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1A03 Exam Review Notes FULL.docx

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Krista Howarth

ANATOMY REVIEW NOTES Four main tissue types: 1. Epithelial 2. Connective 3. Muscular 4. Nervous Epithelial Tissue Epithelium  Covers most surfaces, organs and cavities inside and out  Functions include protection, secretion, absorption, excretion, and sensory reception  Cells arranged in continuous sheets that heal rapidly  Apical (or free) surface faces a body cavity, the lumen, or tubular duct  Lateral surface faces adjacent cells  Basal surface faces towards deeper layers. Basal surface of deepest layer anchors epithelium to basement membrane Basement Membrane  Thin extracellular layer composed of o Basal Lamina  Layer closest to, and produced by, epithelial cells  Contains collagen, laminin, glycoprotiens and proteoglycans  Laminins adhere to integrins in the hemidesmosomes of basal epithelial cells, thereby adhering the epithelium to the basement membrane o Reticular Lamina  Secreted by fibroblasts in underlying connective tissue  Consists of reticular fiber proteins  Serves as point of attachment and support for overlying epithelium  Resists stretching and tearing  Acts as diffusion barrier: epithelium is avascular, therefore blood vessels in connective tissue must provide nutrients to epithelial cells by diffusion through basement membrane  Regulates cells migration and proliferation. Cancerous cells that have crossed the basement membrane are said to have metastasised. Classifying Epithelial Tissue  Two ways of classifying: 1) Number of Cell Layers a. Simple Epithelium  Single Layer of cells  Functions in diffusion, secretion and absorption b. Pseudostratified Epithelium  All cells attached to basement membrane 1  Not all cells extend to apical surface  Nuclei are at different levels, giving stratified appearance  Cells reaching apical surface may have cilia or secrete mucus c. Stratified Epithelium  Two or more layers of cells  Mostly function in protection from wear and tear 2) Cell Shapes a. Squamous cells  Flat and shaped like floor tiles  Wider than they are tall  Allows for rapid diffusion and passage of substances b. Cuboidal cells  Equal height and width. May be cubed or hexagonal in shape  May have microvilli at apical surface c. Columnar cells  Taller than they are wide  Protect underlying tissues Connective Tissue Connective Tissues 1) Found throughout the body; most abundant tissue by weight 2) Provides binding and support, protection against infection, insulation and repair for issue damage 3) Highly vascular, except cartilage (avascular) and tendons (small blood supply) 4) Consist of Cells and Extracellular Matrix (ECM) Cells of Connective Tissue 1) Fibroblasts  Large flat cells with branching processes  Usually most numerous cell in connective tissue  Migrate through connective tissue, secreting fibres and Ground substance for ECM 2) Macrophages  Irregularly shaped cells that develop from monocytes  Phagocytic cells that engulf bacteria and cellular debris  Either reside in particular area, or migrate through connective tissue and gather at site of infection 3) Plasma Cells  Small cells that develop from B-lymphocytes.  Secrete antibodies and are crucial in immune response  Found in many places, but mostly in connective tissues and lymph 4) Mast Cells  Abundant alongside blood vessels that supply connective tissues  Produce histamine : dilates small blood vessels (inflammation)  Also produce heparin: anticoagulant 2 5) Adipocytes  Connective tissue cells that store triglycerides (fats)  Found deep to the skin and around organs such as kidneys 6) White Blood Cells  Not normally found in connective tissue, but migrate in large numbers in response to certain conditions Extracellular Matrix  Composed of ground substance and fibres  Ground Substance o Component of connective tissue between cells and fibres o May be fluid, semi-fluid, gelatinous, or calcified depending on type of tissue o Contains water, complex polysaccharides and proteins o Polysaccharides include hyaluronic acid, chondroitin sulphate, dermatan sulphate, and keratan sulphate, collectively called glycosaminoglycans (GAGs)  Fibres 1) Collagen fibres  Most abundant protein in the body, found in most connective tissues  Strong and resistant to pulling forces, but not stiff, allowing flexibility  Properties differ from tissue to tissue (i.e. cartilaginous collagen attracts more water, giving it a cushioning consistency)  Often occur in parallel bundles, giving great tensile strength (tendons) 2) Elastic fibres  Smaller in diameter than collagen; branch and join to form a network  Consist of elastin surrounded by glycoprotein called fibrillin  Can be stretched to 150% of resting length without breaking  Found in blood vessel walls, skin, and lung tissue. 3) Reticular fibres  Consist of collagen in fine bundles with glycoprotein coating  Provide support to blood vessel walls and stroma (supporting framework) of organs  Thinner than collagen fibers  Help form basement memberane (reticular lamina) Classification of Connective Tissue 1) Connective tissue proper a. Loose connective Tissue i. Areolar connective Tissue ii. Adipose tissue iii. Reticular tissue b. Dense Connective Tissue i. Regular Connective Tissue ii. Irregular Connective Tissue iii. Reticular Connective Tissue 2) Cartilage a. Hyaline cartilage b. Fibrocartilage c. Elastic Cartilage 3 3) Bone 4) Blood Loose Connective issue 1) Areolar  Widely distributed: contains all 6 cells types  All 3 types of fibres are arranged randomly throughout ECM  Combined with adipose tissue, areolar tissue makes the subcutaneous layer 2) Adipose Tissue  Adipocytes, derived from fibroblasts, are used for fat storage  Adipocytes fill with single large fat droplet, pushing nucleus and cytoplasm to periphery  Found with areolar tissue – provides good insulation  Adipocytes increase in number with weight, causing more blood vessels to form 3) Reticular  Fine interlacing reticular fibres  Forms stroma of liver, spleen, and lymph nodes  Mesh-like arrangement helps filter blood and lymph Dense Connective Tissue 1) Regular  Collagen fibres “regularly” arranged in parallel strands  Great tensile strength: resists pulling forces along axis of fibres  Fibroblasts appear between rows of fibres  Examples include tendon and most ligaments 2) Irregular  Collagen packed more closely than loose connective tissue, and in “irregular” arrangement  Found where pulling forces occur in various directions (dermis and pericardium) 3) Elastic  Mostly branching elastic fibres—gives yellowish colour  Fibroblasts present between fibres  Recoils from stretching forces; important in lungs and arteries Cartilage  Dense network of collagen and elastic fibres in gel-like chondroitin sulphate  Can take more stress than Loose or Dense connective tissue  Cells called chondrocytes found in spaces called lacunae in ECM  Dense connective tissue called perichondrium surrounds most cartilage  No blood vessels or nerves except in perichondrium: heals poorly after injury 1) Hyaline  Blue-white appearance—resilient gel as ground substance  Surrounded by perichondrium, except articular cartilage in joints  Most abundant type of cartilage, but also weakest 2) Fibrocartilage  Strongest type of cartilage: threadlike network of collagen fibers  Lacks a perichondrium; found in intervertebral discs 4 3) Elastic cartilage  Network of elastic fibres—perichondrium present  Provides strength and elasticity—found in pinnae of outer ear The Integument The Integument  Includes skin, hair and glands  Functions include 1) Thermoregulation – Blood vessels dilate or constrict, release sweat, direct conduction 2) Blood reservoir – 8-10% of total blood volume 3) Protection – Repel water water, UV, and germs through various barriers 4) Cutaneous sensation – Pressure, touch, pain, and temperature receptors 5) Metabolism – storage of nutrients 6) Excretion + Absorption – minor role  Layers 1) Epidermis 5 2) Dermis 3) Hypodermis (Subcutaneous Layer) Epidermis  Composed of keratinized stratified epithelium  4 major cell types: 1) Keratinocytes  Arranged in 4-5 layers – compose 90% of epidermis  Produce keratin, a tough, fibrous protein that protects cells  Also produce lamellar granules, which produce a water repellent sealant 2) Melanocytes  Comprise 8% of epidermal cells  Produce melanin, a pigment that absorbs UV radiation  Long projections extend between keratinocytes and transfer melanin to them  Melanin clusters around keratinocyte nuclei and shields them from UV 3) Langerhans Cells  Arise from red bone marrow and migrate to epidermis  Participate in immune response against microbes  Easily damaged by UV light 4) Merkel Cells  Least numerous cell type, located in deepest layer of epidermis  Contact flattened processes of sensory neurons called tactile discs  Merkel cells and tactile discs detect various touch sensation  Layers of Epidermis 1) Stratum Corneum  Most superficial stratum: 25-30 layers of flattened dead keratinocytes  Continuously shed and replaced by deeper strata  Interior contains mostly keratin  Between cells are lipids from lamellar granules, making it water-repellant  Protects deeper layers of skin 2) Stratum Lucidum  Only present in “thick skin” of palms, soles and fingertips  3-5 layers of flat, dead and clear keratinocytes  Large amounts of keratin and thickened cellular membrane 3) Stratum Granulosum  3-5 layers of keratinocyes undergoing apoptosis  Include membrane-enclosed lamellar granules, which fill top 3 strata with lipids  Marks transition between deep, active layers and superficial dead layers 4) Stratum Spinosum  8-10 layers of many-sided keratinocytes fit closely together  Have intermediate filaments called tonofilaments which attach to desmosomes  Tonofilaments are converted to keratin in more superficial layers 5) Stratum basale  Also called stratum germanitivum: 1 row of cuboidal/columnar keratinocytes  Some are stems cells undergoing division to form more keratinocytes  Tonofilaments attach to hemidesmosomes and desmosomes  Desmosomes join cells; hemidesmosomes attach layer to basement membrane 6 Dermis nd  2 , deeper layer of the skin; thicker than the epidermis  Contains blood vessels, nerves, glands and hair follicles  Divided into papillary region and reticular region: 1) Papillary Region  One-fifth of thickness of dermis  Consists of areolar connective tissue containing fine elastic fibres  Elastic fibres provide skin tone  Has several dermal papillae: finger-like projections into epidermis  Papillae contain capillaries, free nerve endings and Meissner corpuscles  Free nerve ending sense pain, Meissner corpuscles sense touch 2) Reticular Region  Attached to subcutaneous layer; very flexible  Dense irregular tissue containing fibroblasts, collagen bundles and coarse elastic fibres  Few adipose cells, follicles, nerves, and glands occupy spaces between fibres Subcutaneous Layer (Hypodermis)  Deep to dermis, but not technically part of skin (subcutaneous = below skin)  Attaches skin to underlying structures such as muscles  Contains areolar and adipose tissue, with serve to insulate and cushion the body  Contains Pacinian corpuscles that sense pressure (sometimes also found in dermis)  Highly vascular; supplies skin with nutrients and whatnot Accessory structures of the skin 1) Hairs  Columns of dead, keratinized cells  Superficial portion called shaft, deep portion called root  Both shaft and root consist of 3 concentric layers: i. Medulla o Inner layer which may be missing in thinner hair o Composed of 2-3 rows of irregularly shaped cells ii. Cortex o Forms major part of shaft o Consists of elongated cells iii. Cuticle o Outermost layer: single layer of keratinized cells o Thin flat cells arranged like shingles  Surrounding root is hair follicle, consisting of external and internal root sheath  External root sheath is downward continuation of epidermis  Internal root sheath is produced by cells called the matrix 7  Base of follicle has in indentation called papilla, which contains areolar tissue and blood vessels  Papilla also contains germinal layer of cells called matrix: responsible for growth 2) Sebaceous Glands  Glands that secrete oily substance called sebum into neck of hair follicle  Sebum coats hairs and skin to prevent water evaporation 3) Sudoriferous Glands  Sweat glands that secrete sweat—divided into two main types: i. Eccrine Glands secrete sweat onto surface of skin ii. Apocrine glands secrete sweat into hair follicles Membrane Potential and Neurotransmission Membrane Potential  Resting membrane pote+tial maintained by selectively permeable membrane and Na/K pumps  The cytosol is rich in K ions and is largely negative due to negatively charged protiens, while the extracellular fluid (ECF) is rich in Na  Due to concentration gradient, K attempts to leave the cell and Na attempts to enter  However, cell membrane is much more permeable to K than to Na, causing more K to leave than Na to enter.  This creates a makes the inside of the cell negative, creating an electric potential  Potential is maintained by electrogenic Na/K pump that pumps in 3 K for every 2 Na it pumps out  Resting potential of neurons is approximately -70 mV, but not lower -40 mV Changes in Potential  Two kinds of possible changes: graded and action potential  Graded Potentials o Short lived local changes in membrane potential that vary in amplitude o Causes either hyperpolarization or depolarization o Can be spatially or temporally summed, but only travel 5 microns o Can be caused by mechanically- gated or ligand-gated channels o Mostly occur on neuron cell bodies or dendrites. Rarely axonal.  Action Potential o All-or-Nothing phenomenon: APs are either triggered once the voltage reaches the threshold level, or are not triggered at all o Cannot be summed due to refractory period 1) Sufficient stimulus or change in voltage caused by graded potential opens voltage gated Na ion channels 2) Na rushes into cell, causing depolarization. Potential reaches +30 mV 3) This causes more voltage gated Na channels to open further down in the axon, sending a wave of depolarization down the axon 8 4) Then, voltage gated K channels open just as Na channels are closing, causing K ions to rush out of the cell, causing repolarization 5) Excess outflow of K cause potential to drop below -70 mV. This is known as the after-hyperpolarization phase 6) Once potential is back at -70 mV, K channels close 7) Na/K pump restore concentrations of Na and K inside and outside the cell o Period between rise in potential to over threshold to fall back below threshold is absolute refractory period. No new APs can be made in this time o Afterhyperpolarization is known as relatively refractory period. New APs are harder to generate in this time Muscular System Muscles  Muscle cells are specialised for motility  Each muscle is an organ including muscle tissue, nervous tissue and connective tissue  Three types of Muscle 1) Smooth Muscle  Found in walls of blood vessels, organs, airways as well as digestive, urinary and reproductive tracts  Spindle shaped with single nucleus; smaller than skeletal muscle cells  Involuntary contraction usually regulated by autonomic nervous system  30 times slower contraction than skeletal muscle  Two levels of organization I. Single unit (visceral) o Stimulating one fibre stimulates all o Fibres connected by gap junctions II. Multi-unit o Fibres contract separately o Each fiber has a motor neuron terminal  Contain both thick and thin filaments but less organised than skeletal muscle  Lack T-tubules and have small sarcoplasmic reticulum  Thin Filaments anchored to dense bodies 2) Cardiac Muscle  Striated muscle with branching fibres  Connective tissue with blood vessels and nerves between layers of muscle  Fibres connected by intercalated discs containing gap junctions, allowing cardiac fibres to contract synchronously, and desmosomes for adhesion  Involuntary contraction regulated by autonomic nervous system 9 3) Skeletal muscle  Over 600 voluntary muscles  Accounts for over 40% body weight  Have rich blood supply – need constant O 2upply  Structure: o Made of muscle cells (myocytes) o Myocytes are long, multinucleated fibres o Contain thick and thin filaments in bundles called myofibrils o Muscle fibers are surrounded by endomysium o Several muscle fibres (10-100) are grouped together into fascicles held by perimysium o Several fascicles are bundled together into a muscle surrounded by epimysium o Epimysium, perimysium and endomysium are all continuous with tendons attaching muscle to bone Skeletal Muscle Fibres  Between 10 to 100 micrometers in diameter and 10-30 cm long  Each muscle cell has 100 or more nuclei, formed when myoblasts fuse together in early development  The number of myocytes in body is set at birth; growth occurs by hypertrophy not hyperplasia  Cell membrane of muscle cells referred to as sarcolemma. Nuclei lie just below the surface  Cytosol of muscle cells referred to as sarcoplasm—filled with glycogen and myoglobin  Transverse tubules (T-tubules) small invaginations leading to center of muscle fiber  Each T-tubule is flanked by the terminal cisterns of two sarcoplasmic reticulum, forming a triad  Muscle fibres are filled with strands called myofibrils  Each myofibril has thick and thin filaments in structures called sarcomeres  Sarcomeres repeat within a muscle fibre— separated by Z-discs  Overlap of fibres in sarcomeres cause striations 10  Thick filament has 300 molecules of myosin  Thin filaments are actin anchored to z discs Muscle Contraction Basic outline:  Action potential arrives at axon terminal of neuromuscular junction  Neurotransmitter (ACh) is released from axon terminal into synaptic cleft  ACh binds to receptors on motor end plate of sarcolemma  Depolarization (Action potential) propagates across sarcolemma and down T-tubule  Calcium is mobilised fro m sarcoplasmic reticulum into sarcoplasm  Muscle contracts Generation of muscle action potential  Action potential arrives at axon terminal. Calcium is taken into axon terminal and cause release of ACh into synapse  ACh diffuses across synaptic cleft and binds to receptors. Two ACh required per receptor  ACh receptor activation opens ion channels in sarcolemma, allowing Na enter cells  The change in voltage triggers a muscle action potential which travels across sarcolemma and down T-tubules  Arrival of AP into T-tubule causes release of calcium from terminal cisterns of sarcoplasmic reticulum into cell  Calcium ions bind to troponin, causing a conformational change. This removes the blocking action of tropomyosin, revealing actin active binding sites  Myosin cross-bridges alternately attach and detach, pulling actin filament towards center of sarcomere (detailed below)  Calcium is actively transported back into the sarcoplasmic reticulum and held there by calsequesterin. This causes troponin to revert to original shape and causes tropomyosin to block actin binding sites  Acetylcholinesterase (AChE) breaks down ACh in synaptic cleft, causing ion channels to close Sliding filament mechanism of contraction  Requires both ATP and increase in Ca ions  Thin actin filaments slide over thick myosin filaments 1) Thick filament  Consists of myosin: protein with rod-like tail with globular head  Myosin head has ATP binding site and an ATPase  Several join together to make thick filament 2) Thin filament  Consist of globular actin molecules that aggregate to form a helical filament, with globular troponin and helical tropomyosin  Troponin consists of three polypeptide chains:  TnI: binds to actin (inhibitory subunit) 11  TnT: binds to tropomyosin  TnC: binds to Ca ions (2 at rest, 4 when Ca levels are high)  Contraction cycle begins with rise in Ca ion levels in the sarcoplasm, which expose actin binding sites (detailed above) 1) ATP hydrolysis:  Myosin head hydrolyzes ATP, which cause it to become reoriented and energised.  ADP and phosphate group still attached to myosin head 2) Formation of crossbridges  Energized myosin heads attach to myosin binding site on actin, forming a crossbridge  This causes release of hydrolyzed phosphate group 3) Power Stroke  After formation of crossbridge, ADP binding site opens and releases ADP  This causes myosin head to rotate towards center of sarcomere  This creates a force which pulls the actin filament towards the M line 4) Detachment  At the end of power stroke, myosin head is still attached to actin head  Once the ATP binding site binds another ATP molecule, actin is released  Cycle can now begin again  Contraction cycle continues as long as sufficient Ca ions and ATP are present ATP generation  ATP for muscles is generated in one of 3 ways 1) Direct  Creatine phosphate dephosphorylation  Fast regeneration of ATP from ADP and P i  Provides energy for 15 seconds: useful for 100 m sprint 2) Aerobic Respiration  O required, provides 95% of ATP 2  Stored muscle glycogen is converted to glucose  Provides most of ATP needed during moderate exercise  When muscle glycogen supplies are exhausted, blood glucose and fatty acids are broken down. Glucose yields 36 ATP, fatty acids yield about 100 ATP  Provides energy for hours: useful in marathon 3) Anaerobic glycolysis  When respiratory and circulatory systems cannot provide enough oxygen to sustain muscle contraction, glycolysis occurs 12  Glucose is broken down into lactic acid and pyruvic acid  Faster than aerobic respiration, but less effective (only 2 net ATP per glucose)  Provides energy for 30-40 seconds: useful in 400 m dash Muscle fiber types 1) Slow oxidative  Slow twitch fibres with small diameter and rich blood supply  Use aerobic respiration to generate ATP  Used to maintain posture and in endurance activities such as marathons 2) Fast Oxidative-glycolytic  Intermediate diameter between slow oxidative and fast glycolytic  Contain large amounts of blood vessels and myoglobin, giving a red appearance  Use both aerobic and anaerobic respiration  ATPase in myosin 3 to five times faster than in slow-oxidative fibres, thus refered to as fast-twitch fibres 3) Fast glycolytic  Largest in diameter and contain most myofibrils, thus provide strongest contractions  Fast-twitch fibres with low myoglobin, capillaries and and mitochondria  Mainly use glycolysis to provide energy. Used in weight lifting and throwing motions Autonomic Nervous System Overview  Branch of nervous system that controls involuntary muscles such as heart and smooth muscle  Small sensory part of system is seen in referred pain  Maintains homeostasis  Divided into parasympathetic and sympathetic divisions ANS vs SNS  In the somatic nervous system, a single myelinated motor neuron extends from the CNS all the way to the skeletal muscle fibres in its motor unit.  In the autonomic nervous system, there are two neurons in series. The first has a cell body in the CNS and its myelinated axon extends to the autonomic ganglion. The second neuron has its cell body in the ganglion and its unmyelinated axon extends to the effector  All somatic motor systems use ACh  ANS neurons use ACh at the ganglion and ACh or nor epinephrine at the effector Sympathetic vs. Parasympathetic 1. Sympathetic Nervous System: Fight or flight  Pre ganglionic nerves have cell bodies in lateral horns of the gray matter in the 12 thoracic and 2 lumbar segments of the spinal cord  Ganglia located in the sympathetic chain ganglia  Short preganglionic axons: ganglia are far from the effectors  Uses nicotinic ACh at the ganglion and norepinephrine at the effector  Much faster acting and longer lasting effects than the parasympathetic branch because: 13 i. Sympathetic postganglionic neurons diverge more: allows for more widespread activation on effectors ii. Norepinephrine is broken down very slowly by MAO iii. Norepinephrine is also released as a stress hormone into the blood, increasing their effects in the body  Effects of sympathetic division include: i. Tachycardia – increase blood flow and blood pressure ii. Bronchial dilation – increase 2 intake for muscle activity iii. Pupil dilation – allow more light into eyes to perceive threat iv. Release of glucose – more energy for muscles v. Constriction of gastric vasculature – lunch can wait vi. Dilation of muscle vasculature – allow more blood to muscles vii. Glycogenolysis in liver – Activate more glucose for body 2. Parasympathetic Nervous System: Rest and Digest  Pre ganglionic neurons have cell bodies in the cranial nerve nuclei or lateral horns of the nd th 2 -4 sacral segments of the spinal cord  Ganglia are located very close to, or sometimes even on, the effector organs  Long preganglionic axons: ganglia are close to effectors  Uses nicotinic ACh at ganglia, but muscarinic ACh at the effector  Cranial nerve X (Vagus nerve) carries approximately 80% of craniosacral outflow  Vagus nerve innervates almost entire viscera  Effects Include SLUDD i. Salivation ii. Lacrimation iii. Urination iv. Defacation v. Digestion Receptors 1. Cholinergic receptors  Found in sympathetic and parasympathetic ganglion synapses  Found in postganglionic parasympathetic effectors  Use ACh as their neurotransmitter  Nicotinic ACh receptors i. Found in the postganglionic cell bodies and dendrites of both parasympathetic and sympathetic branches ii. Generally causes excitation  Muscarinic ACh receptors i. Found in effectors innervated by the parasympathetic postganglionic neurons ii. Cause excitation and inhibition 2. Adrenergic receptors  Found on sympathetic postganglionic effectors  Use epinephrine and norepinephrine (but only NE is used as a neurotransmitter)  α sub-type: generally stimulate contraction i. α1: Causes contraction of smooth muscle. Found in visceral blood vessels, except for the heart ii. 2 : Presynaptic receptor used in clotting (not important for this course) 14  β sub-type: generally inhibits contractions i. β1: Causes tachycardia and dilation of blood vessels that feed the heart ii. 2 : Causes bronchiodilation and vasodilation in skeletal muscle vasculature. Relaxes some organ walls such as the bladder iii. 3 : Breaks down brown fat (lipolysis) Central Nervous System Central Nervous system  consists of brain and spinal cord: protected by bone  Neuroglia of the CNS: 1. Astrocytes  Largest and most numerous of neuroglia in the CNS  Many short branching processes that wrap around capillaries to form the blood- brain barrier between the...blood and the brain (duh?)  Also support neurons 2. Oligodendrocytes  Myelinate axons of CNS and inhibit regrowth of axons  Each oligodendrocyte myelinates several axons 3. Microglia  Phagocytic cells that clear microbes and cellular debris 4. Ependymal cells  Line ventricles of the brain and central canal of spinal cord  Produce and monitor CSF, and form the blod-CSF barrier  Neuroglia of PNS 1. Schwann cells  Myelinate PNS axons by encircling them them several times  Each Schwann cell mylinates a section of a single axons  Also support up to 20 unmyelinated axons  Encourage axon regeneration (1 mm per day) 2. Satellite cells  Surround cell bodies of PNS neurons  Provide support and regulate material exchange Protective coverings: the meninges  Cranial meninges are continuous with the spinal meninges: smae structure and names  Has three layers: 1. Dura mater  Thick Durable outer most layer  Firmly attached to skull; impossible to remove  Has its own arteries, veins and nerves  Irritation of dura causes headaches 2. Arachnoid layer  Plastered to underside of dura  Spiderweb-like appearance  Creates subarachnoid space between arachnoid layer and pia mater 3. Pia mater  Plastered on to brain 15  Extremely thin: lines the brain surface  Extensions of the dura separate the brain: 1. Falx cerebri seperates brain into left and right hemispheres 2. Falx cerebella separate cerebellum into left and right hemispheres 3. Tentorum cerebella seperates cerebellum from cerebrum  Cerebral blood sinuses o Cavities within dura where blood drains from cerebral blood vessels o Lack the layers of veins  Trauma 1. Epidural hematoma  Blunt force to skull ruptures meningeal vessels  Blood fills between skull and dura 2. Subdural hematoma  Rapid movement of head causes rupture of cerebral vessels  Blood fills underneath dura 3. Coning  Extreme movements of the brain restricted by dural extensions  Causes damage to brain or nerves  Spinal Meninges o Similar to cranial meninges, except dura is not attached to vertebrae o Layer of fat between dura and vertebrae called epidural fat space o Provides flexibility for spine during bending Cerebrospinal Fluid  Clear colourless liquid that protects from physical and chemical injury  Basically blood without cells  Serves as a physical shock absorber  Allows circulation of nutrients and waste  Formed during early development: brain is formed as a hollow tube filled with CSF  In adults, CSF is present within ventricles in the brain  Drains into the superior saggital sinus through arachnoid villi  Produced in the 3 and 4 ventricles by choroid plexuses  Leakage from ventricular system to subarachnoid space through thin roof of the 4 ventricle The Brain The Brain  Grey matter on the outside: unmyelinated cell bodies of neurons arranged in columns  White matter on the inside: myelinated neuronal axons  Deep grey matter consists of thalamus and basal ganglia  Parts of the Brain: 16 o Cerebral Cortex o Diencephalon o Brain Stem o Cerebellum Cerebral Cortex  Responsible for thinking, memory, sensory perception and voluntary motor movement  Marked by fissures, sulci and gyrii: o Gyrii: Folds of cortex caused by faster growth of grey matter than white matter o Fissure: Deep grooves between folds o Sulcus: Shallow grooves between folds  Lateral Fissure seperates frontal lobe from temporal lobe  Longitudinal fissure separates the two hemispheres of the brain (falx cerebri)  Central Sulcus separates primary motor cortex (precentral gyrus) from primary sensory cortex (postcentral gyrus) Lobes of the Cerebral Cortex 1. Frontal Lobes  Association cortex: Intellect  Premotor cortex: Anterior to central sulcus (precentral gyrus)  Broca’s area: Involved in formulation of words (motor component of speech) 2. Temporal Lobes  Auditory Cortex: Hearing from ears  Wernicke’s Area: Hearing and understanding what words mean (sensory portion of speech) 3. Parietal Lobe  Somatosensory cortex: Touch, pressure, temperature and pain (postcentral gyrus)  Association cortex: Feel touch, texture and temperature and put them together to form an accurate picture of what is being sensed 4. Occipital Lobe  Visual Cortex: processes input from eyes  Frontal eye field: projects into motor cortex to coordinate eye movement 5. Insular Cortex  Balance: Found under temporal lobe (pull apart Lateral fissure to reveal it)  Taste: found under parietal lobe  Smell: Olfactory bulb found on underside of front of the brain Homonculus  Shows which part of the brain is responsible for sensory/motor input from various part of the body  Face and limbs have more innervations than the trunk  Different blood supplies  strokes to different areas will lead to paralysis of different parts of the body 17 k Lateralization of Function:  Hemispheres have different functions  Left Hemisphere: o Responsible for logic, math and language o Controls right side of body  Right Hemisphere: o Responsible for visual-spatial skills, emotion, intuition, arts and creativity o Controls left side of body  Two halves connected by corpus callosum, allowing coordination of two halves White matter tracts 1. Commissures:  Connect the hemispheres  Most important is the corpus callosum 2. Association fibres:  Connect areas within the same hemisphere  Connect different lobes (frontal eye field to visual cortex) 3. Projection fibres  Connect to different parts of CNS  Most importantly connect to spinal cord, brainstem, and thalamus Deep Nuclei  Found underneath to the superficial grey matter and lateral to diencephalon (core of brain)  Consists of limbic system and basal ganglia 1. Limbic System – Responsible for emotions and memory a) Hippocampus – Involved in long term memory formation 18 b) Mammillary bodies – Olfactory relay nucleus. Responsible for strong connection between olfaction and emotion c) Fornix – Provides output to overlying cerebral cortex via axons d) Amygdala – Analyses fear and anger in facial expressions. Also involved in forming emotional memories. Connected to hypothalamus and receives input from visual cortex. 2. Basal Ganglia (Corpus striatum) – Responsible for motor planning and skills memory in slow stereotypical movements such as walking. a) Lenticular Nucleus – bean shaped nucleus lateral to the thalamus. Consists of the putamen and globus pallidus b) Caudate Nucleus – consists of head and tail which tapers to the amygdala Memory Formation Pathways 1. Fact memory: i. You have an experience: buy a car. Brain receives sensory input from 5 senses ii. Amygdala analyses emotional context of experience: good car or bad car iii. Hippocampus remembers spatial relationships: when you bought it, name of dealer, cost, etc. iv. If experience important, hippocampus sends message to diencephalon (thalamus and hypothalamus) and will overlay pleasurable or negative experience with first experience was processed and store them in frontal cortex v. This results in association of those specific sensory memories with the emotional memories that accompanied them. vi. Repeating this cycle help solidify connections and strengthen memories 2. Skills memory: i. New skills are learned using visual cortex and motor planning area in basal ganglia ii. Both two areas feed into motor cortex where skill is stored in precentral gyrus iii. Skills can then be recalled 3. Amnesia  Caused by atrophy of cerebral cortex o Seen in patients of Alzheimer’s Disease o Neurofibrillary plaques and tangles form o Inability to recall past and recent memories, lack of attention, disorientation etc. o Parts of long term memories are forgotten  Caused by lesion or atrophy of hippocampus o Inability to form any new memories: Anterograde amnesia 19 o Inability to recall past events: retrograde amnesia How to drink a beer...for scientific purposes of course i. Eyes pick up image of beer. Image is relayed through the thalamus to the visual cortex. ii. Sensory association cortex in parietal lobes puts image of beer together sensation of dry tongue to tell you you’re thirsty and could use a cold, refreshing brew with a smooth easy-drinking taste iii. This information is sent to the frontal cortex where there is a shift from sensory to motor pathways. You frontal cortex decides whether or not to get the beer after considering moral/logical/religious/legal factors. iv. Frontal cortex sends three simultaneous signals to different parts of the brain: primary motor cortex, cerebellum and basal ganglia. v. Primary motor cortex tells muscles to go grab the beer vi. Cerebellum tells muscle how to grab the beer by coordinating movement of different limbs vii. Basal ganglia tells muscles how fast to do it while eliminating unnecessary movement viii. By coordinating the three, you grab the beer, drink it, and good times are had by all. Diseases of the basal ganglia  Cause difficulty initiating, continuing and stopping movements especially slow stereotypical movements  Cause involuntary movement in the form of tremors  Parkinsons disease caused by degeneration of substantia nigra, the midbrain nucleus that connects to the basal ganglia  Huntington’s Chorea is caused by degeneration of lenticular nucleus and substantia nigra Diencephalon  Consists of thalamus, hypothalamus, and pineal gland.  Thalamus: o Left and right halves connected by intermediate mass o Is a collection of several different nuclei o Sensory relay centre Sorts sensory input to brain and filters out unnecessary information to allow selective attention o Regulates transmission of vision, hearing, touch, pressure, proprioception, pain and temperature o Input from cerebral cortex determines which signals should be relayed to cortex  Hypothalamus o Also collection of several different nuclei o Controls the autonomic nervous system: BP, heart rate, pupil size respiratory rate etc. o Controls emotions such as pleasure, fear and rage and sexual activity o Also involved in thermoregulation, appetite, thirst and sleep o Produces hormones that control the endocrine system along with the pituitary  Pineal Gland o Generates circadian rhythms o Secretes melatonin—the sleep hormone Brainstem 20  Located in front of fourth ventricle  Consists of the midbrain, pons and medulla  Contains most of the cranial nerve nuclei  Midbrain (mesencephalon) o Located just under the hypothalamus o Contains cerebral peduncles: pair of tracts that contain axons of descending corticospinal motor neurons as well as ascending sensory neurons from the medulla to the thalamus o Superior colliculi (bumps on the side of the pineal gland) serve in visual reflex relay i.e. tracking moving objects, reading sentences o Inferior colliculi serve in auditory reflex relay i.e. jumping from loud sounds o Contains nuclei of origin of cranial nerves III and IV  Pons o Connects parts of the brain to each other o Has a big connection to the cerebellum via the pontine nuclei o Other parts connect hemispheres of cerebellum to each other o Nuclei of origin of cranial nerves V, VI, VII and VIII  Medulla o Continuous with superior part of the spinal cord o White matter has corticospinal tracts (pyramids) merging from underneath pons: sensory in dorsal area, motor in ventral area. o Decussation of pyramids: crossing over of corticospinal tracts. Results in left hemisphere controlling right half of body and vise versa o Nuclei of grey matter regulate vital functions such as breathing and heartbeat o Origins of cranial nerves IX, X, XI, and XII Nuclei of the brainstem  Reticular formation o Found in core of brainstem o Receives input from all senses along with thalamus o Responsible for wakefulness and alertness o Released opioids and enkephalins to control pain  Substantia Nigra o Motor pathways that control subconscious motor activity o Pigmented dopaminergic neurons that project to the basal ganglia  Red Nuclei o Red due to large blood supply and iron-containing pigment o Regulate motor pathways of flexion Cerebellum  Located behind brainstem (immediately behind 4 ventricle and pons)  Responsible for producing coordinated muscle movement as well as balance and posture  Outer cortex receives input from proprioceptors and vestibular apparatus. The deep nuclei then provide output into the pons which relays it to the cerebral cortex in order to provide a blueprint for motion 21  Central part responsible for coordinating axial skeleton and outer part responsible for appendicular skeleton  Three paired cerebellar peduncles connect it to the brainstem o Inferior cerebellar peduncles carry sensory information from proprioceptor and vestibular apparatus to the cerebellum o Middle cerebellar peduncles carry commands for voluntary motor movements that originate in the motor cortex from the pontine nuclei to the cerebellum o Superior cerebellar peduncles carry output from cerebellum to red nuclei and thalamus  Diseases or trauma to the cerebellum causes ataxia: an inability to coordinate movement that presents as “permanent drunkenness” The Cranial Nerves Cranial Nerves I. Olfactory Nerve  Entirely sensory: responsible for sense of smell  Olfactory neurons project an odour-sensitive dendrite into the mucosa, and have axons connecting to the olfactory bulb  Olfactory bulb leads to olfactory tracts, which lead to the temporal lobe II. Optic Nerve  Entirely sensory: responsible for sense of sight  Connects rods and cones in eye to occipital lobe  2 optic nerves merge to form the optic chiasm, where axons from the medial half of each eye cross over to opposite sides  Posterior to the chiasm, the regrouped axons form the optic tracts.  Optic tracts lead to the thalamus, where they synapse with axons leading to the occipital lobe III. Occulomotor Nerve  Motor nerve: Superior branch moves extrinsic eye muscles and the upper eyelid.  Inferior branch also supplies extrinsic eye muscles. It also provides parasympathetic innervations to intrinsic eye muscles, including ciliary muscle (adjusts lens) and circular muscles of the iris (constricts pupil) IV. Trochlear Nerve  Motor nerve. Smallest of cranial nerves  Innervates extrinsic eye muscle (superior oblique) V. Trigeminal Nerve  Both sensory and motor components: mixed nerve with three branches  Opthalmic branch contains sensory axons from upper eyelid, eyeball, side of nose, forehead and anterior half of scalp  Maxillary branch has sensory axons from nose, palate, pharynx, upper lip and teeth, and lower eyelid  Mandibular branch has sensory axons from anterior two thirds of tongue (not taste), cheek, lower teeth, lower jaw and side of the head anterior to the ear  Mandibular branch also provides motor axons that innervate the muscles of mastication as well as the tensor tympani VI. Abducens Nerve  Motor nervethat innervates lateral rectus (extrinsic eye muscle) 22  Causes abduction of eyeball VII. Facial Nerve  Both sensory and motor components, as well as parasympathetic  Sensory part is responsible for sensing taste from anterior two thirds of tongue  Motor component controls muscles of facial expression as well as the stylohoid muscle and the posterior belly of the digastric muscle(throat muscles). Also innervates the stapedius  Parasympathetic outflow goes to lacrimal glands, nasal glands, palatine glands, and the sub-mandibular and sub-lingual salivary glands VIII. Vestibulocochlear Nerve  Sensory nerve responsible for hearing and balance  Cochlear branch receives auditory input from cochlea (duh)  Vestibular branch receives information about equilibrium from the semi-circular canals IX. Glossopharyngeal Nerve  Both sensory and motor  Sensory input comes from taste buds on posterior third of tongue as well as stretch receptors (baroreceptors) in the carotid sinuses  Motor output goes to stylopharyngeus (elevates larynx when swallowing)  Parasympathetic outflow goes to parotid gland (salivary gland) X. Vagus Nerve  Both sensory and motor components  Innervates almost entire viscera: heart, lungs, liver, gallbladder, stomach, small intestine and most of the large intestine  Motor component regulates parasympathetic activation of viscera  Sensory component receives input from skin of the external ear, baroreceptors in the aortic arch and visceral sensory receptors XI. Accessory Nerve  Both sensory and motor components  Originates from both the brainstem and spinal cord  Cranial root is motor and innervates voluntary muscles of the pharynx, larynx and soft palate used in swallowing  Spinal root is mainly motor, innervating the sternocleidomastoid and trapezius muscles. Its sensory input is from proprioceptors of aforementioned muscles XII. Hypoglossal Nerve  Both sensory and motor components  Motor component controls muscles of the tongue used in swallowing and speech  Sensory component receives input from proprioceptors in tongue Special Senses – Hearing The Ear  External Ear o Collects sound waves and channels them inwards o Consists of the auricle, external auditory canal and eardrum  Auricle (pinna) is a flap of elastic cartilage covered by thin layer of skin. The rim of the auricle is the helix and the inferior portion is the lobule. 23  The external auditory canal (meatus) connects the auricle to the eardrum and has ceruminous glands that secrete earwax (cerumen). Only inner 1/3of meatus is formed by the bone; outer 2/3 is formed by cartilage. Skin attached to bony part of meatus is extremely thin, leading to painful inflammation when infected.  The eardrum (tympanic membrane) is a thin semitransparent layer of simple cuboidal epithelium covered in epidermis externally and mucosa internally  Middle ear o Air-filled cavity in temporal lobe lined with epithelium. It is separated from the external ear by the eardum, and from the inner ear by the round and oval windows. o Houses the three auditory ossicles held in place by ligaments o Ossicles are connected by synovial joints, and provided a mechanical relay of sound  Malleus (hammer) connects to internal surface of eardum and articulates with incus. It receives vibrations from the eardum and passes them on to the incus.  Incus (anvil) articulates with the stapes and passes vibrations on to it  Stapes (stirrup) transfers vibrations to the oval window. o Two muscles attach to ossicles to dampen loud sounds and protect inner ear from damage  Tensor tympani (supplied by mandibular branch of trigeminal nerve) connects to the malleus. It increases tension on the eardrum and limits its movement.  Stapedius (supplied by facial nerve) is the smallest skeletal muscle in the body and attaches to the stapes. It limits large vibrations of the stapes to protect the oval window, but also decreases sensitivity of hearing o Eustachian (auditory) tube connects the anterior wall of the middle ear to the nasopharynx and is made of both bone and cartilage o Pharyngeal end is usually closed, but opens during yawning and swallowing to equalize pressure between the middle ear and the atmosphere o Middle ear also connects to mastoid air cells in the mastoid process of the temporal bone o Middle ear infections  Common in children as they sneeze improperly, causing germs to be pushed into auditory tube and into the middle ear  Pressure of pus and fluid formed by infection can rupture the eardum. Eardrum can repair itself in a few days, but chronic infections can be dangerous  Infection can get into mastoid air cells, causing chronic mastoiditis  Roof of the temporal bone is very thin, and can be eroded by infection, leading the infection into dura of the brain, causing meningitis  Inner Ear o System of channels in the petrous portion of the temporal bone o Outer bony labyrinth encloses inner membranous labyrinth o Bony labyrinth is a series of cavities in the temporal bone. It is lined with periosteum and contains perilymph, a fluid similar to CSF o The perilymph surrounds the membranous labyrinth, which in+turn is lined with epitherlium and filled with endolymph. Endolymph has high K ion concentration. o Cochlea is spiral canal divided into three channels:  Cochlear duct is continuous with the membranous labyrinth and is filled with endolymph. It lies in the middle of the three canals  The channel above the cochlear duct is the scala vestibuli, which ends at the oval window. It is part of the bony labyrinth and filled with perilymph. 24  The channel below the cochlear duct is the scala tympani, which ends at the round window. It is part of the bony labyrinth and filled with perilymph o The scala tympani and scala vestibule are joined by an opening at the apex of the cohlea called the helicotrema. o The cochlear duct is separates from the scala vestibule by the vestibular membrane and from the scala tympani by the basilar membrane. The tension of fibres in the basilar membrane varies: fibres are shorter and stiffer at the base of the cochlea, and longer and more flexible near the apex. o Resting on the basal membrane is the organ of Corti, which contains epithelial cells and 16,000 hair cells that synapse with neurons of the vestibulocochlear nerve. Inner hair cells are in a single row while outer hair cells are in 3 rows o Hair cells have stereocilia that extend into the endolymph of the cochlear duct. Hearing  The steps involved in hearing and processing sound: 1. Auricle directs sound waves to external auditory canal 2. Sound vibrations strike the eardrum and cause it to vibrate 3. The central area of the eardrum is connected to the malleus, which in turn connects to the incus and stapes. The vibration travels along these three bones. 4. The stapes transmits the vibration to the membrane of the oval window. The oval window vibrates 20 times more vigorously than the eardum due to amplification of the vibrations by the ossicles (smaller oval window compared to larger eardum) 5. The movement of the oval window sends pressure through the perilymph of the scala vestibule in the cochlea. 6. The pressure waves travel through the scala vestibuli and are transmitted to the scala tympani at the helicotrema. The pressure waves in the perilymph of the scala tympani cause the round windows to vibrate. 7. Pressure waves in the perilymph of the scala vestibuli and scala tympani also deform the vestibular membrane, causing pressure in the endolymph of the cochlear duct. 8. Pressure waves in the cochlear duct cause the basilar membrane to vibrate, which moves hair cells against the tectorial membrane. Each segment of the basilar membrane is tuned for a specific frequency. The stiffer fibres near the base of the cochlea pick up higher-pitched sounds. The more flexible fibres near the apex pick up lower sounds. 9. As the hair cells move against the tectorial membrane, the stereocilia bend and send nerve impulses down the sensory neurons of the vestibulocochlear nerve which terminates at the cochlear nuclei of the medulla. 10. From there, axons carry the signal to the thalamus, the inferior colliculi, and the auditory cortex Deafness 1. Conduction Deafness  Caused when sound does not transmit to the nerves in cochlea  Can be caused by ruptured tympanic membrane, wax build-up, or arthritis or fusing of the ossicles  Affects low tones and gives a ringing in the ears 2. Sensory deafness  Caused by destruction of hair cells or by diseases of the vestibulocochlear nerve 25  Can be caused by constant exposure to loud sounds, infarction of blood supply, drug toxicity and tumours.  Affects high tones and gives a low rumbling in the ears  Destruction of hair cells or CNS is irreversible  Cochlear implants can bypass damage to hair cells by converting sounds to electrical signals that are transmitted to the vestibulocochlear nerve Special Senses – Taste and Smell Taste  Taste (salty sour or bitter sensation) from anterior 2/3 received by facial nerve. Facial nerve also innervates muscles of facial expression and salivary glands  Glossopharyngeal nerve receives taste from posterior 1/3 of tongue, and innervates muscles of swallowing  Texture, pain and temperature of food is carried by trigeminal nerve, which also innervates muscles of mastication Taste buds  Tongue is skeletal muscle covered in stratified squamous epithelium similar to skin  Tip of tongue is the apex and root is located near the epiglottis and tonsils. Rest is called body.  Epithelium of tongue is covered in folds called papillae that increase surface area  Four types of papillae: 1. Vallate papillae  Form an inverted V shape at back of tongue  Houses 100-300 taste buds 2. Fungiform papillae  Mushroom shaped elevations scattered over entire tongue  About 5 taste buds each 3. Foliate papillae  Leaf-like papillae located in small trenches on lateral margins of tongue  Most taste buds degenerate in early childhood 4. Filiform papillae  Thread like structures all over tongue  No taste buds: increase friction between food and tongue  Taste buds are not found on top of papillae, but on the side of their folds  Sensory pathway of taste: 1. Chemicals must dissolve in saliva and enter the folds in order to activate receptors 2. Chemical binds to receptor on taste buds and triggers production of second messenger (cAMP) 3. cAMP is hydrolyzed to open or close ion channel, causing an influx or outflux of ions 4. Receptor cells then releases neurotransmitter to postsynaptic cells and the impuls is carried away  Sweet tastes are sensed mainly by taste buds at the front of the tongue, salty on the anterior sides, sour on the posterior sides, and bitter at the back of the tongue. Areas of salty and sour tastes overlap on the sides of the tongue. The Nose 26  Sense smell is carried by the olfactory nerve, but pain and temperature is carried by trigeminal  The nose is mostly cartilage. Septal cartilage forms wall between nasal cavities.  Medial side of nasal cavity is smooth, but lateral side has turbinate bones covered in epithelium protruding inwards. The rich blood supply to this epithelium warms inhaled air and traps dust in mucous membrane.  Air sinuses within head make head lighter and communicate with naso-pharynx  Inflammation of nasopharyngeal epithelium can lead to blockage of sinus openings, preventing sinus drainage and equilibration and causing pain.  Eustachian tubes and lacrimal ducts also drain into nasopharynx Smell  Olfactory receptors are found solely on roof of nasal cavity  Inhaled air is warmed and moistened by nasal mucosa. Some odorants dissolve into mucosa  Dissolved odorants bind to dendrites of olfactory receptors and activate them in a similar fashion to taste buds  Olfactory receptors send axons through pores in the cribiform plate to the olfactory bulb  The olfactory nerve then transmits the signal to the pyriform lobe of the olfactory cortex (olfactory perception), the mammillary bodies of the limbic system (memory) and the amygdale (fear/sexual response) Special Senses – Vision Innervation of the eyes  Visual information is carried by optic nerve  Cranial nerves III, IV and VI control movement of eyeballs  Trigeminal nerve provides general sensory perception, especially in corneas  Facial nerve provides parasympathetic innervations of lacrimal glands Visual areas of the cerebral cortex  Primary visual cortex is located in the occipital lobe at the back of the brain  Visual association area is just anterior to occipital lobe  Eye movements are coordinated by an area in the frontal cortex just anterior to the precentral gyrus  Over 50% of the brain is involved with vision in someway  Over 70% of all sensory receptors are in the eyes, making it the dominant sense Eyes  Eyeballs are located in bony cavity called orbit and are imbedded in fat for easy movement  Eyes are actually part of the central nervous system: sclera is analogous with the dura mater, blood vessels of eye are branches of internal carotid  Fields of vision overlap to provide stereoscopic (3-D) vision  Two chambers of the eye divided by the lens of the eyes: anterior portion filled with watery aqueous humour, posterior portion filled with gel-like vitreous humour  Wall of the eyeball consists of three layers: fibrous tunic, vascular tunic and retina  Fibrous tunic 27 o Back layer is the sclera: white of the eye. Dense connective tissue consisting of collagen fibres and fibroblasts. Important for support and shape o Front area is the cornea: transparent avascular layer responsible for 80% of refractive power (air/water interface) and focussing of incoming light onto retina o Outer layer of cornea consists of stratified squamous epithelium, middle layer is connective tissue called stroma and inner layer is simple endothelium. o Stroma consists of collagen fibres secreted by fibroblasts in regularly spaced and parallel arrays: form a crystalline structure. o Epithelium and endothelium constantly transport Na and Cl ions out of stroma to dehydrate it and ensure it retains its crystalline structure. o Conjuctiva is a thin protective mucous membrane that covers the sclera (not the cornea) and is reflected on the inside of the eyelids. It is Continuous with corneal epithelium. o Infection or irritation causes reddening of the conjunctiva: bloodshot eyes  Vascular tunic o Posterior portion is the highly vascular choroid. It lines the internal surface of the sclera and provides it with nutrients. It also produces melanin to prevent glare o In the anterior portion, the choroid becomes the ciliary body, which contains ciliary muscles and ciliary processes. o Ciliary processes are folds on the inner surface of the ciliary body. They contain capillaries that secrete aqueous humour, which drains through the pupil into the anterior chamber, then out through the sclera venous sinus (circular canal of Schlemm). o Ciliary muscle adjust the lens for accommodation. They are attached to the lens via zonular fibres which extend from the ciliary processes o The iris is the coloured portion of the eyeball. It is suspended between the cornea and the lens and is attached at its outer edge to the ciliary processes. o The iris consists of melanocytes that absorb light and smooth muscle fibres that alter the size of the pupil. Parasympathetic input from cranial nerve III causes the circular muscles (sphincter pupillae) to contract and constrict the pupil. Sympathetic neurons cause the radial muscles (dilator pupillae) to contract, dilating the pupil  Retina o Innermost coat of the eyeball that serves as beginning of visual pathway. o Retina consists of a pigmented layer and neural layer o Pigmented layer consists of melanin-containing epithelial cells that absorb light and prevent glare similar to the choroid o Neural layer consists of photoreceptor layer, bipolar cell layer and ganglion cell layer o Photoreceptor layer contains two types of photoreceptors: rods and cones  Rods are used for vision in dim light, and only provide black and white vision  Cones require more light to be stimulated but can differentiate colour  Three cone types register specific colours: red, blue and green  The ventral fovea is located in the centre of the visual axis, and contains only cones. Fovea is the area of highest visual acuity.  Rods are found more towards the periphery; dim objects such as stars are more visible if you look slightly to the side of them o Bipolar cell layer is found above the photoreceptor layer. Bipolar cells synapse with rods and cones and send the signal to ganglion cells o Ganglion cells converge at the optic disc to form the optic nerve o The optic nerve connects to the retina at the optic disk, which forms the blind spot 28 o Outer layer of veins and arteries also enters the eye with the optic nerve and provides blood supply to the retina from the front (in front of the photoreceptors) o Central fovea lacks bipolar layer, ganglion layer and superficial blood supply in order to maintain high visual acuity. Lens  Regularly arranged lens fibres: essentially cells that lack organelles. Instead filled with proteins called crystallins. Only cells at periphery contain organelles.  Crystallins are exactly the same shape and arranged in a regular array in order to be completely transparent (like the cornea)  Lens fibres articulate with adjacent fibres with “ball-and-socket joints”. This allows them to move freely when the lens is adjusted for accommodation  Lack of organelles means fibres and proteins within are not renewed, and degrade past the age of 40. The fibres stiffen up and lens cannot be adjusted. Known as presbyopia Glands of the eyes 1. Lacrimal glands  Located under the bone beneath the eyebrow. Almond-sized gland that secretes lacrimal fluid (tears) onto the conjunctiva through 6-12 excretory lacrimal ducts  Tears wash over eye and enter lacrimal caruncle, draining into the lacrimal duct, which in turn drains into the nasal cavity  Supplied by parasympathetic branch of facial nerve  Lacrimal fluid serves as lubrication and cleanser. It washes away irritants and kill bacteria with a bactericidal enzyme called lysozyme 2. Tarsal glands  Glands imbedded in the tarsal plate (connective tissue that gives eyelids shape).  Can be seen as yellow bands on underside of eyelid  Produce oily substance that is secreted just under eyelashes. Prevents lacrimal layer on eyes from drying out and lubricates eyelids when they blink 3. Sebaceous glands  Found at the base of eyelash  Similar to sebaceous glands found in every other hair Vision problems 1. Myopia (near-sightedness)  Caused when eye ball is too long or the lens is too thick  Found in 30% of population (but is either not severe or is correctable)  Correctable by concave lenses 2. Hyperopia (far-sightedness)  Caused when eyeball is too short or lens is too thin  Found in 60% of population (but is either not severe or is correctable)  Correctable by convex lenses 3. Astigmatism  Caused by irregular curvature of cornea or lens  Causes a directional blur of vision  Can be corrected by lenses that correct specific irregularities 4. Presbyopia 29  Caused by stiffening of the lens fibres  Lens loses elasticity and is unable to accommodate near vision  Particularly affects hyperopic individuals  Affects persons over the age of 40; can be corrected with bifocals 5. Cataracts  Caused by damage to corneal epithelium, either by chemical or physical injury  As corneal cells die and ion pumps stop, cornea fills with water and becomes cloudy  Can be fixed by corneal transplant; cornea is avascular so there is no immune response 6. Lens Cataracts  Caused when fibres of lens become irregular and become cloudy or opaque  Can be fixed by removing lens and inserting an artificial lens.  Artificial lens cannot be adjusted, and patients still require glasses for near vision 7. Glaucoma  Caused by overproduction of aqueous humour causing increased intraocular pressure  Causes strangulation of the optic nerve, and can lead to blindness.  Medical emergency that can be helped by topical drugs that increase venous drainage MSK – Peripheral Nervous System Peripheral Nerves  Mixed spinal nerves are named from which segment of the vertebral column they originate from  8 cervical nerves from 7 cervical vertebrae (C1 nerve originates above C1 vertebrae)  12 thoracic nerves from 12 thoracic vertebrae  5 lumbar nerves from 5 lumbar vertebrae  5 sacral nerves from 5 levels of sacrum  Spinal cord ends at L1 vertebra; spinal nerves L2-S5 exit vertebral column from cauda equine Limb compartments  Muscles in limbs are divided into compartments divided by fascia  Connective tissue underneath skin (fat and collagenous tissue) known as superficial fascia  Superficial fascia dives inwards to fuse with periosteum, forms interosseus membrane in limbs with two bones (ie forearm or leg), and fuses with superficial fascia on other side  Deep fascia separates muscles into compartments: flexor and extensor  Flexor and extensor compartments have their own vascular and nerve supply. This means every nerve is either a flexor nerve or extensor nerve.  As motor and sensory axons exit the spinal cord from the ventral and motor roots, they merge to form a mixed spinal nerve
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