Muscles Flashcards
Muscles
Three types:
Smooth (internal organs),
Cardiac (heart, endogenous activity)
and Striate (Skeletal, Facial)
Striate
Band of parallel fibers, each fiber made of many cells but acts as unit; Attached by tendons to bones;
- Come in Antagonistic Pairs:
Striae Antagonistic Pairs
Flexor and Extensor
Flexor
moves bone toward body
Extensor
move same bone away from body
Neuro-Muscular Junction
(primarily involving Striate Muscles);
- Motor Neurons (“Alpha Motor Neurons”) exit Ventral Root of Spine»_space; Striate muscles
- Neuron synapses directly onto muscle, releasing Acetylcholine (ACh), always sufficient to trigger response
- Usually 1 axon branches to multiple muscle fibers; the fewer fibers per axon the more precise the control
- Like in a neuron, Muscle fiber response is all/nothing depolarization
usually 1 axon branches to…
…multiple muscle fibers
the fewer fibers per axon…
….the more precise the control
muscle fiber response
Like in a neuron, is all/nothing depolarization => Na+ and then K+ gates open/close
- Ca++ enters muscle cells => triggers energy-requiring process that causes muscle contraction
- Afterward, Ca++ is actively pumped out, and a Na+/K+ Pump repolarizes fiber for next contraction
Contractile Mechanism
- Within each fiber is a string of Sarcomeres
Sacromeres
(the contractile units) each consisting of….
Myosin and
Actin
Myosin
thick protein filament with knobby bead-like clusters (“Cross Bridges”) along it,
Actin
thin protein filament, a coiled double-strand braid, anchored to muscle
Contraction
Myosin Cross Bridges hook into (grab) coiled Actin, bend to tighten coil, release, repeat
the only active muscle response is…
…Contraction!!
