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The Nervous System A System for Communication & Regulation of Life Process What Does the Nervous System Do? It Helps Maintain Homeostasis How? It brings messages from one place to another. By Using Special Cells Neurons (Nerve cells) are the basic functional unit of the nervous system. Neurons receive, conduct, and send impulses. A Typical Neuron Terminal Bulbs Dendrite Terminal Branches Cyton Axon Cyton How Do Impulses Start? They Need a Stimulus Stimulus (plural = stimuli) a change in the external or internal environment that an organism responds to. Examples External Light, Sound, Pressure, Cold, Hot, etc.. Examples Internal Chemicals Changes, Temperature Changes, etc... Different Types of Neurons next slide Inter-neuron Sensory Neuron Motor neuron ??? Parts of the Neuron Explained The Dendrite Dendrites receive stimuli from sense organs or from other neurons in the form of a neurotransmitter. Cell Body Cell Body conducts impulses from the dendrites toward the axon Axon Axon conducts impulses from the cyton toward the terminal branches Myelin Sheath Myelin Sheath - an arrangement of cells around the axon. It helps protect the axon and speed up impulses. Terminal Branches Terminal Branches a fork in the axon. Synaptic Knobs Synaptic KnobsReleases chemicals called Neurotransmitters, which allow the message to be received by the next neuron, or a muscle, gland, organ etc… Terminal (Synaptic) Knobs Neurotransmitters Impulse Direction Neurotransmitters Synapse How Neurotransmitters Work neurotransmitters Neurotransmitters diffuse from the end of one neuron to receptors on the next neuron. When they land on the specific receptor they allow gates to open that allow sodium to enter - this ignites the electro-chemical impulse to begin in the the next neuron. Impulses What are impulses? The cell membrane of a neuron conducts electrical signals from on end to another - in one direction. The inside of a neuron has an overall negative charge, and the outside has an overall positive charge. Outside Neuron Inside neuron Channels The outside of a neuron has sodium ions (Na+). The inside has negatively charged proteins. Neither of these chemicals can pass through the cell membrane. They are attracted to each other because of their opposite charge. There are many protein channels along the membrane where sodium (Na+) can enter, but only when the gate is open. Stimuli cause the gates to open The flow of charge (negatives or positives)across the membrane is electricity. This is why the impulse of a neuron is said to have an electrico-chemical nature. Steps in making an impulse Steps in making an impulse A stimulus occurs Either an external (sound, light, etc..) source or an internal source (such as a neurotransmitter). Steps in making an impulse Gates Open This allows the sodium to enter the cell. Steps in making an impulse Adjacent Gates Open The opening of one gate cause the next gate to open - like dominos Steps in making an impulse The Impulse Travels to the End of the Neuron Steps in making an impulse Neurotransmitters are released when the impulse reaches the Terminal Knobs The Reflex Arc A special pathway The Advantage of a Reflex The advantage of a reflex is that we can respond quickly to a stimulus. A reflex pathway does not involve the brain which is an advantage because the reflex is quicker. Pathway of a Reflex Sensory Organ Stimulus Sensory Neuron Interneuron Effector (Muscle or Gland) Motor Neuron Diseases of the Nervous System Cerebral Palsy Results from brain damage, usually at birth. It is a term used to describe a group of diseases that affect the ability to control movement. Multiple Sclerosis (MS) Results from damage to the Myelin Sheath. Symptoms vary but may include: shaking, blurred vision, slurred speech, and weakness. Parkinson’s Disease Involves a particular group of brain cells in the brain. Symptoms: Tremors, poor balance, stiffening of the muscles. * The thinking functions is usually OK. Alzheimer's Disease Degenerative disease of the brain. The person usually loses the ability to remember, think correctly and speak. The condition usually gets worse over time once it starts. It may take years to notice. Notes This slide presentation is a work in progress. Please feel free to notify the author of any mistakes or suggestion for improvement.