Structure and Processes of the Nervous System

(pg 351-353)

<Structure of a Neuron>

• neurons have specialized cell structure that allow them to transmit nerve impulses 
• 4 common features: dendrites, cell body, axon, branching end 

dendrite

• receive impulses from other neurons or sensory receptors and relay the impulse to the cell body
•  cover a lot of surface area to receive info w/ their numerous branches 

cell body

• has nucleus, site of cell's metabolic reactions
• processes input from dendrite
• impulse, if big enough, is then relayed to axon (where impulse is initiated) 

axon

• conducts impulses away from cell body
• axon terminal releases chemical signals to communicate w adjacent neurons, glands, or muscles
• axons of some neurons enclosed in fatty (white) layer called myelin sheath (protects neurons and speeds rate of nerve impulse transmission) 
• myelin sheath formed by schwann cells 

Classifying Neurons 
-based on structure and function
STRUCTURE: multipolar, bipolar, unipolar

multipolar: several dendrites, single axon, found in brain and spinal cord
bipolar: single main dendrite, single axon, found in inner ear, retina of eye, olfactory of brain
unipolar neuron: single process that extends from cell body, dendrite and axon fused, found in peripheral nervous system

FUNCTION: sensory, interneurons, motor

• sensory, interneurons, motor nuerons form basicimpulse transmission pathway of nervous system 
• 3 overlapping functions: sensory input, integration, and motor output 

sensory input: sensory receptors (ex in skin) receive stimuli and form nerve impulse- sensory neurons transmit impulse from sensory receptors to the central nervous system (brain and spinal cord)
integration: interneurons found within CNS- act as link between sensory and motor neurons. process and integrate incoming sensory info and relay outgoing motor info
motor output: motor neurons transmit info from CNS to effectors (muscles, glands, other organs that respond to impulses from motor neurons)

Reflex Arc: simple connection of neurons that results in a reflex action in response to a stimulus

• reflexes- sudden, involuntary responses to certain stimuli (ex jerking hand away from something hot) 
• reflex arcs-simple connections of neurons that explain reflexive behaviours 
• usually involve only 3 neurons to transmit messages (ex withdrawal reflexes- 3 neurons)