Nervous Tissue A&P Chapter 12

What is the nervous system About 3% of total body weight, one of the smallest but most complex systems. What are some structures of the nervous system? Brain, cranial nerves and their branches, ganglia, enteric plexuses, sensory receptors. The brain is... enclosed by the skull, contains 100 billion neurons, and 12 pairs (rgt and lft) of cranial nerves. What is a nerve? A bundle of hundreds to thousands of axons w/ associated tissue and blood vessels that lies outside of the brain and spinal cord. What is the function of the spinal cord? Connects the brain through the foramen magnum of the skull and is encircled by the bones of the vertebral colum, contains 100 million neurons. Spinal nerves 31 prs, that emerge from the spinal cord, each serving a specific region on the right and left side of the body. ganglia small masses of nervous tissue, consisting mostly of neuron cell bodies, located outside of brain and spinal cord enteric plexuses extensive neurons that help regulate the digestive system sensory receptor used to refer to dendrites of sensory neurons as well as separate, specialized cells that monitor changes in internal or external enviroment Function of the nervous system carries out a complex array of tasks, grouped into 3 basic functions: sensory, integrative, motor Sensory function detect internal stimuli. Info carried to brain/spinal cord through spinal & cranial nerves Integrative function nervous system integrates information by analyzing & storing. Connects Sensory and motor functions.Important function, perception Perception the conscious awareness of sensory stimuli Motor function activates effectors (muscles and glands) through cranial and spinal nerves. Stimulation of the effectors causes contraction and secretion. What are the two subdivisions of the nervous system? Central nervous system (CNS), Peripheral nervous sytem (PNS). CNS consists of... brain and spinal cord PNS includes... all nevous tissue outside of the CNS What are neurons also known as nerve cells, possess electrical excitability. Electrical excitability the ability to respond to a stimulus and convert it into AP Stimulus any change in the environment that is strong enough to initiate an AP An AP or nerve impulse is a.... electrical signal that propagates (travels) along the surface of the membrane neuron, it begins and travels due to K+ and Na+ ions. In what manner does the electrical signal travel? once begun they travel at a rapid and constant strength What are the three parts of a neuron cell body, dendrites, and axons cell body known as the periaryon or soma, contains nucleus and cytoplasm with organelles. What are the three unique features of the cell body -there are nissil bodies located in the rough ER -hypofusion/lipofuscion the yellow pigment -neurofibrils (maintains shape and support) Dendrites structures that receive stimulus and send info to cell body, tree-shaped Axon takes all info from cell body and it is a strong enough stimulus it will send out information, long thin cylindrical w/ branches Where are the places an Axon will send a stimulus? Towards/Away from: neuron along the path, the brain, the spinal cord, glands, muscles, cells, organs Parts of an Axon: Hillock, initial segment, trigger zone, axon collateral, axolemma, axoplasm, axon terminal, myelin sheath Hillock cone-shaped, cell body of axon Initial segment first part of the axon closest to the axon hillock Trigger Zone junction of hillock and initial segment axolemma plasma membrane of the axon asoplasm cytoplasm of the axon axon terminal the many fine processes at the end of the axon myelin sheath only on myelinated axons/ Ex: PNS NTS stands for neurotransmitters What are neurolgia and how large is it? also known as glial, smaller than neurons, 5 to 50X more, take up 1/2 volume of CNS What do neurolgia do? They do not generate AP's, can divide, nourish/insulate/support/protect neurons How many types or neurolgia are there? 6 types. 4 in CNS, 2 in PNS 4 types of neurolgia in CNS Astrocytes, Oligodendrocytes,Microbial cells, ependymal cells astrocytes takes up the excess NTS's and maintains the K+ balance, star shaped cells, largest and most numerous oligondendrocytes produces and secretes myelin, which increases the speed of AP's microbial/ microglia small phagocytic with spinelike projections, eats microbes and cell debris ependymal cells possess cilia and microvilli, lines the surface, secretes CSF (cerebrealspinal fluid) 2 types of neurolgia schwann cells and satellite cells schwann cells myelin sheath (speeds up AP) satellite cells supports neuron cell bodies in the ganglion Nerve Repair -occurs only in PNS -neurolemma repairs damadged axon (schwann cells) nodes of ranvier "sausages" gaps in the myelin sheath, appear in intervals along the axon RMP resting membrane potential electrochemical gradient a concentration (chemical) difference plus an electrical difference what happens when ion channels open? they allow specific ions to move across the plasma membrane how to ions move from a higher concentration to a lower concentration, postively charged cations move toward a neg. charged area ion charges open and close due to... gates/channels leakage channels randomly alternate b/w open and closed. Permeabililty to K+ much higher than to NA+ ligand-gated channel opens and closes in response to a specific chemical stimulus, a wide variety of chemical ligands can open and close channels What are some examples of chemical ligands neurotransmitters and hormones What does the neurotransmitter acetylcholine do? opens cation channels that allow Na+ and Ca+ to diffuse inward and K+ to diffuse outward Mechanically gated channels open or close in response to mechanical stimulation in the form of vibration, touch, pressure or tissue stretching voltage gated channels opens in response to a change in membrane potential (voltage) how does resting membrane potential exist because of a small buildup of -ions in the cytosol along the inside of the membrane and equal buildup of +ions in ECF along outer surface potential energy is measured in... millivolts (mv) what is potential energy a separation of positive and negative electrical charges what is true about the difference in charge across the membrane the greater the difference the larger the membrane potential (voltage) what is graded potential a small deviation from the membrane potential that makes the membrane more polarized or less polarized more polarized the inside is more negative less polarized the inside is less negative hyperpolarizing when the response makes the membrane more polarized depolarizing graded potential when the response makes the membrane less polarized decremental conduction the mode of travel by which graded potentials die out as they spread along the membrane summation the process by which graded potentials add together propagagtion the AP keeps its strength as it spreads along the membrane continous conduction involves step by step depolarization and repolarization of each adjacent segment of the plasma membrane salatory conduction the special mode of AP propagation that occurs along myelinated axons, occurs b/c of uneven distribution of voltage-gated channels nodes of Ranvier (no myelin sheath) the axolemma has many voltage-gated channels what are the two consequences of a current crossing the membrane AP appears to leap from node to node as each nodal area depolarized to threshold=saltatory, opening a small # of channels, energy efficient what three things effect the speed of propagation of an AP amount of myelination, axon diameter, and temperature amount of myelination AP propagates more rapidly along myelinated axons than along unmyelinated axons axon diameter larger-diameter axons propagate AP faster than smaller ones due to their larger surface areas temperature axons propagate AP's at lower speeds when cooled presynaptic neuron the synapse b/w neurons, it is the neuron sending the signal postsynaptic neuron neuron receiving the message axodendritic from axon to dendrite axoaxonic from axon to axon What are the two types of synapses electrical and chemical what are synapses essential for homeostasis b/c they allow info to be filtered and integrated what can come from the disruptions of synaptic communication diseases and neurological disorders electrical synapse AP's conduct directly b/w adjacent cells through structures called gap junctions where are gap junctions common visceral smooth muscle, cardiac muscle, developing embryo, CNS What are two main advantages to electrical synapses Faster communication and Synchronization Faster communication faster communication, b/c AP conduct directly through gap junctions, they are faster Synchronization coordination of the activity of a group of neurons or muscle fibers, can produce AP's in unison Chemical synapses plasma membranes of presynaptic and postsynaptic neurons that are close but do not touch postsynaptic potential type of grade potential caused when postsynaptic neuron recieves chemical signal epsp excitatory and inhibitory posysynaptic potential (neurotransmitter deploarizes the postsynaptic membrane bringing it closer to threshold Inhibitory postsynaptic potential IPSP, neurotransmitter that causes hyperpolarization, membrane potential becomes more negative and farther than threshold iontropic receptor a type of neurotransmitter receptor that contains a NT binding site and an ion channel, are components of the same protein what kind of channel is an iontropic receptor ligand-gated channels when does ESPS or IPSP occur in the postsynaptic cell w/out the ligand, the ion channel component of ionotropic receptor is closed, when correct neurotransmitter binds ion channel opens what do epsp's result in opening of cation channels and allow K+, Na+, and Ca+ through the cell membrane what do ipsp's result from opening Cl channels, when these open chloride ions diffuse inward spatial summation... is the summation of postsynaptic potentials in response to stimuli that occur at different locations in membrane at the same time temporal summation summation of postsynaptic potentials in response to stimuli that occur at the same location in membrane at different times (gradual) acetylcholine (ACh) released by many PNS neurons and by some CNS neurons, when binding occurs w/ ionotropic receptors cation channels open Glutamate glutamic acids (amino acid) powerful excitatory affect asparate aspartic acid (amino acid) powerful excitatory affect gamma aminobutyric acid and glycine GABA and glycine are important inhibitory neurotransmitters, opens Cl channels norepinephrine (NE) plays roles in arousal (awakening from deep sleep), dreaming, regulating mood, serves as hormones epinephrine neurotransmitter, serves as hormones dopamine are active during emotional responses, addictive behavior and pleasurable experiences, help regulate skeletal muscle tone and some mvmnt serotonin concentrated in the neurons in a part of the brain, involved in sensory perception, temp regulation, control of mood, appetite and sleep nitric oxide important w/ widespread effects throughout the body neuropeptides numerous and widespread in both CNS and PNS, bind to metabotropic receptors, have excitatory and inhibitory actions enkephalins 200x stronger than morphine endorphins and dynorphins bodies natural painkillers