1. Receptor Afferent path Integration Efferent Path Effect
Nervous System
Brain, spinal cord, efferent and afferent neurons
Pattern of information flow:
Receptor Afferent path Integration Efferent Path Effect
Central Nervous System (CNS)
Main cell types are neurons and glial cells

3. Typical Arrangement of Neural Connections
Neurons communicate via electrical signaling
They are excitable
Structurally the soma (cell body) has an extensive ER and prominent nucleoli
Long appendages or processes:
Dendrites (receive info)
Axons (deliver info); some are covered by myelin
A collection of axons is called a NERVE

5. Types of glial cells:
CNS = oligodendrocytes, astrocytes, microglia, ependymal cells
PNS = Schwann cells, satellite cells

6. Myelin acts as an insulator and inhibits ion movement in the axonal membrane that it surrounds.

7. Neurons as Excitable Tissue
Excited by altering the resting membrane potential (-90 mV)
Depolarize
Hyperpolarize
Most changes in membrane potential occur through the opening or closing of certain ion channels (they are voltage-gated or gated via second messenger system activation).
Ion
Intracellular (mM)
Extracellular
(mM)
Na+ 2
140
Cl- 10
105
Ca2+
10-8
2.5 K+
150 5
Proteins (-) 65

8. Gates can be chemically opened by neurotransmitters
Gates can be opened via signal transduction mechanisms linked to neurotransmitter binding to receptor
Gates can be opened by stretch, pressure, etc.

9. Stimulus = anything that can cause the opening or closing of gated channels in a neuronal membrane
What happens to the resting membrane potential of the membrane adjacent to the site of Na+ entry?
How about here?

10. What determines whether an action potential will occur or not?
The axon hillock (trigger zone) is sensitive to changes in ion concentration and is the site at which an action potential is initiated.
An action potential is a self-propagating depolarization of the axonal membrane that initiates at the hillock and runs to the axon terminus without diminishing in strength.
All action potentials are the same “size”.
What determines whether an action potential will occur or not?

11. If the graded potential doesn’t change the resting membrane potential enough, the signal from the stimulus will die out and the neuron will not respond with an action potential.
The amount of change in membrane potential necessary to generate an action potential is called a threshold stimulus.

12. Action Potential = depolarization along the axon1 3 2

14. If the trigger area of the axon reaches threshold, the influx of Na+ and the generation of the action potential will be repeated over and over again in one direction, at each segment of membrane, down the axon.

15. What will happen at this area of membrane?

16. One portion of the membrane has just been depolarized and is relatively insensitive to changes in cation concentration. It is said to be refractory to stimulus. Downstream membrane is at resting potential, and can be influenced by cation influx.

18. Saltatory conduction in myelinated neurons

19. Action potentials cause the release of neurotransmitter from the presynaptic axon terminus

20. What will happen to the resting membrane potential if the activation gate is opened?
How could a cell open this activation gate?

21. Strength of stimulus determines neuronal response

22. EPSP mV
time
time mV
time
IPSP

23. Neurotransmitter activity is stopped by: diffusion away from the synapse, transport into cells (glial or back into presynaptic neuron), or degradation by specific enzymes.

25. What is the response in the post-synaptic neuron?

27. What will determine whether this postsynaptic neuron will respond?

29. A B
Red neuron is releasing serotonin which causes an IPSP. The neuron is firing at 70 APs/sec
Neuron A is releasing dopamine, causing and EPSP. The neuron is firing at 40 APs/sec
Neuron B is releasing acetylcholine to create an EPSP. It is firing at 20 APs/sec.
What will the outcome be in the postsynaptic cell?

30. Transmitter Molecule Derived From Site of Synthesis
Acetylcholine
Choline
CNS, parasympathetic nerves
Serotonin 5-Hydroxytryptamine (5-HT)
Tryptophan
CNS, chromaffin cells of the gut, enteric cells
GABA
Glutamate
CNS
Aspartate
Glycine
spinal cord
Histamine
Histidine
hypothalamus
Epinephrine
Tyrosine
adrenal medulla, some CNS cells
Norpinephrine
CNS, sympathetic nerves
Dopamine
Adenosine
ATP
CNS, periperal nerves

31. Result in postsynaptic cell Target
Neurotrans.
Types of receptors
Mode of action
Result in postsynaptic cell
Target
Acetylcholine
Nicotinic
Muscarinic
Opens ion channels
EPSP
CNS neurons; skeletal muscle
Serotonin
Two main classes; multiple subclasses
G-protein coupled receptors; both AC and IP3/DAG
Depends on receptor type
Platelet aggregation, smooth muscle contraction, satiety, vomiting
GABA
GABA-A
GABA-B
Receptor Cl- channel
G-linked K+ channel
IPSP in all cases
Throughout CNS and in retina
Norepinephrine
Receptor
b receptor
G-protein linked to cAMP
IPSP
Relaxes smooth muscles of gut, bronchial tree, and vessels to skel. muscle
Increases rate and strength of cardiac contraction; excites smooth muscle in vessels
Dopamine
D1, D2, D3, D4, and D5
G-protein linked to cAMP, direct channel opening, cAMP to K+ channel opening
EPSP and IPSP
D1-3 are located in the striatum of the CNS, and the basal ganglia
D3-5 play a role in mood, psychosis and neuroprotection