neuron synapses i.anatomy of the synapse ii.chemical synapse iii.epsp & ipsp...

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

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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!