The Muscular System

Question 1

What are the 3 muscle types?

Answer 1

• Cardiac
• Smooth
• Skeletal

Question 2

Isometric contraction

Answer 2

= muscles contract but no shortening (no movement)

Question 3

Concentric contraction

Answer 3

= muscles contract and shorted to lift weight

Question 4

Eccentric contraction

Answer 4

= muscles contract but lengthen to control the lowering of the weight

Question 5

At what point is muscle the strongest and why?

Answer 5

Mid-range
…because it’s the optimum point for the development of cross-bridges which allow strong contractions

Question 6

What is muscle strength affected by?

Answer 6

• metabolic factors
• endocrine factors
• neural output
• psychological factors
• range of joints
• age
• gender
• muscle architecture
• biomechanical set up

Question 7

Inner range

Answer 7

= muscle shortened

Question 8

Mid-range

Answer 8

= mid-length of muscle

Question 9

Outer range

Answer 9

= muscle lengthened

Question 10

Skeletal muscle

Answer 10

• multinucleate and myofilaments precisely aligned and packaged by connective tissue
• contraction is under voluntary control

Question 11

Cardiac muscle

Answer 11

• One nucleus, branching and connected by specialised junctions – intercalated discs
• Forms walls of the heart

Question 12

Smooth muscle

Answer 12

• One nucleus, no striations
• Arranged in sheets and line walls of hollow organs
• Specialised for propelling substances along internal passaged (e.g.: urine in bladder, food in the gut)

Question 13

Epimysium

Answer 13

covers whole muscle

Question 14

Perimysium

Answer 14

surrounds muscle fascicles

Question 15

Endomysium

Answer 15

surrounds muscle fibre

Question 16

What does a thin filament consist of?

Answer 16

• two strands of actin subunits twisted into a helix
• two types of regulatory proteins (troponin and tropomyosin)

Question 17

What does the thick filament consist of?

Answer 17

many myosin molecules whose heads protrude at opposite ends of the filament

Question 18

What are thin myofilaments known as?

Answer 18

actin

Question 19

What are thick myofilaments known as?

Answer 19

myosin

Question 20

Describe a neuromuscular junction (synapse)

Answer 20

• Nerve fibre makes a functional connection with its target cell
• Presynaptic neurons have synaptic vesicles with neurotransmitter and postsynaptic have receptors
• Neurotransmitter (acetylcholine/ACh) release causes stimulation of muscle cell

Question 21

Excitation

Answer 21

action potentials in the nerve lead to formation of action potentials in muscle fibre

Question 22

Excitation-contraction coupling

Answer 22

action potentials on sarcolemma activate myofilaments

Question 23

Contraction

Answer 23

tensing or shortening of muscle fibre

Question 24

Relaxation

Answer 24

return of fibre to its resting length

Question 25

Describe skeletal muscle contraction, initiation and execution

Answer 25

• action potential (AP) travels along a motor nerve to its ending on muscle fibres
• at each motor nerve ending, the nerve secretes acetylcholine (Ach)
• Ach acts locally on the muscle fibre membrane to open Ach-gated cation channels
• the opening of Ach-gated channels allows large quantities of Na ions to diffuse to the interior of the muscle fibre membrane
• this action potential causes a local depolarisation, leading to the opening of voltage-gated Na channels, which initiates an action potential at the membrane
• the action potential depolarises the muscle membrane, causing the sarcoplasmic reticulum (SR) to release large quantities of Ca ions stored within the reticulum
• the Ca ions produce attractive forces to act between actin and myosin filaments, causing them to slide alongside each other leading to the contractile process
• after a fraction of a second, the Ca ions are pumped back into the SR by a Ca-membrane pump and remain stored in the SR until a new muscle action potential occurs
• the removal of Ca ions from the myofibrils causes muscle contraction to cease

Question 26

What muscle adaptations are there to resistance training?

Answer 26

Muscle fibre hypertrophy
Neural activation
- recruit more motor units
- synchronous recruitment

Question 27

What muscle adaptations are there to aerobic training?

Answer 27

• Muscle fibre type (more type 1 fibres)
• Capillary supply
• Myoglobin levels
• Mitochondrial function
• Storage of more glycogen and fat
• Adaptations of CV system

Question 28

What are (6) adaptations due to immobilisation or stopping training?

Answer 28

• Rate of protein synthesis decreases
• Atrophy (loss of protein)
• Decreased neuromuscular activity
• Decreased flexibility
• Endurance decreases even after 2/52 inactivity
• Can recover if training resumed but the period of time is longer than that to lose adaptations