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  1. Melatonin is synthesized by pineal parenchymal cells and secreted by them into the blood and CSF.
  2. It is synthesized from serotonin by N-acetylation and O-methylation. Q
  3. Formation and metabolism of melatonin –

Regulation of Melatonin Secretion

  • In humans and all other species studied to date, melatonin synthesis and secretion are increased during the dark period of the day and maintained at a low level during the day-light hours. The remarkable diurnal variation in secretion is brought about by training of the hypothalamus to the light-dark cycle via retino-hypothalmic nerves
  • The hypothalamus in turn causes norepinephrine secretion by the postganglionic sympathetic nerves (nervi conari) that innervate the pineal gland.
  • The norepinephrine acts via adrenergic receptors in the pineal gland to increase interacellular cAMP, and the cAMP in turn produced a marked increase in N-acetyl transferase activity. This results in increased melatonin synthesis and secretion.

Higher Functions of CNS


1.  Cortical organization (Cerebral cortex)

  1. The neocortex is generally arranged in six layers
  2. The neurons are mostly pyramidal cells with extensive vertical dendritic trees
  3. Afferents from the specific nuclei of the thalamus terminate primarily in cortical layer 4, where the non specific afferent are distributed to layers 1 to 4.

2.  Histological structures of cerebral cortex:

  1. Most of the cells are three types: -
    1. Granular (stellate) cells
    2. Fusiform cells and
    3. Pyramidal cells
  2. Granule cells — short axon function mainly as intracortical interneurons. Some are excitory (releasing —glutamate) and others are inhibitory (releasing à GABA)
  3. Pyramidal cells and fusiform cells: à
    1. They give rise to almost all the out put fibers from the cortex.
    2. Pyramidal cells are larger and more numerous than fusiform cells
    3. Pyramidal cell are the source of long large nerve fibers that go all the way to the spinal cord and also give rise to most of the large subcortical association fiber bundles that pass from one major part of the brain to the other.

Brodmann’s Areas


S. No.





Primary sensory area

(Post central gyrus)


3, 1, 2


Primary Motor area

(Pre – central gyrus)




Premotor area




Frontal eye field




Sensory association area


5, 7


Primary visual area

(Visual association area)






Primary auditory area

Auditory association area




41, 42


Broca’s area

Wernicke’s area






Cingulete gyrus

Angular gyrus







  1. Prosopagnosia: the inability to recognize faces due to lesion in the fusiform gyrus on the inferior surface of the right temporal lobe.
  2. Acalculia: a-selective impairment of mathematical ability (calculation), due to lesion in the inferior portion of the left frontal lobe.
  3. Construction Apraxia: Lesions that involves the posterior parietal cortex in the right hemisphere lead to severe difficulties in copying-simple line drawings.
  4. Anosmia à inability to smell.

Prosopagnosia and Visual Agnosia

  • Prosopagnosia - no difficulty with the generic identification of face as face or of a car as       a car, but they cannot recognize the identity of individual face or the make of an individual car.
  • Visual obiect agnosia: when recognition problems become more generalized and extend to the generic identification of common objects, the condition is known as visual object agnosia; the patient is unable either to name a visually presented
  • object or to describe its use.
  • The characteristic lesions in prosopagnosia and visual object agnosia consists of bilateral infarctions in the territ of the posterior cerebral arteries and involve the lingual and fusiform gyri of occipitotemporal cortex. Q\

Balint's syndrome: - (Severe spatial disorientation)

  1. This syndrome is a combination of: ­
    1. Oculomotor apraxia (deficiet in the orderly visuo-motor scanning of the environment)
    2. Optic ataxis (Deficits in accurate manual reaching towards visuat target) and (c) Simultanganosia: - (an inability to integrate visual information in the centre of gaze with more peripheral information for eg - the patient "misses the forest for the trees".
  2. Balint's syndrome results from bilateral dorsal parientallesions Q, common settings include: ­
    1. Water - shed infarction between the middle and posterior cerebral artery territories,
    2. Hypoglycemia
    3. Sagittal sinus thrombosis or
    4. Degenerative disease such as Alzheimer disease.


Gerstmann's syndrome

1.  It is a combination of: ­

a.  Acalculia (impairment of simple arithmetic)

b.  Dysgraphia (impaired writing)

c.   Fingeranomia (inability to name individual fingers)

d.  Right Left confusion (an inability to tell whether a hand, foot or arm of the patient a examiner is an right or left side of the body)

2.   Cause; - Gerstmann's syndrome is commonly associated with damage to the inferior parietal lobule (=Angular gyrus) in the left hemisphere (Dominant side)


Cerebral dominance


Cerebral dominance: Specialization of one hemisphere.

1.  Left hemisphere (Dominant or Categorical hemisphere):

a.  More adept in language and analytical abilities.

b.  Damage:

c.   Severe speech problems.

Right hemisphere (Representational hemisphere):

a.  Most adept at visuospatial tasks,Emotion, Non verbal communication

b.  Damage:

  • Difficulty finding way around house. 08_12



i.     Broca’s area: Inferior frontal gyrus Area 44

  • Involves articulation of speech.
  • Broca’s area sends fibers to the motor cortex which directly controls the musculature of speech.
  • In damage less speech but comprehension is unimpaired. MOTOR or FLUENT APHASIA

ii.     Wernicke’s area: Superior Temporal Gyrus Area 22

  • Involves language comprehension.
  • In damage, language comprehension is destroyed, but speech is rapid without any meaning(senseless). SENSORY or FLUENT APHASIA

iii.     Angular gyrus:

  • Center of integration of auditory, visual, and somatesthetic information.
  • Damage produces aphasia.

Arcuate fasciculus:

  • To speak intelligibly, words originating in Wernicke’s area must be sent to Broca’s area. Connects the two structures.


Limbic System

The limbic system is applied to the part of brain that consist of a rim of cortical tissue around the hilum of cerebral hemisphere and a group of associated deep structures.

Also called rhinocephalon & is phylogenetically the oldest part of cerebral cortex (allocortex) It consists of:

  1. Cingulate gyrus
  2. Septal nuclei
  3. Hippocampal formation:Hippocampus & Dentate nucleus
  4. Amygdala
  5. Median forebrain bundle (MFB) act as pleasure centre

Papez circuit links limbic system to hypothalamus & thalamus and is concerned with Emotions & Memory Fornix from hippocampus à mamillary body of hypothalamus à Anterior nucleus of thalamus


Function of limbic system

  1. Role in Olfaction related memory
  2. Emotional and Behavioural responses
  3. Autonomic responses
  4. Limbic system with Hypothalamus ~ it concerned with ~ sexual behaviour, the emotion of rage  and fear  and motivation
  5. Rage responses - minor stimuli evoke violent episodes - are observed after removal of the neocortex and after destruction of ventro-medial hypothalamic nuclei and septal nuclei in animal with intact cerebral cortices. i.e. emotional effect to a physical stimuli (Rage) is given by cerebral cortices.
  6. Learning & Memory

Emotions have 3 components:

  1. Cognition: Awareness         
  2. AFFECT: feeling itself
  3. Conation: desire to act        
  4. Peripheral Expression: via Hypothalamus i.e HR, BP etc.

The nucleus accumbens is a collection of neurons within the forebrain. It is thought to play an important role in reward, laughter, pleasure, addiction, fear, and the placebo effect. The principal neuronal cell type found in the nucleus accumbens is the medium spiny neuron. The neurotransmitter produced by these neurons is gamma-aminobutyric acid (GABA). Major inputs to the nucleus accumbens include prefrontal association cortices, basolateral amygdala, and dopaminergic neurons located in the ventral tegmental area (VTA). Dopaminergic input from the VTA is thought to modulate the activity of neurons within the nucleus accumbens. These terminals are also the site of action of highly-addictive drugs such as cocaine and amphetamine, which cause a manifold increase in dopamine levels in the nucleus accumbens.


Kluver-Bucy syndrome (KBS) has been considered a direct consequence of bilateral anterior temporal lobe damage resulting from disease or injury.

Features: Hyperphagia, Hypersexuality, Fearlessness, Decreased Emotions, Agnosia & Rage


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