Basal Nuclei, Limbic System & Interpeduncular Fossa

Basal Nuclei/ Basal Ganglia:

The basal nuclei are intra-cerebral masses of grey matter situated within the white core of the cerebral hemisphere which forming important parts of the extrapyramidal system.
 
Components:
1.Corpus striatum
  • Caudate nucleus
  • Lentiform nucleus
Larger lateral part - Putamen
Medial smaller part - Globus pallidus
2. Amygdaloid body
3. Claustrum


Note:
Functionally basal ganglia also include substantia nigra of the midbrain & subthalamic nuclei of diencephalon.
Corpus striatum is divided into lentiform & caudate nucleus by a band of nerve fibers called internal capsule.


Function of Basal Nuclei:
Control automatic & associated movements. (such as swinging of arms during walking)
Influences premotor cortex to control extrapyramidal activities
It controls abnormal involuntary movements
It control group movement for emotional expression
Concerned with planning & programming of voluntary movement
Inhibit unwanted muscular activity & decrease muscle tone


Note:
Basal ganglia does not receive any sensory input from the spinal cord.
Without sending fibers to the spinal cord modify the effect on the spinal cord through projection to motor cortex & extra-pyramidal fibers.
 
They do not initiate movements but are able to adjust the motor commands.
* Basal ganglia sometimes termed as extrapyramidal nuclei as it influences the quality of motor performance.
 
 
Connection of Basal Nuclei or Corpus Striatum with other parts
 
Caudate nucleus & putamen is the main afferent nuclei while globus pallidus is the outflow part (efferent part).
*  Caudate nucleus receives fibers mainly from the cerebral cortex, thalamus & substantia nigra.
*  Globus pallidus sends fibers to the thalamus, subthalamus, substantia nigra, red nucleus.
 
Different pathways are related to different neurotransmitters like dopamine, glutamate, acetylcholine & GABA.
Nigrostriate fibers are related to the dopamine pathway.
 
Main Afferents Fibers:
Corticostriate Fibres:
Caudate nucleus & putamen receives axons from cerebral cortex.
Thalamostriate Fibers:
Thalamus send large no. of axons to caudate nucleus & putamen.
Nigrostriate fibers:
Neurons in the substantia nigra sends axons to caudate nucleus & putamen.

Important efferent fibers:
Striatonigral fibers:
Fibers pass from caudate nucleus & putamen to substantia nigra
Straiatopallidal fibers:
Fibers from caudate & putamen to globus pallidus.


Disorders of basal nuclei:
Lesion of basal ganglia & cerebellum do not cause paralysis.
*  These produce abnormal movements or unwanted involuntary movements or posture or change in tone.
 
Hyperkinetic disorders:
Excessive & abnormal movements like chorea, athetosis, ballism
 
Hypokinetic disorder:
There is a lack of slowness of movements such as Parkinson’s disease.
 
Parkinson’s disease:
Occur due to Dopamine deficiency in corpus striatum result from the destruction of substantia nigra or lesion in nigrostriate fibers.
 
Sign-symptoms
  • Hypertonicity or muscular rigidity
  • Involuntary tremors / Resting tremor
  • Gait disturbance
  • Akinesia:
    Voluntary movements may be impossible.
    Serious difficulty in initiating movements
  • Loss of facial expression / Mask like face
 
L-dopa (a precursor of dopamine) is used as a replacement therapy in Parkinsonism.
Because dopamine, the normal neurotransmitter in the striatum, is reduced in these cases.
 
The nigrostriate fibers are considered important in the genesis of Parkinsonism tremor, since its neurons utilize dopamine in the neurotransmission.
 
Dopamine is not directly used in treatment because of its high polarity, it cannot easily cross the Blood-Brain Barrier (BBB).
It is very hard to treat the patient of the brain because normal drugs cannot cross the BBB easily.
 
Chorea:
Means dancing involuntary movements
 
 
Limbic system:

The limbic system means entire neural circulation that controls the emotional, behavior & motivational drives.
(Limbus=means ring-shaped)
 
The limbic lobe is a composite bordering zone between the cerebrum and diencephalon.
*  It is somehow ring-shaped.
* It is associated with basic survival behavioral control system
 
Constituents of limbic system:
Olfactory nerve, Olfactory bulb & tract
Septal region
Anterior nucleus of thalamus
Mammilothalamic tract
Hypothalamus (mainly mammillary bodies)
Limbic Lobe consisting of cingulate gyrus, uncus, parahippocampal gyrus
Hippocampus Formation including hippocampus, dentate gyrus, longitudinal striae, indusium griseum
Fornix


Tips:
Mammilothalamic tract is the bundle of nerve fibers connecting the mammillary body & anterior nucleus of the thalamus.
 
Function of the limbic system
The main object of the limbic system is to meet the needs of primitive life that is food and sex.
Food is necessary for survival of individual & sex for survival of the species.
  1. It controls food habits necessary for the survival of the individual.
  2. It controls sex behavior necessary for the survival of the species.
  3. It controls emotional behavior like joy, sorrow, fear.
  4. Convert recent memory to long term memory.
 
Applied anatomy:
Hippocampus can be regarded as the cortical center for autonomic reflexes.
Hippocampal amygdala complex is related to the memory of recent events. Lesions related to a loss of recent memory only.
The patient is unable to commit any new facts to memory and does not remember recent events.
Destruction of olfactory nerve results in loss of the sense of smell (anosmia).


 
Interpeduncular fossa:
Interpeduncular fossa is a rhomboid-shaped fossa when seen from the inferior surface of the base of the brain.
 
Boundary:
Anteriorly:
Optic chiasma
Anterolaterally:
Optic tract
Posterolaterally:
Crus cerebri of midbrain
Posteriorly:
Upper part of Pons
 
Content of fossa
  • Mammillary body
  • Posterior perforated substances
  • Infundibulum
    (A narrow stalk that connects the pituitary gland)
  • Oculomotor nerve
Note: This fossa is surrounded by a circle of Willis
 
Clinical importance:
In head injury, the contents of the interpeduncular fossa is usually injured.