The muscular system

Question 1

What is the function of a muscle tissue?

Answer 1

Contraction & relaxation
Chemical energy changed into mechanical energy

Question 2

What is the function and structure of a skeletal muscle?

Answer 2

Attaches to bone, skin or fascia
Striated: light & dark bands visible with microscope.
Voluntary control

Question 3

What is the function and structure of a cardiac muscle?

Answer 3

Striated
Involuntary control
Auto rhythmic: built in pacemaker

Question 4

What is the function and structure of smooth muscle?

Answer 4

Hair follicles in skin
Walls of hollow organs: blood vessels & GI
Non-striated
Involuntary

Question 5

Main functions of the muscle tissue….

Answer 5

Body movements
Stabilizing position
Regulating organ volume: (smooth muscle: sphincters)
Movement of substances within body: (blood, lymph, urine, air, food & fluids)
Producing heat: (involuntary contractions of skeletal muscle = shivering)

Question 6

What are the properties of a muscle tissue?

Answer 6

Excitability: (respond to neurotransmitters)
Conductivity: (propagate electrical signals over membrane)
Contractility: (shorten & generate force).
Extensibility: (can be stretched without damage).
Elasticity: (return to original shape after being stretched).

Question 7

What is the structure and the membrane involved in the skeletal muscle fibre or myofibre?

Answer 7

Long, cylindrical & multinucleated
Sarcolemma = muscle cell membrane
Sarcoplasm filled with myofibrils & myoglobin (red-coloured, oxygen-binding protein)

Question 8

What are the types of proteins found in muscle?

Answer 8

Contractile proteins (myosin & actin)
Regulatory proteins: turn contraction on & off (troponin & tropomyosin)
Structural proteins: provide proper alignment, elasticity & extensibility (titin, myomesin, nebulin & dystrophin).

Question 9

What is the function of titin?

Answer 9

Anchors thick filament to Z disc.
Between Z disc & end of thick filament can stretch to 4 X resting length & spring back.
Recovery of muscle from being stretched.

Question 10

What is the function of myomesin?

Answer 10

Connects to titin & adjacent thick filaments.

Question 11

What is the function of nebulin?

Answer 11

Inelastic protein, aligns thin filaments.

Question 12

What is the function of dystrophin?

Answer 12

Links thin filaments to sarcolemma & transmits tension generated to tendon.

Question 13

What is the sliding filament mechanism?

Answer 13

Myosin cross bridges pull on thin filaments.
Thin filaments slide inwards.
Z discs come toward each other,
Sarcomeres shorten.
Muscle fibre shortens.
Muscle shortens
Thick & think filaments do not change length.

Question 14

How does relaxation occur?

Answer 14

Troponin holds tropomyosin in position to block myosin-binding sites on actin.

Question 15

How does contraction occur?

Answer 15

Ca^2+ binds to troponin which changes the shape of the troponin-tropomyosin complex and uncovers the myosin-binding sites on actin.

Question 16

What are the 4 steps of the contraction cycle?

Answer 16

1) Myosin heads hydrolyize ATP and become reoriented and energized.
2) Myosin heads bind to actin, forming cross bridge.
3) Myosin heads rotate toward centre of the sarcomere (power stroke).
4) As myosin, heads bind ATP, the cross bridges detach from actin.

Question 17

What are the steps that occur in the relaxation cycle?

Answer 17

Acetylcholinesterase (AChE) breaks down Ach in synaptic gap.
Muscle action potential stops.
Ca^2+ release channels close.
Active transport pumps Ca^2+ back into sarcoplasmic reticulum.
Tropomyosin-troponin complex recovers binding site on actin.

Question 18

What is myasthenia gravis and what does it do and who does it effect?

Answer 18

Progressive autoimmune disease.
Damages Ach receptors at neuromuscular junction.
More common in women 20 to 40.
Possible links to thymus tumours?

Question 19

What are the symptoms of myasthenia gravis?

Answer 19

Double vision & swallowing difficulties.
Progresses to paralysis of respiratory muscles.

Question 20

What is the treatment for myasthenia gravis?

Answer 20

Steroids that reduce antibiotics that bind to Ach receptors.
Inhibitors of acetylcholinesterase.