basal ganglia - wordpress.com · damage to the basal ganglia esp. caudate circuit timing and...

BASAL GANGLIA

Dr. Ayisha QureshiProfessor

MBBS, MPhil

We have completed three levels of the motor system hierarchy: 1. Spinal cord,

2. Brainstem, and the3. Motor cortex,

Both Basal Ganglia & Cerebellum, can be considered as “side loops” in the motor hierarchy.

They influence the processing of motor control and modulate the outputof the descending pathways without directly causing motor output.

Because the most obvious clinical signs of damage to these areas are a wide variety of motor impairments, they are still generally considered to

be motor structures.

BASAL GANGLIA

Also called the Basal Nuclei, it consists of several masses of gray matter located deep within the

cerebral white matter.

CEREBRAL CORTEX

THALAMUS BASAL GANGLIA

It consists of the following nuclei:

1. caudate nucleus, 2. putamen,3. globus pallidus, 4. substantia nigra, and 5. subthalamicnucleus.

One of the principal roles of Basal Ganglia is to function in association with the

corticospinal system to control complex patterns of motor activity.

BASAL GANGLIA

Executing Motor Activity

Putamen Circuit

Cognitive control of Motor Activities

Caudate Circuit

Has 2 major circuits

PUTAMEN CIRCUIT(Executing learned patterns of

movements)

• Writing • Cutting with scissors • Hammering nails • Shooting a basketball• Passing a football• Talking • Controlled eye movements.

CAUDATE CIRCUIT(cognitive control of sequences of

motor patterns)

• Role of cognition and cognitive control of motor activity (motor actions as a consequence of thought)

• Sequential pattern of movements requiring thought and planning and then execution.

• E.g: seeing a lion, turning away from the lion, beginning to run and even climbing a tree.

PUTAMEN CIRCUIT (subconscious execution of learned

patterns of movement)

CAUDATE CIRCUIT(cognitive planning of

sequential & parallel motor patterns)

DISORDER OF THE PUTAMEN CIRCUIT leads to hemiballismus (injury to subthalamus

causing flailing of an entire limb), athetosis (injury to GP causing writhing movement of a hand, an arm

or face) and chorea (injury of putamen causing flicking movements in hands, face and other parts of

the body).

Damage to the Basal Ganglia esp. Caudate Circuit

Timing and scaling is a function of the caudate cognitive motor control circuit working in

association with the association areas of the cerebral cortex.

E.g. How large the writing should be and whether it should be written slowly or rapidly.

Because Basal Ganglia works in combination with Parietal Posterior Cortex (most association areas),

damage to this area leads to 2 conditions: 1. Agnosia- inability to accurately perceive

objects through normally functioning sensory mecahnisms.

2. Personal Neglect Syndrome in which the patient fails to use or clean or be aware of the side

of the body opposite to the side of the damaged posterior cortex.

(Note in the figure that the ability of the person to copy the left side of the drawing is severely

impaired.)

GABA & Dopamine make Negative Feedback Loops, thus, acting as stabilizers to the motor control systems.

PARKINSON’S DISEASE Also known as paralysis agitans, it results

from widespread destruction of the portion of the substantia nigra that sends dopamine-

secreting nerve fibers to the caudate nucleus & putamen.

TREATMENT

• L-DOPA • MAO inhibitors (L-DEPRENYL) • Transplanted Fetal Dopamine Cell• Destroying part of Feedback circuitry in the

Basal Ganglia

Huntington’s Disease (Huntington’s Chorea)

It is an autosomal dominant hereditary disorder, characterized by flicking movements in individual muscles & progressive severe distortional movements of entire body.

(dementia & motor dysfunction is also seen)

CAUSE: Loss of GABA secreting & Ach secreting neurons in many parts of the brain.

Gene involved: Huntingtin

Question: Summarize the integration of the many parts

of the total motor control of the body.