SYNAPSES

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SYNAPSES
D. C. Mikulecky Professor of Physiology http//v
iews.vcu.edu/mikuleck/
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TWO TYPES OF SYNAPSE

• ELECTRICAL
• CHEMICAL

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ELECTRICAL
GAP JUNCTION PROVIDES PATH FOR IONS TO FLOW
FROM ONE CELL TO ANOTHER
CELL 1
CELL 2
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CHEMICAL THE SYNAPSE
INCOMING NERVE
POST SYNAPTIC NERVE
SPACE
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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
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HOW ARE WE WIRED?CONNECTIONS BETWEEN NERVE CELLS
AXON
CELL BODY
AXON TERMINALS
AXON HILLOCK
DENDRITES
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THE NATURE OF CHEMICAL TRANSMISSION BETWEEN NERVES

• PRESYNAPTIC EVENTS
• POSTSYNAPTIC EVENTS
• IN THE SPACE

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PRESYNAPTIC EVENTS

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

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INCOMING ACTION POTENTIAL

• DEPOLARIZES
• TRIGGERS CALCIUM CHANNELS
• CALCIUM ENTERS THE CELL

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THE SYNAPSE
INCOMING ACTION POTENTIAL
CALCIUM CHANNEL

RECEPTOR
SYNAPTIC VESSICLES





ION CHANNEL



ENZYME
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THE SYNAPSE INCOMING ACTION POTENTAL
INCOMING ACTION POTENTIAL
CALCIUM CHANNEL

RECEPTOR
SYNAPTIC VESSICLES





ION CHANNEL



ENZYME
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CALCIUM INFLUX

• CAUSES VESSICLES TO BE RELEASED
• VESSICLES MIGRATE TO MEMBRANE
• EXOCYTOSIS
• NEUROTRANSMITTER ENTERS SPACE

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THE SYNAPSE CALCIUM CHANNELS OPEN
INCOMING ACTION POTENTIAL
CALCIUM CHANNEL

RECEPTOR
SYNAPTIC VESSICLES





ION CHANNEL



ENZYME
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THE SYNAPSE NEUROTRANSMITTER ENTERS SPACE
CALCIUM CHANNEL

RECEPTOR

SYNAPTIC VESSICLES





ION CHANNEL


ENZYME
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POST SYNAPTIC EVENTS

• IONOTROPIC (LIGAND GATED) CHANNELS
• VOLTAGE GATED CHANNELS
• ELECTROPHYSIOLOGICAL PRINCIPLES

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IONOTROPIC CHANNELS

• BIND NEUROTRANSMITTER
• OPEN CHANNEL
• HYPER OR DE-POLARIZATION

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THE SYNAPSENEUROTRANSMITTER BINDS TO
POSTSYNAPTIC RECEPTOR
CALCIUM CHANNEL

RECEPTOR
SYNAPTIC VESSICLES







ION CHANNEL


ENZYME
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HOW ARE WE WIRED?CONNECTIONS BETWEEN NERVE CELLS
AXON
CELL BODY
AXON TERMINALS
AXON HILLOCK
DENDRITES
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POSTSYNAPTIC POTENTIALS
EPSP
RESTING POTENTIAL
TIME
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SPATIAL SUMMATION
SIMULTANEOUS INPUT FROM TWO SYNAPSES
ABOVE THRESHOLD
THRESHOLD
TIME
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SPATIAL SUMMATION
SIMULTANEOUS INPUT FROM TWO SYNAPSES
ABOVE THRESHOLD
THRESHOLD
TIME
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TEMPORAL SUMMATION
TOO FAR APART IN TIME NO SUMMATION
TIME
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TEMPORAL SUMMATION
CLOSER IN TIME SUMMATION BUT BELOW THRESHOLD
THRESHOLD
TIME
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THE GOLDMAN-HODGKIN-KATZ (GHK) EQUATION
Ko ?Nao Vm 60 LOG
-------------------------- Ki ?Nai
? IS THE RATIO OF SODIUM TO POTASSIUM
PERMEABILITY
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TEMPORAL SUMMATION
STILL CLOSER IN TIME ABOVE THRESHOLD
THRESHOLD
TIME
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EPSP-IPSP CANCELLATION
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HOW EXCITATION OCCURS-THE ROLE OF DEPOLARIZATION
AND HYPERPOLARIZATION

• SUMMATION CAN DEPOLARIZE THE CELL BEYOND
  THRESHOLD
• HYPERPOLARIZATION BLOCKS

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(No Transcript)
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NEURO TRANSMITTERS

• ACETYL CHOLINE
• DOPAMINE
• NOREPINEPHRINE
• EPINEPHRINE
• SEROTONIN

• HISTAMINE
• GLYCINE
• GLUTAMINE
• GAMMA-AMINOBUTYRIC ACID (GABA)

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IN THE SPACE

• ENZYME CHEWS UP LIGAND
• MASS ACTION CAUSES LIGAND TO DISSOCIATE FROM
  RECEPTOR

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THE SYNAPSE
CALCIUM CHANNEL

RECEPTOR
SYNAPTIC VESSICLES




ION CHANNEL




ENZYME
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THE SYNAPSE
CALCIUM CHANNEL

RECEPTOR
SYNAPTIC VESSICLES





ION CHANNEL



ENZYME