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Nursing
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The Nervous SystemLecture #5
The Nervous System Is Responsible For:
Allowing us to interact w/ environment Regulation of activities involving internal organs ‘Driving’ the other sys. of the body
Network composed of complex structures, that transmit signals:
Electrically Chemically
… b/w the body’s organs, tissues & brain
Organization of the Nervous System
Organization of the Nervous System
Central Nervous System:
comprised of the Brain
& Spinal Cord
Organization of the Nervous System Peripheral Nervous System (PNS) pathways are
differentiated: Afferent pathways (sensory): ascending.
sensory impulses toward CNS Efferent pathways (motor): descending.
motor impulses away from CNS Somatic NS: voluntary control (i.e. skeletal muscle
contraction) Autonomic NS: involuntary control (i.e. subconscious
reg. of body’s internal environment: resp., HR, digestion)
Autonomic NS:
Sympathetic NS:
Nerves originating from thoracic & lumbar regions
of spinal column
Parasympathetic NS:
Nerves originating from the brain & sacrum
2 Basic Cells w/in the N. System Neuron
Primary cell of N.Sys. Fxnal unit of N.Sys. Different types
(Neuroglial Cells) Supporting cells:
Structural support Nutrition
Schwann Cells Astrocytes Microglial Cells
100 Billion neurons present in our NS ~7 miles of axons (connections)
One neuron connects with 10,000 other neurons (on average)
Some of the more important connections are up to 6ft long
Therefore increased metabolic demands! Many diseases that affect energy affect the Nervous
System. Organ of consciousness, emotions, behavior, intellect &
humanity.
The Neuron Can work alone, or in units
Detect environmental changes & initiate body responses
to maintain a dynamic steady state (Homeostasis)
Structures differ, so that each neuron is adaptable to
perform specialized fxns. {differentiated}
Cannot regenerate entirely
Cell division stops at birth: (G1)
3 Parts to a Neuron:1. Cell Body: Soma
2. Dendrites: thin processes / extensions:• carries impulses toward cell body
The Three Parts to a Neuron3. Axon: projection away from cell body.
• Carries impulses away from it. • Covered with myelin (lipid insulating layer - called
‘myelin sheath’). • Increases the velocity of impulse transmission• Diameter of axon also influences impulse
transmission velocity. De-myelinating Diseases:
MS & Guillain-Barre Syndrome
Integrating the INPUT with the OUTPUT The NS has only 3 main (overlapping) jobs:
Sensory Input: Informing
the CNS:
Organizing what is happening inside
& outside the body
Allows info from body receptors (i.e.
Skin) to create an impulse
that shoots up to the Spinal Cord
& then to the brain
Integrating the INPUT with the OUTPUT Integration: CNS makes ‘sense’
of received input from around the body. i.e. Interneurons: neuron
(nerve cell) sits b/w a sensory fiber & a motor fiber.
Interneurons bring an impulse / stimulus to the CNS, and back to the nerves that can make an action happen
Integrating the INPUT with the OUTPUT
Motor Output:
The stimulation of
muscles to move
The stimulation of
glands to secrete
substances
i.e. Motor fibers- are
‘action making’
nerves
Transmission of the Nerve Impulse
Impulses have a domino-like effect
When a neuron get a signal, it passes it onto the next
neuron; which passes it onto the next neuron; which
passes it onto the next neuron; etc.
def. Nerve-a long collection of neurons
Entire impulse passes through a neuron in about 7
milliseconds
How? The Action Potential
Transmission of the Nerve ImpulseThe Action Potential
When neuron at rest: ‘resting membrane potential’ Cell membrane is Polarized
More Na+ outside; More K+ inside When a stimulus reaches resting neuron:
Gated Na+ channels open on the surface of membrane Na+ rushes into the cell
Inside of the cell becomes (+) This Depolarizes the cell
Creates an ACTION POTENTIAL Transmits the stimulus
ALL–or–NONE: need to overcome threshold
Transmission of the Nerve ImpulseThe Action Potential
Movement of K+ Outside the Cell:
K+ gates open, cause K+ to escape outside
Na+ gates close
Closing of K+ gates:
More K+ outside the cell than Na+ inside the cell
The cell is now in a HYPERPOLARIZED STATE
Transmission of the Nerve ImpulseThe Action Potential
Refractory Period: puts everything back to normal
K+ returns inside & Na+ returns outside
Because of the Na+/K+ Pump!
During refractory period, the neuron DOES NOT
respond to ANY incoming stimuli
Transmission of the Nerve Impulse:The Synaptic Cleft
This is the gap that separates the axon of one neuron & the dendrites of another.
Neurons NEVER touch each other! How does the signal get transmitted?
The depolarization wave reaches the end of the axon & causes Ca2+ ion channels to open, on the presynaptic neuron
Ca2+ enters the presynaptic axonal terminal & fuses with the NT vesicles (synaptic vesicles)
NT then gets released into the synapse
Transmission of the Nerve ImpulseThe Synaptic Cleft
NT binds with protein receptors on the dendrites of the
postsynaptic neuron. (NTs have specific receptors)
2 things can now occur. The NT can: stimulate Na+ channels to open. This continues the
impulse [EPSP] stimulate K+ channels to open. This hyper-polarizes
the cell & stops the impulse [IPSP]
The NT then goes back to the presynaptic neuron & gets
recycled for the next impulse transmission
Sympathetic Response Cardiovascular Increases in:
B/P ; HR ; Contractility ; B.flow to Skeletal Muscles. Respiratory Efficiency Increases:
Bronchial dilation ; RR increases Pupil Dilation & Sweating Increase Piloerection Shunting of blood way from GI Tract. Shunting of blood away from kidneys. Glyconeogenesis & Glycogenolysis. Release of Corticosteroids. Suppression of Immune & Inflammatory responses.
Sympathetic Transmission Termination Once NEpi has been released in the synaptic cleft it
must be removed. Effective recycling of NEpi. Enzymatic metabolization by:
Monoamine oxidase (MAO) Catechol-o-methyltransferase (COMT)
Click on right answer to go to next page
The nurse monitors for which clinical manifestations in the client receiving a medication that stimulates the sympathetic division of the autonomic nervous system?a.Decreased heart rate, decreased force of contractionb.Increased heart rate, increased force of contraction
c.Decreased heart rate, increased force of contractiond.Increased heart rate, decreased force of contraction
Correct Answer is BStimulation of the sympathetic nervous system initiates the fight-or-flight response, increasing both the heart rate and force of contraction.
Parasympathetic Response Increase motility and secretions in the GI tract to
promote digestion and absorption.
Relaxation of GI/GU sphincters - evacuation of wastes.
Decrease HR, B/P & contractility- to conserve energy &
provide rest to the heart
Bronchial Constriction & Increased secretions from
bronchial mucosa.
Pupillary constriction, thereby decreasing light entering
eye (decreases stimulation of the retina).
Parasympathetic Transmission Termination
Once ACh has been released in the synaptic cleft it must
be removed.
Effective recycling of Ach.
Enzymatic metabolization by:
Acetylcholinesterase
Click on correct answer to move to next slide:
In preparation for magnetic resonance angiography, the nurse asks the client which question?
a.“Have you had a recent blood transfusion?”b.“Do you have allergies to iodine or shellfish?”
c.“Do you have a history of urinary tract infections?”
d.“Do you currently use oral contraceptives?”
Correct Answer :B
Allergies to iodine and/or shellfish need to be explored because the client may have a similar reaction to the dye used in the procedure. In some cases, the client may need to be premedicated with antihistamines or steroids before the test.
Neurotransmitters >30 NTs:
NEpi & Epi
ACh
Dopamine
Histamine
Serotonin
AAs (i.e. GABA)
Enkephalins
Endorphins
Thinking about your Brain The brain weighs only 3
pounds & requires 15-20% of the total CO
Different parts of your brain are responsible for different fxns
Major parts of brain: Cerebrum Cerebellum Brain Stem Diencephalon 4 connective cavities of
the brain (ventricles)
Cerebrum Largest part of brain
Controls consciousness
Divided in L / R halves
called Cerebral
Hemispheres
Each 1/2 has 4 lobes: Frontal Parietal Temporal Occipital
Cortex (cerebrum’s outer layer)- is gray
The ‘curvy bumps’ are called gyri
Shallow grooves that separate the gyri are called sulci.
Deeper grooves are called fissures
The Corpus Callosum is located at the base of the
longitudinal fissure
network of myelinated fibers that join the L & R
cerebral hemispheres
Frontal Parietal Temporal Occipital
Speech Production
General Interpretation
Area
Interpretation of
Sensations
Recognizing objects visually
Concentration Understanding speech
Remembering visually
Vision
Problem solving
Ability to use words
Remembering through sounds
Combining images received
visually
PlanningExec. Fxns
Sensations felt
Hearing
Voluntary muscle control
Learning
Which deficit will the nurse expect to find in a client who has experienced an injury to the frontal lobe of the brain?Choose the right answer to move to the next slide:
a. Inability to interpret taste sensations
b. Inability to interpret sound c. Impaired judgment d. Impaired learning
Yes, the answer is “C”: Impaired judgment
The frontal lobe is responsible for many functions, including judgment, reasoning, voluntary eye movement, and motor functions.
Cerebellum Lies just below the cerebrum
Divided by a fissure
Gray on the outside
Controls & coordinates
skeletal muscle mvmts. [The
cerebrum sends out the
signal to the cerebellum for
mvmt]
Maintains muscle tone (at all
times)
The Brain Stem Comprised of 3 structures:
Midbrain: “station” for info. passing b/w: SC & cerebrum SC & cerebellum
Pons: “bridge” that joins the cerebellum with the cerebrum
Filled w/ axonal bundles that integrate info. from eyes & ears
Controls respirations Medulla Oblongata:
HR; Resps; B/P regulation Centers for coughing, vomiting,
sneezing, swallowing & hiccups Becomes the SC after it passes through the
foramen magnum
The Reticular Formation Collection of nerve cell bodies (nuclei)
within the brainstem called the
Reticular Formation
Controls vital reflexes:
Cardiovascular fxning
Respiration
Maintains wakefulness
Bypassing the Brain-The Reflex Arc Happen automatically (i.e. When you touch something
very hot or sharp)
Sensory neurons detect: Pain / Temp / Pressure
If a sensory neuron detects something that could harm
your body (i.e. Sharp object)
An impulse passes from the receptor throughout
the sensory neuron, to the SC & then to a motor
neuron, which stimulates muscles to retract your
finger from the sharp object.
Bypassing the Brain - The Reflex Arc Reflexes occur so fast - you don’t even think
(cognitively) about how to react!
The impulse does not make it to the brain in time to
generate a rxn!
By the time the impulse gets to the brain, the SC has
already taken care of the problem.
Reflex Arcs:
Save time & damaging consequences
The Ventricles 2 Lateral: one on each side of the brain
3rd: in the center of the brain
4th: lies on the top of the brainstem
Cerebral Aqueduct connects the 3rd & 4th ventricles
together & becomes the central canal of the SC
The ventricles & cerebral aqueduct serve as a system to
circulate CSF
CSF is a clear fluid that is made by the cells that line the
ventricles
CSF is contained in the 4 ventricle, the subarachnoid
space & the central canal of the SC. Fxns to:
Pick up wastes
Cushions the CNS
Keeps the ions in balance
Stabilizes the membrane potentials.
Spinal Tap CSF is drawn through a
needle for analysis from
the subarachnoid space
Can be tested for: presence of bacteria
(which may cause meningitis)
presence of proteins that can indicate other diseases (i.e. Alzheimer's)
Regulating Systems : The Diencephalon Made up of the Hypothalamus & Thalamus
Hypothalamus regulates: Sleep Hunger & Thirst Body Temp B/P Fluid Levels Maintains Homeostasis
Controls pituitary gland signaling to the
Endocrine System, for secreting hormones
Regulating Systems : The Diencephalon
Thalamus is the gateway to the cerebrum.
Whenever an impulse travels from somewhere in your
body, it passes through the Thalamus
The Thalamus then relays the impulse to the proper
location in the cerebral cortex, which then interprets
the message
Click on right answer to move to next slide:During electroencephalography, the client is instructed to breathe deeply (hyperventilate). What is the nurse’s interpretation of this action?a.Seizure activity may be increased because of cerebral vasodilation associated with hyperventilation.
b.Seizure activity may be increased because of cerebral vasoconstriction secondary to hyperventilation.
c.Seizure threshold is lowered by acidosis associated with hyperventilation.
d.Seizure threshold is lowered by hypoxemia associated with hyperventilation.
Correct Answer BHyperventilation produces cerebral vasoconstriction and alkalosis, which increases the likelihood of seizure activity. The client is asked to breathe deeply 20 to 30 times for 3 minutes.
The Limbic System
The Limbic System
Disorders of the NS Multiple Sclerosis (MS)
Affects the myelin sheath that covers the axon of a nerve
The myelin sheath develops lesions that become inflamed & irritated.
Leads to demyelination of the white matter of the brain & spinal cord
After the myelin destruction, neuroglial tissue proliferates in the white matter of the CNS. When the lesion heals, hard yellow scar tissue (plaques) are left behind.
As the disease affects more nerves, the number of
scleroses increases, leading to multiple damage sites
The hard scar tissue interferes w/ the nerve’s ability to
conduct an impulse through the axon
If an impulse can’t be transmitted, a mvmt or
response cannot occur
As the dx progresses, mvmt becomes increasingly
difficult & then impossible
Structures most commonly involved are the optic &
occulomotor nerves & the spinal tract nerves. Does not
affect the Peripheral NS
Characterized by exacerbations & remissions
Seen primarily in ages 18 – 40 y/o. [ F > M ]
Exact cause is unknown: Slow acting viral infection? An autoimmune response? GENETICS? An allergic response? Trauma; anoxia; toxins; nutritional deficiencies;
vascular lesions; anorexia?
Alzheimer’s Disease ‘mind’ slipping away Progressive degenerative disorder of the cerebral cortex
{Cortical Degeneration} Accounts for >1/2 of all cases of Dementia Pt’s can’t care for themselves. They’ve forgotten how to
perform ADLs. Bundles of a fibrous protein [ADAP: Alzheimer’s Dx
Assoc. Protein] , are tangled around the nucleus of a neuron
Amyloid plaques (globs of protein) also surround axonal branches. Plaques are thought to kill / destroy the neuron
Cause unknown: Neurochemical factors:
Possible deficiencies: *ACh; Somatostatin; Substance-P; NEpi
Slow-growing CNS virus?; Trauma ? Genetics (abnormal chromosome 21)
Insidious Onset & Cannot be completely confirmed till after death
Tests that can help diagnose possibility: PET (Positron Emission Tomography) CT ; MRI; EEG CSF analysis; Cerebral Angiogrophy
http://web.kamogawa.ne.jp/~miyake/ADunrabelingADEAR/ADEAR2003.htm