EK B2 Ch2 Nervous System COPY Flashcards
axon hillock
where action potential originate
myelination
speeds up signal transmission so if have to go a long way usually lots of myelins, longest axons in body go all the way down your leg to muscles in toes, all the way from spinal cord to toes, axons bundled together into nerve if not myleinated have serious movement disorders signal doesnt travel fast enough over long distance if not insulated in myelin
pattern usually
electrical signaling through a neuron, chemical neurotransmitters diffusing across the synapse, then electrical again, so goes electrical chemical electrical
-system set up to propagation signals one direction only, doesn’t go backwards, down an axon signaling happens only in one direction under normal circumstances
presynaptic neuron
before synapse, and second one is post-synaptic neuron
anterograde
forward normal direction, retrograde is not what naturally occurs but word that describes backward direction, mcat has a weird fondness for things, normal signaling will never be retrograde but if inject a radioactive dye at end of this second neuron! can get dye to migrate in retrograde manner backward through this pathway, so if have retrograde tracer where would it go after dendrites of second neuron, across synapse and totally backwards for what normal signaling can be
ion channels
-all along axon ion channels for Na, K, can be gated by either ligands or by voltage, so in action potential just talking about voltage gated ion channels when membrane around them reaches a certain threshold then ion channels around them will open
resting potential
-of cell around -70 mV means inside of cell negative 70 mV relative to outside! reason this is resting potential is largely thanks to sodium, potassium pump, 3 Na+ and pumps in 2 K pluses per turn of pump, means sodium potassium pump work horse in cells pumps out more positive charge which leads the inside of the cell a little bit negative compared to the outside
excitatory inputs
all of this stimuli that come in and basically the cell is adding them up, process called summation
what the cell is always doing in its constant book keepign is figuring out if membrane potential has reached threshold or not, can be three excitatory inputs that would nudge the cell toward threshold but then inhibitor inputs nudge it away from threshold, and all of those stimuli are considered graded stimuli, not all or nothing each can nudge cell toward threshold, a little bit of inhibition can drag further down from threshold, threshodl means - 55mV all this kind of stimuli gets cell to that threshold then action potential triggered, which is an all or nothign event
excitatory inputs
all of this stimuli that come in and basically the cell is adding them up, process called summation, what the cel is always doing in its constant book keeping is figuring out if membrane potential has reached threshold or not, can be three excitatory inputs that would nudge the cell toward threshold but then inhibitor inputs nudge it away from threshold, and all of those stimuli are considered graded stimuli, not all or nothing each can nudge cell toward threshold, a little bit of inhibition can drag further down from threshold, threshold means - 55mV all this kind of stimuli gets cell to that threshold then action potential triggered, which is an all or nothing event
action potential
all or nothing, if cell trips that wire -way to think about it all these inputs to cell and cumulatively either good enough to spark an action potential or not, by good enough means either get cell to - 55mV or they don’t
When a threshold stimulus is received (–55 mV), an action potential is triggered
Action potential is “all or none”
Stronger stimulus increases the firing frequency/number of neurons firing
action potential
when cell reaches threshold, both Na and K channels open, voltage gated channels these are the ion channels that open in response to voltage, these kinds of channels describe both K and Na channels**** change in voltage and change in membrane potential trigger for membrane ion channels to open
Calicium also voltaged gated ion channel
contrast with voltage gated ion channels is ligand gated channels, we do not have ligand gated channels that is second pathway IP3 bind sto membranae receptors on ER, endoplasmic reticium causing calcium channels to open that is ligand gated calcium channel because lgiand is Ip3****
- thing about it though is sodium channels open quickly, and potassium channels open very very slowly, whole first part of action potential is about movement of sodium, second part about movement of potassium
sodium gradient
active transport pump sodium potassium pushes sodium out of cell, meaning if open channel sodium will come back into the cell, passive direction is into the cell, opposite of sodium potassium pump!
- positively charged sodium comes rushing into the cell, if look at graph see spike that goes up, voltage of cell, measuring voltage inside relative to outside voltage goes up very sharply, thanks to sodium rushing into the cell= DEPOLARIZATION, when inside of cell gets more positive, say that it is being depolarized membrane potential goes up really high, all the way up ot +35 mV
voltage starts to come back down again…. repolarization!
membrane potential comes back down thanks to repolarization - thanks to movement of potassium, said sodium channels open quickly potassium opens slowly, potassium now finally open, which were opening slowly, so now ions mainly moving is potassium, if think abotu direction of potassium, passive direction for potassium is out of the cell, opposite of what happens in sodium ptoassium pump, K+ losing positive charge from inside of cell, makes inside more negative, can see that as cell being repolarized, it actually dips down really low around #5 then comes back up to resting potential
stronger stimulus
DO NOT get bigger action potential -amplitiude or shape* of action potential doesn’t change, what we mean when say all or none event, stimulus causes cell to reach threshold, get action potential but if stimulus really large just get more frequent action potentials how our body encodes stronger signals
atributes of action potential
-starts at axon hilock, moves down, can go faster if diameter of axon is larger
-doesn’t get any weaker as it goes, just keeps renewing itself
-ion channels that keep going after action potential goes by something called refractory period, corresponds to end of repolarization, cell during refractory period the cell cannot do another action potential that would be the absolute refractory period or cell can only do another action potential if stimulus was insanely strong and that would be the relative refractory period
myelination gaps
-have to be gaps for ion channels because sodium and potassium cannot go through myelin sheath, so those areas where you have the ion channels and breaks in myleination are called nodes of Ranvier
saltatory conduction
action potentials originating in nodes, almost action potential jumping down axon one to the next, not passing through myelin sheath have to go at these regular intervals gaps ins heath and nodes of ranvier
Saltatory conduction: myelinated axons undergo discontinuous membrane polarization
Saltatory conduction “jumps” and is faster than continuous conduction
image
Neurotransmitters made in cell body -how do neurotransmitters get released into synapse, what happens is action potential we just talked about causes voltage changes all along the axon, axon potential has propagated all teh way down the axon, talked about voltage gated sodium channels, voltage gated action potential, but down here at end of axon one other kind of ion channel, also voltage gated calcium channels, the purple channel on the left side of axon terminus -when voltage changes associated with action potential each axon termins causes Ca 2+ channels to open, passive direction for ca2+ is to move into axon, more calcium outside cell then inside, calcium rushes in and triggers some steps that cause vesicles ot be exocytosis
So vesicles containing neurotansmiter- means neurotransmitter released into synapse then on the post synaptic membrane receptors receive neurotransmitter and that is how the information signal gets passed onto the next cell, so the signal can cause the next cell to do a g protein pathway, can cause ion channels ot open directly here there is a note about ligand gated channels, when neurotransmitter binds can cause something inhibitor or excitatory in post synaptic cell, how postsynaptic cell decides whether todo an action potential because getting these inputs
3 ways to get neurotransmitter out of synapse so signal stops, 3 mechanisms
- some pumped back into the presynaptic cell, always efficient because can be recycled (naturally happens with serotonin)
- neurotransmitters can be broken down by enzymes, most famous ex of that acetylcholine is broken down by enzyme aceytlcholineestertase, comes up a lot, this is the neurotransmitter used at neuro musclar junction, have nerve cells intervening skeletal muscle, acetylcholine goes and binds to muscle cell, more acetylcholine more muscle contraction, more acetylcholinesterase less muscle contraction, and then problem set question if you were to inhibit acetylcholine esterase, then inhibit breakdown have more acetylcholine more muscle contraction
- neurotransmitters can diffuse out of synapse
serotonin SSRIs
ex of neurotransmitter thought ot elevate mood, big impact on sleep, actions really complex but one thing it seems ot do is elevate mood in some ppl, normally removed from a synapse by a reuptake pump, gets pumped back for recycling into presynaptic neuron SSRIs- inhibit reuptake pump, meaning serotonin lingers for longer in synapse, meaning has more opportunities to bind to its receptors on postsynaptic cell, and theoretically that should inc serotonin signaling
recycling
efficient doesn’t have to make more serotonin from scratch
-use it store it and use it again, know that it is a pump requires ATP to do this pump back into axon terminal, but energy expended on pumping serotonin back into presynaptic cell is worth it because cell doesn’t have to synthesize as much serotonin from scratch
hypothalamus in nervous system
appetite, sex drive, body temperature, autonomic and hormonal control
brain structure
- as animals more complex new functions added on higher up in brain -most primitive, survival oriented functions are in lower parts of the brain that we share with other animals and have similarities with our medulla oblongata, but other things in top of brain pretty unique to humans
afferent signals
INPUTS
-enters spinal cord on dorsal side, out back
efferent signals
outputs, away from spinal cord
-information comes out on ventral side
gray matter versus white matter
gray matter- cell bodies of axons
white matter- axons, its white because of myelin around axons, where the name white matter comes from think the fatty tissue! mylein is made up of fatty stuff, blubbery
a nerve or track
is a bundle of axons
ganglion
-groupings of cell bodies outside of nervous system one is ganglian and plural is ganglia
reflex circuit
-most simple -so fast information only travels later all the way up to the brain -an see why this is adaptive, allows for a super super fast response to a stimulus -sensory information goes along blue neuron, pathway where blue sensory neuron connects to red motor neuron, motor neuron goes out ot quad muscles, that contracts and causes the leg to kick up and that is the test, when you hit a patient on the knee and bottom part of leg swings up and kicks you in the shins is a good sign means reflex arc is in tact, that is the essence of it, sensory neuron synapses directly with a motor neuron right there in spinal cord, fastest possible signaling
reflex circuit 2
- do not want opposing muslce on back of leg, hamstring to also contract, just want leg to move one way, also an inhibitory signal has to go to back of the leg, what that green connector is about, interneuron - direct pathway and then other loop blue sensory neuron interacts with intermediate convertor and then an inhibitory signal gets set back to leg, so don’t have opposing muscles contracting at the same time
autonomic nervous system
- have two neurons btw spinal cord and effector, ultimate target of pathway, true for sympathetic and parasympathetic
- two neurons that are different, from the spinal cord, there is first a short axon, then a synapse and then there is a long neuron, neuron with a long axon that goes all the way to a synapse and then to a target, muscle cell or endocrine gland, in the synapses the neurotransmitters are involved, ACH is acetylcholine in first synapse and then NE is norephinephrine in the second one, the first neuron called pre ganglionic neuron, the second neuron is called post ganglionic neuron, to put it all together, in sympathetic pathway there are two neurons btw spinal cord and target, preganglionic neuron has a short axon and it releases acetylcoA
- postganglionic neuron has a long axon and releases NE, the NE that binds to the target does the fight or flight response, and that is intuitive becuase NE is neurotransmitter version of Epinehphrine, which as a hormone does fight or flight, that target showing could easily be the heart, NE comes through sympathetic pathway, binds to heart and causes heart to be really really fast
autonomic nervous system 2
- fact that there is a short first axon in this pathway, that is significant because when you have something coming out of spinal cord a lot of these sympathetic pathways talk to each other
- when synapses all on top of eachother called sympathetic trunk, what it basically means is that early on as the sympathetic pathways are coming off of the spinal cord they are really talking to eachother, messages coming down sympathetic trunk as well as out to the target
- fight or flight is a whole body response
- all of our bodies experience a fear feeling that is hard to isolate you feel it alll together your heart beating, sweating eyes dialating in a sympathetic response all together partly becuase sympathetic pathways are all coordianted with eachother
parasympathetic
- opposite of sympathetic, long preganglion neuron and short post ganglion neuron
- they have asked questions on mcat, would you expect post ganglonic neuron and parasympathetic pathway= answer very close to whatever the target is, so if have pathway of parasympathetic pathway responses rest and digest
- lots of parasyumpathetic pathways like this end up stimulating differnt cells of digestive tract, or smooth muscle cells to do parastolsis, would expect second neurons would originate buried in walls of small intestine, very short and close to the target!
- also notice for parasympathetic pathway, both synapses use acetylcholine **
enteric nervous system
- surrounds the gut
- can control and sense gut behavior independent of hte brain, very intersting
- also via vagus nerve fibers can transmit information from gut to brain
- can act semi independently with rest of nervous system to influence behavior of diestive system, more evidence to regulate mood* talked about SSRIs and serotonin to try to relieve depression, 90% of serotonin in body actual in gut*** enteric nervous system
- high serotonin levels in gut neurons, antidepressant SSRIs may have an effect in gut, gut on brain very
eye
- light goes in through pupil, bent by lens goes all the way back to retina, layer of cells at the back ot the eye
- on retina are photoreceptors** where physical stimulus of light gets turned into an electrical signal that cna then go to brain, goes to brain via optic nerve
- photoreceptors on retina we have rods and cones!
- rods= dim light vision
- cones= color vision. 3 kinds of cones red, green, blue
fovea
- when light falls on it especially good at seeing image, vs blidn spot where otpic nerve connects no photoreceptors there
photoreceptors
rods and chone, stimulated by light
light causes there to be an electrical signal that propagates, but stimulus is light and sensory system transduces light into an electrical signal, takes input of light and then converts it into the form of action potentials that can then go along the optic nerve to the brain
type of electromagnetic receptor
They detect the physical stimulus of photons that enter the eye
Unlike*** other types of sensory receptors, they do NOT generate action potentails. instead a similar but distinct process the relative level of light in the environment affects the rate of enurotransmitter release by photoreceptors into the synapses that they share with sensory neurons.
chemorecetpors
detect chemical stimuli such as tastes and odors
when small molecule binds to the receptor, like taste and smell
thermodetectors
detect heat
mechanoreceptor
detect mechanical stimuli such as touch and pressure
ear
- should know sound waves come in through pinna
- go down auditory canal to tympanic membrane, also called ear drum which starts vibrating, which causes three bones in middle ear to start vibrating
- fluid in middle ear strengthens virbations, sound waves causing one thing to vibrate after another
- vibrations enter inner ear, specifically cochlea (Sea shell swerve)
- cross section of cochlea= in middle is the organ of corti, business end of the cochlea
- can really see go down to lower right hand part blow up, all thsoe hair cells, on ogan of corti in cochlea big wound up carpet of hair cells sititng on basilar membrane, awning over them called tectorial emmebrane
- tips of those hairs are really really sensitive to pressure or touch, hair receptors, as sound waves cause vibrations that go deeper and deeper into ear, cause basilar membrane like shakign out a carpet undulate, and as that happens different hair cells pop up and hit awning, tectorial membrane, when hair cells hit tecotiral membrane causes them to depolarize, what triggers firing of those cells, then that electrical information goes along to auditory nerve to brain
hair cells
- represent map of all pitches of sound we hear
- if high pitch sound certain hair cells will get pushed up adn depoalrized, low pitch sound different hair cells will pop up and be depolarized
- positioning of hair cells how we code different auditory information for brain
semicircular canals
- thick fluid in semicicrular canals, when tip haead to one or the other pushes fluid ot one side or the other how we know where our head is in space, that sense is called the vestibular sense
- disorders of the semicircular canals horribel siutaitons sea sick all the time, normally gives us a sense of being oriented and knowing where head is in space
- this information also travels along auditiry nerve to brain, full name vestibular cochlea nerve (for vestibular sense, and cochlea for auditory sound information goes through cochlea)
fun fact
- only have 5 kinds of sensory receptors, easy multiple choice: sweet, sour, bitter, salty, umami (MSG)
neuron structure
The nervous system is composed of nerve cells (neurons) and glial cells
In adult nervous system, neurons do not divide
Cell body: contains the nucleus, most organelles, and cytoplasm
Dendrites: one or more short branched processes that receive signals
Axons: processes that transmit electrical signals away from the cell body
Axon hillock joins the axon to the cell body
Some axons are naked, some are wrapped in myelin sheath
Axon terminal forms a synapse with an effector cell (neuron, muscle, or gland)
Neurotransmitters are synthesized in cell body, released from the axon terminal
synapses
Synapse is the junction between axon terminal and effector cell
Synapse is the site at which a nerve impulse is propagated
Axon terminal forms many synaptic knobs with target cell
2 synapse types: chemical and electrical
Most synapses are chemical: mediated by neurotransmitters
Electrical synapse: mediated by gap junction between cells and is faster
Synaptic cleft: the physical gap between the two cells
Presynaptic neuron transmits signal, postsynaptic cell receives signal
Synapse allows unidirectional signal propagation
ALL ABOUT ONE WAY DIRECTION!
anterograde direction
Anterograde direction is “normal” (down axon, presynaptic to postsynaptic)
retrograde direction
Retrograde direction is “reverse” (up axon, from postsynaptic to presynaptic)
Ion channels
Ion channels are protein complexes that allow ions to cross membrane
Ion channels can be passive
Ion channels can be voltage gated: open/close with changes in membrane potential
Ion channels can be chemically gated: open/close with neurotransmitter
resting potential 2
Neuron at rest is polarized: negatively charged inside
Resting potential inside cell is –70 mV
Resting potential results from (1) action of Na+/K+ pump (3 Na+ out/2 K+ in), (2) passive diffusion of K+ out of cell through a second channel
excitatory and inhibitory inputs
A single neuron can have 1000s of synaptic inputs
Each synapse can be excitatory or inhibitory
Excitatory input depolarizes neuron towards threshold level (Na+ in)
Inhibitory input hyperpolarizes neuron away from threshold level (K+ out or Cl– in)
These inputs are graded. They are not “all or none”
Summation: single cell adds inputs; reaching threshold voltage triggers action potential
Electrical inputs spread from dendrites and cell body to axon hillock
action potential 3
- Threshold stimulus (–55 mV) is received, triggering action potential
- Depolarization: voltage gated Na+ channels are activated and open. Na+ rushes down its gradient into cell. Membrane potential transiently spikes to +35 mV
- Voltage gated Na+ channels begin to be inactivated and close. Simultaneously, voltage gated K+ channels are activated and open
- Repolarization: K+ rushes out of the cell and cell returns to its negative state
- Neuron is briefly hyperpolarized (more negative than usual). K+ channel slowly closes
- Neuron returns to resting potential
attributes of action potential 2
Action potential starts at hillock and moves towards axon terminal
Larger diameter axon permits faster conduction
Action potential is rapid < 1 ms
Does not decrease in strength along axon
Refractory period: cell cannot have another action potential during depolarization because Na+ channels are inactivated
Absolute refractory period: no amount of stimulation will evoke action potential
Relative refractory period: increased level of stimulation can evoke action potential
Refractory period
cell cannot have another action potential during depolarization because Na+ channels are inactivated
Absolute refractory period
no amount of stimulation will evoke action potential
Relative refractory period
increased level of stimulation can evoke action potential
myelin 2
Some axons are naked, some are wrapped in myelin sheath
Myelin is produced by Schwann cells (PNS) or oligodendrocytes (CNS)
Myelin is an electrical insulator: portion of axon that is wrapped cannot depolarize
- Myelin makes signal propagate faster** no ions moving through myelin, do have ions moving in and out is called Nodes of Ranvier