Lecture 28: Musculoskeletal System - Physiology and Physics of the Muscles Flashcards
Functions of the muscles
Give stability and postural tone; allow accurate movement; regulate organ movement and volume; generate heat
How much of the body is muscle?
50%
What is shivering?
Rapid muscle contraction that helps the body create heat.
All motion is accomplished by…
Opposing muscle pairs
What are muscles?
Conductors; respond to electrical stimulation by contracting
Three muscle types
- Skeletal
- Smooth
- Cardiac
Skeletal muscles
- Attaches to bone, skin, fascia, and other muscles
- Some nerves activate certain muscle fibers
- Are voluntary
- Are striated (striped); bands of muscle fibers made of actin and myosin
Smooth muscles
- Walls of hollow organs, hair follicles, blood vessels
- Regulates size of intestinal muscles
- Activated by one or multiple nerves (depending on function)
- Is involuntary
Cardiac muscles
- Walls of the heart
- Microscopically striated
- Joins in muscles for coordinated action
- Involuntary and autorhythmic
Nerves - motor neurons; cell bodies
- Motor neurons activate muscles
2. Cell body located in spinal cord; axon ends in the muscle
What does a motor unit contain?
A motor neuron and supplied muscle fibers. When the neuron fires, its muscle fibers fire off too.
What is a synapse?
Location of where the nerve meets another nerve or a muscle. Its ending is a synaptic gap and this separates it from the muscle.
What is a neurotransmitter?
An intermediary for the nerve to directly electrically stimulate the muscle.
Anatomy of a neuron
Axon has an axon terminal. Ends with synaptic bulbs with contain synaptic vesicles. The vesicles have many neurotransmitter molecules.
Most common neurotransmitter
Acetylcholine (Ach)
What do ATP and ADP do?
Adenosine triphosphate (ATP) and diphosphate (ADP) store potential chemical energy in the cells of muscles.
ATP
Converted to kinetic energy (ability to perform work)
ADP
Perform work (moving object any distance)
Skeletal muscle types
Type I (mainly postural muscles) Type IIA (sprinter's muscles in track) Type IIB (typically muscles of shoulders and arms)
Type I skeletal muscle fibers
Are slow oxidative fibers which are fatigue-resistant/slow-twitch. They use oxygen to make ATP which is split slowly and the fibers contract slowly.
Type IIA skeletal muscle fibers
Are fast oxidative fibers that are slightly fatigue-resistant; fast-twitch A. Make ATP using oxygen. Split ATP and contract quickly.
Type IIB
Fast glycolytic fibers/fatigable fibers; fast twitch B. Make ATP without oxygen quickly, but inconsistently.
Anaerobically
Does not require oxygen
Aerobically
Requires oxygen
What is in all three groups of skeletal muscles?
Leg muscles that have postural, walking, and sprinting fibers. They can be altered by changing exercise pattern.
Muscle contraction is…
All or nothing: fired muscle fibers contract all the way or do not contract at all.
Grand mal epileptic seizures
Entire brain fires
Spastic paralysis
All arm muscles fire and the hand bends down; the adductor, biceps, and pronator are stronger than opposing muscles.
What does contraction force depend on?
Frequency (stimulation per second), muscle length before contraction, and stimulated motor units
Muscle tone
The muscle firmness that is caused by continuous involuntary contractions of small motor units
Isotonic contraction
Same tension on all muscles
isometric contraction
Muscle length stays the same
Concentric motion
Positive repetition; angle between two limbs decrease
Eccentric motion
Negative repetition; angle between two limbs increases. This type damages muscles more than concentric motion. Useful for weightlifters since it will slightly damage muscle and will rebuild bigger.
Exercises
Repeated: low-level, aerobic (can meet oxygen needs) like jogging.
Anaerobic: like weight lifting; builds muscle mass
Interval training
Exercises that combines aerobic and anaerobic in the same activity; varies the intensity
Actin
Thin filament
Myosin
Thick filament
