IV] THE NERVOUS SYTEM

1

2

3

4

5

6

dendrites

body of cell

nucleus

Schwann cells

Nodes of Ranvier

axon

receptors of stimuli

source of ions

source of proteins eg. pumps

fats that insulate the neuron

gaps in the insulation

path of electrical signal

1. Dendrite

3. Nucleus

2. Cell body

4. Schwann cells

5. Nodes of Ranvier

6. Axon

7. Axon Terminal

8. Terminal Bouton

9. Axon Hillock

K+ K+

K+ K+

K+ K+

K+ K+

Na+ Na+

K+ gate

Na+ Na+

Na+ Na+

Na+

Na+ Na+

Na+

Na+ gate

Na/K pump

inside of neuron

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+

Na+

C. Propagating signal

Na+

Na+

Na+

Na+

D. Further propagation of signal

Na+

Na+

Na+

Na+

                                                                     

       

4. ACTION POTENTIAL

+40 mV

0 mV

-70 mV

MILLISECONDS

A. RESTING POTENTIAL

B. DEPOLARIZING

C. REPOLARIZING

D. HYPERPOLARIZATION A

E. REFRACTORY PERIOD

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

4. ACTION POTENTIAL

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

- a stronger stimulus results in the sending of MORE signals

-if a stimulus does not reach the threshold level, the neuron isnot activated

or more neuron sending the same signals

5. SALTATORY CONDUCTION - in mylenated cells

A. RESTING POTENTIAL

B. STIMULUS

Na+

Na+

C. PROPAGATING THE SIGNAL

Na+

Na+ Na+

Na+

D. FURTHER PROPAGATION OF SIGNAL

Na+

Na+

Na+

Na+

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

Ca2+

Ca2+

axon dendrite

synaptic cleft

6. PROPAGATING A SIGNAL ACROSS A SYNAPSE

1

Ca2+2

Ca2+

2axon

1. INCOMING ELECTRICAL SIGNAL-arrives at the axon end of the synapse

2. CALCIUM CHANNELS -are triggered to open and let Ca2+ ions enter the axon

3. PRE-SYNAPTIC VESICLES

-the Ca2+ causes pre-synaptic vesicles to move to the end of the axon

3

4

6

7dendrite

synaptic cleft

4. NEUROTRANSMITTER

-the pre-synaptic vesicles release neurotransmitter [acetylcholine] into the synaptic cleft [space]

5. RECEPTORS -the neurotransmitter binds to receptors in the dendrite

6. OUTGOING ELECTRICAL SIGNAL

-the neurotransmitter / receptor complex [N/R complex]initiates an electrical signal in the dendrite

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

5

neurotransmitter

location function

ACETYLCHOLINE nerve / muscle synapses

responsible for muscle contractions

SEROTONIN in brain synapsesrole in emotions such as depression, aggression, impulsive behaviour

NOREPINEPHRINE in brain synapses role in dreaming, arousal, moodiness

BETA-ENDORPHINS & ENKEPHALINS in all synapses

modifies nerve signals eg reduces pain sensitivity

DOPAMINE in brain synapses affects control of movement, emotions, pleasure , pain

GLYCINE & GABA

in brain synapses inhibit signals

GLUTAMINE in brain synapses

most commoninvolved in memory

too much kills brain cells

mylenation proceeds from the back to the front as you age

Now work on…………

“Problems with neurons”