Transcript C17 Nervous_Teacher

Chapter 17 The Nervous System
Nervous Tissue
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2 Major Categories of Nervous System
1. Central Nervous System
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The brain and spinal cord
At midline of body
2. Peripheral Nervous System
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Nerves carrying messages from CNS to muscles and glands
Sensory nerves carrying messages to the CNS
3 Types of Nerves to Know
Sensory Nerves , Interneurons & Motor
Nerves
1. Sensory Nerves - carry information to the CNS
2. Interneuron – a bridge between a sensory and
motor nerve
3. Motor Nerves – carry response from the CNS to
an effector – a gland or muscle that creates an
action
Anatomy of a TypicalNerve Cell
Sensory Neuron shown here
Dendtrites
Axon Bulb
Cell Body
(Soma)
Nucleus
Axon
Myelin Sheath
Node of
Ranvier
Myelin Sheath / Nodes of Ranvier
• Formed by Schwann cells which secrete a fatty coating over the axon
• Acts like an insulation around a wire. Electrical signal jumps gap to
gap because that is easier than travelling down the high resistance of
the axon, itself.
• Gaps where Schwann cells do not myelinate are called the Nodes of
Ranvier (click below for an animation showing Saltatory Conduction
or the jumping of the impulse)
More on Myelin
• Gives nerves white appearance (= WHITE MATTER)
• MS (mutliple sclerosis) is a disorder where myelin is removed from
nerve. Signal passes down axon, weakening. In case of optic nerve,
this can cause loss of vision. Ultimately, muscular control is lost. If
the breathing and respiration centres in the medulla are affected, the
result is fatal.
• Long Axons – usually myelinated to help signal make it
• Short Axons – usually non-myelinated, since signal should not
degrade over short distance
• Unmyelinated nerves = GRAY MATTER
How does a Nerve Cell
Pass an Electrical Signal?
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Nerve impulse carries information
Impulse measured in mV
Stages of Nerve Cell firing off a Signal
1. Resting Potential – electric potential before signal
2. Action Potential – potential of nerve when signal goes
3. Refractory Period – potential after signal has passed
Action potential
• Definition: an “all-or-none” change in voltage that
propagates itself down the axon
• Naturally occurring action potentials begin at the
axon hillock
Resting Potential
• When not conducting an electrical impulse, the
potential difference across the membrane is -65mV
• Inside of axon is negative compared to outside!
• Difference between inside/outside charge of
membrane is needed to start a signal
• Similar to a battery, the ends must have a potential
difference for current to flow
Action potential
• Definition: an “all-or-none” change in voltage that
carries on all the way down the axon, creating
electrical impulse.
• Naturally occurring action potentials begin at the
axon hillock = crest of the axon
• Action potentials do not occur anywhere else in a
neuron – not in dendrites, not in cell bodies
• Let’s watch how a nerve fires using the A.P.
• Click on Hercules over there…
More K+ Sneaks out than Na+ in!
Creates Dipole, enabling an Action Potential (Animation)
Figure 48.11 Saltatory conduction
Action Potential
• Starts ---> -70mV
– Requires Na / K gates in membrane to open
• Ends ---> +45mV
• Lots of repolarizing to do
– Na moves back outside the membrane
– K move back inside the membrane
– Na/K gates must open to allow repolarizing to happen
– Not ready to fire again until this all happens.
SODIUM POTASSIUM PUMP DEMO
How do you get from electrical
signals to chemical signals and
back again?
Axon Bulbs Insert carry Signal
Dendtrites
Axon Bulb
Cell Body
(Soma)
Nucleus
Axon
Myelin Sheath
Node of
Ranvier
Translating signals across Synapses
• The action potential moves
down the axon until it
reaches the terminal
(synapse)
• Electric signal converted to
chemical 
neurotransmitters
• Neurotransmitters cross the
synaptic cleft
• Signal caught on other side
gets the electrical signal
going again.
Click on Synapse to see
Animation
Translating signals
Synapse Animation #2
• The action potential moves down
the axon until it reaches the
terminal (synapse)
• Impulse opens voltage-activated
Ca2+ channels to let the
neurotransmitters through
• Transmitter diffuses across
synaptic cleft and binds to
receptors on post-synaptic cell
Signal Blockers
• Curare – poisonous darts tipped in these in
the Amazon
• Black widow spider venom will cause
bursting of synapses.
• Smoking’s not much good either
Translating signals
• The action potential moves
down the axon until it reaches
the terminal (synapse)
• Its wave of depolarization opens
voltage-activated Ca2+ channels
• Influx of Ca2+ causes vesicles to
fuse with presynaptic cell
membrane
Translating signals
• The action potential moves
down the axon until it reaches
the terminal (synapse)
• Its wave of depolarization opens
voltage-activated Ca2+ channels
• Influx of Ca2+ causes vesicles to
fuse with presynaptic cell
membrane
• Transmitter diffuses across
synaptic cleft and binds to
receptors on post-synaptic cell
Excitatory and inhibitory neurotransmitters
• If a transmitter
depolarizes
(stimulates) the
post-synaptic
neuron, it is said
to be excitatory
•If a transmitter
hyperpolarizes the
post-synaptic
neuron, it is said to
be inhibitory
Excitation or
inhibition
depends on the
receptor!!
Some Things You Should
Know
1.
Acetylcholine
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involved in learning and memory
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Reduced levels in Alzheimers patients
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Excitatory to muscles
NH2 Amine-type Neurotransmitters
2.
3.
4.
NorEpinepherine
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Released by Adrenal Glands
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Excitatory, heightens senses
Dopamine
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Regulates movement, balance, walking
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Generally inhibatory, evening things out
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Reduces levels in Schizophrenics/possible Pathological Gamblers
Serotonin
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Regulates mood, emotion, thought
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Brain cells are bathed in this while you sleep (chemical reset)
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Derived from amino acid Tryptophan (warm milk, turkey). Causes drowsiness
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Related to Melatonin – can get this in pill form. May help with sleep disorders
The Peripheral Nervous System
– The Spinal Nerves leading away from the CNS
– Afferent axons:
• Name for axons directed toward the central nervous system,
conveying sensory information.
– Efferent axon:
• An axon directed away from the central nervous system,
conveying motor commands to muscles and glands.
Reflex Arc Animation 1
Reflex Arc Animation 2
Ever have a Doctor tap your
knee with a hammer? Your lef
moves without conscious
thought. It’s also the reason
beheaded chickens can run.
Gray Matter
White
Matter
2 Divisions of the Peripheral Nervous System (PNS)
1. Somatic nervous system
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2.
Part of the peripheral nervous system that controls the
movement of skeletal muscles or transmits sensory
information (visual, sound, touch, etc.) to the central
nervous system
Quick to respond to changes in the environment
Autonomic nervous system (ANS)
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The portion of the peripheral nervous system that controls
the body’s major systems (on autopilot usually)
» Controls Cardiac, Smooth muscle and glands
» Depending what the somatic nervous system picks up,
kicks the ANS 1st Gear or Reverse
These systems are complete opposites of each other
I. Sympathetic Nervous System - involuntary
II. Parasympathetic Nervous System - involuntary
Fight or Flight Reaction
of ANS
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Is that a cougar on the path in front of you?!
When did it eat last? It looks skinny – gulp!
If it gets on your back each attack has a 33% chance of killing you.
After about 3 attempts, the cougar generally wins with the death
bite to the back of the neck.
1.
2.
Somatic Nervous System – senses the danger
Autonomic Nervous System kicks in
a)
b)
c)
Sympathetic division alerts adrenal glands to secrete adrenalin /
norepinepherine
Senses heighten. Speed increases, pain not so easily felt, strength
increases drastically
Choice now is ---> FLIGHT OR FIGHT???????
Sympathetic
Para-Sympathetic
ADRENAL
MEDULLA
Chromaffin Cells
Epinephrine
(+) Dilates Airways
(+) Cardiac Output
(+) Muscle Contraction & Efficiency
(+) Fatty Acid Release
(+) Mental Alertness
(+) Reaction Time
(+) Glycogenolysis
(-) Digestion
• The Peripheral Nervous System
Autonomic Nervous System
Sympathetic Division of the ANS
– Adrenal medulla:
• The inner portion of the adrenal gland, located atop the kidney,
controlled by sympathetic nerve fibers; secretes epinephrine
and norepinephrine.
• The Peripheral Nervous System
Autonomic Nervous System
Parasympathetic Division of the ANS
– Parasympathetic division:
• Portion of the autonomic nervous system that controls functions
that occur during a relaxed state; supports activities
involved with increases in the body’s supply of stored energy
including salivation, gastric and intestinal motility, secretion of
digestive juices, and increased blood flow to the gastrointestinal
system.
• Returns body to resting state after a “FIGHT OR FLIGHT”
EVENT. So, works opposite to the Sympathetic Nervous
System
The Brain
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Cerebrum
Diencephalon
Brain stem
Cerebellum
Brain Structures
12 Parietal L.
Frontal L.1
Corpus
Callosum
11 Thalamus
2
Hypothalamus 3
10 Occipital
L.
3
Pons 4
9 Cerebellum
Medulla 5
Spinal Cord 6
8 Retic. Activ
Centre
7 Central
Canal
Cerebrum
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Thinking/Processing
Interpretation
Initiation of voluntary muscle movement
Cortex - External Grey Matter
– Processing takes place
• Basal Nuclei - Central Grey Matter
– may have some voluntary muscle control, when
diseased, Parkinson may develop
Cerebrum
Frontal:
Conscious
Thought &
Motor
Control
Temporal:
Hearing,
Smelling,
Perceptual
Judgment,
Visual/auditory Memory,
Parietal:
Sensory
perception
Occipital:
Bilateral
vision
Cerebrum
• Association areas connected with all lobes.
• Concerned with intellect, artistic & creative
abilities, learning, memory
• Brain may be more “plastic” than once
thought.
Cerebrum
• Left/Right halves communicate via Corpus
Callosum
• Left brain controls right body
• Left Brain: spoken/written language,
number & scientific skills, reasoning
• Right Brain: music/art awareness, 3D
forms, insight, imagination
Brain Stem
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Medulla Oblongata
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Heart beat, Breathing, BP
Cough, Sneeze, Hiccup, Vomit
Pons
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Connects Cerebellum to CNS
w/ Medulla regulate breathing/head motion w/
auditory, visual, tactile input
Brain Stem
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Midbrain
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Relay station
Reflexes: Auditory, Visual, Tactile
Reticular Formation - Grey Matter
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Controls wakefulness
Inactive: sleep
Damage: coma
Filters unnecessary stimuli
Cerebellum
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Coordinates movement
Oversees skeletal muscle action
Maintains muscle tone and posture
Interprets info on body position from ear for
balance
• Assists learning of new motor skills
Diencephalon
• Thalamus
– Relays to/from rest of brain
• Hypothalamus
– Regulates homeostasis
– Link to Pituitary Gland
Reticular Activ. Centre
• The RAC acts like a filter, receiving and
sending sensory and motor nerve signals.
• Controls sleep / alertness – wakes you up.
• Allows you to study while watching TV
Limbic System
• Parts of Frontal & Temporal Lobes, Thalamus,
Hypothalamus, Amygdala, Hippocampus
• “Emotional Brain”: creates feelings about occurrences
which influence how person acts in future.
• Memory and Learning: not fully understood, but involve
Limbic. Emotionally charged = vivid memory
Flash Movie – Click Picture
The Reflex Arc
Sensory stimulation
– missed stair, sudden load, heat or pain sends signal to spine
– Interneuron sends signal quickly right back to skeletal muscle
– Muscle contracts: leg muscles tighen for stair / biceps flex for load
/ hand pulled away from heat
Drug Abuse
Perspectives on SubstanceRelated
Disorders: An Overview (cont.)
Figure 11.2 (cont.)
Easy to get hooked on, hard to get off
The Depressants: Alcohol Use
Disorders (cont.)
Figure 11.3
The path traveled by alcohol throughout the body
Alcohol: Some Facts and
Statistics
• In the United States
– Most adults consider themselves light drinkers or
abstainers
– Most alcohol is consumed by 11% of the U.S. population
– Alcohol use is highest among Caucasian Americans
– Males use and abuse alcohol more so than females
– Violence is associated with alcohol, but alcohol alone
does not cause aggression
Alcohol: Some Facts and
Statistics (cont.)
• Facts and Statistics on Problem Drinking
– 10% of Americans experience problems with alcohol
– Most persons with alcoholism can moderate or cease
drinking on occasion
– 20% of those with alcohol problems experience
spontaneous recovery
– Anhedonia – Lack of pleasure, or indifference to
pleasurable activities
– Affective flattening – Show little expressed emotion, but
may still feel emotion
Stimulants: An Overview
• Nature of Stimulants
– Most widely consumed drugs in the United States
– Such drugs increase alertness and increase energy
– Examples include amphetamines, cocaine, nicotine, and
caffeine
Stimulants: An Overview
• Nature of Stimulants
– Most widely consumed drug in the United
States
– Such drugs increase alertness and increase
energy
– Examples include amphetamines, cocaine,
nicotine, and caffeine
Stimulants: Amphetamine Use
Disorders
• Effects of Amphetamines
– Produce elation, vigor, reduce fatigue
– Enhance the release of dopamine and norepinephrine,
while blocking reuptake
– Such effects are followed by a “crash” (e.g., feeling
depressed and tired)
• Ecstasy and Ice
– Produces effects similar to speed, but without the crash
– 2% of college students report using Ecstasy
– Both drugs can result in dependence
Stimulants: Cocaine Use Disorders
• Effects of Cocaine
– Produce short lived sensations of elation, vigor, reduce
fatigue
– Effects result from blocking the reuptake of dopamine
– Cocaine is highly addictive, but addiction develops
slowly
– Cocaine use in the United States has declined over the
last decade
Stimulants: Nicotine Use
Disorders
• Effects of Nicotine
– Stimulates the central nervous system, specifically
nicotinic acetylcholine receptors
– Results in sensations of relaxation, wellness, pleasure
– Nicotine is highly addictive & found in cigarettes
Opiates:
ex. Codeine, Morphine, Heroin
• Nature of Opiates
– Opium = Natural chemical in the opium poppy with narcotic
effects (i.e., pain relief)
– a class of nature and synthetic substances with narcotic effects
– Such drugs are often referred to as analgesics
• Effects of Opiates
– Activate body’s enkephalins and endorphins
– Low doses induce euphoria, drowsiness, and slowed breathing
– High doses can result in death
– Withdrawal symptoms can be lasting and severe
Disorders
Relapse rates for nicotine compared to alcohol
and heroin
An Integrative Model of
Substance-Related Disorders
(cont.)
Stimulants: Caffeine Use
Disorders
• Effects of Caffeine – The “Gentle” Stimulant
– Found in tea, coffee, cola drinks, and cocoa products
– Caffeine blocks the reuptake of the neurotransmitter
adenosine
– Small doses elevate mood and reduce fatigue
– Used by over 90% of Americans/Canadians
– Regular use can result in tolerance and dependence
Cannabis
• The drugs produced from varieties of the hemp plant are, as
a group, called cannabis
– They include:
• Hashish, the solidified resin of the cannabis plant
• Marijuana, a mixture of buds, crushed leaves, and flowering
tops
• The major active ingredient in cannabis is
tetrahydrocannabinol (THC)
– The greater the THC content, the more powerful the drug
Cannabis
• When smoked, cannabis produces a mixture of hallucinogenic,
depressant, and stimulant effects
– At low doses, the user feels joy and relaxation
• May become anxious, suspicious, or irritated
• This overall “high” is technically called cannabis intoxication
– At high doses, cannabis produces odd visual experiences, changes
in body image, and hallucinations
• Most of the effects of cannabis last three to six hours
– Mood changes may continue longer
Cannabis
• Marijuana abuse and dependence
– Marijuana was once thought not to cause abuse or
dependence
– Today many users are caught in a pattern of abuse
• Some users develop tolerance and withdrawal, experiencing
flu-like symptoms when drug use is stopped
• About 1.5% of people in the U.S. displayed marijuana abuse or
dependence in the past year
– About 5% will fall into these patterns at some point in
their lives