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630: Medical Physiology > Neurophysiology (Part 3) > Flashcards

Neurophysiology (Part 3) Flashcards

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USMLE® Step 1 flashcards
1
Q

Descending motor pathways are divided among what 2 tracts?

A

pyramidal and extrapyramidal tracts

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2
Q

What are the 2 types of pyramidal tracts?

A
  • corticospinal tract

- corticobulbar tract

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3
Q

Where do the pyramidal tracts descend down to?

A

They pass through the medullary pyramids and descend directly onto lower motor neurons in the spinal cord

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4
Q

What are the 5 types of extrapyramidal tracts?

A
  • rubrospinal tract
  • potine reticulospinal tract
  • medullary reticulospinal tract
  • lateral vestibulospinal tract
  • tectospinal tract
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5
Q

Where does the rubrospinal tract originate from and where does it project to?

A

It originates in the red nucleus and projects to the motoneurons in the lateral spinal cord

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6
Q

Stimulation of the red nucleus (rubrospinal tract) produces what?

A

activation of flexor muscles and inhibition of extensor muscles

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7
Q

Where does the pontine reticulospinal tract originate from and where does it project to?

A

It originates in nuclei of the pons and projects to the ventromedial spinal cord

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8
Q

Stimulation of the pontine reticulospinal tract produces what?

A

General activation of both flexor and extensor muscles, with its predominant effect on extensors

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9
Q

Where does the medullary reticulospinal tract originate from and where does it project to?

A

It originates in the medullary reticular formation and projects to motoneurons in the spinal cord

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10
Q

Stimulation of the medullary reticulospinal tract produces what?

A

General inhibition of both flexor and extensor muscles, with its predominant effect on extensors

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11
Q

Where does the lateral vestibulospinal tract originate from and where does it project to?

A

It originates in the lateral vestibular nucleus and projects to the ipsilateral motoneurons in the spinal cord

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12
Q

Stimulation of the lateral vestibulospinal tract produces what?

A

Activation of extensors and inhibition of flexors

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13
Q

Where does the tectospinal tract originate from and where does it project to?

A

It originates in the superior colliculus and projects to the cervical spine

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14
Q

What is the tectospinal tract involved in?

A

Control of neck muscles

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15
Q

If a brainstem lesion occurs above the pontine reticular formation and lateral vestibular nucleus, but below the midbrain what will occur and why?

A

It will cause a dramatic increase in extensor tone (called decerebrate rigidity) because the pontine reticular formation and lateral vestibular nucleus have powerful excitatory effects on extensor muscles

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16
Q

Will lesions above the midbrain cause decerebrate rigidity?

A

No

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17
Q

What does the cerebellum regulate and play a role in?

A

movement and posture and plays a role in certain kinds of motor learning

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18
Q

What does the cerebellum help to control?

A

The rate, range, force, and direction of movements (collectively called synergy)

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19
Q

The cerebellum is connected to the brainstem via what?

A

3 cerebellar peduncles that contain both afferent and efferent nerve fibers

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20
Q

What are the 3 main divisions of the cerebellum?

A
  • vestibulocerebellum
  • spinocerebellum
  • pontocerebellum
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21
Q

What is the vestibulocerebellum dominated by and what does it control?

A

It is dominated by vestibular input and controls balance and eye movements

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22
Q

What is the spinocerebellum dominated by and what does it control?

A

It is dominated by spinal cord input and controls synergy of movement

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23
Q

What is the pontocerebellum dominated by and what does it control?

A

It is dominated by cerebral input and controls the planning and initiation of movements

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24
Q

How many layers are there to the cerebellar cortex and how are they described?

A

3, all of which are described in relaation to its output cells, the Purkinje fibers

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25
Q

List the 3 layers of the cerebellar cortex staring with the innermost layer

A
  • granular layer
  • Purkinje cell layer
  • molecular layer
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26
Q

What does the granular layer contain?

A

the granule cells, Golgi II cells, and glomeruli

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27
Q

Mossy fibers from which 2 tracts synapse on dendrites of the granule and Golgi type II cells in the granular layer of the cerebellar cortex?

A

spinocerebellum and pontocerebellum tracts

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28
Q

What does the Purkinje cell layer contain?

A

Purkinje cells

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29
Q

Output from the Purkinje cell layer is always ______.

A

inhibitory

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30
Q

What does the molecular layer contain?

A

Outer stellate cells, basket cells, dendrites of Purkinje and Golgi II cells, and axons of granule cells

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31
Q

What 2 input systems provide excitatory input to the cerebellar cortex?

A
  • the climbing fiber system

- the mossy fiber system

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32
Q

Excitatory projections from the cerebellar cortex modulates the output of what? How?

A

These excitatory projections activate secondary circuits, which modulate the output of the cerebellar nuclei via the Purkinje cells

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33
Q

Which of the 2 fiber systems constitutes the majority of the cerebellar input?

A

the mossy fiber system

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34
Q

Describe the synapses between the climbing fibers and the Purkinje cells

A

Each Purkinje cell receives input from only one climbing fiber, however a single AP from a climbing fiber can elicit multiple excitatory bursts (complex spikes) in the dendrites of the Purkinje cell

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35
Q

Describe the synapses between the mossy fibers and the Purkinje cells

A

Mossy fibers project to excitatory granule cells, that ascend to the molecular layer and give rise to parallel fibers that contact the dendrites of many Purkinje cells

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36
Q

In summary one climbing fiber activates __ Purkinje cell and one mossy fibers activates ___ Purkinje cells

A

one

many

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37
Q

In summary climbing fibers cause ____ spikes that produce multiple action potentials whereas mossy fibers cause _____ spikes that produce single action potentials.

A

complex

simple

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38
Q

What is the function of cerebellar intenreurons?

A

to modulate Purkinje cell output

39
Q

With the exception of the granule cells, all of the cerebellar interneurons are ______.

A

inhibitory

40
Q

The only output of the cerebellar cortex is via what?

A

axons of Purkinje cells

41
Q

Purkinje cell output is always inhibitory, why?

A

Because the NT released at these synapses is GABA which is an inhibitory neurotransmitter

42
Q

What do cerebellar lesions result in?

A

an abnormality of movement called ataxia

43
Q

Cerebellar ataxia is a lack of coordination due to what?

A

errors in rate, range, force, and direction of movement

44
Q

What are the 5 ways in which ataxia can be exhibited?

A
  • Delayed onset
  • Overshoot
  • Dysdiadochokinesia
  • Intention tremors
  • Rebound phenomenon
45
Q

Describe delayed onset ataxia

A

Movement or poor execution of the sequence of a movement is delayed causing the movement to appear uncoordinated

46
Q

Describe overshoot ataxia

A

A limb may overshoot its target or stop before reaching its target

47
Q

Describe dysdiadochokinesia ataxia

A

A person is unable to perform rapid, alternating movements

48
Q

Describe intention tremors

A

These are tremors that occur perpendicular to the direction of a voluntary movement, increasing near the end of the movement

49
Q

Intention tremors are seen in what type of pathology?

A

Parkinson’s disease

50
Q

Describe the rebound phenomenon

A

A person is unable to stop a movement

51
Q

The basal ganglia are the deep nuclei of the telencephalon, list the 4 nuclei

A
  • Striatum which consists of the caudate nucleus and the putamen
  • Globus pallidus
  • Amygdala
52
Q

What are the associated nuclei of the basal ganglia?

A
  • Ventral anterior and ventral lateral nuclei of the thalamus
  • Subthalamic nulceus of the diencephalon
  • Substantia nigra of the midbrain
53
Q

What is the major function of the basal ganglia?

A

to influence the motor cortex via pathways through the thalamus

54
Q

What are the 2 other functions of the basal ganglia?

A

To aid in planning and execution of smooth movements, and to also contribute to affective and cognitive functions

55
Q

What are the 2 pathways into and out of the basal ganglia?

A
  • indirect

- direct

56
Q

The overall output of the indirect pathway is ______, whereas the overall output of the direct pathway is _____.

A

inhibitory

excitatory

57
Q

What are 2 diseases of the basal ganglia?

A

Parkinson’s disease and Huntington’s disease

58
Q

Describe Parkinson’s disease

A

Occurs when cells of the pars compacta of the substantia niagra degenerate, which reduces inhibition via the indirect pathway and reducing excitation via the direct pathway

59
Q

What are the characteristics of Parkinson’s disease?

A
  • resting tremor
  • slowness and delay of movement
  • shuffling gait
60
Q

How is Parkinson’s disease treated?

A

By replacing dopamine by treatment with L-dopa or administration of dopamine agonists

61
Q

Describe Huntington’s disease

A

It is a hereditary disorder caused by destruction of striatal and cortical cholinergic neurons and inhibitory GABAergic neruons

62
Q

What are the symptom of Huntington’s disease?

A

choreic (writhing) movements and dementia

63
Q

Where are voluntary movements directed by?

A

the motor cortex via descending pathways

64
Q

What is the function of the motor plan

A

The motivation and ideas necessary to produce voluntary activity are organized in the cerebral cortex and then transmitted to the supplementary motor and premotor cortices to develop the plan. This plan will identify the specific muscles that need to contract, how much they need to contract, and in what sequence

65
Q

After the motor plan is developed, where is it transmitted?

A

to upper motoneurons in the primary motor cortex, which send it through descending pathways to lower motoneurons in the spinal cord

66
Q

What are the planning and execution stages of the motor plan influenced by?

A

motor control systems in the cerebellum and basal ganglia

67
Q

What are the 3 areas of the motor cortex?

A
  • primary motor cortex
  • supplementary motor cortex
  • premotor cortex
68
Q

The supplementary motor cortex and premotor cortex are responsible for what?

A

generating a plan of movement

69
Q

When is the supplementary motor complex active?

A

during “mental rehearsal” of a movement

70
Q

Once the plan of movement is generated is transferred to the primary motor cortex, for what?

A

execution

71
Q

Describe what happens as programmed patterns of motoneurons are activated from the primary motor cortex

A

This activation excites upper motoneurons which transmits the plan to the brain stem and spinal cord, where lower motoneurons are activated and produce coordinated contraction of the appropriate muscles

72
Q

The primary motor cortex is topographically organized and is described as what?

A

the motor homunculus

73
Q

The topographic organization of the primary motor cortex is dramatically illustrated by what type of seizures?

A

jacksonian seizures

74
Q

The brain is composed of 80% fluid, most of which is what?

A

cerebrospinal fluid (CSF)

75
Q

CSF is formed at a rate of ___ml/day by what cells?

A

500

by the epithelial cells of the choroid plexus

76
Q

Describe the path the CSF takes after it is produced by the choroid plexus

A

It flows into the ventricles and the subarachnoid spaces, which surround the brain and spinal cord

77
Q

The rate at which CSF is transferred to venous blood is equivalent to what?

A

the rate of CSF formation

78
Q

How is CSF sampled?

A

Using a lumbar puncture in the lumbar cistern

79
Q

What is the barrier between the cerebral capillary blood and CSF called?

A

the choroid plexus

80
Q

What are the 3 layers of the choroid plexus?

A
  • capillary endothelial cells and basement membrane
  • neuroglial membrane
  • epithelial cells of the choroid plexus
81
Q

What is the barrier between the cerebral capillary blood and the interstitial fluid of the brain called?

A

blood-brain barrier

82
Q

What are the 2 ways in which the blood-brain barrier differs from the analogous barrier in other tissues?

A
  • the junctions between endothelial cells in the brain are so “tight” that few substances can cross between the cells
  • only a few substances can pass through the endothelial cells (lipid-soluble substances can; water-soluble substances cannot)
83
Q

What is CSF formed by?

A

the epithelial cells of the choroid plexus

84
Q

What molecules are excluded from CSF?

A

Protein and cholesterol because of their large molecular size

85
Q

Which molecules move freely and equilibrate between the CSF and the brain interstitial fluid?

A

Lipid-soluble substances such as oxygen and carbon dioxide

86
Q

What substances are present at approximately the same concentration in the CSF and in the brain interstitial fluid?

A
  • sodium
  • chloride
  • bicarbonate
  • osmolarity
87
Q

What substances are present at higher concentrations in the CSF compared to in the brain interstitial fluid?

A
  • magnesium

- creatinine

88
Q

What substances are present at higher concentrations in the brain interstitial fluid compared to in the CSF?

A
  • potassium
  • calcium
  • glucose
  • amino acids
  • pH
89
Q

What are the functions of the CSF?

A
  • provide a constant, controlled environment for the brain cells
  • to protect the brain from endogenous or exogenous toxins
  • prevent escape of local transmitters into the general circulation
90
Q

Do ionized or nonionized drugs readily penetrate the brain readily and why?

A

nonionized drugs do because they are lipid-soluble

91
Q

What things may increase the permeability of the blood-brain barrier and allow substance normally excluded to enter the brain?

A

inflammation, irradiation, and tumors

92
Q

What part of the brainstem do the rubrospinal and tectospinal tracts originate?

A

midbrain

93
Q

What part of the brainstem does the pontine reticulospinal tract originate?

A

Pons

94
Q

What part of the brainstem do the medullary reticulospinal lateral vestibulospinal tracts originate?

A

medulla

630: Medical Physiology (24 decks)

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