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difference in electrical charge between the inside and outside of a cell


neuron resting potential

Potential inside the resting neuron is about 70mV less than that outside the neuron
Neuron’s resting potential is -70mV, and is polarised


there is pressure for Na+ to enter the neuron

Electrostatic pressure from RMP, the -70mV inside attract the Na+ outside
Random motion of Na+ down conc gradient


generation and conduction of PSPs

When neurotransmitters bind to postsynaptic receptors they may:
Depolarisations AKA EPSPs: increase likelihood that neuron will fire
Hyperpolarisations AKA IPSPs: decrease likelihood that neuron will fire
Both are graded: amplitudes of EPSPs and IPSPs proportional to intensity of the signals that elicit them
Transmission of postsynaptic potentials is rapid and decremental (decrease in amplitude as they travel along neuron)


integration of PSPs and APs

Whether a neuron fires depends on the balance between the excitatory and inhibitory signals reaching its axon
APs generated at axon initial segment
EPSPs and IPSPs are conducted to axon initial segment, if the depolarisations and hyperpolarisations are sufficient to depolarise the membrane to a level of threshold of excitation (-65mV), an AP is generated
AP is a massive but momentary reversal of MP from -70 to +50mV
AP are not graded, rather all-or-none


spatial summation

how local EPSPs and IPSPs produced simultaneously affect each other


temporal summation

sum of the postsynaptic potentials produced in rapid succession at the same synapse to form a greater signal


ionic basis of APs

When the MP of the axon is depolarised to the threshold of excitation by EPSP, voltage activated Na+ channels in axon membrane open and Na+ rush in, driving MP from -70mV to 50mV
Influx of Na+ triggers opening of voltage activated K+ channels
K+ driven out first by high concentration gradient and then when AP is near peak, by positive internal charge
After about 1milisecond, Na+ channels close- marking the end of the rising phase and beginning the repolarisation by continued efflux of K+
Once repolarisation has been achieved, K+ channels close
Because they close too gradually, too many K+ leave and neuron is left hyper polarised for brief time
AP involves only ions close to membrane, so AP has little effect on most ions in and outside the neuron


absolute rp

1-2ms after initiation of an AP where it is impossible to elicit a second one


relative rp

possible to fire neuron again but only by applying higher-than-normal levels of stimulation


AP conduction

One AP is activated, travels passively to Na+ channels which opens them, then conducted passively to next Na+ channels, where another AP is triggered and repeated
Wave of excitation triggered by generation of an AP near the axon hillock always spreads passively back through cell body and dendrites


antidromic conduction

if electrical stimulation of sufficient intensity is applied to the terminal end of an axon, an AP will be generated and will travel along the axon back to cell body


orthodromic conduction

axonal conduction in natural direction


axonal conduction in myelinated neurons

In myelinated axons, ions can pass through axonal membrane only at nodes of Ranvier
When an AP is generated, signal is conducted passively (instantly and decremental) along first myelin segment to next node of Ranvier
Signal is diminished but still strong enough to open the voltage activated sodium channels at the node and generate another full blown AP
Then repeated along
Called saltatory conduction
Faster than in unmyelinated


the hodgkin-huxley model in perspective

Based on study of squid motor neurons- difficult to apply to mammalian brain
Used because they are very large
Motor neurons used rather than cerebral neurons
Cerebral neurons fire continually even when no input
Axons can actively conduct both graded signals and APs
APs of different classes of cerebral neurons vary greatly in duration, aptitude and frequency
Many do not display Ads
Dendrites of some cerebral neurons can actively conduct APs


axodendritic synapse

synapses of axon terminal buttons on dendrites


axosomatic synapse

synapses of axon terminal buttons on somas


dendrodendritic synapse

capable of bidirectional transmission


axoaxonic synapse

mediate presynaptic facilitation and inhibition


directed synapse

synapses at which the site of neurotransmitter release and site of neurotransmitter reception are in close proximity


non directed synapse

synapses at which site of release is at some distance from site of reception
Neurotransmitters released from varicosities and dispersed to surrounding target (string of beads synapses)


large neurotransmitters

are neuropeptides (short amino acid chains composed of between 3-36AA)


small neurotransmitters

are made in cytoplasm of terminal buttons, packaged in synaptic vessels by terminal button Golgi complex, stored next to the presynaptic membrane


neuropeptides are made in

made in cytoplasm of ribosomes, packaged in vesicles by cell body Golgi complex, transported by microtubules to terminal buttons (vesicles larger)



each neuron contains two neurotransmitters, usually one small-molecule neurotransmitter and one neuropeptide, or two small molecule neurotransmitters


release of neurotransmitter molecules

Vesicles with small molecule neurotransmitters congregate to areas with many voltage activated calcium channels
When AP happens, Ca2+ enter cell through these and prompts vesicles to fuse with presynaptic membrane and empty contents into synapse via exocytosis
Small molecule neurotransmitters are released in a pulse each time an AP triggers info of Ca2+, whereas neuropeptides are typically released gradually



associated with ligand-activated ion channels
Neurotransmitter binds, ion channel opens or closes immediately inducing an immediate PSP



associated with signal proteins and G proteins
More prevalent, and effect is slower, longer-lasting, more diffuse and more varied
Each receptor is attached to a serpentine signal protein that winds its way back and forth through the cell membrane seven times
Metabotropic receptor is attached to a portion of the signal protein outside the neuron, G protein is attached to a portion of the protein inside neuron
Neurotransmitter binds, subunit of G protein breaks, depending on particular G protein, subunit may move along inside membrane surface and bind to a nearby ion channel and induce a PSP or it may trigger the synthesis of a second messenger
Second messenger diffuses through cytoplasms and influences activities of neuron



metabotropic receptors that bind to their neurones own neurotransmitter molecules and are located on the presynaptic (rather than postsynaptic) membrane
Monitor the number of neurotransmitters in synapse, reduce release while levels are high and increase when levels are low


small molecule neurotrasmitter receptors

Small molecule neurotransmitters are released into direct synapses and activate either inotropic or metabotropic receptors that act directly on ion channels


neuropeptide receptors

Neuropeptides tend to be released diffusely and all bind to metabotropic receptors that act via 2nd messengers


gap junctions

Gap junctions AKA electrical synapses: narrow spaces between adjacent cells that are bridged by fine, tubular, cytoplasm-filled protein channels called connexins
Most gap junctions are between cells of like kind- synchronise the activities of like cells in a particular area


tripartite synapse

hypothesis that synaptic transmission depend on communication among the three cells: presynaptic neuron, postsynaptic neuron and astrocyte


conventional small neuortransmitters

amino acids, monoamines and acetylcholine


unconventional neurotransmitters

various small molecule neurotransmitters, mechanisms of action are unusual



large molecule neurotransmitters


amino acid neurotransmitters

Neurotransmitters in the vast majority of fast acting, directed synapses in the CNS
glutamate (excitatory) , aspartate, glycine and GABA (inhibitory, sometimes excitatory)



Small molecule neurotransmitters synthesised from a single AA
Slightly larger than AA neurotransmitters and effects more diffuse
In small groups of neurons in brain stem, with highly branched axons and varicosities
dopamine, epinephrine, norepinephrine (catecholamines, made from tyrosine) and serotonin (indolamine, made from tryptophan)
Catecholamines or indolamines based on structure



neurons that release norepinephrine



neurons that release epinephrine



Small molecule neurotransmitter
At euro-muscular junctions, synapses in ANS and several parts of CNS
Broken down in synapse by acetylcholinesterase
Neurons that release it are called cholinergic


unconventional neurotransmitters

Soluble-gas neurotransmitters (nitric oxide and carbon monoxide) diffuse through cell membrane into nearby cells, stimulate production of 2nd messenger and are deactivated by being converted into other molecules
Involved in retrograde transmission, transmit info from post to presynaptic neuron, to regulate activity of presynaptic neurons




similar to THC (psychoactive element in marijuana), one type is anandamine
Produced immediately before released
Synthesised from fatty compounds in cell membrane
Released from dendrites and cell body
Tend to have most effects on presynaptic neurons, inhibiting synaptic transmission



action depends on AA sequence
pituitary, hypothalamic, brain-gut, opiod and miscellaneous peptides


pituitary peptides

neuropeptides that were first identified as hormones released by the pituitary


hypothalamic peptides

first identified as hormones released by hypothalamus


brain-gut peptides

first discovered in gut


opioid peptides

similar in structure to active ingredients of opium


miscellaneous peptides

contains all neuropeptides that do not fit into above categories



facilitate neurotransmitters, ACh, nicotine



inhibit the effects of a neurotransmitter, caffeine, botox


nictonine receptors

PNS: NR at junctions between motor neurons and muscle fibres


muscarine receptors