1. Chapter 55: Cortical and Brain Stem Control Of Motor Function
Unit Eleven: The Nervous System: C. Motor and Integrative Neurophysiology
Chapter 55: Cortical and Brain Stem Control
Of Motor Function
Guyton and Hall, Textbook of Medical Physiology, 12 edition

2. Motor Cortex and Corticospinal Tract
Fig Motor and somatosensory functional areas of the cerebral cortex

3. Motor Cortex (cont.) Primary Motor Cortex
Fig Degree of representation
of the different muscles of
the body in the motor
cortex

4. Motor Cortex (cont.) Primary Motor Cortex
Fig Representation of the different muscles of the body in the motor cortex and location
of other cortical areas responsible for specific types of motor movements

5. Transmission of Signals from the Motor Cortex to the Muscles
Motor Cortex (cont.)
Transmission of Signals from the Motor Cortex to
the Muscles
Corticospinal (Pyramidal) Tract
Fig. 55.4

6. Red Nucleus As An Alternate Pathway
Motor Cortex (cont.)
Red Nucleus As An Alternate Pathway
Fig. 55.5

7. Motor Cortex (cont.)
Function of the Corticorubrospinal System
Accessory route for transmission of discrete signals
from the motor cortex to the spinal cord
Extrapyrimidal System- all portions of the brain and
brain stem that contribute to motor control but are
not part of the direct scorticospinal-pyramidal system
Include the basal ganglia, reticular formation, and
the vestibular nuclei

8. Motor Cortex (cont.)
Excitation of the Spinal Cord Motor Control Areas by
the Primary Motor Cortex and the Red Nucleus
Vertical columnar arrangement of the neurons in the
motor cortex
Each column functions as a unit, usually stimulating
a group of synergistic muscles (sometimes a single muscle)
Each column operates as an integrative operating system
Each column can also function as an amplifying system
Dynamic neurons-excited at a high rate for a short period
of time at the beginning of a contraction
Static neurons-fire at a slower rate but maintain the force
of contraction

9. Motor Cortex (cont.)
Somatosensory Feedback
Vertical columnar arrangement of the neurons in the
motor cortex
Each column functions as a unit, usually stimulating
a group of synergistic muscles (sometimes a single muscle)
Each column operates as an integrative operating system
Each column can also function as an amplifying system
Dynamic neurons-excited at a high rate for a short period
of time at the beginning of a contraction
Static neurons-fire at a slower rate but maintain the force
of contraction

10. Stimulation of Spinal Motor Neurons
Motor Cortex (cont.)
Stimulation of Spinal Motor Neurons
Fig Convergence of different motor control pathways on the
anterior motor neurons

11. Role of the Brain Stem in Controlling Motor Function
Brain Stem Provides Special Control Functions
Control of respiration
Control of the cardiovascular system
Partial control of GI function
Control of many stereotyped movements of the body
Control of equilibrium
Control of eye movements

12. Role of the Brain Stem in Controlling Motor Function
Support of the Body Against Gravity
Reticular Nuclei
Pontine reticular nuclei- transmit excitatory signals; receive strong signals from vestibular nuclei and from nuclei of the cerebellum
Medullary reticular nuclei- transmit inhibitory signals to the same neurons as the pontine nuclei

13. Role of the Brain Stem in Controlling Motor Function
Support of the Body Against Gravity
Vestibular Nuclei- transmit strong excitatory signals to control antigravity muscles

14. Role of the Brain Stem in Controlling Motor Function
Fig Locations of the reticular and vestibular
nuclei in the brain stem
Fig Vestibulospinal and reticulospinal descending
tracts to excite or inhibit anterior motor neurons

15. Vestibular Sensations and Maintenance of Equilibrium
Fig Membranous labyrinth
and organization of the
crista ampullaris and the
macula

16. Vestibular Sensations and Maintenance of Equilibrium
Vestibular Apparatus- sensory organ for detecting
sensations of equilibrium
Encased in the bony labyrinth
Within are the membranous labyrinth which is the
functional part of the vestibular apparatus
Membranous Labyrinth- composed of
Cochlea
Three semicircular canals
Utricle
Saccule

17. Vestibular Sensations and Maintenance of Equilibrium
Maculae
Sensory organs of the utricle and saccule for detecting
orientation of the head with respect to gravity
Covered with a gelatinous layer that contains calcium
carbonate crystals (statoconia)
Hair cells project into the gel layer; synapse with
sensory endings of the vestibular nerve

18. Vestibular Sensations and Maintenance of Equilibrium
Maculae
Calcified statoconia have a specific gravity 2-3X the
specific gravity of the surrounding fluid and tissues;
Weight of the statoconia bends the hair cells (cilia)
in the direction of gravitational pull

19. Vestibular Sensations and Maintenance of Equilibrium
Directional Sensitivity of the Hair Cells—Kinocilium
Fig Hair cell of the equilibrium
apparatus and its synapses
with the vestibular nerve

20. Vestibular Sensations and Maintenance of Equilibrium
Directional Sensitivity of the Hair Cells—Kinocilium
Each hair cell has small cilia (stereocilia) and
one large kinocilium
The kinocilium is located to one side and the cilia get
progressively shorter toward the other side of the cell
When the stereocilia and the kinocilium bend in the
direction of the kinocilium, this opens fluid channels
capable of conducting large numbers of positive ions

21. Vestibular Sensations and Maintenance of Equilibrium
Directional Sensitivity of the Hair Cells—Kinocilium
Positive ions pour into the cell causing receptor membrane
depolarization (hyperpolarization occurs the bending is
in the opposite direction)
At rest: impulses are conducted continuously at a rate of
100 per second
When cilia are bending, impulses increase; as the
orientation of the head in space changes and the weight
of the statoconia bends the cilia, appropriate signals are
transmitted to the brain to control equilibrium

22. Vestibular Sensations and Maintenance of Equilibrium
Semicircular Ducts- arranged at right angles so that
they represent all three planes in space
Anterior
Posterior
Lateral (horizontal)

23. Vestibular Sensations and Maintenance of Equilibrium
Fig Movement of the cupula and its embedded hairs at the onset of rotation

24. Vestibular Sensations and Maintenance of Equilibrium
Semicircular Ducts (cont.)
Each has an enlargement at one end called the ampulla
Ducts and ampulla are filled with endolymph
Each ampulla has a crest called the crista ampullaris
On top of the crista is the cupula

25. Vestibular Sensations and Maintenance of Equilibrium
Semicircular Ducts- Rotation
When a person’s head starts to rotate in any direction, the
inertia of the fluid causes the fluid to remain stationary
while the duct rotates with the head
This causes the fluid to flow from the duct through the
the ampulla, bending the cupula to one side
Rotation of the head in the opposite direction causes the
cupula to bend to the opposite side

26. Vestibular Sensations and Maintenance of Equilibrium
Semicircular Ducts- Rotation
Hundreds of cilia project into the cupula from hair cells
on the crest
Kinocilia are oriented in the same direction, bending
the cupula in that direction causing depolarization of
the hair cells
f. Stimulates the vestibular nerve

27. Vestibular Sensations and Maintenance of Equilibrium
Function of the Utricle and Saccule in Static Equilibrium
Function to maintain equilibrium when the head is in
a near vertical position
Do not operate for the detection of linear velocity
Dectection of Head Rotation by the Semicircular Ducts

28. Vestibular Sensations and Maintenance of Equilibrium
Fig Response of a hair cell when a semicircular canal is stimulated first by
the onset of head rotation and then by stopping rotation

29. Other Factors Concerned With Equilibrium
Neck Proprioceptors
Visual Information
Proprioception and Exteroceptive Information
from Other Parts of the Body