Muscle 1 (skeletal)

Question 1

What are skeletal muscles responsible for?

Answer 1

• voluntary movement of bones that underpins locomotion
• control of inspiration by the contraction of the diaphragm
• skeletal muscle pump - help with venous return to the heart

Question 2

what are fascicles?

Answer 2

Fascicles are bundles of muscle fibres. They are the building blocks of skeletal muscles, responsible for the voluntary movements of our bodies.

Question 3

what are myofibrils?

Answer 3

Myofibrils are the basic rod-like units of muscle cells. They are composed of thin and thick filaments that slide past each other, allowing for muscle contraction

They are made of multiple sacromeres

Question 4

what are sarcomeres?

Answer 4

Repeating segments within myofibrils that give skeletal muscle its striated appearance

Question 5

what is the structure of muscle fibres like?

Answer 5

They have a structural arrangement with myofibril and repeating sarcomere units

Question 6

what is the structure of skeletal muscles like?

Answer 6

striated- visible bands or stripes that can be seen under a microscope when looking at certain types of muscle tissue

Question 7

What’s the difference between Slow and Fast muscle fibres?

Answer 7

Slow: half diameter of fast fibres / take longer to contract after nerve stimulation / can continue to keep contracting for a longer period of time at a high voltage

Fast: take 10msec or less to contract / cant sustain continuous contraction

Question 8

what are the 2 classes of muscle contractions?

Answer 8

Isometric - muscle at fixed length, tension generated but nor change in length
Isotonic - muscle contraction causes a change in length

Question 9

What happens when actin and myosin interact together?

Answer 9

Contraction

Question 10

How is contraction initiated in the muscle?

Answer 10

Action potential comes down the nerve and triggers the release of ACh

Release of Acetylcholine at the neuromuscular junction initiates an action potential in the plasma membrane of the muscle fibre.

Wave of depolarization passes along the sarcolemma and through the T-tubule network to reach interior of the cell

Depolarization triggers an increase in intracellular calcium

Question 11

what does the release of calcium trigger?

Answer 11

muscle contraction

Question 12

how does cross bridge formation of actin and myosin lead to the contraction of the sarcomere?

*This process is an active process meaning it is dependent on ATP phosphorylation

Answer 12

1-The myosin head is in a tight configuration with actin (absence of ATP)

2- ATP comes in to the myosin head which changes how tightly actin is bound to myosin. DISSOCIATION OF MYOSIN HEAD FROM ACTIN

3-ATP is hydrolysed into ADP which are both attached to the myosin head

4- The myosin head changes configuration from a closed to an open position due to ATP and ADP

5-The confirmational change results in increased length of the myosin head

6- The myosin head is able to loosely bind to another molecule on the actin filament

7-Release of phosphate allows tight binding between the myosin head and actin

8- The myosin head changes configuration again into a closed state

9-ADP is released
CYCLE REPEATS

Question 13

What happens when we stimulate a muscle fibre?

Answer 13

an electrical stimulus
depolarisation of sarcolemma
release of calcium and contraction

Question 14

What is the latent period during muscle twitch?

Answer 14

The period where the action potential passes down the sarcolemma
(brief delay between the application of a stimulus and the onset of muscle contraction)

Question 15

What is a muscle twitch?

Answer 15

A single contraction-relaxation cycle in response to a single stimulus

Question 16

What is summation in skeletal muscle?

Answer 16

The process where multiple stimuli can combine to produce a stronger contraction than a single stimulus alone

Question 17

Q: What is the key difference between isotonic and isometric contractions?

Answer 17

Isotonic: Muscle changes length while maintaining constant tension. For example when lifting weights or doing a dumbbell curl

Isometric: Muscle maintains constant length while generating tension. For example when doing a plank

Question 18

Compare the three main types of skeletal muscle fibers

Answer 18

Type I (Slow oxidative): Red color, fatigue resistant, low glycogen, aerobic ATP synthesis, high mitochondria

Type IIa (Fast oxidative): Red color, resistant, abundant glycogen, aerobic ATP synthesis, higher mitochondria

Type IIx/IIb (Fast Glycolytic): White color, fatigable, high glycogen, anaerobic ATP synthesis, fewer mitochondria

Question 19

What is the key difference between slow and fast muscle fibers in terms of contraction time?

Answer 19

Fast fibers (eye) take 10msec or less to contract, while slow fibers (soleus) take longer to contract after nerve stimulation. Slow fibers are also half the diameter of fast fibers.

Question 20

What is botulinum toxin?

Answer 20

They are bacterial toxins that inhibit the release of ACh in the neuromuscular junction. By inhibiting the release of ACh, vesicle fusion is prevented so muscle contraction cannot happen

Question 21

What are the potential clinical effects of disrupting the neuromuscular junction, as seen with botulinum toxin?

Answer 21

1. First symptoms: dry mouth, double vision
2. Second symptoms: gastrointestinal issues (diarrhoea, vomiting)
3. Third symptoms: limb paralysis and respiratory muscle paralysis
4. Can be fatal if untreated

Question 22

What are the therapeutic uses of botulinum toxin?

Answer 22

1. Treatment of strabismus (cross-eyedness)
2. Treatment of blepharospasm (uncontrolled eyelid movements)
3. Cosmetic treatments (Botox)

Question 23

What is dendrotoxin?

Answer 23

Potassium channel inhibitor