Neuron Synapses
I. Anatomy of the Synapse
II. Chemical Synapse
III. EPSP & IPSP
IV. Neurotransmitters
• Neurons signal is One Way
• Communication between neurons at synapse
• AP converted to chemical signal, a ________________
• Stimulation of neuron might lead to an AP
Communication Between Neurons
The Neuron Synapse
Junction between 2 neurons
Ion Channels
Presynaptic Neuron
PostsynapticNeuron
Synaptic Cleft
Secretory Vesicles w/ neurotransmitters
Release of Neurotransmitters
Postsynaptic Neuron
Presynaptic Neuron
The Neuron Synapse
Each neuron has 1,000 – 10,000 axon terminals forming a synapse
The Neuron Synapse
Types of Synapses:
1. Axon – Dendrite synapse
2. Axon – Muscle synapse
3. Axon – Gland synapse
Each neuron has 1,000 – 10,000 axon terminals forming a synapse
Neuron Synapses
I. Anatomy of the Synapse
II. Chemical Synapse
III. EPSP & IPSP
IV. Neurotransmitters
Nerve Communication Across Synapses
AP must reach axon terminal
Nerve Communication Across Synapses
1. AP opens voltage-gated _________ channels. _________ enters axon terminal
Nerve Communication Across Synapses
2. Synaptic vesicles fuse with _________ membrane
Nerve Communication Across Synapses
3. Neurotransmitter release into synaptic _________
4. Neurotransmitters bind to chemically-gated ionchannels
Nerve Communication Across Synapses
5. Ions (Na+ or K+) enter/leave postsynaptic neuron through chemically-gated ion channel
Nerve Communication Across Synapses
6. Neurotransmitter effect terminated
1. Removal by _____________
2. Diffusion
Nerve Communication Across Synapses
Clinical Application: Botulinum toxin
Clinical Application: VX Nerve Gas
Clinical Application: VX Nerve Gas
Neuron Synapses
I. Anatomy of the Synapse
II. Chemical Synapse
III. EPSP & IPSP
IV. Neurotransmitters
Function of Neurotransmitters
• Effect may be fast or slow
Function of Neurotransmitters
• Effect may be fast or slow
• Can excite or inhibit AP in ___________ neuron
Function of Neurotransmitters
• Effect may be fast or slow
• Can excite or inhibit AP in ___________ neuron
• Determined by neurotransmitter interaction with receptor on postsynaptic membrane
Excitatory Postsynaptic Potential (EPSP)
• Neurotransmitter causes small depolarization
Excitatory Postsynaptic Potential (EPSP)
• Neurotransmitter causes small depolarization
• Na+ enters postsynaptic neuron and/or K+ leaves postsynaptic neuron Self-defeating?
Inhibitory Postsynaptic Potential (IPSP)
• Neurotransmitter causes small hyperpolarization
Inhibitory Postsynaptic Potential (IPSP)
• Neurotransmitter causes small hyperpolarization
• K+ leaves postsynaptic neuron
• Produce graded potential in post-synaptic membrane
EPSP’s & IPSP’s
• Produce graded potential in post-synaptic membrane
• Cause slight change in membrane potential (~1 mV)
EPSP’s & IPSP’s
• Produce graded potential in post-synaptic membrane
• Cause slight change in membrane potential (~1 mV)
• Axon Hillock keeps “running account”
EPSP’s & IPSP’s
1) AP initiated at axon hillock (voltage-gated channels)
Axon hillock
1) AP initiated at axon hillock (voltage-gated channels)
2) IPSPs can prevent axon hillock from reaching threshold
Axon hillock
1) AP initiated at axon hillock (voltage-gated channels)
2) IPSPs can prevent axon hillock from reaching threshold
3) Multiple EPSPs are required to reach threshold
Axon hillock
Summation of Graded Potentials Can Trigger Action Potential
EPSP’s Reach Threshold Via:
Temporal Summation occurs when a single synapse is activated repeatedly over a short time period.
Summation of Graded Potentials Can Trigger Action Potential
EPSP’s Reach Threshold Via:
Temporal Summation occurs when a single synapse is activated repeatedly over a short time period.
Spatial Summation occurs when multiple synapses are activated at the same time.
Summation of EPSP’s & IPSP’s
No summation Temporal summation
Spatialsummation
Summation ofEPSP and IPSP
Me
mbr
an
e P
ote
ntia
l (m
V)
E1 & E2 = EPSP ; I1 = IPSP
Spatial & Temporal Summation Analogy
EPSP is student popping bubblegum
AP is professor getting annoyed
Spatial & Temporal Summation Analogy
EPSP is student popping bubblegum
AP is professor getting annoyed
Temporal Summation:How frequently one student pops a bubble
Spatial & Temporal Summation Analogy
EPSP is student popping bubblegum
AP is professor getting annoyed
Temporal Summation:How frequently one student pops a bubble
Spatial Summation:Every student in front row popping bubbles
EPSP’s, IPSP’s & Your Bladder
EPSP’s & the Lesson of Tyco Brahe
EPSP’s & the Lesson of Tyco Brahe
Tyco’s overstretched bladder exploded
Died 11 agonizing days later
Moral of the Story: Listen to your EPSP’s!