nervous system Flashcards
what does the nervous system do
- perceive events (receive information ffrom environment)
- process information
- cause an appropriate response if necessary
two types of cells in nervous system
neurons
glial cells
neurons vs glial : neurons
neurons:
receive, encode, and transmit information
use electrical impulses (action potentials)
have neurotransmitters (chemical components of neurons)
glial
- in charge of protection, support, and nourishment of neurons
three types: oligodendrocytes, astrocyte, ependymal
describe the three glial cells we discussed in class
oligodendrocytes:
- myelinate neurons
- speed up transmission of nerve impulses
- form myelin sheath around axons in CNS
astrocyte
- immune system
-protect neurons
- provide structural support for neurons
ependymal
- regulate the production and flow of cerebrospinal fluid
epithelial cell
cell body of neuron
aka soma
contains the nucleus and most of the cell’s organelles
- where transcribing rna and transcription occurs
dendrites
bring in information to the neuron from other neurons or sensory cells
(looks like ends of leaves)
axon
sends electrical impulses to other neurons
carries information away from the cell body to target cells (other neurons, muscle cells, glands)
axon terminal
swelling at tip of nerve endings (end of axon)
-close to target cells
- nerve impulses cause the release of neurotransmitters into the synapse
- at the terminal a synapse is formed
- send info from presynaptic to post synaptic cell
nervous system processes information in what three stages
sensory input, integration, and motor output
sensory neurons
- receive information from the environment
- transmit info about external stimuli such as light, smell, or touch
- converts signals from the environment to language of nervous system via changes to membrane potential (transduction)
interneurons
in between sensory and output neurons
- integrate and analyze and interpret information
motor neuron
transmit signals to muscle cells causing them to contract
does the brain have more neurons or synapses
The human brain has an estimated 1011 neurons and 1014 synapses
more synapses
Which neurons are responsible for processing, analyzing, and integrating information
Interneurons
vertebrates have a central nervous system including ___
it is the site of ____
the brain and spinal cord
most information processing, storage, and retrieval
also where memories are stored
peripheral nervous system function
brings in and processes information and causes actions
how do we receive and send signals in the nervous system?
step by step
sensory event occurs and this stimulates a circuit of neurons
1. transmission of electric signal : where action potential moves down an axon of one synapse ; this is an electrical signal of ions
2. at synapse the transmission is converted from an electrical signal to a chemical signal aka a neurotransmitter
3. transmission returns to electrical signal in receiving cell
all cells including the nerve cells have an _____–across their membranes
electrical potential
membrane potential
all nerves have a membrane potential
^^ the difference in voltage across the plasma membrane of a neuron
resting potential
in an unstimulated neuron, this is the voltage difference
^ about -70mV
the inside of the cell is more negative than the outside
The resting potential is the result of
unequal distribution of ions: Na+, K+, Cl-, and negatively charged proteins
what is the extracellular vs intracellular concentration of potassium
140 intra
5 extra
more conc on the intracellular
what is the extracellular vs intracellular concentration of sodium
15 intra
150 extra
more on extracellulR
what is the extracellular vs intracellular concentration of chloride ions
10 intra 120 extra
more on outside
what creates this difference in ion concentration
Caused by plasma membrane lipid bilayer that acts as an insulator and doesn’t allow ions across
Within the lipid bilayer are large transmembrane protein molecules
what type of transmembrane proteins does the lioid bilayer have
ion channels that have selective pores that allow ions to move across membrane
pumps
which move ions against their concentration gradient
major ion pump in neuronal membrane is
sodium potassium pump
sodium potassium pump
what it does/how it works
expels three Na+ ions from cell, exchanging them for two K+ ions from the outside cell
unequal exchange creates part of the membrane potential
energy omes from ATP hydrolases
ion channel
-if there is a difference in charge it allows ions to move
-don’t consume atp and don’t create concentration differences
-selectively allow ions to pass through
-pores formed by proteins in lipid bilayer
-some like the K+ leak channel is always open
others are gated
more sodium out for potassium in creates a negative charge
how do we generate the resting potential
the neuron at rest
the gated Na+ and K+ channels are closed
Na+/K+ ATPase pump is always active
the neuron always has small number of K+ leak channels that are always open
because Na+/K+ ATPase made K+ concentration higher in the cell than out, K+ moves out of the cell from high to low concentration
open leak channels diffuse K+ out the cell
this takes the positive charge out of the cell
what are the two forces that act on K+ in resting neurons
-concentration difference (more inside than out) drives K+ out the cell
- net negative charge inside the cell drives it back in (electrical gradient)
- never really changes concentration (constant concentration gradient)
- these forces are balanced out at -90mV –> equilibrium potential
a very small Na+ current drives the resting potential to around -70mV
the Na+/K+ ATPase..
1. Generates ATP by pumping Na+ out of the cell
2. Generates ATP by pumping Na+ into the cell
3. Creates an electric potential by moving more positive charges into the cell than out
4. Creates an electric potential by moving more positive charges out than in
5. 1 and 3
4
The ion will only reach its equilibrium potential if the membrane is permeable to the ion(open channels)
Neurons can change their permeability to particular ions by
opening or closing channels
Membranes can be depolarized or hyperpolarized
what does that mean
When the inside of a neuron becomes less negative in comparison to its resting condition, its plasma membrane is said to be depolarized
Conversely, when the inside of a neuron becomes more negative in comparison to its resting condition, its plasma membrane is said to be hyperpolarizes
Voltage-gated ion channels
Ion channels open and close depending on potential across the membrane
Voltage gated Na+ channels
Voltage-gated K+ channels
Voltage gated Na+ channels
Two gates both closed at resting potential
One gate opens quickly in response to the membrane becoming more positive
The other gate called the inactivation loop, closes slowly in response to the membrane becoming more positive
Voltage-gated K+ channels
Has one gate that opens slowly in response to the membrane becoming more positive
what does the membrane potential graph look like before durign and after an actionpotential occurs
at rest there is -70mV and then there will be some stimulus which causes some depolarizing to occur and then the membrane potential will drastically change from negative to positive quickly (shoot up) and then down again frequently
nerve impulses
action potentials that travel along axonse
describe more thoroughly the changes in membrane potential you see in the action potential graph
there is initial depolarization of the membrane which causes some voltage gated Na+ channels to open (tiny bump= initial dep.)
this causes positive charged (Na+) to move into the cell, thereby opening more voltage gated Na+ channels (chain reaction)
if the initial depolarization is big enough, threshold is reached
leads to rapid opening of many voltage gated Na+ channels, and the membrane potential shoots to +50mV
now describe what gates and channels are open at each stage of action potentials
resting state –> both voltage gated Na+ and K+ channels are closed
depolarization –> some voltage gated Na+ channels open and some Na+ enters the cell
the rising depolarization causes more voltage gated Na+ channels to open and lots of Na+ enter the cell (positive feedback of membrane potential)
falling phase –> depolarization at step 2 causes two slower events to start about a msec after the start of step 2
1. the inactivation loop closes the voltage gated Na+ channel
2. the voltage gated K+ channels open
Na+ stops rushing into the cell and K+ rushes out of the cell (membrane potential becomes negative)
the undershoot is caused by the large # of voltage gated K+ channels being open. –> membrane gets even more negative than at rest but at the negative membrane potential the voltage gated K+ channels close again and you get back to resting state
so how does your nervous system Receive information, processing information, and send out commands if necessary
Occurs via sequence of neurons talking to one another
Action potential (communication between neurons)
Presynaptic cell is having an action potential and the postsynaptic COULD if it receives the signal
resting potential is formed by
leak channels that allow potassium to go through that creates our resting potential
Voltage gated sodium channels are closed, potassium channels are closed
what is the language of the cell
changes in membrane potential caused by charged ions movement
We have a great potential for sodium to come into the cell
Action potential is opening up channels and letting sodium come into the cell, making the inside of the cell positive with respect to the outside
depolarization
Neuron is being tickled by another neuron
Being depolarized → made more positive
Reaches a threshold that sets off a positive feedback
Output creates more of itself → chain reaction
Sodium channels open and open and open
A little sodium comes in and then it becomes really permeable to sodium and then the membrane potential shoots up to positive
Sodium and potassium start at the same time but the inactivation loop closes the Na+
what is also happening
Voltage gated potassium channels open
Increasing phase we have high sodium permeability but then we suddenly close them
The membrane potential shoots down because potassium channels are still open and potassium starts to leave the cell because its higher conc. On the inside than outside → takes positive charge out
Lots of potassium leave → get very negative
what determines how information is sent out
Frequency at which you send action potential
Conduction of Action potentials
Information moves down the
axon
Action potentials start at
axon hillock
The entire nerve cell membrane doesn’t have the action potential simultaneously but
it is conducted down the length of the axon to the synaptic terminals
True or false : In the same neuron you can have part of it having an action potential and the neighboring region could be at resting potential
true
how does action potential move down an axon
The inside of the neuron at resting potential will still have negative charges so the positive charge of the sodium from the region in action potential will attract to the negative charges of the region in resting potential
The region in rest will be depolarized by the adjacent region in action potential because of this attraction (sodium moving down the neuron)
Continues as positive feedback where every adjacent region then becomes depolarized by the sodium from the previous region
In summary
Conduction occurs because t
the entering Na+ at a local region having an action potential can bring the neighboring segment ahead of it to threshold. This new region then has an action potential etc etc
Why does the action potential move in only one direction (towards the synaptic terminals)
Because in the region behind it the Na+ channels are still inactivated
Called the refractory period
The region that starts action potential goes through the process then inactivates the voltage gated sodium channel and can’t have an action potential for a while
There is also an influx of potassium
One way to achieve faster conduction is
to have bigger axons
myelination
Galil cells are the myelinating cells
Myelin is an insulating membrane produced by Schwann cells
Schwann cells in the PNS(peripheral nervous system) and oligodendrocytes in the central nervous system
Basically there are layers and layers of myelin wrapped around the axon
Creating regions of wrapped insulator around the axon
Leave little gaps called nodes of ranvier
Exposed regions of axon
The schwann cells encourage movement of charges down the axon without losing them out → allows for action potential to move down axon
Concentrates voltage gated sodium channels at the exposed nodes
Ion channels are clustered at nodes of ranvier
When an action potential fires at one node of ranvier, it jumps to the next via saltatory conduction (jumps)
Multiple sclerosis
Immune system is supposed to look for invading viruses, bacteria, etc and kills them
If immune system goes haywire and starts attacking good cells it causes an autoimmune disease
Caused by loss of myelination
Cause appears to be either failure of myelinating cells or autoimmune destruction of myelin
Synapses
A junction between a neuron and another cell
In a chemical synapses
The electrical signal of the presynaptic cell is converted to a chemical signal (a neurotransmitter) that diffuses across the synaptic cleft to the postsynaptic cell
Chemical synapses are essential to
the complex computational functions of the nervous system and for learning and memory
In a chemical synapses
Neurotransmitters are released into a ___
they then have to do what
cleft (space between presynaptic and postsynaptic neuron)
Neurotransmitter has to diffuse between the space and find a specific receptor and may initiate an action potential in the postsynaptic neuron
Every neuron receives multiple synaptic input and the integration of all that input is the basis of our neuro system
Pharmaceuticals target this synaptic transmission for treatment
Gap junction channels
Channel-like things that join the cytoplasm of two cells
A certain number of our neurons are joined by gap junctions
what do gap junctions allow for
Allow depolarization to directly move between cells
Neuron 1 depolarizes and all the positive charge ends up at the axon terminus, brings the next neuron to threshold and moves on
Why aren’t all synapses like this
^ gap junction depolarization –> electric synpase
Chemical synapses is where all the computation of the nervous system takes place
Electrical synapses doesn’t allow for computation
Our fast reflexes is were electrical synapses occur
How do we change the electrical signal to a chemical signal
The presynaptic neuron has at the synaptic terminus, little packets of neurotransmitters (membrane bound internal compartments)
They are always there waiting for a signal
The signal is the arrival of the depolarization and action potential at the synaptic terminus
This opens up the voltage-gated Ca2+ channel and calcium flows into the axon terminus
This is the signal for synaptic vesicles to fuse with the membrane and dump their neurotransmitters into the cleft
Each neurotransmitter has its own flavor of receptor that specifically recognizes it
Most common is a
ligand gated ion channel
whta is the ligand in a ligand gated ion channel
neurotransmitter
Neurotransmitters open the receptors
Might be permeable to sodium allowing sodium to rush in, causing an action potential to occur and depolarizing the next neuron
Average neuron has about 1,000 synapses
Usually the release of neurotransmitter from one presynaptic neuron is not enough to cause an action potential in the postsynaptic neuron
what creates a postsynaptic potential
The opening of ligand gated channels in the postsynaptic cell will create a postsynaptic potential
These can be either excitatory or inhibitory, depending on whether positive or negative ions enter the neuron
what is the root of decisions being made and memories being stored
Integration of potentially thousand different inputs and whether or not they result in an action potential or not
Excitatory neuron creates a
positive postsynaptic potential
Inhibitory neuron creates a
negative postsynaptic potential
spatial summation
The relative combination of both positice and inhibitory potential stimuli getting integrated integrated in the postsynaptic neuron cause it to reach relative threshold
Two different spots on neuron and they are signaling
Synaptic transmission
synaptic inputs will sometimes summate to bring the postsynaptic cell to threshold. The summation can occur across time(temporal) summation, or space(spatial summation)
Subthreshold, no summation
Excitatory neuron fires once and depolarizes but then goes back to normal/resting →clear neurotransmitter out of synaptic cleft
Charges up again and membrane potential increases and drops again and again
Temporal summation
→ close enough together in time
Excitatory neuron fires and another fires immediately after
Both firings add together and threshold can be reached and action potential occurs
Spatial summation
→ neither alone can occur but when they come together and happen simultaneously it can overcome threshold
Two firings at the same time and action potential is reached
What are the neurotransmitters?
give the three discussed in class
Acetylcholine –> widely used excitatory neurotransmitter
^ used at neuromuscular junctions in vertebrates
- used at special synapse where motor neurons activate muscles
Glutamate
- Widely used excitatory neurotransmitter in vertebrate CNS
Used in eyes
GABA and glycine
Inhibitory neurotransmitters
Acetylcholine receptor
Each neurotransmitter has a receptor that can be found on the postsynaptic membrane
The acetylcholine receptor mediated channel is normally closed
When ACh binds at specific sites on the receptor, the channel opens, allowing Na+ to enter the postsynaptic cell
Depolarizes the postsynaptic membrane
Excitatory → making less negative and bringing to threshold
Acetylcholinesterase
Job is to destroy acetylcholine
Want to immediately get rid of acetylcholine so that we can do it all over again
Norepinephrine
Major excitatory neurotransmitter in PNS
Can also act as a hormone
Fight or flight
Dopamine
Involved in complex behaviors like emotions, motivation, reward
The drug cocaine targets the dopamine system
Serotonin
Also involved in complex behaviors like mood and attention
Drugs like LSD and SSRIs target the serotonin system
The neurotransmitter for GABA is a ligand-gated Cl- channel. What do you predict would happen to a resting neuron that has GABA gated channels in its membrane, in the presence of GABA?
The neuron will become hyperpolarized (extracellular conc of Cl- is 120 so it will rush into the cell making it more negative)
