Download The Nervous System

The Nervous
System
• In order to maintain homeostasis, organisms
must be able to respond to internal and external
stimuli.
• In order to be able to respond to stimuli, the
human body needs the nervous system to bring
messages from one place to another.
• Nerve cells (neurons) are the basic fundamental
unit of the nervous system.
Nerve Cells:
A cell for rapid communication
• Nerve Cells - specialized cells that
can receive, conduct, and send
impulses.
Neurons
The following slide has
some illustrations of
different kinds of
neurons
Parts of the Neuron
The Dendrite
1. Dendrites- receive
stimuli from sense
organs or from other
neurons in the form of a
neurotransmitter.
• Stimuli – are changes in the
external and internal
environments that the organisms
responds to.
Axon
3. Axon- conducts the
impulse from the cell
body to the terminal
branches.
Cell Body
2. Cell body- has the
nucleus - conducts
impulse from dendrite
to axon.
Myelin Sheath
4. Myelin Sheath- a lipid
cellular arrangement of
cells around the axon. It
helps protect and speed
up impulses.
Terminal Branches
5. Terminal Branchesa fork in the axon.
Synaptic Knobs
6. Synaptic KnobsReleases chemicals
called
Neurotransmitters. They
allow the message to be
received by the next
neuron, or a muscle,
gland, organ etc…
Impulses
What are impulses?
• The cell membrane of a neuron
conducts electrical signals from
on end to another.
• The inside of a neuron has an
overall negative charge, and the
outside has an overall positive
charge.
• The outside of a neuron has
sodium ions (Na+). The inside
has negatively charged proteins.
• Neither of these chemicals can
pass through the cell membrane.
They are attracted to each other
because of their opposite
charge.
• A neural impulse is electrical and
chemical in nature.
• There are many protein channels
along the membrane where
sodium (Na+) can enter, but only
when the gate is open.
• The flow of charge (negatives or
positives) is electricity. This is why
the impulse of a neuron is said to
have a electrical and chemical
nature.
Steps in making an
impulse
Steps in making an impulse
A stimulus occurs. Either an
external (sound, light, etc..)
source or an internal source
(such as a neurotransmitter).
The stimuli causes the gates
to open. Which allows the
sodium to enter the cell.
The sodium rushes into the
cell which causes a stimulus
in the next cell. This happens
until the stimulus reaches the
Terminal Branches.
The Reflex Arc
A special pathway
The Advantage of a Reflex
• The advantage of a reflex is that we can respond quickly
to a stimulus.
• A reflex pathway does not involve the brain which is an
advantage because the reflex is quicker.
Pathway of a Reflex
Stimulus
Sensory
Organ
Sensory
Neuron
Interneuron
Effector
(Muscle or Gland)
Motor Neuron
Diseases of the
Nervous System
Cerebral Palsy
• Results from brain damage, usually at
birth. It is a term used to describe a
group of diseases that affect the
ability to control movement.
Multiple Sclerosis (MS)
• Results from damage to the Myelin
Sheath.
• Symptoms vary but may include: shaking,
blurred vision, slurred speech, and
weakness.
Parkinson’s Disease
• Involves a particular group of brain
cells in the brain.
• Symptoms: Tremors, poor balance,
stiffening of the muscles.
* The thinking functions is usually OK.
Alzheimer's Disease
• Degenerative disease of the brain.
The person usually loses the ability to
remember, think correctly and speak.
• The condition usually gets worse over
time once it starts. It may take years
to notice.
Credits
Power point presentation assembled by the Venerable J. R.
Graphics provided by google.com/images
Notes provided by Mr. Hutchinson
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