Lec 15 - Nervous Tissue Flashcards
What is the basic structural unit of nervous tissue?
The neuron is the basic unit of structure in nervous tissue.
Describe the primary function of a neuron.
A neuron receives stimuli from internal (interoceptive) and external (exteroceptive) environments and transmits information to effector organs.
Which two characteristics make neurons highly specialized?
Neurons are highly specialized for irritability (responsiveness to stimuli) and conductivity (signal transmission).
What structures enable neurons to conduct signals?
Neurons conduct signals through well-developed cellular processes, including dendrites and axons.
How do neurons communicate with each other?
Neurons communicate through synapses, which are functional contact points between neurons and their processes.
What is the role of neuroglia?
Neuroglia are supporting cells of the nervous system that provide protection, nutrition, and structural integrity to nervous tissue.
What is the origin of a neuron?
Each neuron originates from an embryonic stem cell called a neuroblast.
Do neurons have structural continuity?
No, neurons are separate and distinct units that make contact with each other but lack structural continuity.
What forms the conduction mechanism of the nervous system?
Chains of neurons form the conduction mechanism, allowing signal transmission.
What are the main components of a neuron?
A neuron consists of a cell body (cyton, soma, perikaryon) and processes (dendrites and axon).
What are the two functional classifications of neurons?
Neurons can be classified as transmission (conducting) neurons and neurosecretory neurons based on function.
What are transmission (conducting) neurons?
Transmission neurons make up the majority of neuronal types and consist of dendrites, a cell body, and an axon.
How are transmission neurons further classified?
They are classified into:
• Golgi Type I Neurons – Have numerous dendrites and a very long axon.
• Golgi Type II Neurons – Have numerous dendrites and a short axon.
Give examples of Golgi Type I neurons.
Examples include:
• Ventral horn cells of the spinal cord gray matter
• Sympathetic and parasympathetic preganglionic neurons
• Sympathetic postganglionic neurons
Give examples of Golgi Type II neurons.
Examples include:
• Interneurons
• Pyramidal cells of the cerebral cortex
• Purkinje cells of the cerebellar cortex
What are neurosecretory neurons?
Neurosecretory neurons are specialized nerve cells that synthesize, transport, and release hormones into the blood.
How do neurosecretory neurons transport hormones?
They transport hormones via Herring bodies, which are large axon dilatations containing neurosecretory vesicles.
Give an example of neurosecretory neurons and their function.
The neurosecretory cells of the hypothalamus secrete oxytocin and antidiuretic hormone (ADH) into the neurohypophysis (posterior pituitary).
How are neurons classified based on morphology?
Multipolar Neurons:
- Have numerous dendritic processes.
Examples: Golgi Type I and Golgi Type II neurons.
Bipolar Neurons:
- Have one dendrite and one axon located at opposite poles of the cell body.
- Found in areas responsible for special visceral and somatic sensation.
Unipolar (Pseudounipolar) Neurons:
- Have an axon and a dendrite fused near the cell body but separating at a distance.
- Both processes structurally resemble axons.
- Common in cranial and spinal ganglia.
What are the functional relationships of the components of neurons?
• Dendrites: Become stimulated and carry information toward the cell body.
• Axon: Carries information away from the cell body.
• The information is then transferred to the next neuron or effector organ.
What are the key features of a neuronal cell body?
- The nucleus is large, pale, and centrally located within the cytoplasm.
- The cytoplasm (perikaryon) contains filamentous, membranous, and granular organelles arranged concentrically around the nucleus.
What are the major organelles found in the cytoplasm of neuronal cell bodies?
Neurofibrils
Nissl Bodies
Golgi Apparatus
Mitochondria
Centrosome
Other Organelles (SER, lysosomes)
Inclusions (melanin granules, lipofuscin, lipid droplets, secretory granules)
What are neurofibrils?
Neurofibrils are slender, interlacing threads that form the cytoskeleton of the neuron.
They consist of microtubules, intermediate filaments, neurofilaments, and microfilaments (actin) and extend throughout the cytoplasm to connect dendrites and axons.
What are Nissl bodies?
Nissl bodies are basophilic materials in the perikaryon that contain ribonucleic acids (RNA).
They are associated with protein synthesis and are abundant in the cytoplasm, particularly in dendrites but absent in the axon hillock and axis cylinder.
The role of the Golgi apparatus in neurons?
The Golgi apparatus produces secretory vesicles and synaptic vesicles, which contain transmitter molecules.
What is mitochondria in neurons?
Mitochondria in neurons are smaller than those in non-nervous tissue.
Describe centrosome
The centrosome contains a pair of centrioles. However, since neurons do not proliferate, its role in adult neurons is unclear.
What are some other organelles found in the neuronal cytoplasm?
Other organelles include the smooth endoplasmic reticulum (SER) and lysosomes, which contribute to the metabolism and maintenance of the neuron.
What are inclusions in the neuronal cytoplasm?
Inclusions in neurons can include melanin granules, lipofuscin, lipid droplets, and secretory granules.
Explain the structure and function of the axon.
The axon is a single, long process with a smooth surface and uniform diameter. It branches extensively as the telodendrion before its termination on the effector.
What is the role of dendrites in neurons?
Dendrites are cellular processes that increase the surface area. The surface of these processes as well as that of
the cell body, are covered with numerous spines or gemmules which represent the synaptic connections
with axon terminals of nerve cells.
What is the function of neuroglia in the central nervous system (CNS)?
Neuroglia serve as the connective and supportive tissue of the CNS, protecting and nourishing the neurons.
What is neuropil?
Neuropil refers to the interwoven cytoplasmic processes of neurons and neuroglial cells in the CNS.
Which is the most numerous neuroglial cell in the CNS, and what are its functions?
Oligodendrocytes are the most numerous neuroglial cells in the CNS.
Their functions include:
- nourishing neurons
- producing myelin
- becoming phagocytic if needed.
What are the two types of astrocytes, and where are they abundant?
Fibrous astrocytes
- Have long unbranched processes, less cytoplasm, and are abundant in the white matter.
Protoplasmic astrocytes
- Have short branched processes, more cytoplasm, and are abundant in the gray matter.
List two major functions of astrocytes.
- Provide structural support to the CNS.
- Repair nervous tissue defects and form CNS scars.
What is the function of ependymal cells, and where are they found?
Ependymal cells line the neural canal and brain ventricles.
Function:
- producing cerebrospinal fluid (CSF)
- aiding in transport and secretory activities.
What are tanycytes, and how do they differ from regular ependymal cells?
Tanycytes are non-ciliated ependymal cells found on the walls of the ventricular system, unlike regular ependymal cells, which are ciliated.
Why are amphicytes not considered true neuroglia?
Amphicytes are found in the peripheral nervous system (PNS), surrounding ganglion cells, whereas true neuroglia are found in the CNS.
What is the role of Schwann cells in the PNS?
Schwann cells produce myelin to insulate nerve fibers in the PNS and can become phagocytic if nerve damage occurs.
Where are Muller cells found?
Muller cells are associated with neurons in the retina.
What is the origin and primary function of microgliocytes?
Microgliocytes originate from the bone marrow and act as macrophages in the CNS, performing phagocytic functions during minor injury.
What happens in case of extensive CNS injury regarding microgliocytes?
In case of extensive injury, phagocytic cells from the blood migrate to the CNS to perform phagocytic functions.
What is the function of amphicytes in neurons?
Amphicytes provide cellular investment for ganglion cells.
Which cells form the sheath of Schwann, and what is its alternative name?
Schwann cells form the sheath of Schwann, also known as the neurolemmal sheath.
What are mesaxons in unmyelinated nerve fibers?
Mesaxons are the juxtaposed plasmalemmal components of the Schwann cell that encircle the axis cylinder.
What type of nerve fibers have slow impulse-conducting speed?
Unmyelinated nerve fibers have relatively slow impulse-conducting speed.
Which cells produce the myelin sheath in the PNS and CNS?
In the PNS, Schwann cells produce myelin, while in the CNS, oligodendrocytes produce myelin.
What is neurokeratin, and where is it found?
Neurokeratin is the nonlipid component of the myelin sheath.
Describe how the myelin sheath is formed around the axon.
- The cytoplasm of the Schwann cell surrounds the axon, thus the axon occupies an invagination in the
Schwann cell. - The Schwann cell then begins to rotate around the axon. During this rotation, the cell membrane
lining one side of the groove in which the axon lies comes into contact with the cell membrane that lines
the other side of the groove. - As the winding continues, the cytoplasm is squeezed back forward the cell body of the Schwann cell
or lost in some other way. - Accordingly, the myelin sheath evolved from 2-layered rings of the cell membrane.
What are the major dense lines in electron micrographs of myelin?
Major dense lines represent the apposition of the inner (cytoplasmic) processes of the Schwann cell unit membrane.
What is represented by the intraperiod lines in myelin?
Intraperiod lines represent the union of the outer surfaces of the Schwann cell unit membrane.
What are Schmidt-Lantermann incisures?
These are oblique cone-shaped discontinuities in the myelin, representing local separations of the spirally wrapped myelin lamellae.
