PHYSIOLOGY

Physiology Is the branch of biology which deals with normal functions of

living things and their parts. The normal functioning of the body is

controlled by sense organs. Coordination is accomplished through a set of

signals channeled into a series of nerve cells. Coordination in mammals

involves three main components which are receptors, coordinators and

effectors.

receptors. Coordinators include the brain and the spinal cord. A

coordinator uses messages to link activities in the body. The messages

received are called nerve impulses.

Effectors: These are the cells, organs or organelles which receive motor

impulses from the brain or spinal cord and bring about an appropriate

response. The effectors include: Muscles, cilia, flagella and glands.

Response: This is any change shown by the organism responding to

stimulus. Response may involve the movement of the whole or part of the

organism’s body. This movement can be either towards or away from the

stimulus. Examples include the quick removal of the leg if pricked by a

mammals, there are five major sense organs namely; the ear, the eye, the

nose, the tongue, and the skin. Each sensory receptor responds to only one

specific stimulus.

Sensory receptors are the specialized region of the body detecting the

stimulus.

Types of receptors.

Classification of sensory receptors based on type of stimuli

Based on the type of stimulus they detect in the environment, there are

several types of sensory receptors, which include: mechanoreceptor,

vibration. Mechanoreceptors are responsible for detecting changes

that are perceived such as sound or touch.

❖ They are also responsible for maintaining equilibrium balance and

proper tone in muscles and joints

Photoreceptors

These are receptors which detect electromagnetic stimuli such as light.

There are two types of photoreceptors namely; rods and cones. These

are found in the retina of an eye for detecting dim and bright light

respectively

Thermoreceptors

Examples of thermoreceptors are bulbs of Krauze which sense

coldness and organ of Ruffin which detects heat. These cells are

connected to heat gain and heat loss centres of the hypothalamus

Nociceptors (pain receptors)

These are receptors that can detect pain and they are found in the skin,

muscles, bones, blood vessels, and some organs

Chemoreceptors

These are receptors which detect chemical stimuli such as smell, taste,

and humidity. They have the ability to respond to a diverse range of

impulses to pass to the olfactory bulb and then to the brain.

Osmoreceptor

They detect the changes in osmotic pressure. The osmoreceptors are

primarily found in the hypothalamus and kidney of most

homoeothermic organisms. They contribute to regulate fluid balance in

There are five sense organs

The Ear

The ear is the organ for hearing and maintenance of body balance. It

detects sound waves and vibration. It also provides information on the

position of the organism. The mammalian ear is composed of three parts;

the outer ear, the middle ear and the inner ear.

Function of the ear

Adaptation of the ear to its functions

The following are the adaptations of the ear to its functions:

❖ The presence of pinna which helps to collect the sound waves from

The eye is an organ for vision which receives light from the environment

and converts it into electrical impulses. It is roughly spherical in shape and

located in a bony socket called orbit in the skull. The orbit protects the eye

against physical damage.

Function of the eye

❖ To enhance a person to determine distance.

❖ To bring sense of sight/vision

The contraction and relaxation of these muscles control the size of

the pupil and amount of light entering the eye

❖ Pupil allow light to enter the eye.

❖ Eye lashes, protects the eye from entering of small particles and

dusts

❖ Ciliary body When the eyes focus on an object they contract and

relax, and they change the shape of the lens.

❖ Eyelid is a thin fold of skin that covers and protects the eye

externally against entry of foreign particles. There are two eyelids

foreign particles such as sand and dust.

❖ The eyebrow is an area of thick, short hairs above the eye that

follows the shape of the lower margin of the brow riges. Their

main function is to prevent sweat, water, and other debris from

falling down into the eye socket. They are also important in human

communication and facial expression

❖ Sclera This layer protects, supports, and maintains the shape of the

eyeball. The sclera is white in colour except the front part which is

transparent and it is called cornea. It also contains elastic

connective tissues.

❖ The cornea is the transparent part of the eyeball which is

continuous with the sclera and is covered with a thin membrane

called conjunctiva. Cornea is convex so that light rays can be

refracted, and since it is transparent, it allows light to pass through.

❖ The conjunctiva is a thin transparent membrane which is found

inside of the eyelids covering the front of the sclera. Conjunctiva

❖ Short sightedness (myopia)

❖ Long sightedness (hypermetropia).

❖ Astigmatism

❖ Presbyopia

This is a defect of vision in which far objects appear blurred but

near objects are seen clearly. The image of an object is focused in

front of the retina in vitreous humour rather than on the retina

This defect occurs when the eye does not focus light evenly on the

retina, instead some light is focused on the retina while some is

non-uniform curvature of the cornea.

item (i) – (iv) and then answer the questions that follow:

(i)

Look at your body and observe the sense organ that covers the

whole hands.

(ii)

Take a tooth pick and prick slightly the upper part of your hand

and note the feeling.

(iv)

Take cotton wool and soak into methylated spirit. Rub it on your

hand and observe what is happening.

Questions

and locate the regions corresponding to the taste of the following

food samples: (i) A (ii)B (iii)C.

food samples.

❖ Ears

Skin: