5.5.10: Muscle

Question 1

What are muscles composed of?

Answer 1

• Cells arranged to form fibres.

- These fibres can contract to become shorter, which produces a force.

Question 2

Which two protein filaments help to achieve contraction?

Answer 2

-Actin and myosin protein filaments in the muscle cells.

Question 3

How are muscle cells arranged and why?

Answer 3

• Muscle cells are arranged in opposing pairs so that one contracts and the other elongates.
• because muscle cannot elongate without an antagonist.

Question 4

In some cases, the antagonist isn’t another muscle, what could it be?

Answer 4

-In some cases, the antagonist may be elastic recoil or hydrostatic pressure in a chamber.

Question 5

What are the three types of muscle?

Answer 5

• Involuntary (smooth)
• Cardiac
• Voluntary (skeletal or striated) muscle.

Question 6

What does involuntary (smooth) muscle consist of?

Answer 6

• Individual cells, tapered at both ends (spindle shaped)
• At rest, each cell is about 500 um long and 5 um wide.
• Each cell contains a nucleus and bundles of actin and myosin.

Question 7

Describe the contraction of smooth muscle.

Answer 7

• Contracts slowly and regularly.

- Does not tire quickly

Question 8

What is smooth muscle controlled by?

Answer 8

-The autonomic nervous system

Question 9

Where is involuntary muscle found and how is it arranged?

Answer 9

• In the walls of tubular structures, such as the digestive system and blood vessels.
• Arranged in longitudinal and circular layers that oppose each other.

Question 10

What does cardiac muscle form?

Answer 10

The muscular part of the heart.

Question 11

How does the arrangement of cardiac muscles help to ensure that electrical stimulation spreads evenly over the walls of the chambers of the heart and that the contraction is a squeezing action rather than one dimensional?

Answer 11

-The individual cells of cardiac muscle form long fibres, which branch to form cross-bridges between fibres.

Question 12

What are cardiac muscles joined by?

Answer 12

-Intercalated discs

Question 13

What are intercalated disks?

Answer 13

• Specialised cell surface membranes fused to produce gap junctions that allow free diffusion of ions between the cells.
• Action potentials pass easily and quickly along and between the cardiac muscle fibres.

Question 14

Describe the contractions of cardiac muscles.

Answer 14

• Cardiac muscle contracts and relaxes continuously throughout life.
• It can contract powerfully and does not fatigue easily.

Question 15

What are some fibres in the heart such as Purkyne fibres modified to do?

Answer 15

• Carry electrical impulses.

- These coordinate the contraction of the chamber walls.

Question 16

Heart muscle is myogenic. What does this mean?

Answer 16

It can initiate its own contractions.

Question 17

What is the rate of contraction of the heart controlled by?

Answer 17

The SAN

Question 18

How do cardiac muscles appear when viewed under the microscope?

Answer 18

Striated

Question 19

Where are voluntary (skeletal) muscles found and what does their contraction cause?

Answer 19

• At the joints in the skeleton.

- Contraction causes movement of the skeleton by bending or straightening the joint.

Question 20

How are voluntary muscles arranged?

Answer 20

• In pairs called antagonistic pairs.

- When one contracts, the other one elongated.

Question 21

Describe how the muscle cells in voluntary muscles are arranged into fibres.

Answer 21

• Muscle cells form fibres of about 100um in diameter.

- Each fibre is multinucleate and is surrounded by a membrane called the sarcolemma.

Question 22

What is the muscle cell cytoplasm in voluntary muscle called and what does it contain?

Answer 22

• Sarcoplasm

- Specialised to contain many mitochondria and extensive sarcoplasmic reticulum.

Question 23

What are the contents of the fibres in voluntary muscles arranged into?

Answer 23

• Myofibrils, which are contractile elements.
• These myofibrils are divided into a chain of subunits called sarcomeres which contain the protein filaments actin and myosin.

Question 24

What gives voluntary muscles their striated appearance?

Answer 24

• Actin and myosin are arranged in a particular banded pattern.
• Dark bands are known as the A bands and lighter bands are the I bands.

Question 25

What are the contractions of skeletal muscles stimulated by?

Answer 25

-The somatic nervous system.

Question 26

Describe the contraction of voluntary muscles.

Answer 26

- Voluntary muscle contracts quickly and powerfully. | - It also fatigues quickly.

Question 27

What us the junction between the nervous system and the muscle called?

Answer 27

A neuromuscular junction.

Question 28

There are five steps to the stimulation of a contraction. | Step 1:

Answer 28

Action potentials arrive at the end of the axon and open calcium ion channels in the membrane. Calcium ions flood into the end of the axon.

Question 29

There are five steps to the stimulation of a contraction. Step 1: Action potentials arrive at the end of the axon and open calcium ion channels in the membrane. Calcium ions flood into the end of the axon. Step 2:

Answer 29

Vesicles of acetylcholine move towards and fuse with the end membrane.

Question 30

There are five steps to the stimulation of a contraction. Step 2: Vesicles of acetylcholine move towards and fuse with the end membrane. Step 3:

Answer 30

Acetylcholine molecules diffuse across the gap and fuse with receptors in the sarcolemma.

Question 31

There are five steps to the stimulation of a contraction. Step 3: Acetylcholine molecules diffuse across the gap and fuse with receptors in the sarcolemma. Step 4:

Answer 31

This opens sodium ion channels, which allow sodium ions to enter the muscle fibre, causing depolarisation of the sarcolemma.

Question 32

There are five steps to the stimulation of a contraction. Step 4: This opens sodium ion channels, which allow sodium ions to enter the muscle fibre, causing depolarisation of the sarcolemma. Step 5:

Answer 32

A wave of depolarisation spreads along the sarcolemma and down transverse tubules into the muscle fibre.

Question 33

What is a motor unit?

Answer 33

- Many motor neurones divide and connect to several muscle fibres. - All these muscle fibres contract together, providing a stronger contraction.

Question 34

How can the electrical activity of muscles be investigated using an electromyograph?

Answer 34

- When a muscle cell is stimulated, the motor neurone created action potentials in the muscle fibres. - Electrodes applied to the surface of the skin detect the combined effects of the action potentials. - The amplitude of the EMG recording reflects the number and size of the motor units involved in the contraction.

Question 35

What does the amplitude of the EMG recording reflect?

Answer 35

-The number and size of the motor units involved in the contraction.