motor system4 basal ganglia undergraduates

Basal ganglia• These are a set of deep nuclei located

in and around the basal part of the brain that are involved in motor control, action selection, and some forms of learning

Basal ganglia• Caudate nucleus • Putamen• Globus pallidus

–(internal and external)• Subthalamic nuclei• Substantia nigra

International Basal Ganglia Society

(Ref. Guyton)

thalamus

globus pallidus

putamencaudate

basal ganglia• caudate nucleus

• putamen

• globus pallidus

• subthalamic nuclei

• substantia nigra

corpus striatum

lentiformnucleus

• Interconnecting circuitry through these nuclei

• These circuits start from the cortex and ends in the cortex

• These circuits are very complex

• Their effect is excitatory or inhibitory on motor functions (depending on the neurotransmitter involved)

• They also have a role in cognitive functions.

PUTAMEN CIRCUIT

• Starts from premotor Cx, SMA & 1° sensory area.

• Then goes to putamen (striatum)

• Then to globus pallidus

• Then to thalamus

• Return to 1° motor Cx

Cortex

Putamen

globuspallidus

Thalamus

PUTAMEN CIRCUIT

• This circuit functions to control complex patterns of movement in association with the motor Cx

• eg. – writing letters of alphabet, – cutting papers with scissors, – hammering nails, – passing a football, – vocalisation

CAUDATE CIRCUIT

• Starts from all parts of the Cx: frontal, parietal, occpital, temporal. and association Cx

• Then to caudate nucleus

• Then to globus pallidus

• Then to thalamus

• Finally to Premotor Cx, SMA

Cortex

Caudate

globuspallidus

Thalamus

CAUDATE CIRCUIT

• This circuit functions in the cognitive control of movement.

• Some of these circuits are excitatory and some inhibitory• This depends on the neurotransmitter involved.

• Inhibitory: dopamine and GABA• Excitatory: Ach• Others: glutamate (from cortical projections)

enkephalin etc

Following pathways are known:

• Dopamine pathway from substantia nigra to caudate nucleus and putamen

• GABA pathway from caudate and putamen to globus pallidus and substantia nigra

• Ach pathway in the caudate and putamen

Cortex

Putamen

globuspallidus

Thalamus

Caudate

Substantia nigra

Subthalamic nucleus

Reticular formation

Dopamine

Thalamus Reticular formation

glutamate

GABA

Interneurons: Ach

stri

atum

GABA

+

+

Functions of Basal Ganglia

• Motor control

• Learning

• Sensorimotor integration

• Reward

• Cognition

Cortico–Basal Ganglia Motor Loop• Basal ganglia

receives information from cerebral cortex (frontal, prefronal and parietal)

• Complex mechanisms occur inside basal ganglia

• Output goes to the thalamus

• From the thalamus to the frontal cortex (premotor and supplementary motor areas)

Basal ganglia inhibit muscle tone

Basal Ganglia disorders

• Parkinsonism• Athetosis• Chorea• Hemiballismus

• Basal ganglia disorders are also called extrapyramidal disorders

Parkinsonism• due to destruction of dopamine secreting pathways

from substantia nigra to caudate and putamen.– also called “paralysis agitans” or “shaking palsy” – first described by Dr. James Parkinson in 1817.

• In the west, it affects 1% of individuals after 60 yrs

Classical Clinical features:

• Tremor, resting

• Rigidity of all the muscles

• Akinesia (bradykinesia): very slow movements

• Postural instability

– expressionless face– flexed posture– soft, rapid, indistinct speech– slow to start walking– rapid, small steps, tendency to run– reduced arm swinging– impaired balance on turning– resting tremor (3-5 Hz) (pill-rolling tremor)

• diminishes on action

– cogwheel rigidity– lead pipe rigidity– impaired fine movements– impaired repetitive movements

other areas

Cortex

Putamen

globuspallidus

Thalamus

Caudate

Substantia nigra

Subthalamic nucleus

Reticular formation

Dopamine

Thalamus Reticular formation

glutamate

GABA

Interneurons: Ach

stri

atum

GABA

+

+

Parkinsonism

• this could be caused by– idiopathic causes (no definite cause)– drugs– toxins– MPTP (1 methyl 4 phenyl tetrahydropyridine)

• experimentally induced parkinsonism

– associated with other disorders

Parkinsonism

• Treatment is to – increase dopamine content by giving

dopaminergic drugs• Ldopa

– decrease Ach activity by giving anticholinergic drugs

Chorea• Lesions in the caudate nucleus

• jerky movements of the hand, face and other parts

• patient is unable to control them

• may get worse with anxiety

• disappears in sleep

video

Athetosis• Lesions in putamen

• spontaneous slow writhing movements (twisting movements) of fingers, hands, toes, feet.

Hemiballismus

• Lesions in subthalamus

• violent, flailing movements of arm & leg on one side of the body