Muscular System

Chapter 9

3 types of muscular tissue:

Functions of muscular system

Stabilize joints Muscle tone Movement Maintain constant body temperature

Muscle structure Fascia – connective tissue around muscle, becomes the tendon

Origin – on stationary bone

Insertion – on the moveable bone

Fascicle – bundle of muscle fibers

Muscle fiber – muscle cell

Myofibril – made of sarcomeres (in-between two Z bands)

Myo-filaments – actin and myosin

Group Actions

Prime mover – the muscle that causes the desired movement

Antagonist – relax during the action

Synergists – muscles that steady the movement (helpers)

The Neuromuscular Junction: Neurons

Parts of : Cell body Dendrites – receive

impulse Axon – carries impulse

away Myelin sheath- white

fatty material• Schwann cells (pns)• Neurilemma (outside the

sheath)• Nodes of Ranvier

The Nerve Impulse

Action potential – steps in the nerve impulse

3 stages of : polarization, depolarization, repolarization

Step 1: Polarization

Resting state of a neuron Sodium/potassium pump – sodium ions

out of cells and potassium ions into cells

Polarization continued

Inside of the cell is – charged Outside of cell is + charged Due to sodium-potassium pump

– 2 K+ ions go in as 3 Na++ go out

http://faculty.washington.edu/chudler/introb.html

Step 3: repolarization

Return to resting state Due to the pumping out of K+. Na+ blocked Inside of cell negative

Continues to synapse

The Sliding Filament theory: Step 1: Neuromuscular Junction

Action potential – the reversal of charges across the plasma membrane.

Nerve impulse arrives at axon terminal releasing acetylcholine (Ach)

Step 1: Neuromuscular Junction

Ach diffuses across synaptic cleft, binds to receptors in the motor end plate.

Triggers action potential

Acetylcholinersterase in cleft destroys Ach to stop action potential

Disorders at the neuromuscular junction

Myasthenia gravis

Botulism

Curare

tetanus

Step 2:

Sarcoplasmic reticulum stimulated to release calcium ions.

Step 3

Release of Calcium causes shift in troponin (actin)

Active site on Actin is uncovered

Step 4

Myosin and ATP combines with active site on actin causing formation of a crossbridge

Step 5 - 7

Energy released causing filaments to slide past each other (power strokes)

ATP converted ADP Troponin slides back Cycle repeats if enough

calcium and ATP are present

Energy for contraction

ATP (respiration) Creatine phosphate-can be stored

longer and more abundant than ATP Glycogen-storage of glucose in liver

Oxygen Debt-strenuous exercise

Lack of oxygen availability

Accumulation of lactic acid (soreness)

Become short of breath to metabolize lactic acid

Muscular Responses

All or nothing response single fiber contracts only maximally– Threshold stimulus

Recruitment -

Types of Whole muscle contraction

Twitch contraction – not a usual method of muscle contraction

Summation -

Muscle not allowed to relax in-between contractions

Stronger contraction

Tetanus

sustained muscle contraction (maintaining posture or tone)

Usual means of movement

Isotonic vs. Isometric

Isotonic contraction Movement produced

as a muscle pulls on an attached bone toward a stationary structure

Isometric contraction

Muscle tension, no shortening of muscles

No movement

Muscle Fiber types

Based on genetics Classified by respiration and the speed

of contraction Strength Training can influence

Fast Twitch Fibers

Energy for quick, forceful contractions

Contraction 2-3 times faster than slow twitch

Anaerobic respiration Short term activities –

basketball, sprinting, volleyball

Slow twitch muscle fibers

Aerobic respiration Slow contracting Endurance type

activities Ex. Long distance

running, soccer, football, basketball