Muscles- responsing to changes in the environment

Question 1

What are the 3 types of muscle?

Answer 1

-Cardiac
-Smooth (involuntary)
-Skeletal (voluntary)

Question 2

What word describes cardiac muscle?

Answer 2

Myogenic

Question 3

Where is smooth muscle found?

Answer 3

Gut, blood vessels, rhythmical

Question 4

What is skeletal muscle?

Answer 4

Attached by tendons to bones

Question 5

Describe how muscles work in antagonistic pairs

Answer 5

-Skeletal muscles work together to move bones
-One muscles will contract whilst the other relaxes
-The contracting muscle is the agonist and the relaxing is the antagonist.
-Tendons attach muscles to bones
-Ligaments attach bones to other bones

Question 6

Briefly describe muscle fibres

Answer 6

-Skeletal muscles are made of muscle fibres which are long bundles of long cells.
-Cell membrane is called the sarcolemma, where sections fold inwards and stick to the sarcoplasm (cytoplasm)
-The folds are called transverse tubules or T-tubules and help spread impulses throughout the sarcoplasm.
-Contain lots of mitochondria to provide ATP.

Question 7

What are fast twitch fibres?

Answer 7

white muscle

-Adapted to sudden bursts of energy
-Consume ATP quickly, O2 consumption is not enough, therefore energy is gained from anaerobic respiration
-The enzymes of the glycolosis pathway are plentiful and have few mitochondria.
-High store of phosphocreatine
-Thicker and more numerous myosin fibres

Question 8

What are slow twitch muscles fibres?

Answer 8

red muscle

-Sustained low levels of activity
-Oxygen demand keeps up with pace with ATP supply
-Glucose broken down in glycolosis, krebs and oxidative phosphorylation.
-Many mitochondria
-Good blood supply
-Contain lots of myoglobin to act as an oxygen store

Question 9

Put single muscle fibres, whole muscle, myofibril, and bundle of muscle fibres in order from largest to smallest.

Answer 9

Whole muscle

Bundle of muscle fibres

Single muscle fibres

Myofibril

Question 10

How does an action potential trigger muscle contractions?

Answer 10

1. Like synaptic transmission: Ca+ channels open, stimulates vesicles to fuse, release acetylcholine.
2. Acetylcholine binds to receptors on muscle membrane, opening Na+ channels, Na+ floods in.
3. Postsynaptic membrane depolarises, an action potential if threshold is met. This travels along the muscle cell membrane and into the special structures called T-tubules.
4. The T-tubules channel the action potential into the cell towards the sarcoplasmic reticulum. this organelle releases stored Ca2+ ions into the cell cytoplasm in response to the depolarisation.
5. Increase in conc of Ca2+ in muscle cell cytoplasm that causes the cell to contract. the acetylcholine is recycled by enzyme action and returned to the neuron.

Question 11

Outline differences between neuromuscular and cholinergic

Answer 11

Neuromuscular:
-Only excitatory
-Only links neurons and muscles
-Only motor neurons
-Action potential ends here

Cholinergic:
-Excitatory or inhibitory
-Neuron to neuron or effector
-Motor, sensory, intermediate
-New action potential may be produced

Question 12

What do myofibrils contain?

Answer 12

Bundles of thick and thin myofilaments that move past each other to make the muscle contract.

Question 13

What are the thick myofilaments made of?

Answer 13

Myosin

Question 14

What are the thin myofilaments made of?

Answer 14

Actin

Question 15

During contraction, what happens to the A band and I band?

Answer 15

A band stays the same
I band gets smaller

Question 16

Explain ‘Sliding Filament Theory’

Answer 16

• In contraction, Z lines are pulled closer together by the movement of actin and myosin filaments. Filaments become more interlocked.
• Myosin heads form cross-bridges with the surrounding actin filaments by attaching themselves to binding sites on the actin.
• Upon binding to actin, the myosin heads change shape. They pull actin filaments towards the centre of the sacromere: this is called the power stroke.
• Myosin heads use energy in ATP to detach from the actin and return to their original position. This entire process repeats, causing the sacromere to contract fully.
• When the muscle relaxes, the myosin heads are prevented from binding from actin. The actin and myosin can now be separated by the action of an antagonistic muscle.

Question 17

Explain how calcium ions and ATP are involved in muscle contraction

Answer 17

Tropomyosin blocks the binding.

1. Nerve impulses stimulate the release of calcium ions (Ca+) from the sarcoplasmic reticulum.
2. Ca+ cause the tropomyosin to change shape exposing the actin binding site.
3. Binding to actin causes myosin head to change shape. This causes the entire myosin filament to be pulled along by the actin. ADP can now be released from the myosin head.
4. ATP binds to the myosin head. This is broken down to produce ADP, Pi and energy. The energy allows the myosin head to release the actin and return to its original state.
5. The cycle can now repeat, dragging the myosin filament further along the actin. The sacromere will continue to contract if there is a ready supply of ATP.
6. Calcium is actively removed from the sarcoplasm when the muscle is no longer stimulated by a nerve. This causes the tropomyosin to return to its original shape.

Question 18

Muscle contractions will only occur is simulation is…

Answer 18

above a certain threshold

Question 19

What is a ‘refractory period’?

Answer 19

The time taken for the muscle to return to resting potential.

There is an absolute refractory period followed by a relative refractory period.

Question 20

What are A bands?

Answer 20

Darker bands in a myofibril, consists of overlapping myosin and actin filaments.

Question 21

What is a H zone?

Answer 21

The lighter region in the centre of each A band

Question 22

What is a neuromuscular junction?

Answer 22

An excitatory synapse formed between a motor neuron and a muscle fibre that uses the neurotransmitter, acetylcholine.

Question 23

What is a sacromere?

Answer 23

Each repeating unit of striations between adjacent z-lines.

Question 24

What is the Z-line?

Answer 24

The line in the centre of each I band.