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Biology 3201
Maintaining Dynamic Equilibrium
II
Nervous System
The nervous system is the body system that
allows us to feel things. This happens by
a network of nerves.
There are two main parts of the nervous
system
1. Brain
2. Spinal Cord
Human Nervous System
How the Brain and Spinal Cord
are Protected…
By
1. Meninges- Spaces around the brain and
spinal chord that act as buffer zones.
2. Bone (Skull/Vertebrae)- Act as a shield.
3. Cerebral Spinal Fluid – Absorbs energy
when the brain of spinal cord receive a
blow.
Meninges
The Brain
Parts we must know:
1. Cerebrum – Sorts and interprets all information
from our senses.It is the center of human
consciousness.
2. Cerebellum – Controls muscle coordination.
Contains 50% of the brain’s neurons.
3. Medulla Oblongata – Controls heart rate, and
force of heart contractions. Also controls reflex
centers for hiccupping, vomiting, coughing,
swallowing.
4. Pons – Functions with medulla to regulate
breathing rate; has the reflex centers involved
in head movement.
5. Hypothallamus – Controls hunger, body
temperature, aggression.
6. Thalamus – Sorts sensory information.
7. Midbrain – Involved in sight and hearing.
8. Corpus Callosum – Series of nerve fibers that
connect the left and right sides of the brain.
The Peripheral Nervous System
• Consists of the autonomic nervous
system and the somatic nervous
system.
– The autonomic nervous system is not
consciously controlled.
– The autonomic nervous system is made up of
the sympathetic and parasympathetic nervous
system.
• The sympathetic nervous system gets the body
prepared for a fight or flight response.
• It causes such things as increased heart rate,
dilation of pupils, release of adrenaline, etc. (Refer
to Figure 12.5)
• The parasympathetic nervous system has the
opposite effect of the sympathetic nervous system.
• The somatic nervous system is in some
cases under our control.
– It is made up of:
• Sensory neurons that carry impulses from the
body’s sense organs to the CNS.
• Motor neurons that carry impulses away from the
CNS to effectors (muscle fibers) that cause a
response. (eg. Moving your hand away from a hot
stove.)
Nervous System Response
In order for a nervous system response to occur
there must be:
1. Information taken in by the senses (eyes, ears,
skin, etc.)
2. Transmission of an impulse by neurons.
3. Interpretation of the impulse by the brain or
spinal cord.
4. Effectors (muscle or glands).
The result is an impulse giving rise to a response if
called a reflex arc.
The Neuron
The functional Unit of the Nervous system is
called the neuron.
The PNS consists of nerves, which are
neurons held together by connective
tissue.
90% of the body nerves are found in the
CNS.
Capable of living over 100 years.
The Neuron
The neuron consists of three main parts.
1. Cell body – Contains a nucleus, cytoplasm
with mitochondria, lysosomes, a golgi complex
and rough ER.
2. An axon – Is the long, cylindrical portion of the
neuron. Can be 1mm to 1 m in length.
Impulses are passed along the axon by a wave
of depolarization.
3. Dendrites – The fingerlike projections that
extend from the cell body. The receive signals
from other neurons.
The Neuron
How an impulse is passed
The neuron at rest
Outside the neuron membrane
• +vely charged.
• High [] of Na+ ions. Lower []’s of K+ and Cl-.
Inside the neuron membrane
• High [] of K+. Lower []’s of Na+
• Dominant anions are proteins, amino acids,
phosphates and sulfates.
At rest the Na+/K+ pump keeps the ion
distribution.
Resting potential of the neuron is –70mV.
Depolarization
• As an impulse passes, there is a change
in the charge of the membrane. This is
called an action potential.
• Na+ channels open that allow ions to
pass.
• K+ channels close.
Repolarization
• After the impulse passes the Na+ channels
close.
• The K+ channels open to allow the ions out of
the membrane.
• The Na+/K+ pump helps reestablish polarity.
The time between neuron impulses in called
refractory period. For many neurons this can be
~0.001s.
The All-Or-None Response

In order for an impulse to occur the stimulus
need to be sufficient for the impulse to be sent.
Ie. There is a Threshold that needs to be met in
order for an impulse to occur.

If the Threshold is met then an impulse will be
sent along the length of the axon.

The strength of the impulse is always the
same, there is no mild of stronger impulse.

The impulse either occurs or it doesn’t ie.
Either all-or-none.
The Synapse
Once an impulse reaches the Axon terminals, it
needs to cross the synaptic gap.
Neurotransmitters are released from the
presynaptic neuron by exocytosis.
Receptor sites on the post synaptic neuron
recieves the neurtransmitter.
This can cause either an excitatory response or
inhibitory response.
The enzyme cholinesterase is released quickly to
break down the neurotransmitter Acetylcholine.
Neurotransmitters
• Acetylcholine – Primary neurotransmitter of the
somatic and parasympathetic nervous systems.
May be excitatory or inhibitory.
• Noradrenaline (norephnephrine) – primary
neurotransmitter of the sympathetic nervous
system.
• Glutamate- the neurotransmitter of the cerebral
cortex. Makes up ~ 75% of the neurotransmitters
in the brain.
• GABA (gamma aminobutyric acid) – Most
common inhibitory neurotransmitter in the brain.
Neurotransmitters
Dopamine – Elevates mood and controls
skeletal muscles.
Seratonin – Involved in alertness,
sleepiness, thermoregulation, and mood.
Requirements of the Nerve cell
Cells within the nervous system require enormous
amounts of energy to function. This energy is
provided by the processing of glucose and the
production of ATP within these tissues, requiring
an adequate supply of carbohydrates and
oxygen (Na+/K+ pump). ATP energy is required
to operate the sodium-potassium pump which
convert cellular chemical signals into electrical
signals along a nerve cell and in between
individual nerve cells (i.e., synapse).
Core Lab #1 - Reflex Arc
What is a reflex arc?
It is the nerve pathway that leads from
stimulus to reflex action.
Complete Pre-lab Question.
Technology for Viewing the
Brain
1. EEG (electroencephalograph): Invented
by Dr. Hans Borger in 1924.
  This technology measures electrical
activity in the brain.
  Allows doctors to detect and locate
brain tumors and disorders such as
epilepsy.
EEG
Technology Continued
2. Cat Scan: taking a series of crosssectional X-rays to give a computer
generated 3-D picture of any part of the
body, including the brain.
Technology Continued
3. MRI (Magnetic Resonance Imaging): This
technology uses a series of large
magnets, radio frequencies and a number
of computers to create a detailed view of
the brain and other structures in the body.
MRI
Treating Stroke and Spinal Cord
Injury
Stroke: Is caused by lack of oxygen to a particular
part of the brain causing that portion of the brain
to die.

Treatments for stroke involve:
1. clot-busting drugs- drawback is that they need
to be administered within three hours after the
stroke occurs.
2. Asprin may also be administered to a person
showing signs of stroke. Asprin decreases the
chance of a clot by reducing stickiness of
platelets (like the oil that you put in the engine
of a car)

Treatments for spinal cord injury (none as of
yet): There is a large amount of medical
research dedicated to finding a way to treating
spinal cord injuries.
§
-Scientists have found a gene that inhibits the
regeneration of the spinal cord and the CNS.
§
-Researchers hope to use this discovery to
develop a therapy that will promote regeneration
of the neurons in the CNS
EEG
MRI
PET Scan
• Shows activity of the
brain by giving a
coloured scan on a
monitor. The more
intense the colour the
greater the activity.
Section 12.3 – The Sense
Organs
Eye and Ear
The Sense Organs: The Human
Eye
What are the eyes protected by?
1.
2.
3.
4.
Eyelashes
Eyebrows
Eyelids
Bones in skull
The different parts of the eye:
How many can you think of?
1. Lens: The lens is a clear and flexible part of the
eye.

Its purpose is to focus light onto the retina.

The lens is adjusted by ciliary muscles. These
adjust the shape of the lens.
2. Iris: The iris opens and closes to control the
size of the pupil. Which inturn restricts or allows
more light to get into the eye.

your iris is the coloured part of your eye. If
you have green eyes, it’s because you have a
green iris.
3. Retina: The retina is the inner layer of the eye.
It is composed of the photoreceptors of the eye,
the rods and the cones

The retina contains approximately 6 million
cones.
4. Rods: The rods are very sensitive to light, but
they do no distinguish between different colors.
5. Cones are less sensitive to light but they
are able to distinguish between colours.
6. Cornea: The cornea is the transparent,
dome-shaped window covering the front of
the eye.

it is normally clear and has a shiny
surface
7. Choroid Layer: Is the middle layer of the
eye. Located between the retina and the
outer layer of the eye.
a. It absorbs light
b. Prevents reflection of light within the eye
c. The choroids becomes the iris at the
front of the eye
8. Fovea: The fovea is located directly
behind the lens of the eye.
 The cones of the eye are concentrated
within the fovea.
 This area of the eye is responsible for
producing the most distinct image
9. Pupil: The pupil is the opening in the center of
the iris. The size of the pupil determines the
amount of light that enters the eye.
10. Blind spot: There is one area in the eye where
there are no photoreceptors

Because of this there is one place in the eye
where you cannot see.

Look at page 413
The Eye
Links
• http://www.nei.nih.gov/health/eyediagram/i
ndex.asp
• http://www.exploratorium.edu/learning_stu
dio/cow_eye/step01.html
Go to unitedstreaming.com
Pathway of Light Through the
Eye
1. Light passes through the cornea
• 2. . Then through the iris
• 3. If there is a lot of light the pupil then
constricts, if there is low amounts of light the
pupil will dilate
• 4. The lens then adjusts its shape in order to
aim the image at the retina.
• 5. Light hits the retina.

The retina is composed of three layers: 1.
ganglion layer 2. Bipolar layer 3. the rod and
cone layer.
•
The rods and cones form the image

The image is then transmitted to the
ganglion layer via the bipolar layer of the
eye.

The impulse then exits the eye via
the optic nerve
Layers of the retina (pg 412)
Disorders of the Eye
In this course we will learn about 5 disorders of the eye.
1. Cataracts – cloudy or opaque areas on the lens
• Get worse with age
• Damaged lens can be replaced with an artificial
one.
2. Glaucoma – Buildup of aqueous humor between lens
and cornea.
• The duct that normally drains the fluid becomes
blocked.
• Can cause nerve damage to nerves that aid in
peripheral vision.
• Can be helped with drugs.
3. Myopia (Near-sightedness) – Can see objects close up.
– Usually caused by the eyeball being too long.
– Therefore the image is focused in front of the retina.
– Treated with concave lens
4. Hyperopia (Far-sightedness) – Can see objects far away
but not close up.
– Usually caused by short eyeballs.
– The image is focused behind the retina.
– Treated with convex lens
5. Astigmatism – Abnormal shaped lens or cornea,
resulting in uneven focus.
– Treated with uneven lens.
Refer to Figure 12.22 in text.
Treatments of eye disorders
1. Laser treatment
1. Photorefractive keratectomy (PKU)
•
•
•
Outpatient procedure
Reshapes cornea by removing microscopic amounts of
tissue.
Controlled by computer
2. Laser in situ keratomileusis (LASIK)
•
•
•
•
•
Helps repair near-sightedness
Knife is used to cut the corneal flap.
Laser is used to remove tissue underneath and flap is
replaced.
Controlled by surgeon.
Both treatments are highly successful.
2. Corrective lenses
3. Cornea transplant
– When the cornea is beyond repair, a
transplant can be performed.
– Cornea comes from a donor, but doesn’t need
to be matched. Ie any cornea can be used by
any person.
– Recovery can be up to 12 months.
– Prognosis is usually very good.
The Ear
Parts of the ear
1. Pinna – Channels sound waves into the
auditory canal.
2. Tymphanic membrane (ear drum) acts like a
drum head and vibrates as sound waves hit it.
3. Ossicles
–
–
–
Malleus (hammer) – picks up vibrations from the ear
drum. Vibrates and hits the incus (anvil)
Incus (anvil) – Passes vibrations to the stapes.
Stapes (Stirrup) – Passes vibrations to the Oval
Window.
4. Eustachian tube (Auditory tube) – Tube behind
the ear drum that allows pressure behind the
eardrum to equalize.
5. Semicircular canals – Involved in balance and
equilibrium. (Fluid filled)
6. Cochlea – Fluid filled – involved in hearing.
Contains very tiny hairs that pick up sound
vibrations.
7. Auditory nerve – Takes message away from ear
to the CNS.
Pathway of Sound in the Ear
1. Pinna focuses sound waves into the auditory
canal.
2. Tymphanic membrane vibrates.
3. Vibrations are passed through the ossicles.
4. Sound waves pass through the oval window
into the cochlea.
5. Hairs in the cochlea pick up sound and are
changed to nerve inpulses.
6. Nerve impulses are taken away by the auditory
nerve.
Disorders of the Ear
There are two main types of deafness that a
person can have; they are as follows:
1. Nerve deafness: Nerve deafness is caused by
damage to hair cells in the spiral organ of the
ear.
a. This type of deafness is usually uneven, ie.
People with the disorders can hear certain
frequencies better than others.
b. Damage cannot usually reversed and it
continues to get worse as a person gets older.
2. Conduction deafness: This type of
hearing disorder is caused by damage to
the outer and middle ear
a. Conduction deafness affects the
transmission of sound waves into the ear.
b. This type of hearing disorder doesn’t
usually cause total hearing loss.
c. Hearing can usually be improved with the
use of a hearing aid.
1. Eustachain tube implants: Many
children have inner middle ear infections
because their Eustachian tube is on an
angle that does not allow proper drainage.
a. To prevent these infections, doctors can
put tubes in the patients ears to allow
proper drainage and pressure release.
Treatments for Ear Disorders
1. Hearing aids: There are several different types
of hearing aids available; 1. Conventional
2. Programmable, and 3. digital aids.
a. Conventional hearing aids have a
microphone to receive sounds and an amplifier
to increase their volume
b. Programmable hearing aids have an analog
circuit that a professional such as an
audiologists can program to the patients needs.
c. Digital Hearing aids can shape amplifications
across various pitches and frequencies
according to individual needs.