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FSU PET 3322 - The Nervous System

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Anatomy and Physiology Exam 2- Figueroa GOOD LUCK! :)The Nervous System•The nervous system controls our behaviors, memories, and movements•Functions:•Sensory- sense changes both internally and externally via sensory receptors•Afferent •muscle -> brain•Integrative- allows us the ability to analyze the sensory info received, store aspects, and make decisions •Motor function- response via movement in reaction to stimuli by initiating action•Efferent•brain -> muscle•Easy way to remember which comes first: A comes before E... so the sensory neurons need to be stimulated first -> then it sends impulse to the brain which processes it -> then the brain says what to do by stimulating the motor neurons to give a reaction movement•Synapse = connection•If reaction involves the brain it is NOT a reflex. It is only a reflex when it is involuntary and the brain is not involved•the Nervous system has 2 main divisions: •Central Nervous system (CNS)•“Central” = center of the body. The brain, midbrain, and spinal cord are all in the center of the body•Peripheral Nervous system (PNS)•consists of cranial and spinal nerves•these nerves contain both sensory and motor fibers•connects CNS to muscles, glands, and all sensory receptors•made up of 2 systems:•Somatic Nervous system (SNS)•control muscles connected to bone•“soma” = “body”•Autonomic Nervous system (ANS)•controls internal organs•Enteric Nervous system is part of the ANS•**do NOT focus on the ANS for exam 2**•Sensory (Afferent)•Somatic fibers carry impulses FROM the skin, skeletal muscles, and joints TO the brain•Visceral fibers carry impulses FROM visceral organs TO the brain•organ -> brain•Motor (Efferent)•impulses are sent FROM CNS TO effector organs•brain -> organ•Neurons •a neuron is the main functional unit of the Nervous system•produce action potential ( electrical signal)•excitability•made up of a single nucleus with a prominent nucleolus•2 kinds (sensory and motor)•sensory = afferent neurons•motor = efferent neurons•Structure:•have 2 propagations (processes)•Dendrites- receive signals•Axons- contains plasma membrane. End in a axon terminals•transmits electrical impulses produced by the soma•Soma-the “body.” Everything (organelles) in a cell is in the soma•receptive or input region•contains receptors•receives stimulus•connected to dendrites•produce neurotransmitters and electrical impulses• Axon terminal- where neurotransmitters are stored and released upon stimulation•Action Potential- the signal that will propagate (travel/transport)•can travel long distances•Think of baseball:•player= receptor •ball = neurotransmitter•pitcher= axon terminal•Myelin = a lipid (fat)•increases the speed of nerve impulse conduction from the soma to the axon terminal• myelinated axons are surrounded by myelin•Unmyelinated axons have slower nerve conduction•Myelin AND axon diameter are factors for how fast a neurotransmitter can travel•the larger the diameter, the faster the impulse•fastest= myelinated, wide axon•White matter- mostly myelinated axons•Gray matter-neuronal cell bodies, dendrites, unmyelinated axons, and axon terminals•the different colors are caused by which part of the neurotransmitter is on the inside/outside•Soma is more dense; therefore, it makes up gray matter•the brain consists of the gray matter surrounding the white matter•the spinal cord consists of white matter surrounding the gray matter•Neurons are excited due to the voltage difference across their membrane•Types of Ion Channels •Ligand- gated channel•open and close in response to a stimulus•Figueroa gave the example of the teacher parking lots on campus•Na+ = car•key/card= neurotransmitter (Acetlycholine or Ach)•gate= gate•receptor= the little box that reads the card•the gate can only be opened when a neurotransmitter connects with a receptor in an instant ( doesn’t need to stay), then the gate opens and the Na+ can travel in•Na+ diffuses into the cell•Voltage- gated channel•open in response to a direct change in the membrane potential•Resting Membrane Potential (the electrical charge inside the membrane) •Negative ions (ex. Cl-) and sodium are inside the cell membrane•Positive ions are outside the cell membrane•Potential energy difference at REST is -70mV•this is caused by:•the extracellular fluid containing a high amount of Cl- and Na+•the cytosol containing a high amount of K+, organic phosphate, and amino acids•membrane permeability•the membrane is 50-100 times more permeable for K+•Na+/K+ pump removes Na+ as soon as it leaks in•K+ flows out of the cell at a higher rate than the flow of Na+ into the cell•Action Potentials! •a nerve impulse/ stimulation•triggers the release of neurotransmitters•a sequence of events that causes the membrane potential to decrease so much that it reverses (becomes positive) and then it restores itself by becoming more negative until it reaches its resting state•during an action potential: voltage-gated Na+ and K+ channels are OPEN•a stronger stimulus will NOT cause a larger impulse•REMEMBER: polar means it is NEGATIVE•Neurotransmitter opens the gate of the channel, allowing Na+ to enter the cell•Na+ goes into the cell -> causes depolarization•once a cell becomes positive, the K+ channels open and K+ leaves the cell, Na+ channels have already closed -> repolarization•this causes the cell to become more negative since potassium is positive and it is leaving•REMEMBER: even though Na+ is traveling into the cell, there is ALWAYS more Na+ outside of the cell than inside•Depolarization- make less negative (aka to more positive)•stimulus causes potential to exceed threshold (-55mV)/ become more positive than the threshold•Na+ diffusion•Positive Feedback process!•Repolarization- to make more negative, back to normal polarity•Hyperpolarization- more negative than at rest (so more negative than -70mV)•is a part of the stimulation due to an action potential•hyperpolarization occurs once the potential reaches -90mV, causing the K+ channels to close, and the membrane potential returns to resting potential•Resting potential = -70mV•Threshold = -55mV•if it does not reach the threshold, then the action potential doesn’t occur•Propagation - moving or traveling of an action


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