Lecture 31 Skeletal Muscle II

Question 1

Describe the length tension relationship

Answer 1

Optimum length: 2.2um, every myosin head binds to a actin binding site, maximum tension developed
Overstretched: Less overlap between myosin and actin and thus less tension developed
Understretched: Actin and myosin are overlapping, meaning there is a 50/50 chance of myosin binding to the correct binding site on actin (going in the right direction)

Question 2

What is the total tension in muscle composed of

Answer 2

Passive force and active force

Question 3

What is the relationship between the stretch in a muscle and its passive force?

Answer 3

As muscle stretches more, the passive force increases

Question 4

What is a motor unit

Answer 4

A motor neuron and all the muscle fibers it innervates

Question 5

How is ACh released into the neuromuscular junction

Answer 5

Action potential travels down a motor neuron, causing calcium channels to open. Calcium enters the axon terminal, causing vesicles filled with acetylcholine to fuse with the terminal membrane. Acetylcholine then binds to the acetylcholine receptors in the terminal membrane, releasing ACh into the neuromuscular junction

Question 6

What happens during the activation of ACh receptors

Answer 6

Ach binds to receptors on the muscle end plate, which causes opening of the ligand gated ion channels, opening of these channels allows movement of predominantly Na+ into the muscle cell making it less negative

Question 7

How is a muscle action potential triggered

Answer 7

If sufficient ligand gated channels are opened, the end plate potential reaches threshold. Voltage gated Na+ channels open and an action potential is triggered. Action potential is then propagated along the sarcolemma into the T tubule system

Question 8

How is the terminal cisternae and the T tubule linked

Answer 8

By voltage gated calcium channels

Question 9

How do calcium levels fall

Answer 9

Calcium is actively pumped back into the sarcoplasmic reticulum via Ca2+ATPase pumps

Question 10

What are sources of ATP for muscle metabolism

Answer 10

Creatine phosphate, anaerobic glycolysis, aerobic metabolism

Question 11

Why is creatine phosphate useful

Answer 11

Creatine phosphate is a store of free phosphate, which means that recombination of ADP and Pi can make ATP again

Question 12

Why is anaerobic glycolysis

Answer 12

fast but inefficient, short intense exercise

Question 13

What is type 1 slow twitch

Answer 13

units with neurons innervating the slow efficient aerobic cells

Question 14

What is type 2 fast twitch

Answer 14

units with the neurons innervating the large fibres that fatigue rapidly but develop large forces

Question 15

What is the regulation of force dependent on

Answer 15

The rate of stimulation and the number of motor units recruited

Question 16

What is the rate of stimulation

Answer 16

One stimulus results in the muscle contracting and relaxing, if another stimulus is applied before the muscle relaxes completely, more tension results. This is a temporal summation and results in a unfused tetanus
If there is a high stimulation frequency, it results in a fused tetanus where the tension adds up

Question 17

What is recruitment

Answer 17

This also increases the force created. You recruit fibres from small to large