Nervous System Flashcards
Neurons
Neurons (nerve cells) are network that form the human nervous system. They typically have numerous long processes.
Neurons form the parenchyma.
Neuron is a functional unit in both CNS and PNS.
Glial cells descriptions, functions, embryonic development, and compositions
Glial cells are supporting cells of the nerve cells which have short processes. (They are like glue)
Glial cells form the stroma
They suppport neuronal survival and activities.
They are 10X more abundant than neurons.
They develop from progenitor cells of the embryonic neural plate (neural tube and the neural crest).
They substitute for cells of connective tissue. The collagen-like structure are neuropils.
Anatomical divisions of the Nervous System
Central Nervous system and Peripheral Nervous System
Components of the Central Nervous System
Cerebrum, Cerebellum, and Spinal Cord
Components of the Peripheral Nervous System
Cranial nerves, Spinal nerves, and Peripheral nerves or Ganglia
Define Nuclei, Tracts, Ganglia, and Nerves
Nuclei are somas or cell bodies in CNS.
Tracts are collection of axons in CNS (sheathed by oligodendrocytes).
Ganglia are somas or cell bodies in PNS.
Nerves are collection of axons in PNS (sheathed by Schwann cells or neurolemmocytes).
Functional divisions of the Nervous System
- Sensory (Afferent)
a. Somatic- sensory input perceived consciously (skin)
b. Visceral- sensory input not perceived consciously (heart) - Motor (Efferent)
a. Somatic - motor outpur controlled voluntarily (skeletal muscle)
b. Autonomic Nervous System - motor output NOT controlled voluntarily (heart, gland, effectors)
Somatic (Voluntary) Nervous System and Autonomic(Involuntary) Nervous System
Remember: SAME DAVE
Division of the Autonomic Nervous System
Sympathetic division (fight, flight, freeze) and Parasympathetic division (rest and digest)
Neuronal pathways of the ANS (autonomic nervous system)
Preganglionic (cell body in CNS) and Postganglionic (cell body in a ganglion)
Depolarization Wave
Stimuli by environment changes->
Membrane Depolarization: Neurons respond by altering ionic gradient [(electrical potential) cells that rapidly change its potential are excitable]->
Action potential/ Depolarization wave/Nerve impulse
Development of Nerve tissue
Nervous tissue develops from ectoderm (outermost)[3rd week of development]->
Thickens to form epithelial neural plate [signal comes from the underlying axial structure, the notochord]->
Sides of the plate fold upward and grow toward each other medially->
Neural tube forms [within few days]- gives rise to CNS, neurons, glial cells
Neural crest (mesenchymal) above neural tube-> gives rise to PNS and non-neuronal cell types
All the rest of will become epidermis
3 main parts of a Neuron
- Cell body/ Perikaryon/ Soma - contains nucleus and organelles. Synthetic or Trophic center.
- Dendrites - elongated processes-> Receive stimuli from other neurons at synapses.
- Axon - single long processes ending at synapses. Conduct nerve impulse to other cells. May also receive information from other neurons.
Neurolemma
Neuronal cell membrane
Smallest neuron
Cerebellar granule cell
Neuronal classifications
Structural:
- Multipolar neurons- (most common) 1 axon and 2 or more dendrites (interneurons, motor)
- Bipolar neurons- 1 dendrite + 1 axon (sensory neurons of the retina, olfactory epitehlium, inner ear- SPECIAL sensory)
- Unipolar or Pseudounipolar neuron- axon bifurcates close to perikaryon. Peripheral process connects the dendrites. Central process leads to the CNS. (general sensory)- dorsal root ganglia
- Axoaxonic neuron- many dendrites but no true axon. Do NOT produce action potential but regulate electical changes of adjacent CNS neuron.
Functional:
Sensory, Interneuron, Motor Neuron
Interneurons
Interneurons:
- connect 2 brain regions to form functional circuits in CNS.
- play a vital role in reflexes
- either multipolar or anaxomic
- comprise 99% of all neurons in adults
Locations of Soma in CNS, Axons in CNS, Cell bodies in PNS, Axons in PNS
Soma in CNS are found in gray matter (cortex).
Axons in CNS are found in white matter (medulla).
- Medulla oblongata- mixture of white matter tract and gray matter nuclei
Cell bodies in PNS are found in ganglia and some sensory regions (olfactory mucosa)- (gray matter in medulla)
Axons in PNS are bundled in nerves (white matter forming a path)
In cerebellum:
Cortex: outer layer (gray mater)
Medulla: inner layer (white matter)
Nuclei: gray matter in medulla
Tract: white matter-> arbor vitae
What is Parkinson’s disease and state its treatment
Parkinson’s disease is a gradual loss by apoptosis of dopamine-producing neurons which cell bodies lie within the nucleus of the CNS substantia nigra. It is treated by L-dopa (dopamine percursor)
Describe the cell body of a typical neuron with regard to its nucleus, cytoplasm, golgi, mitochondria, cytosketelal components, and pigmentation
Nucleus- unusually large, euchromatic (intense synthetic activity), prominent nucleolus
Cytoplasm- numerous free polyribosomes & highly developed RER (active production of cytoskeletal proteins & proteins for transport and secretion). Basophilic (chromatophilic substances or Nissl bodies) are abundant in large neuron cells like motor neurons.
- Axon hillock- origin of axon
Golgi apparatus- is only found in cell body
Mitochondria- can be found throughout the cell (abundant in axon terminals)
Microtubules, Actin filaments, Intermediate filaments (Neurofilaments- type IV intermediate filaments) are abundant in both cell body and processes
Lipofuscin- residual bodies left from lysosomal digestion can be seen
Neurofilaments
Neurofilaments are Type IV Intermediate filaments (neurofibrils) that can be seen on light microscopy by a silver stain.
Function of dendrites and location of the cytoskeletal element
Dendrites are principal signal reception and processing sites of neurons. Their cytoskeletal elements are predominantly in distal region.
Dendritic spine
Dendritic spine is the initial processing site for synaptic signal. It depends on actin filaments and changes continuously as synaptic connections on neurons are modified (key important in neural plasticity), It can be visualized with silver staining through confocal or electron microscopy to see as most synapses occur.
Axolemma
Axon plasma membrane
Axoplasm
Axon cytoplasm
Axon Hillock
where concentrated ion channels generate action potential. It is the origin of axon.
Collaterals
Major branches of interneurons and some motor neurons which influence activity of many other neurons
Terminal buoton
A dilation at the end of the axon
Describe an axon with regard to its organelle and mechanism of injury
Axon is a single, long cell extension emerging from the axon hillock of the cell body. It contains mitochondria, microtubules (with kinesin and dynein), neurofilaments, transport vesicles but few polyribosomes or cisternae of RER. Maybe, myelinated by glial cells to increase the speed of action potential propagation (node of ranvier). If severed, distal part quickly degenerates and undergoes phagocytosis.
Anterograde and Retrograde transport in the axon
Anterograde transport- movement of organelles & macromolecules from cell body to synaptic terminals along microtubules via kinesin (K+ :)->
Retrograde transport- movement of macromolecules taken up by endocytosis (including virus and toxins) from the periphery to the cell body by dynein. This process can be used to study pathways of neuron (peroxidase injected into axon terminals). Rate of axonal transport=axon growth
Microtubules is the cytoskeletal component as the track
Nerve impulse
Nerve impulse or Action potential is an electrical process initiated at axon hillock when other impulses received at the cell body or dendrites meet a certain threshold. Membrane depolarization is produced by volage-gated Na+ & K+ channels in the axolemma.
Axon’s resting potential
-65mV (electical difference) as K+ is many times greater than the extracellular concentration
Describe the components of the eletrical and chemical synapse
Threshold->
Voltage-gated Na+ channels open->
Influx of Na+
Axoplasm shifts the resting potential from -65mV to +30mV (depolarization)->
Voltage-gated Na+ channels close & K+ channels open->
Returns to resting potential->
Refractory period wherein neuron is ready to repeat the process & generate another action potential->
Impulse arriving at the synaptic nerve endings promote the discharge of stored neurotransmitters->
Nerve impulse opens Ca2+ channels->
Ca2+ influx NT release by exocytosis->
NT diffuses across the synaptic cleft->
NT inhibits or stimulates action potentials
Describe the chemical synapse component to application in anesthesia
Local anesthesia are low molecular weight molecules that bind the voltage regulated Na+ channels to the axolemma interfering the sodium ion influx inhibiting action potential.
Describe excitatory and inhibitory neurotransmitters
Excitatory NT opens postsynaptic Na+ channels that causes Na+ influx which then causes depolarization.
Inhibitory NT opens Cl- channels that causes Cl- influx (or other anion) which then causes hyperpolarization
Synapses
Synapese are sites where nerve impulse are transmitted from one neuron to another or to other effector cells. Its structure ensures transmission is unidirectional. It converts an electrical signal from presynaptic cell to chemical signal that affects the post-synaptic cell.
Synaptic cleft: 20-40nm gap
Neurotransmitters
NT are small molecules that bind specific receptor proteins to either open or close ion channels or to initiate secondary messenger cascade.
Components of synapse
Presynaptic axon terminal (terminal buoton)- contains mitochondria & numerous synaptic vesicles
Synaptic cleft- separates pre and post synaptic membrane
Postsynaptic cell membrane- contains receptors and ion channels
Ways NT are cleaned up at synapses
a. Diffusion – from greater to lesser concentration. The only method of clean up for nitric oxide and endocannabinoids which are lipid soluble
b. Enzymatic degradation – NMJ with acetylcholinesterase like PACMAN 😊 e.g. MAO (Monoamine Oxidase) uses oxygen to clip amine group off of mono amines
- Occurs within the neuron (it’s a mitochondrial enzyme)
- Targets for Monoamine oxidase inhibitors
c. Reuptake – transporter or method on presynaptic that picks up neurotransmitter either for recycling or enzymatic breakdown. Common target for drugs such as SSRI (selective serotonin reuptake inhibitor)
d. Glial activity
e. Endocytosis of receptor-NT complex by postsynaptic cell
SSRIs
Selective Serotonin Reuptake Inhibitor is a treatment for depression and anxiety. It augments level of serotonin at postsynaptic membrane by inhibiting reuptake by presynaptic membrane.
Types of synapses
- Axosomatic- Axon to cell body
- Axodendritic- Axon to dendritic spine
- Axoaxonic- Axon to axon (modulates synaptic activity)
Depending on the type of NT if it can stimulate or inhibit action potential
Neuropil
Network of fine cellular processes emerging from neurons & glial cells that resembles collagen by light microscopy
Describe the CNS glial cells
- Oligodendrocytes- Origin: neural tube. Extend many processes-> becomes sheet-like-> wraps a nearby CNS axon-> most cytoplasm moves out of the growing extension-> leaving cell membrane (myelin). Predominant glial cells in white matters. Morphology in light microscopy: small cells with rounded, condensed nuclei & unstained cytoplasm (d/t abundant Golgi). Funtions:
- Myelin production in more than 1 axon
- Electrical insulation
- Astrocytes- Origin: neural tube. Large # of long radiating, branching processes. Glial fibrillary acid protein (GFAP) makes up bundles of intermediate filaments located at proximal region (unique marker for astrocytes). Distal lack GFAP which then is not readily seen by microscopy and its synaptic sites. Most common glial cells of the brain. Fibrocytic astrocytes have long delicate processes, abundant in white matter. Protoplasmic astrocytes have many short processes, predominates in the gray matter. Astrocytes communicate via the gap junctions.
- Ependymal cells- Origin: neural tube. Columns or cuboidal cells that line the fluid filled ventricles of brain & central canal of spinal cord. In some apical ends, have cilia that facilitates movement of CSF and long microvilli involved in absorption. It is joined apically by apical junction complexes similar to epithelial cells. NO basal lamina- basal ends extend into the adjacent neuropil.
- Microglia- small cells and actively mobile processes evenly distributed throughout gray and white matter. They are NOT interconnected since they are constantly used in immune surveillance of the CNS tissue. They do NOT originate from progenitor cells but form blood monocytes. Morphology in H&E: nuclei-> small. dense, slightly elongated. Immunohistochemistry: demonstrates microglial process.
Myelin sheath
Composed of mostly lipid that which appears white under the microscope.They encapsulate the axon and facilitate rapid transmission of nerve impulse.
Astrocytoma
Atrocytoma is a tumor derived from fibrous astrocytes. They can be distinguished by their expression of the GFAP.
Meninges and the 3 layers
Meninges are membrane of connective tissue between bone and nervous tissue that covers the CNS.
3 layers:
- Dura mater (tough mother)- Dense irregular connective tissue organized as an outer periosteal layer continuous with the periosteum of the skull and an inner meningeal layer. Along the superior sagittal surface, they separate to form a blood-filled dural venous sinus. Separated from the arachnoid by thin subdural space.
Epidural space- contains a plexus of thin walled veins and loose connective tissue that separated dura mater from the periosteum
- Arachnoid- CT is avascular- 2 components:
- Sheet of loose connective tissue in contact with the dura mater
- System of loosely arranged trabeculae composed of collagen and fibroblasts continuous with the underlying pia mater
Arachnoid villi- functions in releasing excess fluid into the blood
Subarachnoid space- sponge-like cavity that surrounds the trabeculae. Filled with CSF. Protects CNS from minro trauma. Communicates with the ventricles of the brain where CSF is porduced.
Leptomeninges- also called Pia-arachnoid which arachnoid has a very close association with the Pia mater
- Pia mater- most delicate innermost part consists of flattened, mesenchymally derived cells.
Glial limiting membrane or glia limitans- thin superficial layer of astrocytic processes that separate pia from nerve cells or fibers
Spinal Meninges:
1)Dura Mater – “Tough Mother”
- No periosteal layer
- Epidural space filled with adipose tissue
2)Arachnoid Mater – “Spider Mother”
- No arachnoid villi
- Subarachnoid space still filled with CSF
3)Pia Mater – “Tender Mother”
•Tightly adheres to spinal cord
Identify the glial cell in CNS
Astrocytes
Euchromatin and Heterochromatin within the astrocytes are sometimes described as salt and pepper
Identify the glial cell in CNS
Oligodendrocytes
Smaller-sized nuclei that are a lot heterochromatic
Much more punctate, smaller nuclei than astrocytes.
Identify the glial cell in CNS
Microglia
Can be identified by their spindly and flattened nuclei that often occur in solitary fashion
Identify the glial cell in CNS
Ependymal cells- cuboidal-looking cells that are lining the ventricular spaces of the CNS (filled with CSF)
May resemble an epithelial tissue-> but to verify, ependymal cells do not have basement membrane
Also see the lining of choroid plexus (lack BBB)
Identify the glial cell in PNS
Schwann cells-
Rich with phospholipid bilayers that is repeatedly wrapped around the axon (pale staining)
Notch in between is node of ranvier
Flattened nuclei belong to schwann cells- pushed to the periphery of the wrappings
Identify the glial cell in PNS
Satellite cells
Form a barrier between neuron cell body and extracellular environment inside the Ganglion.
Layers of cerebral cortex and cerebellar cortex
There are 6 layers of the cerebral cortex.
There are 3 layers of the cerebellar cortex:
- Molecular- thick outer layer with many neuropil and scattered neuronal cell bodies
- Purkinje cell layer- thin layer consists only of very large neurons (purkinje cells) with dendrites extending throughout the molecular layer
- Granular layer- thick inner layer that contains various very small, densely packed neurons (including granule cells) & little neuropil
Anterior horn, Posterior horn, and Cental canal
Remember SAME DAVE!
Anterion horn- contains cell bodies of motor neuron (axons make up the ventral root of spinal nerve)- MULTIneuron
Posterior horn- (interneurons) receive sensory fibers from neurons in the spinal (dorsal root) ganglia- MULTIneuron
- Dorsal root ganglion- collection of unipolar sensory neuron cell bodies
- Spinal nerve- combination of motor and sensory axons
Central canal- developed from the lumen of neural tube. Continuous with ventricles of brain. Lined by ependymal cells. Contains CSF.
Capillary Endothelium
Main structural component of BBB
Tightly sealed by occluding junctions
Little or no transcytosis activity
Surrounded by basement membrane
Limiting layer of perivascular astrocytic feet envelopes the basement membrane of capillaries
Illustrate and describe supporting tissues of the nerve
Nerves- bundles of nerve fibers in PNS. Whitish glistening appearance because of myelin and collagen content.
Endoneurium- external lamina of Schwann cells. Consists of reticular fibers, scattered fibroblasts, and capillaries. Loose connective tissue to reticular connective tissue.
Perineurium - sleeve that covers fascicles (bundles of axons with Schwann cells). Contains flat fibroblasts and edges are sealed together by tight junctions. Dense irregular to loose connective tissue. 2-6 layers of this make up the blood-nerve barrier.
Epineurium - Dense irregular connective tissue- toughest of all the layers- fibrous coat of peripheral nerves that fills the space between fascicles.
Describe Regeneration after injury to axon
Injury to CNS or PNS->
(when neuronal cell body is intact)
2 weeks: Chromatolysis ( color degeneration d/t RER degeneraion)- cell body swells lightly. Nissl bodies is initially diminished. Nucleus migrates to a peripheral position within the perikaryon->
Nerve fibers distal to injury degenerates along with its myelin sheath->
Debris is phagocytosed by macrophages->
3 weeks: Muscle fiber shows denervation atrophy but Schwann cell or Oligodendrocyte proliferates to form a component cord penetrated by the growing axon->
3 months: Regeneration success and functional connections with muscle fibers are restored.
Identify the dark staining and the pink staining regions
Dark staining- cell bodies of neuron
Pinkish- neuropil (neuron extension and glia)
Identify the classification of neurons
Polygonal structure with extension-> cell body of neurons-> multipolar neurons
Clear area on the center of the body- nucleus with the nucleolus
Nissl bodies- basophilic staining-> quite active in terms of transcription and translation
Identify the cells in the backround
Glial cells on the background
Salt and pepper speckles-> nuclei that belong to the astrocytes
More punctate, smaller more condensed nucleoli-> belong to the oligodendrocytes
Background-> all neuropil (dendrite extensions, axon extensions and glial cells)
Microglia or endothelia?
Endothelial cells lining the capillary-> when flattened cells are grouped together and not solitary
When its solitary-> it belongs to Microglial cells
Classify this neuron from gray matter
Multipolar neuron in gray matter
Identify backgound cells
Astrocyte nuclei-> more euchromatic
Oligodendrocyte nuclei->smaller, darker, more punctate, heterochromatic
Neuropil-> fibery structures in the backgound
Identify the light staining areas
Many tracts emerging from the ventral horn of the spinal cord
Pale staining structures-> myelin sheaths by the oligodendrocytes
Identify the blue structure
Meninges
Identify cell bodies
Dorsal root ganglion (spinal ganglion)-> oval and large cell bodies-> unipolar neurons-> site where unipolar cell bodies are all aggregate together in the PNS
Identify the glial cell
glial cells (satellite cells) outline just outside of the unipolar neuron cells
neuron cell bodies- large euchromatic nucleus with punctate nucleolus & large cytoplasm containing lots of Nissl bodies
Identify the middle portion
Central canal-> contains CSF-> lined by ependymal cells
Describe the cerebrum neural tissue
Gray matter- more cell bodies
White matter- more axons
Gyri- folds or hills 😉
Sulci- grooves or sulken or sunken 😊
NEURAL TISSUE CEREBRUM IS QUITE VASCULAR!
Identify cell pointed
Oval, large, euchromatic of neuron cell bodies-> distinct and punctate nucleoli-> cytoplasm are basophilic d/t Nissl bodies
Identify cell pointed
Astrocytes-> euchromatin, heterochromatin cytoplasm, punctate nucleoli
Identify cell pointed
Oligodendrocytes
Identify the region in cerebrum
White matter-> majority of nuclei are those of glial cells
Identify the location and name the external layer
Cerebellum-> with gyri and sulci too
External layer: Molecular layer contains lots of neuron cell bodies, neuropil
Identify layer
2nd layer: Purkinje cell layer-> contains interneurons (multipolar Purkinje cells) that have elaborate dendrites that extend to the molecular layer and axon fibers that branch extensively into the inner layer of cerebellar cortex-> allows communication and neural network and inner most layer
Identify layer
Inner layer: Granular cell layer-> most cellular-> layer that contains the smallest sized neuron cell bodies in our anatomy d/t the granular appearance
What does the medulla of the cerebellum comprise of?
Medulla of the cerebellum-> comprised of white matter
Classify neuron and state location
Unipolar neurons-> from the cell body, short cytoplasmic extension coming out & branching immediately into the proximal and distal branches with the proximal branch plugging into the spinal cord synapse with the multipolar interneurons that are in the dorsal horn of the spinal cord
Euchromatic nuclei-> highly active
Punctate nucleolus-> suggesting construction of ribosomes
Speckled cytoplasm-> full of Nissl bodies consistent
Found in Dorsal Root Ganglion
Identify pale staining regions
Axons-> Pale-staining regions are with myelination
Identify the structure pointed
Node of ranvier-> where axon cell membrane would depolarize
Identify the structures on the topmost and bottommost parts of the image. State how to distinguish from different connective tissue and muscle types.
Perineurium which contains flat fibroblasts
To distinguish: Smooth muscle will have more regularity in shapes of the nuclei and tissue will be more cell dense and no pale staining regions
Dense irregular CT-> collagen fibers run in 1 parallel direction, and it will be less cellular. Also, nuclei will be flatter and highly condensed (fibrocytes)
Identify the structures
- Dura mater- dense CT
- a. epidural space (above the dura)
- b. subdural space (below the dura
-
Arachnoid mater- delicate loss CT
* d. subarachnoid space- actual space filled with CSF - Pia mater- delicate and thin CT
Identify the structures
- Epineurium- dense CT
- Perineurium- around a fascicle
- Endoneurium- delicate basement membrane around each axon or Schwann cell
