Session 6 - Muscles

Question 1

Histologically distinguish between skeletal, cardiac and smooth muscle types

Question 2

Describe the ultrastructural appearance of striated muscle and state which bands contain actin, myosin or both

Question 3

Explain the hierarchical composition of a typical skeletal muscle outlining the principal components at the molecular, organelle, cellular, histological and regional anatomical levels

Question 4

Compare and contrast the structural significance of fast and slow striated muscle fibres

Answer 4

Question 5

Fast vs slow twitch Muscle fibres when they are working

Answer 5

Question 6

Describe the limited nature of repair possible in a mature muscle

Question 7

Recognise the following in photomicrographs, discuss their anatomical locations and salient histological features in relation to their function:
* skeletal muscle in longitudinal and transverse section (and be able to distinguish it from tendon)
* cardiac muscle (and be able to distinguish it from skeletal muscle)
* smooth muscle (and be able to distinguish it from connective tissue)

Question 8

Understand the concepts of the origin and insertion of a muscle, and relate these to its actions

COME BACK TO

Answer 8

• To contract, a skeletal muscle needs at least two points of attachment, an origin and an insertion.
• In most cases, one end of the muscle is fixed in position (usually the origin), while the other end moves during contraction (usually insertion)
• The insertion is usually distal, or further away, while the origin is proximal, or closer to the body, relative to the insertion.
  (For example, one could say the wrist is distal to the elbow. Conversely, you can say the elbow is proximal to the wrist.)
• Points of origin
• Points of insertion
• If these cross a joint, then movement occurs
• Movement is dependent on the direction of muscle fibre (cell) contraction
• Lots of different shapes of mucscle
• Movement is always along the direction of a fascicle
• Tension created at the origin tendon point
• Movement created at the insertion tendon point

Question 9

Describe the structure and organisation of skeletal muscle fibres

Question 10

Understand the different roles muscles can play in coordinated movement e.g. agonist, antagonist, synergist, neutraliser and fixator

Answer 10

Question 11

Understand the difference between superficial and deep fascia

Question 12

Outline the function of the Purkinje fibres of the heart

Answer 12

• The Purkinje fibres conduct action potentials rapidly (3-4 m/s, compared to 0.5 m/s for cardiac muscle fibres)
• This rapid conduction enables the ventricles to contract in a synchronous manner

Question 13

Outline the structure Purkinje fibres of the heart

Answer 13

Purkinje fibres are large cells with: - abundant glycogen
- sparse myofibrils
- extensive gap junction sites

Question 14

What is this arrow pointing to?

Answer 14

Purkinje Fibres

Question 15

Label this diagram (the 3 arrows) and describe what is happening in the image

Answer 15

Tracts of Purkinje fibres (modified myocytes) transmit action potentials to the ventricles from the atrioventricular node

Question 16

What are Purkinje fibres?

Answer 16

• Large modified myocytes with: abundant glycogen, sparse myofilaments and extensive gap junction sites.
• Conduct APs rapidly, enabling ventricles to contract in a synchronous manner.

Question 17

describe the process of skeletal muscle remodelling and its relevance to atrophy, hypertrophy and during injury

Question 18

describe the mechanism of innervation of muscle and excitation contraction coupling (the motor end plate)

Question 19

Outline the physiology of the neuromuscular junction

Question 20

Describe the clinical features of myasthenia gravis

Answer 20

Ptosis (Ptosis is when the upper eyelid droops, sometimes restricting or blocking vision)

Question 21

Describe the pathogenesis of myasthenia gravis

Answer 21

• Autoimmune disease
• Antibodies directed against Ach
  receptor (block)
• 30% reduction in receptor number sufficient for symptoms
• Endplate ‘invaginations’ in synaptic clefts reduced
• Reduced synaptic transmission
• Intermittent muscle weakness

Question 22

outline the mechanisms of the sliding filament model of muscle contraction

Question 23

State how neuromuscular transmission is disrupted in botulism

Answer 23

• Toxin produced by Clostridium botulinum
• Blocks neurotransmitter release at the motor end plate
• Causes non-contractile state of skeletal muscle - Flaccid paralysis

Question 24

Describe the use of Botulism toxin and botox

Answer 24

• Clinically used to treat muscle spasms (e.g. cervical dystonia)
• Used cosmetically to treat ‘wrinkles’

Question 25

State how neuromuscular transmission is disrupted in organophosphate poisoning

Answer 25

Organophosphates are used as pesticides * Inhibits the normal function of Ach esterase * Ach activity at the neuromuscular junction is potentiated * Leads to multiple symptoms and signs: * Effects on both somatic and autonomic signalling

Question 26

describe the pathophysiology of Duchenne muscular dystrophy

Answer 26

* Most common muscular dystrophy * Inherited through X-linked recessive pattern * Mutation of the dystrophin gene * Absence of dystrophin allows: - Excess calcium to enter the muscle cell - Calcium taken up by mitochondria - Water taken with it - Mitochondria burst - Muscle cells burst (rhabdomyolysis) - Creatine kinase and myoglobin levels are extremely high in the blood*(*sodium, phosphate, uric acid, potassium are also released) * Multiple skeletal muscle related symptoms and signs * Muscle cells replaced by adipose tissue

Question 27

What are the signs and symptoms of Duchenne muscular dystrophy? (10)

Answer 27

Question 28

What is happening in this image?

Answer 28

Muscle cells are being replaced with adipose tissue (occurs in Duchenne muscular dystrophy)

Question 29

Break down the word 'rhabdomyolysis'

Answer 29

Rhabdo = striated; myo = muscle; lysis = destruction

Question 30

Describe the pathophysiology of malignant hyperthermia

Answer 30

* Severe reaction to anaesthetics – Succinylcholine Autosomal dominant inheritance pattern - RyR1 gene Males>Females * Massive contractile fasciculation Muscle rigidity caused by ↑Ca2+ release Outcome – excessive heat and metabolic acidosis * ↑Muscle breakdown and hyperkalaemia (high blood [K+]) * Mortality risk 5% with treatment; 75% without treatment

Question 31

State the muscarinic and nicotinic symptoms of cholinergic toxidrome

Answer 31