LABORATORY STUDY OF THE SHEEP BRAIN
WEEK 2 Medial Structures
You should be able to work on the cranial nerves before Wednesday. (Possible extra credit? Know the role of each CN – for example optic nerve = incoming vision signals)
Cranial Nerves. Human Brain 5.7 – KNOW THE LOCATION AND NAME *NOT JUST CNX or Cranial Nerve 3* FOR EACH CRANIAL NERVE – Color code the pairs of nerves, it will help! Sheep Brain Handout will help you, there are good labeled images on the Online Sheep Brain Dissection Guide (http://www.uofs.edu/sheep/framerow.html) – I will only ask you to name cranial nerves where it is absolutely clear which nerve it could be.
a. The origins of the olfactory (CNI) and optic (CNII) nerves have been indicated on the week 1 sheet.
b. The oculomotor nerve (CNIII) arises from the ventral surface of the cerebral peduncles close to its medial border.
c. The trochlear nerve (CNIV) is found caudal and lateral to the oculomotor nerve and rostral and medial to the trigeminal nerve.
d. The trigeminal nerve (CNV) is a very large flat nerve extending forward from the lateral border of the pons. It arises by two roots; the larger sensory root is placed lateral to the smaller motor root.
e. The abducens nerve (CNVI) arises from the trapezoid body about 1/8 inch from the ventral median fissure.
f. The facial nerve (CNVII) arises from the trapezoid body lateral to the abducens.
g. The vestibulocochlear nerve (CNVIII) is seen just caudal to the facial nerve. Having arched downward from the dorsolateral border of the medulla, it appears from under the flocculus of the cerebellum.
h. The glossopharyngeal (CNIX) and vagus (CNX) nerves arise by a series of filaments from a groove along the lateral border of the medulla. CNIX arises from this groove just caudal to the trapezoid body and just lateral to the olive. CNX arises caudal to CNIX.
i. The accessory nerve (CNXI) is on the same line with CNIX and X, but caudal to them; it is seen running forward along the side of the spinal cord and medulla, receiving filaments from both.
j. The hypoglossal nerve (CNXII) arises as a series of roots from the ventral surface of the medulla, near the caudal end of the lateral border of the pyramid.
Medial sagittal section of brain.
2. The cingulate gyrus (gyrus cinguli) is the gyrus just dorsal to the corpus callosum, bounded dorsally by the cingulate sulcus (sulcus cinguli).
i. the lamina terminalis, a thin plate joining the two hemispheres. It is the original rostral boundary of the telencephalon. In this section it extends from the optic chiasm upward to the anterior commissure, a fiber bundle connecting olfactory regions of the two hemispheres, which appears here in cross section as a round white spot.
ii. a small caudally-running portion of the rostrum of the corpus callosum.
iii. a small part of the fornix just above the anterior commissure. Just caudal to this part of the fornix are located, on either side, the interventricular formina (sing. foramen), the opening by which the third ventricle communicates with the lateral ventricles of hemispheres.
i. rostrally, a very thin ependymal layer which is thrust downward into the ventricle by a fold of richly vascular pia mater. Thus is formed the choroid plexus of the third ventricle, which extends rostrally and laterally through the interventricular foramina to form the choroid plexus of the lateral ventricles.
ii. caudally, the pineal body or epiphysis, a small pinecone-shaped body whose caudal surface rests upon the midbrain.
iii. The habenular trigone, a small triangular area just rostral to the pineal body. It contains a nucleus concerned with olfactory reflexes.
iv. the posterior commissure appears as a round white spot in the roof just caudal to the pineal body. Some of its fibers connect the two superior colliculi; the connections of the rest are not certain. The posterior commissure is dorsal to the junction of the third ventricle and the cerebral aqueduct (aqueduct of Sylvius), the cavity of the mesencephalon.
Any of the above bold and underlined structures are fair game in the human Neuroanatomy book but it particular pay attention to the following plates:
CRANIAL NERVES 5.7
OVERALL MIDLINE STURCTURES: 10.4 10.5
NOTES ON TAKING THE LAB PRACTICALS:
Remember that the lab practicals are CUMULATIVE.
On the lab practical you must be as specific as possible. If a pin is in the hippocampal gyrus and the sheet does not say “lobe” then you must answer hippocampal gyrus and not temporal lobe. If the pin is in the vermis, you will not get credit for answering cerebellum.
Ventricles, Gyri, Sulci, Fissures, and Nerves will be so marked on your lab practical sheet.
To help prepare for the lab practical, you should quiz your lab partner and have them quiz you on more than 1 brain (they don’t all look alike!).