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Coordination - Biology Form 4

Background.

In form one, we learnt that one of the characteristics of living things is that they respond to changes in their environment. The responses are necessary for their survival. These responses are made possible due to hormones and the nervous system. You learnt about hormones under the topic Growth and development.

Play the animation to see organisms responding to changes to environment.

Objectives.

By the end of these lessons, you should be able to:

  1. Define the term irritability, stimulus and response
  2. Explain differences between tactic and tropic responses
  3. Explain the production of plant hormones and their effect on tropisms
  4. Relate the structure of the mammalian nervous system to its functions.
  5. Distinguish between simple and conditioned reflex actions.
  6. Explain the role of endocrine system in humans.
  7. State the effects of drug abuse on the human health
  8. Relate the structure to function of the human eye and ear.
  9. Explain defects of the eye and ear and their corrections

RECEPTION, RESPONSE AND COORDINATION IN PLANTS AND ANIMALS.

Introduction.

In order to survive in any environment, living organisms need to be able to detect or perceive external and internal changes in their environment and respond appropriately to the changes. Animals have two different but related systems of coordination namely nervous system and endocrine system. Plants do not posses nervous system and rely entirely on chemical coordination system equivalent to hormones. Plants responses are therefore slow and often involve growth.

The extra possession of a nervous system in animals is probably related to their need to seek food, which requires sense organs and locomotion, which are controlled by a nervous system. In this topic, we will learn how these processes take place

The mammalian eye

The eye contains light receptors (photo receptors) which enable an organism to perceive and distinguish objects in its environment. It is located in a socket in the skull called orbit which offers protection against physical damage. Within the orbit there is a fatty layer lining which cushions the eye therefore providing protection against shock.

In the socket the eye is suspended by sets of rectus muscles which move the eye. The lateral rectus muscles move the eye left and right. The superior and inferior rectus muscles move the eye up and down. The oblique muscles steady the up and down movements of the eye.

Play animation of the eye to see how the eye moves as the various muscles work on it.

There are two thick folds of skin in front of the eye. These are called eye lids. They protect the eye. Many hairs called eye lashes arise from the eye lids these protect the eye from the entry of small foreign particles. Above the eye are portions of raised skin thickly covered with hair which prevents sweat and dust from entering the eye.

The illustration shows the eye lashes, eye brows, eye lids.

Within the inside corner of each eye are lacrimal glands which continuously produce a watery saline and antiseptic fluid called tears. The fluid moistens the surface of the eyes and protects them from foreign matter and infections. Normally tears drain from the eye through the lacrimal duct into the nasal cavity.

Excess tears produced due to strong irritation of the eyes or emotion that is not taken by the lacrimal ducts spills over the eye lids carrying with it any foreign bodies that might have entered the eye. The mammalian eye is spherical and filled with fluid. Its wall consists of three distinct layers.

Play the animation to see the internal structure of the eye

The outer layer is called sclera or sclerotic layer. This is fibrous. It protects the delicate parts of the eye ball and maintains the shape of the eye. The middle layer is called choroid this is heavily pigmented and prevents internal reflection of light.

The inner layer is the retina. This contains photoreceptors it is the part on which images are focused. Lens, this is a transparent biconvex structure separating the chamber of the eye into two, the anterior containing aqueous humour and the posterior containing a more viscous vitrous humour. The lens in position by suspensory ligaments.When these ligaments become tout the lens is stretched and become less convex, when the ligaments become loose, the lens thickens and becomes more converging.

The animation shows the changes in shape of lens as toutness of ligaments changes. Click on the play button to view the animation.

  Iris: This is a thin round sheet of muscular tissue. It is pigmented and contains two sets of muscles, circular and radial which control the diameter of the pupil therefore controlling the amount of light entering the eye.

Cornea: The transparent part of the sclera in front of the lens. It allows light to pass through to the eye. It is refractive and helps focus the image on the retina. The cornea is covered by a tough thin transparent membrane called conjunctiva. This is moistened by tears and frequently cleaned by the blinking of eyelids.

Pupil: This is an adjustable opening in the iris directly in front of the lens. It's size is determined by the contraction and relaxation of the muscles of the iris.

Aqueous humour: This is a watery and transparent liquid in front of the lens. It allows light to pass through to the lens.

Vitrous humour: This is the jellylike mass in the posterior chamber of the eye ball. It refracts light to the retina and give shape to the eye ball.

Retina: Contains the light sensitive cells called rods and cones. These are in close association with neuronees from the optic nerve. These cones contain a chemical pigment called iodopsin which perceives light of high intensity as the colour.When cones are exposed to light of high intensity they iodopsin chemical breaks down, the chemical reaction results in a nerve impulse being created and transmitted through the optic nerves to the brain. The brain interprets the image impulses and gives meaning to the image.

 

Rods contain a photochemical substance called rhodopsin or visual purple. This perceives light of low intensity. It is not sensitive to colour. Rods share neuronees in the retina. Rhodopsin breaks down and releases chemicals that set off an impulse in the neuronees in the retina. The impulse is transmitted to the brain through the optic nerve where interpretation takes place. Norcturnal animals have a higher concentration of rods which enhances their sight in darkness.

The animation shows the rods and cones within the retina. Click on the play button to view the animation.

Accommodation of the eye.

Accommodation refers to the ability of the eye to adjust so as to bring the image of a near or a distant object into sharp focus on the retina. Play the animation to see the accommodation of near and far objects.

Accommodation of a close object.

The lens curvature is altered by the action of the cilliary muscles acting on the suspensory ligaments. To focus on a near object, the cilliary muscles contract thereby relaxing the tension on the suspensory ligaments. This leads to increase in the curvature of the lens. The light rays are sufficiently refracted and brought to focus on the retina. Play the animation to see the accommodation of near objects.

Accommodation of a distant object.

To focus on distant object, the ciliary muscles relax, increasing the tension of the suspensory ligaments. This stretches the lens decreasing its curvature. Light rays from a far object are less refracted and hence focused on the retina. Play the animation to see the accommodation of distant objects.

In bright light

The circular muscles of the iris contract while the radial muscles relax The iris becomes smaller reducing the size of the pupil. Less light therefore enters the eye. Play the animation to see relaxation of radial muscles and contraction of circular muscles.

The function of the iris.

The iris regulates the amount of the light entering the eye.

In dim light

The radial muscles of the iris contract while the circular muscles relax Contraction of the radial muscles pulls the iris outwards enlarging the pupil More light gets into the eye.

Play the animation to see contraction of radial muscles and relaxation of circular muscles.

In bright light

The circular muscles of the iris contract while the radial muscles relax The iris becomes smaller reducing the size of the pupil. Less light therefore enters the eye. Play the animation to see relaxation of radial muscles and contraction of circular muscles.

Defects of the eye.

Sometimes, the eye undergoes some structural changes which make the focusing mechanism difficult. Most of these changes otherwise known as defects can be corrected carefully after diagnosis by an optician. The common eye defects are:

  1. Short sightedness
  2. Long sightedness
  3. Astigmatism
  4. Squintedness
  5. Old sight (presbyopia)
  6. Cataracts
  7. Colour blindness

The photograph shows an optician using detection equipment to diagnose eye defects

Short sightedness

It is a condition in which light rays from a distant object are brought to focus in front of the retina while those from near object are clearly focused on it. Play the animation to see short sightedness.

Short sightedness is also known as myopia. It is caused by a long eyeball. It may also be as a result of the lens becoming less elastic, such a lens may develop a greater curvature which may not be easily adjustable. The illustration shows a long eyeball.

Myopia is corrected by use of diverging or concave lenses. Such lenses spread out (diverge) the distant rays so that the defective eyeball is able to focus effectively onto the retina. Play the animation to see diverging of the rays by the concave lens & focus on the retina

Long sightedness

This is a condition in which light rays from a near object are not brought to focus by the time they reach the retina, while those from a distant object are sharply focused.

Play the animation to see long sightedness.

Longsightedness is also known as hypermetropia, is caused by too short eyeball or an extremely thin lens.

The illustration shows a short eyeball.

Hypermetropia is corrected by use of converging or convex lens. The lens refracts light rays before reaching the eye lens thereby enhancing refraction in order to focus rays sharply onto the retina.

The illustration shows a convex lens.

Play the animation to see converging of the rays by the convex lens.

Astigmatism

Astigmatism is a condition in which light rays from an object are brought to focus in different places. The animation shows image formation in astigmatism. Click the play button to view the animation.

The condition is caused by uneven surface of cornea or lens. This leads to uneven light refraction from an object. The shape of the image formed is therefore destroyed. Astigmatisation is corrected by use of a cylindrical lens in front of the eye. The illustration shows correction of astigmatisation by use of cylindrical lens

Squintedness

Squint refers to the inability to align both eyes simultaneously. Its a condition in which the extrinsic muscles of the eye that control the turning of the eyeball do not coordinate accordingly on stimulation. In this condition, the eye face different directions hence focusing and accommodation are achieved differently. The photograph shows a person with squinted eyes

Old sight (presbyopia)

The ageing process in humans may cause hardening of the lens, which loses elasticity. This leads to progressive reduction in the eyes ability to focus on near objects. Distant objects are however focused on retina. The ciliary muscles become weak and are unable to function well. It can be corrected by wearing a convex lens. In some people bifocal lens is used. The illustration shows bifocal lens for correction of presbyopia.

Cataracts

This is another defect associated with old age. In this condition the eye lens becomes cloudy or opaque hence blocking transmission of light rays. The protein fibres in the lens are coagulated forming the opaqueness in the lens The defect can be corrected surgically by replacing the defective lens with a good one. The Illustration shows an eye with cataracts.

Colour blindness

Its one of the sex linked conditions due to genetic mutation. It leads to inability to distinguish certain colours in humans one is unable to distinguish between red and green colours. Colour blindness so far has no corrective measure.

THE EAR.

The ear is a complex sense organ whose functions are:

  • sound perception
  • maintains body balance

The ear can be divided into 3 parts namely:

  • Outer ear
  • Middle ear
  • Inner ear

     

    The illustration shows the three parts of a mammalian ear

     

     

    The animation shows the structure of the mammalian ear.

     

     

    The Structure of the human ear.

     

    Play the animation to view the structure of the mammalian ear

    The Structure of the human ear.

     

    Outer ear.

     

    This consists of the pinna and the auditory canal.

    Pinna: This is a flap of skin and cartilage which \covers the opening of the external auditory in meatus

     

    Functions -Collecting and concentrating sound waves to the auditory meatus

     

    Auditory meatus (canal): This is a tubular structure that is lined with hairs and has wax secreting cells connected to the pinna and tympanic membrane (eardrum)

    Functions -Direct sound waves to the ear drum. The hairs trap dust/solid tympanic membrane. The was helps in maintaining the flexibility of ear drum

     

    The illustration shows the pinna and the auditory canal

     

     

    Middle ear.

     

    This is an air filled cavity. This part of the ear consists of tympanic membrane, ear ossides, eustdian tube, oval and round window.

     

    i) Tympanic membrane (ear drum): This is a thin tough membrane that covers the external opening of middle ear. Functions - it vibrates when hit by sound waves from external ear and transfers the waves into vibrations. - It transmits the vibrations to the ear ossicles.

     

    ii) The ossicle: These are three tiny bones namely malleus, incus and stapes. They are held by muscles, tensor tympant and stapedius which prevent them from excessive vibrations which may damage the ear drum. Functions - Amplify the sound vibrations from the ear drum. - Transmits the vibration from the ear drum to the fenestra ovals (oval window)

     

    iii) Eustachian tube: This is a short canal that connects the middle ear to the pharynx Functions. It equalizes air pressure between the middle ear and outer ear to prevent distribution of the ear drum

     

    iv) Oval window: this is a flexible membranous tissue that connects the middle ear to the inner ear. Functions It receives vibrations from the ear ossicles and transmits them to the cochlea.

     

    v) Round window: This is a flexible membranous tissue that vibrates following vibrations of the oval window. Functions It dissipates vibrations from the fluid in the inner ear back into the middle ear.

     

     

    The illustration shows parts of the middle ear.

     

     

    The inner ear.

     

    This is a fluid filled cavity connecting to the middle ear by the oval window. It consists of - Semicircular canals - Vestibule - Cochlea i) Semicircular canal and vestibule The Semicircular canals, are inner tubular cavities lying at right angle to each other and are filled with a fluid called endolymph. Two of the semicircular canals lie at tight angle vertically white the third on is horizontal. Each canal has a swelling contains sensory cells for body balance. The semi circular canal maintains balance in relation to the movement. The vestibule consists of the utriculus and succules. The two contain sensory cells, which detect body posture in relation to gravity.

     

    ii) Cochlea Is a series of spiral hollow conical shaped structure filled with an endolymph and perilymph fluids. It is divided into three chambers by the Reissners membrane and Basilar membrane. The three chambers are - Scala vestibule - Scala media - Scala tympani The scala vestibule and scala tympani are perilymph filled while scala media is endolymph filled. The organ of corti is found in cochlea duct which runs in the middle of the cochlea. It is responsible for hearing It contains hair like nerve cells which convert sound vibrations into nerve impulses leading to hearing.

     

    The illustration shows parts of the inner ear

     

     

    The illustration shows parts of the inner ear

     

     

    The process of hearing

    • Pinna collects and concentrates sound waves into the auditory meatus.
    • Sound waves strikes ear drum covering it to vibrate.
    • Ear drum transforms sound waves into vibrations
    • Ear drum transmits vibrations to the ear ossicles, malleus, incus and stapes.
    • The stapes passes vibrations to the oval window from where the vibrations are transmitted to the cochlea causing the fluids to vibrate.
    • The vibrations is stimulates the sensory cell hairs generating nerve impulses which are transmitted to the brain by the auditory nerves for interpretation
    • To discriminate frequencies only specific small parts of the ear cochlea are stimulated
    • The direction of sound is detected accurately as a result of both ears functioning together.If the sound is from one side one ear pick the waves easier than the other hence the intensity of impulses transmitted to brain from one ear will be different to the other ear allowing for the determination of direction and distance.

     

    Play the animation to view the hearing process

     

    Defects of the ear

     

    Ear defects are conditions which makes the ear to be unable to perform its functions. Such as deafness, inability to perceive sound. It may be permanent or partial.

    • Damage to cochlea as a result of round sound or some microbial infection and antibiotics.
    • Partial deafness is brought about by impartment of any of the structure that transmit sound waves or vibrations to the cochlea e.g. eardrum can be damaged by infection or physical blow, ear ossicles may have abnormal growth of the connective tissue in the middle ear making them not vibrate well. The auditory canal may be blocked by production of too much wax.

    Corrections.

    Permanent deafness is hard to correct but partial deafness is corrected by surgery or by use of a learning aid. Deaf people can be assisted by us of sign language. Click on the play button to watch the video.

    Meaning of stimulus, response and irritability.

     

    Stimulus refers to variation in condition which can produce a change in activity of part or the whole organism. Response on the other hand refers to change in activity by the organism with respect to stimulus. The ability to respond to stimuli is a characteristic of all living organisms. Many stimuli originate from outside .However organisms also respond to internal changes. The ability to detect and respond to changes in the environment is known as irritability. This is possible due to presence of receptors and effectors.

     

    Receptors are the parts of the body which receive stimuli, while those bringing about the response are called effectors. Effectors are parts of the body which respond to stimuli. Coordinators integrate the information received. This can be represented diagrammatically as shown below.

     

     

    Responses are brought about by external stimuli such as:

    • Temperature
    • Light
    • pH
    • Humidity
    • Mineral salt
    • Concentration in a habitat
    • Population density
    • Absence or presence of predator

     

     

     

     

     

     

     

     

     

     

    Response to variety of stimuli.

     

    Responses are grouped depending on the types of stimuli. This may involve the whole organism or part of the organism.

     

     

    Play the animation to see movement of whole or part of the organism.

    Positive response is the movement response towards the stimuli, while movement away from the stimuli is negative response.

     

     

    Play the animation to see positive and negative response.

     

    Taxes.

     

    Taxis are the movement of organisms as a whole towards or away from stimulus. This term is used in reference to small organisms. Such as euglena, termites, maggots and amoeba. These responses are usually rapid and necessary for the survival of the organism. The stimuli that elicit tactic responses include light, oxygen, changes in osmotic pressure, chemical substances and heat. The taxes are named based on the stimuli that elicit them.

    Rheotaxis.

     

    Refers to response of an organism to variations in water currents or air currents.eg fish move against water currents.

     

     

    The animation shows fish moving against water currents. Click on the play button to view the animation.

    Butterflies move against wind currents. This helps them to detect the scent of flowers.

     

     

    The animation shows butterflies moving against wind currents. Click on the play button to view the animation.

     

    Chemotaxis.

     

    Refers to response to variation in chemical substances.eg movement of the male gametes towards the female gamete. This enables fertilization to take place.

     

    Play animation to see a sperm moving towards the ovum.

    Mosquitoes move away from insecticides. This helps them to avoid harmful stimuli.

     

    Play the animation to see a person spraying mosquitoes and the mosquitoes flying away.

     

    Thermotaxis

     

    This is a Locomotory response due to temperature changes. E.g. Aquatic parasitic organisms move towards homeotherms. This enables them to bore into the skin or suck blood from the living organisms. E.g. Paramecium moves from a lower temperature of 15 degrees C to a higher temperature of 25 degrees C.

     

     

    The animation shows a paramecium moving from dark cold site of water to blight warm areas. Click on the play button to view the animation.

     

    Phototaxis

     

    This is movement of organism in response light intensity and direction. Euglena and spirogyra move towards the direction of light in order to photosynthesize more effectively. This is positive phototaxis

     

     

    On this animation spirogyra and euglena are moving towards the direction of light. Click on the play button to view the animation.

     

    Termites move away from bright light .This is negative phototaxis. It enables them avoid dehydration due to the heating effect of light.

     

     

    Play the animation see termites moving from a lit box to a dark one.

     

    Aerotaxis.

     

    This is movement of organisms in response to variation in concentration of oxygen. For example amoeba moves from an area of low oxygen concentration to high oxygen concentration. Salmon fish also move to areas of water with higher oxygen concentration.

     

     

    Play the animation to see an amoeba moving from an area of low oxygen concentration to high oxygen concentration.

    The video clip below shows salmon fish moving towards turbulent part of a fish pond. Click on the play button to view the video.

     

     

    Osmotaxis

     

    This is movement in response to changes in osmotic pressure of the environment in which it is. For example sea crabs that find themselves exposed to low tides dig into seashore sand in order to maintain balance in osmotic pressure.

    Play the animation to see sea crabs digging into coral sand at low tide.

     

    The video clip below shows sea crabs digging into coral sand at low tide. Click on the play button to view the video.

    Reception, Response And Co-ordination in Plants.

     

    Tropisms. Plants do not carry out locomotion like animals. Movement in plants is restricted through growth. Tropism is a growth movement of plants parts in response to unilateral stimulus. Tropic movements are manifested through growth curvatures towards the stimulus (positive) or away from the stimulus (negative)

    Types of tropisms

    Plants exhibit the following forms of tropisms:

    1. Phototropism
    2. Chemotropism
    3. Geotropism
    4. Hydrotropism
    5. Thigmotropism / Haplotropism

     

    Phototropism

    This is a growth curvature in response to a source of light. Shoots are positively phototropic while roots are negatively phototropic.

     

     

    Play the animation to see plant shoot bending towards light (positive phototropism).

     

     

    Chemotropism

     

    This is a growth curvature in response to a gradient of chemical concentration. The animation shows pollen grain germinating and pollen tube growing towards the embryo sac of the ovary.

    Click on the play button to view the animation.

     

    Geotropism

     

    Growth curvature in response to gravity. Roots show positively geotropic response while shoots show negative geotropic responses.

    Play the video to see negative and positive geotropism.

     

    Hydrotropism

     

    The growth curvature of plants parts in response to source of water or moisture. Roots are positively hydrotropic.

    Plant roots growing towards water depicting positive hydrotropism.

     

    Thigmotropism/ Haplotropism

     

    Growth curvature of plant parts in response to contact with a solid substance. Roots tips are negatively thigmotropic and grow away from any solid material e.g rocks.

     

     

    The photograph shows the stem of money plant twining around a tree. This shows thigmotropism / haptotropism.

     

     

    Survival value of tropism responses.

     

    Phototropism enables plants to expose their leaves towards sources of light for maximum light absorption for photosynthesis.

     

    The photograph shows trees in a forest growing to expose leaves to light

    .

     

    Hydrotropism

     

    This response enables plant root to grow towards water. Plants need water for photosynthesis transport and support.

    Play the animation to see roots growing towards water.

     

    Haptotropism

     

    This response enables plants with weak stem to obtain mechanical support.

     

     

    The illustration shows a morning glory plant twining around a tree to obtain support.

    Geotropism

     

    This response enables roots to grow towards gravity in order to obtain water and mineral salts and anchor the plant.

     

    The illustration shows plant shoot bending away from gravity and root towards gravity

     

    Chemotropism:

    This response enables plants parts like pollen tubes to reach the embryo sac.

    Play the animation to see pollen tube growing towards the embryo sac for fertilization to occur.

     

    Role of auxins in tropic responses.

     

    Growth responses are mostly influenced by the hormone auxin. Auxins are a class of plants growth substances. One of the most common on the class is indole acetic acid (IAA). Auxins are produced at the roots and shoot tips of plants. They influence cell division and elongation within the meristem region at varying concentrations. In roots high auxin concentrations inhibits growth while in shoots it stimulates faster growth. Roots require very low auxin concentration to stimulate faster growth. Very high auxin concentration in roots and shoots stops growth.

     

    Auxin and Phototropism.

     

    Auxins migrate away from the illuminated plant parts to the non illuminated side. Within the shoot region a high auxin concentration increases rate of growth. The non illuminated side of the plant shoot registers a faster growth than the laminated side.

     

    This leads to bending curvature of the plant shoot towards the direction of light source. When light is evenly distributed on the shoot tip, the auxin concentration is evenly distributed in the shoot causing uniform cell elongation. When light is from a unilateral source auxins migrate away from the source of light to a dark side of the plant.

     

    This causes a high auxin concentration on dark side of plant than illuminated side. A higher auxin concentration on one side of the shoot leads to curvature of the shoot tip towards the source of light.

     

    Play the animation to see the role of auxins in phototropism

     

     

    Auxins and Geotropism.

     

    When a plant is placed horizontally auxins moves down from the upper side of the plant to the lower side. The concentration of auxin on the upper side will be lower than that on the lower side. In the shoot region a higher concentration of auxin on the lower side causes faster growth.

     

    The shoots bends upwards away from gravity. In the root region a higher concentration of auxins on the lower side slows down growth and as a result faster growth on upper cells of the shoot causes root to bend down towards gravity.

     

    The animation shows the effect of auxins on geotropism.

     

    Click on the play button to view the animation.

     

    When the germinating seed is placed horizontally held on a klinostat, auxins are evenly distributed in the shoots and roots. Cell elongation is even in shoots and roots hence curvature fails to occur in both.

     

    Play the animation to see how seedlings respond to gravity when a Klinostat is used.

     

    Auxin and Thigmotropism.

     

    Auxin migrates away from some plant part when in contact with solid objects. This is common in roots of all plants, tendrils and stems of climbing plants. The plants parts with a higher auxin concentration grow faster than those parts with a lower auxin concentration. Faster growth on one side of the plant part causes growth curvature of the plant around the solid object.

     

    Play the animation to see the stem of a money plant coiling around the support post due to difference in auxin concentration.

    Reception, response and Co-ordination in animals.

    Components of the mammalian nervous system.

     

    Animals like plants are able to perceive change in their external and internal environment. They detect those changes through special cells and organs called receptors. Mammalian nervous system includes:

    1. Central Nervous System
    2. Peripheral Nervous System.

    The animation shows the central Nervous System and the Peripheral nervous system

    The Mammalian neurone.

    This is the basic functional unit of the nervous system. It is also called the nerve cell. -The neuron contains all the basic organelles found in other ordinary cells. The only difference is that it has special structural adaptations to enable it transmit nerve impulse. Bundles of neurons form a nerve -there are cranial nerves which arise from the brain while spinal nerve arises from the spinal cord.

     

    The animations show the sensory, motor and relay neuron.

     

    Structure of a neurone.

     

    Play the animation to view the structure of a neurone.

     

    Types of neurones.

     

    There are three main types of neurones:

    1. Sensory neurone: relaying impulse from receptor to central nervous system
    2. Motor neurone: relay impulses from central nervous system to effectors
    3. Intermediate or Relay neurone: relay impulse from sensory to motor neurones

    Play the animation to see the three types of neurones

     

    Sensory neurone.

     

    Play the animation to view the structure of a Sensory neurone.

     

    Motor neurone.

     

    Play the animation to view the structure of a Motor neurone.

     

    Intermediate or Relay neurone.

     

    Play the animation to view the structure of intermediate or Relay neurone.

     

    Functions of the Major parts of the human Brain.

    The brain is divided into two hemispheres: the left and the right hemisphere. The hemispheres are organised into a number of parts which include:

    1. Cerebrum
    2. Cerebellum
    3. Medulla oblongata
    4. Hypothalamus
    5. Pituitary bodies

     

    The illustration shows the main parts of the mammalian brain

     

     

    Play the animation to see the functions of the major parts of the brain

     

     

     

     

     

     

     

    \

     

     

     

    Reflex action.

    A reflex action is a rapid and automatic response to a stimulus usually aimed at enabling the body to avoid harm. The path followed by an impulse in a reflex action is called a reflex arc. A reflex action consists of the following:

    • A receptor
    • A sensory neurone
    • Central nervous system (spinal cord or brain)
    • Motor neurone
    • Effector (muscle or gland)

    b) Conditioned reflex.

    This is automatic response to a stimulus which is substituted for the normal or natural stimulus associated with the response. This comes about when the individual is repeatedly exposed to the stimuli together for a long time for example students responding to a bell at lunch time. When the bell rings students stand up and leave their classroom and go to the dining hall. This is due to associating the bell with food.

     

    The endocrine system.

     

    The endocrine system comprises of glands which secrete hormones. It is another system for coordination in animals in addition to nervous system. Hormones are organic chemical substances which are secreted in one area and usually have an effect in another part of the body of a living organism. The endocrine glands are located in various parts of the body.

     

    The illustration shows the location of various glands in human body.

     

     

     

    The production of hormones from the ductless glands is directly or indirectly influenced by the nervous system. The pituitary gland is the master gland which controls the activities of the endocrine gland. However, the hypothalamus influences the activities of the pituitary gland by monitoring the levels of the hormones in the blood. This is done through negative feedback.

     

    The negative feedback control of thyroxin can be illustrated as shown below.

     

     

    The scheme shows that if thyroxine gland is producing too much thyroxine, the signal levels will be sent to pituitary gland to secrete less thyroid stimulating hormone, which is also called thyrotrophine. In effect, the amount of thyroxine falls.

     

    Thyroxine.

    This hormone is produced by the thyroid gland found in the neck region. The illustration shows the location of thyroid gland in human.

     

     

    Thyroxine hormone controls basal metabolic activities, this is achieved by:

    • Increasing glucose oxidation.
    • Enhances effect of growth hormone i.e. somatotrophin ensuring normal growth and development. Undersecretion of thyroxine, also known as hypothyroidism leads to:
    • Insufficient iodine in the diet.
    • Cretinism in children and myxoedema in adults.

    A cretin child has the following characteristics.

    • Slow growth
    • Very low IQ
    • Long tongue
    • General body sluggishness

     

    The photograph shows cretin children.

     

     

    Myxoedema on the other hand is characterised by swelling of the thyroid gland called goitre. Goitre results due to overworking of the thyroid gland in the attempt to synthesize enough thyroxine. Myoedema is characterised by the following:

    • Low metabolic rate leading to reduced heartbeat and breathing rate and low body temperature
    • The victims are mentally and physically sluggish.
    • Swollen feet and puffy face due to retention of excess fluids.

    Myxoedema can be controlled by use of iodine table salt and administration of iodine tablets.

     

    The photograph shows a person suffering from goitre.

     

    Oversecration of thyroxine, also known as hyperthyroidism also may occur due to defective enzymatic reactions. It could lead to increased metabolic rate resulting in increased heartbeat, breath rate and high temperature.

     Hyperthyroidism victims show nervousness, restlessness and are easily irritable. Extreme hyperthyroidism could lead to heart failure, a condition known as thyrotoxicosis.

     

    Adrenaline.

     

    This hormone is secreted by the adrenal gland, which are attached above the kidney.

    The photograph shows the position of adrenal gland in human body.

     

     

    Adrenaline prepares the body for emergency. It prepares the body to defend itself from danger by fighting or running away. Therefore its also known as fight or flight hormone. This hormone therefore increases the rate of activity so that the body can deal with emergencies. The extra energy required to fight or flee the energy is not produced quickly enough.

     

     

     

    Over secretion of adrenaline may lead to the body being hyperactive. This in turn puts pressure on all the organs concerned. The heartbeat increases increasing the rate of circulation, breathing rate becomes faster and deeper and skeletal muscles increases the rate of contraction and relaxation leading to movement.

    Functional similarities between endocrine and nervous system.

    • Both systems provide means of communication within the body of an organism.
    • Response brought about by both systems increase choices of survival for the organism.
    • Both involve chemical transmission.
    • The target organs are the effecter organs.

    Functional differences between the endocrine and nervous system.

    The table below illustrates the Functional differences between the endocrine and nervous system.

     

     

    Effects of drug abuse on human health.

     

    A drug is a chemical substance which when taken into the body, affects chemical process that occur in the cell. Medicinal drugs are used to restore health when one becomes sick Other drugs are taken for other purposes for which they are intended. Such drugs include alcohol. This leads to drug abuse.

    The effects of drug abuse on human health are destructive and can be illustrated as follows.

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