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Objectives:
1.
What is
the nervous system and what does it do?
2.
Define
and be able to use the following: Neurons, Action Potentials, Chemical synapses, Memory
3.
Know
the divisions of the Nervous System: The central nervous system (CNS) is composed of the
brain and spinal cord: The peripheral nervous system (PNS) includes all the nerves that carry
signals to and from the brain and spinal cord.
4.
States
of consciousness: Central nervous system governs sleeping, dozing daydreaming and full
alertness: Neurons of the reticular activating system control the
changing levels of consciousness by releasing serotonin
5.
Describe
the effects of drugs
on the Central Nervous System:
6.
What is
the result of demyelination of axons?
An example is multiple
sclerosis?
7.
Why
does drinking large amounts of coffee or other caffeine-containing beverages tend
to make a person “nervous”
or “jittery”?
Important figures
11.1 nervous system, 11.2
types of neurons, 11.3 the neuron, 11.4 membrane potential, 11.6 action
potentials, 11.7 synaptic transmission 11.9 spinal reflexes, 11.15 cerebrum
1. Three Classes of neurons work together to form a
circuit:
a. Sensory neurons of the PNS are receptors for specific sensory stimuli.
b. Interneurons
in the brain and spinal cord (CNS)
integrate input and output signals.
c. Motor neurons send information from integrator to muscle or gland cells (effectors)
1. The cell body contains the nucleus and
metabolic machinery for protein synthesis.
2. Dendrites
are numerous, usually short extensions that receive stimuli (input zones) from
other neurons.
3. Axon is a
single, long extension that transmits impulses to other cells. Electrical signals are initiated at the axon
hillock and the place where the axon and cell body are joined. The axon ends in a small rounded tip called
an axon bulb.
C. Neurons
are usually supported by other cells.
1.
Only 20% of the cells
in the nervous system are Neruons
2.
the rest are neuroglial
cells which provide physical support and protection to the neurons.
D. A neuron
at rest then moved to action
1.
A neuron at rest
maintains a voltage difference across the plasma membrane, called the resting
membrane potential
2. A strong signal causes an action potential (an
abrupt, brief reversal of the voltage difference across the plasma membrane)
E. Restoring
and Maintaining Readiness
1. Neurons maintain voltage differences because
a. The lipid bilayer restricts passage of sodium, potassium
and other ions
b. Channel proteins control ion flow: some are always
open, others are controlled or gated.
2. The following conditions exist when a neuron is in
between action potentials:
a.
There are more
potassium ions inside the membrane that outside and more sodium ions outside
than inside
b. The channels for potassium are open, and potassium
tends to leak out until their is no net movement of potassium
c. Pump proteins such as those in the sodium-potassium pump use ATP to actively pump
potassium ions in and sodium ions out of the neuron to keep the concentration
of sodium ions higher outside.
4.
Node to node hopping along Sheathed Axons
A. Many axons are covered by myelin sheath
derived in part from schwann cells
B. Each section of the sheath is separated from adjacent
ones by a region (node of Ranvieer) where the axon membrane is exposed.
C. The action potentials jump from node to node (saltatory
conduction) which is fast and efficient.
D. In a process called demyelination the sheaths of myelinated neurons in the brain and
spinal cord become damaged and hardened with scar tissue. These scarred areas can no longer insulate
the neurons effectively and it disrupts and slows the transmission of
impulses. For an example see MS or ALS
at the end of these notes.
A. A chemical synapse is a junction between a
neuron and an adjacent cell, separated by a synaptic cleft into which a
transmitter substance is released.
B. The neuron that releases the transmitter into the
cleft is called the presynaptic cell
C. The neuron that has receptors and receives the
transmitter is the postsynaptic cell.
1)
Neurotransmitters include
a. Acetylcholine: for neuromuscular junctions, glands, the brain and spinal cord
b. Norepinephrine affects brain regions concerned with emotions, dreaming, and awaking
c. Two debilitating diseases, Parkinson’s and Alzheimer’s
are testimony to the effects of the loss of neurotransmitters can effect.
D. Neuromodulators like endorphins can enhance or reduce membrane responses to
action potential in neurons
5. Paths of
Information Flow (Nerves)
A. Signals between brain or spinal cord and body regions
travel by nerves
B. Sensory and
motor neurons of many nerves take part in reflexes, which are
stereotyped movements made in response to sensory stimuli.
7.
Divisions of the Nervous System
A. The central nervous system (CNS) is composed of the brain and spinal cord,
receives, processes, stores and transfers information.
B. The peripheral nervous system (PNS) includes all the nerves that carry signals to
and from the brain and spinal cord.
8. The
Peripheral Nervous System (PNS)
1) Sensory division carries info to the CNS
2) Motor division carries information from the CNS
1)
Somatic
nerves relay commands to and from
skeletal muscle (voluntary control)
2) The autonomic nerves
send signals to and from smooth muscles, cardiac muscle, and glands (involuntary control)
D.
The autonomic
subdivision is further divided into the Sympathetic and Parasympathetic
Nerves
1) Parasympathetic nerves tend to slow down body
activity when the body is not under stress
2) Sympathetic nerves increase overall body activity
during times of stress, excitement, or danger: they also call on the hormone
epinephrine to increase the “flight-fight” response.
9. Components
of the Central Nervous system (While our neurons cannot think or have emotions, we do? Somehow the arrangement of these neurons
allows this action. In the next few
topics we will look closer at this arrangement)
1)
The spinal cord lies
within a closed channel, protected by the surrounding bones of the vertebral
column.
2)
The spinal cord
(and the brain) is covered with 3 tough membranes-the meninges.
3)
Cerebrospinal fluid fills the space between the meninges.
Cerebrospinal fluid is made for the brain and the spinal cord in the
entricles of the brain. This fluid is
special because it has to pass through a cell in order to be exposed to the
brain.
4) Signals move up and down the spinal cord in nerve
tracts, which are bundles of sheathed axons.
This is the white matter.
5) It is a pathway for signal travel between the
peripheral nervous system and the brain: it is also the center for controlling
some reflex actions
a. Some reflex actions do not require input form the
brain, like bladder emptying
b. These reflexes occur in the grey
matter
B.
Divisions of the
Brain: whose function is to control the body, is protected by meninges,
bones and cerebrospinal fluid. An Atlas
of the brain is located at http://www.med.harvard.edu/AANLIB/home.html
1) Hindbrain
a. medulla
oblongata –respiration, heart rate,
swallowing sleep wake responses
b. cerebellum- acts a
reflex center for maintaining posture and coordinating limbs
c. pons (bridge) possesses nerve tracts that bas between
brain centers
2) Midbrain
a.
Midbrain where visual
and sensory input are merged before going on too higher centers, it can be
considered a switching center.
b. Works together with pons and medulla to form the brainstem
that coordinates muscles and higher brain activities.
3) Forebrain
a. Forebrain is the most developed portion of the brain
in humans and higher animals
b. Cerebrum
integrates sensory input and selected motor responses
c. Thalamus
(below cerebrum) relays and coordinates sensory signals
d. Hypothalamus
monitors internal organs and influences responses to thirst, hunger, and sex.
10.
Other aspects of CNS Structure
A.
The cerebral
Hemispheres, Left and right, communicate through the corpus
collosum, the left lobe is responsible
for verbal skills, nonverbal skills such as music, mathematics and abstract
abilities reside in the right lobe.
B. Brain Cavities and Canals.
1)
The brain and spinal
cord are surrounded by cerebrospinal fluid and fills cavities in the brain.
2) Blood brain
barrier controls which substances will pass to the fluid and
to the neurons
a.
Lipid soluble
substances such as alcohol, nicotine and drugs diffuse quickly through the
lipid bilayer of the plasma membrane.
11. A closer
Look at the Cerebral Cortex
A.
Structure of the
Cerebral cortex
1) Occipital lobe in the rear has centers for vision
2) Temporal lobe near temple is processing center of hearing an influences emotional
behavior
3) Parietal lobe house the somatosensory cortex and is receiving area for signals from
the skin and joints.
4) The frontal lobe includes the motor cortex and areas
used in thinking and memory.
1) Central nervous system governs sleeping, dozing
daydreaming and full alertness
2) Neurons of the reticular activating system control
the changing levels of consciousness by releasing serotonin
A.
Memory is the storage
and retrieval of information about previous experiences
1) Association
is the linkage of information in packages due to chemical and structural
changes in brain regions
a.
short term memory lasts from seconds to hours and is limited to a few
bits of information
b.
Long term memory is more permanent and seems to be limitless
B.
Information that seems
most important to the individual moves most rapidly into long term storage
1) epinephrine stimulates glucose production, fueling
the brain’s memory work
2) Memory information is encoded in a form resistant to
degradation.
13. The Brain
and Behavior
A.
Our emotions are
governed by the limbic system, which consists of several brain regions.
B.
The cerebral cortex and
thalamus plus the “gatekeeper” hypothalamus are able to regulate reactions to
emotional situations
14. Drugs
Effect on the Central Nervous System
A.
A drug is any
substance introduce into the body to provoke a specific physiological response
1) Drug abuse
is defined as use of a drug in a way that harms health or interferes with a
person’s ability to function in society
2) In general, drug abuse involves psychoactive drugs,
which act on the CNS to alter mental and physical states
B.
Drug Effects
1) As body develops tolerance to a drug, larger and more
frequent doses are needed to produce the same effect, this reflects physical
drug dependence
2) Physchological drug dependence or habituation,
develops when a user begins to crave the feelings associated with using a
particular drug and cannot function without it.
3) Habituation
and tolerance are evidence of addiction.
C.
Drug Action and
Interactions.
1) In a synergistic interaction, two drugs used
together have a much more powerful effect than they would have if used
separately.
2) Some drugs combinations are antagonistic, one
drug blocks the effects of another
3) Others are potentiating; one drug enhances the
effects of the other.
14. Commonly Abused Drugs
A.
Stimulants
1)
Caffeine stimulates the
cerebral cortex, causing increased alertness, higher doses act at the medulla
oblongata to disrupt motor coordination and intellectual functions.
2)
Nicotine mimics
Acetylcholine, directly stimulating receptors such as those in the brain that
in turn stimulate the adrenals to releases hormones the increases the heart
rate and blood pressure
3)
Amphetamines resemble
dopamine and Norepinephrine, causing increased alertness initially, but
increased dependence over prolonged use.
4)
Cocaine stimulates the
pleasure centers by blocking natural signaling molecules released at synapses;
thus the body needs a rather constant supply to achieve the feeling
B.
Sedatives,
hypnotic and Antianziety Drugs
1)
As a group, these drugs
lower the activity of nerves and grain.
2)
Alcohol acts directly
on the plasma membrane to alter cell activity leading initially to relaxation
but eventually to disorientation, diminished judgement, and uncoordinated
muscular movements.
3)
Barbiturates are prescribed
to reduce epileptic seizures and induce relaxation, but can be used abusively
as downers
C.
Analgesics
1)
The body produces its
own pain relievers, such as endorphins and enkephalins
2)
Narcotic analgesics
such as codeine, morphine, and heroin are derived form opium: they have medical
uses but are habit forming and seriously addictive
D.
Psychedelics
and Hallucinogens
1)
LSD affects the
activity of serotonin, a brain hormone, causing increases in blood pressure as
well as hallucinations
2)
Marijuana contains the
active ingredient THC, which acts as a depressant
E.
Deliriants
1)
PCP leads to toxic
psychosis or delirium, impairment of
perceptions, and outbursts of violent behavior
2)
Inhalants of chemicals
in cleaning fluids and spray paint work their magic on the brain but also lead
to toxicity in the liver, kidneys, respiratory system and heart with long-term
use.
Methods used to look at brain and nervous tissue
function
A)
PET
scan
15. Disorders of the nervous system
A)
Trauma or physical
injury
1) Concussions are caused by a violent blow to the
head or neck. A brief period of
unconsciousness occurs when the brains electrical activity is briefly
disrupted. The biggest dangers are
due to subdural hemotomas or bleeding into the space between the meninges.
3)
Spinal cord injuries
due to trauma to the vertebrae surrounding the spinal cord, causing a
disruption in the transmission of the signals form the body to the brain. The extent of the damage depends on the
location of the damage in the spinal cord.
4)
Infections
a.
Encephalitis: Inflammation of the brain caused by
infections that cause swelling of the brain.
Symptoms vary but include headache, fever, fatigue, hallucinations and
confusion.
b.
Meningitis: Inflammation of the meninges usually
bacterial. Symptoms include headache,
fever, nausea and vomiting.
c.
Rabies: an infections viral brain of mammals can be
transmitted by an animal bite. Signs include
swollen lymph glands, painful swallowing, vomiting choking. All cases result in death after about 6 to 9
months.
B)
Disorders of neural and
synaptic transmission
1)
Epilepsy: recurring episodes of abnormal electrical
brain activity. Mostly results in seizures
with involved jerky body movements and loss of consciousness.
2)
Parkinson's disease: A
loss of dopamine-releasing neurons.
Symptoms include stiff joints, muscle tremors in the hands and
feet. They eventually loose mobility.
3)
Alzheimer's disease: shortage
of acetylcholine resulting in an impairment of the memory.
4)
Multiple sclerosis: an
Autoimmune disorder where the sheaths of myelinated neurons in the brain and
spinal cord become progressively damaged and hardened thereby impeding the
movement of signals. Common symptoms
are muscle weakness, visual impairment and urinary incontinence.
5)
Amyotrophic lateral
sclerosis (ALS) loss of myelin
typically occurs in the lower spine.
primary symptoms are weakening and wasting of skeletal muscle tissue. Usually die of respiratory failure due to
the weakening of the diaphragm.
C)
Brain tumors and
abnormal growths.
1) Any abnormal growth in the brain can cause
problems because of the limited space in the skull. To pack more tissue into the skull increases the pressure and
affects the function of the nervous system.
Many can be surgically removed or treated.
Discussion:
1.
What is the result of
demyelination of axons such as occurs in multiple sclerosis?
2.
Why does a physician’s
tapping of the knee or elbow reveal the general status of the nervous system in
general, not just the condition of those two joints?
3.
Why does drinking large
amounts of coffee or other caffeine-containing beverages tend to make a person
“nervous” or “jittery”?
1)
Which of the following
are correct concerning action potentials
a)
they always move at the
maximal rate, the speed of light
b)
can move faster by
hopping across the nodes of Ranvieer
c)
is caused by higher
numbers of sodium on the outside of the membrane than on the inside
d)
always stay the same
2)
the distance between a
chemical synapse
a)
is bridged by electric
sparks
b)
is bridged by a
chemical called a neurotransmitter
c)
is a space called the
synaptic cliffs
d)
Is very large and is
rapidly crossed by diffusion
e)
There is no distance, the
cells are held together by gap junctions
3)
the loss of
neurotransmitters has been implicated in diseases such as
a)
kidney stones b) Parkinson’s c) cancer d) Alzheimer’s e) The fish
4)
Nicotine has the
following effects on the body
a)
stimulates the cerebral
cortex, causing increased alertness
b)
Act at the medulla
oblongata to disrupt motor coordination and intellectual functions.
c)
mimics Acetylcholine, directly stimulating
receptors in the brain
d)
dopamine and Norepinephrine, causing
increased alertness
5)
A reflex is a
stereotyped movement made in response to a stimuli. Which of the following are nervous structures involved in a
reflex?
a) Sensory neuron b)
Midbrain c)
motor neuron d) forebrain e) Thalamus
6)
the portion of the
nervous system that is most involve in the fight or flight response of the body
to a stimulus is the
a)
limbic system b) autonomic c) somatic d) parasympathetic e)sympathetic
Answers: 1) b
2) b,c 3) b,d 4)c 5) a,c 6) e
Some interesting web sites.
For more information on Alzheimer's see http://www.alz.org/
For more information of Parkinson's see http://www.parkinson.org/
Caffeine and jolt cola http://www.geocities.com/SiliconValley/9692/joltcola.html
Parkinson's
disease
http://www.nhgri.nih.gov/DIR/LGDR/PARK/about_parks.html
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http://www.vh.org/Providers/Textbooks/BrainAnatomy/BrainAnatomy.html a live dissection of the human brain.
http://www.med.harvard.edu/AANLIB/home.html the whole brain atlas.
An interesting site showing fetal anatomy of the brain
ect. http://www.vh.org/Providers/Textbooks/FetalYoungCNS/FetalYoungCNS.html
Not being able to recognize faces http://www.choisser.com/faceblind/