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

• 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.

Drugs and the Nervous System

The end