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Anatomy and Cell Biology
Anatomy and Cell Biology 3319
Kem Rogers

preMajor Points & Things to Remember Embryology • Day 4-6 – early blastocyst (inner cell mass & blastocoele) • Day 9 – trophoblast invades wall – epiblast & hypoblast, yolk sac & amniotic sac • Day 11 – bilaminar embryonic disc – epiblast, hypoblast, yolk sac & amniotic sac • Day 16 – gastrulation & trilaminar embryo o Raised primitive node & streak o Some epiblast cells migrate inwards at streak to make mesoderm & to move hypoblasts down (endoderm – epithelial lining of tracts) o Rest of epiblast cells make surface ectoderm – epidermis, brain & spinal cord, neural crest sensory nerve cells & other nervous system cells o Epiblast cells (mesoderm) migrate anteriorly through node to form notochord • Day 17 – Neurulation o Notochord signals overlying ectoderm to start forming spinal cord & brain o Neural plate is forming • Day 19 o Neural crest cells are pulled into body o Neural groove starts to deepen overlying notochord • Day 20 o Neural folds form by folding of neural plate  which deepens to make neural groove o Neural fold cells migrate to form neural crest o Neural crest cells will leave ectoderm and move to mesoderm o Mesoderm differentiation  Notochord • Intervertebral discs  Somites • Starts off paraxial • Forms subectodermal bulges on the back – makes first body segments • Cranial  caudal • Dermis of dorsal cavity, part of vertebrae or ribs, muscles of trunk & limbs  Intermediate • Beside paraxial mesoderm & influenced by it • Divides into spherical segments • Cranial  caudal • Each attaches to somite  Lateral • Splanchnic mesoderm – next to endoderm (visceral) o Wall of digestive & respiratory tracts, visceral serosa, heart • Somatic mesoderm – next to ectoderm (body) o Connective tissues, dermis of ventral cavity & parietal serosa • Coelom in the middle of two mesoderms o Pleural, pericardial & peritoneal cavities • Day 22 - Neural folds have closed – neural tube is formed – detached from surface ectoderm Spinal Bifida – doesn’t zip in caudal (tail) region, leads to malformation of spine, spinal cord & lower limb nerves Anencephaly - doesn’t zip in rostral (cranial/head) region, rudimentary brain stem (no cerebral hemispheres) - die Ectopic pregnancy – tubal pregnancies (rupture possibility) & implantation can occur in cervix, ovaries, & abdomen Twins • 1 sperm, 1 egg – 1 zygote o Splitting at 2-cell stage – two blastocysts – different placenta, different amnions o Complete split of inner cell mass – one blastocyst – same placenta, different amnions o Split of inner cell mass later in development – one blastocyst – same placenta, same • 2 sperm, 2 egg – 2 zygotes o Different placenta, different amnions Introduction to CNS CNS – brain & spinal cord PNS – nerves & ganglia (collection of neuronal cell bodies) • Sensory (afferent) division o Somatic sensory  Touch, pain, pressure, vibration, temperature & proprioception, hearing, equilibrium & vision o Visceral sensory  Stretch, pain, temperature, chemical changes, irritation in viscera, nausea, hunger, taste & smell • Motor (efferent) division o Somatic motor  Motor innervation of all skeletal muscle o Visceral motor (autonomic nervous system)  Motor innervation of smooth muscle, cardiac muscle & glands • Parasympathetic – rest & digest • Sympathetic – fight or flight Neuron • Cell body o Contain chromatophillic substance (clusters of RER & ribosomes) & other organelles o Neurofibrils (intermediate neurofilaments) run between chromatophillic substances o Most located in CNS but ganglia (clusters of neuron cell bodies) lie along nerves in PNS • Neuron processes o Axon  No chromatophillic substance or organelles involved in protein synthesis  Neurofilaments, actin filaments & microtubules are important  Vary in length (if long called nerve fibre)  Can branch (axon collaterals) • Usually branches a lot at one end – terminal aborization • End in knobs – terminal boutons o Dendrites  Contain organelles & chromatophillic substances  Enlarged surface area, bring signals toward cell body • Synapse o Axodendritic – axon to dendrite o Axosomatic – axon to cell body o Terminal boutons contain synaptic vesicles  Plasma membranes of two neurons are separated by synaptic cleft Types of neurons • Multipolar (99%) o Motor neurons, interneurons (linkers) o Have more than 2 processes: many dendrites & 1 axon o Some have no axon • Unipolar o Sensory neurons (found in sensory ganglia in PNS) o No dendrites o Receptor  AP  down peripheral process  central process  brain & spinal cord • Bipolar o Sensory neurons o 2 processes that extend out from cell body o Only occur in special organs (inner ear, olfactory system & retina) o AP goes through cell body then onto central process • Sensory neuron – most pseudounipolar & cell bodies are in ganglia outside CNS, 2 processes function as 1 (carry impulses from receptors to CNS), some are bipolar • Motor neuron – multipolar & cell bodies are located in CNS (except for some of the ANS) • Interneurons – lie between sensory & motor neurons, multipolar neurons, confined entirely to CNS, chain linkers, 99% of neurons in the body Neuroglia – in CNS • Branching processes, & central cell body • Can divide throughout life & more numerous than neurons • Astrocytes o Most abundant glial cells of CNS o Radiating processes with bulbous ends – cling to neurons or capillaries o Regulate neurotransmitter levels by regulating uptake o Signaling increased blood flow through capillaries in the brain o Control ionic environments around neurons (calcium) o Promote neural growth • Microglial cells o Smallest & least abundant o Elongated cell bodies & cell processes o Engulf invading organisms o Do not originate in nervous tissue • Ependymal cells o CNS originates in embryo as a hallow neural tube and retains central cavity o Form simple epithelium that lines central cavity of spinall cord & brai o Permeable layer between cerebrospinal fluid and tissue fluid that bathes the cells of the cns o Help circulate cerebrospinal fluid • Oligodendrocytes o Fewer branches than astrocytes o Small groups & wrap their cell processes around the thicker axons in the CNS o Produce insulating covering – myelin sheath Neuroglia – in PNS • Schwann cell o Surround all axons in PNS o Produce insulting covering – myelin sheath • Satellite cell o Surround neuron cell bodies within ganglia PNS CNS Group of neuronal cell bodies Ganglion Nucleus – collection of neuronal cell bodies Basal ganglia – special collection of neuronal cell bodies Bundle of axonal fibres Nerve Tract/fasciculus column/funiculus lemniscus Development of CNS • Nervous system develops from dorsal ectoderm • Neural tube’s walls – Neuroepithelial cells – become CNS • Divide & migrate externally to form neuroblasts (future neurons) & neuroglial cells • Just external to neuroepithelium – neuroblasts cluster to form: (future gray matter) o Alar plate dorsally  interneurons (remain in CNS) o Basal plate ventrally  motor neurons (** some interneurons form from basal plate) • Axons that sprout from the young interneurons become the white matter • Neurons grow until 6 month of development – neuron formation slows • Just before slow down – neuroglial cells differentiate into astrocytes & oligodendrocytes • Neuroepithelium differentiates into a layer of ependymal cells • Sensory neurons arise from neural crest cells – cell bodies lie outside CNS • Axons elongate at growth cones – attracted by chemical signals (neurotrophins released from other neurons & astrocytes) • Neuroblasts sprout axons, which grow toward their targets o Receiving dendrites send out extensions to reach approaching axons & form synapses o Synaptic connections – determined by two factors  Amount of neurotrophin initially received by axon  Degree to which a synapse is used after being established o Overproduction of neurons – some die via apoptosis Embryonic development of the brain • Rostral portion of neural tube becomes the brain, caudal portion becomes the spinal cord • Starts to expand & 3 primary brain vesicles o Prosencephalon – forebrain & most anterior o Mesencephalon – midbrain o Rhombencephalon – hindbrain & most posterior • Week 5 - formation of 5 secondary brain vesicles o Prosencephalon  telencephalon (endbrain) & diencephalon (through-brain) o Mesencephalon  mesencephalon - remains undivided o Rhomencephalon  metencephalon (afterbrain) & myelencepahlon (brain like spinal cord) • Formation of 2 flexures cause telencephalon & diencephalon to angle toward brain stem o Midbrain flexure o Cervical flexure – around neck of future fetus • Each secondary brain vesicle develops major structures o Telencephalon: 2 lateral swellings become cerebral hemispheres (& white matter and basal nuceli) o Diencephalon: thalamus, hypothalamus & epithalamus, retina o Mesencephalon: brain stem - midbrain o Mentecephalon: brain stem - pons & cerebellum o Myelencephalon: brain stem – medulla oblongata o Spinal cord • Central cavity of neural tube enlarges to form hallow ventricles of brain – filled with cerebrospinal fluid • Hemispheres grow posteriorly over brain – envelop diencephalon & midbrain (superior part of brain stem) • As each cerebral hemispheres grows & it bends into a horseshoe shape (c-shape) & by week 26 – growth causes creasing Basic parts & organization of the brain • 4 parts - brain stem, cerebellum, diencephalon & cerebrum • Gray matter of CNS contains: short, non-myelinated neuron & neuron cell bodies • White matter: non-myelinated & myelinated axons • Spinal cord & brain have inner region of gray matter adjacent to ventricles - surrounded by white matter • Difference occurs because during brain development – certain groups of neurons migrate externally to form collections of gray matter in regions that otherwise consist of white matter • Surface sheets of gray matter: cortex o Sheet covering cerebellum – cerebellar cortex o Sheet covering cerebrum – cerebral cortex • All other gray matter – from of clusters of neuron cell bodies: brain nuclei • Ependymal cells from a simple epithelium that lines the central cavity of spinal cord & brain • Ependymal cells form permeable layer between cerebrospinal fluid that fills cavity & tissue fluids that bathe cells of the CNS • Ependymal cells bear cilia that help circulate cerebrospinal fluid Ventricles • Paired lateral ventricles – lie in cerebrum, horseshoe shape (bending of hemispheres), lie close together anteriorly and separated by thin membrane septum pellucidum rd • 3 ventricle – lies in diencephalon, anteriorly connects to each lateral ventricle through interventricular foramen • In midbrain – thin tube-like central cavity is cerebral aqueduct - connects 3 & 4 ventricle • 4 ventricle – lies in brain stem, dorsal to pons and superior half of medulla, three openings occur in walls: paired lateral apertures & median aperture (roof) – holes connect ventricle with subarachnoid space – allows cerebrospinal fluid to fill ventricles, connects caudally to central canal of inferior medulla & spinal cord Comparison of 5.5 weeks & adult CNS • Spinal cord - ventral horn: basal plate  motor neurons • Spinal cord – dorsal horn: alar plate  interneurons & cell processes of sensory neurons from dorsal ganglia Cerebral Hemispheres • Most rostral part of brain • Important fissures (deep grooves) o Transverse cerebral fissure – separates cerebrum from cerebellum o Longitudinal fissure – separates two hemispheres • Composed of o Superficial gray matter (cortex) – neuron cell bodies o Cerebral white matter – fibre tracts (white because of myelination) o Deep gray matter (basal ganglia) – deep collection of neuron cell bodies • Sulci - shallow grooves Gyri – ridges of tissue Lobes • Frontal o Extends posteriorly to central sulcus – separating it from parietal lobe  Precentral gyrus (primary motor cortex) – voluntary movement  Premotor cortex (motor association area) – planning movement  Frontal eye field – eye movement  Broca’s area – speech production  Anterior association area (prefrontal cortex) - executive control (decision making, task management, working memory, complex tasks)  Limbic association area (cingulate gyrus) – emotional response • Parietal o Extends anteriorly to central sulcus and posteriorly to parietal-occipital sulcus  Postcentral gyrus (primary somatosensory cortex) – somatosensory  Somatosensory association cortex – interpreting somatosensory stimuli  Wernicke’s area – speech understanding (within posterior association area)  Posterior association area – spatial awareness of objects, sound & body parts • Occipital o Posterior lobe o Separated anteriorly from posterior lobe by parietal-occipital sulcus  Visual cortex – vision  Visual association area – interpreting visual stimuli • Temporal o Lateral side of each hemisphere o Separated from parietal & frontal lobes by lateral sulcus  Auditory cortex – hearing  Auditory association cortex – interpreting auditory stimuli  Olfactory cortex – smell  Limbic association area – emotional response & memory • Insula o Buried deep within lateral sulcus o Covered by temporal, parietal & frontal lobes – need to peal back along lateral fissure  Gustatory cortex – taste  General visceral sensations  Equilibrium Sensory Association Areas Somatosensory Area • Primary somatosensory cortex – post-central gyrus o Input: general somatic senses (touch, pressure, pain, vibration, temperature from skin & proprioception of muscles/joints) o Conscious awareness o Sensory receptors  spinal cord  thalamus  primary somatosensory cortex o Cortical neurons process information & identify area being stimulated o Sensory input map: sensory homunculus  Representation is upside down – face on inferolateral postcentral gyrus & toes at the superomedial  Amount devoted to each body part reflects sensitivity – fingers & lips = most sensitive o Contralateral projection – right hemisphere receives input from left side of the body o Damage: destroys conscious awareness of sensations • Somatosensory association cortex o Lies posterior to primary somatosensory cortex o Integrates sensory inputs into comprehensive understanding Visual Areas • Primary visual cortex o Posterior & medial part of occipital lobe – buried within calcarine sulcus o Largest of all sensory areas o Input: visual information that originates from retina o Contralateral projection – right half of visual space is represented on left visual cortex o Processing is very low – orientation of objects & merging sensory stimuli from both eyes o Damage: person has no conscious awareness of what is being viewed – functional blindness • Visual association area o Surrounds primary visual cortex – covers much of occipital lobe o Continues processing visual information – analyzing colour, form & movement Auditory Areas • Primary auditory cortex o Input: conscious awareness of sound (loudness, rhythm, pitch) o Located on superior edge of temporal lobe – inside lateral sulcus • Auditory association cortex o Lies just posterior & lateral to primary auditory area o Evaluation of sound (talking, screech, thunder or music) Vestibular (Equilibrium Cortex) • Conscious awareness of sense of balance • Position of head in space • Located in posterior part of inslu – deep to lateral sulcus Gustatory Cortex • Conscious awareness of taste stimuli • Lies in insula Olfactory Cortex • Primary olfactory cortex o Conscious awareness f smell o Lies on medial temporal lobe – small region piriform cortex o Dominated by hook-like uncus o Olfactory nerves in nasal cavity  olfactory cortex o Part of area: rhinecephalon: olfactory related cerebral areas - piriform cortex, olfactory tract & olfactory bulb Visceral Sensory Area • Located deep to lateral sulcus on insula • Receives general input: pain, pressure, hunger from thoracic and abdominal organs Motor Areas • All lie in posterior part of frontal lobe • Primary motor cortex – precentral gyrus o Anterior to primary sensory cortex o Contains large neurons: pyramidal cells o Long axons of pyramidal cells form massive pyramidal tracts – descend through brain stem & spinal cord o Axons synapse on motor neurons to allow movements o Contralateral projection – right motor cortex sends information to left side of the body o Motor output map: motor homunculus  Represented upside down – head on inferolateral part of gyrus & toes at superomedial end  Face & hand muscles • Premotor cortex o Anterior to pre-central gyrus o Plans & coordinates complex movements & relays plan to motor cortex o Receives highly processed information from sensory & multimodal regions of cortex o Control voluntary actions that depend on sensory feedback about spatial relations (moving hand through a maze) • Frontal eye field o Anterior to premotor cortex o Controls voluntary movement of the eyes • Broca’s Area o Anterior to inferior part of premotor cortex in left hemisphere o Left hemisphere controls motor movements required for speaking o Connected to language comprehension areas (Wernicke’s area) o Right hemisphere controls emotional overtones given to spoken words o Damage: deliberate, non-fluent speech with impaired articulation – understands speech Multimodal Association Areas • Posterior association area o Located at interface of visual, auditory & somatosensory association areas in parietal & temporal lobes o Integrates sensory information to form a unified perception o Function One:  Body sense: awareness of spatial location of body in reference to itself and environment (ongoing input) • Integrated to determine how to move limbs through space and relays information to anterior association area (motor) o Visual streams  Dorsal stream • Extends through posterior parietal cortex, postcentral gyrus • Where pathway – location of objects  Ventral stream • Extends through inferior part of temporal lobe • What pathway – identifying what things are o Auditory streams  Posterolateral • Through parietal lobe to lateral part of frontal lobe • Where pathway - evaluates location of sound  Anterolateral • Anterior temporal lobe to inferior frontal lobe • What pathway – sound identification o Function Two  Left Side • Regions that function in speech comprehension – Wernicke’s area (coordinates with Broca’s area) • Coordination of auditory and visual aspects of language (naming objects & reading words) • Damage: difficulties with language comprehension – speech is not impaired  Right side • Creative interpretation of words • Control emotional overtones of speech • Anterior association area o Large anterior region of frontal lobe o Input: highly processed sensory information from posterior association area o Plans & initiates motor responses o Coordinated movements require ongoing sensory input o Cognitive functions – thinking, perceiving, remembering & recalling information, processing abstract ideas, reasoning & judgment, impulse control, long-term planning, complex problem solving, mental flexibility, social skills, appreciating humor, empathy & conscious o Damage – mental & personality disorders, mood swings, loss of attentiveness, loss of inhibitions/judgment o Last parts of brain to mature • Limbic association area o Located on medial side of cerebral hemisphere in portions of temporal, parietal, & frontal lobes o Includes cingulate gyrus, hippocampus & parahippocampal gyrus o Involve din memory & emotion o Integrates sensory & motor behaviour with past experiment and helps form memories Lateralization of cortical functioning • Most people o Left hemisphere has greater control of: language abilities, math & logic o Right hemisphere has greater control of: creative thinking, visual spatial skill, facial expressions, emotion, facial expressions White Matter of Cerebrum • Underlies gray matter • Many fibres – allow communication between various areas • Most are myelinated & bundled into large tracts • Commissural fibres o Cross from one side of the CNS to the other o Interconnect hemispheres o Largest: corpus callosum • Association fibres o Connect different parts of the same hemisphere o Short connect neighbouring areas and long connect widely separated areas • Projection fibres o Descend from cerebral cortex to more caudal parts of CNS or ascend to cortex from lower regions o Fibres run vertically unlike commissural & association fibres which run horizontal o Deep to cerebral white matter – internal capsule  Passes between thalamus and basal ganglia o Corona radiate  Superior to internal capsule  Running to and from cerebral cortex fan out Clinical Applications • Hemispherectomy – one hemisphere is removed or disabled • Alzheimer’s & dementia • Seizures – interconnectivity of white matter – strong signal is passed uncontrollably from one hemisphere to another • Prosopagnosia – face blindness – ability to recognize faces is impaired while other aspects of visual processing are intact • Agnosias – loss of ability to recognize objects, persons, sounds, shapes or smells – specific sense is not defective nor is there memory loss • Aphasias – disturbance of comprehension & formulation of language cause by dysfunction in different areas o Broca’s aphasia o Wernicke’s aphasia • Apraxias – loss of ability to execute learned purposeful movements – despite desiring and having the physical ability o Distribution of motor planning Basal Ganglia • Deep gray matter of cerebrum o Basal nuclei - involved in motor control o Basal forebrain nuclei – associated with memory o Claustrum – brain nucleus of unknown function o Amygdaloid body – part of limbic system • Basal part of forebrain/telencephalon - cluster of neurons in PNS deep within cerebral white matter • Striatum = caudate nucleus & putamen (some fibres of internal capsule passing through them created a striated appearance) • Pallidum = globus pallidus (internal & external) & ventral pallidum • Substantia nigra = pars reticular and pars compacta • Claustrum • Amygdala • Subthalamic nucleus • Corpus striatum – striatum & globus pallidus • Lentiform nucleus – globus pallidus & putamen • Clinical definition – corpus55 striatum, substantia nigra & subthalamic nuclei • Anatomical definition – striatum, pallidum, claustrum, amygdala • Caudate nucleus – arches superiorly over thalamus & lies medial to internal capsule • Globus pallidus & putamen – lateral to internal capsule • Function o Start, stop & regulate intensity of voluntary movement ordered and executed by cerebral cortex o Select appropriate muscles for the task and inhibit antagonistic muscles o Control rhythmic, repetitive tasks & participate in learning of habits o Involved in estimating passage of time Motor control hierarchy • Strategy/goal – association area of the cortex: prefrontal & ideomotor & basal ganglia • Tactics – muscle contractions: motor cortex, premotor cortex, cerebellum • Execution – activation of motor neurons: brainstem & spinal cord Direct Pathway – Movement 1. Motor cortex sends excitatory response (glutamate) to striatum (D1 receptors) 2. Increase in firing of neurons in caudate & putamen 3. Increased inhibitory response (GABA) directed towards globus pallidus (internal) & substantia nigra (pars reticular) 4. Less inhibition of thalamus 5. Thalamus is activated and stimulates motor cortex (glutamate) 6. Motor cortex is activated 7. Muscle contraction Indirect Pathway – Stop 1. Motor cortex sends excitatory response (glutamate) to striatum (D2 receptors) 2. Increase in firing of neurons in caudate & putamen 3. Increased inhibitory response (GABA) directed towards globus pallidus (external) 4. Less inhibition of subthalamic nucleus 5. Stimulate (glutamate) globus pallidus (internal) 6. Increased inhibition on thalamus 7. Decreased excitatory stimulus (glutamate) from thalamus to motor cortex 8. Less movement Substantia nigra pars compecta – stimulates D1 but inhibits D2 • Parkinson’s o Degeneration of dopaminergic cells in substantia nigra o Direct: Less excitation of D1 recetLess inhibition of internal globus plGreater inhibition of thalmus Less activation of motor areas o Indirect: Less inhibition of D2 receptors  More inhibition of external globus pallidus  Less inhibition of subthalamic nuclei  More activation of globus pallidus internal  More inhibition of thalamus  Less activation of motor areas o Symptoms: slow, jerky movements, muscle rigidity, slow tremors, bradykinesia, difficulty initiating movement • Huntington’s o Atrophy of striatum, damage of intrinsic inhibitory circuits o Direct: No inhibition of striatum  greater activation of neurons  more projections to internal globus pallidus  less inhibition of internal globus pallidus  less inhibition on thalamus  greater activation of motor areas o Indirect: More activation of D2 receptors  More inhibition of external globus pallidus  Less inhibition of subthalamic nuclei  More activation of globus pallidus internal  more inhibition of thalamus  Less activation of motor areas o Symptoms: brisk, jerky purposeless movements of limbs • Dyskinesia o Lesions of basal ganglia o Unwanted voluntary movements • Schizophrenia o Changes in dopamine release in nucleus accumbens (basal part of striatum) o Connections to lateral prefrontal cortex & involved in addictive behaviors Diencephalon Thalamus • Paired structure that makes up 80% of diencephalon • Inferior to corpus callosum – forms superolateral walls of 3 ventricle - 3 ventricle separates two halves of thalamus • Right and left parts – joined by interthalamic adhesion (intermediate mass) • Categories of nuclei o Modality specific: primary cortical, sensory or motor areas o Association: anterior, LD, LP, MD & pulvinar o Non-specific: reticular to thalamus – (reticular to thalamic for arousal & intralaminar group to areas for cortical arousal • Internal medullary lamina – divides the thalamic nuclei into 3 groups: o Anterior nuclei o Medial group including medial dorsal nucleus o Large lateral nuclear groups • Afferent impulses from all senses except olfaction converge in the thalamus which then amplifies or tones signals • Descending tract passes lateral to thalamus as internal capsule • Nuclei (12 major – bilateral distribution) o Ventral posterolateral nucleus – pain & temperature, tactile, pressure, conscious proprioception o Ventral posteromedial nucleus – pain & temperature, tactile, pressure, sensations from head, conscious proprioception o Medial geniculate nucleus – auditory relay required for auditory perception & discrimination o Lateral geniculate nucleus – visual relay required for vision & visual perception o Mediodorsal thalamic nucleus – olfactory relay o Ventral anterior nucleus – provides feedback pathway to motor regions of cortex necessary for motor functions
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