Nerve 1 Flashcards
Describe the cell body of the typical neuron
-portion of the cell with the nucleus and other organelles (e.g, noiseless bodies- rER)
Describe the nerve fibers of the typical neuron(dendrite)
Dendrite:
-Unmyelinated arborizations extending from a neuronal cell body
- receive stimulus from the environment and other neurons and carries impulse towards the cell body from another neuron
- contains cytoplasmic contents similar to the perinulcear
Describe the nerve fibers of the typical neuron (axon)
- myelinated portion of nueron
- output portion of a neuron that carries nerve impulse from the cell body toward another neuron, muscle cell or gland
- contains microtubules, microfilaments, mitochondria, vesicles (with proteins including neurotransmitters )
What are the fibers of the typical neuron ?
Dendrite and axon
What are the categories of neurons ?
- sensory
- type of fiber =afferent (so,stick or visceral)
- structure- pseudo polar or unipolar
- carry - sensory (voluntary/involuntary) impulses
Interneurons
- type of fiber- afferent and/or efferent
- structure= multipolar
- carry- sensory/motor impulses
Motor
- type of fiber: efferent( somatic or visceral)
- structure: multipolar
- carry motor (voluntary/involuntary ) impulses
What is the normal structure of a sensory neuron ?
a) general sensory- pseudo-unipolar), e.g. pain, (with cell bodies in DRG)
b) special sensory (bipolar) e.g. eyes (with cell bodies in retina
What is the general structure of a motor neuron?
a) somatic voluntary (e.g., skeketal muscle)
b) autonomic involuntary (e.g. smooth muscle)
What are the structures of integrative (communicating network ) neurons?
A. Pyramidal
B. Interneuron
C. Purkinje
Summarize the interaction of a sensory neuron
Have part of their nerve fibers (axons) begin in the skin or an organ in the PNS and the other part of their axons are directed towards the CNS. Cell bodies are in the dorsal root ganglia (DRG)
Summarize the interactions of integrative neurons
Interconnect eg. Interneurons in spinal cord. Have cell bodies in dorsal horn of spinal cord
Summarize the interactions of motor neurons
Have their cell bodies located in the CNS eg. Ventral and intermediolateral horns of the spinal cord, and their axons are directed towards the peripheral nervous system (PNS) eg. to skeletal muscles or smooth muscles, cardiac muscles and glands
What is axonal transport?
Bidirectional movement of materials between cell body and processes
What are the types of axonal transport ?
Anterograde:
- motor protein involved-kinesin
- slow or fast
Retrograde:
- motor protein involved- Dynein
- fast
Clinical importance: route used by toxins abs viruses to enter nervous system
Contrast anterograde and retrograde axonal transport
Anterograde: towards synapse; flow of synaptic vesicles, mitochondria etc.
Retrograde: towards CB; recycled membrane vesicles , neuromodulators
Contrast ganglia and nuclei
Ganglia are clusters of nerve cell bodies outside the CNS
Nuclei are clusters of nerve cell bodies inside the CNS
Summarize location and structure of sensory neurons
Location- craniospinal (DRG, cranial nerves)
- Pseudo-unipolar neurons (general sensory)
- larger cell bodies
- close together
- thick fascicles of fibers alternating with bundles of cell bodies
- Bipolar neurons (for special senses)
Summarize the autonomic nervous system
Sympathetic and parasympathetic nervous system
Multipolar neurons
-relatively smaller cell bodies
- further apart from each other
- diffuse nerve fibers between cell bodies
Summarize the histology of sensory ganglia- DRG
- centrally located cell bodies
- large pale staining central nuclei
- No synaptic connections
- Groups of pseudo-unipolar cell bodies alternating with thick fascicles of nerve fibers (axons)
Summarize the histology of sympathetic ganglia
- eccentric cell bodies with multiple processes
- random bundles of fibers mingled with the somas
- dispersed multipolar cell bodies
- Synapsing occurs between neurons
Explain in DETAIL neuroglia
Neuroglia Or glia - are non- neuronal cells that support, insulate or nourish neurons. They can be found in both the central nervous system (CNS) and the peripheral nervous system (PNS). Peripheral neuroglia includes- Schwann cells and satellites cells. Central neuroglia includes- astrocytes, oligodendrocytes, ependymal cells and microglia cells
What is the function of a protoplasmic astrocyte?
- prevalent in the gray matter
- branching cytoplasmic processes
- maintain the blood CSF barrier
-contains GFAP (protein of the intermediate filament family) helps provide structural support/strength to cells
What is the function of fibrous astrocytes?
- prevalent in white matter
- Has straight cytoplasmic processes
- contain GFAP
What do fibrous and protoplasmic astrocytes have in common?
- support and regulate movement of metabolites and wastes in neurons
- maintain the blood-brain barrier
- protect bare areas of neurons
What are microglia?
Smallest type of central microglia
- originate from hematopoietic (blood cell line)
- functions in phagocytosis of bacteria, removal of debris & injured tissue
- Has abundant spikes/ ruffled border cytoplasmic processes
What are oligodendrites?
- myelinate axons in the CNS
- have tongue-like cytoplasmic processes
- larger nodes of fancier - increases efficiency of nerve conduction
- one oligodendrocyte myelinates portions of several axons
What is the function of ependymal cells?
- epithelium lining of the CNS cavities
- cuboid to columnar cell type
- have characteristic of fluid transporting/absorbing cells ( cilia, microvilli, basal in folding)
- found in choroid plexus- modified cells that interact with capillaries and help secrete cerebrospinal fluid
What is the Schwann cell?
- myelinate neurons in PNS. Several Schwann cells myelinate portions of the axon
- provide support for both myelinated and unmyelinated axons in the PNS
- clean up debris
- scaffolding for regeneration of nerve tissue
What are satellite cells?
- small cuboidal cells
- surround the cell body of neurons in PNS
- regulate the perineuronal environment
- electrical insulator, does NOT MAKE MYELIN
- Regulate metabolic exchange
What is myelin?
- lipid rich layer around the axons of neurons
- formed by the mesoaxon of the Schwann cells
- serves to insulate/ support axons of nerves fibers from the environment surrounding the endoneurium
- facilitates rapid conduction of nerve impulses
What are the myelinating cells?
- Schwann cells (PNS)
- Oligodendrocite(CNS)
Explain the formation of myelin sheath
-Axon lies in a groove of the Schwann cell’s surface
- Schwann cell plasma membrane forms two distinct polarized domains
- abaxonal plasma membrane
- adaxonal plasma membrane
Mesoaxon-formed when the abaxonal and adaxonal membranes connects, which closes off the extracellular environment
- Concentric sheaths of myelin are laid around the axon
- Thickness of the myelin sheath is determined by the diameter of the axon, regulated by neuregulin-1 protein
As myelin is laid down, the sheaths contain small amounts of cytoplasm allowing for connections within the Schwann cell:
-inner collar of Schwann cell cytoplasm
+between axon and myelin
- Schmidt-Lanternmann clefts
- small islands of cytoplasm within lamellae of myelin
Perinodal cytoplasm at node of fancier
- Outer collar of Schwann cell cytoplasm
- around myelin (most times where cell nucleus is located)
Contrast myelin vs nerves
Myelinated nerves-
-they have multiple concentric layers of myelin sheath around one axon
-the nerves are devoid of myelin at the nodes of ranvier, axon hillock, and terminal arborizations
Unmyelinated nerves
- Axon/axons rests in a cleft of Schwann cell cytoplasm, each with a single mesoaxon
- No myelin sheaths formed
What is impulse conduction?
- Impulses received by the dendrites are conducted to the cell body
- Action potential is triggered
- Nerve impulse is conducted along the axon
- Wave of depolarization passes along the axon through the nodes of Ranvier
- Faster in myelinated vs Unmyelinated axons
