The muscular system produces movement and maintains posture.

There are three kinds of muscles: skeletal, cardiac, and smooth.

Muscles are excitable, contractile, extensible, and elastic.

Muscles are attached to bone by tendons and are arranged in opposing or antagonistic pairs.

Sarcomeres are the contractile units of muscle.

Muscle striations are caused by the arrangement of myofibrils within the muscle cell. Each myofibril contains groups of myofilaments composed of actin and myosin proteins.

A muscle contracts when myosin binds to actin causing the filaments to slide past one another.

Contraction is powered by ATP and controlled by two regulatory proteins and calcium ions (sliding filament theory).

Nerves stimulate muscle contraction at the neuromuscular junction.

Acetylcholine, released from the motor neuron, causes a change in muscle cell permeability resulting in the release of calcium ions and contraction.

A motor neuron and all the muscle cells it stimulates are called a motor unit.

A muscle twitch is the contraction caused by a stimulus to the muscle.

The ATP required for muscle contraction comes from creatine phosphate, aerobic respiration, and lactic acid fermentation.

Slow-twitch muscles, found in the abdomen and back, contract slowly, powerfully, and with endurance.

Fast-twitch muscles, found in the arms and legs, contract rapidly and powerfully, but with less endurance.

Aerobic exercise increases endurance while resistance exercise builds muscle mass.

1. Excitability – receive and respond to stimuli

2. Contractility – shorten and thicken

3. Extensibility – stretch and extend

4. Elasticity – return to original shape after contraction or extension

1. Motion2. Maintenance of posture3. Heat production4. Protection of internal

organs

Forms from the mesoderm germ layer

Triploblasts simplest: flatworms

Segmentation annelids, arthropods, vertebrates

Vertebrate musclesInvertebrate muscles

1. Skeletal◦ Attached to

bones◦ Striated and

voluntary2. Cardiac

◦ Heart wall◦ Striated and

involuntary

3. Smooth◦ Walls of hollow

internal structures

◦ Nonstriated and involuntary

1. Striated◦ Voluntary movements◦ Longitudinal or circular

in shape2. Smooth

◦ Involuntary movements

Motion produced by action of muscles on bones levers

Tendons attach muscles to bones (e.g. Achilles tendon)

1 fixed point of attachment (origin) and 1 moving point of attachment (insertion)

Fascia sheets that cover muscles

Muscles work in antagonistic or opposing pairs

Adduction Abduction Flexion Extension Rotation Sphincters Levators Depressors Supination Pronation

Skeletal muscle fiber (cell)

Muscle Fascicle

Surrounded by perimysium

Surrounded by endomysium

endomysium

perimysium

Skeletal muscle

Surrounded by epimysium

epimysiumtendon

The muscle fiber is stimulated.

Ca2+ ions are released.

Thin filaments move to middle of sarcomere.Muscle fiber contracts.Muscle tension increases.

Cycle of contraction and relaxation generated from one stimulus

Force Summation◦ Increasing # and size of fibers

contracting◦ Increasing frequency at which action

potentials are sent to muscle fibers Types of Twitches

◦ Slow Twitch More ATP from aerobic respiration Continuous extended contractions

over time◦ Fast Twitch

Anaerobic metabolism (creatine phosphate and lactic acid fermentation)

Short bursts of speed Fatigue quickly

Aerobic exercise◦ Moderate

intensity◦ Extended

periods of time

Anaerobic exercise◦ High

intensity◦ Shorter

periods of time

Painful sensations caused by contraction/overshortening of muscles

Causes◦ Hyperflexion◦ Inadequate oxygenation◦ Changes in temperature◦ Dehydration◦ Low amount of electrolytes

in blood Treatment

◦ Correct breathing◦ Increasing intake of water

and electrolytes