Skip to main content

Coordination Biology Secondary School Notes




It is defined as the linking together of various processes in the body. It is brought about by the nervous system and the endocrine system. Coordination which is brought about by the nervous system is called nervous coordination while coordination that is brought about by the endocrine system is called chemical (hormonal) coordination.

The Nervous System

It is made up of three parts namely;

  1. The central nervous system (CNS) which is made up of the brain and spinal cord.
  2. The autonomic Nervous System (ANS) which is made up of nerves that link all internal organs to the brain and the spinal cord.
  3. The Peripheral Nervous System (PNS) which is made up of a network of nerves linking the brain and the spinal cord to all parts of the body.

1. The Central Nervous System (CNS)

The brain

It is located in the head in the skull which protects it from external forces. It is surrounded by three membranes called meninges. These membranes protect it from shock. The meninges are separated by a fluid called cerebrospinal fluid which brings nutrients to the brain. The brain is the organ that controls most of the activities in the body. It is divided into three parts;


It is the largest part of the brain. It occupies the anterior part of the brain. It has grey matter outside and white matter outside. It is highly folded on the surface to increase the surface area. It is divided into two halves by a deep fissure which runs from the front to the back. The two halves are called hemispheres or lobes i.e. therefore there is a left lobe/hemisphere and the right lobe/hemisphere joined together by a bundle of nerves called the corpus callosum.

Functions of the cerebrum

  1. It controls memory, thinking and emotions. These three makes up intelligence.
  2. It also controls reasoning
  3. It interpret sensory messages e.g. sight, taste, smell, touch and pain.


It is the second largest part of the brain. It is located behind or just below the cerebrum. It is less folded hence has a smaller surface area. It also has grey matter outside and white matter inside.


  1. Maintains muscle tone for balance.
  2. Controls muscular co ordination during walking, dancing, running etc.
  3. It controls posture.

Medulla oblongata

It is the smallest part of the brain. It is located below the cerebellum. It has got white matter and grey matter. It is not folded on the surface hence has got a very small surface area.


It controls most of the vital processes in the body such as breathing, heart beat, blood pressure, regulation of body temperature, etc. therefore any damage to the medulla oblongata leads to death.

Spinal Cord

It arises from the base of the brain (medulla Oblongata). It runs through the vertebrae up to the last bone in the pelvis. The back bone provides protection to the spinal cord. The spiral cord is also surrounded by the meninges which are also separated by the cerebrospinal fluid. In the spinal cord there is white matter out side and grey matter inside. At the centre of the spinal cord there is a hole called the central canal which contains cerebrospinal fluid. The spinal cord is joined to nerves that link various part of the body. The nerves enter through the Dorsal root and leave through the ventral root. On the dorsal root there is a swelling called the Ganglion which is made up of cell bodies of the nerve cells.


  1. To conduct impulses from the sensory nerves to the brain.
  2. To control reflex actions of all organs below the head.
  3. To conduct impulses from the brain to motor nerves linking organs below the head.

Nerve Cells

A nerve is a thread like structure which conducts impulses in the body. Nerves that carry impulses from sensory organs to the central nervous are called sensory nerves. Nerves that carry impulses from the central nervous to the muscles or organs that carry out a response are called Motor Nerves. In the brain and spinal cord there are nerves that link the sensory nerve to the motor nerve these are called Association or relay Nerves. Each nerve fibre is made up of small units called Nerve cells or Neurones.

Structure of a neuron

Structure of Neutron

Structure of Neutron

Functions of the parts of a neuron

  1. Dendrites.These are structures that radiate from the cell body. Their function is to trap impulses crossing the synapse. Once trapped the impulses is transported to the cell body.
  2. Cell body. This receives impulses from the dendrites. It coordinates them and send them out to the axon. It contains a nucleus which controls all the activities of the neurone.
  3. Axon. It is an elongated structure that is joined to the cell body. It carries impulses away from the cell body.
  4. Myelin sheath. This is a layer of fat cells that cover the axon. Its function is to provide insulation to the axon so that impulses are not conducted by other body cells. This insulation also helps to increase the speed at which the impulses are conducted.
  5. Node of ranvier. This is a gap between myelin sheaths. It is used as a point where food and oxygen are supplied to the axon.
  6. Dendron. This is the longest dendrite. It carries impulses towards the cell body.

How impulses cross a synapse

A synapse is a gap between neurones. Impulses travelling through a neurone have to cross a synapse to reach another neurone. When impulses reach the end plate of an axon, a liquid called the Neurotransmitter (acetylcholine) is secreted into the synapse. Acetylcholine is a good conductor of impulses. Therefore the impulses are transported across until they are picked up by dendrites of the next neurone. After impulses have crossed the synapse, the Acetylcholine is later destroyed by enzymes.

Reflex Actions

A reflex action is a rapid and automatic response to stimulus. Most reflex actions are carried out to protect the body from injury. They are usually carried out before the brain could interpret the impulses. Interpretation of the impulses involved in a reflex action occurs after the response has been carried out. Examples of reflex actions are blinking of the eye, knee jerk, withdrawal of a hand from a hot object, sneezing.

Types of reflex actions

There are two types of reflex actions

  1. Cranial reflexes. These are reflex actions that are carried out by organs in the head region. Examples of cranial reflexes are blinking and sneezing. Cranial reflexes are controlled by the brain.
  2. Spinal reflexes. These are reflex actions that are carried out by organs below the head. They are controlled by the spinal cord. Examples include; knee jerk and withdrawal of a hand from a hot object.
Scroll to Continue

Reflex arc

This is a path that is followed by impulses in a reflex action. The reflex arc is made up of the following components. Receptor; this is sensory organ that detects the stimulus. When the stimulus has been detected, nerve impulses are produced and are carried by the sensory Neurones.

Sensory neurones

These are nerve cells that carry impulses into the brain and the spinal cord.

Association neurones

These are found in the brain and the spinal cord. They pick up impulses from the sensory neurones. Instead of sending impulses straight to the brain for interpretation the impulses are sent to the motor neurones.

Motor neurones

These pick up the impulses from the association neurones. They send the impulses to the effectors.


An effector is an organ or tissue that carries out a response. Examples of effectors include muscles.

Conditioned reflexes

These are reflex actions which come about after a period of learning or training. In most cases conditioned reflexes, the responses are not related to stimulus. Examples are, fear of white gowned nurses by children, fear of the lizard, riding a bicycle etc. Conditioned reflexes usually develop into behaviour.

Effects of drugs on the nervous system

A drug is a substance which changes the way in which the body works. There are four groups of drugs, namely;

Painkillers. These are drugs that suppress the part of the brain responsible for interpretation of pain. Examples are heroine and morphine which are usually given to people in great pain.

Stimulants. These speed up the rate at which the brain works. They make the brain more alert. Examples are cocaine, nicotine and caffeine.

Sedatives. These are drugs which slows down the brain and make a person feel sleepy. Examples include valium and piriton.

Hallucinogens. These are drugs that causes hallucinations or illusions when taken. A hallucination is an imagination of something that may be felt but does not exist. Examples are cannabis and marijuana.

Dangers of drugs

  1. They may impair the persons judgement and make him/her clumsy. A persons takes longer to respond e.g. alcohol.
  2. They may injure the body by damaging cells. E.g. alcohol kills cells in the brain and liver. Marijuana kills cells in the brain.
  3. They may make a person to become addicted. A person can not do without taking the drug.

Chemical Coordination

This is a type of coordination that is brought about by hormones. Hormones are chemicals that are produced by the endocrine glands and transported by the blood to target organs where they produce an effect. Endocrine glands are also called ductless glands because they do not have tubes that link them to the blood vessels.

Endocrine glands

Pituitary gland

This is located in the head if the base of the brain. It is small in size, the size of a pea. It produces the growth hormone, Anti Diuretic Hormone (ADH) and a group of other hormones called Trophic hormones.

Growth hormone

This is a hormone that controls growth in a person. When the hormone is produced in excess a person becomes a giant and if the hormone is under produced a person becomes dwarf.

Trophic hormones

This is a group of hormones which controls the functioning of other endocrine glands. The pituitary gland is called the master glands because it controls other endocrine glands.

Anti diuretic Hormone (ADH)

This is a hormone which helps in regulation of the amount of water in the body. It works in conjunction with the kidneys. When there is less water in the body, ADH is produced and it makes the kidneys to reabsorb the water filtered out of the blood back into the blood. When there is too much water in the body, no ADH is produced and the kidneys do not reabsorb water back into the blood.

Thyroid gland

It is located in the neck region in front of the voice box (larynx). It produces a hormone called thyroxin. This is a compound of iodine. Without iodine, the hormone can not be produced and the gland swells forming a simple goitre. Thyroxin helps in cellular metabolism such as respiration. Too much thyroxin increases metabolism. The person becomes overactive, thin has protruding eyes. Too little thyroxine reduces metabolism. The person becomes sluggish, fat and mentally retarded.


This is a gland that also produces digestive enzymes. It also has special groups of cells called Islets of Langerhans which produces hormones.


It is produced when the blood sugar level rises. It makes the liver to absorb glucose from the blood and store it as glycogen. Lack of insulin leads to a sugar disease called Diabetes Mellitus which can be treated by administration of insulin tablets or intravenous injection.


This is another hormone that is produced by the pancreas. It main function is to increase the sugar level in the blood when it is low. It makes the liver to release glycogen back into the blood as glucose.

Adrenal gland

These are hormones that are located just above the kidneys. Each gland produces a hormone called adrenaline. This hormone prepares the body for action i.e. either running away or to fight. Because of this the hormone is therefore referred to as a fight or flight hormone. The body is prepared by; making the pupil in the eye to dilate to improve vision. The heart beat increases to supply as much oxygen as possible to the muscles.The blood vessels dilate to carry a lot of blood with oxygen and glucose.

Related Articles