Flashcards in Nervous Tissue Deck (51):
Two cell types and functions of nervous tissue
Neurons - receptive, integrative, and motor function
Neuroglial cells - Support and protection of neurons
Derived from ectoderm
What is the CNS?
Central nervous system consisting of brain and spinal cord. Integrative and control centers of body
What is PNS?
Peripheral nervous system consisting of cranial nerves and spinal nerves. Communication lines between the CNS and the rest of the body
What are afferent neurons?
Sensory nerves, somatic and visceral fibers that conduct impulses from receptors to the CNS.
What are efferent neurons?
Motor nerve fibers that conduct impulses from the CNS to the effectors (muscles and glands)
Efferent neurons are subdivided into? What do they do?
Somatic - voluntary, conducts impulses from the CNS to skeletal
Autonomic - Visceral motor, conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands
Autonomic nervous system is subdivided to? Functions?
Sympathetic - mobilizes body systems during activity
Parasympathetic - Conserves energy, promotes house-keeping functions during rest
T or F: There are cell bodies in the PNS
F, only in the CNS or peripheral ganglia
Describe the general structure of a neuron
Cell body (perikaryon, soma), dendrites (receptive region), nucleus, nucleolus (enlarged), Nissl bodies, axon (axon hillock)
What are nodes of Ranvier?
Spacing between neurilemma (myelin) and Schwann cell where saltatory signals are propagated
What are Nissl bodies?
Aggregates of rough ER that stain dark purple in H&E
T or F: Golgi is found in dendrites
F (only organelle not found in neuron extensions)
What is a bipolar neuron?
One axon and one dendrite extension in line with cell body. Very rare, found in olfactory and retina.
What is a unipolar neuron?
Two axons that extend from a common channel off the cell body. Sensor cell type found in dorsal root ganglia
What is a multipolar neuron?
Most common. Motor neuron with dendrites off of cell body and a single axon.
Where are pyramidal neurons found?
Function of sensory/afferent neurons?
Receive stimulus from internal and external environment and conduct to CNS
Function of motor/efferent neurons
Conduct impulses from CNS to other neurons, muscles, glands
What is the function of interneurons?
Connect other neurons in chain or sequence. Important in regulating activity within a network
What three types of cytoskeleton are found in neurons?
Actin microfilaments - 6 nm diameter associated with plasma membrane, structural support
Neurofilaments - 10 nm diameter intermediate filaments in cytoplasm for structural support
Microtubules - 24 nm diameter found in cytoplasm, structural support and transport
Describe axon transport
Anterograde transport to plus end of axon (kinesin active, dynein inactive)
Retrograde transport to negative end of axon (dynein active, kinesin inactive)
Where is the MTOC for neurons located?
Cell body (negative end of microtubule)
What is fast axonal transport?
20-40 cm/day, antero and retrograde, membrane bound vesicles and mitochondria
What is slow axonal transport?
~1 mm per day, anterograde only!, cytoskeleton components and other soluble proteins
What are synapses?
Sites of impulse transmission between pre and post synaptic cells
Two types of synapses?
Electric and Chemical
Define electrical synapses. Common?
Use gap junctions. Not common in mammals
Describe chemical synapse structure
Axon terminal bouton where NT is packaged and released, post-synaptic apparatus containing receptors for NT, synaptic cleft is the gap between the pre and post synaptic membranes which the NT diffuses through
Describe the function of the neuromuscular junction (motor endplate)??
Nerve stimulate release of NT into the cleft (ACh for example) stimulating change in the sarcolemma down the T tubules for fiber contraction. Enzymes in the cleft break down ACh to limit the twitch.
What is myasthenia gravis?
Autoimmune disease against ACh receptor leading to muscle weakness (seen in eyelids first!)
What is botulism?
Toxin from clostridium botulinum which blocks NT release most notably at the Neuromuscular junction
Neurotoxins are common in what?
Snake, spider, insect venoms
Function of oligodendrocyte
CNS myelin production and electrical insulation
Function of microglial cells
CNS macrophage activity (part of MPS)
Function of astrocyte
CNS structural support, BBB, ion homeostasis, NT uptake, growth factors
Function of nervous satellite cell
Peripheral ganglia, structural support, growth factors
Function of Schwann cells
Peripheral nerves, myelin production, electrical insulation
T or F: Peripheral nerves can be made up of both sensory and motor neurons
T (dont typically specify until close to site of innervation)
Describe packaging of a peripheral nerve
Axon surrounded by endoneurium, bundled into fasicles by perineurium, then bundles are bundled b epineurium
Myelin formers in CNS? In PNS?
Oligodendrocytes. Schwann cells.
Describe myelination in PNS
Can be done by Schwann cell which envelops the axon and rotates around in successive layers. Cytoplasm is forced out between membranes to form the sheath
Describe unmyelinated axon in PNS
Schwann cell wraps around multiple axons in a bundle.
Perineurial epitheloid cells are used to?
Establish BBB via tight junctions
T or F: Oligodendrocytes myelinate multiple axons at many points
What is a node of ranvier?
Space between Schwann cells where action potentials are propagated in saltatory transmission
Loss of myelin leads to?
Lesser ability to conduct signal. Disorientation and muscle weakness
Describe hereditary motor and sensory neuropathy Type I
Mutation in PMP-22 causes demyelination of PNS though loss of PMP-22 activity
What is Charcot-Marie-Tooth syndrome Type I
Duplication of PMP-22 results in Schwann cell hyperplasia in PNS. Leads to constriction of nerves and loss of function
What is Wallerian degeneration?
Damaged axon degrades down to last node before cell body. Cell body bloats and loss of Nissl bodies.
T or F: PNS can regenerate