Essen%al Idea Neurons transmit the message, synapses modulate the message. Neurons & Synapses

Essen%al Idea Neurons transmit the message, synapses modulate the message. Neurons & Synapses

Neuron Structure Cell Membrane

Nerve Impulse Informa8on passed rapidly in your body by electrical signals à Result of changes in concentra8on of sodium (Na + ) and potassium (K + ) ions across the membrane This is how we measure the electrical ac8vity of a neuron

How do impulses work? It s all or nothing. à Nerve impulse occurs only when a s8mulus is strong enough to depolarize the neuron and pass the threshold.

The players Voltage gated channels Sodium, Potassium Ac%ve Transport Sodium/ Potassium Pump 3 Sodium out 2 Potassium in

Nerve Impulse Res3ng poten3al (-70mV) The electrical poten8al across the plasma membrane of a cell that is not conduc8ng an impulse Maintained by ac8ve transport (Na + /K + Pump) & diffusion Plasma membrane is 50 8mes more permeable to K+ ions than Na+

Nerve Impulse Ac8on Poten8al Ac8on poten8al is the rapid change in membrane poten8al as an impulse travels along it. Two parts: Depolariza8on & Repolariza8on

Ac8on Poten8al Depolariza8on (+30mV) A change from nega8ve to posi8ve à In response to a s8mulus some voltage gated Na + channels open and sodium enters the neuron by diffusion. à If a threshold poten8al is reached, all the voltage gated Na + channels open. The entry of Na + causes the membrane poten8al to become posi8ve

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San8ago Ramón y Cajal

Ac8on Poten8al - Repolariza8on A change back from posi8ve to nega8ve à The depolariza8on of the membrane poten8al causes the voltage gated Na + channels to close and the voltage gated K + channels open. à K + diffuses out of the neuron rapidly and the membrane poten8al becomes nega8ve again

Okay.. Now back to res8ng, right? Hyperpolariza8on The K+ channels close slowly The membrane is more nega8ve than the res8ng poten8al. Refractory period where the neuron cannot be further s8mulated.

Pass it on. Ac8on Poten8als, once started, are passed on down the axon automa8cally. How does the nerve impulse travel down the neuron?

Refractory Poten8al (RefP) Acer an ion channel has opened, it needs a rest period before it can reopen Can t be reopened by the ac8on poten8al down axon Ac8on poten8als are one-way. Only downstream channels open Delay prevents the summa8on of ac8on poten8als (one impulse cannot catch up to another impulse)

Ac8on Poten8al High concentra8on of Na + in the axon (Channels open) diffuses to the next set of voltage gates causing depolariza8on Threshold (TH): The ion channels are either open or closed; there is no halfway posi8on. Ac8on poten8al = +40mV (the en8re length of the axon)

Res8ng Poten8al Na + diffuses If threshold is reached then the channel will open Na + will flood in and a new ac8on poten8al begins

Speed maiers.

Myelina8on and saltatory conduc8on from the La8n saltare, to hop propaga8on along myelinated axons from one node of Ranvier to the next node increases conduc8on velocity of ac8on poten8als. Reduces energy cost up to 200 m/s versus 2 m/s.

It s the end of the neuron. But the beginning of the message. The Synapse the space between the axon and the dendrite. Pre-synap8c Post-synap8c

In the synapse The electric signal is converted to a chemical message called neurotransmiders. NeurotransmiDers (NTs) are made and stored in synap8c vesicles at the end of the axon. The the post-synap8c neuron has chemical-gated ion channels called neuroreceptors. specific binding sites for the neurotransmiiers

Synapse Overview

Synap8c Transmission (7 steps) Nerve impulse reaches terminal end of presynap8c neuron Ca 2+ causes synap8c vesicles to move to the membrane and fuse Depolariza8on causes voltage gated calcium channels to open. Ca + rushes in.

Synap8c Transmission (7 steps) NTs that were stored in the vesicle diffuse across the gap NTs bind with post-synap8c receptors (these are specific) Enzymes in the gap break down NTs. Pieces are taken up by pre-synap8c neuron via ac8ve transport. Sodium channels open (Na + enters) à depolariza8on and an ac8on poten8al begins

Neurotransmiier found in neurons and muscle cells 2 parts: acetyl (from respira8on) choline (from diet) Acetylcholine Travels across the synapse to bind its receptor Broken down by enzyme acetylcholinesterase in the synapse Choline is absorbed by presynap8c neuron and re-used

6.5.A2 Blocking of synap8c transmission at cholinergic synapses in insects by binding of neonico8noid pes8cides to acetylcholine receptors. Neonico8noids: insec8cide synthe8c chemical similar to nico8ne Safe for mammals Non-specific insec8cide binds the acetylcholine receptor irreversibly leads to paralysis and death in insects