Neuro - Micro Lab - Exam 1 Flashcards
Grey matter
Red (Triangles) - pyramidal cells
Blue - astrocytes
The gray matter of the cerebrum is further divided into 6 discrete layers, called the CORTEX. The characteristic neuron cell type of the cortex is the PYRAMIDAL CELL, so-called because of their triangular shape, and which can be identified histologically. Pyramidal cells have a thick, branching dendrite located at the apex and a long axon that extends toward the white matter. Numerous ASTROCYTES with round nuclei are also present.
Red circles - Oligodendrites
WHITE MATTER
Note the parallel arrangement of the cell nuclei in the deeper white matter of the brain. OLIGODENDROCYTES are the most common GLIAL CELL seen in the CNS white matter. They produce myelin sheaths surrounding the axons. The processes and sheaths are not visible by routine light microscopy staining. Myelinated axons are seen making the parallel arrangements, or TRACTS, with embedded OLIGODENDROCYTES. The minute blue, dot-like nuclei likely represent MICROGLIAL CELLS.
These are ventral horn cells
VENTRAL HORN – the bilateral anterior horns contain the cell bodies of motor neurons. These neurons’ axons extend out of the spinal cord through the ventral root. You should be able to identify them at low power. They have large polygonal nuclei, prominent nucleoli, and cytoplasm rich in Nissl, all of which indicate extensive protein synthesis to maintain the axons of these cells that extend great distances.
DORSAL HORN – the bilateral posterior horns of the spinal cord contain cell bodies of ascending secondary sensory neurons which receive sensory fibers from neurons in the spinal ganglia (dorsal roots). The primary sensory neurons have their cell bodies outside, but just adjacent to, the spinal cord in the DORSAL ROOT GANGLION (DRG).
White matter
Unlike in the brain, the WHITE MATTER of the spinal cord is peripherally located with myelinated axons wrapped by oligodendrocytes as vertically arranged tracts. At high power you can see the blue nuclei representing oligodendrocytes. The axons, cut cross-sectionally, with their lipid-rich myelin sheaths are difficult to see at this resolution
Red - Perikarya
Green arrows - Satellite cells
Blue arrows - Schwann cells
Motor end plates
This is an AWESOME section of a muscle that has been dissected with a portion of the innervating motor nerve. The muscle fibers appear pink (as in a typical H&E stain) and the nerve fibers are stained black with a silver impregnation stain. Before it terminates in a skeletal muscle, each motor axon bundled in the nerve forms many branches, each of which forms a synapse with a muscle fiber. Motor neurons are typically multipolar with an axon that terminates in a NEUROMUSCULAR JUNCTION (NMJ) on the surface of skeletal muscle fibers. Receptor binding by the neurotransmitter acetylcholine initiates muscle fiber depolarization, which is carried to the deeper myofibrils by the T-tubules.
A motor neuron innervates one or many muscle fibers to control muscle contraction. A motor unit is defined as the neuron and the muscle fibers it supplies. Muscles that require fine control have fewer muscle fibers innervated by each neuron; muscles that participate in less controlled movements may have many fibers innervated by one neuron.
Three layers of connective tissue surround nerve fibers to help support the nerve structure.
ENDONEURIUM – individual axons and Schwann cells are surrounded by a thin, delicate layer of reticular fibers, scattered fibroblasts and capillaries.
PERINEURIUM - bundles of nerve fibers are surrounded by a thicker, 2-6 layers of connective tissue composed of flat squamous fibroblasts with edges sealed together by tight junctions. The resulting “Blood-Nerve Barrier” helps regulate the microenvironment inside the fascicle.
EPINEURIUM - consists of a dense irregular fibrous region with looser deep region that contains larger blood vessels (arteriole, venule, lymphatics).
Blue - axons
Yellow - Schwann cells
Black line - endoneurium
AXONS are easier to identify in cross section, however, SCHWANN CELLS are easier to identify in the longitudinal nerve. Basically, the only nuclei observed in peripheral nerve fascicles belong to SCHWANN CELLS.
You cannot see the NODES OF RANVIER which lie between the SCHWANN CELLS due to the processing artifacts from the amount of lipid composition of myelin. During processing, the myelin lipid gets eliminated, and leaves an artifactual space, or “halo,” surrounding the axons. See Insert.
Pacinian Corpuscles
Sensory neurons are pseudounipolar. Impulses are carried to the spinal cord by the sensory nerves. Sensory nerves have various types of receptors. EXTEROCEPTORS – sensations of external stimuli: pain, temperature, touch, and pressure from the skin and connective tissue. Among the numerous exteroceptors are:
PACINIAN CORPSUSCLES - widely distributed throughout the body and respond to pressure, tension, and vibrations. Typically, they are found in the dermis (but also connective tissue of organs, e.g. wall or rectum and bladder), and appear as cylindrical cores surrounded by 20-70 concentric lamellae of Schwann cells and thin collagen fibers. The neuron’s axon passes through the corpuscle center and terminates in an expanded end.
Multiple sclerosis is an autoimmune demyelinating disease of the CNS resulting in damage to the nerve cells in the brain and spinal cord. The axons become stripped of ___ __ by invading ___.
Processes of astrocytes penetrate the space previously occupied by myelin to form plaques. To what type of cell is the auto-antibody in MS produced? Since peripheral nerves also contain myelin sheaths, why are these nerves not affected?
A: The antibody must be to the ___ or membrane of the ____, but not to Schwann cells.
Multiple sclerosis and Guillain-Barré are two autoimmune demyelinating conditions. Patients with either of these conditions have a loss of myelin . While both of these conditions affect the myelin sheath, they affect different types of myelin.
Guillain-Barre disease involves antibodies against myelin derived from ____ cells but not ___ - the peripheral nervous system is affected instead
Multiple sclerosis is an autoimmune demyelinating disease of the CNS resulting in damage to the nerve cells in the brain and spinal cord. The axons become stripped of myelin sheaths by invading macrophages. Processes of astrocytes penetrate the space previously occupied by myelin to form plaques. To what type of cell is the auto-antibody in MS produced? Since peripheral nerves also contain myelin sheaths, why are these nerves not affected?
A: The antibody must be to the myelin or membrane of the oligodendrocyte, but not to Schwann cells.
Multiple sclerosis and Guillain-Barré are two autoimmune demyelinating conditions. Patients with either of these conditions have a loss of myelin . While both of these conditions affect the myelin sheath, they affect different types of myelin.
Guillain-Barre disease involves antibodies against myelin derived from Schwann cells but not oligodendrocytes - the peripheral nervous system is affected instead
Astrocytes in the CNS and maintain ___ ____ ____.
Schwann Cell is in ___ and myelinates a __ __.
Oligodendrocyte in __ and myelinates ___ axons.
___ cells in CNS and produces cerebral spinal fluid.
Microglia in CNS and involved in ___ __ ___ via phagocytosis.
__ __ in PNS and provides structural and metabolic support to motor neurons.
A: Astrocytes in the CNS and maintain blood-brain barrier.
Schwann Cell is in PNS and myelinates a single axon.
Oligodendrocyte in CNS and myelinates multiple axons.
Ependymal cell in CNS and produces cerebral spinal fluid.
Microglia in CNS and involved in removing cellular debris via phagocytosis.
Satellite cell in PNS and provides structural and metabolic support to motor neurons.
A: dorsal root ganglia - contain pseudounipolar neurons –the neuron shown is MULTIpolar.
Nissl
ER
: Ventral Horn (grey matter). They appear as multipolar motor neurons with abundant Nissl.
Depolarzation and saltatory conduction
A is the unmyelinated nerve and B is myelinated nerve. Note the white “halos,” which is myelin, around the axons in B. The lipid-rich myelin gets washed out during tissue processing, leaving white spaces “halos” surrounding the axons.
A: Peripheral nerve bundle
You can see the endoneurium
