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BIO 141 Lecture 2 notes

by: Camryn McCabe

BIO 141 Lecture 2 notes Biol 141

Marketplace > Science > Biol 141 > BIO 141 Lecture 2 notes
Camryn McCabe
Penn State
GPA 3.81

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on the nervous system notes from 1/22-1/29
Janelle Malcos
Class Notes
nervous system, Bio
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This 7 page Class Notes was uploaded by Camryn McCabe on Saturday January 30, 2016. The Class Notes belongs to Biol 141 at a university taught by Janelle Malcos in Spring 2016. Since its upload, it has received 33 views.


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Date Created: 01/30/16
BIOL 141 notes 3: 1/22-1/29 The Nervous System o Regulation- maintaining homeostasis (stable internal environment) o Systems that work for regulation  Endocrine- sends chemical messages  Works slowly; hormones  Nervous- sends electrical signals and chemical messages  Works fast; neurotransmitters o Structure o Two major subdivision  Central nervous system (CNS)- brain and spinal cord  Integration center  Peripheral nervous system (PNS)- nerves  Delivers/sends information to CNS o Nervous tissue o Neurons- specialized cells that make up nervous tissue  Main characteristics:  Excitability (uses ions) o Cells respond to stimuli from environment OR other cells o Results in electrical signal (action potential) – form of communication o Major evolution pressure to maintain this function for communication  Conductivity- sending the message o Neurons propagate an electrical signal over a distance from its origin  Secretion- passing on the signal o Neurons translate electrical signal to chemical signal  Neuron structure  Cell body (Soma) o Contains ONE nucleus  Dendrites- short and thick extensions off cell body o Receives signals from other neurons  Axon- extension away from cell body o Some are covered by myelin sheath (myelinated)- improves conductivity  Synapse- site of communication between neurons or between neuron and target tissue o Secretion BIOL 141 notes 3: 1/22-1/29  Structural classes  Multipolar- cell body at the end o Most common  Bipolar- cell body is more centrally located  Unipolar- cell body is off to the side o Axon comes after the cell body  Functional classes  Afferent neurons (sensory) o Sometimes called receptors o Specialized to detect stimuli o Start in PNS and travel to CNS o Delivers information about environment/condition of body to CNS  Internuerons o In CNS o Receives and integrates information  Efferent neurons (motor) o Send signals from CNS to effectors (targets)  Muscles, organs, glands  All of these pathways work by communication through electrical and chemical signals o Neural circuits  Allows the body to monitor the environment (or itself) and decide on an appropriate response to maintain homeostasis o Electrical/chemical function of neurons  Use electrical currents to communicate  This speedy diffusion of ions across the membrane has been favored as form of rapid communication throughout evolution  No concentration gradient = no communication o If potential is 0  no flow of ions  no communication  Electrical potential (voltage)  Voltage- concentration gradient of charged particles (the separation)  Requires potential to create a current  Electrochemical gradient- concentration gradient of charged particles  Electrical current  Flow of charged particles from one point to another BIOL 141 notes 3: 1/22-1/29  Current- flow of charged particles from high to low o Example of passive transport  In a battery…  Flow of electrons in a battery circuit produces an electrical current  A semipermeable membrane separates charges, creating voltage  Flow of ions in/out of a cell (through protein channel) produces an electrical current  Extracellular fluid (ECF)- outside the cell  Intracellular fluid (ICF)- inside the cell  EFC and ICF are separated by semipermeable membrane  Main ions separated: Na and K + o Electrochemical gradient o Consists of a concentration gradient of charged particles  Na and K + o 2 components  Chemical gradient- uneven distribution of molecules  Electrical gradient- uneven distribution of charge  Because molecules are ions  Movement of ions through protein channels  Driven by chemical gradient (diffusion) AND  Electrical gradient (attraction/repulsion of charges) o How electrochemical gradient is established  Chemical gradient- created by Na /K protein pumps  The pump (active; requires energy) + +  Moves 3 Na ions out and 2 K ions in  Creates slightly more positive environment outside the cell, and slightly more negative environment inside the cell  The pump works to move Na ions out of the cell, but they can leak back in if there are leak channels + o Same goes for K ions; they will leak back out of the cell if there are leak channels  These leak channels counteract the pump o But the pump works hard enough that the gradient is still there o The leak channels keep the gradient from getting bigger and bigger  Electrical gradient- permeability and trapped anions BIOL 141 notes 3: 1/22-1/29  More K leak channels than Na channels o More K leaves the cell than Na entering the cell +  Cell is more permeable to K  Inner membrane is more negative than outer membrane  Trapped anions inside the cell o More anions are proteins and huge o They can’t get through  trapped inside  make inside more negative o Sodium- chemical and electrical gradient go in the same direction; enforce each other  Wants to get into the cell because of chemical gradient  (+) is attracted to (-) electrical gradient inside o Potassium- chemical and electrical gradient go in the opposite direction  Coming out because of the chemical gradient  But goes in because of the electrical gradient  (+) attracted to (-) o Resting Membrane Potential (RMP)- balance of diffusion between chemical and electrical gradients o At rest; unexcited o Balance between chemical and electrical gradients = Electrochemical gradient o RMP = -70mV in neurons o All cells have a resting membrane potential o Changes in RMP lead to currents  Currents are the communication (flow of charged molecules from high to low)- local action potential o Local action potential- when a stimulus causes a change in RMP o Usually occurs at dendrite/cell body  At stimulus sight, communication btw neuron 1 and 2, communication btw neuron 2 and 3  Effects are close to the origin, not down axon o If local potential is large enough (reaches the threshold) it activates action potential  Threshold = -55mV o Usually excitartory in PNS  From stimuli in the environment OR from organs inside the body o Excitatory or inhibitory in CNS  Communication btw neurons via neurotransmitters o Ion movement is regulated by gated protein channels BIOL 141 notes 3: 1/22-1/29  Certain stimulus opens it, allows current o Reversible to a certain point (like when dust lands on you) o Stimulus  local potential  reach threshold  action potential  communication to CNS o Ion movement during Local Potentials o Regulated by gated protein channels  Respond to stimuli  All passive o These function in addition to pumps and leak channels already working o Chemical gated channels (ligand)  Usually a chemical binds and causes channel to open  Ex. Taste, smell o Voltage gated channels (potential)  Open in response to change in voltage o Mechanical gated channels  Respond to force (vibration, touch); forces channel to open  Ex. Hearing (vibrations), touch o Can result in excitatory response  depolarization  Na+ channels open and Na+ ions diffuse INTO cell  Membrane potential becomes more POSITIVE (closer to zero) (closer to neutral) o Can result in inhibitory response  hyperpolarization  K+ channels open and K+ ions diffuse OUT of the cell  Membrane potential becomes more NEGATIVE (farther from zero/neutral) o Type of gated channel depends on location in NS  In PNS  Usually ligand or mechanical  At interneurons  Usually ligand o Ligands are neurotransmitters  In CNS  Chemical (ligand) o Example of Local potential o Depolarization  This example is taking place at interneurons (chemical communication)  Ligand binds Na+ chemical-gated channel  Na+ channel opens and Na+ enters cell  Membrane potential becomes LESS NEGATIVE (towards 0) BIOL 141 notes 3: 1/22-1/29  If potential reaches -55mV (threshold) in cell body, action potential is triggered  Electrical signal transmitted down axon o Action potentials o Always depolarize o Regulated by voltage-gated channels  Located at axon hillock  AP goes down axon  Secretion at axon terminal o In LP- lots of (+) coming in, going to reach action potential o Na+ voltage-gated channels open at -55mV  Na+ rushes in (to the first part of the axon only) o Membrane depolarizes (becomes LESS NEGATIVE) o Membrane potential reaches +30mV (peak depolarization)  Na+ channels close  K+ voltage-gated channels open  K+ diffuses out of the cell  Cell starts to repolarize (become MORE NEGATIVE) o Repolarization  K+ channels stay open over a longer voltage  More K+ leaves the cell than Na+ enters  Hyperpolarization o Na+/K+ pumps actively transport ions back to original state  Na+ comes out, K+ back in  back to RMP  Necessary to get back to RMP before another action potential can occur  Absolute refractory period- from when it hits -55 til it gets back to RMP  Relative refractory period- when it’s below RMP  Very strong local potential needed to overcome this o Conduction o Dendrites/cell body  axon o After initial action potential  Sodium diffuses in cytoplasm from entry point  Causes adjacent voltage-gated channels to open  Continues down axon  One-way bc refractory period o Myelin Sheath o Electrically insulates axons o In CNS- made of oligodendrocytes o In PNS- made of Schwann cells  Lipid/protein dense BIOL 141 notes 3: 1/22-1/29 o Important for conductivity  Allows for fast propagation o Action potentials only occur at nodes of Ranvier  Myelin sheath allows ions to diffuse further bc they can’t be transported to ECF by pumps o Saltatory propagation- allows action potential (signal) to jump down axon between nodes o Not all neurons are myelated  That would take up too much space  Only ones that need fast conduction are o LP v. AP o LP  Triggered by receptors and neurotransmitters  Can depolarize or hyperpolarize the membrane  Are graded (proportional to strength of stimuli)  Reversible (to a certain point…threshold!)  Local (effects are close to the origin)  Decremental (signal gets weaker as it moves away from origin) o AP  Triggered by voltage-gated channels  Always depolarizes the membrane  Are all-or-nothing (exhibits same peak regardless of stimulus strength  Irreversible  Self-propagating (effects have a great distance from origin)  Non-decremental (signal is the same each time)


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