Basal Ganglia1. Neostriatum Caudate nucleus Putamen Ventral striatum (nucleus accumbens)

2. Paleostriatum Globus pallidus external segment (GPe)

Globus pallidus internal segment (GPi)

3. Substantia Nigra Pars compacta (SNc) Pars reticulata (SNr)

4. Subthalamic nucleus (STN)

Basal Ganglia

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.

And claustrum

And substantia

innominata Nucleus accumbens

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 capsule.

1- Putamen:

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.

The four principal nuclei of the basal ganglia are (1) the striatum, (2) the globuspallidus (or pallidum), (3) the substantianigra (consisting of the pars reticulata and pars compacta), and (4) the subthalamic nucleus. The striatum consists of three important subdivisions: the caudate nucleus, the putamen, and the ventral striatum (which includes the nucleus accumbens). The striatum is divided into the caudate nucleus and putamen by the internal capsule, a major collection of fibers that run between the neocortex and thalamusin both directions.

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 ventricle.

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.

5- Claustrum:

It is a thin plate of grey matter placed lateral to lentiform nucleus. Its anteroinferior part fuses with the anterior perforated substance and the amygdaloid nucleus.

Forebrain

Midbrain

Circuit of the Circuit of the basal gangliabasal ganglia

AFFERENT FIBERS Corticostriate fibers 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.

Thalamosriate fibers The intralaminar nuclei of the

thalamus send large numbers of axons to the caudate nucleus & putamen

Nigrostriate fibers 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 function.

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.

Striatopallidal fibers these fibers pass from the caudate

nucleus & putamen to the globus pallidus. They have gamma aminobutyric acid ( GABA ) as their neurotransmitter.

Striatinigral fibers 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.

AFFERENT FIBERS Striatopallidal fibers these fibers pass from the caudate &

putamen to the globus pallidus. GABA as their neurotransmitter.

Pallidofugal fibers these fibers can be divided into groups: 1. Ansa lenticularis , which pass to the

thalamic nuclei2. Fasciculus lenticularis , which pass to

the subthalamus3. pallidotegmental , fibers terminate in

the caudal tegmentum of the midbrain4. 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 motor activity)

Cerebral Cortex

Striatum

SNc

Thalamus

Glutamate Glutamate

Glutamate

D2GABA-enk

D1GABA-dyn

GABA

DA

Brainstem andSpinal Cord Globus pallidus interna/Substantia Nigra reticulata

Globus Pallidus externa

Subthalamic Nucleus

IndirectPathway

DirectPathway

Cerebral Cortex

Brainstem andSpinal Cord

Corticospinal tract and Corticobulbar projections

Cerebral Cortex

StriatumGlutamate

Brainstem andSpinal Cord

Cerebral Cortex

Striatum

Substantai Nigra compacta

Glutamate

D1

Dopamine

Brainstem andSpinal Cord

D2

Cerebral Cortex

Striatum

SNc

Globus pallidus interna/Substantia Nigra reticulata

Thalamus

GlutamateGlutamate

D1GABA-dyn

GABA

DA

Brainstem andSpinal Cord

DirectPathway

Cerebral Cortex

Striatum

Globus Pallidus externa

Subthalamic Nucleus SNc

Gpi/SNr

Thalamus

Glutamate Glutamate

Glutamate

D2GABA-enk

D1GABA-dyn

GABA

DA

Brainstem andSpinal Cord

Cerebral Cortex

Striatum

SNc

Thalamus

Glutamate Glutamate

Glutamate

D2GABA-enk

D1GABA-dyn

GABA

DA

Brainstem andSpinal Cord Globus pallidus interna/Substantia Nigra reticulata

Globus Pallidus externa

Subthalamic Nucleus

IndirectPathway

DirectPathway

• The corpus striatum regulates muscle tone & thus help in smoothening voluntary movements.

• 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 movements subconsciously.

Corpus striatum , cerebellum & motor areas of cerebrum jointly are responsible for planning , execution & control of movements.

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.

3- Sydenham’s 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

disease)

It is an inherited disorder ( autosomal recessive ) of copper metabolism.

5- Hemiballism

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

tracts.

1. Basal Ganglia2. Midbrain giving rise to following

bulbospinal tracts.A. Rubrospinal tract.B. Vestibulospinal Tract.C. Reticulospinal TractD. Tectspinal Tract.E. Olivospinal Tract.

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

› Rubrospinal› Vestibulospinal› Reticulospinal› Tectospinal tracts

Regulate:› 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› Cortex› Basal Ganglia (caudate, putamen, globus

pallidus, Subthalamic nucleus and substantia nigra)

› Thalamus› Cerebellum› Red nucleus› Reticular nucleus

Function Dysfunction

1. Regulation and integration of voluntary motor activity

Involuntary motor activity:

rhythmic & regular (static tremor)

Dysrhythmic and irregular (chorea, athetosis, dystonia)

2. Regulation and maintenance of muscle tone

Hypertonia or rigidity

3. Regulation and maintenance of emotional & associative movement

Bradykinesia, mask face, infrequent blinking, loss of swinging during walking.

Note:1. UMN cell body location2. UMN axon decussates in pons3. Synapse between UMN and LMN occurs in anterior horn of sc3. LMN exits via ventral root4. LMN axon stimulates skeletal muscle

Red Nucleus in Midbrain

Decussation at the level of red nucleus

Occupies the lat. White column of spinal cord

Pass down through Pons & Medulla

Ends in ant. Horn of spinal cord

Functions: Facilitatory influence on flexor muscle tone

Afferent from cerebellum, vestibular apparatus & vestibular nuclei

Spinal motor neuron

Innervating axial & postural muscles

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

Function:

Allow turning of the head in response to visual or Auditory stimuli.

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 proprioceptors.

Origin : vestibular nucleus, reticular formation, superior colliculus

Course : uncrossed fibers. Extend up to upper cervical segments

Function : coordination of reflex ocular movements , Integration of movements of eye & neck

Akinetic rigid syndrome (Parkinsonism) Dyskinesias

› Tremor› Chorea› Myocolonus› Tics› Dystonia

Tremors is a rhythmic, involuntary, oscillatory movement of body parts

It is the most common movement disorder.

Tremors are classified as rest or action tremors.

Rest tremor occurs when the affected body part is completely supported against gravity.

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 random sequence.

It affects limbs and face and caused by lesion in caudate nucleus

Causes› Hereditary: huntington’s disease› Birth injury: Kernicterus› Rheumatic: Sydenham’s chorea› Pregnancy: chorea gravidarum› Vasculitic› Thyrotoxicosis› Drugs: L-Dopa

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 each movement.

Repetitive, stereotyped, semipurposeful movement.

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)