Neurons Flashcards
Be able to describe the function of each structure in a motor neuron.
- Dendrites: short, branched fibers (branching off the cell body)
receive chemical signals (from sensory receptors or other neurons) and transform them into electrical signals which are sent to cell body (into neuron) - Cell body (soma): nucleus & cytoplasm + organelles
(metabolism and summation of input signals) - Axons: long nerve fibers
carry signals away from cell body to the end of the axon/ axon terminal/ synaptic terminal buttons (where neurotransmitters are released for communication with other neurons or effectors)
Be able to define membrane potential
the difference in electrical charge across the plasma membrane
Know the relative (where there is more versus where there is less) concentrations of sodium and potassium inside and outside of a neuron when it is “at rest”
3 Na+ OUT for every 2 K+ IN
Know what an action potential is and which direction it travels through a neuron.
- and that it is an all or nothing event
- Neurons become “excited,” when a stimulus causes a voltage-gated ion (Na+) channel to open in the axon membrane (ONLY opens if a “threshold” voltage is reached)- once this threshold voltage is reached, an ACTION POTENTIAL (nerve impulse) is generated and propagated (sent) down the axon
Be able to explain how an impulse is generated in a neuron and propagated down the axon (events of an action potential)
- Depolarization: Voltage-gated Na+ channels open (when threshold potential of -55mV is reached) and Na+ rushes INTO axon (more Na+ outside of cell), causing more Na+ channels to open – domino effect (propagation) down the axon – membrane potential becomes more POSITIVE
- Repolarization: K+ channels open (Na+ channels close) and K+ rushes OUT of axon – domino effect down the axon – membrane potential becomes more NEGATIVE - becomes hyperpolarized)
- Resting potential restored (by sodium-potassium pumps: 3 Na+ OUT for every 2 K+ IN): This period called refractory period (another action potential CANNOT be fired until this period is complete - until the resting potential AND Na+/ K+ ion concentration gradients are restored)
Be able to explain the role of the myelin sheath in saltatory conduction.
In myelinated neurons, action potentials travel FASTER down the axon because ion channels are ONLY positioned BETWEEN myelinated portions (at the Nodes of Ranvier) - called SALTATORY CONDUCTION (also require LESS ATP to return to resting potential)
Be able to explain the steps of synaptic transmission.
1.An action potential arrives at END of the axon (the axon terminal/ synaptic knob)
2.Calcium channels open and calcium ions rush INTO the axon terminal/synaptic knob
3.Calcium ions interact with vesicles (containing neurotransmitter) stored in the axon terminal, causing them to migrate to and fuse with the membrane of the axon terminal/synaptic knob
4.Neurotransmitter is released (by exocytosis) into the synaptic cleft (space between neurons/ neurons and effectors) and diffuses across the synaptic cleft
5.Neurotransmitters bind to receptor proteins on the post-synaptic membrane (dendrites, etc. )
6.Binding of neurotransmitter causes ion channels to open (changes their 3° structure) and:
Na+ ions rush in the post-synaptic cell (causing depolirzation: excitatory) OR
Cl-ions rush into the post-synaptic cell (causing hyperpolarization: inhibitory)
7.Enzymes break down neurotransmitters into two or more fragments (ion channels close on postsynaptic membrane) and their pieces diffuse back into presynaptic neuron (reuptake) to be assembled in vesicles again
Be able to explain the steps involved in synaptic transmission (at the neuromuscular junction) when ACh (acetylcholine) is the neurotransmitter.
- Ach is usually released by presynaptic neurons at neuromuscular junctions in order to trigger muscle contractions by binding to receptors (cholinergic/ nicotinic) in the membrane of postsynaptic muscle fibers to allow Na+ ions to diffuse into post-synaptic muscle fiber cells.
- Acetylcholinesterase/ Cholinesterase (AchE) - released by presynaptic cell or found in membrane of postsynaptic cell - continually breaks Ach down (back into choline and an acetyl group), as overstimulation of muscle fibers by Ach can lead to fatal convulsions and paralysis!
- Choline is taken back into the presynaptic cell (reuptake/ reabsorption) to be used to make Ach again
Be able to explain how neonicotinoid pesticides work, why they are effective (and not harmful to humans), and what concerns there are with their use.
- Neonicotinoid pesticides bind IRREVERSIBLY to Ach receptors (in postsynaptic muscle fiber cell membranes) in insects
- Block normal Ach binding (block synaptic transmission)
- AchE is NOT able to break down neonicotinoids, so effect is PERMANENT (paralysis/ no muscle contraction/ death)
Be able to explain the role of the sodium potassium pump in maintaining the resting potential of a neuron (and be able to define resting potential and know that it is negative for neurons)
• Using ACTIVE transport (ATP), sodium-potassium pumps pump 3 Na+
ions OUT of the axon while pumping 2 K+ ions INTO the axon
• Result: OUTSIDE of neuron is more positive compared to inside of
neuron (outside of axon and inside of neuron are POLARIZED)
– Creates a negative resting membrane potential of -70mV
