Nerve Tissue and Nervous System Overview

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Questions and Answers

What role do monocyte-derived macrophages play in the response to neuronal injury?

They facilitate the formation of blood–nerve barriers.

They are responsible for the process of myelin removal. (correct)

They enhance the phagocytic activity of microglia.

They promote the regeneration of nerves.

What is the effect of limited disruption of the blood–brain barrier on neuronal injury recovery?

It leads to excess myelin debris in the CNS.

It restricts infiltration of monocyte-derived macrophages. (correct)

It allows for rapid clearance of myelin debris.

It supports axon regeneration.

What consequence does apoptosis of oligodendrocytes have during neuronal injury response?

It causes rapid recovery of the blood–nerve barrier.

It enhances myelin debris clearance.

It promotes effective nerve regeneration.

It leads to inefficient phagocytic activity of microglia. (correct)

What is the impact of astrocyte-derived scar formation on nerve recovery in the CNS?

It contributes to failure in nerve regeneration. Signup and view all the answers

What allows for axon regeneration following neuronal injury?

Rapid clearance of myelin debris. Signup and view all the answers

What type of connective tissue surrounds a group of nerve fibers, contributing to the blood-nerve barrier?

Dense irregular connective tissue Signup and view all the answers

Which structure serves as a relay station for transmitting nerve impulses located outside the central nervous system?

Ganglion Signup and view all the answers

What are the two types of ganglia based on their functions?

Sensory and autonomic ganglia Signup and view all the answers

Which of the following correctly describes the role of autonomic ganglia?

They contain postganglionic visceral efferent neurons. Signup and view all the answers

What type of nerve fibers carry information from sensory organs to the central nervous system?

Afferent fibers Signup and view all the answers

The neurons in sensory ganglia are described as which of the following?

Pseudounipolar neurons Signup and view all the answers

Which structure encases the entire nerve, providing support and protection?

Epineurium Signup and view all the answers

The direction of the nerve impulse through a ganglion determines its type. What type of ganglion is characterized by afferent input?

Sensory ganglia Signup and view all the answers

What is the function of the myelin sheath in large diameter axons?

To provide insulation that speeds up nerve impulse conduction Signup and view all the answers

What is the primary component of the blood-brain barrier?

Capillary endothelium Signup and view all the answers

Which type of astrocyte is more prevalent in gray matter?

Protoplasmic astrocytes Signup and view all the answers

What role do the perineurium layers play in nerve organization?

Provide a blood-nerve barrier and regulate diffusion Signup and view all the answers

How are small diameter axons different from large diameter axons regarding myelination?

They are engulfed by one Schwann cell without myelin formation Signup and view all the answers

What tissue layer surrounds individual nerve axons?

Endoneurium Signup and view all the answers

Which statement accurately describes the interior structure of white matter?

Contains fibrous astrocytes that are curved Signup and view all the answers

What distinguishes saltatory conduction from other forms of conduction in nerves?

It allows action potentials to jump between nodal segments Signup and view all the answers

What is the primary role of the myelin sheath formed by Schwann cells?

To insulate the axon and enhance action potential propagation Signup and view all the answers

How many axons can a single Schwann cell myelinate at one time?

One axon only Signup and view all the answers

What is contained within the Schmidt-Lanterman clefts?

Schwann cell cytoplasm Signup and view all the answers

What structure acts as a partial barrier at the nodes of Ranvier?

The axolemma Signup and view all the answers

What initiates the myelination process around an axon?

The formation of the mesaxon membrane by Schwann cells Signup and view all the answers

What happens to the cytoplasm during the myelination process?

It is extruded and compacted to form myelin Signup and view all the answers

Which of the following describes the relationship between Schwann cells and unmyelinated axons?

Several unmyelinated axons can be enveloped by a single Schwann cell Signup and view all the answers

What role do nodes of Ranvier serve in the conduction of nerve impulses?

They allow for ion exchange necessary for action potentials Signup and view all the answers

What is NOT one of the basic functions of nerve tissue?

Transporting oxygen to brain cells Signup and view all the answers

Which component of the nervous system includes the brain and spinal cord?

Central Nervous System Signup and view all the answers

Which type of cells in nerve tissue are responsible for mitotic activity?

Glial cells Signup and view all the answers

What structure separates nerve cells from connective tissue in the brain?

Blood brain barrier Signup and view all the answers

Where do CNS neurons and central glia originate from?

Neuroectodermal cells Signup and view all the answers

Which of the following best describes a synaptic bouton?

A swelling located at the terminal ends of axons Signup and view all the answers

Which of the following is NOT derived from neuroectodermal cells?

Microglial cells Signup and view all the answers

What is the primary role of dendrites in the neuron?

Receive stimuli from the environment Signup and view all the answers

Study Notes

Nerve Tissue

Nerve tissue is responsible for controlling and integrating organ and organ system functions.
Nerve tissue has three main functions:
- Sensing changes using sensory receptors.
- Interpreting and remembering detected changes.
- Reacting to changes using effectors.

Anatomical Organization

The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
CNS components include:
- Brain (cerebrum)
- Cerebellum
- Spinal cord (Medulla Spinalis)
PNS components include:
- Ganglions:
  - Autonomic (sympathetic and parasympathetic) ganglia
  - Dorsal root (spinal or sensory) ganglia
- Nerves:
  - Cranial nerves (emerge from the brain)
  - Spinal nerves (emerge from the spinal cord)
- Nerve endings

Nervous System

The nervous system consists of a network of neurons and glial cells.
Both the CNS and PNS contain neurons and glial cells.

Features of Nerve Tissue

Nerve tissue contains neurons, neuroglia cells, and minimal connective tissue.
Neurons are separated from connective tissue by the blood-brain barrier.
Neurons do not undergo mitosis.
Neuroglia cells can divide through mitosis.

Origin of Nerve Tissue Cells

CNS neurons and central glial cells, except microglial cells, originate from neuroectodermal cells within the neural tube.
Microglial cells develop from mesodermal macrophage precursors, specifically from granulocyte/monocyte progenitor (GMP) cells in bone marrow.
PNS ganglion cells and peripheral glial cells originate from the neural crest.

Neuron

Cell body (Perikaryon, soma): Contains the nucleus and cytoplasm.
Projections:
- Dendrites: Multiple, receive stimuli.
- Axon: Single, conducts impulses away.
  - Synaptic boutons: Small swellings found at the terminal ends of axons.

Unmyelinated Axon

Multiple unmyelinated axons can be wrapped by the cytoplasm of a single Schwann cell.
While a Schwann cell can only myelinate one axon, it can envelop multiple unmyelinated axons.

Myelination of PNS Axons

A Schwann cell engulfs a portion along the length of a large diameter axon.
The Schwann cell membrane fuses around the axon, and a thin Schwann cell extension repeatedly wraps around it to form compacted layers, creating the myelin sheath.
The myelin sheath is rich in lipids and provides insulation for the axon, facilitating action potential formation along the axolemma.
Each Schwann cell is responsible for forming one internodal length of myelin.

Myelin Sheath Formation

The axon initially sits in a groove on the Schwann cell surface.
The Schwann cell completely surrounds the axon.
The mesaxon membrane initiates myelination by wrapping around the embedded axon.
The mesaxon membrane extends and wraps around the axon, forming multiple membrane layers.
During wrapping, cytoplasm gets pushed out between the Schwann cell membrane layers, and they become compacted to form myelin.

Schmidt-Lanterman (Myelin Cleft)

Axons enveloped by the myelin sheath contain some Schwann cell cytoplasm in spaces between the membrane layers, known as Schmidt-Lanterman clefts.
This cytoplasm moves along the myelin sheath, creating temporary spaces (clefts) for the renewal of membrane components, maintaining the sheath.

Nodes of Ranvier

Between adjacent Schwann cells on an axon, the myelin sheath shows small nodes of Ranvier (nodal gaps).
These gaps are specialized regions of the axonal membrane not insulated by myelin.
They act as partial barriers to the movement of materials into and out of the periaxonal space between the axolemma and Schwann cell sheath.

Myelination

Enables saltatory conduction.

Unmyelinated Axons

Small diameter axons are enclosed by the cytoplasm of one Schwann cell.
Each axon is separated and enclosed within its own fold of Schwann cell surface.
No myelin formation occurs through wrapping in this case.
These axons use action potentials that don't depend on the insulation provided by myelin, unlike larger axons.

Unmyelinated Nerve

In unmyelinated nerves, axons are surrounded by Schwann cell cytoplasm.

Astrocyte

Protoplasmic astrocytes are prevalent in the gray matter (outermost brain covering).
They have numerous and short branching cytoplasmic processes.
Fibrous astrocytes are more common in the white matter (inner core of the brain).
They have fewer and straighter processes than protoplasmic astrocytes.

Blood Brain Barrier

Allows tighter control of substances moving from blood into CNS tissue.
The main structural component of the BBB is capillary endothelium surrounded by the basement membrane.
Perivascular astrocytic feet that envelop the capillary basement membrane in most CNS regions contribute to the BBB.

Nerve Organization

Axons and Schwann cells are enclosed within layers of connective tissue:
- Endoneurium: A thin, protective layer of connective tissue surrounding each nerve axon.
- Perineurium: A connective tissue with a lamellar arrangement, enclosing nerve fascicles containing multiple axons.
  - Regulates diffusion into the fascicle.
  - Forms the blood-nerve barrier.
- Epineurium: The outermost layer of dense connective tissue encompassing the (peripheral) nerve.

Endoneurium

Thin, loose connective tissue rich in reticular fibers.
Mast cells, macrophages, and few fibroblasts are present.
Surrounds individual fibers.
In contact with the Schwann cell basal lamina.

Perineurium

Dense irregular connective tissue.
Surrounds a group of fibers (fascicles).
Specializes in contributing to the blood-nerve barrier.
Two or more cell layers thick.

Epineurium

Dense irregular connective tissue.
Surrounds the entire nerve from the outside.

Peripheral Nerve

Establishes communication between CNS centers and sense organs and effectors (muscles, glands).
Generally contain both afferent (sensory) and efferent (motor) fibers.
Nerve fibers:
- Afferent fibers: Convey information from the internal body and environment to the CNS.
- Efferent fibers: Carry impulses from the CNS to effector organs.

Ganglions

Ovoid structures.
Clusters of neuron cell bodies outside the CNS.
Surrounded by a connective tissue capsule.
Serve as relay stations for nerve impulse transmission.
Typically, one nerve enters and another exits each ganglion.
The direction of nerve impulse determines whether a ganglion is sensory or autonomic.

Ganglion Types

Sensory Ganglia:
- Dorsal root ganglia (Spinal Ganglia): Emerge from the spinal cord.
- Ganglia associated with cranial nerves (V, VII, VIII, IX, X): Emerge from the brain.
Autonomic Ganglia:
- Sympathetic chain ganglia
- Parasympathetic ganglia

Sensory Ganglia

Receive afferent impulses destined for the CNS.
Neurons here are pseudounipolar and relay information from the ganglion nerve endings to the spinal cord gray matter.
Satellite cells: Glial cells of ganglia arranged around neuron cell bodies.
Contains minimal connective tissue with blood vessels.

Autonomic Ganglia

Found within autonomic nerves.
Contain postganglionic visceral efferent neurons that receive synaptic input from preganglionic visceral efferent neurons.
Contain multipolar neuron cell bodies with eccentric nuclei.

Neuronal Injury Response

In the PNS, Schwann cells divide and dedifferentiate, disrupting the blood-nerve barrier along the injured axon.
This allows for the infiltration of monocyte-derived macrophages, which remove myelin debris.
This occurs quickly, promoting axon regeneration and restoration of the blood-nerve barrier.
In the CNS, disruption of the blood-brain barrier is limited.
This restricts the infiltration of macrophages, significantly slowing myelin removal.
Oligodendrocyte apoptosis, inefficient microglial phagocytosis, and astrocyte-derived scar formation impede nerve regeneration within the CNS.

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Description

Explore the key functions and anatomical organization of nerve tissue and the nervous system in this quiz. Understand how the central and peripheral nervous systems operate, including the roles of various components such as neurons and glial cells.