Anatomy and Physiology of Cells of the NS

Question 1

Soma

Answer 1

-Cell body of neuron
-Contains nucleus and most other organelles
-Common site of synaptic input (afferent)
-Contain receptors for neurotransmitters (subsynaptic membrane)

Question 2

Dendrites

Answer 2

-Extension of the soma
-Common site of synaptic input (afferent)
-Contain receptors for neurotransmitters (subsynaptic membrane)

Question 3

Axon hillock

Answer 3

-Anatomical transition from soma to axon
-Physiological transition from graded potential to action potential (AP)
-initial segment - has lowest graded threshold for AP

Question 4

Axon

Answer 4

-Long thin, efferent process
-Many microtubules and microfilaments to maintain shape

Question 5

Axon transport

Answer 5

-Up to 400mm per day

Question 6

Anterograde transport

Answer 6

-Movement of materials (neurotransmitters, proteins, etc) from soma towards synaptic knobs

Question 7

Kinesin

Answer 7

-Protein motor molecule

Question 8

Retrograde transport

Answer 8

-Movement of materials (often waste) from synaptic knobs towards soma

Question 9

Dynein

Answer 9

-Protein motor molecule

Question 10

What surrounds the axon?

Answer 10

-May be surrounded by myelin with nodes of Ranvier

Question 11

AP conduction speed _________ with _________ diameter & ________myelin.

Answer 11

increases, increased, increased

Question 12

Fibers with largest diameter, most myelin

Answer 12

Sensory (afferent) A-alpha
Motor (efferent) Ia, Ib, II
Conduction speed: 70-120m/sec

Question 13

Fibers in between

Answer 13

Sensory (afferent) A-beta
Motor (efferent) III
Conduction speed: 5-30m/sec

Question 14

Fibers with smallest diameter, least myelin

Answer 14

Sensory (afferent) C
Motor (efferent) IV
Conduction speed: 0.5-2m/sec

Question 15

Synaptic knobs (terminal boutons)

Answer 15

-Swelling at end of axons
-Contain structures of synaptic transmission (esp. vesicles of neurotransmitter)

Question 16

Membrane potential

Answer 16

-Due (primarily) to differences in [Na] & [K] between ICF and EFC
-Also [Cl] & [Ca]
-When no signal is being sent = resting membrane potential
[-70mV] varies among neurons & types of neurons

Question 17

Changes in membrane potential (=information)

Answer 17

-Depolarization: toward 0mV
-Repolarization: return from depolarization toward -70mV
-Hyperpolarization (overshoot): more negative than -70mV

Question 18

Graded (local) potentials

Answer 18

-Small, decremental voltage changes in response to some stimulus (receptor, neurotransmitter, etc.)
-Larger stimulus causes larger voltage change (=graded)
-Can be excitatory (depolarizing) or inhibitory (hyperpolarizing)
-Created/located in the dendrites and soma

Question 19

Action potential (AP)

Answer 19

-Huge, stereotypical, non-decremental, unidirectional change in membrane potential that is propagated along axon

Question 20

AP is formed if threshold voltage is met (All or none rule)

Answer 20

-Initial segment of axon hillock (site of transition from local potential to AP)
-Threshold varies among neurons, even of the same type (usually around -55mV)

Question 21

Propagation along axons

Answer 21

Contiguous or Saltatory

Question 22

Contiguous Conduction

Answer 22

-On unmyelinated fibers
-Slower
-Must be recreated on every portion of the membrane

Question 23

Saltatory Conduction

Answer 23

-On myelinated fibers
-Much faster
-AP “jumps” from one Node of Ranvier to the next

Question 24

Synapses

Answer 24

-Functional connection between neurons
-Usually axodendritic or axosomatic (but can be axoaxonic)
-Usually functions by transforming AP signal into chemical signal (neurotransmitter) that crosses the synaptic cleft

Question 25

Presynaptic neuron

Answer 25

Releases neurotransmitter (sends information)

Question 26

Postsynaptic neuon

Answer 26

Senses neurotransmitter (receives information)

Question 27

EPSP - Excitatory Post-Synaptic Potential

Answer 27

-Depolarizes postsynaptic cell -Moves membrane potential closer to threshold -Makes it more likely to fire an AP

Question 28

IPSP - Inhibitory Post-Synaptic Potential

Answer 28

-Hyperpolarizes postsynaptic cell -Moves membrane further from threshold -Makes it less likely to fire an AP

Question 29

Neurotransmitters

Answer 29

Chemical messengers (hundreds)

Question 30

Excitatory (fast) [neurotransmitter]

Answer 30

Acetylcholine (ACh), glutamate (primarily CNS; estimated at 90%+ of synapses)

Question 31

Inhibitory (fast) [neurotransmitter]

Answer 31

GABA (gamma-aminobutyric acid; mostly brain), glycine (mostly spinal cord)

Question 32

Second messenger mediated (slow; many are either excitatory or inhibitory, depending on receptor)

Answer 32

-Catecholamines (epinephrine & norepinephrine; dopamine) -Serotonin -Neuropeptides (neuromodulators) -Several neurotransmitters have both fast & slow receptors (ACh, glutamate, GABA)

Question 33

Drugs and diseases acting at synapse

Answer 33

-Curare -Botulsim -Tetanus -Myasthenia Gravis

Question 34

Curare

Answer 34

-Toxin that blocks ACh receptors (nicotinic receptors) -Causes flaccid paralysis

Question 35

Botulsim

Answer 35

-Toxin prevents exocytosis of ACh (esp @ neuromuscular junction) -Causes flaccid paralysis

Question 36

Tetanus

Answer 36

-Toxin is transported by retrograde axonal transport to inhibitory neurons of spinal cord -Blocks glycine release -Prevents inhibition of motor neurons; causes spastic paralysis

Question 37

Myasthenia Gravis

Answer 37

-Autoimmune destruction of ACh receptors; although ACh release is normal -Muscle contraction decreases (esp. to repeated contractions) -Causes weakness, double vision, etc.

Question 38

Glial cells

Answer 38

90% by number; 50% by volume

Question 39

Astrocytes (CNS)

Answer 39

-Connective tissue of the CNS -Hold neurons in position -Blood-brain barrier - chemically protect neurons

Question 40

Oligodendrocytes (CNS)

Answer 40

-Myelinate axons in CNS -Larger, myelinate many regions of multiple axons

Question 41

Schwann cells (PNS)

Answer 41

-Myelinate axons in PNS -Smaller, myelinate specific region of one axon -Provide support, myelinate, and have phagocytotic role

Question 42

Ependymal cells (CNS)

Answer 42

-Line ventricles, central canal of the spinal cord -Choroid plexus: specialized ependymal cells within the ventricles that produce CSF -Function: secretory, absorptive and CSF circulatory role

Question 43

Microglia (CNS)

Answer 43

-Phagocytosis of degenerative debris of CNS -Immune function

Question 44

Charcot-Marie Tooth Disease (family of disorders)

Answer 44

-Uncurable; genetic (most common inherited neurological disorder: 40 in 100,000) -Peripheral neuropathy – caused by gap junction channelopathy -Progressive loss of touch sensation, muscle weakness & wasting -Affects longest axons first -(i.e., feet first, then legs, then hands, then arm) -Mechanism/molecule unknown, but causes demyelination of PNS

Question 45

Guillain-Barre Syndrome

Answer 45

-Autoimmune inflammation (after viral infection) where macrophages attack and destroy myelin in the PNS (fairly rare: 1 in 100,000) -Can cause rapid (12 hours! to 2 week) symptoms of weakness, loss of sensation -often affects breathing muscles & patients require ventilation -Patients often recover significantly, but 20% are unable to walk unaided after 6 months

Question 46

Multiple Sclerosis

Answer 46

-Autoimmune attack on CNS myelin (approx. 28 in 100,000) -Symptoms vary widely – depending on specific area of damage -Chronic & debilitating changes in sensation, movement, mood and/or cognition