Control and Coordination Part-1

  • In lower animals, or every phylum of invertebrates (apart from sponges), the fundamental form of the nervous system is used to achieve control and coordination.
  • In contrast to vertebrates, who have well-developed nervous and endocrine systems that control the entire process of control and coordination, sponges depend on their cilium to generate the signals necessary to react to any stimuli.

Nervous System


The structural and functional unit of the nervous system is the neuron.

  • The three primary components of each neuron are the axon, dendrites, and cyton/soma/cell body.
  • Other neurons' impulses are received by dendrites.
  • The impulse is processed by the Cyton/soma.
  • The impulse is transmitted by the axon to another neuron, muscles, glands, etc.
  • Axon may be myelinated or non-myelinated.
  • Myelinated neurons have a faster rate of impulse transmission.

Structure of neuron

The neuron consists of the following parts

  • Cyton or cell body: The cell body or cyton is somewhat star-shaped, with many hairs like structures protruding out of the margin. These hair-like structures are called dendrites. Dendrites receive the nerve impulses.
  • Dendrites: These are numerous, short; branched cytoplasmic processes that project out of the cell body. They act as the receiver of impulses and then transmit them to the cyton.
  • Axon: This is the tail of the neuron. It ends in several hair-like structures, called axon terminals. The axon terminals relay nerve impulses.
  • Myelin sheath: There is an insulator cover around the axon. This is called myelin sheath. The myelin sheath insulates the axon against nerve impulse from the surroundings.


  • Synapse refers to the point of contact between the terminal axon branches of one neuron and the dendrite of another neuron.
  • In between the axon and dendrite or axon and another cell, there is a fine gap called the synaptic cleft.
  • The synaptic cleft helps in the transfer of information in the form of neurotransmitters like acetylcholine.

Human Nervous System

  • The human nervous system consists of three parts-Central nervous system, Peripheral nervous system and Autonomous nervous system.

Central Nervous System

  • Central nervous system: It consists of two main parts that is the brain and the spinal cord.
  • They actually control the major part that refers to what to do when to do and how to do i.e. a response towards all stimulus.
  • The cerebrum is responsible for reasoning, logic, emotions, speech, memory, visual processing, recognition of auditory and taste stimuli, etc.
  • Cerebellum regulates and coordinates body movements, posture and balance.
  • Pons relays signals from the hindbrain to the forebrain.
  • Medulla Oblongata controls all involuntary movements like vomiting, sneezing, yawning, heartbeat, breathing, blood pressure, etc.
  • Medulla oblongata continues as the spinal cord, which runs through the vertebral column and it controls reflex actions.

Peripheral Nervous System

  • It refers to all the nerves that enter or leave the brain and the spinal cord.
  • It is composed of the cranial nerves and spinal nerves.
  • There are 12 pairs of cranial nerves. The cranial nerves come out of the brain and go to the organs in the head region.
  • There are 31 pairs of spinal nerves. The spinal nerves come out of the spinal cord and go to the organs which are below the head region.

Autonomic Nervous System

  • All the nerves of the peripheral Nervous System that control the involuntary actions in the body form the autonomic nervous system. E.g. respiration, heart rate, blood pressure, digestion, etc., are controlled by the autonomic nervous system.
  • There are two types of autonomic nervous system is present -sympathetic and parasympathetic nervous systems.
  • The sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response, while the parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high-energy functions.