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1
Chapter 11
The Nervous System
The Brain, Cranial Nerves,
Autonomic Nervous System
and the Special Senses
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Introduction
• Brain is divided into four main parts
– Brainstem ( Medulla oblongata, Pons,
Midbrain) : controls breathing, heartbeat rates
and reactions to auditory and visual stimuli
– Diencephalon: controls homeostasis
– Cerebrum: controls intellectual processes and
emotions
– Cerebellum: maintains body posture and
balance
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Blood supply and the Brain
Barrier System:
• Although the brain constitutes only 2% of the adult
body weight, it receives 15% of the blood (750
ml/min)
• Consumes 20% of the body’s oxygen and glucose.
• 10 seconds of interruption in blood flow can cause
unconsciousness (4 min = irreversible brain
damage)
• A blood-brain barrier regulates what substances can
get from the blood stream into the brain. Injury,
inflammation, toxins may break it down.
• Permeable to water, glucose, oxygen, carbon
dioxide, alcohol, caffeine, nicotine and anesthetics.
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The Principal Parts of the
Brain
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The Principal Parts of the Brain
(cont’d.)
• Main parts: brainstem, diencephalon,
cerebrum and cerebellum
• Protection
– Cranial bones (fontanels close ~2 yrs old)
– Meninges
– Cerebrospinal fluid
• Ventricles
– Interventricular foramen
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The Principal Parts of the Brain
(cont’d.)
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Ventricles of the brain:
• 4 internal chambers called ventricles
• Several “canals” interconnect the ventricles and
a central canal extends through the medulla
oblongata into the spinal cord.
• These ventricles and canals are lined with
ependymal cells – CSF
• Each ventricle contains a choroid plexus –
network of blood capillaries anchored to the floor
or wall of the ventricle and covered by
ependymal cells.
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Cerebrospinal fluid /CSF
• Serves as a shock absorber – fills the arachnoid
space so the brain & spinal cord “float”
• Provides some nutrients and removes some wastes
• Optimizes chemical levels for accurate neuronal
signaling
• Produced by the ependymal cells of the choroid
plexus which is located in some ventricles within the
brain.
• Production equals reabsorption so the volume of
CSF remains the same.
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The CSF circulates
Through the ventricles and then
flows to the
Sub-arachnoid space where it will
flow around the brain & spinal cord
– finally it will be reabsorbed by villi
within the arachnoid layer
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The Anatomy and Functions of
the Brainstem
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The Anatomy and Functions of the
Brainstem (cont’d.)
• Medulla oblongata
–
–
–
–
–
Ascending and descending tracts
Connects spinal cord with the brain
Some tracts cross over in medulla
Reticular formation: controls consciousness
Reflex centers – involuntary, simplest path able to
receive a stimulus & produce a response.
• Vital=heart rate, breathing & blood vessel size, BP.
• Less vital=vomiting, swallowing, coughing,
sneezing and hiccuping
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The Anatomy and Functions of the
Brainstem (cont’d.)
• Pons varolii
– Connects spinal cord with brain – between
medulla and midbrain
– Connects parts of brain with each other –
relays impulses from one side of cerebellum
to the other
– Helps control breathing (back up) along with
Medulla oblongata –even breaths
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The Anatomy and Functions of the
Brainstem (cont’d.)
• Midbrain
– Ventral cerebral peduncles: convey impulses
from cortex to pons and spinal cord
– Dorsal tectum: reflex center
– Controls movement of head and eyeball
(visual stimuli) – survival activity
– Controls movement of head and trunk
(auditory stimuli) – you automatically turn
toward a noise or movement
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Inferior (underside) of brain:
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The Anatomy and Functions of
the Diencephalon
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Location of Diencephalon:
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The Anatomy and Functions of the
Diencephalon (cont’d.)
• Optic tracts
• Mamillary bodies: memory and emotional responses
• Thalamus
– Relay station for sensory impulses
– Interpretation center for pain, temperature and
touch (if damaged, sensitivity to pain or loss of
consciousness)
• Epithalamus: contains pineal gland
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Example of relaying information:
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The Anatomy and Functions of the
Diencephalon (cont’d.)
• Hypothalamus: homeostasis
– Lies inferior to the thalamus and attached by a small
stalk to the pituitary gland
– Controls and integrates autonomic nervous system
– Receives sensory impulses from internal organs
– Controls thirst, hunger, body temp, memory, emotion
( rage) and sleep
– Controls pituitary gland and links endocrine and
nervous systems
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The Anatomy and Functions of
the Diencephalon (cont’d.)
• Pineal gland:
– Pine cone shaped growth attached to the roof
of the third ventricle.
– Decreases in size with age.
– Regulates the gonads and the annual
breeding cycle.
– Produces serotonin by day and melatonin at
night.
– May regulate timing of puberty.
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Sagittal cut:
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Other areas: Reticular formation
(or activating system)
• neural network” involves neurons from the
medulla, pons, hypothalamus, midbrain and
cerebrum & cerebellum
– Controls consciousness
– Stimulates nerve cells to be active’
– During sleep, RAS shuts down areas so they can
recover (form more neurotransmitters). Sleep
runs in 90 minute cycles (REM vs. non-REM sleep)
– Coordination – as you get tired, you slump
– “filters” incoming sensory information and
passes on only important stuff (like pain)
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Means “network”
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The Cerebrum: Structure and
Function
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The Cerebrum: Structure and
Function (cont’d.)
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The Cerebrum: Structure and
Function (cont’d.)
• Cerebral cortex: gray matter surface
• Longitudinal fissure separates two hemispheres (R & L)
– Control muscles on opposite sides
– Right: artistic, spatial & pattern awareness
– Left: language, scientific, reasoning, logic
• Premotor area involved in learning –how to walk before
doing it)
• Gyri: folds
• Sulci: grooves
• Corpus callosum: bridge connecting two hemispheres
(coordinates) – women’s larger (intuition?)
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The Cerebrum: Structure and
Function (cont’d.)
• Surface of the cortex
– Motor areas control muscular movements
– Sensory areas interpret sensory impulses
– Association areas process emotions and
intellect
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The Cerebrum: Structure and
Function (cont’d.)
• Basal ganglia/cerebral nuclei
– Composed of structures from the cerebrum,
thalamus, and midbrain
– Basal ganglia are not easily seen and work
with the cerebellum to coordinate muscle
activities associated with rhythmic movements
like walking, running, etc.
– Limits unwanted muscle activity
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The Limbic System;
• Involved in the involuntary emotional aspects of
behavior – memories of past pleasant or
unpleasant experiences affect how we act in
certain situations.
• Associated with emotions such as pain, pleasure,
fear, rage, sorrow, sexual feelings, affection, anger
and docility depending on the area of the “system”
which is stimulated.
• Amygdala – emotion
• Hippocampus – memory (determines where a
memory is to be stored) – Alzheimers?
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Way inside the brain…
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The Cerebrum: Structure and
Function (cont’d.)
• Cerebral hemispheres
– Frontal lobe:
•
•
•
•
•
•
•
muscle movement (planned – like dancing)
moods, aggression (lobotomy?)
Smell
Motivation & personality (part is genetic…)
problem solving, reasoning (right from wrong)
visual scanning (phone book)
Broca’s area – motor speech center (thoughts into
words) – stroke?
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The Cerebrum: Structure and
Function (cont’d.)
• Parietal lobe:
– touch, pain, balance, taste, temperature (sensory)
– Common integration center – gathers information
from different areas of cerebrum and analyzes see someone in the hall ( visual, perfume, voice,
etc)
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The Cerebrum: Structure and
Function (cont’d.)
• Temporal lobe:
– hearing, smell, memory, abstract thought,
judgment
– Taste center – taste buds
– Olfactory center – nasal receptors
– Wernicki’s area – sensory speech – determines if
it is speech being heard or something else
(music, noise)
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The Cerebrum: Structure and
Function (cont’d.)
• Occipital lobe:
• posterior part of the brain
• Visual center – info from eyes ( color, shape & movement)
• Visual association area: uses past visual experiences in
memory to recognize what is being seen
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The Cerebrum: Structure and
Function (cont’d.)
• Insula – 5th lobe:
– Also called “Island of Reil”
– Inside lobe of cerebrum
– Deep to the parietal, frontal & temporal (these
need to be removed in order to see it)
– Not sure of function, but has been associated
with spoken language, taste, sensing info from
visceral receptors.
– Social emotions – disgust, pride, moral intuition,
craving drugs (cigarettes?) – being human?
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The Cerebellum: Structure
and Function
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The Cerebellum: Structure and
Function (cont’d.)
• Butterfly-shaped – clump of cauliflower?
• Two partially separated hemispheres
connected by vermis
• Functions – same side control
(ipsilaterally)
– Coordinating muscular movements
– Maintaining posture
– Maintaining balance
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The Cerebellum: Structure and
Function (cont’d.)
• Arbor vitae – called the “tree of life”
• is the cerebellar white matter, so called for
its branched, tree-like appearance. It
brings sensory and motor information to
and from the cerebellum.
• Proprioception – awareness of the location
and action of a particular body part
(gymnast)
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Arbor vitae
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The Autonomic Nervous
System
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The Autonomic Nervous System
(cont’d.)
• Subdivision of efferent PNS
• Functions without conscious effort
• Controlled mostly by hypothalamus, some
by medulla
• Regulates functions of internal organs
• Assists in maintaining homeostasis
• Helps deal with emergency situations
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General Characteristics of the ANS:
• It is a two-neuron pathway:
– Sensory signals from viscera and skin send signals to
autonomic neurons in brain and spinal cord.
– A preganglionic neuron cell body is located within the
CNS (brain stem or spinal cord).
– Preganglionic fibers (efferent fibers) synapse with a
ganglionic neuron located in the PNS
– A postganglionic fiber terminates on the effector
organ (heart, stomach, etc).
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The Autonomic Nervous System
(cont’d.)
• Includes nerves, ganglia, and plexuses which carry
impulses to all smooth muscle, secretory glands, and heart
muscle.
• Regulates the activities of the visceral organs (heart and
blood vessels, respiratory organs, alimentary canal,
kidneys, bladder, and reproductive organs)
• The sympathetic and parasympathetic may be antagonistic
in their action:
– The sympathetic may accelerate the heartbeat in
response to fear whereas the parasympathetic
slows it down.(dual innervation)
– You wont knit and run from a tiger at the same time!
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The Autonomic Nervous System
(cont’d.)
• Sympathetic
– Energy and stressful situations – FIGHT or FLIGHT!
– Increases heartbeat, BP and breathing rates
– Neurotransmitters: acetylcholine and norepinephrine –
occurs in the ganglions
• Causes an increase in activity in most organs
( except digestive system) – uses lots of energy
– Preganglionic neurons in the thoracic and lumbar
regions of spinal cord
– Synapse alongside vetebrae or collateral (bonus)
ganglion
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The Autonomic Nervous System
(cont’d.)
• Parasympathetic
– Restores body to nonstressful state
– Neurotransmitter: acetylcholine
– Stimulates digestion, urination and defecation,
decreases others (Rest and Repose)
– Preganganglionic neurons in brain stem or sacral
regions
– Over 75% are found in the Vagus nerve
(CN X)
– Synapse (ganglia) close to target organs
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The 12 Cranial Nerves and
Their Functions
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Cranial Nerves:
• Part of the Peripheral Nervous System
• 12 pairs of nerves which begin in the brain. More
precise & accurate than other nerves.
• Designated by number and name (gives clue to
the function)
• Most are “mixed” nerves; they carry both
sensory and motor fibers.
• The olfactory, optic and vestibulocochlear nerves
only carry sensory fibers (pick up only the
stimuli)
• SEE HANDOUT
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KNOW THESE!
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The 12 Cranial Nerves and Their
Functions (cont’d.)
• (I) Olfactory: smell
• (II) Optic: sight
• (III) Oculomotor: movement of eyeball,
constriction of pupil
• (IV) Trochlear: movement of eyeball
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The 12 Cranial Nerves and Their
Functions (cont’d.)
• (V) Trigeminal: chewing, sensations in teeth
– Ophthalmic V1
– Maxillary V2
– Mandibular V3
• (VI) Abducens: movement of eyeball (outward)
• (VII) Facial: facial expression, taste, tear and salivary
glands
• (VIII) Vestibulocochlear: equilibrium, hearing
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The 12 Cranial Nerves and Their
Functions (cont’d.)
• (IX) Glossopharyngeal: swallowing, taste,
salivary glands
• (X) Vagus: certain muscle movements – throat,
affects heart, digestive system, sensory
impulses
• (XI) Accessory: swallowing, head movement,
voice
• (XII) Hypoglossal: swallowing, speech, tongue
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An aid to memory:
•
•
•
•
•
•
•
Old = Olfactory (I)
Opie = Optic (II)
Occasionally= Oculomotor (III)
Tries = trochlear (IV)
Trigonometry = trigeminial ( V)
and =abducens (VI)
feels = facial (VII)
Very= vestibulocochlear (
VIII)
Gloomy, =
glossopharyngeal ( IX)
Vague = vagus ( X)
And = accessory ( XI)
Hypoactive = hypoglossal
(XII)
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Neurological Diseases &
Disorders
•
•
•
•
•
•
•
•
•
•
•
Hydrocephalus
Aging
Seizures/convulsions
Alzheimer’s disease
Parkinson’s disease
Reye syndrome
TIA
Cerebrovascular accident/CVA
Concussion
Shingles
Multiple Sclerosis
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Hydrocephalus:
• Excessive build-up of CSF
• Either excessive production or inability to
reabsorb the fluid (perhaps a tumor)
• Results in pressure on the brain tissue and
eventual damage to the neurons
• Treatment usually a shunt and fluid drains
into abdomen.
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Treatment:
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Aging:
• Neurons lost – up to 1000 a day! (minor
considering we have several billion) so may not
see changes until over 75 yrs old
• Studies show better function & decision making
at 60 than 30!
• Decreased capacity for sending impulses (esp.
hearing, vision, smell, taste)
• Voluntary muscular activity can decrease
significantly
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Seizures/convulsions:
• Caused by abnormal neuronal signaling.
• 2 types:
– Petit mal – “blanking out”
– Grand mal – violent muscle contractions
• Causes:
– Epilepsy- certain parts of the brain are overactive,
producing convulsive seizures & possible loss of
consciousness.
– Brain trauma
– Fever
– Allergic reactions
– Increased intercranial pressure – due to hemorrhage, tumor
or swelling
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Alzheimer’s disease:
• Disabling senile dementia – unknown
cause but most patients have similar
things in common:
– Loss of neurons in certain brain area –
especially those that use ACH
– Abnormal protein deposition within the
neurons
– Tangled protein filaments within the neurons
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CAT scan of Alzheimer’s brain:
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Parkinson’s Disease
• Common with aging
• Caused by a deficiency of dopamine
• Characterized by tremors, a shuffling gait,
pill-rolling (movement of thumb and index
finger), and muscular rigidity.
• Has difficulty initiating movement
• Treated with the drug L-dopa & other
drugs for the symptoms.
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© 2010 Delmar, Cengage Learning
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Reye Syndrome;
• Swelling with certain viral infections (chicken
pox, flu) in children.
• Aspirin use appears to increase risk – could
result in irreversible damage to the liver (toxins)
and brain - can be fatal.
• Cerebral edema, high ammonia levels, other
toxic wastes in serum
• Results in lethargy, headache, vomiting,
disorientation, seizures, coma
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TIA = Transient ishemic attack
• Episode of temporary interruption of blood
supply to the brain
• A sign of impending stroke
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Cerebrovascular accident /CVA
• Stroke: destruction of brain tissue
following an interruption of blood supply
due to:
– Clot formation
– hemorrhage
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Concussion:
• Traumatic injury to the
brain
• Leading to brain
edema (swelling)
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Shingles:
• Acute infection of
nerves of the
PNS caused by
the herpes virus
which causes
chicken pox
• Causes severely
painful blisters
and discoloration.
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Multiple Sclerosis:
• Sclerosis: Greek > sklero means “hard”, scarring
•
•
•
•
•
or plaques result from demyelination.
Myelin sheath is slowly deteriorating
Autoimmune disease: body confuses virus
proteins and own myelin
Increased protein in CSF
Fatigue, spasticity, bladder & bowel dysfunction,
tremors, facial & other pain, sexual dysfunction,
depression,etc.
Drugs used: steroids, immunosuppresants
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The Special Senses
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Sensations:
• Interpretation of impulses in the cerebral
cortex
– Determined by the area of the cortex ( frontal
=smell, occipital=sight)
• Intensity depends on frequency of stimuli
– More stimuli, more receptors are active ( a
“touch” is less, a “punch” stimulates more
receptors)
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Factors in sensation:
• Projection (helps out)
– Sensation is recognized where the stimulus
occurs ( hurt finger or cookies smell from
kitchen)
• Adaptation
– With repeated stimuli the receptor decreases
its response
– This prevents over-stimulation (frequently with
smell – perfumes, barn, etc.)
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General Senses:
• Found throughout the body, esp. skin, muscles, tendons
and visceral organs (guts) i.e. heartburn felt in torso
• Proprioceptive – awareness of location & action of a part of
the body (driving a car)
– Thermal – temperature
• Heat receptors – sensitive above 77 degrees, above
113 degrees painful
• Cold receptors – sensitive below 68 degrees, below
50 degrees painful
• Comfort zone (Rm temp) 69-76 degrees – no
adjustment (no shiver, no sweat)
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General Senses:
Mechanoreceptors
• Tactile: touch, pressure, vibration, tickle
– Stereognosis – ability to identify an object by touch only
• Pacinian corpuscles (pressure)
– Deep in dermis or hypodermis – more force
• Meissner’s corpuscles
– In dermal papillae (fingerprint bumps)
– Detect very light touch (lips)
• Free nerve endings – in epithelial & connective tissue
– Some attached to hair to detect bending (fly on arm)
– Other detect pain in guts (spleen has pain , not itchy)
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Pain:
• Free nerve endings are stimulated whenever tissue is
damaged (protective detectors)
– Acute – sudden, rapid onset
– Chronic – slow onset>worsens
• Referred pain:
– Occurs if projection is not accurate – feels pain
“originating” from an area where stimulus is not
occuring (heart attack or appendicitis)
– Probably occurs because some nerves carry
impulses from the body wall and internal organs
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Common sites for referred pain:
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The Sense of Smell
• Molecules in air dissolve in nasal mucus
• Bipolar sensory neurons transfer chemical
impulse
• Olfactory bulbs receive impulse
• Impulse sent to olfactory tract, which carries
impulses into the cerebral cortex
• Odor variety dependent on brain interpretation –
adapts quickly for perfume, slowly for smoke
(toxic)
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© 2010 Delmar, Cengage Learning
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The Sense of Taste
• Taste buds on tongue, palate and pharynx &
epiglottis ( maybe esophagus?)
• Taste buds (on papillae) cell types
– Exterior capsule: epithelial cells
– Interior: taste cells
• Taste depends on chemicals dissolved in saliva
(chemoreceptors)
• Taste influenced by olfactory sensations
• Spicy foods can stimulate pain receptors!
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The Sense of Taste
• Impulses are sent to cerebral cortex for
evaluation
– Receptors adapt fairly quickly (can over eat)
– 5 primary tastes
• Salty, bitter, sweet, sour and umani ( metallic
MSG)
– “flavors” are a combination of basic tastes –
pepperoni pizza (salty & sweet)
• Decreased saliva due to drugs can change taste
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The Sense of Sight
• Eyes protected by eyelids and eyelashes
• Tears
– Lubricate the eyes
– Contain bacteriolytic lysozyme enzyme
– Contain salt and gamma globulin
• The inner lining of the eyelid is the conjuctiva.
When inflamed = pink eye
• The extrinsic eye muscles move the eye around
within the orbit. You don’t always have to turn your
head!
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Vision:Internal eye structures:
• Outer fibrous layer: puncture resistance
– Sclera – white portion
– Cornea – clear window-like structure on anterior of
the eye
• Middle vascular layer
– Choroid – provides nutrients and has melanin which
will absorb light rays after they have been “seen” by
the receptors
– Iris – colored part that controls the amount of light
by regulating the size of the pupil.
– Ciliary body – controls shape of the lens to assist
with focusing of the image in the eye.
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The Sense of Sight (cont’d.)
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Vision: Internal eye structures
• Inner neural layer:
– Retina: Contains the photoreceptors
• Rods: non-color, low light stimulus, crude
image. Located in nearly all areas of retina
• Cones: color, high light stimulus, detailed
image. Located primarily in the macula region
but randomly scattered throughout retina
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Vision:Internal eye structure
– Macula lutea: area of best visual acuity- high
concentration of cones. Located directly opposite
the pupil. The fovea centralis is a depression in the
center
– Optic disc: lacks photoreceptors, no light can be
detected (blind spot) where the beginning of the
optic nerve is.
• Optic nerve (CN II): transmits information from the eye to
the brain.
• Optic fluids:
– Aqueous humor: between cornea & lens
– Vitreous humor: gelatinous mass between lens and
retina
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© 2010 Delmar, Cengage Learning
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Vision:
• As light enters the eye, refraction occurs>
REFRACTION is a bending of light which occurs
as the light passes through different densities.
– 60% of refraction caused by the cornea, this is
fixed and cannot be changed without reshaping
the cornea.
– 40% of refraction takes place in the lens, this is
adjustable.
• Accommodation: changing the shape of the lens to
adjust focusing
• Image which eye detects is upside down and
backward (inverted) due to refraction.
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© 2010 Delmar, Cengage Learning
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Disorders of the eye:
• Myopia: nearsightedness
– Focal point in front of the retina
• Hyperopia: farsightedness
– Focal point is behind the retina
• Presbyopia: old age –loss of accommodation so it is
difficult to focus on near objects
• 20/20 vision means at 20 feet you are seeing what a
normal eye can see at 20 feet.
• 20/30 means at 20 feet, you are seeing what the normal
eye would see at 30 feet away
(you need to be 10 feet closer!)
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MYOPIA
Presbyopia corrected
With glasses
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The Sense of Hearing and
Equilibrium
• Outer ear
– Auricle: external, visible, flexible part
• Sound waves enter
– External auditory meatus
• Lined with hair and ceruminous glands which
make cerumen (ear wax)
– Tympanic membrane: vibrates in response to
sound
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The Sense of Hearing and
Equilibrium (cont’d.)
• Structures of the ear shown in cross
section
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The Sense of Hearing and
Equilibrium (cont’d.)
• Middle ear
– Auditory ossicles: malleus, incus and stapes
• Amplifies vibrations to oval window
– Openings: oval and round windows
– Eustachian tube: equalizes pressure
• children have a tube parallel to the ground which
means more infections: otitis media
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Myringotomy – drainage tube
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The Sense of Hearing and
Equilibrium (cont’d.)
• Inner ear
– Cochlea: hearing
• Fluid moves against round window which releases
sound waves from inner ear, this also causes
movement of “hair’ receptors (bends) which send
impulses to the brain
– Equilibrium – unconscious
• Combines with visual input & info on body position
• Static: vestibule
• Kinetic: semicircular canals
© 2010 Delmar, Cengage Learning
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© 2010 Delmar, Cengage Learning
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