Nerve Tissue: Structure and Function

Questions and Answers

What is the external layer of gray matter in the brain called?

gyri

Which of the following types of neurons are found in the cerebrum?

Pyramidal cells (correct)

Granule cells (correct)

Purkinje cells

Fusiform cells (correct)

The most external layer of gray matter in the cerebellum is called the ______ layer.

molecular

What are the large neurons in the Purkinje cell layer called?

Purkinje cells Signup and view all the answers

What is the internal layer adjacent to the white matter in the cerebellum called?

granular layer Signup and view all the answers

White matter in the brain has more blood supply compared to gray matter.

False Signup and view all the answers

In which part of the central nervous system is white matter external to gray matter?

Spinal cord Signup and view all the answers

What are the two major components of nerve tissue?

Neurons and support cells (neuroglia or glial cells). Signup and view all the answers

Which of the following are functional categories of neurons? (Select all that apply)

Sensory Signup and view all the answers

What structure in neurons is responsible for protein synthesis, visible in the light microscope?

Nissl bodies. Signup and view all the answers

What is the typical resting membrane potential of a nerve cell?

-70 mV Signup and view all the answers

What are the two types of axonal transport?

Anterograde flow and retrograde flow. Signup and view all the answers

Dendrites are typically myelinated.

False Signup and view all the answers

Which of the following types of neurons has a single large process that branches?

Pseudounipolar neurons Signup and view all the answers

What type of synapses allow direct passage of ions from one cell to another?

Electrical synapses. Signup and view all the answers

Match the following types of chemical synapses with their functions:

Excitatory synapses = Depolarize the membrane Inhibitory synapses = Hyperpolarize the membrane Signup and view all the answers

What is the role of neurotransmitters at chemical synapses?

They bind to receptors on the postsynaptic cell to generate depolarization or hyperpolarization. Signup and view all the answers

What clinical conditions are associated with oligodendrocytes?

Oligodendrocytoma and multiple sclerosis. Signup and view all the answers

What is the function of astrocytes in the CNS?

Support and maintain the blood-brain barrier. Signup and view all the answers

How is the neurotransmitter reincorporated into vesicles?

By endocytosis Signup and view all the answers

What are acetylcholine broken down into in the synaptic cleft?

Acetate and choline Signup and view all the answers

Inhibition of the enzyme that breaks down norepinephrine has detrimental effects in the treatment of depression.

False Signup and view all the answers

What type of synapse is formed between an axon and a dendrite?

Axodendritic Signup and view all the answers

What is the specialized type of synapse called that represents the neuromuscular junction?

Motor end-plate Signup and view all the answers

The virus responsible for rabies is carried by wild ______.

mammals Signup and view all the answers

What do Schwann cells form around axons in the peripheral nerves?

Myelin sheath Signup and view all the answers

Match the cell types in the central nervous system (CNS) with their characteristics:

Astrocytes = Support for neurons and blood vessels Oligodendrocytes = Form segments of myelin sheath Microglial cells = Phagocytic properties to remove debris Ependymal cells = Line ventricles and produce cerebrospinal fluid Signup and view all the answers

Multiple sclerosis is caused by damage to the myelin sheath in the CNS.

True Signup and view all the answers

What is gliosis?

Formation of a glial scar Signup and view all the answers

What type of neuron do sensory craniospinal ganglia contain?

Pseudounipolar neurons Signup and view all the answers

What are the two major types of support cells in the peripheral nervous system (PNS)?

Schwann cells and satellite cells Signup and view all the answers

What do free nerve endings mediate?

Pain Signup and view all the answers

Which sensory nerve ending is sensitive to vibrations and deep pressure?

Pacinian corpuscle Signup and view all the answers

What is a primary function of the myelin sheath in neurons?

It allows electric impulses to travel rapidly through the axons. Signup and view all the answers

Which of the following best describes axons?

They are designed to carry signals from the perikaryon to other cells. Signup and view all the answers

What role do lysosomes play in neurons?

They maintain waste management and recycling of cellular materials. Signup and view all the answers

Which of the following statements about the cytoskeleton of neurons is true?

It includes a variety of filament types, including neurofilaments and microtubules. Signup and view all the answers

Which type of cell is primarily responsible for producing myelin in the peripheral nervous system?

Schwann cells Signup and view all the answers

What characterizes the processes of neurons?

Dendrites primarily convey signals toward the neuron cell body. Signup and view all the answers

Which statement about neuroblasts in the adult brain is accurate?

Only a few neuroblasts can divide and reproduce in small numbers. Signup and view all the answers

What is a key function of synapses in neurons?

They enable communication between neurons and other cell types. Signup and view all the answers

What is the primary function of inhibitory synapses in the postsynaptic cell?

To hyperpolarize the membrane potential Signup and view all the answers

What size are synaptic vesicles typically found in the presynaptic knob?

40-60 nm in diameter Signup and view all the answers

Which part of the neuron typically has receptor sites for neurotransmitters?

Postsynaptic membrane Signup and view all the answers

What initiates local depolarization in the postsynaptic cell?

Binding of neurotransmitters to receptors Signup and view all the answers

How is excess plasma membrane removed after synaptic vesicle fusion?

Via endocytosis with clathrin-coated vesicles Signup and view all the answers

What type of synapse primarily occurs on the perikaryon of neurons?

Inhibitory synapse Signup and view all the answers

What is the primary role of neurotransmitters in a synapse?

They bind to receptors and generate depolarization or hyperpolarization Signup and view all the answers

What occurs first when an action potential reaches the presynaptic terminal?

Opening of Ca++ channels Signup and view all the answers

What mechanism allows for the recapture of neurotransmitters in the synaptic cleft?

High-affinity reuptake Signup and view all the answers

What type of synapse is characterized by a connection between an axon and a perikaryon?

Axosomatic Signup and view all the answers

Which neurotransmitter is primarily broken down by enzymes in the synaptic cleft?

Acetylcholine Signup and view all the answers

What is the main effect of inhibiting the enzymes that break down norepinephrine?

It aids in the treatment of depression. Signup and view all the answers

Which of the following is NOT a morphotype of synapse?

Axotroponin Signup and view all the answers

What is the primary role of the motor end-plate in the neuromuscular junction?

To transmit signals between the muscle and nerve cell Signup and view all the answers

In the context of synaptic transmission, what does endocytosis refer to?

The reinternalization of neurotransmitters into vesicles Signup and view all the answers

Which of the following components of the nervous system primarily supports nerve fibers in the peripheral nervous system?

Schwann cells Signup and view all the answers

What is the primary function of dendrites in a neuron?

To deliver signals from the cell periphery to the cell body. Signup and view all the answers

Which statement accurately describes dendritic spines?

They have a mushroom shape and house postsynaptic receptors. Signup and view all the answers

Which characteristic distinguishes dendrites from axons?

Dendrites branch profusely while axons do not. Signup and view all the answers

What type of neuron is primarily associated with pseudounipolar neurons?

Sensory neurons involved in transmitting peripheral sensory information. Signup and view all the answers

What structural feature allows dendrites to increase their synaptic connection potential?

The branching nature forming a dendritic tree. Signup and view all the answers

Which component is NOT typically found in dendrites?

Golgi apparatus Signup and view all the answers

In terms of signal transmission, what is the role of the peripheral process of a pseudounipolar neuron?

To collect information from sensory areas. Signup and view all the answers

What distinguishes the surface of dendrites from axons?

Dendrites are covered with spines that increase surface area for synapses. Signup and view all the answers

Which of the following describes the role of Schwann cells in the peripheral nervous system?

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

Which type of cell in the central nervous system primarily functions in the repair of nervous tissue?

Astrocytes Signup and view all the answers

Which statement about excitatory chemical synapses is correct?

They enhance the likelihood of an action potential. Signup and view all the answers

What is the main function of astrocytes in the central nervous system?

To support and regulate neuronal activity. Signup and view all the answers

Which structure forms the gap between the presynaptic and postsynaptic neurons in a chemical synapse?

Synaptic cleft Signup and view all the answers

Which type of synapse is commonly associated with neurotransmitter release from axon terminals?

Axodendritic Signup and view all the answers

What is the primary characteristic of retrograde axonal transport?

It involves the movement of degraded materials back to the cell body. Signup and view all the answers

Which type of neuron is commonly involved in sensory pathways and has one main process that splits into two branches?

Pseudounipolar neurons Signup and view all the answers

Study Notes

Characteristics of Nerve Tissue

Provides rapid, specific communication between body organs.
Comprises two major components: neurons (electrically excitable) and neuroglia (support cells).
Average human body contains about 100 million neurons.

Functional Categories of Neurons

Sensory Neurons: Gather information from receptors.
Interneurons: Form communication networks between neurons.
Motor Neurons: Convey impulses from the nervous system to effector cells.

Structure of Neurons

Contain a large, rounded nucleus with a prominent nucleolus.
Perikaryon (cell body) size ranges from 5 to 135 µm.
Well-developed rough endoplasmic reticulum (RER) forms Nissl bodies visible in light microscopy.
Well-developed Golgi complex for membrane and neurotransmitter production.
High mitochondrial content for energy; may lack centrioles, limiting cellular division.

Cell Processes of Neurons

Neurons have two types of processes: axons and dendrites.
Synapses are formed for communication with other cells.

Axon Structure and Function

Each neuron has one axon, designed to convey signals from the perikaryon.
Axons can be very long (up to 1 meter), maintaining consistent diameter.
Initiate from the axon hillock, which lacks Nissl bodies.
Myelin sheath insulates many axons, facilitating rapid impulse transmission.

Axonal Transport

Microtubules involved in transport within axons.
Anterograde Flow: Materials move from perikaryon to axon terminal; consists of fast and slow axonal transport.
- Fast Transport: Up to 100-400 mm/day, for organelles and synaptic vesicles.
- Slow Transport: ~1-6 mm/day, for structural proteins.
Retrograde Flow: Moves materials from axon terminal back to perikaryon, utilized by viruses and toxins.

Dendrites

Typically several per neuron, designed to receive signals.
Form extensive dendritic trees for increased synaptic contact area.
Surface covered with dendritic spines where synapses form.
Cytoplasmic composition similar to perikaryon, includes ribosomes and RER.

Major Types of Neurons

Pseudounipolar Neurons: Sensory neurons with a single process that bifurcates into peripheral and central branches.
Bipolar Neurons: Found in sensory organs, have one axon and one dendrite.
Multipolar Neurons: Most common type; includes one axon and many dendrites, subclassified into:
- Golgi type I cells (long axons, motor neurons).
- Golgi type II cells (short axons, interneurons).

Electrophysiology of Nerve Tissue

Nerve cells exhibit an electric membrane potential (~ -70 mV at rest).
Action potentials are rapid positive changes in membrane potential, propagating at speeds up to 120 m/sec.
Depolarization occurs with Na+ influx, hyperpolarization makes depolarization more difficult.

Types of Synapses

Electrical Synapses: Represented by gap junctions, allowing direct ion transfer.
Chemical Synapses: Predominant in mammals, convey signals via neurotransmitter release.

Chemical Synapse Structure

Presynaptic Knob: Contains synaptic vesicles housing neurotransmitters.
Synaptic Cleft: Narrow gap (~20 nm) between pre- and postsynaptic cells.
Postsynaptic Membrane: Contains receptors for neurotransmitters, which trigger depolarization or hyperpolarization.

Morphotypes of Synapses

Axodendritic: Connection between axon and dendrite.
Axosomatic: Connection between axon and neuron body.
Axoaxonic: Connection between two axons.
Motor End-Plate: Specialized synapse between motor neurons and muscle cells, featuring junctional folds.

Clinical Comments

Various toxins, such as curare and botulinum toxin, inhibit synaptic function and muscle depolarization, showcasing the importance of chemical synapses in bodily function.

Support Cells

PNS Support Cells:
- Schwann Cells: Form myelin sheath; create Nodes of Ranvier.
- Satellite Cells: Support ganglia.
CNS Support Cells:
- Astrocytes: Maintain blood-brain barrier, respond to CNS injuries (astrocytoma, glial scar).
- Oligodendrocytes: Form myelin sheath; involved in pathologies like oligodendrocytoma and multiple sclerosis.
- Microglial Cells: Act as immune cells in CNS.
- Ependymal Cells: Line ventricular cavities in the brain.

Peripheral Nervous System Structure

Nerves:
- Endoneurium: Surrounds individual nerve fibers.
- Perineurium: Encloses bundles of fibers.
- Epineurium: Outer layer of nerve.
Ganglia:
- Sensory craniospinal ganglia and autonomic ganglia.
Special Ending Nerve Types:
- Meissner’s corpuscle (touch) and Pacinian corpuscle (pressure).
- Proprioceptors like muscle spindle.

Central Nervous System Structure

Distinction between gray matter (neuronal cell bodies) and white matter (myelinated axons).### Curare Toxin
Originally used by South American Indians for hunting.
Binds to acetylcholine receptors as a muscle relaxant.

Botulinum Toxin

Produced by the bacterium Clostridium botulinum, functioning as a neurotoxin.
Prevents the release of acetylcholine from synaptic vesicles.
Botox is a cosmetic application of botulinum toxin, used to relax facial muscles.

Autoimmune Diseases

Diseases such as myasthenia gravis impact neuromuscular junctions, leading to extreme muscle weakness.
Autoantibodies target acetylcholine receptor proteins, weakening muscle responses to nerve stimuli.

Rabies Virus Transmission

Carried by wild mammals like skunks and raccoons; transmitted via bites.
Virus replicates in muscle tissue for 1-2 weeks, during which vaccination can be effective.
After replication, the virus reaches the motor neurons, spreading through retrograde axonal transport.
Most of the CNS becomes affected, causing severe inflammation and seizures, also known as hydrophobia.
Ultimately spreads to salivary glands for transmission between animals; no cure is available after symptoms appear.

Support Cells of the Nervous System

Peripheral Nervous System (PNS)

Composed of Schwann cells and satellite cells.
Schwann Cells: Form myelin sheath around axons, providing insulation for rapid impulse conduction.
- Nodes of Ranvier formed by gaps in myelin sheath facilitate saltatory conduction.
- Envelop unmyelinated axons; action potentials in these fibers propagate in a wave-like manner.
Satellite Cells: Surround neuron cell bodies in ganglia, offering electrical insulation and supporting metabolic exchange.

Central Nervous System (CNS)

Contains astrocytes, oligodendrocytes, microglial cells, and ependymal cells.
Astrocytes: Largest neuroglial cells, offering structural support, forming the blood-brain barrier, and involved in metabolic substance transport.
- Two types: Protoplasmic (in gray matter) and Fibrous (in white matter).
- Astrocytomas are common tumors arising from astrocytes.
Oligodendrocytes: Smaller neuroglial cells that myelinate axons in the CNS.
- Resemble Schwann cells but form multiple segments of the myelin sheath.
- Damage to myelin sheath is a hallmark of multiple sclerosis.
Microglial Cells: Small phagocytic cells that increase in number with injury, believed to aid in debris removal.
- Associated with Alzheimer's and Parkinson's diseases due to their role in plaque formation and demyelination.
Ependymal Cells: Line ventricles and spinal cord cavities, responsible for cerebrospinal fluid (CSF) production and absorption.
- Have microvilli and cilia to aid in CSF absorption.

Peripheral Nervous System Structure

Comprises cranial, spinal, and peripheral nerves, ganglia, and special nerve endings.
Nerves consist of myelinated and non-myelinated fibers, maintained by connective tissue layers:
- Endoneurium surrounds individual fibers.
- Perineurium surrounds nerve fascicles.
- Epineurium encloses entire nerves.

Ganglia Types

Clusters of neuron cell bodies outside the CNS, encapsulated by connective tissue.
Sensory Craniospinal Ganglia: Contain pseudounipolar neurons with processes extending to receptors and CNS.
Motor Ganglia: Part of the autonomic nervous system, consisting of multipolar neurons.

Sensory and Motor Endings

Motor End-plates: Specialized endings in skeletal muscles.
Sensory Nerve Endings:
- Special Senses: Responsible for smell, sight, hearing, and equilibrium.
- Somesthetic Receptors: Distributed throughout the body; include free nerve endings for pain and encapsulated endings like Meissner’s and Pacinian corpuscles.
  - Meissner’s Corpuscle: Provides touch sensation, located in skin of fingers and toes.
  - Pacinian Corpuscle: Largest encapsulated sensory ending, detects vibrations and deep pressure.

Proprioceptors

Collect information about joint angulations and muscle tension.
Muscle Spindle: Specialized stretch receptor in skeletal muscle, containing intrafusal fibers surrounded by sensory and motor nerve fibers.

Central Nervous System Organization

Composed of the spinal cord and brain, with clusters of neurons known as nuclei and organized nerve fibers into tracts.
Gray Matter: Contains neuron bodies and unmyelinated fibers; vascularized by capillaries.
- In the spinal cord, gray matter is internal; organized into anterior (ventral) and posterior (dorsal) horns.
- In the brain, gray matter is external and features folds (gyri).
White Matter: Composed of myelinated axons and fewer glial cells; denser with limited blood supply, and organized oppositely in the brain compared to the spinal cord.

Neurotransmitter Deactivation

Released neurotransmitters are deactivated mainly through recapture and degradation.
High-affinity reuptake allows up to 80% of catecholamines (e.g., dopamine, norepinephrine) to be recaptured into vesicles via endocytosis.
Enzymes on the synaptic membrane break down remaining neurotransmitters; for instance, acetylcholine is converted into acetate and choline.
Inhibiting norepinephrine breakdown or high-affinity reuptake is beneficial for depression treatment.

Morphotypes of Synapses

Axodendritic synapses connect axons to dendrites.
Axosomatic synapses link axons to neuron bodies (perikaryon).
Axoaxonic synapses connect one axon to another axon.
Motor end-plates are specialized synapses at neuromuscular junctions, containing presynaptic vesicles with acetylcholine.
Type II inhibitory synapses hyperpolarize postsynaptic cells, reducing action potential likelihood.

Chemical Synapses

Presynaptic knobs contain synaptic vesicles (40-60 nm), rich in neurotransmitters.
Over 100 known neurotransmitters can induce depolarization or hyperpolarization, acting as either excitatory or inhibitory.
The synaptic cleft is a narrow (~20 nm) gap between presynaptic and postsynaptic membranes.
Action potential triggers calcium channel opening, facilitating neurotransmitter release into the synapse.
Endocytosis removes excess plasma membrane after neurotransmitter release.

Dendrites

Dendrites are numerous, short, tapered processes designed to convey signals toward the perikaryon.
Dendritic trees can have up to 200,000 synapses, maximizing synaptic contact area.
Dendritic spines, shaped like mushrooms, host most postsynaptic receptors.
Dendrites lack myelin and contain ribosomes and rough endoplasmic reticulum but no Golgi apparatus.

Major Types of Neurons

Neurons can be classified as pseudounipolar, bipolar, or multipolar based on shape and process number.
Pseudounipolar neurons are primarily sensory, with one large process branching into peripheral and central processes that transmit sensory information to the central nervous system.

Axonal Transport

Axonal transport occurs in two directions: anterograde (moving materials away from the cell body) and retrograde (moving materials toward the cell body).
Anterograde transport includes both fast and slow transport mechanisms.

Neuron Structure

Neurons feature distinct structures: one axon per cell, dendritic processes, and axon terminals.
Axons vary in length (up to 1 meter), maintain a constant diameter, and lack Nissl bodies at the axon hillock.
Myelinated axons enhance signal transmission speed, while myelin sheath formation abnormalities can lead to disorders.

Cytoskeleton of Neurons

Neuronal cytoskeleton is well-developed, consisting of neurofilaments, microfilaments, and microtubules.
Neurons generally lack centrioles, preventing cellular division, with limited neuroblast replacement in adults, notably in olfactory neurons.

Support Cells in Nervous System

Peripheral nervous system support cells include Schwann cells (involved in myelination) and satellite cells.
Central nervous system support cells encompass astrocytes (with multiple types), oligodendrocytes, microglial cells, and ependymal cells, each with distinct functions and clinical relevance.

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Description

This quiz focuses on the characteristics and structure of nerve tissue, including neurons and their processes. You will be tested on your ability to identify nerve tissue in various specimens and understand its functional properties. Prepare to describe the intricacies of neurons, including dendrites and axons.