test 2 ._.

functions of the nervous system

they encode, process, and store a wide variety of information from the external and internal environments and they used that information to control and regulate the physiology and behavior of the organism.

what is a neuron

a nerve cell

what do all neurons have in common

they all generate and conduct electric signals

what are the type major types of glia

• macroglia

• microglia

what is macroglia

macroglia support and modulate the functions of neurons

what is microglia

phagocytic cells derived from blood-forming stem cells, they are motile and are the first and major immune defense mechanism in the nervous system

what are the two types of nervous systems

• central nervous system (CNS)

• peripheral nervous system (PNS)

what does the central nervous system do

the central nervous system has lots of densely populated neurons that process and store information and generate commands

what is the central nervous system

the brain and spinal cord

what does the peripheral nervous system do

it provides communication between the central nervous system and all the rest of the body

how do new neurons form

the neural tube contains rapidly dividing neuronal stem cells. Division is usually symmetrical - all stem cells. but it can be asymmetrical - one stem cell, neuroblast or gliablast (progenitor cells)

what do progenitor cells produce

progenitor cells like the neuroblasts and gliablasts produce the neurons and glia that together form the various structures of the nervous system

what are the four regions of the neuron

1. cell body

2. dendrites

3. axon

4. axon terminals

what is the cell body of the neuron

the cell body contains the nucleus and most of the cell’s organelles.

what is the dendrites of the neuron

dendrites are the shrub-like projections that extend from the cell body.

dendrites receive information from other neurons or sensory cells and bring it to the cell body

what are the axons of the neuron

in most neurons, one projection - the axon is much longer than the others.

Axons carry information from the cell body to target cells

what are the axon terminals of the neuron

the axon divides into a spray of fine nerve endings. the tips of these nerve endings have swellings called axon terminals

neurons with few dendrites

they receive information from specific and limited sources

neurons with large array of dendrites

they can collect and integrate information from a wide range of sources

in all cells, where is the electric change negative

the electric charge on the inside of the neuronal cell membrane is slightly negative in comparison with the outside

what is an action potential (AP)

stimuli create electrical changes that travel along till the base of the cell’s axon, where a small change in membrane potential generates a large, rapidly reversed change in membrane potential

what happens when the action potential reaches the axon terminals

axon terminals come extremely close to the membrane of the target cell. here synapses transfers the information conveyed by the action potential from the presynaptic cell to the postsynaptic cell

what are the type kinds of synapses

• electrical

• chemical

what do electrical synapses do

they allow the action potential to pass directly between two neurons

what do chemical synapses do

At chemical synapses, there is a small gap between the pre and postsynaptic membrane.

when an action potential arrives at an axon terminal it causes the release of neurotransmitters who diffuse across the synaptic space and bind to receptors on the cell membrane of the target cell.

types of macroglia

• oligodendrocytes

• schwann cells

• astrocytes

• ependymal cells

what are oligodendrocytes

they wrap around the axons of neurons of the brain and spinal cord, covering them with concentric layers of cell membranes . it prevents electric current from leaking out of the axon

what are schwann cells

schwann cells wrap around the axons for the peripheral nerves. it prevents the electric current from leaking out of the axon

what is myelin

myelin is the wrapping produced by oligodendrocytes and schwann cells. cells that are myelinated conduct action potentials more rapidly than those without

what are epdendymal cells

it lines the central fluid-filled chambers in the brain called ventricles and produce the cerebrospinal fluid that bathes the brain and spinal cord

nodes of ranvier

at the intervals between schwann cells - the nodes of ranvier - the axon is exposed

what are astrocytes

it contributes to the blood-brain barrier that protects the brain from toxic chemicals in the blood.

why are astrocytes important

blood vessels throughout the body are very permeadble to many chemicals, including toxic ones. astrocytes surround the blood vessels in the brain

what is perivascular space

in the blood-brain barrier there is a small space between the membranes of the blood vessels and the astrocyte end-feet that surround them

the glymphatic system

interstitial fluid enters the brain through the perivascular spaces between blood vessels and the astrocytes that surround them. the astrocytes have aquaporins that enable them to take up fluid from the perivascular spaces and distribute it to the interstitial fluid compartment of the brain. that fluid leaves the brain through the perivascular spaces of the vein, taking metabolic waste products with it.

functions of astrocytes at the synapse

• they can take up neurotransmitters

• they can supply neurons with nutrients

• they have signaling properties - release neurotransmitters

• they aid in the repair and regeneration of neurons

• they can signal changes in the composition of the blood

why is the inside of a cell more negative relative to the outside

this is due to the cell membrane being differentially permeable to certain ions. for neurons at rest, their membranes are most permeable to potassium, and that permeability is primarily responsible for the electric charge across their membranes.

what will happen because the concentration of potassium is higher inside the cell than out

potassium tends to diffuse out of the cell down its concentration gradient.

what happens when potassium leaks out of the cell

it leaves behind an unbalanced negative electric charge that tends to pull potassium back into the cell

what is membrane potential

the resulting charge difference across the membrane

resting potential

in neurons it is the steady-state membrane potential

what is action potential in terms of membrane potential

the action potential is a sudden, large, transcient change in membrane potential generated by sudden changes in permeability to sodium ions.

how is electric current carried in a solution

electric current is carried by ions

what are the major ions that carry electric charges across the cell membranes of neurons

• sodium

• potassium

• calcium

• chloride

what is resting potential in millivolts

-60 and - 70 mV

what does the resting potential allow to happen

this resting potential provides a means for a neuron to respond to stimuli.

if some determinant of this balance of forces is altered, the membrane potential will change.

what happens if physical or chemical stimulus changes the permeability of the cell membrane to ions

it will cause a change in the cell’s membrane potential

what would happen to the membrane potential if there was a sudden increase in the permeability of the membrane to sodium ions?

it would cause a change of the membrane potential in the positive direction. if that change in sodium permeability were transient, the membrane potential would rapidly return to resting. and such rapid change is an action potential

where are sodium ions most abundant

outside the cell

why do ions need transporters and channels to get into neuron cells

like any cell, the membrane are lipid bilayers that are impermeable to ions so they’ll contain protein molecules that serve as ion transporters and ion channels.

what does the sodium-potassium pump do

it actively expels sodium ions from inside the cell, exchanging them for potassium ions from outside the cell

what is the purpose of the sodium-potassium pump

it keeps the concentration of potassium inside the cell greater than the potassium concentration of the extracellular fluid, and the concentration of sodium inside the cell less than that of the extracellular fluid.

how do the concentration differences established by active transport relate to the electrical gradients

ion channels permit the diffusion of ions across membranes in either direction. the direction and magnitude of ion movement depend on the concentration gradient and on the voltage difference across that membrane

electrochemical gradient

the two motive forces (concentration and voltage differences) that drives the movement of ions through channels

potassium leak channels

an open channel which make resting neurons more permeable to potassium than to any other ion.

how are potassium leak channels responsible for the resting membrane potential

the combination of potassium leak channel and Na-K pumps keep potassium concentration higher inside than out. thus potassium tends to diffuse out of the cell but when they leave they leave behind unbalanced negative change, generating an electric potential which pull potassium back into the cell

potassium equilibrium potential

the membrane potential at which the net diffusion of potassium out of the cell ceases

(the diffusion out is balanced by inward movement)

what are the different types of gated ion channels

• voltage-gated channels

• chemically gated channels

• mechanically gated channels

what are voltage-gated channels

ion channels that open or close in response to a change in the voltage across the cell membrane

what are chemically gated channels

ion channels that open or close depending on the presence or absence of a specific molecule that binds to the channel protein/ receptor

what are mechanically gated channels

ions channels that open or close in response to mechanical force applied to the cell membrane

opening and closing gated channels alters what?

openings and closings of gated channels alter the membrane potential

what happens when the sodium gated channel opens

sodium ions move down their electrochemical gradient until the membrane approaches the equilibrium potential for sodium which makes the inside of the cell less negative

what is a depolarized membrane

when the inside of a neuron becomes less negative (or more positive) than it is in its resting condition its cell membrane is depolarized

what happens when a gated potassium channel opens

potassium moves out of the cell, and the membrane potential becomes even more negative than when only the potassium leak channel were open

what is a hyperpolarized cell membrane

when the inside of a neuron becomes more negative than it is in its resting condition

what are the basic mechanisms for how neurons respond to stimuli

the openings and closings of ion channels that result in changes in the voltage across the cell membrane

what do local changes in membrane potential cause

it causes a flow of ions that spreads the change in membrane potential to adjacent regions of the membrane.

what is a graded membrane potential

it is a change from the resting potential that is proportional to the magnitude of a stimulus

what are graded membrane potentials a means of

integrating stimuli because the membrane can respond with proportional amount of depolarization or hyperpolarization to each stimulus

limitations of graded membrane potential

the spread of graded potentials can only be local and cannot be transmitted down long axons

explain what happens to voltage when an action potential travels down the axon

at resting potential voltage differences would be ~60-~70mV. when an action potential travels down the axon, a rapid change in membrane potential occurs, going from ~-60mV to +50mV, followed by a rapid return to the resting level.

what are action potentials generated by?

the openings and closings of voltage gated sodium and potassium channels in the cell membrane of the axon

what can cause some voltage gated sodium channels to open

a slight depolarization of the membrane

where are voltage gated sodium channels most concentrated

at the axon hillock

what happens when a neuron is stimulated sufficiently

it causes the membrane of its ell body to depolarize slightly, that graded potential spread by local current flow to the axon hillock which causes some of the voltage gated channels to open briefly

what happens when the voltage gated channels are opened briefly

the increased sodium permeability depolarizes the membrane even more, causing more sodium channels to open

what is a threshold

when the membrane is depolarized about 5-10 mV above the resting potential

what happens when a threshold is hit

a large number of sodium channels open and the membrane potential becomes positive - an action potential

what causes the axon to return to resting potential after active potential

1. the voltage gated sodium channels close

2. voltage gated potassium channels open

how do the voltage gated potassium channels respond to depolarization

they open, but they do so more slowly and they stay open longer than the sodium channels

what happens when voltage gated potassium channels open

the membrane potential returns to a negative value and usually becomes even more negative than the resting potential until the channels close again

what is the refractory period of voltage gated sodium channels

it’s the 1-2 milliseconds during which the voltage gated sodium channels cannot open again

what are the two types of gates of voltage gated sodium channels

• activation gate

• inactivation gate

which gate is closed under resting conditions

an activation gate

which gate is open under resting conditions

an inactivation gate

how does the refractory period work

depolarization of the membrane to the threshold level causes both gates to change state, but the activation gate responds faster. Thus the activation channel is open along with the inactivation channel for a brief moment. the inactivation channel will then close briefly before spontaneously opening again.

what is after-hyperpolarization or undershoot

the dip in the membrane potential following an action potential

what is an action potential that is an all-or-none event?

it is the process where slight depolarization of the membrane opens voltage gated sodium channels, leading to further depolarization through a positive-feedback mechanism and the generation of an action potential

what is an action potential that is self-regenerating

it spreads by local current flow to adjacent regions of the cell membrane. the resulting depolarization brings those neighboring areas of membrane to threshold. therefore when an AP occurs at one location, it stimulates an adjacent region to generate an AP and so on.

why do action potentials only propagate in one direction

it goes away from the cell body and cannot reverse itself because the voltage gated sodium channels in the region of the membrane it came from are in their refractory period

at what kinds of axons are action potentials conducted the fastest

• they travel faster in large-diameter axons than in small-diameter axons

• they travel faster in myelinated than in unmyelinated axons

why do action potential conduct faster in large-diameter axons

the resistance to ionic current flow decreases as an axon’s diameter gets bigger

why do axons conduct action potentials faster with myelinated axons

they can move down the axon in short jump.

write out all phases of an action potential

1. leak potassium channels create the resting potential. Gated channels are closed.

2. some voltage gated sodium channels open, depolarizing the cell to threshold

3. additional voltage gated sodium channel activation gates open causing a rapid spike of depolarization

4. sodium channel inactivation gates close; gated potassium channels open, repolarizing and even hyperpolarizing the cell.

5. all gated channels close. the cell returns to its resting potential

how are action potentials able to jump from node to node

Action potentials cannot propagate under the myelin sheath but jump from node to node (Nodes of Ranvier) as local electric fields spread quickly between them. Depolarization at one node leads to the depolarization of the next which triggers action potentials down the axon.

saltatory action potentials

action potentials jump from node to node in myelinated axons, allow faster transmission of information

how do saltatory action potentials work

a sodium channel opens, generating an action potential, that current is taken through the myelin and brings the next node to threshold

how do neurons communicate with each other and with other cells

neurons communicate at synapses

electrical synapses

common among invertebrates, the action potential spreads directly from presynaptic to postsynaptic