Updated for 1999
Lecture Notes-Chapter 8

Week 4

3 types of muscles:

1) Smooth muscle - controlled by the autonomic nervous system; may either be generally inactive and then respond to neural stimulation or hormones or may be rhythmic

2) Cardiac muscle - found in the heart, acts like rhythmic smooth muscle, modulated by neural activity and hormones

3) Skeletal muscle - move us around and responsible for most of our behavior; most attached to bones at each end via tendons

movement:

anatomy: Muscular contraction: Sensory feedback from muscles: Monosynaptic stretch reflex: Weight placed in a personís hand -

1) afferent impulses from the muscle spindle are conducted to the terminal buttons in the gray matter of the spinal cord

2) terminal buttons synapse onto an alpha motor neuron

3) alpha motor neuron synapses on motor endplate on the extrafusal muscle fibers of the same muscle

4) if arm starts to drop, then muscle spindle afferent neurons start to fire as they detect muscle lengthening, they then synapse on alpha motor neurons and rate of firing increases, and then muscle contraction increases

example: posture - if pushed forward, muscles in back of calves stretch, causing contractions in the toes

Gamma motor system:

Brain sends message for movement:
  1. alpha motor neuron and gamma motor neurons activated
  2. alpha motor neurons start the muscle contracting
  3. if no resistance, both extrafusal and intrafusal muscle fibers contract at the same rate, sending little info from muscle spindles
  4. if resistance, then extrafusal muscle fibers are halted, but intrafusal continue to contract, as told to by the gamma motor neuron
  5. then, sensory info from the intrafusal fibers goes to the spinal cord, where there is a synapse onto the alpha motor neuron, which then increase muscular contraction
Polysynaptic reflexes:

Golgi tendon organs have 2 kinds of receptors:

Agonist-antagonist muscle groups

Muscle spindles send terminal buttons to:

  1. alpha motor neurons
  2. the brain
  3. inhibitory interneurons
Organization of the motor cortex:
Cortical control of movement:

Pathways that originate in the cortex:

1) corticospinal tract - axons terminate in gray matter of spinal cord, mostly originating in primary motor cortex, through pyramidal tracts, then at the end of the medulla they cross and descend through the contralateral spinal cord, forming the lateral corticospinal tract (control distal part of limbs); the remaining fibers stay on the same side and form the ventral corticospinal tract (control upper legs and trunk)

2) corticobulbar tract - projects to the medulla, ending at cranial nerves which control movements of the face and tongue

Pathways that originate in the brainstem:

1) rubrospinal tract - originates in the red nucleus, which receives info from motor cortex and cerebellum; axons terminate on motor neurons in the spinal cord (control arms and legs, but not fingers)

2) ventromedial pathways - terminate in gray matter of spinal cord; include vestibulospinal, tectospinal, and reticulospinal tracts (control movement of the truck and proximal limb muscles, such as walking, head turning, autonomic functions)

apraxia - inability to properly execute a learned skilled movement

1. limb apraxia - moving wrong part of limb, moving correct part in the wrong way, or correct movements in the wrong sequence (assessed by pantomiming)

2. constructional apraxia - caused by lesions of the right parietal lobe

Basal ganglia - know Parkinsonís & Huntingtonís

Cerebellum - know definitions of terms in bold and section about lesions of the lateral zone

Reticular formation - controls activity of the gamma motor system - regulates muscle tone (remember association with arousal and autonomic functioning)