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4.3 Nervous System
Introduction
The body's intricate command center.
Coordinates actions, transmits signals, responds to stimuli.
Regulates basic bodily functions to complex thought and emotion.
Divisions of the Nervous System
Central Nervous System (CNS):
Primary control center.
Brain:
Control center for intelligence, learning, memory, emotions.
Spinal Cord:
Relays information to/from brain, mediates reflex actions.
Peripheral Nervous System (PNS):
Network of nerves extending from CNS to rest of body.
Somatic Nervous System:
Controls voluntary movements, relays sensory info.
Autonomic Nervous System (ANS):
Regulates involuntary functions.
Sympathetic:
"Fight or flight."
Parasympathetic:
"Rest and digest."
Cells of the Nervous System
Neurons:
Primary functional units; specialized cells transmitting electrical and chemical signals.
Structure:
Cell body, dendrites (receive signals), axon (sends signals).
Glial Cells (Glia):
Supporting cells; provide physical and metabolic support to neurons.
Types of Nerves
Sensory Nerves:
Carry signals from sense organs to the brain.
Motor Nerves:
Carry signals from the brain to muscles and glands.
Mixed Nerves:
Contain both sensory and motor fibers.
Cranial and Spinal Nerves
Cranial Nerves:
Emerge directly from the brain.
Number:
12 pairs.
Spinal Nerves:
Emerge from the spinal cord.
Number:
31 pairs.
Structure of a Motor Neuron
Cell Body:
Contains the nucleus.
Dendrites:
Branch-like extensions that receive signals.
Axon:
Long, slender projection that carries signals away.
Reflex Action
Definition:
An involuntary and nearly instantaneous movement in response to a stimulus.
Basic Terms:
Stimulus:
Evokes a reaction.
Response:
Reaction to a stimulus.
Impulse:
Signal transmitted along a nerve fiber.
Receptor:
Responds to stimulus, transmits signal to nerve.
Effector:
Organ/cell that acts in response to stimulus.
Common Examples:
Withdrawing hand from hot object, blinking.