Nervous System: Behaviour, Brain and Parts for Competitive Exams

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Central Nervous System (CNS) and Peripheral Nervous System (PNS)

  • The brain and its constituent parts are the most complex system ever known. With one trillion separate cells, each one in a continuous process of changing in response to chemical signals.
  • From the moment of conception to the moment of death, the biology of the individual is changing.
  • It is in this complexity that our species has found the capability to store the accumulated experience of thousands of generations – to create human culture.
  • Our language, religions, governments, childrearing practices, technologies, economies are all man-made; yet all depend upon the remarkable capacity of the brain to make internal representations of the external world.

Biological Bases of Behavior

The Nervous System

  • Endocrine Glands

The Nervous System

  • The system that controls and regulates the structure and function of the brain, spinal cord, nerves, and the nerve cells; it maintains coordination between the nervous system and the rest of the bodily systems.
  • It is responsible for the internal communication system that ensures the integrated functioning of the various systems.

Some Interesting Facts About the Nervous System

  • The nervous system consists of billions of highly specialized nerve cells called neurons.
  • Nerve impulse is an electrical impulse that travels along the nerves at a speed of around 400km/hour.
  • Every second, a number of these impulses can pass along nerves.
  • Brain cells never re grow; once destroyed or dead, they cannot be replaced.
  • Nerve fibers are very thin and fine in size; a hundred of them lying side by side would fit into just 1mm.
  • The brain is divided into two visible parts or hemispheres; the left hemisphere controls the right side of the body, and the right controls the left side.
  • The total surface area of the cerebral cortex is approximately 2.5sq. ft. If you spread it flat.


A nervous system cell is constituted in such a way that it is specialized in receiving, processing, and/or transmitting information to other cells.

Structure of a Neuron

  • Dendrites: Receivers of incoming signals; branch fibers extending outward from the cell body.
  • Soma: The cell body containing the cytoplasm and the nucleus of the cell; cytoplasm keeps it alive.
  • Axon: The nerve impulses travel from the soma to the terminal buttons through the extended fiber of a neuron i.e.. , axon.
  • Terminal Buttons: Swollen, bulblike structures at one end of the axon; the neuron stimulates the nearby glands, muscles, or other neurons Connection between nerve cells
  • Synapse: the gap between one neuron and the other.
  • Synaptic Transmission: the procedure through which information is relayed from one neuron to another across the synaptic gap.
  • Neurotransmitters: The post synaptic neuron is stimulated by the chemical messages released from neurons; they cross the synapse from one neuron to another.

The Chemical Messages

  • The neurons follow an all-or-none law … . either a neuron will be firing or resting/off.
  • Excitatory Message: The chemical message that makes it more likely that the receiving neuron will fire and the action potential will travel down its axon.
  • Inhibitory Message: The chemical message that inhibits a receiving neuron from firing so that the action potential does not travel down its axon.

Major Varieties of Neurons

  • Sensory Neurons (afferent) : they carry messages toward the Central Nervous System from the sensory receptor cells.
  • Motor Neurons (efferent) : they carry messages away from the Central Nervous System toward the muscles and glands.
  • Inter-Neurons: they relay messages from sensory neurons to other inter-neurons and/or to motor neurons.

Main Parts of the Nervous System

  • The Peripheral Nervous System
  • The Central Nervous System

Central Nervous System (CNS)

  • Brain receives the information from all over the body (primarily in terms of stimulation via sensation) , interprets it, and decides how to respond.
  • The brain՚s function is similar to that of a computer; there is a central processing unit (CPU) , the output comes in, and the CPU analyses it and responds to it.

The Brain

  • The center of the nervous system.
  • The vital organ that is responsible for the functions of seeing, hearing, smelling, tasting, thinking, feeling, remembering, speaking, dreaming, information processing, and a lot more.
  • The regulator of basic survival functions such as breathing, resting and feeding.
  • It is responsible for abstract level functions such as decision making, foresight, and problem solving.
  • The spinal cord is an information highway connecting the PNS to the brain.
  • Information travels to and from the brain by way of spinal cord.

Functions of the Various Structures of the Brain

  • Regulation of the internal systems
  • Reproduction
  • Sensation
  • Motion
  • Adaptation to the varying environmental demands

Structure of Brain

  • The deeply grooved structure lies safely and securely in our skull.
  • The average adult human brain weighs 1.3 to 1.4 kg (approx. 3 pounds) .
  • If you look at it from the outside the brain is pinkish gray in color; soft, spongy, and mottled.
  • The brain contains billions of nerve cells (neurons) and trillions of “support cells” .

Parts of the Brain

The brain is made of three main parts:

a. Fore brain

b. Mid brain

c. Hind brain

Fore Brain

i. Cerebrum

ii. Thalamus

iii. Hypothalamus

iv. Limbic system

Mid Brain

i. Tectum

ii. Tegmentum

iii. Reticular formation

iv. Substantia nigra

Hind Brain

i. Cerebellum

ii. Pons

iii. Medulla oblongata

Brain Stem and Cerebellum

  • Located underneath the limbic system the brain stem, containing four structures, is found in all vertebrates.

It contains four structures:

1. Medulla

  • Located at the top of the spinal cord and continuous with it.
  • Damage to Medulla can be fatal as it is the center responsible for vital functions i.e.. , respiration, heartbeat, and blood pressure.
  • Contains ascending & descending tracts that communicate between the spinal cord & various parts of the brain.
  • At medulla, nerves ascending from the body and descending from the brain cross over; hence the left side of the body is connected to the right side of the brain and vice versa.
  • Contains 3 vital centers:
    • Cardio inhibitory center: regulates heart rate.
    • Respiratory center: regulates the basic rhythm of breathing.
    • Vasomotor center: regulates the diameter of blood vessels.

2. Pons

  • Pons = Latin word for bridge
  • Bridge connecting spinal cord with brain and parts of brain with each other.
  • The pons seems to serve as a relay station carrying signals from various parts of the cerebral cortex to the cerebellum.
  • Nerve impulses coming from the eyes, ears and touch receptors are sent on the cerebellum.
  • The pons also participates in the reflexes that regulate breathing.
  • It has parts that are important for the level of consciousness and for sleep.

3. Reticular formation

  • The reticular formation is a region running through the middle of the hindbrain and into the midbrain.
  • A dense network of nerve cells.
  • It keeps the brain alert even during sleep.
  • It makes the cerebral cortex attend to new stimulation by arousing it.
  • Long fibrous tracts of reticular formation run into the thalamus.
  • Needed for arousal from sleep & to maintain consciousness.
  • Serious damage to reticular formation may result into a coma.

4. Thalamus

The pair of egg-shaped structures located at the top of the brainstem.

  • Incoming sensory information is channeled to the appropriate area of the cerebral cortex by thalamus, so that it is processed there.
  • Thalamus acts like a relay station … . the brain՚s sensory switchboard; it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla.
  • It receives information from the sensory neurons and routes it to the higher brain regions that deal with vision, audition, taste and touch.
  • Cerebellum
  • “Cerebellum” comes from the Latin word for “little brain” . The cerebellum is located behind the brain stem.
  • Cerebellum is somehow similar to the cerebral cortex: the cerebellum is divided into hemispheres and has a cortex that surrounds these hemispheres.
  • It carries 10 % of the weight of the brain.
  • It contains as many neurons as in the rest of the brain.
  • Its function is to coordinate body movements i.e.. coordination, maintenance of posture & balance.
  • Damage to cerebellum results into jerky and uncoordinated body movements.

Responsible for basic survival functions such as breathing, heartbeat, and blood pressure.