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Download 36.1: The Nervous System
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19: The Nervous System Section Objectives: Analyze how nerve impulses travel within the nervous system. Interpret the functions of the major parts of the nervous system. Compare voluntary responses and involuntary responses. The Nervous System • • • • • • • Controls and coordinates the body’s responses to changes in the environment HOW: Stimulus: a change in the external or internal environment which initiates an impulse Impulse~ an electro-chemical charge generated along a neuron Receptors~ structures specialized to detect certain stimuli Response~ a reaction to a stimulus Effectors~ what responds to a stimulus such as muscles or glands Neurons: Basic Units of the Nervous System • Neurons conduct impulses throughout the nervous system. • A neuron is a long cell that consists of three regions: a cell body, dendrites, and an axon. Neurons: Basic Units of the Nervous System • Dendrites~ receive impulses and carry them toward the cell body • Axon~ carries impulses away from the cell body and toward other neurons, muscles, or glands. • Cell body~ contains the nucleus Myelin coating signal direction Axon coated with insulation made of myelin cells speeds signal signal hops from node to node 330 mph vs. 11 mph myelin coating Multiple Sclerosis 2003-2004 immune system (T cells) attacks myelin coating loss of signal Fun facts about neurons • Most specialized cell in animals • Longest cell – blue whale neuron • 10-30 meters – giraffe axon • 5 meters – human neuron • 1-2 meters Nervous system allows for 1 millisecond response time 2003-2004 Neurons: Basic Units of the Nervous System 3 Types of neurons. • 1. Sensory neurons: carry impulses from the body to the spinal cord and brain (sense receptors) • 2. Motor neurons carry the response impulses away from the brain and spinal cord to a muscle or gland. (effectors) • 3.Interneurons: connect sensory &motor neurons within the brain and spinal cord Types of neurons sensory neuron (from senses) interneuron (brain & spinal chord) 2003-2004 motor neuron (to muscle) How an impulse is transmitted • 1. Resting: no impulse, cell is polarized ( + on outside & - on inside) – Sodium/Potassium pump in axon using ATP maintains this polarity How an impulse is transmitted • 2.Impulse: stimulus excites neuron – Na+ gates open – Na+ goes inside, therefore inside becomes more + – Depolarization occurs ~ a nerve impulse – Impulse moves in one direction Synapse ~ connection between neurons & effector cells Junction between nerve cells – 1st cell releases chemical (neurotransmitter) to trigger next cell – where drugs affect nervous system synapse 2003-2004 Nervous System cerebrum cerebellum spinal cord • Central nervous system (CNS) cervical nerves thoracic nerves – brain & spinal cord lumbar nerves • Peripheral nervous system (PNS) femoral nerve – nerves from senses – nerves to muscles 2 systems work together sciatic nerve tibial nerve 2003-2004 Anatomy of the brain • Cerebrum: – – – – – Conscious activities Intelligence Memory Language Voluntary activity • Cerebellum: -Coordinates motor activity -balance Medulla Oblongata: involuntary activities such as breathing,&heart rate Nervous System Central Nervous System (CNS) Somatic Nervous System (voluntary) Relays information to and from skin and skeletal muscles. Peripheral Nervous System (PNS) Autonomic Nervous System (involuntary) Relays information to internal organs. Sympathetic Nervous System Parasympathetic Nervous Controls organs in times of stress. Controls organs when body is at rest System