PHYSIOLOGY OF BASAL GANGLIAPHYSIOLOGY OF BASAL GANGLIA

Prof. Sultan Ayoub Meo MBBS, M.Phil, Ph.D (Pak), Med Ed, Med Ed, (Dundee), FRCP (London), FRCP (Dublin), FRCP (Glasgow), FRCP

(Edinburgh) Prof. Department of Physiology

College of Medicine, King Saud University

• Enumerate different nuclei of basal ganglia

• Know different neurotransmitters that have a role

in basal ganglia functions

• Appreciate general functions of basal ganglia

• Physiological basis of basal ganglia disorders

Lecture Objectives

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BASAL GANGLIA: BASAL GANGLIA: NUCLEI NUCLEI

Five nuclei : Caudate Nucleus Putamen Globus Pallidus – external & internal

segments. Subthalamic Nucleus Substantia Nigra- pars compacta,reticulataBasal ganglia: A group of nuclei, act as a unified functional unit. Basal ganglia: A subcortical nuclei of grey matter located in the interior part of cerebrum / base of the forebrain connected with cerebral cortex, thalamus, and other brain areas. Play a role in action selection, decision of possible behaviors to execute at a given time

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BASAL GANGLIA: NUCLEI BASAL GANGLIA: NUCLEI

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BASAL GANGLIA: NUCLEI BASAL GANGLIA: NUCLEI

1. Parietal cortex (primary and secondary somatosensory information, secondary visual information), 2. Temporal cortex (secondary visual and auditory information), 3. Cingulate cortex (limbic and emotional status information), 4. Frontal cortex (primary and secondary motor information), 5. Prefrontal cortex.

Basal ganglia Input

Basic Circuits of basal ganglia

Motor loop (putamen circuit): Learned moment.

Cognitive loop (Caudate circuit): Cognitive control of

sequences of motor pattern. Mainly it is concerned with

motor intentions. (Cognition means thinking process using

sensory input with information already stored in memory.)

Limbic loop: Giving motor expression to emotions like,

smiling, aggressive or submissive posture.

Occulomotor loop: Voluntary eye movement (saccadic

movement)

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Motor loop (putamen circuit): Concerned with learned moment. Putamen circuit is inhibitory. Executes skilled motor activities for example cutting paper with a scissor, hammering on nail, shooting a basket ball & like throwing a base ball.

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Cognitive loop (Caudate circuit): Concerned with cognitive control of sequences of motor pattern. Motor intentions (Cognition means thinking process using sensory input with information already stored in memory)

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Neurotransmitters of basal ganglia

Neurotransmitters of basal ganglia

Dopamine pathway: From substantia nigra to caudate nucleus and putamen.Gama amino butyric acid pathway: From caudate nucleus and putamen to globus pallidus and substantia nigra.Acetylcholine pathway: From cortex to the caudate nucleus to putamen.Glutamate: Provide the excitatory signals that balance out the large no. of the inhibitory signals transmitted specially by the dopamin, GABA & serotonin inhibitory transmitters.Dopamine: excites areas of caudate/putamen with D1 receptors to promote the direct pathway, inhibits areas of caudate/putamen with D2 receptors to inhibit the indirect pathway

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Dopamine: Neuromodulatory neurotransmitter, excites areas of the caudate/putamen with D1 receptors to promote the direct pathway, inhibits areas of the caudate/putamen with D2 receptors to inhibit the indirect pathway Glutamate: Excitatory neurotransmitter Subthalamic nucleus projects glutamate to stimulate the ventrolateral thalamus. Ventrolateral thalamus projects glutamate to stimulate the primary localized motor cortex GABA: Inhibitory neurotransmitter: Caudate/Striatum (direct) projects GABA to inhibit the Gpi GPi projects GABA to inhibit the ventrolateral nucleus Caudate/Striatum (indirect) projects GABA to inhibit the GPe

GPe projects GABA to inhibit the subthalamic nucleus

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Cerebral cortexPrefrontal,

premotor, primary motor area,

somatosensory area

Putamen

Thalamus

Via globus pallidus

subthalamic nucleus

Caudate nucleus

Thalamus

IndirectInhibitory

Direct Excitatory

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RED: Excitatory glutamatergic pathways, BLUE: Inhibitory GABAergic pathways, Magenta: Modulatory dopaminergic pathways GPe: globus pallidus external; GPi: globus pallidus internal; STN: subthalamic nucleus; SNc: substantia nigra compacta; SNr: substantia nigra reticulata

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Cortex (stimulates) → Striatum (inhibits) → "SNr-GPi" complex (less inhibition of thalamus) → Thalamus (stimulates) → Cortex (stimulates) → Muscles, → (hyperkinetic state)

Cortex (stimulates) → Striatum (inhibits) → GPe (less inhibition of STN) → STN (stimulates) → "SNr-GPi" complex (inhibits) → Thalamus (stimulating less) → Cortex (stimulating less) → Muscles, → (hypokinetic state)

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FUNCTIONS OF BASAL GANGLIA

Voluntary motor activities

Regulatory

Procedural learning

Routine behaviors (Habits)

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FUNCTIONS OF BASAL GANGLIA

1.Voluntary motor activities

Plan, Programming

Initiate

Maintain (Tone)

2. Regulatory

Cognitive (thinking)

Emotional functions

Voluntary control of eye movement

3. Procedural learning

4. Routine behavior ( habits)

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Functions 1. Planning & programming (discharge before

movement begins ) . 2. Motor control of the final common pathway . 3. Muscle tone (lesion increases). 4. Cognitive functions (Frontal cortex) Lesions disrupt

performance . 5. Speech , lesion of left caudate results in disturbed

speech dysarthria .

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Metabolic characteristics High Copper content . Wilsons disease (Copper

intoxication): Ceruloplasmin is low, Lenticular degeneration .

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Disorders of movement in Basal ganglia disease

1. Hyperkinetic: Excessive abnormal movement i.e.

chorea, athetosis, ballism

2. Hypokinetic: Slow movements i.e. akinesia,

bradykinesia .

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HYPERKINESIA

Chorea: Rapid involuntary “ dancing” movements

Athetosis: Continuous , slow writhing movements .

Ballism (Hemiballismus): Involuntary flailing ,

intense and violent movements

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HYPOKINESIA

Akinesia: Difficulty in initiating movement

Braykinesia :Slowness of movement .

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Parkinson’s disease: Paralysis Agitans

Parkinson 1. Slow degeneration / loss of dopaminergic

nigrostriatal neurons (60-80 %).

2. Phenthiazines(tranquilizers drugs) .

3. Methyl-Phenyl-Tetrahydro-Pyridine (MPTP). Toxic to SN.

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FeaturesTremors: The tremor most apparent at rest

Rigidity: Simultaneous contraction of flexors and extensors, which tends to lock up the limbs. Rigidity agonists and antagonists ( spacticity). Lead-pipe rigidity; cogwheel -catches (mixture of tremer and rigidity)

Akinesia –Bradykinesia: Movements (swinging of arms during walking. Facial expression is masked. Bradykinesia, or "slow movement", is a difficulty initiating voluntary movement, as though the brake cannot be released

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Features

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Pathogenesis

Excitation imbalance Inhibition loss of dopamine inhibition of putamen increases in inhibitory output to GBes decreases inhibitory output of STN increases excitatory output GBis increases inhibitory output to thalamus reduces excitatory drive to cerebral cortex

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Parkinson’s Disease: Treatment(FYI)

Drug Therapy L-DOPA Cholinergic Pallidectomy

Electrical stimulation of Globus pallidus

Tissue transplants

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Huntington’s Disease (Chorea)

Rare onset 30-40s

early as 20s

Degeneration of Striatum Caudate Putamen

GABA & ACh neurons

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Huntingtons Disease

Hereditary , autosomal dominant . Disease of caudate & putamen. Jerky movement of hands toward end of reaching an

object . Chorea Slurred speech and incomprehensive. Progressive Dementia

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Loss of GABA – Cholinergic neurons .

Loss of GABAergic neurons leads to chorea

Loss of Dopaminergic neurons leads to Parkinson's disease .

Huntingtons Disease

Summary of functions of basal ganglia

It play important motor function in starting and stopping motor functions and inhibiting unwanted movement.

It changes the timing and scales the intensity of movements.

Putamen circuit is inhibitory. Executes skilled motor activities for example cutting paper with a scissor, hammering on nail, shooting a basket ball & like throwing a base ball.

Putamen circuit has indirect connection to cortex via thalamus. while caudate has direct connection to the cortex from thalamus.

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Caudate circuit is excitatory, has instinctive function which works without thinking and need quick response. eg. response after seeing a lion.

[Note: effects of basal ganglia on motor activity are generally inhibitory.]

Lesions of the basal ganglia produce effects on contra lateral side of the body

Damage to basal ganglia does not cause paralysis. However it results in abnormal movements

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Summary of functions of basal ganglia

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