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Flashcards in Muscles Deck (58):
1

What's a fasciculation

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

2

Describe the origin of a skeletal muscle

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

3

Describe the insertion of a skeletal muscle

Bone, tendon or CT
Usually distal
Usually moved by contraction

4

What are the 3 arrangements of skeletal muscle

Circular
Parallel
Pennate

5

Describe circular skeletal muscle
Give examples

Fibres form concentric rings around sphincter or opening
Orbicularis occuli, orbicularis oris

6

What do circular skeletal muscles attach to

Skin
Ligaments
Fascia of other muscles

7

Describe parallel skeletal muscles

Fibres run parallel to force generating axis

8

What are the types of parallel skeletal muscle
Give an example of each

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

9

Describe Pennate skeletal muscle

Has 1 or more aponeuroses through muscle body from tendon
Fascicles attach to aponeuroses at an angle (pennation angle) to direction of movement

10

Types of Pennate skeletal muscle
Give an example of each

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

11

What separates compartments of muscle

Fascia

12

What is compartment syndrome

Bleeding within compartment exerts pressure on nerves and blood vessels

13

Symptoms of compartment syndrome

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

14

Treatment of compartment syndrome

Fasciotomy

15

Define agonist

Main muscle responsible for a particular movement

16

Define antagonist

Opposes action of agonist

17

Define synergist

Assists agonist
Acting alone it can't perform the movement of the agonist

18

Define neutraliser

Prevents unwanted actions that an agonist performs
Example: rotator cuff muscles prevent shoulder Flexion during elbow Flexion (biceps brachii)

19

Define fixator/stabiliser

Holds a body part immobile whilst another is moving

20

What are the types of muscle contraction

Isotonic contraction
Isometric contraction
Passive stretch

21

Describe isotonic contraction

Tension is constant
Muscle length changes

22

Types of isotonic contraction (describe)

Concentric - muscle shortens
Eccentric - muscle exerts force while extending

23

Effect of eccentric isotonic contraction

Damages muscles and causes delayed onset muscle pain

24

Describe isometric contraction

Muscle length is constant
Tension changes

25

When does isometric contraction occur

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

26

Describe passive stretch
Give an example

Muscle is lengthened while in passive state
Example: hamstrings lengthen when touching toes

27

Describe first class lever
Give example

Effort at one end, load at other end
Extension/Flexion of head

28

Describe second class lever
Give an example

Effort at one end, load between effort and fulcrum
Plantar Flexion of foot

29

Describe third class lever
Give an example

Effort between load and fulcrum
Lifting weight

30

What's a motor unit

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

31

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

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

32

How do types of muscle fibres differ

Myosin heavy chain expression

33

What are the main types of muscle fibre

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

34

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

All the same type
Therefore a motor unit is either fast, intermediate or slow contracting

35

Properties of type 1 muscle fibres

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

36

Properties of type 2a muscle fibres

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

37

Properties of type 2x muscle fibres

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

38

What factors control contractile force

Size principle
Rate code

39

Describe size principle

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

Describe rate code and summation

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

What causes baseline muscle tone

Elasticity of muscle
Low level of motor neurone activity

42

What controls skeletal muscle tone

Motor control centres in brainstem

43

What is hypotonia

Lack of skeletal muscle tone

44

Causes of hypotonia

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

45

Describe excitation contraction coupling

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

Describe malignant hyperthermia

Rare dominant condition triggered by volatile anaesthetic agents and succinylcholine

47

Effect of malignant hyperthermia

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

Treatment of malignant hyperthermia

Dantrolene
Antagonist of ryanodine receptor

49

Most common cause of malignant hyperthermia

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

50

What is myotonia

Inability to relax muscles at will

51

Symptoms of myotonia congenita

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

52

Cause of myotonia congenita

Mutations in chloride channel (CLCN1)

53

What are intrafusal muscle fibres

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

54

What are muscle spindles

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

55

Innervation of intrafusal fibres and function of neurones

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

What happens in patients with large fibre sensory neuropathy

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

57

Functions of skeletal muscle

Movement
Posture
Joint stability
Thermogenesis

58

What is sarcopenia

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

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