Lesson Notes By Weeks and Term v5 - Grade 12
Human nervous system and senses – Week 7 focus
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Human nervous system and senses – Week 7 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Life Sciences
Class: Grade 12
Term: 3rd Term
Week: 7
Theme: General lesson support
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The human nervous system is an incredibly complex and vital network that allows us to perceive the world, react to stimuli, and maintain homeostasis. This week, we will delve deeper into the intricate workings of the human nervous system and explore the fascinating world of our senses. Understanding this system is crucial because it impacts our everyday lives in countless ways – from avoiding danger in the streets of Johannesburg to experiencing the joy of listening to Maskandi music in KwaZulu-Natal or smelling braaied meat at a shisa nyama.
2. 1. The Central Nervous System (CNS) The CNS is the control center of the body, consisting of the brain and the spinal cord. It receives information from the peripheral nervous system (PNS), processes it, and initiates responses.
Brain: The brain is the most complex organ in the human body.
It's divided into three main regions: Cerebrum: The largest part of the brain, responsible for higher-level functions like thinking, learning, memory, emotions, and voluntary movements. It is divided into two hemispheres (left and right), each further divided into lobes: Frontal Lobe:* Involved in planning, decision-making, personality, and motor control (e.g., controlling muscles used for writing is driven by this region).
Parietal Lobe:* Processes sensory information like touch, temperature, pain, and spatial awareness (e.g., knowing where your hand is in relation to your body without looking).
Temporal Lobe:* Involved in hearing, memory, and language comprehension (e.g., understanding the words spoken by a news anchor on SABC).
Occipital Lobe:* Processes visual information (e.g., recognizing the colors of the South African flag).
Cerebellum: Located at the back of the brain, responsible for coordinating movement, balance, and posture (e.g., allows you to walk smoothly without stumbling even after taking a taxi ride on bumpy roads).
Brainstem: Connects the brain to the spinal cord. It controls vital functions like breathing, heart rate, blood pressure, and sleep-wake cycles (e.g., ensuring your heart continues to beat automatically even when you are asleep).
Spinal Cord: A long, cylindrical structure extending from the brainstem down the back. It serves as a pathway for communication between the brain and the PNS. It also controls reflexes, allowing for quick responses to stimuli without involving the brain (e.g., quickly pulling your hand away from a hot stove). 2.
2. The Peripheral Nervous System (PNS) The PNS consists of all the nerves that extend from the brain and spinal cord to the rest of the body.
It's divided into two main branches: Somatic Nervous System: Controls voluntary movements of skeletal muscles (e.g., raising your hand to answer a question in class). It relays sensory information from the body to the CN
S. Autonomic Nervous System: Controls involuntary functions of internal organs and glands (e.g., digestion, heart rate, breathing).
It is further divided into two branches: Sympathetic Nervous System:* "Fight or flight" response – prepares the body for action in stressful situations (e.g., increased heart rate and breathing when encountering a snake while walking in the Kruger National Park).
Parasympathetic Nervous System:* "Rest and digest" response – conserves energy and promotes relaxation (e.g., slowing down heart rate after exercise). 2.
3. The Human Eye: Structure and Function The eye is the organ of sight.
Key structures include: Cornea: The transparent outer layer that refracts light entering the eye.
Iris: The colored part of the eye that controls the size of the pupil.
Pupil: The opening in the iris that allows light to enter the eye.
Lens: Focuses light onto the retina. Its shape is adjusted by the ciliary muscles for near and far vision.
Retina: The light-sensitive layer at the back of the eye containing photoreceptor cells (rods and cones).
Rods:* Sensitive to dim light and responsible for black and white vision.
Cones:* Responsible for color vision and function best in bright light.
Optic Nerve: Transmits visual information from the retina to the brain.
Eye Defects and Correction: Myopia (Nearsightedness):* Difficulty seeing distant objects clearly. Corrected with concave lenses. Imagine trying to see the soccer ball from across the field, appearing blurry. Concave lenses help spread the light rays slightly before they enter the eye, allowing for proper focusing on the retina.
Hyperopia (Farsightedness):* Difficulty seeing near objects clearly. Corrected with convex lenses. An example would be a tailor struggling to thread a needle. Convex lenses converge the light rays slightly before they enter the eye, allowing for proper focusing.
Astigmatism:* Blurred vision due to an irregularly shaped cornea or lens. Corrected with cylindrical lenses.
Cataracts:* Clouding of the lens, causing blurry vision. Treated with surgery to replace the cloudy lens.
Glaucoma:* Damage to the optic nerve, often caused by increased pressure inside the eye. Treated with medication or surgery. 2.
4. The Human Ear: Structure and Function The ear is the organ of hearing and balance.
It consists of three main parts: Outer Ear: Collects sound waves and directs them towards the middle ear. Includes the pinna (the visible part of the ear) and the auditory canal.
Middle Ear: Amplifies sound waves. Includes the tympanic membrane (eardrum) and three tiny bones (malleus, incus, and stapes).
Inner Ear: Converts sound waves into nerve impulses and detects changes in head position for balance.