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MOTOR UNIT Flashcards

1
Q

What does motor unit consist of?

A

Motor neurone
Skeletal muscle
NMJ
Connective tissue

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2
Q

Purpose of motor unit

A

Set muscle tone of the body
Bring about voluntary movement via antagonistic muscle pairs

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3
Q

Definition of motor unit

A

Minimal functional unit of motor system

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4
Q

Innervation ratio?

A

The number of muscle fibres innervated by a single motor neurone
Smaller the ratio the more precise the movement

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5
Q

Examples of innervation ratios. Extra-ocular and quadriceps ?

A

Extra ocular 1 neurone: 10 fibres
Quadriceps 1:1000

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6
Q

Where motor unit originates from?

A

From somatic motor efferents

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7
Q

Myogenic?

A

Generate own electrical activity

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8
Q

Importance of skeletal muscle

A

Movement
Stability of joints
Heat generation (only 20% efficient)
Posture

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9
Q

Single cell of a muscle known as?

A

Myocyte

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10
Q

What is a tendon?

A

Organised tough band of fibrous connective tissue
Attaches muscle to bone

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11
Q

Importance of tendon

A

Forms a point of confluence bringing together the individual contractions of the myocytes to produce a combined action usually at a joint

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12
Q

How can skeletal muscles be classified?

A

According to the assemblies of their fascicles

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13
Q

Types of skeletal muscles

A

Convergent
Circular
Strap
Fusiform
Pennated

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14
Q

Three types of pennated muscles

A

Unipennate
Bipennate
Multipennate

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15
Q

What are myocytes?

A

Muscle cells
Skeletal myocytes are tubular
Made from myofibrils

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16
Q

Role of lower motor neurone

A

Transmit signals from upper MN to effector

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17
Q

Where are lower motor neurones located

A

Cell body in lamina IX of the grey matter of the spinal cord then to effector

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18
Q

Characteristics of muscle fibres of a motor unit

A

Same contraction speed
Same susceptibility to fatigue
Same myosin fibre typing

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19
Q

Importance of the motor unit

A

Allows uniform development of force throughout muscle
Nervous system regulate rate and speed of contraction
Muscle contraction to be distributed throughout the muscle

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20
Q

How muscle fibres categorised

A

How quickly they develop force
How long they take to relax

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21
Q

Three broad classes of muscle fibres?

A

Fast twitch
Intermediate twitch
Slow twitch

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22
Q

Fast twitch?

A

Muscle develops force at a high speed but fatigues very quickly
E.g. eye

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23
Q

Intermediate twitch

A

Muscle develops force at medium speed and fatigues at moderate rate
E.g.

24
Q

Slow twitch

A

Muscle develops force at slow speed and fatigues very slowly

25
Tetanus?
When increase frequency of twitches Summation of twitches occurs Tetanus contraction is sustained and smooth Body stimulates muscle at high frequency so summation occurs quicker and contraction smoother
26
Stretch reflex?
Contraction of muscle in response to its passive stretching Increase length of muscle automatically by increasing contractility
27
Muscle tone?
Amount of tension or resistance to movement in the muscle Change in muscle tone allows us to move
28
Neurone pathway of skeletal muscles
Somatic
29
Neurone supply of glands and smooth muscle
Autonomic
30
Causes for degeneration of nerves
1. Injury 2. Genetics of the body 3. Aging
31
Injured peripheral nerves have a capacity to regenerate and re- innervate effectors. True or False
True
32
Do CNS or PNS regenerate more easily
PNS
33
Structural features of neurone likely to be affected by insult:
1. Epineurium - (interfascicular bands attach adjacent nerve fascicle) 2. Perineurium 3. Endoneurium 4. Myelin sheaths 5. Axon (deepest)
34
Neuropraxia ?
Mildest form of traumatic peripheral nerve injury Temporarily loses its ability Injury would be at level of myelin sheath
35
Axonotomesis
Axon and myelin sheath is damaged but surrounding CT is intact Result of severe crush injury Can be recovered
36
Neurotmesis
Entire nerve fibre is completely transected or severed Most sever class of nerve damage Recovery of function doesn’t occur
37
Seddons classification of nerve injuries
Neuropraxia Axonotomesis Neurotmesis
38
When nerve damaged, divided into 2 segments:
Proximal segment - receives support of cell body Distal segment - cut off from cell body
39
Distal segment of neurone?
• often cut off from cell body • Loses potential for repairs • Loses potential for nutritional support •Becomes vulnerable to phagocytosis by glia
40
What 3 glial cells are important when nerve is damaged
1. Myelin forming cells Oligodendrocytes + Schwann cells 2. Astrocytes - create environment for neurones 3. Microglia - immune cells of NS
41
Reaction to injury (minutes after)
- neurone stop conducting AP - cut axon start leaking Intracellular fluid - cut ends pull apart and start swelling
42
Reaction to injury an hour after injury sustained
- Synaptic terminal degenerates. Accumulation of neurofilaments (significant role in determining the shape of cells, caliber of axonal projections, and maintenance of axonal transport) - Astroglia surround terminal - Microglia infiltration
43
Fate of distal segment of a severed nerve?
- Not viable - Dies due to nutritional loss - axonal segment undergoes Wallerian degeneration - axon digested by phagocytes
44
Tissues that might be preserved after damage:
Myelin sheaths Epineurium Perineurium Endoneurium
45
Importance of tissues that may be preserved after damage
These form hollow tubes to guide any new regrowth of the end of the proximal end
46
Reactions to injury after days/ weeks?
The distal segment undergoes wallerian degeneration Digested by phagocytes
47
Fate of proximal segment of a severed nerve?
- Undergoes process chromatolysis - Cell body very active and prod. Proteins for repair - Soma becomes bloated -Nucleus displace to periphery - Injured nerve seals wounded stump: neuroma - sometimes nerve stump regenerates to innverate peripheral structures
48
What is neuroma?
Injured nerve seals the wounded stump
49
Regeneration of axonal stump in proximal segment
Forms many sprouts Some which find Schwann cell tubes
50
What is innervation?
Term used to describe the normal state of nerve supply to a muscle or other target Alpha motorneurones innervates skeletal muscle
51
Re innervation?
Re growth of the nerve supply to the muscle
52
Is re innervation successful?
Reinnveration to the right organ is not always successful Most nerves reinnervate a different target This leads to unexpected results (or syndromes)
53
Acute phase of denervated muscle that is not reinnervated?
- Muscle is immediately paralysed (flaccid paralysis) - muscle becomes areflexic (absence of deep tendon reflexes) - Muscle start to fasciculate (twitching) If muscle not reinnervated the fasciculations will subside
54
Chronic phase of denervated muscle that is not reinnervated?
Fasciculations subside and muscles: - loose bulk due to lack of use and dennervation Muscle will die Muscle replaced with CT and fat State of fibrosis
55
Processes that distal and proximal segment undergo when nerve damaged
Proximal - chromatolysis (redistribution of nissl substance in the cell body to prod proteins for regeneration) Distal - wallerian degeneration

NAS (17 decks)

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