Ch 4: Neural Conduction And Synaptic Transmission Flashcards
Membrane potential
Difference in electron charge between inside and outside cell
Resting membrane potential
Inside neuron is negative with respect to outside
Resting membrane about -70 mV
Membrane polarized (carries a charge)
Ionic basis of resting potential (even distribution)
Factors contributing to even distribution. Of ions
- random motion: particles move down their concent. Gradient
- electrostatic pressure: like repels like, opposites attract
Ionic basis of resting potential (uneven distribution)
Factors contributing to uneven distribution
- selective permeability to certain ions
- sodium-potassium pump
Ionis contributing to resting potential
Na+
Cl-
K+
Negative charged proteins within neuron
Neural membrane
Passive and active factors that influence the dist. Of Na, K, Cl ions across neural membrane
Neuron is prepared to respond to strongly and rapidly to stimulus
Postsynaptic potential (psp)
Neurotransmitters bind at postsynaptic receptor
Depolarization: making membrane less negative
Hyperpolarization: making membrane potential more negative
Generation of action potential
One Epsp not enough to cause neuron to fire
Threshold of activation near axon hillock to generate firing
Integration of Psp and Epsp result in a potential of -65 mV to generate AP
Integration
Adding and combining a number of individual signals into one overall signal
Spatial summation
Integration of events at different places
Temporal summation
Integration of events at different times
Sodium and potassium channels
Opening and closing of voltage activated Na and K channels during the 3 phases of action potential: rising, repolarization, Hyperpolarization
Action potentials
- Occur in axons
- Any simulation beyond there’s hold = same AP
- In neuron all AP are equal in size and shape
All or none law
Size and shape of AP is independent of intensity of stimulus that initated it
Refractory periods
Absolute: impossible to imitate another AP
Relative: harder to imitate another AP
Limit rate of firing and prevent backward movement of AP
Psp
Decremental
Fast
Passive (energy not used)
AP
Nondecremental
More slow
Passive and active (use Atp)
Axonal conduction of AP
Passive conduction along each mylin segment to next node ranvier
New AP generated at each node
Mylinated axon: instant, faster than nonmylinated
Structure of synapse
Axodendrite: most common. Synapse onto dendrite spines
Directed synapse: site of release and contact are close proximity
Non directed: site of release and contact are spereated by some distance
7 steps of NT action
- NT synthesized from enzymes
- NT stored in vesicles
- NT that leak are destroyed by Enzymes
- AP vesicles to fuse with presynaptic membrane and release NT into synapse
- released NT molecules bind with autorec.
- released NT bind to postsynaptic receptors
- released NT are deactivated by reuptake or enzymatic degradation
Synthesis of proteins
Small NT are synthesized in bouton and packaged in vesicles
Large NT synthesized in cell
Body by ribosomes and transported by Microtubules
Release of NT
Exocytosis: NT release
Arrival of AP at terminal opens voltage activated Ca channel
Entry of Ca causes vesicles to fuse with terminal membrane and release their contents
Release and diffusion of NT
Usually 2 or 3 NT released from each neuron
Ligand
Molecule that binds to another
A NT is a ligand of its receptor
Ionotropic receptors
Associated with ligand activated ion channels
NT binds and an associated ion channel opens/ closes
If Na+ channels opened for example EPSP occurs
If K+ channels open for example IPsP occurs
Metabolic receptors
Associated with signal
Effects slower, longer lasting, more diffuse, more varied,
- NT 1st messenger binds
- G protein subunit breaks away
- Ion channel open/ close or a 2nd message me
- 2nd messenger wide variety effects
Postsynaptic receptors
On terminal at tip of an axon
2 types
- Autoreceptor: sensitive to the NT released by terminal bouton acts as negative feedback
- Hetereorecpetor: responds to chemical other than the NT released by terminal bouton
Reuptake
Scoop up and recycle NT
Enzymatic degradation
A NT broken down by enzymes
Seretonin
Mood and temperature regulation, aggression, sleep cycles
Glutamate
Main excitatory NT, participates in relay sensory info and learning
GABA
Main inhibitory NT
Norepinephrine
Brain arousal and other functions like mood hunger and sleep
Anandamide
Pain reduction, increases in appetite
Acetylcholine
Muscle contraction (PNS) cortical arousal (CNS)
Dopamine
Motor function and reward
Amino acid NT
Found at fast acting directed synapses in CNS
Glutamate and GABA
Aspertate and glycine
Monoamines NT
Effects tend to be diffused
Atecholamines: synthesized from tyrosine (dopamine, norepinephrine, epinephrine)
Indolamines: synthesized from tryptophan (serotonin)
Unconventional NT
Soluble gases: exsist only briefly (nitric acid and carbon monoxide)
Retrograde transmission: backwards communication
Endadcannabinoids: anandamine is 1 of 2 known Endo.
Agonists
Increase or facilitate activity (nicotine)
Inc. synthesis of NT
Inc. # NT molecules by destroying degrading enzymes
Inc. release of NT molecules from terminal bouton
Antagonistic
Decrease or inhibit activity
Blocks synthesis of NT
Cause NT to leak from vesicles and be destroyed
Blocks the release of NT from terminal bouton
Activates autoreceptors and inhibit NT release
Drug is a receptor blocker. Binds to postsynaptic receptors and blocks effect of NT
