Task 2 Flashcards
Membrane potential
The difference between the electrical charge between the inside and the ouside of a cell
How to record membrane potential
Position the tip of one elctrode inside of the neuron and the tip of another neuron in the extracellular fluid.
Intracellular electrodes
Microelectrodes
what is the potential inside a resting neuron?(resting potetntial of a neuron)
70 mvV less than outside
When do we say that a neuron is polarised?
When it is at its resting potential
Ions
Positively and negatively charged particles
Anion
Negativelt charged ion
Cation
Positively charged ion
4 most important ions
And levels in intracellular and extracellular space
Sodium ions na+(high levels extracellular)
potassium ions K+(high levels intracellular)
Calcium ions Ca2+ (Low levels intracellular and low levels extracellular)
Cl- ions ( high levels extracellular)
IPSP
inhibitory postsynaptic potential (IPSP) is a kind of synaptic potential that makes a postsynaptic neuron less likely to generate an action potential.
IPSP and cl- ions relation
IPSPS result from opening operational channels permitting cl- to enter the cell making the cell more negative
Resting neurons and ions
They have more Na+ ions outside the cell and more K+ inside
Concentration is maintained although there are ion channels in the neural membranes. Each ion channel is specialized for the passage of particular ions.
Concentration of the cell and ion channels.
Concentration is maintained although there are ion channels in the neural membranes. Each ion channel is specialized for the passage of particular ions.
2 types of pressure of Na+ to enter resting neurons for moving across the membrane
what is more likely?
Electrostatic pressure from resting membrane potential (opposite charges atract)
Random motion of Na+ ions to move down the concentration gradient
Is more likely to move from areas of high concentration to areas of low concentration
What is a concentration gradient
A concentration gradient occurs when the concentration of particles is higher in one area than another. In passive transport, particles will diffuse down a concentration gradient, from areas of higher concentration to areas of lower concentration, until they are evenly spaced.
When are sodium ion channels closed?
When are potassium ion channels open?(why dont they usually use this channel)?
Na+ channels are closed while neuron is at resting potetnial while K+ are open
K+ dont tend to pass the ion channel because they want to maintain the negative resting of the membrane potential
Hodgkin and huxley model
Why does the resting potetntial stays fixed
At the same rate Na+ ions leak into resting neurons, other Na+ ions are actively transported out. At the same rate K+ ions leak out of the membrane, other K + ions are actively transported in.
There are sodium potassiulm pumps and also existence of ohter kind sof transporteers
What is released when a neuron fires?what does it do?
A neurotransmitter that diffuses across the synapti cleft and interacts with receptor molecules on receptive membranes of the next neuron.
what are the two effects of a neurotransmitter interacting with the receptor molecule on the receptive membrane of a neuron?
It either depolarizes the recptive membrane ( Excitatory post synaptic potential (EPSP) increasing likelihood of a neuron firing
or it hyperopolarizes it inhibitory postsynaptic potential (IPSP) decreasing th elikelihood of a neuron firing
What are graded responses?
reflection of the nature and magnitude of neurotransmitters released at the synapse at any given point in time.( same energy ans recived)
Transmission postsynaptic potentials 2 important characteristics
Rapid( can be assumed to be instantaneous)
Decremental(decrease in amplitude)
EPSP and IPSP dying tendencies?
Most EPSP and IPSP do not travem more than a couple of mm from the site of generation before they fade out only a few travel along the axon
What are the receptve areas of most neurons covered with?
Thousands of synapses
What does a neuron depend on to fire?
Net of activity (balance between inhibitory and excitatory signals)
Where are action potentials generated?
At the axon initial segment NOT THE AXO HILLOCK
If the sum of depolarisations and hyperpolarisations are able to depolarize the membrane threshold to -§( mv?
An action potential occurs
What does it mean tht an action potential occurs?
That a massive but momentary (1ms) reversal of the membrane potential from -70mV to -50mV happens( it is not a graded response is an all or nothing situation)
Whic synapses are more likely to fire a neuron?
Those closer to the the axon
Spatial and temporal summation
Spatial=is a mechanism of eliciting an action potential in a neuron with input from multiple presynaptic cells.
Temporal summation=emporal Summation Allows Integration of Successive PSPs
Temporal summation can be illustrated by firing action potentials in a presynaptic neuron and monitoring the resultant EPSPs
What happens when two simultaneous EPSPS sum?and when IPSPS?
Produce a greater EPSP +
Produce a greater IPSP -
What happens when a simultaneous IPSP and EPSP?
They cancel each ohter out
How are APS produced and conducted?
Through action of voltage activated ion channels
When does the membrane potential of a resting neuron change?
When the membrane potential of the axon is depolarized to the threshold by EPSP
Depolarizing the membrane potential of a restig neuron
Sodium channels opne and Na+ ions rush in (h-the membrane potential goes from -70mV to 50 mV
Potassium channels open and K+ is driven out
First by relatively high internal concentration
Then by positive internal change
After 1 ms sodium channels close= end of the rising phase
Repolarization
Continued efflux of K+ ions once repolarization has been achieveed K+ channels close but gradually there are still a lot of K+ ions out there
Hyperpolarization
Brief time period
What is an absolute refractory period?
When it is impossiblle to fire a second time
What is a relative refractory period?
Possible to fire but only by higher than normal levels of stimulation
What is the refractory period responsible for?
For APS to travel in only one direction
Rate of neural firing related to intensity of stimulation
Neuron subjected to continual stimulation, it will fire and then again after the refractory period, up to 1000x per second
Orthodromicand antidromic conductions?
Orthodromic conductio is the traditional way for travleig of an AP from cell body to terminal buttons
Antidromic conduction is the axonal conduction generated at terminal end of an axon traveling along bck to the cell body
Nodes of ranvier on myelinated axons
They only structure Aps can go through to get pass the axon because of axona sodium channels are concentrated there
The conduction in myelinated axons is active or passive?
Why is myelin useful?
Passive
Myelin increases speed of axonal conduction
What is the conduction in myelinated axons due to thenodes of ranvier?
A saltatory conduction
In what depends the velocity of axonal conduction?
It depends on two properties of the axon:
It conducts faster in large diameter axons
And it is faster in lyelinated axons
Mammalian motor neurons characteristics
They are large and myelinated
Do neurons without axons conduct anything?
If they do how is it?
Many neurons in mamalian brains do either not have axons or they have very short ones. Many of these normally dont display Aps
Conduction is passive and decremental
Hodgkin huxley modle in perspective
Based on a study on squid motor neurons
There are hundred kinds of neurons i mammalian brains
Model should be applied with caution to cerebral neurons
Cerebral neurons move varied and complex than motor neurons
