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