Biology 306 - L8

Front 1

Primary Motor Cortex (Area 4)
3 Functions?

Back 1

1. A convergence point for information from other areas of cortex.
2. Motor cortex directs movements that require cortical processing, e.g. fine movements of the fingers, via corticospinal axons that project to the spinal cord.
3. Corticobulbar axons project to brainstem to control facial expression, eye movements, etc.

Front 2

Brain Stem
4 functions?

Back 2

1. Receives ascending sensory information relevant to movement, plus afferent information about the head and neck from the cranial nerves.
2. Contains the components of the Vestibular System, crucial for postural control.
3. Contains motor neurons for the head and neck, as well as for eye muscles and muscles of facial expression.
4. With the exception of the cortico-spinal tract, all descending motor pathways to the spinal cord originate in the brainstem extra-pyramidal system.

Front 3

Spinal Cord
3 functions?

Back 3

1. Ventral horn of the Spinal Cord contains the motor neurons for limb and trunk movements.
2. On its own, the spinal cord is responsible for simple, automatic types of movements, like the knee-jerk reflex, or the alternating contraction and relaxation of muscles during walking.
3. The circuitry that exists in the Spinal Cord for these types of movements enables higher brain centers to control these behaviors with relatively simple neural signals. They can tell the spinal cord to begin the “walking program” without having to worry about the many signals that must be sent to individual muscles.

Front 4

Purpose of Motor Cortex in Primates?

Back 4

The generation of discrete, fine, voluntary movements, particularly of distal musculature. For example, manipulative movements of the fingers.

Front 5

Outpur of the

Back 5

The motor cortex exerts its effect by way of corticobulbar (to cranial nerve nuclei) and corticospinal (to spinal cord) projections.
Of the total number of corticobulbar and corticospinal fibers, not all are from Area 4:
30% - Area 4, Precentral Gyrus, Primary Motor Cortex
30% - Area 6, Premotor & Supplementary Motor cortex
40% - Areas 3,1,2, Postcentral Gyrus, Somatosensory Cortex

Front 6

3 types of lateral pathways?

Back 6

Lateral Pathways:
1) Fibers from somatosensory cortex synapse on sensory neurons in dorsal horn.
2) Motor cortex axons synapse on interneurons in intermediate zone of spinal gray.
3) Motor cortex axons synapse on motor neurons innervating the distal limb musculature. E.g. fingers, wrist, arm, and forearm.

Front 7

Columnar Organization of Motor Cortex - 3 Characteristics?

Back 7

1. Columns are 0.5 to 1 mm in diameter.
2. A single column appears to control movement of a single muscle, or at most a small group of muscles.
3. Cells within a column receive sensory input from peripheral receptors that would be affected by the contraction of the muscle represented by the column.

Front 8

Evarts’ Experiment Findings

Back 8

1. Activity of CTN’s changes with direction of wrist movement, some preferring flexion, others preferring extension.
2. Cell discharge begins before start of movement.
3. Frequency of discharge encodes force rather than the actual change in position of the limb.

Front 9

Role of Supplementary and Premotor Cortex

Back 9

Damage to these areas result in loss of the ability to correctly plan a coordinated sequence of movements.

Front 10

3 Functions of Supplementary Cortex

Back 10

1. Stimulation can produce opening and closing of hand. I.e. more complex, patterned movements.
2. The activity of neurons is not related to details of the movement, e.g. individual muscle movements.
3. Experiment by Roland and colleagues, used PET to examine cerebral blood flow in humans:

Front 11

Role of Premotor Cortex

Back 11

Not well understood, but appears to play a role in the initial preparation for and sensory guidance of movement – Motor Set

Front 12

2 Roles of Basal Ganglia?

Back 12

Selection and Initiation of Willed Movements
Cognition?