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Chapter 8 : Nervous System (8.3 Events Involved in the Generation and…
Chapter 8 : Nervous System
8.2 Neurons & Neuroglia
Neuron : Structural and functional unit of the nervous system; a nerve cell.
Neuron Structure
Each neuron is composed of a cell body and many extensions from the cell body called neuron processes or nerve fibers
Cell body = central portion of neuron; contains usual organelles, except centrioles.
Neuron processes/Nerve Fibers = extensions from cell body
Dendrites
Many per neuron, receives signal, start action potential
Axons
One per neuron, carry impulses away from the cell body.
Axons in PNS
Large axons are surrounded by a myelin sheath produced by many layers of Schwann Cells
Axons in CNS
Myelin is produced by oligodendrocyte
Neuroglial Cells = Accessory cells of nervous system from supporting network for neurons
PNS = Schwan Cells produces myelin and satellite cells nourish neurons
CNS = 4 types to provide bulk of brain and spinal cord tissue.
Oligodenrocyte : Function is to produce myelin
Astrocyte : Function is to nourish neurons
Microglia : Function is phagocytosis
Ependymal Cells : Function is to line spaces in CNS
Classification of Neurons
Sensory neurons
afferent neurons carry sensory impulses from sensory receptors to CNS
Somatic receptor
Visceral receptors
Interneurons
Motor neurons
Efferent neurons
Structural Classification
Multipolar Neurons
Bipolar Neurons
Unipolar Neurons
8.1 Major Anatomical Divisions & Functions
Organs of Nervous System
Central Nervous System : Brain & Spinal Cord
Peripheral Nervous System : Nerves that Extend from Brain & Spinal Cord
Functions Of Nervous System
Sensory Input Function
PNS
Sensory Receptors
Transmit a Sensory Impulse to CNS
Sensory Impulse is carried on a Sensory Neuron
Integrative Function
CNS (Brain & Spinal Cord)
Integration occurs in Interneurons
Motor Function
PNS
Motor Impulse is carried on a Motor Neuron
2 Types of Effectors : Muscles & Glands
8.3 Events Involved in the Generation and Propagation of an Action Potential
Resting Nerve Cells
Polarized = electricity charged
Potential Difference : the difference in electrical charge between 2 points
RMP : -70 m/v
More negative = Hyperpolarization
Less negative : Depolarization Approx. -55mv (Threshold potential)
3 Different types of Neurons : Multipolar, Unipolar, Bipolar
Generation of action potential
Continous propagation
Salutatory propgation
Reach threshold, depolarization, respolarization
Factors responsible for Membrane Potential
Intracellular Fluid
Extracellular Fluid
Nerve Impulse Transmission
Def : Propagation of AP along a nerve fiber
Its an electrical impulse, begins on a dendrite
Characteristics
All or Nothing Response : Nerve cell responds at all, it responds completely
Refactory Period : Period following a NI when a threshold stimulus can't produce another NI
Summation : Many subthreshold stimuli received one after another may allow threshold potential to be reached
Conduction : The manner in which the NI runs down the neuron/nerve fiber
Unmyelinated Nerve FIbers
Myelinated Nerve Fiber : Saltatory Conduction
Synapse : The junction between 2 neurons where a nerve impulse is transmitted
Synaptic cleft : gap between 2 neurons
Neurotransmitter
Acetylcholine : released by all motor neurons & some CNS neurons
Fate in synaptic cleft
Destruction of Neurotransmitter
Enzymes that are presented in the synaptic cleft destroys NT
Reuptake of Neurotransmitter
NT is transported back into pre-synpatic knob.
Efferent pathway : Automatic & Somatic