BIOLOGY O LEVEL(FORM THREE) NOTES – COORDINATION -1

COORDINATION -1

Coordination refers to the linking together of the activities of different organs, so that they work at an appropriate time and rate required by the body.

During physical exercise, several organs are involved; these include the heart, skeletal muscles, blood vessels, and lungs. Hence, for any activity to take place smoothly, these organs must function in a coordinated manner.

Without coordination, body activities become disordered and the body may fail to function properly.

Coordination of various organs in the body requires a system which can detect changes in the environment and transfer information to the appropriate organs so that the body can change in such a way as to ensure its survival.

Coordination is affected by the nervous system and hormonal coordination. Hormonal coordination involves organs which secrete chemical substances in response to certain changes in the environment, both internal and external stimuli.

COORDINATION IN ANIMALS

All animals, from simple unicellular organisms to large multicellular ones, need to coordinate body activities. All animals respond to changes in their surroundings and react in an appropriate way.

Coordination in animals consists of five components.

The following figure shows the nervous coordination:

STIMULUS

Refers to a factor which causes an organism to react (respond).

Example: Changes in external or internal environment (outside or inside animal body). Examples include pain, smell, taste, and sound.

RECEPTORS

Refers to the parts of an animal which detect the changes (stimulus), e.g., tongue, nose, skin, ears. Receptors are called sense organs. A receptor produces a type of message called nerve impulses, which are then transmitted from one part of the body to another.

COORDINATOR

Consists of the brain and spinal cord which receive messages as sensory nerve impulses from receptors. It coordinates these and generates motor nerve impulses which pass to the appropriate organs of the body which respond. In this way, the activities of the body are coordinated.

EFFECTOR

An organ which receives motor nerve impulses from the brain or spinal cord and brings about an appropriate response, e.g., muscles and glands.

RESPONSE

A body activity provoked by stimulus. E.g., pulling your hand away from a hot object.

NERVOUS COORDINATION IN HUMANS

The nervous system includes specialized cells called nerve cells or neurons.

A neuron has the following basic properties:

• It is highly capable of responding to stimulus. This property is referred to as excitability.
• It is highly capable of conducting messages (nerve impulses) along it. This property is referred to as conductivity.
• It has cytoplasm which extends forming long fine threads.

NEURONS

Neurons, like other animal cells, have a plasma membrane surrounding the cytoplasm.

The cytoplasm contains the nucleus and other organelles and is contained in one part of the cell called the cell body.

• Axon is a projection arising from the cell body.
• Axon carries nerve impulses away from the cell body.
• The shorter projections are called dendrites which conduct impulses towards the cell body.
• The axon is made up of cells called Schwann cells, which form a sheath around the axon called the myelin sheath.
• The small gap between adjacent Schwann cells is called a node of Ranvier.
• Myelin sheath serves to insulate axons from one another and prevents impulses in one axon from interfering with impulses in another axon.

Also, nerve impulses travel faster in myelinated than in non-myelinated nerve fibres.

Classification of neurons

Neurons are classified as:

1. Sensory (afferent)
2. Motor (efferent)
3. Relay neurons (Intermediate)

1. SENSORY (AFFERENT) NEURONS

They transmit impulses from sense organs towards the central nervous system (brain and spinal cord).

Each sensory neuron has an axon and dendron. The dendron originates in a sense organ. When there are changes in the environment, the sense organ is stimulated at the tip of the dendron.

The nerve impulses are transmitted along the dendron to the cell body and from there via the axon to the finely branched ends of the nerve cells in the brain or spinal cord.

Note: There will be no sensation until the nerve impulses have been interpreted.

2. EFFERENT (MOTOR) NEURONS

They transmit impulses from the central nervous system to effector organs.

3. RELAY NEURONS

Form intermediate links between afferent and efferent neurons. They are found in the brain and spinal cord. The terminal part of the dendron of relay neurons receives impulses from the terminal part of the axon of a sensory neuron.

Impulses from the axon of a relay neuron are passed to the dendron of a motor neuron.

CENTRAL NERVOUS SYSTEM

The central nervous system (CNS) consists of the brain and spinal cord.

The CNS analyses the impulses received. It also determines what actions are to be taken in response to stimulus.

The central nervous system has two main components:

1. Brain
2. Spinal cord

1. THE BRAIN

Situated in the skull and covered by a system of membranes called meninges. Between the innermost membrane and the middle membrane is a space filled with a fluid called cerebrospinal fluid.

This fluid cushions the brain against shock. The brain is very sensitive to insufficient supply of oxygen and glucose which causes rapid damage.

The brain is divided into three regions: forebrain, midbrain, and hindbrain.

a) FOREBRAIN

This is the anterior portion of the brain. It is composed of the olfactory lobes and cerebrum. The outer portion is grey, hence called grey matter; the inner part is whitish, hence called white matter.

The cerebrum interlinks impulses and coordinates responses. Nerve impulses from the eyes, ears, and tongue are interpreted in the cerebrum.

The cerebrum is responsible for speech, reasoning, memory, decision making, behavior, and imagination.

Activities such as running, walking, eating, and playing are under voluntary control, meaning they are consciously done. In humans, the cerebrum is extremely active compared with other animals, which is why we can reason and recall past experiences.

The olfactory lobes receive impulses of smell via olfactory nerves from the organ that senses smell (nose).

b) MIDBRAIN

The midbrain is smaller compared to other regions. This part of the brain is called the optic lobes. It lies between the forebrain and the hindbrain. It is composed of the thalamus and hypothalamus together with the pituitary gland.

• Its function is to relay information between the forebrain and hindbrain.
• It also relays information between the forebrain and the eyes. The optic nerve linking the brain and eyes originates here.

c) HINDBRAIN

The hindbrain is composed of the cerebellum and medulla oblongata.

• The cerebellum regulates and coordinates body movements concerned with equilibrium.
• It receives impulses from skeletal muscles, tendons, and the inner ear, then relays them to the forebrain.
• In the forebrain, the impulses are analyzed and the animal is made aware of its posture.
• The cerebellum also relays impulses from the inner ear to the appropriate muscles. These muscles act to change the body position to maintain balance.
• The medulla oblongata: is the most posterior part of the brain which merges with the spinal cord.
• It controls all unconscious activities of the body, e.g., breathing, heartbeat, digestion, dilation and contraction of blood vessels, secretion of juices from glands, and temperature regulation.
• The medulla oblongata is essential to life because it controls breathing and heartbeat. If the medulla oblongata is severely damaged, the animal dies immediately. The parts of the nervous system that control these unconscious activities are collectively called the autonomic nervous system.

Note: Meningitis is a disease resulting from infection of the meninges by certain types of bacteria or viruses.

• Meningitis caused by bacteria can be treated with antibiotics, but viral meningitis is very difficult to treat with antibiotics. If the infection reaches the brain, the person may die.

2. THE SPINAL CORD

The spinal cord is the extension of the central nervous system (CNS) from the brain to the tail. It is encased in meninges and protected by the vertebral column. The spinal cord is made up of two halves fused together called the spinal canal, which is filled with cerebrospinal fluid.

The spinal cord gives rise to 31 pairs of spinal nerves which exit between the bones of the vertebral column and connect to all parts of the body.

• The spinal cord serves as a nerve impulse conduction pathway. Nerve impulses transmitted by the spinal nerves are relayed to the brain, then from the brain to the spinal cord, and finally transmitted to the effector organs.
• The spinal cord acts as a coordinating centre. It controls actions called involuntary actions, which are fast and automatic. They cannot be controlled by willpower and need not be learned.
• Such responses are called reflex actions, e.g., sneezing, coughing.

STRUCTURE OF SPINAL CORD

GREY MATTER

• Is the central part of the spinal cord.
• It consists of the central canal filled with cerebrospinal fluid.
• It consists of relay neurons which connect information between the afferent and efferent neurons.
• The cell bodies are found inside the grey matter.

WHITE MATTER

Is the outer part of the spinal cord, consisting of axons of sensory and motor neurons.

VENTRAL ROOT

This part of the spinal cord carries motor nerve fibres.

DORSAL ROOT

This part of the spinal cord carries sensory nerve fibres.

Function of the spinal cord

• Conducts sensory nerve impulses from the receptors of the sense organs to the brain.
• Conducts motor nerve impulses from the brain to the effectors.
• Enables animals to attain an upright position through the maintenance of muscle tone.

Protection of nervous system

The nervous system is very delicate and vital to the well-being of animals; it is therefore highly protected from damage.

• The brain is protected from mechanical damage by the bones which make up the cranium/skull.
• The meninges are tough membranes that protect the brain from shock.
• The cerebrospinal fluid provides a floating environment.
• The fluid also helps to protect the brain from blows on the skull and from abrupt head movement.
• The spinal cord is protected by the vertebrae from mechanical damage.
• The nerves are sheathed by membranes.

PERIPHERAL NERVOUS SYSTEM

The peripheral nervous system is made up of sensory and motor nerves. These nerves run to and from the central nervous system and the rest of the body.

REFLEX ACTION

A reflex action is a sudden, automatic, and uncontrolled response of parts of the body or the whole body to external stimuli. For example, when a hot object is accidentally touched, the hand is quickly withdrawn.

The eyelids close quickly when a small object comes very close.

All these activities are responses which help to protect the individual. Actions occur as a result of impulses that travel along neurons arranged in a path called the reflex arc (the neural pathway linking a receptor and effectors).

These responses are fast and automatic. They cannot be controlled and are not learned.

The sensory neuron transmits impulses from a receptor and enters the spinal cord via the dorsal root of a nerve. Impulses travel from the receptor to the spinal cord or brain.

The relay neuron in the spinal cord receives impulses from the sensory neuron and passes them to the motor neuron via a relay neuron.

The motor neuron then sends the impulses to an effector via the ventral root so that a very quick response is produced. As a spinal reflex action takes place, impulses are sent to the brain. The brain takes note of what has happened, records it, and the individual then becomes aware of what has happened.

CONDITIONED REFLEX ACTION

Conditioned reflex action refers to reflex actions which result from experience or learning. That is, the reflex action was not there before.

Example of coordinated reflex action: A dog produces a lot of saliva at the sight of food. The production of saliva is a reflex action in response to the sight of food.

An experiment was carried out on dogs in which a bell was rung every time food was supplied to the dog. After the experiment was repeated several times, it was noticed that when the bell was rung even without supplying food, the dog salivated.

Usually, the sound of a bell does not cause a dog to salivate. The dog had learned to associate the sound of the bell with the presence of food. Thus, the sound of the bell induced the secretion of saliva in the same way as did the sight of food.

Through conditioned reflex actions, it is possible to change an animal’s behavior, helping the animal to learn new ways of behaving and produce favorable responses.

SENSE ORGANS

A sense organ is a mass of specialized sensory receptor cells compacted together. Sensory receptor cells detect stimuli from the environment. Each type of receptor is responsible for registering a particular kind of stimulus.

Receptors will not respond to stimuli other than those for which they are specialized. For example, a sense organ sensitive to touch will not detect heat, and a cell sensitive to chemicals will not detect pressure.

The sense organs or sense cells are connected to the brain or the spinal cord by nerve fibres. When the sense organs receive an appropriate stimulus, they set off an electric impulse which travels along the nerve fibre to the brain or spinal cord.

When the impulse reaches one of these centers, it may produce an automatic or reflex action.

The sense organs of one kind and in a definite area are connected with one particular region of the brain. It is the region of the brain to which the impulse comes that gives rise to the knowledge about the nature of the stimulus and where it was received. Each part of the body has its own sensory area in the brain. For example, nerve fibres from one’s thumb run to one area in the brain, while those from one’s big toe run to another area.

SENSORY ADAPTATION

When the sensory nerve in the receptor is stimulated for the first time, transmission of nerve impulses is very fast. Continued stimulation soon leads to a slowing down of impulse transmission and finally it ceases altogether.

Sensory adaptation is useful for the comfortable life of an organism.

For example, when a person is cut or bruised, they feel sharp pains initially. These pains may lessen over time due to sensory adaptation.

SENSORY RECEPTORS

Human beings have different types of sensory receptors located in different parts of the body. They are found in the skin, eyes, ears, blood vessels, muscles, tendons, nostrils, and tongue.

I. EAR

There are three types of sensory receptors in the human ear:

• Those concerned with hearing.
• Those concerned with equilibrium (balance).
• Those concerned with acceleration (structure concerned with detection).

The mammalian ear is divided into three parts:

1. The outer ear.
2. The middle ear.
3. The inner ear.

1) OUTER EAR

The pinna, ear canal, and the eardrum form the outer ear.

a. The pinna is the outermost part of the ear and is made up of cartilage. Its function is to trap sound waves and direct them into the ear canal.

b. The ear canal is the tube through which sound waves travel. The walls of the ear canal secrete wax and have hairs which trap dust. This tube directs sound waves to the eardrum.

c. The eardrum (tympanum) is a thin double membrane that forms the boundary between the outer ear and middle ear. The eardrum vibrates when hit by sound waves.

2) MIDDLE EAR

This is an air-filled cavity behind the eardrum. The middle ear consists of three tiny bones: malleus (hammer), incus (anvil), and stapes (stirrup). These ear ossicles amplify the vibrations and transmit them towards the inner ear. The cavity is connected to the mouth by a tube called the Eustachian tube.

Usually, the tube is closed, but when the pressure in the middle ear increases, the tube opens until the air pressure in the middle ear is equal to that in the throat and therefore to the atmosphere.

• The Eustachian tube equalizes the air pressure between inside and outside of the eardrum.
• If this tube is blocked by mucus, as in the case of a cold, hearing is impaired.
• Opposite the eardrum, there are two openings: one oval-shaped called the oval window (fenestra ovalis), and the other round called the round window (fenestra rotunda).

3) INNER EAR

The inner ear consists of a cavity filled with a fluid called perilymph, two sac-like structures called the sacculus and utriculus, three semi-circular canals, and a coiled tube called the cochlea.

The sacculus, utriculus, semi-circular canals, and cochlea are filled with a liquid called endolymph.

The cochlea detects sound vibrations (hearing), and the semi-circular canals, sacculus, and utriculus control balance and posture.

MECHANISM OF HEARING

• The pinna collects sound waves and directs them to the eardrum through the ear canal.
• When sound waves hit the eardrum, it vibrates. The vibrations are transmitted to the ossicles and amplified. The vibration of the stapes causes the membrane at the oval window to vibrate. The vibrations of the oval window are transmitted to the perilymph and then to sensory nerve fibres. The impulses are transmitted to the brain for interpretation.

SENSE OF ACCELERATION

The semi-circular canals are concerned with the detection of motion. The ampullae of the semi-circular canals contain sensory cells attached to sensory nerve endings. The sensory cells have hairs enclosed in a core of jelly-like substance called the cupula.

Whenever the body or head moves, the semi-circular canals lag in their motion and apparently move in the opposite direction.

The moving fluids cause the cupula to tilt, thus pressing the hairs of the sensory cells. The pressing of the sensory hairs creates nerve impulses in the sensory nerve endings. The nerve impulses are transmitted to the brain. The brain then interprets the direction and speed of motion of the body or head.

SENSE OF EQUILIBRIUM

The utriculus and sacculus are concerned with the sense of balance and posture. The inner surface of these structures contains sensory cells. The sensory hair cells have protruding hairs embedded in a jelly-like substance containing tiny particles of chalk called otoliths.

When the head is tilted to one side, the otoliths move in the opposite direction, pulling or pressing the sensory hairs. They initiate nerve impulses which are transmitted to the brain. The brain then directs the angle which tends to return the body to its normal position.

HEARING DEFECTS

Loss of hearing and deafness can be caused by:

1. Blockage of the ear canal: Production of too much wax may harden and block the external auditory canal.
2. Rupture of the eardrum: The eardrum may be perforated or burst due to loud noise, physical blow, or infection.
3. Fusion of the ear ossicles: Due to abnormal growth of connective tissues in the middle ear which fuses the ear ossicles and prevents them from vibrating.
4. Nerve destruction: Caused by damage to the auditory nerve due to nervous disease.
5. Infection of the middle ear: When the eardrum is infected, it becomes thick and rigid such that it cannot vibrate even when struck by sound waves.

II. SENSE OF VISION (EYE)

Receptors concerned with the sense of vision are located in the eyes.

Front view of mammalian eye

From the front view, the eye has three well-marked regions:

• Pupil – a small dark central portion surrounded by the iris.
• Sclerotic layer – the layer which surrounds the iris. This is the largest part of the eyeball.
• Cornea – a transparent region in front of the eyeball that passes over the iris and pupil.

Cross-section of the mammalian eye

Function and adaptation of the parts of the eye

The eyeball has a cavity which is divided into two portions:

I. VITREOUS HUMOUR

A large posterior portion filled with jelly-like fluid called vitreous humour, found between the lens and retina. The vitreous humour maintains the shape of the eyeball. The fluid also reflects light and, since it is transparent, allows light to pass through.

II. AQUEOUS HUMOUR

A watery fluid filling a small anterior portion found between the cornea and lens. Aqueous humour is transparent, allows light to pass through, reflects light, and maintains the shape of the eyeball.

The two chambers are separated by the lens.

The lens is held in position by fibres called suspensory ligaments. The lens is transparent to allow light to pass through.

1. RETINA is the innermost layer of the eyeball. It is elastic and contains many blood vessels. It contains photoreceptors called cones and rods.
2. CONES are sensitive to light of high intensity (bright light) and colour.
3. RODS are sensitive and function in dim light.
4. FOVEA is a region where the cones are packed together. The fovea is directly opposite the lens and is the most sensitive part of the retina.
5. CILIARY BODY contains ciliary muscles that contract to control the shape of the lens.
6. IRIS is a ring of contractile muscles (circular and radial) that control the amount of light entering the eye.
7. PUPIL is a hole or opening in the iris which allows light to enter the eye.
8. SCLERA is the outermost layer of the eye. This layer protects, supports, and maintains the shape of the eyeball. The sclera continues and becomes a transparent layer at the front of the eye called the cornea.
9. CORNEA is the transparent front of the eyeball covered by a thin membrane known as conjunctiva. It is convex to reflect light and also allows light to pass through.
10. CONJUNCTIVA is a transparent membrane that covers and protects the cornea.
11. CHOROID LAYER is a layer next to the sclerotic layer. It extends to the front of the eye to form the ciliary body and iris. The pigment of the choroid absorbs stray rays of light to prevent reflection of light within the eye.
12. BLIND SPOT is the area in the retina through which the optic nerve leaves the eyeball. The blind spot has neither rods nor cones. So images from objects falling on the blind spot cannot be perceived by the brain.

IMAGE FORMATION

Vision depends upon image formation. The formation of an image depends on the refraction of light. When light passes from one medium to another, its velocity changes. If light goes from air into a denser medium, the rays bend. This bending of light is called refraction.

The formation of an image depends on the law of refraction. Light rays from the object enter the eye through the cornea. Then they pass through the aqueous humour, pupil, lens, vitreous humour, and finally reach the retina where the image is recorded as real, upside down, and smaller than the object.

When light rays fall on the retina, they stimulate the photoreceptors and impulses are sent to the brain through the optic nerve. The cerebrum then interprets the impulses, making the object visible. The interpretation also means that a person will be able to see the object in its correct orientation and size.

ACCOMMODATION OF THE EYE

Accommodation is the ability of the eye to focus on both near and distant objects or the ability of the eye to produce clear images of objects at different distances by altering the focal length of the eye lens.

This is brought about by the action of the ciliary muscles and elasticity of the lens.

When the eye is focusing on a distant object, the ciliary body muscle relaxes, while the suspensory ligaments become tighter and pull on the lens. The lens gets thinner and gives a clear image of the object.

When the eye is focusing on a near object, the tension of the suspensory ligament is relaxed or decreased and the lens becomes thick and more convex. This allows light rays to be focused onto the retina.

THE COMMON EYE DEFECTS

Defects of the mammalian eye are structural deviations of the eye which alter the focusing mechanism of the eye.

There are two common eye defects:

1. HYPERMETROPIA (long sight)
2. MYOPIA (short sight)

1. HYPERMETROPIA (long sight)

This condition is due to compression of the eyeball, resulting in shortening of the normal distance between the lens and the retina.

In this condition, light rays from distant objects are focused on the retina, whereas light rays from near objects fall behind the retina.

This means:

• A person cannot see near objects clearly.
• Images of near objects fall behind the retina.
• Caused by the eyeball being too short or the lens being too thin, so that it does not converge the light rays enough.
• These defects are corrected by using spectacles with convex lenses.
• Convex lenses converge the light rays before they reach the eye.

2. MYOPIA

A short-sighted person focuses distant objects improperly. This individual can only focus near objects clearly. This is because the light rays of distant objects converge at a point in front of the retina.

This may be due to the eyeball being too large. This may be corrected by a biconcave lens. This helps to diverge the light rays from distant objects so that they can be focused on the retina.

COLOUR VISION

There are three kinds of cones in the human retina. All three respond to more than one colour, but each particular cone is sensitive either to blue, green, or yellow. Yellow light stimulates the green and yellow cones, but red light affects the yellow-sensitive cones.

When all three types of cones are equally stimulated, we get the sensation of white light.

3. ASTIGMATISM

This is a condition in which the cornea or lens is uneven such that it is not focused properly on the retina. The defect can be corrected by using spectacles with special cylindrical lenses.

4. PRESBYOPIA

In this condition, the lens cannot change its shape. It is brought about by loss of elasticity of the lens and ciliary muscle due to old age. It can be corrected by the use of convex lenses.

5. CATARACT

The lens gradually becomes cloudy so that light cannot pass through easily and the person cannot see properly. It may become gradually worse. The lens may have to be removed by operation and can be replaced by a plastic lens inside the eye.

6. GLAUCOMA

This defect is common in old people. Glaucoma is caused by pressure in the eye.

7. COLOUR BLINDNESS

This is a genetic disorder in which a certain colour cannot be distinguished by a person. A common type is red-green blindness, where the individual is not able to distinguish between red and green colours.

8. TRACHOMA

This is a viral disease which affects the lining of the eyelids. If not treated, trachoma can cause blindness.

III. SKIN

There are different types of sensory receptors in the skin.

1) Touch receptors

Are sensitive to light touch; they enable a person to distinguish between different textures, e.g., rough and smooth, hard and soft, liquid and solid substances. Touch receptors are scattered all over the body surface but not evenly distributed. They are more concentrated in areas such as fingertips and others attached to the base of hairs.

2) Pain receptors

These are evenly distributed throughout the skin. They are also found in muscles, tendons, ligaments, and walls of the digestive system but not in the brain.

3) Heat receptors

Are sensitive to temperature.

4) Cold receptors

Are also sensitive to temperature.

5) Proprioceptive and visceral senses

These receptors receive information about the condition of the body itself. Proprioceptive receptors are found in the muscles and tendons. Stretch provides the brain with information about the degree of tension in muscles and the angle at which each joint is bent. Such information makes the brain aware of the movement of parts of the body.

TRANSVERSE SECTION OF A MAMMALIAN SKIN

SENSORY RECEPTORS OF THE TONGUE AND NOSTRILS

The sensory receptors of the tongue and nostrils are sensitive to solutions of certain chemical substances. The sensory receptors of taste are located on the upper surface of the tongue and the pharynx. The receptors for smell are located in the upper parts of the nasal passages.

There are four (4) basic taste sensations:

1. Sweet is detected at the tip of the tongue.
2. Sour is detected at the sides of the tongue.
3. Bitter is detected at the back of the tongue.
4. Salt is detected all over the tongue.

The combined cavity of taste buds and smell receptors gives the sensation of flavor. Sensation of taste is important as it helps animals distinguish between suitable and unsuitable substances for ingestion.

It also stimulates the salivary glands to secrete saliva containing digestive enzymes.

The receptors of taste and smell are similar in function. Much of what is called “taste” is in fact a function of the sense of smell.

QUESTIONS

Why does hot food often have more taste than cold food?

– This is because hot food vaporizes more; the vapour passes from the mouth up into the nasal passages where it stimulates smell receptors.

Why can we not taste food well when suffering from a cold?

– This is because the nasal passages are inflamed and coated with mucus. The smell receptors are essentially non-functional.

In each case of taste and smell, chemicals must go into solution in the film of liquid coating the membrane of the receptor cells to be detected.

The major functional difference between the two kinds of receptors is that smell receptors are more specialized for detecting vapour coming to the organism from distant sources. Taste receptors are specialized for detection of chemicals present in the mouth itself. Furthermore, smell receptors are much more sensitive than taste receptors.

DRUGS AND DRUG ABUSE

DRUG

A drug is any substance, natural or synthetic, which has a physiological action on a living body.

It can be used for the treatment of disease or alleviation of pain.

PSYCHOACTIVE DRUGS

Psychoactive drugs are drugs that affect the central nervous system. They produce a false sense of well-being and relieve someone from tension, anxiety, stress, and pain.

Types of psychoactive drugs

1. Stimulants e.g., cocaine, heroin, and nicotine.
2. Sedatives/depressants e.g., alcohol, diazepam, and mandrax.
3. Painkillers/volatile solvents e.g., glue, kerosene, toluene, and petroleum.
4. Hallucinogens.
5. Narcotics.

Forms of drug taking

1. Intravenous: injecting a chemical substance into blood through a vein.
2. Inhalation: some people prefer to inhale volatile solvents such as petrol, glue, or paint.
3. Oral: some drugs are taken through the mouth.
4. Smoking: some drugs like marijuana (bhang or ganja) are smoked.
5. Sniffing: some drugs like cocaine are sniffed through the nose.

DRUG ABUSE

Drug abuse is when drugs are used for non-medical reasons with no regard to their side effects.

When drugs are used regularly, they can cause a state of dependence called addiction. Drug addiction is dependence on a drug so that life becomes unbearable without it. If there is a sudden cut-off of the drug, a person suffers withdrawal symptoms.

1. CAFFEINE

This is a bitter substance found in tea, soft drinks, chocolate, kola nuts, and certain medicines. It has the same effects on the nervous system: accelerates the heart rate and increases the amount of sugar in the blood. These have negative effects on the well-being of the human body.

2. NICOTINE

Found in tobacco, it has the same effects on the nervous system as caffeine. Smoking is linked with cancer of the lungs, mouth, throat, larynx, gullet, bladder, and pancreas. It also thins and weakens lung tissue, delays the healing of stomach ulcers, and reduces the sense of smell and taste.

3. COCAINE

Found in the leaves and nuts of the coca plant, it has similar effects as nicotine.

4. ETHYL ALCOHOL

Found in alcohol and beer, it interferes with the transmission of nerve impulses at synapses. Small amounts have a stimulating effect; large amounts distort vision and interfere with hearing.

The person becomes insensitive to touch and experiences difficulty speaking. Ethyl alcohol slows reflexes and interferes with concentration and distance judgment. This is why people are advised not to drink when driving.

5. OPIUM, MORPHINE, HEROIN, AND METHADONE

These are found in capsules of the poppy plant. These drugs cause feelings of euphoria and power. They interfere with nerve impulse transmission resulting in a positive effect on the well-being of the body. If inhaled in appreciable amounts with either chlorofluorocarbon or benzene, they induce unconsciousness similar to that produced by alcoholic intoxication.

6. VALIUM

Interferes with impulse transmission; others tested with Valium interfere with the function of the medulla.

7. MARIJUANA & HASHISH

Produced from a plant called Indian hemp. These drugs disturb the sense of judgment so that a person becomes careless and foolish.

EFFECTS OF DRUG USE ON HEALTH AND SOCIAL LIFE

Social hazards

• Users may lose their jobs as a result of repeated failure to show up for work.
• Users often turn to crime to support their habit.
• Loss of esteem by the user as he or she may be rejected by their family.
• Loss of work hours as many users take time off to recover from side effects of their habits.
• Relationships may break up as a result of the increasing impotence of the user’s habits.

Health hazards

1. Smoking may lead to lung cancer or heart disease.
2. Alcohol causes brain damage and liver cancer.
3. Some drugs affect the reproductive system by slowing down the rate of sperm production.

CAUSES OF DRUG ABUSE

• Social pressure, fear of being rejected in a social group.
• Taking drugs might ease anxiety or unpleasant feelings.
• Escapism: some take drugs because they think it is the only way to have a pleasant time socially.

PREVENTION

• Avoid taking any form of drugs without a prescription from a doctor.
• If one realizes that they are addicted, they should seek help from health officials.
• To avoid boredom and idleness, one needs to get engaged in activities such as games and sports during leisure time.
• Form counseling clubs in the community to advise people, especially youth, on how to keep off drugs.
• Cultivation of drug-producing plants can also be prevented.
• Drug dealing can also be controlled or eliminated by communities.
• Drug abusers can obtain help in drug rehabilitation centers.

HORMONAL COORDINATION IN HUMANS

Hormonal coordination involves organs which secrete chemical substances. This system is known as the endocrine system, which is composed of glands that secrete chemical substances known as hormones.

These glands have no ducts; their secretions enter directly into the bloodstream or body fluid by diffusion. The hormones are then transported through these media to the target tissues or organs, where they initiate a response.

Therefore, hormonal coordination refers to the regulation of body functions through the release of hormones.

Hormones are vital in the body because they coordinate body functions. Some hormones act directly on effector organs such as muscles; some regulate metabolic activities while others activate other endocrine glands.

Still others regulate normal growth and development of young animals and keep the adult animal in a healthy state.

Hormones are produced in small quantities and in most cases their effects are slow.

The endocrine system and the nervous system are similar in two ways:

1. They are both set into action by a stimulus to produce a response.
2. They both involve chemical transmission.

Difference between nervous and hormonal coordination

Position of endocrine glands in human body

The endocrine system consists of the following glands: pituitary, parathyroid, thyroid, pancreas, adrenal gland, ovaries, and testes.

1. PITUITARY GLAND

Found at the base of the forebrain. It controls the functioning of the body directly by producing its own growth hormone. It is also known as the master gland because it controls other ductless glands, e.g., it controls the production of thyroxin hormone in the thyroid gland.

The pituitary gland produces thyroid-stimulating hormone (TSH) which stimulates the thyroid to release more thyroxin.

The pituitary gland secretes at least nine hormones which include the following:

1. Growth hormone (somatotropin)

This influences protein metabolism and growth of bones. Normal secretion of the hormone produces normal growth.

• Over secretion of the hormone results in abnormal large size of the body; the condition is called gigantism.
• Under secretion results in dwarfism which may be due to delayed growth or permanently retarded growth.

2. Follicle stimulating hormone (FSH) stimulates development of Graafian follicles in the ovary.
3. Testis stimulating hormone causes sperm production in males.
4. Anti-diuretic hormone (ADH) increases the absorption of water from kidneys.
5. Luteinizing hormone brings about ovulation.
6. Prolactin hormone stimulates milk production in lactating mammals.
7. Oxytocin brings about contraction of the uterus at birth and causes expulsion of milk from the mammary gland. Hypo secretion delays birth while hyper secretion results in premature birth.

2. THYROID GLAND

Found in the neck, it produces thyroxin. It regulates the rate of metabolism, stimulates growth and development in young animals, and controls birth to old age.

Under secretion causes cretinism (stunted growth) and severe mental retardation in children.

Over secretion in adults causes exophthalmic goiter and premature ageing. The condition is called myxoedema.

Excess in adults causes underweight, restlessness, and mental instability.

Goitre is characterized by enlargement of the thyroid gland. The cells in the thyroid gland enlarge in an attempt to contract as much iodine as possible from the blood.

3. PARATHYROID

Found within the thyroid gland. It produces parathormone in response to a lack of calcium in the blood, resulting in increased absorption.

4. ADRENAL GLAND

Found above the kidney. They produce adrenaline hormone which prepares the body for action in an emergency by raising blood pressure, increasing heart and breathing rates, increasing blood sugar levels, and increasing supply of blood to the muscles. These actions prepare the individual to run away or to fight the enemy.

Adrenaline is thus referred to as the hormone of flight or fight.

Aldosterone regulates blood sugar and deposition of glycogen into the liver. It is also concerned with the reabsorption of sodium and chloride ions as well as osmotic pressure.

5. PANCREAS (Islets of Langerhans)

Produces insulin which lowers the level of glucose in the bloodstream by causing the liver to store more glycogen.

Too little insulin causes diabetes mellitus (excess glucose in the bloodstream), which is diagnosed by the presence of sugar in the urine.

6. TESTES

Male reproductive organs produce testosterone hormone which is responsible for sperm production and development of male secondary sexual characteristics.

7. OESTROGEN

Produced by the ovary in females. Oestrogen controls the development of female secondary characteristics, promotes development of reproductive organs, and prepares the uterus to receive a ripe fertilized ovum.

• Progesterone is also produced by the ovary. It is concerned with maintenance of pregnancy. It encourages the development of the uterus lining after ovulation. It inhibits ovulation and prevents the uterus from contracting during pregnancy.
• Relaxin is also produced by ovaries beginning at the time of birth. This hormone causes the ligaments between the pelvic bones to loosen, providing a more flexible passage for the baby during birth.