Ch.5-Muscle Structure and Function

Question 1

Types of Human Muscle

Answer 1

660 muscles
1/2 body weight
Various structures and types
Numerous Functions:
Ventilation
Digestion
Pumping of blood
Movement

Question 2

Skeletal Muscle Properties

Answer 2

Formed by muscle fibres (cell) bound together by connective tissue.
Linked to bone by bundles of collagen fibres (tendons)
Shorten during contraction and pull onto tendons and bones to create movement
Capable of rapid contraction
Fatigue as a result of intensive activity

Question 3

Muscle Teamwork

Answer 3

Skeletal muscles work together in synchrony to produce a desired movement

Question 4

Agonist-Antagonist

Answer 4

Flexion: Primary move/agonist contracts: biceps
Antagonist relaxes: triceps

Extension: Primary mover/agonist contracts: triceps
Antagonist relaxes: biceps

Question 5

Synergists and Fixators

Answer 5

Example: Rope climbing
Prime mover/agonist contracts to flex shoulder: pectoralis major
Synergist contracts to complement flexion: deltoid anterior
Fixator contracts to steady scapula closer to body: serratus anterior

Question 6

Tendon

Answer 6

Attaches muscle belly to bone

Question 7

Muscle Belly

Answer 7

Made up of muscle fibre bundles

Question 8

Muscle Fibre Bundle

Answer 8

Numerous muscle fibres wrapped by a thick connective tissue

Question 9

Muscle Fibre

Answer 9

Cylinder-shaped muscle cell
Contains contractile machinery and organelles for cell respiration

Question 10

Myofibrils

Answer 10

Make up muscle fibre
Contain contractile machinery: sarcomeres and myofilaments

Question 11

Sarcolemma

Answer 11

Connective tissue sheath
Wraps each muscle fibre

Question 12

Machinery

Answer 12

Myofibril contains contractile machinery:
Sarcomeres: Contractile units. Organized longitudinally in series (end to end)
Myofilaments: Thin filaments with actin proteins. Thick filaments with myosin proteins

Question 13

Skeletal Muscle=Striated Muscle

Answer 13

Alternating light and dark bands under microscope due to organization of sarcomeres and myofilaments.
Sarcomere: Z line: proteins anchoring thin filaments.
H Zone: space between thin filaments.
M line: Proteins anchoring thick filaments
I band: Actin filaments
A band: Myosin filaments

Question 14

Sliding Filament Theory

Answer 14

Muscle contraction occurs due to actin sliding over myosin:
1. Motor nerve activates muscle fibre
2. Myosin head attaches to actin; cross bridge formation
3. Cross bridges move similar to stroking of the oars
4. Actin filaments move and sarcomere shortens
1% of sarcomere
25-40% of myofibril length
I band and H zone shrink, A band remains the same

Question 15

Optimal Joint Angle

Answer 15

Sarcomeres at optimal distance.
Optimal number of cross bridges
Maximal force developed
90 degree

Question 16

Large joint angle

Answer 16

Sarcomeres too far apart
Fewer cross bridges
Smaller force developed
Obtuse angle (120 ish)

Question 17

Small joint angle

Answer 17

Sarcomeres too close together
Cross bridges interfere
Smaller force developed
Acute angle

Question 18

Muscle Fibre Types

Answer 18

Fast twitch muscle fibres
Slow twitch muscle fibres

Question 19

Slow Twitch Muscle Fibres

Answer 19

ST or Type 1
Appear red
Slow contraction
Aerobic
Fatigue resistant
Small fibres

Question 20

Fast Twitch Muscle Fibres

Answer 20

FT or Type 2
Appear white
Fast contraction
Anaerobic
Fatigue fast
Large fibres

Question 21

Muscle Biopsy

Answer 21

Biopsyt=bio (life) + opsis (sight)
A tiny piece of muscle is removed and analyzed under a microscope

Question 22

Nervous System

Answer 22

Skeletal muscle contraction is initiated through nervous system activation and is under conscious control.
Central Nervous System: Brain and spinal cord
Peripheral Nervous System: Sensory nerves: transmit information from sensory receptors to CNS
Motor nerves: Transmit information from CNS to skeletal muscles

Question 23

Motor Unit

Answer 23

Group of fibres activated via the same nerve.
Basic functional entity of muscular activity.
One motor unit per muscle fibre
Each motor unit can consist of different muscle fibers but of the same type.
Delicate and precise movement: Many (1,500-3000) motor units per muscle
Few (8-50) muscle fibers per unit

Unrefined and powerful movements: Few (600-2,000) motor units per muscle
Many (1,500) muscle fibres per unit

Question 24

Motor end plate

Answer 24

End of a motor neuron
Transmits neural impulses to a muscle fibre

Question 25

All-Or-None Principle

Answer 25

An impulse of a certain magnitude is required to cause fibres to contract. All muscle fibres that make up a single motor unit will contract maximally i the magnitude is reached An impulse of smaller magnitude will not cause a muscle contraction

Question 26

Activation Threshold

Answer 26

Every motor unit has a specific threshold that must be reached for activation A weak nerve impulse activates only those motor units that have a low threshold A stronger nerve impulse will additionally activate motor units with higher thresholds As the resistance increases, more motor units must be activated by stronger, more intensive impulses

Question 27

Activation Threshold P.2

Answer 27

Nerve's electric current (action potential) is not capable of exciting muscle fibres At the endplate electrical current triggers a chemical reaction Neurotransmitter (acetylcholine) is released and diffuses across the neuromuscular junction, causing excitation of the sarcolemma Calcium ions are released and diffuse into the actin-myosin overlap zone Troponin and tropomyosin change shape and position and expose the active sites on the actin molecule to the myosin Cross bridge binding and muscle contraction occur ATP molecule breakdown provides energy for the cross bridge binding

Question 28

Intramuscle coordination

Answer 28

Capacity to activate different motor units simultaneously Impossible to simultaneously activate all motor units of a muscle: Trained athletes (85%) Untrained individuals (60%) Muscle force deficit: difference between assisted and voluntarily generated maximal force: Trained athlete: 10% deficit Untrained individuals 20-35% deficit Trained athletes: Exploit a larger number of muscle fibres. Larger muscle mass and more limited in further strength gains

Question 29

Intramuscle coordination

Answer 29

The capacity to activate different muscles to produce a movement. Of particular importance is the interplay between agonists and antagonists. Agonist motor units must be synchronously activated. Antagonist motor units must synchronously relax. The greater the participation of muscles/groups the higher the importance of intermuscle coordination. Complex movements are often broken down so that individual muscle groups are first trained in isolation.

Question 30

Muscles adaption to strength training

Answer 30

Biological adaptation: Perormance improvements through strength training. Reflected in increased strength Performance capacity of a muscle is determined by several factors Trainable factors: fibre diameter, intra/inter-muscle coordination, nerve impulsve frequency, muscle and tendon elasticity, energy stores, capillary density. Non-trainable factors: muscle fibre number and type structure Different factors adapt at different rates