Neurons & Nerve Impulses - Fall River Public Schools

Neurons & Nerve Impulses

Objectives
• Explain the function of the nervous system
• Contrast the three types of neurons
• Identify the 4 main parts of a neuron
• Identify where nerve impulses are transferred

Introduction
• The nervous system controls
and coordinates functions
throughout the body and
responds to internal and
external stimuli
• The nervous system is the
communication system of
the body
• Messages carried by the
nervous system are electrical
signals called impulses

Neurons
• Neurons – cells that transmit
nerve impulses
• 3 Types of Neurons
– Sensory neurons carry
impulses from sense organs to
the spinal cord and brain
– Motor neurons carry impulses
from the brain and spinal cord
to muscles and glands
– Interneurons connect sensory
and motor neurons and carry
impulses between them

Parts of a Neuron
• Cell body – the largest part of a neuron that
contains the nucleus and most of the cytoplasm
• Dendrites – short, branched extensions that carry
impulses from the environment or from other
neurons toward the cell body
• Axon – long fibers that carry impulses away from
the cell body
– the ends of the axon are called axon terminals
– Axons and dendrites are clustered into bundles of
fibers called nerves

Parts of a Neuron
• Some neurons have a myelin sheath, which is an insulating
membrane that surrounds an axon
• The myelin sheath has gaps in it called nodes which allow
impulses to move quickly up the axon

The Nerve Impulse
• An impulse begins when a neuron is stimulated by another
neuron or by the environment
• An impulse is a sudden reversal of the membrane potential
• Sodium channels open to allow Na + to flow into the cell
• The inside of the membrane temporarily becomes more
positive than the outside
• Action potential – the reversal of charges across the cell
membrane from negative to positive, also called a nerve
impulse
• As the impulse passes, potassium channels open, allowing K+
to flow out, restoring resting potential
• Nerve impulses at one point trigger an impulse at the next
point, like a row of falling dominoes

The Synapse
• Impulse reaches the end of a
neuron at the axon terminal,
where it makes contact with
another cell
– The neuron may pass the impulse
to the second cell
• Synapse – the location at which
a neuron can transfer an impulse
to another cell
• Axon terminals contain vesicles
with neurotransmitters
• Neurotransmitter – chemicals
used by a neuron to transmit an
impulse across a synapse to
another cell

Notes Review
• Explain the function of the nervous system
– The nervous system controls and coordinates
functions throughout the body and responds to
internal and external stimuli

Notes Review
• Contrast the three types of neurons
– Sensory neurons carry impulses from sense organs
to the spinal cord and brain
– Motor neurons carry impulses from the brain and
spinal cord to muscles and glands
– Interneurons connect sensory and motor neurons
and carry impulses between them

Notes Review
• Identify the 4 main parts of a neuron
– Cell body, dendrites, axon, myelin sheath

Notes Review
• Identify where nerve impulses are transferred
– Nerve impulses are transferred at the synapse.