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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