IV] THE NERVOUS SYTEM

dendrites receptors of stimuli 1 body of cell source of ions 2 3 nucleus source of proteins eg. pumps 4 Schwann cells fats that insulate the neuron 5 Nodes of Ranvier gaps in the insulation 6 axon path of electrical signal

1. Dendrite 5. Nodes of Ranvier 2. Cell body 4. Schwann cells 8. Terminal Bouton 7. Axon Terminal 5. Nodes of Ranvier 2. Cell body 4. Schwann cells 9. Axon Hillock 3. Nucleus 6. Axon

K+ K+ Na+ Na+ Na+ Na/K pump K+ gate Na+ gate Na+ Na+ K+ K+ K+ K+ inside of neuron Na+ Na+ Na+ Na+ Na+ outside of neuron

1. The Na/K pump - pumps 2 K+ in and 3 Na+ out of the neuron 2. The K+ gate - allows K+ to freely move out of neuron 3. The Na+ gate - usually these are partly closed, and so only allows some of Na+ to move back into neuron

4. The result - there are more Na+ ions outside of neuron which gives it a positive charge outside - because there are Cl- ions equally inside and out, the inside of the neuron now has a negative charge after some of the Na+ ions have moved outside - the net result is a -70 mV negative charge inside the neuron compared to outside

A. Resting potential

B. Stimulus Na+

C. Propagating signal Na+ Na+

D. Further propagation of signal

4. ACTION POTENTIAL                                                                             

+40 mV 0 mV -70 mV MILLISECONDS C. REPOLARIZING B. DEPOLARIZING A A. RESTING POTENTIAL D. HYPERPOLARIZATION E. REFRACTORY PERIOD

4. ACTION POTENTIAL A. RESTING POTENTIAL - the Na/K pumps are ON - Na+ gates are CLOSED B. DEPOLARIZING - the Na/K pumps are OFF - the Na+ gates are OPEN C. REPOLARIZING - the Na/K pumps are ON - the Na+ gates are CLOSED

D. HYPERPOLARIZATION - the Na/K pumps are ON - the Na+ gates are CLOSED - extra positive ions are pumped out, making a larger electrical difference E. REFRACTORY PERIOD - the time during which the neuron can NOT respond to a new signal

F. THRESHHOLD VALUES - a neuron is either ON or OFF, there are no part signals if a stimulus does not reach the threshold level, the neuron is not activated - a stronger stimulus results in the sending of MORE signals or more neuron sending the same signals

5. SALTATORY CONDUCTION - in mylenated cells

A. RESTING POTENTIAL

B. STIMULUS Na+

C. PROPAGATING THE SIGNAL

D. FURTHER PROPAGATION OF SIGNAL

mylenated neurons send the signal faster mylenated neurons send the signal faster as the signal jumps under the Schwann cells thicker neurons have more pumps and more ions and so they can depolarize and repolarize faster

Synapses between neurons

6. PROPAGATING A SIGNAL ACROSS A SYNAPSE synaptic cleft Ca2+ axon dendrite

1. INCOMING ELECTRICAL SIGNAL-arrives at the axon end of the synapse 2 1. INCOMING ELECTRICAL SIGNAL-arrives at the axon end of the synapse axon 3 1 2. CALCIUM CHANNELS -are triggered to open and let Ca2+ ions enter the axon Ca2+ 2 3. PRE-SYNAPTIC VESICLES -the Ca2+ causes pre-synaptic vesicles to move to the end of the axon

RECEPTORS -the neurotransmitter binds to receptors in the dendrite -the pre-synaptic vesicles release neurotransmitter [acetylcholine] into the synaptic cleft [space] synaptic cleft RECEPTORS -the neurotransmitter binds to receptors in the dendrite 7 dendrite 4 6. OUTGOING ELECTRICAL SIGNAL -the neurotransmitter / receptor complex [N/R complex]initiates an electrical signal in the dendrite 6 5 7. ENZYME - an enzyme [acetylcholinesterase] is released from the dendrite to get rid of acetylcholine and stop the N / R complex from initiating another electrical signal

responsible for muscle contractions nerve / muscle synapses neurotransmitter location function ACETYLCHOLINE responsible for muscle contractions nerve / muscle synapses role in emotions such as depression, aggression, impulsive behaviour SEROTONIN in brain synapses role in dreaming, arousal, moodiness NOREPINEPHRINE in brain synapses modifies nerve signals eg reduces pain sensitivity BETA-ENDORPHINS & ENKEPHALINS in all synapses affects control of movement, emotions, pleasure , pain DOPAMINE in brain synapses GLYCINE & GABA in brain synapses inhibit signals in brain synapses most common involved in memory GLUTAMINE too much kills brain cells

mylenation proceeds from the back to the front as you age

“Problems with neurons” Now work on………… “Problems with neurons”