Lecture 11Outline of Last Lecture I. Basic parts of the nervous systemII. General functions of the nervous systemIII. Introduction to the neuronIV. Reflex ArcsV. Gray and White Matter VI. Segmentation of the Spinal CordVII. CNS vs. PNSVIII. Parts of the BrainIX. Development of the Brain and Spinal CordOutline of Current LectureI. Nervous TissueII. Neuronsa. General information b. Parts of the neuronc. Axonsd. Synapses e. Dendrites f. Grouping of neuron cell bodiesIII. Supporting CellsCurrent LectureI. Nervous Tissuea. Nervous tissue consists of the nerve cells, neurons, plus supportive cells around the neuronsb. Both cell types arise from neural tube or neural crestc. Contains capillaries surrounded by a bit of connective tissue II. Neurons (Nerve Cells)a. Our nervous system contains trillions of neurons, called sensory neurons, motor neurons, and interneuronsb. General Informationi. Each neuron has a cell bodyii. The cell body, which contains the nucleus, is also called the soma and the perikaryoniii. Axons vs. dendrites1. Dendrites: processes that carry electrical activity toward the cell bodya. Graded potential: dendrites do not conduct charge reversal like axon2. Axon: carries an impulse away from the cell bodyiv. Multipolar vs. pseudo-unipolar neurons1. Neurons are classified structurally by the number of processes that have 2. Vast majority have more than 2 BIOL_315 1nd Edition3. Multipolar: have more than 2 processesa. Motor neurons and most interneurons are multipolar4. Unipolar: only 1 process, a single, short, process arises from the cell bodyand divides into two long branchesa. Sensory neurons are unipolarb. One of these branches runs centrally into the CNS: central processc. The other branch extends out to the body’s periphery to pick up the sensory stimuli: peripheral process5. Pseudo-unipolar: seems to have just one process, but actually has two fused togetherv. Nerve fiber: a long neuronal process, long axons, not whole cellsc. Parts of the neuron: the cell body (soma)i. Nucleus: 1. Large, spherical, prominent nucleolus2. Nucleus is clear (unlike other cells) with no condensed chromatin around the inside of the nuclear envelopea. Neurons are active cells with almost all their chromosomes unraveled and extended for frequent transcription of their DNAii. Nissl Substance (made of chromatophilic bodies, or Nissl bodies)1. Collection of closely packed cisterns of RER and free ribosomes within theneuron cell body2. Make the many membranes and structural proteins needed by the neuronsiii. Neurofibrils:1. Bundles of intermediate filaments that run in a network throughout the cytoplasm of the neuron cell body, between the Nissl bodies2. Resist tension placed on celld. Axonsi. One axon per neuronii. Thinner than dendritesiii. Do not branch as much as dendritesiv. Axon collateral: rare branch of an axonv. Can be very long or shortvi. Axon hillock: cone-shaped region of the cell body, lacking Nissl substancevii. End branches (telodendria): branches near the end of the axon1. end in knobs called axon terminals e. Synapsesi. Communication between different neuronsii. Specialized cell junctions that give directionality to the flow of information in the nervous systemiii. Synaptic vesicles: secrete NT chemicalsiv. Synaptic Cleft: the narrow space between the pre- and post- synaptic membranesv. NOT ALL SYNAPSES INVOLVE AXON TERMINALS COMMUNICATING WITH DENDRITES vi. Most synapses are in the CNS, because most communication between neurons is in the CNSf. Dendritesi. Receive information from other neuronsii. Synapsing with axon terminals iii. Neurons with more dendrites receive more synaptic input than neurons with fewer dendritesiv. Appearance of neuron is determined by the pattern and complexity of its dendrites v. Spines projection from the dendrite = dendritic spines1. Sites of synapse with axon terminals g. Grouping of Neuron Cell Bodiesi. Neuron cell bodies are not scattered randomly , but are collected into groups within the PNS and CNSii. CNS:1. Columns, nuclei, and cortexes2. Collection in CNS makes up gray matteriii. PNS: 1. Collection in PNS = GangliaIII. Supporting Cellsa. General Functioni. Supportive functionii. Nutritive function, maintaining the dendrites and axons, and neuron cell bodies in a healthy condition iii. Provide insulation1. Act like rubber coating on wires in a cableb. Neurogliai. In the CNSii. More numerous than neurons iii. Differ from neurons in:1. Being smaller, with smaller nuclei2. Having chromatin on the inside of the nuclear membrane3. Lacking Nissl bodiesiv. The 4 types of neuroglial cells:1. Astrocytes: a. have numerous cell processesb. end feet that touch both small blood vessels and neurons in the CNSc. signal the vessels to bring more blood to supply the tissue when more active d. pump ions to control ionic content of the tissue fluid around neuronse. help synapses work better2. Microglia a. Small phagocytic cells that resemble thorny bush b. Engulf and destroy infectious micro-organisms that enter the CNSc. Phagocytize dead or injured neurons3. Oligodendrocytesa. Have only a few cell processes b. Form myelin in the CNS4. Ependymal cellsa. Line the hollow central region of the spinal cord and brainb. Form a simple ciliated columnar epithelium called