333 EXAM 1

What are the three structural classifications of neurons?

Unipolar (pseudounipolar), bipolar, and multipolar.

What is a unipolar (pseudounipolar) neuron?

A neuron with the dendrite and axon emerging from the same process; only one branch.

What is a bipolar neuron?

A neuron with the axon (information in) and dendrite (information out) on opposite ends of the soma.

[PURPLE] Why do Bipolar Neurons have this shape?

A straight input to output line keeps sensory pathways crisp and low noise for fine detail like our speciality senses; vision, hearing, and smell.

What is a multipolar neuron?

A neuron with more than two dendrites. Most common structural type of neuron in CNS.

What are Golgi I neurons?

Neurons with long-projecting axons.

What are Golgi II neurons?

Neurons whose axons project locally.

What are the three functional action classifications of neurons?

Excitatory, inhibitory, and modulatory.

What is an excitatory neuron/signal (EPSP)?

It facilitates firing of an action potential via depolarization. Examples in the notes: glutamatergic signaling and acetylcholine.

What is an inhibitory neuron/signal (IPSP)?

It inhibits firing of an action potential via hyperpolarization. Examples in the notes: GABA and glycine.

What is a modulatory neuron/signal?

It adjusts how other neurons and circuits respond rather than sending fast excitatory/inhibitory signals; it can make some signals stronger and others weaker. Examples: dopamine and serotonin.

How do modulatory signals generally differ from excitatory/inhibitory signals?

They tend to diffuse and change how the environment and/or neurotransmitters work, and they tend to work more slowly.

What are the three connectivity classifications?

Afferent, efferent, and interneurons.

What is an afferent signal?

It conveys sensory information toward the CNS ('arrive').

What is an efferent signal?

It transmits signals away from the CNS to effector cells, such as motor neurons ('exit').

What are interneurons?

Neurons that connect neurons within specific regions of the CNS to allow integration and influence other neurons; they are local to one area such as the spinal cord or brain.

[RED] Where does protein/mRNA translation occur in a neuron?

In the soma (majority of protein synthesis) and dendrites (local protein synthesis for plasticity), NOT in the axon.

What is the 'factory' of the neuron?

The soma.

What is the 'fine-tuning' part of the neuron?

The dendrite.

What is the 'delivery route' of the neuron?

The axon/axon hillock, which transmits information.

Why is the tip of the axon dependent on the nucleus/soma?

The soma supports protein synthesis and the axon depends on that support.

What is anterograde (antegrade) transport?

Transport away from the soma.

What is slow anterograde transport used for?

Moving/removing large structural proteins and maintaining the neuron; it is a limiting factor on how fast a neuron can develop.

What is fast anterograde transport used for?

Moving functional proteins, enzymes, vesicles, and neurotransmitter-related materials.

[RED] How does fast anterograde transport compare with fast retrograde transport?

Fast anterograde transport is about 2× faster than fast retrograde transport.

Why does fast anterograde transport need to be fast?

Functional proteins are needed quickly so the neuron can function and replenish them quickly

What is retrograde transport?

Transport toward the soma.

Why is fast retrograde transport important?

It provides general support to the nucleus and helps maintain neuronal survival by keeping the connection with the neuron alive.

[RED] What is the difference between oligodendrocytes and Schwann cells?

Oligodendrocytes are in the CNS and Schwann cells are in the PNS; both make myelin.

How does myelin production differ between oligodendrocytes and Schwann cells?

Oligodendrocytes make tons of myelin, whereas Schwann cells have a 1:1 relationship with the myelin they make.

What are microglia?

Glial cells described in the notes as activating when there is an infection; they are part of the immune system.

What are macroglia?

Glial cells including oligodendrocytes, Schwann cells, and astrocytes.

What are key characteristics of astrocytes?

They are the most numerous glial cells'; found in the brain, connect neurons and capillaries, and provide extensive support.

[RED] What do glial cells do, and what is the one thing they do NOT do?

They support and protect neurons. They do NOT conduct action potentials.

What are major astrocyte functions listed in the notes?

Removing debris; reuptake of neurotransmitters; guiding migrating neurons and axonal growth; releasing growth factors; and providing nourishment to neurons.

How do astrocytes provide nourishment according to the notes?

They take glucose and 'chew' it to lactose.

What two forces form concentration gradients?

Diffusion and electrostatic pressure.

What is the force of diffusion?

Movement of particles from high concentration to low concentration.

What is electrostatic pressure?

Opposites attract and like charges repel.

[RED] What are the major ion concentration gradients described in the notes?

Inside: increased K+. Outside: increased Na+ and Cl-.

Why does K+ tend to move out of the cell by diffusion?

K+ concentration is higher inside, so diffusion pushes K+ toward the lower concentration outside.

Why does electrostatic pressure keep K+ inside?

K+ is positively charged and is attracted to the negatively charged inside of the cell.

Why does both forces cause Na+ move into the cell?

Na+ is higher outside, so diffusion pushes it inward, and its positive charge is attracted to the negative interior.

Why does Cl− tend to stay outside?

Diffusion pushes Cl− inward because its concentration is higher outside, but electrostatic pressure repels the negatively charged Cl− from the negative interior.

[RED] What is the sodium-potassium transporter ratio?

3 Na+ out and 2 K+ in.

What is depolarization?

A decrease in membrane potential toward 0 (becoming more positive), associated in the notes with opening Na+ channels and making an action potential more likely.

What is hyperpolarization?

An increase in membrane potential, making the cell more negative relative to resting potential and making an action potential less likely.

What are cable properties?

Passive conduction of electrical current in a decremental fashion down the length of an axon that determine how changes in membrane potential spread through a neuron; the notes emphasize that dendrites use cable properties rather than action potentials.

[PURPLE] How do Cable Properties compare to Action Potentials?

Cable properties are good for short distances, they are fast, and they dont require a lot of energy. However, there is a limited distance to which they can travel (only short distances), and only one intensity.

Action Potentials require more energy but they can travel further, and they have a stronger intensity (all or none).

What is an action potential?

A brief electrical impulse that provides the basis for conduction of information along an axon; it is an active mechanism.

What is threshold of excitation?

The membrane potential value that must be reached to produce an action potential.

[RED] What is the all-or-none law?

Once an action potential is triggered in an axon, it is propagated without decrement to the end of the fiber.

How do action potentials differ from depolarization/hyperpolarization in terms of magnitude?

Depolarization and hyperpolarization have magnitude; an action potential is all-or-nothing.

What is saltatory conduction?

Action potential conduction that jumps from one node of Ranvier to the next.

[RED] What determines action potential speed?

Axon diameter and amount of myelin. Heavier myelin allows the action potential to jump farther and travel faster.

Where is the action potential created according to the notes?

At the node of Ranvier.

How is action potential intensity represented?

By firing rate/frequency, population of neurons, and type of neurons.

What is the rate law for action potentials?

Variations in stimulus intensity are represented by variations in the rate at which the axon fires.

[RED] How does firing frequency relate to stimulus intensity?

Higher firing frequency corresponds to greater intensity.

How does population size relate to signal strength?

A smaller group of neurons represents a weaker signal; a larger group represents a stronger signal.

What is an ion channel?

A specialized protein molecule that permits specific ions to enter or leave cells.

What is a voltage-dependent ion channel?

An ion channel that opens or closes according to the membrane potential.

[RED] How do K+ and Na+ voltage-dependent channels differ in the notes?

K+ channels are strictly voltage dependent and slower to react. Na+ channels are voltage dependent and also have an inactivation mechanism that acts like a timer.

What is Na+ channel inactivation?

After the voltage threshold is passed, the Na+ channel opens and then inactivates/closes after a certain amount of time even if the membrane is still above the voltage.

[RED] How does Na+ channel inactivation contribute to action-potential directionality?

The Na+ channel needs time to reactivate after closing, creating a refractory period that contributes to the directionality of the action potential.

Why does the sodium-potassium transporter move ions?

To prevent sodium from accumulating inside the cell; sodium accumulation would depolarize the cell.

Can ligand-gated and voltage-dependent mechanisms both be involved?

Yes. The notes state that ligand and voltage are not mutually exclusive.

What is the presynaptic membrane?

The membrane of an axon terminal button adjacent to the postsynaptic membrane through which neurotransmitter is released.

What is the postsynaptic membrane?

The cell membrane opposite the terminal button in a synapse; it receives the message.

What is the synaptic cleft?

The space between the presynaptic and postsynaptic membranes.

What is a synaptic vesicle?

A small, hollow, beadlike structure in terminal buttons that contains molecules of a neurotransmitter.

What is the release zone?

A region of the presynaptic membrane where synaptic vesicles attach and release neurotransmitter into the synaptic cleft.

What are classical neurotransmitters?

Neurotransmitters made in the presynaptic unit/axon terminal, packed into vesicles, released at the active zone, and cleared by reuptake or enzymes.

What are examples of classical neurotransmitters?

Acetylcholine; monoamines such as serotonin, dopamine, and norepinephrine; glutamate; GABA; and histamine.

Why are classical neurotransmitters easier to replenish than non-classical neurotransmitters?

Classical neurotransmitters are made in the presynaptic unit/axon terminal and packed into vesicles, whereas non-classical examples such as neuropeptides are made in the soma/cell body.

What are semi-classical NT?

Larger and usually co-released alongside classical neurotransmitters during periods of high-frequency stimulation to act as slower, long-lasting neuromodulators that diffuse across broader areas (volume transmission).

Examples of semi-classical NTs

Neuropeptides

What is retrograde neurotransmission?

Neurotransmitter/signaling released by the postsynaptic unit that travels back to the presynaptic unit; information can travel both ways.

What are examples of non-classical NT’s?

Lipids, nucleosides, and soluble gases.

What are non-classical neurotransmitters?

These molecules freely diffuse across cell membranes rather than relying on standard vesicular exocytosis. They frequently act as retrograde messengers, traveling backward from the postsynaptic cell to the presynaptic terminal to dynamically modulate and suppress future neurotransmitter release.

What are the three dimensions of neurotransmission?

Space, time, and function.

What is an anatomically addressed nervous system?

A hard-wired series of connections between neurons that communicate across synaptic clefts. Physical point-to-point wiring.

What is chemical/volume transmission?

Neurotransmitter signaling that occurs outside physical synapses when neurotransmitter spills over and diffuses through extracellular space. Widespread diffusion.

What determines diffusion in volume transmission?

Proximity and the presence of matching receptors.

What is the time difference between fast-onset and slow-onset signaling?

Fast-onset: glutamate + immediate, short-lasting. Slow-onset: GABA + delayed, long-lasting, including monoamines/neuropeptides.

Why are slow-onset signals important?

They help maintain changes because some functions need to be prolonged.

What are neuromodulators?

Signals that modulate a different signal from other neurotransmitters.

Where can modulation occur?

On the soma, axons, and dendrites; the notes say dendritic terminals may have the most effect because they have many connections and can bypass the rest of the neuron.

Why is timing important in neurotransmission?

The signal needs to reach a particular level of excitation at a particular time.

What are autoreceptors?

Receptors on the presynaptic side for classical neurotransmitters.

[RED] What is the overall direction of neuronal signaling across the synapse?

Signals can travel both retrograde and anterograde.

What are the major steps of neuronal development?

Neurogenesis → selection → migration (with astrocytes) → differentiation → presynapticgenesis → postsynapticgenesis.

Where does neurogenesis mostly occur, and what adult exception is noted?

It mostly occurs around birth, but the notes state that it also happens in the hippocampus in adults.

What guides neuronal migration?

Attraction and repulsion, with growth factors noted in the surrounding material.

How does regeneration differ between the CNS and PNS?

Long-distance regeneration is limited in the CNS, whereas the notes state that it is possible in the PNS.

What is neuronal plasticity?

Local changes that happen often, referring to changes within the synapse.

What are the steps of synapse formation?

Decision making (most time-consuming) → adhesion molecules via vesicles → 'decorating' by increasing functional proteins.

Connections are formed and strengthened through communication and growth signals.

Connections that are NOT needed can later be weakened or eliminated through synaptic pruning/loss.

What is a perforated synapse?

A complicated and functional synapse that makes more connections around it.

[RED] What does 'Cells that fire together, wire together' mean?

Neural activity occurring together is associated in the notes with strengthening/formation of connections.

What is synaptic pruning?

The ongoing removal of synaptic connections based on signals from outside the neuron; it happens more during development and less in adulthood.