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Myology
Bio 250
Human Anatomy & Physiology
Types of Muscle Tissue
Skeletal, striated, voluntary
Visceral, smooth, involuntary
CardiacCardiac , heart muscle, involuntaryheart muscle involuntary
Functions of Muscle
Motion: e.g.walking, running, writing,
chewing, swallowing or breathing
Heat production: muscles make upp p
nearly half of body and are in a
constant state of activity producing heat
as by-product
Posture and body support: muscles give
form and stability to the body
Skeletal Muscles are Organs
composed of muscle,
nerve, vascular and
various types of
connective tissues
Connective tissue
coverings include:
Epimysium (surrounds entire muscle) Perimysium (surrounds fasciculi) Endomysium (surrounds each muscle cell i.e. muscle fiber)
Skeletal Muscle Cells
Transverse tubules
extend from
sarcolemma to
terminal cisternae
which connect to the
sarcoplasmic reticulum
Note triad
Unit of contraction
called a sarcomere
Review of Skeletal Muscle Structure
Neuromuscular Junction
Muscle fibers stimulated to contract by motor neurons
Motor end plate of a muscle fiber lies on one side of the myoneuralside of the myoneural junction In response to a nerve impulse, the end of the motor nerve secretes a neurotransmitter which binds to receptors sites and stimulates the sarcolemma
Eventually causes muscle contraction
Skeletal Muscle Contraction
Structural and functional unit of contraction called SARCOMERE Muscle fiber contraction results from a sliding movement within myofibrilsy Actin and myosin filaments slide past each other Sacromeres shorten and muscle fiber as a whole shortens
Stimulus for Muscle
Contraction
Muscle fiber is stimulated by acetylcholine at
myoneural (neuromuscular) junction
Acetylcholine binds to receptors on the
sarcolemma and initiates an action potential
Action potential travels along the sarcolemma
and enters sarcoplasm at T-tubules
T-tubules stimulate terminal cisternae to
release stored Calcium ions
Role of Calcium Ions
Calcium ions diffuse throughout sarcoplasm
Ions expose myosin binding sites on the actin
molecule
Myosin cross bridges form with actinMyosin cross bridges form with actin
Activated myosin breaks down ATP
Energy released from ATP used to slide Actin
and Myosin filaments together
Sarcomere and muscle fiber shorten
This is called CONTRACTION
Note that ATP is needed to release myosin
heads from actin in order for relaxation to
occur
Review of Muscle Contraction
What happens to ADP?
ADP is rebuilt within the mitochondria
During periods of high muscle activity,
CREATINE PHOSPHATE is used toCREATINE PHOSPHATE is used to
restore some of the ADP to ATP
Activity: ADP + CP -> ATP + C
During rest periods, creatine is
recharged to creatine phosphate
At rest: C + ATP -> CP + ADP
What happens to acetylcholine?
An enzyme in the synaptic cleft called
ACETYLCHOLINESTERASE destroys
acetylcholine stopping the stimulation
of the receptors on the sarcolemmaf
Acetylcholine ->acetate + choline
This insures that one nerve stimulus
causes one muscle fiber contraction
Motor nerve rebuilds acetylcholine from
acetate acid and choline
Muscle Fatigue
Fatigued muscles lose ability to contract Usually due to accumulation of lactic acid
Athletes usually produce less lactic acid because of increased ability to supply oxygen and nutrients toincreased ability to supply oxygen and nutrients to muscles Physiological contracture results from lack of ATP needed to break myosin bridges and “pump” Ca++^ back into the sarcoplasmic reticulum
Rigor mortis- contraction of all the muscles of the body within a few hours of death. Lasts 15-72 hours depending on conditions like temperature. Lysosomal enzymes eventually break bridges.
Muscular Responses
Threshold stimulus vs sub-threshold
stimulus
All or none responseAll or none response
Muscle fibers follow A or N response
Motor units follow A or N response
Muscles DO NOT follow A or N response
Recruitment of Motor Units
Low intensity of stimulation of muscle
stimulates small numbers of motor units
High intensity of stimulation causesHigh intensity of stimulation causes
additional motor units to be RECRUITED
Muscles have graded responses
Twitch contraction
Myogram is a
recording of muscular
contraction
Twitch includes:
latent period contraction phase relaxation phase
Refractory period is
time following
contraction when
muscle remains
unresponsive to
stimulation