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The NERVOUS System
Functions of the Nervous System
Sensory
senses stimuli from both within the body and from the
external environment
Integrative
analyzes, interprets, and stores information about the
stimuli it has receives from the sensory portion of the
nervous system
Motor
responds to stimuli by some type of action
muscular contraction
glandular secretion
Divisions of the Nervous System
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
Somatic Nervous System (SNS)
Autonomic Nervous System (ANS)
Sympathetic Division
Parasympathetic Division
Nervous System Schematic
Nervous System Schematic
Nervous System Schematic
The Central Nervous System
Consists of the brain and the spinal cord
Sorts incoming sensory information
Generates thoughts and emotions
Forms and stores memories
Stimulates muscle contractions
Stimulates glandular secretions
The Brain
We’ll talk about it more later…
The Spinal Cord
The spinal cord is the main pathway for information
connecting the brain and peripheral nervous system
The length of the spinal cord is about 45 cm in men
and 43 cm in women.
The spinal cord is shorter than the vertebral column
Nerves that extend from the spinal cord from the
lumbar and sacral levels must run in the vertebral canal
for a distance before they leave the vertebral column.
This collection of nerves in the vertebral canal is called
the cauda equina
horse tail
The Spinal Cord
The Peripheral Nervous System
Connects sensory receptors, muscles, and glands in the
peripheral parts of the body to the central nervous system
Consists of spinal and cranial nerves
Afferent Neurons (Sensory)
conduct nerve impulses from sensory receptors toward the
CNS
Efferent Neurons (Motor)
conduct nerve impulses from the CNS to muscles and
glands
Consists of the somatic and autonomic systems
Spinal Nerves
Also called nerve roots
Branch off the spinal cord and pass out through the vertebral foramen
Carry information from the spinal cord to the rest of the body, and from
the body back up to the brain.
31 pairs total
Four main groups of spinal nerves, which exit different levels of the spinal
cord:
Cervical Nerves "C" : (nerves in the neck) supply movement and feeling
to the arms, neck and upper trunk. Also control breathing.
Thoracic Nerves "T" : (nerves in the upper back) supply the trunk and
abdomen.
Lumbar Nerves "L" : (nerves in the lower back) supply the legs, the
bladder, bowel and sexual organs
Sacral Nerves "S" : (nerves in the lower back) supply the legs, the bladder,
bowel and sexual organs
Spinal Nerves
Cranial Nerves
I-XII
12 pairs
Lead directly from the brain to various parts of the head, neck, and trunk
Some involved in the special senses (such as seeing, hearing, and taste)
Others control muscles in the face or regulate glands
The nerves are named and numbered (according to their location, from the
front of the brain to the back)
Cranial Nerves
Cranial Nerves
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olfactory, optic, oculomotor, trochlear, trigeminal,
abducens, facial, vestibulocochlear, glossopharyngeal,
vagus, spinal accessory, hypoglossal
Divisions of the PNS
Somatic Nervous System
Autonomic Nervous System
Sympathetic
Parasympathetic
The Somatic Nervous System
Made up of sensory neurons that convey information
from the cutaneous and special sense receptors in the
head, body wall, and extremities to the CNS
Also contains the motor neurons from the CNS that
conduct impulses to the skeletal muscles
The Autonomic Nervous System
Contains sensory neurons mainly from the viscera that
convey information to the CNS
Contains the efferent neurons that conduct impulses to
smooth muscle, cardiac muscle, and glands
Unconscious control
Divisions include:
Sympathetic nervous system
Parasympathetic nervous system
Sympathetic Division
Sympathetic Division— “Fight or
Flight”
Cope with stress or emergency
situations
Increase in heart rate, blood
glucose levels, breathing rate
Pupils dilate
Increased blood flow to muscles,
lungs, heart
Reduced digestive activity due to
decreased blood flow to visceral
organs
Parasympathetic Division
Parasympathetic Division— “Rest
and Relaxation”
Helps body return to homeostasis
Decrease in heart rate, breathing
rate, and blood glucose levels
Reduced blood flow to skeletal
muscle
Increased digestive activity due to
increased blood flow to visceral
organs
Activity
Directions: Choose the responses that best correspond to the
descriptions provided in the following statements. Insert the appropriate
letter in the answer blanks.
A. Autonomic Nervous System
C. Peripheral Nervous System
B. Central Nervous System
D. Somatic Nervous System
________________1. Nervous System subdivision that is
composed of the brain and spinal cord.
________________2. Subdivision of the PNS that controls voluntary
activities.
________________3. Nervous system subdivision that is composed
of the cranial and spinal nerves.
________________4. Subdivision of the PNS that regulates the
activity of the heart and smooth muscle
(involuntary).
Neurons
The nerve cells responsible for the special functions of the nervous
system
sensing
remembering
thinking
controlling muscle activity
controlling glandular secretions
Synapse - the functional relay points between two neurons or between a
neuron and an effector organ
Neuromuscular Junction
Neuroglandular Junction
Parts of A Neuron
Cell Body (Soma or Perikaryon)
nucleus, cytoplasm, organelles of a neuron
Dendrites - tapered, highly branched processes protruding
from the cell body
usually very short
AFFERENT FUNCTION
Axons - long, thin,
cylindrical process
usually myelinated
EFFERENT FUNCTION
Neuron
Neurons
Neuroglia
Nervous system cells that support, nurture and protect the
neurons
Not actual neurons
Do not conduct electrical impulses
Types of Neuroglia found in the CNS
Astrocytes
Oligodendrocytes
Microglia
Ependymal Cells
Types of Neuroglia found in the PNS
Satellite Cells
Neurolemmocytes (Schwann Cells)
Neuroglia of the CNS
Astrocytes
Star-shaped cells with many processes
Participate in metabolism of neurotransmitters
Maintain K+ balance for generation of nervous
impulses
Participate in brain development
Help form the blood brain barrier
Provide a link between neurons and blood vessels
Astrocyte
Oligodendrocytes
Small cells with few
processes
Form a supporting
network around the
neurons by twining
around neurons and
producing a lipid and
protein wrapping around
the neurons (myelin
sheath)
Microglia
Small phagocytic cells that protect the central nervous
system by engulfing and invading microbes
Clears away debris from dead cells
Ependymal Cells
Neuroglia cells that line the brain ventricles
Line the central canal of the spinal cord
Helps form and circulate cerebral spinal fluid
Help form the blood-CSF barrier (different from the
blood-brain barrier)
Ependymal Cells
Neuroglia of the PNS
Satellite Cells
Provide physical support to neurons in the peripheral
nervous system
Neuroglia of the PNS
Schwann Cells Neurolemmocytes
Cells responsible for
producing the myelin
sheaths around the
PNS neurons
Can also wrap thinly
around bundles of
axons without
wrapping multiple
layers around each
axon
Unmyelinated
neurons
Schwann Cell
(Neurolemmocyte)
Neuroglia Overview
Myelination
The process of developing or producing a Myelin Sheath
Insulates the axon of a neuron
Increases the speed of nerve impulse conduction
CNS - oligodendrocytes
PNS - neurolemmocytes (Schwann Cells)
Diseases such as Tay-Sachs disease and Multiple Sclerosis
involve destruction of the myelin sheaths around the nerve
Myelination
Myelinated Axon
Unmyelinated Axon
Activity
Match the anatomical terms that best correspond to the following
statements. Place the correct letter in the answer blanks.
A. Axon
D. Myelin Sheath
B. Axon Bulb
E. Cell Body
C. Dendrite
__________1. Releases neurotransmitters
__________2. Directs messages toward the cell body
__________3. Increases the speed of the message
__________4. Location of the nucleus
__________5. Long extension that takes messages to the target
Neurophysiology
The transmission of nerve (electrical) impulses from nervous tissue to
other nervous tissue, organs, glands, and muscles.
Transmission of Nerve Impulses
Nerve Impulse: An electrical event due to movement of
ions across a membrane
Also called an action potential
Lasts about 1 msec (1/1000 of a second)
Dependent upon diameter of the axon
larger diameter axons - 0.4 msec (1/2500 sec)
2500 impulses per second
smaller diameter axons - 4 msec (1/250 sec)
250 impulses per second
All or None Principle
If depolarization reaches a threshold, an action
potential (impulse) is conducted
Each action potential (impulse) is conducted at
maximum strength unless there are toxic materials
within the cell or the membrane has been disrupted
Neuron Membrane Potential
Neuron Action Potential
Action Potential
Resting phase (polarization)
The axon is not actively conducting nerve impulses. Sodium is the ion found in the
greatest concentration in the extracellular fluid. Potassium is the ion found in the
greatest concentration in the intracellular fluid. The outside charge of the polarized
membrane is positive while the inside charge of the polarized membrane is negative.
Depolarization phase
As the action potential propagates down the length of the axon, the sodium channels
open in the axon membrane. Sodium, which is found in greater concentration in the
extracellular fluid, rushes through the protein channels creating a negative charge in the
extracellular fluid and a positive charge in the intracellular fluid.
Repolarization phase
Just split seconds after the opening of the sodium channels, the potassium channels in
the axon membrane open. Since potassium is found in greater concentration within the
cell, potassium ions rush outward. This flow of positively charged ions restores the
positive charge outside of the cell and the negative charge inside of the cell.
Refractory period
During this period of time, no nerve impulses (action potentials) can be sent. The
sodium-potassium pump (using ATP) functions to restore the ion concentration of the
polarized cell by pumping sodium ions out of the cell and bringing potassium ions into
the cell.
Neuron Impulse
Neuron
Action
Potential
Types of Impulse Conduction
Continuous Conduction - step by step depolarization of
each sequential, adjacent area of of the nerve cell
membrane
typical of unmyelinated nerve fibers
type of action potential in muscle fibers
Saltatory Conduction - the jumping of an action potential
across specialized neurofibril nodes along the axon
Nodes of Ranvier
Nerve Conduction
Nerve Conduction—Myelinated
Axon
Transmission of Nerve Impulses at
Synapses
Most nervous conduction is from neuron to neuron
(interneurons - 90%)
Types of Synapses
Axon to dendrite
Axon to soma
Axon to axon
Two ways to transmit impulses across a synapse
Electrical Synapses
Chemical Synapses
Reflexes
Fast, predictable, automatic responses to changes in the
environment that help maintain homeostasis
Somatic Reflexes - involve skeletal muscles
Visceral (Autonomic) Reflexes - involve responses of
smooth muscles, the heart, and glands
Involve the spinal nerves
The Reflex Arc
A response by the body involving only the body
segment being affected and the spinal cord
Brain does not have to be involved
Receptor - the distal end of a sensory neuron (dendrite)
Responds to a specific stimulus
a change in internal or external environment
Triggers a nerve impulse
Receptor - the distal end of a sensory neuron (dendrite)
Responds to a specific stimulus
a change in internal or external environment
Triggers a nerve impulse
Sensory Neuron - the neuron located in the gray matter of the
spinal cord
conducts impulses from the receptor to the spinal cord
Integrating Center - a region within the CNS (spinal cord or
brain) that interprets the information from the sensory neuron
and initiates an appropriate response
Motor Neurons - the neurons arising from the integrating center
that relay a nerve impulse to the part of the body that will
respond to the stimulus
Effector - the part of the body that responds to the motor nerve
impulse (usually a muscle or a gland)
Effector - skeletal muscle - somatic reflex
Effector - cardiac, smooth muscle, or gland -visceral reflex
The Reflex Arc
Reflex Arc Examples
Stretch Reflex - results in the contraction of a muscle if it
has been stretched suddenly
Tendon Reflex - results in the contraction of a muscle
when a tendon is stretched suddenly
Flexor (Withdrawal) Reflex - sudden contraction and
removal of a body segment as a result of a pain stimulus
Tendon Reflex
Withdrawal
Reflex
Also called the
Flexor/Withdrawal
Reflex
The BRAIN
The BRAIN
One of the largest organs in the body
Controls all mental functions
Component of the CNS
Composed of over 100 billion neurons
Comprises 2-3% of body weight
Utilizes over 20% of body’s energy
Brain Video
The Brain
Gray and White Matter
White Matter - the aggregation of myelinated processes
from many neurons
Visible upon freshly dissected brain or spinal tissue
White color is due to myelination
Gray Matter - unmyelinated nerve cell bodies, axons,
dendrites, ganglia, and axon terminals
Appears gray because of lack of myelin
Gray and White Matter
Ventricles
Cavities within the brain
Lateral ventricles (2) - located within each hemisphere
in the cerebrum
Third ventricle - a vertical slit between the lateral
ventricles and inferior to the right and left halves of the
thalamus
Fourth ventricle - space between the brainstem and the
cerebellum
Ventricles of the Brain
Choroid Plexus
Network of capillaries in the walls of the
ventricles
Formation of CSF by the choroid plexus is
facilitated by the very high rates of blood flow
to the choroid plexus
Covered with ependymal cells that form the
cerebrospinal fluid
In the choroid plexus the ependymal cells are,
in contrast to elsewhere in the brain, tightly
bound by tight junctions
That means, these ependymal cells are so
close together they form the blood-CSF
barrier (different than the blood-brain barrier).
Selectively permeable barrier
White cells are capillary
endothelial cells
Blue cells are ependymal
cells
The structure of cell layers in
the choroid plexus/BCB
(blood-CSF barrier) is shown
in the top of the figure.
The structure of cell layers
elsewhere in the brain/BBB
(blood-brain barrier) is
shown in the lower part of
the figure.
Blood-CSF vs Blood-Brain Barriers
Protection and Coverings of the
Brain
Protected by the cranial bones and the cranial meninges
Dura Mater - outer layer
Arachnoid - middle layer
Pia Mater - inner layer
Also protected by cerebrospinal fluid
fluid that nourishes and protects the brain and spinal cord
continuously circulates through the subarachnoid space
around the brain and throughout the cavities within the
brain
Spinal Cord
Protective
Coverings
Dura Mater
Arachnoid
Pia Mater
Meninges
Connective tissue covering found around the brain and
spinal cord
Three layered membrane
Dura Mater - outer most layer
dense irregular connective tissue
Arachnoid - middle layer
spider web arrangement of collagen fibers
Pia Mater - inner most meninges
very delicate layer of thin tissue
Meninges of the Brain
Subarachnoid Space
Wide space between the arachnoid and pia mater
Contains Cerebrospinal Fluid (CSF)
Spinal cord ends at about the level of the L2 vertebra but the
subarachnoid space continues to S2 making it possible to access
CSF fluid with needle puncture (lumbar puncture)
Cerebrospinal Fluid
Mechanical Protection
Serves as a shock absorbing medium
Buoys the brain so it literally floats within the cranial cavity
Chemical Protection
Provides an optimal chemical environment for neural
signaling
Circulation
Acts as a medium for exchange of nutrients and waste
products between the blood and nervous tissue
Flow of
CerebroSpinal
Fluid
Flow of
CerebroSpinal
Fluid
Blood Supply to the Brain
One of the most metabolically active organs in the body
Makes up only 2-3% of body weight but uses about 20% of
available O2 at rest
Well supplied with O2 and nutrients
Only nutritional source for brain metabolic activity is
glucose
Capillaries in the brain are much less leaky than other
capillaries in the body and form a blood brain barrier
Major Divisions of the BRAIN
CEREBRUM - occupies most of the cranium and is
divided into right and left halves called hemispheres
CEREBELLUM - the posterior-inferior portion of the
brain
BRAIN STEM - consists of the medulla oblongata, the
pons, and the midbrain
it is continuous with the spinal cord
DIENCEPHALON - located above the brainstem,
composed primarily of the:
Thalamus
Hypothalamus
The Brain Stem
The most inferior portion of the brain
Connects the brain to the spinal cord
Composed of Three Areas
The Medulla Oblongata
The Pons
The Midbrain
The Medulla Oblongata
Most inferior portion of the brain stem
Connects the brain stem to the spinal cord
Respiratory Center
Adjusts rhythm and depth of breathing
Cardiovascular Center
Regulates heart rate and contraction force
Influences vasoconstriction and vasodilation
Also controls coughing, vomiting, swallowing, and
hiccupping
The Medulla Oblongata
The Medulla Oblongata
The Pons
Lies superior to the medulla oblongata
Together with the respiratory center in the medulla
helps control respiration
The Midbrain
Superior to the pons
Connects the brain stem to the diencephalon
Pons and Midbrain
The Diencephalon
Area of the brain containing the:
Thalamus
Hypothalamus
The Thalamus
Oval structure that makes up 80% of the diencephalon
Comprised of a pair of oval masses (mostly gray matter)
Principle relay station between the various sections of
the brain
The Hypothalamus
A small portion of the diencephalon located below the
thalamus
One of the main regulators of homeostasis in the body
Lacks a blood brain barrier
Partially protected by the sella turcica of the sphenoid bone
Functions of the Hypothalamus
Coordinates nervous system and endocrine system
activities to maintain homeostasis
Thirst, Hunger, Satiety
Sleep Patterns and Waking States
Temperature regulation
Sex Drive, Maturation, Aggression, and Rage
Influences movement of food through the Gastrointestinal
Tract
production and secretion of hormones that control other
Endocrine Glands
Hypothalamus
The Cerebrum
Largest division of the brain
Occupies most of the cranium
Accounts for 85% of brain mass
Divided into right and left hemispheres
Longitudinal Fissure
Corpus Callosum
Connects the two hemispheres
Cerebral cortex - the outer surface area of the cerebrum
Composed mainly of gray matter
Contains billions of neurons
The Cerebrum
Terms associated with the Cerebrum
Gyri
A series of folds in the cortex that increase surface area
Sulci
A groove or furrow that separates the gyri of the brain
Lobes of the Cerebrum
Named after the bones that cover them
Frontal Lobe
Parietal Lobe
Temporal Lobe
Occipital Lobe
A Note about the Cerebral Cortex
The cerebral cortex is the most highly developed part of
the human brain and is responsible for thinking,
perceiving, producing and understanding language
It is also the most recent structure in the history of brain
evolution
Frontal Lobe
Motor Areas
Controls movement of voluntary skeletal muscles
Association Areas
Carry on high level intellectual processing
Problem Solving
Reasoning
Planning
Concentration
Memory
Behavior
Emotions
Expressions
Broca’s area
One of the main areas responsible for speech production
Parietal Lobe
Sensory Areas
Interprets sensations from the skin such as:
touch
temperature
pressure
pain
Association Areas
Understanding of speech
Using words to express thoughts and feelings
Temporal Lobe
Sensory Areas
Hearing and balance
Association Areas
Interpret sensory experiences
Memory of visual scenes - music - smells and other complex
sensory patterns
Wernicke’s Area
region of the brain where spoken language is understood
(speech comprehension)
Occipital Lobe
Sensory Areas
Visual processing and interpretation
Association Areas
Combines visual images with sensory experience
Left Brain vs Right Brain
Right side of brain
controls left side of
body
Left side of brain
controls right side of
body
New research at the U
of U indicates left and
right brain attributes
aren’t as clear cut as
once thought
A little rap to help you
remember…
The occipital lobe controls your sight. Why it does, we don’t
know why.
The temporal lobe controls how you hear, like the clucking of a
chicken or the stomping of a deer.
The parietal lobe processes what you touch whatever you can
squeeze or grab or clutch.
The frontal lobe helps you think and memorize so you can
process what you need right before your eyes.
These are the lobes of the brain and now you know them so call
up all your friends and don’t forget to show em’
WORD!
The Cerebellum
Second largest portion of the brain
Occupies the inferior and posterior aspects of the cranial cavity
Processes sensory information
Balance
Coordination
Maintains postural equilibrium
Cerebellum and Brainstem
Nervous System Disorders and
Homeostatic Imbalances
Alzheimer’s Disease (AD)
Disabling neurological disorder that effects about 11% of
the population
6th leading cause of death in the U.S.
It is the only cause of death among the top 10 in America
without a way to prevent it, cure it or even slow its
progression.
A chronic, organic, mental disorder, a form of pre-senile
dementia due to atrophy of neurons of the frontal and
occipital lobes
AD patients usually die from complications due to being
bedridden
Alzheimer’s vs. Dementia
Dementia is not a disease itself, it is the symptoms
language difficulty,
loss of recent memory
poor judgment
Alzheimer’s accounts for 60-70% of dementia cases
Other types of dementia include:
Vascular dementia
Parkinson's disease
dementia with Lewy Bodies
Frontotemporal dementia.
Amyotrophic Lateral Sclerosis
(ALS)
Also known as Lou Gehrig’s Disease
A relatively rare neurological disorder
A syndrome marked by muscular
weakness and atrophy with spasticity
and hyperflexion due to
degeneration of the motor neurons
of the spinal cord, medulla, and
cortex
A degenerative disease
No known cure
Bacterial Meningitis
Infection of the meninges
by the bacterium
Haemophilus Influenzae
Usually affects children
under age 5
Symptoms include severe
headaches and fever
Can lead to brain damage
and even death if not
treated
Cerebral Palsy (CP)
A group of motor disorders due to loss of muscle control
Caused by damage to the motor areas of the brain during
fetal development, birth, or infancy
About 70% of CP individuals are somewhat mentally
retarded due to the inability to hear well or speak fluently
Not a progressive disease but the symptoms are irreversible
Epilepsy
Short, recurrent, periodic,
attacks of motor, sensory, or
psychological malfunction
Characterized by seizures
which can result in involuntary
skeletal muscle contraction,
loss of muscle control, inability
to sense light, noise, and smell,
and loss of consciousness
Most epileptic seizures are
idiopathic
Multiple Sclerosis (MS)
The progressive destruction of the
myelin sheaths of neurons of the CNS
The sheaths deteriorates to scleroses
hardened scars or plaques
“short circuits” nerve transmission
Cause is unknown
May be a type of an autoimmune
disease
No known cure
Progressive loss of function with
intermittent periods of remission
Parkinson’s Disease (PD)
A chronic nervous disease characterized by a
fine, slowly spreading tremor, muscle
weakness and rigidity, and a peculiar gait
Usually affects people over 60
Cause is unknown but a toxic
environmental factor is suspected
Chemical basis of the disease appears to be
too little dopamine and too much Ach
Treatment includes increasing levels of
dopamine and decreasing Ach
Difficult because dopamine does not cross
the blood brain barrier
Usually can be controlled with drug therapy
GABA - gamma aminobutyric acid
Attempting to transplant fetal nervous
tissue into the damaged area of the brain of
some Parkinson’s Disease patients
Guillan-Barré Syndrome
Rare disorder in which a person’s own immune system
damages their nerve cells
Causes muscle weakness and sometimes paralysis
Symptoms that usually last for a few weeks
Most people recover fully from GBS, but some people have
long-term nerve damage
Risk factors
Infection with Campylobacter jejuni (diarrhea)
People can develop GBS after having the flu or other infections
(such as cytomegalovirus and Epstein Barr virus)
On very rare occasions, they may develop GBS in the days or
weeks after getting a vaccination
Guillan-Barré Syndrome
Cerebral Vascular Accident
(CVA) - Stroke
The most common brain disorder
Characterized by slurred speech, loss of or blurred
vision, dizziness, weakness, paralysis of a limb or
hemiplegia, coma, and death
Ischemic CVA - due to lack of blood supply to a
particular area of the brain
Hemorrhagic CVA - due to the rupture of a blood
vessel in the brain
Risk Factors for Stroke
hypertension
heart disease
smoking
diabetes
atherosclerosis
hyperlipidemia
obesity
excessive alcohol intake
Symptoms of a Stroke
Sudden numbness, tingling, weakness, or loss of
movement in your face, arm, or leg, especially on
only one side of your body (facial drooping)
Sudden vision changes.
Sudden trouble speaking.
Sudden confusion or trouble understanding simple
statements.
Sudden problems with walking or balance.
A sudden, severe headache that is different from past
headaches.
Is it a stroke?
Reye’s Syndrome
Acute childhood illness that causes fatty
infiltration of the liver and brain,
encephalopathy, and increased
intracranial pressure
Almost always follows within 1 to 3 days
of an acute viral infection, flu, or chicken
pox
Common in infants and children.
The incidence often arises during flu
outbreaks
May be linked to aspirin use
Symptoms include vomiting, mood
changes, confusion, tachycardia, and
tachypnea
Treatment involves treating the
symptoms
Hydrocephalus
Excessive accumulation of cerebrospinal fluid within the
ventricles of the brain.
Occurs most often in newborns
The head is enlarged and the brain may be compressed
causing brain damage
Early detection and surgical intervention improves the
prognosis
Complications of the surgery include infection of the shunt.
Hydrocephalus
Spina Bifida
Congenital defect where the neural arch fails to unit
Usually involves the lumbar vertebrae
Symptoms may be mild to severe
usually results in paralysis
partial or complete loss of bladder control
absence of reflexes
Can be diagnosed during pregnancy by sonography,
amniocentesis, blood tests
Spina Bifida
Spina Bifida
Spina Bifida
Spina Bifida
Headaches
Most commonly begins as a patient complaint, but is usually a
symptom of an underlying disorder
Ninety percent are caused by vascular problems or muscle contractions
Tension headaches
mild, dull pressure without other accompanying symptoms
Cluster headaches
severe pain (sometimes described as “stabbing” pain) behind one eye, and
may be accompanied by redness and nasal congestion
Sinus headaches
pain and pressure behind the brow and cheek bones
Migraines
pounding headache, nausea, vomiting, and light sensitivity
Headaches
Concussion
Most common head injury resulting from a blow to the head – a blow hard
enough to jostle the brain and make it hit against the skull causing temporary
neural dysfunction.
Precipitating causes include a fall to the ground, a punch to the head,
automobile accidents and child abuse
Most victims recover within 24 to 48 hours after the injury
Symptoms
a loss of consciousness
vomiting
possible amnesia
dizziness
headache
Lethargy
Treatment
Monitoring vital signs, mental status, level of consciousness, and pupil size
Whiplash
Results from a sharp hyperextension and flexion of the neck that damages the
muscles, ligaments, disks and nerve tissue
Common after rear-end automobile accidents.
Padded headrests and shoulder harnesses reduce the risk of this type of injury.
Symptoms can include:
pain in the interior and posterior neck
dizziness
headache
neck rigidity
numbness in the arms
Treatment includes:
immobilizing the neck at the scene of the accident
ruling out spinal cord injury
analgesics
warm compresses
a cervical collar
possible physical therapy
Whiplash
Spinal Cord Injury (SCI)
Commonly referred to as a broken neck
Involves injury to the spinal cord
The more superior the injury, the more permanent damage results to the patient
Causes of the injury include:
motor vehicle accidents
falls
sporting injuries (football, skiing)
diving into shallow water
gunshot wounds.
Paralysis of the body may occur
Paraplegia:
lower half of the body is paralyzed
Quadriplegia:
body from the neck down is paralyzed
Treatment:
maintaining vital functions and rehabilitation to maintain the use of muscles.
Depression
This is a sad mood, which may be a primary disorder, a response to a disease
process or a drug reaction.
Causes include:
Genetic
Familial
Biochemical
Physical and physiological processes
The person may have feelings of helplessness, anger, hopelessness, low selfesteem, and pessimism
Other symptoms include weight loss or weight gain, sleep disturbance, depressed
mood most of the day, energy loss, fatigue, difficulty thinking or concentrating
Treatment may involve:
Psychotherapy
drug therapy
Counseling
Light therapy
Sensations
and
Special Senses
Senses
Specialized structures of the nervous system which
provide information about the environment in which
we live to help maintain homeostasis
Functions of Special Senses
Sensory - monitoring the body and the external
environment for changing conditions
Sensory Pathways
All pathways begin with a receptor and the sensory
information is transmitted to the CNS
Always begins with a stimulus
change in the environment
Receptors
Structures which provide feedback about the environment
Are impulse specific—Only respond to one type of stimulus
Mechanoreceptor
Any information about mechanical changes in its environment,
such as movement, tension and pressure.
Photoreceptor
able to detect, and react to light
Chemoreceptor
Sense organ, or one of its cells (such as those for the sense of
taste or smell), that can respond to a chemical stimulus
Thermoreceptor
sensitive to changes in temperature
Nociceptor
sends signals that cause the perception of pain in response to a
potentially damaging stimulus.
Many have sensory function adaptations
May end as bare dendrites or be a complex organ
Vision
The most complex of the special senses
Over 70% of the sensory receptors in the body are
photoreceptors for sight
Visual organs, the eyes are supported by a number of
accessory structures and internal organs
Dependent upon photoreceptors in the eyes
The Eye
Accessory Structures of the Eye
Eyelids - protects the anterior surface
Conjunctiva - the mucous membrane of the eyelid
Helps moisten and lubricate the eyeball
Lacrimal Apparatus - secretes tears
lacrimal gland
lacrimal sac
lacrimal canals
nasolacrimal duct
moistens and lubricates the eyeball
fights against infection (enzymes in tears)
Extrinsic Muscles of the Eyeball (6)
skeletal muscles that move the eyeball
Accessory
Structures
of the
Eye
Structure of the Eye
The wall consists of three layers of tissue or tunics
Fibrous Tunic - outer layer
Vascular Tunic - middle layer
Nervous Tunic - inner layer
Fibrous Tunic
Thick, outermost layer of the eyeball
Sclera - the posterior “white” portion
Forms most of the fibrous tunic
The “whites” of the eye
Cornea - the anterior transparent portion of the
fibrous tunic
Bulges outward slightly
Fibrous Tunic
Vascular Tunic
Extremely vascular
Supplies blood to numerous structures of the eye
Choroid
Ciliary Body
Iris
Lens
Vascular Tunic
Choroid - posterior, thin portion of the vascular
tunic
A thin, dark brown membrane that lines most of the
internal surface of the sclera
Ciliary Body - anterior, thick portion of the
vascular tunic
Thickest part of the vascular tunic
Consists of smooth muscle fibers
Attaches to the lens by ligaments
Changes the thickness and shape of the lens.
Ciliary Body
Iris - anterior, colored portion of the Vascular Tunic
contraction of it’s smooth muscle accounts for dilation or
constriction of the Pupils (openings to the inner cavities of
the eyes)
Lens - special tissue which focuses and directs light
entering the eye
suspended by the Ciliary Body
located behind the Iris
alteration of the shape of the lens to accommodate for near
or far vision focusing (Accommodation)
The Lens
Iris – Pupil Diameter
Nervous Tunic
The inner layer of the eye
Retina - a thin fragile layer of neurons that
forms the inner lining of the eyeball’s posterior
wall
Lines the posterior cavity and contains the
photoreceptor cells (rods and cones), bipolar
neurons, and ganglion cells
Optic Nerve - axons and ganglion cells
Transmits images to the occipital lobe of the brain
for interpretation of what we see
Nervous Tunic
Rods and Cones
Rods - elongated cylindrical dendrites that are sensitive
to varying light conditions
Allows us to see under varying light intensities (night
vision)
Cones - dendrites with tapered ends
Color sensitive
Determines the “sharpness” of vision
Rods
and
Cones
Rods and Cones
Other Structures of the
Nervous Tunic
Optic Disc - blind spot where the optic nerve exits the
retina
Fovea Centralis - an area of the retina containing many
cone cells
the area of sharpest vision
Retina
Elements of Vision in the Eye
Vision spectrum of the eye
only detect three colors
Red
Green
Blue
Aspects of vision of the eye
color
motion
form
depth
Refraction
the “bending” of light rays as it travels through the
eye
the pathway of light as it travels through the eye
influenced by:
shape of the lens
shape and thickness of the cornea
amount and consistency of the Aqueous and Vitreous
Humor
Refraction
Vision
Abnormalities
related to
Refraction
Physiology of Vision
Rods and cones convert light waves into a series of
signals that results in the generation of an action
potential in the ganglion cells
Both rods and cones contain pigments that decompose
when exposed to light
The decomposition of the pigments is what generates
the action potential
Visual Pathways
From the rods and cones, the nervous impulse is
passed on to bipolar neurons and then on to
ganglion cells
Axons from the ganglion cells extend out of the
eye and converge to from the optic nerve
The optic nerves cross behind the eye at an area
known as the optic chiasma
The optic nerve terminates at the thalamus
Visual impulses from the thalamus are transmitted by
other neurons to the occipital lobe of the cerebral
cortex where the impulses are interpreted as the sense
of sight.
Visual Pathway
Hearing
Dependent upon special organs within the ear
The ears are also associated with maintaining
equilibrium and balance
Three Regions of the Ears
Outer Ear
Middle Ear
Inner Ear
The Ear
The Ear
Outer Ear
Direct sound waves toward the eardrum
Auricle - the outer appendage
Auditory Canal - a tube that extends into the temporal
bone
The Outer Ear
Middle Ear
Middle Ear
An air-filled space within the temporal bone
Tympanic Cavity - contains the auditory ossicles
Smallest bones in the body
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
Auditory (Eustachian) Tube - a tube from the middle ear to
the pharynx
Allows for pressure equalization between the middle ear and
the atmosphere
Tympanic Membrane (Eardrum) - thin, semitransparent
membrane separating the outer and the middle ear
Vibrates in response to sound waves striking it
The vibrations are then transmitted to the auditory ossicles
Middle Ear Structures
The tympanic membrane and auditory ossicles convert
sound waves into mechanical movement within the middle
ear and then transmit that motion to the “oval window”
The oval window opens into the cochlea of the inner ear
Within the inner ear the vibrations of the stapes causes the
fluid within the inner ear to move stimulating the
receptors for hearing
The Three Regions of the
Inner Ear
Formed by the canals of the bony labyrinth and
the series of sacs of the membranous labyrinth
Involved in both the sense of hearing and the
maintenance of balance and equilibrium
Cochlea
Vestibule
Semicircular Canals
The Inner Ear
Inner Ear Structures
Inner Ear Structures
The Semicircular Canals - three loops that lie at
right angles to each other
The Vestibule - the chamber between the cochlea
and the semicircular canals
Both the semicircular canals and the vestibule are
involved with maintaining balance or equilibrium
The Cochlea - shape resembles a snail shell
Contains the organs of hearing (Organ of Corti)
Receptor cells that move in response to endolymph motion
Releases neurotransmitters that stimulate nerve impulses
The Cochlea
The Cochlea
Organ of Corti
Cross Section of Cochlea
Inner Ear (Labyrinth)
Consists of a winding, complicated series of
passageways or canals
Bony Labyrinth - a series of canals within the
temporal bone
Contains perilymph
Membranous Labyrinth - an internal series of sacs
and tubes
Contains endolymph
Conforms to the bony labyrinth shape
Also helps form the shape of the three regions of the
inner ear
Vestibulocochlear Nerve
Nerve Pathways
Sound waves cause the tympanic membrane to
vibrate
The vibration of the tympanic membrane
causes the stapes to move back and forth
Movement of the stapes back and forth pushes
the oval window in and out producing waves in
the perilymph of the inner ear
Pressure waves in the perilymph push the vestibular
membrane inward increasing the pressure of the
endolymph within the cochlear duct
The hair cells in the Organ of Corti convert the motion of
the endolymph to the release of neurotransmitters
These neurotransmitters stimulate a nerve impulse in a
sensory branch of the Vestibulocochlear Nerve (CN #VIII)
The impulse is then transferred through the midbrain and
the thalamus and finally terminates in the temporal lobe of
the cerebral cortex where the sound is interpreted
Physiology of Hearing
Physiology of Hearing
Nervous System Disorders
Homeostatic Imbalances
Clinical Terms
Diseases and Disorders
Ametropia
Myopia - nearsightedness
Imaged focused in front of the retina
Presbyopia
A defect in vision in advancing age involving loss of
accommodation or recession of near point (results in
farsightedness)
Hyperopia - farsightedness
Image focused in back of the retina
Cataracts
Abnormal loss of transparency of the lens
Vision becomes blurry or cloudy
Can be removed and have an artificial lens inserted
Most often occurs to individuals over the age of 50.
Exposure to sunlight and smoking increases the risk.
Conjunctivitis
Inflammation of the conjunctiva, the mucous membrane
that lines the eyelid and is reflected to the eyeball.
Also known as “Pink Eye”
Strabismus
Disorder in which the two eyes do not line up in the same
direction, and therefore do not look at the same object at
the same time.
Also known as "crossed eyes."
Glaucoma
A group of eye diseases characterized by elevated
intraocular pressure in the eye resulting in atrophy of
the optic nerve which may lead to blindness
Caused by an obstruction of the outflow of the
aqueous and vitreous humor
Minor cases can be treated with eye drops
More severe cases may require a surgical incision into
the iris of the eye
Macular Degeneration
The destruction or tearing away of the retina from
the back of the eye
Commonly occurs in the region of the retina
known as the macula lutea
Can be caused by:
Vascular diseases (diabetes)
Chronic increased pressure (glaucoma)
Sudden blow or impact to the head or eye (Detached
Retina)
Vertigo
A condition of dizziness and spatial disorientation
A spinning sensation that may result in loss of balance
and equilibrium
In some individuals it is due to heights or fear of high
places
Tinnitus
Ringing or tinkling sounds or sensations in the ear
Middle Ear Infection
Infection of the tympanic membrane or other
structures associated with the middle ear (Otitis Media)
Deafness
Loss of the ability to hear
Conductive Deafness: deafness resulting from any
condition that prevents sound waves from being
transmitted to the auditory receptors
Sensorineural Deafness: deafness due to
defective function of the cochlea, organ
of Corti, or the auditory nerve