Cell & Molec Neuro (Exam 1)

What are the parts of a neuron? (6)

• soma

• dendrite

• nucleus

• axon

• myelin sheath

• synaptic terminal

Dendrites

receives signals from other neurons via neurotransmitters

Myelin Sheath (2)

• insulates axon allowing the ions to move more efficiently

• made of glial cells

Axon Terminal

releases neurotransmitters, which passes information to the next cell

Nodes of Ranvier

carry information from the cell body through the movement of ions

Axon Hillock

where action potentials are initiated

What can differ between the distinct compartments of neurons? (4)

• morphology

• organelles

• cell membrane phospholipids

• transmembrane and intracellular proteins

How do most neurons communicate?

via chemical synapses

How does neurotransmitter release work? (2)

• presynaptic axon releases neurotransmitters

• neurotransmitters come from synaptic cleft and travel in vesicles

Electron Microscopy

allows neuroscientists to observe synapses

What is a way to study the structure of neurons?

histology

Histology

the study of tissue structure

What stains can be used in histology? (2)

• Nissl stain

• Golgi stain

Nissl Stain (2)

• dyes that bind to negatively charged nucleic acids

• good for looking at how many neurons are present

Which parts of neurons will be stained by the Nissl Stain?

the nucleus

Golgi Stain (3)

• stains the whole cell

• stains a small percentage of neurons at random

• useful for understanding precise morphology

What are examples of structures Nissl stains can be used on? (3)

• cortex

• olfactory bulb

• cortical layers

What are examples of structures Golgi stains can be used on? (4)

• pyramidal cell

• purkinje cell

• interneuron

• retinal cells

What did Ramon y Cajal do?

used the Golgi stain to map out the circuitry of the brain

Neuron Doctrine (2)

• neurons are individual cells

• the individual neuron is the structural and functional unit of the nervous system

In various nerve cell morphologies, what is structure related to?

function

How does a single genome produce different cell types? (2)

• cells have the same DNA template

• proteins produced creates differences in structure and function

The Central Dogma

DNA → RNA → Protein

Proteins (3)

• chains of amino acids held together by peptide bonds

• they have complicated 3D structures

• they do most of the work of the cell

What determines when and where a gene is expressed? (3)

• promoter sequences

• distal sequences

• transcription factors

RNA Polymerase (2)

• the protein that completes the process of transcription

• synthesizes mRNA for a given name

What do antibody stains do?

recognize specific proteins in cells

What is the process of obtaining and using an antibody? (3)

• inject a protein in an animal

• collect and isolate the proteins produced

• label antibody with a tag for visualization

What happened in the Volkmar study? (2)

• they had enriched and isolated mice then Golgi stained neurons within the visual cortex

• they found that the enriched group had more branching

What are the benefits of increased neuron branching? (3)

• increased surface for synaptic contacts

• greater potential for interneuronal interaction

• suggests a greater capacity for information processing

Dendritic Spines (3)

• important post-synaptic compartments

• increased surface area

• isolate chemical reactions

What are the cells of the nervous system? (2)

• neurons

• glia

Neurons

process information

Glia

support neurons

In what ways do the subtypes of neurons and glia differ? (4)

• gene expression

• morphology

• electrical activity

• function

What are the types of glial cells? (5)

• astrocytes

• microglia

• Schwann cells

• oligodendrocytes

• radial glia

Astrocytes (4)

• wrap around synapses

• regulate the extracellular concentration of various ions and neurotransmitter

• maintain the appropriate chemical environment for neurons

• can release gliotransmitters that activate neuronal receptors

Blood-brain Barrier (2)

• protects the brain from chemicals in the blood and infection

• endothelial cells surrounded by astrocytes

What can cross the BBB? (4)

• lipid soluble molecules

• oxygen and CO₂

• ethanol

• sugars and some amino acids

What cannot cross the BBB? (4)

• large molecules

• antibiotics

• large proteins

• ions and charged particles

Microglia

perform immune-like functions, such as removing dead cells

Myelinating Glia

form myelin sheath that surrounds and insulates certain vertebrate axons

What are the types of myelinating glia? (2)

• Schwann cells

• Oligodendrocytes

Schwann Cells (2)

• in the peripheral nervous system

• each cell myelinates a single axon

Oligodendrocytes (2)

• in the central nervous system

• each oligodendrocyte myelinates multiple axons

Radial Glia

guide the migration of neurons and the growth of their axons and dendrites during embryonic development

How are electrical signals carried?

by changes in membrane potential induced by movement of ions

What is the process of nerve signaling for external stimuli? (5)

1. sensory neurons have ion channels that open or close in response to sensory stimuli

2. electrical signal carried through sensory neuron leads to synaptic released of neurotransmitters

3. neurotransmitters directly or indirectly open or close ion channels on postsynaptic cell

4. electrical signal carried through motor neuron, leads to synaptic released of neurotransmitters

5. neurotransmitters signal to muscle cells to contract

What are the components of the lipid bilayer? (2)

• hydrophilic head

• hydrophobic tail

Hydrophilic Head (2)

• faces outward with regards to the bilayer

• both towards the inside and outside

Hydrophobic Tail

middle of the bilayer

Lipid Bilayer (2)

• allows cells to maintain different intracellular and extracellular concentrations

• limited permeability

Which ions have a higher concentration in the extracellular space? (3)

• Na⁺

• Cl^-

• Ca²⁺

Where is the [K⁺] the highest?

intracellular space

Permeability

how easy it is for something to pass over the membrane

What types of molecules cannot pass through the lipid bilayer easily? (2)

• charged molecules

• large molecules

How can large and charged molecules pass through the lipid bilayer?

membrane-spanning transport proteins

What is responsible for the movement of ions across neuronal membranes? (2)

• active transporters

• ion channels

Why can electrical potentials be generated? (2)

• differences in ion concentrations across membrane

• selective permeability of membrane

Active Transporters (6)

• requires energy

• actively move selected ions against electrochemical gradient

• create ion concentration gradients

• selective to certain ions

• ions must bind to transporters to cross membrane

• slower movement than through channels

Ion Channels (2)

• allow ions to diffuse down the electrochemical gradient

• are selectively permeable to certain ions

What are the types of neuronal electrical signals? (2)

• membrane potential (V_m)

• resting membrane potential (V_rest)

V_m (5)

• electrical potential inside the cell

• can be measured in mV by sticking an electrode into a neuron

• always refers to the inside of the cell

• based on the movements of ions along the membrane

• creates the electrical gradient

V_{rest (2)}

• in absence of stimulation

• typically around -60 or -65 mV for neurons

Depolarizing

V_m becomes more positive

Hyperpolarizing

V_m becomes more negative

Passive Response (3)

• graded

• the movement of ions is passive

• at the axon hillock, the passive inputs are summed together leading to the action potential

Graded

magnitude of the stimulation is encoded by magnitude of change

Active Response (4)

• all or none

• if the V_m is depolarized above a threshold voltage level, the neuron produces and active response

• action potential

• rate coding

Rate Coding

magnitude of stimulation encoded by rate of action potentials

Why is an active response active? (2)

• ion channels open and close

• energy is not required

Threshold (2)

• specific membrane potential needed for the action potential to fire

• ~ 50 mV

What is the chemical driving force based on? (3)

• concentration gradient

• moving from high to low

• passive process

What is the electrical chemical gradient based on? (2)

• difference in charge across the membrane

• movement occurs because ions are attracted to opposite charge

Electrochemical Gradient (2)

• net force that acts on an ion due to both the electrical and chemical gradients

• for a particular ion and location, those forces may act in the same or different directions

What is the typical charge on the inside of a cell?

negative

What are the directions of the concentration and electrical gradient for K⁺?

typically they are in opposite directions

When is equilibrium reached for the electrochemical gradient?

when the electrical and chemical gradients are equal and opposite

When is the chemical gradient stronger?

when there is a greater difference in ion concentration

When is the electrical gradient stronger?

when the membrane potential is further from 0

Equilibrium Potential (E_ion)

the electrical potential that creates an electrical gradient that would balance the concentration gradient leading to net 0 ion flow

Nernst Equation (2)

calculate equilibrium potential of an ion given intracellular and extracellular concentrations

What happens to E_x when the concentration gradient is big?

you get a big E_x

What happens to E_x when the concentration gradient is small?

you get a small E_x

How does the change in electrochemical gradient affect intracellular and extracellular concentrations?

it does not significatntly change them

What is affected when you move further from E_ion?

electric gradient only

Which gradient is stronger when V_m is greater than E_K? (2)

• concentration

• movement will follow the concentration gradient

What happens when V_m = 0?

there is no electrical gradient

Which gradient is stronger when V_m is less than E_K? (2)

• electrical

• movement will follow the electrical gradient

What happens to the gradients for K⁺ when the V_m is positive? (2)

• both push K⁺ out

• net movement out

Which gradient is stronger when V_m is greater than E_Na? (2)

• electrical

• movement will follow the electrical gradient

Which gradient is stronger when V_m is less than E_Na? (2)

• concentration

• movement will follow the concentration gradient

What happens to the Na⁺ gradients when the V_m is negative? (2)

• both push Na⁺ in

• there is net movement in

What is the typical E_K?

-80 mV

What is the typical E_Na?

55 mV

What is the range in V_m for membranes permeable to Na⁺ and K⁺?

between E_Na and E_K

What does V_m depend on? (2)

• equilibrium potentials for each ion

• relative permeability of each ion

Relative Permeability

how many ion channels open

GHK Equation

What is happening in this picture? (4)

1. At rest P_K >> P_Na more K⁺ channels open than Na⁺ channels, V_m close to E_K

2. Depolarizing stimulus moves V_m above threshold, opens voltage-gated Na⁺ channels, increasing P_Na

3. As V_m approaches E_Na, the flux of Na⁺ becomes less

4. Voltage-gated Na⁺ channels close and voltage-gated K⁺ channels open, making V_m more negative