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Receptor: Receives stimuli from the environment. Effector: Brings about a response based on the received stimulus. Eye The retina responds to light. Impulses are sent from the retina to the brain via the optic nerve. The brain detects changes in shape, color, brightness, and distance....

Receptor: Receives stimuli from the environment. Effector: Brings about a response based on the received stimulus. Eye The retina responds to light. Impulses are sent from the retina to the brain via the optic nerve. The brain detects changes in shape, color, brightness, and distance. Ear Sensitive hairs in the inner ear respond to sound waves. Impulses travel through the auditory nerve to the brain, allowing the brain to detect quality, tone, pitch, and loudness. Nose Air flowing into the nose during breathing touches the sensitive hairs in the nostrils. Chemical molecules trigger signals to the brain, enabling the detection of scents. Tongue Taste buds on the tongue respond to chemicals in food. Different areas of the tongue are sensitive to flavors: sweet, salt, bitter, and sour. Signals are sent to the brain to detect flavor changes. Skin The largest sense organ in the body, covered with nerve endings and sensory cells. It detects pain, touch, temperature, and pressure. Impulses are sent to the brain to identify what has been touched. The Nervous System Neurons: The nerve cells that transmit electrical impulses to and from the brain. Nervous system consists of: ○ Central Nervous System (CNS): Brain and spinal cord. ○ Peripheral Nervous System (PNS): All other nerves. The PNS forms a vast communication network, linking stimulus reception to responses. Types of Neurons: Sensory Neurons: Conduct impulses from the receptors to the CNS. Motor Neurons: Conduct impulses from the CNS to the effectors. Relay Neurons: Intermediate neurons that link sensory and motor neurons, found in the CNS. Pathway Example: Response to a Hot Object 1. Stimulus: A hot object touches a pain receptor in the skin. 2. Sensory Neuron: The signal travels along the sensory neuron to the Central Nervous System (CNS). 3. Relay Neuron: In the CNS, a relay neuron carries the signal to the brain or passes it directly to a motor neuron. 4. Motor Neuron: The signal travels along the motor neuron to the effector (muscle or gland). 5. Response: The effector triggers an action, such as pulling your hand away from the hot object. Synapse A synapse is a small gap where two neurons meet. Electrical impulses cannot pass across this gap, so they are converted into chemical signals to cross the synapse. Once the chemical signal reaches the next neuron, it is converted back into an electrical impulse. Reflex Actions Reflex actions are rapid and automatic responses that do not require conscious control. Examples include knee-jerk, blinking, and sneezing. Types of Reflexes:  1. Spinal Reflexes: Nerve impulses pass through the spinal cord without involving the brain (e.g., knee-jerk reflex). 2. Cranial Reflexes: Reflexes in the head region (e.g., blinking). The Brain The brain is the most important part of the nervous system, responsible for thinking and reasoning. It is made of gray matter on the outside and white matter on the inside, protected by meninges and cerebrospinal fluid, which cushions it from impact. The brain is also surrounded by the bones of the skull for further protection. Different areas of the brain coordinate complex physical and mental activities, receiving stimuli and bringing about the appropriate responses. The Spinal Cord Like the brain, the spinal cord is composed of grey matter and white matter, but in the spinal cord, the white matter is on the outside and the grey matter is on the inside. Parts of the Brain:[ 1. Cerebrum: ○ Responsible for conscious actions and thought processing. ○ Processes signals from the five senses. 2. Hypothalamus: ○ Controls the body’s internal environment (homeostasis). 3. Cerebellum: ○ Controls balance and coordinates muscular activity. 4. Medulla Oblongata: ○ Regulates involuntary actions such as heartbeat, breathing, and swallowing. 5. Pituitary Gland: ○ An endocrine gland that secretes hormones. Autonomic Nervous System  Comprises all the nerves that control the functioning of internal organs. It helps maintain homeostasis and a constant internal environment. Endocrine System The endocrine system consists of a number of glands known as endocrine glands. It controls growth, development, and the regulation of various body functions. Endocrine glands secrete chemicals known as hormones directly into the bloodstream, where they travel to target organs. Types of Glands: 1. Endocrine Glands: ○ Secrete hormones directly into the blood (e.g., pituitary gland, thyroid gland). 2. Exocrine Glands: ○ Transport their secretions via ducts to other parts of the body (e.g., salivary glands, tear ducts). Reflex Arc A reflex arc is the pathway that controls a reflex action. It involves the following steps: 1. Stimulus: A change in the environment (e.g., touching something hot). 2. Receptor: Detects the stimulus (e.g., sensory cells in the skin). 3. Sensory Neuron: Sends the signal to the spinal cord. 4. Relay Neuron (in the spinal cord): Processes the information and transfers it to a motor neuron. 5. Motor Neuron: Sends a signal to the effector. 6. Effector: The muscle or gland that acts (e.g., pulling your hand away). Diagram of the Reflex Arc Receptor → Sensory Neuron → Relay Neuron → Motor Neuron → Effector Example: Knee-jerk reflex or withdrawing hand from heat. Structure of the Eye The eye is a sensory organ that detects light and sends visual information to the brain. Key parts include: 1. Cornea: Transparent outer layer; refracts light. 2. Iris: Colored part; controls the size of the pupil. 3. Pupil: The opening that regulates the amount of light entering the eye. 4. Lens: Focuses light onto the retina. 5. Retina: Contains photoreceptor cells (rods for low light, cones for color). 6. Optic Nerve: Carries visual information to the brain. 7. Sclera: Tough white outer layer of the eye. 8. Choroid: Contains blood vessels; nourishes the eye. 9. Ciliary Muscles: Adjust the shape of the lens for focusing. From Stimulus to Response 1. Stimulus Detection: Sensory organs (like the eye or skin) detect stimuli. 2. Signal Transmission: ○ Sensory neurons carry the signal to the central nervous system (CNS). 3. Processing in the CNS: ○ The brain or spinal cord processes the signal. ○ If it's a reflex, the spinal cord immediately sends a response signal without involving the brain. 4. Response Transmission: ○ Motor neurons carry signals to the effector. 5. Effector Action: ○ A muscle contracts or a gland secretes a substance (response). Example (Eye Reflex to Bright Light): Stimulus: Bright light. Receptor: Photoreceptors in the retina. Sensory Neuron: Carries the signal to the brain. Brain: Signals the iris muscles. Effector: Iris muscles contract, shrinking the pupil to reduce light intake.