NEURO EXAM 1 HELP SESSION

Equilibrium Potential Equation

E= 58mV/-1 * log extracellular conc. / intracellular conc.

Driving Force Equation

Vm - E ion : tells you the electrical driving force (leaking in or out of cell)

Vm - actual membrane potential

E ion - ion equilibrium potential

In a neuron at rest is the passive sodium influx equal in size as the active sodium efflux?

Yes passive = active for neuron at rest

Length Constant (λ)

Describes the DECAY of the membrane voltage along the axon due to leakiness of the membrane

(How FAR a voltage can spread)

→ position where the voltage reaches 37% of the intial peak voltage

Does increasing the axonal diameter increase or descrease the length constant (λ)?

INCREASE, the wider it is the less resistance and therefore easier to spread

*You want high length constant for optimal flow

→ think of a narrow hallway, there is more resistance so it’ll be harder to spread

Do you want high or low value for the TIME CONSTANT ( τ ) to speed up propagation of action potential ?

LOW = fastest , voltage changes the quickest

→ how FAST the membrane voltage can change

What factors of electrical properties are affected passive properties ?

Local Graded Only

• Time Course

• Amplitude

Both Local and Action

• Speed of propagation

Benefits for each 3 recording methods

1) Extracellular: longer recordings → no cellular damage

2) Intracellular: control of intracellular condition

3) Patch Clamp: single ion channel recording

The further away from the neuron of interest the electrode is placed…

The SMALLER the signal gets (weaker with more distance)

Why is neuroscience an important discipline in life science?

1) Understanding brain development, anatomy, physiology = major challenge

2) Understanding & Treating Neurological Disorders

3) Knowledge can improve computers, sensors, robotic devices

Two Cell Types - mediate the nervous system

Neuron and Glial Cells

Function of neurons

Signaling

Functions of glial cell

Maintenance and support

Common properties - Neuron and Glial Cells

Ion channels, pump transmitter receptors, membrane potential, produce transmitters, ecto-derm derived

Differences - neuron and glial cells

Glial cells ARE NOT polarized, don’t form action potentials, they can divide

3 properties - Local Graded Potential vs Action Potential

Local:

• Small amplitude changes

• Stimulus intensity reflects size of amplitude

• Travels only short distances

Action-Potential:

• Large amplitude changes

• Stimulus reflects frequency, amplitude stays constant!

• Travels long distances

Function of Local-Graded Potential

Local change in potential due to neurotransmitter binding, or response to a physical or chemical stimulus

→ typically dendrites on cell bodies that cant travel far

Function of action potentials

All-or-none signal triggered upon integration of the various local potentials, travels larger distances

→ important for long range signaling, amplitude stays constant

Why are neurons described as POLARIZED cells

They have morphologically and functionally distinct compartments

2 major compartments in neurons

1) Axonal compartment: sending signals and transmitter release

2) Somatodendritic compartment: receive signals and metabolic functions

Another polarized cell type that has been compared with neurons in respect to polarity

Epithelial cells

Three different types of glial cells

1) Schwann - myelination

2) Oligodendrocyte - myelination

3) Astrocytes - homeostasis, nutrition, support

4) Radial Glia - guides for neuronal migration

Does monomer in G-actin have polarity?

NO - F-actin has ± polarity

Ratio of axon to neuron

1 axon : 1 neuron

Tubulin binds…

GTP

Actin binds…

ATP

All MT have their plus ends oriented towards…

THE TERMINAL

Cell body (-) > > > Terminal / Growth cone (+)

Dendrites are thinner/thicker than axons?

THINNER

Role of axonal transport - how is it accomplished?

• Axon can be very long and majority of protein synthesis occurs in the cell body (transport is needed)

• In order to build and maintain the axon is through transport

• Directed by motor proteins that move cargo along microtubules (MTs)

Protein synthesis in neurons can happen…

Mainly in the cell body/ soma, but it can also happen locally (dendrites)

Plus end directed MT motor

Kinesin

Minus end directed MT motor

Dynein

Spinal cord

Sensory input transmission

Medulla

BP and Respiration

Pons

Transmission station: cortex and cerebellum

Cerebellum

Fine control of movements

Midbrain

Connects the motor systems

Diencephalon

Sensory transmission station (thalamus)

Telencephalon

Cognition and Memory Storage

Part of the brain - memory formation

Hippocampus

Where is the hippocampus located?

Medial temporal lobe of the telencephalon

How did researchers figure out that the hippocampus was important for memory formation?

Patients that had their medial temporal lobe removed from stroke had problems with memory formation afterwards.

What part of the epithelial cell is similar to the axonal compartment of the neuron?

The apical (lower) domain

What part of the epithelial cell is comparable to the Somatodendritic compartment of the neuron?

The basolateral domain (upper)

How does the GOLGI STAIN work and why is it useful?

Stains a small % of neurons, allowing the entire morphology of individual neurons (soma, dendrites, axon) to be seen and not the surrounding neurons.

Which scientists used the GOLGI STAIN for the first time?

Ramon y Cajal

Where does the name “Glia” from?

Greek word meaning GLUE

Does the original meaning of the name GLIA (glue) accurately describe the functions of glial cells?

NO - they perform many active and essential functions: supporting neurons, immune defense, maintaining extra cellular environment, forming myelin, etc.

What is the main function of OLIGODENDROCYTES?

Form myelin around axons in the CNS → can wrap around multiple different axons

Electrically insulates axons and increases action potential conduction

Function of SCHWANN CELLS

Form myelin around axons in the PNS

Name of GLIAL CELL that plays a role in the DEVELOPMENT of the nervous system

RADIAL GLIAL CELLS - guides migrating neurons to their appropriate locations during nervous system development

Purpose of Local Grade vs Action potential

LOCAL GRADE POTENTIAL:

• Carries info over SHORT distances

• Integrates incoming signals to determine whether an AP should occur

• Dendrites and Soma

• Strength decreases with distance

ACTION POTENTIAL:

• Carries info rapidly & reliably over LONG distances

• Along axon to the axon terminal

How is stimulus intensity encoded by each electrical signal?

Local Graded: Intensity is encoded by the AMPLITUDE of the graded potential

Action: Intensity is encoded by action potential FREQUENCY

True or false: All microtubules in axons have their plus ends oriented toward the terminal

FALSE - not ALL MT have that orientation, a small number can have the opposite orientation, most of them do have their plus ends oriented toward the terminal

True or false: dendrites are thicker than axons

FALSE - dendrites get smaller and taper off as they extend away from the cell body and branch extensively

True or false: One of the main functions of the intermediate filaments is providing tracks for organelle transport

FALSE - MT (microtubules) are the highways that motor proteins travel along not IFs (IFs are just for support)

True or false: Microtubule dynamics depends on GTP

TRUE - GTP on beta-tubulin is hydrolyzed GTP→GDP

Cap present = MT is able to grow

Cap lost = MT becomes unstable and rapidly shrinks

True or false: ATP bound actin has a higher preference for assembly than ADP bound actin

TRUE -

• ATP bound= more likely to ADD to an actin filament

• ADP bound= more likely to LEAVE the filament

True or false: the GOLGI is important for protein modification such as glycosylation and for protein targeting the appropriate subcellular compartment

TRUE -

Golgi is in charge of modifying and sorting/shipping proteins

True or false: different types of neurons have different compositions of membrane proteins such as ion channels

TRUE -

Different membrane properties give neurons different electrical properties and functions

True or false: protein Glycosylation is important for molecular recognition

TRUE - glycosylation adds sugar ID tags that other cells and molecules recognize

True or false: protein synthesis can occur in different parts of the cell

TRUE - protein synthesis (translation) can occur in different locations; 2 major ones being free ribosomes in cytoplasm and ribosomes on rough ER

→ can occur in the cell body / soma of neurons

→ or locally in dendrites of the neuron

True or false: the longest axon in the human body is 1mm long

FALSE-

Can be around 1 METER long not 1mm