Transcript Nervous System

Nervous System
Nervous system
• The organs of the nervous system form
two subsystems
– The brain and the spinal cord make-up the
central nervous system (CNS)
– All the nervous tissue outside the brain and
spinal cord make up the peripheral nervous
system (PNS)
Basic Unit of the Nervous System
• The basic unit of the nervous system is the
nerve cell or NEURON.
• Although there are different kinds of
neurons, they share certain characteristics
– Axons
– Dendrites
– Cell body
The Neuron
• All neurons have three common
characteristics
– Axon: A fiber called an axon carries electrical
signals away from the cell body. It is the
output cable
– Dendrite: Fibers called dendrites receive
signals and carry them toward the cell body
Resting potential
• When a neuron is not transmitting a signal,
it has an energy potential.
• Just like water behind a dam, ions of
opposite charges are seperated by the cell
membrane.
Triggering the nerve signal
• If a neuron is stimulated – by a tap on the
knee, for example – the voltage across the
membrane changes, this is called
depolarization.
• A neuron will only fire if the stimulus is
strong enough to depolarize the
membrane to a certain level, called the
threshold (-50 mV)
Transmitting a signal
• Once the neuron’s membrane is
depolarized to the threshold level, an
action potential occurs.
• An electrical signal travels via the axon to
the next neuron.
– At the end of the axon, the signal causes the
release of neurotransmitters that jump the
space between cells called the synapse
Need for Speed
• Neurons have a “turbo” called myelin
sheath.
– A nerve signal can travel along a nerve from
your spinal cord to your toes in less than 7
milliseconds! (150 meters per second)
Drugs and the Nervous System
Drugs and the Nervous System
• Different drugs have different affects on the body
– Stimulants generally increase activity in the CNS
– Cocaine is a highly addictive stimulant. It blocks the
normal removal of pleasure neurotransmitters. The
excess neurotransmitters cause a temporary “high”
that is soon followed by depression as the
neurotransmitters fall to below normal levels.
– Addiction to cocaine causes permanent chemical
changes in the brain.
Every day stimulants
Drugs and the Nervous System
• Depressants slow CNS activity
– Alcohol is a strong depressant that interferes with
coordination, judgment, and damages the liver as well
as can cause esophagus cancer.
– Marijuana contains over 400 chemicals (THC being
the main one). It cause many problems in the brain
including memory and learning. The more a person
smokes - to escape what ever is causing them
emotional pain – will make the person seem like
things are ok when in reality they are just getting
dumber and dumber and the problems will still be
there. And will cause lung cancer.
The end