Problem 2 Flashcards
Structural Division of a Neuron
- Dendrite
- Soma
- Axon
- Axon terminals
Dendrite
Input Zone
receives information from other neurons across synapses
Soma
Integration Zone
Combines / Integrates the received information
Contains cells nucleus
Axon
Conduction Zone
Carries the cells electrical signal (AP) away from soma
leads away from cell body
Axon Collaterals
multiple branches at end of axon
Axon Terminals
Output Zone
transmit neurons activity across synapses to other cells
Neuron
basic unit of the nervous system
- receives inputs from other cells
- integrates the inputs
- then distributes processed information to other neurons
Multipolar Neuron
many dendrites, single axon
--> most common
Bipolar Neuron
single dendrite, single axon
Unipolar Neuron
axon branches in two directions
one side has the dendrite, other has the collaterals and terminals
Motor Neuron
governs movement
part of CNS
Sensory Neurons
carry information from the periphery to other neurons
Interneurons
perform functions of the brain
Astrocyte
Type of glial cell
involved in formation of new synapses
Oligodendrocyte
Type of glial cell
Myelinates in CNS
Schwann Cell
Type of Glial cell
Myelinates in PNS
Node of Ranvier
small uninsulated patches of axonal membrane
Microglial cell
removes debris / lesion from injured or dead cells
Type of glial cell
Ion channel
tubelike pore that allows ions of a specific type to pass through the membrane
Precondition of Resting Potential
- 65mv
- neuron contains a majority of anions (-) which cannot exit the cell
- intra - and extracellular fluid are separated by cell membrane
- intracellular –> more negatively charged ions
(Anions- & K+)
extracellular –> more postively charged ions (Na+ & Cl- ions) - neuron is studded with K+ Channels
Process of Resting potential
At rest, membrane is much more permeable to Potassium (K+ Ions)
- K+ ions leave interior through K+ channels
- -> build up of negative charges inside cell
- Concentration gradient pushes K+ ions out of extracellular f.
+ electrostatic pressure pulls K+ ions in the intracellular fluid- -> Equilibrium is reaches
- Further movement of potassium into the cell is matched by movement out of cell
Maintenance of the Resting Potential
- little but steady influx of Na+ through leakage current leads to decrease of negative potential
- K+ ions leaving the cell leads to high loss of potassium
–> Sodium potassium pump pumps 3 Na+ out of call and 2 K+ into call ( always 1 cation (+) is pumped out of intracellular fluid.
What is an Action Potential ?
Very brief, but large changes in a neurons polarization that arise at the axon hillock
–> it is then propagated at high speed along the axon
Depolarization
I. Phase of an AP
Cell becomes depolarized to threshold levels
- -> channels shape changes - -> voltage gated Na+ Channels open - -> Na+ ions are allowed through
Rapid change from -65mv to +40mv
Repolarisation
II. Phase of an AP
- Axon membrane contains voltage - gated potassium channels (K+) which require more depolarization to open
- -> open later than Na+ channels
- K+ channels (that are always open) + Voltage-gated K+ channels
= High permeability for K+ ions - Na+ permeability decrease at the same time
- -> Na+ channels close
- High number of cations left cell
=> Membrane potential is negative again
Sodium
Natrium (Na+)
Anion
negatively charged ions
Cl-
Cations
Positively charged ions
K+, Na+
Hyperpolarisation
III. Phase of an AP
- K+ channels close
- -> number of K+ ions that left is so high that membrane potential is lower than resting potential
- Axonal membrane is refractory ( unresponsive ) to a second stimulus
Absolute refractory phase
Threshold –> Repolarisation
- Na+ channels are unresponsive
- -> no amount of stimulus can induce a new AP
Relative refractory phase
Hyperpolarisation
- Right after the Absolute refractory phase
- -> only a very strong stimulus can produce another AP
Active transport
uses / requires energy (ATP)
Passive transport
doesn’t require energy
All or none property
Either an AP fires at full magnitude or not at all
Axonal transport
- Important substances needed at the axon terminals are loaded onto motor proteins
- Proteins act between soma and terminals
Anterograde transport
toward terminals
Retrograde transport
towards cell body
Glial Cell
- surround neurons + provide support
Why can’t an AP travel backwards ?
- AP can only occur when the Na+ channels are open
- -> as they close as soon as the AP happens, it can’t travel backwards (refractory period)
Axon hillock
thickening at soma - border crossing of soma and axon
--> determines/decides whether the sum of EPSPs and IPSPs will lead to an AP
