Lectur 3,4 Flashcards
What are the 2 primary functions of neurons?
1.) rapid transmission of information from specific sources to selected targets: done via action potentials
2.) The integration of information / electrical activity from many sources
Anatomical structure of neurons?
Basis structure →
- cell body
- dendrites
-Axon
-Axon terminal
Define dendrites?
Receive info from other neurons
Define cell body
Contain nucleus & most cell organelles
Define axon hillock?
Information is collected by dendrites is integrated generating an action potential
Define axon ?
Conducts action potentials away from the cell body
Define axon terminal
Synapses with target cell
Define neurotransmitters?
The release of chemicals substances
The neuronal membrane at ‘rest’?
Cell is at rest = not generating an impulse / AP
Resting neurone →cytosolic side of plasma membrane has a negative electrical charge
Steady difference in electrical charge across membrane is called resting membrane potential ( RMP)
Define solutes?
Dissolved materials that con move across cell membrane and epithelia
Electrolytes → charged species: Na t k+ .
Conc of potassium ions is higher inside the cell vs outside whereas sodium & chionde Ians are more concentrated..
What does the phospholipid bilayerdo?
Separates ICF from ECF: forms a barrier
Water soluble ions
Membranes are selectively permeable to water, small molecules and ions pass through “special “ proteins
Define channel protein?
Ion channels: proteins assemble to form a pore
Ion selectivity
Gating
Ion pumps → nat/ki atlases
What does a carrier protein?
Used for glucose transport
Molecule binds to carrier
Carrier changes shape & molecule passes through
What is passive transport mechanism?
Transport ↓ the concentration gradient, or facilitated diffusion ( via channel/ carrier protein )
Can carry material only in direction of equilibrium
Define active - transport mechanism?
Transport against conc gradient; requires energy
→ primary & secondary
→ can carry material in direction opposing eqm
Movement of ions across membrane?
Direction of movement →
1.) concentration of gradient
Net movement of ions from a , region of high to a region of low concentration (down a conc gradients )
2.) charge of ions or molecule ( electrical gradient)
“Opposite charges attract like charges repel “
Electrical potential (V) reflects diff in charges
3.) The membrane potential (mv )
Inside surface of cell membrane is always negative compared to outside
What is neuronal resting membrane potential (RMP)?
Membrane potential: voltage across the national membrane.at rest inside neuron surface is electrically negative vs outside
Equilibrium potential: potential at which tendency of an ion to move ↓ its conc gradient is exactly balanced by the membrane potential0
Result: net movement of ion ceases → when electrochemical forces are equal & opposite
The Nernst equation?
Con calculate the equilibrium potential for a given ion
What does generating an RMP depend on?
1.) differences in conc of sodium & potassium both inside & outside of cell
2.) differences in the permeability of the plasma/ cell membrane to these ions
What is the sodium-potassium pump ?
an ion pump that breaks down ATP in the presence of internal Na+
-Chermical energy relaesed drives the pump :exchanges internal Na+ for external K+ both pumped against their concentration gradient (ACTIVE TRANSPORT -needs energy)
-> ensures K+ is concentrated inside and Na+outside ->pump maintains both K+ and Na+ gradients-critical for brain function
Establishing the ionic-concentration gradients:role of sodium -potassium pump?
1.)Outside of the cell :High Na+ conc low K+conc
3Na+ and 1 ATP bind to the protein pump
2.)Hydrolysis of ATP phosphorylates the pump protein which then changes its shape .Inorganic phosphate (Pi) binds to the pump.
3.)shape change-releases Na+ outside the cell enabling K+ to bind to pump
4.)Release of Pi returns the pumpto its original shape releasing K+ to the cells interior and once again exposing yhe Na +binding sites-repeats cycle
Relative ion permabilties ?
at rest -membrane is highly permeable to K+(leak channels) also seady leak of Na+ into cell
-Neuronal membrane is permeably different ions helps explain RMP (-65mV)
RMP can be calculated-Goldmans equation
What is the K+ efflux ?
neuronal membrane is higly permeable to K+ becuase of the membrane leak K+ channels (major contributor to RMP)
k+ions move down their concentration gradient to the outside of the cell->leaves the inside of the neuron -ve charged
What experiment showed the existance of voltage-gated ion channels ?
Hodgkin and Huxley (1949)
experiment on Squid axons revealed the existence of voltage gated ion channels and their critical role in the gneration of AP
-during AP membrane is more permeable to Na+ than K+
After membrane potential gated ion channels?
gated in channels open/close under certain conditins
-chemically (ligand) gated ion channels e,g)NaChR,s
-Voltage gated ion channels
Activation can lead to depolarisation /hyperpolarisation
What are the 2 properties of Action potential ?
1.)Na+ current :inward,depolarising current
2.)K+ current :outward ,hyperpolarising current
APs are sudden transcient large chains in Vm
How are APs generated ?
By opening and closing of voltage gated Na+ and K+ channels
Voltage gated Na+ channels are oncentrated atthe axon hillock .Sufficient depolarisationcauses an AP
PASSESthrugh threshold
How are voltage gated channels controlled?
Na channels → activation m-gate
Inactivation h-gate
K+ channel → activation n-gate
(Slide 34 )
Course of AP?
1.) leaky K + channels create the resting potential
Gated channels are closed
2.) some voltage gated Nat channels open depolarising the cell to threshold
3.) additional voltage gated Nat channels activation gates open → A rapid spike depolarisation _ AP
4.) Na channels inactivation gates close, gated K t channels open replanting & even hyper polarising the cell
5.) all gated channels close. The cell returns to its resting potential. Nat inactivation gates reopen
What are the “ups” & “downs” of an AP?
If threshold is exceeded → AP → “all or nothing”
Nat channels open or inactivated a 2nd AP cannot he elicited → absolute refractory period ( ARP)
K+ channels open um is hyperpolarised so only stronger dep. Stimulus con elicit 2nd AP relative refractory period (rrp)
Myelin: Nodes of Ranvier
CNS: oligodendrocytes myelinate axons
PNS:Schwann cells myelinate axons
Nodes of Ranvier :Interruptions in myelin sheath
Factors affecting conduction
velocity ?
Velocity-varies
Axon Diameter:The larger the diameter the faster the propagation -important for invertebrates
Myelination: Provides insulation = important for vertebrates
Nodes of Ranvier :Saltatory conduction AP jump node to node -current faster &farther
Define synapse ?
Junction between a nerve ending (axon terminal )& target cell
-Presynaptic terminal
-Postsynaptic terminal
-Synaptic Cleft
Define Synaptic Transmission ?
Process by which nerve cells (neurons) pass information onto target cells
2
-Chemical transmission :chemical neurotransmitters diffuse across the synaptic cleft POSTSYNAPTIC
-Electrical transmission:pre and postsynaptic elements are electrically connected via junctions
Define structure of CNC chemical synapse ?
draw or explain
Chemical synaptic transmission ?
1: Action potential arrives sat axin terminal
2.)Na+ channels open depolarisation causes voltage gated Ca 2+ channels to open
3.)Ca 2+ enters the cell and triggers fusion of acetylcholine vesicles with preresynaptic membrane.
4.)Acetylcholine molecules diffuse across the synaptic cleft and bind to receptors on the postsynpatic membrane
5.) When receptors bind acetylcholine they open the cation channels and depolarise the postsynaptic membrane
6.)Spreading depolarisation fires an action potential in the postsynaptic membrane
7.)AChE breaks dwon ACh snd the components are taken back up the presynaptic cell.Acetylcholine and vesicels are recycled
Define Excitatory neurotransmiiters ?
eg.)glutamate ,acetylcholine
-Increase nerve activity
-cause depolariation
-initiate excitatory post-synaptic potentials (ESPS)
more likely for AP to be prod
Defie Inhibitory neurotransmitters ?
Decrease nerver activity
Cause hyperpolarisation
Initiate inhibitory post synaptic potentials (IPSP)
Define Summation ?
The balance of ESPS and ISPS coverging on to a neuron at any given moment -
SYNAPTIC INTEGRATION
Define Dendrites
axo dendritic synapses
Defien soma
Axo-somatic synapses
Other axons :
Axo axonal synapses
What is the Excitatory synapse ?
When the presynaptic activity increases the excitability of the postsynaptic neuron
How are ESPS graded ?
In intensity and outlast the APs that generated them in the first place .Thus they can be temporally and spatially summated.
Define Spatial Summation ?
Occurs when several excitatory postsynaptic potentials (ESPS) arrive at the axon hillock simultaneously .
Define Temporal Summation ?
means that postsynaptic potentials crerated at the same synapse in rapid succession can be summed
Explain GABergic syanpse ?
explain
