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motor control 1 Flashcards

1
Q

types of motor control

A

voluntary
goal directed
habit
involuntary

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2
Q

examples of voluntary motor control

A

running
walking
talking

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3
Q

what is goal directed motor control

A

conscious
explicit
controlled

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4
Q

what is habit motor control

A

unconscious
implicit
automatic

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5
Q

what is involuntary motor control

A

eye movements
facial expression,jaw,
tongue,
postural muscles

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6
Q

describe activation of muscle fibres

A

its either all or none

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7
Q

how is a skeletal muscle attached to the bone

A

by a tendon

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8
Q

what is a muscle fascicle

A

a bundle of skeletal muscle fibres

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9
Q

what is skeletal muscle made of

A

several muscle fasiculi (group of muscle fibres)

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10
Q

what is a muscle fibre made of

A

several myofibrils

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11
Q

what do myofibrils contain

A

protein filaments; actin & myosin myofilaments

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12
Q

what happens when a muscle fibre is depolarised

A

actin and myosin slide against each other and produce muscle contraction

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13
Q

define motor unit

A

a motoneuron and all of its associated muscle fibers that it innervates

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14
Q

is an alpha motor neurone an upper or lower motor neurone

A

lower motor neurone

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15
Q

describe muscle fibres in a single motor unit

A

located in one muscle but they are distributed throughout the muscle and are not necessarily adjacent to each other

this is to provide evenly distributed force

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16
Q

do different motor neurones innervate different numbers of muscle fibres

A

yes

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17
Q

what does it mean if a motor neurone innervates less fibres

A

greater variation of movement
eg fingertips and tongue

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18
Q

what does activation of an alpha motor neurone cause

A

depolarisation and contraction of all the fibres in that unit

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19
Q

what is the final common pathway for motor control

A

the motor unit

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20
Q

the more a motor neurone fires…

A

… the more fibres that contract

resulting in more power

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21
Q

where are alpha motor neurones controlling distal muscles located

A

laterally in the spinal cord

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22
Q

where are alpha motor neurones controlling proximal muscles located

A

medially in the spinal cord

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23
Q

what does the average number of muscle fibres innervated by a single motor neurone depend on

A

on 2 functional requirements for that muscle

  1. level of control
  2. strength
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24
Q

where does the myelin sheath surrounding the axon of each motor neurone end

A

near the surface of a muscle fibre

and the axon divides into a number of short processes that lie embedded in the grooves on the muscle fibre surface

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25
Q

what do the axon terminals of a motor neurone contain

A

vesicles similar to those found in
the synaptic junctions between two neurones

the vesicles contain the neurotransmitter acetyl-choline (ACh)

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26
Q

what is the motor end plate

A

the region of the muscle fibre plasma membrane that lies directly under the
terminal portion of the axon

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27
Q

what is the neuromuscular junction

A

the junction of an axon terminal with the motor end plate

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28
Q

what happens when an action potential in a motor neurone arrives at the axon terminal

A

it depolarises the plasma membrane, opening voltage-gated Ca2+ channels and allowing Ca2+ ions to diffuse into the axon terminal from the extracellular fluid

29
Q

what do Ca2+ ions bind to

A

to proteins that enable the membranes of the acetyl-choline containing vesicles to fuse with the neuronal plasma membrane, thereby releasing ACh into the extracellular cleft separating the axon terminal and the motor end plate

30
Q

where does ACh diffuse from

A

diffuses from the axon terminal to the motor end plate where it binds to
cholinergic nicotinic receptors

31
Q

what does binding of ACh do

A

opens an ion channel in the receptor protein (both sodium & potassium can pass through these channels)

32
Q

what is the end-plate potential (EPP)

A

due to the differences in the electrochemical gradients across the plasma membrane,

MORE Na+ moves in than K+ out -

producing a local depolarisation
of the motor end plate

the end-plate potential (EPP)

(this is equivalent to an
EPSP (excitatory postsynaptic potential) at a neuron-neuron synapse

33
Q

compare magnitudes of EPP and EPSP

A

the magnitude of a single EPP is much larger than that of an EPSP
because the neurotransmitter is released over a larger surface area,

thereby binding to many more receptors and opening many more ion channels

SO one EPP is more than sufficient to depolarise the muscle plasma
membrane adjacent to the end-plate membrane to its threshold potential
thereby initiating an action potential

34
Q

where is the action potential propagated

A

over the surface of the muscle fibre and
into the T-tubules (to spread throughout the muscle)

35
Q

where are most neuromuscular junctions located

A

near the middle of a muscle fibre
with newly generated action potentials propagating from this region in both
directions towards the ends of the fibre

36
Q

how are action potentials in motor neurones different to synaptic junctions

A

EVERY ACTION POTENTIAL in a motor neurone normally produces an action
potential in each muscle fibre in its motor unit

  • whereas in synaptic junctions
    multiple EPSPs must occur in order for threshold to be reached and an
    action potential elicited in the postsynaptic membrane
37
Q

are all neuromuscular junctions excitatory

A

yes

38
Q

which enzyme is present in the synaptic junction of the neuromuscular junction

A

acetylcholinesterase

  • breaks down ACh
  • the choline is then transported
    back into the axon terminals where it can be used for the synthesis of new ACh
39
Q

what are muscle spindles

A

delicate sensory receptors that inform the CNS about changes in
1. the length of individual muscles
2. the speed of stretching

receptors in the spindle will detect stretch regardless of the current muscle length

40
Q

structure of stretch receptors

A

consist of peripheral endings of afferent nerve fibers wrapped around modified muscle fibers

41
Q

what are intrafusal fibres

A

The modified muscle fibres within the
spindle

42
Q

what are the 2 ends of intrafusal fibres innervated by

A

GAMMA MOTOR NEURONES
(type of lower motor neurone)

43
Q

what do gamma motor neurones do

A

keep the intrafusal fibres set at a length that optimises muscle stretch detection

44
Q

what part of muscle spindle is contractile

A

the two ends of the muscle spindle are
contractile whilst the central portion is
non-contractile

45
Q

how many types of stretch receptor are there in the spindle

A

2

46
Q

what are the 2 types of stretch receptors

A
  1. nuclear chain fibres
  2. nuclear bag fibres
47
Q

what do nuclear chain fibres respond to

A

to how much muscle is stretched

48
Q

what do nuclear bag fibres respond to

A

both the magnitude of stretch AND the
speed with which it occurs

49
Q

what is the middle third of the spindle associated with

A

fast type 1a afferent
sensory nerves

50
Q

what are the inferior and superior thirds of the spindle associated with

A

slower conducting type 2 afferent sensory nerves

51
Q

describe arrangement of muscle spindle in regards to extrafusal fibres

A

muscle spindles are attached by
connective tissue in parallel to the
extrafusal fibers

52
Q

what activates receptor endings of intrafusal fibres

A

an external force stretching the muscle
pulls on the intrafusal fibers,
stretching them and activating their
receptor endings

53
Q

impact of more or faster stretching of a muscle

A

greater rate of receptor firing

54
Q

what happens if action potentials along motor neurons cause the contraction of extrafusal fibers

A

the resultant shortening of the muscle removes tension on the spindle and thus slows the rate of firing in the stretch receptor -
thereby resulting in a reduction of sensory information

55
Q

what is used to prevent loss of sensory information

A

alpha-gamma coactivation

56
Q

how does alpha gamma coactivation work

A
  1. the contractile ends of the intrafusal fibers are too small & weak to
    contribute to force or shortening of the entire muscle
  2. However, they can maintain tension and stretch in the central receptor
    region of the intrafusal fibre
  3. so activating the gamma-motor neurones ALONE will increases the
    sensitivity of the muscle to stretch
  4. Coactivating BOTH the alpha and gamma motor neurones will prevent the central region of the muscle spindle from going slack during a shortening
    muscle contraction - ensuring that information about muscle length will be
    continuously available to provide for adjustment during ongoing actions
    and to plan and program future movements
57
Q

what does tension depend on (3)

A
  • muscle length
  • the load on the muscles
  • the degree of muscle fatigue
58
Q

why is tension feedback necessary

A

to inform the motor control
system of the tension actually achieved

59
Q

how is tension feedback provided

A
  • some provided by vision (you can
    see whether you are lifting or
    lowering an object)
  • some by afferent input from the
    skin, muscle & joint receptors
60
Q

what are the golgi tendon organs

A

a receptor type that specifically monitors how much TENSION the
contracting motor units are
exerting

(or is being imposed
on the muscle by external
forces if the muscle is being
stretched)

  • they measure the force developed by the muscles & any resultant
    change in length
61
Q

structure of golgi tendon organs

A

they are endings of afferent fibres that wrap around collagen bundles in the tendons near their junction with the muscles - these collagen bundles are slightly bowed in their resting state

62
Q

what are the afferent fibres leading from the golgi tendon organ to the spinal cord

A

1b fibres that run to the anterior horn of the spinal cord

63
Q

what causes tension to be exerted on the tendon

A

when the muscle is stretched or the attached extrafusal muscle fibres
contract - tension is then exerted on tendon

this straightens the collagen bundles and distorts the golgi tendon receptor endings thereby activating them

64
Q

what causes the tendon to stretch more

A

the tendon is stretched much more by an active contraction of the
muscle than when the whole muscle is passively stretched - thus golgi
tendon organs discharge in response to the tension generated by the
contracting muscle and initiate action potentials that are transmitted to the
CNS

65
Q

what is the INVERSE STRETCH (MYOTATIC) REFLEX

A

Branches of the afferent neurone (1b fibres) from the golgi tendon organ
cause the inhibition of ALPHA MOTOR NEURONES of the contracting
muscle (thereby inhibiting muscle contraction) and its synergists (muscles
whose contraction assists the intended motion) via interneurons in order to
regulate muscle tension at a normal range and to protect it from overload

66
Q

what is the output produced by the golgi tendon proportional to

A

muscle tension
(force)

67
Q

do golgi tendon organs possess slower or faster afferent fibres than muscle spindles

A

slower

68
Q

what else do golgi tendon organs stimulate

A

the motor neurones of the antagonistic muscles

69
Q

what are Pacinian corpuscles

A

(occur in the skin & deep tissue)
detect vibrations

neuro lectures (15 decks)

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