Neurons Flashcards
Signaling
Coordinates body functions
Difference between endocrine system and nervous system?
Endocrine system: has hormones as signalers, is slow-acting, prolonged effects
Nervous system: neurotransmitters as signalers, fast-acting, ephemeral effects (stimulus -> action -> over)
Neurons
Highly specialized for information processing; has dendrites, cell body w/nucleus, axon hillock, axons covered w/ myelin sheath, nodes of Ranvier, axon terminals, and synapses
Dendrites
Top of the neuron that receives signals
Cell body
Also called soma contains nucleus
Axon hillock
Determines whether or not to fire the signal through the neuron
Axon
Includes myelin sheath and nodes of Ranvier where the signal travels through
Myelin sheath
Covers the axon and acts as a fatty insulator; makes the signal travel faster)
Nodes of Ranvier
Gaps between myelin sheath that the signal lands on after jumping over myelin sheath
Axon terminals
End of an axon and has synapses
Synapses
Connect w/ another neuron and transfers signal
How many neurons typically make up a circuit?
2-3
How many sodium ions are pumped for how many potassium ions?
3 sodiums for 2 potassiums
What does it mean when there is more Na+ ions outside and K+ ions inside?
More positive outside and more negative inside
Hyperpolarization
Removing positive charges and resting potential becomes more negative; cell does not fire
Depolarization
Resting potential becomes more positive due to more positive ions being entering the cell; cell does not fire
Graded potentials
Stimulated neuron but not enough to fire; “false alarm”
Action potential
Massive energy change when tons of ions flood in and out of cell; enough energy to pass the threshold allowing for neuron to fire; a lot of positive energy
List the steps of an action potential.
- Resting state-all voltage gated channels are closed
- Depolarization-stimulus opens some Na channels causing the resting potential to become less negative (Na ions are outside)
- Rising phase-membrane voltage exceeds threshold, causes all voltage gated ion Na channels to open
- Falling phase-K channels open, Na channels close; becomes more negative as Na+ goes in
- Hyperpolarization-K channels remain open longer than Na channels causing potential to return to resting potential (-70 V)
All or nothing
Either a neuron fires or it does not
Unidirectional
A signal moves through the neuron unidirectionally (in one direction cannot go back); signal jumps over myelin sheath and lands on Nodes of Ranvier
Difference between neuron w/ myelin sheath and w/o.
W/ myelin sheath: fast
W/o myelin sheath: slow, increases radius of neuron to offset speed deficiency, in squids and other molluscs
Saltatory conduction
Speeds up signal propogation
What happens once neurotransmitters reach the synapse?
- Action potential triggers release of synaptic vesicles
- Neurotransmitters cross the synaptic cleft and bind to ligand gated channels
- Ion channels open and changing of membrane potential occurs on the other neuron
What would happen if the membranes directly touched?
The action potential will continue to trigger leading to a continuous signal. It will function as one cell. No touching would’ve allowed the signal to stop.
Summation
Inputs are integrated in the axon hillock
Excitatory potential (EPSP)
More likely to fire
Inhibitory potential (IPSP)
Less likely to fire
Sub threshold, no summation
Not enough to fire; involves excitatory potentials
Temporal summation
Excite close in time=fire; involves excitatory potentials
Spatial summation
Signals firing at the same time at diff. Parts of the target cell leads to firing; involves two different excitatory potentials
Spatial summation of EPSP and IPSP
a lot of neuron signals but no firing; involves excitatory and inhibitory signals
How are neurontransmitters returned?
Neurotransmitters are cleared from the synaptic cleft to reset the process. This is done by enzymes breaking down inactivated neurotransmitters in the synaptic cleft and the reuptake of neurotransmitters by the presynaptic neuron.
Some medications block the reuptake of neurotransmitters by the presynaptic neuron in the synaptic cleft. What happens to the postsynaptic neuron as a result?
Neurotransmitters remain bound to ligand gated ion channels longer, triggering more graded potentials (don’t fire)
The neuron becomes hyper stimulated, increasing the magnitude of action potentials
Neurotransmitters remain bound to voltage gated ions channels longer, triggering more action potentials
The response rate of the postsynaptic neuron stays the same because it does not respond to neurotransmitters
Neurotransmitters remain bound to ligand gated ion channels longer, triggering more graded potentials
Greater magnitude leads to taller action potentials. T or F?
False, greater magnitude means more action potentials
