Basal Ganglia (Edit)

Objectives: Anatomy of the basal ganglia and

describe the parts

Describe the main connections and its functions

Functions and disorders of the basal ganglia

BASAL GANGLIA BASAL : relating to, situated at, or

forming the base

GANGLIA : any of certain masses of gray matter in 

the brain

The Basal ganglia located mainly lateral to and surrounding the thalamus, occupying a large portion of the interior regions of both cerebral hemispheres

Constitutes another accessory motor system that functions usually not by itself but in close association with the cerebral cortex and corticospinal motor control system

Receive most of their signal from the cerebral cortex itself and also return almost all their output signals back to the cortex.

The term basal ganglia, as generally used by anatomists, refers to some or all of the major telencephalic subcortical nuclear masses lying at the base of the forebrain.

Paired clusters of gray matter deep in each cerebral hemisphere.

BASAL GANGLIA COMPONENTS

a) Caudate Nucleus -comma or C shaped mass of gray

matter related throughout its extent to the surface of the lateral ventricle.

Parts:

head – lies rostral to the thalamus and bulges into the anterior horn of the lateral ventricle. The head of the caudate nucleus and the putamen are separated by fibers of the anterior limb of the internal capsule.

*Internal Capsule: - is a space that lies between the caudate

and the putamen. - formed by fibers projecting to and from the

cerebral cortex. Forms two major limbs: a. Anterior limb

: separates the head of the caudate nucleus and the putamen

b. Posterior limb : Larger: Between the thalamus and the Globus Pallidus

body – extends along the dorsolateral border of the thalamus, from which it is separated by the stria terminalis and the terminal vein.

tail – caudal portion that sweeps into the temporal lobe in the roof of the inferior horn of the lateral ventricle and comes into relationship with the central nucleus of the amygdaloid complex.

b) Putamen - Largest and most lateral portion of the corpus

striatum- Lies between the external capsule and the lateral

medullary lamina of the globus pallidus

* Corpus Striatum - caudate nucleus and the putamen together

c) Globus pallidus or pallidum -forms the smaller and inner part of the

lentiform nucleus, lies medial to the putamen

* Lentiform or Lenticular nucleus : The putamen and the globus pallidus together

subdivisions:Lateral medullary lamina/external segment – external

surface of the pallidum at its junction with the putamen

Medial medullary lamina/internal segment – divides the globus pallidus into:

a. internal b. external segments

Accessory medullary lamina/– divides the internal segment into:

a. outer b. inner portions.

d) subthalamic nucleus - located in the midbrain just below the thalamus- has the shape of a thick biconvex lens

e) substancia nigra- Lies anterior;y in the superior mesencephalon.sheet

of neurons containing dark pigment neuromelanin present to the crus cerebri in midbrain

- divide into: Pars compacta – dopaminergic and cholinergic

neurons Pars reticulate - GABAergic neurons

* Internal capsule – a separate entity, is a space that lies between the caudate and the putamen.

* The caudate nucleus and the putamen together are referred to as the corpus striatum

* The putamen and the globus pallidus together form the lentiform or lenticular nucleus

* The striatum and pallidum form the core structures of the basal ganglia.

• The substancia nigra and the subthalamic nucleus are the control structures because they are thought to exert a profound modulatory influence on the core structure of the basal ganglia.

NEURONAL CIRCUITRY OF THE

BASAL GANGLIA

What are the primary functions of the basal ganglia? A) Functions in executing patterns of

motor activity

B) Functions in cognitive control of sequences of motor patterns

C) Functions in changing the timing and scaling he intensity of movements

2 major circuits:

1. Putamen circuit

2. Caudate circuit

A) Executing patterns of motor activity - the putamen circuitFunction in association with the corticospinal

system to control complex patterns of motor activity.

Eg: writing of letters of alphabet.

When there is a serious damage to the basal ganglia, the cortical system of motor control can no longer provide these patterns. Instead, one’s writing becomes crude, as if one were learning for the first time how to write.

-other patterns that require the basal ganglia are:

cutting paper with scissorshammering nailsshooting a basketball through a hooppassing a footballthrowing a baseballthe movements of shoveling dirtmost aspects of vocalizationcontrolled movements of the eyes

…etcMost of which are performed subconsciously.

THE PUTAMEN CIRCUIT

The putamen circuit begin mainly in the premotor and supplementary areas of the motor cortex and in the somatosensory areas of the sensory cortex.

Next they pass to the putamen (mainly bypassing the caudate nucleus), then to the internal portion of the globus pallidus, next to the ventroanterior and ventrolateral relay nuclei of the thalamus, and finally return to the primary motor cortex.

Ancillary circuit- Pass from the putamen through the

external globus pallidus, the subthalamus, and the substancia nigra – finally returning to the motor cortex by way of the thalamus

Main inputs: - main inputs to the putamen circuit are

mainly from those parts of the brain adjacent to the primary motor cortex but not much from the primary motor cortex itself.

Main outputs:- Its outputs go mainly back to the primary

motor cortex or closely associated premotor and supplementary cortex.

Abnormal functions in the Putamen circuit:

How the putamen circuit function to help execute patterns of movement is poorly known.

However…

When a portion of the circuit is damaged or blocked, certain patterns of movement become severely abnormal.

Examples:Athetosis- a lesion in the globus pallidus.- a writhing, involuntary movement especially affecting the hands, face, and tongue. Usually a form of cerebral palsy.

Hemiballismus- a lesion in the subthalamus- sudden flailing movements of an entire limb.

Chorea- multiple small lesions in the putamen - flicking movements in the hands, face, and other parts of the body.

Parkinson’s disease-Lesion in the substancia nigra- severe disease of rigidity, akinesia, and tremors

B) Cognitive Control of Sequences of Motor Patterns – Caudate Circuit

Cognition- Thinking processes of the brain, using

both sensory input to the brain, plus information already stored in memory.

Cognitive Control of Motor Activity - Motor actions that occur as a consequence

of thoughts generated in the mind.

THE CAUDATE CIRCUIT

The caudate nucleus extends into all lobes of the cerebrum, beginning anteriorly in the frontal lobes, then passing posteriorly through the parietal and occipital lobes, and curving forward again like the letter “c” into the temporal lobes.

After the signals pass from the cerebral cortex to the caudate nucleus, they are next transmitted to the internal globus pallidus, then to the relay nuclei of the ventroanterior and ventrolateral thalamus, and finally back to the prefrontal, premotor and supplementary motor areas of the cerebral cortex.

But, with almost none of the returning signals passing directly to the primary motor cortex.

Instead, the returning signals go to those accessory motor regions in the premotor and supplementary motor areas that are concerned with putting together sequential patterns of movement lasting 5 seconds or more instead of exciting individual muscle movements.

Example: A person seeing a lion approach and

then responding instantaneously and automatically by:

- Turning away from the lion- Beginning to run- And even attempting to climb a tree or

play dead.

Thus, cognitive control of motor activity determines subconsciously, and within seconds, which patterns of movement will be used together to achieve a complex goal that might itself last for many seconds.

C. Change the timing and to scale the intensity of movements

2 Important capabilities of the brain in controlling movements:

1. To determine how rapidly the movement is to be performed

2. To control how large the movement will be.

The basal ganglia is not alone in performing these functions. It however works in close association with the cerebral cortex.

One especially important cortical area is the posterior parietal cortex.

Since the caudate circuit functions mainly with the association areas of the cerebral cortex such as the posterior parietal cortex, presumbaly, the timing and scaling of movements are functions of this caudate cognitive motor control circuit.

Posterior parietal cortex - the locus of the spatial coordinates for

motor control of all parts of the body, as well as for the relation of the body to its parts to all its surroundings.

Damage to the posterior parietal cortex causes:

Agnosia -an inability to accurately perceive objects through normally functioning

sensory mechanisms.

The px ability to copy the left side of the drawings is severely impaired. Also, such a person will try to avoid using his/her L hand, L arm, or other portions of his/her L side of the body for the performance of tasks, or even wash this side of the body (personal neglect syndrome), almost not knowing that these parts of his/her body exist.

PUTAMEN CIRCUIT VS CAUDATE

CIRCUIT

PUTAMEN CIRCUIT CAUDATE CIRCUITPARTS COVERED Extends only to parts of

the cerebral cortexExtends to all lobes of the cerebral cortex

INPUT From parts of the brain adjacent to the primary motor cortex of the cerebral cortex

From association areas of the cerebral cortex

OUTPUT Almost all signals go back to the primary motor cortex or closely associated premotor and supplementary cortex

Almost none of the signals go back to the primary motor cortex

SIGNALS Does not pass through the caudate nucleus

Pass through the caudate nucleus

ANCILLARY CIRCUIT Yes None

MAIN FUNCTION Execute patterns of motor activity

Cognitive control of sequences of motor patterns

SPECIFIC NEUROTRANSMITER SUBSTANCES IN THE

BASAL GANGLIA SYSTEM

1. Dopamine Pathway (I and E) - From substancia nigra to the caudate

nucleus and putamen

2. Gamma-aminobutyric acid (GABA) pathway (I)

- From caudate nucleus and putamen to the globus pallidus and substancia nigra

3. Acetycholine (Ach) Pathway (I)- From the cortex to the caudate nucleus and

putamen

4. Other pathways - From the brain stem that secrete

norepinephrine (E), serotonin (I), enkephalin (I), and several other neurotransmitters in the basal ganglia, and other parts of the cerebrum.

Glutamate pathways - provide most excitatory signals that

balance out the large numbers of inhibitory signals transmitted especially by the dopamine, GABA, and serotonin inhibitory transmitters.

CLINICAL SYNDROMES RESULTING FROM A

DAMAGE TO THE BASAL GANGLIA

2 classifications1. HYPOKINETIC DISORDERS- Characterized by significant impairments

in movement initiation (akinesia)- Reduction in the amplitude and velocity

of voluntary movement (bradykinesia)- Accompanied by muscular rigidity and

tremor at rest.- Parkinson’s Disease is the best known

example

Parkinson’s disease Results from wide destruction of the

substantia nigra (the pars compacta) that sends dopamine-secreting nerve fibers to the caudate nucleus and putamen.

characteristics:

a. Muscular rigidity - - Heightened resistance to passive movement, but independent of velocity

of that stretch or movement

b. Involuntary/resting tremor - - occurs during all waking hours - occurs when the person is at rest - involves primarily the digits, the head, and the lips

c. akinesia - serious difficulty in initiating movement

d. Postural instability - Stooped posture - caused by impaired postural reflexes, - Leads to poor balance and falls

e. Dysphagia – difficulty in swallowing

f. Mask-like face,

g. Infrequent blinking of the eyes

h. shuffling gait with small steps disturbances

i. speech disorder (slow dysarthric speech)

j. fatigue

Tx: L-Dopa administration

ameliorates many of the symptoms, especially therigidity and akinesia.

provide transient symptomatic relief but does not reverse the neuronal destruction or arrest disease progression

Treatment with L-Deprenyl.

inhibits monoamine oxidase (destroys dopamine after it has been secreted).

Slows the destruction of the dopamine-secreting neurons in the substantia nigra.

Treatment with transplanted fetal dopamine cells

*disadvantage: cells do not live for more than a few months; from aborted fetuses

Treatment by destroying part of the feedback circuitry in the basal ganglia.

*disadvantage: can cause serious neurological damage

2. HYPERKINETIC DISORDERS

- Characterized by excessive motor activity in the form of involuntary movements (dyskinesia) and varying degrees of hypotonia.

- Huntington’s Disease is the best known example

Huntington’s Disease Hereditary disorder that usually begins causing

symptoms at age 30 to 40 years Caused by an abnormal gene CAG

characteristics: Flicking movements in individual muscles Progressive severe distortional movements of

the entire body. Severe behavioral disturbances with dementia Motor dysfunctions.

TYPES OF DYSKINESIA OCCURRING IN

ASSOCIATION WITH BASAL GANGLIA DSE’S:

1. TREMOR- most common form of dyskinesia- rythmic, alternating, abnormal, involuntary

activity, with regular frequency and amplitude

A. Resting tremor B. Intention Tremor - evident during voluntary and associated

movements, ceases when patient is “at rest”.

- Tremor is exaggerated when the patient is anxious, self-conscious, or exposed to cold.

2. ATHETOSIS- slow, writhing, vermicular, involuntary movements involving

particulary the extremities.

- May also involve axial muscle groups and the muscles of the face and neck.

- Movements blend with each other giving the appearance of a continuous mobile spasm.

- Occurs contralateral to the lesion

TORSION DYSTONIA – movements producing severe torsion of the neck, shoulder girdle, and pelvic girdle.

3. CHOREA- brisk, graceful series of successive complex, involuntary

movements

- Resemble fragments of purposeful voluntary movements

- Involve primarily distal portions of the extremities, muscles of facial expression, tongue, and deglutitional musculature.

A. Sydenham’s chorea- Occurs in childhood- Recover in a short time- Associated with rheumatic heart dse

B. Huntington’s chorea

4. BALLISM- Represents most violent form of dyskinesia- Violent, puposeful, flinging, movement- Involves primarily the proximal appendicular

musculature and muscles about the shoulder and pelvic girdles.

- Represents most violent form of dyskinesia- With marked hypotonus

HEMIBALLISM – unilateral lesion on the subthalamic nucleus occurring on the contralateral side

Carpenter’s Human Neuroanatomy – Andre Parent

Medical Physiology – Guyton and Hall

Pathologic Basis of Diseases - Robins and Cotran

Reporters: Donna BalancioEloisa FoyaganMylene Precious Sapida