Transcript The nervous system

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EVOLUTIONARY DEVELOPMENT OF THE NERVOUS
SYSTEM
These facts prove the evolutionary development of the nervous system…
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Cnidarians have a have a nerve net
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Cephalization is a trend toward clustering sensory neurons and interneurons at
the anterior end. Basically, it is the forming of a head.
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Flatworms show cephalization, with a small brain and longitudinal nerve cord.
They have the simplest clearly defined central nervous system.
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Annelids such as the earthworm and arthropods have a ventral nerve cord.
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Vertebrates have a hallow dorsal nerve cord.
With cephalization come more complex nervous systems.
WHY IS THE NERVOUS SYSTEM IMPORTANT?
Nerves send messages to everything from the brain.
if there was no nervous system...
1.you're heart wouldn't be told to beat
2. your legs wouldn't be told to walk, and your arms wouldn't be told to move
3. your lungs wouldn't be told to expand and collapse
4. messages wouldn't be able to send messages to the brain, such as tastebuds (no
taste) skin, (no feeling,) eyes (no sight), no hearing, and no smelling.
The vertebrate nervous system consists of
central and peripheral components
- the central nervous system (CNS) consists
of the brain and spinal cord (nerve bundle
that communicates with body)
- the peripheral nervous system (PNS)
consists of all nerves outside the CNS.
PERIPHERAL SYSTEM
Sensory system: conveys information from sensory receptors or nerve endings.
Motor system:
1. Somatic system: controls the voluntary muscles
2. Autonomic system: Controls involuntary muscles
Sympathetic:
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Flight or fight response
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Increase heart and breathing rate
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Liver converts glycogen to glucose
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Bronchi of lungs dilate and increase gas exchange
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Adrenalin raises glucose levels
Parasympathetic:
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Rest and digest
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Calms the body
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Decreases heart/breathing rate
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Enhances digestion
THE SCHWANN CELL
Schwann cells are part of the peripheral nervous system
(PNS.) They have two major functions, they produce
the myelin sheath which covers the Schwann cell,
which helps to repair and regenerate nerves that have
been damaged. In addition, they help the nerve
impulse to be passed on quicker so that the brain can
send a impulse to ones bones and muscles.
Functional composition of the PNS.
cerebrum
corpus
callosum
thalamus
Pineal gland
hypothalamus
cerebellum
pituitary
pons
spinal cord
medulla
oblongata
CEREBRUM
Involved with higher brain functions.
Processes sensory information.
Initiates motor functions.
Integrates information.
Frontal lobe.
Contains the primary motor cortex.
Parietal lobe.
Contains the primary somatosensory
cortex.
Integrative Function of the Association Areas.
Much of the cerebrum is given over to
association areas.
Areas where sensory information is integrated
and assessed and motor responses are
planned.
Lateralization of Brain Function.
 The left hemisphere.
 Specializes in language, math, logic operations, and the
processing of serial sequences of information, and visual and
auditory details.
 Specializes in detailed activities required for motor control.
 The right hemisphere.
 Specializes in pattern recognition, spatial relationships, nonverbal
ideation, emotional processing, and the parallel processing of
information.
FIG. 49-17
Max
Hearing
words
Seeing
words
Min
Speaking
words
Generating
words
Language and Speech.
Broca’s area.
 Usually located in the left hemisphere’s frontal lobe
 Responsible for speech production.
Wernicke’s area.
 Usually located in the right hemisphere’s temporal lobe
 Responsible for the comprehension of speech.
Emotions.
In mammals, the limbic system is composed of
the hippocampus, olfactory cortex, inner portions
of the cortex’s lobes, and parts of the thalamus
and hypothalamus.
Mediates basic emotions (fear, anger), involved in
emotional bonding, establishes emotional memory
 For example,
the amygdala
is involved in
recognizing
the emotional
content of
facial expression.
Memory and Learning.
Short-term memory stored in the frontal
lobes.
The establishment of long-term memory
involves the hippocampus.
The transfer of information from short-term to
long-term memory.
 Is enhanced by repetition (remember that when you are
preparing for an exam).
 Influenced by emotional states mediated by the
amygdala.
 Influenced by association with previously stored
information.
Different types of long-term memories are
stored in different regions of the brain.
Memorization-type memory can be rapid.
Primarily involves changes in the strength of
existing nerve connections.
Learning of skills and procedures is slower.
Appears to involves cellular mechanisms
similar to those involved in brain growth and
development.
Human Consciousness.
Brain imaging can show neural activity
associated with:
Conscious perceptual choice
Unconscious processing
Memory retrieval
Working memory.
Consciousness appears to be a whole-brain
phenomenon.
MIDBRAIN
Contains ascending and descending
tracts to the cerebrum and
thalamus.
Reflex center for eye muscles.
Also involved with processing visual
and auditory information (connects
head movements with visual and
auditory stimuli).
MEDULLA
OBLONGATA
• Composed of nerve tracts
to and from the brain
(these tracts cross over
left to right and right to left)
• May be regarded as an
extension of the spinal
cord
• Almost all of the cranial
nerves arise from this
region
MEDULLA OBLONGATA
Contains control centers for
many subconscious
activities
• Respiratory rate
• Heart rate
• Arteriole constriction
• Swallowing
• Hiccupping
• Coughing
• Sneezing
CEREBELLUM
Controls and coordinates
muscular activity.
Important in equilibrium, posture
and movement.
THE NEURON
The neuron consists of a cell body, which contains the nucleus and other organelles,
and two types of cytoplasmic extensions called dendrites and axons.
Dendrites are sensory; they receive incoming messages from other cells
and carry electrical signal to the cell body. Axons transmit an impulse
from the cell body outward to another cell.
3 types of neurons:
Sensory neurons: receive an initial stimulus from a sense organ
Motor neuron: stimulates effectors (muscles or glands)
Interneuron/association neuron: resides within the spinal cord and brain,
receives sensory stimuli, and transfers the information directly to a
motor neuron or to the brain for processing.
SYNAPSE
• Each branched end of an exon transmits information to another
cell at a junction called a synapse.
• The part of each axon branch that forms this specialized junction
is a synaptic terminal.
• Chemical messengers called neurotransmitters pass information
from the transmitting neuron to the receiving cell. With the
signaling of influx of Calcium ions into the neuron. The
neurotransmitters will match up with another ion channel, and
change it’s shape so it can take in ions. Now, sodium can flow in
into the next neuron
• The transmitting neuron is the presynaptic cell
• The neuron, muscle, or gland cell that receives the signal is the
postsynaptic cell
THE REFLEX ARC
The simplest nerve response.
It is inborn, automatic, and protective. i.e the knee-jerk reflex: consists of
only 2 neurons: sensory and motor. A stimulus, a tap from a hammer, is
felt in the sensory neuron of the kneecap, which sends an impulse to the
motor neuron, which directs the thigh muscle to contract.
Complex reflex consists of 3 neurons: sensory, motor and interneuron
a sensory neuron transmits an impulse to the interneuron in the spinal
cord, which sends one impulse to the brain for processing and also one
to the motor neuron to effect change immediately (jerk hand away from
hot iron).
1. The reflex is initiated artificially by tapping the tendon connected to the quadriceps
muscle.
2. Sensors detect a sudden stretch in the quadriceps
3. Sensory neurons convey the information to the spinal cord.
4. In response to signals, motor neurons convey signals to the quadriceps, causing it to
contract and jerking the lower leg forward.
5. Sensory also communicate with interneurons in the spinal cord.
6. The interneurons inhibit motor neurons that lead to the hamstring muscle. This
inhibition prevents contraction of the hamstring which would resist the action of the
quadriceps.
RESTING POTENTIAL
All living cells have a membrane potential: a difference in electrical
charge between the cytoplasm (negative ions) and extracellular
fluid (positive ions). This potential should be between -50mV and
-100mV. A neuron in its unstimulated/polarized state (resting
potential) has a membrane potential -70mV. The sodiumpotassium pump maintains the polarization by actively pumping
ions that leak across the membrane. In order nerve to fire, a
stimulus must be strong enough to overcome resting potential.
The larger the membrane potential, the stronger the stimulus
must be to cause the nerve to fire.
GATED CHANNELS
Neurons have gated-ion channels that open or close in response to
a stimulus and play an essential role in transmission of electrical
impulses. Allow one kind of ion, i.e. sodium or potassium, to flow
through. If stimulus triggers sodium ion-gated channel to open:
sodium flow into cytoplasm -> decrease in polarization (-60mV);
membrane becomes depolarized-> easier for nerve to fire.
Potassium ion-gated channel: membrane potential increases,
membrane becomes hyperpolarized (-75mV), harder for neuron
to fire.
ACTION POTENTIAL
- generated only in the axon of a neuron
- when axon is stimulated sufficiently to overcome resting potential, permeability of
the region suddenly changes and impulse can pass
- sodium channels open and sodium flood into the cell
- in response, potassium channels open and potassium floods out of the cell
- rapid movement of ions (wave of depolarization) reverses the polarity of the
membrane -> action potential
- the sodium-potassium pump restores the membrane to its original polarized
condition by pumping sodium and potassium ions back to original position ->
Period of repolarization called refractory period, neuron cannot respond to
another stimulus.
THE INTERDEPENDENCE
The nervous and muscular systems work together and are very
unique systems that could not function without each other.
The muscular system gets messages from the nervous system,
telling it what to do, how to do it, and exactly when to perform the
action.
Without the nervous system, the muscular system would not be able
to move us, because it would have nothing to tell it what to do.
And without the muscular system, we wouldn't be able to move
even if we did have the nervous system.
Also, the skeletal system, female reproductive system, male
reproductive system, endocrine system.
Your conscious mind relays a command to your
central nervous system, which translates it
into electrical impulses. When the muscles are
ready, a chemical, acetylene, is released from
the nerve endings, stimulating the
membranes of muscle fibers, and causing
them to contract.
COMMON DISEASES FROM THE NERVOUS
SYSTEM
SCHIZOPHRENIA
The symptoms of schizophrenia include hallucinations and delusions, blunted emotions,
distractibility, lack of initiative, and poverty of speech.
The cause of schizophrenia is unknown, although the disease has a strong genetic component.
There is an active effort to find the mutant genes that predispose a person to schizophrenia.
Available treatments for schizophrenia focus on the use of dopamine as a neurotransmitter.
Two lines of evidence suggest that this approach is suitable.
 First, amphetamine, which stimulates dopamine release, can produce symptoms identical to
those of schizophrenia.
 Second, many of the drugs that alleviate the symptoms block dopamine receptors.
Additional neurotransmitters may also be involved because other drugs successful in
treating schizophrenia have stronger effects on serotonin and/or norepinephrine
transmitters.
The street drug PCP blocks glutamate receptors and induces strong schizophrenialike symptoms. Many current schizophrenia medications have severe side effects.
Dopamine: It is an inhibitory neurotransmitter, which means that when it comes to its
receptor sites, it blocks the tendency of that neuron to fire. Dopamine is
associated with reward mechanisms in the brain.
Severe deficiency and overabundance of this neurotransmitter can cause drastic
results. It is often the neurotransmitter involved with drugs, like cocaine heroin,
etc. People that suffer from Schizophrenia are often seen with vast amounts of
dopamine in their system. People that suffer from Parkinson's disease are often
seen with insufficient amounts of dopamine in their system.
ALZHeimer’s disease
Alzheimer’s disease is a mental deterioration or dementia. It is characterized by confusion,
memory loss, and a variety of other symptoms.
Its incidence is age related, rising from 10% at age 65 to 35% at age 85.
The disease is progressive, with patients losing the ability to live alone and take care of
themselves. There are also personality changes, almost always for the worse.
It is difficult to diagnose Alzheimer’s disease while the patient is still alive.
However, it results in characteristic brain pathology.
Neurons die in huge areas of the brain, often leading to shrinkage of brain tissue.
The diagnostic features are neurofibrillary tangles and senile plaques in the remaining brain
tissue.
 Neurofibrillary tangles are bundles of degenerated neuronal and glial processes.
 Senile plaques are aggregates of ß-amyloid, an insoluble peptide that is cleaved from a
membrane protein normally found in neurons.
 Membrane enzymes, called secretases, catalyze the cleavage, causing ß-amyloid to
accumulate outside the neurons and to aggregate in the form of plaques.
 The plaques seem to trigger the death of the surrounding neurons.
Parkinson’s disease
Approximately 1 million people in the United States suffer from Parkinson’s
disease, a motor disease characterized by difficulty in initiating
movement, slowness of movement, and rigidity.
Parkinson’s disease results from death of neurons in a midbrain nucleus
called the substantia nigra.
These neurons normally release dopamine from their synaptic terminals in
the basal nuclei.
The degeneration of dopamine neurons is associated with the accumulation
of protein aggregates containing a protein typically found in presynaptic
nerve terminals.
The consensus among scientists is that it results from a combination of
environmental and genetic factors.
At present, there is no cure for Parkinson’s disease, although various
approaches are used to manage the symptoms, including brain surgery;
deep-brain stimulation; and drugs such as L-dopa, a dopamine precursor
that can cross the blood-brain barrier.
One potential cure is to implant dopamine-secreting neurons, either in the
substantia nigra or in the basal ganglia.
Embryonic stem cells can be stimulated or genetically engineered to develop
into dopamine-secreting neurons.
 Transplantation of these cells into rats with an experimentally induced
condition that mimics Parkinson’s disease has led to a recovery of motor
control.
 It remains to be seen whether this kind of regenerative medicine will work
in humans.
MULTIPLE CHOICE QUESTIONS
1. The function of a Schwann cell is to
a) Produce esterases to break down neurotransmitters
b) Form the myelin sheath around the axon of a neuron
c) Act as an interneuron in the spinal cord
d) Receive impulses and send them to the neuron
e) Act as an effector for a neuron
2. Which of the following are the parts of neurons?
a) Brain, spinal cord, and vertebral column
b) Sensory and motor
c) Dendrite, axon, and cell body
d) Cortex, medulla, and sheath
e) Sympathetic and parasympathetic
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