Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Year 2 Term 3 Control > Sensory and motor innervation of muscle > Flashcards

Sensory and motor innervation of muscle Flashcards

1
Q

The descending motor system is not a linear system, from what 2 places can motor signals originate, what is each involved in?

A

1) Motor cortex - planning, initiating and directing voluntary movements
2) Brainstem centers - basic movements and postural control

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Which 2 parts of the brain can give inputs to the motor cortex and brainstem centers where motor signals originate, what is the role of each?

A

1) Basal ganglia - has a role in dampening down the level of movements we carry out (called proper initiation of movement)
2) Cerebellum - has a role in sensory motor coordination, making sure the correct movement has been carried out and coordinating patterns of movement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

By which 2 circuits can UMNs make contact with LMNs?

A

1) Directly - straight from UMNs to LMN pools

2) Indirectly - via local circuit neurones - interneurones - involved in reflex coordination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the 3 basic roles of the brain in terms of the motor system?

A

1) Initiation
2) Integration
3) Coordination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the 2 basic roles of the spinal cord in terms of the motor system?

A

1) Simple reflexes

2) Pattern generation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the clinical consequence of the route taken by UMNs to reach LMNs?

A

Those which go via local circuits - ie interneurones - have a greater capacity for neuronal plasticity and thus recovery of function if damage occurs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the 4 brain stem centers involved in the motor system?

A

1) Red nucleus
2) Reticular formation
3) Vestibular-nuclear complex
4) Also houses the LMNs responsible for movements of head and neck

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

The motor cortex is mainly confined to which 2 Brodmann areas?

A

4 & 6

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

The primary motor cortex is found within which lobe?

A

Frontal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the role of the motor cortex?

A

Responsible for planning and initiating voluntary movement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Upper motor neurons are what kind of cells?

A

Pyramidal cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

The pyramidal cells which are the UMNs are located within which of the 6 layers of the cortex?

A

Located within the 5th layer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Via which 2 tracts do UMN axons descend?

A

1) Corticobulbar

2) Corticospinal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Motor signals to below the neck are carried within which tract?

A

Corticospinal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Motor signals to the head, neck and face are carried within which tract?

A

Corticobulbar

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the other name for the corticospinal tract?

A

Pyramidal tract

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Where in the spinal cord do UMNs terminate either directly or indirectly via interneurones on the LMNs?

A

In the ventral horn

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

In the medulla 95% of corticospinal fibres cross the midline, why do 5% continue to descend ipsilaterally?

A

It is thought to be because postural muscles require input to both sides in order for left and right postural muscles to act in a coordinated fashion thus you need corticospinal fibres running down both sides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

The 95% of UMNs which cross the midline to travel contralaterally do so within which tract?

A

Lateral/ posterior CST

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

The 5% of UMNs which continue to descend ipsilaterally do so within which tract?

A

Anterior/ ventral CST

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

LMNs are localised within which lamina of the ventral grey horn?

A

Lamina IX

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are the 2 types of LMNs?

A

1) Alpha motor neurons

2) Gamma motor neurons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How many axons is each muscle fibre innervated by?

A

A single axon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Does each LMN give off a single axon?

A

No - give off many collaterals - each motor neuron can give off many different axons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Which type of LMNs are directly responsible for the generation of force by muscle?

A

Alpha motor neurones

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is a muscle fibre composed of?

A

Each muscle fibre is composed of fibrils which are composed of sarcomeres

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Why is damage to LMNs often catastrophic?

A

Because the only route by which impulses can reach muscles is via LMNs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

How does the size of lamina IX within the ventral grey horn vary?

A

Varies rostro-caudally, the size variation reflects demands of peripheral musculature and its innervation
Lamina IX is largest within the cervical and upper lumbar segments which control upper and lower limb musculature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

How many alpha motor neurons are there estimated to be on each side of the cord?

A

150,000

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is meant by the motor neuron pool?

A

The motor neuron pool of a muscle is all the motor neurons which innervate that single muscle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What is the distribution of a motor neuron pool within the spinal cord?

A

Each motor neuron pool extends rostro-caudally along the spinal cord axis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

How would the motor neuron pools for a powerful muscle such as gastrocnemius and a more postural muscle such as soleus vary?

A

There motor neuron pools would lie close to each other as they come from similar spinal cord levels (Gastrocnemius is L5-S2 and soleus is L4-L7) but gastrocnemius’ pool is likely to be larger as it is a more powerful muscle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

How does the segmental distribution of LMNs in the ventral grey horn vary depending on position and function of peripheral muscle?

A

1) Motor neurons that control flexors lie dorsal to those which control extensors
2) Motor neurons that control axial muscles lie medial (closer to the spinal canal) to those which control more distal muscles

34
Q

What is a motor unit?

A

It is comprised of the alpha motor neuron and all of the muscle fibres that it innervates
As each motor neuron gives off more than one axon (and each muscle fibre is innervated by one axon) then each motor neuron innervates more than one muscle fibre so motor units contain more than one muscle fibre

35
Q

What are the 3 sizes of motor unit, give an example of each?

A

1) Small motor unit - ratio of 3 muscle fibres per single alpha motor neurone eg. extraocular muscles of the eye (need fine movement)
2) Medium motor unit - ratio of 180 muscle fibres per single alpha motor neurone eg. soleus muscle
3) Large motor unit - ratio of 1000-2000 muscle fibres per alpha motor neurone eg. gastrocneumius (need less fine but more powerful movement)

36
Q

How does the size of motor neurons vary between different sized motor units?

A

Small motor units = small motor neurons

Large motor units = large motor neurons

37
Q

In muscles with motor units of more than one size, in what order are motor units recruited and why?

A

Small motor units are recruited before large motor units to get an increase in force

38
Q

Motor units vary in the type of muscle fibres they innervate, what are the 3 types of motor units in terms of force and fatigability?

A

1) Slow motor units
2) Fast fatigable motor units
3) Fast fatigue-resistant motor units

39
Q

Slow motor units, innervate what kinds of muscle fibres with what kinds of adaptations?

A

Slow motor units are composed of a small motor units and small red muscle fibres. These red muscle fibres generate low force but are resistant to fatigue. They are red because:
1) They have high levels of myoglobin
2) Good vascular supply to bring O2 and take away wast products ie CO2 to avoid acidosis
3) High levels of mitochondira
All the above lead to resistance to fatigue

40
Q

Give an example of a type of muscle which would contain lots of slow motor units?

A

Postural muscles - dont need to produce high force but need to be resistant to fatigue

41
Q

Fast fatiguable motor units are composed of what types of muscle fibre with what adaptations?

A

Fast fatigable motor units are composed of large motor units and larger paler muscle fibres that generate large forces, pale muscle fibres are fatiguable as:
1) They contain lower amounts of myoglobin
2) Contain less mitochondria
Thus they resort to anaerobic respiration more readily so are fatigued by lactic acidosis

42
Q

Give an example of a muscle containing many fast fatigable motor units?

A

Biceps muscle - generates large amounts of force over short periods of time

43
Q

What is the role of fast fatigue resistant motor units?

A

They are an intermediate type and can produce moderate force and some fatigue

44
Q

How does the percentage of maximum force generated differ between 3 types of motor unit?

A

Slow motor units - produce 100% of maximum force over a sustained period of time but their maximum force is not that high
Fast fatigable motor units - maximum force is v high but only produce 100% maximum force for a short period of time before it declines
Fast fatigue-resistant motor units - maximum force is moderate, can produce 100% maximum force for a moderate length of time before it reduces

45
Q

How can motor unit activity be recorded?

A

Using electromyography (EMG) - place a fine gauge needle into the selected muscle to pick up the electrical activity of the motor unit

46
Q

How does the appearance of the electromyograph vary with mild voluntary effort to maximal effort?

A

1) Mild voluntary effort - fewer peaks
2) Moderate effort - more peaks and motor units recruited following the size principle - ie. smaller followed by larger
3) Maximal effort - Many more peaks

47
Q

How is a clinical diagnosis made using an electromyograph?

A

Degradation in the EMG or spontaneous or asynchronous activity forms the basis for clinical diagnosis

48
Q

Can complete fused tetanus be achieved in one motor unit in vivo?

A

No - cannot reach the level of Hz needed. Only unfused tetanus can be achieved in each individual motor unit

49
Q

Why can a smooth muscle contraction still be achieved despite the fact that fused tetanus cannot be achieved in individual motor units in vivo?

A

Because different motor units are being recruited at slightly different time, so the fluctuation in unfused tetanus are at slightly different points and the overall effect of all the motor units working together is smooth muscle contraction

50
Q

What is meant by tetanus in muscles?

A

Each AP produces a muscle twitch, in tetanus muscle fibres are innervated by the next AP before they have chance to relax leading to a maintenance of tension

51
Q

Name the 3 main sources of inputs to the alpha motor neurons?

A

1) Sensory inputs from peripheral proprioceptors
2) Local inputs from spinal interneurons
3) Descending inputs from UMNs

52
Q

Which 3 kinds of proprioceptor is found within the joint capsule?

A

Ruffini-like proprioceptor
Pacinian-like proprioceptor
Bare nerve endings

53
Q

What is the role of the proprioceptors found within the joint capsule?

A

Protective function against hyperextension

54
Q

Which type or proprioceptor is found in tendons?

A

Golgi tendon organ

55
Q

What do golgi tendons detect?

A

Muscle tension

56
Q

The muscle spindle is made up of what type of muscle fibres?

A

Intra-fusal muscle fibres - ie. within a capsule

57
Q

What do muscle spindles detect?

A

Change in muscle length

58
Q

What is the function of muscle spindles?

A

Enable detection of body position in space and enables regulation of muscle contraction and precisely matches force generated to the task

59
Q

What is the role of muscle spindle in maintaining muscle tone?

A

Interaction between muscle spindles and alpha motor fibres ensures the muscle is always under some degree of stretch - this is muscle tone

60
Q

What are the 2 main classes of muscle spindle?

A

1) Chain spindles

2) Bag spindles

61
Q

What is the difference between chain and bad muscle spindles?

A
  • Chain spindles innervated by Ia and II afferent fibres and they encode the static response of the fibre - ie they continue firing for as long as the muscle is stretched
  • Bag spindles are innervated by Group Ia afferents and only encode mainly the dynamic response of the fibre ie. the rate of change during dynamic stretch
62
Q

Extrafusal muscle fibres receive innervation from what type of motor neurones?

A

Alpha motor neurones

63
Q

Intrafusal fibres have a sensory function and do not generate tension but they have to receive some motor innervation, which type of motor neurons provide this motor innervation?

A

Gamma motor neurones

64
Q

Describe the mechanism of muscle contraction and the role of gamma motor neurons in ensuring sensitivity of muscle spindles?

A

1) Alpha MN cause extrafusal fibres to contract
2) Intrafusal fibres not innervated by alpha MN so dont contract, the intrafusal fibres thus lose tension and sensitivity to changes in muscle length as muscle spindle collapses
3) This is corrected by the gamma motor neuron which matches the length of the intrafusal fibres to the extrafusal fibres thus restoring the sensitivity of the muscle spindle to the muscle length

65
Q

What kind of receptor is the golgi tendon organ?

A

Mechanoreceptor

66
Q

What is the rough structure of golgi tendon organ?

A

Axons of the Ib afferent neurons are intertwined with the collagen fibrils of the tendon

67
Q

What do golgi tendon organs detect?

A

change in muscle tension as when the muscle contracts the force acts directly on the tendon, acts like a strain gauge ie monitors muscle tension and the force of contraction

68
Q

What kind of fibres are golgi tendon organs innervated by?

A

Ib afferents

69
Q

What is the difference in the firing of golgi tendon organs and muscle spindles during isometric and isotonic contraction?

A

During isometric contraction (tension without a change in muscle length) - Ib (golgi tendon organ) is firing but Ia (muscle spindles are not)
During isotonic contraction (change in muscle length with no change in tension) - the Ia axon (muscle spindle) is active and Ib axon (golgi tendon organ) is not

70
Q

What are the relative conduction velocities of Ia, Ib and II afferent nerve fibres, what is this related to?

A

Ia>Ib>II

Large diameter and greater myelination

71
Q

Group Ia afferents innervate what receptors involved in proprioception?

A

Both bag and chain spindles

72
Q

Group II afferent nerve fibres innervate which receptors involved in proprioception?

A

Chain spindles

73
Q

Group Ib afferent nerve fibres innervate which receptors involved in proprioception?

A

Golgi tendon organ

74
Q

What is the babinski sign?

A

To do with plantar response
When sharp object scraped along the plantar surface of the foot the toes should plantar flex
Babinski’s sign is when the toes instead dorsiflex and span out
This is a symptoms of upper motor neurone syndrome
NB. it also occurs in babies for the first few days of life

75
Q

Damage to descending motor pathways gives rise to what syndrome?

A

Upper motor neurone syndrome

76
Q

After several days what are the symptoms of upper motor neurone syndrome? 4

A

1) Babinski sign
2) Spasticity
3) Hyporeflexia
4) Loss of fine movements

77
Q

Why is it thought that fine movements are lost in damage to descending motor pathways?

A

Fine movement signals travel via UMN which make direct contact with LMNs - thus no involvement of interneurones so less capacity for neuronal plasticity and recovery of function than the less fine movements whcih travel via interneurones

78
Q

What disease is caused by damage to lower motor neurones?

A

Amyotrophic lateral sclerosis/ Motor neurone disease

79
Q

What are the symptoms of motor neurone disease?

A

1) In early stages weakness of muscles and atrophy
2) Inexorable decline with loss of all voluntary movement (walking, speaking, swallowing, breathing)
3) No loss of cognitive function

80
Q

What kind of neurons degenerate in motor neuron disease?

A

Progressive alpha neuron degeneration

Year 2 Term 3 Control (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions