The Basal Ganglia

Dr. NimirDr. Safaa

Objectives

Understand the anatomical and functional definition of the basal ganglia.

Identify the different components of the basal ganglia.

Describe the connections of the different components of the basal ganglia and the indirect pathways from the basal ganglia to the lower motor neurons.

Describe signs and symptoms of lesions which affect different components of the basal ganglia.

Basal ganglia are masses of gray matter situated deep within each cerebral hemisphere.

The basal nuclei play an important role in control of posture and voluntary movement, but have no direct input or output connections with spinal cord.

They are: Corpus striatum. Amygdaloid nucleus. Claustrum. Substantia Nigra.Subthalamic Nuclei.

Corpus striatum:Is lateral to thalamus and

divided by internal capsule, into caudate nucleus and lentiform nucleus.

Caudate nucleus has head, body & tail which terminates in amygdaloid nucleus.

Lentiform nucleus is lateral to internal capsule & medial to external capsule.

It is divided into dark putamen & light globus pallidus.

Neostriatum means putamen & caudate nucleus.

Amygdaloid nucleus: Is in temporal lobe

close to uncus.It is part of the limbic

system.Claustrum: Is thin gray matter

lateral to external capsule and medial to subcortical white matter of insula.

Substantia nigra and subthalamic nuclei:

Substantia nigra of midbrain and subthalamic nuclei of diencephalon are functionally related to basal nuclei.

Connections:Caudate nucleus and

putamen are main sites for receiving input to the basal nuclei.

The globus pallidus is major site of output from basal nuclei.

Connections of the Corpus Striatum:

Afferent fibers:Corticostriate.Thalamostriate.Nigrostriate.Brainstem.

Efferent fibers:Striatopallidal.Striatonigral.Connections of the

globus pallidus:Afferent:Striatopallidal.Efferent :Pallidofugal Fibers which

are:Ansa lenticularis to

thalamic nuclei.Fasciculus lenticularis to

subthalamus.Pallidosubthalamic to

subthalamic nuclei.Pallidotegmental to

tegmentum of the midbrain.

Functions of the basal nuclei:

Basal nuclei control muscular movements by influencing cerebral cortex.

They have no direct control through descending pathways to brainstem and spinal cord.

They assist in regulation of voluntary movement and learning of motor skills.

Disorders of the basal nuclei:

Are of two types: Hyperkinetic disorders are those in which there are excessive and abnormal movements (chorea, athetosis, and ballism).

Hypokinetic disorders are those in which there is a lack or slowness of movement.

Parkinson disease includes both types of motor disturbances.