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The Nervous System Section 3.5 p. 146-151 Learning outcomes • I can describe how the role and function of the nervous system • I can list and describe the individual organs that make up the nervous system, and how they work together • I can describe how the nervous system responds to changing conditions Remember what a stimulus is?? Responding to a stimulus • Stimulus: is a change in your environment • Can occur in many forms • pressure, heat, cold, light, sound, or body chemistry. • Can be external or internal • External – outside of your body • i.e. walking in from the cold outdoors to a warm room • Internal – Inside your body • i.e. the arrival of food in your stomach • It is the job of the nervous system to monitor and respond to these stimuli Nervous Tissue • Remember the four types of tissues? •. •. •. •. • The nervous system is made up almost entirely of Nervous tissue • The nervous tissue is made up entirely of one type of specialized cell called Neurons • A neurons job is to send and receive messages The Neuron • The neuron receives messages from small branches of the cell called dendrites • Messages are passed from the dendrites through the cell body to the axon • The axon is a long extension of the cell that ends in small branches • It carries impulses away from the cell body to its branches. • These branches transmit the message to the dendrites of neighboring cells • Signals travel very fast • Myelinated cells up to 100 M/s • Unmyelinated around 2-3 M/s Organization of Nervous System • All though there are many divisions of the Nervous system • There are two main important components • Central Nervous system: is composed of the brain and spinal cord • This is where the info processing occurs • Peripheral Nervous system: is composed of the cranial and spinal nerves that travel to all parts of the body • So all other nervous tissue that is contained outside of the brain and spinal cord Peripheral Nervous system • Each nerve of the peripheral nervous system is composed of two types of neurons. • Sensory Neurons: carry information from the body to the central nervous system • Motor Neurons: carry information from the central nervous system to the muscles and organs The Peripheral Nervous system can be divided again • Within the peripheral nervous system, there are two types of smaller systems • Somatic Nervous System: System that refers to actions that you have conscious control over • These are voluntary responses, you choose to perform them • i.e. when you hear a noise you decide to turn and investigate what it might be • Automatic Nervous System: controls the actions that you respond to unconsciously ( without thought) • You don’t think about these reactions, they occur automatically • i.e. adjusts size of pupils to amount of light, heart rate, breathing rate, peristalsis in your digestive tract • If you had to think of all these things you wouldn’t be able to think of much else The Reflex Response • Reflex: is an automatic response by the nervous system to an external stimulus • Reflex Response: is when sensory neurons and motor neurons work together with out the Brain (CNS) • So lets say you touch a hot stove element • Your sensory neurons still send a message to the brain(CNS) • But interneurons recognize the severity of the stimulus, and relay the message directly to the motor neurons in your arm • This way by the time your brain tells you to scream out in pain, you’ve already removed your arm from the danger • Reflex's protect you from injury by reducing the time it takes to reduce harmful stimuli The Central Nervous System (CNS) • Protected by the bones of the skull and spinal cord • Made up of two types of tissue • Grey matter • White matter • The brain receives stimuli information from your sense organs • i.e. eyes, nose, mouth, skin, ears • It also receives internal stimuli from your body • i.e. greater need for oxygen in a certain area of the body due to increase in activity • It reacts to these stimuli, and sends messages to the appropriate body parts 3 main Components of the Brain • The brain is generally divided into three main sections • Cerebrum • Conscious events including thoughts • Cerebellum • Programs and fine-tunes voluntary and involuntary movements • Medulla • Controls your cardiac, respiratory, and balance system • There are around a 100 billion neurons in your brain • It accounts for 2% of your body weight • Consumes about 25% of the oxygen your body uses CNS Cont’d • The spinal cord connects the brain to the peripheral nervous system • It acts like a highway for messages between the brain the body • It contains Interneurons (these connect one neuron to another) An uneven sense of touch • Unlike other senses such as vision, hearing, smell, and taste, the sense of touch is not found in one specific place • The sense of touch is found in all areas of your skin, making it the largest sense organ • Not all areas have the same amount of touch receptors • Which area’s do you think will have the most