Microanatomy Quiz #3c - Nervous Tissue

3 parts of a neuron, top to bottom:
cell body (soma or perikaryon)
dendrites (usually multiple)
axon (single
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3 parts of a neuron, top to bottom:
cell body (soma or perikaryon)
dendrites (usually multiple)
axon (single
Image: 3 parts of a neuron, top to bottom: cell body (soma or perikaryon) dendrites (usually multiple) axon (single
Nissil Body
Image: Nissil Body
•The function of nervous tissue is to provide a system for communication within the body and between the body and the external environment

•Cellular organization is:
•Neurons
•Neuroglia
Nervous tissue - function and cellular organization
•Basic anatomical organization of nervous tissue is:
•Central nervous system (CNS) = brain and spinal cord
•Peripheral nervous system (PNS) = cranial and spinal nerves and associated ganglia


•Functional organization of nervous tissue is:
•Sensory (afferent)
•Motor (efferent) - Somatic and Autonomic
Nervous tissue - anatomical and functional organization
Basic functional unit that receives and transmits nerve impulses

Consist of three basic parts:
cell body (soma or perikaryon)
dendrites (usually multiple)
axon (single)
Neuron - definition and 3 parts
cell body (soma or perikaryon) contains:
-nucleus that is large and euchromatic and has 1 nucleolus or occasionally several nucleoli
-cytoplasm has abundant RER and polysomes that appear as clumps of basophilic material called Nissl substance or Nissl bodies (chromatophilic substance)


dendrites (usually multiple):
processes extending from the soma; are sites for synapses

axon (single):
-most neurons have just one axon; are very long; transmit signals to neurons or cells of effector organs
-originate from the soma at a region called the axon hillock (no ribosomes in the axon hillock)
-distal end of axon forms a terminal arborization to form synapses
Parts within three basic parts of neuron
Top 2: dendrites
Then top to bottom -
Axon hillock
Axon
Terminal aborization
Image: Top 2: dendrites Then top to bottom - Axon hillock Axon Terminal aborization
Neurons are cells that live a long time.
Lipofuscin is the name for fine yellow-brown pigment granules composed of lipid-containing residues of lysosomal digestion and accumulates in the cytoplasm of muscle and nerve cells. It is considered to an aging or "wear-and-tear" pigment.

Lipofuscin is found in the liver, kidney, heart muscle, retina, adrenals, nerve cells, and ganglion cells.
Image: Neurons are cells that live a long time. Lipofuscin is the name for fine yellow-brown pigment granules composed of lipid-containing residues of lysosomal digestion and accumulates in the cytoplasm of muscle and nerve cells. It is considered to an aging or "wear-and-tear" pigment. Lipofuscin is found in the liver, kidney, heart muscle, retina, adrenals, nerve cells, and ganglion cells.
Lipofusion granules
Image: Lipofusion granules
G: cell body, P: nucleus, yellow - nucleolis, blue - axon
Image: G: cell body, P: nucleus, yellow - nucleolis, blue - axon
L to R: Bipolar, unipolar, multipolar Neuron classification based on shape •Bipolar •Unipolar (pseudounipolar) •Multipolar•Sensory (afferent neurons) - primarily unipolar neurons •Motor (efferent neurons) - primarily multipolar neurons •Interneurons (intercalated neurons - in amygdala) - primarily multipolar neurons Bipolar neurons are primarily sensory cells of the retina, olfactory mucosa, and inner earNerve types based on function and the SHAPE of neurons found there•Protect neurons and support neuronal survival and activities; also participate in the regulation of neuronal propagation of impulses •Gap junctions occur between neuroglial cells •There are more neuroglial cells in the mammalian brain than neuronsNeuroglia (glia)•4 kinds of glial cells are found in the CNS •Oligodendrocytes •Astrocytes •Microglia •Ependymal cells •2 kinds of glial cells are found in the PNS •Neurolemmocytes (Schwann cells) •Satellite cellsTypes of glial cells in CNS and PNS•Oligodendrocytes•Astrocytes•Provide structural and metabolic support to neurons •Remove ions and neurotransmitters that have been released into the extracellular space •Release glucose that can be used for neuronal energy metabolism •Help maintain the blood-brain barrier (BBB) by forming a continuous layer over CNS capillaries via their perivascular feet (end-feet) •Are recruited to areas of damage in the CNS to form cellular scar tissue (glial scar)AstrocytesAstrocyte•Produce and maintain the myelin for myelinated axons in the CNS •Smaller somas than astrocytes •Each oligodendrocyte has multiple processes (up to 50); each process produces myelin for a segment of an axon in the CNS. Thus, one oligodendrocyte can provide a myelin segment for multiple axonsOligodendrocytesOligodendrocyteThe plasma membrane of an oligodendrocyte process flattens out into a sheet-like shape and elongates. As this sheet-like process contacts a segment of an axon, it wraps around the axon multiple times. This happens along the length of the axon and as a result, many oligodendrocytes contribute to the myelin sheath of one axon. The spaces between the segments of myelin are called Nodes of Ranvier. A similar process occurs in the PNSMyelin formationL to R: axon, node of ranvier, oligodendrocyte (myelin sheath formation)myelin sheath formation•Small cells with short, irregular processes. •Migrate through the CNS tissue •Phagocytic; remove debris, viruses and other microorganisms in the CNS •Have other functions, including immune functions •Derived from progenitors in bone marrow; are considered part of the mononuclear-phagocytic cell population.MicrogliaMicroglia •Small cells with short, irregular processes. •Migrate through the CNS tissue •Phagocytic; remove debris, viruses and other microorganisms in the CNS •Have other functions, including immune functions Derived from progenitors in bone marrow; are considered part of the mononuclear-phagocytic cell population.Ependymal cells •Low columnar to cuboidal cells lining the ventricles of the brain and central canal of the spinal cord to form a selective barrier between the brain parenchyma and the CSF; zonula adherens and gap junctions are present; tight junctions are present in some places and absent in others •In some areas ependymal cells are ciliated, facilitating movement of cerebrospinal fluid (CSF); microvilli also are present for absorption of water and other substances from the CSF • Ependymal cells that are part of the choroid plexus participate in producing CSF•Small cells with short, irregular processes. •Migrate through the CNS tissue •Phagocytic; remove debris, viruses and other microorganisms in the CNS •Have other functions, including immune functions Derived from progenitors in bone marrow; are considered part of the mononuclear-phagocytic cell population.Microglia•Low columnar to cuboidal cells lining the ventricles of the brain and central canal of the spinal cord to form a selective barrier between the brain parenchyma and the CSF; zonula adherens and gap junctions are present; tight junctions are present in some places and absent in others •In some areas ependymal cells are ciliated, facilitating movement of cerebrospinal fluid (CSF); microvilli also are present for absorption of water and other substances from the CSF • Ependymal cells that are part of the choroid plexus participate in producing CSFEpendymal cellsEpendymal cellsEpendymal cellsEpendymal cellsEpendymal cellsNeurolemmocytes (Schwann cells) and Sattelite cells2 kinds of glial cells are found in the PNS•Produce the myelin sheaths of axons located outside the CNS (axons in the PNS) •Each neurolemmocyte provides one segment of the myelin sheath for one axon •Collectively, many neurolemmocytes make up the myelin sheath for one axon •The plasma membrane of the neurolemmocyte wraps around the segment of axon many times; these axons are called myelinated axons •The gap between adjacent neurolemmocytes is called a Node of Ranvier where the axon is unmyelinatedNeurolemmocytes (Schwann cells)Top: One neurolemmocyte Bottom: Node of RanvierNuerolemmocytesatellite cellssatellite cellssatellite cells•Collections of neuronal cell bodies outside the CNS are found in structures called ganglia (singular = ganglion) •Satellite cells are small support cells that form a layer over the surface of the neuronal cell bodies in ganglia •Satellite cells provide trophic support for the neurons and regulate their microenvironmentSatellite cellsdescribe organized areas or subdivisions of the CNS; the differences are due to the amount of myelin that is present White matter •The main component of white matter is the myelin from myelinated axons •There are few neuronal cell bodies in white matter, but astrocytes and microglia are present •Looks white in the fresh, unfixed CNS Gray matter •consists of abundant neuronal cell bodies and dendrites •Where most of the synapses occur •Astrocytes and microglia are present •Looks gray (tan-gray) in the fresh, unfixed CNSWhite verse gray matterWhite and grey matterbrain •Gray matter is superficial •White matter is deeperIn the brain.... •Gray matter is ____ •White matter is ____Grey matter •arrows indicate neuronal cell bodies •arrowheads indicate various neuroglia cells •N indicates the area containing a network of axons, dendrites, and glial cell processes which is called neuropilWhat tissue is this, what do arrows, arrowheads, and N indicateWhite matter •arrows indicate myelinated axons •arrowheads indicate various neuroglia cells (mostly oligodendrocytes and astrocytes) •The clear spaces are where the lipid of the myelin was located but was lost during tissue processingWhat tissue is this, what do arrows, arrowheads, and clear spaces indicateSpinal cord •White matter is peripheral •Gray matter is central (this is reversed from the orientation in the brain) Note the following structures central canal ganglion - dorsal rootPoint out white and grey matterWhite matter •Contains myelinated axons organized into tracts •Tracts are collections of axons performing a similar function that run together. Tracts carrying sensory information to the brain are ascending tracts. Tracts carrying motor information to the spinal cord are descending tracts. Gray matter •Has the general shape of an "H" or butterfly •Ventral horn - contains large motor neuron somas (cell bodies) •Dorsal horn - contain the somas of interneuron associated with sensory input •Gray matter also has myelinated axons, but only a few compared to white matter, which is what causes the color differencesSpinal cord organization•Dorsal root ganglia of the spinal cord are sensory ganglia •They contain the neuronal cell bodies of sensory neurons, which are unipolar (pseudounipolar) neurons •These are large neurons have a characteristic appearance in that the nucleus is centrally located in the soma (cell body)•Dorsal root ganglia of the spinal cord are sensory ganglia •They contain the neuronal cell bodies of sensory neurons, which are unipolar (pseudounipolar) neurons •These are large neurons have a characteristic appearance in that the nucleus is centrally located in the soma (cell body)(singular = meninx) •Specialized membranes that provide protection, physical stability, and shock absorption for the CNS •Three layers •Dura mater •Arachnoid •Pia materMeninges and the 3 layersMeninges 3 layers Top to bottom: •Pia mater •Arachnoid •Dura materR to L: •Pia mater •Arachnoid •Dura mater•dense irregular collagenous connective tissue •between the dura mater covering the spinal cord and overlying bone is an epidural space, usually filled with fat and blood vesselsDura mater•middle meningeal membrane •a sheet with fibroblasts, collagen fibers and some elastic fibers •Pressed against the dura mater by CSF that is in the subarachnoid space •The subarachnoid space separates the arachnoid from the pia mater. •The subarachnoid space is spanned by modified fibroblasts and collagen fibers that form bundles called arachnoid trabeculaeArachnoid•Innermost of the three meninges •Adheres to the surface of the spinal cord and brain and follows all of the contours •Composed of a thin layer of flat, modified fibroblasts •The pia mater is separated from neurons by neuroglial cellsPia mater•Innermost of the three meninges •Adheres to the surface of the spinal cord and brain and follows all of the contours •Composed of a thin layer of flat, modified fibroblasts •The pia mater is separated from neurons by neuroglial cellsPia materThe same meninges cover the brain The outer layer of the dura mater serves as the periosteum of the inner surface of the skullWhat meninges cover brainArachnoid trabeculae, meninge in brainsubarachnoid space on left, subdura on right•Folds of tissue that extend into the ventricles of the brain •Folds are composed of a core of pia mater that is covered by a single layer of ependymal cells •The folds contain numerous capillaries •Choroid plexus produces the cerebrospinal fluid (CSF) •CSF fills and circulates in the ventricles of the brain, central canal of the spinal cord and the subarachnoid spaceChoroid plexusChoroid plexus top, ventricle bottomChoroid plexus?Pia matterChoroid plexusBrain ventricles System of interconnected spaces in the brain and spinal cordChoroid plexus tumors (CPTs) comprise approximately 10% of all primary brain tumors in dogs. MRI - A large contrast-enhancing globular 4th ventricular mass is seen An additional smaller contrast enhancing subarachnoid mass also is seen (arrow) Histology sections: A)choroid plexus papilloma (low grade tumor) B)choroid plexus carcinoma (higher grade tumor) a, b, c) CSF cytology from (B)Peripheral nerves are bundles of axons located outside the CNS They have three layers of connective tissue Epineurium - outermost layer; composed of dense irregular collagenous connective tissue; covers the entire nerve Perineurium - surrounds bundles of axons called fascicles; composed of dense irregular collagenous connective tissue but is thinner than epineurium Endoneurium - surrounds each individual myelinated axon; composed of reticular fibers; contacts the basal lamina of the neurolemmocytesPink = epineurium Blue = perineuriumGreen= endoneuriumA nerve fascicle stained with a special stain, so the collagen is green. Red = mylein Blue = perineurium Green= endoneurium black and light blue = axon cytoplasmMyelinated axons cut in cross section; myelin is stained black Each axon is in its own myelinated sheathMyelinated axons seen longitudinallyMyelinated axons seen longitudinally that have been "teased" apart. Notice that the myelin sheath is discontinuous along the length of the axon. These are Nodes of Ranvier (NR)Node of Ranvier is indicated in an H&E-stained section of a nerve seen to the right •Neurokeratin is the pink-stained protein component of the myelin sheath that is "left over" after the lipids have been removed from the myelin sheath by the dehydration process during tissue preparation •The neuronal axon stains pale blue with H&E usually, (as seen in the top photomicrograph) •The neurolemmocytes (Schwann cells) form the the myelin sheathNode of RanvierNode of Ranvier - Longitudinal section of a nerveNode of Ranvier - Longitudinal section of a nerveLongitudinal sections of two nerves at a low magnificationCross section of a nervecollections of neuronal cell bodies located in the tunica muscularis of the intestine These are autonomic motor gangliaMyenteric gangliaMyenteric gangliaMyenteric gangliaWhat would be located hereUnmyelinated axons •Not all axons of peripheral nerves are myelinated. •With non-myelinated axons the neurolemmocyte only envelopes the axon with one fold of their plasma membrane instead of many. •Cerebral cortex on left (the outer layer) Cerebellum on rightArroa - pia matter in the inset: P & G are neurons N is a nucleus of a neuroglial cellSection from a rodent brain that has cerebrum (cerebral cortex)Section from a rodent brain that has cerebrum (cerebral cortex)L: White matter R: Gray matter of cerebrumGrey matter - top White - bottomGrey matter - top White - bottomLight blue - purkinje cell dendrites, pink - their bodies, dark blue - Purkinje cell layer orange - ganglia cell layerdark blue - Purkinje cell layer orange - ganglia cell layerOutermost layer of the cerebellar cortex is the molecular layer, a region relatively free of neuronal somata. composed of the projected axons of the cells of the granule cell layer (see below) and the immensely ramified dendritic trees of the Purkinje cells (see below). The Purkinje cells are the principal integrating neurons of the cerebellum, the classic example of an integrator. From each a large axon descends into the deeper portions of the cerebellum. Its function is to receive input from various sources, make a "decision" to fire or not, and to send a single integrated on/off signal from its own axon reflecting that decision.•Collections of neuronal cell bodies in the CNS are called nuclei and collections of neuronal cell bodies outside the CNS are called ganglia. However, there are exceptions. For example, there are collections of neuronal cell bodies in the brain called basal ganglia. •In the dorsal root ganglion, you cannot "see" that the neurons are unipolar (pseudounipolar) neurons. You know that is the case because you are looking at a sensory ganglion. •Do not confuse the word nerve with neuron.Additional information and some reminders...the appearance of fresh, unfixed tissue. When these tissues are fixed and stained with H&E or other stains, they will take on different characteristics. For example, it is often the case that with H&E, white matter will stain darker than gray matter.The terms gray and white matter refer to .....Collections or groupings of axons in the CNS are called tracts and they are called nerves in the PNSCollections or groupings of axons in the CNS are called ____ and they are called ____ in the PNS