The Musculoskeletal SystemSupport, Protection, Movement and Locomotion

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◦ Highly branched◦ Striated and

involuntary3. 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

All or none response of muscle fibers Force Summation

◦ Increasing # and size of fibers contracting◦ Increasing frequency at which action potentials are sent to

muscle fibers

Slow Twitch◦ More ATP from aerobic

respiration◦ Continuous extended

contractions over time◦ More myoglobin

Fast Twitch◦ Anaerobic metabolism (creatine

phosphate and lactic acid fermentation)

◦ Short bursts of speed◦ Fatigue quickly

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