Neurons Flashcards
Dendrites
LOTS of little extensions off of the soma that recieve signals from other neurons
Soma
Body of a neuron
* Has a nucleus
* Protein synthesis
* Most of cells metabolism
Axon terminal
End of an axon that touches multiple other neurons
Axon
Long extension of the neuron covered with myelin
Synapses
Where the axon terminal of one neuron touches another neuron and signals it
Action Potential (AP)
Very fast electrical signal that travels down the axon from the soma to the axon terminal and can continue traveling far - When AP reaches the axon terminal → the 1st neuron fires the 2nd (at the synapse)
Myelin
Layers of fat wrapped (plasma membrane) around the axons of many neurons to Insulate and speed up AP.
Afferent
(A= ad = towards)
Sensory neurons carrying signals into the CNS from the PNS.
Efferent
(E= ex = exit)
neurons that carry info out from the CNS into the PNS
Motor Neurons
Efferent neurons that control muscles
Interneuron
Neurons that are between other neurons - almost all in the CNS
Multipolar Neuron
Most common neurons with many dendrites coming off the soma.
* Efferent neurons
* Most interneurons
Bipolar neuron
Bi-polar - 2 extensions - 1 dendrite + 1 axon
Neurons with only one dendrite coming off the soma at the end
Afferent in most of special senses:
Eyes, ears, nose
Pseudounipolar neurons
Sensory neurons where the soma is off to the side in the middle of the axon and the dendrites are at the start of the axon not coming off the soma.
AP starts where dentrites turn into axons
Somatic senses = senses of body: touch, pain, temp, tastes, etc
Anaxonic Neurons
Rare neurons only in CNS with many extensions and no clear axon.
Electrochemical Gradient
The difference in distribution of ions between 2 sides of membrane
Extracellular Fluid (ECF) Ions
Contains more Na+, Ca++, Cl-
Intracellular Fluid (ICF) makeup
More K+, amino acids + neucleotides.
Inside of the cell is negative relative to outside of the cell
Na+K+ Pump in relation to the electrochemical gradient
The most important protein for maintinaining the difference in ECF + ICF
Does active transport
Uses 1 ATP
Moves 3 Na+ from ICF → ECF
Moves 2 K+ from ECF → ICF
Resting membrane potential
The usual membrane potential of cell - when cell isn’t doing anything to change it. Has a charge of -70mV
Membrane potential effectors
Difference in concentration of ions between the fluids
Permeability of membrane to ions = how easily is if for ions to pass through the membrane
Open Ion Channels
- Ions flow in + out of cell changing the membrane potential
- Minimal effect on the concentration of ions on either side of the membrane
Leak Channels
- Always open protein channels
- Mostly responsible for a resting membrane potential
Mechanically Gated Channels
Opens in response to some sort of force
Ex: sense of touch
Ligand Gated Channel
Open when they bind a chemical
Allows cells to change membrane potential in response to a chemical signal
ex: Smell
Voltage Gated Ion Channels
Open in response to a change in membrane potential
That allows changes in membrane potential to lead to more changes in the membrane potential –> Positive or negative feedback
Effects of more Na+ & Ca++ in the ECF
Open Na+ & Ca++ ion channels
* Na+ & Ca++ flow into the cell
* Makes the cell more positive
More K+ in the ICF
Opens K+ channels
* K+ flowing out
* cell is more negative
Polarized Membrane
membrane at resting potential:
* Inside of cell is negative
* Na+ & K+ leak channels open
* More K+ channels open - the membrane is more negative
Cell Membrane Depolarization
cell becomes more positive due to:
* Open Na+ or Ca+ channels
* Close K+ or Cl- channels
Cell Membrane Repolarization
cell becomes negative again after depolarization due to:
* Open K+ or Cl- channels
* Close Na+ or Ca++ channels
Cell Membrane
Hyperpolarization
Cell becomes even more negative than the resting potential (more - than -70) due to:
* Open K+ or Cl- channels
* Close Na+ or Ca++ channels
Graded Potential
A change in membrane potential that can be big or small, positive or negative
Occurs in response to stimulus
Bigger stimulus → bigger change
Almost all cells are capable
Action Potential (AP)
Wave of depolarization that travels down the axon
At each point down the axon - they become slightly depolarized
→ leads to a big depolarization
→ followed by a swift repolarization
Voltage-Gated Na+ Channel
Composed of 2 gates:
1st gate opens in response to a slight depolarization
2nd gate closes in response to big depolarization
Voltage-Gated K+ Channel
Opens in response to a big change (when very depolarized → repolarization)
Action Potential Steps
- Resting potential
- Threshold Depolarization
- Depolarization
- Repolarization
- Hyperpolarization
- Return to resting membrane potential
Resting potential for AP
Resting potential is -70mV
* Leak channels are open
* Voltage-gated Na+ & K+ channels are closed
Membrane’s ready for an action potential
Threshold Depolarization
A small depolarization that’s sufficient to open volage-gated Na+ channel
Na+ moves down the axon from further up the axon
→ Slight depolarization → reaches threshold → Voltage-gated Na+ channels open
→ depolarization
Depolarization
membrane becomes positive +40mV
Voltage gated Na+ channels open -> increased permeability of Na+ -> depolarization
Repolarization
Membrane potential becomes negative again.
When the membrane reaches +40mV:
Voltage-gated Na+ channels closed
Voltage-gated K+ channels open
Both lead to repolarization
Hyperpolarization
Membrane potential overshoots - more negative than -70mV
1. Voltage gated K+ channels open to make cell negative
2. Refactory period = a new AP can’t start
Refactory period
A new AP can’t start
membrane cannot depolarize again, because K+ channels open and second gate of Na+ channel closed
Voltage-gated Na+ channels
during action potential
Resting: Closed
Depolarization: Open
Repolarization: Closed
Hyperpolarization: Closed
Voltage-Gated K+ channels
during action potential
Resting: Closed
Depolarization: Closed
Repolarization: Open
Hyperpolarization: Open
Action potential propagation
how an AP moves down an axon
Soma → axon terminal
Have an AP → Na+ enters axon from AP → Na+ diffuses down axon → slight depolarization further down the axon → threshold → starts AP
Na+ will diffuse back up the axon too – further back up the axon is in Refractory period but AP can never go backwards
Action potential frequency
How often a neuron has an AP
On any given neuron, all APs are:
1. Same size
2. Same speed
= APs are all or nothing - binary
Higher frequency APs = stronger signal
Myelin sheath gaps
Spots along the axon where there’s no myelin
* APs happen only at gaps
* No APs between where there’s myelin
Saltatory conduction
AP jumps from gap to gap
How:
1. AP at one gap - Na+ ions flow into the cell (depolarizes the membrane)
2. Na+ ions diffuse through myelin
3. Na+ ions lead to a threshold at the next gap
Glial Cells
All cells in the nervous system that aren’t neurons
Develop from the same tissue as neurons
Located in the PNS & CNS
Astrocytes
Glial cells in the CNS that maintain the environment in the CNS → ion concentrations in ECF
* Identifiable by the many long extensions coming off
* Feed neurons
* Provide structure to neurons
Blood-brain burrier
Hard for substances to pass from blood into the CNS
Astrocytes wrap around blood vessels to help maintain the burrier
Oligodendrocytes
Glial cells that make myelin in the CNS
Each one wraps the plasma membrane around the axons of multiple neurons
Microglia
Glial immune cells of the CNS
* Not neural tissue
* They’re WBCs that live in the CNS
Phagocytes - Eat cells + large particles (Pathogens + old dead tissue)
Ependymal
Glial cells of the CNS that line the inside of the dorsal cavity.
* Neural epithelial cells
* Cerebrospinal flood on one side / Nervous tissue on the other
* Cilia beat - moves Cerebrospinal fluid around the CNS
* Different than other glial cells
Schwann cells
Glial cells that make myelin in the PNS.
Each one wraps around 1 axon.
Satellite cells
Glial cells that wrap around cell bodies of neurons in the PNS + support them
