Download Neuron Signal Movement: Graded Potentials and Action Potentials and more Slides Human Biology in PDF only on Docsity! Four Basic Components of Signal Movement Through Neuron 1. Input signal (graded potential) 2. Integration of input signal at trigger zone 3. Conduction signal to distal part of neuron (= Action Potential) 4. Output signal (usually neurotransmitter) Chapter 8: Neurons, Part 2 Docsity.com Review of Solute Distribution in Body Fluids •The [ ] gradient of K+ is the main source of the membrane potential •Change in permeability ot Na+ can allow influx of Na+ •Depolarization •Electric signal created •Controlled by gated channels Docsity.com AP Subthreshold potential vs. Suprathreshold potential Fig 8-8 Graded potential starts here Docsity.com Location ? Travel over long distances Do not lose strength as they travel Are all identical (all-or-none principle): 100mV amplitude Represent movement of Na+ and K+ across membrane Conduction Signals: Action Potentials (AP) Ability to propagate the AP = Excitability Docsity.com Ion Movement across Cell Membrane During AP Sudden increase in Na+ permeability Na+ enters cell down electrochemical gradient (+ feedback loop for ~ .5 msec) Influx causes depolarization of membrane potential = electrical signal What stops + feedback loop? The Na+ inactivation gate closes. Docsity.com Graded potentials A. Produce an effect that increases with distance from the point of stimulation B. Produce an effect that spreads actively across the entire membrane surface C. May involve either depolarization or hyperpolarization D. Are all-or-none E. All of the above Docsity.com Absolute & Relative Refractory Periods No movement of Na+ possible Na+ channels reset to resting state, K+ channels still open higher than normal Stimulus necessary Fig 8-12 Docsity.com Refractory Periods 1. Limit signal transmission rate (no summation!) 2. Assure one way transmission! 3. Remember that the Na+ and K+ concentration gradients remain nearly unchanged! Forward current excites, backward current does NOT re-excite ! Animation Docsity.com 1. Axon Diameter
One giant
axon from
a squid
'
0.8 mm diameter
400 myelinated
mammalian axons
'
would require a nerve this size
if each mammalian axon were
the size of a squid giant axon
(i ™
(
Fig. 8-18 Demyelination diseases (E.g. ?) 2. Signal Transduction in Myelinated Axon: Animation Docsity.com Output Signal: Communication at Synapses Synapse = point where neuron meets target cell (e.g. ?) 2 types chemical electrical 3 components of chemical synapse presynaptic cell synaptic cleft postsynaptic cell What’s this? Docsity.com Synapse
Action
potential
Axon
terminal
. An action potential depolarizes
Synaptic the axon terminal.
vesicle
The depolarization opens voltage-
gated Ca2+ channels and Ca2+
enters the cell.
Calcium entry triggers exocytosis
of synaptic vesicle contents.
protein Neurotransmitter diffuses across
the synaptic cleft and binds with
receptors on the postsynaptic cell.
Postsynaptic Receptor e peer:
cell
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3 Classes of Neurotransmitters (of 7) 1. Acetyl Choline (ACh) – Made from Acetyl CoA and choline – Synthesized in axon terminal – Quickly degraded by ACh-esterase – Cholinergic neurons and receptors – Nicotinic (agonistic) and muscarinic (antagonist) 2. Amines – Serotonin (tryptophane) and Histamine (histidine) – SSRI = antidepressants – Dopamine and Norepinephrine (tyrosine) – Widely used in brain, role in emotional behavior (NE used in ANS) – Adrenergic neurons and receptors - and 3. Gases – NO (nitric oxide) and CO 4. Others: AA, (e.g., GABA), lipids, peptides, purines Fig 8-22 Docsity.com Postsynaptic Responses Can lead to either EPSP or IPSP (p.277) Any one synapse can only be either excitatory or inhibitory Fast synaptic potentials Opening of chemically gated ion channel Rapid & of short duration Slow synaptic potentials Involve G-proteins and 2nd messengers Can open or close channels or change protein composition of neuron Docsity.com
