Neurons

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Biology Unit 1 – Maintaining Dynamic Equilibrium II

Section 1 – Nervous System

“The Neuron”

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The Neuron

The basic functional unit of the nervous system.

Function: Send impulses to and from the CNS and PNS and the effectors (muscles/glands)

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Neuron Structure

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Dendrite  Fine hair-like extensions on the end of a neuron.

Function: receive incoming stimuli.

Cell Body or Soma  The control center of the neuron.

Function: Directs impulses from the dendrites to the axon.

Nucleus  Control center of the Soma.

Function: Tells the soma what to do.

Axon Pathway for the nerve impulse (electrical message) from the soma to the opposite end of the neuron.

Myelin Sheath  An insulating layer around an axon. Made up of Schwann cells.

Nodes of Ranvier  Gaps between schwann cells.

Function: Saltatory Conduction (Situation where speed of an impulse is greatly increased by the message ‘jumping’ the gaps in an axon).

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Types of Neurons

There are 3 types of neurons.

Sensory Neurons  Neurons located near receptor organs (skin, eyes, ears).

Function: receive incoming stimuli from the environment.

Motor Neurons  Neurons located near effectors (muscles and glands)

Function: Carry impules to effectors to initiate a response.

Interneurons  Neurons that relay messages between other neurons such as sensory and motor neurons. (found most often in Brain and Spinal chord).

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Types of Neurons

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Nerves

Nerves  Collections of neurons that are joined together by connective tissue.

Responsible for transferring impulses from receptors to CNS and back to effectors.

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How Do Neurons Operate?

Neuron at Rest  Resting Potential

Occurs when the neuron is at rest.

A condition where the outside of the membrane is positively(+) charged compared to the inside which is negatively(-) charged.

Neuron is said to be polarized.

Neuron has a voltage difference of -70 mV

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