Neuroscience: Structure and Function of Neurons

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What role do microtubules play in neurons?

They assist in intracellular transport. (correct)

They generate electrical signals.

They provide structural support only.

They store neurotransmitters.

Which part of the neuron is primarily responsible for receiving information?

Dendrites (correct)

Presynaptic neuron

Myelin sheath

Axon

What is the function of the synapse in a neuron?

It produces neurotransmitters.

It allows communication between the presynaptic and postsynaptic neurons. (correct)

It protects the neuron from injury.

It transmits electrical signals along the axon.

What is the initial part of the axon where signals are generated called?

Axon hillock Signup and view all the answers

In which structure does intracellular transport primarily occur within neurons?

Microtubules Signup and view all the answers

What is the main function of sensory neurons?

Send electrical impulses to the CNS from sensory receptors Signup and view all the answers

Which type of neuron is primarily responsible for processing information within the CNS?

Interneurons Signup and view all the answers

What is the structural classification of a typical motor neuron?

Multipolar Signup and view all the answers

Where are dendrites primarily located in a neuron?

Near sensory receptors Signup and view all the answers

What is the role of the axon in a typical neuron?

Transmit action potentials away from the cell body Signup and view all the answers

Which region of a neuron is primarily responsible for receiving signals?

Dendrites Signup and view all the answers

What is the primary characteristic of an anaxonic neuron?

Absence of an axon Signup and view all the answers

How does the nucleus of a neuron contribute to its function?

By producing proteins necessary for cell function Signup and view all the answers

What term is used to describe the neurons that send signals away from the CNS?

Efferent neurons Signup and view all the answers

Which part of the neuron is primarily involved in synaptic communication?

Axon terminals Signup and view all the answers

What occurs during depolarization of a neuron's membrane potential?

The membrane potential becomes less negative than the resting membrane potential. Signup and view all the answers

Which equation primarily determines the equilibrium potential of an ion at rest?

Nernst equation Signup and view all the answers

Which type of neuron is specifically responsible for transmitting sensory information from the peripheral nervous system to the central nervous system?

Sensory neurons Signup and view all the answers

What physiological change occurs during repolarization of a neuron?

The membrane potential returns to its resting membrane potential. Signup and view all the answers

What structural characteristic differentiates pseudounipolar neurons from bipolar neurons?

Bipolar neurons have two equal-length processes, while pseudounipolar neurons have a single axon. Signup and view all the answers

What is the effect of metabolic energy on ionic gradients across a neuron's membrane?

It must be used to maintain the ionic gradients. Signup and view all the answers

In what way do excitable cells like neurons alter their membrane potential?

By opening or closing ion channels. Signup and view all the answers

Which type of structural category do interneurons belong to?

Anaxonic Signup and view all the answers

What primarily influences the equilibrium potential at rest for a given ion?

Concentration gradient of the ion Signup and view all the answers

What happens to the membrane potential during hyperpolarization?

The membrane potential becomes more negative than resting potential. Signup and view all the answers

Which component allows motor proteins to bind with organelles during axonal transport?

Tail Signup and view all the answers

What is the primary energy source required for motor proteins to facilitate axonal transport?

ATP Signup and view all the answers

Which type of axonal transport mechanism is responsible for moving the varicella zoster virus from the soma to the skin?

Anterograde transport Signup and view all the answers

In which region of a neuron are action potentials initiated?

Axon hillock Signup and view all the answers

What type of signals do axons carry in a unidirectional manner?

Electrical signals Signup and view all the answers

What happens to old membrane components in a neuron?

They are digested in lysosomes. Signup and view all the answers

During axonal transport, which structure facilitates the movement of proteins and vesicles?

Microtubule network Signup and view all the answers

What describes the movement of the heads of motor proteins along microtubules?

They alternately bind and release. Signup and view all the answers

What is a key feature of neuronal connectivity described in the content?

Each neuron is an isolated unit. Signup and view all the answers

Which of the following is a characteristic of synaptic vesicle recycling?

It is part of the exocytosis process. Signup and view all the answers

What is the primary role of axons in a neuron?

To transform electrical signals into chemical signals Signup and view all the answers

What determines whether electrical signals from the dendrites can proceed through the axon?

The axon hillock Signup and view all the answers

What is a synapse?

The region where an axon terminal communicates with a dendrite Signup and view all the answers

Which part of the neuron is primarily involved in the release of neurotransmitters?

Axon terminals Signup and view all the answers

What is the function of myelin sheath in neurons?

To enhance the electrical signal transmission speed Signup and view all the answers

What type of synapses are associated with the release of excitatory neurotransmitters?

Excitatory synapses Signup and view all the answers

What are dendritic spines thought to be associated with?

Learning and memory Signup and view all the answers

What is the process known as axonal transport responsible for?

Transporting vesicles and organelles to and from axon terminals Signup and view all the answers

Which structure is primarily involved in integrating and processing incoming signals?

Cell body Signup and view all the answers

What role do retrograde messengers play in neurotransmission?

They regulate feedback and neurotransmitter release in presynaptic terminals. Signup and view all the answers

What is the primary function of dendrites in a neuron?

To receive input signals and integrate them Signup and view all the answers

What does the term anterograde neurotransmission refer to?

Forward motion of signals down the axon Signup and view all the answers

Which part of the neuron is responsible for converting chemical signals back into electrical signals?

Postsynaptic dendrite Signup and view all the answers

What role does the synaptic cleft play in neuron communication?

It is the area between the presynaptic and postsynaptic neurons Signup and view all the answers

What distinguishes excitatory synapses from inhibitory synapses?

Excitatory synapses enhance the likelihood of an action potential Signup and view all the answers

What is the significance of dendritic spines in neurons?

They enhance communication by increasing contact sites Signup and view all the answers

What type of signals do dendrites primarily receive?

Both electrical and chemical signals Signup and view all the answers

What role do polyribosomes in dendritic spines play?

They produce proteins for local modifications Signup and view all the answers

What happens to neurotransmitters released by the presynaptic neuron?

They bind to receptors on the postsynaptic dendrites Signup and view all the answers

What does retrograde transport refer to in neuron communication?

Movement of neurotransmitters to the presynaptic terminal after signaling Signup and view all the answers

What primarily characterizes the cell body of a neuron?

Site for integration of graded potentials Signup and view all the answers

How is neurotransmission initiated in neurons?

When graded potentials reach the axon hillock Signup and view all the answers

What is the role of the myelin sheath in neuronal signaling?

To insulate the axon and speed up transmission Signup and view all the answers

Why are dendritic spines capable of synthesizing their proteins?

Because they contain polyribosomes Signup and view all the answers

Study Notes

Nervous System - Resting Membrane Potential and Neuron

Objectives:
- Understand the basic principles of resting membrane potential generation.
- Describe the anatomy of a typical neuron and its functions.

Membrane Permeability

Phospholipid bilayer of cell membranes are impermeable to charged molecules (e.g., Na+, K+, Cl-, Ca++).
These molecules are also insoluble in the hydrophobic membrane core.
Large, water-soluble molecules (e.g., proteins, nucleic acids, sugars) also require channels for transport across the membrane.
Small uncharged polar molecules (e.g., CO2, O2, NH3, and water—mostly via aquaporins) can cross freely.

Electrolytes Distribution

Interstitial Fluid: Major electrolytes include Na+, Cl-, and HCO3-.
Intracellular Fluid: Major electrolytes include K+, HPO42- (phosphate ion), and negatively charged proteins.

Dominant Ions and Distribution

Extracellular fluid: Cations: Na+ Anions: Cl-
Intracellular fluid: Cations: K+ Anions: Phosphate ions & negatively charged proteins
Selective permeability of the plasma membrane creates unequal electrolyte distribution, resulting in electrochemical disequilibrium across the membrane.

Electrical Properties of the Cell Membrane

Plasma membranes act as ionic conductance, allowing ionic currents.
Concentration gradients dictate ion flow direction across the membrane.
Membranes act as capacitors, holding charges.
Electrical gradients generate the transmembrane potential (voltage difference between intra and extracellular spaces).

Generation of Membrane Potential

At equilibrium, cell and solution are electrically and chemically balanced.
The cell membrane acts as an insulator, preventing free ion movement between compartments.
Loss of positive ions (K+) intracellularly, due to Na+-K+ ATPase and K+ leak channels, creates an electrical gradient (more negative ions intracellularly).
Negative ions and molecules pull K+ back inside the cell.
Opposing forces (concentration and electrical gradients) balance, resulting in membrane potential measured as equilibrium potential (Eion).

K+ Leak Channels

Plasma membranes have more K+ leak channels than Na+ leak channels.
K+ leaks out to the extracellular space due to concentration gradients.
Negative ions inside the cell follow K+ efflux, due to attraction.
The membrane's impermeability to negative ions traps negative charges inside the cell.
K+ leakage through channels contributes to resting membrane potential.

Equilibrium Potential

Loss of positive ions (K+) intracellularly results in an electrical gradient.
Negative ions and molecules pull K+ back inside the cell.
When concentration and electrical gradients balance, net movement is zero.
The resulting membrane potential is the equilibrium potential.

Resting Membrane Potential

All living cells have a membrane potential.
Chemical and electrical disequilibrium exists between intracellular/interstitial fluid at rest.
Electrical disequilibrium generates an electrical gradient between intracellular and interstitial fluid.
Transmembrane potential (resting membrane potential) measures electric charges inside relative to outside the cell.
Resting membrane potential is typically negative in value (due to more negative than positive charges inside).

Stimulation of Plasma Membrane

A stimulus leads to Na+ influx.
This depolarization causes the intracellular environment to become more positive.
Repolarization follows depolarization, returning charges to the baseline.
Na+-K+ ATPase restores electrolyte distribution to resting conditions.

Resting State of Plasma Membrane

Some K+ and Na+ leak channels exist in the plasma membrane, especially K+.
Na+-K+ ATPase is required to maintain ionic concentration gradients.

At Resting State

Extracellular and intracellular compartments are in a dynamic steady state, not equilibrium.
They are in osmotic equilibrium but with chemical and electrical disequilibrium; intracellular space has more negative ions.

Equilibrium Potential of a Living Cell

The Nernst equation can calculate equilibrium potential for a single ion type.
Variables include: equilibrium potential (Eion), valence (charge, Z), ion concentration outside (extra) and inside (intra) the cell, and constant(2.303 RT/F @ 37°C).

Ion Distribution for K+

Higher intracellular K+ concentration produces a net efflux of K+ into the extracellular space.
The tendency of K+ efflux is balanced by negative equilibrium potential (-85.6 mV).

Additional concepts

Resting state, although a dynamic steady state, is not equilibrium, as it requires energy to maintain ion gradients.
Depolarization, repolarization, and hyperpolarization are events in which membrane potential changes either more or less negative than the resting membrane potential.

Neuron Anatomy and Function

Neurons are the functional units of the nervous system, responsible for transmitting and processing information.
Signals are both electrical (graded, action potentials) and chemical (neurotransmitters) enabling communication between nervous system and body systems.
Neurons receive information (sensory input), process it (integration), and respond (motor output).

Neuron Types

Sensory neurons: Typically unipolar or bipolar, carrying information from sensory receptors to the central nervous system (CNS).
Interneurons Found in CNS, can be anaxonic or multipolar, they integrate sensory information and communicate with other neurons.
Motor neurons: Multipolar, carrying signals from the CNS to effector organs (e.g., muscles, glands); conveying information, in the form of action potentials toward the effector.

Neuron Structure: Cell body

Contains nucleus and organelles.
Occupies a proportionally small volume compared to the whole neuron.
Proteins produced in the nucleus are transferred outward along the cytoskeleton (microtubules).

Neuron Structure: Dendrites

Highly branched extensions receiving signals from other neurons.
Can contain dendritic spines, increasing contact surface area and enabling protein production.
Signals are propagated from dendrites to the cell body then the axon.

Neuron Structure: Axon

A single, long projection originating from the axon hillock (trigger zone).
The axon hillock determines whether electrical signal generated by dendrites travels down the axon.
Axons branch into axon terminals with synaptic end bulbs.
These contain neurocrine molecules and mitochondria used to communicate with other cells.

Axonal Transport

Movement of materials along the axon, essential for transporting neurotransmitters, vesicles, and organelles.
This transport can be anterograde (away from soma—towards terminal) or retrograde (towards soma).
The molecular mechanism is associated with motor molecules using ATP.

Neuron Information Transmission

Information flows from the receiving site (dendrites/cell body) to the axon hillock as graded potentials.
Electrical signals (action potentials) arise in the axon hillock and are propagated unidirectionally to the presynaptic terminal.
Axons carry electrical signals unidirectionally, while chemical signals can be bi-directional.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the essential roles and structures of neurons, including microtubules, synapses, and various neuron types. Test your knowledge on how neurons communicate and process information within the nervous system.