NERVOUS SYSTEM

Biology

NERVOUS SYSTEM

What is the nervous system?

Components of the nervous system in humans

  • Every organ is the human body is connected to nerves.
  • The nervous system is made up of nerve cells (neurons) which transmit impulses from one part of the body to another.

It consists of the following:

  • The Central Nervous System (CNS) is a concentrated mass of interconnected nerve cells which make up the brain and the spinal cord.
  • The peripheral nervous system is made up of nerves which link the CNS to the receptors and the effectors.
  • Sensory nerves link the sensory cells (receptors) to the central nervous system and transmit nerve impulses from a sense organ to the CNS.

Structure and Functions of Neurons

  • A nerve cell consists of a cell body (centron) where the nucleus is located, and projections called dendrites arise.
  • One of the projections is drawn out into an axon i.e. the longest process.
  • Each axon contains axoplasm which is continuous with the cytoplasm in the cell body.
  • The axon is enclosed in a fatty myelin sheath which is secreted by Schwarm cell.
  • The myelin sheath is interrupted at approximately 1 mm intervals by constrictions known as nodes of Ranvier.
  • The myelin sheath is enclosed by a thin membrane called the neurilemma, which is part of the Schwann cell in contact with axon.
  • The myelin sheath and nodes of Ranvier enhance transmission of the impulse.
See also  KINGDOM FUNGI

There are three types of neurons:

Sensory neurone

  • Also known as afferent neurone.
  • Transmits impulses from sensory cells to the CNS.
  • The cell body of a sensory nerve cell is located at some distance along the length of the axon outside the CNS.

Motor neurone

  • Known as efferent or effector neurone
  • Transmit impulses from the CNS to the effectors(muscles and glands)
  • Its cell body is located inside the CNS.

Intermediate or connector neurone

  • Also called relay neurone
  • Found inside the CNS.
  • The connect sensory and motor neurons with each other and with other nerve cells in the CNS.
See also  HYDROPHYTES (WATER PLANTS)

Functions of the neurone

  • The nerve impulse is electrical in nature.
  • Its transmission depends on differences in electrical potential between the inside and the outside of the axion.
  • The outside is positive while the inside is negative.
  • The stimulus triggers a change that affects the permeability of neurone membrane.
  • The result is a change in the composition of ions on either side of the membrane.
  • The outside becomes negative as the inside becomes positive due to sodium ions rushing in.
  • The above constitutes a nervous impulse which is transmitted along the sensory neurone to the CNS.
  • The speed of transmission is very high.
  • Certain mammalian axions transmit impulses at the rate of 100m/s.
  • The dendrites of neurons do not connect directly to each other, but they leave a small gap called synapse.
  • The transmission of an impulse from one cell to the next takes place through synapse.
  • Synaptic knobs are structures found at the ends of dendrites.
  • Thus the dendrites of one nerve cell make contact with the dendrites of the adjacent nerve cell through the synapses.
  • Impulses are transmitted in the form of a chemical transmitter substance which crosses the gap between one dendrite and the next.
  • The transmitter substance is found within synaptic vesicles.
  • The chemical substance is either acetylcholine or noradrnaline.
  • The synaptic vesicles burst and release the transmitter substance when an impulse arrives at the synaptic knob.
  • Impulses in motor neurone s are trans mitted to effectors.
  • The space between motor end dendrite and muscle is known as neuro-muscular Junction.
  • Synaptic vesicles in the ends of the dendrites release the transmitter substance across the neural muscular junction.
See also  POLLINATION

See also:

PRODUCTION OF AUXINS AND THEIR EFFECTS ON PLANT GROWTH

RECEPTION, RESPONSE AND CO-ORDINATION IN PLANTS

BIOLOGY PRACTICAL ACTIVITIES

EVOLUTION

PRACTICAL ACTIVITIES TO DEMONSTRATE CONTINUOUS VARIATIONS

Leave a Reply

Your email address will not be published. Required fields are marked *