a2 nervesystemscolstons
TRANSCRIPT
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Nervous Systems
Colston’s School
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Structure of a Vertebrate Neuron
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Diversity of Nervous Systems
Simple, slow moving animals like hydra have neurons arranged in a network of bipolar neurons called a nerve net.
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Basic Tasks of the Nervous SystemSensory Input: Monitor both external and internal environments.
Integration: Process the information and often integrate it with stored information.
Motor output: If necessary, signal effector organs to make an appropriate response.
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• Cell body: functional portion
• Dendrites: short extensions that receive signals
• Axon: long extension that transmits impulses away
Anatomy of a nerve
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Nerve Impulse – Nerve Impulse – The Action PotentialThe Action Potential
Threshold potential will trigger an action potential or nerve impulseThe action potential is an all-or-none response
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Nerve Impulse – Nerve Impulse – The Action PotentialThe Action Potential
A nerve is stimulated, (A.P.) usually at one point, and then is propagated along the axon.
The role of sodium and potassium ions in propagating an Action Potential is crucial.
Na+ and K+ both move in apposing directions to generate a potential difference all along the axon. Positive and negatives attract.
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Myelinated Neurons
• Many vertebrate peripheral neurons have an insulating sheath around the axon called myelin which is formed by Schwann cells.
• Myelin sheathing allows these neurons to conduct nerve impulses faster than in non-myelinated neurons.
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Saltatory Conduction in Myelinated Axons
Myelin sheathing has bare patches of axon called nodes of Ranvier
Action potentials jump from node to node
Fig. 48.11
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How does a signal move from one neuron to another?
• A synapse divides 2 neurons• The action potential will not move
across the synapse• Neuro transmitters
– Released by the signal cell to the receiver cell
– Move by diffusion
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Types of chemical synapse
• Acetylcholine: neuromuscular junctions, glands, brain and spinal cord
• Norepinepherine: affects brain regions concerned with emotions, dreaming
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Spinal Reflex
• Knee-patellar is the classic example, but there are many reflexes
• Blinking your eye
• Salivating when expecting food
• Going to the toilet as an infant
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The Autonomic Nervous System
• The outer nervous system controls the body’s activities that you don’t think about
• The outer nervous system controls activities in your small intestine, your breathing, and your heartbeat.
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The sense organs - eye
• Sense organs carry messages about the environment to the central nervous system
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Parts of the EyeDetectors on the Fovea
– Rods• light intensity and motion sensitive
– Cones• color sensitive
The blind spot for the eye is cause by the optic nerve.
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Myopia (Near-Sightedness)
People with near-sightedness cannot see clearly at distance.
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Hyperopia (Farsightedness)
People with far-sightedness cannot see clearly up close
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Addictive Drug Use: Tobacco, Alcohol, &
Illicit Drugs
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• All addictive drugs produce:
• Short-term pleasure to some degree
• Long-term negative consequences
• Tolerance & physical dependence
• A withdrawal syndrome
• Activation of dopamine neurons in the Nucleus Accumbens
Pharmacology of Addictive Drugs
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Source: Gray
Transmission Across the Synapse
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How Drugs Become Addictive
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Detail of Axon
Terminal
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Neurotransmitter Neurotransmitter molecules molecules
(e.g., Acetylcholine (e.g., Acetylcholine or Dopamine)or Dopamine)
Postsynaptic membrane
Detail of the Synapse Itself
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Binding site
How binding
sites work
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Neurotransmitter re-uptake helps keep binding sites clear
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Cocaine Cocaine inhibits the re-uptake of dopamine producing effects such as increased heart rate and
blood pressure
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NicotineNicotine fills & activates acetylcholine binding sites producing effects such as increased heart rate and blood pressure
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What is Addiction?
• All definitions describe behaviour which produces positive sensations in the short term, but negative consequences in the long term
• A straightforward definition:
–Compulsive use
–Loss of control
– Use despite harmUse despite harm* Portnoy
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How People Start Using Drugs• Genetics• Predisposing risk factors:
– Age 11-22 for onset– Primitive character structures
• Especially Conduct Disorder– Peer influence– Parental influence– Smoking and alcohol use
• Constricted temporal focus?
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Nicotine Use is Associated With Other Drug Use
0
10
20
30
40
50
60
70
80
Cigarettes smoked per day
% o
f S
tudents
"
5+drugs
1 drug
2-4 drugs
Kozlowski, Coambs, et al., 1989
Nicotine Use is Associated With Other Drug Use
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Some People Never Start
• Factors which reduce risk:–Age 35+–Nuanced character structures–No Peer influence–No Parental drug use history–No other smoking or alcohol abuse
• E.G., the SISAP
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Basic Treatment For Addiction
• Treat the urges directly, if possible
• Establish why the person uses the drug
• What needs are being fulfilled by that drug?
• Find methods to fulfil those needs without the drug
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How People Quit Drug AbuseHow People Quit Drug Abuse• Most quit on their own (cold turkey)
• Most use no medication
• Probably those people who can quit easily do so
• Clinicians tend to see the difficult cases
• Ambivalence is normal
• Most quit by age 40
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Relapse Prevention• Plan for relapse: Abstinence Violation
Effect
• Relapse is common: it is not failure!
• Repeated relapse is associated with
success in quitting
• Learn from it in next attempt
• Find a way to control urges