Skeletal Muscle

Question 1

How are Z disks connected

Answer 1

Fine threads of intermediate filaments (desmin) via latitudinal and longitudinal strands

Question 2

Costameres

Answer 2

Strengthened areas on the sarcolemma

Question 3

Where do connections between sarcomeres end

Answer 3

Beyond the sarcolemma/muscle fibre membrane; they go to costameres on the sarcolemma which form rings around the fibre and reach out into the interstitial space

Question 4

Titin

Answer 4

Protein that surrounds actin and myosin and is the main protector against overstretch

Question 5

Sarcolemma

Answer 5

Muscle Fibre Membrane

Question 6

Lumbrical Muscles

Answer 6

Muscles deep in the palm of the hand which tighten the grips of our fingers

Question 7

Endomysium

Answer 7

Loose connective tissue surrounding each muscle fibre

Receives some force from desmin

Question 8

Perimysium

Answer 8

Mixed connective tissue (dense or loose) separating groups of muscle fibres into fasicles

Question 9

Epimysium

Answer 9

Loose connective tissue between connective tissue covering the muscle (Fascia) and muscle body

Question 10

Motor End Plate

Answer 10

Synapse between nerve and muscle fibre; one synapse per fibre

Question 11

How is SkM fibre AP generated (simply)

Answer 11

Motor End Plate stimulation (or electrical stimulation)

There are no gap junctions

Question 12

Motor Unit

Answer 12

A motor neuron and the muscle fibres it innervates. Contains more than one muscle fibre but all fibres of one unit are of the same type

Question 13

Difference between muscle fibre types/myosin isoforms

Answer 13

Type I are slow twitch and have higher oxidative capacity (more mitochondria), stain darker

Type IIa and IIX are fast twitch and have lower oxidative capacity better higher glycolytic capacity (anaerobic respiration)

Type I and IIX are extremes, IIA is like an intermediate

Question 14

Which Fibre type/isoform has the highest resistance to fatigue

Answer 14

Type I (Slow-twitch)

Question 15

Are all fibres in a given motor unit the same type/isoform?

Answer 15

Yes - being commanded by the same nerve, they do the same amount of work

Question 16

Storage fuels in each muscle fibre type

Answer 16

I - Triglycerides
IIA - Triglycerides, Glycogen
IIX - Creatine Phosphate, Glycogen

**Lipids as fuel source for long distance, carbs (and creatine) for intense exercise

Question 17

Describe size principle

Answer 17

As more force is needed, motor units are recruited in order according to their size with small units (type I) being recruited before bigger ones (type IIA then IIX) based on demand

Question 18

Compare Type I vs Type II muscle distribution between a marathon runner and bodybuilder

Answer 18

Marathon - More type I and bigger, normal or even relatively small type II
Higher oxidative capacity (more mitochondria)

Bodybuilder - More type II and bigger, and also bigger than average type I (size principal)
Lower oxidative capacity due to more myofibrils packed into a fibre

Question 19

Development of embryological skeletal muscle

Answer 19

Mononucleic precursor cells migrate into space where muscles form and multiply and align to fuse into muscle fibre precursors before starting to synthesise myofibril proteins

**DONT STRESS THIS YOU’LL DO MORE LATER (PROBABLY)

Question 20

Satellite cells (muscle)

Answer 20

Stem cell reserve of muscles; most precursors had fused into fibres during embryological development but these did not

They stay closely apposed to a muscle fibre but do not fuse and can replace damaged muscle cells and fuse to form myofibrils as done to embryos

**Double arrow head is basement membrane

Question 21

Look at this… that’s all