MMW 13 Lecture 19: Lecture Notes copy (Lectures 1-19)
19 May 2018
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Review for exam → monday may 14, 7-8:20 pm in peterson 110
Motor processes - may 10, 2018
● 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
find more resources at oneclass.com
find more resources at oneclass.com
■ Motor neuron stimulates same muscle to contract, counters passive
stretch
■ Reflexive response - only one synapse that reflexes in body
○ Golgi reflex - golgi tendon organ
■ Over-contracting muscle pulls so hard on tendon that the golgi tendon
organ (proprioceptor) signals the spinal cord
● Activates an inhibitory interneuron in spinal cord that
○ Inhibits motor neuron to signal muscle, reducing
contraction
■ Golgi tendon organ splits in half
● Other half can activate an excitatory interneuron in spinal cord that
○ Excites motor neuron to antagonistic muscle, increasing its
contraction, which decreases original’s contraction
○ Pain withdrawal reflex
■ nociceptor (pain receptor) detects noxious stimulus
● Synapses in spinal cord on excitatory interneuron
○ Excites motor neuron for flexor muscle to pull sensor away
from noxious stimulus
○ Scratch reflex
■ Oscillator circuit
■ Cerebellar reflex
● Like the human - tongue/lip vibration
○ Infant reflex
■ Cerebellar reflex
■ Babkin reflex - press palms, fingers grasp and mouth opens
■ Rooting reflex - touch cheek, head turns, and infant suckles
○ Corticospinal (pyramidal) tracts
■ For control of voluntary motion, on contralateral side of body
■ From motor cortex
● Most fibers cross to contralateral spinal cord in medulla
○ Activates motor neurons to contralateral skeletal muscles
■ Corticobulbar tract
● For face movements - crosses over in the pons
○ Ventromedial tracts
■ Bilateral and ipsilateral
■ Primarily for control of posture, neck, shoulders, and trunk, where one
side cannot move separately from the other
find more resources at oneclass.com
find more resources at oneclass.com
■ Includes circuits for walking, since two sides must be in tight coordination
■ Make multiple connections in tectum, vesigular nucleus, reticular
formation, integrating with sensory and arousal systems
● Cerebellum
○ For rapid, well-coordinated movements requiring precise timing
■ Include preprogrammed (like saccades) and learned-through-practice
behaviors
● Including shifts of attention
● Depends on real-time sensorimotor feedback
○ Purkinje cell
■ Cerebellar circuits
■ How cerebellum converts time into space
● These cells fold into deep nuclei - send info up motor pathway →
sensory and motor feedback
● This circuit codes time as distance signals travel
● Purkinje's correspond to different muscle groups
○ Activity along parallel tracks represent timing of different
moves by changes in purkinje
○ Sobriety test for cerebellum function
■ Smooth ballistic motion of hand to face
■ Walking a straight line, requires balance (integration of vestibular input)
● Basal ganglia
○ Organises activity into tasks
○ Striatum - output
○ GP (globus pallidus - medial) - output
○ A “re-entrant” system that keeps track of status of “sub-goals”
○ “Automates” - complex sequential process selects what’s appropriate when
○ Pathologies include OCD, ADD, and Parkinson’s disease
■ Parkinson’s: Insufficient dopamine from substantia nigra in tegmentum to
striatum
● Greater inhibition from globus pallidus to motor nucleus (VLP) of
thalamus
○ Produces tremors, difficulty with smooth execution
■ Cures: treated with L-dopa, dopamine precursor
that crosses blood-brain barrier but many side
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Review for exam monday may 14, 7-8:20 pm in peterson 110. 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.
