NEUROMUSCULAR AND
SYNAPTIC TRANSMISSION
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
TYPES OF CHEMICAL
SYNAPSES
• DISCRETE
• DIFFUSE
DISCRETE SYNAPSES
DIFFUSE SYNAPSES
CHEMICAL: THE SYNAPSE
INCOMING NERVE
POST SYNAPTIC
NERVE
SPACE
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
CELL
BODY
AXON
AXON
TERMINALS
AXON
HILLOCK
DENDRITES
THE NATURE OF CHEMICAL TRANSMISSION
BETWEEN NERVES
• PRESYNAPTIC EVENTS
• POSTSYNAPTIC EVENTS
• IN THE SPACE
PRESYNAPTIC EVENTS
• THE ALL OR NONE ACTION
POTENTIAL TRIGGERS THE
RELEASE OF CHEMICAL
TRANSMITTER
INCOMING ACTION POTENTIAL
• DEPOLARIZES
• TRIGGERS CALCIUM CHANNELS
• CALCIUM ENTERS THE CELL
THE SYNAPSE
INCOMING
ACTION
POTENTIAL
CALCIUM
CHANNEL
•••
SYNAPTIC
VESSICLES
•••
•••
•••
RECEPTOR
•••
•••
•••
•••
•••
ENZYME
ION
CHANNEL
THE SYNAPSE: INCOMING ACTION POTENTAL
INCOMING
ACTION
POTENTIAL
CALCIUM
CHANNEL
•••
SYNAPTIC
VESSICLES
•••
•••
•••
RECEPTOR
•••
•••
•••
•••
•••
ENZYME
ION
CHANNEL
CALCIUM INFLUX
• CAUSES VESSICLES TO BE
RELEASED
• VESSICLES MIGRATE TO
MEMBRANE
• EXOCYTOSIS
• NEUROTRANSMITTER ENTERS
SPACE
THE SYNAPSE: CALCIUM CHANNELS OPEN
INCOMING
ACTION
POTENTIAL
CALCIUM
CHANNEL
•••
SYNAPTIC
VESSICLES
•••
•••
•••
RECEPTOR
•••
•••
•••
•••
•••
ENZYME
ION
CHANNEL
THE SYNAPSE: NEUROTRANSMITTER
ENTERS SPACE
CALCIUM
CHANNEL
•••
SYNAPTIC
VESSICLES
•••
•••
•••
•••
•••
•••
RECEPTOR
•••
•••
ENZYME
ION
CHANNEL
POST SYNAPTIC EVENTS
• IONOTROPIC (LIGAND GATED)
CHANNELS
• VOLTAGE GATED CHANNELS
• ELECTROPHYSIOLOGICAL
PRINCIPLES
IONOTROPIC CHANNELS
• BIND NEUROTRANSMITTER
• OPEN CHANNEL
• HYPER OR DE-POLARIZATION
THE SYNAPSE:NEUROTRANSMITTER
BINDS TO POSTSYNAPTIC RECEPTOR
CALCIUM
CHANNEL
•••
SYNAPTIC
VESSICLES
•••
RECEPTOR
•••
•••
•••
•••
••• •••
•••
•••
ENZYME
ION
CHANNEL
HOW ARE WE WIRED?CONNECTIONS
BETWEEN NERVE CELLS
CELL
BODY
AXON
AXON
TERMINALS
AXON
HILLOCK
DENDRITES
POSTSYNAPTIC
POTENTIALS
IPSP
RESTING
POTENTIAL
TIME
EPSP
SPATIAL SUMMATION
SIMULTANEOUS
INPUT FROM TWO
SYNAPSES: ABOVE
THRESHOLD
THRESHOLD
TIME
SPATIAL SUMMATION
SIMULTANEOUS
INPUT FROM TWO
SYNAPSES: ABOVE
THRESHOLD
THRESHOLD
TIME
TEMPORAL SUMMATION
TOO FAR APART IN TIME:
NO SUMMATION
TIME
TEMPORAL SUMMATION
CLOSER IN TIME:
SUMMATION BUT
BELOW THRESHOLD
THRESHOLD
TIME
THE GOLDMAN-HODGKIN-KATZ
(GHK) EQUATION
[Ko] + [Nao]
Vm = 60 LOG -------------------------[Ki] + [Nai]
 IS THE RATIO OF SODIUM TO
POTASSIUM PERMEABILITY
TEMPORAL SUMMATION
STILL CLOSER IN
TIME: ABOVE
THRESHOLD
THRESHOLD
TIME
EPSP-IPSP CANCELLATION
HOW EXCITATION OCCURS-THE ROLE OF
DEPOLARIZATION AND HYPERPOLARIZATION
• SUMMATION CAN DEPOLARIZE THE
CELL BEYOND THRESHOLD
• HYPERPOLARIZATION BLOCKS
NEURO TRANSMITTERS
•
•
•
•
•
ACETYL CHOLINE
DOPAMINE
NOREPINEPHRINE
EPINEPHRINE
SEROTONIN
•
•
•
•
HISTAMINE
GLYCINE
GLUTAMINE
GAMMAAMINOBUTYRIC
ACID (GABA)
IN THE SPACE
• ENZYME “CHEWS UP” LIGAND
• MASS ACTION CAUSES LIGAND TO
DISSOCIATE FROM RECEPTOR
THE SYNAPSE
CALCIUM
CHANNEL
•••
SYNAPTIC
VESSICLES
•••
RECEPTOR
•••
•••
•••
•••
•••
•••
•••
ENZYME
ION
CHANNEL
THE SYNAPSE
CALCIUM
CHANNEL
•••
SYNAPTIC
VESSICLES
•••
•••
•••
RECEPTOR
•••
•••
•••
•••
•••
ENZYME
ION
CHANNEL