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physio - e2 - lecture slides > L1-Spinal Cord, brainstem, cortex control of motor function > Flashcards

L1-Spinal Cord, brainstem, cortex control of motor function Flashcards

1
Q

groups of neurons in spinal cord:

A
  • sensory (afferent)
  • anterior motor neurons (efferents)
  • interneurons
  • renshaw cells
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2
Q

what do alpha motor neurons give rise to?

A

alpha fibers

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3
Q

describe characteristics of interneurons

A
  • 30x as numerous as anterior motor neurons
  • small and highly excitable
  • capable of spontaneous activity
  • responsibility for most of spinal cord integrative function
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4
Q

describe the characeristics of renshaw cells

A
  • inhibitory cells in anterior horns of spinal cord
  • receive collateral branches from alpha motor neurons
  • transmit inhibitory signals to surrounding motor neurons: result in lateral inhibition; enhance fluidity of limb movement
  • transmit inhibitory signals to same motor neuron: results in recurrent inhibition
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5
Q

describe motor neurons (efferent):

A
  • cell body is in the motor cortex, brainstem or spinal cord
  • axon projects to SC or to effector organ/muscle
  • upper motor neuron synapse onto interneurons in SC or to lower motor neuron
  • lower motor neuron go from spinal cord to effector
  • lower motor neurons are classified as alpha, beta, or gamma
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6
Q

describe upper motor neuron:

A
  • descends the spinal cord to level of the appropriate spinal nerve root
  • synapses with lower motor neuron or interneuron
  • neurotransmittor of UMN to LMN is GLUTAMATE, which binds to glu receptors
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7
Q

describe lower motor neurons:

A
  • typically found in anterior gray portion of SC or cranial nerve nuclei of brainstem
  • terminate at effector with acetylcholine as neurotransmitter
  • cranial nerves are unique LMN
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8
Q

describe the motor unit components:

A
  • motor unit
  • motor neuron pool
  • recruitment
  • small motor neurons
  • larger motor neurons
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9
Q

describe the motor unit

A
  • composed of a single motor neuron and the muscle fibers it innervates
  • composed of extrafusal fibers
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10
Q

describe motor neuron pool

A

group of motor neurons that innervate fibers within the same muscle

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11
Q

recruitment

A

recruitment refers to the increase in tension of muscle contractions by the activation of additional motor units (size principle)

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12
Q

describe small motor neurons

A
  • innervate a few muscle fibers
  • lowest thresholds
  • fire first
  • generate smallest force
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13
Q

describe large motor neurons

A
  • innervate many muscle fibers
  • highest thresholds
  • fire LAST
  • generate largest force
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14
Q

differentiation upper motor neuron lesions:

A
  • muscle bulk: preserved
  • muscle tone: spastic
  • spontaneous movements: none
  • reflexes: increased
  • babinski reflex: present
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15
Q

differentiation of lower motor neuron lesions:

A 
muscle bulk: atrophy
muscle tone: flaccid
spontaneous movements: fasciculations
reflexes: absent
babinski reflex: absent
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16
Q

describe interneurons

A
  • 30x as numerous as anterior motor neurons
  • bipolar (shape)
  • capable of spontaneous activity
  • responsible for most of spinal cord integrative function
  • most are inhibitor - GABA is neurotransmitter
  • excitatory - glutamate is nt
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17
Q

neural connections in the SC: renshaw cells

A
  • inhibitory cells use GLYCINE as nt
  • receive collateral branches from alpha-MNs
  • may be supplied by more than 1 alpha-MN and may synapse with multiple MNs
  • transmit inhibitory signals to surrounding MNs: results in lateral inhibition // enhances fluidity of limb movement
  • transmit inhibitory signals to same MN: negative feedback.
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18
Q

what are the two inhibitory neurons:

A

I-alpha and I-beta

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19
Q

describe I-alpha

A
  • inhibits antagonistic muscle
  • signal from muscle spindle
  • avoids spasticity
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20
Q

describe I-beta

A
  • autogenic inhibition reflex
  • golgi tendon activated with stretch
  • connects with l-beta to inhibit same muscle
  • responsible for smooth contraction and protects muscle from tears
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21
Q

describe excitatory interneurons

A
  • involved in spinal reflex to remove extremity from damaging stimulus
  • place foot on track, sensory information must be translated into motor output
  • sensory group 3 afferents send signal to excitatory interneurons that send ipsilateral and contralateral signals
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22
Q

list the muscle sensors

A
  • muscle spindle (group Ia and II afferents)
  • golgi tendon organ (group Ib afferents)
  • Pacinian corpuscles (group II afferents)
  • Free nerve endings (groups III and Iv afferents)
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23
Q

describe muscle spindle groups Ia and II

A
  • arranged in parallel with extrafusal fibers

- detect both dynamic and static changes in muscle length

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24
Q

describe golgi tendon organ

A
  • arranged in series with extrafusal fibers

- detect muscle tension

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25
Q

what do pacinian corpuscles detect?

A

vibration

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26
Q

what do free nerve endings detect?

A

noxios stimuli

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27
Q

what groups are and are not myelinated?

A

is: I, II, III

is not: IV

28
Q

list and describe fiber types:

A

A FIBERS: somatic, myelinated; alpha: largest, AKA type 1; beta, aka type II; gamma; delta, smallest aka Type IV

B FIBERS: lightly myelinated, preganglionic fibers of ANS

C FIBERS: unmyelinated, found in somatic and autonomic systems, aka Type IV Fibers

29
Q

sensory fiber types and description

A
  • A-alpha or A-beta fibers (conduction rate = 30-120 m/sec)
  • A-delta fibers (4-30 m/sec)
  • C fibers (less than 2.5 m/s)
30
Q

what are nociceptors and thermoreceptors related to?

A

C fibers or A-delta fibers

31
Q

describe the muscle spindle

A
  • 3-10 mm long
  • consists of 3-12 intrafusal fibers: innervated by small gamma motor neurons (group II fibers); encapsulated within a sheath to form muscle spindle; run parallel to extrafusal fibers

-central region of spindle has NO contractile fibers; functions as a sensory receptor. (sensory fibers originate from central region; stretching of central region of intrafusal fiber stimulates sensory fibers)

32
Q

what happens with finer movements?

A

the number of MSs required increases

33
Q

what are they innervated by?

A

small gamma motor neurons

34
Q

overall, what does a muscle spindle do?

A

detects CHANGES in muscle length

35
Q

what are the types of intrafusal fibers?

A

nuclear bag fibers

nuclear chain fibers

36
Q

describe the nuclear bag fibers

A
  • detect rate of change in muscle lenght
  • innervated by group Ia afferents and dynamic gamma efferents
  • multiple nuclei concentrated in “bag” in center of receptor area
37
Q

describe nuclear chain fibers

A
  • detect static change in muscle lenght
  • innervated by group II afferents and static gamma efferents
  • more numerous than nuclear bag fibers
  • multiple nuclei arranged in a single row
38
Q

alpha motor neuron (related to MS)

A
  • most numerous
  • innervate effector - skeletal muscle
  • neurotransmitter - acetylecholine
39
Q

gamma motor neuron (related to MS)

A
  • innervates intrafusal muscle fibers
  • keeps muscle spindles taut
  • neurotransmitter - acetylcholine
40
Q

what does the muscle spindle correct for?

A

increase in muscle length (stretch)

when muscle is stretched, spindle is stretched

41
Q

what does stimulation result from?

A
  • lengthening of entire muscle
  • contraction of ends of intrafusal fibers

*stimulation results in stimulation of alpha-motor neurons, resulting in contraction and shortening of muscle

42
Q

describe the muscle spindle gamma motor neurons

A
  • innervate intrafusal fibers
  • adjust sensitivity of muscle spindle
  • coactivated with alpha-motor neurons (stimulation results from lengthening of entire muscle)
  • equal to about half the number of alpha motor neurons
43
Q

what types of gamma MNs are there?

A

A-gamma: 5 mue-meters diameter, supply small intrafusal fibers in middle of muscle spindle

Gamma-dynamic: excite nuclear bag intrafusal fibers

Gamma-static: excite nuclear chain intrafusal fibers

44
Q

what brain areas control gamma fibers?

A
  • bulboreticular region of brain stem
  • cerebellum
  • basal nuclei
  • cerebral cortex
45
Q

what are the three muscle spindle functions?

A
  • dynamic stretch reflex
  • static reflex
  • prevents jerkiness of body movements (damping)
46
Q

describe dynamic stretch reflext

A
  • signals transmitted from primary nerve endings
  • elicited by rapid stretch or unstretch
  • opposes sudden changes to muscle length
47
Q

describe static reflex

A
  • transmitted by both primary and secondary endings

- causes degree of muscle contraction to remain relatively constant

48
Q

describe the general stretch reflex

A
  • stretching of muscle stretches group Ia afferent fibers
  • group Ia afferents synapse directly on alpha-motor neurons of same muscle
  • the muscle contracts and decreases tension on muscle spindle
  • synergistic muscles are activated and antagonistic muscles are inhibited
49
Q

describe the golgi tendon organ

A
  • encapsulated sensory receptor through which muscle tendon fibers pass
  • arranged in series with extrafusal fibers
  • 10-15 muscle fibers attached to each golgi organ
  • golgi organ is stimulated by contracting or stretching of muscle
  • detects muscle tension
  • gogli tendon reflex is opposite of the stretch reflex
  • has no motor component
50
Q

what is the circuitry of the golgi tendon organ?

A

type Ib afferent (+) —> inhibitory interneuron (-) —> anterior motor neuron

51
Q

what does after-discharge result from?

A

it is the result of persistent neural activity in polysynaptic circuits; it prevents muscle from relaxing for some time

52
Q

what is the function of the premotor and supplementary motor cortices?

A

they generate a plan for movement

they transfer plan to primary motor cortex

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

53
Q

what does the anterior part of the premotor cortex do?

A

develops a “motor image” of the total muscle movement that is to be performed

54
Q

describe what the supplementary motor cortex does

A

it programs complex motor sequences and is responsible for mental rehearsal for a movement.

55
Q

what else does the premotor and supplementary motor areas do?

A

image in posterior motor cortex excites each successive pattern of muscle activity required to achieve the image

56
Q

where does the posterior motor cortex sends signals to?

A

–> primary motor cortex –> basal nuclei and thalamus –> primary motor cortex

57
Q

how are cells in the motor cortex organized?

A

vertical columns

58
Q

describe the verticle columns

A
  • each column stimulates a group of synergistic muscles or even a single muscle
  • each column has 6 distinct layers
  • neurons arising in the 6th layer communicate with other regions of the cerebral cortex
59
Q

what layer are the pyramidal cells found in?

A

5th layer

60
Q

where do input signals enter through?

A

layers 2-4

61
Q

describe the generalizations of the motor paths

A

typical descending pathways consists of a series of two motor neurons

62
Q

what are those two?

A

UMNs and LMNs

does not take into consideration the association neurons between UMNs and LMNs

63
Q

descibe UMNs

A
  • are entirely within the CNS
  • originate in: cerebral cortex, cerebellum, and brainstem
  • form descending tracts
64
Q

describe LMNs

A
  • begin in CNS: from anterior horns of SC, from brainstem cranial nerve nuclei
  • made up of alpha motor neurons (A-alpha)
  • make up spinal and cranial nerves
65
Q

describe UMN classification

A

they are classified according to where they synapse in the ventral horn:

  • medial activation system: innervate postural and girdle muscles
  • lateral activation system: associated with distally located muscles used for fine movements
  • nonspecific activating system: facilitate local reflex arcs
66
Q

medial UMN axial and girlde muscles: vertical organization of motor control

A
  • medial corticospinal tract
  • lateral vestibulospinal tract
  • tectospinal tract
  • medial reticulospinal tract
  • medial vestibulospinal tract
67
Q

lateral UMN limb muscles: vertical organization of motor control

A
  • rubrospinal tract
  • lateral corticospinal tract
  • medullary (lateral) reticulospinal tract

physio - e2 - lecture slides (8 decks)

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