Biological Psychology Kalat 12E Week 3 Chapter 2

When the membrane is at rest:

Sodium channels are closed. Potassium channels are partially closed allowing the slow passage of sodium

Chemicals that can pass through the membrane:

Sodium, potassium, calcium, and chloride

Glucose

simple sugar that is the primary source of nutrition for neurons

Ribosomes

sites at which the cell synthesizes new protein molecules

sodium potassium pump

a protein complex that continually pumps three sodium ions out of the cells while drawing two potassium ions into the cell.

EPSPs/ depolarisation

(excitatory post-synaptic potentials) takes neuron towards the threshold, occur when the excitatory neurotransmitters open sodium channels on the postsynaptic membrane, these sodium channels allow positively charged sodium ions to enter the cell by the same processes of diffusion and electrostatic pressure that occur during an action potential, this influx of sodium ions causes depolarization of the membrane making the inside of the cell more positively charged, this influx of positively charged sodium ions in an epsp increases the likelihood that the cell will fire an action potential

auto receptors

-auto receptors are a type of receptor that can be located on any part of the cell, unlike the receptors talked about so far these do not open ion channels or change the membrane potential, instead auto receptors are a type of metabotropic receptor that activates three proteins and second messenger systems, their role in the neuron appears to be that they detect the amount of neurotransmitter floating in the extracellular fluid and they regulate the amount of neurotransmitter that is produced and released (Kalat's auto email example) if too much neurotransmitter has been released auto receptors will inhibit further production, alternately if there's not enough neurotransmitter being released into the synapse auto receptors will detect this and stimulate further release of neurotransmitters

fast synaptic transmission- different image

-different image- in this image we have the presynaptic membrane or terminal button at the top of the screen and the postsynaptic membrane or dendrites of the receiving cell at the bottom of the screen, between these we have the synapse or extracellular space, you can see sodium ions that exist in high concentration floating in the extra cellular space, -in this image the sodium channels on the postsynaptic membrane in purple at the bottom of the screen are closed, and so ions cannot enter through these sodium channels

temporal/ summation combination example

-example shows a combination of temporal and spatial summation, as with the previous example the top left synapse is activated in blue, normally this activation alone wouldn't be enough for the excitatory input to reach the axon hillock however because there is a second synapse in the bottom left-hand corner that's also activated at the same time these additional excitatory inputs are strong enough for the threshold of activation to be reached and for the cell to fire

G Proteins- basic

-g proteins are coupled with an energy storing molecule called guanosine triphosphate or GTP, the G proteins which are located on the membrane near the metabotropic receptors activate enzymes, and these enzymes stimulate the production of a second messenger chemical, the second messenger chemical travels into the cytoplasm of the cell and may serve a couple of different functions, for example they may open or close certain ion channels, they may alter the production of proteins within the cell or even activate chromosomes -slow synaptic transmission (binding to metabotropic receptors) may involve a number of different steps i.in the most simple form of slow synaptic transmission which you can see here the neurotransmitter binds to the receptor ii.as we move across to the middle box the binding of the neurotransmitter to the receptor activates the g-protein on the membrane near the metabotropic receptor iii.third step on the right the g-protein opens the ion channel-g proteins are coupled with an energy storing molecule called guanosine triphosphate or GTP, the G proteins which are located on the membrane near the metabotropic receptors activate enzymes, and these enzymes stimulate the production of a second messenger chemical, the second messenger chemical travels into the cytoplasm of the cell and may serve a couple of different functions, for example they may open or close certain ion channels, they may alter the production of proteins within the cell or even activate chromosomes -slow synaptic transmission (binding to metabotropic receptors) may involve a number of different steps i.in the most simple form of slow synaptic transmission which you can see here the neurotransmitter binds to the receptor ii.as we move across to the middle box the binding of the neurotransmitter to the receptor activates the g-protein on the membrane near the metabotropic receptor iii.third step on the right the g-protein opens the ion channel

axoaxonic/ dendrodendritic synapses

-the synapses we've covered so far are the junction between a terminal button of one cell and the dendrite of another cell, however synapses or connections between neighboring neurons can also occur between two axons, we call this axoaxonic, these axoaxonic synapses appear to modulate neurotransmitter release, dendrodendritic synapses are a connection between two dendrites, these neurons don't have long axons like normal cells and it's believed that these are more related to organizing groups of neurons rather than synaptic connection and transmission

Step 1- synthesis (production) of neurotransmitter

-there are two different types of neurotransmitters and these are synthesized in different ways i.peptide neurotransmitters (Kalat: chains of amino acids): synthesized in the cell body or soma, these peptide neurotransmitters are more complex and require protein synthesis using messenger RNA, covered last topic??, these peptide neurotransmitters are packaged in the Golgi apparatus and then transported to the terminal buttons where they're stored until they need to be released ii.small molecule neurotransmitters: on the other hand are synthesized in the terminal button, the precursor molecules and enzymes that are used to synthesize small molecule neurotransmitters are created in the cell body but transported via axoplasmic transport to the terminal button, there they can be synthesized and stored until they need to be released Summary: 1.Synthesis of neurotransmitters •Peptide neurotransmitters •synthesised in cell soma •Require protein synthesis using mRNA •Packaged in the Golgi apparatus •Small molecule neurotransmitters •Precursor molecules and enzymes transported to terminal button •These are synthesised into neurotransmitters in terminal button Summary: >recap the steps we've covered so far -left-hand side of the image in step 1 neurotransmitters were synthesized either in the cell body or in the terminal button -in step 2 neurotransmitters or their precursors were carried down the axon via axoplasmic transport -in step three the action potential travels down the axon depolarizing the membrane -right-hand side of the image for step four, action potential causes calcium to enter the terminal button evoking the release of neurotransmitters picture- pore diffusion

temporal/ spatial summation of epsps and ipsps (cancelling out)

-this example almost identical to the previous diagram with the two synapses on the left-hand side being activated and producing excitatory postsynaptic potentials however there is a green synapse activated on the right and this green synapse is producing inhibitory signals indicated by the minus signs inside the cell, these inhibitory signals cancel out some of the excitatory inputs produced by the blue synapses, because of this the membrane potential is not positive enough to reach the threshold of excitation and the cell cannot fire

spatial/ temporal summation of signals

-when receptors on dendrites receive incoming signals from neighboring neurons the depolarization from excitatory inputs needs to spread all the way across to the axon hillock in order for the cell to reach the threshold of excitation and fire an action potential -whether these excitatory and inhibitory signals make it all the way across to the axon hillock depends on "spatial and temporal summation of signals" -spatial summation refers to the location of activation at dendrites, that is how far away are the dendrites from the axon hillock and can these signals on the dendrites travel all the way across to the hillock -temporal summation refers to the rate of activation at dendrites, talked about the rate of firing to create strong versus weak signals, a weak signal produces a slow rate of firing and so the signals are less likely to reach the axon hillock, a strong signal on the other hand has a rapid rate of firing, this increases the likelihood that the excitatory signals will travel to the axon hillock and activate an action potential --example we have excitatory inputs indicated by the little plus signs being pumped into the cell by the single active synapse which you can see in blue on the top left, because this activation of the dendrite is a long way away from the axon hillock these positive excitatory inputs aren't strong enough to reach the axon hillock and so the cell doesn't fire

Step 2 - transport (summary)

2.Transport •Neuropeptides use fast axoplasmic transport •Stored in dense core vesicles •Small molecule neurotransmitters use fast transport •Enzymes needed for catalysing synthesis use slow transport •Transport molecules and proteins help fill vesicles at terminal •Stored in clear core vesicles

Step 3-4 Action Potential Travelling Down Axon, Release of Action Potential

3) the third step in synaptic transmission is the action potential traveling down the axon 4) once the action potential reaches the terminal button the action potential evokes the release of neurotransmitters, remember that the action potential involves depolarization of the membrane along the axon, that is the influx of positively charged sodium ions makes the inside of the cell more positively charged, once the action potential reaches the terminal button these calcium channels work in a similar way to sodium channels, calcium is highly concentrated outside of the cell and so when the membrane is depolarized by the action potential there's an influx of calcium into the cell propelled by diffusion and electrostatic pressure, as we saw with postsynaptic potentials calcium can change the biological processes within cells, in the terminal button calcium binds with protein molecules that join neurotransmitter vesicles with the presynaptic membrane or the terminal button, we call this joining of the vesicles into the membrane docking, this docking causes protein molecules to move apart creating a fusion pore in the membrane, basically a hole that opens up, molecules of the neurotransmitter then exit the terminal button into the synaptic cleft via the process of diffusion

Steps 3-4 Summary (action potential travels down, neurotransmitter release)

3.Action potential travels down axon 4.Neurotransmitter release •Action potential depolarisation terminal button •Opens calcium ion channels •Calcium binds with protein causing vesicles to dock to pre-synaptic membrane (terminal button) •Fusion pore in membrane opens •Neurotransmitter diffuses into synaptic cleft

Step 5 Neurotransmitter attaches to receptor

5) neurotransmitters in the synapse bind to or attach to receptors, these receptors are made of protein molecules on the postsynaptic membrane, the binding of neurotransmitters to receptors works a bit like a key and a lock, the receptors are different shapes and sizes and are intended for specific neurotransmitters to fit to them, just like certain keys are designed to fit certain locks, similar to a key and a lock if there is already a key in the lock another key cannot fit in there, the same goes with neurotransmitters, if a neurotransmitter is already bound to a receptor site no other neurotransmitters can bind at that site, neurotransmitters activate the postsynaptic cell by attaching to the receptor, just like a key opens a lock the binding to the receptor unlocks or opens a particular ion channel in the postsynaptic dendrite or membrane, the opening of the ion channel then either causes an excitatory postsynaptic potential or inhibitory postsynaptic potential, depending on whether a sodium, potassium, chloride or calcium channel was opened by the receptor

Step 5 neurotransmitter attaches to receptor

5) neurotransmitters in the synapse bind to or attach to receptors, these receptors are made of protein molecules on the postsynaptic membrane, the binding of neurotransmitters to receptors works a bit like a key and a lock, the receptors are different shapes and sizes and are intended for specific neurotransmitters to fit to them, just like certain keys are designed to fit certain locks, similar to a key and a lock if there is already a key in the lock another key cannot fit in there, the same goes with neurotransmitters, if a neurotransmitter is already bound to a receptor site no other neurotransmitters can bind at that site, neurotransmitters activate the postsynaptic cell by attaching to the receptor, just like a key opens a lock the binding to the receptor unlocks or opens a particular ion channel in the postsynaptic dendrite or membrane, the opening of the ion channel then either causes an excitatory postsynaptic potential or inhibitory postsynaptic potential, depending on whether a sodium, potassium, chloride or calcium channel was opened by the receptor

5. Binding to receptors- summary

5.Binding to receptors •Neurotransmitters bind to receptors on post-synaptic membrane •Keys and locks •Opens ion channels in dendrite •Ion channel opening causes EPSP and IPSP

Step 5 Summary

5.Binding to receptors •Neurotransmitters bind to receptors on post-synaptic membrane •Keys and locks •Opens ion channels in dendrite •Ion channel opening causes EPSP and IPSP

Steps 6,7,8 summary

6.Separation of neurotransmitter molecules from receptor 7.Reuptake of unused neurotransmitter into pre-synaptic membrane OR decomposition in synaptic cleft 8.Vesicles without neurotransmitter transported back to cell body

reuptake

>reuptake happens when the presynaptic membrane or terminal button that released a neurotransmitter in the first place sucks the remaining neurotransmitter back into the presynaptic cell, this is done by special transporter molecules that work a little bit like the sodium potassium pump, bringing the neurotransmitter back into the cell where it can be recycled

iotropic synapses - kalat

At ionotropic synapses, a neurotransmitter attaches to a receptor that opens the gates to allow a particular ion, such as sodium, to cross the membrane. Ionotropic effects are fast and brief. Most excitatory ionotropic synapses use glutamate, and most inhibitory ionotropic synapses use GABA.

metabotropic synapses

At metabotropic synapses, a neurotransmitter activates a second messenger inside the postsynaptic cell, leading to slower but longer-lasting changes.

neurons contain the following structures:

Membrane, Nucleus, Mitochondria, Ribosomes, Endoplasmic reticulum

All neurons have the following major components:

Dendrites, Soma/ cell body, Axon, Presynaptic terminals

What is brought to the brain via active transport?

Glucose, hormones, amino acids, and vitamins

graded potential - kalat

Kalat: Unlike action potentials, which are always depolarizations, graded potentials may be either depolarizations (excitatory) or hyperpolarizations (inhibitory) -A graded depolarization is known as an excitatory postsynaptic potential (EPSP). It results from a flow of sodium ions into the neuron. If an EPSP does not cause the cell to reach its threshold, the depolarization decays quickly.

neurotransmitter release kalat (relevant?)

Kalat: Whereas other neurotransmitters are released at the axon terminal, the neuropeptides are released mainly by dendrites, and also by the cell body and by the sides of the axon. A single action potential can release a neurotransmitter, but neuropeptide release requires repeated stimulation. However, after a few dendrites release a neuropeptide, the released chemical primes other nearby dendrites, including those on other cells, to release the same neuropeptide also.

Electrical Gradient

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

electrical gradient

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

Polarization

a difference in the electrical charge of two locations

fusion pore

a hole through both membranes that enables them to fuse together, opening through which NT is released, Diagram- in blue at the bottom of the screen we have clusters of proteins in the presynaptic membrane, when the action potential reaches the terminal button and calcium channels open the entry of calcium opens the fusion pore, as we move across to the right of the screen you can see that the fusion pore starts to widen and neurotransmitters begin to diffuse into the synaptic cleft

IPSP (inhibitory postsynaptic potential)

a kind of synaptic potential that makes a postsynaptic neuron less likely to generate an action potential, Inhibitory postsynaptic potentials stop the cell from firing by cancelling out any excitatory inputs, in picture see a chloride channel is opened, negatively charged chloride ions move into the cell making the cell more negatively charged, this hyper-polarization causes an inhibitory postsynaptic potential that decreases the likelihood that the cell will fire, in picture d a calcium channel is opened, the influx of positively charged calcium ions activates enzymes, these enzymes then have carry on effects by activating a second messenger system, the second messenger system makes changes within the cell that influence how the cell will fire in the future summary: •Inhibitory neurotransmitters •Open chloride channels (Cl-), negative ions enter •Open potassium channels (K+), positive ions leave cell •hyperpolarizes the membrane •¯ the likelihood that a cell will fire

Threshold of Excitement

a levels above which any stimulation produces a massive depolarization

G Proteins- complex

a more complex version of slow synaptic transmission involves the second messenger system i. as with the previous example the neurotransmitter binds to a metabotropic receptor ii. this binding activates a g-protein which you can see in the second square iii. in the middle square you can see that the g-protein activates an enzyme that causes the production of a chemical known as the second messenger, for example the enzyme adenylate cyclase converts ATP our energy producing molecule into a second messenger called cyclic AMP or CAMP, this second messenger cyclic AMP then opens the ion channel

ionotropic synapses

a neurotransmitter attaches to a receptor that opens the gates to allow a particular ion, such as sodium, to cross the membrane. Ionotropic effects are fast and brief. Most excitatory ionotropic synapses use glutamate, and most inhibitory ionotropic synapses use GABA. Kalat: Note the contrast- an ionotropic synapse has effects localized to one point on the membrane, whereas a metabotropic synapse, by way of its second messenger, influences activity in much or all of the cell and over a longer time.

Action Potential

a rapid depolarization of the neuron, action potential summary: •Dendrites receive input from neighbouring synapses •Graded potentials >Excitatory (depolarisation) >Inhibitory (hyper polarisation) >Integration of excitatory and inhibitory signals at axon hillock •Must reach the threshold of approximately -20 mV •If threshold of activation is reached = action potential

action potentail

a rapid depolarization of the neuron.

Nucleus

a structure that contains the chromosomes

Membrane

a structure that separates the inside of the cell from the outside environment

post synaptic potential

a voltage change, movement of ions at a receptor site on a postsynaptic cell membrane, summary: •Neurotransmitters from neighbouring neurons attach to receptors on postsynaptic membrane (dendrite) •Opens ion channels •Movement of ions into and out of the cell depolarises (excitatory) or hyperpolarises (inhibitory) the cell •These are called postsynaptic potentials

Dendrites

branching fibers with a surface lined with synaptic receptors responsible for bringing information into the neruon

deactivation or breaking down of neurotransmitter after it has activated postsynaptic cell

broken down in the synaptic cleft by enzymes, the enzyme breaks down the neurotransmitter into smaller molecules so that the neurotransmitter can no longer activate nearby neurons, waste products are then cleaned up and recycled by glia, finally vesicles in the terminal that don't contain neurotransmitter as well as some other waste product are transported back to the cell body via retrograde and axoplasmic transfer

Oligdendrocytes & Schwann cells

build the myelin sheath that surrounds the axon of some neurons

Neurotransmitters

chemical messengers (that transmit information from one neuron to another) that cross the synaptic gaps between neurons, neurotransmitters from neighboring neurons attach to receptors on the postsynaptic membrane or the dendrite, the neurotransmitter itself doesn't enter the postsynaptic cell, instead the neurotransmitter unlocks or opens an ion channel on the postsynaptic membrane or dendrite, this opening of ion channels in the postsynaptic membrane lets either positive or negatively charged ions move in and out of the cell

Thiamine

chemical that is necessary for the use of glucose

Cell body/ Soma

contains the nucleus, mitochondria, ribosomes, and other structures found in other cells

Depolarization

decreasing the polarization towards zero.

polarization

difference in the electrical charge of two locations

excitatory graded potential

excitatory graded potentials depolarize the cell and make it more positively charged -example we again have four little positive excitatory signals this time though the synapse that's activating these is in blue on the right right next door to the axon hillock because this synapse is spatially close to the axon hillock the excitatory inputs are able to increase the membrane potential at the axon hillock and the cell will fire, this diagram shows temporal summation

Dedndritic Spines

further branch out and increase the surface area of the dendrite

radial glia

guide the migration of neurons and the growth of their axons and dendrites during embryonic development

Motor Neuron

has its soma in the spinal cord and receives excitation from other neurons and conducts impulses along it axon to a muscle

Astrocytes

helps synchronize the activity of the axon by wrapping around the presynaptic terminal and taking up chemicals released by the axon

activation of postsynaptic receptors- slow synaptic transmission

i.slow synaptic transmission on the other hand occurs when a neurotransmitter opens a metabotropic receptor, the name metabotropic comes from the fact that these receptors require the cell to use metabolic energy, neurotransmitters do not directly open channels when they bind to metabotropic receptors, instead of opening ion channels directly they activate a g-protein located on the membrane which then activates an enzyme, this enzyme then creates a second messenger chemical and this second messenger then opens the ion channel or it causes physiological changes within the cell, because binding to metabotropic receptors requires extra steps in opening the ion channel synaptic transmission is much slower

slow synaptic transmission

i.slow synaptic transmission on the other hand occurs when a neurotransmitter opens a metabotropic receptor, the name metabotropic comes from the fact that these receptors require the cell to use metabolic energy, neurotransmitters do not directly open channels when they bind to metabotropic receptors, instead of opening ion channels directly they activate a g-protein located on the membrane which then activates an enzyme, this enzyme then creates a second messenger chemical and this second messenger then opens the ion channel or it causes physiological changes within the cell, because binding to metabotropic receptors requires extra steps in opening the ion channel synaptic transmission is much slower

Millivolts

in order for the neuron to fire and reach the threshold of excitation the membrane potential at the axon hillock must depolarize (become more positive) by approximately 20 millivolts so it should reach around minus 50 - minus 55 millivolts for an action potential to be triggered

fast synaptic transmission- different image

in this image neurotransmitters in dark blue have been released into the synapse, these will diffuse across to the postsynaptic membrane, here the neurotransmitter in blue binds to the receptor site at the bottom and opens the ion channel in the chemically gated neurotransmitter dependent ionotropic receptor, when the neurotransmitter binds to the receptor site and the ion channel is opened the sodium ions in the pale blue will enter the postsynaptic cell depolarizing the membrane and creating an excitatory postsynaptic potential

Hyperpoalrization

increasing the polarization or the difference between the electrical charge of two places.

potassium (ipsp)

inhibitory postsynaptic potentials also occur if potassium channels are opened, remember that potassium is highly concentrated inside the cell and is positively charged, so if inhibitory neurotransmitters open a potassium channel positively charged potassium leaves the cell making the cell more negative inside, that is it hyperpolarizes the membrane by making it more negative, and because the cell is more negative it decreases the likelihood that the cell will fire by cancelling out any excitatory postsynaptic potentials

Myelin Sheath

insulating material covering the neurons

nodes of Ranvier

interruptions in the Myelin Sheath

second messenger system- diagram 2 (complex)

moving over to the image on the right we have the more complex involvement of the second messenger system i.neurotransmitter binds with the metabotropic receptor ii.in step 2 the receptor activates the g-protein iii.step 3 the subunit of the g-protein breaks away unlike the example on the left where the G proteins open to the ion channel in this example the G protein activates an enzyme that produces the second messenger chemical iv.step 4 the second messenger opens the ion channel v.step 5 ions enter and produce a postsynaptic potential vi.step 6 the second messenger can also travel into the nucleus and to other parts of the cell to modify chromosomes and other proteins or affect cellular processes, this might include altering chromosomes or protein production the process can

Blood Brain barrier

mechanism that surrounds the brain and blocks most chemicals from entering.

Graded Potentials

membrane potentials that vary in magnitude and do not follow the all-or-none law?? -so how and why does the neuron fire? the dendrite at the beginning of the neuron receives incoming input from neighboring synapses and there's usually multiple inputs coming in at the one time from multiple neurons these incoming signals are called graded potentials, graded potentials can either be excitatory or inhibitory -usually multiple excitatory and inhibitory inputs coming in at once so whether the cell fires or not depends on the integration or balance between these positive and negative signals (equation eg. half/ half or one dominates etc)

Endoplasmic Reticulum

network of thin tubes that transport newly synthesized proteins to their location

Step 6- when the neurotransmitter has activated the postsynaptic cell

neurotransmitters only stay bound to receptors on the postsynaptic membrane for a brief moment, that is only a matter of milliseconds, once they have activated the postsynaptic cell and caused a postsynaptic potential these neurotransmitters undock from the receptor and float back into the synaptic cleft, after they've done their job and activated the postsynaptic cells neurotransmitters either get recycled in a process called reuptake or they are deactivated and broken down in the synaptic cleft

Sodium Potassium Pump

protein complex that continually pumps three sodium ions out of the cells while drawing two potassium ions into the cell.

Presynaptic Terminals

refer to the end points of an axon where the release of chemicals to communicate with other neurons occurs

Afferent Axon

refers to bringing information into a structure

Efferent Axon

refers to carrying information away from a structure.

Hyperpolarization

refers to increasing the polarization or the difference between the electrical charge of two places

synaptic transmission, what happens when action potential reaches end of the axon at terminal button

relaying of information across the synapse by means of chemical neurotransmitters sequence of events at chemical synapse: 1)left top hand side of the image you can see that the neurotransmitters are synthesized and packaged into vesicles within the cell body 2)these neurotransmitters are transported down the axon via axoplasmic transport 3)action potential travels down the axon 4)move over to the right side of image, action potential causes calcium to enter the terminal button evoking the release of neurotransmitters into the synapse 5)down the bottom the neurotransmitter crosses the synaptic cleft and attaches to receptors on neighboring dendrites either exciting or inhibiting the postsynaptic neuron 6)neurotransmitter molecules separate from the receptor after they've done their job 7)reuptake occurs whereby neurotransmitters are recycled by the terminal button in the presynaptic neuron 8)finally in step eight on the bottom-left, vesicles without neurotransmitters in the terminal button are transported back to the cell body via retrograde axoplasmic transport for recycling

Microglia

remove waste material and other microorganisms that could prove harmful to the neuron

slow synaptic transmission (more)

slow synaptic transmission is also sometimes referred to as the second messenger system, slow synaptic transmission occurs when the neurotransmitters bind to metabotropic receptors on the postsynaptic membrane i.you can see this in the image in step 1, however binding to the receptor does not directly open the ion channel ii.instead in step 2 you can see there is a g-protein in blue that is activated when the neurotransmitter binds to the metabotropic receptor iii.in step 3 the g-protein activates an enzyme that stimulates the production of a second messenger chemical, note here that the neurotransmitter is the first messenger iv.the second messenger chemical then travels into the cyber cytoplasm of the cell and attaches to nearby ion channels opening them, you can see this in step 4 v.ions enter the cell in step 5

Sensory Neuron

specialized at one end to be highly sensitive to a particular type of stimulation (touch, light, sound, etc.)

Resting Potential

state of the neuron prior to the sending of a nerve impulse a dendrite with lots of synapses attaching to receptors on it, in this diagram though the cell's not receiving any active incoming signals, therefore we have a resting potential where the cell is resting at about minus 72 minus 75 millivolts, and because there's no incoming inputs there's no action potential being fired

Resting Potential

state of the neuron prior to the sending of a nerve impulse.

Mitochondrian

structure that performs metabolic activities and provides energy that the cells requires.

Step 2- transport of neurotransmitters (and transmitter molecules)

synaptic transmission is transport of neurotransmitters and neurotransmitter molecules: -neuro peptides (synthesized in the cell body) are packaged into dense core vesicles by the Golgi apparatus in the soma, these vesicles are then transported to the terminal button via fast axoplasmic transport -small molecule neurotransmitters are synthesized in the terminal button, the enzymes needed to catalyze and synthesize these neurotransmitters are produced in the cell body and then transported using slow axoplasmic transport down to the terminal button, once these reach the terminal button transport molecules and proteins help fill the vesicles at the terminal button with neurotransmitters, vesicles that store these small molecule neurotransmitters are called clear core vesicles -in image you can see the difference between peptide neurotransmitters and small molecule neurotransmitters, at the top of the image can see small molecule neurotransmitters stored within clear core vesicles ie. look a little bit empty inside, in the bottom image you can see the dense core vesicles, less see through, these are neuropeptides

Concentration Gradient

the difference in distributions of ions

Glia

the other major components of the nervous system that exchange chemicals with adjacent neurons

third messenger system

the process can even get more complex, here you can see the involvement of a third messenger system, i.as with the previous examples the neurotransmitter binds to the metabotropic receptor in step 1 ii.in the second box the G protein activates the second messenger iii.in the middle box the second messenger has its effect on intracellular processes, iv.now building on what we've already covered the fourth box shows that the second messenger can also activate enzymes that create or synthesize a third messenger chemical v.the final box shows that the third messenger can also set off intracellular processes, for example third messengers can modulate the activity of the sodium potassium pump which will affect how the cell functions during future action potentials, alternately the third messenger can also open ion channels itself now we've completed up to step five in

Active transport

the protein mediated process by which useful chemicals are brought into the brain.

inhibitory graded potential

they cause hyper-polarization to occur (make membrane potential more negative)

Axon

thin fiber of a neuron responsible for transmitting nerve impulses toward other neurons, organs, or muscles

second messenger system- diagram 2

this diagram summarizes the process again from a different viewpoint, on the left we have a more basic g-protein activation i.can see the neurotransmitter binds to the receptor in step one ii.this metabotropic receptor activates the g-protein in step two iii.in step three a subunit of the G protein breaks away and opens the ion channel iv.in step 4 ions enter the cell and produce a postsynaptic potential

intrinsic neurons

those whose dendrites and axons are completely contained within a single structure.

chloride channels (ipsp)

when chloride channels are opened remember that in a resting potential chloride stays put in the extracellular fluid, because diffusion and electrostatic pressure balance it out perfectly, however if a membrane is already depolarized or excited by nearby excitatory synapses the negatively charged chloride is attracted to the inside of the cell that is now depolarized and positively charged, therefore there's an influx of negatively charged chloride which hyperpolarizes the membrane, making the cell which was previously positively charged more negative, as the cell becomes more negative it returns to the resting potential, therefore the influx of chloride hyperpolarizes the membrane and this negative input neutralizes or cancels out any excitatory postsynaptic potentials and stops the cell from firing, that is its inhibitory and decreases the likelihood that the cell will fire

fast synaptic transmission

when neurotransmitters bind to protein molecules or receptors on the postsynaptic membrane they transmit information in two different ways i.Fast synaptic transmission occurs when the neurotransmitter opens an ionotropic receptor, an ionotropic receptor opens neurotransmitter dependent ion channels, because binding of the neurotransmitter directly opens the ion channel, this makes synaptic transmission fast

activation of postsynaptic receptors- fast synaptic transmission, also known as ligand gated ion channels

when neurotransmitters bind to protein molecules or receptors on the postsynaptic membrane they transmit information in two different ways i.Fast synaptic transmission occurs when the neurotransmitter opens an ionotropic receptor, an ionotropic receptor opens neurotransmitter dependent ion channels, because binding of the neurotransmitter directly opens the ion channel, this makes synaptic transmission fast ionotropic tropic receptors are involved in fast synaptic transmission, sometimes these are also known as ligand gated ion channels i. can see in the image on the right the neurotransmitter in green binds to a protein molecule receptor on the postsynaptic membrane ii. in step 2 in this image the neurotransmitter opens to ion channel iii. in step 3 the red ions go through the ion channel and cause a postsynaptic potential *note that ionotropic receptors are chemically gated, that is only specific neurotransmitters can unlock or open the ion channels

regulation of synaptic transmission- summary

•Auto receptors Located on any part of the cell Metabotropic receptor Detects and regulates amount of neurotransmitter released •Axoaxonic synapses Junction between axon and axon Modulate neurotransmitter release •Dendrodendritic synapses Junction between 2 dendrites Organise groups of neurons

postsynaptic calcium channels

•Calcium works similarly to sodium •High concentration outside the cell •Opening of calcium channels depolarises membrane = EPSP •Activates enzymes that trigger chemical and structural changes •2nd messenger system >when a neurotransmitter attaches to a receptor and opens the calcium channel positively charged calcium enters the cell and creates a depolarization, but rather than just increasing the membrane potential and opening an ion channel just like sodium does calcium is quite special in the postsynaptic membrane, calcium binds with and activates enzymes, these enzymes influence the production of certain chemicals which we call second messengers that change the structure and function of cells Cengage quiz: 9.When the action potential reaches the presynaptic terminal, which ion must enter the presynaptic terminal to evoke release of the neurotransmitter? Answer Calcium????

G proteins - summary

•G proteins are coupled with guanosine triphosphate (GTP) •an energy storing molecule •Increases the concentration of a "second-messenger" •The second messenger communicates to areas within the cell •May open or close ion channels, alter production of activating proteins, or activate chromosomes

neural signals

•Neuron firing depends on the balance of excitatory and inhibitory input •Excitatory - fire signal •Inhibitory - no fire signal -example of temporal summation though there's a rapid rate of firing in that synapse this rapid firing creates a strong signal that produces lots of excitatory inputs and these are able to reach the axon hillock and trigger the action potential

slow synaptic transmission- summary

•Second messenger system •Metabotropic receptors •Neurotransmitters bind to receptors •Receptors DO NOT directly open ion channels •G proteins near receptor activate intracellular processes