Unit #1: Wellness And HomeostasisControlling Homeostasis (2)
“Neurons and Nerve Impulses”
What is Nervous Tissue?
Why is Nervous Tissue important to Controlling and Maintaining Homeostasis?
How does a Nerve Cell Work?
Neuron Structure:
(A) Cell Body
(C) Dendrites
(D) Axon
• main portion of the cell
• contains a nucleus (B) and other
organelles
• extensions at one end of the neuron
• nerve impulses enter the cell body
through the dendrites
• A long extension that extends away from
the cell body
• carries the nerve impulse AWAY from the
cell body
(E) Axon Terminal
(F) SchwaanCells
(H) Nodes of Ranvier
• Thousands of microscopic branches
located at the end of the axon
• release Neurotransmitters that carry
nerve impulses to neighbouring neurons
and target muscles and glands
• these cells are wrapped around the axons
of the cells and form Myelin Sheaths (G)
• Myelin Sheaths insulate the axon which
speeds up nerve impulses
• Gaps between Schwaan cells
• found in longer Myelinated Axons
• allows the nerve impulse to “jump” from
node to node (moves further faster)
What is a Nerve?
Sensory Neurons
Motor Neurons
Interneurons
• A Nerve is a series of connected neurons that
form a pathway that an impulse can travel
through
• Neurons that build Sensory Nerve pathways
• carry impulses from the body to the CNS
• Dendrites are connected to body surfaces or
organs and axons lead to the CNS
• Neurons that build Motor Nerve pathways
• carry impulse from CNS to the body
• Dendrites are connected to the CNS and
axons lead to target areas of the body
• Neurons that connect Sensory and Motor
Neurons
• usually are found in reflex arcs in the spinal
cord
What is a Nerve Impulse?
How it works:
1. Resting Potential
A signal that is carried along a nerve
• The neuron is at “rest” - no impulse is
being transmitted
• Sodium Ions (I) are being actively
pumped out of the nerve cell while
Potassium Ions are equally concentrated
inside and outside of the cell
• cell membrane is “polarized” (inside is - ,
outside is + )
2. Action Potential
• the neuron is “firing”
• an electrical chemical, chemical or
mechanical stimulus alters the structure
of the cell membrane of the neuron
• Sodium Ions rush into the cell and the
membrane depolarizes
• the Action Potential (Impulse) is passed
down the axon and depolarizes the areas
in front of it)
• After the action potential passes the
neuron “re-polarizes” and returns to its
resting potential
• the entire process takes less than a
millisecond
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