Basal Ganglia

Motor functions of the basal ganglia

*The basal ganglia & cerebellum work  in association with the cortex to give the power and precision of muscle activity.

* Include 3 large  cerebral basal nuclei :

1.Caudate nucleus.

2.Putamen.

3.Globbus pallidus.

 functionally related nuclei:

1.Subthalamic nucleus. 

2.Substantia nigra.

* Connections of the basal ganglia:-

-Functionally important pathways connect the basal ganglia with each other and with other areas of the C.N.S.

* Neurotransmitters in Basal ganglia :

- GABA, dopamine and serotonin are inhibitory

 neurotransmitters.

- Glutamate & Acetylcholine are excitatory neurotransmitters.   

 The balance between the different transmitters is important for normal function of the basal ganglia. 

* Functions of the basal ganglia

1.They help the corticospinal system in executing slow sustained movements (i.e. ramp movement) like writing, some aspects of vocalization, etc., This is executed by the putamen circuit.

*Damage to the basal ganglia causes gross abnormality in this patterns, even in the presence of a normally functioning cortical motor system. 

2. the caudate nucleus+cortical association area, plays an important rule in cognitive control of motor activity.).

3.The basal ganglia are inhibitory to muscle tone through-out the body.

This is brought about by sending impulses which activate the inhibitory reticular formation of the brain stem.

Therefore, the widespread damage of the basal ganglia produces rigidity.

4. the basal ganglia are also responsible for the initiation and regulation of gross, subconscious, associated movementsof the body (e.g. swimming of the arms while walking, facial expressions). 

5. the globus pallidus is responsible for the posture taken by the body to perform a particular voluntary movement (e.g. one assumes a certain posture of trunk and limbs to be able to write).

Clinical syndromes associated with damage to the basal ganglia :

* chorea :

 A syndrome which occurs due to degeneration of the caudate nucleus mainly, but the putamen may be involved too.

Characterized by spontaneous, uncontrolled, flicking movements which occur one after the other at rest and are ↑ by the muscular activity and emotions.

The normal progression of voluntary movements is interrupted and replaced by dancing movement.

A pendular knee-jerk.

 Choriec movements are due to absence of the inhibitory effect of GABA on the globus pallidus and substantia nigra. 

* Parkinson's disease (paralysis agitans ) 

 Results from widespread degeneration of nigro-striate fibers which secretes dopamine into the neostriatum and the thalamic nuclei.

* Causes:

- Senility mainly after age of 65 years

- Repeated head trauma.  

- Use of Dopamine antagonists as antitpsychotic drugs .

- Use of synthetic heroin containing .

The syndrome is characterized by three principal features:

1.Rigidity of muscles.

2.Tremor.

3. Akinesia.