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BME 201 > Nervous System - Spinal Reflexes and Control of Movement > Flashcards

Nervous System - Spinal Reflexes and Control of Movement Flashcards

1
Q

skeletal muscle structure

A
  1. skeletal muscles
  2. skeletal muscle fibers
  3. muscle fascicle
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2
Q

skeletal muscles

A
  • muscles connected to the skeleton

- muscle fibers contain myofibrils, organized in sarcomeres

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3
Q

myofibrils

A
  • bundles of contractile proteins called myosin and actin
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4
Q

skeletal muscle fibers

A

elongated cylindrical multinucleate cells

- connective tissues surround muscle fibres and nerves that innervate them

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5
Q

muscle fascicle

A

bundle of skeletal muscle fibers

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6
Q

spinal nerve

A
  • connected to the spinal cord by a dorsal root

- mixed nerve (carries both sensory and motor info)

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7
Q

fibers in a dorsal root

A

sensory

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8
Q

fibers in a ventral root

A

motor

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9
Q

types of muscle fibers

A
  1. extrafusal fibers

2. intramural fibers

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10
Q

extrafusal muscle fibers

A
  • majority of skeletal muscle fibers
  • generate force to move or rigidly fix body parts
  • innervated by efferent motor fibers (alpha motor neurons)
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11
Q

intrafusal muscle fibers

A
  • specialized fibers (muscle spindle)
  • inform CNS about muscle length and its rate of change
  • innervated by both sensory and motor nerves
    - afferent sensory fibers Ia, II
    • efferent motor fibers: gamme motor neuron
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12
Q

muscle spindle

A
  • spindle-shaped organ
  • composed of intrafusal muscle fibers
  • intramural muscle fibers are arranged in // with extrafusal muscle fibers
  • detect muscle stretch
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13
Q

types of intrufsal muscles fibers

A
  1. nuclear bag fibers

2. nuclear chain fibers

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14
Q

co-activation of the gamma and alpha motor neurons

A

co-activation of the gamma efferents occur to maintain muscle spindle sensitive to changes in muscle length, even as the muscle contracts and shortens

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15
Q

events occurring when a muscle is stretched

A
  1. muscle stretched
  2. extrafusal muscle fibers lengthened
  3. intrafusal muscle fibers lengthened
  4. sensory afferent fibrs (Ia/II) are activated
  5. alpha motoneurons are activates (innervate extrafusal fibres)
  6. muscle contracts
  7. gamma motoneurons are co-activated (innervate intrafusal fibers)
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16
Q

purpose of muscle spindle reflexes

A

operate to return muscle to its resting length after has been shortened or lengthened

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17
Q

principles of the skeletal muscle (5)

A
  1. motor unit
  2. motoneuron pool
  3. size principle
  4. population code
  5. frequency code
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18
Q

neuromuscular junction

A

a chemical synapse formed by the contact between a motor neuron and a muscle fiber

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19
Q

junction: pre-synaptic cell, type of synapse, neurotransmitter, class of receptors, type of receptor, post-synaptic cell

A
  1. alpha motor neuron
  2. chemical
  3. acetylcholine
  4. ionotropic
  5. nicotinic
  6. muscle fiber
20
Q

motor end plate = neuromuscular junction

A
  • motor neurons typically branch to innervate multiple muscle fibers
  • each branch ends in a neuromuscular junction or motor end plate
  • motor end plate consists of a number of terminal enlargements of the nerve (terminal buttons)
21
Q

terminal buttons

A
  • terminal enlargements of nerve

- make up motor end plate

22
Q

motor unit

A
  • single motoneuron and the muscle fibers it innervates

- alpha motor neuron (lower motor neuron) and the set of muscle fibers it innervates

23
Q

producing more force

A
  1. activation of more motor neurons
  2. activation of more muscle fibers
  3. produces more force
24
Q

motor neuron pool

A
  • set of alpha motor neurons innervating fibers within the same muscle
25
Q

where are lower motor neurons located?

A

ventral horn of the spinal cord

26
Q

where are upper motor neurons located?

A

cortex of the brain

27
Q

gradation of muscle force

3 points

A

muscle force can vary from delicate control to maximum activation

  1. size principle
  2. population code
  3. frequency code
28
Q

size principle

A
  • successive engagement of larger populations of motor units occurs according to their size
  • smaller motor units (with smaller motoneurons) recruited first
  • large motor units are recruited last
29
Q

population code

A
  • successively larger fractions of the motor units are engaged
  • encodes the strength of the muscle force
30
Q

frequency code

A
  • motor units activated with higher frequencies

- increases the muscle force but also increases its duration

31
Q

somite

A

body segment

32
Q

dermatome

A
  • skin part supplied by a single spinal nerve

- enabling the clinician to determine the level of a lesion of the spinal cord or nerve roots

33
Q

myotome

A
  • muscle part of a body segment

- controlled by areas of the motor cortex adjacent to the sensory cortex

34
Q

spinal reflex

A
  • stereotyped muscular response to a specific sensory stimulus
    • “hard wired”
    • reflection of the stimulus onto the musculature
    • may be suppressed or enhanced, but not eliminated
    • no conscious deliberation
35
Q

reflex arc

A

type of conduction pathway that allows impulses to travel in only one direction

36
Q

reflex arc components (5)

A
  1. receptor
  2. sensory (afferent) neuron
  3. integration center
  4. motor (efferent) neuron
  5. effector
37
Q

spinal reflexes (4)

A
  1. myotatic
  2. inverse myotatic
  3. withdrawal
  4. crossed-extensor
38
Q

myotatic reflex

A
  • muscle stretch reflex (knee-jerk reflex = patellar reflex)
  • monosynaptic
  • causes muscle contraction in response to muscle stretch
  • involves muscle spindles which detect stretch)
39
Q

inverse myotatic reflex

A
  • golgi tendon reflex (clasp-knife reflex)
  • disynaptic
  • causes muscle relaxation in response to muscle contraction
  • prevents damage to muscles due to excessive force production
40
Q

withdrawal reflex

A
  • flexor-withdrawal reflex
  • polysynaptic
  • occurs in response to painful or noxious stimulus
  • causes movement of limbs towards the body (activates flexors, inhibits extensor)
    (pain afferent fibers)
41
Q

crossed-extensor reflex

A
  • activate to maintain balance in response to pain
  • polysynaptic
  • limb on opposite side of stimulus extended (flexion on ipsilateral side, extension on contralateral side)
    (pain afferent fibers)
42
Q

motor control

A
  • posture and movement depend on a combination of:
    • voluntary actions controlled by higher brain centers
    • involuntary reflexes coordinated by the spinal cord (spinal cord reflexes + central pattern generators)
43
Q

all reflexes and voluntary control of muscles act through their effect on what type of motorneurons

A

lower motoneurons

44
Q

major descending motor pathways

A
  • higher control of muscles originates in the cerebrum and is coordinated with inputs and from other parts of the brain
  • descending tracts contain axons that make contact with the lower motor neurons and help control them
45
Q

how descending tracts are named

A
  • first from their point of origin and secondly from their termination
    ex. rubrospinal tract, ventral corticospinal tract

BME 201 (10 decks)

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