BIOLOGY NOTES FOR FORM FIVE
Notes 1
RESPIRATION and GASEOUS EXCHANGE
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IMPORTANCE OF REGULAR HEALTH CHECK-UPS – PART 1
1. Lower Healthcare Costs
The
thought of a huge doctor’s bill is daunting to the best of us. If one wants to
cut down on the healthcare costs they may incur it is important that one
schedules a regular health screening. These regular check-ups ensure that you
save money in the long run. This is the case because regular health check-ups
mitigate the risk of potential health ailments that can turn out to be
dangerous. It can also, in certain cases, help reduce the risks of undergoing
surgery and other serious medical expenditure.
2. It can reduce your risk of getting sick
Regular
medical check-ups include a number of physical and mental checks, making sure
that your body and mind are fit and fine. These check-ups are known as full
body check-ups for this reason – because they examine you from head to toe,
almost literally. The reason this is done is to catch any disease early on, and
so that you can be prescribed the right treatment for it.
3. Detect diseases early on
Regular
medical check-ups allow doctors to pick up signs of diseases that the patients
may not even know to exist. With routine screenings, the doctor can diagnose
potentially severe or life-threatening conditions and prevent any
kinds of risks before it is too late or it takes a turn for the worse.
4. Awareness of Personal Health
Many
individuals pass through their daily lives, completely oblivious to the signs
their body is giving them. This ignorance of personal health often causes
treatable conditions to escalate. On the other hand, regular appointments with
your general physician can keep you aware of your body’s health. This awareness
will enable you to take better care of yourself, and take the correct lifestyle
measures to maintain your overall health.
5. Increases life span
By
doing a regular check-up of your body and health, you can be assured of how
healthy you are. By taking the preventive advice from the doctor and following
the doctor’s prescriptions can increase your lifespan as well.
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COORDINATION
Concept of Coordination.
The Concept of Coordination in Organisms
Explain the concept of coordination in organisms
Coordination is the working together of the various organs of an organism in a systematic manner so as to produce a proper response to the stimuli. Without coordination the body becomes disorderly and it may fail to function properly.
The Ways in Which Coordination is Brought About
Outline the ways in which coordination is brought about
The coordination in simple multicellular animals takes place through nervous systemonly. The control and coordination in higher animals called vertebrates (including humanbeings) takes place through nervous system as well as hormonal system called endocrinesystem. Coordination in plants is under the control of hormones.
All the living organisms (plants and animals) respond and react to changes in the environment around them. The changes in the environment to which the organisms respond and react are called stimuli (singular: stimulus). The living organisms show response to stimuli such as light, heat, cold, sound, smell, taste, touch, pressure, pain,water, and force of gravity, etc. The ability to perceive, interpret and respond to stimuli is called irritability or sensitivity.
There are two types of stimuli: external and internal. External stimuli are associated with the surrounding environment such as wind temperature, light, pressure, touch, water and gravity. Internal stimuli occur within the organism, for example, a decrease or an increase in the amount of water and glucose in the blood.
When an organism detects a stimulus, it initiates a response. A response is a behavioural,physiological or muscular activity initiated by a stimulus. For example, if a man touches a very hot utensil accidentally, he quickly pulls his hand away from the hot utensil. Here,heat is the stimulus and the man reacts (responds) by moving his hand away from the hot utensil. Similarly, when the sun is bright, we close our eyes. In this case, light is the stimulus and we react by closing our eyes. Likewise, when the amount of water in the blood drops, the pituitary gland secretes an anti-diuretic hormone (ADH) which stimulates the reabsorption of water in the kidneys.
Multicellular organisms detect stimuli through sense organs called receptors. A receptor is a sense organ (e.g. eye) or sensory nerve ending (e.g. in the skin or internal organ) which receives stimuli and sets nervous impulses. Impulses are electrical transmissions or chemical stimuli that are sent from the receptor to the coordinating system in the organism. The organs that respond to the stimuli are called effectors. A coordinator is an organ (e.g. the brain and spinal cord) that receives messages from the receptors,translates them and sends the information back to an effector for action. An effector is a muscle or gland which receives impulses from nerves, brain or spinal cord and responds to them. Response is the end-action, such as a muscle contracting to cause the movement of the arm. The diagram below illustrates the five components of coordination in mammals.
Nervous Coordination in Human, Neurons
The Structure of Motor Sensory and Relay Neurons
Describe the structure of motor sensory and relay neurons
Neurones
Neurones are nerve cells. They carry information as tiny electrical signals. A neuroneconsists of a cell body (with a nucleus and cytoplasm), dendrites that carry electricalimpulses to the cell, and a long axon that carries the impulses away from the cell. Theaxon of one neurone and the dendrites of the next neurone do not actually touch eachother. The gap between neurones is called the synapse
Structure and functions of neurones
The diagram below shows a typical neurone: in this case, a motor neurone. It has tinybranches at each end (dendrites) and a long fibre (axon) that carries the signals or nervousimpulses. The axon is surrounded by a fatty layer known as the myelin sheath. Thishelps to protect the neurone and allow impulses to travel faster. The sheath is produces bySchawnn cells. The myelin sheath has nodes (Nodes of Ranvier) that speed uptransmission of nervous impulses. The cell body consists of cytoplasm enclosing thenucleus. There are also other organelles in the cytoplasm such as mitochondria thatsupply energy to for metabolic functions.
Synapses
Where two neurones meet, there is a tiny gap called a synapse. Signals cross this gap using chemicals (neurotransmitters) released by a neurone. When the chemical diffuses across the gap it makes the next neurone transmit an electrical signal. The transmission of nervous impulses across synapses occurs thus:
- An electrical impulse travels along an axon.
- This triggers the nerve-ending of a neuron to release chemical messengers calledneurotransmitters.
- These chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the next neuron.
- The receptor molecules on the second neuron bind only to the specific chemicals released from the first neuron. This stimulates the second neuron to transmit the electrical impulse.
Types of Neurones:
There are three types of neurones namely motor neurone, sensory neurone and relay(or intermediate) neurone. Each of these neurones has a different structure and performsdifferent functions.
Motor neurone
A motor neurone is a nerve cell that transmits impulses from the central nervous system(CNS) to the effector organs such as muscles or glands where response is made. The cell body of a motor neurone is at one end of the neurone and lies entirely within the central nervous system (see the diagram above).
Sensory neurone
A sensory neurone is a nerve cell that transmits impulses from the receptors to the CNS.Sensory neurones have their cell bodies off the axon and outside the central nervoussystem.
Relay (intermediate or inter) neurone
A relay neurone conveys messages between neurones in the CNS. Relay neurones are located in the CNS between the sensory and the motor neurones.
Central Nervous System (CNS)
The Meaning of Central Nervous System
Give the meaning of central nervous system
The CNS is the part of the nervous system consisting of the brain and spinal cord. Itcoordinates all the neural functions. The chart below shows subdivisions of the nervoussystem.
The brain
The human brain is a specialized organ that is ultimately responsible for all thought and movement that the body produces. This allows humans to successfully interact with their environment, by communicating with others and interacting with inanimate objects near their surroundings. If the brain is not functioning properly, the ability to move, generate accurate sensory information or speak and understand language can be damaged as well.
The brain has many different parts. Each part has a unique function that allows humansobserve and interact with their environment effectively. The following are parts of thehuman brain and their functions:
Cerebrum
The cerebrum is the largest portion of the brain, and contains tools which are responsible for most of the brain’s function. It is divided into four sections: the temporal lobe, the occipital lobe, parietal lobe and frontal lobe.
Parietal Lobe: Located in the cerebral hemisphere, this lobe focuses on comprehension.Visual functions, language, reading, internal stimuli, tactile sensation and sensory comprehension are monitored here.
Temporal Lobe: The temporal lobe controls visual and auditory memories. It includesareas that help manage some speech and hearing capabilities, behavioural elements, andlanguage. It is located in the cerebral hemisphere.
Occipital Lobe: the occipital lobe is located in the cerebral hemisphere in the back of thehead. It helps to control vision.
Cerebellum
This is commonly referred to as “the little brain‖. The cerebellum controls essential bodyfunctions such as balance, posture and coordination, allowing humans to move properlyand maintain their posture.
Limbic system
The limbic system contains glands which help relay emotions. Many hormonal responses that the body generates are initiated in this area. The limbic system includes the amygdala, hippocampus, hypothalamus and thalamus.
Amygdala: The amygdala helps the body responds to emotions, memories and fear.
Hippocampus: This portion of the brain is used for learning memory, specificallyconverting temporary memories into permanent memories which can be stored within thebrain.
Hypothalamus: The hypothalamus region of the brain controls mood, thirst, hunger and temperature. It also contains glands which control the hormonal processes throughout the body.
Thalamus: The thalamus is located in the centre of the brain. It helps to control theattention span, sensing pain and monitors input that moves in and out of the brain to keeptrack of the sensations the body is feeling.
Brain stem
All basic life functions originate in the brain stem, including heartbeat, blood pressure and breathing. In humans, this area contains the medulla, midbrain and pons.
Midbrain: This part of the brain helps regulate body movement, vision and hearing.
Pons: The pons interprets information that is used in sensory analysis or motor control.The pons also creates the level of consciousness necessary for sleep.
Medulla: The medulla or medulla oblongata is an essential portion of the brain stemwhich maintains vital body functions such as the heart rate and breathing.
The diagram below shows and summarizes the basic functions of different parts of thebrain.
The Components of the Central Nervous System and their Functions
Identify the components of the central nervous system and their functions
The table below summarizes the structure and functions of the major components of the brain.
The Structure of the Spinal Cord and Brain
Describe the structure of the spinal cord and brain
Spinal cord
The spinal cord functions primarily in the transmission of neural signals between the brain and the rest of the body but also contains neural circuits that can independently control numerous reflexes and central pattern generators. It carries out two main functions:
- It connects a large part of the peripheral nervous system to the brain. Information(nerve impulses) reaching the spinal cord through sensory neurons is transmitted up into the brain. Signals arising in the motor areas of the brain travel back down the cord and leave in the motor neurones.
- The spinal cord also acts as a minor coordinating centre responsible for some simplereflexes like the withdrawal reflex.
The intermediate neurones carrying impulses to and from specific receptors and effectors are grouped together in spinal tracts.
The diagram shows various sections of the spinal cord and the functions of each section.
Peripheral Nervous System (PNS)
The Meaning of Peripheral Nervous System
Give the meaning of peripheral Nervous System
The peripheral nervous system is made up of a network of nerves linking various parts of the body to the brain and spinal cord. It includes the cranial nerves, spinal nerves and their roots and branches, peripheral nerves, and neuromuscular junctions.
The peripheral nervous system (PNS) has two components: the somatic nervous systemand the autonomic nervous system. The PNS consists of all of the nerves that lie outsidethe brain and spinal cord.
The Components of the Peripheral Nervous System and Their Functions
Identify the components of the peripheral nervous system and their functions
The somatic nervous system is made up of nerves that connect to voluntary skeletal muscles and to sensory receptors. It is composed of afferent nerves that carry information to the central nervous system (spinal cord) and efferent nerves that carry neural impulses away from the central nervous system. This system is responsible for the involuntary control of the skeletal muscles, bones and sense organs.
The autonomic nervous system is further subdivided into sympathetic andparasympathetic nervous system.
- The sympathetic nervous system activates the ‗fight or flight’ response under sudden or stressful circumstances, for instances by raising the heart rate and dilating the pupils.
- The parasympathetic nervous system helps the body return to normal activity after an emergency, which conserve energy and replenishes the system.
Together, these two systems regulate homeostasis within the body – one preparing the body for action, and the other repairing the body afterward.
Reflex Action
The Meaning of Reflex Action
Give the meaning of reflex action
When a receptor is stimulated, it sends a signal to the central nervous system, where thebrain co-ordinates the response. But sometimes a very quick response is needed, one thatdoes not need the involvement of the brain. This is a reflex action.
The reflex action is a rapid, involuntary response to a certain stimulus. The route that is followed by impulses during a reflex action is called a reflex arc.
Reflex actions are rapid and happen without us thinking. For example, you would pully our hand away from a hot flame without thinking about it. The diagram below shows a simplified reflex arc.
This is what happens:
- receptor detects a stimulus – change in the environment
- sensory neurone sends signal to relay neurone
- motor neurone sends signal to effector
- effector produces a response
The above process appears to be a long one but, in reality, the process takes a very shorttime. It happens within seconds.
The way the iris in our eye adjusts the size of the pupil in response to bright or dim lightis also a reflex action. It happens without our thinking and beyond our control.
The Neuronic Path of a Reflex Action
Describe the neuronic path of a reflex action
A reflex action can either be simple or conditioned reflex.
Simple reflex action
An example of a simple reflex found in humans is the pupil reflex, where the pupil of the eye gets larger in dim light and smaller in bright light.The eye needs to control the amount of light entering it in different light conditions. In dim conditions, more light is allowed to enter so that a clear image can be formed on the retina. In bright conditions, less light is allowed to enter so that the retina is not damaged.
Conditioned reflex action
A conditioned reflex is some action or feeling that is learned in response to a specificsituation or stimulus.
A Russian scientist called Pavlov trained dogs to expect food whenever he rang a bell.The dogs eventually produced saliva when they heard the bell ring. The dog salivates naturally when given food. Pavlov rung a bell every time the dogs were to be given food.After much repetition the dogs salivated when they heard the bell ringing, even when there was no food. This is an example of a conditioned reflex.
The dogs were conditioned to salivate when the bell rang. A ringing bell does not normally cause salivation in dogs. However, when the ringing bell becomes a secondary stimulus, it does cause salivation, even though the dog will not be able to eat the bell as food.
This is now called a conditioned reflex. In a conditioned reflex the final response(salivation) has no direct connection with the stimulus (ringing bell).
Another example of a conditioned (learned) reflex is when the driver comes across a hurdle on the road such as a ditch or a pedestrian. In such circumstances, the first thing the driver will do is to move his leg towards the brake pedal to apply the brakes. He has learned to do this action for so long that he finds himself applying the brake in any of such circumstances.
The Difference between Simple Reflex and Conditioned Reflex Action
Distinguish simple reflex from conditioned reflex action
Differences between conditioned reflex action and simple reflex action
| Conditioned reflex | Simple reflex | |
| 1 | It involves more than one stimuli | Requires only one stimulus |
| 2 | Involves the brain | Mostly involve the spinal cord |
| 3 | It is an immediate action (no time to learn) | It is an immediate action (no time to learn) |
| 4 | It is acquired in one‘s life | It is inborn |
Modifying a reflex response
In some circumstances the brain can modify a reflex response. It does this by sending an impulse along a motor neuron of the reflex arc. This enables us, for example, to hold a hot dinner plate when normally we would drop it.
Sense Organs
The Meaning of a Sense Organ
Explain the meaning of a sense organ
Sense organs are organs of the body that detect and respond to changes in the environment (stimuli) so as to survive.
Types of Sense Organs and Their Relative Position
Identify types of Sense organs and their relative position
There are five sense organs in our body: eyes,ears, nose, tongue and skin. We receive a variety of information from the environmentaround us through the sense organs. The sense organs contain receptors. A receptor is acell (or a group of cells) in a sense organ which is sensitive to a particular type ofstimulus (or a particular type of change in the environment) such as light, sound, smell,taste, heat, pressure, etc. The different sense organs contain receptors for detectingdifferent stimuli.
The eyes have light receptors (which can detect light), ears have sound receptors (which can detect sound), nose has smell receptors (which can detect smell), tongue has taste receptors (which can detect taste) whereas skin has receptors for detecting touch,pressure, heat (or cold) and pain, etc.
The Structure of Each Sense Organ
Describe the structure of each sense organ
The human eye
The eye is the organ for vision. The eye is one of the most complex parts of the body.The different parts of the eye allow the eye to take in light and perceive objects around usin the proper colour, detail and depth. This allows people to make more informeddecisions about their environment. If a portion of the eye becomes damaged, you may notbe able to see effectively. You may even lose your vision completely.Parts of the eye and their functionsThere are several physical and chemical elements that make up the eye. The table belowshows different parts of the human eye and their functions.Eye part Description and function(s)Cornea The cornea is the outer, transparent covering of the eye. This layerprotects the eye from elements that could cause damage to the innerparts of the eye. The cornea also helps to focus light on the retina at theback of the eye.Sclera The sclera is commonly referred to as the “white” of the eye. It protectsthe eye and maintains the shape of the eye ball.Pupil The pupil appears as a black dot in the middle of the eye. This blackarea is actually a hole that takes in light to enable the eye focus on theobjects in front of it. The pupil, thus, controls the amount of light thatenters the eye.Iris The iris contains the pigment which gives the eye its colour. It has radialInternal structure
Parts of the eye and their functions
There are several physical and chemical elements that make up the eye. The table belowshows different parts of the human eye and their functions.
| Eye part | Description and function(s) |
| Cornea | The cornea is the outer, transparent covering of the eye. This layer protects the eye from elements that could cause damage to the inner parts of the eye. The cornea also helps to focus light on the retina at the back of the eye. |
| Sclera | The sclera is commonly referred to as the “white” of the eye. It protects the eye and maintains the shape of the eye ball. |
| Pupil | The pupil appears as a black dot in the middle of the eye. This black area is actually a hole that takes in light to enable the eye focus on the objects in front of it. The pupil, thus, controls the amount of light that enters the eye. |
| Iris | The iris contains the pigment which gives the eye its colour. It has radial and circular muscles that control the size of the pupil by dilation and contraction. This allows the eye to take in more or less light depending on how bright it is around. The iris allows more light into the eye when the environment is dark and allows less light into the eye when the environment is bright. |
| Conjunctiva | This is a membrane that covers the cornea. It is thin and transparent so as to allow light to enter the eye. It is tough and protects the eye from mechanical damage. |
| Lacrimal glands | These glands are located on the outer corner of each eye. They produce tears which help moisten the eye when it becomes dry, and flush out particles which irritate the eye. As tears flush out potentially dangerous irritants, it becomes easier to focus properly. |
| Lens | This is a transparent structure filled with a jelly-like substance. The lens focuses light into the retina. It is held in place by the suspensory ligaments attached to the ciliary muscles, which allow the lens to change shape depending on the amount of light entering the eye. Through the ciliary muscles, the lens becomes thicker to focus on nearby objects and thinner to focus on distant objects. |
| Retina | Retina is the sensory tissue that lines the inner layer of the eye. It is the layer of the eye where images are formed, and it is connected to the optic nerve that transmits the images to the brain to be interpreted. The retina is made up millions of photoreceptors known as rods and cones. |
| Ciliary body | Ciliary body, also called ciliary muscles, is a ring-shaped tissue which holds and controls the movement of the eye lens, and thus, it helps to control the shape of the lens. The ciliary body contains glandular cells which secrete the aqueous humour. |
| Suspensory ligaments | The suspensory ligaments attach the lens to the ciliary muscles. When the ciliary muscles contract, they pull the suspensory ligaments and the lens gets long and thin to accommodate rays of light from distant objects. When the ciliary muscles relax, there is less tension on the suspensory ligaments and the lens becomes more spherical in shape. This enables the accommodation of light rays from near objects. |
| Choroid | The choroid lies between the retina and the sclera, which provides blood supply to the eye. Just like any other portion of the body, the blood supply gives nutrition to the various parts of the eye. |
| Vitreous humour | The vitreous humour is the gel located in the back of the eye which helps it hold its shape. This gel takes in nutrients from the ciliary body, aqueous humour and the retinal vessels so the eye can remain healthy. The gel in the vitreous humour is transparent to allow light to get to the retina and also helps maintain the shape of the eyeball. |
| Aqueous Humor | The aqueous humour is a watery substance that fills the eye. The aqueous humour gives the front of the eye its shape as well as nourishes the cornea and lens. This liquid is drained through the Schlemm canal so that any build-up in the eye can be removed. If the person’s aqueous humour is not draining properly, s/he can develop glaucoma. |
| Optic nerve | Optic nerve is a cranial nerve which contains sensory neurones. The neurones transmit impulses from the rods and cones of the retina to the brain for interpretation. The optic nerve exits the eye at the blind spot. |
| Blind spot | It is located at the point where the optic nerve leaves the eye. The blind spot is not sensitive to light because it has no rods or cones. |
| Fovea | The fovea is the centremost part of the macula*. This tiny area is responsible for our central, sharpest vision. A healthy fovea is important for reading, watching television, driving, and other activities that require the ability to see detail.*Small and highly sensitive part of the retina responsible for detailed central vision. The retina is the very centre of the macula. |
Adaptations of the eye to its functions
The eye is adapted to its functions by possessing the following features:
- Conjunctiva, cornea and lens are transparent to allow light to pass through them.
- Sclerotic layer is made up of (collagen) fibres; it maintains shape of eyeball/protectsthe eye from mechanical damage.
- Cornea is transparent and curved thus refracts light rays and allows light to passthrough.
- Choroid (a layer of a tissue) has black or dark pigments that prevent internalreflections of light in the eye.
- The eye contains blood vessels in the choroids layer that supply oxygen and nutrientsto the eye, giving the eye energy to perform its function, and removes the metabolicwastes from the eye.
- Retina is made of photoreceptors known as rods and cones, which trap light rays toenable the eye to do its function of vision.
- Yellow spot (fovea) has the highest concentration of cones for accurate and sharp,central vision.
- Optic nerve has sensory neurones for transmission of nerve impulses to the brain (forinterpretation).
- Lens is biconvex and made up of elastic, transparent material which adjusts to focusfar or near objects and allows light rays to pass through.
- Suspensory ligaments are fibrous to hold the lens in place.
- . The ciliary body contains ciliary muscles which are contractile to for controlling thecurvature and hence focal length of the lens. It also contains glands that secrete theaqueous and vitreous humours.
- The iris is opaque and contractile for controlling the amount of light entering the eye(by adjusting the size of the pupil).
- Ocular muscles coordinate eye movement so that both eyes can follow a movingobject together.
- The eyelid covers an eye and prevents it from mechanical damage and invasion byforeign bodies.
- Eye lashes help to prevent dust and small insects or particles from entering the eyeby trapping them on their hairs.
- The presence of aqueous and vitreous humours helps the eye to bend light raystoward retina to process the signal and send impulse to the brain.
The Functions of Sense Organs and their Adaptive Features
Explain the functions of sense organs and their adaptive features
Adaptations of the eye to its functions
The eye is adapted to its functions by possessing the following features:
- Conjunctiva, cornea and lens are transparent to allow light to pass through them.
- Sclerotic layer is made up of (collagen) fibres; it maintains shape of eyeball/protectsthe eye from mechanical damage.
- Cornea is transparent and curved thus refracts light rays and allows light to passthrough.
- Choroid (a layer of a tissue) has black or dark pigments that prevent internalreflections of light in the eye.
- The eye contains blood vessels in the choroids layer that supply oxygen and nutrientsto the eye, giving the eye energy to perform its function, and removes the metabolicwastes from the eye.
- Retina is made of photoreceptors known as rods and cones, which trap light rays toenable the eye to do its function of vision.
- Yellow spot (fovea) has the highest concentration of cones for accurate and sharp,central vision.
- Optic nerve has sensory neurones for transmission of nerve impulses to the brain (forinterpretation).
- Lens is biconvex and made up of elastic, transparent material which adjusts to focusfar or near objects and allows light rays to pass through.
- Suspensory ligaments are fibrous to hold the lens in place.
- . The ciliary body contains ciliary muscles which are contractile to for controlling thecurvature and hence focal length of the lens. It also contains glands that secrete theaqueous and vitreous humours.
- The iris is opaque and contractile for controlling the amount of light entering the eye(by adjusting the size of the pupil).
- Ocular muscles coordinate eye movement so that both eyes can follow a movingobject together.
- The eyelid covers an eye and prevents it from mechanical damage and invasion byforeign bodies.
- Eye lashes help to prevent dust and small insects or particles from entering the eyeby trapping them on their hairs.
- The presence of aqueous and vitreous humours helps the eye to bend light raystoward retina to process the signal and send impulse to the brain.
The human ear
The ear is the organ of hearing and maintaining balance and posture. The outer earprotrudes away from the head and is shaped like a cup to direct sound waves toward thetympanic membrane, which transmits vibrations to the inner ear through a series of smallbones (ossicles) in the middle ear called the malleus, incus and stapes. The inner ear, orcochlea, is a spiral-shaped chamber covered internally by nerve fibres that react to thevibrations and transmit impulses to the brain via the auditory nerve. The brain combinesthe input of our two ears to determine the direction and distance of sounds.
The inner ear has a vestibular system formed by three semicircular canals that areapproximately at right angles to each other and which are responsible for the sense ofbalance and spatial orientation. The inner ear has chambers filled with a viscous fluid andsmall particles (otoliths) containing calcium carbonate. The movement of these particlesover small hair cells in the inner ear sends signals to the brain that are interpreted asmotion and acceleration. The figure below shows the internal structure of themammalian ear.
Adaptations of the mammalian ear to its functions
The ear is adapted to its functions by possessing the following features:
- The outer ear (pinna) is a flap of tissue which collects sound waves and directs theminto the inner ear via the auditory canal.
- The lining of auditory canal contains wax-secreting cells which produce wax. Thewax in the canal traps dust particles and other foreign bodies and hence protects theinner delicate parts of an ear from mechanical damage or microbial infections.
- The ear drum is thin and membranous, a fact that enables it to vibrate when soundwaves hit it before converting the waves into vibrations and passing them on to theear ossicles in the middle ear.
- The ear ossicles (malleus, incus and stapes) act as a lever system which can moveforward and backward to amplify and transmit vibrations to the oval window.
- The Eustachian tube is hollow, a fact which allows air in and out of the middle ear toequalize the pressure between the inside and outside of the ear drum—whichimproves the drum‘s ability to vibrate
- The cochlea is coiled to increase the surface area for sound reception. It also cariesauditory nerves which transmit sound impulses to the brain for interpretation.pinnaear drumskull bonesemi-circular canalsauditory canaleustachian tuberound windowcochleaauditory nerveInternal structure of the human earoval window
- The presence of fluid-filled vestibular apparatus (semi-circular canals, sacculus, andutriculus) in the inner ear facilitates balancing of sound when the fluid is displaced.
The tongue
The tongue is an organ responsible for taste. It is the primary organ of taste (gustation), asmuch of its upper surface is covered in taste buds. The tongue’s upper surface is alsocovered with numerous lingual papillae. The tongue is sensitive and kept moist by saliva,and is richly supplied with nerves and blood vessels.
The receptors for taste, called taste buds, are situated chiefly in the tongue, but they arealso located in the roof of the mouth near the pharynx. They are able to detect four basictastes: salty, sweet, bitter, and sour.
Generally, the taste buds close to the tip of the tongue are sensitive to sweet and saltytastes, whereas those in the back of the tongue are sensitive to bitter tastes. The taste budsin the sides of the tongue are sensitive to sour tastes. At the base of each taste bud there isa nerve that sends the sensations to the brain. The sense of taste functions in coordinationwith the sense of smell.
The number of taste buds varies substantially from individual to individual, but greaternumbers increase sensitivity. Women, in general, have a greater number of taste budsthan men. As in the case of colour blindness, some people are insensitive to some tastes.
Adaptation of the tongue to its functions (as a sense organ)
The tongue is adapted to its functions by possessing the following features:
- The tongue has taste buds which help it to respond the stimuli such as sweet, bitter,sour and salty.
- At the base of each taste bud there is a nerve that sends the sensations to the brain.
The human nose
The nose is the organ responsible for the sense of smell. The cavity of the nose is linedwith mucous membranes that have smell receptors connected to the olfactory nerve. Thesmells themselves consist of vapours of various substances. The smell receptors interactwith the molecules of these vapours and transmit the sensations to the brain. The smellreceptors are sensitive to seven types of sensations that can be characterized as camphor,musk, flower, mint, ether, acrid, or putrid. The sense of smell is sometimes temporarilylost when a person has a cold. Dogs have a sense of smell that is many times moresensitive than man’s.
When we want to ―smell‖ food we draw air high up into the nasal cavity where thechemicals come into contact with hairs on the sensory cells. Different chemicalsstimulate different sensory cells and nervous impulses are set up which pass along theverves to the brain to be interpreted.
When our nose is blocked with cold, our food may become ―tasteless‖ because we nolonger smell it.
Adaptations of the nose to its functions
The nose is adapted to its functions by possessing the following features:
