12th Zoology

The Brain – Fore Brain, Midbrain, Hindbrain

The Brain 

There are more than a thousand million neurons in the adult human
brain. An estimate shows that the cerebral cortex alone has about 102783000
synapses. Thus the brain is a complex organ.

On structural and functional basis the brain can be divided into 3
regions. They are (1). Fore brain, (2). Midbrain, (3). Hind brain.

Fore Brain (Prosencephalon)

This region of the brain comprises Diencephalon and the cerebrum.
The diencephalon is formed of thalamus and hypothalamus.

Thalamus (Fore brain)

It is the largest part of the diencephalon. This region contains a
cluster of nuclei. Most of the sensory inputs are conducted to the cerebral
cortex through the thalamus. Axons carrying auditory, visual and other
sensory informations synapse with specific nuclei of this region. This
region may also influence mood and general body movements due to strong
emotions such as fear or anger.

Hypothalamus (Fore brain)

This region contains small nuclei and nerve tracts. The nuclei called
mamillary bodies are involved in olfactory reflexes and emotional responses
to odours. The funnel shaped infundibulum from the hypothalamus
connects it to the posterior pituitary or neurohypophysis. This region
controls the secretions of the pituitary gland.

The hypothalamus receives inputs from several sensory systems such
as tongue, nose and external genitalia. It is associated with emotional and
mood relationships. It provides a relaxed feeling. Feeling good after a meal,
rage and fear are also due to this region. It also coordinates responses to the
sleep-wake cycle with other areas.

Cerebrum (Fore brain)

It is the largest part of the brain. It weighs about 1400g in males and
1200g in females. Larger brains are normally associated with larger bodies
and not with greater intelligence.

The grey matter on the outer surface of the cerebrum is the cortex. It
forms clusters deep inside the brain called nuclei. The inner part of the brain,
in between the cortex and the nuclei has white matter named as
cerebral medulla.

Cerebral cortex (Fore brain)

The cortex contains several primary sensory areas. These areas
include taste area, primary auditory cortex for processing auditory stimuli,
visual cortex for perceiving visual images and areas for other cutaneous

The cortical areas adjacent to the primary sensory centers are called
the association areas. These areas are involved in the process of
recognition. For example the sensory stimulus from the retina of the eye
reaches the visual association area of the cortex. Here the visual
information is compared with past experiences. Further this area has
connections with other parts of the cortex, which influence decisions. Thus
visual information is judged several times. This may be one of the reasons
why two people who witness the same event can present somewhat
different versions of what happened.

The primary motor area of the cortex controls many voluntary
movements, especially the finer motor movements of the hands. Muscle groups
such as facial muscles, that have many motor units have greater innervation. They are represented by a large area of the motor cortex.

Anterior to the primary motor area are the premotor area. It is the
staging area in which motor functions are organized before they are
initiated in the motor cortex. For example, if a person decides to lift a hand,
the neurons of the premotor area are stimulated first. This area determines
the order and the degree to which the muscles must contract.

The prefrontal area provides motivation and foresight to plan and
initiate movements. This area is well developed only in primates and
especially in humans. Our emotional behaviour and mood are controlled by
this area.

The midbrain or Mesencephalon

The roof of this region contains four nuclei. The nuclei form mounds.
They are collectively called corpora quadrigemina. It is formed of 2
superiour colliculi or mounds and 2 inferior colliculi or mounds. The
superior colliculi are involved in visual reflexes. They control eye and head
movements. They aid in visual tracking of moving objects. The inferior colliculi
are involved in hearing.

The hindbrain or Rhombencephalon

This part of the brain comprises Cerebellum, Pons and Medulla


This region communicates with other region of the CNS through three
large nerve tracts called the cerebellar peduncles.
The cerebellum consists of following three parts Parts Control

1. flocculonodular balance and maintenance
of muscle tone.

2. vermis – anterior part motor coordination and muscle tone.
3. vermis – posterior part and fine motor coordination and
lateral hemispheres muscle tone.

Cerebellar disfunction may cause decreased muscle tone, imbalance and lack
of co-ordination.


This region relays information from the cerebrum to the
cerebellum. It also contains sleep center and respiratory centers. These
centers along with medulla help to control respiratory movements.

Medulla oblongata

It is the most inferior part of the brain stem. It acts as a conduction
pathway for both ascending and descending nerve tracts. The nuclei inside
medulla oblongata function as centers of several reflexes involved in the
regulation of heart rate, blood vessel contractions, breathing, swallowing,
vomiting, coughing and sneezing.

Related Topics in Zoology:

Bio Zoology All Important Topics

  1. Human Physiology Introduction

  2. Nutrition

  3. Carbohydrates Poly hydroxyaldehydes (or) ketones

  4. Proteins (Polypeptides)

  5. Lipids

  6. Vitamins – Functions Of Vitamins

  7. Deficiency of Vitamin

  8. Minerals – Water – Role of water

  9. Balanced diet

  10. Obesity

  11. Digestive System

  12. Dental Caries (Tooth decay)

  13. Root Canal Treatment

  14. Peptic ulcer

  15. Hernia and Types

  16. Appendicitis (Appendix)

  17. Gall Stones

  18. Hepatitis

  19. Fractures – Types of fractures

  20. Mechanism of fracture

  21. Dislocation of joints

  22. Arthiritis

  23. Rickets and Osteomalacia – Orthopedics

  24. Muscles

  25. Mechanism of muscle contraction

  26. Types of muscle contraction

  27. Myasthenia Gravis

  28. Respiration – Process of pulmonary respiration

  29. Mechanism of Breathing

  30. Regulation of Respiration

  31. Pneumonia Tuberculosis Symptoms Treatment

  32. Bronchitis – Acute bronchitis, Chronic Bronchitis Causes

  33. Circulatory System – Functioning of Human heart

  34. Cardiac Cycle

  35. Coronary blood vessel and its significance

  36. Myocardial infarction

  37. Angina pectoris

  38. Angiogram – Angioplasty

  39. Atherosclerosis

  40. Heart block Echo cardiography Heart Valves

  41. Rheumatic Heart Disease (RHD), ICCU – (Intensive Coronary Care Unit)

  42. Blood Pressure

  43. Heart transplantation

  44. Pulse rate

  45. Cardio Pulmonary Resuscitation (CPR)

  46. Blood – Composition of plasma – Blood cells

  47. Clotting of Blood or Haemostasis

  48. Thrombosis

  49. Nervous system Co-ordination systems

  50. The Brain – Fore Brain, Midbrain, Hindbrain

  51. Memory

  52. Sleep – Types of sleep

  53. Stroke – Brain haemorrhage

  54. Alzheimer – Meningitis (Brain fever)

  55. Conditioned reflex

  56. Electroencephalography EEG

  57. Right and Left brain concept

  58. Spinal cord functioning

  59. Chemical co-ordination – Functions of Endocrine glands

  60. Hypothalamus

  61. Pituitary gland – hormone

  62. Hormones of Neurohypophysis – vasopressin

  63. Thyroid gland

  64. Parathyroid Gland

  65. Pancreas

  66. Adrenal gland

  67. Gonads

  68. Receptor Organs – Eye

  69. Photochemistry of Retinal visual Pigments

  70. Errors of refraction

  71. Optometry – Retinopathy

  72. Cataract – Lens Replacement – Glaucoma – Nyctalopia

  73. Eye Infections and Eye Care

  74. Ear

  75. Mechanism of hearing

  76. Defects of the ear

  77. Hearing Aid – Noise pollution

  78. Skin and functions of skin

  79. Melanin functions

  80. Effects of solar radiation / UV radiation – Skin grafting

  81. Dermatitis

  82. Tongue – Mechanism of Stimulation

  83. Excretion Ureotelism Nephron

  84. Mechanism of urine formation

  85. Renal Failure, Dialysis, Kidney Machines

  86. Kidney stone – Kidney transplantation

  87. Diabetes mellitus

  88. Functioning of male reproductive system

  89. Functioning of female reproductive system

  90. Ovulation and fate of the ovum – Menstrual cycle

  91. Fertilization

  92. Birth control

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