Lecture 9- Skeletal Muscle Neurophysiology 1

Question 1

What is skeletal muscle specialized for?

Answer 1

Has a highly order structure in order to generate force through contraction and extension. In this way skeletal muscles act as the motor pulling bones into place and allowing for movement.

Question 2

Skeletal muscle has what construction?

Answer 2

Parallel, fibers run in the same direction ensuring maximum force is produce through contraction.

Question 3

Order these words from the biggest to the smallest in terms of the structure of muscle....
Fiber
Muscle
Fasciculus
Myofibril

Answer 3

Muscle
Fasciculus
Fiber
Myofibril

All of these are long tube like structures running in parallel which bundle together to make the structure above in list.

Question 4

Name three things that skeletal muscle is rich in….

Answer 4

• Nerves= connection between the brain and muscles
• Blood vessels= Skeletal muscle uses a lot of energy and therefore needs oxygen + nutrients shipped to it constantly and waste products from metabolism removed.
• Connective tissue= exists throughout every layer of the muscle to provide structure keeping all the fibers correctly orientated. Having it in-between also acts like cushioning preventing rubbing/ friction.

Question 5

What is the appearance of muscle like?

Answer 5

Striated

Question 6

True or false: each muscle fiber is a muscle cell?

Answer 6

True

Question 7

What are sarcomeres? How they are defined in skeletal muscle?

Answer 7

They are the individual contractile units of skeletal muscle.
1 sarcomere is the distance between two Z lines.

Question 8

What is the outer membrane of a skeletal muscle fiber called?

Answer 8

Sarcolemma

Question 9

Describe the filaments that make up a myofibril? What are their roles in sarcomere contraction?

Answer 9

• Thin filament= actin. Gets pulled to the center of the sarcomere. The space between the thin filaments in the middle of the sarcomere gets smaller throughout contraction and bigger when relaxed.
• Thick filament= myosin. Is what does the pulling.

Question 10

Which filament forms the structure of the skeletal muscle fibers themselves?

Answer 10

Actin (thin)

Question 11

Where does contraction occur in skeletal muscle?

Answer 11

With contraction every sarcomere shortens its length in unison.

Question 12

What are the two aspects of the muscle excitation problem?

Answer 12

• Muscle fibers respond but don’t think i.e they don’t have pacemaker cells like the heart does and cannot act independently of the brain
• Muscle fibers need to contract simultaneously along their entire length otherwise will get staggered movement (think wave)

Question 13

What are the two aspects of the muscle excitation problem?

Answer 13

• Muscle fibers respond but don’t think i.e they don’t have pacemaker cells like the heart does and cannot act independently of the brain
• Muscle fibers need to contract simultaneously along their entire length otherwise will get staggered movement (think wave)

Question 14

What structure is responsible for solving the muscle-excitation problem?

Answer 14

The neuromuscular junction (NMJ)

Question 15

Describe the events that occur at the NMJ in transferring signals….

Answer 15

-Action potential moves down the myelin-coated axon and arrives at the
pre-synaptic terminal
-Triggers the movement of vesicles to the active zones, releasing acetylcholine (Ach)
-Ach moves into the synaptic cleft and down into the junctional folds
-Ach then interacts with receptors on the sarcolemma, depolarizing the fibre and propagating an action potential

Question 16

What are active zones?

Answer 16

This is where vesicles containing acetylcholine can bind and release neurotransmitter into the synaptic clef. Need this mechanism others would bind in places we don’t want release.

Question 17

What is the function of junctional folds?

Answer 17

They increase the surface area between the synaptic clef and sarcolemma. This is lined with acetylcholine receptors therefore, increasing the action that can occur here.

Question 18

Finnish the sentence:

Depolarisation of a muscle fiber leads to an….

Answer 18

Action potential

Question 19

How many APs in the muscle fiber result from 1 AP in the terminal?

Answer 19

1, not like in CNS when multiple inputs or multiple actions potentials from the same input

Question 20

What does a muscle fiber AP trigger?

Answer 20

Contraction (excitation- relation coupling)

Question 21

True or false: we have the ability to both synthesize and break down acetylcholine?

Answer 21

True

Question 22

What enzyme do we need for acetylcholine synthesis?

Answer 22

Choline Acetyltransferase

Question 23

What enzyme do we need for acetylcholine breakdown?

Answer 23

Acetylcholinesterase

Question 24

What is the acetylcholine lifecycle?

Answer 24

• Acetylcholine is synthesized is presynaptic terminal from choline and acetyl cholA via ChAT
• It is transported into a vesicle and then released at the synaptic clef where it binds to receptors on the post-synaptic membrane to have an effect
• Acetylcholine is then broken down into choline and acetic acid in order to prevent continuous activation.
• Choline is then transported back into the presynaptic terminal via sodium co-transport (takes advantage of favorable sodium gradient)
• Choline can then be made into more acetylcholine

Question 25

Why don’t we just make Acetylcholine from scratch every time?

Answer 25

It’s too inefficient energy wise (wastes too many resources)