AP1, Lab 8

AP1, Lab 8 - Central Nervous System
The 12 Pairs of Cranial Nerves
# Name Function
I Olfactory Sensory impulses from nose for sense of smell
II Optic Sensory impulses from eye for vision
III Oculomotor Motor impulses to eye muscles for movements of the eyes
IV Trochlear Motor impulses to eye muscles for movements of the eyes
V Trigeminal Sensory impulses info from face, scalp, and teeth;
Motor impulses to temporal and masseter muscles for closing
the mandible as when chewing
VI Abducens Motor impulses to eye muscles for abduction of the eyes
VII Facial Sensory impulses from some taste buds of tongue;
Motor impulses to muscles controlling facial expressions like
frowning, smiling, etc.
VIII Vestibulocochlear Sensory impulses from ear for senses of both sound and balance
IX Glossopharyngeal Sensory impulses from throat and some taste buds at the back of
the tongue (salty);
Motor impulses to muscles of throat for swallowing and to
salivary glands
X Vagus Sensory impulses from throat, larynx, thoracic and abdominal
organs;
Motor impulses to stimulate digestive organs, to slow heart rate,
to cough, and to swallow.
XI Accessory Motor impulses to trapezius and sternocleidomastoid muscles of
the neck and upper shoulder for shoulder movements and
movements of the head.
XII Hypoglossal Motor impulses to muscles of the tongue for most tongue
movements.
MNEMONIC DEVICES for Names of Cranial nerves:
On occasion, our trusty truck acts funny - very good vehicle anyhow Or:
Oh, Oh, Oh—To Touch And Feel Very Good Velvet, A-H!
MNEMONIC DEVICE for Sensory, Motor, or Both:
Some say Marry Money, but my brother says Big Business makes money Or:
Some Say Marilyn Monroe, But My Brother Says Bridget Bardot, My, My!
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Visual learning: The figure below is especially useful to visual learners:
There are 12 pairs of cranial nerves in humans.
Their Roman numeral designations and
names are:
� I Olfactory
� II Optic
� III Oculomotor
� IV Trochlear
� V Trigeminal
� VI Abducens
� VII Facial
� VIII
Vestibulocochlear
(auditory)
� IX Glossopharyngeal
� X Vagus
� XI Accessory (spinal
accessory)
� XII Hypoglossal
The cranial nerves mostly innervate structures in the head and neck.
The cartoon codes for at least one major functional innervation of each cranial nerve. This drawing is
based on one done by Beatrice Humphris, R.N. published in Nursing 1984.
http://www.sci.uidaho.edu/med532/cranialnervebackgroundinfo.html
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12 pairs of cranial nerves are associated with the ventral aspect of the brain.
—The first 2 pairs attach to the forebrain, the rest originate from the brainstem.
**Note: The Intermediate nerve included in the diagram above is actually the smaller root of the facial nerve (VII).
Most images do not illustrate it separately. This one just happens to do so.
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Test Your Cranial Nerves
Now that you know the names and functions of the cranial nerves, let's test them. These tests will help you
understand how the cranial nerves work. These tests are not meant to be a "clinical examination" of the cranial
nerves.
You will need to get a partner to help...both of you can serve as the experimenter (tester) and the subject. Record
your observations of what your partner does and says.
Olfactory Nerve (I): sensory for smell
Gather some items with distinctive smells (for example, cloves, lemon, chocolate or coffee). Have your
partner smell the items one at a time with each nostril. Have your partner record what the item is and the
strength of the odor. Now you be the one who smells the items...have your partner use different smells
for you.
Optic Nerve (II): sensory for sight
Use an eye chart (a "Snellen Chart") and have your partner try to read the lines at various distances away
from the chart.
Cranial nerves III, IV and VI are tested together. They each control muscles involved with eye movement.
In addition, the oculomotor also functions in pupil dilation.
Oculomotor Nerve (III), Trochlear Nerve (IV) and Abducens Nerve (VI): Motor
These three nerves control eye movement and pupil diameter. Hold up a finger in front of your partner.
Tell your partner to hold his or her head still and to follow your finger, then move your finger up and
down, right and left. Do your partner's eyes follow your fingers?
Check the pupillary response (oculomotor nerve): look at the diameter of your partner's eyes in dim light
and also in bright light. Check for differences in the sizes of the right and left pupils.
Trigeminal Nerve (V): sensory for touch/pain in face
motor for chewing (mastication)
The trigeminal nerve has both sensory and motor functions. To test the motor part of the nerve, tell your
partner to close his or her jaws as if he or she was biting down on a piece of gum. Temporal and
masseter muscles of the face should have equal strength
To test the sensory part of the trigeminal nerve, lightly touch various parts of your partner's face with
piece of cotton or a blunt object. Be careful not to touch your partner's eyes. Although much of the
mouth and teeth are innervated by the trigeminal nerve, don't put anything into your subject's mouth.
Facial Nerve (VII) Sensory for taste on anterior 2/3 of tongue and salivary glands
Sensory to transmit information from ear to brain
Motor for controlling muscles used in facial expression
The motor part of the facial nerve can be tested by asking your partner to smile or frown or make funny
faces. Check for symmetry.
The sensory part of the facial nerve is responsible for taste on the front part of the tongue. You could try
a few drops of sweet or salty water on this part of the tongue and see if your partner can taste it.
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Vestibulocochlear Nerve (VIII): Sensory for sound and balance
The vestibulocochlear nerve is a branching nerve. The cochlear nerve is responsible for hearing and the
vestibular controls balance.
Hearing: Have your partner cover one ear and close his or her eyes. Stand about 2 feet from the subject
and whisper a word with 2 distinct syllables, like mailman, or football and observe for difficulties
distinguishing words. You may also determine the distance at which he or she can hear the ticking of a
clock or stopwatch.
Balance: Test for balance by having the subject stand with his feet close together and eyes closed. The
subject may sway a little, but should not fall.
Cranial nerves IX and X can be tested together since they both serve to innervate the pharynx.
Glossopharyngeal Nerve (IX): Sensory for taste on the posterior 1/3 of the tongue and conveying
information from the tongue, tonsils and pharynx
Motor for swallowing
Have your partner drink some water and observe the swallowing reflex. Also the glossopharyngeal nerve
is responsible for taste on the back part of the tongue. You could try a few drops of salty (or sugar) water
on this part of the tongue and see if your partner can taste it.
Vagus Nerve (X): Sensory from throat, larynx, thoracic and abdominal organs
Motor for heart rate, swallowing, esophagus and stomach (digestion)
Have the subject speak or cough. Her voice should be clear and strong. Cough should be strong. Subject
should have a strong gag reflex.
Spinal Accessory Nerve (XI): Motor to control the sternocleidomastoid and trapezius muscles involved in head
movement
Put your hands on your partner’s shoulders from the back. As you apply slight resistance, have him shrug
his shoulders upward. Contraction should be symmetrical.
Now place one hand on one side of your partner's jaw. Tell your partner to move his or her head toward
your hand while you apply slight resistance. Repeat on the opposite side. Strength in the
sternocleidomastoid should be symmetrical.
Hypoglossal Nerve (XII): Motor for tongue movement
Have your partner stick out his or her tongue and move it side to side. Check for symmetry.
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DO YOU KNOW……?
Which cranial nerve is the largest? _______________________________
Which cranial nerves are responsible for eye movements? ______________
What does "abducens" refer to? _________________________________
Which cranial nerves carry gustatory (taste) information? ______________
Which cranial nerve is the longest? _______________________________
Which nerve or nerves are involved in:
Rotating the head? _________________________________________
Smelling a flower? _________________________________________
Raising the eyelids, pupillary constriction? ________________________
Slowing the heart rate? _____________________________________
Increasing motility of the digestive tract? _______________________
Bell’s Palsy? ______________________________________________
Chewing food? ____________________________________________
Listening to music? _________________________________________
Seasickness? _____________________________________________
Secretion of saliva? ________________________________________
Sensation of taste? ________________________________________
Rolling the eyes? (3 nerves)__________________________________
Feeling a toothache? _______________________________________
Reading a newspaper? ______________________________________
Purely sensory in function? __________________________________
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HOW THE BODY BLOCKS PAIN
1. The Gate Control Theory:
� Pain impulses are BLOCKED at the dorsal horns of the spinal cord and/or in the hypothalamus and/or
midbrain by the release of natural opiates called ENDORPHINS and ENKEPHALINS. These (and possibly
SEROTONIN) create IPSPs to cancel out EPSPs.
� Fewer messages get through. The gate is partially “closed.”
2. Pain messages aren’t really blocked at all but rather are “smothered” by pleasurable ones in the brain.
� ENDORPHINS and ENKEPHALINS released in the brain inhibit the inhibition of the release of DOPAMINE.
� DOPAMINE, a “feel-good” NT, floods the frontal lobes of the brain and smothers the unpleasant
sensations with pleasant ones.
3. In reality there is probably truth in both theories.
HOW MEDICATIONS BLOCK PAIN:
� ASPIRIN and IBUPROFEN inhibit prostaglandin activity thereby reducing inflammation and pain.
� ACETAMINOPHEN (Tylenol) blocks pain but not inflammation by inhibiting activation of the COX
enzyme.
� NSAIDS are anti-inflammatory in a variety of ways; often as COX2 inhibitors
� NARCOTICS such as morphine, Demerol, and heroin reduce pain by mimicking the effects of
endorphins and enkephalins.
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HOW A T.E.N.S. UNIT BLOCKS PAIN
TENS = Transcutaneous Electrical Nerve Stimulation
� Every day, ordinary afferent sensory impulses enter the spinal cord at the posterior horns of the gray
matter. Here they must pass through synapses before traveling up to the brain via ascending tracts
of the spinal cord. Pain messages follow the same pathway.
� Applying continuous or repetitive stimulation through the skin of an appropriate area using TENS
‘annoys’ the brain with a flood of sensory input. In response, the brain increases the frequency of
impulses down the spinal cord to create IPSPs to “block” both the incoming messages from the
skin as well as the pain messages.
� Electrical stimulation of nerves using TENS also stimulates the release of endorphins so that fewer
pain generating impulses reach the brain, so pain is not felt or at least is felt less.
REFERRED PAIN
� A painful sensation felt in a region of the body that is not the origin of the stimuli.
� Usually, it’s a painful sensation of visceral origin felt in a somatic region of the body that is not the
origin of the stimuli.
Examples:
1. Heart attack – the origin of the impulses is the heart muscle but the pain is often felt in the upper
chest, left side of the mandible, and on the medial surface of L arm.
2. Gallbladder and Liver – often felt at the top of the R shoulder.
3. Kidney and Ureters – often felt in the lower back.
� Happens because the visceral and somatic sensory neurons converge on the same ascending tracts of the
spinal cord. When messages arrive on these tracts the brain can’t always distinguish between the two
points of origin.
PHANTOM PAIN
� The sensation of pain experienced in a body part you no longer have – a missing foot, leg, arm, etc.
� The brain receives no sensory information from the missing limb to inhibit pain sensations. If an action
potential is initiated anywhere along the neuronal pathway from the severed limb, the idea of pain will be
projected back to the missing limb even though the limb is not there.
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Dissection of Cow Brain with Dura Mater
� Use images from the dissection manuals in lab and your knowledge of the brain to identify the following.
Recall the functions of those with an *.
� Your group will be evaluated on the quality of your dissection. FOLLOW INSTRUCTIONS CAREFULLY.
1. Glove up – your choice of latex or polyethylene.
2. Safety – practice caution with the knives and other implements.
3. Housekeeping (Your mother does not work here, kindly clean up after yourself) – Don’t put pieces of
tissue in the sink. If you notice, there is no garbage disposal. At the end of lab, we will put brains back
in the bag. Don’t get “slime” on the brain models. When you are finished, wash everything and return it
where you found it.
4. Open your bag and rinse away as much preservative as possible. Observe the dull white DURA MATER
covering the surface of the brain.
5. The two, large fatty masses dangling from the anterior and inferior surface are the tissues that were
behind the eyes. Find the two OPTIC NERVES in these and then cut the fatty mass off.
6. Use scissors to cut away the superior 90% of the DURA MATER. Leave the bottom portion intact as it will
contain the pituitary gland. The ARACHNOID LAYER will come off with the dura mater leaving only the
PIA MATER on the surface of the brain.
7. Observe the LONGITUDINAL and TRANSVERSE FISSURES containing DURAL SINUSES as you remove the
dura mater. What occurs at your dural sinuses? _______________
1. Identify the following externally visible structures while the brain is still whole. No cutting necessary.
CEREBRUM
L and R CEREBRAL HEMISPHERES
Various SULCI & GYRI
OLFACTORY BULBS and OLFACTORY TRACTS. This is CRANIAL NERVE #1 carrying sensory
messages to the brain for the sense of smell.
Observe the delicate PIA MATER anchoring blood vessels to the cerebrum mostly in the sulci. These
vessels are dark brown/black in color.
CEREBELLUM
OPTIC NERVES and OPTIC CHIASMA. Cut the optic nerves (cranial nerve #2) and other motor nerves as
far out as you can clearly see them to get rid of those dangling lumps of fatty tissue that were
located behind the eyes.
Pituitary gland - usually appears as a nodule or “lump” approximately ¼ inch in diameter on the ventral
side of the brain.)
TRIGEMINAL NERVES - The lateral edges of the dura mater containing the pituitary gland also contain the
large trigeminal nerves (cranial nerve #5). Cut the nerves near the dura mater to leave stumps on the
lateral walls of the pons. Remove the dura mater containing any branches of this nerve but do not
remove the pituitary gland.
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OCULOMOTOR NERVES – Gently lift the pituitary gland from its anterior edge while looking for the
oculomotor nerves (cranial nerve #3) to be raised with the dura mater and the pituitary gland. Go
ahead and remove the dura mater and pituitary gland. The stumps of the oculomotor nerves will
either be lying on the midbrain, projecting forward or they will have torn loose and be attached to the
dura mater above the pituitary gland.
BRAIN STEM
Spinal cord – function?
Medulla Oblongata – functions?
Pons – functions?
**Confirm identifications of everything up to this point with your instructor.
2. Bisect the brain on the mid-sagittal plane along the longitudinal fissure all the way through the brain stem.
Make one clean, straight cut all the way through. Try to cut as precisely in the middle as possible. Identify the
following.
Corpus Callosum and Fornix– recall function?
Thalamus – recall functions?
Hypothalamus – recall functions?
Lateral ventricles - Use your metal probe to separate the corpus callosum and the fornix in order to see
better into the lateral ventricles. The corpus callosum will be the roof and the fornix
will be the floor of each ventricle.
Third ventricle – Look above the thalamus but below the fornix.
Choroid plexus - specialized capillaries for production of CSF. They are delicate and dark brown in color
similar to the vessels on the surface of the cerebrum. Use your forceps to gently reach deep into the
posterior portion of a lateral ventricle and pull some of this out. You might also find some in the 3 rd
and 4 th ventricles.
Cerebral aqueduct – passageway for CSF to flow from 3 rd to 4 th ventricle.
Fourth ventricle – space between the cerebellum and spinal cord.
3. Locate your thalamus again. Put the two hemispheres back together and perform a coronal section such that
your cut passes through the thalamus. Hold the two posterior portions together and view them from the
anterior side.
Identify the following:
Cerebral white matter
Cerebral cortex - The term “cortex” refers to the outer layer of any structure.
On the cow brain it’s the darker, more superficial layer that borders the white matter and follows
the contour of the sulci. The majority of the synapses of the brain are found in the cortex.
Corpus callosum
Lateral ventricles
Fornix
Third ventricle
Thalamus
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