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ACVIM General Boards > Neurophysiology > Flashcards

Neurophysiology Flashcards

1
Q

autonomic nervous system

A

= set of pathways to and from the CNS that innervate and regulate

  1. smooth muscle
  2. cardiac muscle
  3. glands
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2
Q

three divisions of the ANS

A
  1. sympathetic
  2. parasympathetic
  3. enteric nervous systems
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3
Q

parasympathetic NS features

  • origin of preganglionic nerve
  • preganglionic axon length
  • nt to autonomic ganglia
  • receptor type at ganglia
  • postganglionic axon length
  • nt to effector organ
  • receptor type at effector organ
A
  • origin of preganglionic nerve = CN 3, 7, 9, 10; spinal segments S2-S4 (craniosacral)
  • preganglionic axon length: long
  • nt to postganglionic: Acetylcholine (ACh)
  • receptor type at ganglia: nicotinic
  • postganglionic axon length: short
  • nt to effector organ: ACh
  • receptor type at effector organ: muscarinic
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4
Q

sympathetic NS features

  • origin of preganglionic nerve
  • preganglionic axon length
  • nt to autonomic ganglia
  • receptor type at ganglia
  • postganglionic axon length
  • nt to effector organ
  • receptor type at effector organ
A
  • origin of preganglionic nerve = T1-12, L1-3 (thoracolumbar)
  • preganglionic axon length: short (terminates in the paravertebral chain of ganglia)
  • nt to postganglionic: ACh
  • receptor type at ganglia: nicotinic
  • postganglionic axon length: long
  • nt to effector organ: norepinephrine (except sweat glands, which use ACh)
  • receptor type at effector organ: alpha-1, alpha-2, beta-1, beta-2
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5
Q

effector organs of the somatic nervous system

A

skeletal muscle

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6
Q

neurotransmitter of the somatic NS

A

ACh

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7
Q

receptor type of the somatic NS

A

nicotinic

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8
Q

adrenal medulla and special anatomy

A

= specialized ganglion of the sympathetic nervous system; pregangllionic fibers synapse directly on chromaffin cells in the adrenal medulla–> secretion of epinephrine (80%) and norepinephrine (20%)

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9
Q

pheochromocytoma

A

= tumor of the adrenal medulla that secrete excessive amts of catecholamines and is associated with increased excretion of 3-methyoxy-4-hydroxymandelic acid (VMA)

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10
Q

adrenergic nerve fiber

A

= a neuron for which the neurotransmitter is either epinephrine, norepinephrine, or dopamine; usually norepinephrine

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11
Q

cholinergic neuron

A

= a neuron for which the neurotransmitter is acetylcholine (ACh); present in both the sympathetic and parasympathetic NSs

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12
Q

receptors types of the ANS

A
  1. adrenergic (nt = norepinephrine)

2. cholinergic (nt = ACh)

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13
Q

special parasympathetic receptors of the GIT

A

= nonadrenergic, noncholinergic receptors of some postganglionic parasympathetic neurons in the GIT, which release

  1. substance P
  2. vasoactive intestinal peptide (VIP)
  3. nitric oxide (NO)
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14
Q

types of adrenergic receptors

A
  1. alpha-1
  2. alpha-2
  3. beta-1
  4. beta-2
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15
Q

two broad categories of cholinergic receptors (cholinoreceptors) and specific types of cholinergic receptors

A

categories of cholinergic receptors

  1. nicotinic receptors
  2. muscarinic receptors

specific types of cholinergic receptors

  1. Nm (N1)
  2. Nn (N2)
  3. M1
  4. M2
  5. M3
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16
Q

alpha-1 receptors

  • location
  • result of activation
  • nt sensitivity
  • G protein
  • mechanism
A
  • location = 1. smooth muscle (vascular smooth muscle of the skin and splanchnic regions, GIT, and bladder sphincters), 2. radial muscle of the iris
  • result of activation = excitation (contraction/constriction)
  • nt sensitivity = equally responsive to norepi and epi but ONLY norepi released from adrenergic neurons is present in high enough concentrations to activate alpha-1 receptors
  • G protein = Gq
  • mechanism = Gq–> stimulation of phospholipase C–> increase IP3 and intracellular Ca2+
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17
Q

alpha-2 receptors

  • location
  • result of activation
  • nt sensitivity*
  • G protein
  • mechanism
A
  • location: 1. walls of GIT (heteroreceptors), 2. sympathetic postganglionic nerve terminals (autoreceptors), platelets, fat cells
  • result of activation: inhibition (relaxation/dilation)
  • nt sensitivity*
  • G protein: Gi
  • mechanism: Gi–>inhibition of adenylate cyclase–> decrease in cAMP
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18
Q

beta-1 receptors

  • location
  • result of activation
  • nt sensitivity
  • G protein
  • mechanism
A
  • location: Heart (1. SA node, 2. AV node, 3. ventricular muscle)
  • result of activation: excitation (increase HR, increase contraction velocity, increase contractility)
  • nt sensitivity: equally sensitive to norepi and epi; more sensitive than alpha-1 receptors
  • G protein: Gs
  • mechanism: Gs–>activate adenylate cyclase–>increase cAMP
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19
Q

beta-2 receptors

  • location
  • result of activation
  • nt sensitivity
  • G protein
  • mechanism
A
  • location: smooth muscle (1. bronchial smooth muscle, 2. vascular smooth muscle of skeletal muscle, 3. walls of GIT and bladder)
  • result of activation: relaxation (dilation of bronchioles, dilation of vascular smooth muscle, relaxation of the bladder wall)
  • nt sensitivity: more sensitive to epi than norepi (epi>norepi); more sensitive to epi than alpha-1 receptors
  • G protein: Gs
  • mechanism: Gs–>activate adenylate cyclase–>increase cAMP
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20
Q

Nm (N1) nicotinic cholinergic receptors

  • location
  • result of activation
  • nt sensitivity
  • G protein
  • mechanism
A
  • location: skeletal muscle neuromuscular junction (somatic nervous system)
  • result of activation: excitation
  • nt: ACh or nicotine
  • G protein: n/a
  • mechanism: opening Na/K channels (because nicotinic ACh receptors are also ion channels for Na and K)
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21
Q

Nn (N2) nicotinic cholinergic receptors

  • location
  • result of activation
  • nt sensitivity
  • G protein
  • mechanism
A
  • location: autonomic ganglia (of both the sympathetic and parasympathetic NS); adrenal medulla
  • result of activation: excitation
  • n: ACh or nicotine
  • G protein: n/a
  • mechanism: opening Na/K channels
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22
Q

M1 muscarinic cholinergic receptors

  • location
  • result of activation
  • nt sensitivity
  • G protein
  • mechanism
A
  • location: CNS
  • result of activation
  • nt: ACh or muscarine
  • G protein: Gq
  • mechanism: Gq–>increase phospholipase C activity–>increase IP3/Ca
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23
Q

M2 muscarinic cholinergic receptors

  • location
  • result of activation
  • nt sensitivity
  • G protein
  • mechanism
A
  • location: heart
  • result of activation: inhibition (decreased HR, decreased conduction velocity of the AV node)
  • nt: ACh or muscarine
  • G protein: Gi
  • mechanism: Gi–>inhibit adenylate cyclase–>decrease cAMP–>opening of K channels–>slowing of the rate of spontaneous phase 4 depolarization–>decreased heart rate
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24
Q

M3 muscarinic cholinergic receptors

  • location
  • result of activation
  • nt sensitivity
  • G protein
  • mechanism
A
  • location: glands, smooth muscle
  • result of activation: excitatory (increased GI motility, increased secretion)
  • nt: ACh or muscarine
  • G protein: Gq
  • mechanism: Gq–>increase phospholipase C activity–>increase IP3/Ca
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25
Q

hexametonium

A

= ganglionic blocker in the autonomic ganglia but NOT at the neuromuscular junction (i.e. NOT the Nm (N1) nicotinic cholinergic receptors

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26
Q

atropine

A

= anticholinergic by blocking muscarinic cholinergic receptors

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27
Q

alpha-1 adrenergic receptor agonists (pro-sympathetic = sympathomimetic)

A
  1. norepinephrine

2. phenylephrine

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28
Q

alpha-1 adrenergic receptor antagonists (anti-sympathetic = sympatholytic; parasympathomimetic)

A
  1. phenoxybenzamine
  2. phentolamine
  3. prazosin
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29
Q

alpha-2 adrenergic receptor agonists (sympathomimetic)

A

clonidine

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30
Q

alpha-2 adrenergic receptor antagonists (sympatholytic; parasympathomimetic)

A

yohimbine

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31
Q

beta-1 adrenergic receptor agonists (sympathomimetic)

A
  1. norepinephrine
  2. isoproterenol
  3. dobutamine
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32
Q

beta-1 adrenergic receptor antagonist (sympatholytic; parasympathomimetic)

A
  1. propranolol

2. metroprolol

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33
Q

beta-2 adrenergic receptor agonists (sympathomimetic)

A
  1. isoproterenol

2. albuterol

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34
Q

beta-2 adrenergic receptor antagonists (sympatholytic; parasympathomimetic)

A
  1. propranolol

2. butoxamine

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35
Q

nicotinic cholinergic receptor agonists

A
  1. ACh
  2. nicotine
  3. carbachol
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36
Q

nicotinic cholinergic receptor antagonists

A
  1. curare (NMJ N1 (Nm) receptors

2. hexamethonium (ganglionic N2 (Nn) receptors

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37
Q

muscarinic cholinergic receptor agonists

A
  1. ACh
  2. muscarine
  3. carbachol
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38
Q

muscarinic cholinergic receptor antagonists

A
  1. atropine
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39
Q

Table 2.4

A

Effect of the ANS on organ systems - REVIEW

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40
Q

locations of ANS centers within the brainstem and hypothalamus

A
  1. medulla - vasomotor center, respiratory center, swallowing/coughing/vomiting centers
  2. pons - pneumotaxic center
  3. midbrain - micturition center
  4. hypothalamus - temperature regulation center; thirst and food intake regulatory centers
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41
Q

major divisions of the CNS

A
  1. spinal cord
  2. brain stem (medulla, pons, midbrain)
  3. cerebellum
  4. diencephalon (thalamus, hypothalamus)
  5. cerebral hemispheres (cerebral cortex, basal ganglia, hippocampus, amygdala)
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42
Q

dendrites

A

= components that arise from the cell body and receive information from adjacent neurons

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43
Q

glial cells

A

= support cells for neurons

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44
Q

types of glial cells

A
  1. astrocytes
  2. oligodendrocytes and Schwann cells
  3. microglial cells
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45
Q

astrocyte functions

A
  1. supply metabolic fuels to neurons
  2. secrete trophic factors
  3. synthesize neurotransmitters
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46
Q

oligodendrocyte function

A

synthesize myelin in the CNS

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47
Q

Schwann cell function

A

synthesize myelin in the PNS

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48
Q

microglial cell function

A

proliferate following neuronal injury and serve as scavengers for cellular debris

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49
Q

sensory receptors

A

= specialized epithelial cells or neurons that transduce environmental signals into neuronal signals

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50
Q

environmental signals that can be detected by sensory receptors

A
  1. mechanical force
  2. light
  3. sound
  4. chemicals
  5. temperature
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51
Q

4 types of sensory transducers (general categories)

A
  1. mechanoreceptors
  2. photoreceptors
  3. chemoreceptors
  4. nociceptors
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52
Q

5 types of mechanoreceptors

A
  1. pacinian corpuscles
  2. joint receptors
  3. stretch receptors in muscle
  4. hair cells in auditory and vestibular systems
  5. baroreceptors in carotid sinus
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53
Q

2 types of photoreceptors

A
  1. rods

2. cones of the retina

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54
Q

4 types of chemoreceptors

A
  1. olfactory receptors
  2. taste receptors
  3. osmoreceptors
  4. carotid body O2 receptors
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55
Q

sensation of nociceptors

A

extremes in pain and temperature

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56
Q

A-alpha fibers

  • example
  • sensory fiber types and examples
  • diameter
  • conduction velocity
A
  • example: large alpha-motoneurons
  • sensory fiber types and examples
    1. Ia sensory fibers (e.g. muscle spindle afferents)
    2. Ib sensory fibers (e.g. Golgi tendon organs)
  • diameter: largest
  • conduction velocity: fastest (because largest diameter)
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57
Q

A-beta fibers

  • example
  • sensory fiber types and examples
  • diameter
  • conduction velocity
A
  • example: touch, pressure
  • sensory fiber types and examples: II (e.g. secondary afferents of muscle spindles; touch and pressure)
  • diameter: medium
  • conduction velocity: medium
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58
Q

A-gamma

  • example
  • sensory fiber types and examples
  • diameter
  • conduction velocity
A
  • example: gamma-motoneurons to muscle spindles (intrafusal fibers)
  • sensory fiber types and examples: n/a
  • diameter: medium
  • conduction velocity: medium
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59
Q

A-delta

  • example
  • sensory fiber types and examples
  • diameter
  • conduction velocity
A
  • example: touch, pressure, temperature, pain
  • sensory fiber types and examples: III (e.g. touch, pressure, fast pain, and temperature)
  • diameter: small
  • conduction velocity: medium
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60
Q

B fibers

  • example
  • diameter
  • conduction velocity
A
  • example: preganglionic autonomic fibers
  • diameter: small
  • conduction velocity: medium
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61
Q

C fibers

  • example
  • sensory fiber types and examples
  • diameter
  • conduction velocity
A
  • example: slow pain; postganglionic autonomic fibers
  • sensory fiber types and examples: IV (e.g. unmyelinated pain and temperature fibers)
  • diameter: smallest
  • conduction velocity: slowest (because they have the smallest diameter and they are unmyelinated)
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62
Q

receptive field

A

= an area of the body that, when stimulated, changes the firing rate of a sensory neuron

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63
Q

excitatory receptive field

A

= the firing rate of the sensory neuron is increased

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64
Q

inhibitory receptive field

A

= the firing rate of the sensory neuron is decreased

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65
Q

steps in sensory transduction

A
  1. stimulus arrives at the sensory receptor
  2. ion channels are opened in the sensory receptor, allowing current to flow (usually inward current–>depolarization of the sensory receptor; EXCEPTION = photoreceptor - light–>DECREASED inward current–>hyperpolarization)
  3. change in membrane potential produced by the stimulus = receptor potential (or generator potential)
  4. if the receptor potential is large enough, the membrane potential will exceed threshold–>action potential in the sensory neuron
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66
Q

important point about receptor potentials

A

they are NOT action potentials; receptor potentials are graded in size depending on the size of the stimulus; if the receptor potential is depolarizing, it brings the membrane potential closer to threshold

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67
Q

two types of adaptations of sensory receptors

A
  1. slowly adapting (tonic) receptors

2. rapidly adapting (phasic) receptors

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68
Q

examples of slowly adapting (tonic) receptors

A
  1. muscle spindle receptors
  2. pressure receptors
  3. slow pain receptors
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69
Q

features of slowly adapting (tonic) receptors

A
  1. respond repetitively to prolonged stimulus

2. detect a steady stimulus

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70
Q

examples of rapidly adapting (phasic) receptors

A
  1. pacinian corpuscles

2. light touch

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71
Q

features of rapidly adapting (phasic) receptors

A
  1. decline in action potential frequency with time in response to a constant stimulus
  2. primarily detect onset and offset of a stimulus
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72
Q

general sensory pathway from sensory receptor to cerebral cortex

A
  1. sensory receptor activated by environmental stimuli–>transduce the stimulus into electrical energy (i.e. receptor potential
  2. first-order neurons
  3. second-order neurons
  4. third-order neurons
  5. fourth-order neurons in the appropriate sensory area of the cerebral cortex
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73
Q

1st-order neurons

A

= the primary afferent neurons that receive the transduced signal and send info to the CNS; cell bodies are located in the dorsal root or spinal cord ganglia

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74
Q

2nd-order neurons

  • location
  • function
A
  • location = spinal cord or brainstem
  • function = receive information from one or more primary afferent neurons in relay nuclei and transmit it to the thalamus; **axons of 2nd order neurons may cross midline in a relay nucleus in the spinal cord before they ascend to the thalamus–>THEREFORE, sensory information originating on one side of the body ascends to the CONTRALATERAL thalamus
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75
Q

3rd-order neurons

  • location
  • function
A
  • location = the relay nuclei of the thalamus

- function = direct

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76
Q

4th-order neurons

  • location
  • function
A
  • location = cerebral cortex

- function = receives information of the stimulus and forms conscious proprioception

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77
Q

four senses of the somatosensory system

A
  1. touch
  2. movement
  3. temperature
  4. pain
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78
Q

two pathways of the somatosensory system

A
  1. dorsal column system

2. anterolateral system

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79
Q

dorsal column system

  • function
  • fiber type
  • course
A
  • function: processes sensations of 1. fine touch, 2. pressure, 3. two-point discrimination, 4. vibration, 5. proprioception
  • fiber type: group II fibers
  • course: primary afferent neurons have cell bodies in the dorsal root; their axons ascend ipsilaterally to the nucleus gracilis and nucleus cuneatus of the medulla–>2nd orrder neurons cross midline and ascend to the contralateral thalamus where they synapse on 3rd order neurons–>3rd order neurons ascend to the somatosensory cortex, where they synapse on 4th order neurons
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80
Q

anterolateral system

  • function
  • fiber types
  • course
A
  • function: processes sensations of 1. temperature, 2. pain, 3. light touch
  • fiber type: group III and IV fibers (terminate on dorsal horn)
  • course: 2nd order neurons cross the midline to the anterolateral quadrant of the spinal cord–>ascend to the contralateral thalamus where they synapse on 3rd order neurons–>3rd order neurons ascend to the somatosensory cortex, where they synapse on 4th order neurons
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81
Q

sensation within the thalamus

A

is for the CONTRALATERAL side of the body; arranged somatotopically

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82
Q

four types of mechanoreceptors for touch and pressure

A
  1. pacinian corpuscle
  2. Meissner corpuscle
  3. Ruffini corpuscle
  4. Merkel disk
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83
Q

Pacinian corpuscle

  • description
  • sensation encoded
  • adaptation
A
  • description: onion-like structures in the SQ skin (surrounding unmyelinated nerve endings)
  • sensation encoded: vibration, tapping
  • adaptation: rapidly adapting
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84
Q

Meissner corpuscle

  • description
  • sensation encoded
  • adaptation
A
  • description: present in nonhairy skin
  • sensation encoded: velocity
  • adaptation: rapidly adapting
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85
Q

Ruffini corpuscle

  • description
  • sensation encoded
  • adaptation
A
  • description: encapsulated
  • sensation encoded: pressure
  • adaptation: slow adapting
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86
Q

Merkel disk

  • description
  • sensation encoded
  • adaptation
A
  • description: transducer is on epithelial cells
  • sensation encoded: location
  • adaptation: slowly adapting
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87
Q

largest areas of the sensory homunculus

A
  1. face
  2. hands
  3. fingers
    i. e. where precise localization is important
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88
Q

pain (nociceptors)

  • receptors
  • neurotransmitter
A
  • receptors = free nerve endings in the skin, muscle, and viscera
  • neurotransmitters for nociceptors = substance P
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89
Q

fast pain fibers

  • fiber type
  • features
A
  • fiber type: group III fibers

- features: rapid onset and offset; localized

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90
Q

slow pain fibers

  • fiber type
  • features
A
  • fiber type: C fibers

- features: aching, burning, throbbing that is poorly localized

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91
Q

referred pain

A

= pain of visceral origin that is referred to sites on the skin and follows the dermatome rule; innervated by nerves that arise from the same segment of the spinal cord

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92
Q

diopters definition

A

= the reciprocal of the distance

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93
Q

emmetropia

A

= normal; light focuses on the retina

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94
Q

hyperopia

A

= farsighted; light focuses behind the retina and is corrected with a convex lens

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95
Q

myopia

A

= nearsighted; light focuses in front of the retina and is corrected with a biconcave lens

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96
Q

astigmatism

A

= curvature of the lens is not uniform and is corrected with a cylindrical lens

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97
Q

presbyopia

A

= a result of loss of the accommodation power of the lens that occurs with age; the near point moves farther from the eye and is corrected with a convex lens

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98
Q

near point

A

= the closest point on which one can focus by accommodation of the lens

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99
Q

listed layers of the retina

A
  1. pigmented epithelial cells
  2. receptor cells (rods and cones)
  3. bipolar cells
  4. horizontal and amacrine cells
  5. ganglion cells
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100
Q

pigmented epithelial cell function

A
  1. absorb stray light and prevent scatter

2. convert 11-cis retinal to all-trans retinal

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101
Q

blind spot

A

= the optic disc where there are no rods or cones

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102
Q

rods

  • sensitivity to light
  • acuity
  • dark adaptation
  • color vision
A
  • sensitivity to light: sensitive to low-intensity light; adapted for night vision
  • acuity: lower visual acuity; not present in fovea
  • dark adaptation: rods adapt later
  • color vision: no
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103
Q

cones

  • sensitivity to light
  • acuity
  • dark adaptation
  • color vision
A
  • sensitivity to light: sensitive to high-intensity light; day vision
  • acuity: higher visual acuity; present in fovea
  • dark adaptation: cones adapt first
  • color vision: yes
104
Q

bipolar cells

A

= the receptor cells onto which rods and cones synapse; bipolar cells then synapse on ganglion cells

105
Q

structure of rod and cone synapses on bipolar cells

A
  • cones: few cones synapse on a single bipolar cell–>synapses on a single ganglion cell–>basis for high acuity and low sensitivity of cones
  • rods: many rods synapse on a single bipolar cells–>less acuity in the rods than in the cones, but greater sensitivity in the rods bc light striking any one of the rods will activate the bipolar cell
106
Q

function of horizontal and amacrine cells

A

form local circuits with the bipolar cells

107
Q

ganglion cells

A

receive input from the bipolar cells; are the output cells of the retina (axons of the ganglion cells form the optic nerve–>optic tract–>lateral geniculate body of the thalamus)

108
Q

fovea

A

= point of highest acuity where the ratio of cones to bipolar cells is 1:1; NO rods located in the fovea

109
Q

optic chiasm

A

= location where fibers from each nasal hemiretina cross (vs. the fibers from each temporal hemiretina remain ipsilateral)

110
Q

geniculocalcarine tract

A

= fibers from the lateral geniculate body that pass to the occipital lobe of the cortex

111
Q 
lesions:
- cutting the optic nerve-->
- cutting the optic chiasm-->
- cutting the optic tract-->
cutting the geniculocalarine tract-->
A
  • cutting the optic nerve–>blindness in the ipsilateral eye
  • cutting the optic chiasm–>heteronymous bitemporal hemianopia?? blindness of the outer vision?
  • cutting the optic tract–>homonymous contralateral hemianopia
    cutting the geniculocalarine tract–>homonymous hemianopia with macular sparing
112
Q

rhodopsin

A

= the photosensitive element in the rods; composed of opsin (a protein) belonging to the superfamily of GPCRs and retinal (an aldehyde of vitamin A)

113
Q

steps in photoreception in the rods

A
  1. light on the retina converts 11-cis retinal to all-trans retinal (= photoisomerization); a series of intermediates then forms, one of which is metarhodopsin II
  2. metarhodopsin II activates the G protein called transducin (Gt), which–>activates a phosphodiesterase
  3. phosphodiesterase catalyzes the conversion of cyclic guanosine monophosphate (cGMP) to 5’-GMP and cGMP levels decrease
  4. decreased levels of cGMP–>closure of Na channels, decreased inward Na current, and as a result–>hyperpolarization of the photoreceptor membrane
  5. when the photoreceptor is hyperpolarized, there is decreased release of glutamate (= an excitatory neurotransmitter)
114
Q

two types of glutamate receptors on bipolar and horizontal cells (which determines whether the cell is excited or inhibited)

A
  1. inotropic glutamate receptors = excitatory

2. metabotropic glutamate receptors = inhibitory

115
Q

inotropic glutamate receptors

A

= excitatory; decreased release of glutamate from the photoreceptors actin on ionotropic receptors–>hyperpolarization (inhibition) because there is decreased excitation

116
Q

metabotropic glutamate receptors

A

= inhibitory; decreased release of gluamate from photoreceptors actin on metabotropic receptors–>depolarization (excitation) bc there is decreased inhibition

117
Q

on-center, off-surround

A

= one pattern of ganglion cell receptive feed in which light striking the center of the receptive field–>depolarizes (excites) the ganglion cell vs. light striking the surround of the receptive field–>hyperpolarizes (inhibits) the ganglion cell

118
Q

possible patterns of a ganglion cell receptive field

A
  1. on-center, off-surround

2. off-center, on-surround

119
Q

features detected by neurons in the visual cortex

A
  1. shape

2. orientation of figures

120
Q

three cortical cell types involved in the visual cortex

A
  1. simple cells
  2. complex cells
  3. hypercomplex cells
121
Q

simple cells

A
  • center-surround, on-off patterns
  • elongated rods rather than concentric circles
  • respond best to: bars of light that have the correct position and orientation
122
Q

complex cells respond best to

A

moving bars or edges of light with the correct orientation

123
Q

hypercomplex cells respond best to

A

lines with particular length and to curves and angles

124
Q

components of the middle ear

A
  1. tympanic membrane
  2. auditory ossicles (malleus, incus, stapes)
  3. oval window = a membrane between the middle ear and the inner ear
    * air filled
125
Q

mechanisms of sound amplification

A
  1. the lever action of the ossicles

2. the concentration of sound waves from the large tympanic membrane onto the smaller oval window

126
Q

components of the inner ear

A
  1. bony labyrinth (= semicircular canals + cochlea + vestibule)
  2. membranous labyrinth
  3. perilymph = fluid outside the ducts; high Na concentration
  4. endolymph = fluid within the ducts; high K concentration
    * fluid-filled
127
Q

structure of the cochlea

A

= three tubular canals

  1. scala vestibuli
  2. scala tympani
  3. scala media
    - scala vestibuli and scala tympani contain perilymph
    - scala media contains endolymph
128
Q

basilar membrane

A

borders the scala media; the site of the organ of Corti (the cell bodies of the hair cells contact the basilar membrane while the cilia of the hair cells are embedded in the tectorial membrane

129
Q

Organ of Corti structure

A

= contains the receptor cells (inner and outer hair cells) for auditory stimuli; cilia protrude from the hair cells and are embedded in the tectorial membrane

130
Q

inner vs. outer hair cells

A
  • inner hair cells: arranged in single rows; few in number

- outer hair cells: arranged in parallel rows; great in number

131
Q

spiral ganglion

A

contains the cell bodies of the auditory nerve (cranial nerve 8), which synapses on the hair cells

132
Q

steps in auditory transduction by the organ of Corti

A
  1. sound waves cause vibration of the organ of Corti (NOTE: because the basilar membrane is more elastic than the tectorial membrane, vibration of the basilar membrane causes the hair cells to bend by shearing force as they push a against the tectorial membrane)
  2. bending of the cilia–>changes in K+ conductance of the hair cell membrane (bending in one direction causes depolarization vs. bending in the other direction causes hyperpolarization)–>cochlear microphonic potential (oscillating potential)
  3. the oscillating potential of the hair cells causes intermediate firing of the cochlear nerves
133
Q

note about frequency and hair cell location

A

the frequency that activates a particular hair cell depends on the location of the hair cell along the basilar membrane

134
Q

base of the basilar membrane (near the oval and round windows) features

A

stiff and narrow; responds best to high frequencies

135
Q

apex of the basilar membrane (near the helicotrema) features

A

wide and compliant; responds best to low frequencies

136
Q

central auditory pathway

A
  1. fibers ascend through the lateral lemniscus–>
  2. inferior colliculus–>
  3. medial geniculate nucleus of the thalamus–>
  4. auditory cortex
    fibers may be crossed or uncrossed–>a mixture of ascending auditory fibres represents BOTH ears at all higher levels
137
Q

lesions of the cochlea of one ear–>

A

unilateral deafness

138
Q

central unilateral lesions–>

A

bilateral deafness

139
Q

features detected by the vestibular system

A
  1. angular acceleration of the head

2. linear acceleration of the head

140
Q

vestibular organ structure

A

= a membranous labyrinth consisting of

  1. three perpendicular semicircular canals
  2. utricle
  3. saccule
141
Q

function of the semicircular canals

A

contain endolymph and bathed in perilymph; detect angular acceleration or rotation

142
Q

functions of the utricle and saccule

A

detect linear acceleration

143
Q

receptors of the vestibular organ

A

hair cells located at the end of each semicircular canal; the cilia are embedded in a gelatinous structure (= the cupula); kinocilium = a single long cilium; stereocilia = smaller cilia

144
Q

steps in vestibular transduction of angular acceleration

A
  1. during counterclockwise rotation of the head (left), the horizontal semicircular canals and its attached cupula also rotate to the left - initially the cupula moves more quickly than the endolymph–>the cupula is DRAGGED through the endolymph–>the cilia on the hair cell bend to the right toward the kinocilium–>the hair cell depolarizes
  2. after several seconds, the endolymph “catches up” with the movement of the head and the cupula–>cilia return to their upright position and are no longer depolarized or hyperpolarized
  3. when the head stops moving, the endolymph continues to move counterclockwise (left), dragging the cilia in the opposite direction–>therefore if the hair cell was depolarized with the initial rotation, it will now hyperpolarize and if it was hyperpolarized initially (e.g. the ones on the right), it will depolarize
145
Q

if the stereocilia are bend away from the kinocilium–>

A

the hair cell hyperpolarizes (inhibition)

146
Q

nystagmus

A

= when the eyes slowly move in the OPPOSITE direction to maintain visual fixation and when the limit of eye movement is reached, the eyes rapidly snap back (nystagmus) then move slowly again

147
Q

definition of nystagmu

A

defined by the fast phase; therefore, the nystagmus occurs in the same direction as head rotation

148
Q

postrotatory nystagmu

A

occurs in the OPPOSITE direction of the head rotation

149
Q

receptor cells of the olfactory pathway

A

= located in the olfactory epithelium; true neurons that conduct action potentials into the CNS

150
Q

basal cells of the olfactory epithelium

A

undifferentiated stem cells that continuously turn over and replace the olfactory receptor cells (neurons)

151
Q

axon features of the olfactory nerves

A

= unmyelinated C fibers (smallest and slowest in the nervous system)

152
Q

2 innervations of the olfactory epithelium

A
  1. CNI

2. CN V (trigeminal) - detects noxious or painful stimuli (e.g. ammonia)

153
Q

fractures of the cribriform plate–>

A

sever input to the olfactory bulb and reduce (hyposmia) or eliminate (anosmia) the sense of smell; NOTE the response to ammonia will be INTACT because the response is carried by CN V

154
Q

mitral cells of the olfactory bulb

A

= 2nd order neurons; output forms the olfactory tract, which projects to the prepiriform cortex

155
Q

steps in transduction in the olfactory receptor neurons

A
  1. odorant molecules bind to specific olfactory receptor proteins on the cilia of the olfactory receptor cells
  2. when receptors are activated, they activate G proteins (Golf), which in turn activate adenylate cyclase
  3. adenylate cyclase–>increase in cAMP–>opens Na channels in the olfactory receptor membrane–>depolarizing receptor potential
  4. the receptor potential depolarizes the initial segment of the axon to threshold, and action potentials are generated and propagated
156
Q

note about taste receptors

A

they are NOT neurons, unlike olfactory receptors

157
Q

features of the anterior 2/3 of the tongue

  • papillae
  • tastes detected
  • innervation
A
  • papillae: fungiform
  • tastes detected: salty, sweet, umami
  • innervation: CN7
158
Q

features of the posterior 1/3 of the tongue

  • papillae
  • tastes detected
  • innervation
A
  • papillae: circumvallate and foliate
  • tastes detected: sour, bitter
  • innervation: CN9
    NOTE: the back of the throat and epiglottis are innervated by CNX
159
Q

taste pathway

A

CN7, 9, and 10 enter the medulla–>ascend in the solitary tract–>terminate on 2nd order taste neurons in the solitary nucleus–>project, primarily ipsilaterally to the ventral posteromedial nucleus of the thalamus–>taste cortex

160
Q

steps in taste transduction

A
  1. taste chemicals bind taste receptors–>produce depolarizing receptor potential in the receptor cell
161
Q

components of a motor unit

A

single motoneuron + the muscle fibers it innervates

162
Q

fine control motor unit components

A

= single motoneuron innervates only a few muscle fibers

163
Q

larger movement motor unit components

A

= single motoneuron innervates thousands of muscle fibers

164
Q

motoneuron pool

A

= a group of motoneurons that innervates fibers within the same muscle

165
Q

force of muscle contraction determinant

A

graded by recruitment of additional motor units (size principle)

166
Q

size principle

A

= as additional motor units are recruited, more motoneurons are involved and more tension is generated

167
Q

features of small motoneurons

A
  • innervate a FEW muscle fibers
  • have the LOWEST thresholds = fire first
  • generate the smallest force
168
Q

features of large motoneurons

A
  • innervate MANY muscle fibers
  • have the HIGHEST thresholds = fire last
  • generate the largest force
169
Q

types of muscle sensors

A
  1. muscle spindles
  2. Golgi tendon organs
  3. pacinian corpuscles
  4. free nerve endings
170
Q

muscle spindles

  • fiber groups
  • structure
  • detect
A
  • fiber groups: group Ia and II afferents
  • structure: arranged in parallel with extrafusal fibers
  • detect: both static and dynamic changes in muscle length
171
Q

Golgi tendon organs

  • fiber groups
  • structure
  • detect
A
  • fiber groups: Ib afferents
  • structure: arranged in series with extrafusal muscle fibers
  • detect: muscle tension
172
Q

Pacinian corpuscles

  • fiber groups
  • structure
  • detect
A
  • fiber groups: group II afferents
  • structure: distributed throughout the muscle
  • detect: vibration
173
Q

Free nerve endings

  • fiber groups
  • detect
A
  • fiber groups: III and IV afferents

- detect: noxious stimuli

174
Q

types of muscle fibers

A
  1. extrafusal fibers

2. intrafusal fibers

175
Q

extrafusal fibers

  • definition
  • innervation
  • function
A
  • definition = the bulk of the muscle
  • innervation = alpha-motoneurons
  • function = provide the force for muscle contraction
176
Q

intrafusal fibers

  • definition
  • innervation
  • structure
  • function
A
  • definition = smaller than extrafusal muscle fibers
  • innervation = gamma-motoneurons
  • structure = encapsulated in sheaths to form muscle spindles; run in parallel with extrafusal fibers but not for the entire length of the muscle
  • function = too small to generate significant force; used for fine movement?
177
Q

types of intrafusal fibers in muscle spindles

A
  1. nuclear bag fibers

2. nuclear chain fibers

178
Q

nuclear bag fibers

  • detect
  • innervation
  • structure
A
  • detect: rate of change in muscle length (fast, dynamic changes)
  • innervation: group Ia afferents
  • structure: nuclei collected in a central “bag” region
179
Q

nuclear chain fibers

  • detect
  • innervation
  • structure
A
  • detect: static changes in muscle length
  • innervation: group II afferents
  • structure: nuclei arranged in rows
  • more numerous than nuclear bag fibers
180
Q

how the muscle spindle works

A
  • muscle spindle reflexes oppose (correct for) increases in muscle length (stretch)
  • sensory information about muscle length is received by group Ia (velocity) and group II (static) afferent fibers
  • when a muscle is stretched, the muscle spindle is stretched–>stimulating group Ia and II afferents–>stimulates alpha-motoneurons to the spinal cord–>contraction and shortening of the muscle
181
Q

function of gamma-motoneurons

A

innervate intrafusal muscle fibers and adjust the sensitivity of the muscle spindle so that it will respond appropriately during muscle contraction

182
Q

three types of muscle reflexes

A
  1. stretch reflex (knee-jerk)
  2. Golgi tendon reflex (clasp-knife)
  3. flexor withdrawal reflex (after touching a hot stove)
183
Q

stretch reflex = knee jerk reflex

  • number of synapses
  • stimulus
  • afferent fibers
  • pathway
  • response
A
  • number of synapses: monosynaptic
  • stimulus: stretching of muscle
  • afferent fibers: Ia
  • pathway: stretching of muscle–>stimulates group Ia afferent fibers–>group Ia afferents synapse directly on alpha-motoneurons in the spinal cord that innervate the homonymous muscle–>contraction in the muscle that was stretch - ALSO synergistic muscles are activated and antagonistic muscles are inhibited
  • response: contraction of the stretched muscle
184
Q

Golgi tendon reflex (inverse myotactic)

  • number of synapses
  • stimulus
  • afferent fibers
  • pathway
  • response
A

= the inverse (opposite) of the stretch reflex

  • number of synapses: disynaptic
  • stimulus: active muscle contraction
  • afferent fibers: Ib
  • pathway: active muscle contraction–>stimulates the Golgi tendon organs and group Ib afferent fibers–>group Ib afferents stimulate inhibitory neurons in the spinal cord–>inhibit alpha-motoneurons–>relaxation of the muscle that was originally contracted
  • response: relaxation of the muscle
185
Q

myotactic reflex

A

= the stretch reflex

186
Q

alpha-motoneurons versus gamma-motoneurons

A

Alpha motor neurons control muscle contraction involved in voluntary movement, whereas gamma motor neurons control muscle contraction in response to external forces acting on the muscle.

187
Q

flexor withdrawal reflex

  • number of synapses
  • stimulus
  • afferent fibers
  • pathway
  • response
A
  • number of synapses: polysynaptic
  • stimulus: pain (e.g. stepping on a hot stove)
  • afferent fibers: II, III, and IV
  • pathway: pain–>stimulates the flexor reflex afferents of groups II, III, and IV–>the afferent fibers synapse polysynaptically (via interneurons) onto motoneurons in the spinal cord
  • on the ipsilateral side–>flexors are stimulated (contract) and extensors are inhibited (relax)–>arm is pulled away from the stove
  • on the contralateral side–>flexors are inhibited and extensors are stimulated (contract)–>crossed extension reflex to maintain balance
  • response: ipsilateral flexion; contralateral extension
188
Q

homonymous muscle

A

= the same muscle that was stimulated

189
Q

convergence

A

= when a single alpha-motoneuron receives its input from many muscle spindle group Ia afferents and produces spatial and/or temporal summation

190
Q

divergence

A

= when the muscle spindle group Ia afferent fibers project to all of the alpha-motoneurons that innervate the homonymous muscle

191
Q

Renshaw cells

A

= inhibitory cells in the ventral horn of the spinal cord

192
Q

recurrent inhibition

A

= when Renshaw cells receive input from collateral axons of motoneurons and, when stimulated, negatively feedback (inhibit) the motoneuron

193
Q

two major tracts controlling posture

A
  1. pyramidal tracts

2. extrapyramidal tracts

194
Q

pyramidal tracts

A

= pass through the medullary pyramids

  1. corticospinal
  2. corticobulbar
195
Q

extrapyramidal tracts

A
  1. rubrospinal
  2. pontine reticulospinal
  3. medullary reticulospinal
  4. lateral vestibulospinal tract
  5. tectospinal tract
196
Q

rubrospinal tract

  • origin
  • projection
  • stimulus
A
  • origin: red nucleus
  • projection: to interneurons in the lateral spinal cord
  • stimulus: –>stimulation of flexors and inhibition of extensors
197
Q

pontine reticulospinal tract

  • origin
  • projection
  • stimulus
A
  • origin: nuclei in the pons
  • projection: to ventromedial spinal cord
  • stimulus: –>general stimulatory effect on both flexors and extensors, with predominant effect on extensors
198
Q

medullary reticulospinal tract

  • origin
  • projection
  • stimulus
A
  • origin: medullary reticular formation
  • projection: to spinal cord interneurons in the intermediate gray area
  • stimulus: –>general inhibitory effect on both extensors and flexors, with predominant effect on extensors
199
Q

lateral vestibulospinal tract

  • origin
  • projection
  • stimulus
A
  • origin: dieters nucleus
  • projection: to ipsilateral motoneurons and interneurons
  • stimulus: –>powerful stimulation of extensors and inhibition of flexors
    = OPPOSITE function of the rubrospinal tract
200
Q

tectospinal tract

  • origin
  • projection
  • stimulus
A
  • origin: superior colliculus
  • projection: to cervical spinal cord
  • stimulus: involved in control of neck muscles
201
Q

spinal shock

A

= initial loss of reflexes; immediately after transection, there is loss of the excitatory influence from alpha and gamma motoneurons; limbs become flaccid and reflexes are absent

202
Q

lesion at C7–>

A

loss of sympathetic tone to the heart–>decrease HR and arterial BP

203
Q

lesion at C3–>

A

stops breathing

204
Q

effects of transection at lesions above the lateral vestibular nucleus

A

–>decerebrate rigidity = extensor posturing = exaggerated extensor contraction of all extremities

205
Q

lesions resulting in decerebrate rigidity

A
  1. lesions above the lateral vestibular nucleus

2. lesions above the pontine reticular formation and below the midbrain

206
Q

lesion above the red nucleus

A

–>decorticate posturing (flexion of arms and wrists) and intact tonic neck reflexes

207
Q

three functional sections of the cerebellum

A
  1. vestibulocerebellum
  2. pontocerebellum
  3. spinocerebellum
208
Q

role of vestibulocerebellum

A

= control of balance and eye movement

209
Q

role of pontocerebellum

A

= planning and initiation of movement

210
Q

role of spinocerebellum

A

= synergy = control of rate, force, range, and direction of movement

211
Q

layers of the cerebellar cortex

A
  1. granular layer
  2. Purkinje cell layer
  3. molecular layer
212
Q

granular layer

  • location
  • contains
A
  • location: innermost layer
  • contains
    1. granule cells
    2. golgi type II cells
    3. glomeruli = within which axons of mossy fibers form synaptic connections on dendrites of granular and golgi type II cells
213
Q

purkinje cell layer

  • location
  • contains
  • output
A
  • location: middle layer
  • contains: purkinje cells
  • NOTE output of the Purkinje cell layer is always inhibitory
214
Q

molecular layer

  • location
  • contains
A
  • location: outermost layer
  • contains
    1. stellate cells
    2. basket cells
    3. dendrites of purkinje and golgi type II cells
    4. parallel fibers (= axons of granule cells)
215
Q

inputs into the cerebellar cortex

A
  1. climbing fingers

2. mossy fibers

216
Q

climbing fingers

  • origin
  • synapses
  • function
A
  • origin: single region of the medulla (inferior olive)
  • synapses: multiple synpses onto Purkinje cells–>high frequency bursts or complex spikes
  • function: condition the purkinje cells (role in cerebellar motor learning)
217
Q

mossy fibers

  • origin
  • synapses
  • function
A
  • origin: many centers in the brainstem and spinal cord; includes vestibulocerebellar, spinocerebellar, and pontocerebellar afferents
  • synapses: multiple synapses on Purkinje fibers via interneurons
  • function:
    1. synapses on Purkinje cells–>simple spikes
    2. synapses on granule cells in glomuli
218
Q

output of the cerebellar cortex

A

Purkinje cells = ONLY output of the cerebellar cortex and the output of the purkinje cells is ALWAYS INHIBITORY; neurotransmiitter = GABA

219
Q

clinical disorders of the cerebellum

A
  1. ataxia
  2. dysdiadochokinesia
  3. intention tremor
  4. rebound phenomenon
220
Q

components of basal ganglia

A
  1. striatum
  2. globus pallidus
  3. subthalamic nuclei
  4. substantia nigra
221
Q

function of the basal ganglia

A

modulates thalamic outflow to the motor cortex to plan and execute smooth movements (i.e. control of movements); many synaptic connections are INHIBITORY and use GABA as the neurotransmitter

222
Q

two pathways of the striatum to the thalamus and cerebral cortex

A
  1. indirect = inhibitory

2. direct = excitatory

223
Q

neurotransmitter btwn striatum and substantia nigra

A

dopamine = inhibitory in the Indirect pathway (D2 receptors) and excitatory on the direct pathway (D1 receptors); the OVERALL action of dopamine is EXCITATORY

224
Q

lesions of the globus pallidus–>

A

inability to maintain postural support

225
Q

lesions of the subthalamic nucleus

  • cause
  • result
A
  • cause: release of inhibition on the contralateral side

- result: wild, flinging movements (hemiballismus)

226
Q

lesions of the striatum

  • caused by
  • result
A
  • caused by: release of inhibition
  • result = quick, continuous uncontrollable movements
    occurs in patients with Huntington disease
227
Q

lesions of the substantia nigra

A
  • caused by: destruction of dopaminergic neurons (since dopamine INHIBITs the INDIRECT (inhibitory) pathway and excites the direct (excitatory; D1) pathway, destruction of the dopaminergic neurons is, overall, inhibitory
  • result: lead-pipe rigidity, tremor, and reduced voluntary movement
    occurs in patients with Parkinson disease
228
Q

function of supplementary motor cortex

A

programs complex motor sequences and is active during “mental rehearsal” for a movement

229
Q

primary motor cortex (area 4)

  • function
  • organization
A
  • function: the execution of movements

- organization: somatotopically (motor homunculus)

230
Q

predominant EEG wave in awake adult with eyes open

A

beta waves

231
Q

predominant EEG wave in awake adult with eyes closed

A

alpha waves

232
Q

predominant EEG wave during sleep

A

slow waves

233
Q

driver of circadian periodicity

A

suprachiasmatic nucleus of the hypothalamus; input from the retina

234
Q

features of REM sleep

A
  1. rapid eye movements
  2. loss of muscle tone
  3. pupillary constriction
  4. penile erection
235
Q

factors that decrease duration of REM sleep

A
  1. benzodiazepines

2. increasing age

236
Q

functions of the right cerebral cortex hemisphere

A
  1. facial expression
  2. intonation
  3. body language
  4. spatial tasks
237
Q

functions of the left cerebral cortex hemisphere

A
  1. language
238
Q

lesions of the left hemisphere–>

A

aphasia

239
Q

damage to the Wernicke area–>

A

sensory aphasia = difficulty understanding written or spoken language

240
Q

damage to the Broca area–>

A

motor aphasia = speech and writing are affected but understanding is intact

241
Q

short term memory

A

involves synaptic changes

242
Q

long term memory

A

involves structural changes in the nervous system; is more stable

243
Q

lesions that block ability to form new long-term memories

A

bilateral lesions of the hippocampus

244
Q

components of the blood-brain barrier BBB

A
  1. endothelial cells of the cerebral capillaries

2. choroid plexus epithelium

245
Q

transport across the BBB

A
  • freely movable and equilibrate = lipid soluble substances (CO2, O2) and water
  • carriers = other substances
    composition of the CSF is approximately the same as the interstitial fluid of the brain but differs significantly from blood
246
Q

CSF versus blood:

  • equal in
  • CSFblood
A
  • equal in: Na, Cl, HCO3, osmolarity

- CSFblood: Mg, creatinine

247
Q

functions of the BBB

A
  1. maintains a constant environment for neurons
  2. protects the brain from endogenous or exogenous toxins
  3. prevents escape of neurotransmitters from their functional sites in the CNS into general circulation
248
Q

heat-generation mechanisms

A
  1. thyroid hormone–>increase metabolic rate and heat production by stimulating Na-K-ATPase
  2. cold temperatures activate the sympathetic nervous system and beta receptors in brown fat–>increase metabolic rate and heat production
  3. shivering (orchestrated by the hypothalamus)
249
Q

most potent mechanism for increasing heat production

A

shivering

250
Q

heat loss mechanisms

A
  1. radiation
  2. convection
    orchestrated by the anterior hypothalamus
  3. evaporation (depends on activity of sweat glands, which are under sympathetic muscarinic control)
251
Q

hypothalamic set point for body temperature

A
  • anterior hypothalamus compares detected core temperature to set point temperature
  • posterior hypothalamus is responsible for heat generating or heat loss mechanisms
252
Q

pyrogens

A

increase the set-point temperature by increasing production of IL-1 by phagocytic cells–>IL-1 and other cytokines cross the BBB–>IL-1 acts on the anterior hypothalamus to increase production of prostaglandin E2–>prostaglandins increase the set-point temperature

253
Q

aspirin MOA

A

inhibits cyclooxygenase–>inhibits production of prostaglandins–>decreases set point temperature–>decreases fever

254
Q

steroid MOA

A

block the release of arachidonic acid from brain phospholipids, thereby preventing the production of prostaglandins

255
Q

heat exhaustion

A

caused by excessive sweating–>blood volume and arterial blood pressure decrease–>syncope occurs

256
Q

heat stroke

A

occurs when body temperatures increase to the point of tissue damage; sweating is impaired and core temperature increases further

257
Q

malignant hyperthermia

A

characterized by massive increase in O2 consumption and heat production by skeletal muscles–>rapid rise in body temperature

ACVIM General Boards (3 decks)

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