Histology 4 - Nervous System Flashcards
Steps for Preparing Histology Slides
- Fixation 2. Cutting 3. Staining
Fixation
tissues fixed in formalin or other substances that cross-link tissue proteins and prevent decomposition
Cutting
tissue sectioned, embedded in paraffin wax, cut into translucent 4-6 micron slices, attached to glass slide
Staining
- Hemotoxylin (basophillic) - stains DNA and RNA purple/blue 2. Eosin (eosinophillic) - stains collagen and other components pink 3. Immonohistochemical stains: antibodies tage antigens
Neurons Characteristics
Size: Cell bodies 4μm-150μm
Roles: Motor (efferent) Sensory (afferent) Interneurons
Neuron Structural Class
Multipolar: most neurons
Bipolar: retina, olfactory mucosa, cochlear and vestibular ganglia
Pseudounipolar: spinal sensory and most cranial ganglia
Parts of the Neuron
Perikaryon
Dendrites
Axon
Perikaryon
Appearance: Cell Body
Function: synthetic receptor for nerve
Contains: Nissel/Chromatophillic Substance = RER and free ribosomes (amount depends on type and functional state)
Dendrites
Appearance: numerous, elongated processes extending 1-3μm from the perikaryon
Function: location of must neuronal synapses, specialized to recieve environmental or neuronal stimuli
Axon
Appearance: single process of uniform diameter originating from axon hillock, can be very long (motor cells of spinal cord to foot muscle = 100cm)
Function:
- Transport of molecules and organelles - motor protiens along microtubles
- Propagation of of action potential
Contains:
- Axon Plasma Membrane = Axolemma
- Axon Cytoplasm = Axoplasm
(+)mitochandria, microtubles, neurofilaments, cisternae of smooth ER
(-)rolyribosomes, RER, gogli
Glial Cells
CNS
- Oligodendricytes
- Astrocytes
- Microglia
- Ependymal Cells
PNS
- Schwann Cells
- Satellite Cells
Think: Physiology lecture
(O-AME has GaSS call the COPS)
Oligodendrocytes
Appearance: extended proccesses that wrap around parts of multiple axons. “Fried Egg” appearance when fixed in formulin
Function: produce myelin sheath for CNS neurons (electril insulation)
predominant cell type in CNS white matter
Astrocytes
Appearance:
- Fibrous Astrocytes -few processes, found in white matter
- Protoplasmic Astrocytes - numerous processes, found in gray matter
Function:
- control ionic environment
- form CNS scar tissue
- secrete metabolits
- perivascular feet contribute to BBB
most numerous glial cell
Microglia
Appearance: dense, elongated nuclei
Function: phagocytic and secretes cytokines
When activated, retract processes and migrate to need
Evenly distributed to gray and white matter
Originate from bone marrow, same family as macrophages and APC
Ependymal Cell
Appearance: low columnar/cuboidal, sometiems cilliated cells lining the ventricle sof brain and central canal of spinal cord
Function - produces CSF in choroid plexus
No basal lamina, branched processes at the basal ends
Schwann Cells
Neurolemmocytes
Appearance: single Schwann cell form segment of myelin on a single axon
Function: provide myelination for PNS
neural crest origin
Satellite Cell
Appearance: covering layer over lare neuronal cell bodies in PNS ganglia
Function: trophic or supportve role to ganglionic neurons
neuronal crest origin
Central Nervous System
Cerebrum
Cerebellum
Brain Stem
Spinal Cord
Virtually no connective tissue
Divided into white and gray matter
White Matter
- Myelinated axons ←main component
- Oligodendrocytes
- No neuronal cell bodies
Cortex: white central, gray peripheral
Spinal Cord: gray central, white peripheral
Gray Matter
- adundant neuronal cell bodies
- dendrites
- astrocytes
- microglia
- initial unmyelinated protions of axons
synapses occur in gray matter
Cortex
neurons are stratified
6 distinct lamina in gray matter
pyramidal neurons
Meninges
Dura Mater
Arachnoid Mater
Pia Mater
Dura Mater
- thick, external layer
- internal surface = simple squamous epithelium of mesenchymal origin
- consists of dense fibroelastic connectie tissue
- continuous with skull periosteum
- separated from arachnoid by the subdural space
Arachnoid Mater
- “spiderweb-like”
- Components
- sheets of connective tissue in contact with dura
- system of loosely arranged trabeculae of fibroblasts and collagen = continuous wiht pia mater
- Subarachnoid Space
- filled with CSF for protection and cushion
- communicates with brain ventricles
- lacks nutriative capillaies, but larger vessels traverse it
- Arachnoid Villi
- arachnoid perforates the dura forming wneous sinuses covered by endothelium
- functions to transport CSF from subarachnoid space to veins
Pia Mater
- innermost meningeal layer
- thin layer, mesenchymally derived cells
- lays upon layer of astrocytes forming a barrier
- blodd vessels travel through perivascular spaces within pia
- Pia and arachnoid intimately assocaited (leptomeniges/pia-arachnoid layer)
Choroid Plexus
Location: projects into
- roofs of the third and fourth ventricles
- part of the walls of the two lateral ventricles
Architecture:
- elaborate folds with many villi
- layers of vascularized pia mater
- covered cuboidal ependymal cells
Function:
- produce CSF - shock absorber, important for brain metabolism
Peripheral Nervous System
Nerve Fibers - axons enclosed within Schwann Cells
Myelinated vs. Unmyelinated
Myelinated
- Schwann cell wraps portion of axon
- cytoplasm and plasma membrane form consecutive layers
- overlapping inner layers = myelin sheath
- cytoplasm and nuclues pushed to periphery of cell
Unmyelinated
- Schwan cells envelopes multiple axons
- Axon surrounded by Schwann cell, but no consecutive layers
PNS Myelination Facts
- Schwann cell membrane = ↑proportion of lipids
- Myelin = protects axon and maintians ionic environment for propagation of action potential
- Nodes of Ranvier = gaps between Schwann cells
→allows for rapid nerve conduction
Structure of Nerves
Endoneurium - CT surrounding individual axons
Perineurium - CT surrounding bundles of neurons
Epineurium - CT surroudning multiple fascicle of neurons
View matters with identfying structures
