Human Nervous System: Structure, Function, and Physiology

Posted on Dec 11, 2024 in Biology

Nervous System

BIOL 201 Human Anatomy & Physiology I

Michael Powers, PhD, ATC, CSCS, EMT

Nervous System Function

  • Receive sensory information (sensory input)
  • Integrate & process information
  • Produce an action or response (motor output)

Nervous System Organization

  • Central Nervous System (CNS)
    • Components
      • Brain
      • Spinal cord
    • Functions
      • Command center (the boss) – integrates sensory input & directs motor output
      • Higher order functions
        • Learning, memory, decisions, emotions, sleep, etc.
  • Peripheral Nervous System (PNS)
    • Originates from pairs of cranial nerves & pairs of spinal nerves

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  • Sensory nervous system (afferent)
    • Input from receptors
      • General Somatic Afferent Receptors (GSA)
        • Temperature
        • Touch/pressure
        • Pain
        • Proprioception/kinesthesia
      • General Visceral Afferent sensory receptors (GVA)
        • Cardiovascular
        • Respiratory
        • Digestive
        • Reproductive
        • Endocrine
      • Special senses
        • Sight, hearing, balance, smell, taste

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  • Motor nervous system (efferent)
    • Output to glands, adipose, muscle & other organs
      • Somatic nervous system
        • Output to skeletal muscle
      • Autonomic nervous system
        • Output to smooth & cardiac muscle, glands, & adipose (visceral output)
        • Parasympathetic nervous system (PSNS)
        • Sympathetic nervous system (SNS)

Nervous Tissue

  • Like other tissues, two components
    • Extracellular (less than 20% of the tissue)
    • Cells (densely packed & tightly intertwined)
      • Neurons
      • Neuroglia
  • Neurons
    • Functional Unit
    • ~100 billion
    • Rapid communication by generating action potentials
    • Limited regeneration
  • Neuroglia
    • “Support Cells”
    • Outnumber neurons (~20:1)
    • No conventional communication
    • Ability to divide

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Neuronal (Cell) Anatomy

  • Cell Body (Soma)
    • Peripheral nerve cell bodies are located in the CNS or ganglia
    • Organelles
      • Nucleus
      • Endoplasmic reticulum
      • Golgi apparatus
      • Mitochondria
  • Dendrites
    • Extensions from the cell body
    • Can be 90% of surface area
    • Receive information & deliver it to the cell body via graded potentials
  • Axon
    • Each neuron usually has a single axon
    • Arises from a cone-shaped area of the soma called the axon hillock
    • Sometimes the entire length of the neuron
    • Some have collaterals, all have terminal branches or telodendria
    • Typically transmits information (action potentials) away from the cell body

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  • Do not contain Golgi apparatus
    • Relies on cell body for production
    • Relies on delivery via neurofilaments & neurotubules

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Neuronal (Cell) Physiology

  • Axon Terminal
    • Synapse with next cell
    • Organelles
      • ER
      • Few mitochondria
      • Vesicles with neurotransmitters
  • Axonal Transport
    • Anterograde
      • Moves towards axon terminal
      • Kinesin: Motor protein that carries material along microtubule
      • Mitochondria, membrane components, enzymes, vesicles, neurotransmitters
      • Requires ATP
    • Retrograde
      • Moves towards soma
      • Dynein: Motor protein that carries material along microtubule
      • Organelles for recycling or lysis, vesicles, signals
    • Both require ATP

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  • Rabies Virus
    • Can infect any mammal
      • U.S. → Raccoon, fox, skunk, bats (dogs & cats usually vaccinated, but not always)
      • Worldwide → #1 dogs
    • Peripheral bite usually on limb
      • The saliva containing virus first comes in contact with muscle cells
      • Rabies virus replicates in these cells until enough of a concentration exists in the region of the bite that some viral particles come in contact with sensory or motor nerve cells
      • Viruses enter the axons where they are unmyelinated & move towards the nucleus by retrograde flow
      • Rabies virus capitalizes on this mechanism to reach the spinal cord, moving at 8 to 20mm per day
  • Herpes Virus (HSV1 & HSV2)
    • Following primary infection, the virus enters sensory nerve endings & travels to ganglia via retrograde transport
    • The viral genome persists in the nucleus (a state of latency may persist for many years)
    • In a percentage of people, the virus will reactivate (stimuli?)
    • A cycle of viral replication occurs in the neuron & virus particles travel down the axon to reinfect the skin or mucous membrane in the area supplied by the nerve

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CNS Glial Cells

  • Astrocytes “star cells”
    • Most abundant & versatile
    • Connected by gap junctions
    • Maintain extracellular ion composition
      • Especially K+ & some Na+
      • Some ability to regulate nutrients & dissolved gas concentrations
    • May form glial scar following CNS injury
      • Walls off injured neuronal tissue
    • Bind to synaptic endings & capillaries
      • Provide exchange between capillary & neuron
      • Critical part of the blood-brain-barrier (end feet cover CNS capillaries limit passage)
    • Pickup & recycle neuronal neurotransmitters
      • Particularly glutamate & GABA
  • Microglia
    • Smaller cells with “thorny” processes
    • Migrate towards injured or unhealthy neurons
    • Remove cellular debris & pathogens by phagocytosis

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  • Ependymal Cells
    • Squamous & columnar cells lining the brain ventricles & central canal of spinal cord
    • Apical surfaces have cilia & microvilli
    • Help in the production & circulation of cerebral spinal fluid (CSF)
    • Purpose of CSF??
  • Oligodendrocytes
    • Produce myelin for CNS neurons
    • Wraps around axonal region
    • Unmyelinated region = nodes

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PNS Glial Cells

  • Satellite Cells
    • Associated with neuronal cell bodies of ganglia
    • Many of the same functions as astrocytes in the CNS
    • Help regulate gases & nutrients of neuronal ganglia
    • Ganglia → cluster of neuronal cell bodies in PNS
  • Schwann Cells
    • Produce myelin for PNS neurons
    • Wraps around axonal region
    • Unmyelinated region = nodes

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  • Myelin
    • Protecting & electrically insulating phospholipid & protein layers
      • Different composition made by oligodendrocytes & Schwann cells
      • Interactions between the proteins & the lipids hold together
    • Wrapped around axon → acts as insulation
      • Good insulators due to few channels
      • Limits leakage of ions out (or in) of the axon
      • Speeds the conduction of electrical signals
    • Dendrites are unmyelinated
    • Adjacent Schwann cells are not connected
    • Gaps between cells (& myelin) are known as nodes of Ranvier
  • Neurilemma
    • The outermost nucleated cytoplasmic layer of Schwann cells
    • It forms the outermost layer of the axon (not found in the CNS – difference between Schwann cells & oligodendrocytes)
    • Forms a regeneration tube through which the growing axon re-establishes its original connection

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  • White vs. Gray Matter of CNS
    • Axon = white matter (myelin appears “white”)
    • Cell bodies = gray matter
    • Axonal damage in the PNS has limited regeneration
    • Research looking into differences in PNS & CNS myelin
    • Many nervous system disorders are associated with myelin abnormalities

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  • Multiple Sclerosis
    • CNS Demyelination
    • Damage to oligodendrocytes
    • Signs & symptoms of CNS dysfunction with remissions & recurring exacerbations
    • Sensory & motor problems
  • Diphtheria Toxin
    • Corynebacterium diphtheriae infection of skin or respiratory tract
    • CNS & PNS Demyelination → toxin damages Schwann cells
    • Sensory & motor problems
    • Vaccine available (often coupled with pertussis & tetanus vaccine)
  • Guillain–Barré syndrome (GBS)
    • An acute inflammatory demyelinating polyneuropathy (AIDP)
    • An autoimmune disorder affecting the peripheral nervous system, usually triggered by an acute infectious process
    • Frequently severe & usually exhibits as an ascending paralysis noted by weakness in the legs that spreads to the upper limbs & the face
    • Death may occur if severe pulmonary complications & autonomic nervous system problems are present

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Neuronal (Cell) Physiology

  • Resting Membrane Potential
    • Potential difference between the inside & the outside of cell
    • Cell membrane is polarized (opposite charges)
    • Cytoplasmic side of membrane is negative relative to the interstitial side
  • Why is it negative inside cell?
    • Ion leak channels → always open
      • K+ leak channels >>>> Na+ leak channels (~100:1)
      • So permeability of K+ greater at RMP
    • Na+ /K+ ATPase → electrogenic
      • Protein carrier moves 3 Na+ out & 2 K+ in
    • Many negatively charge proteins trapped inside the cell
  • What influences ion movement
    • Electrochemical gradient
      • Chemical gradient
      • Electrical gradient

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  • Graded Potentials
    • “Local” change in membrane potential occurring on the dendrites & soma
      • Can be depolarization or hyperpolarization
      • Due to neurotransmitter action on postsynaptic receptor or other stimulus that opens a gated channel
    • Characteristics
      • Magnitude depends on strength of stimulus (e.g. amount of neurotransmitter)
      • Can be summed
      • Decays as it moves along membrane
      • Short distance signal (current flows farther with stronger stimulus)
    • All dendrite & soma graded potentials summed
      • This potential moves toward axon hillock
    • Is threshold (~ -50 or -60 mV) reached at axon hillock?
      • No → no action potential
      • Yes → action potential occurs (all or nothing)
  • Action Potential
    • When threshold is reached
      • Voltage gated Na+ channels open (Na+ influx)
      • Upstroke of AP (rising phase – depolarization)

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  • Restoration toward RMP
    • Voltage gated Na+ channels close
    • Voltage gated K+ channels open (K+ efflux)
    • Downstroke of AP (falling phase – repolarization)
  • Action potential is propagated along axon length away from the point of origin
  • All or nothing principle
  • Continuous conduction (propagation)
    • Unyelinated axons
    • Ion exchange takes place along entire length of axon
  • Saltatory conduction (propagation)
    • Myelinated axons
    • Ion exchange takes place at nodes of Ranvier

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  • Action potential is propagated at a constant velocity, which is determined by,
    • Axon diameter = faster due to less resistance
    • Myelination = faster

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  • Fiber types
    • A-fibers
      • Large myelinated
      • Somatic sensory & motor
      • Alpha, beta, gamma, delta
    • B-fibers
      • Thin myelinated
      • Autonomic motor
    • C-fibers
      • Thin unmyelinated
      • Nociceptors (pain) & other sensory information
  • Synapses
    • Terminal axon → dendrite
    • Terminal axon → soma
    • Terminal axon → other cell
    • Electrical
      • Via gap junctions
    • Chemical
      • Via synapses
  • Chemical Synapse
    • Presynaptic nerve (axon) terminal
      • Contains synaptic vesicles with neurotransmitters
    • Synaptic cleft → space

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  • Postsynaptic Cell (neuron, muscle or gland)
    • Presynaptic neurotransmitters act at postsynaptic receptors
    • If neuron, most will be on postsynaptic dendrites or soma
    • Excitatory post synaptic potentials
      • Graded potentials (local depolarization)
      • If strong enough, continued action potential
    • Inhibitory post synaptic potentials
      • Hyperpolarization of post synaptic membrane
      • Usually due to outward movement of K+ or inward movement of Cl–

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  • Temporal vs spatial summation

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Neurotransmitters

  • Acetylcholine
  • Amino acids
    • Glutamate
    • Aspartate
    • Glycine
  • Amino Acid Derivatives
    • Epinephrine
    • Norepinephrine
    • Dopamine
    • Serotonin
    • Histamine
    • GABA (gamma-amino butyric acid)
  • Purines
    • Adenosine
  • Peptides
    • Opioids (Endorphins, etc)
    • Substance P
    • Neuropeptide Y
  • Gases (Neuromodulators)
    • Nitric Oxide
    • Carbon Monoxide

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Medication Effects on Nerve Transmission

  • Lidocaine
    • Local anesthetic
    • Blocks voltage gated Na+ channels
    • The neuron fails to transmit an action potential
  • Opioids
    • Act presynaptically to block Ca++ uptake & consequently inhibit neurotransmitter release (Substance P, acetylcholine, norepinephrine, glutamate, & serotonin)
    • Hyperpolarize postsynaptic neurons by increasing outward K+ currents
  • Tetrodotoxin
    • Blocks voltage gated Na+ channels
    • The neuron fails to transmit an action potential
    • Results in paresthesia, anesthesia, & paralysis

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Functional Classification

  • Sensory Neurons (Input)
    • Also referred to as afferent neurons
      • Interoceptors (visceroreceptors)
      • Exteroceptors (stimuli outside the body)
      • Proprioceptors (also internal stimuli)
  • Interneurons
    • Integration
    • All in CNS
    • Very small (~1-2mm)
  • Motor Neurons (Output)
    • Also referred to as efferent neurons
    • Somatic motor neurons
    • Visceral motor neurons (ANS)

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Sensory Stimulus Classification

  • Mechanoreceptors
    • Tactile
    • Baroreceptors
    • Proprioceptors
  • Thermoreceptors (temperature)
  • Photoreceptors (light)
  • Chemoreceptors (chemicals)
  • Nociceptors (noxious stimuli)

Sensory Nerves Types

  • Free nerve endings
    • Unencapsulated dendrite endings
    • Usually C-fibers
    • Temperature
    • Nociceptors: extreme temperature changes, mechanical damage, chemicals
    • Itch: activated by chemicals including histamine
    • Touch: connected to Merkel discs & hair follicles

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  • Encapsulated dendritic endings
    • Terminal ends are enclosed by a connective tissue capsule
      • Meissner’s (tactile) corpuscles
        • Mechanoreceptor: fine (discriminative) touch, pressure & vibration
        • Distributed at the papillary dermis
        • Numerous in lips, feet, fingertips, nipples, genitalia (hairless areas)
        • Rapidly adapting
      • Pacinian (lamellated) corpuscles
        • Mechanoreceptor: deep pressure, vibration
        • Throughout dermis & subcutaneous tissue
        • Fingertips, feet, genitalia, tendon, ligament, capsule, walls of bladder
        • Very rapidly adapting → most sensitive to pulsing stimuli
      • Ruffini corpuscles
        • Mechanoreceptor: pressure – deep (continuous) pressure
        • Distributed in deep dermis, subcutaneous tissue, joint capsules
        • Slowly adapting

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  • Muscle spindles
    • Consist of a fusiform nerve fiber surrounding an intrafusal fiber
    • Found in the perimysium
    • Monitor skeletal muscle length
    • Reflex contraction when stimulated
  • Golgi Tendon Organs
    • Similar to Ruffini corpuscles
    • At musculotendinous junction
    • Monitor skeletal muscle tension
    • Tension compresses GTO
    • Reflex inhibition when stimulated
  • Joint receptors
    • Monitor stretch in joint capsules
    • Pacinian, Ruffini, GTO-like receptors (& even free nerve endings)
    • Joint position & motion

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  • How does it work?
    • Begins with a stimulus
    • e.g. pacinian corpuscle: mechanical deformation opens the stretch-gated Na+ channels creating a graded potential
    • If stimulus reaches threshold, AP occurs
    • Thermoreceptors??

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Perception

  • Conscious interpretation of stimuli
  • Determines response
    • Sensory receptors (1st order)
    • Ascending pathways (2nd order)
    • Perceptual level (3rd order)
  • Sensory receptors (1st order)
    • Afferent nerves
    • Cell bodies located in DRG
    • 1st synapse occurs in the dorsal horn

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  • Ascending pathways (2nd order)
    • Cell bodies are located in the dorsal horn
    • Send AP to the brain for 2nd synapse
    • Decussation
    • Send information via specific tracks or pathways (white matter)
      • Spinocerebellar → cerebellum
      • Spinoolivary → medulla oblongata → thalamus
      • Spinothalamic → thalamus

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  • Perceptual level (3rd order)
    • Send information from the thalamus to the cerebral cortex

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  • Dermatomes “skin segment”
    • Area of skin innervated by cutaneous branches of a spinal nerve (C2-S5)
    • Level of the body follows segmental levels for the most part (S2-S5 are exceptions)
      • Upper limb – ventral rami of C5-T1 (T2)
    • In reality there is an overlapping of segmental innervation
      • Areas can be isolated for each spinal & peripheral nerve – C5 over deltoid tuberosity

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Motor Control

  • Levels of motor control
    • Precommand level
      • Motor behavior
    • Projection level
      • Descending pathways
    • Motor nerves
      • Segmental level
  • Precommand level
    • Cerebellum & basal nuclei regulate motor activity
      • Receives somatosensory input
      • Receives & controls the output of the cortex & brain stem motor centers
      • Coordinates movement, position, posture, etc.
      • Chiari Malformation
      • Syringomyelia

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  • Projection level
    • Upper motor neurons of the motor cortex (pyramidal cells)
    • Descending signals are sent via the spinal cord
      • Amyotrophic Lateral Sclerosis (ALS)
        • Slow progressive disease
        • Degeneration of motor neurons
        • Atrophy
        • Weakness → Paralysis

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  • Segmental level
    • Projection level neurons synapse with somatic & autonomic motor neurons
    • Motor neurons from each segment to specific skeletal & smooth muscles & glands
  • Hilton’s Law
    • Any nerve that innervates a muscle producing movement at a joint also innervates the joint itself & the skin overlying the joint
      • Axillary nerve (C5/C6)
        • Deltoid
        • Glenohumeral joint
        • Skin overlying inferior deltoid area “regimental badg” area) innervated by superior lateral cutaneous nerve
    • So what information does each nerve carry?

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Autonomic Nervous System

  • Effectors
    • Cardiac muscle
    • Smooth muscle
    • Glands
  • Pathways
    • 2-neuron chain
      • Pre-ganglionic
      • Post ganglionic
    • Motor ganglia
      • Primarily located near the vertebrae (sympathetic) or the viscera they innervate (parasympathetic)
      • Contain cell bodies
      • Synapses occur here

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  • Sympathetic Ganglia
    • Typically 23 ganglia in the chain on either side of the spinal column
      • 3 in the cervical region
      • 12 in the thoracic region
      • 4 in the lumbar region
      • 4 in the sacral region

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  • The cervical & sacral levels are not connected to the spinal cord directly through the spinal roots, but through ascending or descending connections through the bridges within the chain
  • Lateral horn of spinal cord
    • Found only in the thoracic & upper lumbar spinal segments (T1 to L2).
    • Gives rise to preganglionic sympathetic efferent neurons, which reach out to the sympathetic chain ganglia on either side of the vertebral column.
    • Within the sympathetic chain, the preganglionic neurons either synapse immediately inside the ganglia or ascend & descend within the sympathetic chain to synapse with ganglia above & below.

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  • Neurotransmitters
    • Sympathetic
      • Acetylcholine – preganglionic (cholinergic)
      • Norepinephrine – post ganglionic (adrenergic)
        • Excitatory or inhibitory
    • Parasympathetic
      • Acetylcholine – preganglionic
      • Acetylcholine – post ganglionic
        • Excitatory or inhibitory
  • Neurotransmitter receptors
    • Acetylcholine (cholinergic)
      • Nicotinic – stimulatory (excitatory)
        • Sarcolemma
        • All ANS post ganglionic
        • Adrenal medulla cells
      • Muscarinic – stimulatory or inhibitory
        • Parasympathetic targets
        • Eccrine sweat glands
        • Some skeletal muscle vasculature
    • Norepinephrine (adrenergic)
      • Alpha – stimulatory or inhibitory
        • α1
        • α2
      • Beta – stimulatory or inhibitory
        • β1
        • β2
        • β3

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  • Autonomic motor ending
    • Smooth muscle terminal axon branches become varicose (contain varicosities)
    • The branches intermingle with other axons in the area (plexus)
    • Innervates bundles of muscle
    • Each varicosity contains synaptic vesicles
      • Acetylcholine
      • Norepinephrine

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Reflexes ▪ Visceral (autonomic) ˗ Reflex arc = receptor → afferent neuron → integration center → motor neuron → effector ˗ Afferent information regarding chemical changes, stretch, pressure, pain ˗ Integration @ spinal cord (GI tract?) ˗ 2 neuron motor response ▪ Somatic ˗ Reflex arc = receptor → afferent neuron → integration center → motor neuron → skeletal muscle ˗ Afferent information regarding movement, position, pain ˗ Integration @ spinal cord o Monosynaptic o Polysynaptic ˗ Single neuron motor response NERVOUS SYSTEM Michael Powers, PhD, ATC, CSCS, EMT Page 44 of 49 NERVOUS SYSTEM Michael Powers, PhD, ATC, CSCS, EMT Page 45 of 49 NERVOUS SYSTEM Michael Powers, PhD, ATC, CSCS, EMT Page 46 of 49 NERVOUS SYSTEM Michael Powers, PhD, ATC, CSCS, EMT Page 47 of 49 Discussion Questions 1. Describe the general functions of nervous system. 2. What R the 2 primary comp1nts of the central nervous system? Where R they found? 3. How many pairs of cranial nerves exist? 4. How many pairs of spinal nerves exist? (How many cervical, thoracic, lumbar, sacral & coccygeal?) 5. What is the functional difference between afferent & efferent nerves? 6. What is the functional difference between somatic & autonomic efferent nerves? 7. What R the function differences between the sympathetic & parasympathetic nervous systems? 8. What R the comp1nts of nervous tissue? Regarding these comp1nts, how does nervous tissue differ from the other tissues w’v discussed? 9. Describe the structure of a neuron including dendrites, soma, & axons. 10. What occurs @ the axon hillock? 11. What R axon collaterals? 12. What R telodendria & what occurs there? 13. Describe the processes of anterograde & retrograde axonal transport. Why R these important? Which motor proteins function in each type of transport? Is this movement active or passive? 14. How do the rabies & polio viruses travel from their point of invasion 2 the CNS? 15. Where do the herpes viruses hide in the body & what happens when they R active? 16. Describe the structure & function of the CNS glial cells; astrocytes, microglia, ependymal cells & oligodendrocytes. 17. Where is cerebrospinal fluid found & what is its function? 18. Describe the structure & function of the PNS glial cells; satellite cells & schwann cells. 19. What is myelin & how does it affect ion movement across an axon membrane? 20. Describe the etiology of multiple sclerosis, diptheria, & Guillain–Barré syndrome. How do they affect the body functionally? 21. Describe what is meant when a cell is said 2 be excitable. Explain the 2 comp1nts of this property. Which cells R excitable? 22. Every cell hs a resting membrane potential. What does this mean & how is it maintained? 23. What determines the rate & direction of movement 4 diffusion? 24. What is Coulomb’s Law (simplified)? 25. What is the difference between a leak channel & a gated channel? 26. What does the K+-Na+ pump do? NERVOUS SYSTEM Michael Powers, PhD, ATC, CSCS, EMT Page 48 of 49 27. Due 2 the electrochemical gradient across an axon membrane, a rapid influx of Na+ should occur. Why doesn’t it when the nerve is in a resting state? 28. What is the difference between a graded potential & an action potential? 29. How does local depolarization normally occur? 30. How does local hyperpolarization normally occur? How does this relate 2 inhibition? 31. Is it possible 4 a local change in polarity 2 occur in a membrane without a resultant action potential? Why or why not? 32. What mechanisms R responsible 4 axon depolarization (as part of an AP)? 33. What mechanisms R responsible 4 axon repolarization (as part of an AP)? 34. What is meant by the absolute & relative refractory periods? When & why do they occur? 35. What is the difference between continuous & saltatory conduction (propagation)? 36. Which 2 factors effect conduction (propagation) velocity? 37. Describe the differences between Type A, B, & C nerve axons. 38. How do electrical & chemical synapses differ? 39. During a chemical synapse, what occurs @ the presynaptic & post synaptic membranes? 40. How do excitatory & inhibitory post synaptic potentials differ? 41. What is the mechanism of action 4 a local anesthetic like lidocaine? 42. How do endogenous (endorphin, enkephalin) & exogenous (heroin, morphine, oxycod1) opioids affect pain sensation & perception? 43. U jst 8 a puffer fish. What might happen & why? 44. What stimuli would excite tactile mechanoreceptors, baroreceptors, proprioceptors, thermoreceptors, chemoreceptors, & nociceptors? 45. Where R the muscle spindles located & what do they sense? 46. Where R the golgi tendon organs located & what do they sense? 47. Describe the structure, function, & location of free nerve endings, Meissner’s (tactile) corpuscles, Pacinian (lamellated) corpuscles & Ruffini corpuscles. 48. What is found in the white & grey matter of the spinal cord? 49. Where does all afferent (sensory) information enter the spinal cord? 50. Where does all efferent (motor) information leave the spinal cord? 51. Explain (in detail) the pathway from the point of sensory stimulation 2 perception. 52. Where R the cell bodies of peripheral afferent (1st order) neurons located? 53. Where R the terminal ends of the peripheral afferent (1st order) neurons found? What do they do there? 54. Where R the dendrites & cell bodies of ascending spinal cord neurons found? What happens 2 them there? NERVOUS SYSTEM Michael Powers, PhD, ATC, CSCS, EMT Page 49 of 49 55. Where R the terminal ends of the ascending spinal cord neurons found? What do they do there? 56. Where is the somatosensory cortex & what does it do? 57. Explain (in detail) the pathway of a motor signal from its point of origination 2 its effector. 58. Where is the primary motor cortex & what does it do? 59. Where R the dendrites & cell bodies of descending spinal cord neurons found? What happens 2 them there? 60. Where R the terminal ends of the descending spinal cord neurons found? What do they do there? 61. Where R the dendrites & cell bodies of peripheral efferent (motor) neurons located? What happens 2 them there? 62. What would be found within a peripheral nerve (e.g. ulnar nerve)? What information would it carry? 63. What is a dermatome? 64. What is a myotome? 65. Draw the brachial plexus & identify all roots, trunks, divisions, cords, terminal branches & side branches. 66. List the cranial nerves (roman numeral & name) & identify their function. Autonomic Nervous System 67. What R autonomic ganglia & where R they found? What occurs there? How do they differ between the sympathetic & parasympathetic systems? 68. Explain the beginning & end & the function of preganglionic & post ganglionic autonomic neurons. 69. Describe the relationship between neurotransmitters, receptors & somatic & autonomic effectors. 70. What R the 2 types of cholinergic receptors? How do they differ? 71. Which horm1s/neurotransmitters bind 2 adrenergic receptors? 72. What R the adrenergic subtypes? 73. Why would Botox be used 4 excessive sweating? 74. How do autonomic motor endings differ from the neuromuscular junction? 75. What R varicosities? What is their functional significance? 76. Describe the pathway 4 the visceral reflex arc. 77. Describe the pathway 4 the somatic (monosynaptic) visceral reflex arc. 78. How do monosynaptic & polysynaptic reflexes differ? 79. What is the mechanism behind the stretch reflex & what is the end result?