Basal Ganglia Flashcards
What is the basal ganglia
The basal ganglia are the scattered masses of
gray matter submerged in the subcortical
substance of the cerebral hemisphere
The basal ganglia is part of what system
It is part of the extrapyramidal system which modulates motor activities.
Components of the basal Ganglia
Corpus Striatum
Substantia nigra
Subthalamic nucleus of Luys.
Where is the corpus striatum located
It is situated at the base of the cerebral hemisphere in close relation to the thalamus.
Corpus striatum is divided into two by
Internal capsule.
Parts of corpus striatum
Caudate nucleus.
Lenticular nucleus.
Caudate nucleus is related to what part of the brain throughout its length
The lateral ventricle of the ventricular system of the brain
Caudate nucleus has two portions
A head portion and a tail portion.
Caudate nucleus lies where
It lies medial to the internal capsule.
Describe the head portion
It bulges into the lateral ventricle and
is situated rostral to the thalamus.
Describe the tail portion
The tail is long and arched. It extends along the
dorsolateral surface of the thalamus and ends
in the amygdaloid nucleus.
Lenticular nucleus is located where
It is situated lateral to internal capsule
What divides the lenticular nucleus into two portions
A vertical plate of white matter called external medullary lamina.
What are the two portions of the lenticular nucleus
Outer putamen
Inner globus pullidus
Where is substantia nigra located
Below the red nucleus
Substantia nigra is made up of
Large pigmented cells( contains high quantity of iron )
Small non pigmented cells
Where is subthalamic nucleus of Luys located
It is situated lateral to red nucleus and dorsal or posterior to substantia nigra
Next 4 questions will be on connections of the basal ganglia
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How does different components of the corpus striatum on the same side gets connected
They get inter connected by intrinsic fibers
What of different components of corpus striatum on each side
They get connected to those of the opposite side by commisural fibers
Mention some connections of the basal ganglia
1.Putamen to globus pallidus
2. Caudate nucleus to globus pallidus
3. Caudate nucleus to putamen.
List five functions of the basal ganglia
CONTROL OF MUSCLE
TONE.
Control of motor activity
Control of reflex muscular activity.
CONTROL OF AUTOMATIC
ASSOCIATED MOVEMENTS.
Role in Arousal mechanism.
How does the basal ganglia control muscle tone
The basal ganglia control the muscle tone.
The gamma motor neurons of spinal cord are responsible for development of tone in the
muscles.
The basal ganglia decrease the muscle tone by inhibiting gamma motor neurons through
descending inhibitory reticular system in the brainstem.
During lession of basal ganglia what happens
Muscle tone increases leading to rigidity
Three things are involved in control of motor activity what are they
Regulation of voluntary movements
Regulation of conscious movements
Regulation of unconscious movements
Describe how basal ganglia regulate voluntary movement
Movements during voluntary motor activity
are initiated by the cerebral cortex.
▣ However, these movements are controlled by
the basal ganglia, which are in close association
with the cerebral cortex.
▣ The basal ganglia control the motor activities
because of the nervous (neuronal) circuits
between the basal ganglia and other parts of
the brain involved in motor activity.
Neuronal circuits arise from three areas of the
cerebral cortex:
a. Premotor area
b. Primary motor area
c. Supplementary motor area
▣ All these nerve fibers from the cerebral cortex
reach the caudate nucleus. From here, the fibers
go to the putamen.
▣ Some of the fibers from the cerebral cortex go
directly to the putamen also.
The putamen sends fibers to globus pallidus.
Fibers from here run towards the thalamus,
subthalamic nucleus of Luys and substantia
nigra.
▣ The subthalamic nucleus and substantia nigra
are in turn, projected into thalamus.
▣ Now, the fibers from the thalamus are projected
back into the primary motor area and other two
motor areas, i.e. premotor area and
supplementary motor area.
Describe how basal ganglia regulate conscious movements
Fibers between the cerebral cortex and caudate
nucleus are concerned with regulation of
conscious movements.
▣ This function of the basal ganglia is also known
as the cognitive control of activity.
▣ For example, when a stray dog barks at a man,
immediately, the person understands the
situation, turns away and starts running.
Describe how basal ganglia regulates unconscious movement
Cortical fibers reaching the putamen are
directly concerned with regulation of some
subconscious movements, which take place
during trained motor activities, i.e. skilled
activities such as writing the learnt alphabet,
paper cutting, nail hammering, etc.
How does basal ganglia control reflex muscular activity
The basal ganglia are responsible for the
coordination and integration of impulses for reflex activities e.g visual
and labyrinthine reflexes which are important in
maintaining the posture.
During lesion of basal ganglia, the postural
movements, especially the visual and labyrinthine
reflexes become abnormal.
These abnormal movements are associated with rigidity.
Rigidity is because of the loss of inhibitory influence from the cerebral cortex on spinal cord
via basal ganglia.
How does basal ganglia control automatic associated movements
Automatic associated movements are the
movements in the body, which take place along
with some motor activities.
▣ Examples are the swing of the arms while
walking, appropriate facial expressions while
talking or doing any work.
▣ The Basal ganglia are responsible for the
automatic associated movements.
Describe the role of basal ganglia in arousal mechanism
.Globus pallidus and red nucleus are involved
in arousal mechanism because of their
connections with reticular formation
Extensive lesion in globis pullidus cause
Drowsiness leading to sleep
List neurotransmitters released by the basal ganglia and their functions
- Dopamine released by dopaminergic fibers from
substantia nigra to corpus striatum (putamen and
caudate nucleus: dopaminergic nigrostriatal fibers):
deficiency of dopamine leads to parkinsonism - Gammaaminobutyric acid (GABA) secreted by
intrinsic fibers of corpus striatum and substantia nigra.
Acetylcholine released by fibers from cerebral
cortex to caudate nucleus and putamen - Substance P released by fibers from globus pallidus
reaching the substantia nigra - Enkephalins released by fibers from globus pallidus
reaching substantia nigra - Noradrenaline secreted by fibers between basal
ganglia and reticular formation - Glutamic acid secreted by fibers from subthalamic
nucleus to globus pallidus and substantia nigra.
Which neurotransmitters are inhibitory fibers
GABA
Dopamine
