Microstructure and Function (S1)

Question 1

What is muscle?

Answer 1

any contractile tissue

Question 2

What are the 5 types of tissue?

Answer 2

• epithelium
• connective
• blood
• muscle
• neural

Question 3

What are the 3 main muscle types?

Answer 3

• Striated
• Skeletal
• Cardiac
• Non-striated:
• Smooth

Question 4

What are other non-striated muscles apart from smooth?

Answer 4

• myoepithelium (in glands, iris of eye)
• myofibroblasts (in healing wounds)

Question 5

How quick is contraction and voluntariness within each of the 3 muscles?

Answer 5

• Skeletal
• rapid contraction, subject to fatigue, voluntary
• Cardiac
• quite rapid, resists fatigue, involuntary
• Smooth
• slower but powerful, energy-efficient, little fatigue, involuntary (apart from internal bladder sphincter)

Question 6

Describe the microstructure arrangement of skeletal muscle

Answer 6

• Epimysium (thick outermost CT layer surrounding muscle)
• Perimysium (CT layer surrounding fascicles)
• Within fascicle, there is a muscle fibre surrounded by endomysium and sarcolemma
• Furthest subdivision = myofibrils within the muscle fibre cells

Question 7

Why are skeletal muscle fibres multinucleated?

Answer 7

Skeletal muscle fibres are formed by thousands of precursor cells in the embryo (myoblasts) fusing together.

Question 8

What is a myofibril?

Answer 8

Bundles of thick myosin and thin actin filaments

Question 9

What is a sarcomere?

Answer 9

Contractile unit, from one Z line to the next

Question 10

What is the Z line?

Answer 10

Where actin filaments meet / separating sarcomeres

Question 11

What are the A and I bands?

Answer 11

A band is in the middle of a sarcomere, where the myosin and actin filaments overlap.

The I band is between the myosin filaments (so just the actin)

Question 12

What happens during the sliding filament model?

Answer 12

The sarcomere contracts - the Z lines get closer so the I band gets narrower but the A band stays the same.

Question 13

How does skeletal muscle know when to contract?

Answer 13

There is neural stimulation via motor end-plates, special membrane systems carry the signal to all parts of this very large cell.

Question 14

What is Duchenne muscular dystrophy?

Answer 14

Inherited genetic condition in whcih the muscle fibres are smaller and there is more connective tissue.

Question 15

What are the main differences between cardiac and skeletal muscle fibres?

Answer 15

Cardiac has much smaller fibres, joined end-to-end by specialised junctions called intercalated disks, fibres also only have 1 or 2 nuclei.

Question 16

How does cardiac muscle resist fatigue?

Answer 16

The numerous mitochondria allow continuous supply of energy

Question 17

How does cardiac muscle resist high blood pressure?

Answer 17

It has branching fibres which provide extra strength

Question 18

Describe the myogenic stimulus of cardiac muscle?

Answer 18

AP starts from pacemaker in R. Atrium and carries wave of contraction across heart, assisted by ion diffusion through gap junctions in intercalated disks.

Question 19

Where is smooth muscle found?

Answer 19

Generally internal organs (except heart), eg. digestive tract, uterus, lungs, bladder, glands, blood vessels etc

Question 20

What is the shape and structure of smooth muscle fibres like?

Answer 20

smooth, sausage spindle shaped, with one nucleus

Question 21

What does the contractile structure of smooth muscles look like?

Answer 21

No myofibrils/striations/complex membrane systems, but there are caveolae and ER.

Also some actin and very few myosin filaments.