1. 11-3

2. Conduction Velocities of Axons
Conduction velocities vary widely
Rate of impulse is determined by:
Axon diameter –
Presence of a myelin sheath –

3. Saltatory conduction of the AP

4. Saltatory Conduction (sauter = “to jump (Fr.)”
Current passes through a myelinated axon only at the nodes of Ranvier
Voltage regulated Na+ channels are concentrated at these nodes
Action potentials jump from one node to the next

5. Synapses HOW NEURONS COMMUNICATE WITH: IF NEURON TO NEURON:
another neuron
An effector cell (muscle or gland)
IF NEURON TO NEURON:
Presynaptic neuron –
Postsynaptic neuron –synapse

6. Synapse NEURON TO NEURON
Axodendritic
Axosomatic
Axoaxonic
PREsynaptic neuron / POSTsynaptic neuron
Figure 11.17

7. Electrical synapse

8. Electrical Synapses Electrical synapses: less common Correspond to
Contain intercellular
Permit ion flow from one neuron to the next
BI-directional !!!
Are found in the brain and embryonic tissue

9. Chemical synapse
Figure 11.18

10. Chemical Synapses release and receive neurotransmitters
Typically composed of two parts:

11. Synaptic Cleft
Fluid-filled space separating the presynaptic and postsynaptic neurons
Prevent nerve impulses from directly passing from one neuron to the next as in an electrical synapse
Transmission across the synaptic cleft:

12. Synaptic cleft
Postsynapse
presynapse

13. 9-23

15. Synaptic Delay
Neurotransmitter must be released, diffuse across the synapse, and bind to receptor
Synaptic delay – time needed to do this ( ms)

17. excitatory postsynaptic potential (EPSP)
Internal membrane at rest (before EPSP)

18. Inhibitory postsynaptic potential (IPSP)30
Inhibitory postsynaptic potential
(IPSP)
Internal membrane at rest (before IPSP)

19. Neurotransmitters
Chemicals used for neuronal communication with the body and the brain
50 different neurotransmitter have been identified
Classified chemically and functionally

20. Excitatory & inhibitory presynaptic inputs

21. FUNCTIONS Two classifications: excitatory and inhibitory
Excitatory neurotransmitters cause depolarizations ( glutamate)
Inhibitory neurotransmitters cause hyperpolarizations ( GABA and glycine)
Some neurotransmitters have both excitatory and inhibitory effects
Determined by the receptor type of the postsynaptic neuron
Example: aceytylcholine
Excitatory at neuromuscular junctions
Inhibitory with cardiac muscle

22. Termination of Neurotransmitter Effects
Neurotransmitter bound to a postsynaptic neuron:
Produces a continuous postsynaptic effect
Blocks reception of additional “messages”
Must eventually be removed from its receptor
Removal of neurotransmitters occurs when they:
Are degraded by enzymes
Are reabsorbed by astrocytes or the presynaptic terminals
Diffuse from the synaptic cleft