1. 6.5 Neurons & Synapses

2. The Nervous System Divided into 2 parts CNS: Central Nervous System
Consists of brain and spinal cord
Composed of neurons
PNS: Peripheral Nervous System
Consists of all the nerves that branch from the CNS and go to the rest of the body
Made up of sensory receptors and nerves
Afferent and efferent

3. Neurons

4. Neurons transmit electrical impulses
Send out rapid electrical impulses called action potentials
must be changed into a chemical message in order to cross the synapse (space between 2 neurons)
Carry message to a relay neuron inside the CNS
Relay neuron turns it into an electrical impulse
Then it travels to an effector cell (elicits a response)

5. Resting potential & Action Potential
Difference in electrical charge inside (cytoplasm) and outside (extracellular fluid)
Membrane potential
Controlled by sodium NA+ and potassium k+
Neurons pump sodium and potassium ions across their membrane to generate a resting potential

6. Resting potential
The charge of a cell at “rest”. The neuron is not sending an action potential. Resting potential is maintained by the sodium-potassium pump.
At rest charge inside cells is more negative by -70mv
Uses ATP to pump 3Na+ out of cell and 2K+ into cell
Some “leaky” channels (always working to maintain resting potential)

8. Action Potential
The changing charge in a cell due to the opening of sodium-gated ion channels (depolarization) followed by the opening of potassium-gated ion channels (repolarization)
Occur when a stimulus is detected
If cells depolarized to a charge around -50 mv and action potential is propagated (threshold potential)

9. Propagation of an action potential

10. Nerve Impulses
When action potential is propagated it moves down the axon to the terminal buttons
Axon is depolarized and then repolarized
Wave of traveling membrane charge changes
Myelinated axons speed up the transmission
Axon potential generated between nodes (between myelination, across Schwann cells)
Jumping of the impulse from one node to another is called saltatory conduction

12. Graph of an Action Potential

13. Synaptic Transmission
Synapse: space between two neurons or a neuron and a muscle cell
In order to carry and impulse across a synapse it needs to be changed from and electrical signal to a chemical signal
Chemical form is called a neurotransmitter
Stored in the terminal buttons of neurons
Arrival of action potential at terminal buttons triggers the opening of the calcium gated channels in the presynaptic membrane
Causes the release of neurotransmitters

14. Neurotransmitters Excitatory: when they open sodium channels
Inhibitory: when they open potassium channels
Examples
Acetylcholine (cholinergic synapses)
Cholinergic synapses control muscle contractions
Dopamine
Serotonin
Epinephrine
norepinephrine

15. Useful applications for blocking cholinergic synapses
Pesticides: neuroactive insecticides bind to acetylcholine receptors causing the paralysis of insects.
Botox: toxin derived from the bacteria that causes botulism, stops muscle contractions by blocking the release of acetylcholine. The relaxed muscles reduce the appearance of wrinkles.

16. Removal of neurotransmitters
Must be removed from the synapse to stop the message being sent
Removed by enzymes
Removed by terminal buttons by reuptake (endocytosis)

18. Receptor  Interneuron  Effector = Reflex
Does not involve the brain
Involuntary (ex. pain)
Adaptive behavior for survival