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Anatomy and Physiology of Muscles: Types, Functions, Structure, and Contraction - Prof. Th, Study notes of Physiology

An in-depth exploration of the various types of muscles, their functions, and the structure of skeletal muscles, including the role of neuromuscular junctions and motor units in muscle contraction. It also covers the energy sources and muscle fatigue.

Typology: Study notes

Pre 2010

Uploaded on 08/08/2009

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Myology
Bio 250
Human Anatomy & Physiology
Types of Muscle Tissue
Skeletal, striated, voluntary
Visceral, smooth, involuntary
Cardiac heart muscle involuntary
Cardiac
,
heart
muscle
,
involuntary
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pfa
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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