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SYNAPSES. D. C. Mikulecky Professor of Physiology http://views.vcu.edu/~mikuleck/. TWO TYPES OF SYNAPSE. ELECTRICAL CHEMICAL. ELECTRICAL. GAP JUNCTION: PROVIDES PATH FOR IONS TO FLOW FROM ONE CELL TO ANOTHER. CELL 1 . CELL 2. CHEMICAL: THE SYNAPSE. INCOMING NERVE. POST SYNAPTIC

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Synapses
SYNAPSES

D. C. Mikulecky

Professor of Physiology

http://views.vcu.edu/~mikuleck/


Two types of synapse
TWO TYPES OF SYNAPSE

  • ELECTRICAL

  • CHEMICAL


Electrical
ELECTRICAL

GAP JUNCTION: PROVIDES PATH FOR IONS TO

FLOW FROM ONE CELL TO ANOTHER

CELL 1

CELL 2


Chemical the synapse
CHEMICAL: THE SYNAPSE

INCOMING NERVE

POST SYNAPTIC

NERVE

SPACE


Events in cellular communication
EVENTS IN CELLULAR COMMUNICATION

INPUT SIGNAL (CHEMICAL,MECHANICAL, PHOTO,

ELECTRICAL)

RECEPTOR

TRANSDUCER

EFFECTOR

ENZYMES,GENOME,CONTRACTILE FILAMENTS,

SECRETORY GRANULES

RESPONSE (OUTPUT)

SECRETION CONTRACTION/RELAXATION DIVISION

PHAGOCYTOSIS


How are we wired connections between nerve cells
HOW ARE WE WIRED?CONNECTIONS BETWEEN NERVE CELLS

AXON

CELL

BODY

AXON

TERMINALS

AXON

HILLOCK

DENDRITES


The nature of chemical transmission between nerves
THE NATURE OF CHEMICAL TRANSMISSION BETWEEN NERVES

  • PRESYNAPTIC EVENTS

  • POSTSYNAPTIC EVENTS

  • IN THE SPACE


Presynaptic events
PRESYNAPTIC EVENTS

  • THE ALL OR NONE ACTION POTENTIAL TRIGGERS THE RELEASE OF CHEMICAL TRANSMITTER


Incoming action potential
INCOMING ACTION POTENTIAL

  • DEPOLARIZES

  • TRIGGERS CALCIUM CHANNELS

  • CALCIUM ENTERS THE CELL


The synapse
THE SYNAPSE

INCOMING

ACTION

POTENTIAL

CALCIUM

CHANNEL

•••

RECEPTOR

SYNAPTIC

VESSICLES

•••

•••

•••

•••

•••

ION

CHANNEL

•••

•••

•••

ENZYME


The synapse incoming action potental
THE SYNAPSE: INCOMING ACTION POTENTAL

INCOMING

ACTION

POTENTIAL

CALCIUM

CHANNEL

•••

RECEPTOR

SYNAPTIC

VESSICLES

•••

•••

•••

•••

•••

ION

CHANNEL

•••

•••

•••

ENZYME


Calcium influx
CALCIUM INFLUX

  • CAUSES VESSICLES TO BE RELEASED

  • VESSICLES MIGRATE TO MEMBRANE

  • EXOCYTOSIS

  • NEUROTRANSMITTER ENTERS SPACE


The synapse calcium channels open
THE SYNAPSE: CALCIUM CHANNELS OPEN

INCOMING

ACTION

POTENTIAL

CALCIUM

CHANNEL

•••

RECEPTOR

SYNAPTIC

VESSICLES

•••

•••

•••

•••

•••

ION

CHANNEL

•••

•••

•••

ENZYME


The synapse neurotransmitter enters space
THE SYNAPSE: NEUROTRANSMITTER ENTERS SPACE

CALCIUM

CHANNEL

•••

RECEPTOR

•••

SYNAPTIC

VESSICLES

•••

•••

•••

•••

•••

ION

CHANNEL

•••

•••

ENZYME


Post synaptic events
POST SYNAPTIC EVENTS

  • IONOTROPIC (LIGAND GATED) CHANNELS

  • VOLTAGE GATED CHANNELS

  • ELECTROPHYSIOLOGICAL PRINCIPLES


Ionotropic channels
IONOTROPIC CHANNELS

  • BIND NEUROTRANSMITTER

  • OPEN CHANNEL

  • HYPER OR DE-POLARIZATION


The synapse neurotransmitter binds to postsynaptic receptor
THE SYNAPSE:NEUROTRANSMITTER BINDS TO POSTSYNAPTIC RECEPTOR

CALCIUM

CHANNEL

•••

RECEPTOR

SYNAPTIC

VESSICLES

•••

•••

•••

•••

•••

•••

•••

ION

CHANNEL

•••

•••

ENZYME


How are we wired connections between nerve cells1
HOW ARE WE WIRED?CONNECTIONS BETWEEN NERVE CELLS

AXON

CELL

BODY

AXON

TERMINALS

AXON

HILLOCK

DENDRITES


Postsynaptic potentials

IPSP

POSTSYNAPTIC POTENTIALS

EPSP

RESTING

POTENTIAL

TIME


Spatial summation
SPATIAL SUMMATION

SIMULTANEOUS

INPUT FROM TWO

SYNAPSES: ABOVE

THRESHOLD

THRESHOLD

TIME


Spatial summation1
SPATIAL SUMMATION

SIMULTANEOUS

INPUT FROM TWO

SYNAPSES: ABOVE

THRESHOLD

THRESHOLD

TIME


Temporal summation
TEMPORAL SUMMATION

TOO FAR APART IN TIME:

NO SUMMATION

TIME


Temporal summation1
TEMPORAL SUMMATION

CLOSER IN TIME:

SUMMATION BUT

BELOW THRESHOLD

THRESHOLD

TIME


The goldman hodgkin katz ghk equation
THE GOLDMAN-HODGKIN-KATZ (GHK) EQUATION

[Ko] + [Nao]

Vm = 60 LOG --------------------------

[Ki] + [Nai]

 IS THE RATIO OF SODIUM TO

POTASSIUM PERMEABILITY


Temporal summation2
TEMPORAL SUMMATION

STILL CLOSER IN

TIME: ABOVE

THRESHOLD

THRESHOLD

TIME



How excitation occurs the role of depolarization and hyperpolarization
HOW EXCITATION OCCURS-THE ROLE OF DEPOLARIZATION AND HYPERPOLARIZATION

  • SUMMATION CAN DEPOLARIZE THE CELL BEYOND THRESHOLD

  • HYPERPOLARIZATION BLOCKS


Neuro transmitters

ACETYL CHOLINE HYPERPOLARIZATION

DOPAMINE

NOREPINEPHRINE

EPINEPHRINE

SEROTONIN

HISTAMINE

GLYCINE

GLUTAMINE

GAMMA-AMINOBUTYRIC ACID (GABA)

NEURO TRANSMITTERS


In the space
IN THE SPACE HYPERPOLARIZATION

  • ENZYME “CHEWS UP” LIGAND

  • MASS ACTION CAUSES LIGAND TO DISSOCIATE FROM RECEPTOR


The synapse1
THE SYNAPSE HYPERPOLARIZATION

CALCIUM

CHANNEL

•••

RECEPTOR

SYNAPTIC

VESSICLES

•••

•••

•••

•••

ION

CHANNEL

•••

•••

•••

•••

ENZYME


The synapse2
THE SYNAPSE HYPERPOLARIZATION

CALCIUM

CHANNEL

•••

RECEPTOR

SYNAPTIC

VESSICLES

•••

•••

•••

•••

•••

ION

CHANNEL

•••

•••

•••

ENZYME


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