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MSK > Muscles > Flashcards

Muscles Flashcards

1
Q

What’s a fasciculation

A

Small, local, involuntary skeletal muscle contraction and relaxation (twitch)

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2
Q

Describe the origin of a skeletal muscle

A

Bone
Usually proximal
Greater mass and more stable during contraction than the insertion

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3
Q

Describe the insertion of a skeletal muscle

A

Bone, tendon or CT
Usually distal
Usually moved by contraction

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4
Q

What are the 3 arrangements of skeletal muscle

A

Circular
Parallel
Pennate

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5
Q

Describe circular skeletal muscle

Give examples

A

Fibres form concentric rings around sphincter or opening

Orbicularis occuli, orbicularis oris

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6
Q

What do circular skeletal muscles attach to

A

Skin
Ligaments
Fascia of other muscles

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7
Q

Describe parallel skeletal muscles

A

Fibres run parallel to force generating axis

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8
Q

What are the types of parallel skeletal muscle

Give an example of each

A

Strap - sartorius
Fusiform - biceps brachii
Fan shaped/convergent - Pectoralis major

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9
Q

Describe Pennate skeletal muscle

A

Has 1 or more aponeuroses through muscle body from tendon

Fascicles attach to aponeuroses at an angle (pennation angle) to direction of movement

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10
Q

Types of Pennate skeletal muscle

Give an example of each

A

Unipennate (fascicles on same side as tendon) - extensor digitorum longus
Bipennate (fascicles on both sides of tendon) - rectus femoris
Multipennate (central tendon branches) - deltoid

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11
Q

What separates compartments of muscle

A

Fascia

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12
Q

What is compartment syndrome

A

Bleeding within compartment exerts pressure on nerves and blood vessels

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13
Q

Symptoms of compartment syndrome

A 
Constant poorly localised pain
Paresthesia 
Compartment feels tense 
Swollen shiny skin
Bruising and blistering 
Prolonged capillary refill time
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14
Q

Treatment of compartment syndrome

A

Fasciotomy

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15
Q

Define agonist

A

Main muscle responsible for a particular movement

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16
Q

Define antagonist

A

Opposes action of agonist

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17
Q

Define synergist

A

Assists agonist

Acting alone it can’t perform the movement of the agonist

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18
Q

Define neutraliser

A

Prevents unwanted actions that an agonist performs

Example: rotator cuff muscles prevent shoulder Flexion during elbow Flexion (biceps brachii)

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19
Q

Define fixator/stabiliser

A

Holds a body part immobile whilst another is moving

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20
Q

What are the types of muscle contraction

A

Isotonic contraction
Isometric contraction
Passive stretch

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21
Q

Describe isotonic contraction

A

Tension is constant

Muscle length changes

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22
Q

Types of isotonic contraction (describe)

A

Concentric - muscle shortens

Eccentric - muscle exerts force while extending

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23
Q

Effect of eccentric isotonic contraction

A

Damages muscles and causes delayed onset muscle pain

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24
Q

Describe isometric contraction

A

Muscle length is constant

Tension changes

25
Q

When does isometric contraction occur

A

Load against muscle equals contractile force being generated
E.g. Holding weight in fixed position

26
Q

Describe passive stretch

Give an example

A

Muscle is lengthened while in passive state

Example: hamstrings lengthen when touching toes

27
Q 
Describe first class lever 
Give example
A

Effort at one end, load at other end

Extension/Flexion of head

28
Q 
Describe second class lever
Give an example
A

Effort at one end, load between effort and fulcrum

Plantar Flexion of foot

29
Q 
Describe third class lever 
Give an example
A

Effort between load and fulcrum

Lifting weight

30
Q

What’s a motor unit

A

Alpha motor neurone and muscle fibres it innervates (connected by neuromuscular junction)

31
Q

Demonstrate with examples the variety in muscle fibre number in motor units

A

Muscles that produce precise movements have few muscle fibres - inferior rectus has 9
Powerful movements have lots of muscle fibres - gastrocnemius has 2000

32
Q

How do types of muscle fibres differ

A

Myosin heavy chain expression

33
Q

What are the main types of muscle fibre

A

Slow oxidative type 1
Fast oxidative type 2a
Fast glycolytic type 2x

34
Q

What’s the significance of the muscle fibres in each motor unit

A

All the same type

Therefore a motor unit is either fast, intermediate or slow contracting

35
Q

Properties of type 1 muscle fibres

A 
Aerobic 
High myoglobin
Red
Many mitochondria 
Rich capillary supply
Fatigue resistant 
Recruited in standing and walking
36
Q

Properties of type 2a muscle fibres

A 
Aerobic 
High myoglobin
Red/pink
Many mitochondria 
Rich capillary supply
Moderate fatigue resistance
Recruited in walking and running
37
Q

Properties of type 2x muscle fibres

A 
Anaerobic 
Low myoglobin
Pale
Few mitochondria 
Poorer capillary supply
Rapidly fatiguable
Recruited in running, sprinting and jumping
38
Q

What factors control contractile force

A

Size principle

Rate code

39
Q

Describe size principle

A

Small motor neurones are recruited before larger ones
Therefore motor units are recruited in order of:
Slow type 1
Fast type 2a
Fast type 2x

40
Q

Describe rate code and summation

A

More APs gives higher contractile force
Subsequent APs results in summation giving a slightly larger contractile force with each contraction. Limit where no further force can be produced is called tetany

41
Q

What causes baseline muscle tone

A

Elasticity of muscle

Low level of motor neurone activity

42
Q

What controls skeletal muscle tone

A

Motor control centres in brainstem

43
Q

What is hypotonia

A

Lack of skeletal muscle tone

44
Q

Causes of hypotonia

A

Cerebellum lesions
Lesions of sensory afferents from muscle spindles
Lower motor neurone lesions
Degeneration of muscle

45
Q

Describe excitation contraction coupling

A

ACh release at neuromuscular junction opens L-type calcium channels in T tubules
These channels are in close association with ryanodine receptors in SER
Ryanodine receptors are activated by calcium influx
Calcium is released into sarcolemma and binds to troponin
Bonding sites on actin are revealed

46
Q

Describe malignant hyperthermia

A

Rare dominant condition triggered by volatile anaesthetic agents and succinylcholine

47
Q

Effect of malignant hyperthermia

A

Uncontrolled increase in oxidative metabolism and resulting increase in body temperature
Increase in intracellular Ca leads to increased rate of SERCA which leads to massive heat production

48
Q

Treatment of malignant hyperthermia

A

Dantrolene

Antagonist of ryanodine receptor

49
Q

Most common cause of malignant hyperthermia

A

Polymorphism (2 or more alleles at 1 locus) in ryanodine receptor

50
Q

What is myotonia

A

Inability to relax muscles at will

51
Q

Symptoms of myotonia congenita

A

Muscle stiffness enhanced by cold/inactivity and relieved by exercise
Muscle hypertrophy

52
Q

Cause of myotonia congenita

A

Mutations in chloride channel (CLCN1)

53
Q

What are intrafusal muscle fibres

A

Type of muscle fibre that facilitates proprioreception (unconscious perception of own body’s movement and spacial orientation)
Contains muscle spindle

54
Q

What are muscle spindles

A

Sensory receptors in belly of intrafusal muscle fibres that respond to muscle stretch/length

55
Q

Innervation of intrafusal fibres and function of neurones

A

Gamma motor neurone - keep fibres taught
Type 1a sensory neurone - relays rate of change in muscle length to CNS
Type 2 sensory neurone - provides position sense

56
Q

What happens in patients with large fibre sensory neuropathy

A

Can perform accurate movements with eyes open but with eyes closed they are grossly inaccurate

57
Q

Functions of skeletal muscle

A

Movement
Posture
Joint stability
Thermogenesis

58
Q

What is sarcopenia

A

Loss of muscle mass due to loss of muscle fibres and reduced muscle cross sectional area

MSK (87 decks)

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