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Biology A2: 5.5 > 5.5.10: Muscle > Flashcards

5.5.10: Muscle Flashcards

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1
Q

What are muscles composed of?

A
  • Cells arranged to form fibres.

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

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2
Q

Which two protein filaments help to achieve contraction?

A

-Actin and myosin protein filaments in the muscle cells.

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3
Q

How are muscle cells arranged and why?

A
  • Muscle cells are arranged in opposing pairs so that one contracts and the other elongates.
  • because muscle cannot elongate without an antagonist.
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4
Q

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

A

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

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5
Q

What are the three types of muscle?

A
  • Involuntary (smooth)
  • Cardiac
  • Voluntary (skeletal or striated) muscle.
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6
Q

What does involuntary (smooth) muscle consist of?

A
  • 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.
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7
Q

Describe the contraction of smooth muscle.

A
  • Contracts slowly and regularly.

- Does not tire quickly

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8
Q

What is smooth muscle controlled by?

A

-The autonomic nervous system

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9
Q

Where is involuntary muscle found and how is it arranged?

A
  • In the walls of tubular structures, such as the digestive system and blood vessels.
  • Arranged in longitudinal and circular layers that oppose each other.
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10
Q

What does cardiac muscle form?

A

The muscular part of the heart.

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11
Q

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?

A

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

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12
Q

What are cardiac muscles joined by?

A

-Intercalated discs

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13
Q

What are intercalated disks?

A
  • 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.
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14
Q

Describe the contractions of cardiac muscles.

A
  • Cardiac muscle contracts and relaxes continuously throughout life.
  • It can contract powerfully and does not fatigue easily.
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15
Q

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

A
  • Carry electrical impulses.

- These coordinate the contraction of the chamber walls.

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16
Q

Heart muscle is myogenic. What does this mean?

A

It can initiate its own contractions.

17
Q

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

A

The SAN

18
Q

How do cardiac muscles appear when viewed under the microscope?

A

Striated

19
Q

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

A
  • At the joints in the skeleton.

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

20
Q

How are voluntary muscles arranged?

A
  • In pairs called antagonistic pairs.

- When one contracts, the other one elongated.

21
Q

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

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

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

22
Q

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

A
  • Sarcoplasm

- Specialised to contain many mitochondria and extensive sarcoplasmic reticulum.

23
Q

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

A
  • Myofibrils, which are contractile elements.
  • These myofibrils are divided into a chain of subunits called sarcomeres which contain the protein filaments actin and myosin.
24
Q

What gives voluntary muscles their striated appearance?

A
  • 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.
25
Q

What are the contractions of skeletal muscles stimulated by?

A

-The somatic nervous system.

26
Q

Describe the contraction of voluntary muscles.

A
  • Voluntary muscle contracts quickly and powerfully.

- It also fatigues quickly.

27
Q

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

A

A neuromuscular junction.

28
Q

There are five steps to the stimulation of a contraction.

Step 1:

A

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.

29
Q

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:

A

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

30
Q

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:

A

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

31
Q

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:

A

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

32
Q

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:

A

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

33
Q

What is a motor unit?

A
  • Many motor neurones divide and connect to several muscle fibres.
  • All these muscle fibres contract together, providing a stronger contraction.
34
Q

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

A
  • 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.
35
Q

What does the amplitude of the EMG recording reflect?

A

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

Biology A2: 5.5 (11 decks)

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