Muscular Function IB SEHS

Functions of muscles

• Movement ( Skeletal)

• Move substances through body (smooth and cardiac)

• Stabilize & maintain body positions

• Generate body heat

Motor units

Muscles are organized into moto units. 1 motor neuron and the muscle fibers it activates. Anywhere between 2,000(glutes) and 10 (eye) muscle fibers per motor neuron.

All or none principle

all muscle fibers in a motor unit are either relaxed at once or contracted at once.

Types of motor units (slow/fast twitch muscle fibers)

Type I

• slow twitch

• Slow transmission speed

• Small muscle forces ( output)

• Fatigue resistant

• Aerobic - high myoglobin and mitochondria

• Thin and slender

Type IIa

• fast twitch

• Fast transmission speed

• Stronger muscle contraction force

• Fatigue resistant

Type IIx

• fast twitch

• Fastest transmission speed

• Strongest muscle contraction forces

• Low fatigue resistance

Origin of muscle

non- mobile part the muscle connects to (scapula to bicep)

Insertion

mobile part the muscle connects to (radius to bicep). When a muscle contracts it pulled the insertions closer to the origin.

Isometric contraction

tensing muscles without producing any movement (no change in muscle length)

isotonic contraction

typical muscle contraction

• Concentric (positive): muscle shortens

• Eccentric (negative): muscle lengthens. Using a muscle to slow what gravity would do for you.

Isokinetic contraction

muscle changes in length but action repeats at a constant speed requiring no change of force during action (almost non-existent in daily life).

Sarcomere

smallest functional unit within a muscle cell. Enables contraction.

Myosin

thick filament

Actin

Thin filament

Titin

Protein spanning Z-line to M-line that functions like a spring

M- line

Central line

H- zone

zone with only myosin

A- band

spans full length of the myosin filaments

I - zone

extends both sides of the z-line

Troponin

located on actin. calcium binds to it.

Tropomyosin

prevents muscle contraction at rest by covering myosin binding sites

Outline of sliding filament/ contraction

nerve impulse → calcium released from endoplasmic reticulum → calcium bonds to troponin on actin → binding displaces tropomyosin → myosin binding sites on actin exposed → myosin heads are bound to an ADP & phosphate molecule from previous reaction → myosin heads release phosphate → myosin heads bind to actin → ADP released & heads move → the filaments glide past each other (contraction) → gliding stops when ATP binds to myosin heads and sever bonds between filaments → ATP turns to ADP & energy from transformation is stored in myosin head.

Reciprocal inhibition

turning off a muscle’s antagonist during a movement.