Brain Mechanisms of Movement

1

• Brain Mechanisms of Movement
• Stretch Reflex (8.1)
• proprioceptors
• sensory neurons
• motor neurons
• Role of the Cerebral Cortex in Movement Control
  (8.2)
• multiple motor areas
• Connections from Brain to Spinal Cord
• dorsolateral tract
• ventromedial tract

2
The Stretch Reflex Proprioceptors
Proprioceptor receptor that is sensitive to the
stretch and tension within a muscle. Important
for 1) maintaining posture, 2) controlling limb
movements, 3) providing information about limb
position.
3
The Stretch Reflex Proprioceptors
Muscle spindle parallel to the muscle responds
to stretch produces contraction of surrounding
muscle.

• Golgi tendon organ connects the muscle to the
  bone responds to tension prevents muscle
  contractions that would result in damage to the
  muscle.

How is movement affected by loss of proprioceptor
function????
4
The Stretch Reflex Sensory and Motor Neurons
5
The Stretch Reflex Sensory and Motor Neurons
6
Role of the Cerebral Cortex in Movement Control

7
Role of the Cerebral Cortex in Movement Control

• Primary motor cortex
• located in the precentral gyrus, just anterior to
  the central sulcus
• no direct connections to muscles
• sends axons to brain stem and spinal cord
• contains a map of the body (motor humunculus)
• involved in controlling complex movements (e.g.,
  gymnastics, figure skating)
• Not activated by simple, reflexive movements
  (e.g. swallowing, laughing)
• Posterior parietal cortex
• responds to visual somatosensory stimuli
• involved in keeping track of body position in
• relation to the world
• allows one to convert perception into action

8

• Motor Humunculus
• Penfield Rasmussen, 1950
• electrical stimulation causes muscle movements
• somatotopic organization
• but map is not a 11 correspondence
• head, fingers, toes are over-represented
• brain imaging (fMRI) muscle movements
• increase activity in specific areas

9
Role of the Cerebral Cortex in Movement Control

• Prefrontal cortex
• responds to sensory stimuli (e.g., light, sound,
  odor)
• involved in the planning and carrying out of
  movements
• Premotor cortex
• involved in planning movements
• much less active during the movement
• Supplementary motor cortex
• involved in planning a rapid series
• of movements (e.g., playing the piano)

10
Connections from the Brain to the Spinal Cord

• How does the brain interact with the spinal
  cord to control complex movements?
• Where are muscles controlled?
• There are two main descending axonal tracts to
  the spinal cord -- dorsolateral tract and the
  ventromedial tract

11
Dorsolateral Tract
12

• The Dorsolateral Tract
• tract originates in the primary motor cortex
  surrounding areas, and the red nucleus of the
  midbrain
• tract crosses at the pyramids of the medulla
• involved in the control of distal limb movements
  (hands, fingers, toes)
• damage loss of fine movement

13
Ventromedial Tract
14

• The Ventromedial Tract
• tract originates in the primary and supplementary
  motor cortices and some nuclei from the midbrain
  (e.g. reticular formation, tectum, vestibular
  nucleus)
• tract does not cross but can branch to both sides
  of the spinal cord
• involved in control of proximal muscles (neck,
  shoulders, trunk)
• damage loss of coordinated walking movements
  poor balance