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Lecture 5 - Nervous system - 6 per page JZ.pdf - 20171004...

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Unformatted text preview: 2017‐10‐04 Outline Nervous system Spinal cord and spinal nerves (Ch. 13) • Organization • Cross section organization • Ascending, descending tracts • Spinal nerves • General anatomy of nerves and ganglia • Plexuses – networks of intersecting nerves • Nervous tissue (Ch. 12) • Overview of the nervous system • Properties of neurons • Neuroglia, myelination Resources: 12.1‐12.3 13.1‐13.2 Labs 16‐17 Endocrine: Producing hormones, blood stream, affect physiology of distant cells Behavour/perception is rapid. Fast electrical signalling, chemical Immune: Stress responce Urinary: Water in blood, hormones urinary system, detirmine 7-9 minutes Internal communication Endocrine and nervous system maintain internal coordination 1. Endocrine system • uses hormones secreted into blood • “long‐distance” communication • slow • Nervous system is tightly integrated with all other body systems 2. Nervous system • uses electrical and chemical means • sends message from cell to cell • very quick (e.g. reflexes, perception) CNS, PNS CNS: Brain spinal cord PNS: Nerves, distributed throughout body, long cells, bundles of axons Gangilon, knot like 5-7 minutes 3-4 minutes Nervous system components Central nervous system (CNS) • Brain and spinal cord • Enclosed by cranium and vertebral column Peripheral nervous system (PNS) • Everything else distributed through body: cranial and spinal nerves, ganglia • Composed of nerves and ganglia • Nerves ‐ bundle of nerve fibres (axons) wrapped in fibrous connective tissue • Ganglion ‐ knot‐like swelling in a nerve where neuron cell bodies are concentrated • Two divisions (sensory and motor), each with somatic and visceral subdivisions Nervous system organization: input/ output 1. Sense organs receive information and transmits coded messages to the CNS Information: patterned changes in body or external environment 2. CNS processes the information, determines appropriate response 3. CNS issues commands to muscles and gland cells to carry out the response 1 2017‐10‐04 Sensory: Somatic, skeletal muscles Motor: output Visceral: Motor output Reflexive involuntary control 1-2 minutes 5-7 minutes Functional classes of neurons Afferent neuron Efferent neuron Peripheral Nervous System 1. Sensory (afferent) division Somatic • Signals from skin, muscles, bones, and joints Visceral • Signals from the viscera (heart, lungs, stomach, and urinary bladder) Interneuron 1. Afferent (sensory) neurons • Detect stimuli and transmit the information toward the CNS 2. Interneurons in CNS 2. Motor (efferent) division Somatic • Carries signals to skeletal muscles • Produces muscle contractions Visceral (autonomic nervous system) • Signals to glands, cardiac, and smooth muscle • Involuntary responses are visceral reflexes • Connecting neurons ‐ carry out integrative functions (make decisions) • About 90% of our neurons are interneurons 3. Efferent (motor) neurons • Sends signals to muscles and/or gland cells 1 minute or less 1 minute Visceral motor division (autonomic nervous system) • Subdivisions: 1. Sympathetic division • Tends to arouse body for action (“fight or flight”) • Accelerates heart beat and respiration • Inhibits digestive and urinary systems 2. Parasympathetic division • Tends to have a calming effect (“rest and digest”) • Slows heart rate and breathing • Stimulates digestive and urinary systems important differences in structure: Discuss later next week **Both output systems, two neurons involoved, short preglyanic nerve, synpase between two, closer NOTE GENERAL DIFFERENCE Vagus nerve: Goes down *** 7 minutes Sympathetic Note general differences in nerve organization Neurons cannot be stretched Secretion on terminal end **Structure, dentrites branches one end recieving signal from other neurons ** Explained the route of signal transmittion (diagram) 5 minutes NOTE: Information flow (action potential) is one-way Parasympathetic Properties of neurons 1. Excitability ‐ will respond to stimuli (environmental changes) 2. Conductivity ‐ produce electrical signals that are quickly conducted to other cells at distant locations 3. Secretion ‐ when signal reaches the end of a nerve fiber, a neurotransmitter will be released that crosses the gap and influences the next cell Note: information flow (action potential) is one‐way Excitation Conduction Secretion 2 Axon: Trigger zone: Membrane potential axon hillok One axon per neuron, can get branches 2017‐10‐04 Schwan cells: Myolin sheath Synaptic knobs: Filled neuron transmitters Synapse: Neurons are communicating More dendrites: more connection, more info can receive soma: Protein synthesis, nucleous is there 3-4 minutes 8-9 minutes Neuron structure • Dendrites • receiving signals from other neurons • branches off of the soma • more dendrites a cell has, the more information it can receive • Soma (a.k.a. neurosoma or cell body) • single, centrally located nucleus • cytoplasm contains organelles (mitochondria, lysosomes, Golgi apparatus, inclusions) • extensive rough ER and cytoskeleton Neuron structure Axon • Nerve fibre, originates from a mound on the soma called the axon hillock • Only one axon per neuron (some have none) • axon collaterals – branches of axon • branch extensively on distal end • Cylindrical, relatively unbranched for most of its length • For rapid conduction of signals to distant points • Axoplasm – cytoplasm of axon • Different from other cytoplasm in the cell, well equipped to facilitate an electrical signal • Axolemma – plasma membrane of an axon **kinrsin and dynein Neuron structure Axon • Myelin sheath may enclose it • Distal end has terminal arborization • Extensive complex of fine branches • Synaptic knob (terminal button) is a little swelling that forms a junction (synapse) with the next cell • Contains synaptic vesicles full of neurotransmitter • Many different neurotransmitters, vary depending on circuit • Examples: dopamine, acetylcholine, norepinephrine, glutamate • May be excitatory (increase probability of action potential in post‐synaptic neuron) or inhibitory (decrease probability of AP) Anterograde and retrograde Slow: bigger components - regernderation ** Retergrade: Bring back to recycled. Pathogens will invade CNS this way ex. Polio, HEP, entering nverous system through these transport 3-5 minutes Axonal transport • Axonal transport = two‐way transport of proteins, organelles, and other material along an axon • Anterograde – movement down axon away from soma • Retrograde – movement up axon toward the soma 1. 2. Fast – 20‐400 mm/day • Anterograde transport • Organelles, enzymes, synaptic vesicles, and small molecules • Retrograde transport • Recycled materials and • Some pathogens hitch a ride this way (rabies, herpex simplex, tetanus, polio) • Delay between infection and symptoms is time needed to transport up axon Slow – 0.5‐10 mm/day • Always anterograde • Stops and starts • Moves enzymes, cytoskeletal components, and new axoplasm for repair/regeneration Axonal transport • Axons are long (>1 m in PNS) and have a dense cytoskeleton aiding transport • Many proteins made in soma must be transported to axon and axon terminal • i.e. proteins to repair axolemma, channel proteins, enzymes, neurotransmitters Microtubules guide materials along axon (Ch. 3.4) • Motor proteins carry materials while the move along microtubules (similar to myosin head ratcheting on actin) • Kinesin – anterograde transport • Dynein – retrograde transport ‐uuk4Pr2i8 ; Most common: Brain Multipolar, branching dentrites, recieve lots info Bipolar: special sensories Unipolar: Single process rapid reflexes Anaxonic: no axon, no action potential minor electrical effects on surrounding cells **no axons, some graded effect on adjacent cells** Neuron types Multipolar • Most common type; most neurons in CNS are this kind • Multiple dendrites, one axon Bipolar • Olfactory cells, retina, inner ear (special senses) • One dendrite and one axon Unipolar • Sensory cells from skin and organs to spinal cord (dorsal root ganglion) • Has a single process leading away from soma Anaxonic • Retina, brain, and adrenal gland • Many dendrites, no axon • Non‐spiking (AP), but has effects on electric potential of adjacent cells 3 2017‐10‐04 5 minutes Protect, nourishing, help singnal, structure support Neuroglia (supportive glial cells) Neuroglia in CNS • Protect neurons and help them function Four types in CNS: • Bind neurons together and form framework for nervous tissue Ependymal cells – line internal cavities of the brain, secrete and circulate cerebrospinal fluid (CSF) • cilia on apical end help circulate CSF Oligodendrocytes – form myelin sheaths in brain and spinal cord that speed conduction Microglia – type of white blood cell (macrophage) • wander through CNS looking for damage/debris; phagocytose dead materials • accumulate at sites of injury • also involved in synaptic remodeling (neuroplasticity) Schwann, binds keeps wrapping around Satellite cells: Elcectrical insulation Regulaitng chemical enviroment Know asterocytes Neuroglia in CNS Astrocytes • most abundant glial cell in CNS, covers brain surface and most non‐synaptic regions of neurons in the gray matter Neuroglia in PNS Two types in PNS: 1. Schwann cells • Functions: 1. 2. 3. 4. 5. Form supportive framework Extensions (perivascular feet) that contact blood capillaries and stimulate them to form a tight junction seal (blood‐brain barrier) Secrete nerve growth factors – neuropeptide aiding growth, survival of neuronse Communicate electrically with neurons Regulate chemical composition of tissue fluid by absorbing excess neurotransmitters and ions • When a neuron is damaged, have asterocytosis/sclerosis, which is astrocytes forming scar tissue to fill the space Myelination • Myelin sheath is insulation around a nerve fibre Text • Envelop nerve fibres, winding repeatedly around each fibre • Produce a myelin sheath similar to oligodendrocytes in CNS • Assist in regeneration of damaged fibres 2. Satellite cells • Surround neurosomas in ganglia of the PNS and provide electrical insulation around the soma • Regulate chemical environment of the neurons • Similar role to astrocytes in CNS Myelin sheath segmentation • Many Schwann cells or oligodendrocytes cover one nerve fibre • Formed by: A. Oligodendrocytes in CNS B. Schwann cells in PNS • Consists of the plasma membrane of glial cells • 20% protein, 80% lipid (phospholipids, glycolipids, cholesterol) • Speed of conduction linked to: myelination, diameter (larger diameter faster) • Sheath is segmented: • Axon hillock – tapering of soma before axon • Trigger zone for action potential • Nodes of Ranvier • gaps between segments • Internodes • myelin covered segments fromone gap to the next Fig. 12‐6 4 2017‐10‐04 Myelin: Mostly liquids Schwan cells wraps around, leaves cell membrane behind Myelination in the PNS vs. CNS Neurilemma • thick, outermost coil of myelin sheath • contains nucleus and most of cytoplasm • Each Schwann cell spirals repeatedly around a single nerve fibre • as many as 100 layers of membrane • no cytoplasm between inner membranes • Oligodendrocytes • myelinate several nerve fibres in its immediate vicinity • cannot migrate around any one of them like a Schwann cell • must push newer layers of myelin under the older ones, so myelination spirals inward toward nerve fibre • no neurilemma or endoneurium Unmyelinated nerve fibres • Many CNS and PNS fibres are unmyelinated • In PNS, Schwann cells hold small nerve fibres in surface grooves • Membrane folds once around each fibre • Slower signal, however, usually small cells so it is not essential to be fast • Found in gray matter on the exterior of the brain MS ** note!! Neuron resilience • Mature neurons have no centrioles (long lived) • But regeneration of neural stem cells can occur in some areas of the brain (hippocampus – medial temporal lobe, limbic system) Nerve regeneration in PNS: • Can regenerate if some endoneurium in tact • Need endoneurium and schwann cells for regeneration Steps: • Macrophages remove degenerated axon and schwann cells • Muscle atrophies without innervation • New schwann cells align along endoneurium, followed by axon growth Spinal cord • ‘Information highway’ that connects the brain and lower body Brain tumors (gliomas) and myelin diseases • Most brain tumors arise from glial cells (others from meninges or metastasized) • Glial cells are mitotically active throughout life, unlike the long‐lived neurons • Often treatment via radiation or surgery due to blood‐brain barrier for some drugs • Diseases of myelin: • Multiple sclerosis (MS) ‐ oligodendrocytes deteriorate, disrupting neuronal signaling. • Tay‐Sachs disease– overproduction of glycolipid in myelin (insufficient catabolic enzyme activity). High incidence in eastern European jewish ancestry. Frontal section of the brain with a large tumor (glioblastoma) in the left cerebral hemisphere Spinal cord functions 1. Conduction • nerve fibers conduct sensory and motor information up and down the spinal cord 2. Neural integration • Cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull • Occupies upper 2/3 of vertebral canal • Inferior margin ends at L1 or slightly beyond (L3 at birth) • spinal neurons receive input from multiple sources, integrate it (may involve brain), and execute appropriate output 3. Locomotion • spinal cord contains central pattern generators: groups of neurons that coordinate repetitive sequences of contractions for walking (flexion/extension repeat) 4. Reflexes • Gives rise to 31 pairs of spinal nerves • involuntary responses to stimuli that are vital to posture, coordination and inury protection Cross Section of Nerve Fibers (Fascicles) 5 2017‐10‐04 ********* The vertebral column Spinal cord divided into four regions: 1. 2. 3. 4. Cervical (C1‐C7) (breakfast) Thoracic (T1‐T12) (lunch) Lumbar (L1‐L5) (dinner) Sacral (5 fused vertebrae) (dessert) – named for where nerves emerge Spinal cord surface anatomy Two enlargements: 1. 2. Cervical enlargement – cord thickening where nerves emerge to upper limbs Lumbar enlargement – cord thickening where nerves to pelvic region and lower limbs • Medullary cone • cord tapers to a point inferior to lumbar enlargement • Cauda equine • Cauda = tail, equine = horse • bundle of nerve roots that occupy the vertebral canal from L2 – S5 • innervates pelvic organs, lower limbs ** space in middle ** SPENT A LOT OF TIME Meninges Meninges • Separates soft tissue of CNS from the cranium and vertebral canal • Three fibrous membranes that enclose the brain and spinal cord Arachnoid Mater Lumbar puncture Epidural • adheres to the dura • separated from pia by the subarachnoid space: • filled with cerebrospinal fluid • lumbar puncture (spinal tap) takes samples of CSF at L3/L4 or L4/L5 (no risk of spinal cord injury) • Consist of (superficial to deep): Pia Mater 1. Dura mater – dura = tough 2. Arachnoid mater 3. Pia mater • Dural sheath surrounds spinal cord and is separated from vertebrae by the epidural space • delicate membrane that follows the contours of the spinal cord • continues inferiorly as the fibrous terminal filum that fuses with the dura to form the coccygeal ligament NOTE!!** Know this disease Spina bifida • Congenital defect • One or more vertebrae fail to form a complete vertebral arch for enclosure of the spinal cord • 1 baby in 1,000 • Common in lumbosacral region Cross‐sectional anatomy of the spinal cord • Gray matter • Central area • Neuron cell bodies with little myelin (site of synaptic integration) • White matter • Surrounds gray matter • Abundantly myelinated axons (carry signals in the CNS) • Folic acid (leafy greens) reduces incidence • Note ‐ start 3 months before conception, as defect occurs in the first 4 weeks Note: grey matter in cerebral cortex of brain (not a medullary position) 6 2017‐10‐04 Gray matter – central core Reflex example • Posterior (dorsal) horns • Posterior root carries sensory nerve fibres • Anterior (ventral) horns • Anterior (ventral) root of spinal nerve carries only motor fibres • Gray commissure connects right and left sides • Central canal lined with ependymal cells and filled with CSF • Lateral horn • Visible from T2 through L1 • Contains neurons of the sympathetic nervous system White matter Spinal cord tract organization • Surrounds gray matter • Bundles of axons up and down the cord providing communication between different levels of CNS Columns (funiculi): 1. Posterior (dorsal) 2. Lateral 3. Anterior (ventral) • Each column/ funiculus consists of subdivisions = Tracts or fasciculi • Fibres within a given tract have similar origin, destination, and function • Ascending tracts – carry sensory information up • Descending tracts – carry motor information down • Tract decussation ‐ crossing of the midline that occurs in many tracts so that brain senses and controls contralateral side of body (i.e., tracts go left to right, or vice versa) • Different points of decussation for different tracts (spinal cord, medulla, midbrain) Posterior Lateral Anterior Cuneate fasciculus Ascending tracts • Sensory signals travel across three neurons from origin (receptors) to destinations in the sensory areas of the brain • First‐order neurons • Detects stimulus and transmits signal to spinal cord or brainstem Descending tracts • Involve two motor neurons (upper and lower) • Upper motor neuron ‐ soma in cerebral cortex or brainstem • Terminates on the lower motor neuron, which leads to target • Second‐order neurons • Continues to the thalamus at the upper end of the brainstem • Third‐order neurons • Carries the signal the rest of the way to the sensory region of the cerebral cortex Lateral and Anterior Corticospinal Tracts 7 2017‐10‐04 Gracile fasciculus • signals for vibration, visceral pain, deep and discriminative touch, proprioception (sense of position/movement) • signals from mid‐thoracic and lower parts of body Cuneate fasciculus • 1st‐order neurons carrying same signals as gracile fasciculus • for the upper limbs and chest Posterior (dorsal) and anterior (ventral) spinocerebellar tracts • proprioceptive signals from limbs and trunk up to the cerebellum Spinothalamic tract • signals for pain, pressure, temperature, light touch, tickle, and itch Spinoreticular tract • carries pain resulting from tissue injury Corticospinal tracts • precise, finely coordinated movements Lateral and medial reticulospinal tracts • posture and balance for upper and lower limbs Tectospinal tract • reflex turning of head in response to sights and sounds Lateral and medial vestibulospinal tracts • receives impulses for balance from inner ear, control extensor muscles of limbs for balance • reflex for balance Some myelated and some unmyelated Spinal nerves • Nerve ‐ cord‐like organ composed of numerous nerve fibres (axons) bound together by connective tissue Ganglia • Ganglion ‐ cluster of neurosomas outside the CNS • Enveloped with an epineurium continuous with that of the nerve • Posterior and anterior rootlets merge into spinal nerve Organization of connective tissue: • Endoneurium ‐ loose connective tissue external to neurolemma • Perineurium ‐ layers of overlapping squamous cells that wrap fascicles (bundles of nerve fibres) • Epineurium ‐ dense irregular connective tissue that wraps entire nerve • Dorsal/posterior root ganglion • Blood vessels penetrate connective tissue coverings; schwann cells overy many fibres (myelinated) Spinal nerve plexuses • 31 pairs of spinal nerves (mixed) • 8 cervical • 1st cervical exits between skull and atlas, all others at intervertebral foramina • • • • • Sympathetic chain ganglion • Posterior ramus –skin and muscles of spine and back regions • Anterior ramus – anterior and lateral; skin, muscles, trunk, limbs; form nerve plexuses 12 thoracic 5 lumbar 5 sacral 1 coccygeal • Except in thoracic region, nerves branch and merge repeatedly to form five webs = nerve plexuses 8 2017‐10‐04 Phrenic Nerve ** involoved...
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