EXAM 3 REVIEW:Chapter 12- Nervous Tissueo Nervous System Cellso Neurons- nerve cells, conduct electrical signals (action potential) Neurogilia= provide support to neurons - Make up about ½ volume of CNS- Astrocytes (of CNS): star-shaped cells, largest and most numerous of neuroglia- Oligondedrocytes (of CNS) - smaller and contain fewer processes compared to astrocyteso Responsible for forming and maintain the myelin sheath around CNS axon- Shwann Cells (of PNS)- myelinates a single axon, participatein axon regeneration Neurons have excitable tissue cause a change in voltage to become either more positive or negative- Fast process- Short duration and specific Parts of neuron:- Dendrites: receive input- Axon- carries impulse/action potential- Cell body- basic functions of neuron- Axon hillock- sums graded potentials - Axon terminal- forms synapse and releases neurotransmitterso Myelinationo Function: to speed up operationo Sheath consists of fat and protein coveringo Node of Ranvier- gaps in myelin sheath What allow action potential to move along axon propagate speedo types that produce myelin sheaths: Schwann cells in PNS Oligodendrocytes in CNSo White vs. Grey Mattero White Composed primarily of myelinated axons Whitish color To try to help secrete linkage from one to another Conduction Brain and spinal cord are highly myelinated - Speed=fast- Provides link between areas/regiono Grey Contains neuronal cell bodies, dendrites, unmyelinated axons, axonterminals, and neuroglia Grey because the Nissl bodies impart appears gray color and there is little or no myelin in the areas Neural processing Analysis Interpretation Higher order of thinkingo Blood brain barriero Barrier around the brain that controls permeability of different substances Very selectiveo To transport glucose for neuron tissue, keep drugs out as well as pathogenso Astrocytes help form blood brain barriero To get through blood brain barrier: Fat soluble materials (O2,CO2, C2H5OH)= free diffusion Glucose= active transport Water soluble materials= slow process in Drugs/proteins= blocked o Disruption: dizziness, unconsciousness, death Trauma to head can cause leakage of proteins into plasmao Ion Channelso Leak Channels randomly open & close Plasma membrane have many more potassium ion (K+) leak channels than sodium ion (Na+) leak channels, and the potassium ion leak channels are leakier than the sodium ion lean channels Membranes permeability to K+ is much higher than its permeability to Na+ Move down its gradient Leak channels and ion pumps complement each other to maintain a constant electrical potential Found in all cells of all types of neuronso Ligand-gated channels open when ligand-chemical binds with receptor- neurotransmitters, hormones, and particular ions can open or closeo ex: acetylcholine (neurotransmitter) opens cation channels that allow Na+ and Ca2+ to diffuse inward and K+ to diffuse outward located in the dendriteso mechanically-gated channels open through a mechanical stimulus- touch=pressure- vibration (sound waves) - tissue stretching force distors the channel from its resting position, opening the gate found at dendrites found in sensory receptorso voltage-gated channels opens in response to a change in membrane potential (voltage)- electrical signal open when meeting threshold (-55mV) participate in the generation and conduction of action potentials in the axons and axon terminal of all types of neuronso Resting Membrane Potential o Small buildup of charges along the potential membraneo This causes a potential energy because of the positive and negative charges The greater the difference in charge across the membrane, the larger the membrane potential (voltage)o Overall net charge between the extracellular fluid and cytosol are equal/neutralo Normally -70mV Due to sodium potassium pump, K+ leak channels let even more positives outo Established by leak channels There are more potassium leak channels than there are sodium channels, so more positive potassium ions go out of cell than positively sodium ions that diffuse ino Maintained by the Na+/K+ pump Maintain high (K+) inside neuron and high (Na+) outside neurono Establishing Membrane Potential o Factors that contribute to RMP Na/K pumps: - Sodium in, potassium out- Na+ moves against gradient- ATP- 3 potassium (K+) moves out, 2 sodium (Na+) move ino more positive out, more negative inside Anion impermeability:- inability of most anions to leave the cell- Anions inside cell are not free to leave because they are attached to non-diffusible molecules such as ATP and large proteinso Na+ increases inside= becoming more negative Ion and ion channel disparities: unequal distribution of ions- Large and charged- Permeability of Na+ is low because of few sodium leak channelso Sodium ions diffuse slowly inward, down gradient- As more K+ move out of cell= inside becomes more negativeo Graded potentialo Small deviation (local change) from the resting membrane potential that makes the membrane either more polarized (inside more negative) or lesspolarized (inside less negative) Travel few mm only Very local changes, occurring in dendrites and cell body of a neurono Occurs when a stimulus causes mechanically-gated or ligand-gated channels to open or close in an excitable cell’s plasma membraneo Establishing resting membrane potential o Membrane potential becomes more positive (excitatory) or more negative (inhibitory) Excitatory potential - More positiveo Ex: ligand gated Na+ channel Ligand binds= activation Positive moves in to make less negative As it opens, ligand dissociated from receptor, increases in potential and then it closes and goes back to resting membrane potential Quick bc it needs to go back to rmp (-70mV) Inhibitory potential- More negativeo Ex: ligand gated Cl- channelo Hyperpolarizing=negative potentialo More negative because Cl- ions move into cello Graded Potential Strengtho Directly proportional to signal Bigger signal= more changeo Local, quick, travel across dendriteso Do not exhibit a refractory periodo Temporal Summationo Process by which graded potentials add together As they get closer= bigger summationo Spatial Summationo Magnitude directiono All graded potential has to arrive simultaneouslyo Sum of inputs from different sourceso Dendrites receive both excitatory
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