Lecture 8 - Skeletal Muscle Strucutre And Function

Question 1

What are the three types of muscles?

Answer 1

1. Smooth (lines hollow organs)
2. Cardiac (only in the heart)
3. Skeletal (muscles applies to the bones to control posture and body movements)

Question 2

What are the three primary jobs of skeletal muscle?

Answer 2

1. Skeletal muscles are under voluntary control (we choose when we activate them)
2. The primary job is to develop TENSION or FORCE
3. Muscles develop force on only one direction (developing force by shortening)

Question 3

What are the other secondary jobs that skeletal muscles provide?

Answer 3

1. Support and protection for soft internal organs (e.g muscles of abdominal wall)
2. Provides voluntary controls over major openings (allow passage of substances into or out of the body)
3. Converts energy (in part) to hear which is used to maintain core temperatures (e.g shivering)
4. Provides a major “store” for energy and protein

Question 4

Skeletal muscle is a complex tissue which what several major cell types?

Answer 4

1. Skeletal muscle fibres are huge, multinucleate cells containing large amounts of protein
2. Connective tissues ensheath the muscle fibres, and connects fibres to the bones
3. Skeletal muscle is richly supplied with blood vessels
4. Skeletal muscle is richly supplied with nerve fibres

Question 5

What are fascicles?

Answer 5

Muscle fibres are gathered into bundles

Question 6

Fascicles are gathered into bundles called….

Answer 6

Muscles

Question 7

Connective tissue is ensheathed by which three things?

Answer 7

Fibres, fascicles and muscles

Question 8

Connective tissue investments are gathered together to form what?

Answer 8

Tendons

Question 9

What do tendons connect?

Answer 9

Muscle to bone

Question 10

Each muscle fibre has hundreds to thousands of nuclei. Fibres are typically what length in diameter?

Answer 10

20-40 um

Question 11

What are myofibrils?

Answer 11

A myofirbil is a long cylindrical organelle found in muscle cells formed by two transverse filament systems - thick and thin. Myofibrils are made up of repeating units known as sacromeres.

Question 12

What are the two names of thin and thick filaments?

Answer 12

Actin (thin) and myosin (thick) filaments

Question 13

What is a sacromere?

Answer 13

A sacromere is the basic contractile unit of each muscle fibre.

Question 14

What are transverse tubules and their jobs?

Answer 14

T-tubules are extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscle cells. Through these mechanisms, T tubules allow heart muscle cells to contract more forcefully by synchronizing calcium release throughout the cell

Question 15

What is sacroplasmic reticulum?

Answer 15

Sacroplasmic reticulum is an extensive membranous tubular network associated with the T-tubules at regular intervals

Holds Ca ions

Question 16

Where does a triad come from?

Answer 16

The terminal chambers (terminal cisternae) of each SR structure associated with the T-tubules to form a membrane triplet called a triad

Question 17

What is the job of the SR?

Answer 17

To take up and store calcium, then to release Ca into the cytoplasm on receipt of an action potential conducted along the associated T-tubules

Question 18

The sacromere structure of the myofilamets arises due to what?

Answer 18

The arrangement of contractile proteins

Question 19

What does a myosin look like?

Answer 19

A long thin tail and a globular head

Question 20

What is the sliding filament theory?

Answer 20

How we can produce force and be able to contract

Question 21

What is the pr less of sliding filament?

Answer 21

These contractile proteins develop force by triggered molecular interaction that allows association of the myosin head with the nearby thin actin filament followed by the flexing of the myosin head to allow it to “walk” along the thin.

In this process the interlaced thick and thin filaments slide past one another

Question 22

The arrangement of the myosin heads in a sacromere means what?

Answer 22

That when this process is activated, the ends of the sacromere are drawn closer together by the flexing of the myosin heads (the sacromere Z-lines are drawn close to the central M-line)

Question 23

What are muscle contractions triggered by?

Answer 23

Action potentials

Question 24

Once action potentials arise in the brain, what happens next?

Answer 24

They’re conducted down the spinal cord to motor neurons in the spinal cord

Question 25

The myelinated axon of a motor neuron terminates at what?

Answer 25

A single point on the muscle fibre

Question 26

What is a motor unit?

Answer 26

A motor neuron and all the muscle fibres it controls

Question 27

What does the arrival of action potential at NMJ (neuromuscular junction) initiate?

Answer 27

The synaptic transmission which results in generation of AP in postsynaptic muscle fibre

Question 28

Excitation contraction coupling is what?

Answer 28

When AP in muscle fibre triggers a process that results in development of force within the fibre