CTO Quiz #3 Flashcards
What are some synonyms for “cell body” of a neuron?
Perikaryion; Soma.
What does a neuron look like?
Typically there is a large, euchromatic nucleus with a prominent nucleolus with lots of rER (Nissl Substance) in the cytoplasm. Some neurons contain lipofusin because of longevity.
Where do axons arise from the neuron?
Axons arise from the axon hillock, which is often called the “initial segment” of the axon (where action potentials are first generated).
Where does protein synthesis take place in the neuron?
Protein synthesis takes place in the cell body and, to a lesser extent in the dendrites. There is little (if any) protein synthesis in axons.
What is found in greater abundance in the cytoplasm axon than in the neuronal cell body?
Neurotubules and neurofilaments.
How are things transported within the axon?
Kinesin motors transport things in an anterograde manner along microtubules (toward synapse). Dynein transports things in a retrograde (toward the soma) manner.
What is transported within the axon?
Organelles, such as mitochondria and vesicles. Also proteins and cytoskeletal elements.
What is the difference between fast and slow axoplasmic transport?
How far the kinesin or dynein motor carries something before it detaches and has to be picked up by another transport molecule.
What is the general speed of fast and slow axoplasmic transport?
Slow transport is about 0.2-4mm/day, while fast is 20-400 mm/day.
What are synaptic vesicles?
These are membrane bound structures that contain neurotransmitter.
What are the presynaptic and postsynaptic densities?
The presynaptic density contains the proteins required for docking and release of vesicles of neurotransmitter. The postsynaptic density contains the receptors and associated regulatory molecules and enzymes.
What is an action potential and what ions are responsible for it?
An action potential (nerve signal) is the sudden depolarization of the neuron due to movement of sodium ions through voltage gated sodium channels.
Why do action potentials move in one direction and not “double back” on themselves?
After an action potential, the voltage-gated sodium channel inactivates for a period of time, producing a period in which it cannot be activated (absolute refractory period) and preventing the signal from “doubling back”.
What ion is responsible for the processes that result in release of neurotransmitter from the nerve terminal?
Depolarization at axon terminal opens voltage-gated calcium channels that result in calcium entry which causes docking and fusion of synaptic vesicles (with release of transmitter).
How does neurotransmitter cross the synapse?
Neurotransmitter crosses by simple diffusion. That is why the synapse must be narrow.
What are the possible effects of a nuerotranmsitter on the postsynaptic cell?
Neurotransmitters can be stimulatory (i.e., increase the chances of generating an action potential), inhibitory (decrease the chances of generating an action potential) or modulatory (having some longer term effect on the postsynaptic cell through second messengers).
What are the three mechanisms for termination of action of neurotransmitter?
Inactivation of neurotransmitters occurs by reuptake, enzymatic degradation or diffusion away from the synapse (usually to be taken up by glia).
What are the two broad types of receptors for neurotrasmitters?
Neurotransmitters bind to ionotropic (ligand-gated ion channels) or metabotropic receptors. The latter type consist of transmembrane proteins that are linked to 2nd messenger systems.
What is a Schwann cell?
A Schwann cell is derived from neural crest cells and interacts with axons in the peripheral nervous system. It may simply encase them (as unmyelinated axons) or it may wrap them tightly (as the myelin sheath).
What is the process of myelination of peripheral nerve fibers?
Schwann cells interact with specific signals (glycoproteins) on the axon and on their own membranes to wrap plasma membrane around axons. Gap junctions interconnect the wraps of myelin to allow communication within the sheath.
What transmembrane proteins would be in high concentration at the node of Ranvier?
There is a high concentration of voltage-gated sodium channels at the nodes of Ranvier (to make them sensitive sites of action potential generation).
What is the function of the myelin sheath?
Myelin allows that rapid propagation of signals via salutatory conduction, where the action potentials only need to be generated at the nodes of Ranvier and conduction is very rapid in between (longer break between nodes = faster conduction).
What is the range of conduction speeds from unmyelinated axons to the fastest myelinated axons?
The range is from <100 m/sec.
What are the connective tissue sheaths of peripheral nerves?
Nerve divided like muscle by connective tissue. The epineurium: surrounds the entire nerve. The perineurium: surrounds individual fascicles of the nerve and the enodneurium surrounds each axon.
What are the two general types of ganglia?
The two types of ganglia are the sensory and the autonomic ganglia.
What are satellite cells ?
Satellite cells surround ganglion cells and maintain proper environment.
Where is the gray matter in the CNS ?
The gray matter is located deep in the brain, near the ventricles, or on the surface of the brain (where it is called cortex).
What are the four types of glia found in the CNS and which type is not derived from neuroepithelial cells?
The astrocytes, oligodendrocytes and ependymal cells are glia that is derived from the neuroepithelium. Microglia are derived from mesoderm and migrate into the CNS.
