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MVST1B NHB > Movement L2+3 > Flashcards

Movement L2+3 Flashcards

1
Q

The major motor area of the spinal cord is the ___ ______

A

The major motor area of the spinal cord is the ventral horn

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2
Q

which neurones are locate din the ventral horn of the spinal cord?

A

alpha-motoneurons that innervate muscle fibres

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3
Q

Most synapses on motoneurons are from where?

located?

A

Most synapses on motoneurons are from spinal interneurons located in the intermediate zone grey matter.

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4
Q

how many motor neurones innervate a given muscle?

A

The group of 200-500 motoneurons that innervate a given muscle (the motoneuron pool) are located close together in the ventral horn

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5
Q

The group of 200-500 motoneurons that innervate a given muscle (the motoneuron pool) are located close together in the ventral horn usually extending _____________ over several spinal segments

A

The group of 200-500 motoneurons that innervate a given muscle (the motoneuron pool) are located close together in the ventral horn usually extending rostro-caudally over several spinal segments

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6
Q

There is a somatotopic organisation with distal muscles being represented _______.

A

There is a somatotopic organisation with distal muscles being represented laterally.

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7
Q

which neurones are in the dforsal horn?

A

somatosensory neurones

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8
Q

D: Motor unit:

A

Each motorneuron axon branches to innervate many muscle fibres which are distributed throughout the muscle.

These form motor units: the basic unit of force production.

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9
Q

how many types of motor unit are there?

A

3

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10
Q

3 types of motor unit

A

Slow

intermediate

fast

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11
Q

describe slow motor units

A

Slow motor units are ideal for continuous generation of small forces,

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12
Q

describe fast motor untis

A

fast fatigueable units produce high forces, but over a short period.

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13
Q

which motor units contains the most myoglobin?

A

myoglobin (red) - in slow fibres

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14
Q

which motor units have the most capillaries?

A

slow

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15
Q

describe motor neurones firing rate as a means to control the force output of a muscle

A

rate coding - varing rate of APs sent to muscle to vary force.

bad because the twitches generated by muscles fuse into a tetanus at quite low frequencies = little control.

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16
Q

describe ‘motor neurone recruitment’ as a means to control how much force a muscle generates

A

motor units are recruited in an orderly sequence as force increases, the lowest force motor units first, the highest force units last.

Force therefore always increments by finest available motor unit and is thus as smooth as possible.

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17
Q

describe the mechanism underlying motorneuron recruitment

A

developmental plasticity: motoneurons with low firing threshold innervate few muscle fibres and induce them to become slow twitch, low force and fatigue resistant.

Motoneurons with the highest firing thresholds (which are recruited last) innervate many muscle fibres and induce them to become fast twitch and high force, but fatiguable.

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18
Q

Motorneuron damage leads to …..

A

Motorneuron damage leads to complete paralysis (flaccid)

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19
Q

what makes motor neureons fire?

(3)

A
  1. • muscle spindle afferents (ONLY from muscle spindles!)
  2. •Descending fibres (direct pathways from brain stem or cerebral cortical structures, relatively rare, with an important exception in primates)
  3. •Spinal interneurons (most numerous, in most cases receiving inputs from both sensory pathways and descending pathways from the brainstem and/or cerebral cortex)
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20
Q

2 ‘types’ of reflex

A

It is important to draw clear distinctions between reflex actions targeted at specific small groups of muscles and involve in regulation of their force (examples are stretch reflexes and associated reciprocal and recurrent inhibition which we shall see later),

and more complex reflexes that generate functional movements that involve multiple muscles (an example is the nociceptive withdrawal reflex).

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21
Q

proprioceptors vs proprioception?

A

Proprioceptors (sensory fibres from muscles and joints) and proprioception (or Kinaesthesia, the sense of position and movement of the body) should not be confused:

although proprioceptors can provide some information used in proprioception, cutaneous sensation (exteroceptors), the eyes and vestibular systems and other sources of information also play a large role in proprioception.

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22
Q

There are _ major groups of proprioceptors

A

3

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23
Q

There are 3 major groups of proprioceptors

what are they?

A
  1. muscle spindle afferents are muscle stretch receptors
  2. Golgi tendon organ afferents are muscle tension receptors
  3. joint receptors signal joint position and movement, especially at the extremes
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24
Q

what are muscle spindles?

hoew many per muscle?

A

The spindles are spindle-shaped structures embedded in muscles that give rise to afferents that signal muscle length and change in muscle length.

Typically a muscle will contain between 20 and 100 spindles.

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25
Q

describe the structure of muscle spindles

A

Structure: each muscle spindle is an
encapsulated bundle of small specialised intrafusal muscle fibres – (literally within-spindle muscle fibres).

intrafusal fibres are very small. generating no forace at tendon

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26
Q

There are 2 distinct morphological types of intrafusal fibres

what are they?

A

bag fibres

chain fibres

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27
Q

describe bag fibre muscle spindles

A

Bag fibres have a swollen central region containing many nuclei (the bag) and contractile ends,

(2 types of bag fibre too)

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28
Q

describe chaiun fibres muscle spindles

A

Chain fibres are of uniform diameter and are uniformly contractile along their length.

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29
Q

describe the sensory innervation of muscle spindles

A

2 types:

  1. primary (or 1a) spindle afferents- very large (and thus very fast conducting) axons which have terminal branches that end in coils (annulospiral endings) around the central region of the intrafusal muscle fibres.
  2. Smaller, slower conducting afferent fibres (secondary or II spindle afferents) end adjacent to the central region of the intrafusal muscle fibres.
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30
Q

describe what happens when you stretch a bag fibre muscle spindle

A
  1. central region is not contractile but elastic
  2. so central region stretched first
  3. rapidly activates afferents
  4. this stretch is then relieved by the end of the fibres stretching - reducing stretch on the central region

As a result, during the stretch the central region is greatly elongated, generating a strong initial response but this declines to be distributed across the whole fibre at the end of the stretch.

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31
Q

describe the out put of chain fibres in response to stretch

A

Chain fibres have uniform mechanical properties throughout their length, so the sensory endings on them (especially secondary endings) signal muscle length approximately linearly (a static response).

32
Q

which motor afferents have dynamic responses?

A

intrafusal bag fibres

33
Q

describe the efferent control of muscle spindle terminals

A

ends innervated by smal slow conducting gamma neurones

contract ends- stretching the central bag region.

gamma motorneuron firing thus increases both the firing and the sensitivity the receptors: this complicates the sensory signal.

34
Q

how do gamma efferent neurones allow sensitivity of muscle spindles to be modulated?

A
  • allows psindles to be able to change length
  • allowing signalong from different starting positions
  • rather tha nsaturating at extremes.
  • form of adaptation - adjusting receptor sensitivity to extend the range over which the sense organ operates, analogous to adaptation in other sensory (e.g. visual) systems.
35
Q

Activity in muscle spindle afferent fibres therefore represents interplay between……

A

Activity in muscle spindle afferent fibres therefore represents interplay between externally generated muscle stretch (e.g. from different loads on the muscle) and internally generated ‘stretch’ produced by contraction of intrafusal fibres in response to gamma motoneuron activation.

36
Q

Adjustability of spindle afferent sensitivity complicates the interpretation of their signals

how

A

A change in muscle spindle afferent firing could be generated by muscle length changes OR by altered gamma motoneuron activity (or, more likely, by combinations of both!).

If the signals were to be used to generate reflexes or sensation, then to interpret the muscle spindle signals unambiguously in terms of muscle length or length change the brain needs to ‘know’ the gamma motoneuron activity.

This could be provided by efference copy (knowing the command to the gamma motoneuron). Without that information the spindle afferent signals are ambiguous.

37
Q

what are golgi tendon organs?

A

activated by tension in the tendon.

38
Q

when are golgi tendon organs activated?

A

in passive stretches of relaxed muscle, tension in the tendon does not rise much due to the elasticity of the muscle fibres.

Muscle contractions on the other hand generate tension directly in the tendon and make tendon organs fire briskly - i.e. they signal active tension – the force generated as the muscle contracts.

39
Q

do golgi tendon organs signal active tension?

A

yes

40
Q

T or F for golgi tendon organs?

This signal will be strongly proportional to the load on the muscle.

A

T

41
Q

T or f

Most muscles respond to being stretched by contracting.

A

T

42
Q

Most muscles respond to being stretched by contracting.

where is this reflex gernertaed?

A

This reflex is generated by the nervous system: it disappears if the muscle nerve is cut (or if the muscle is paralysed).

43
Q

classic stretch reflex situation?

A

knee jerk or tendon tap reflex: tapping the patellar tendon stretches muscle spindles in quadriceps leading to a reflex contraction of quadriceps (the knee jerk).

44
Q

where might stretch reflex be useful?

A

mainly homeostatic - maintain muscle length

This might be particularly useful in postural control: if the body sways then the stretched leg muscles will automatically contract to counteract the sway, helping maintain an upright stance.

45
Q

describe the only monosynaptic reflex?

A

Monosynaptic connections from muscle spindle afferents to the alpha-motoneurons that innervate the same muscle underly the stretch reflex.

Note that this is the ONLY monosynaptic reflex;

all other reflexes involve spinal interneurons.

46
Q

which muscles have no stretch reflex?

A

The large majority of muscles have a stretch reflex, but eye and tongue muscles are notable exceptions.

47
Q

does the stretch reflex branch out? if you catch my drift

A

As well as contractions of the muscle in which the spindle is located, muscle spindles also excite the motoneurons of close synergists (e.g. stretch of brachialis at the elbow produces a reflex in biceps as well as brachialis).

48
Q

describe reciprocal inhibition in the stretch reflex

A

excite interneurons that inhibit antagonist muscles (reciprocal inhibition - later), preventing further stretch (e.g. stretch of brachialis and or biceps will produce inhibition of triceps motorneurons, and vice versa). These actions are seen across most limb joints.

49
Q

why dont eye muscles have stretch reflexes?

A

Eye muscles are also an exception in that they do not encounter unexpected loads, which seems to support a role for the stretch reflex in counteracting unexpected loads.

50
Q

why doesnt the stretch reflex mediate the reaction to unspecified loads?

A
  1. GAIN. For this to work there must be a compensatory contraction for any given stretch. The stretch reflex should have a gain of 1. (any given amount of stretch will elicit contraction to precisely counteract it with the same amount of contraction). When measured, the gain of the stretch reflex is less than 1 in normal situations.
  2. DELAYS. Remember the disadvantage of feedback systems is the delay in sensing errors and generating responses.
51
Q

which characteristic changes are seen following damage to descending systems?

A

stroke or cerebral palsy:

  1. the stretch reflex is exaggerated (a high gain) - brisk responses are evoked to tapping tendons and muscles have tonic contraction
  2. Oscillating muscle contractions follow stretch (MYOCLONUS or just CLONUS).
52
Q

t or F

the sensitivity of the muscle spindle afferents (and therefore the strength or gain of the stretch reflex) can be set by activity in the gamma-motoneurons

A

T

53
Q

can the brain control the gain of the stretch reflex?

A

in slow movements and situations where precision is needed then gain may be set high (high spindle sensitivity and therefore a strong stretch reflex), whereas for fast movements such a gain might generate clonus, so gain may be set low.

through varied gamma motor neurone firing rates

54
Q

proprioception: eye position is mainly signalled by?

A

efference copy

55
Q

MOST IMPORTANTLY proprioceptors provide information for…..

A

proprioceptors provide information for supraspinal motor systems, which are involved in predictive feedforward control of movement (e.g. cerebellum and motor cortex) using model systems

56
Q

The principal central projection of proprioceptors is to the cerebellum via ….

A

The principal central projection of proprioceptors is to the cerebellum via spinocerebellar pathways

57
Q

describe Reciprocal Inhibition

A

Reciprocal Inhibition parallels the stretch reflex.

Muscle spindle primary afferents excite glycinergic inhibitory interneurons that inhibit motoneurons of antagonist muscles when a muscle is stretched.

These are effects are mediated by a group of Ia Inhibitory interneurons associated with each motoneuron pool.

58
Q

describe recurrent inhibition

A

Recurrent Inhibition is generated by Renshaw cells Motoneuron axons have branches (recurrent collaterals) within the spinal cord that innervate inhibitory Renshaw cells.

Renshaw cells are likely to regulate the timing of motoneuron firing, preventing synchrony.

59
Q

t or F

Most reflexes are context dependent

A

T

60
Q

T or F

Most reflexes evoke multijoint responses

A

T

61
Q

T or F

Different types of afferents can contribute to the same reflex pathway

A

T

62
Q

T or F

Reflex pathways are controlled by descending pathways

A

T

63
Q

d: NOCICEPTIVE WITHDRAWAL REFLEXES

A

Noxious stimuli generate a coordinated pattern of muscle contraction that moves the stimulated part of the body away from the stimulus (withdrawal reflexes).

64
Q

where in the spinal cord are nociceptive reflexes mediated?

A

These reflexes are mediated by interneurons that process information relayed from the dorsal horn.

65
Q

which basic properties of reflex do nociceptive reflexes show?

A
  • spatial and temporal summation – stimuli at adjacent sites or closely timed sum to give larger responses
  • local sign – different reflexes are evoked from different locations. Stimulation of the plantar surface of the foot evokes leg flexion, stimulation of the foot dorsum evokes leg extension: both remove the skin surface from the source of the stimulus.
  • context dependance
66
Q

For many years tendon organs were considered to mediate the clasp-knife reflex, which can be seen after stroke.

is this true?

A

NO

67
Q

the clasp knife reflex can be seen after what>

A

stroke

68
Q

no reflexes change with age?

A

yes

69
Q

describe babinskis sign?

A
70
Q

Following brain damage changes in spinal reflex patterns occur, and neonatal reflexes may ______

A

Following brain damage changes in spinal reflex patterns occur, and neonatal reflexes may reappear

71
Q

D: Spasticity

A

Exaggerated stretch reflexes (Spasticity). Muscles are tense and stiff. Stretch elicits strong reflexes and clonus (a negative feedback system oscillating)

72
Q

T o F

Locomotion can be spinally
generated in most vertebrates, including most
mammals

A

T

73
Q

note Functional locomotion is not generated after spinal transection in man.

A

T

74
Q

describe the walking movements babies make in their first few month

A

Although babies make stepping movements in the first few months after birth, these movements have a different pattern to the stepping that appears at about 12 months when walking first appears.

75
Q

There is a general pattern that greater encephalisation (a larger cerebral cortex) is associated with…..

regarding motor patterns in spinal cord

A

There is a general pattern that greater encephalisation (a larger cerebral cortex) is associated with a weaker ability to generate locomotion in the spinal cord:

76
Q

fat

A

mamba

MVST1B NHB (25 decks)

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