The basal ganglia are sub-cortical brain structures that include the corpus striatum, globus pallidus, thalamus, subthalamic nuclei, and substantia nigra. The corpus striatum is divided into the caudate nucleus and lentiform nucleus. The basal ganglia receive input from the cerebral cortex and thalamus and send output to the thalamus, brainstem, and other structures. They play an important role in controlling voluntary motor activity, timing and scaling of movements, and maintaining muscle tone and posture. Disorders of the basal ganglia can cause either hypokinetic or hyperkinetic movement abnormalities.

1. BASAL GANGLIA
- CHAITRA CHINMAYEE

2. BASAL GANGLIA
Basal Ganglia are sub-cortical masses of gray matter located within the
white matter at the basal part of the cerebral hemisphere.
COMPONENTS OF BASAL GANGLIA :-
a. Corpus Striatum/Striatum
b. Globus Pallidus/Pallidum
c. Thalamus
d. Subthalamic nuclei
e. Substantia Nigra

3. CORPUS STRIATUM
Corpus Striatum comprises of sub-cortical masses of gray matter within the
white matter of cerebral hemisphere. It is divided by the fibres of internal
capsule into :-
a. Caudate nucleus – a highly curved comma shaped band of gray matter. It
consists of head, body and tail. It is almost entirely separated from the
lentiform nucleus by the fibres of internal capsule except at the lower part,
where it is continuous with the putamen
b. Lentiform nucleus – it is in shape of a biconvex lens which is divided by the
fibres of external lamina of the white matter into –
i. Putamen – outer dark quadrilateral part
ii. Globus Pallidus – inner small part which is divided by the fibres of the
internal lamina of the white matter into :-
* Globus Pallidus Externus
* Globus Pallidus Internus

4. SUBTHALAMIC NUCLEI
Biconvex masses of gray matter lateral to red nucleus and dorsal to
substatia nigra. It lies below the thalamus, and separated from the
ventral nuclei of the thalamus by a thin sheet of gray matter known as
zona inserta.
SUBSTANTIA NIGRA
Sheet made up of small un-pigmented & large pigmented nerve cells. It
extends along the entire length of mid-brain. It is divided into :-
a. Pars Compacta – dorsal part which contains dopaminergic (75%) and
cholinergic (25%) fibres
b. Pars Reticulata – ventral part which contains mostly GABAergic fibres.

5. CONNECTIONS OF BASAL GANGLIA
AFFERENTS:-
Striatum forms the major input of the basal ganglia
a. Corticostriate Projections – from the cerebral cortex (pre motor,
supplementary motor, primary somatosensory areas) and terminate in
striatum. They are mainly glutamatergic.
b. Thalamostriate fibres – from centromedian nucleus of thalamus to
striatum.
c. Nigrostriate fibres – from S.Nigra Pars Compacta to striatum. They are
dopaminergic.
d. Raphestriate fibres – from raphe nuclei in reticulat formation to
striatum. They are serotoninergic fibres.
e. Locus coeruleus striate fibres – from locus coeruleus to striatum. They
are noradrenergic fibres.

6. PROJECTIONS FROM STRIATUM/INTERMEDIATE FIBRES
• Striatum to Pallidum – most fibres project on
pallidum. They are GABAergic.
• Striatum to S. Nigra – GABAergic meurons to Pars
Reticulata
CONNECTIONS OF BASAL GANGLIA

7. CONNECTIONS OF BASAL GANGLIA
EFFERENTS:-
a. Thalamus – fibres are called thalamic fasciculus/ansa fascicularis. They
arise from internal segment of pallidum and terminate on the ventral-
anterior, ventral-lateral and centro-median nuclei of the thalamus. They
further project on pre-frontal and pre-motor cortex.
b. Subthalamic – which in turn project on S. Nigra
c. S. Nigra – fibres from pallidum to S. nigra via 3 routes
i. directly
ii. via subthalamic nucleus
iii. via pedunculopontine nucleus
S. nigra in turn sends descending projections to:-
* brain stem reticular formation – reticulospinal tract pathway
* superior colliculus – tectospinal tract pathway
* habenula
d. Red nucleus – rubrospinal tract pathway

8. CONNECTIONS OF BASAL GANGLIA

9. FUNCTIONS OF BASAL GANGLIA
a. Role in control of voluntary motor activities :-
The basal ganglia controls the motor activities initiated by the motor cortex. Role
of BG in control of voluntary movements include -
i. Cognitive control of motor activity :
The BG plans and programs the movements of the body, like the cerebellum
ii. Timing and scaling of motor activities :
The BG controls the timing (how rapidly the movement has to be performed) and
scaling (how large the movement has to be made) of the movements
iii. Subconscious execution of some movements :
The BG coordinates subconscious movements of the body during performance of
skilled movements like movements of limbs while swimming, swinging of arms while
walking, crude movement of facial expression accompanying emotions, etc

10. FUNCTIONS OF BASAL GANGLIA
b. Role in control of reflex activity :-
The BG exerts inhibitory effect on spinal reflexes & regulate the activity of
muscles which maintain posture. Visual and labyrinthine reflexes are important in
maintenance of posture.
c. Control of muscle tone :-
Muscle spindles & gamma motor neurons of spinal cord are controlled by the S.
Nigra of the BG. Lesions of the BG increases muscle tone leading to muscle
rigidity, as in parkinsonism.
d. Role in arousal mechanism :-
Pallidum and red nucleus are involved in arousal mechanism because of their
connections with the reticular formation. Extensive lesions of the pallidum are
associated with drowsiness, leading to sleep.

11. DISORDERS OF BG
Hypokinetic Disorders –
Parkinsonism
Hyperkinetic Disorders –
Athetosis
Ballismus
Chorea
Torsion spasm