Module 8: The Muscular System Flashcards
3 types of muscle
Skeletal
Smooth
Cardiac
Functions of muscles (4)
Produces movement
Maintains posture
Stabilizes joints
Generates heat
Produces movement
Skeletal muscles - walk, blink, turn around, chew, laugh etc
Smooth muscles line blood vessels and transport blood
Cardiac muscle operates as a pump for the blood
Maintains posture
Skeletal muscles defy gravity by making adjustments that allow us to sit or stand erect
Stabilizes joints
Skeletal muscles hold bones together and assist in stabilizing and strengthening joints
Generates heat
Muscle activity of ALL muscles general heat (skeletal muscles generate the most)
Coverings of skeletal muscle
- covered by fascia (layers of fibrous connective tissue)
- fascia extends beyond muscle and turns into the tendon
- Epimysium of fascia is the layer that attaches to the muscle
- Muscle fibers (cells) are grouped into fascicles (bundles)
- Perimysium surrounds each bundle
- Endomysium surrounds each muscle fiber
Structure of muscle fiber (cell)
- Elongated cells with hundreds of nucleoli
- Plasma membrane called sarcolemma
- Cytoplasm called sarcoplasm
- Each fiber is made of many myofibril which consist of myofilaments
- Sarcoplasmic reticulum surrounds each myofibril
- each myofilament is made of thin (actin) and thick (myosin) filaments
- Myfilaments arranged in sarcomeres (give muscle striated look)
- T tubules carry nerve stimulus into muscle fiber
Sliding filament mechanism
sliding of the thin filaments toward the center of the sarcomere causes the unit to shorten
Contracting muscles:
-nerve impulse stimulates sarcolemma
-t tubules allow stimulus to reach sarcolemma
-myosin heads make contact with actin to form temporary cross bridges
-myosin heads rotate, pulling actin inwards
Motor neuron
transmits nerve impulses from the brain and spinal cord to the skeletal muscles
Motor unit
a single motor neuron and the muscle fibers it stimulates
Neuromuscular Junction (NMJ)
The area where the motor neuron meets the muscle fibers
Structures include: plasma membrane @ end of neuron, Synaptic cleft (space between end of neuron and sarcolemma/plasma membrane of muscle fiber), sarcolemma/plasma membrane and its receptor sites
The neuron releases chemicals that diffuse across NMJ and stimulate the muscle fiber
Action potential
electrical impulse resulting from stimulation of the neuron to move along the neuron towards the axon terminal with vesicles (containing ACh, acetylcholine)
Acetylcholinesterase
NMJ enzyme that breaks down ACh
What happens to the electrical signal in the sarcolemma
- signal travels along sarcolemma
- travels through T tubules and then stimulates the sarcoplasmic reticulum to release Calcium
- Calcium floods the sarcomeres and allows interaction of actin, myosin and ATP to cause muscle contraction
- Calcium is pumped back into the sarcoplasmic reticulum, away from actin and myosin causing muscle relaxation
All or none principle
The muscle fibers are either ON (contracting completely) or OFF (relaxing)