Transcript Chapter 21
Chapter 21 Control and Coordination Section 1- The Nervous System • Homeostasis – The regulation of steady, life-maintaining conditions inside an organism, despite changes in its environment. • Neurons – Working unit of the nervous system; a nerve cell • Neurons consist of a cell body, axons, and dendrites. • Dendrite – Part of neuron; they receive messages and send them to cell body. • Axon – Part of neuron; it carries messages away from cell body. • Synapse – Small space between neurons Types of Nerve Cells • Motor Neurons – Conduct impulses from brain or spinal cord to body parts • Sensory Neurons – Receive info. and send impulses • Interneurons – Relay impulses to motor neurons The Brain • Coordinates all of your body activities. • Cerebrum – Thinking takes place – Largest part of your brain – Interprets impulses from the senses • Cerebellum – Part of the brain that coordinates your muscle movement. Helps maintain balance. • Brain stem – Connects brain to the spinal cord – Includes the midbrain, pons, and the medulla – Medulla- involuntary actions (heartbeat, breathing and digestion) – Midbrain & pons- acts as pathways that connect various parts of the brain with each other • Spinal cord – Controls reflex responses – Ex. Withdrawing your hand from a hot stove, your foot from a sharp piece of glass, putting your hands out in front of you to stop a fall. • Central Nervous System (CNS) – Made up of the brain and spinal cord • Peripheral Nervous System (PNS) – Made up of nerves outside the central nervous system. • Connects the brain and spinal cord to other body parts. Sensory neurons send impulses to the brain or spinal cord. • 2 Major Division of PNS – 1) Somatic 2) Autonomic – Somatic- Voluntary Actions – Autonomic- Involuntary Actions • Reflex – Involuntary, automatic response to a stimulus • Stimulus – Change that causes a response in your body • What steps happen when you run an iron over your hand accidentally? • 1. You aren’t paying attention when you run the iron over your hand. • 2. Sensory neurons in your hand send messages to interneurons. • 3. Interneurons relay impulses to motor neurons • 4. Motor neurons relay impulses to muscles of your hand. • 5. Muscles of your hand contract, responding to the impulses. • 6. You pull your hand away from the iron and scream. Drugs and the Nervous System • Caffeine is a stimulant – A drug that speeds up the activity of the central nervous system. – Increases heart rate – Causes restlessness and insomnia – Causes kidneys to produce more urine • Alcohol is a depressant – A drug that slows the activities of the central nervous system. – Impairs judgment – Destroys brain and liver cells Section 2- The Senses • Sense organs intercept different forms of energy, which are then converted into impulses by the nervous system. • Your senses work together – Maintain homeostasis within your body. • • • • • • Senses 1) Vision 2) Hearing 3) Smell 4) Taste 5) Touch Vision • How do you see???? – Light enters the eye – cornea – Next passes through the lens – Lens directs light into the retina • Tissue at back of eye that is sensitive to light energy – Rods (respond to dim light) and cones (respond to bright light and color) are found in the retina. – Light energy stimulates an impulse – Optic Nerve- Carries impulses from the retina to the brain. http://glencoe.mcgraw-hill.com/sites/dl/free/0078617022/161752/00053402.html Rods and Cones Lens Optic Nerve Retina Cornea Hearing • Sound energy is to hearing as light energy is to vision. • When an object vibrates, sound waves are produced. • Outer Ear – Intercepts sound waves and funnels them into the ear canal • Middle Ear – Eardrum vibrates – Contains hammer, anvil, and stirrup • Inner Ear – Cochlea- fluid-filled structure in the inner ear – Causes electrical impulses to be sent to the brain by a nerve Smell • Olfactory cells – Nerve cells in the nose stimulated by molecules – Kept moist by mucus Taste • Taste buds – Major sensory receptors on the tongue • In order to taste something, it has to be dissolved in water. Saliva begins this process. • Smell and taste are related! – Olfactory cells are stimulated through the back of your throat. Other Sensory Receptors • Skin – sensory receptors are located throughout your skin. (Fingertips) – You can tell whether an object is smooth or rough, hot or cold, hard or soft.