Nerve Tissue & Nervous System Flashcards
Los pares craneales se consideran
Del sistema nervioso periférico
Intracelularmente la neurona es rica en…, sirven a la neurona para transportar los neurotransmisores
Neurofilamento
Los neurofilamentos abundan en
Pericarion y dan cuerpo a las neuritas
El conjunto de prolongaciones neuronales y de las células acompañantes se llama
Neropilo
El nucleo es
Eucromatico
El nucleolo en microscopio es evidente
Ojo de búho
El neuroplasma es
Basofilo por riqueza de ergastoplasma
El RER de la neurona se denomina
Cuerpo de Nissl
El número de células nerviosas dentro del sistema nervioso central es sobre pasado por la Glia aproximadamente
5 veces mas
Las células que se consideran neuroglia periférica
Células satélites o capsulares
Células de Shwann
Tres tipos de células neuroglia
Astrocitos
Oligodendrocitos
Microglia
Son llamados colectivamente macroglia
Astrocitos
Oligodendrocitos
Macroglia es de origen
Ectodermico como las células nerviosas
La microglia es de origen
Mesodermico
Son los mas grandes de las células gliales
Astrocitos
Tiene un nucleo mas grande que el oligodendrocitos,abundante citoplasma granular presentes en la sustancia gris
Astrocitos protoplasmáticos
Largas expansiones relativamente delgadas regulares y ramificadas presente en la sustancia blanca
Astrocitos fibrosos
Son las células de defensa del SNC funcionan como los macrofagos aunque con una mayor capacidad migratoria
Microglia
Tres etapas de diferenciación son
La célula precursora totipotencial (glioblasto)
Células son inducidas a expresar los genes para lípidos y proteinas especializadas.
Diferenciación terminal
Comienzan a aparecer hacia el tercer día después del nacimiento , tienen división celular, su citoplasma)
Los oligodendrocitos jóvenes
Antes que inicie la formación de mielina aparece
La Glia de mielinizacion ( la oligodendroglia)
Migran en sentido proximo distal a lo largo de los axones en crecimiento
Células de schwann
Las células de Schwann en contacto con axones de gran tamaño producen una vaina de mielina asociándose a un solo axon cual es el diámetro
1.0 micrometro
Células de Schwann que envuelven a diámetro inferior a 1.0 micrometro los
Envuelven sin producir mielina
Algunos componentes fosfolipidicos de la mielina es de origen axonal ya que existe una transferencia de
Fosfatidilcolina
Las células de Schwann son capaces de fabricar colagena de tipo
I, III, IV
Es el axon de una neurona
Fibra nerviosa
Es la prolongación celular particularmente especializada en transmitir información
Axon
Marcan la interrupción de la vaina de mielina a intervalos regulares (segmentos internodales) la principal función es en la conducción saltatoria del impulso nervioso
Nodos de Ranvier
En los cortes trnasversales consiste de una banda densa dispuesta en espirales multilamelares alrededor del axon
mielina internodal
El extremo exterior de la espiral deriva del estrechamiento de las partes adyacentes de la membrana citoplasmatica de una pequeña lengüeta del citoplasma del oligodendrocito llamado
Mesaxon externo
Consta de la fusión de las hojas internas de la membrana plasmatica de la célula mielinizante
Mielina compacta
Las hojas externas yuxtapuestas y frecuentemente fusionadas en apariencia forman la línea intraperiodica, el espacio entre los dos componentes membranales es de
1 nm
La periodicidad de las lamelas es de
11 nm
El oligodendrocitos está separado de la membrana axonal por una delgada hendidura extracelular el
Espacio periaxonal
Es una región de la vaina de mielina donde terminan las lamelas
Nodo de Ranvier
% de lípidos que contiene la mielina
70%
% de proteinas de mielina
30%
La mielina contiene
Colesterol
Fósfolipidos
Galactolipidos
Las proteínas de mielina
Po, P1 y P2
Proteina específica del SNP
Po
Marca la principal diferencia entre los componentes químicas del SNC y SNP
Po
Se produce como consecuencia de una sección del axon o de una afección local que le es equivalente
Degradación walleriana
En la degeneración walleriana las células de Schwann se multiplican en el segmento distal y se organizan linealmente en bandas de
Bunger en el interior del tubo formado por la lamina basal preexistente
En la degradación walleriana esta actividad de proliferación continua durante
25 días y luego disminuye
En la degradación walleriana la regeneración axonal comienza
Desde las primeras horas
Los muñones en la regeneración axonal se incrustan en los tubos de lámina basal progresan a una velocidad aproximada de
2.0 a 3 mm por día
Es debida a una destrucción primaria de la mielina y se acompaña también de una proliferación de las células de Schwann , alrededor de un eje constituido por el axon intacto
Desmielinizacion segmentaria
El cerebro y la médula espinal contienen vasos sanguíneos derivados de
Mesenquima
Las tres túnicas que envuelven al SNC están compuestas por
Tejido conectivo
La mas externa también conocida como paquimeninge es densa y firme
Duramadre
Constituyen las leptomeninges
Aracnoides y piamadre
Transparente , inodoro e incoloro de aspecto cristalino llamado “agua de roca”
LCR
Se encuentra dentro del encéfalo y del canal medular, amortigua traumatismos cráneo encefálico, aporta metabolitos por difusión e interviene en la compensación de cambios en el volumen de la masa encefálica
Sistema nervioso central
La cantidad de líquido producida en un día es aproximadamente
un promedio de 0.35 ml/min (500ml/dia)
El volumen de recambio de LCR
De cuatro a cinco veces en el transcurso del día, para mantener un volumen promedio de 130ml durante el día
% de LCR que se encuentra en el espacio subaracnoideo
75%
% de LCR que se encuentra en los ventrículos
25%
LCR es producido principalmente en
Plexo coroides Espacio subaracnoideo Ependimo Superficie cerebral glial Espacios extracelulares cerebrales
Se encuentran en los ventrículos III y IV en su suelo del cuerpo, atrio y cuernos inferiores, ventrículos laterales, superficie basal del tallo cerebral
Plexo coroides
Consisten en invaginaciones de la piamadre cubiertas por epitelio cúbico simple o cilíndrico bajo con presencia de capilares fe estrados y dilatados
Plexo coroides
De los ventrículos laterales al tercer ventrículo se comunica por medio de
Agujero de monroe
El tercer ventrículo con el cuarto se comunica por
Acueducto de Silvio
El cuarto ventrículo se comunica con el espacio subaracnoideo por
El agujero medias de Luschka y dos agujeros laterales de Magendie
LCR es absorbido por medio de
Velocidades aracnoideas
Ubicadas en la cara superolateral y medial de los hemisferios cerebrales con predominio en el seno sagital superior
Velocidades aracnoideas
Se hipertrofia las vellocidades subaracnoideo y sufren acumulos de colagena para ser llamados
Granulaciones de Paccioni
Entre los componentes de LCR encontramos
Densidad especifica. 1.004-1.008 pH 7.35 Cloruros 720 mg/dl Glucosa 65 mg/dl Base total 157 mEq/l Proteína total Lumbar 15-45mg/dl Cisternal 10-25mg/dl Ventrícular 5-15mg/dl
Regula las concentraciones de iones, hormonas, y sustancias en contacto con cerebro y médula espinal
Barrera hematoencefalica
Los vasos se encuentran rodeados por
As trocitos
Las áreas que carecen de barrera hematoencefalica son conocidas como
Órganos cirunventriculares
Órganos cirunventriculares incluyen
Área postrema de la médula oblongada Neurohipofisis Glándula pineal Lamina terminal (órgano vascular) Hipotalamo (tubérculo intercolumnar) Órgano subfornical (tubérculo intercolumnar ) Órgano subcomisural
The nervoous system develops from and beginning
Ectoderm and third week
The NS develops with signals from
Notochord
Ectoderm on the mid dorsal side of the embryo thickens to form the epithelial
Neural plate
The lateral sides of this plate fold upward bend and grow toward each other medially and fuse forming
Neural tube
Are the numerous enlongated processes extending from the perikaryon and specialized to receive stimuli from other neurons at synapses
Dendrites
Measure of the cell body
150 micrometer in diameter
Body’s smallest cells
Cerebellar granule
Have one axon and two or more dendrites
Multipolar neurons
Have one dendrite and one axon
Bipolar neurons
Sigle Process that biffurcates with one longer branch extending to a peripheral ending and the other toward the CNS
Unipolar o pseudounipolar
Many dendrites but no true axon regulate electrical changes of adjacent neurons
Anaxonic neurons
Most neurons are
Multipolar
Bipolar neurons are found in
Retina
Olfatory mucosa
(Inner ear) cochlear and vestibular ganglia
Pseudounipolar neurons are found in the
Spinal ganglia (sensory ganglia) Craneal ganglia
Establish relationships among other neurons forming complex funtion al network or circuits
Interneurons
In PNS cell bodies are found in
Ganglia
Neurulation take place at
Fourth week
Slowly progressing disorder affecting muscular activity characterized by tremors, reduced activity of facial muscle , loss of balance and postural stiffness, caused by gradual loss by apoptosis of dopamine-producing neurons
Parkinson disease
The end of axones have many small branches called
Telodendria
Concentrated RER and other polysomes appear as clumps of Basophilic material called chromatophilic substance or
Nissl bodies
Abundant of Nissl substance or bodies in particulary
Large nerve cells such as motor neurons
Intermediate filaments are abundant both in perikarya and processes and in this cell are often called
Neurofilaments
Neurofilaments forms neurofibrils visible with certain fixatives like
Silver stains
Inclusions of pigmented material that nerve cell contains
Lipofuscin
Consist of residual bodies left from lysosomal digestion
Lipofuscin
Number of axonal ending Make functional contact with the dendrites of a single large Purkinje cell
200,000 axonal ending
Short blunt structures projecting at point along dendrites and most synapses impinging on neurons
Dendritic spines
Dendritic spines occur in vast Numbers for cells of the human cerebral cortex and serve as the initial processing sites for synaptic signals
10^14
Dendritic spines are of key importance in the constant changes of the neutral plasticity for
Underlying adaptation
Learning
Memory
Length of a motor neuron of the spinal cord that innervate the foot muscle
100 cm
Axons originate from a pyramid shaped region of the perikaryon called the
Axon hillock
The plasma membrane of the axon is often called
Axolemma
Citoplasm of An axon
Axoplasm
Site where various excitatory and inhibitory stimuli impinging on the neuron are algebraically summed
Initial segment
The distal end of An axon forms a
Terminal arborization
Axons of interneurons and some motor neurons have branches called…, that end at synapses influencing the activity of many other neurons
Collateral
Each branch ends with dilation called
Terminal bouton
Axoplasm contains
Mitocondria Microtubules Neurofilaments Cisternae of smooth ER No polyribosomes or RER
Organelles and macromolecules synthesized in cell body moves by
Anterograde transport along the axon from perikaryon to the synaptic terminals
Opposite direction carries macromolecules such material Taken by endocytosis
Retrograde transport
Mediate anterograde vesicular transport,a microtubule activated ATPase
Kinesin
Microtubule activated ATPase , provides retrograde transport
Dynein
Anterograde and retrograde transport a rate of
50 - 400 mm/d
The action potential is propagated along the axon as a wave of membrane depolarization produce by
Voltage-gated Na and K channel
Axoplasmic concentration
K
Potential electrical difference across the axolemma of about
-65 mV
Low-molecular weight molecules that bind to the voltage-Gated sodium channel of the axolemma
Local anesthetic
Depolarization resting the potential from negative to positive at
+30 mV
Immediately after the membrane depolarization the
Voltage gated Na channels close and those for K open
Terminal bouton from which neurotransmitters is released by exocitosis from
Synaptic vesicles
Synaptic cleft are separated by
20 to 30 nm
At the presynaptic region the nerve impulse briefly opens
Calcium channel influx that trigger neurotransmitters release by exocytosis or similar mechanism
Neurotransmitters are removed quickly by
enzymatic breakdown diffusion or endocytosis
The chemical transmitter used at neuromuscular junctions is
Acetylcholine
A widely used class of drugs for treatment of depression An axiety disorder
Selective serotonin reuptake inhibitors
The predominant glial cells in CNS
Oligodendrocito
Most common neurotransmitter in the brain, opens Na channels, excites activity in neurons to promote cognitive function in the brain (learning and memory)
Glutamate
Synthesized from glutamate, primary inhibitory neurotransmitter, also influences muscle tone, opens or closes various ions channels
gamma -aminobutyric acid GABA
Inhibits activity between neurons in the CNS including retina , opens Cl channels
Glycine
Functions in the brain related to sleep, appetite, cognition and mood, modulates actions of other neurotransmitters
Serotonin or 5 hydroxytryptamine
A distinct group of monoamines
Catecolamines
Produces inhibitory activity in the brain, important roles in cognition, motivation, behaviors and mood, open K channels , close Ca channel
Dopamine
Neurotransmitter of PNS (sympathetic division of autonomic nervous system) and specific CNS regions
Norepinephrine
Has various effects in CNS , especially the spinal cord , thalamus, and hypothalamus
Epinephrine
Helps regulate response to noxious and potentially harmful stimuli
Enkephalin
Involved in memory regulation and energy balance (increase food in take and decreased physical activity)
Neuropeptide Y
Inhibits activities of neurons in specific brain areas
Somatostatin
Assists with pain information transmission into the brain
Substance P
Stimulates neurons in the brain to help mediate satiation (fullness) and repress hunger
Cholecystokinin
Prevents release of pain signals from neurons and fosters a feeling of well being
Beta endorphin
Helps control and moderate the effects of dopamine
Neurotensin
Inhibits activities in certain CNS neurons
Adenosine
Involved in learning and memory relaxes muscle in the digestive tract important for relaxation of smooth muscle in blood vessels (vasodilatation)
Nitric oxide
Have a large number of radiating processes
Astrocytes
Typical in white matter, with few long processes
Fibrous astrocytes
Many shorter branched processes are called…, predominant in gray matter
Protoplasmatic astrocytes
The larger processes of all astrocytes are reinforced with bundles of intermediate filaments made of …, which serves as a unique marker for astrocytes, the most common source of brain tumors
Glial fibrillary acid protein (GFAP)
Derived from those glial cells and characterized pathologically by their expression of GFAP
Astrocytomas
Astrocytes Forming a barrier layer of expanded processes called …,lining the meninges at the external CNS surface
Glial limiting membrane
Astrocytic processes are seen with
Gold staining
Astrocytes extending processes that cover capillary endothelial cells and contribute to the BBB
Perivascular feet
Common type of dementria in elderly, affect both neuronal perikarya and synapses within the cerebrum
Alzheimer disease
Are columnar or cuboidal cells that line the ventricules of the brain and central canal of the spinal cord , in some CNS locations the apical ends of ependymal cells have cilia,facilitates movement of CSF and long microvilli for absorption
Ependymal cells
Ependymal cells are joined apically by… , but lack a basal lamina
Juntional complexes
Major mechanism of inmune defense in CNS
Microglia
The myelin sheaths surrounding axons are damaged by an autoimmune mechanism
Multiple sclerosis
Funtion of satellite cells
Form An intimate covering layer over the large neuronal cell bodies in the ganglia of the PNS
The main components of white matter are myelinated axons often group together as
Tracts
Deep regions of the CNS have darker aggregates consist of large number of neuronal cell bodies
Nuclei
Number of layers in cerebral cortex
Six layers
Diameter of granular layer cells
4-5micrometers
White matter is peripheral and gray matter is internal
Spinal cord
Consist of dense , fibroelastic connective tissue that is continuous with the periosteum of the skull
Dura mater
Around the spinal cord the dura mater is separated from the periosteum of the vertebrae by
Epidural space which contains a plexus of thin-walled veins and areolar connective tissue
The dura mater is always separated from the arachnoid by the thin
Subdural space
The internal surface of all dura mater as well as the external surface in the spinal cord is covered by
Squamous epithelium of mesenchymal origin
Two components of the arachnoid
A Sheet of connective tissue in contact with dura mater
System of trabeculae composed of collagen and fibroblast
Surrounding the trabeculae is a large sponge like cavity the…, filled with CSF
Subarachnoid space
The connective tissue of the arachnoid is said to be
Avascular
Consists of flattened,mesenchymally derived cells closely applied to the entire surface of the CNS tissue
Pía mater
The pia does not directly contact nerve cells or fibers being separated from the neural elements by the very thin superficial layer of
Astrocytic processes the glia limitans
Blood vessels penetrate the CNS through long
Perivascular spaces covered by pia mater
Is a functional barrier that allows much tighter control than in most tissue over the passage of substances moving from blood into the CNS tissue
Blood brain barrier
Completely envelops the basal lamina of the capillaries in most CNS regions forms another BBB component and further regulates passage of molecules and ions from blood to brain
Limiting layer of perivascular astrocytic feet
Function of the choroid plexus
Is to remove water from blood and release it as the CSF
Provide the main pathways for absorption of CSF back into the venous circulation
Arachnoid villi
Also called neurolemmocytes
Schwann cells
The length of axon ensheathed by one Schwann cell the
Internodal segment
Axonal diameter ranges
300 to 1500 micrometers
Consist of reticular fibers scattered fibroblast and capillaries , immediatedly around the external laminae of the Shwann cells
Endoneurium
Schwann cells and endoneurium are bundled together as fascicles by a sleeve of
Perineurium
Autonomic ganglia are small bulbous dilations in autonomic nerves usually with
Multipolar neurons
Sensory ganglia are associated to
Cranial nerves
Dorsal roots
The chemical mediator present in the synaptic vesicles of all preganglionic axons is
Acetylcholine
Proteins produced by both neurons and glial cells the neural plasticity
Neurotrophins
is the dissolution of the Nissl bodies in the cell body of a neuron. It is an induced response of the cell usually triggered by axotomy, ischemia, toxicity to the cell, cell exhaustion, virus infections, and hibernation in lower vertebrates. Neuronal recovery through regeneration , but most often it is a precursor of apoptosis.
Chromatolysis
