Skeletal Muscle Morphology And Mechanics

Question 1

What are the 4 main functions of Skeletal Muscle?

Answer 1

Movement
Posture
Joint Stability
Heat Generation

Question 2

Briefly describe circular muscles, giving a function and two examples

Answer 2

• Concentric fibres which attach to skin, ligaments, and fascia
• Act as sphincter to adjust opening
• Orbicularis Occuli, Orbicularis Oris

Question 3

Describe parallel muscles and give the three main categories

Answer 3

• Fibres run parallel to force generating axis
• Most common type

Categories:

• Strap: Shaped like belt, fibres run longitudinally to contraction direction eg sartorius
• Fusiform: Wider and cylindrically shaped in centre, taper off at ends eg biceps brachii
• Fan-Shaped: Fibres converge at one end and spread over broad area at other end eg Pectoralis Major

Question 4

Describe pennate muscles and give the three different types

Answer 4

• One or more aponeuroses run through muscle body from tendon
• Fascicles attach to aponeuroses at an angle (pennation angle)

Types:

• Unipennate: all fascicles on same side as tendon eg extensor digitorum longus
• Bipennate: Fascicles on both sides of central tendon eg rectus femoris
• Multipennate: Central tendon branches eg deltoid

Question 5

By what are muscle compartments delineated?

Answer 5

Fascia

Question 6

What are the 5 roles muscles can have in movement?

Answer 6

Agonist - prime movers responsible for movement
Antagonist - oppose prime movers
Synergists - assist prime movers
Neutralisers - prevent unwanted actions of agonist
Fixators - act to hold a body part immobile while another moves

Question 7

What are the two main types of contraction, and their subclasses?

Answer 7

Isotonic - constant tension, variable length
- Concentric: muscle shortens
- Eccentric: muscle exerts force when extended
Isometric - constant length, variable tension eg hand grip

Question 8

What are the 3 classes of lever, giving examples of each?

Answer 8

First Class (See-Saw) - Effort at one end, load at another eg flexion/extension of head

Second Class (Wheelbarrow) - Effort at one end, fulcrum at other eg plantarflexion (load between fulcrum and effort)

Third Class (Fishing Rod) - Effort between load and fulcrum eg biceps brachii

Question 9

What are the 3 main fibre types?

Answer 9

Slow Type I - many mitochondria, red
Fast Type IIA - many mitochondria, red/pink
Fast Type IIX - few mitochondria, white

Question 10

What sense do muscle spindles facilitate?

Answer 10

Proprioception

Innervates by two sensory axons and one motor axon

Ia Sensory neurones relay rebate of change in muscle length to CNS
Type II sensory neurones provide position sense

Spindle walled off from rest of muscle by collagen sheath

Question 11

True or False: Small motor neurons are recruited before large

Answer 11

True