Human Brain: Cerebrum and Diencephalon.

 Human Brain: Cerebrum and Diencephalon.

Human Brain:

  • The brain and the spinal cord are the Central Nervous System, and they represent the main organs of the nervous system. 

  • The spinal cord is a single structure, whereas the adult brain is described in terms of four major regions.

    1. The Cerebrum.

    2. The Diencephalon.

    3. The Brain Stem.

    4. The Cerebellum.

  1. The Cerebrum:

  • The cerebrum makes up most of the mass of the brain.

  • It deals with the ability to read, write, speak, and to make calculations, our creativity and memory.

  • The wrinkled area of the cerebrum is called the “Cerebral Cortex”.

  • The outer portion of the brain appears “gray” in color and called “Gray matter” which mainly contains cell bodies of the neurons.

  • The inner portion appears “White” in color and is called “White matter” which mainly contains the axons.

  • The folds of the gray matter are called “Gyri (Single =Gyrus)”.

  • The deeper grooves between the gyri are called “Fissures” while the shallow ones are called “Sulci (Single =Sulcus)”.

  • These fissure divides the cerebrum into five prominent lobes,

    1. Frontal lobe.

    2. Parietal lobe.

    3. Temporal Lobe.

    4. Occipital lobe.

    5. Central lobe (Insula).

  • The biggest fissure called “Longitudinal fissure” divides the cerebrum into two “Cerebral Hemispheres”.

  • The right and left cerebral hemisphere are joined together by a thick band of white matter called “Corpus callosum”.

Lobes of Cerebrum:

  • Each cerebral hemisphere is further subdivided into four globes,

    • Frontal lobe.

    • Parietal lobe.

    • Temporal Lobe.

    • Occipital lobe.

  • The fifth lobe “Central Lobe (Insula) lies deep.

  • The main sulci and gyri that divide the lobes are as follows,

    • Lateral Sulcus: Separates Frontal lobe and Temporal Lobe.

    • Parieto-occipital sulcus: Separates Parietal lobe and Occipital Lobe.

    • Central Sulcus: Separates Frontal Lobe and Parietal Lobe.

  • The cerebral cortex contains 52 identified areas of specific functions called “Brodmann areas”

  1. Frontal lobe:

  • The Frontal Lobe contains most of the ‘Dopaminergic Neurons’ of the brain.

  • The prominent areas of the frontal lobe are as following,

    • Motor Area: Controls muscles of speech, fine movements of fingers and limbs.

    • Supplementary Motor Area:  Deals with altitudinal movements.

    • Premotor Area: Involuntary muscle movements for specific movements.

    • Broca’s Area: Deals with ability to speech. 

  • It is concerned with emotions, reasoning, planning, movement, and parts of speech.

  • It is also involved in purposeful acts such as creativity, judgment, and problem solving, and planning.

  1. Parietal lobe:

  • Major areas include;

    • Primary Sensory Area: Deals with sensations like temperature, touch and pain.

    • Secondary Sensory Area: It deals with complex sensations of the above.

    • It also has language functions.

  1. Temporal Lobe:

  • This lobe deals with the sensation of sound.

  1. Occipital lobe:

  • This lobe deals with the sensation of vision.

  • The area is involved with the brain's ability to recognise objects.

Diencephalon:

  • Present between Cerebrum and brainstem.

  • The major regions of diencephalon are,

    • Thalamus.

    • Hypothalamus.

    • Epithalamus.

  1. Thalamus:

  • Makes up 80% of the diencephalon but measures only 3cm.

  • Functions:

    • Relay the sensory information from “Skin, Viscera, special organs and pressure” before entering the cerebrum.

    • Regulation of Autonomic Activities.

    • Maintenance of consciousness.

  1. Hypothalamus: 

  • As the name suggests it is situated just below the thalamus and above the pituitary gland.

  • It has four main regions,

    • Mammillary Region.

    • Tuberal region.

    • Supraoptic region.

    • Preoptic region.

  • Functions:

    • Controls the ANS:

      • Regulates the smooth muscles and cardiac muscle contractions.

      • Regulates secretions of many glands.

      • Regulates contraction of urinary bladder,

      • Regulates heart rate.

      • Regulates the peristalsis movement of GIT.

    • Production of Hormones.

      • Has direct control over the Pituitary gland and regulates many secretions.

      • Hypothalamus itself secretes many regulatory hormones such as,

        • corticotropin-releasing hormone.

        • Dopamine

        • Growth hormone-releasing hormone,

        • Somatostatin,

        • gonadotropin-releasing hormone

        • thyrotropin-releasing hormone.

    • Regulation of Emotions and Behaviour.

      • Along with the “Limbic System”  it plays an important role in expression of various emotions like anger, love, pain, pleasure etc.

    • Regulation of Body Temperature:

      • Maintains body temperature at normal values.

    • Regulation of eating and drinking:

      • Regulates eating and drinking habits.

    • Regulates Circadian Rhythms:

      • Regulates pattern of body clock and consciousness.

  1. Epithalamus:

  • It is a small area the size of a pea.

  • Present superior and posterior to thalamus.

  • It consists of,

    1. Pineal Gland

    2. Hearbanuclear nuclei.

  • Pineal gland secretes a hormone called “Melatonin” which is associated with production of sleep and aging.

Commonly asked questions.

  1. Give the functions of cerebrum.

  2.  Describe the functions of hypothalamus.

  3. Draw a well labelled diagram of CNS and describe various parts of the human brain.

  4. Draw a well labelled diagram of CNS

  5. Draw a well labelled diagram of Cerebrum and describe it.

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