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NAS > MOTOR UNIT > Flashcards

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
Q

Tetanus?

A

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
Q

Stretch reflex?

A

Contraction of muscle in response to its passive stretching
Increase length of muscle automatically by increasing contractility

27
Q

Muscle tone?

A

Amount of tension or resistance to movement in the muscle
Change in muscle tone allows us to move

28
Q

Neurone pathway of skeletal muscles

A

Somatic

29
Q

Neurone supply of glands and smooth muscle

A

Autonomic

30
Q

Causes for degeneration of nerves

A
  1. Injury
  2. Genetics of the body
  3. Aging
31
Q

Injured peripheral nerves have a capacity to regenerate and re-
innervate effectors. True or False

A

True

32
Q

Do CNS or PNS regenerate more easily

A

PNS

33
Q

Structural features of neurone likely to be affected by insult:

A
  1. Epineurium - (interfascicular bands attach adjacent nerve fascicle)
  2. Perineurium
  3. Endoneurium
  4. Myelin sheaths
  5. Axon (deepest)
34
Q

Neuropraxia ?

A

Mildest form of traumatic peripheral nerve injury
Temporarily loses its ability
Injury would be at level of myelin sheath

35
Q

Axonotomesis

A

Axon and myelin sheath is damaged but surrounding CT is intact
Result of severe crush injury
Can be recovered

36
Q

Neurotmesis

A

Entire nerve fibre is completely transected or severed
Most sever class of nerve damage
Recovery of function doesn’t occur

37
Q

Seddons classification of nerve injuries

A

Neuropraxia
Axonotomesis
Neurotmesis

38
Q

When nerve damaged, divided into 2 segments:

A

Proximal segment - receives support of cell body
Distal segment - cut off from cell body

39
Q

Distal segment of neurone?

A

• often cut off from cell body
• Loses potential for repairs
• Loses potential for nutritional support
•Becomes vulnerable to phagocytosis by glia

40
Q

What 3 glial cells are important when nerve is damaged

A
  1. Myelin forming cells
    Oligodendrocytes + Schwann cells
  2. Astrocytes - create environment for neurones
  3. Microglia - immune cells of NS
41
Q

Reaction to injury (minutes after)

A
  • neurone stop conducting AP
  • cut axon start leaking Intracellular fluid
  • cut ends pull apart and start swelling
42
Q

Reaction to injury an hour after injury sustained

A
  • 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
Q

Fate of distal segment of a severed nerve?

A
  • Not viable
  • Dies due to nutritional loss
  • axonal segment undergoes Wallerian degeneration
  • axon digested by phagocytes
44
Q

Tissues that might be preserved after damage:

A

Myelin sheaths
Epineurium
Perineurium
Endoneurium

45
Q

Importance of tissues that may be preserved after damage

A

These form hollow tubes to guide any new regrowth of the end of the proximal end

46
Q

Reactions to injury after days/ weeks?

A

The distal segment undergoes wallerian degeneration
Digested by phagocytes

47
Q

Fate of proximal segment of a severed nerve?

A
  • 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
Q

What is neuroma?

A

Injured nerve seals the wounded stump

49
Q

Regeneration of axonal stump in proximal segment

A

Forms many sprouts
Some which find Schwann cell tubes

50
Q

What is innervation?

A

Term used to describe the normal state of nerve supply to a muscle or other target

Alpha motorneurones innervates skeletal muscle

51
Q

Re innervation?

A

Re growth of the nerve supply to the muscle

52
Q

Is re innervation successful?

A

Reinnveration to the right organ is not always successful
Most nerves reinnervate a different target
This leads to unexpected results (or syndromes)

53
Q

Acute phase of denervated muscle that is not reinnervated?

A
  • 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
Q

Chronic phase of denervated muscle that is not reinnervated?

A

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
Q

Processes that distal and proximal segment undergo when nerve damaged

A

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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