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Physiology II > Spinal Cord, Brainstem, Cortex Control of Motor Function (Lec 7) > Flashcards

Spinal Cord, Brainstem, Cortex Control of Motor Function (Lec 7) Flashcards

1
Q

What are the three groups of neurons on the spinal cord?

A

sensory (afferent)
anterior motor neurons
interneurons

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2
Q

What type of fibers to alpha motor neurons give rise to?

A

alpha fibers

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3
Q

True or False?

anterior motor neurons are 30x as numerous as interneurons

A

False; interneurons are 30x as numerous as anterior motor neurons

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4
Q

What are some characteristics of interneurons?

A

small and highly excitable, capable of spontaneous activity, responsible for most of spinal cord integrative function

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5
Q

What type of cells are Renshaw cells and what do they do?

A

Inhibitory cells; transmit inhibitory signals to surrounding motor neurons - results in lateral inhibition

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6
Q

What do Renshaw cells receive collateral branches form?

A

alpha motor neurons

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7
Q

How long is a muscle spindle?

A

3-10 mm long

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8
Q

How many intrafusal fibers does a muscle spindle consist of?

A

3-12 intrafusal fibers

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9
Q

What are intrafusal fibers of a muscle spindle innervated by?

A

innervated by small gamma motor neurons

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10
Q

Does the central region of the muscle spindle have contractile fibers?

A

no

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11
Q

What does the central region of the muscle spindle function as?

A

sensory receptor; sensory fibers originate from the central region

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12
Q

What stimulates sensory fibers in the muscle spindle?

A

stretching of the central region of intrafusal fibers

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13
Q

What does the muscle spindle detect?

A

changes in muscle length - causes ends of intrafusal fibers to contract

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14
Q

What are the two types of sensory fibers in the muscle spindle?

A

Ia (primary fibers)

II (secondary fibers)

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15
Q

The following characteristics describe which type of sensory fiber in the muscle spindle:
forms annulospiral ending
17 micrometers in diameter
Transmits at 70-120 m/sec

A

Ia (primary fibers)

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16
Q

How long are II (secondary) sensory fibers in the muscle spindle?

A

8 micrometers

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17
Q

In regards to muscle spindle function, what is the dynamic stretch reflex?

A

elicited by rapid stretch or unstretch, opposes sudden changes to muscle length

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18
Q

In regards to muscle spindle function, what is the static reflex?

A

causes degree of muscle contraction to remain relatively constant

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19
Q

What do the two muscle spindle reflexes work together to prevent?

A

jerkiness of body movements (damping)

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20
Q

Signals for the dynamic stretch reflex are transmitted by what?

A

primary nerve endings

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21
Q

What transmits the signal for the static reflex?

A

both primary and secondary endings

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22
Q

Which class of intrafusal muscle fibers have nuclei concentrated in “bag” in center of receptor area?

A

nuclear bag fibers

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23
Q

Which class of intrafusal muscle fibers have nuclei aligned in chain throughout receptor area?

A

nuclear chain fibers

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24
Q

The amount of gamma motor neurons is equal to about ___ the number of alpha motor neurons

A

half

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25
Q

In regards to gamma motor neurons, which type has a 5 micrometer diameter and supplies small intrafusal fibers in the middle of the muscle spindle?

A

Alpha Gamma

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26
Q

In regards to gamma motor neurons, which type excites nuclear bag intrafusal fibers?

A

Gamma-dynamic

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27
Q

In regards to gamma motor neurons, which type excites nuclear chain intrafusal fibers?

A

Gamma-static

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28
Q

What are the brain areas that control gamma fibers?

A

Bulboreticular region of brain stem, cerebellum, basal nuclei, and cerebral cortex

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29
Q

The golgi tendon organ is an encapsulated sensory receptor through which ___ ___ fibers pass

A

muscle tendon

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30
Q

How many muscle fibers are attached to each golgi tendon organ?

A

10-15

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31
Q

What stimulates the golgi tendon organ?

A

contracting or stretching of muscle

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32
Q

What does the golgi tendon organ detect?

A

muscle tension

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33
Q

What is the circuitry pathway of the golgi tendon organ?

A

type Ib afferent (16 micrometer diameter) -> inhibitory interneuron -> anterior motor neuron

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34
Q

What does a myogram of the flexor reflex show?

A

rapid onset of reflex, an interval of fatigue, and after discharge after the input stimulus is over

35
Q

What does a myogram of the extensor reflex show?

A

slow onset but prolonged afterdischarge

36
Q

In regards to the motor cortex, signals generated here cause more complex patterns of movement than the more discrete pattern generated by the primary motor cortex

A

premotor area

37
Q

Anterior part of the premotor area of the motor cortex develops a ___ ___ of the total muscle movement that is to be performed

A

motor image

38
Q

True or False?
The motor image in the posterior motor cortex excites each successive pattern of muscle activity required to achieve the image

A

true

39
Q

Where does the posterior motor cortex send signals to?

A

a. ->primary motor cortex

b. -> basal nuclei and thalamus -> primary motor cortex

40
Q

How are cells in the motor cortex organized?

A

into vertical columns

41
Q

Each column of the motor cortex stimulates what?

A

a group of synergistic muscles or even a single muscle

42
Q

How many layers does each column in the motor cortex have?

A

6

43
Q

Pyramidal cells are in which layer of the column of motor cortex cells?

A

5th

44
Q

Which layer of the column of motor cortex cells do input signals enter?

A

2-4

45
Q

Neurons arising in the 6th layer of the column of motor cortex cells communicate with what?

A

other regions of the cerebral cortex

46
Q

A generalization of the motor paths would be that typical descending pathways consist of a series of ___ motor neurons

A

two: upper motor neurons, lower motor neurons

47
Q

Where are upper motor neurons found and where do they originate?

A

entirely within the CNS; originate in cerebral cortex, cerebellum, and brainstem

48
Q

Where are lower motor neurons found and where do they originate?

A

Make up spinal and cranial nerves; begin in CNS

49
Q

What type of neurons make up lower motor neurons?

A

alpha motor neurons

50
Q

What are some characteristics of upper motor neurons?

A

originate in the motor cortices; 75-85% decussate in pyramids and form the lateral corticospinal tracts; remainder decussate near synapse with lower motor neurons and form anterior corticospinal tracts; most synapse with association neurons in spinal cord central gray

51
Q

The corticospinal tract and corticobulbar tract make up what system?

A

pyramidal

52
Q

What makes up the lateral corticospinal tract? What does it supply?

A

corticospinal fibers that have crossed in the medulla; supplies all levels of the spinal cord

53
Q

What makes up the anterior coritcospinal tract? What does it supply?

A

uncrossed corticospinal fibers that cross near level of synapse with LMNs; supply neck and upper limbs

54
Q

What is the origin of the corticospinal tract (aka pyramidal tract)?

A

primary motor cortex, premotor cortex, somatosensory cortex

55
Q

What is the pathway of the corticospinal tract?

A

site of origin -> internal capsule -> medullary pyramids in lower medulla -> lateral columns of spinal cord (lateral corticospinal tract)

56
Q

What happens to the fibers in the corticospinal tract that do not cross?

A

continue down ipsilaterally in ventral corticospinal tract

57
Q 
In regards to the corticospinal tract, the following characteristics describe what type of cell?:
located in motor cortex
large cells
large fibers
transmit 70 m/sec
make up about 3% of fibers in tract
send collaterals back to cortex
A

Giant pyramidal cells

58
Q

In regards to the corticospinal tract, what do other fibers from the cortex do?

A

pass into caudate nucleus and putamen, pass to red nucleus, pass to reticular substance and vistibular nuclei, large numbers of fibers pass to pontine nuclei

59
Q

What are the functions of the corticospinal tract?

A

adds speed and agility to conscious movements - especially movements of hand; provides a high degree of motor control (ex: movement of individual fingers)

60
Q

What do corticospinal tract lesions cause?

A

reduced muscle tone, clumsiness, weakness, not complete paralysis

61
Q

What does the corticobulbar tract innervate?

A

the head

62
Q

Most fibers in the corticobulbar tract terminate where?

A

reticular formation near cranial nerve nuclei

63
Q

Association neurons of the corticobulbar tract leave reticular formation and synapse where?

A

in cranial nerve nuclei with lower motor neurons

64
Q

In regards to red nucleus, fibers from primary motor cortex (corticorubral pathway) and branches from corticospinal tract synapse where?

A

in magnocellular portion of red nucleus

65
Q

In regards to red nucleus, large neurons from magnocellular region of red nucleus give rise to the rubrospinal tract which decussates where?

A

in lower brain stem

66
Q

The magnocellular region of the red nucleus has a ___ representation of all the muscles of the body

A

somatotopic

67
Q

What does the extrapyramidal system include?

A

pathways that contribute to motor control but that are not part of the corticospinal system: rubrospinal tracts, vestibulospinal tracts, and reticulospinal tracts

68
Q

Where does the Rubrospinal tract begin, decussate, and descend?

A

begins in red nucleus
decussates in midbrain
descends in lateral funiculus

69
Q

The function of the rubrospinal tract is closely related to what?

A

cerebellar function

70
Q

What do lesions on the rubrospinal tract cause?

A

impairment of distal arm and hand movement; intention tremors

71
Q

Where does the vestibulospinal tract originate, descend, and synapse?

A

orginates in vestibular nuclei - receives input from
vestibular nerve

descends in anterior funiculus

synapses with LMNs to extensor muscles - primarily involved in maintenance of upright posture

72
Q

Where does the reticulospinal tract originate and descend?

A

originates in various regions of reticular formation

descends in anterior portion of lateral fundiculus

note: thought to mediate larger movements of trunk and limbs that do not require balance or fine movements of upper limbs

73
Q

What do Pontine reticular nuclei do and make up?

A 
excite antigravity (axial) muscles;
make up the pontine reticulospinal tract
74
Q

What do Medullary reticular nuclei do and make up?

A

relax antigravity muscles;

make up the medullary reticulospinal tract

75
Q

What are the vestibular apparatus components?

A

Utricle, Saccule, Semicircular canals

76
Q

Where is the macula of the utricle located and what does it do?

A

located on horizontal plane; plays role in determining orientation of head when head is upright

77
Q

Where is the macula of the saccule located and what does it do?

A

located in a vertical plane; signals head orientation when person is lying down

78
Q

Each macula is covered by a gelatinous layer. Describe this layer.

A

contains large number of embedded small calcium carbonate crystals (statoconia); contains thousands of hair cells which project cilia into the gelatinous layer; the wight of the statoconia bends cilia in the direction of gravitational pull

79
Q

What are some characteristics of hair cells found in macula?

A

50-70 small cilia; 1 large cilium; tips of sterocilia are connected together and to kinocilium; bending of cilia opens hundreds of cation channels causing receptor membrane depolarization; bending of cells in opposite direction causes hyper polarization; oriented such that bending the head in different directions causes different groups of hair cells to depolarize

80
Q

In regards to semicircular canals, what occurs when head is bent forward 30 degrees?

A

lateral ducts are horizontal; anterior ducts are in vertical planes projecting forward and 45 degrees outward; posterior ducts are in vertical planes projecting backward and 45 degrees

81
Q

The following characteristics describe what?:

enlargement at one end of each duct; filled with endolymph

A

ampulla

82
Q

What is the small crest within each ampulla called?

A

crista ampullaris

83
Q

What is the loose mass of gelatinous tissue on top of the crista called?

A

cupula

84
Q

Describe what happens in regards to semicircular canals when the head begins to rotate in any direction

A

inertia of the fluid in one or more of the semicircular canals remains stationary while semicircular canal rotates with the head; hundreds of hair cells within each cupola detect bending and send signals via the vestibular nerve

Physiology II (19 decks)

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