Skeletal Muscle organ structure and function

Question 1

List the components of skeletal muscle tissue

Answer 1

muscle cells + extracellular matrix (minimal)

Question 2

Describe the components of muscle cell/fibre

Answer 2

• multinucleated

- myofibrils

Question 3

What is a myofibril ?

Answer 3

= bundles of myofilaments (actin and myosin contractile proteins)

Question 4

List and describe the 3 types of skeletal muscle cells:

Answer 4

Type 1:
- slow oxidative, slow aerobic, smallest, fatigue resistant, least powerful
Type 2a:
- fast oxidative, fast aerobic, intermediate, some fatigue resistance
Type 2b:
- fast glycolytic, fast anaerobic, largest, fatigue, most powerful, more common

Question 5

List the 5 steps of the skeletal muscle organ

Answer 5

1. Tendon (DRCTP)
2. Deep fascia (DICTP)
3. Muscle epimysium (DICTP)
4. Fascicle perimysium (DICTP)
5. Fibre endomysium (LCTP)

Question 6

List and describe the 3 types of muscle contraction

Answer 6

1. Isometric: muscle force matches load, constant length
2. a. Concentric: muscle force is greater than load, muscle shortens (e.g. lifting weight)
   b. Eccentric: muscle force less than load, muscle lengthens (e.g. lowering weight)
3. Isokinetic: constant speed

Question 7

Describe a motor unit

Answer 7

• a single motor neuron and the muscle fibres it innervates
• all or nothing principle
• small versus large motor units

Question 8

List the 4 arrangement of fascicles

Answer 8

1. Circular
2. Parallel
3. Convergent
4. Pennate (feather)

Question 9

Describe circular fascicle arrangement in more detail

Answer 9

• fibres arranged concentrically around an opening = sphincters
  e. g. orbicularis iris, orbicularis oculi

Question 10

Describe parallel fascicle arrangement in more detail

Answer 10

• fascicles parallel to muscle

e. g. masseter, biceps branchii, rectus abdominis, sartorius

Question 11

Describe convergent fascicle arrangement in more detail

Answer 11

• fibres converge toward a common attachment site

e. g. pectorals major, latissimus dorsi

Question 12

Describe pennate (feather) fascicle arrangement in more detail

Answer 12

• fascicles at an oblique angle to the tendon

e. g. unipennate (extensor digitorum), bipennate (rectus femoris), multipennate (deltoid)

Question 13

Describe how axial muscles are organised

Answer 13

• stabilise or move elements of the axial body

Question 14

Describe how appendicular muscles are organised

Answer 14

• stabilise or move the appendicular body

Question 15

How much force can the muscle produce?

Answer 15

• can be determined by the physiological cross sectional area (PCSA)

Question 16

How efficient is the muscle force in moving the body segment>

Answer 16

• moment arm

- where moment arm = perpendicular distance from axis to the line of action of the muscle