Chapter 10: Muscular tissue

Question 1

Skeletal muscle functions

Answer 1

1. Producing body movements
2. Maintaining posture
3. Stabilizing joints
4. Generating heat

Question 2

Skeletal muscle structure

Answer 2

• Attached to bone by a tendon and covered by a connective tissue layer.
• the entire muscle is surrounded by the epimysium.
• inside are many cylindrical bundles of muscle cells called fascia to support the muscle.
• the fascia are surrounded by layers of perimysium.
• and each individual muscle cell is surrounded by a layer of endomysium.

Question 3

Muscle organization

Answer 3

• Each muscle cell/fibre is elongated and have many nuclei.
• the cytoplasm (called sarcoplasm) contains thousands of tiny myofibrils that extend the length of the cell.
• each myofibril consists of even smaller myofilaments which help in contraction

Question 4

Myofilaments

Answer 4

2 types:
1. Thick myofilaments - composed of myosin protein (2 myosin heads, 1 myosin tail). During contraction, the myosin heads stand up towards the thin filaments and forms cross bridges.

2. Thin myofilaments - composed of 2 chains of actin that bind to myosin heads, tropomyosin which covers the binding site, and troponin binds the two together.

Question 5

Sarcomeres

Answer 5

The arrangement of myofilaments resulting in striations

5 parts:
Z disc - separate the sarcomeres
A band - middle region of sarcomere (contains think and thin myofilaments)
H zone - in center of A band (contains only thick myofilaments)
I band - either side of a band (contains only thin myofilaments)
M line - in center of H zone, contains fine protein strands that hold thick myofilaments together

Note: the junction between the A and I bands forms a T tubule

Question 6

Myofibrils

Answer 6

Each myofibril is surrounded by the sarcoplasmic reticulum (smooth ER). Each myofibril is made up of several sarcomeres. There are sacs called terminal cisterns that join with the T tubule and together they form a triad.

Function:
To store, and release calcium at action potentials

Question 7

Motor unit

Answer 7

A motor neuron that branches to many muscle fibres

Question 8

Acetlycholine (ACh)

Answer 8

The neurotransmitter that is needed for the action potential to leave the axon terminal, cross the synaptic cleft, and excite the sarcolemma

Question 9

How does a muscle become stimulated?

Answer 9

• An action potential goes down the axon to its terminals. The terminals are connected to the muscle by a neuromuscular junction (synapse).
• voltage-gated Ca+ channels open and Ca+ ions diffuse into the terminal, which opens up ACh vesicles.
• ACh diffuses across the cleft and bind to ligand-gated channels which open to send Na+ ions into the muscle fibre and K+ ions out of the muscle fibre . This makes the membrane potential more positive.
• a threshold value is reached and an action potential extends across the sarcolemma (membrane).

Question 10

Excitation-contraction coupling

Answer 10

This is how the excited sarcolemma connects to the muscle contraction.

-The action potential travels down into the T tubules which triggers the sarcoplasmic reticulum to release Ca2+ into the sarcoplasm.
- Ca2+ binds to troponin which changed the shape of the thin myofilament and moves tropomyosin out of the way and frees the myosin binding site on the actin proteins.

Question 11

Sliding filament mechanism

Answer 11

ATP hydrolysis - ATP splits and binds to the myosin head and reorients it.
Cross bridge attachment - the energized myosin head attached to actin (forming a cross bridge), and the phosphate is released.
Power stroke - the cross bridge flicks up and shifts the thin myofilament towards the center of the sarcomere, then the ADP is released.
Cross bridge detachment - a new molecule of ATP binds to myosin head and the cross bridge detaches from actin.

Question 12

3 main pathways to supply muscles with ATP

Answer 12

1. Muscles store creating phosphate which can release ATP
2. Anaerobic glycolysis can be used
3. Aerobic respiration