Histology - Nervous Tissue Flashcards
End bulbs (terminal boutons)
Axon terminal
Perikaryon
Cell body of a neuron
Nissles bodies
= RER + polyribosomes
Basophilic material
Axon hillock
- RER is absent
- Highest concentration of sodium (Na+) gates/ channels
- Pyramidal-shaped region of the soma
Hypolemma cisterna
- SER extending from the axons to the dendrites
- Continous with RER of the cell body and weave between nissls bodies
Golgi complex
Responsible for the packaging of neurotransmitter substances or enzymes essential for their production in the axon
Mitochondria
- Most abundant at the axon terminals
- More slender in neurons
Centriole
- Most adult neuron display one centriole associated with a basal body of a cilium
- Possesses the 9+0 arrangement in microtubules
- Believed to be vestigial structures
Melanin granules
- CNS:
> Substantia nigra
> Locus ceruleus
> Dorsal motor nucelus of the vagus and the spinal cord
- PNS:
> Sympathetic gangliaWhat is the precusor of the melanin granules?
Dihydroxyphenylalanine (DOPA)/methyldopa
Inclucions
- Melanin
- Lipofuscin pigments
- Lipid droplets
Lipofuscin
- Irregulary shaped, yellowish brown pigment granule
- Remant of lysosomal activity
- Increase in number with age
- May crowd the organelles and the nucleus to one side, possibly affecting cellular funtion
- Purkinjie cellsof the cerebellar cortex do not accumulate lipofuscin
Give an example of a cell that does not accumulate lipofuscin?
Purkinjie cells of cerebellar cortex
Lipid droplets
- Observed in neuronal cytoplasm
- May be the result of faulty metanolism or from energy reserves
- Secretory granules are observed in neurosecretory cells; many of them containing signaling molecules.
Secretory granules
Observed in neurosecretory cells; many of them containing signaling molecules
Neuronal cytoskeletal components;
- Exhibit neurofibrils
- 3 filamentous structures:
- Microtubules (MAP-2 and MAP-3)
- Neurofilaments (clumped bundles of neurofilaments)
- Microfilaments (actin filaments)
Dendrites
- Do not contain golgi complex
- Neurofilaments are reduced to small bundles or single filaments, which may be cross-linked to microtubules.
- Mitochondria is abundant
- Some dendrites have spines which permit them to form synapses with other neurons
- Sometimes the dendrites contain vesicles and transmit impulses to other dendrites.
Spines
- Located on the surface of some dendrites
- Permit them to form synapses with other neurons
- Diminish woth age and poor nutrition
Collateral branches
Arise at right angles from the axon trunk.
Terminal arbor
Small branches of the axon terminals
Initial segment =
Spine trigger zone
Axolemma
- Plasmalemma of the axon
- Lacks RER
- Houses abundant microtubules and neurofilaments
Myelin sheath
Surround some axons in poth CNS and PNS
What is the precusor of the neurotransmitters dopamine and noradrenaline?
Dihydroxyphenylalanine (DOPA)/methyldopa
Unmyelinated axon
Axons lacking myelin sheath
Myelinated axon
Axons surroundednby myelin sheath
Axonal transport
Transport of materials between the soma and the axon terminals
Anterograde transport
- Transport of materials from the cell body to the axon terminals.
- Translocation of organelles and vesicles as well as macromolecules such as:
> Actin
> Myosin
> Clathrin
> Some enzymes necessary for neurotransmitter synthesis at the axon terminals
Retrograde transport
- Transport of materials from the axon terminals to the cell body
- include;
> Protein building blocks of neurofilaments
> Subunits of microtubules
> Soluble enzymes
> Materials taken by endocytosis (e.g. viruses, toxins)
Horseradish peroxidase
Enzyme used for axonal retrograde transport.
Tubulin dimers
- Reaches the axoplasm via anterograde transport
- Are assembled onto the microtubules at their plus end and depolarized at their minus end.
Kinesin
- Involve in the anterograde mechanism because one end attaches to a vesicle and the other end interact in a cyclical fashion with a microtubule, thus permitting the kinesin to transport the vesicle.
- A microtubule-associated protein.
Dynein
- Microtubule associated protein
- Responsible for moving vesicles along microtubules in retrograde transport.
Where is the bipolar neurons located?
In the vestibular and the cochlear ganglia and in the olfactory epithelium of the nasal cavity
What does the unipolar neurons develop from?
The unipolar neurons develop from the bipolar neurons
Which neurons are the most common?
Mutlipolar neurons
What kinds of neurons are the purkinji cells?
Multipolar neurons
What kind of neurons are the pyramidal cells?
Multipolar neurons
Motor (efferent) neurons and interneirons are….?
Multipolar neurons
Which cells undergo mitosis?
- Neuroglia;
> Astrocyte
> Oligodendrocyte
> Microglia
> Ependymal cells
> Schwann cellsWhich neuroglial cells are in the CNS?
> Astrocyte
> Oligodendrocyte
> Microglia
> Ependymal cells
Which neuroglial cells are in the PNS?
Scwann cells
Gray matter in the CNS
Protoplasmic astrocyte
White matter in the CNS
Fibrous astrocytes
Unique to astrocytes
Glial fibrillar acidic protein
Protoplasmic astrocyte
- Stellate cells
- Have pedicles (vascular) feet that come in contact with blood vessles
- ## Other protoplasmic astrocyte near the brain or surface of the spinal cord exhibit pedicletipped process that contact the pia mater, forming the pia-glial membrane
Fibrous astrocyte
- Possess a euchromatic cytoplasm
- Few organelles, free ribosomes, and glycogen
- long and mostøy unbranched processes. These processes are closely associated with the pia mater and blood vessles but are separated by these structures by their own basal lamina.
Astrocyte functions
- function in scavenging(remove) ions, neurotransmitters, and remants of neuronal metabolism
- Assist in the maintaining the blood-brain barrier
- Are recruited to damaged areas of the CNS, where they form cellular scar tissue.
Which cells forms the cellular scar tissue?
Astrocytes
Which cell does the oligodendrocye resemble?
Astrocytes
Oligodendrocytes
- Resemble astrocyte
- Darkest-staining neuroglial cell
- Located in both gray matter and white matter of the CNS
- Microtubules are present
Which two types of oligodendrocytes do we have?
- Interfascicular oligodendrocytes
2. Satellite oligodendrocyte
CNS: white matter and gray matter
In the fresh state the myelin sheath imprats a wite appearance to the axon.
Interfascicular oligodendrocytes
- Located in budles beside the axons
- Responisible for manufacturing and maintaining myelin about the axon of the CNS
- A single oligodendrocyte wraps around ceveral axons
- Particapate in myelination of nerve fibers in the brain
Satellite oligodendrocytes
- Closely applied to cell bodies of large neurons
- Function: not clear
Microglial cells
- Resemble oligodendrocyte
- Oval to triangular nuclus
- Spines
- Protect the nervous system from viruses, microorganisms, and tumour formation.
- They act like antigen-presenting cells and secrete cytokinese
- Derive from the bone marrow and are part of the mononucelarphagocytotic cell population.
Where do the neuroglial cells dervie from?
The neuroglial cells derive from the neural tube, exept for the microglial cells which derive from the bone maroow
Ependymal cells
=> Ependymocytes
- low columnar to cuboidal cells linind the ventricles of the brain and the central cana of the spinal cord.
- Derived from embryonic neuroepithelium of the developing nervous.
- Cytoplasm: abundant mitochondria, intermediate fillaments
- Can be ciliated -> to facilitate the movement of the cerebrospinal fluid
- Forms the internal limiting memebrane lining the ventricles.
- Froms the external limiting membrane beneath the pia mater. Both formed by fused pedicles.
- Participate in the fomration of the choroid plexus
- Tanycytes
Internal limiting membrane
Lines the ventricles
External limiting membran
- Beneath the pia mater
- Formed by fused pedicles
Pia mater and the external limiting membrane is formed by…?
Fused pedicles
Tanycytes
- Specialized ependymal cells
- Extend processes into the hypothalamus, where they terminate near blood vessles and neurosecretory cells.
- Tanycytes transport CSF to these neurosecretory cells, and possibly under the control from the anterior lobe of the pituitary, may respond to changes in hormone levels in the CSF by discharging secretory products in the capillaries.
Schwann cells
- In the PNS
- Form either myelinated or unmyelinated coverings
Myelinated nerves
Axons that have myelin wrapped around it
Nodes of ranvier
Interruptions on the myelin sheath at regular intervals along the axon, exposing the axon.
What is covered by a basal lamina?
Nodes of ranvier and the Schwann cells
Internodal segments
Areas of the axon covered in concentretic lamellae of myelin and the single Schwann cell that produced the myelin.
Clefts (incisures) of Schmidt-Lanterman
Oblique clefts in the myelin sheath of each internodal segment
Major dense line
Represent the fused cytoplasmic surfaces of the Schwann cell plasma membrane
Intraperiod line
Represent the apposing outer leaflets of the Schwann cell plasma membrane
Intraperiod gaps
- Small gaps within the period line.
- Provide access for small molecules to reach the axon
Internal mesaxon
The region of the intaperiod line that is in intimate contact with the axon
Extrenal mesaxon
The outermost aspect of the intraperiod line, which is in contact with the bidy if the Schwann cells
Myelination
Process whereby the Scwanncells(in PNS) or the Oligodendrocyte (CNS) concentrically wraps around the axon to form the myelin sheath
How many axons can a Schwann cell myelinate?
Myelinate one internode of a single axon and only in the PNS
How many axons can an oligodendrocyte myelinate?
Can myelinate an internode of several axons and only in the CNS
When are the motor almost muelinated completely?
At birth
When are sensory roots myelinated?
Several months after birth
How many unmyelinated axons may be envelpoed by a single Schwann cell?
Several
Resting potential
- It is about -90 mV
- The inside of a cell is less positive thatn the outside
Refractory period
When the Na+ channles are inactive
Read 198-200
About the “generation and conduction of nerve impulses”
Electrical synapses
- Uncommon in mammals
- Present in the retina and cerebral cortex
- Presented by gap junctions that permit free movements of ions from one cell to another
- Faster than chemical synapses
Chemical synapses
- Gated ion-channel rceptors
- Slower than electrical synapses
Neurotransmitter
- Signaling molecules that act as “first messenger systems”
- Diffuse across the synaptic cleft to gated ions-channel receptors.
- They only activate the response. They do not accomplish the reaction events at the postsynaptic membrane.
Excitatory postsynaptic potential
- Action potential
Inhibitory postsynaptic potential
- Maintainance of a membrane potential or increasing its hyperpolarization.
Axodendric synapse
Synapse between an axon and a dendrite
Synapse between an axon and a spine(which is from a dendrite)
Axosomatic synapse
Synapse between an axon and a soma
Axoaxonic synapse
Synapse between two axons
Dendrodendric synapse
Synapse between two dendrites
Synapsin-I
- Small protein that forms a complex with the vesicle surface.
- Appearsnto assistin the clustering of synaptic vesicles held in reserve
What happens when synapsin-I is phosphorylated?
The synaptic vesicles become free to move to the active zone in prepraration for release of the neurotransmitter.
What happens when the synapsin-I is dephosphorylated?
The results of the phosphorylation will be reversed
Synaptotagmin and synaptophysin
- Synaptic vesicle proteins that control the docking of the synaptic vesicles with the presynaptic membrane
What causes the synaptic vesicles to fuse with the presynatpic membrane, emptrying neurotransmitter into the synaptic cleft via exocytosis?
Ca2+ influx undr the influence of SNARE (SNAP receprot) proteins.
Including synaptobrevin, syntaxin, and soluble N-ethylmaleimide-sensetive fusion protein attachment protein-25 [SNAP-25]
Interactions between synaptotagmin and vesicle coat protein AP-2
Involves in recyclin of synaptic vesicles
Synaptobrevin
The synapstic vesicle protein
Asymmetric synapse
Is usually the site of exitatory responses
Symmetric synapse
Usually the site of inhibitory responses
Neuromodulators or neurohormones
Signaling molecules thatn invoke “second messenger system”
Neurotransmitters
Signaling molecules that act as “first messenger systems”
Neurotransmitters (and neuromodulators) are represented by the following 3 groups;
- Small-molecule transmitters
- Neuropeptides
- Gases
Small-molecule transmitters are of 3 major types:
- Acetylcholine
- The aminoacids
- Biogenic amines
Acetylcholine
- Not an aminoacid derivate
- Small-molecule transmitter
Aminoacids
- Glutamate
- Aspartate
- Glycine
- “Gamma”-aminobutyric acid (GABA)
- Small-molecule transmitter
Biogenic amines
- Monoamines
- Serotonin
- 3 catecholamines;
- Dopamine
- Norepinephrine (noradrenaline)
- Epinephrine (adrenaline)
- Small-molecule transmitter
Neuropeptides
- Neuromodulators
- Include:
- Opioid peptides
- Gastrointestinal peptides
- Hypothalamic releasing hormones
- Hormones
Opioid peptides
- Enkephalins
- Endorphins
Gastrointestinal peptides
- Produced by cells of the diffuse neuroendocrine system.
> Substance P
> Neurotestin
> Vasoactive intestinal peptides
Hypothalamic-releasing factor
E.g:
> Thyrotrompin releasing hormone
> Somatostatin
Hormones
Stored in and released from the neurohypophysis (antiduretic hormone and oxytocin)
Gases
May act as neuromodulators. The ones that do are:
- Nitric oxid (NO)
- Carbon monoxide (CO)
Epineurium
- The outermost layer of the connective tissue investment covering nerves.
- Composed of: dense, irregular, collagenous connecitve tissue containing thick elastic fibers.
Perineurium
- The middle layer of connective tissue investmen.
- Cover each bundle of nerve fibers.
- Composed of dense connective tissue but is thinner than epineurium.
- It inner suraface is covered byseveral layers of epitheloid cells joined by zonulae occuludentes and surrounded by basal lamina that isolates the neuronal enviroment.
- There are sparse collagen fibers between the layers of epitheloid cells adn interwined with a few elastic fibers
Where can we find epitheloid cells?
Perineurium
Endoneurium
- Innermost layer of the three connective tissue investememt of a nerve
- Surrounds individualnerve fibers (axons)
- A loose connective tissue composed of a thin layer of reticular fibers (produced by undrlyibg Schwann cells), scattered fibroblasts, fixed macrophages, capillaries, and perivascular mast cells in extracellular fluid.
- The endoneurium is in contact with the basal lamina of the Schwann cells
- Isolated from the perineurium and Schwann cells
Mixed peripheral nerves
=> spinal nerves
- Carry both sensory and motor fibers
Salatory conduction
- Is when the action potential jumps from node to node.
- Occure in myelinated fibers
Continous conduction
- Is slower and requires more energy than the salatory conduction
- Occure in unmyelinated fibers
Which cranial nerves contains somatic efferent components?
- III
- IV
- VI
- XII
Excluding those nerves supplying muscles of brachiomeric origin
What nerves provide the motor innervation for the skeletal muscles?
The somatic nerves
What nerve provide motor innervation for smooth muscle and cardiac muscle and supply secretomotor innervation to glands?
Autonomic nerves
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