The Nervous System: CNS and PNS1. Define the following: Nissl body, neurofilaments, ganglia, nuclei, tract, nerve, axonal terminals, neurilemma, nodes of Ranvier, endoneurium, perineurium, epineuriumNissl bodyNeurofilamentsGangliaNucleiTract nerveAxon terminalsNeurilemmaNodes of RanvierEndoneuriumPerineuriumEpineurium2. Which part of a neuron is known as the:a. biosynthetic centerCell bodyb. receptive centerDendrites3. Name and describe the function of all 6 types of supporting cellsSupporting cells=neurogliaFour supporting cells are located in the CNSAstrocytesMost abundantNumerous extensions that wrap around neurounsInvolved in forming the blood-brain barrier, a selective barrier that regulates the chemicals environment of the brainRegulate brain functionMicrogliaSince the specific immune system does not have access to the CNS; the microglia act as macrophages to engulf/destroy pathogens and cell debrisEpendymal cellsCiliated columnar cells that line the ventricles—cavities in the brain that contain cerebrospinal fluid (CSF)Currents created by beating of cilia circulate the CSFOligodendrocytesTheir extensions myelinate axons of neurons in the CNSTwo supporting cells are located in the PNSSchwann cells=neurolemmocytesMyelinate axons of neurons in the PNSSatellite cellsSurround cell bodies of neurons and control their chemical environment4. Explain why myelinated axons in the CNS do not regenerate when severed.The microglia poorly clean up area of damage—debridement is not completeNo neurilemma guide growth of severed axonPresence of growth-inhibiting proteins in the CNS inhibit regeneration of a severed axon5. Explain why impulses are conducted faster in a larger myelinated axon than in a smaller unmyelinated axon.Myelinated axons use salutatory conduction where action potentials are generated only at the nodes of ranvier hence, the impulse “jumps from node to node down the axon”Unmyelinated axons use continuous conduction where action potentials developed stepwise across the entire axolemma6. Describe thea. depolarization phase of an action potentialentry of sodium ions=sodium influx, makes membrane potential less and less negativeThreshold potential—action potential develops=an all-or-none phenomenonUpshoot or spike due to an explosive entry of sodium ions=a positive membrane potential reachedb. repolarization phase of an action potentialsodium channels close and potassium channels open and potassium ions rush out=potassium efflux, and reversal of membrane potential toward a negative membrane potential7. What are the absolute and relative refractory periods in an action potential?Absolute refractory period— the depolarization phase of the action potential when sodium channels are opened, another action potential cannot be generatedRelative refractory period— the repolarization phase of the action potential when the sodium channels are closed (potassium channels are open), an exceptionally strong stimulus can cause sodium channels leading to depolarization and the generation of another action potential8. Name and describe the 3 structural classes of neuronsMultipolar neuron has at least three processes—one axon and at least two dendrites; most abundant neuron in the human bodyBipolar neuron has two processes—one axon and one dendritesUnipolar neuron has one short process from the cell body and it bifurcates into a central process and a peripheral process9. Name and describe the 3 functional classes of neuronsMotor or efferent neuron transmits impulses away from the CNS to effector organs=glands, organsSensory or afferent neuron transmits impulses from sensory receptors toward the CNSAssociation neurons or interneuron located in the CNS between the sensory neurons and the motor neuronsMost of the neurons (99%) in the body are associated neurons10. Name and describe the 3 categories (types) of nerve fibers – which type has the fastest conduction velocity and why?Group A fibers—have the largest diameter and heavily myelinated; transmit impulse at the rate of 150 m/s (300 miles per hour)Group B fibers—intermediate diameter and lightly myelinated; transmit impulses at a rate of 15 m/sGroup C fibers—smallest diameters and unmyelinated; transmit impulses at a rate of 1 m/sThe Brain1. Name the 3 structures protecting the brain.Cranium—bony helmet composed of the 8 cranial bones—frontal, parietal (paired), temporal (paired), occipital, sphenoid, ethmoid bonesMeninges—three connective membranes surrounding the brain:Dura mater—outermost meninx; double-layered—outer periosteal layer lining the internal surface of the cranium and the inner meningeal layer separated from the underlying arachnoid mater by the sudural spaceArachnoid mater—middle meninx separated from the underlying pia mater by the subarachnoid space; weblike extensions from the arachnoid mater to the subarachnoid space gives this meninx its name (Arachnida=spider family)The subarachnoid space contains CSFPia mater—innermost meninx that clings to the surface of the brainCerebrospinal fluid (CSF)—filtered from blood; located in the ventricles and also in the subarachnoid space hence, CSF is found inside and outside of the brain acting as a “liquid” cushion; provided buoyancy to the brain; provides nutrients; removes metabolic wastesBlood-brain barrier—a selective barrier that prevents harmful substance in blood from crossing to the brain2. Name and describe the 3 meninges.Dura mater—outermost meninx; double-layered—outer periosteal layer lining the internal surface of the cranium and the inner meningeal layer separated from the underlying arachnoid mater by the sudural spaceArachnoid mater—middle meninx separated from the underlying pia mater by the subarachnoid space; weblike extensions from the arachnoid mater to the subarachnoid space gives this meninx its name (Arachnida=spider family)The subarachnoid space contains CSFPia mater—innermost meninx that clings to the surface of the brain3. Give the function of the CSF.filtered from blood; located in the ventricles and also in the subarachnoid space hence, CSF is found inside and outside of the brain acting as a “liquid” cushion; provided buoyancy to the brain; provides nutrients; removes metabolic wastes4. Define the following: septum pellucidum, interventricular foramen, cerebral aqueductGive the locations of the lateral, third and fourth ventricles.Septum pelluciudum—a thin median membraneInterventricular
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