A&P Chapter 11 - Lecture notes 11 PDF

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A&P – CHAPTER 11: FUNDAMENTALS OF THE NERVOUS SYSTEM

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3 Special Features of Neurons  Extreme longevity o Given good nutrition, they can function optimally for a lifetime  Amitotic o As neurons assume their roles as communicating links of the nervous system, they lose their ability to divide o Neurons cannot be replaced if destroyed (exception= stem cells)  High metabolic rate o Exceptionally high metabolic rate requires continuous and abundant supplies of oxygen and glucose o Cannot survive for more than a few minutes without oxygen 3 Functional Regions  Receptive region o Dendrites  Conducting region o Axon  Secretory region o Axon terminals Neuron  A nerve cell; the basic building block of the nervous system  Transmit messages when stimulated by signals from our senses or when triggered by chemical signals from neighboring neurons

Axon Hillock – part of cell body that connects to the axon

Neuron Cell body

A&P – CHAPTER 11: FUNDAMENTALS OF THE NERVOUS SYSTEM

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Also known as soma or perikaryon The cell’s life-support center Contains nucleus and organelles Plasma membrane of the cell body acts as part of the receptor region that receives information from other neurons Consists of clustered free ribosomes and rough endoplasmic reticulum o Rough ER or chromatophilic substance, stain starkly with basic dyes Golgi apparatus o Well developed and forms an arc or a complete circle around the nucleus

Neuron processes  Dendrites  Axons  Bundles of neuron processes; o CNS- called tracts o PNS- called nerves (ie; optic nerve) Dendrites  Neuron’s bushy, branching extensions  Main receptive or input regions  Receive messages and conduct impulses toward the cell body  Increased surface area to receive messages Axon  The neuron extension that passes messages through its branches to other neurons or to muscles or glands  May be very long, projecting several feet through the body Myelin Sheath  A fatty tissue layer segmentally encasing the axons of some neurons; enables vastly greater transmission speed as neural impulses hop from one node to the next  Sausage like sections of myelin  Insulates axons and speeds impulses (similar to wire; needs insulation so the signal stays strong and does not stray)  Created by glial cells Terminal Branches  Aka terminal buttons  Form junctions with other cells

Glial Cells  “Glia” or “glue cells”

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Cells in the nervous system that support, nourish and protect neurons Provide nutrients and insulating myelin, guide neural connections, and clean up debris (ions and neurotransmitters) They may also play a role in learning, thinking and memory Brain= 50% neurons, 50% glial cells

Neuron at Rest  Selectively permeable membrane o Some things can pass through, while others can not o Relatively impermeable to sodium (Na+) and potassium (K+) at rest  Na+ in higher concentration outside the cell  K+ in higher concentration inside the cell  Chemical or concentration gradient  Overall, inside of the cell is negatively charged, compared to the outside of the cell o Electrical potential (gradient) o Resting (membrane) potential

Negatively charged protein Neuron When Activated: The Action Potential  A neural impulse; a brief electrical charge that travels down an axon  The neuron is “firing”  Speed varies from 2 mph two more then 200 mph  Electrical signal transmitted along the axon by the diffusion of charged atoms o The membrane becomes permeable to sodium (Na+) and Potassium (K+) o Series of channel openings along the axon that allows the diffusion

A&P – CHAPTER 11: FUNDAMENTALS OF THE NERVOUS SYSTEM

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Sodium channels open at the axon hillock o Sodium rushes in o Since sodium is positively charged, the inside becomes positive  Depolarization Resting membrane potential is then restored o Sodium channels close o Potassium channels open and potassium rushes out of the cell, making the cell negative on the inside again o Sodium pumped back out, while potassium pumped back in  Sodium-potassium pump o Repolarization o Refractory period  A period of inactivity after a neuron has fire (the neuron cannot fire)  Relative refractory period- follows absolute refractory period. An exceptionally strong stimulus can reopen Na+ channels This occurs at successively adjacent portions of the axon All-or-none response o Neuron’s reaction of either firing with a full-strength response or not firing

Threshold – the level of stimulation required to trigger a neural impulse

A&P – CHAPTER 11: FUNDAMENTALS OF THE NERVOUS SYSTEM

Chemical Synapse

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A&P – CHAPTER 11: FUNDAMENTALS OF THE NERVOUS SYSTEM

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The junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron The tiny gap at this junction is called the synaptic gap or synaptic clef

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Axon terminals release neurotransmitter o Chemical messengers that cross the synaptic gaps between neurons. When released by the sending are on, neurotransmitters travel across the synapse and find two receptor sites on the receiving are on, thereby influencing whether that neuron will generate a neural impulse

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Axon terminals release neurotransmitter o Synaptic vesicles Neurotransmitter binds to a receptor o Dendrite or cell body of receiving neuron o Lock and key type relationship Trigger the opening (or closing) of ion channels o NOT an action potential

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Dendrites/cell body receive signals from many neurons o Most excitatory, some inhibitory o Summation o Threshold

Reuptake  A neurotransmitter’s reabsorption by the sending neuron (Can also drift away or be broken down by enzymes

Electrical Synapse

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A&P – CHAPTER 11: FUNDAMENTALS OF THE NERVOUS SYSTEM

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Much less common than chemical synapse Electrically coupled neurons Channel proteins = connexons

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A&P – CHAPTER 11: FUNDAMENTALS OF THE NERVOUS SYSTEM

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