intro to neuroscience exam 2

ch 4, 5, 6

what was the debate between Golgi and Cajal?

brain organization, is the brain just a bunch of parts or a greater whole?

what was Cajal’s argument?

neuron doctrine: brain is composed of discrete cells

what was Golgi’s argument?

Reticular theory: brain is a continuous network of fibers

what are the basic parts of a neuron and their functions?

1. cell body or soma with a nucleus: houses the nucleus and receives and integrates incoming electrical signals from the dendrites

2. axon(long thin protrusion): transmit electrical signals

3. dendrites(tree)(thicker shorter protrusions): receive incoming electrical signals

what is the role of the cell body(soma)

houses the nucleus and receives and integrates incoming electrical signals from the dendrites

what is the role of the axon

transmit electrical signals

what is the role of the dendrites

receive incoming electrical signals

what are the types of glial cells

1. astrocytes

2. oligodendrocytes/schwann cells

3. microglia

what is the role of the astrocytes

helps control blood brain barrier and absorbs and release important biological compounds that

support neuronal and endothelial function

what is the role of oligodendrocytes/schwann cells

produces the myelin sheath that wraps around axons

what is the role of microglia

immune cells of the brain, removes clumps of proteins and dead dying cells

cajal

founder of modern neuroscience, won the debate about brain organization

golgi

italian physician and scientist who did the black reaction and found the golgi apparatus

black reaction

created by golgi, silver nitrate on fixed tissue, stains only a few random cells, but filled completely

neuron doctrine

created by cajal, brain is composed of discrete cells, Neurons signal to each other –brain can be

understood by action of its basic parts

reticular theory

created by golgi, brain is a continuous network of fibers, action of the whole is key

dendrite

thicker shorter protrusions, often with spines

soma

similar to dendrites

axon

long thin protrusion

law of dynamic polarization

dendrites → axon hillock → axon → axon terminals

input zone→integration zone→ conduction zone→output zone

axon hillock

where the end of the cell body and the first axon meet

interneuron

integrate and modulate neural signals

monopolar

only one short process extending from the cell body

bipolar

two distinct processes that extend from the cell body(soma)

glia

support cells

myelin

fatty, insulating layer, or sheath, that forms around the axons of many neurons

what is an injury current

electric current generated by damaged excitable tissue, such as a nerve, muscle, or the heart

what is membrane theory

created by Julius Berstein that stated:

1. cells act like leyden jars

2. When depolarized, voltage

   reaches a threshold,

   “discharging” an action

   potential that is propagated

   down the axon

main components of the integrate and fire model

-proposed by Lapique

-synaptic currents are added up to charge/discharge the membrane

-when threshold is reached (all are none action potential)

What were Adrian’s main findings about action potential production in single nerve fibers?

all or none principle: rate not shape

frequency is the code for stimulus intensity

what is spatial integration

more neurons synapsing at different locations in the dendrite

what is temporal integration

spikes come up more rapidly, and they can add up over time

how does spatial integration contribute to total synaptic input current

multiple inputs

how does temporal integration contribute to total synaptic input current

total influence = firing rate X synaptic weight

how does thinking relate to the dominant paradigm

• pattern of firing rates within network

• combination of excitation and inhibition

how does learning relate to the dominant paradigm

• Permanent change in connections

• Rewiring

how does feeling relate to the dominant paradigm

modulating connectivity

Sherrington

A scientist discovered that excitatory and inhibitory synapses that are modified with learning

Bernstein

scientist that discovered cells have graded membrane potentials, acting as charged capacitors (Leyden jars)

Adrian

scientist that discovered how to record from single axons

resting potential

inside nerve has negative voltage relative to outside

spike threshold

critical level of membrane depolarization that must be reached for a neuron to fire an action potential/spike

soups vs sparks

is synaptic input with chemicals(soups) vs. electrical(sparks)

activation dynamics

pattern of firing rates within network, determined by wiring, combo of excitation and inhibition

rate coding

proposes that the intensity or strength of a stimulus is encoded by the frequency or rate at which a neuron fires action potentials (spikes)

synaptic weight

determines the size or the effect per spike

what are the major techniques for recording brain activity

• fMRI

• EEG

• Intracellular recording

amplifier

use small currents to alter much bigger externally supplied currents

micropipette

records small currents

in vitro

in glass(petri dish)

in vivo

in living organism

patch clamp

technique for recording intracellular recording

microwires

invasive, chronic recording of neural activity in live animals and sometimes in human patients (during surgery)

tetrodes

four electrodes

neuropixel silicon probes

chip technology, 100s of recording sites

fMRI

functional magnetic resonance imaging

BOLD

blood oxygen level dependent

charge

electricity that comes from charged particles

voltage

electric potential or electrostatic pressure

current

rate of flow of charge past a point

conductance

A measure of how easily electric current flows through a material

resistance

measure of an object’s opposition to the flow of electric current

charge in the water analogy

amount of water

current in the water analogy

current-I

voltage in the water analogy

pressure - V

conductance in the water analogy

width of pipe -g

resistance in the water analogy

narrowness of pipe - R (g=1/R)

what is ohm’s law

two forms: V=IR or I=gV

I

current

g

conductance

What are the two causes pushing ions to move across the membrane through selective ion channels?

the concentration gradient and the electrical gradient

How does a concentration gradient alter the formula for Ohm’s Law?

while the concentration gradient doesn’t do much and stays constant, the voltage changes rapidly

What is the reversal potential?

a point in which the voltage exactly cancels the concentration gradient and at this point, the current reverses between inward and outward

electrostatic gradient

Movement of charged ion due to differences in voltage between inside and outside of cell

concentration gradient

Ion diffusion due to different concentrations inside and outside cell

driving force

net gradient is the difference between the voltage and the reversal potential

driving force in equation

V-Erev

I_X = g_X(V-E_X)

net pressure equation

Erev

reversal potential

How can changing the relative conductance of multiple ion channels be used to control the membrane voltage?

increase in Na conductance: depolarization

Increase in G conductance: hyperpolarization

increase in CL conductance: stabilization/inhibition

How do Na and K voltage-dependent conductances cause action potentials?

The Na will be fast and the K will be slow because it depends on voltage and time

What technique allowed Hodgkin and Huxley to untangle the currents contributing to the action potential?

voltage clamp

What functional properties of action potential generation arise from the mechanisms?

voltage gated NA+ channel activation, delayed opening of K+ voltage gated channels

How does myelin speed up signal propagation?

it decreases capacitance between nodes and there is high density of Na at nodes of Ranvier, causing saltatory conduction

Squid giant axon

specialized neurons they have, with the largest diameter axons in the animal kingdom

overshoot

where V=0, phase of the action potential where the membrane potential temporarily becomes positive

Na hypothesis

reducing NA concentration reduces early phase, and the late phase is similar

after-hyperpolarization (AHP)

where Na and K become largely inactive, with Na completely inactive and K still lingering

voltage clamp

an experiment technique in which you set the desired voltage(like a thermostat) and wrap thin wire around a glass tube that measures voltage and injects a current to keep V constant 

spike threshold

particular voltage where Na channels activate, which triggers an action potential

refractory period

happens right after a spike and K is open while Na inactivated and cannot spike again

activation gates

fast, opens fast when V is depolarized

inactivation gates

slow(like K), slowly closes(inactivates channel) when V is depolarized

channel subunits

individual protein components that assemble to form an ion channel

myelin

the sheath that wraps around axons

nodes of Ranvier

short periodic gaps found in the myelin sheath along a myelinated axon

saltatory conduction

the mechanism by which an action potential is rapidly transmitted along a myelinated axon

What were the main arguments around the discovery of chemical transmission?

sparks: favored electrical transmission at synapse

soups: scientists favoring chemical transmission

What sequence of steps results in a presynaptic action potential causing neurotransmitter to bind at receptors on the postsynaptic membrane?

1. Vesicles filled with neurotransmitter

   are docked to the membrane

2. Action potential enters terminal

3. Ca enters via voltage-gated Ca

   channels

4. Ca reacts with proteins binding

   vesicles to membrane

5. Neurotransmitter has to be cleared  

Post synaptic

6. Neurotransmitters diffuse across synaptic cleft

7. Transmitters bind to receptors on the post-

   synaptic neuron

8. binding leads to opening of ligand-

   gated ion channels

9. Current flows through channels

   • Post-synaptic current (PSC)

10. Current causes change in post-synaptic

    membrane voltage

    • Post-synaptic potential (PSP)

What are gap junctions

(also known as electrical synapses) a type of synapse in which there is direct connection between the cells and no neurotransmitters are needed