Skeletal Muscle Structure & Function

Question 1

What are the 3 types of muscle?

Answer 1

Striated = skeletal and cardiac. Non-striated = smooth

Question 2

Outline the features of skeletal muscle

Answer 2

Multinucleated, fused cells, attached skeleton, voluntary

Question 3

Describe cardiac muscle

Answer 3

Branched uninucleated, heart only, intercalated disks, involuntary

Question 4

Outline the characteristics of smooth muscle

Answer 4

Distinct cells, spindle shaped, wall of internal organs, involuntary

Question 5

Define fasciculation

Answer 5

Small local involuntary muscle contractions and relaxation – may be visible under skin

Question 6

Describe the structure, function and placement of circular muscles

Answer 6

Concentric fibres, act as sphincter to adjust opening, attach to skin/ligaments and fascia rather than bone e.g. orbicularis occuli/oris

Question 7

What are the 3 main categories of parallel muscles?

Answer 7

Strap, fusiform, fan shaped

Question 8

Describe a parallel strap muscle

Answer 8

Shape = belt, fibres run longitudinally to contraction direction

Question 9

Outline a parallel fusiform muscle

Answer 9

Shape = wider in the centre, taper off at the ends

Question 10

What is a parallel fan shaped muscle?

Answer 10

Shape = fibres converge at one end and spread over broad area at other end

Question 11

What are the 3 types of pennate muscle and what distinguishes them?

Answer 11

Unipennate = all fascicles on same side as tendon.

Bipennate = fascicles on both sides of central tendon.

Multipennate = central tendon branches

Question 12

What is the difference between a muscle origin and insertion?

Answer 12

Origin = greater mass and more stable during contraction. Insertion = tends to be moved by contraction, tends to be distal, may be bone/tendon/CT

Question 13

What is compartment syndrome?

Answer 13

Trauma in one compartment (limbs divided into sections by fascia) = internal bleeding which exerts pressure on blood vessels and nerves

Question 14

What role can a muscle assume in movement?

Answer 14

Agonist, antagonist, synergist (assists), neutralisers (prevents unwanted), fixator (hold part immobile)

Question 15

Describe an isotonic contraction

Answer 15

Constant tension, variable muscle length: 1) concentric = shortens 2) eccentric = extended

Question 16

Outline an isometric contraction

Answer 16

Constant length, variable tension

Question 17

What is a first/second/third class lever?

Answer 17

First = load and effort on either side of the fulcrum (see-saw).

Second = load and effort on the same side, effort is furthest away (wheelbarrow).

Third = load and effort on the same side, load is furthest away (fishing-rod)

Question 18

What is rigor mortis?

Answer 18

ATP depleted, myosin heads can’t detach

Question 19

How any motor neurons innervate a single muscle fibre?

Answer 19

1

Question 20

How many muscles fibres can a motor neuron innervate?

Answer 20

Many

Question 21

What are the 3 main muscle fibre types?

Answer 21

Slow oxidative type I (many mitochondria),

fast oxidative type IIA (many mitochondria),

fast oxidative type IIX

Question 22

What is the name given to sensory receptors located in intrafusal muscle fibres that detect change?

Answer 22

Proprioceptors

Question 23

How is muscle force controlled?

Answer 23

Rate code = more AP the more force. Size = small motor neurons recruited before large

Question 24

How is baseline tone maintained?

Answer 24

Healthy muscle never fully relaxed = retain tension and stiffness = tone

Question 25

What is hypotonia?

Answer 25

Lack of skeletal muscle tone – symptom rather than a condition e.g. muscular dystrophies

Question 26

Besides K+ leak channels, skeletal muscles fibres also have high conc of?

Answer 26

Cl- leak channels

Question 27

What is myotonia?

Answer 27

Inability to relax muscle at will caused by mutations to chloride channel CLCN1, recessive or dominant

Question 28

In skeletal muscle which ion provides the most conductance?

Answer 28

Cl-

Question 29

What are the sources of ATP in muscle?

Answer 29

Short term stores ATP, creatine phosphate, glycolysis, oxidative phosphorylation

Question 30

What causes acidosis?

Answer 30

Current thinking is that acidosis is not caused by lactate but other reactions like ATP hydrolysis