1. Nervous System
FUNCTION: Senses, processes, interprets, and determines the response to stimuli from the environment
Central Nervous System (CNS) - made of the brain and spinal chord
Peripheral Nervous System (PNS) - all nerve cells outside of the CNS

2. Divisions of the Nervous System (see pages 388-89 for more detail on each)
Sensory division - receives
Information (senses)
Motor division - relays
information to organs/glands
involuntary
voluntary
“Fight or flight”
“rest & digest”

3. Cells of the Nervous System
Neurons - cells that conduct nerve impulses (action potentials) to communicate with organs and glands
Neuroglia (glial cells) - support, protect and nourish neurons (do not send nerve impulses

4. Structure of a Neuron
Axon - transmits nerve impulses to communicate with other cells and organs
Dendrites - receive signals from other neurons
Myelin sheath - fatty coating on axon that speeds up action potential
Nodes of Ranvier - gaps in the myelin sheath where the axon is exposed
Cell body - part of neuron from which dendrites arise (also contains nucleus of cell)
Axon terminals - end of axon/part that releases neurotransmitters to communicate with other neurons

5. Functional Regions of the Neuron
Receptive zone
Receives
input from other
neurons
Conducting zone
generates action potential
(nerve impulse)
Secretory zone
Releases
neurotransmitters

6. Functional Classification of Neurons
Sensory (afferent) neurons
Receive information from the environment (senses)
Motor (efferent) neurons
Send signals to muscles/glands/organs to carry out response
Interneurons
Relay signals between sensory and motor neurons

7. Nerves vs. Neurons
Nerves are bundles
of neurons

8. Synapse - area where two or more neurons communicate with each other

9. Action Potentials A brief reversal in charge across a membrane
Happens in the axon membrane at Nodes of Ranvier (Saltatory conduction)
Voltage gated ion channels for Na+ and K+ open and close in response to changes in membrane potential (charge)
Action potential
is initiated by the
axon hillock

10. Stages of an Action Potential
More Na+ outside cell/more K+ inside
Na+ enters the axon (charge becomes more positive - depolarization)
K+ leaves axon (charge becomes more negative)
Too much K+ has left (hyperpolarization - more negative than resting)
Na/K pump restores original conditions
View action potential stages in action

11. Neurotransmitters
Chemical messengers that cross the synapse allowing one neuron to communicate with another
Can be excitatory (cause post-synaptic neuron to depolarize (become more positive))
Can be inhibitory (cause post synaptic membrane to hyperpolarize (become more negative))

12. Neurotransmitters (cont.)
Stored in vesicles in axon terminals
Ca2+ rushes into the terminal in response to arriving action potentials
Ca2+ causes vesicles to release neurotransmitters into synaptic cleft (example)
Neurotransmitters bind to their receptors on the post-synaptic membrane
Neurotransmitters are broken down by enzymes in the synaptic cleft or are taken back up by the pre-synaptic neuron via transporter proteins

13. Neurotransmitters (cont)
Examples:
GABA (inhibitory)
Glutamate (excitatory)
Dopamine, serotonin, norepinephrine (excitatory or inhibitory depending on the nature of the synapse)
Over 50 identified

14. IPSP vs. EPSP
Inhibitory post-synaptic potentials (IPSP) decrease the likelihood of the post-synaptic neuron sending an action potential (hyperpolarizes post-synaptic neuron: lets Cl- in or lets K+ out)
Excitatory post-synaptic potentials (EPSP) increase the likelihood of the post-synaptic neuron sending an action potential (depolarizes post-synaptic neuron: lets Na+ in)

15. Summation Additive effect of the inputs of all pre-synaptic neurons
If there are more excitatory than inhibitory signals, then depolarization may occur and an action potential may be sent by the post-synaptic neuron

16. Long-term Potentiation (LTP)
LTP is the long-lasting strengthening of synapses between two neurons
Post-synaptic neurons become more sensitive to neurotransmitters coming from the pre-synaptic neuron(s) by:
1) making more receptors
2) increased sensitivity of existing receptors
Involved in learning and memory formation

17. BEFORE:
Glutamate (excitatory
neurotransmitter) stimulates
NMDA receptors (in green) at a
high frequency
AFTER:
Because of the frequency of
stimulation, there is an increase
in the number and sensitivity
of receptors on the
post-synaptic neuron (increasing
the strength of the synapse)
What causes this to happen?