Basal nuclei By Dr. Roberton Gautam - PowerPoint Presentation

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Basal nuclei

By Dr. Roberton Gautam

SR, JNMC ALIGARH

BASAL NUCLEI

The

basal nuclei (or ganglia) are large

subcortical

masses

of grey

matter located inside the white matter in the basal

part of

the cerebral hemisphere

.

Anatomically, the term

basal ganglia include:

(a) corpus striatum,

(b)

claustrum

, and

(c)

amygdaloid

body

.

Functionally, basal ganglia also include

substantia

nigra

,

red nucleus

, and

subthalamus

.

Horizontal section of brain

AXIAL SECTION OF BRAIN

CORONAL SECTION OF BRAIN

CORPUS STRIATUM

The

corpus striatum is situated lateral to the thalamus.

D

ivided

into

the

caudate

nucleus and

the

lentiform

nucleus by a band

of

nerve

fibres

, the

internal capsule.

The

lentiform

nucleus

consists of two

parts

a darker lateral

part

putamen

and

a

medial paler part

globus

pallidus

.

Phylogenetically

, corpus striatum forms two

distinct functional units

the

paleostriatum

and the

neostriatum

.

The

globus

pallidus

is relatively ancient and

termed

paleostriatum

/

pallidum

.

The

caudate nucleus and

putamen

being

recent in development, together form the

neostriatum

/striatum

.

The anterior aspect of a coronal section through the leftcerebral hemisphere.

CAUDATE NUCLEUS

Caudate

nucleus is a large comma-shaped mass of

grey matter

, which surrounds the thalamus and is

itself surrounded

by the lateral ventricle.

The

whole length of

its convexity

projects into the cavity of lateral ventricle

.

Its rounded anterior part in front of

interventricular

foramen

is called its

head

.

The

head

gradually

and

imperceptibly

tapers caudally into the

body

then

into

a tail

,

which merges at its anterior extremity with an

almond shaped

mass

of grey matter called

amygdaloid

body.

The striatum within the left cerebral hemisphere

LENTIFORM NUCLEUS

A

large lens-shaped (biconvex) mass

of grey

matter beneath the

insula

forming the lateral

boundary of

the internal capsule.

In

horizontal section of cerebrum,

it appears

wedge shaped with broad convex base

directed laterally

.

D

ivided

into two parts by a vertical plate of

white matter

(external

medullary

lamina):

an

outer darker part,

the

putamen

and

an

inner lighter part the

globus

pallidus

.

The larger lateral part, the

putamen

consists of

densely

packed

small cells, and is structurally similar to the

caudate nucleus

.

The

globus

pallidus

is smaller medial part and consists

of

large

(motor) cells.

The

globus

pallidus

is

further

subdivided by an

internal

medullary

lamina of white

matter

into

outer and inner segments.

CONNECTIONS OF CORPUS STRIATUM

The

striatum (caudate nucleus and

putamen

) is the

receptive part

while

globus

pallidus

is the

efferent part

(

outflow centre

) of the corpus striatum.

The striatum

receives

fibres

mainly from the

cerebral cortex

, thalamus, and

substantia

nigra

.

The

globus

pallidus

sends

fibres

to the thalamus,

subthalamus

,

substantia

nigra

, reticular

formation, and red nucleus.

Different pathways involve different

neurotransmitters, which

include dopamine, acetylcholine, glutamate,

and

γ-

aminobutyric

acid (GABA).

CLAUSTRUM

Claustrum

is a thin saucer-shaped mass of grey matter

situated between the

putamen

and

insula

.

Its significance is not known.

AMYGDALOID BODY (OR AMYGDALA)

Amygdaloid

body is an almond-shaped mass of grey

matter in

the temporal lobe, lying

anterosuperior

to the tip

of inferior

horn of lateral ventricle.

It

is situated deep to

uncus

.

The

fibres

arising from

amygdaloid

body form

stria

terminalis

.

The

stria

terminalis

is the main efferent tract of the

amygdaloid

body

.

Developmentally it is related to the basal nuclei

but functionally

it is included in the limbic system, and

therefore, shares

its

functions.

SUBSTANTIA NIGRA AND RED NUCLEUS

SUBTHALAMUS (SUBTHALAMIC NUCLEUS)

This small nucleus in the ventral part of the diencephalon,

which looks like a biconvex lens in coronal section. It

is located

caudal to the lateral half of the thalamus

and

inferomedial

to

globus

pallidus

.

It

is separated from

thalamus by

a smaller nucleus called

zona

inserta

.

Caudate nucleus, Amygdaloid Body and

Stria

Terminalis

FUNCTIONS OF THE BASAL NUCLEI

Concerned

with planning and programming

of voluntary movements.

Determine

how rapidly a movement is to be

performed and

how large the movement must

be.

Decrease

muscle tone and inhibit unwanted

muscular activity.

Regulate

the muscle tone and thus help in

smoothening the

voluntary motor activities of the

body.

Control

automatic associated movements, like

swinging of

arms during

walking.

Control

group of movements responsible for

emotional expression.

Control

reflex muscular activity.

Clinical

Lesions of basal ganglia: The lesions of basal

ganglia

result

in various forms of unwanted involuntary

movements and

disturbance in the muscle tone.

These

disorders

include Parkinsonism

chorea,

athetosis

, and

ballismus

.

The Parkinsonism

being the commonest

disorder.

•

Parkinsonism (also called Parkinson’s

disease/paralysis

agitans

): This disease usually occurs after 50 years of

age due

to deficiency of the neurotransmitter dopamine in

the corpus

striatum following a lesion in

substantia

nigra

and/ or

its

nigrostriate

fibres

.

Characteristic

features of Parkinsonism:

–

Resting tremors.

–

Lead-pipe or cogwheel type of muscular rigidity.

–

Pill-rolling movements of hands.

–

Mask-like face or loss of facial expression.

–

Stiff, shuffling gait.

–

Stooped posture.

–

General slowing-down of movements and absence

of associated

movements, such as arm swinging

during walking

.

THANK YOU