chapter 15 nervous tissue Flashcards
What are the charcteristics of nervous tissue?
- Irritability
- Specialized to recieve stimuli
- COnductabiltiy
- transmist nerve impulses
- cellular componets
- neurons - conduct impulses
- fundamental structural and functional unit of NS
- Neuroglial cells
- non conductive cells that support and protect neurons
- parts of neuron
- cellbody (soma)
- dendrites
- axon
- neurons - conduct impulses
What is the cell body (soma)?
- contains nucleus
- Nissl bodies (substances) consists of RER and free ribosomes
- Extensive RER visible with light microscopy and elaborate golgi structures
- abundunt mitochondria, microtubles, and intermediate filaments (neurofilaments )
- Lipofucsin granules are formed from lysosomes and accumulate with age of the neuron
- associated with ligand gated channels and local potentials
What are dendrites?
- Connduct impulses (local potentials) toward the cell body
- Contain Nissl Substance, mitochondria, and ect. but NO GOLGI BODY
- may be studded with dendritic spines to increase sa
- tend to taper distally and may branch
- assocated with ligand channels
What is an axon hillock?
(part of the axon)
site for origin of the axon
devoid of nissl substance
associated with action potential generation
What is axon
- Assoc. with volt. gated ion channels and AP
- Contain mito chondria and microtubles
- but lack RER, Ribosomes, and Golgi
- terminates in branching telodendrites
- telodendrites contain synaptic vesicles and related proteins
- form presynaptic vescles
- may be enclosed in myelin sheath
structure of axon pic
structure of axon pic
How are nerve cells classified on function?
- Sensory (afferent)
- To CNS
- Motor (efferent)
- Exit CNS
- Somatic
- skeletal
- automatic
- glands, cardiac, smooth
- divided in to parasymp and sympathetic neurons
- INterneurons
- transmit impulses within CNS and b/w sensory and motor neurons
- most abundant class
how are nerve cells classified on processes?
- multipolar neurons
- most common
- single axon and multiple dendrites
- bipolar
- two processes, one at each end of spindle shaped neuron
- in association of special senses such as olfactory and visual
- pseudounipolar
- single process from the cell body that bifurcates into a central and a peripheral process
- found in ganglia alongside spinal cord (dorsal root gangila )
How are neurons classified according to length?
- Golgi 1
- neurons with long axons which leave the gray matter of which thye are a part of
- Golgi 2
- Neurons with short axons which ramify through the gray matter
what is this?
what is this?
What is a nerve?
a bundle of axons (fibers) in the PNS
What is a tract?
A bundle of axon (fibers) in the CNS
What are ganglion?
An aggregation of cell bodies and dendrites in the PNS
What is a nucleus?
A aggregation of cell bodies and dendrites in the CNS
What is the micro architechure of the nerve?
-
Epineurium
- thick fiborus coat
- covers entire nerve
- cupplied by blood and lymphatic vessels
- type 1 collagen and fibroblasts
-
Perineurium
- dense CT
- covers bundles of axons (fasiciles) within nerve
- Epithelial like fibroblasts on inner surface joined by tight junctions
- zonulae occuldens
- provide permiability barruer
- layer must be regjoined in micro surgery for limb reattachment
-
blood nerve barrier
- Endothelial cells of vessels also linked by tight junctions
-
Endoneurium
- thin layer of recticuar CT
- surrounds indivdual dibers and schwann cells
- type 3 collagen
What is the membrane specializations on a nerve?
- Receptors
- ion channels
- ligand gated channels on dendrites and cell bodies
- potassium channels on axon
- voltage gated sodium channels on axon
- voltage gated calcium channels on axon
- Presynpatic membrane
- synaptic vesicles
- vesucular docking protins and synapsin filaments
- Post synaptic membrane
- receptors
- ligand gated ion channels
microstructure
microstructure
What is anterograde transport?
- Cell body towards distal end of axon
- Kinesin
- Rate of transport
- Slow
- anterogradee only
- SCa (pre assembled microtubles and neurofilament)
- SCb (enzymes, actin, clathrin)
- Slow
- Intermediate
- Mitochondria and other membrane bound organelles
- Fast
- Synaptic vescicles and neurotransmitters
What is retrograde transport?
- Axon toward cell body
- carries endocytosed materials and recycled proteis
- rate of transport
- 100 - 300 mm/day
WHat are glial cells?
- Non Neuronal cells dervived from emboryonic neural crest rissue (except micro gilia)
- serve in support functions of PNS and CNS
- capable of cell division
Types:
- Astrocytes
- Oligodendrocytes
- Schwann Cells
- Microglial Cells
- Ependymal Cells
What are the characteristics of astrocytes?
- from neural crest
- CNS only numerous process with expanded pediceles (fet) that terminate on capillaries or pia mater
- fibrous
- Found in white matter
- long few beanches
- Protoplasmic
- found in gray matter
- shorter with many short branches
What are the functions of astrocytes?
- Regulate composition of intercellular environments or entry of substances into it
- Structural support
- blood-rain barrier
- mediate exchange of nutrients and metabolites between blood and neurons
- end feet form glia limitans
- Development of cerebral cortex
- potassium sink
- secretion of neurotrophic factors
- uptake/metabolism of neurotransmitters
- help forms non collagen scar tissue after injuy to CNS
what is this tissue
What is this tissue
what are Oligodendrocytes?
- Dervived from neuro crest (neuroepithelium)
- only CNS
- Functions:
- Closely assocated with neuron cell bodies in gray matter and act as satellite cells
- surround axons of unmyleinated fibers in gray matter
- myelinate axons in the CNS
- each one myelinates several axons
WHat are schwann cells?
Dervived from the neural crest
myleinate axons in the PNS
(each one myelinates a section of a single axon)
What are microglial cells
- dervived from macrophages precursors (bone marrow)
- Functions
- phagocytic in CNS
- recruti leukocytes across blod brain barrier
- modulate initiation and progression of immune responses along with astrocytes
What are ependymal cells?
Ciliated cubodial cels
dervived from neuroepithelium and line ventricular system of CNS
Used in transport
in choriod plexus, may be principal cell that secretes cerebrospinal fluid
What are satellite cells?
Derived from neural crest
forms moons (crescents) around cell bodies in ganglia
functions as insulators
How does myelination ocur in the PNS?
- Schwann cell plasma membrane wraps around axon
- schwann cell cytopasm is squeezed out leaving behind concentric layers of membranes
- internal and external mesaxon
- outer and innermost points of fusion between the outerleaflets (extracellular leaflets )
- internal and external mesaxon
- intraperoid lie
- eletron dense line created by extracelllar space between adjacent outer leaflets
- major protein zero is a transmembrane protein that forms homodimers
- found in the PNS
- homodimers form homotetramers with the opposing outer leaflets
- mutation are related to charcot-marie-tooth diseases
- In CNS version of this protein - mutation result in pelizaeus merzbacher disease
- major protein zero is a transmembrane protein that forms homodimers
- eletron dense line created by extracelllar space between adjacent outer leaflets
- Major Dense line
- e dense line created by cytoplasmic space remnant between adjacent inner leaflets
- myelin basic protein ( also in PNS) is an abundant protein assocated with the inner leaflets
- stablized lipids in leaflets
- there are a number of forms created by splicing of a single gene
- Schmidt- lanterman clefts ( incisures)
- residual areas of cytoplasm within the major dense lines
What are oligodendrocytes or Nodes of raniver?
Oligodendrites form myelin sheaths in CNS
applies myelin sheath to multiple aaxons
autotypic junctions ar efound in membranes of the same cell
heterotypic junctions are found inbetween axolemma surrounding the axon and cytoplasmic loops adjacent to the nodes of Raniever
what are the componets of a synapse
PreSynaptic Membrane
- voltaged gated calcium channels
- SNAPS bind synpatic vesicles to presynaptic membrane
- soulable NSF
- found in cytosl of terminal
- vescle docking proteins
- snap receptors found in pre and synaptic vesicular membranes
- synapsisns
- filaments in the preynaptic membrane
PostSynaptic Membrane
- Neurotransmitters receptors
What are the types of Snapses?
- Axosomatic
- Axon terminal synapses with the neuron cell body
- Axaxonic
- AXon terminal synapses with another axon terminal
- Axodendritic
- Axon terminal synapses with a dendrite spine
- Excitatory
- More postive end - plate potential ( close )
- Inhibitory
- More negative end plate potential ( farther )
What are meninges and how are they listed from superficial to deep?
- Superfical to Deep
- Epidural space (absent around brain)
- Dura mater
- Subdural Space
- Leptoemninx
- Archnoid membrane
- Archnoid villi Pia Mater
What is the dura mater
- Thick sheet of dense CT
- (in cranial cavity it lines cranial vault bone and serves as periosteum)
- around the Spinal Cord, It forms CT that is seperated from bone via epidural space
- Endothellial-lined venous sinuses that recieve blood from cerebral drainage as well as ceebrospinal fluid via arachnoid vili
- A later of dural border cells seperates the dura mater from the subdural space
What is arachnoid layer?
- Is a meninx compoxed of delicate CT
- Spaced b.w the arachnoid and the pia mater is collectively reffered as the subarachnoid space
- filled with cerebrospinal fluid
- Arachnoid villi allso for Cerebral Spinal Fluid to flow from subarachnoid space into dural sinuses
What is the Pia Mater?
Is a thin sheet of CT lies on the surface of brain and spinal cord
Continous wiht perivascular Ct of cerebral and spinal cord blood vessels
tightly attached to nervous tissue of brain and sponal cord (removal = damage)
are tunnels covered with pia mater
What is the choroid Plexus?
highly infolded simple cubodial epithelium
cells linked via tight junctions form cerbrospinal fluid barrier
increased mitochondria = active transport mechanisms
capillaries are formed from fenestrated ( leaky) (w/ holes) endothelial cells
Na + ; K+; ATPase Pump sends fluids from chorid plexus epithelium to ventricular lumen into Cerebrospinal Fluid
What is the ependymal layer?
- simple cubodial epithelium that lines ventricular walls of the brain
- linked by zonula adherens with microvilli and cilia
- formed glia limitans w/ astrocytic proces
- part of blood brain barrier
- asotrocyts send processes to the surrounding non fenestrated capillaries
- which is part of the blood brain barrier
What is the sensory (dorsal root) ?
- Capsule of connective tissue (epinuerium)
- Clustered pseudounipolar neurons lies within capsul
- postganglionic axons are myelinated
- Satellite cells:
- form single layer around the cell body of each neuron
- surfaces of cells facing aaway from neurons are in contact with basal lamina
What is Autonomic ganglia ?
- Capsule of epineurium
- cluster of multipolar neurons
- recieve input from myelinated preganglioninc neurons
- Post ganglionic axons are not myelinated
- satellite cells:
- Similia to those in dorsal root ganlia but less numerous
