COGS 17 Lecture Notes - Lecture 10: Muscle Spindle, Neuromuscular Junction, Stretch Reflex
19 May 2018
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Motor processes
● Three types of muscles
○ Skeletal/striated muscle - connected to tendons to bones, voluntary movements.
Operate when doing intended activity
○ Cardiac (heart) muscle - has endogenous rhythm of activity, modified by neurons
○ Smooth (organ) muscle - can sustain contraction, mostly autonomically controlled
● Skeletal muscles
○ Come in “antagonistic pairs”
○ For each “flexor” muscle, that moves bones toward body there is a corresponding
“extensor” muscle, that moves same bones away from body
■ E.g biceps contract, triceps relaxed (extended) and vice versa
○ Neuromuscular junction
■ Motor neurons (alpha neurons) release acetylcholine onto muscle fibers
■ Fiber responds like a neuron would
● Na+ gates open, na+ enters cell. Change in polarity opens ca++
gates, ca++ enters cell → instead of causing release of
neurotransmitter, ca++ activates sarcomeres to contract the
muscle
○ Sarcomere - contractile unit in skeletal muscles
■ Made of myofibrils
■ Two key proteins: actin and myosin
■ Actin is fixed/secured to muscle at z disk whereas
myosin isn’t fixed to anything
■ When ca++ enters, muscle cells, cross bridges that
myosin are involved with are activated
● They ‘row’ into pairs of actin coils pulling
them closer together
● Spinal reflexes - simple circuits
○ Stretch reflex → muscle spindle (a proprioceptor) in muscle detects passive
stretch of muscle
■ As from a doctor’s hammer, or from shift of weight while walking
○ Muscle spindle excites motor neuron in spinal cord
■ Motor neuron stimulates same muscle to contract, counters passive
stretch
find more resources at oneclass.com
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Document Summary
Skeletal/striated muscle - connected to tendons to bones, voluntary movements. Cardiac (heart) muscle - has endogenous rhythm of activity, modified by neurons. Smooth (organ) muscle - can sustain contraction, mostly autonomically controlled. For each flexor muscle, that moves bones toward body there is a corresponding. Extensor muscle, that moves same bones away from body. E. g biceps contract, triceps relaxed (extended) and vice versa. Motor neurons (alpha neurons) release acetylcholine onto muscle fibers. Change in polarity opens ca++ gates, ca++ enters cell instead of causing release of neurotransmitter, ca++ activates sarcomeres to contract the muscle. Sarcomere - contractile unit in skeletal muscles. Actin is fixed/secured to muscle at z disk whereas myosin isn"t fixed to anything. When ca++ enters, muscle cells, cross bridges that myosin are involved with are activated. They row" into pairs of actin coils pulling them closer together. Stretch reflex muscle spindle (a proprioceptor) in muscle detects passive stretch of muscle.
