Lab 6: Peripheral NS and the Sheep Brain
Station 1: Torso brain model
The following structures were from the the brain models last week. Keep them in mind as you look
for the corresponding structures in the sheep brain.
o Medulla oblongata
o Transverse cerebral
o Conus medullaris
o Pons
fissure
o Cauda equina
o Midbrain
o Longitudinal fissure
o Spinal dural sheath
o Middle cerebellar
o Central sulcus
o 3rd cervical nerve
peduncle
o Lateral sulcus
o 10th thoracic nerve
o Cerebellum
o Parieto-occipital sulcus
o 1st lumbar nerve
o Arbor vitae
o Precentral gyrus
o 2nd sacral nerve
o Thalamus
o Postcentral gyrus
o Sympathetic trunk and
o Hypothalamus
o Optic (II)
ganglia
o Pituitary gland
o Oculomotor (III)
o Ventral rami
o Corpus callosum
o Trochlear (IV)
o Dorsal rami
o Frontal lobe
o Trigeminal (V)
o Dorsal root ganglia
o Parietal lobe
o Glossopharyngeal (IX)
o Gray matter
o Occipital lobe
o Vagus (X)
o White matter
o Temporal lobe
o Hypoglossal (XII
Station 2: External Sheep Brain:
Rinse the brain under gently running water to remove some of the preservative and keep your
hands more comfortable. Gloves are not required, but we have some out if you prefer to use them.
Place some paper towels on your tray.
1. Place brain on the paper towels, dorsal side up.
a. Observe the outer membrane (dura mater), if present. Cut off the dura mater and
expose the cerebrum.
b. Observe the gyri (ridges) and the sulci (grooves). Blood vessels are found between
the arachnoid and pia mater, and the pia mater may be indestinguishable from the
brain tissue. Carefully remove some of the blood vessels with tweezers if you desire.
c. Identify the longitudinal fissure, which separates the right and left hemispheres of
the brain.
d. Locate the frontal, 2 parietals, 2 temporals, and the occipital lobes of the brain.
Observe the ventral surface of the brain.
2. Locate the following structures:
a. The pituitary gland is easily lost, but find the stem where it used to be attached.
b. Find the pair of olfactory bulbs. What lobe of the brain are they under?
c. Find the optic nerves and optica chiasm, and optic tract. If muscles, other nerves and
tissue are in the way, you can remove them with a scalpel. Where is the dicussation
in this system?
d. The oculomotor nerve should be caudal to these.
e. Find the pons and medulla oblongata. Look for the very large root of the trigeminal
nerve.
3. Several cranial nerves can be seen exiting from the medulla, if you have an obliging brain.
a. At its rostral end, you may be able to see the thin (and easily ripped off) abducens nerve
(VI). The abducens exits from the trapezoid body (a thin transverse band of fibers on
the surface of the brain just caudal to the pons,) at a point just lateral to the
longitudinally coursing pyramidal tracts.
b. Lateral to the abducens is the more substantial facial nerve (VII).
c. Lateral to this, tucked up just under the
cerebellum, you may see the tuft that forms the
vestibulocochlear nerve (VIII).
d. Caudal to the vestibulocochlear nerve you may
see another light tuft of nerves that are made up
of the glossopharyngeal nerve(IX) blending into
the more caudal vagus nerve (X).
e. Caudal to this you may see the spinal accessory
nerve (XI) which appears as a line of connected
filaments running in a rostral-caudal direction
(they may take on the appearance of a broad
yard rake).
f. The hypoglossal nerve (XII) exits in several
branches from the lateral edge of the caudal
medulla
4. Anterior to the medulla is the IV Ventricle and the
cerebellum. If you gently pull the cerebellum away from the cerebrum, you can find the
superior and inferior colliculus.
Examine the Mid-sagittal Section
5. Hold the brain with the dorsal side up, and cut along the longitdinal fissure.
a. Find the lateral ventricle and the third ventricle
b. Find the corpus callosum
c. The pineal body is deep to the lateral ventricle, and caudal to the thalamus and
hypothalamus
d. Note the arbor vitae of the cerebellum
6. Before continuing, use your dissection pins to label the pineal gland, thalamus and lateral
ventricle.
Show your lab instructor before you continue.
Create a coronal section
7. Bring the lateral halves of the brain back together, and do your best to make a coronal cut
through the pineal gland:
(image from http://portal.psy.uoguelph.ca/faculty/peters/labmanual/CoronalCuts.html)
a. In your best slice, be able to find the following: hippocampus, pineal gland, posterior
commisure, midbrain, optic fibers.
What lobe of the cerebellum is visible in the section?
For the lab practical, we will have pins in various structures. Feel free to take labeled pins and
create your own photo study guide using your phone camera. Make friends with groups near you if
they have a particularly nice section and visible structures, and photograph their brains as well.
Station 3: Modeling nerve pathways, human skeleton.
You will model six total nerves in this activity; two cranial and four major nerves that are
parts of the nerve plexuses of the body. We are going to use either WikiStix (wax-covered string) or
string and tape. In the instructions below, “nerve” means your chosen wikistix or string.
NOTE: this model will not be completely accurate, as we are not modeling the nerve
plexuses; rather the nerves will attach directly to the spinal nerves. Also remember that each nerve
is paired – there is a left and right of each nerve. You are only going to model the left or the right,
not both.
Optic nerve
 Take the brain from the torso and identify the origination point of the optic nerve.
 Identify the optic nerve from the envelope of nerves and tape one end to the attachment
point on the brain.
 Where does the optic nerve originate from the brain?
 Remove the skullcap from the human skeleton skull model, and identify the foramen that
the optic nerve passes through.
 What foramen does the optic nerve pass through?
 Carefully place the brain in the cranial fossa and thread the cranial nerve through its
foramen.
 Remove the left eye from the torso and carefully place it in the left orbital socket of the
skull. The optic nerve is now “attached” to the eye!
Vagus nerve
 Remove the brain from the skull and identify the origination point of the vagus nerve. (leave
the optic nerve attached!)
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Where does the vagus nerve originate from the brain? ____________
Identify the vagus nerve from the envelope of nerves and tape one end to the attachment
point on the brain.
In the skull model, identify the foramen that the vagus nerve passes through.
What foramen does the vagus nerve pass through? _______________
Carefully place the brain in the cranial fossa and thread the cranial nerve and vagus nerve
through their foramina.
Thread the vagus nerve to the approximate location where it would innervate the heart.
Show your lab instructor before you continue. Leave your nerves in place.
Phrenic nerve
 Which spinal nerves make up the phrenic nerve? __________________
 What plexus does the phrenic nerve originate from? _______________
 On the human skeleton model, identify the spinal nerves that make up the phrenic nerve.
 Tape the ends of the phrenic nerve to its appropriate spinal nerves.
 Thread the phrenic nerve from its attachment points at the spinal nerves to its most distal
point – use tape to help keep it in place.
Ulnar nerve
 Which spinal nerves make up the ulnar nerve? ____________________
 What plexus does the ulnar nerve originate from? _______________
 On the human skeleton model, identify the spinal nerves that make up the ulnar nerve.
 Tape the ends of the ulnar nerve to its appropriate spinal nerves.
 Thread the ulnar nerve from its attachment points at the spinal nerves to its most distal
point – use tape to help keep it in place.
Show your instructor your phrenic and ulnar nerves before moving on.
Obturator nerve
 Which spinal nerves make up the obturator nerve? _________________
 What plexus does the obturator nerve originate from? _______________
 On the human skeleton model, identify the spinal nerves that make up the obturator nerve.
 Tape the ends of the obturator nerve to its appropriate spinal nerves.
 Thread the obturator nerve from its attachment points at the spinal nerves to its most distal
point – use tape to help keep it in place.
Tibial nerve
 Which spinal nerves make up the tibial nerve? __________________
 What plexus does the tibial nerve originate from? ________________
 On the human skeleton model, identify the spinal nerves that make up the tibial nerve.
 Tape the ends of the tibial nerve to its appropriate spinal nerves.
 Thread the tibial nerve from its attachment points at the spinal nerves to its most distal
point – use tape to help keep it in place.
Take an artisitic photo of your work and post it to your Instagram.
… if you are brave enough…