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The Nervous System 3. Objectives: 1. Describe how the nervous system is divided into different subsystems. 2. Describe (Be able to label) a typical neuron. Be able to trace the path of a reflex arc from stimulus to response. The nervous system enables us to react to our environment Cranial nerves Spinal nerves Peripheral Nervous System (PNS) CNS Spinal cord Sensory nerves -carry messages from inside & outside to the brain 2 parts Somatic Nervous System -under conscious control Brain Autonomic Nervous System -without conscious control motor nerves -carry messages from the brain to the muscles − works on a system of STIMULUS / RESPONSE - change in the environment detected by the body - sensory neurons carry impulses to the brain - ex. Sight, sound, smell, taste, touch (pressure & heat) - body’s reaction to the change - motor neurons send messages to the muscles (for movement) and glands (for hormone secretion) Examples: STIMULUS Cookies Baking Touch a hot stove Watching a scary movie RESPONSE Saliva secreted in mouth Pull hand away Heart Rate increases, sweating, jumping at scary/loud noises Nervous system Central Nervous System (CNS) Peripheral Nervous System (PNS) - Brain - Spinal cord SOMATIC NERVOUS SYSTEM - under conscious control - ex. You need to go to the washroom, but you can hold it. ex. Your nose is itchy, so you scratch it. AUTONOMIC NERVOUS SYSTEM - without conscious control (it happens automatically) - ex. Heart beat, dilation of pupils, saliva secreted. Etc. The Nervous System: Neurons dendrite Cell body nucleus Direction of nerve impulse transmission Myelin sheath axon (Schwann cell) Muscle cell Terminal knob Terminal branches The Nervous System: Neurons • A nerve cell or neuron is: a specialized cell that uses electrical signals to communicate with other cells • An impulse is: an electrical signal travelling through a neuron • A nerve is: a bundle of neurons • Sensory neurons: carry impulses from receptors (e.g. in skin) to the central nervous system (brain/spinal cord) • Motor neurons: carry impulses from brain or spinal cord to muscle or gland • Dendrites: carry impulses toward cell body • Axon: carry impulses away from cell body • Myelin sheath: fatty white tissue that covers some axons • Terminal knobs: part of neuron that attaches to another cell • Synapse: connection between terminal knob of one axon and dendrite of another Reflexes • The PNS receives input from stimuli and transmits it to the CNS for processing. • The brain decides the appropriate responses and send a signal back along the PNS to the part of your body that will respond. • HOWEVER… sometimes your brain gets bypassed! • The spinal cord coordinates reflex (Actions that don’t require your brain.) • Reflexes occur without conscious thought and are quick. • EX. When you step on a tack or put your hand on a hot surface. illustration from http://scienceblogs.com/neurotopia Your Task • Read pp. 170 – 173 • Answer Questions #4, 5, 7 on pp. 176 • Create a diagram or flow chart to explain what happens in our nervous system when we step on tack. (Start with the sensory receptors and end with the movement off of the tack. What nervous structures are involved and in what part of the nervous system are they located.)