basic unit of the nervous system 1. receives inputs from other cells 2. integrates the inputs 3. then distributes processed information to other neurons

Problem 2 Flashcards by Kimberly Brown

Structural Division of a Neuron

Dendrite
Soma
Axon
Axon terminals

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Dendrite

Input Zone

receives information from other neurons across synapses

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Soma

Integration Zone

Combines / Integrates the received information

Contains cells nucleus

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Axon

Conduction Zone

Carries the cells electrical signal (AP) away from soma

leads away from cell body

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Axon Collaterals

multiple branches at end of axon

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Axon Terminals

Output Zone

transmit neurons activity across synapses to other cells

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Neuron

basic unit of the nervous system

receives inputs from other cells
integrates the inputs
then distributes processed information to other neurons

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Multipolar Neuron

many dendrites, single axon

 --> most common

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Bipolar Neuron

single dendrite, single axon

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Unipolar Neuron

axon branches in two directions

one side has the dendrite, other has the collaterals and terminals

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Motor Neuron

governs movement

part of CNS

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Sensory Neurons

carry information from the periphery to other neurons

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Interneurons

perform functions of the brain

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Astrocyte

Type of glial cell

involved in formation of new synapses

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Oligodendrocyte

Type of glial cell

Myelinates in CNS

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Schwann Cell

Type of Glial cell

Myelinates in PNS

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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 1. Axon membrane contains voltage - gated potassium channels (K+) which require more depolarization to open - -> open later than Na+ channels 2. K+ channels (that are always open) + Voltage-gated K+ channels = High permeability for K+ ions 3. Na+ permeability decrease at the same time - -> Na+ channels close 4. 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 1. K+ channels close - -> number of K+ ions that left is so high that membrane potential is lower than resting potential 2. 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