It is a number of nuclear (grey matter) masses which lie within the cerebral hemisphere.
They are corpus striatum; amygdaloid nucleus and claustrum. Its major components are
caudate nucleus; putamen and globus pallidus . These structures are involved in the control
of posture and movement. They are sometimes referred to anatomically as the corpus
striatum but clinically, as basal ganglia. Notice that the function of amygdala is differ.
Gross anatomically, the putamen and globus pallidus are called the lentiform or lenticular
nucleus. The corpus striatum are connected with thalamus ; subthalamus of diencephalon
and substantia nigra of midbrain.
The lentiform nucleus is three- sided, having a convex lateral surface and 2 other
surfaces that converge to a medial apex which lies against the genu of the internal
It lies lateral to the internal capsule and globus pallidus. It is separated from
the globus pallidus by a thin lamina of nerve fibers ( the lateral medullary lamina ).
Lateral to it lies a thin sheet of grey matter ( claustrum ) which separates the
white matter into 2 layers, the external capsule and the extreme capsule. Lateral to
the extreme capsule lies the cortex of the insula ( deep within the lateral fissure of
the hemisphere ).
2- Caudate nucleus:
It consists of a large head and body and a tapering, curved tail. The head of
the caudate is completely separated from the putamen by the internal capsule.
Rostrally, it is continuous with the putamen at the anterior limb of the internal
capsule. At this level, the most ventral portion of the striatum is the nucleus
accumbens which is connected to the limbic system.
The head of the caudate nucleus forms a prominent bulge in the lateral wall of
the anterior horn of the lateral ventricle.
principal nuclei of the basal ganglia are (1) the striatum, (2) the globuspallidus (or pallidum),
substantianigra (consisting of the pars reticulata and pars compacta), and (4) the subthalamic
. The striatum consists of three important subdivisions: the caudate nucleus, the putamen, and
striatum (which includes the nucleus accumbens). The striatum is divided into the caudate nu
tamen by the internal capsule, a major collection of fibers that run between the neocortex an
Striatum = caudate+putamen
The tail of the caudate
passes posteriorly and
follows the curvature of
the lateral ventricle then
descends into the
temporal lobe where it
lies in the roof of the
inferior horn of lateral
3- Globus Pallidus:
It lies medial to putamen, separated from it by the lateral medullary lamina. Its
medial apex nestles into the lateral concavity of the internal capsule.
It consists of 2 division which are separated by a thin sheet of fibers ( the
medial medullary lamina ). The medial segment is the smaller one.
The putamen and globus pallidus ( lentiform nucleus ) lie lateral to the internal
capsule and deep to the cortex of the insula.
4- Substantia Innominata:
It refers to the basal part of the rostral forebrain that lies beneath the corpus striatum.
It contains several groups of neurons. One of them is the nucleus basalis that project to
the cerebral cortex and utilize acetylcholine as their neurotransmitter. These
neurons undergo degeneration in Alzheimer’s disease.
It is a thin plate of grey matter placed lateral to lentiform nucleus. Its anteroinferior part
fuses with the anterior perforated substance and the
all parts of the cerebral cortex send
axons to the caudate nucleus & putamen.
Each part of cerebral cortex projects to a
specific of the caudate putamen complex.
Most of the projections are from the cortex
of the same side. The large input is from the
sensory motor cortex. Glutamate is the
neurotransmitter of the corticostriate fibers.
The intralaminar nuclei of the thalamus
send large numbers of axons to the
caudate nucleus & putamen
Neurons in the substantia nigra send
axons to the caudate nucleus &
putamen & liberate dopamine at their
terminals as the neurotransmitter. It is
believed that these fibers are inhibitory in
Brainsten striatal fibers
ascending fibers from the brinstem
end in the caudate nucleus & putamen
& liberate serotonin at their terminals as
the neurotransmitter. It is thought that
these fibers are inhibitory in function.
these fibers pass from the caudate
nucleus & putamen to the globus pallidus.
They have gamma aminobutyric acid
( GABA ) as their neurotransmitter.
fibers pass from the caudate & putamen
to the substntia nigra. Some of the fiber use
GABA or acetylcholine as the neurotransmit
ter,while other use substance P.
these fibers pass from the caudate &
putamen to the globus pallidus. GABA as
these fibers can be divided into groups:
Ansa lenticularis , which pass to the
Fasciculus lenticularis , which pass to the
pallidotegmental , fibers terminate in the
caudal tegmentum of the midbrain
pallidosubthalamic fibers , which pass to
the subthalamic nuclei.
Direct pathway : cortex –(+) striatum – (-) pallidum
internum/subst. nigra – (-) thalamus – (+) cortex ( increases
the activity of the thalamus and the excitation of cerebral
cortex = increased motor activity)
Indirect pathway : cortex – (+) striatum –
(-) pallidum externum – (-) subthalamic nc. – (+) pallidum
internum – (-)thalamus – (+) cortex (decreases activity of the
thalamus and the excitation of cerebral cortex = decreased
Globus pallidus interna/Substantia Nigra reticulata
Corticospinal tract and
Substantai Nigra compacta
Globus pallidus interna/Substantia Nigra reticulata
Globus pallidus interna/Substantia Nigra reticulata
The corpus striatum regulates muscle tone &
thus help in smoothening voluntary
It controls automatic associated
movements, like the swinging of arms during
waking. Similarly, it controls the coordinated
movements of different parts of the body
for emotional expression.
It influences the precentral motor cortex
which is supposed to control the
extrapyramidal activities of the body
These do not receive any sensory input from spinal cord
unlike the cerebellum. Basal ganglia contribute to
cognitive functions of brain.
These help cortex in execution of learned patterns of
Corpus striatum , cerebellum & motor areas of cerebrum
jointly are responsible for planning , execution & control
Corpus striatum & cerebellum without sending fibres to
spinal cord modify the effect on spinal cord through
projections to motor cortex & extra pyramidal fibres.
Basal ganglia & cerebellum do not initiate movements
but are able to adjust motor commands.
1- Huntington’s Disease
It is an degenerative autosomal dominant inherited disease with the onset occurring in adult
life. Within the striatum, there is progressive ; particular attrition of the cells that project to
the lateral segment of the globus pallidus ( indirect segment ).
This leads to disinhibition of the lateral pallidal neurons and inhibition of subthalamic
nucleus. Medial pallidal neurons , therefore ,become abnormally underactive and unwanted;
involuntary movements.The following signs is present:
1- Choreiform movements first appear as involuntary movements of the extremities and
twitching of the face (facial grimacing). Later, more muscle
groups are involved so the patient becomes immobile and unable to speak or swallow.
2- Progressive dementia occurs with loss of memory and intellectual capacity There is
degeneration of the GABA; P-secreting and acetylcholine-secreting.
2- Parkinson’s disease
It is a neurodegenerative disease of elderly, of unknown cause. It is
characterized by akinesia, flexed posture, rigidity and a resting tremor.
It is due to depletion of striatal dopamine levels. It is treated by levodopa which
restores normal striatal function. When drug therapy fails, neurosurgical ablation
or electrical stimulation of the subthalamic nucleu or medial segment of the
globus pallidus can help the patient.
Chorea ( St Vitus’ dance )
The patient exhibits involuntary, quick,
jerky, spasmodic, irregular movements that
are nonrepetitive. Sudden movements of the
head; trunk or limbs. It is a common
manifestation of rheumatic fever.
4- Hepatolenticular degeneration (Wilson’s
It is an inherited disorder ( autosomal
recessive ) of copper metabolism.
It is rare with choreiform movements of the
limbs on one side of the body. It caused by a
lesion of cerebrovascular origin of the
contralateral subthalamic nucleus.
Definition: Tracts other than corticospinal tract are
known as Extrapyramidal tract.
The word extrapyramidal is slowly being replaced
by Corticonuclear & corticobulbar tracts.
The descending tracts of spinal cord oter than
pyramidal tracts are known as extrapyramidal
Midbrain giving rise to following
Includes all motor pathways not part of the pyramidal system
Upper motor neuron (UMN) originates in nuclei deep in
cerebrum (not in cerebral cortex)
UMN does not pass through the pyramids!
LMN is an anterior horn motor neuron
This system includes
Axial muscles that maintain balance and posture
Muscles controlling coarse movements of the proximal portions of limbs
Head, neck, and eye movement
Reticulospinal tracts – originates at reticular formation
of brain; maintain balance
Rubrospinal tracts – originate in ‘red nucleus’ of
midbrain; control flexor muscles
Tectospinal tracts - originate in superior colliculi and
mediate head and eye movements towards visual
targets (flash of light)
All fibers that influence the motor activity
without passing through the pryamidal tract
› Basal Ganglia (caudate, putamen, globus
pallidus, Subthalamic nucleus and substantia
1. Regulation and integration of
voluntary motor activity
Involuntary motor activity:
rhythmic & regular (static tremor)
Dysrhythmic and irregular (chorea,
2. Regulation and maintenance of
Hypertonia or rigidity
3. Regulation and maintenance of Bradykinesia, mask face,
emotional & associative movement infrequent blinking, loss of
swinging during walking.
1. UMN cell body location
2. UMN axon decussates in pons
3. Synapse between UMN and LMN
occurs in anterior horn of sc
3. LMN exits via ventral root
4. LMN axon stimulates skeletal
Red Nucleus in Midbrain
Decussation at the level of red nucleus
Pass down through Pons & Medulla
Occupies the lat. White column of spinal cord
Ends in ant. Horn of spinal cord
Functions: Facilitatory influence on flexor muscle
Afferent from cerebellum, vestibular apparatus
& vestibular nuclei
Spinal motor neuron
Innervating axial &
Function : Controls reflexes
eg. Postural & righting
Control eye movements.
Superior & Inferior collicili in midbrain
Near Medial longitudinal fasiculus
Cervical spinal motor neuron of anterior horn
Allow turning of the head in response to visual or
The reticular formation makes up a central
core through much of the brainstem. It
contains many different nuclear groups.
Pontine and medullary nuclei projects to
the anterior horn of the spinal cord. It
extend up to thoracic segments.
Functions: Coordination of voluntary &
reflex movement and is also responsible
for the muscle tone. Control of
respiration & diameter of blood vessels.
It arises in the cells of inferior olive of the
medulla and is found only in the cervical
region of the spinal cord.
Functions : are not known clearly. It is
believed that this tracts is involved in
reflex movements arising from the
Origin : vestibular nucleus, reticular
Course : uncrossed fibers. Extend up to
upper cervical segments
Function : coordination of reflex ocular
movements , Integration of movements
of eye & neck
Tremors is a rhythmic, involuntary,
oscillatory movement of body parts
It is the most common movement
Tremors are classified as rest or action
Rest tremor occurs when the affected
body part is completely supported
Action tremors are produced by
voluntary muscle contraction.
› postural, isometric, kinetic tremors.
Is continuous flow of involuntary irregular
movement. The movements are rapid,
jerky, non rhythmic and explosive that flit
from portion of the body to another in
It affects limbs and face and caused by
lesion in caudate nucleus
repetitive involuntary, slow, sinuous, writhing
movements, which are especially severe in
the hands. There are also elements of
postural disturbance. Usually combined with
chorea known as chorea-athetosis
Involuntary, twisting, sustained
movement of the limb or head resulting
in an abnormal posture.
Brief, isolated, involuntary, random, jerk
movement of a group of muscles.
Intermittent with distinct pause between
Repetitive, stereotyped, semipurposeful
Patient could willingly suppress them at expense of
mounting inner tension
There are 2 types of tics
› Simple tics of children: transient or chronic
› Complex tics: Gilles de La Tourette syndrome
(tics, vocalization, obsessive behavior)