Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Sense Organs
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Sense Organs
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Subject: Biology
Class: Senior Secondary 3
Term: 1st Term
Week: 2
Theme: The Organism At Work
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List the major sense or gans and infer the ir locations. Describe the or gans of smell and taste. Identify the different partsof the to ngue as sociated with sweetness, bitterness, salty.taste and sore taste. Draw the skin showing the different receptors present. Describe the structure of the mammalian ear. Explain the functions of the ear -hearing, balance. Describe the mammalianeye and explain the functions of itsvarious parts.
Explain the functions of the eye:- image for mation- accommodation Explain the terms myopia,hyper metropia, as tigmatism,cataracts, night blindness Name the kind of lensthat can be used to correctmyopic and hyper-metropiadefects.
Sweat gland. Blood vessels. Nerve endings (showing different types of receptors). Sensory Receptors in the Skin (Types and Functions):
1. Mechanoreceptors: Respond to mechanical forces.
Meissner's corpuscles: Located in the dermal papillae, sensitive to light touch and fine discrimination (e.g., feeling the texture of Ankara fabric).
Merkel's discs: Located at the epidermal-dermal junction, sensitive to sustained touch and pressure (e.g., feeling the pressure of a handshake).
Pacinian corpuscles: Deep in the dermis, detect deep pressure and vibration (e.g., feeling the vibration of a phone).
Ruffini endings: Located deep in the dermis, sensitive to skin stretch and sustained pressure (e.g., feeling stretching during exercise).
Hair follicle receptors: Detect movement of hairs (e.g., feeling a fly land on the arm).
2. Thermoreceptors: Respond to temperature changes.
Krause end bulbs: Primarily detect cold.
Ruffini endings: Can also detect warmth (though primarily stretch). Free nerve endings also play a role.
3. Nociceptors (Free nerve endings): Widespread throughout the skin, respond to pain caused by tissue damage (e.g., cuts, burns, excessive heat/cold).
Mechanism of Touch:
1. A stimulus (e.g., pressure, heat, cold, pain) activates specific receptors in the skin.
2. The activated receptors generate nerve impulses.
3. These impulses travel along sensory nerves to the spinal cord and then to the somatosensory cortex in the brain.
4. The brain interprets the impulses as distinct sensations, allowing us to differentiate between hot and cold, sharp and blunt, or light touch and deep pressure. D. The Organ of Hearing and Balance (Ear) The mammalian ear is a complex organ divided into three main parts: the outer ear, middle ear, and inner ear.
1. Outer Ear: Pinna (Auricle): The visible, fleshy part of the ear; made of cartilage. It collects and funnels sound waves into the auditory canal.
Auditory Canal (External Auditory Meatus): A tube leading from the pinna to the eardrum. It amplifies sound and contains ceruminous glands that produce earwax (cerumen) to trap dust and protect the ear.
Tympanic Membrane (Eardrum): A thin, oval membrane that vibrates when struck by sound waves. It separates the outer ear from the middle ear.
2. Middle Ear: An air-filled cavity containing three small bones (ossicles).
Ossicles: Malleus (Hammer): Attached to the eardrum.
Incus (Anvil): Connects the malleus to the stapes.
Stapes (Stirrup): Fits into the oval window of the inner ear.
Function: The ossicles amplify and transmit vibrations from the eardrum to the inner ear.
Eustachian Tube (Auditory Tube): Connects the middle ear to the nasopharynx. It equalizes pressure between the middle ear and the external atmosphere, preventing damage to the eardrum (e.g., during changes in altitude).
Oval Window: A membrane-covered opening that separates the middle ear from the inner ear. The stapes vibrates against it.
Round Window: Another membrane-covered opening that allows fluid movement within the cochlea.
3. Inner Ear (Labyrinth): Contains fluid-filled chambers responsible for both hearing and balance.
Cochlea: A snail-shaped, fluid-filled structure containing the Organ of Corti, which houses the hair cells (auditory receptors). Responsible for hearing.
Vestibule: Contains the utricle and saccule, which detect linear acceleration and static equilibrium (head position relative to gravity).
Semicircular Canals (3): Three fluid-filled loops (anterior, posterior, lateral) arranged at right angles to each other. They detect angular acceleration and dynamic equilibrium (rotational movements of the head).
Auditory (Vestibulocochlear)
Nerve: Transmits impulses from the cochlea and vestibular system to the brain.
Functions of the Ear: a)
Hearing:
1. Sound waves are collected by the pinna and travel down the auditory canal.
2. They cause the tympanic membrane to vibrate.
3. These vibrations are amplified and transmitted by the ossicles (malleus, incus, stapes) to the oval window.
4. The stapes pushes on the oval window, creating pressure waves in the fluid (perilymph and endolymph) within the cochlea.
5. These fluid waves stimulate the hair cells (mechanoreceptors) in the Organ of Corti.
6. The hair cells convert the mechanical energy into electrical signals (nerve impulses).
7. These impulses are sent via the auditory nerve to the brain for interpretation as sound. the cornea, which refracts them significantly.
2. They then pass through the aqueous humor, pupil (regulated by the iris), and the lens.
3. The lens further refracts the light rays, focusing them onto the retina.
4. Due to refraction, the image formed on the retina is real, inverted, and diminished.
5. Photoreceptors (rods and cones) in the retina convert the light energy into electrical signals (nerve impulses).
6. These impulses are transmitted via the optic nerve to the visual cortex in the brain.
7. The brain interprets the inverted image as upright and integrates information to form a complete visual perception. b)
Accommodation: The process by which the eye adjusts the focal length of the lens to focus on objects at different distances.
For Distant Objects (more than 6 meters): Ciliary muscles relax, increasing the tension in the suspensory ligaments. This pulls the lens, making it thinner and less convex (flatter), decreasing its refractive power. Light rays from distant objects are nearly parallel and require less refraction.
For Near Objects (less than 6 meters): Ciliary muscles contract, releasing the tension in the suspensory ligaments. This allows the elastic lens to become thicker and more convex (rounder), increasing its refractive power. Light rays from near objects are divergent and require more refraction to be focused on the retina.
Common Eye Defects and Their Correction: Myopia (Short-sightedness): Explanation: Distant objects appear blurry, while near objects are seen clearly. Occurs when the eyeball is too long or the lens is too curved, causing light rays from distant objects to focus in front of the retina.
Correction: Use a concave lens (diverging lens) to spread out the light rays before they enter the eye, pushing the focal point back onto the retina.
Hypermetropia (Long-sightedness): Explanation: Near objects appear blurry, while distant objects are seen clearly. Occurs when the eyeball is too short or the lens is too flat/less curved, causing light rays from near objects to focus behind the retina.
Correction: Use a convex lens (converging lens) to converge the light rays before they enter the eye, pulling the focal point forward onto the retina.
Astigmatism: Explanation: Blurred vision at all distances due to an uneven or irregular curvature of the cornea or, less commonly, the lens. Light rays are focused unevenly on the retina.
Correction: Use a cylindrical lens which has different refractive powers in different meridians, to compensate for the irregular curvature.
Cataracts: Explanation: A clouding or opacification of the natural lens of the eye, leading to blurred vision, faded colours, and difficulty seeing at night. Common with aging but can also be congenital or due to injury.
Correction: Surgical removal of the cloudy lens and replacement with an artificial intraocular lens.
Night Blindness (Nyctalopia): Explanation: Difficulty seeing in low light conditions. Often caused by a deficiency in Vitamin A, which is essential for the production of rhodopsin (the photopigment in rod cells). Can also be due to genetic conditions or retinal diseases.
Correction: Dietary supplementation with Vitamin A (e.g., from carrots, liver, sweet potatoes, green leafy vegetables common in Nigerian diet like ugu and efo), or addressing the underlying retinal condition.
Introduction to Sense Organs: Sense organs are specialized structures containing receptors that detect specific stimuli from the environment and transmit this information to the brain for interpretation. These stimuli can be chemical, mechanical, thermal, or light energy. The major sense organs are the nose (smell), tongue (taste), skin (touch, temperature, pain), ear (hearing, balance), and eye (sight).
A. The Organ of Smell (Nose)
Location: The olfactory receptors are located in the olfactory epithelium, a specialized patch of mucous membrane found in the upper part of the nasal cavity.
Structure: Olfactory receptors: Bipolar nerve cells with dendrites extending into the mucus layer of the nasal cavity and axons forming the olfactory nerve.
Olfactory cilia: Hair-like projections on the dendrites that increase the surface area for detecting odorants.
Mucus layer: Produced by Bowman's glands, it dissolves odorant molecules, allowing them to bind to receptors.
Mechanism of Smell (Olfaction):
1. Odorant molecules (chemicals that evaporate easily) are inhaled into the nasal cavity.
2. They dissolve in the watery mucus layer covering the olfactory epithelium.
3. Dissolved odorants bind to specific protein receptors on the olfactory cilia.
4. This binding triggers a signal (nerve impulse) in the olfactory receptor cells.
5. The impulses travel along the olfactory nerve fibres directly to the olfactory bulb in the brain.
6. From the olfactory bulb, signals are transmitted to the olfactory cortex for interpretation, allowing the brain to identify and differentiate various smells (e.g., the aroma of jollof rice, the pungent smell of onions, or the warning smell of burning kerosene).
B. The Organ of Taste (Tongue)
Location: Taste receptors (taste buds) are primarily located on the tongue, but also found in the soft palate, pharynx, and epiglottis.
Structure: Papillae: Small bumps on the surface of the tongue (e.g., fungiform, circumvallate, foliate papillae). Many papillae contain taste buds.
Taste buds: Clusters of specialized sensory cells (gustatory cells) with microvilli (taste hairs) that project into a taste pore. Support cells and basal cells are also present.
Different Taste Sensations: The tongue can detect five primary tastes: sweet, sour, salty, bitter, and umami (savoury).
Sweetness: Primarily detected at the tip of the tongue (e.g., sugar, fruits).
Saltiness: Primarily detected at the front sides of the tongue (e.g., table salt, salty snacks).
Sourness: Primarily detected at the mid-sides of the tongue (e.g., lemon, unripe mango).
Bitterness: Primarily detected at the back of the tongue (e.g., bitter leaf, quinine, strong coffee).
Umami: Detected more generally across the tongue (e.g., meat, mushrooms, monosodium glutamate).
Mechanism of Taste (Gustation):
1. Tastant molecules (chemicals responsible for taste) from food dissolve in saliva.
2. Dissolved tastants enter the taste pores and bind to receptors on the microvilli of gustatory cells within the taste buds.
3. This binding generates nerve impulses in the gustatory cells.
4. These impulses are transmitted via cranial nerves (facial, glossopharyngeal, vagus) to the gustatory cortex in the brain.
5. The brain interprets these impulses as specific tastes, allowing us to enjoy food and detect potentially harmful substances.
C. The Organ of Touch (Skin)
Location: The skin, the largest organ of the body, contains various sensory receptors distributed unevenly across its surface.
Structure of Skin: Epidermis: Outermost layer, composed of epithelial cells, provides protection.
Dermis: Layer beneath the epidermis, rich in blood vessels, nerves, hair follicles, and glands. Most touch receptors are located here.
Drawing the Skin showing Receptors: A simple diagram of the skin should include: Epidermis and Dermis layers. Hair shaft and Hair follicle. Sweat gland. Blood vessels. Nerve endings (showing different types of receptors). Sensory Receptors in the Skin (Types and Functions):
1. Mechanoreceptors: Respond to mechanical forces.
Meissner's corpuscles: Located in the dermal papillae, sensitive to light touch and fine discrimination (e.g., feeling the texture of Ankara fabric).
Merkel's discs: Located at the epidermal-dermal junction, sensitive to sustained touch and pressure (e.g., feeling the pressure of a handshake).
Pacinian corpuscles: Deep in the dermis, detect deep pressure and vibration (e.g., feeling the vibration of a phone). down the auditory canal.
2. They cause the tympanic membrane to vibrate.
3. These vibrations are amplified and transmitted by the ossicles (malleus, incus, stapes) to the oval window.
4. The stapes pushes on the oval window, creating pressure waves in the fluid (perilymph and endolymph) within the cochlea.
5. These fluid waves stimulate the hair cells (mechanoreceptors) in the Organ of Corti.
6. The hair cells convert the mechanical energy into electrical signals (nerve impulses).
7. These impulses are sent via the auditory nerve to the brain for interpretation as sound. b)
Balance (Equilibrium): Static Equilibrium (Head position): Achieved by the utricle and saccule in the vestibule. These contain otoliths (calcium carbonate crystals) embedded in a gelatinous membrane. When the head tilts, gravity causes the otoliths to pull on the gelatinous membrane, bending hair cells and sending signals to the brain about head position. Dynamic Equilibrium (Rotational movements): Achieved by the semicircular canals. Each canal contains a fluid (endolymph) and a swelling called the ampulla, which houses hair cells. When the head rotates, the fluid lags behind, bending the hair cells and sending signals to the brain about the direction and speed of rotation (e.g., when a student spins during a game or dances). E. The Organ of Sight (Eye) The mammalian eye is a spherical organ specialized for detecting light and forming images.
Structure of the Mammalian Eye: Outer Fibrous Layer: Sclera: The tough, white outer coat that protects the eye and maintains its shape.
Cornea: The transparent, dome-shaped front part of the sclera that covers the iris, pupil, and anterior chamber. It is the primary structure that refracts (bends) light entering the eye.
Middle Vascular Layer (Uvea): Choroid: A highly vascular layer that nourishes the retina and absorbs stray light (prevents internal reflections).
Ciliary Body: Produces aqueous humor and contains ciliary muscles that control the shape of the lens during accommodation.
Iris: The coloured part of the eye, a muscular diaphragm that regulates the amount of light entering the eye by controlling the size of the pupil.
Pupil: The central opening in the iris through which light passes. It constricts in bright light and dilates in dim light.
Inner Neural Layer: Retina: The light-sensitive layer at the back of the eye, containing photoreceptors (rods and cones).
Rods: Responsible for vision in dim light (scotopic vision) and detecting black, white, and shades of grey. Provide peripheral vision.
Cones: Responsible for vision in bright light (photopic vision) and colour vision. Concentrated in the fovea.
Fovea (Macula lutea): A small pit in the retina, rich in cones, responsible for sharp central vision and detailed colour perception.
Blind Spot (Optic Disc): The point where the optic nerve leaves the eye. It contains no photoreceptors, hence is insensitive to light.
Optic Nerve: Transmits visual information from the retina to the brain.
Lens: A transparent, biconvex structure located behind the iris. It changes shape (accommodation) to focus light onto the retina. Held in place by suspensory ligaments.
Suspensory Ligaments: Fibrous strands connecting the ciliary body to the lens, holding it in position.
Aqueous Humor: A clear, watery fluid filling the anterior segment (between cornea and lens). It nourishes the cornea and lens and maintains intraocular pressure.
Vitreous Humor: A clear, jelly-like substance filling the posterior segment (between lens and retina). It maintains the eye's shape and keeps the retina pressed against the choroid.
Functions of the Eye: * a)
Image Formation:
1. Light rays from an object pass through the cornea, which refracts them significantly.
2. They then pass through the aqueous humor, pupil (regulated by the iris), and the lens.
3. The lens further refracts the light rays, focusing them onto the retina.
4. Due to refraction, the image formed on the retina is real, inverted, and diminished.
5. Photoreceptors (rods and cones) in the retina convert the light energy into electrical signals (nerve impulses).
6. These impulses are transmitted via the optic nerve to the visual cortex in the brain.
7. The brain interprets the inverted image as upright
Health and Hygiene: Understanding sense organs emphasizes the importance of proper hygiene and care.
Eye Care: Avoiding rubbing eyes with dirty hands, protecting eyes from excessive sunlight (e.g., wearing sunglasses during the dry season), seeking prompt medical attention for eye infections common in crowded environments or areas with poor sanitation. Knowledge of night blindness encourages consumption of Vitamin A-rich foods common in Nigeria like carrots, palm oil, ugu, and soko leaves.
Ear Care: Avoiding inserting sharp objects into the ear canal, protecting ears from extremely loud noises (e.g., during concerts or traditional festivals where sound systems can be very loud), and timely treatment of ear infections to prevent hearing loss.
Skin Care: Protection from sun exposure, insect bites, and injuries, especially for individuals whose occupations involve outdoor work (farmers, construction workers).
Safety and Environmental Awareness: Smell: Detecting gas leaks in homes (e.g., cooking gas), identifying spoiled food (common concern in markets without refrigeration), and detecting smoke from a fire, all crucial for personal and community safety.
Sight and Hearing: Essential for navigating busy Nigerian roads, avoiding accidents, identifying potential dangers (e.g., a rapidly approaching vehicle, an open drain), and overall situational awareness in crowded public spaces.
Culinary and Cultural Appreciation: Taste and Smell: These senses are central to appreciating the diverse and rich flavours of Nigerian cuisine. Understanding taste helps explain why certain ingredients are combined (e.g., the balance of sweetness, sourness, and spice in a dish). The aroma of suya, pepper soup, or moi-moi is a significant part of the cultural experience, driven by olfactory perception.
Sight: The vibrant colours of Nigerian textiles (e.g., Adire, Aso-oke), traditional artwork, and cultural festivals (e.g., Calabar Carnival, Eyo Festival) are appreciated through the sense of sight.