This document summarizes the cortical and brain stem control of motor function. It discusses how the motor cortex, premotor area, and supplementary motor area initiate voluntary movements by activating patterns stored in lower brain areas like the brain stem and cerebellum. These lower centers then send control signals to muscles. It describes areas of the motor cortex and their functions, as well as pathways involving the brain stem, basal ganglia, cerebellum, and spinal cord that integrate to control motor functions. Damage to different areas can impact speech, eye and head movements, and dexterity.

2. Cortical and Brain Stem
Control of Motor Function

3. Most “voluntary” movements initiated by the
cerebral cortex are achieved when the cortex
activates “patterns” of function stored in lower
brain areas—the cord,brain stem,basal ganglia,
and cerebellum. These lower centers, in turn,
send specific control signals to the muscles.

4. MOTOR CORTEX
Anterior to the central cortical sulcus, occupying
approximately the posterior one third of the frontal
lobes.
Divided into:
(1)the primary motor cortex
(2) the premotor area
(3) the supplementary motor area.

7. Primary motor cortex
 Lies in the first convolution of the frontal lobes
anterior to the central sulcus. It begins laterally in
the sylvian f issure, spreads superiorly to the
uppermost portion of the brain, and then dips
deep into the longitudinal fissure.
 More than one half of the entire primary motor
cortex is concerned with controlling the muscles
of the hands and the muscles of speech.
 Excitation of a single motor cortex neuron usually
excites a specific movement rather than one
specific muscle.

8. Premotor Area
• Nerve signals generated in the premotor area
cause much more complex “patterns” of movement.
• The anterior part of the premotor area first develops
a “motor image” of the total muscle movement that
is to be performed.Then, in the posterior premotor
cortex, this image excites each successive pattern
of muscle activity required to achieve the image.
• This posterior part of the premotor cortex sends its
signals either directly to the primary motor cortex to
excite specific muscles or, often, by way of the
basal ganglia and thalamus back to the primary
motor cortex.

9. Supplementary Motor Area
 It lies mainly in the longitudinal fissure but
extends a few centimeters onto the superior
frontal cortex.
 Contractions elicited by stimulating this area are
often bilateral.
 This area functions in concert with the premotor
area to provide body-wide attitudinal
movements,fixation movements of the different
segments of the body, positional movements of
the head and eyes,and so forth.

10. Specialized Areas of Motor
ControL
Broca’s Area and Speech
- “word formation” area.
-Damage to it does not prevent a person from
vocalizing, but it does make it impossible for the person
to speak whole words .
-closely associated cortical area also causes
appropriate respiratory function, so that respiratory
activation of the vocal cords can occur simultaneously
with the movements of the mouth and tongue during
speech.

12. Voluntary Eye Movement Field.
-Damage to this area prevents a person from voluntarily
moving the eyes toward different objects. Instead, the
eyes tend to lock involuntarily onto specific objects.
-This area also controls eyelid movements such as
blinking.

13. Head Rotation.
•This area is closely associated with the eye
movement field; it directs the head toward different
objects.
Area for Hand Skills
•Destruction in this area, hand movements
become uncoordinated and nonpurposeful, a
condition called motor apraxia.

14. Transmission of Signals from the Motor Cortex to
the Muscles :
•Motor signals are transmitted directly from the
cortex to the spinal cord through the
corticospinal tract and indirectly through
multiple accessory pathways that involve the
basal ganglia, cerebellum, and various nuclei of
the brain stem.

15. Corticospinal (Pyramidal) Tract
 The most important output pathway from the
motor cortex .
 It’s fibers originate from giant pyramidal cells,
called Betz cells , these fibers are large
myelinated fibers with a diameter of 16
micrometers.
 The Betz cells are about 60 micrometers in
diameter, and their fibers transmit nerve impulses
to the spinal cord at a velocity of about 70 m/sec,
the most rapid rate of transmission of any signals
from the brain to the cord.

17. Red nucleus
• Red Nucleus Serves as an alternative pathway
for transmitting cortical signals to the spinal cord
• Red nucleus, located in the mesencephalon,
functions in close association with the
corticospinal tract called “corticorubral tract”
• Fineness of representation of the different
muscles is far less developed than in the motor
cortex.
• The corticospinal and rubrospinal tracts together
are called the lateral motor system of the cord.

19. Extrapyramidal system
Extrapyramidal motor system is all those portions
of the brain and brain stem that contribute to motor
control but are not part of the direct corticospinal-
pyramidal system.
These include pathways through the basal ganglia,
the reticular formation of the brain stem, the
vestibular nuclei, and often the red nuclei.

20.  The cells of the motor cortex are organized in
vertical columns, with thousands of neurons in
each column.
 Each column of cells functions as a unit, usually
stimulating a group of synergistic muscles, but
sometimes stimulating just a single muscle.
 Each column has six distinct layers of cells.
 The pyramidal cells that give rise to the
corticospinal fibers all lie in the fifth layer of cells
from the cortical surface.
 The input signals all enter by way of layers 2
through 4. And the sixth layer gives rise mainly to
fibers that communicate with other regions of the
cerebral cortex itself.

21. • Each column of cells excites two populations of
pyramidal cell neurons:
1-dynamic neurons : exicted for short period ,initial
rapid development of force.
2-static neurons: fire at a much slower rate, to
maintain the force of contraction as long as the
contraction is required.
• The neurons of the red nucleus have similar
dynamic and static characteristics, except that a
greater percentage of dynamic neurons in it.

22. • When nerve signals from the motor cortex cause
a muscle to contract, somatosensory signals
return all the way from the activated region of the
body to the neurons in the motor cortex that are
initiating the action.Most of these somatosensory
signals arise in :
(1) the muscle spindles
(2) the tendon organs of the muscle tendons
(3) the tactile receptors of the skin overlying the
muscles.
These somatic signals often cause positive
feedback enhancement of the muscle contraction.

23.  Removal of the Primary Motor Cortex
(Area Pyramidalis)
• Removal of a portion of the primary motor cortex—
area containing the giant Betz pyramidal cells—
causes varying degrees of paralysis of the
represented muscles.
• If the sublying caudate nucleus and adjacent
premotor and supplementary motor are affected loss
of voluntary control of discrete movements of the
distal segments of the limbs, especially of the hands
and fingers.
• The ability to control the fine movements is gone.

24. • Muscle Spasticity Caused by Lesions That Damage
Large Areas Adjacent to the Motor Cortex.
• The primary motor cortex normally exerts a
continual tonic stimulatory effect on the motor
neurons of the spinal cord; when this stimulatory
effect is removed, hypotonia results.
• Most lesions of the motor cortex, especially those
caused by a stroke, involve not only the primary
motor cortex but also adjacent parts of the brain
such as the basal ganglia, muscle spasm occurs on
the opposite side, because inhibitory pathways
are affected.

25. Role of the Brain Stem in
Controlling Motor Function
•Brain stem control motor and sensory functions for
the face and head regions , also:
1-Control of respiration
2. Control of the cardiovascular system
3. Partial control of gastrointestinal function
4. Control of many stereotyped movements of the
body
5. Control of equilibrium
6. Control of eye movements
• Reticular nuclei and Vestibular nuclei are
present in the brain stem, they control whole-body
movement and equilibrium.

26. Excitatory-Inhibitory Antagonism Between
Pontine and Medullary Reticular Nuclei
The reticular nuclei are divided into:
(1) pontine reticular nuclei, located slightly
posteriorly and laterally .
(2) medullary reticular nuclei.
 These two sets of nuclei function mainly
antagonistically to each other,with the pontine
exciting the antigravity muscles and the
medullary relaxing these same muscles.
 when the pontine reticular excitatory system is
unopposed by the medullary reticular system, it
causes powerful excitation of antigravity muscles.

28. • The specific role of the vestibular nuclei is to
selectively control the excitatory signals to the
different antigravity muscles to maintain
equilibrium in response to signals from the
vestibular apparatus.
• This control is done by lateral and medial
vestibulospinal tracts.

31. Maculae
 Sensory Organs of the Utricle and Saccule for
detecting orientation of the head with respect to gravity.
 The macula of the utricle lies in the horizontal plane
on the inferior surface of the utricle and plays an
important role in determining orientation of the head
when the head is upright.
 Conversely, the macula of the saccule is located
mainly in a vertical plane and signals head orientation
when the person is lying down.

33. • The calcified statoconia have a specific gravity two to
three times the specific gravity of the surrounding fluid
and tissues.The weight of the statoconia bends the
cilia in the direction of gravitational pull.
 In each macula, each of the hair cells is oriented in a
different direction so that some of the hair cells are
stimulated when the head bends forward, some are
stimulated when it bends backward, others are
stimulated when it bends to one side, and so forth.
 Therefore, a different pattern of excitation occurs in
the macular nerve fibers for each orientation of the
head. It is this “pattern” that apprises the brain of the
head’s orientation in space.

34. Semicircular Ducts.
 When a person’s head begins to rotate in any
direction, the inertia of the fluid in one or more of
the semicircular ducts causes the fluid to remain
stationary while the semicircular duct rotates with
the head. This causes fluid to flow from the duct
and through 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.
 Into the cupula are projected hundreds of cilia
from hair cells located on the ampullary crest.

35. From the hair cells, appropriate signals are sent by
way of the vestibular nerve to apprise the central
nervous system of a change in rotation of the head
and the rate of change in each of the three planes
of space.

36. Detection of Head Rotation by the
Semicircular Ducts
The semicircular duct transmits a signal of one
polarity when the head begins to rotate and of
opposite polarity when it stops rotating.
The semicircular duct mechanism predicts that
dysequilibrium is going to occur and thereby
causes the equilibrium centers to make
appropriate anticipatory preventive adjustments.
“anticipatory correction”.

37. Other Factors Concerned with
Equilibrium
1-Neck Proprioceptors
joint receptors of the neck:When the head is leaned in one
direction by bending the neck, impulses from the neck
proprioceptors keep the signals originating in the vestibular
apparatus for giving the person a sense of dysequilibrium.
2-Proprioceptive Information from Other Parts of the Body
Ex .pressure sensations from the footpads tell one
(1) whether weight is distributed equally between the two
feet and (2) whether weight on the feet is more forward or
backward.
3- A person can still use the visual mechanisms for
maintaining equilibrium.

38. • The primary pathway for the equilibrium reflexes
begins in the vestibular nerves, where the nerves are
excited by the vestibular apparatus then passes to
the vestibular nuclei and cerebellum. Next, signals
are sent into the reticular nuclei of the brain stem,
and down the spinal cord by way of the
vestibulospinal and reticulospinal tracts. The signals
to the cord control the interplay between facilitation
and inhibition of the many antigravity muscles, thus
automatically controlling equilibrium.
• The flocculonodular lobes of the cerebellum are
especially concerned with dynamic equilibrium
signals from the semicircular ducts.

40. Functions of Brain Stem Nuclei in
Controlling Subconscious,
Stereotyped Movements
• Many of the stereotyped motor functions of the
human being are integrated in the brain stem.
• Example : anencephaly (baby born without brain
structure), they can still cry, yown, suckling,
stretch, move their eye to follow objects.

41. Contributions of the Cerebellum
and Basal Ganglia to Overall Motor
Control

42. • cerebellum and the basal ganglia always function in
association with other systems of motor control.
• Basically, the cerebellum plays major roles in :
• 1-Timing of motor activities and in rapid, smooth
progression from one muscle movement to the next.
• 2- controls intensity of muscle contraction when the
muscle load changes.
• 3- controls necessary interplay between agonist and
antagonist muscle groups.
• The basal ganglia help to plan and control complex
patterns of muscle movement.

45. • In the vermis, most cerebellar control functions
for muscle movements of the axial body, neck,
shoulders, and hips are located.
• Cerebellar hemisphere is divided into an
intermediate zone and a lateral zone.
• The intermediate zone of the hemisphere is
concerned with controlling muscle contractions in
the distal portions of the upper and lower limbs.
• Without this lateral zone, most discrete motor
activities of the body lose their appropriate timing
and sequence.

47. Afferent Pathways from Other Parts of the Brain.
The dorsal spinocerebellar tract and the ventral
spinocerebellar tract.
The signals transmitted in the dorsal spinocerebellar
tracts come mainly from the muscle spindles about
muscle contraction, tension, positions and rates of
movement of the parts of the body, and forces acting
on the surfaces of the body.
the ventral spinocerebellar are excited mainly by
motor signals arriving in the anterior horns of the
spinal cord from the brain and the spinal cord itself.

48. Deep Cerebellar Nuclei and the Efferent Pathways.
• Located deep in the cerebellar mass on each side
are three deep cerebellar nuclei—the dentate,
interposed, and fastigial.
• Three major layers of the cerebellar cortex are
shown: the molecular layer, Purkinje cell layer, and
granule cell layer.
• Functional Unit of the Cerebellar Cortex is the
Purkinje Cell and the Deep Nuclear Cell.

49. • The afferent inputs to the cerebellum are mainly
of two types :
A. the climbing fiber type originate from the
inferior olives of the medulla, produce action
potential called the complex spike.
• B. the mossy fiber type originate from the higher
brain, brain stem and spinal cord. Action potenial
produce is called simple spike (weaker).

51. • Feedback inhibitory signals from the Purkinje cell
circuit arrive.
• Basket cells and stellate cells are inhibitory cells
with short axons cause lateral inhibition of
adjacent Purkinje cells, thus sharpening the
signals.

52. Function of the Cerebellum in
Motor Control
• cerebellum coordinate motor control functions at
three levels:
• 1.Vestibulocerebellum
• Equilibrium is far more disturbed during
performance of rapid motions.
• It is presumed that information from both the
body periphery and the vestibular apparatus is
used in a typical feedback control circuit to
provide anticipatory correction of equilibrium.

53. 2.Spinocerebellum
• This part of the cerebellar motor control system
provides smooth, coordinate movements of the
agonist and antagonist muscles of the distal
limbs for performing acute patterned movements.

54. • 3.Cerebrocerebellum
• lateral cerebellar zones communicate with the premotor
area and primary motor and associated somatosensory
area.
• concerned with two other important but indirect aspects of
motor control:
• (1) the planning of sequential movements:
• Lateral cerebellar zones are concered with what will be
happening during the next sequential movement a
fraction of a second or perhaps even seconds later.

55. (2) the “timing” of the sequential movements:
• lesions in the lateral zones cause failure of
smooth progression of movements.

56. Clinical Abnormalities of the
Cerebellum
• 1-Dysmetria: movements ordinarily overshoot
their intended mark then the conscious portion of
the brain overcompensates in the opposite
direction,results in uncoordinated movements
that are called ataxia.
• Caused by cerebellar disease or lesions in the
spinocerebellar tracts.
• 2-Past pointing means that in the absence of the
cerebellum, a person ordinarily moves the hand
or some other moving part of the body
considerably beyond the point of intention.

57. • 3-Dysdiadochokinesia: failing to predict where the
different parts of the body will be at a given time, it
“loses” perception of the parts during rapid motor
movements.
• Dysarthria:failure of progression during talking.
• 4-intention tremor or an action tremor: results from
cerebellar overshooting and failure of the cerebellar
system to “damp” the motor movements.
• example: Cerebellar nystagmus is tremor of the
eyeballs that occurs usually when one attempts to
fixate the eyes on a scene to one side of the head.

58. 5-hypotonia :
• Results from loss of cerebellar facilitation of the
motor cortex and brain stem motor nuclei by tonic
signals from the deep cerebellar nuclei.
• Decreased tone of the peripheral body
musculature on the side of the cerebellar lesion.

59. Basal ganglia
• Found on each side of the brain, these ganglia
consist of the caudate nucleus, putamen, globus
pallidus, substantia nigra, and subthalamic
nucleus.
• They are located mainly lateral to and
surrounding the thalamus.
• Nerve fibers connecting the cerebral cortex and
spinal cord pass through the space that lies
between the major masses of the basal ganglia,
the caudate nucleus and the putamen. This
space is called the internal capsule of the brain.

61. • two major circuits,the putamen circuit and the
caudate circuit.
• The putamen circuit has its inputs mainly from
those parts of the brain adjacent to the primary
motor cortex
• circuits pass from putamen through the external
globus pallidus,the subthalamus, and the
substantia nigra—finally returning to the motor
cortex by way of the thalamus.

63. • The caudate nucleus plays a major role in
cognitive control of motor activity.
• After the signals pass from the cerebral cortex
to the caudate nucleus, they are next transmitted
to the internal globus pallidus, then to nuclei of
the ventroanterior and ventrolateral thalamus,
and finally back to the prefrontal, premotor, and
supplementary motor areas of the cerebral cortex.

65. • In patients with severe lesions of the basal
ganglia, the timing of functions are poor; or
sometimes nonexistent.
• Because the caudate circuit of the basal ganglial
system functions mainly with association areas of
the cerebral cortex such as the posterior parietal
cortex, presumably the timing and scaling of
movements are functions of this caudate
cognitive motor control circuit.

66. • Specific Neurotransmitter Substances in the
Basal Ganglial System:
• GABA always functions as an inhibitory agent
found in negative feed back loops.

67. • Clinical Syndromes Resulting from damage to the Basal
Ganglia
• 1-Parkinson’s Disease
• known also as paralysis agitans.
• results from widespread destruction of that portion of the
substantia nigra (the pars compacta) that sends
dopamine-secreting nerve fibers to the caudate nucleus
and putamen.
• The disease is characterized by:
• (1) rigidity of much of the musculature of the body.
• (2) involuntary tremor of the involved areas even when
the person is resting at a fixed rate of 3 to 6 cycles per
second.
• (3) serious difficulty in initiating movement, called
akinesia.

68. Treatment
A. Treatment with l-Dopa:
• L-Dopa passes through blood brain barrier.
• Ameliorates many of the symptoms, especially the
rigidity and akinesia.
• L-dopa is converted in the brain into dopamine, and
the dopamine then restores the normal balance
between inhibition and excitation in the caudate
nucleus and putamen.
B.Treatment with l-Deprenyl:
• This drug inhibits monoamine oxidase, which is
responsible for destruction of most of the dopamine .
• Used in combination with l-Dopa.

69. c.Treatment with Transplanted Fetal Dopamine Cells.
d.Treatment by Destroying Part of the Feedback
Circuitry in the Basal Ganglia.
2-Huntington’s Disease (Huntington’s Chorea):
• Hereditary disorder that usually begins causing
symptoms at age 30 to 40 years.
• It is characterized at first by flicking movements in
individual muscles and then progressive severe
distortional movements of the entire body.
• The cause is loss of most of the cell bodies of the
GABA-secreting neurons in the caudate nucleus and
putamen and of acetylcholine-secreting neurons in
many parts of the brain(which causes denentia).

70. Thank you