Skeletal Muscle

Question 1

Striations in skeletal muscle are due to?

Answer 1

Myofibrils held in register by intermediate filaments (desmin) that link neighbouring Z discs laterally and longitudinally

Question 2

Force is transmitted longitudinally and laterally

Answer 2

The non-myofibrillar cytoskeleton provides link to BM and surrounding connective tissue

Question 3

Fascicles

Answer 3

Bundles of muscle fibres held together by perimysia

Question 4

Endomysium

Answer 4

Loose connective tissue;
Delicate and dense fibres;
Surrounds each muscle fibre;
Connects to BM;

Question 5

Perimysium

Answer 5

Dense and loose connective tissue; mixed;
Separates groups of muscles into fascicles;
Venue for nerves and BV;

Question 6

Epimysium

Answer 6

Loose connective tissue between fascia and muscle body

Question 7

Fascia

Answer 7

Dense connective tissue covering the muscle

Question 8

Muscle types

Answer 8

Unipennate;
Bipennate;
Fusiform;
Quadrate;
Multipennate;

Question 9

Fusiform

Answer 9

Eg. Biceps;

Maximal amplitude and minimal force

Question 10

Unipennate, bipennate

Answer 10

Maximal force and small amplitude

Question 11

Psychological cross section

Anatomical cross section

Answer 11

Perpendicular to fibres, indicative of maximal force;

Perpendicular to space occupied

Question 12

Control of contraction in skeletal muscle

Answer 12

Via motor nerves in somatic nervous system;
Force producing fibres innervated by motor neurons;
1 synapse per fibre;
Motor end plates generate action potential
No gap junction;
Very quick/immediate feedback - proprioception (neural feedback loop) - Signals from muscle spindle provide information about the length change and Golgi tendon organs provide info about strength of contraction;
Therefore, precise control

Question 13

Motor unit

Answer 13

Motor neuron + muscle fibre it innervates

Question 14

Fibre types classified according to

Answer 14

Myofibrillar ATPase;
Oxidative capacity
Glycolytic capacity

Question 15

Myofibrillar ATPase

Answer 15

Indicative of myosin variants;

3 Myosin isoforms: type I (darkest) , IIA (lightest) and IIX;

Question 16

Oxidative capacity

Answer 16

Demonstrative of NADH TR activity;

Type I fibres (slow twitch) have a higher oxidative capacity than type II (fast twitch) and has more mitochondria;

Question 17

Glycolytic capacity

Answer 17

Type II fibres have a higher glycolytic capacity than type I and produce more lactate;
X greater than A;

Question 18

Each fibre in a given motor unit is the same type. What does this mean?

Answer 18

Same myosin isoform, same glycolytic and oxidative capacity, and do the same among of work as commanded by the same nerve fibre.

Question 19

Size principle

Answer 19

Type I (small) fibres are recruited first. When more force is needed type II fibres (larger) are recruited. Type IIX is usually recruited last (maximal force). Type II motor units have more fibres, therefore are larger.

Question 20

Effect of endurance on myosin isoforms

Answer 20

More and larger type I fibres due to higher oxidative capacity and more mitochondria

Question 21

Effect of strength on myosin isoforms

Answer 21

Both fibre types larger; less mitochondria; less endurance; creased strength;

Question 22

Lack of muscle activity leads to

Answer 22

Muscle atrophy

Question 23

Development of skeletal muscle

Answer 23

Not all myoblasts (muscle cell precursors) fuse to form muscle fibres. Some myoblasts are used as stem cell reserves in case the muscle is damaged.

Question 24

Muscle fibre nucleus

Answer 24

Myonucleus

Question 25

Muscle fibre membrane

Answer 25

Sarcolemma

Question 26

Muscle fibre cytoplasm

Answer 26

Sarcoplasm

Question 27

Satellite cells

Answer 27

Stem cells;
Small cells outside sarcolemma but underneath BM;
A small % of nuclei are satellite cells

Question 28

Characteristics of myonuclei

Answer 28

Terminally differentiated and cannot divide anymore;

Underneath the sarcolemma and basement membrane