Neurophysiology II: The Synapse

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Neurophysiology IIThe Synapse
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Synapse Defined

• Space between adjacent neurons!
• Relays information from one neuron to another!
• Neuron ? Neuron
• Neuron ? Muscle
• Neuron ? Gland
• Axodendritic Synapses
• Most common synapse type in body

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How do synapses work?

• ELECTRICAL SYNAPSES
• Allow ion flow from AP to continue from neuron to
  neuron
• Transmission of information is extremely rapid!
• Allow for synchronized neuron activity!

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Electrical Synapses continued

• Isolated in the body!
• CNS
• Sleep arousal
• Concentration
• Emotion/memory centers
• Embryonic Nervous Tissue
• Predominant synapse type!
• Will develop into

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• CHEMICAL SYNAPSES!
• Release chemicals across synapse from neuron to
  neuron (or muscle, gland)
• Chemicals are known as
• N E U R O T R A N S M I T T E R S!

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CHEMICAL SYNAPSES ARE

• THE MOST COMMON TYPE OF SNYAPSE IN THE BODY!
• Composed of Three Major Areas
• Axon terminal on Presynaptic Neuron!
• Synaptic Cleft (the space!)
• Receptor region on Postsynaptic Neuron!

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Axon terminal
presynaptic
Vesicles of
neuron
neurotransmitter
Synaptic
cleft
postsynaptic neuron
Receptors
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Neuron functioning is

• AN
• ELECTROCHEMICAL
• EVENT!!

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The Electro Part

• Generation of Action Potential along axon
• AP will fizzle out at axon terminal!

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The Chemical Part

• Neurotransmitters are
• 1. Released from presynaptic axon terminal
• 2. Diffused across synaptic cleft
• 3. Bound to receptors on postsynaptic cell

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How the Chemical Part Works

• The Players
• NEUROTRANSMITTER
• (stored in vesicles)
• CALCIUM

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The Steps

• AP reaches axon terminal
• Voltage-gated Calcium Channels open!
• Ca rushes into axon terminal membrane!
• (will get pumped back out later)

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• 4. Influx of Calcium causes vesicles (containing
  neurotransmitter) to fuse with axon terminal
  membrane
• Exocytosis occurs!
• Neurotransmitter released into synaptic cleft

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• Neurotransmitter diffuses across synaptic cleft
• Neurotransmitter binds to receptor proteins on
  membrane of postsynaptic neuron.

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• Ion channels on postsynaptic membrane open!
• 10. Membrane permeability changes
• 11. EPSP (Excitatory Post-Synaptic Potential) or
  IPSP (Inhibitory Post-Synaptic Potential) begins!

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EPSP vs. IPSP

• Determined by type of neurotransmitter released
• EPSP? neurotransmitter stimulates the neuron to
  depolarize at the axon (AP occurs!)
• (What axon channels will open to do this?)
  

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• IPSP ? neurotransmitter inhibits depolarization
  at the axon (NO AP!)
• Instead
• neurotransmitter causes hyperpolarization at
  axon!
• K channels open ? K moves out!
• Cl- channels open ?Cl- moves in!

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Now that its over

• HOW DO YOU
• STOP THE EFFECTS OF THE NEUROTRANSMITTER?

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3 OPTIONS!

• 1.Neurotransmitter is broken down by enzymes
• 2. Neurotransmitter is Reabsorbed/recycled by
  presynaptic cell
• 3. Neurotransmitter diffuses out of synapse

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AChneurotransmitter E Enzyme
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Summary of Neurotransmitters

• chemical messengers
• present in terminal and discharged upon
  stimulation
• produce membrane potential changes on
  postsynaptic cell
• naturally removed from synapse
• most cells make and respond to more than one
  neurotransmitter

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• Over 50 chemicals are known to function as
  NEUROTRANSMITTERS!
• BUT 1 chemical is the most well known!

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ACETYLCHOLINE

• 1st neurotransmitter idenitified
• Used at neuromuscular junctions
• Excitatory to skeletal muscles! (EPSP)
• Effect muscle contraction
• Abbreviated ACh

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AChneurotransmitter E Enzyme
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ACETYLCHOLINESTERASE

• ENZYME USED TO BREAK DOWN ACh bound to post
  synaptic receptors!
• Abbreviated AChE

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NERVE AGENTS
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Other Neurotransmitters

• NAME
• Norepinephrine
• Dopamine
• Seratonin
• Histamine
• Endorphins
• GABA

• EFFECT
• Feelings of Euphoria
• Feelings of Euphoria
• Sleep State
• Inflammation
• Pain Inhibitor
• Major IPSP Effect!

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Cholinergic synapses

• Use acetylcholine as NT
• Parasympathetic Division

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Adrenergic Synapses

• Use noradrenaline as NT
• Sympathetic Division

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Endorphins vs. EnkephalinsThe Pain
Killers

• Bind to postsynaptic receptors

• Block calcium channels in presynaptic neuron

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Parkinsons Disease
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Causes of Parkinsons

• Dopamine deficiency!
• Results in contraction of antagonistic muscles!
• Results in uncontrolled shaking