A2 nervesystemscolstons
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Nervous Systems Colston’s School
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Transcript of A2 nervesystemscolstons
Nervous Systems
Colston’s School
Structure of a Vertebrate Neuron
Diversity of Nervous Systems
Simple, slow moving animals like hydra have neurons arranged in a network of bipolar neurons called a nerve net.
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.
• Cell body: functional portion
• Dendrites: short extensions that receive signals
• Axon: long extension that transmits impulses away
Anatomy of a nerve
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
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.
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.
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
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
Types of chemical synapse
• Acetylcholine: neuromuscular junctions, glands, brain and spinal cord
• Norepinepherine: affects brain regions concerned with emotions, dreaming
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
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.
The sense organs - eye
• Sense organs carry messages about the environment to the central nervous system
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.
Myopia (Near-Sightedness)
People with near-sightedness cannot see clearly at distance.
Hyperopia (Farsightedness)
People with far-sightedness cannot see clearly up close
Addictive Drug Use: Tobacco, Alcohol, &
Illicit Drugs
• 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
Source: Gray
Transmission Across the Synapse
How Drugs Become Addictive
Detail of Axon
Terminal
Neurotransmitter Neurotransmitter molecules molecules
(e.g., Acetylcholine (e.g., Acetylcholine or Dopamine)or Dopamine)
Postsynaptic membrane
Detail of the Synapse Itself
Binding site
How binding
sites work
Neurotransmitter re-uptake helps keep binding sites clear
Cocaine Cocaine inhibits the re-uptake of dopamine producing effects such as increased heart rate and
blood pressure
NicotineNicotine fills & activates acetylcholine binding sites producing effects such as increased heart rate and blood pressure
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
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?
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
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
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
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
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
