Chapter 9 Nervous System PDF

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Nine Nervous system Introduction In Standard Six, you learnt about the circulatory sys...

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Nine Nervous system Introduction In Standard Six, you learnt about the circulatory system and the LY reproductive system. In this chapter, you will learn about the concept of the nervous system, its parts and functions. You will also learn about the functions of different sensory organs, their disorders and N how to rectify those disorders. The competencies developed will help you to take care of this system and avoid behaviours that can cause O disorders in the nervous system. The concept of the nervous system SE Think U 1. Reasons for closing eyes when you move from a dim light to a bright light area E 2. Reasons for sweating when the temperature rises N Responding to stimuli is one of the characteristics of living organisms. Living organisms respond to stimuli through the nervous system. These LI stimuli include sound, taste, smell, touch, light, and temperature changes. The nervous system coordinates both voluntary and involuntary actions N in the human body. Examples of voluntary actions are playing ball, eating, talking, and reading. Involuntary actions include sneezing, regurgitating, O breathing and beating of the heart. These actions enable the body to recognize and respond appropriately to the changes that occur outside R and inside the body. FO Parts of the nervous system The nervous system is divided into two main parts. These parts are the central nervous system and the peripheral nervous system. The central nervous system is made up of the brain and the spinal cord. The peripheral 107 SCIENCE AND TECHNOLOGY STD 7.indd 107 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE nervous system is made up all the nerves that lie outside the brain and the spinal cord. See Figure 1. Brain Spinal cord Nerves LY N O SE U Figure 1: The human nervous system Parts of the central nervous system and their functions E The central nervous system is divided into two main parts, namely the brain and the spinal cord. N LI The brain Cerebrum This is the largest and most Cerebellum N important part of the central nervous system. Due to its importance, the O brain is encased inside the skull so that it is not touched or injured by anything. The brain receives R information from various sense Medula FO organs through nerves. The main oblongata function of the brain is to coordinate various actions including learning, Figure 2: Parts of the human brain remembering, speaking, and 108 SCIENCE AND TECHNOLOGY STD 7.indd 108 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE thinking. The brain is divided into three main parts. These are the cerebrum, cerebellum and medulla oblongata, as shown in Figure 2. Cerebrum: This is the largest part of the brain. It is folded to increase its surface area. The cerebrum is divided into two parts: the left and right parts. The right part of the cerebrum coordinates actions of the left part of the body, while the left part coordinates actions of the right part of the body. The cerebrum coordinates many functions of the body, such as thinking, deciding, learning, remembering, and moving. This part also interprets LY senses of touch, sight, hearing, taste and smell. Hence, a person may have eyes and ears, but, if the part of cerebrum involved is damaged, he/ she will not be able to see or hear. N Cerebellum: This part of the brain is found below the cerebrum. Its main O function is to coordinate the movement of the muscles in the body. The cerebellum also receives information from parts of the ear that are involved SE in maintaining body balance. It also coordinates all movements related to voluntary actions of the muscles such as walking, picking up something, riding a bicycle, and swimming. These actions are performed efficiently U after learning and getting used to them. Medulla oblongata: This is a very small part of the brain that is connected to the spinal cord. This part coordinates all involuntary actions such as E breathing, heartbeat and the increase or decrease in body temperature. Other involuntary actions include digesting food, coughing, sneezing, N vomiting and swallowing. This part also coordinates all information LI travelling between the brain and the spinal cord. N The spinal cord This part of the central nervous system is connected to the medulla O oblangata. In the human body, the spinal cord is found in a hollow space of the vertebral column. The spinal cord is encased inside the interlocking R bones within the vertebral column, and it forms a canal from the neck to the waist. The spinal cord is soft and delicate; hence, the vertebral column FO protects it from mechanical injury. In each spine of the vertebral column, two nerves called motor and sensory nerves move from the spinal cord to various parts of the body. These nerves function to transmit and retrieve information from various parts of the body. See Figure 3. 109 SCIENCE AND TECHNOLOGY STD 7.indd 109 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE Spinal canal Sensory nerve Motor nerve LY Figure 3: A section of spinal cord N The spinal cord is a major means of communication between the brain and other parts of the body. That is why, when the spinal cord is injured, O communication between the brain and other parts of the body is lost. The spinal cord communicates with the brain through nerves. The spinal cord functions to coordinate involuntary actions arising from external stimuli. SE Some of these actions include a sudden movement of knee jerk after being touched at its lower part. Other involuntary actions include the dilation and contraction of the urinary bladder and a rapid removal of a U body part upon touching a sharp or hot object. These actions protect the body from being harmed. E The function of the central nervous system is to receive information from outside and inside the body and to produce appropriate responses. These N responses are transmitted to other parts of the nervous system or organs of the body for appropriate responses. LI N Activity 1: Constructing a model of the central nervous system O Materials: Manila sheets, light white paper, glue, wheat or cassava flour or clay, stick, and different watercolour paint R Procedure 1. Fold a manila sheet of about five centimeters wide to form a hollow FO tube. 2. Fold another manila sheet to form a thin long pipe. 3. Moisten the clay and make a soft lump. 110 SCIENCE AND TECHNOLOGY STD 7.indd 110 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE 4. Cut the clay soil lump into four different parts with different sizes. Make sure they do not dry. 5. Wrap one large clay lump from Step 4 in white paper and make folds around it using a thin stick. Put the lump in the manila sheet with a hole that you have made in Step 1. This part represents the cerebrum. 6. Take two small sized clay lumps and construct a model of the cerebellum and medulla oblongata. Then connect it with the cerebrum. LY The portion of the model representing the medulla oblongata should be small. Paint the three parts of the brain model representing the cerebrum, cerebellum and medulla oblongata to distinguish them. N 7. Take the fourth lump and lengthen it to a long stick depending on the length of the hollow manila sheet tube. O 8. Insert a stick of clay lump into the pipe. This stick represents the spinal cord, and the pipe is the vertebral column that protects the spinal cord. SE 9. Connect the spinal cord and the brain model as shown in Figure 1. Then, let it dry. 10. Paint each part of the brain model that you made using different U colours. The peripheral nervous system E The peripheral nervous system is made up of nerves that lie outside the N brain and the spinal cord. Nerves are fibre like cells that connect all parts of the body with the central nervous system. The nerves also connect sensory LI organs with the central nervous system. These sensory organs include the eyes, ears, skin, tongue and nose. The nerves transmit information to the N central nervous system for the body to give appropriate responses, timely and efficiently. For example, the central nervous system receives information O from the nerves when a person is thirsty, hungry, in pain or needs to go to the toilet. This system provides responses to wait or fulfil those needs. These responses enable the body to function properly and safely. R Nerve structure FO Nerves are among the cell types that make up the body of an animal. They are made up of nerve cells or neurones. Each neurone is made up of a nucleus surrounded by cytoplasm. The nucleus and cytoplasm form the cell body. The cytoplasm has branches called dendrites. Dendrites take information from 111 SCIENCE AND TECHNOLOGY STD 7.indd 111 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE their surroundings and transmit them to the cell Dendrite body of the responsible Cytoplasm nerve. On the other side of the cell body, Cell body there is a long thread- Nucleus like extension called the axon. This connects the cell body of one nerve LY Axon with another or a cell body of a nerve and an N organ. See Figure 4. O Nerves have different structures depending on their positions in the body. These structures enable them to function SE properly. For example, U the sciatic nerve that receives and transmits information to the limbs E has long axons starting from the waist to the feet. Figure 4: Structure of a nerve cell N LI Types of nerve cells and their functions Nerve cells are divided into three main types: sensory nerves, motor nerves, N and relay or intermediate nerves. Sensory nerves take information from various parts of the body such as sensory organs and transmit them to the O central nervous system. Motor nerves take information from the central nervous system and transmit them to various parts of the body where the R response occurs. The response is based on the type of information. Relay or intermediate nerves carry information from sensory nerves to motor FO nerves. Thus, the intermediate nerves connect the sensory nerves with the motor nerves. 112 SCIENCE AND TECHNOLOGY STD 7.indd 112 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 2: To examine how nerves work Materials: chair and ruler Procedure 1. Sit on a chair and place one foot on top of the other as shown in Figure 5. 2. Allow your fellow pupil to tap the lower part of the knee of your leg, LY which is above the other leg, using a ruler. Observe what will happen. 3. Exchange the sitting position with your fellow pupil; you should stand and do what your fellow pupil did to you. Write down what you have N observed. O SE U E N LI N O R Figure 5: The ways nerves works FO Question Is the shock experienced on the foot voluntary or involuntary? Explain your answer. 113 SCIENCE AND TECHNOLOGY STD 7.indd 113 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE Differences between the central nervous system and the peripheral nervous system Table: Differences between the central nervous system and the peripheral nervous system Central nervous system Peripheral nervous system (i) This system is made up of the brain (i) This system is made up of nerves and the spinal cord. outside the brain and the spinal cord. LY (ii) Nerves are covered by the skull and (ii) Nerves are not covered by bones. the vertebral column. They freely start at the beginning of a muscle or tissue to the end. N (iii) The main function of the central (iii) The main function of the peripheral nervous system is to receive stimuli nervous system is to connect the central nervous system with other O from outside and inside the body and provide interpretations. body parts. It takes stimuli from the sensory organs and inside the body, then transmits them to the central SE nervous system and returns the translated information to the sensory organs. U Exercise 1 Answer the following questions: E 1. Explain three main types of nerve cells and their functions. 2. Differentiate between voluntary and involuntary actions. N 3. Describe the two main parts of the central nervous system. LI 4. Explain the importance of involuntary actions in securing the safety of the human body. N O Sensory organs Sensory organs are structures of the body that are capable of receiving stimuli from external and internal changes in the body. These organs receive R information and transmit them to the central nervous system. The ability to FO taste, see, hear, smell, and sense temperature changes is done through the sensory organs. In the human body, there are five sensory organs. These sensory organs are eyes, ears, nose, tongue and the skin. These organs are connected to the brain by nerves. 114 SCIENCE AND TECHNOLOGY STD 7.indd 114 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE Any defect or disorder of the sensory organ affects the interpretation of the stimuli arising from the environment. For example, a disorder in the ear can cause deafness to a person, and a defect in the eyes can cause blindness to a person. Thus, sensory organs are important since they help the living organism to carry out its daily activities. The eye Eyes are sense organs that enable us to see. They are located on the face in holes called eye sockets. The eyes are held in place by muscles. These LY muscles rotate the eye to enable it to see different directions. The eyes are the only organs that receive light and form images. The interpretation of an image is given by the brain after receiving information from the eye through N the optic nerve. Light is the energy that enables us to see different objects. O Discuss with your fellow pupils SE The changes that occur in eye vision when a person moves from the bright to dim light U Parts of the eye and their functions The eye is made up of two main parts: the internal and external parts. The E external part is made up of eyebrows, eyelashes and eyelids. The internal part is made up of the conjunctiva, cornea, fluid called aqueous humour, N pupil, iris, lens held by ciliary muscles, a fluid called vitreous humour, retina LI and the optic nerve as shown in Figure 6. N Ciliary muscle Retina Iris O Aqueous humour Pupil Optic nerve Conjuctiva R Cornea FO Vitreous humour Lens Figure 6: The internal structure of the eye 115 SCIENCE AND TECHNOLOGY STD 7.indd 115 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE Functions of the parts of the eye Eyelid: This is a skin that covers the eye to protect it from injury and entrance of foreign objects. On the upper and lower parts of this lid, there are hairs called eyelashes. Eyelashes prevent dirty substances such as dust from getting into the eye. Conjunctiva: This is a transparent thin skin that covers and protects the cornea. LY Cornea: This is a transparent thin membrane of skin that covers the front part of the eye. This membrane refracts light to reach the lens before reaching the retina. N Ciliary muscles: These are muscles that expand and shrink to change O the shape of the lens that allows light to pass through. Lens: This is the part that allows light to pass and refracts it in order to SE fall on the retina to form an image of an object. The muscles holding the lens contract or relax, thus changing the shape of the lens. This process enables the person to see objects at different distances. U Aqueous humour: This is a salty fluid. It is located in a small part between the cornea and the lens. The fluid allows light to pass through. E Iris: This is a coloured membrane that regulates the amount of light entering the eye. N Pupil: This is a space or opening in the iris through which the light passes LI towards the lens. Vitreous humour: This is a jelly-like fluid that fills the back part of the lens N and makes the eye to be circular in shape. O Retina: This part has a layer of cells which are stimulated by light that facilitates the formation of images. R Optic nerve: Is a collection of nerves that carry information in the form FO of image from the retina and transmit it to the brain. The brain interprets that image. 116 SCIENCE AND TECHNOLOGY STD 7.indd 116 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 3: To examine the dilation and contraction of the pupil Materials: Torch, a piece of cloth, a watch and a plane mirror Procedure 1. Use a plane mirror to check the size of the pupil of your eye. 2. Close your eyes and wrap them using a piece of cloth for two minutes. 3. Remove the piece of cloth and open your eyes. 4. Immediately, direct the light of the torch to your pupil. LY 5. Look on the plane mirror to see the change in your pupil size. Note: Use a torch with light intensity which will not affect your iris. N This activity can be done in pairs. O Questions 1. What causes decrease or increase in pupil size? 2. What is the advantage of increasing or decreasing the size of the pupil? SE Defects of the eye and how to correct them U Correct image formation of an object takes place on the retina. The image that reaches the retina is upside down as shown in Figure 7. This image is then transmitted to the brain where it is transformed into a real object. E N LI N Tree Image Image O Optic nerve Lens R FO Figure 7: Image of an object in the eye We often see people wearing spectacles. These spectacles help them to see images of different objects in their reality. A person wears spectacles 117 SCIENCE AND TECHNOLOGY STD 7.indd 117 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE to correct a defect in his/her eyes. Two common defects can occur in the human eye. These are short sightedness and long sightedness. Short-sightedness or myopia This defect occurs when a person is unable to see distant objects but can clearly see nearby objects. This problem is caused by high converging power of the lens or abnormally large eye ball that forms images before reaching the retina. Thus, light rays from distant objects converge before LY reaching the retina. This results into the formation of an image in front of the retina. See Figure 8. N O Retina SE An image formed in U Eye lens front of the retina Figure 8: An eye with a short-sightedness defect E Short-sightedness is corrected by wearing spectacles with concave lenses. N These lenses diverge light rays and bring them to the retina. Thus, the image of the object is seen clearly as shown in Figure 9. LI N O An image formed on the retina R FO Concave lens Eye lens Figure 9: Correction of short-sightedness or myopia 118 SCIENCE AND TECHNOLOGY STD 7.indd 118 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE Long-sightedness or hypermetropia Some people can see far objects but cannot clearly see nearby objects. This defect is caused by low converging power of the lens or the eye ball being smaller than normal. Accordingly, the image of an object is formed behind the retina. The image is then focused behind the retina rather than on it as shown in Figure 10. LY Retina N An image formed O behind the Eye lens retina SE Figure 10: An eye with a long-sightedness defect Long-sightedness is corrected by wearing spectacles with convex lenses. These lenses converge the scattered rays and land them on the retina as U shown in Figure 11. E Retina N Retina LI An image formed on the retina N Convex lens O Eye lens Figure 11: Correction of long-sightedness R The ear FO This is an organ for hearing sounds. The ear is also responsible for balancing the body. It is divided into three main parts. These parts are the outer, middle and inner ear as shown in Figure 12. 119 SCIENCE AND TECHNOLOGY STD 7.indd 119 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE Hammer Semicircular canals Anvil Pinna Auditory nerve Meatus LY N Ear drum Stirrup Cochlea O Outer ear Middle ear Inner ear SE Figure 12: Parts of the human ear The outer ear is made up of a pinna and a canal or meatus that leads to the inner ear. The function of the outer ear is to collect sound waves U and direct them to the middle ear. Sound waves are vibrations that travel through the air. These vibrations cause the ear drum to vibrate and move sound waves to the middle ear. E N The middle ear is made up of the ear drum and three connected bones. The bones are the hammer, the anvil, and the stirrup. These bones LI functions to receive vibrations of sound waves from the ear drum and direct them to the inner ear. N The inner ear is made up of semi-circular canals and cochlea. The function O of semi-circular canals is to balance the body. The cochlea contains fluid- filled channels and microscopic hair fibres. When sound waves reach the cochlea, the fluid present scatters and stimulates the hair fibres. The R microscopic hair fibres receive the sound wave’s vibrations and transmit FO them to the auditory nerve. This nerve transmits sound waves to the brain for interpretation. Excessive sound can hurt the ears and affect the ability to hear. Therefore, it is advised against using devices which produce loud sounds in the ear or to sit near objects that produce loud sounds. 120 SCIENCE AND TECHNOLOGY STD 7.indd 120 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE The tongue This organ is responsible for detecting tastes of various substances. You cannot recognise the taste of anything without using the tongue. This ability is due to the presence of taste buds in the tongue. When eating, a person gets a general taste of food even though every part of the tongue detects a specific type Sour Bitterness Sour LY of taste. The tip of the tongue contains taste buds cells that can detect sweetness. Taste buds that detect N the salty taste are found on both sides of the front part of the tongue. The O central part of the tongue contains many taste buds that detect umami, a taste which is found in foods such as meat, mushrooms and tomatoes. The peripheral parts of the tongue SE contain taste buds that can detect the Salty Umami U sour taste. At the back, the tongue Salty has more taste buds that can detect Sweetness the bitter taste. See Figure 13. The E tongue is also used for talking, eating, Figure 13: Tongue taste buds and swallowing. N The nose LI Brain This is a protruded organ on the N human face with two holes. One of Olfactory the functions of the nose is to allow nerve O air to pass during breathing and speaking. Another function of the Nose nose is to detect smells of different R substances. Smells of substances FO travels through the air and enters the nose. Inside the nose, there are hairs that are connected to nerves as shown in Figure 14. The nerves that Figure 14: Parts of the nose 121 SCIENCE AND TECHNOLOGY STD 7.indd 121 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE carry information from the nose to the brain are called olfactory nerves. When these nerves detect a certain smell, they send information to the brain for interpretation. The skin This is the organ that covers the human body. The skin functions to detect sensations of warmth, cold, touch, pressure, pain, and vibrations. The skin is divided into three main parts, which are the upper layer, the middle layer and the inner layer. See LY Figure 15. The skin also has Hair hairs, sensory nerves, blood vessels, and sweat glands. N The upper layer has numerous Upper O nerves. However, the amounts layer of nerves vary from one part of the body to another. This layer Middle contains melanin substances. Melanin gives the skin its colour. This substance helps to protect SE layer Sweat gland Inner U the body from direct sun rays. layer Some babies are born with Blood vessels Sensory nerve a skin that has a very little E amount or no melanin at all. Figure 15: Parts of the skin N This condition is called albinism. The skin of a person with albinism has LI little ability of protecting the body from direct sun rays. Therefore, they are advised to wear hats and clothes that cover most of their bodies. Examples N are trousers and long-sleeved shirts. They are also advised to use special lotions to reduce the effects of direct sun rays on their skins. This in turn O helps to prevent their skins from getting wounds from sunburn. R Disorders of the nervous system The nervous system can experience various disorders, which can affect FO its functioning. These disorders can be caused by the following factors: (a) Diseases such as meningitis, leprosy, epilepsy and polio: These diseases affect the nerves and make the victim unable to detect the 122 SCIENCE AND TECHNOLOGY STD 7.indd 122 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE changes in the environment. Other disease like high blood pressure can affect the brain, thereby causing stroke. This condition causes paralysis and inability to walk or talk. (b) Accident which affect the brain or spinal cord: These accidents affect the nervous system and make the victim unable to work properly. For example, a defect of the spinal cord can lead to paralysis. (c) Depression and stress which cause stroke and in turn affect the functioning of the nervous system: Drug abuse can also cause LY disorders in the nervous system. A drug addict may fail to make the right decisions. N Caring for the nervous system It is important to take care of the nervous system to enable the body to O function effectively. Ways of caring for the nervous system are as follows: One should give the brain time to rest by getting enough sleep of at least SE eight hours a day. Sleeping calms it down and enables it to function properly. Eating a balanced diet, especially the food rich in vitamin A is important. Physical exercise is essential for the health of the nervous system. It is U better to avoid stress to reduce the risk of having a stroke. It is also good to take care of the sensory organs by getting proper treatments when they are attacked by diseases. It is advised to take precautions by observing road safety rules to avoid accidents that may affect the nervous system. In E addition, it is important to avoid using drugs, alcohol and cigarettes. These N substances affect the proper functioning of the nervous system. LI Exercise 2 N Answer all questions in sections A, B, C and D. Section A O Choose the most correct answer and write its letter in the box provided. 1. The following are the disorders in the sensory organs R EXCEPT__________. FO (a) deafness (b) short-sightedness (c) anaemia (d) long-sightedness 123 SCIENCE AND TECHNOLOGY STD 7.indd 123 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE 2. The sensory organ that is responsible for the sensations of hotness and coldness is the__________. (a) eye (b) ear (c) tongue (d) skin 3. The function of the outer ear of the human is __________. (a) collecting sound waves LY (b) interpreting sound waves (c) dispersing sound waves (d) stimulating the inner ear N 4. The correct arrangement of the three bones in the middle ear is as O follows: __________. (a) anvil, hammer, and stirrup (b) stirrup, hammer, and anvil (c) (d) hammer, stirrup, and anvil hammer, anvil, and stirrup SE 5. The brain is divided into three parts, which are the__________. U (a) cerebrum, medulla oblongata, and vertebral column (b) cerebellum, spinal cord, and medulla oblongata (c) cerebrum, cerebellum, and medulla oblongata E (d) medulla oblongata, cerebrum and spinal cord N 6. The nerve that transmits information from the nose to the brain is called the __________. LI (a) olfactory nerve (b) optics nerve N (c) acoustic nerve O (d) auditory nerve 7. The nerve that transmits information from the retina to the brain is R called the __________. (a) auditory nerve FO (b) optic nerve (c) acoustic nerve (d) olfactory nerve 124 SCIENCE AND TECHNOLOGY STD 7.indd 124 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE Section B 8. Match the items in Section A with the correct statements in Section B by writing the letter of the correct answer in the space provided. Section A Answer Section B (i) Brain (a) Bone joints that are connected from the neck to waist (ii) Spinal cord (b) The organ in the human body that LY coordinates all body actions (iii) Vertebral column (c) The part that allows light to pass and refracts it in order to fall on the retina N (iv) Sensory nerve (d) Part of central nervous system protected within the vertebral column O (iv) Iris (e) A nerve that carries information from one part of the body and transmit it to the central nervous system (v) Myopia SE (f) A nerve that carries information from the central nervous system and transmits it to other parts of the body U (vii) Cornea (g) The part that controls the amount of light passing through the eye (h) Defect of short sightedness E (i) Defect of long sightedness N (j) A transparent membrane that allows light to pass LI Section C N Write TRUE for a correct statement and FALSE for an incorrect O statement in the space provided. 9. The function of the nose is only to smell. __________ 10. The tongue is incapable of detecting the taste of the lemon. R __________ FO 11. The function of the eye lens is to prevent light rays from entering the eye. __________ 12. A convex lens is used to correct long-sightedness. __________ 125 SCIENCE AND TECHNOLOGY STD 7.indd 125 26/07/2021 12:01  FOR ONLINE USE ONLY DO NOT DUPLICATE 13. The upper layer of the skin is made up of more nerves than other layers. __________ 14. One can hear very well even if the ear drum ruptures. __________ 15. The cochlea deals with body balance. __________ Section D 16. Describe four functions of the tongue. LY 17. Explain the changes that occur in the eye when a person moves from a bright light to a dim light area. 18. Explain the advantage of a decrease and an increase in the pupil’s N size of an eye. O 19. Mzee Kalulu went to the hospital for an eye test, and he was then given spectacles with convex lenses. What was wrong with his eyes? Explain how the defect can be correct by spectacles. Vocabulary SE U Melanin a substance or natural pigment found in the upper layer of the skin that gives skin its colour and helps to protect the body from the sunrays E Socket holes on the skull where the eyes are held N Taste buds cells in the tongue with nerves that collect information of various tastes LI Umami a taste which is found in foods such as meat, mushrooms and tomatoes N O R FO 126 SCIENCE AND TECHNOLOGY STD 7.indd 126 26/07/2021 12:01