Neuroscience: Neurons and Neural Crest Cells

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Questions and Answers

What is the primary functional unit of the nervous system?

Glial cells

Synapses

Neurotransmitters

Neurons (correct)

Which type of neuron is responsible for transmitting impulses from receptors to the central nervous system?

Efferent neurons

Sensory neurons (correct)

Interneurons

Motor neurons

What distinguishes motor neurons from sensory neurons?

Motor neurons send impulses to effector organs. (correct)

Motor neurons do not require stimuli to activate.

Motor neurons are typically found in the CNS.

Motor neurons are solely responsible for reflex actions.

What percentage of all neurons in adults are interneurons?

99% Signup and view all the answers

Where are neuronal cell bodies primarily located in the CNS?

Gray matter Signup and view all the answers

What is the main characteristic of neurons that allows them to respond to environmental stimuli?

They can rapidly change their ionic gradient. Signup and view all the answers

Which type of motor nerves control involuntary activities?

Autonomic motor nerves Signup and view all the answers

What is a characteristic function of interneurons in the nervous system?

They connect sensory and motor neurons. Signup and view all the answers

What is the primary function of the cell body of a neuron?

Produce most of the cytoplasm for neuron processes Signup and view all the answers

Which type of neuron has both an axon and multiple dendrites?

Multipolar neurons Signup and view all the answers

What is the role of dendrites in a neuron?

Receive stimuli from other neurons Signup and view all the answers

Which statement best describes anaxonic neurons?

They do not produce action potentials. Signup and view all the answers

What is Nissl substance primarily associated with?

Regions of concentrated RER and polysomes Signup and view all the answers

In which type of neuron do the processes bifurcate close to the cell body?

Pseudounipolar neurons Signup and view all the answers

Where is the Golgi apparatus located in a neuron?

In the cell body Signup and view all the answers

What structural characteristic is common in the nucleus of a neuron?

It generally has a prominent nucleolus. Signup and view all the answers

What initiates the release of neurotransmitters in a synapse?

Influx of Ca2+ ions Signup and view all the answers

What happens to the resting potential of a neuron when it is depolarized?

It becomes +30 mV Signup and view all the answers

How is the transmission of nerve impulses at a synapse described?

Unidirectional and chemical Signup and view all the answers

What role do neurotransmitter receptors play in synaptic communication?

They bind to neurotransmitters and initiate an impulse Signup and view all the answers

What is the primary effect of the influx of Na+ ions during an action potential?

It creates an action potential by depolarizing the membrane Signup and view all the answers

Which component of the synapse contains synaptic vesicles and mitochondria?

Presynaptic axon terminal Signup and view all the answers

What prevents the continuous firing of a neuron after an action potential?

Repolarization of the membrane Signup and view all the answers

Which statement accurately describes the function of neurotransmitters in synaptic communication?

They open or close ion channels initiating a postsynaptic impulse Signup and view all the answers

What is the primary purpose of the myelin sheath around axons?

To insulate axons and maintain an ionic microenvironment Signup and view all the answers

What happens at the Nodes of Ranvier?

There is a higher concentration of voltage-gated Na+ channels Signup and view all the answers

In unmyelinated nerve fibers, how do Schwann cells interact with axons?

They enclose portions of many axons within small folds Signup and view all the answers

What characterizes myelinated nerve fibers as opposed to unmyelinated nerve fibers?

They are covered with multiple layers of Schwann cell membrane Signup and view all the answers

What type of cells are responsible for forming the myelin sheath in the PNS?

Schwann cells Signup and view all the answers

What is the main structural component of myelin?

Lipid bilayers and membrane proteins Signup and view all the answers

What is the role of ganglia in the peripheral nervous system?

Housing neuronal cell bodies and glial cells Signup and view all the answers

What distinguishes saltatory conduction from continuous conduction?

Involves the movement of impulses from one node to another Signup and view all the answers

What effect do neurotransmitters have at excitatory synapses?

They open Na+ channels, leading to depolarization. Signup and view all the answers

Which type of glial cell wraps around axons in the CNS to form the myelin sheath?

Oligodendrocytes Signup and view all the answers

What is the primary role of astrocytes in the central nervous system?

To provide structural support and regulate neurotransmitters Signup and view all the answers

What is the characteristic structural feature of ependymal cells?

They are columnar or cuboidal and may have cilia. Signup and view all the answers

How do inhibitory neurotransmitters affect postsynaptic cells?

They open Cl- channels, causing hyperpolarization. Signup and view all the answers

Which type of glial cell is the most numerous in the brain?

Astrocytes Signup and view all the answers

What is the main function of the myelin sheath in the nervous system?

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

What is a distinguishing characteristic of oligodendrocytes compared to other glial cells?

They form myelin sheaths around multiple axons. Signup and view all the answers

Study Notes

Neural Crest Cells

Neural crest cells migrate extensively to form all cells of the peripheral nervous system (PNS) and various non-neuronal cell types.

Neurons: Functional Units

Neurons are the main functional units of the nervous system, characterized by long processes.
They respond to stimuli by altering ionic gradients, leading to membrane depolarization.
Neurons are excitable cells capable of rapid changes in electrical potential in response to stimuli.

Types of Neurons

Sensory Neurons: Afferent neurons that transmit stimuli from receptors.
Motor Neurons: Efferent neurons that send impulses to muscles and glands, divided into:
- Somatic motor nerves (voluntary control, skeletal muscle)
- Autonomic motor nerves (involuntary control of glands and smooth/cardiac muscles)
Interneurons: Connect other neurons and comprise 99% of neurons in adults; found in the CNS, either multipolar or anaxonic.

Neuron Structure

Cell Body (Perikaryon/Soma): Contains the nucleus and organelles, acting as the synthetic center, rich in Nissl bodies indicative of high synthetic activity.
Dendrites: Processes that receive stimuli and convey impulses to the cell body.
Axon: A single long process that conducts nerve impulses away from the cell body, may include branches to receive additional information.

Classification of Neurons by Processes

Multipolar Neurons: One axon, two or more dendrites; most common type.
Bipolar Neurons: One dendrite and one axon; found in sensory organs such as the retina.
Unipolar/Pseudounipolar Neurons: One bifurcating process; primarily sensory neurons.
Anaxonic Neurons: Multiple dendrites without a true axon; do not produce action potentials.

Nerve Impulses

Triggered when a threshold is met, leading to rapid influx of Na+ ions, causing depolarization.
Membrane potential shifts from negative to +30 mV; returns to resting potential quickly via K+ channels.

Synaptic Communication

Synapses transmit impulses between neurons or from neurons to effectors, ensuring unidirectional flow.
Converts electrical signals (nerve impulses) into chemical signals using neurotransmitters.
Components of a synapse include:
- Presynaptic Axon Terminal: Contains synaptic vesicles and mitochondria; releases neurotransmitters upon calcium influx.
- Postsynaptic Membrane: Contains neurotransmitter receptors and mechanisms to initiate impulses.

Neurotransmitter Effects

At excitatory synapses, neurotransmitters open Na+ channels, leading to depolarization.
At inhibitory synapses, neurotransmitters open Cl- channels, causing hyperpolarization.

Glial Cells

Support and maintain neurons, outnumbering them tenfold in the mammalian brain.
Develop from embryonic neural plate progenitor cells.

Types of Glial Cells

Oligodendrocytes: Form myelin sheaths in the CNS, facilitating rapid impulse transmission.
Astrocytes: The most abundant glial cells with diverse roles; influence signal transmission and maintain the blood-brain barrier.
Ependymal Cells: Line ventricles and central canal; involved in the circulation of cerebrospinal fluid (CSF).

Peripheral Nervous System (PNS) Structure

Nerve Fibers: Enclosed axons by glial cells (Schwann cells) that may form myelin sheaths.
Myelinated Nerve Fibers: Schwann cells create a myelin sheath through multiple layers, resulting in lipid-rich white matter.

Nodes of Ranvier

Gaps in myelinated axons that allow for saltatory conduction, enabling rapid impulse transmission.

Unmyelinated Nerve Fibers

Smaller-diameter axons are enveloped by Schwann cells but not wrapped in a myelin sheath; slower impulse conduction.

Ganglia

Ovoid structures containing neuronal cell bodies and glial satellite cells, supported by connective tissue and enclosed by a denser capsule.

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Description

Explore the fascinating world of neurons and neural crest cells. This quiz covers the structure and function of neurons, types of neurons, and the role of neural crest cells in developing the peripheral nervous system. Test your understanding and enhance your knowledge of these essential components of the nervous system.