Nerves (weeks) Flashcards
`What ar the features of Neuronal Cell Body (perikaryon, soma) ? In the Nucleus, nucleolus, inclusions, axon hillock , golgi, cytoskeletal elements.
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Nucleus:
- Centrally located
- Contains active euchromatin (not always active)
- Nucleolous: sometimes 2 or more
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Inclusions
- lipid, glycogen, melanin or iron
- Lipofucsin (product of lysosomes) brown pigment , byproduct of undigested material- increases with age
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Axon Hillock
- Lacks Nissl substance
- Cytoskeletal elements (microtubules, intermediate filaments, microfilaments) funnel into axon
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Golgi
- Can be extremely ware and well developed in neurons
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Cytoskeletal Element
- Neurofibrils (cluster)
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Neurofilaments (neuron specific intermediate filaments)
- made of 3 different intermediate filaments (70kDa, 150KDa, 200kDa)
- Microtubules (aka neurotubules)
- Microfilaments
Do cell bodies replicate?
No; Neurons don’t divide, they must last a lifetime however cellulary components have a normal turnover rate.
What are dendrites? What is its apppearance? Specifiy the branching patterns. What makes the dendrites different from the other cell parts? Function.
- The number of dendrites could be either single or multiple.
- It has a large diameter, doesn’t extend far from the cell body, ALMOST never myelinted
- Tapered
- Branching: acute angles, branch repeatedly, diameters vary
- The unique difference in organelles.
- Contents are similar to soma
- golgi can extend into dendrites
- contains ribosomes
- microtubules prevalent (evenly spaced)
- Function: receptor processes, recieving info (stimuli from other neurons or external environment,
- graded potentials
- receiving synapses
What are axons? What is its apppearance? Specifiy the branching patterns. What makes the axons different from the other cell parts?
- Not all neurons have axons
- The appear: 1-30 nm
- small constant diameter
- smooth contours and cylindrical shape
- may extend long distances from the cell body (some axons in humans over 1 m long)
- Can be myelinated
- Branching
- branches infrequently
- branches obtuse angles
- Unique differences in organelles
- Lack Nissl bodies and golgi
- NEVER contains ribosomes
- Neurofilaments and microtubules prevalent (no regular arrangement)
- Function:
- Action potential
- Conduction and transmission
- Action potential
What are dendritic spines?
- Thay have mushroom shaped structures that are connected to the dendritic shaft.
- SER and filamentous proteins extend into spines- no ribosomes
- Function: increase receptive area
- occur in the vast numbers in order of 10^14 in the human cerebral cortex
- Size: 1-3 micrometerx long
- increase binding site surface area (axons come and form synapsis)
- Dynamic structures
What is a Biopolar neuron? What is it used for?
- One dendrite, one axon
- rare
- special senses:
- Cochlear (hearing)
- Vestilandar (balance,eye movemeny
- Retina
- taste
- smell
What is Pseudounipolar neuron?
- one process close to soma
- extends short distance, then divides in to a T
- Stimuli are received from dendrites passed directly to Axon Terminal
- found in sensory neurons
- and in gnglia such as dorsal root ganglia (DRG)
What is Multipolar neuron?
- More than 2 cellular processes
- Most in the body are mulitpolar
What is a synapse (Bouton) responsible for?
- Responsible for the unidirectional transmision of nerve impulses
- converts electrical impulse into a chemical signal
- sites of functional contact between neurons
- other neurons
- effector neurons
What are the types of synapses?
- Chemical synapses (99%)
- two types
- without reuptake (20%)
- Ex: Ach, achetycholesterase degrades Ach as fast as it is produced
- with uptake (80%)
- without reuptake (20%)
- two types
- electrical synapses (rare)
- found in the retina
- do NOT require NTs
What happens when someone takes cocaine?
- )cocaine inhibits the reuptake of dopamine and serotonin in the pleasure center of the brain
- ) overtime the post synaptic receptors down regulate (not as many embedded). crash b/c not enough receptors
What are the morphologies and sizes of Ach, NE, inhibioty, serotonin (5HT, 5 hydroxytrptamine)?
- Ach: clear in color, ~40-50 nm
- NE: 40-60 nm range, small clark centrally located dot
- Inhibitory: tend to be flattened out
- (GABA;gama -amino butyric acid)
- Serotonin, aka (80-150nm) damso dark staining core
What are the assigned classification of neurotransmitter?
Over 50 and more types of neurotransmitters.
- GABA:most abundant neurotransmitter in CNS
- Dopamine: associated w/ pleasure center, also found in substantia nigra and basal ganglia
- Glutamate: most abundant excitatory neurotransmitter in CNS
- Peptides
- Substance P: involved in pain
- Vasoactive intestinal polypeptide (VIP)
- Somatostatin (GHIH)
What are non-directed synapses?
Synapes without distinct postsynaptic targets.
What is glia (neuroglia)?
- 10/1 glia: neurons
- provide protection and support for neurons
- proliferation/ constant slow turnover
What are the 4 types of glia?
- Astrocytes
- Myelin producing cells
- Microglia
- Ependymal cells
What is te must numerous type of glia cells?
Astrocytes have morphological and functional diversity.
What are the morphological subtypes of astrocytes? What is the size of its soma? what are the common markers? What is the tumor of astrocytes called?
- Fibrous (in white matter): few long processes
- protoplasmic (in gray matter): many short processes
- others in unique brain regions (bergmann glia, cerebellum)
- Soma: 10-20 micrometers
The common markers: glial fibrillary acidic protein (GFAP), and glutamate synthetase
- Astrocytomas: tumors arising from fibrous astrocyes; account for ~80% adult brain tumors
What is the function of astrocytes in metabolic and reaction to injury?
Metabolic:
- store gycogen
- K+ sink
- store neurotransmitter enzymes
- proccesses surround neurons (can extend 100 micrometers)
- have perivascular end feet that cover blood vessels
Reaction to injury:
- increase in size
- increase in number
- glial scar
What are types of myelin producing cells?
Olgiodendrocytes for several CNS axons
Schwan cells: Single PNS axon
What is the description of oligodendrocytes (CNS)?
- size: 10-12 micromenters soma
- small, dark, round nucleus
- cytoplasm difficult to see at LM level without markers
- Stain light-dark (EM) depending on age of oligo
- common markers: myelin basic proteins, galactocerebroside (gal C)
- produces myelin for several CNS axons
- tumors: oligodendrocytomas
- produces myelin for several CNS axons
- A single oligo sends out multiple tongue like processes that wrap portions that wrap multiple axons.
- Distance of oligo may be some distance from an axon it myeleniates.
What are Schwann Cells (PNS)?
It surround myelinated (one) or unmyelinated (several) PNS axons?
What is mylein?
Lipid rich cellular extrusion acts as an insulator
What is the role of Microglia?
- assists with macrophagic action–> phaocytotic–>ingest cellular debris
- (bone marrow region) Mesodermal origin
- created from blood monocytes
- realease cytokines attracting t cells
- can act as antigen presenting cells
- increase in size and number with disease
Explain morphology of Ependymal Cells.
- Form the simple epithelial like lining of ventricles of brain of centeral of the spinal cord
- cubodial/columnar epithelia
- line ventricles/ central canal of brain
- cilated–>facilitates movement of CSF
- processes can extend far into the CNS
- markers: vimentin
- tumor: ependymona
What is the Central Nervous System?
- Brain and spinal cord
- contains white matter and gray matter
What does white matter contain?
- No or few neuron cell bodies
- Many myelinated axons
- Glia (oligodendrocytes,astrocytes, and microglia)
What does gray matter contain?
- Neuron cell bodies
- network of unmyelinated axons and dendrites (neurophil)
- glia
- many blood vessels compared to white matter
What is Ganglia?
collection of neurons in PNS
What is the PNS? What are the components of PNS?
- cell bodies and nerve processes outside the brain and spinal cord
- Sympathetic ganglia, parasympathetic ganglia,
What is the basic funtional unit of the reflex arc?
- Afferent (input): coming in to the brain of spinal cord
- Synapse
- Efferent (output): sending out from CNS to PNS
What are the 2 types of ganglia?
Sensory and autonomic
Where can sensory ganglia be found?
- Cranial: cranial nerves
- Spinal–> aka DRG
- Sensory ganglia (peripheral nervous system)
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What are the two types of motor ganglia (autonomic)? Describe the features of each type.
- Sympathertic–> Not found in cranium
- CT capsule
- Non-distinct fiber tracts (unmyelinated) as seen at the LM level
- cells distributed throughout
- satellite cells
- Scattered
- non-uniform
- multipolar neurons
- Eccentric Nucleus
- Multiple processes
- Parasymphatethic-
- 2-3 or 100 neurons
- located near organ of innervation–> often located in the wall of organ innervated
- capsule may be indistinct
- usually fewer neurons than in symphathetic ganglia
- otherwise similar to sympathetic ganglia
What type of cells lines the ventricles?
epidymal cells
What produces the cerebral spinal fluid? Where does CSF circulate?
Choroid Plexus
It circulates through the ventricles, central canal, the subarchnoid space and perivascular space.
What is meningitis and what the cause associated with?
Infflammation of the meniges (usually pia and subarchoid)
What is the structural continuity of the connective tisse covering of the peripheral nerves/ ganglia?
- Dura- epineurium –> fibrous coat of dense CT, rich in nerve endings
- arachnoid- perineurium–> flatted epithelial-like cells
- subarachoid space- sub perineurial space
- pia: endoneurium; thin layer of reticular fibers-> produced by schwann cells
What are the characteristics of ependymal cells?
- Cubodial/ columnar epithelia
- line ventricles/ central canal
- cilated–> help circulate CSF
- processes can extend far into the CNS
- possess microvilli
What are the characteristics of choroid plexus?
- modified ependyma and blood vessels extend into the ventricles
- located in each ventricle
- secretes CSF
- endothelium
- contains choroid cell
- made up of dilated penestrate capillaries enveloped invaginated folds of pia matter.
What is the function of Olgiodendrocytes?
produces myelin for several CNS axons
In PNS all axons (myelinated and unmyelinater are surrounded by what?
Schwann cells
Unmyelinated nerve has no nodes of ranvier. T or F?
T
How many axons does schan cover in mylinated?
One axon. Multiple schwanns over entire length.
How many axons does unmyelinated schwann cover?
multiple axons
In the CNS, myelinated axons are surrounded by what type of cells? Up to how many axons can it myelinate?
Oligodendrocytes
1 olgiodndrocyte can myelinate several (5-10) axons
What are the characteristics of unmyelinated axons?
- contain either no myelin sheath or surrounded by astrocytes
What is the function of astrocytes?
- Invests all neurons
- support, both physical and metabolic
- end feet regulate transport
- forms pia-glial barrier
- help control ionic an chemical enviornment of neurons
- store glycogen
- have role in synaptic activity
- help confine NT’s to synaptic clefts
- remove excess NT’s by phagocytosis
What is another structure and function of astrocytes in the anatomical blood brain barrier?
- created by endothelial cells linked by zonula occludens
- has basement membrane
- surrounded by astrocyte end feet
- passagage across is severly restricted.
- substance that cross well after certain lipid soluble molecules (02, CO2, EtOH)
- Macromolecules are transported by specific receptor mediated endocytosis
- help control ionic and chemical enviornment in neurons.
What are the types of axoplasmid transport (movement of material in the neuron)?
- ) anterograde transport
- ) retrograde transport
What is anterograde transport?
It carries material away from cell body
- fast (20-400mm/day)
- moves organelles (mitochondria,vesicles)
- moves molecules (neurotransmitters)
- Slow (.6-4mm/day)
- moves cytoskeletal componenets (tubilin, actin)
- moves axolemma components
What is retrograde transport ?
(carries material toward cell body)
- dyenein used
- fast-there is no slow retrograde transport
- pathway followed by toxins of viruses that enter CNS nerve endings
- material take up endocytosis
Describe regeneration for mammalian neurons.
- mammaalian neurons don’t typically divide
- degeneration usually represent permanant lose
- neuronal proccesses in CNS have narrow limits on sympathetic activity after injury
- glial scaring limit agent
- peripheral nerves can regenerate if their cell bodies aren’t destroyed
What happens at proximal to lesion of Neurons?
- primary degeneration
- chromatolysis
What is chromatolysis?
- cellualredema and loss of nissl substance form cell body in primary lesion
What happens when the lesion is distal of neurons?
secondary degeneration (wallerian); anterograde degeneration
axon degeneration
What is Nissl Substance made of?
Contains Nissl Substance (RER and free ribosomes;alternating pattern)
What does the axon hillock lack? what is it used to differentiate from?
It lacks nissl substance and golgi. its used to differentiate from the axon from dendrites
what are neurofibrils?
Cluster of neurofilaments
All neurons have axons. True or false?
False
What is pia analogous to? what is it made of? what is it made by?
Endoneurium, thin reticular fibers, produced by schwann cells.
What is the chloroid plexus?
Modified ependyma and blood vessels extend into ventricles.
Where is CSF circulated?
Through ventricles, central canal, subarachoid space and perivascular space.
What type of areas does astrocytes cover?
Astrocytes provide a covering for the bear areas of mylein axons (nodes of ranvier and synapses)
What are the characteristics of microglia?
- markers: MAC-1, MAC-3, OX42
- 10 micrometers soma
- usually found near blood vessels
What is the main function of microglia?
Function: monitor CSF
- line ventricles/ central canal of brain
What is the function of ependymal cells?
funtion monitor and modify CSF content
all axons both myelinated and unmyelinated in the PNS are surrounded by what cell?
schwann cell
All unmyelinated axons in the CNS are surrounded by what type of cells?
Astrocytes
Which cell helps confine NTs to synaptic clefts and remove excess NTs by phagocytosis?
astrocytes
What main microtuble protein is used for anterograde?
Kinesin
tubulin and acting for cytoskeletal movement
What main microtuble protein is used for retrograde?
Dynenin
What is the limiting agent of symphathetic activity after injury?
Glial scarring
Where are electrical synapses found? and what don’t they require?
Found in retina
don’t require NTs
What is the most abundant NT in CNS? What is the most abundant excitatory in CNS?
GABA, Glutamate
other than the exception microglia, where do all the other glia originated from?
Ectroderm (nerual tube)
Which neurotransmitter are mainly used in the parasymphatetic and symphatetic?
Parasymphatetic: Ach
symphathetic: NE
What are astrocytes roles in synaptic activity?
Help confine NTs to synaptic clefts. remove excess NTs by phagocytosis.
