NSC EXAM 2

synaptic transmission

info transfer at synapse, plays a role in all operations of nervous system

electrical synapse

speed of synaptic transmission, electrical current flowing from one neuron to the next (frog’s heart)

chemical synapse

chemical neurotransmitters transfer info from one neuron to another (crayfish)

gap junctions

occur between cells in nearly every part of the body and interconnect many non-neuronal cells, electrical synapses occur at these specialized sites

connexins

membranes of cells separated by 3nm, spanned by proteins

gap junction channels

connexons form together, allows ions to pass directly from one cytoplasm another cytoplasm

asymmetrical

Gray’s type I, excitatory

symmestrical

Gray’s type II, inhibitory

postsynaptic neuron

two neurons are electrically coupled and causes small ionic current to flow across gap junction channel into other neuron, second neuron can generate action potential because it induces PSP in first neuron

synaptic cleft

pre/postsynaptic separation, filled with fibrous extracellular protein, glue

presynaptic element

(presynaptic synapse) usually is an axon terminal, contains dozens of small membrane closed spheres (synaptic vesicles)

secretory granules

axon terminals that contain larger vesicles, contain soluble proteins that appear dark in electron microscope (dense-core vesicles)

membrane differentiations

dense accumulations of protein adjacent to and within membrane on either side of synaptic cleft

active zones

proteins jutting into cytoplasm of terminal along intracellular face of membrane that look like tiny pyramids

postsynaptic density

protein thickly accumulated in and just under the postsynaptic membrane, contains NT receptors

axodentric

postsynaptic membrane on a dendrite

axosomatic

post synaptic membrane on a cell body

dendrodentritic

dendrites form synapses with each other

neuromuscular junction

chemical synapses between axons of motor neurons of spinal cord and skeletal muscles, largest active zones/largest synapses

motor-end-plate

seiers of shallow folds, postsynaptic membrane

3 major categories of NTs

1. amino acids

2. amines

3. peptides

amino acids/amines

stored and released from synaptic vesicles with nitrogen

peptides

stored and released from secretory granules

most common amino acids

glutamate (Glu), gamma-aminobutyric (GABA), glycine (Gly), acetylcholine (ACh), mediates for transmission at all neuromuscular junctions

glutamate and glycine

building blocks of proteins and abundant in neurons

GABA and amines

made by neurons that release them

transporters

special proteins that are embedded in vesicle membranes, job is to concentrate the neurotransmitters inside the membrane

what causes voltage-gated channels to open

depolarization of terminal membrane

exocytosis

vesicles release contents, membrane of synaptic vesicle fuses to presynaptic membrane at the active zone, allowing contents to spill out

endocytosis

recycled vesicle is refilled with neurotransmitters

transmitter-gated ion channels

membrane spanning proteins consisting of 4/5 subunits that come together to form a pore between, induces con formative changes

excitatory postsynaptic potential (EPSP)

transient postsynaptic membrane depolarization caused by presence of presynaptic release

inhibitory postsynaptic potential (IPSP)

transient hyperpolarization of the postsynaptic membrane potential caused by presynaptic release of neurotransmitter

G-protein coupled receptors

slower, longer lasting, more diverse synaptic actions

1. NT molecules bind to receptor proteins embedded in postsynaptic membrane

2. receptors activate small proteins (G-proteins) free to move along intracellular face

3. activated G-proteins activate “effector” proteins

second messengers

enzymes that synthesize, diffuse away in cytosol

metabotropic receptor

G-protein coupled receptors can trigger widespread metabolic effects

autoreceptors

presynaptic receptors that are released by presynaptic terminal, typically are G-protein receptors that stimulate second messenger formation

neuropharmacology

effect of drugs on nervous system tissue

inhibitors

inhibit normal function of specific proteins involved in synaptic transmission

receptor antagonists

bind to receptors and block normal action of transmitters

receptor agonists

drugs bind to receptors and mimic action of naturally occurring neurotransmitters

nicotonic ACh receptors

ACh-gated ion channels in muscles

synaptic integration

process which multiple synaptic potentials combine with one synaptic neuron

quantized

post synaptic EPSPs at a given synapse, multiples of quantum

miniature postsynaptic potential

tiny post synaptic responses to released neurotransmitters measured electrophysiologically

quantal analysis

method of comparing amplitudes of miniature and evoked PSPs, used to determine how many vesicles release neurotransmitters during normal transmission

integration of EPSPs

sophisticated neuron computations require EPSPs add together to produce depolarization

EPSP summation

simplest form of synaptic integration in CNS

spatial summation

adding together of EPSPs generated simultaneously at many different synapses

temporal summation

adding together of EPSPs generated at same synapse in rapid succession

length constant

distance where depolarization is about 37% of the origin, how far it can spread

internal resistance

resistance current flowing longitudinally down dendrite (ri)

membrane resistance

resistance to current from flowing across the membrane (rm)

inhibitory synapse

action of synapse taking membrane potential awayfrom action potential threshold

inhibition shunting

synapse inhibits current flow inward movement of (-) charged Cl ions which equals outward positive current flow

modulation

synaptic activation does not directly evoke EPSPs and IPSPs but modifying EPSPs generated by other synapses

adenlylcyclase

catalyzes the chemical rxn that converts ATP into cAMP free to diffuse in cell

protein kinase

catalyzes phosphorylation (transfer of phosphate groups from ATP to specific sites on cells)

conductance, resistance correlation and consequence

decrease in K+ conductance = increase in dendritic membrane resistance = increase in length constant, consequence: distant/weak excitatory synapses more effective depolarization, more excitable cell

cholenergic

cells that produce and release ACh

noradrenergic

neurons that use amine NT NE

glutamatergic

synapses that use glutamate

GABAmergic

synapses that use GABA

peptidergic

synapses that use peptides

criteria that must be met for a molecule to be considered a NT

1. molecule must be synthesized and stored in presynaptic neuron

2. molecule must be released by presynaptic axon terminals upon stimulation

3. molecule when experimentally applied must produce response in postsynaptic cell that mimics response produced by release of NT from presynaptic neuron

immunochemistry

used to anatomically localize particular molecules to particular cells, chemically purified and injected into skin and stimulates immune response, distinguished by different colors of antibodies

in situ hybridization

method for localizing specific mRNA transcripts, confirming that a cell synthesizes a particular protein or peptide

autoradiography

viewing distribution of radio activity, (-) images = white dots

in vitro

alive

microntophoresis

assess postsynaptic actions of transmitter candidate very small glass pipetter ejects candidate with pulses of high pressures

receptor subtype

each different receptor a NT binds to

nicotinic ACh receptor

ion channel, agonist in skeletal muscle

receptor subtypes

each different receptor a NT binds to

muscarinic ACh receptor

agonist in cholinergic region of heart

3 subtypes of receptors

1. AMPA

2. NMDA

3. Kainate

ligand

chemical compound that binds to a specific site on a receptor

Dale’s principle

idea that a neuron has only one NT, many peptides violate this

co-transmitters

when 2 or more transmitters are released from one nerve terminal

acetylcholine (ACh)

NT at neuromuscular junction and synthesized by all motor neurons in spinal cord and brain stem, requires choline acetyltransferase (ChAT) to synthesize

transporter

NT is concentrated in synaptic vesicles by actions of vesicular transporter

ChAT

transfers an acetyl group from acetyl CoA to choline

acetylcholinesterase (AChE)

ACh degradative enzyme, secreted into synaptic cleft, one of fastest catalytic rates among all known enzymes

rate-limiting step in ACh synthesis

availability of choline limits how much ACh can be synthesized

tyrosine

precursor for 3 different amine NT that contain catechol

catecholamines

found in regions involved with movement/mood/attention/visceral function, dopamine (DA)/norepinephrine (NE)/adrenaline, all contain tyrosine hydroxylase (TH) rate limiting

end-production inhibition

catecholamine released at high rate, elevation of [Ca2+], triggers increase in activity of TH therefore transmitter keeps up with demand

dopa decarboxylase

dopa converted to NT DA by this enzymes, in parkinson’s these die

dopamine B-hydroxylase (DBH)

converts DA to NE

phentotamine N-methyltransferase (PNMT)

converts NE to norepinephrine, in cytosol of adrenergic axon terminalsm

monoamine oxidase (MAO)

enzyme found on outer membrane of mitochondria, enzymatically destroy

serotonin

amine NT, 5-HT, derived from amino acid tryptophan, 2 step synthesis, tryptophan → 5-HTP (by tryptophan hydroxlase) → 5-HT (by deoxycarboxylase)

glutamate transporters

concentrate glutamate until about 50mU in synaptic vesicles

adenosine triphosphate (ATP)

key molecule in metabolism, NT, can be co-transmitter

endocannabinoids

small lipid molecules, released from postsynaptic neurons, act on presynaptic terminals

1. not packaged in vesicles, manufactured rapidly and on demand

2. are small membrane permeable, can diffuse rapidly across membrane of their cell origin to contact neighboring cells

3. bind selectively to CB1 type of cannabinoid receptor, located on a certain presynaptic terminal

retrograde messenger

“post to pre” travel, feedback system to regulate synaptic transmission

CB1 receptors

G-protein-coupled receptors, main effect to reduce opening of presynaptic Ca channels, inhibited calcium channels = impaired ability to release NT

nitric oxide (NO)

gaseous molecule proposed for intracellular communication, “gasotransmitter” (CO, H2S), released from endothelial cells and causes smooth muscle blood vessel to relax

ACT I

presynaptic and culminates in transient elevation of NT concentration in synaptic cleft

ACT II

generation of electrical/biochemical signals in postsynaptic cleft