Synapses and Graded Potentials

EX - Reflex Arc

Knee-Jerk (Drawing on board; Simple - Spinal Cord X Section)

Receptors - send signal to

interneurons (spinal cord) in turn send info to

motor neuron which innervates muscles

---> reflex

Excitatory Synapses

A) Electrical - Gap Junctions

B) Chemical Basis

1) Synthesis

2) Transmitter stored

3) AP depols terminal ---> release of transmitter

4) Transmitter diffuses across synaptic cleft

5) Transmitter binds to receptors in postsynaptic terminal

• alpha-bungarotoxin

6) Postsynaptic Potential

7) Transmitter Action Removed from synapse

Two Mechanisms

1) ACh - ACh-ase is in cleft

Prostigmine - inhibits

2) A) NE -

B) Prozac

OVERALL:

• Action is usually v short lived

• both release and receptor binding is over in a few ms

• normally - transmitter must not be allowed to hang around

--> VIP - neurons would keep firing

IPSPs

----> hyperpolarization

Ionic basis of IPSPs?

• permeability to K+ and Cl- is increased

 

Information Processing

Graded Potentials

Dif Membrane than axon ---> different potentials

1) refractory

2) duration

APs - over within 4 msec

graded - last sev msec->minutes

3) summation

4) all or none

5) regeneration

6) Size

FUNDAMENTAL PRINCIPLE OF NERVOUS SYSTEM

PROCESSING:

Summation

Temporal

Spatial

Integration

Summary:

• most neurons receive thousands of inputs and

• each input contributes less than 1 mV

• output of a neuron is a rather complex function of its synsptic input

 

Transmitters

Types

1) Cholinergic

ACh - most info

2) Monoamines - NE and epinephrine

3) Amino acids

4) neuropeptides (amino acid chains)

EX - enkaphalins, endorphins - sim in structure to opium

A few Concepts

1) Multiple Receptors

2) Permeability and Metabolic Effects

Other second messengers:

• Ca++, cGMP (cyclic guanosine monophosphate), and