Psychology Study Material: Nervous System and Biological Bases of Behaviour

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Nervous System

Nervous System

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 Behaviour

  • 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 fibres 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 fibres 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 fibre 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.