The nervous system

Yes- we will do a little experiment

CNS and PNS• The nervous system is made up of the central

nervous system and the peripheral nervous system.

• The CNS is made up of the the nerves of the spinal chord and the brain- the CNS deciphers signals sent by the PNS and sends messages out to respond.

• The peripheral nervous system is made up of all the other nerves of the body. The PNS detects changes in the environment and rceives messages from the CNS to respond

Pathway of a nerve impulse

stimuli sensory receptors sensory neurone CNS (spinal chord) brain or motor neurone Effector (muscle or gland)

Basic Nerve Structure

Electro-chemical pathway

• Messages travel along the nerve as an electrical impulse

• Messages travel between nerves as a chemicals called neurotransmitters

Electrical impulse• The membrane is very important in nerves.

• Potassium and sodium ions move in an out of the cell through protein channels (this uses ATP produced from cellular respiration).

• When resting, these ions cause a negative charge inside the nerve cell.

• When stimulated sodium ions rush into the cell causing a negative charge along the cell which needs to be rebalanced.

• This is the basis of the electrical impulse along the cell

For more information

• http://www.biologymad.com/nervoussystem/nerveimpulses.htm

Action potential- summary

• At rest the cell is negative.• When stimulated positive sodium ions rush.• Potassium is pumped out the resting state.• This change from negative to positive back to

negative is how the electrical charges moves along the nerve.

Chemical signal• Often nerves are not physically connected– The gap between nerves is called the synapse

• When the electrical impulse reaches the axon terminal a neurotransmitter is released

• This is a protein! Complex in structure, denatures when heated!

• The neurotransmitter drifts across the gap and fits into a receptor on the membrane of the nerve receiving the signal.

• The message is converted back into an electrical signal.

When the wrong message is sent

• Many recreational drugs exploit this part of the neural pathway by mimicking a neurotransmitter and either blocking or stimulating the pathway.– Heroin for example mimics our natural endorphins

which give us a feeling of well being during exercise or reduce pain

Different types of nerves

Activity: Two point threshold• You will need 5 paper clips and a ruler• Unfold the paper clips so the two ends are nearly touching• Set the distances of the ends using your ruler (see chart)• Working in pairs- one will be the subject and one will be

the experimenter• Lightly touch the two ends of the paper clip on the skin of

the subject• The subject will report whether they felt one or two points

– Be honest– Mix up the order of distance being tested– Test each distance twice

• Switch roles when you are done

Complete the following table

Activity: reflex action

• Sometimes it is important that we react quickly to a stimulus eg. When we experience pain or heat.

• In this case the nervous system by-passes sending information to the brain.

• This is called a reflex action and the nerve pathway is called a reflex arc.

The somatic reflex arc

Test your knee reflex

• The knee jerk reflex is one that you may have had tested at a check up at the doctor's office. In this test, the doctor hits your knee at a spot just below your knee cap and your leg kicks out. Try it! Have a partner sit with his or her legs crossed so that his leg can swing freely. Hit his leg just below the knee with the side of your hand. DO NOT USE A HAMMER!!!! The leg will kick out immediately (if you hit the right place).