Neurobiology Exam 1

soma/ cell body

contains nucleus carries out normal cell function

dendrites

receive input from many neurons

axon

has initiation site, release neurotransmitters at presynaptic terminal

where is the initiation site

in the axon usually close to the soma

how do neurons have polarity

one end receives-dendrites and postsynaptic

one end transmits- axon and presynaptic terminal

anterograde transport

molecular signals carried from the soma to the axon terminal

retrograde transport

from axon terminals to the nucleus

fast axonal transport is used to transport what

membrane bound organelles

what is transported in fast axonal transport for anterogade

mitochondria, neurotransmitter vesicles, elements of the ER, ribosomes, and mRNA

what is transported in fast axonal transport for retrograde

mitochondria, lysosomes, and signaling endosomes

how is fast axonal transport carried out

an active process of kinesins(motor proteins carrying cargo)  moving along cytoskeletal proteins, microtubules, 

what does slow transport move

cytoplasmic and cytoskeletal proteins using anterograde and retrograde

how does slow transport work

smaller pieces of microtubules sliding across linger lengths of microtubules, no motor proteins involved

what way are mRNAs and proteins moved

anterograde

glia

cells that provide physical and chemical support to neurons and maintain their environment

what do glia do

do not produce action potential, but they secrete neurotransmitters and use ion channels for signaling

what is unique about glia

you form new ones throughout life(gliogenesis), unlike neurons(neurogenesis)

what are the five types of glia

astrocytes, microglia, oligodendrocytes, Schwann cells, and ependymal cells

astrocytes

star shaped, make contact with neurons and wrap around synapses.

what are some functions of astrocytes

absorbing neurotransmitters, maintaining proper ionic balance, growth development and repair in CNS

microglia

the host defense system because immune system doesn’t reach the brain, when brain is damaged, they accumulate at the cite and phagocytosis the damage

oligodendrocytes

responsible for myelination of the axons in the CNS

Schwann cells

responsible for myelination in PNS

ependymal cells

regulate communication through fluids brain and spinal cord

white vs gray matter

grey- neuron cell bodies

white- regions with myelinated axons(because lipids and fats appear white)

where are nuclei found

brain stem, cerebellum, and subcortical parts of brain

ganglia

groups of neurons in the peripheral nervous system(no ventral root)

commisure

tract of axons that   cross midline of the brain or brainstem(corpus callosum)

what are bundles of axons called in PNS and CNS

PNS- nerves

CNS- tracts(in spinal cord -column)

what are ways that neurons are diverse

1. morphology

2. bioelctric properties

3. types of synaptic transmission

4. what parts of nervous system they connect to

hyper polarization 

becoming more negative

depolarization

becomes less negative(but still below 0).

passive response

when the current lets it return to resting potential staying below a certain point

EPSP

a depolarization makes it more likely for a action potential

IPSP

less likely to fire action potential because it hyper-polarizes

electrical potential

all cells have one, the difference in distribution of charge particles between two points

membrane potential

Vm, inside of cell is negative compared to outside the cell

current

the movement of charge particles from one point in an electrical current to another

electrochemical gradient

made up of chemical and electrical gradient, which act independently 

equilibrium potential

when the chemical and electrical gradients balance each other out

inside vs outside with K

high K inside, low k outside

Nernst Potential

when the equilibrium potential is reached

if membrane potential is set above the EK what direction would k move

what is resting potential

-70

if the membrane potential of k is set above Ek

the K will move out

if the membrane potential of K is set below the Ek

K moves into the cell

what determines the distribution of each ion to the resting potential

the permeability of the membrane to a given ion

why does K have an outward current

because the Vm is higher then the Ek

why does more Na move in

the Vm is much further from the Ena. This makes the current much stronger, but since there is a low permeability of na only 3 go in

how many na and k pumped

3 na out 2k in counteracts the normal k going out and na going in

passive propagation

as the membrane potential passes down the axon, it leaks and loses voltage

Why does an electrical potential move/propagate?

the inside of the neuron is electrically conductive but the membrane is not so it spreads throughout inside of cell

what generates passively propagating signals

sensory input(caused by receptors hyper or depolarizing) and synaptic transmission(EPSP or IPSP)

active propagation

action potentials do not decay as they travel the axon

how do action potentials not decay

The inward Na+ current during the action potential depolarizes the neighboring membrane, activating enough of the Na+ channels in that region to initiate an a.p. there

rising phase

depolarization phase

falling phase

repolarization phase

undershoot phase

afterhyperpolarization phase

what is the most important ion to resting potential

k

what ion is necessary to generate an action potential

Na

conductance

the capacity for ions to move across the membrane; is a function of the number of ion channels that
are open

resistance

the inverse of conductance; we usually talk about overall resistance of a cell (not ion specific). Input
resistance is measure of how “leaky” a cell is when current enters the cell.

capacitance

the ability of the membrane to store charge

Intracellular Recordings

can measure membrane potentials, record action potentials of a single neuron, and measure EPSPs and IPSPs

Extracellular recordings

just shows if a neuron has fried an action potential or not

is calcium normally high or low in the cell

low

what does a voltage clamp measure

currents and membrane potential

voltage clamp technique

1. an electrode measures Vm and is connected to voltage clamp amplifier

2. amplifier compares membrane potential to the command voltage set by the experimenter

3. when they are different, the amplifier injects current into a separate electrode, which changes it to the command potential

4. the current flowing back into the axon is measured

what happened in the squid axon when there was a hyper polarized potential

it made a capacitive current, but no membrane current.

what was observed in the squid axon when it was depolarized

there was an early, transit inward current, and then a delayed persistent current

current which way is positive and negative

+=outward

-=inward

what happens as the voltage clamp is set to more depolarized potentials

the outward current grows, and the inward current get larger but at 52mV it disappears and turns outwards

which ion is mediating the outward current

K because it is flowing outward

which ion is mediating the inward current

Na because it has a positive equilibrium potential that it reaches

what is shown in an IV curve

the maximum current recorded at each voltage-clamped membrane potential

what is the threshold potential

where the current start to be shown

what is the maximum inward or outward current you see

the highest or lowest peak

what is the reversal potential

the membrane potential at which the current direction switches

how did removing na show that na did the inward current

there was no longer an inward current, but there was a small outward current beucase they only removed extracellular Na

what was another way to test if it was na or K causing the current on IV curve

drugs the block na or k, like TEA or TTX

TEA

blocks voltage gated K

TTX

blocks voltage activated Na Chanels 

how does TTX work

the TTX blocks the Na channel, it resembles the Na ion and can enter the outer part of the pore

conductance

the ease with which ions pass through the membrane, in this class it is equivalent to membrane permeability

how does conductance work

voltage dependent, but not affected by the equilibrium potential of the ions being conducted, shows a view to how many channels open at given voltage

inactivation

a process where the current/conductance stops even though the membrane is still being depolarized

when is an action potential initiated

when there is a suffice depolarization to open a critical number of voltage gated Na channels(threshold)

delayed rectifiers

terminates the action potential by delayed opening of voltage-gates K channels

what also terminates the action potential

the inactivation of the Na channels(repolarization)

what happens immediately after repolarization

hyper polarization of the membrane potential(afterhyperpolarization AHP) caused by the delayed closing of K channels and opening of additional channels

what stage is caused by delayed rectifiers

repolarization

what is the permeability usually to na and k

k is 100 open and only like 5 for Na

absolute refractory

during repolarization phase due to na channel inactivation, can not start another action potential

relative refractory period

during the AHP and due to the K channels that mediate the AHP, can sometimes start another action potential but its hard

active propagation features

can widen the axon diameter or myeline to increase the velocity of action potential down axon

saltatory conduction

to jump from one node of rhaniver to the next

why do we need nodes of rhanvier at all

because na needs a plane to enter

how is myelination different in Schwann cells vs oligodendrocytes

Schwann can only myeline one at a time, oligodendrocytes can myeline different regions and axons

what is important about myelination

it is electron dense

multiple sclerosis

axons lose myelin and can result in axons breaking, since action potentials are in trains some get through and some don’t