Nervous_Teacher - Chapter 17 The Nervous System Nervous...

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Chapter 17 The Nervous System
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Nervous Tissue 2 Major Categories of Nervous System 1. Central Nervous System The brain and spinal cord At midline of body 1. Peripheral Nervous System Nerves carrying messages from CNS to muscles and glands Sensory nerves carrying messages to the CNS
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3 Types of Nerves to Know Sensory Nerves , Interneurons & Motor Nerves 1. Sensory Nerves - carry information to the CNS 2. Interneuron – a bridge between a sensory and motor nerve 3. Motor Nerves – carry response from the CNS to an effector – a gland or muscle that creates an action
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Anatomy of a TypicalNerve Cell Sensory Neuron shown here Dendtrites Cell Body (Soma) Nucleus Axon Bulb Axon Myelin Sheath Node of Ranvier
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Myelin Sheath / Nodes of Ranvier Formed by Schwann cells which secrete a fatty coating over the axon Acts like an insulation around a wire. Electrical signal jumps gap to gap because that is easier than travelling down the high resistance of the axon, itself. Gaps where Schwann cells do not myelinate are called the Nodes of Ranvier
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More on Myelin Gives nerves white appearance (= WHITE MATTER) MS (mutliple sclerosis) is a disorder where myelin is removed from nerve. Signal passes down axon, weakening. In case of optic nerve, this can cause loss of vision. Ultimately, muscular control is lost. If the breathing and respiration centres in the medulla are affected, the result is fatal. Long Axons – usually myelinated to help signal make it Short Axons – usually non-myelinated, since signal should not degrade over short distance Unmyelinated nerves = GRAY MATTER
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How does a Nerve Cell Pass an Electrical Signal? Nerve impulse carries information Impulse measured in mV Stages of Nerve Cell firing off a Signal 1. Resting Potential – electric potential before signal 2. Action Potential – potential of nerve when signal goes 3. Refractory Period – potential after signal has passed
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Action potential Definition: an “all-or-none” change in voltage that propagates itself down the axon Naturally occurring action potentials begin at the axon hillock
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Resting Potential When not conducting an electrical impulse, the potential difference across the membrane is -65mV Inside of axon is negative compared to outside! Difference between inside/outside charge of membrane is needed to start a signal Similar to a battery, the ends must have a potential difference for current to flow
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Action potential Definition: an “all-or-none” change in voltage that carries on all the way down the axon, creating electrical impulse. Naturally occurring action potentials begin at the axon hillock = crest of the axon Action potentials do not occur anywhere else in a neuron – not in dendrites, not in cell bodies
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K+ Sneaks out than Na+ in! Creates Dipole, enabling an Action Potential
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This note was uploaded on 10/28/2010 for the course BIOLOGY BIO-1B taught by Professor Dehaan during the Spring '10 term at Berkeley College.

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Nervous_Teacher - Chapter 17 The Nervous System Nervous...

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