Ch48NervousSystem

January 13, 2018 | Author: Anonymous | Category: Science, Biology, Neuroscience
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Ch 48: Nervous System 2016

Ch 48: Nervous System From Topic 6.5 Nature of science: Cooperation and collaboration between groups of scientists—biologists are contributing to research into memory and learning (4.3). Essential idea: Neurons transmit the message, synapses modulate the message. Understandings: • Neurons transmit electrical impulses. • The myelination of nerve fibres allows for saltatory conduction. • Nerve impulses are action potentials propagated along the axons of neurons. • Neurons pump sodium and potassium ions across their membranes to generate a resting potential. • An action potential consists of depolarization and repolarization of the neuron. • Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential. • A nerve impulse is only initiated if the threshold potential is reached. • Synapses are junctions between neurons and between neurons and receptor or effector cells. • When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. Guidance: • The details of structure of different types of neuron are not needed. • Only chemical synapses are required, not electrical, and they can simply be referred to as synapses. Applications and skills: • Application: Secretion and reabsorption of acetylcholine by neurons at synapses. • Application: Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors. • Skill: Analysis of oscilloscope traces showing resting potentials and action potentials. • Skill: Analysis of oscilloscope traces showing resting potentials and action potentials. Utilization: • An understanding of the workings of neurotransmitters and synapses has led to the development of numerous pharmaceuticals for the treatment of mental disorders. Aim 8: The social effects of the abuse of psychoactive drugs could be considered, as could the use of the neurotoxin Botox for cosmetic treatments.

Parts of the Nervous System • Central nervous system (CNS) – Brain and spinal cord • Both contain fluid-filled spaces which contain cerebrospinal fluid (CSF). – The central canal of the spinal cord is continuous with the ventricles of the brain. – White matter is composed of bundles of myelinated axons – Gray matter consists of unmyelinated axons, nuclei, and dendrites.

• Peripheral nervous system (PNS) – Everything outside the CNS. Nervous System: https://www.youtube.com/watch?v=x4PPZCLnVkA

Peripheral Nervous System (PNS)

Neuron Anatomy

Neuron Anatomy

Membrane Potential • Membrane Potential: a term used

to illustrate there is an electrical potential difference between the inside of the cell and the surrounding extracellular fluid. • -70 mV is the resting membrane potential of a neuron, which means that the inside of the cell is negative compared to the outside. Membrane Potential: http://www.sumanasinc.com/webcontent/animations/content/electricalsignaling.html

Normal Levels • Sodium-Potassium Pump: is used in establishing the membrane potential in neurons (1) it makes the [Na] high in the extracellular space and low in the intracellular space (2) it makes the [K+] high in the intracellular space and low in the extracellular space (3) it creates a negative voltage in the intracellular space compared to the extracellular space.

Hyperpolarization • Gated K+ channels open  K+ diffuses out of the cell  the membrane potential becomes more negative

Depolarization • Gated Na+ channels open  Na+ diffuses into the cell  the membrane potential becomes less negative

Action Potential • Action Potential: All or Nothing Depolarization • If graded potentials sum to  -55mV a threshold potential is achieved. • This triggers an action potential. • Axons only Action Potential: http://www.sumanasinc.com/webcontent/animations/content/action_potential.html Action Potential w/ Graph: http://bcs.whfreeman.com/thelifewire/content/chp44/4402002.html

Action Potential Diagram

• Step 1: Resting State.

Fig. 48.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Step 2: Threshold.

Fig. 48.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Step 3: Depolarization phase of the action potential.

Fig. 48.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Step 4: Repolarizing phase of the action potential.

Fig. 48.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Moving Potential

Saltatory Conduction • In myelinated neurons, only unmyelinated regions of the axon depolarize. Signal jumps from one node to the next, making the impulse travel 100x faster than on a unmyelinated neurons. Khan Academy: https://www.khanacademy.org/science/biology/human-biology/neuron-nervous-system/v/saltatory-conduction-neurons Saltatory Conduction: http://wps.aw.com/bc_goodenough_boh_3/104/26721/6840613.cw/content/index.html

Fig. 48.11

Synapses • Electrical Synapses. – Action potentials travels directly from the presynaptic to the postsynaptic cells via gap junctions.

Chemical Synapses • More common than electrical synapses. • Postsynaptic chemically-gated channels exist for ions such as Na+, K+, and Cl-. • Depending on which gates open the postsynaptic neuron can depolarize or hyperpolarize.

Fig. 48.12

Routes of Nerve Transmission

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