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Nervous System Components: Brain, spinal cord, nerves, sense organs, and associated structures. Functions: Works with endocrine system to coordinate body activities. Integrates and processes information from sense organs. Sends signals (instructions) to muscles and glands. Responds to internal stimuli. Homeostatic Role: Regulates most organ activities along with endocrine system. 1 Human Nervous System 2 Functions of Nervous Tissue 1. Sensory Input: Conduction of signals from sensory organs (eyes, ears, nose, skin, etc.) to information processing centers (brain and spinal cord). 2. Integration: Interpretation of sensory signals and development of a response. Occurs in brain and spinal cord. 3. Motor Output: Conduction of signals from brain or spinal cord to effector organs (muscles or glands). Controls the activity of muscles and glands, and allows the animal to 3 respond to its environment. Nervous System Allows Us to Respond to Our Environment 4 Cells of Nervous Tissue 1. Neuron: Nerve cell. Structural and functional unit of nervous tissue. Carry signals from one part of the body to another. 2. Supporting cells: Nourish, protect, and insulate neurons. There are roughly 50 supporting cells for every neuron. In humans, Schwann cells wrap around the axons of neurons, forming a myelin sheath that is essential for transmission of nerve impulses. 5 Neuron Structure Cell body : Contains nucleus and most organelles. Dendrites: Extensions that convey signals towards the cell body. Short, numerous, and highly branched Axon: Extension that transmits signals away from the cell body to another neuron or effector cell. Usually a long single fiber. Axon is covered by a myelin sheath made up of many Schwann cells that are separated by small spaces (Nodes of Ranvier). 6 Structure of the Neuron 7 Neuron Structure Myelin sheath and nodes of Ranvier greatly speed up nerve impulses, which jump down axon from node to node. Speed of signal Myelinated axon 100 meters/second Unmyelinated axon 5 meters/second Multiple sclerosis: A disease in which a person’s immune system destroys the myelin sheaths on their neurons. • Loss of muscle control • Impaired brain function • Death 8 Neurons and Synapses Types of Neurons Sensory Motor Interneurons 9 Sensory Neurons INPUT From sensory organs to the brain and spinal cord. Drawing shows a somatosensory neuron Brain Sensory Neuron Spinal Cord Vision, hearing, taste and smell nerves are cranial, not spinal 10 Motor Neurons OUTPUT From the brain and spinal cord To the muscles and glands. Sensory Neuron Brain Spinal Cord Motor Neuron 11 Interneurons Interneurons carry information between other neurons only found in the brain and spinal cord. Brain Sensory Neuron Spinal Cord Motor Neuron 12 Structures of a neuron 13 The cell body Contains the cell’s Nucleus Round, centrally located structure Contains DNA Controls protein manufacturing Directs metabolism No role in neural signaling 14 Dendrites Information collectors Receive inputs from neighboring neurons Inputs may number in thousands If enough inputs the cell’s AXON may generate an output 15 Dendritic Growth Mature neurons generally can’t divide But new dendrites can grow Provides room for more connections to other neurons New connections are basis for learning 16 Axon The cell’s output structure One axon per cell, 2 distinct parts tubelike structure branches at end that connect to dendrites of other cells 17 Myelin sheath White fatty casing on axon Acts as an electrical insulator Not present on all cells When present increases the speed of neural signals down the axon. Myelin Sheath 18 How neurons communicate Neurons communicate by means of an electrical signal called the Action Potential Action Potentials are based on movements of ions between the outside and inside of the cell When an Action Potential occurs a molecular message is sent to neighboring neurons 19 Neuron to Neuron Axons branch out and end near dendrites of neighboring cells Axon terminals are the tips of the axon’s branches A gap separates the axon terminals from dendrites Gap is the Synapse Dendrite Axon Cell Body 20 Synapse axon terminals contain small storage sacs called synaptic vesicles Sending Neuron Axon Terminal Synapse vesicles contain neurotransmitter molecules 21 Neurotransmitter Release Action Potential causes vesicle to open Neurotransmitter released into synapse Locks onto receptor molecule in postsynaptic membrane 22 Locks and Keys Neurotransmitter molecules have specific shapes Receptor molecules have binding sites When NT binds to receptor, ions enter positive ions (Na+ ) depolarize the neuron negative ions (Cl-) hyperpolarize 23 Some Drugs work on receptors Some drugs are shaped like neurotransmitters Antagonists : fit the receptor but poorly and block the NT e.g. beta blockers Agonists : fit receptor well and act like the NT e.g. nicotine. 24 Summary 3 types of neurons The cell membrane Ion movements Action potentials Synapse Neurotransmitters Receptors and ions Agonists and antagonists 25 In this experiment you are required to say the color of the word, not what the word says. For example, for the word, RED, you should say "Blue." Green Red Blue 26