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Basal ganglia


  1. The basal ganglia, like the cerebellum, constitute another accessory motor system that function not by itself but in close association with the cerebral cortex and corticospinal motor control system. In fact, the basal ganglia receive most of their input signals from the cerebral cortex itself and also return almost all their output signals back to the cortex.
  2. The basal ganglia consist of caudate nucleus, Putamen, Globus pallidus, Subthalamic nucleus and substantia nigra. Substantia nigra is divided into pars compacta and pars reticulata. Caudate nucleus and putamen are collectively called the striatum which receive most of the afferent input coming to the basal ganglia. Globus pallidus and Substantia nigra are the principal output nuclei, i.e., the efferents arise from these.
  3. The basal ganglia are involved in planning and programming of movement or more broadly, in the process by which an abstract thought is converted into a voluntary action. Like, lateral cerebellum, neurons in the basal ganglia discharge before the movements begin. They influence the motor cortex via the thalamus, and corticospinal tract is the final common pathway to motor neuron. Putamen circuit is involved in complex pattern motor activity and skilled movement.
  4. Basal ganglia is part of extrapyramidal system and therefore are involved in regulation of tone and posture.
  5. The basal ganglia, particularly the caudate nuclei, also play a role in some cognitive process so, caudate nucleus plays a major role in cognitive control of motor activity.

Limbic system

In the vicinity of corpus callosum and diencephalon are a number of features that have come to be known collectively as limbic system. It plays a role in abstract functions as emotion, behavior, mood and memory. The limbic system consists of:-

  1. Olfactory pathway comprising olfactory nerves, olfactory bulb, olfactory nucleus and olfactory tracts.
  2. Pyriform lobe (including uncus and entorhinal area).
  3. Amygdaloid body and its efferent pathways (stria terminalis, ventral amygdalofugal fibres)
  4. Hippocampal formation comprising indusium griseum and longitudinal striae, gyrus fasciolaris, dentate
  5. gyrus, hippocampus, parahippocampal gyrus, subicular complex, entorhinal cortex, alveus, fimbria and fornix.
  6. Limbic lobe which includes septal area, cingulate gyrus, parahippocampal gyrus.
  7. Hypothalamus, anterior nucleus of thalamus, habenular nucleus, interpeduncular nucleus, mid brain tegmental nuclei, stria medullaris thalami, fasciculus retroflexus, medial forebrain bundle.

Anterior perforated substance

  1. It is an irregularly quadrilateral area perforated by numerous small blood vessels penetrating lateral lenticulostriate arteries arising from I st part of middle cerebral arteries and lying in front of optic tract and behind olfactory trigone.
  2. It is a part of basal forebrain, is a region of gray matter in limbic system immediately posterior to gyrus rectus. Its gray matter is confluent above with corpus striatum. It is bounded: -
    1. Medially: Medial relations are :-
      1. Anteromedial: Medial olfactory striae.
      2. Immediate medial: Optic tract and chiasma.
      3. Posteromedial: Optic tract.
    2. Laterally: Lateral relations are :-
      1. Anterolateral: Lateral olfactory stria.
      2. Immediate lateral: Limen insulae (gyrus ambiens)
      3. Posterolateral: Uncus.

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