Lecture 14: Neurons

How do the nervous system and endocrine system differ in communication?

The nervous system uses neurotransmitters for fast, specific signals, while the endocrine system uses hormones for widespread, prolonged effects.

What are the three main types of neurons?

Afferent (sensory), efferent (motor), and interneurons.

What is the function of glial cells?

They support neurons: Schwann cells (PNS), oligodendroglia (CNS), astrocytes (metabolic support), and microglia (immune function).

What is membrane potential and how is it maintained?

Membrane potential is the electrical charge difference across a cell membrane, maintained by selective permeability and ion pumps (e.g., Na+/K+ ATPase).

What is the Nernst equation used for?

It determines the equilibrium potential for a specific ion based on its concentration gradient.

How does an action potential occur?

A neuron depolarizes when voltage-gated Na+ channels open, allowing Na+ influx, followed by K+ efflux for repolarization.

What is the Hodgkin cycle?

A positive feedback loop where Na+ influx during depolarization triggers more Na+ channels to open, causing rapid action potential generation.

Why do action potentials travel in one direction?

The inactivation of Na+ channels prevents backward propagation.

How is stimulus strength encoded in neurons?

By the frequency of action potentials fired, not their amplitude.

What is the refractory period?

A period after an action potential when a neuron cannot fire (absolute) or requires a stronger stimulus (relative).

How does myelination affect nerve conduction speed?

Myelin sheaths increase conduction velocity by allowing saltatory conduction between nodes of Ranvier.

What is the difference between depolarization and hyperpolarization?

Depolarization makes the membrane potential less negative (closer to 0), while hyperpolarization makes it more negative.

What are the key ions involved in generating membrane potential?

Sodium (Na⁺), potassium (K⁺), and chloride (Cl⁻).

What is the Goldman equation used for?

It calculates the resting membrane potential considering multiple ion permeabilities.

What role does the Na⁺/K⁺ ATPase pump play in neurons?

It actively transports 3 Na⁺ out and 2 K⁺ in, maintaining the resting membrane potential.

What is threshold potential?

The critical level of membrane potential (-55mV in many neurons) required to trigger an action potential.

What is saltatory conduction?

The jumping of action potentials between nodes of Ranvier in myelinated neurons, increasing conduction speed.

What are the two types of refractory periods?

Absolute refractory period (no action potential possible) and relative refractory period (stronger-than-normal stimulus needed).

How does neuron diameter affect conduction velocity?

Larger-diameter axons conduct action potentials faster due to lower resistance.

What is the role of voltage-gated ion channels in action potentials?

They open or close in response to voltage changes, allowing ion flow that drives depolarization and repolarization.

What is the difference between graded potentials and action potentials?

Graded potentials vary in strength and decay over distance, while action potentials are all-or-nothing and travel without losing strength.

What factors influence the resting membrane potential?

Ion concentration gradients, selective permeability of the membrane, and the Na⁺/K⁺ pump.

How does the inactivation of Na⁺ channels contribute to the refractory period?

It prevents the neuron from firing again immediately after an action potential, ensuring one-way propagation.

What is the function of nodes of Ranvier?

They are gaps in the myelin sheath where action potentials are regenerated, enabling saltatory conduction.

What are the two types of synapses?

Electrical synapses (direct ion flow via gap junctions) and chemical synapses (neurotransmitter release).

What happens at a chemical synapse?

An action potential triggers Ca²⁺ influx, causing neurotransmitter release into the synaptic cleft, which binds to receptors on the postsynaptic neuron.

What is the difference between excitatory and inhibitory synapses?

Excitatory synapses (e.g., glutamate) depolarize the postsynaptic neuron, while inhibitory synapses (e.g., GABA) hyperpolarize it, making action potentials less likely.

What are the main types of neurotransmitters?

Amino acids (glutamate, GABA), monoamines (dopamine, serotonin), peptides (endorphins), and acetylcholine.

What is summation in neurons?

The process where multiple synaptic inputs combine to determine if an action potential is generated. Includes temporal summation (rapid signals from one synapse) and spatial summation (multiple synapses firing together).

What is the role of G-protein-coupled receptors in neurotransmission?

They mediate slower, longer-lasting effects by activating second messengers inside the cell, unlike fast ligand-gated channels.

How does myelin loss (as in multiple sclerosis) affect neurons?

It slows or blocks action potential conduction, leading to muscle weakness, coordination issues, and sensory problems.