The Neuron Flashcards
Neurons
Specialized cells of the nervous system that carry information using electrical impulses (action potentials)
Nerves
Bundles of neuron fibers wrapped in connective tissue to create cable-like structures
Neuroglia or “Glial Cells”
cells that support, protect and nourish neurons
Cell Body
contains the cell’s organelles, relay action potentials from dendrites to axon(s)
Nissl Substance
rough ER of a neuron, makes neurotransmitters (amino acids, small peptides or proteins)
Dendrites
receives incoming messages and direct them toward the cell body
Axon
Conducts electrical signals (action potentials) away from the cell body
Synaptic Terminal
At the end of the axon, relays messages to other neurons or body cells, usually in the form of neurotransmitters
Myelin Sheath
Insulates the axon and helps it conduct electricity more quickly (like Sheath on a wire)
made of closely spaced supporting (glial) cells, these are called Schwann Cells in nervs
Nodes of Ranvier
small gaps in between the supporting cells
Helps nerve signals “hop” along the axon more quickly
Membrane Potential
The driving force for the movement of ions across a membrane due to a difference in ion concentration inside relative to outside neuron cell membrane
What happens when a neuron is “at rest”?
High [Na+] outside the cell, high [K+] inside the cell
the resting membrane potential is Negative: [K+] inside <[Na+] outside (inside more negative)
If positive Ions leave the cell what happens to the cell membrane potential?
decreases (repolarizes)
if positive ions enter what happens to the cell membrane potential
increases (depolarizes)
Voltage-gated ion channels
passively allow the movement (diffusion) of one type of ion down their concentration gradient (from [high] to [low])
what do ion pumps do?
actively move ions up (against) their concentration gradient using ATP (dephosphorylation)
the sodium-pottasium pump (Na+/K+ pump) is ALWAYS pumping to restore/maintain the restin potential
3 Na OUT 2K+ IN
What is an action potential?
a wave of depolarization (positive membrane) that travels along a neuron
starts at the dendrites and ends at the synaptic terminals
Action Potential Phases: Stimulation
a stimulus causes a slight increase in Na+ ions inside the cell which raises the membrane potential
sodium channels open if the stimulus raises the membrane potential above the threshold
Action Potential Phases: Rising Phase (depolarization)
Sodium Ions diffuse (move) down their concentration gradient into the cell
the membrane potential rises and quickly becomes positive (depolarized)
Action Potential Phases: Peak
Sodium channels close and inactivate (can’t open again right away during this refractory period)
potassium channels open
Action Potential Phases: Falling Phase (repolarization)
potassium ions flow down their concentration gradient out of the cell
membrane potential decreases and becomes negative
potassium channels close
Action Potential Phases: Recovery Phase
the sodium-potassium pump restores the resting potential and ion concentration gradients
for every ATP used:
- 3 sodium ions are pumped out
- 2 potassium ions are pumped in
Action Potential Propagation (4 steps)
- Stimulus: brings a section of neuron membrane above the threshold
- Sodium: flow into the cell through voltage-gated Na+ channels
- Na+ ions spread further down inside the membrane and cause nearby Na+ channels to reach their threshold and open
- the Na+ channels that opened first quickly close and become inactive preventing the action potential from propagating (spreading) backwards
How does Myelin Sheath speed up action potentials?
instead of ions needing to diffuse in and out all the way along the neuron membrane the action potential “hops” when Na diffuses through the cytoplasm to the next Node of Ranvier
What is a Synapse
the connection between two neurons or between a neuron and another type of cell
allows the sending neuron (presynaptic neuron) to deliver its signal to a receiving cell (post-synaptic cell)
Types of Synapse: Electrical Synapses
provides a direct channel between cells so that the action potential can physically “jump” from one cell to the next when Na+ ions flow through connexions (holes between cells)
Types of Synapse: Chemical Synapses
convert the electrical signal (action potential) from the sending neuron (presynaptic neuron) to a chemical signal (in the form of neurotransmitters) that can cross the synaptic cleft and trigger a response in the receiving cell (either postsynaptic neuron or cell)
Synaptic Cleft
small space between the synaptic terminal of one neuron and the next neuron
