Exam #1 - Fundamentals of Neuroscience

What is the neuron hypothesis?

States that the brain is made up of neurons which are basic signaling units for the nervous system

What are the three types of neurons?

Sensory neurons, interneurons, and motor neurons

Sensory neurons

Inputs: sensory receptors (information from world)

Outputs: other neurons

Made for quick relay, not much processing (like reflexes)

Interneurons

Inputs: other neurons

Outputs: other neurons

Lots of processing

Motor neurons

Inputs: other neurons

Outputs: muscles and glands

Some processing, only 1 output

What is a primary example of the use of sensory neurons?

Myotatic/knee-jerk reflex

What are the three unique factors of neurons?

Plasticity, longevity, and shape

What is plasticity?

Plasticity is how neurons routinely change structure and biochemical properties even after the primary developmental period has passed

What is longevity?

Most neurons are never replaced

What is shape (neurons)

Neurons are long and thick

What are neurons?

Specialized nerve cells that transmit information using electrical and chemical signals

What are glial cells?

Non-neuron cells in the nervous system that provide crucial support, protection, and nourishment for neurons

What are the functions of astrocytes?

Serve as supporting elements to the brain and provide firmness and structure, help form the blood-brain barrier, and dilate blood vessels to support increased brain activity

What are the functions of oligodendrocytes and Schwann cells?

Oligodendrocytes in the CNS and Schwann cells in the PNS form myelin, the insulating sheath that covers most neurons and helps electrical impulses travel faster

What are the functions of ependymal cells?

Secrete cerebrospinal fluid, which is a shock absorber, helps eliminate waste, may be a source of nutrients, and helps in brain cooling

What is the dendrite of a neuron?

Branchy extensions of a neuron that receive neurotransmitters from other neurons and transmit them toward the cell body. Dendrites play a crucial role in the neuron's ability to communicate, significantly contributing to synaptic integration and plasticity.

What is the function of the cell membrane?

The cell membrane acts as a selective barrier, regulating the movement of substances in and out of the cell, containing ion channels and pumps to generate and transmit action potentials by controlling the flow of ions (Na+, K+)

What is the difference between transcription and translation?

Transcription makes RNA from DNA while translation makes protein from RNA.

What is a nucleus’ purpose in a neuron?

The nucleus functions as the neuron’s control center to direct protein synthesis, regulate gene expression, and manage cell activities.

What is the function of a ribosome in a neuron?

The ribosome acts as the machinery for protein synthesis (translation), converting the genetic code from mRNA into functional proteins for neurons.

What is the direction of information flow in a neuron?

The information goes from the dendrites (who receive signals) to the cell body (soma) for processing, then to the axon terminals to communicate with other cells.

The majority of the cell membrane is made up of this macromolecule

Lipids

This compartment of the neuron sends action potentials to neurons that follow it in a circuit

Axon

Which of the following methods allows scientists to tell whether a gene or gene product is necessary for a behavior?

Genetic knockout

Membrane potential of a neuron is typically measured in

Millivolts (mV)

What is the abbreviation for the potassium ion?

K+

What is an fMRI?

A functional magnetic resonance imaging, a scan that detects changes in blood flow

What is an EEG? ERP?

Electroencephalography (EEG) is the method of measuring the brain’s overall electrical activity. An event-related potential (ERP) is a specific, time-locked component with the EEG that reveals the brain’s response to a specific event.

What is a brain lesion?

An area of abnormal tissue in/around the brain caused by injury/disease/etc

What is potential in a neuron?

The electrical voltage across the cell membrane

What is resting potential?

When neurons have a means of generating a constant voltage across the membrane while at rest

What is synaptic potential?

Allows transmission of information from one neuron to another, serves as the means of exchanging information in the complex neural circuits found in the CNS and PNS

What is action potential?

Brief electrical signal that travels down the axon

What is threshold potential?

The critical level of electrical charge that the neuron’s membrane must reach in order to trigger an action potential

What is depolarization?

When a current of the opposite polarity is delivered, so that the membrane potential of the nerve cell becomes more positive than the resting potential

What is hyperpolarization?

The membrane potential of the nerve cell becomes more negative than the resting potential

What are electrostatic forces?

The interactions (attraction between opposite charges, repulsion between like charges) that drive the movement of ions across the cell membrane

What are diffusion forces? Concentration gradient?

Diffusion or chemical forces in neurons represent the passive, natural movement of ions down the concentration gradient which consists of unequal ion distributions across the membrane to create potential energy for signaling

What is the difference between electrostatic and diffusion forces?

Diffusion is the movement of ions from high concentration to low concentration areas. Electrostatic force is the attraction of opposite charges and the repulsion of like charges.

What is equilibrium potential?

The specific electrical charge difference across a cell membrane that exactly balances the concentration gradient for a particular ion (calculated using the Nernst equation)

What is the difference between the Nernst and the Goldman equation? When would you use each?

You would use the Nernst equation to calculate equilibrium potential. You would use the Goldman equation to calculate resting membrane potential.

What is necessity?

Taking away a biological process to take away a behavior (ex. gene knockout, ion channel blockers, neurotransmitter antagonists)

What is sufficiency?

Including a biological process to induce a behavior (ex. electrophysiological stimulation, neurotransmitter agonists)

What does it mean to show a brain function is necessary vs. sufficient for a cognitive function?

Necessity: taking it away to see if it is necessary. Sufficiency: inducing it (is it sufficient enough to cause xyz)

Are K+ ions more concentrated inside or outside the cell?

Inside

Is K+’s equilibrium potential positive or negative?

Negative

Are Na+ ions more concentrated inside or outside of the cell?

Outside

Is Na+’s equilibrium potential positive or negative?

Positive

At the resting potential, the cell membrane is most permeable to which ion species?

Potassium ions K+

At the peak of the action potential, the cell membrane is most permeable to which ion species?

Sodium ions Na+

A solution of 1 millimolar KCl is on both sides of a semi-permeable membrane, permeable to K+ only. When the ions are allowed to reach equilibrium, the resulting membrane potential will be what?

0 mV

An ion channel is a ____ that selectively allows ions to move ____ the electrostatic and diffusion forces acting on them.

Protein; with

Increasing the concentration of ___ outside the cell, will increase the ____ potential of the squid giant axon.

Potassium, resting

The ____ equation is used to calculate the predicted membrane potential, when there are multiple ion species that can be permeable across the membrane.

Goldman

For an equilibrium potential to develop, this force must act on ions first:

Diffusion force (diffusion is what creates the charge separation to begin with, electrostatic occurs after diffusion has started)

What are leakage ion channels?

Ion channels are open all the time

When are leakage channels the most influential on membrane potential?

During resting potential

Which ion are leakage channels most permeable to?

Potassium (because of the resting potential)

What are voltage-gated ion channels?

Ion channels that are normally closed, but open in response to depolarization or hyperpolarization of the cell membrane

When do voltage-gated Na+ channels open?

At the threshold potential, leading to an action potential

What are ligand-gated ion channels?

Normally closed, but open when a ligand (a specific chemical such as a neurotransmitter) binds to the channel and is how information is carried from one neuron to the next

What are stretch-activated ion channels?

Open when something mechanical or physical presses on them (myotatic reflex, pressing on the skin)

What is a voltage clamp?

A voltage clamp is an electrophysiological technique that maintains a neuron at a specific membrane potential (clamped voltage) while measuring the ionic current flow across the membrane.

What is special about tetrodotoxin (TTX) and tetraethylammonium (TEA)?

Tetrodotoxin is an alkaloid neurotoxin found in fish/frogs/etc that blocks the Na+ current WITHOUT affecting the K+ current. Tetraethylammonium ions block K+ currents WITHOUT affecting Na+ currents

Ion channel activation vs. inactivation

Activation: ion channel transitions from a resting/closed state to an open state

Inactivation: a separation inactivation gate blocks the pore, stopping ion flow

What is the refractory period?

The brief interval after an action potential during which it is difficult or impossible to generate another one

What is passive current flow?

The passive spread of electrical charge along the axon/dendrites which does not involve voltage-gated ion channels

What is saltatory conduction? What are the nodes of Ranvier?

Saltatory conduction is the quick “jumping” of action potentials along myelinated axons, where the signal skips between uninsulated gaps called nodes of Ranvier

Why was the voltage clamp technique so important to early ion channel experiments?

Allowed researcher to control membrane potential while observing ionic currents, allowing scientists to separate and measure specific Na+ and K+ currents

What two currents are evident under voltage clamp conditions when the membrane is depolarized?

Inward sodium current (rapid), outward potassium current (delayed/sustained)

What currents are evident under voltage clamp conditions when the membrane is hyperpolarized?

Very little current

Describe the order and time course of Na+ and K+ channels opening and closing and their consequent effects on the voltage during an action potential

1. Resting state, Na+ and K+ channels are closed, inside of neuron is negative

2. Threshold is reached via stimulus, Na+ channels open quickly, inside of neuron is positive (depolarization)

3. Action potential peaks, Na+ channels close and are temporarily unusable

4. K+ channels open slowly, K+ flows out

5. K+ channels open too long, voltage drops below resting level, membrane becomes negative (hyperpolarization)

6. Returns to resting state

True or false: passive current flow moves in both directions on an axon

False

True or false: propagation of action potentials moves in both directions on an axon

False

Voltage-gated channel: closed state

Channel is not conducting, but ready to; occurs at resting membrane potential and prepares channel for depolarization

Voltage-gated channel: open state

Channel is conducting, occurs during depolarization, generates rising phase of an action potential

Voltage-gated channel: inactivated state

Channel is closed, not ready to conduct; occurs at peak/falling phase of action potential, prevents immediate re-excitation

What is an active transporter?

Transmembrane proteins that actively move ions into or out of cells AGAINST their concentration gradients. Their source of energy may be ATP or the electrochemical gradients of various ions

What is ATP?

Adenosine triphosphate, provides energy when broken down to ADP, universal energy currency

What is the Na-K pump?

What moves Na+ and K+ against their concentration gradients

True or false: Voltage-gated ion channels are specific to individual ion species

True

True or false: Voltage-gated ion channels are always open

False

True or false: K+ ion channels are never voltage-gated.

False