----------------Dissection of a Sheep Brain----------------
I have ordered a sheep brain which I shall dissect so to parallel my findings with my studies in school. I will be using a dissection manual to help me. I will post pictures and detailed information about sensory systems, cortical areas, the limbic system, and more.
The defenition of terms in this thread pertain to the human brain. I am dissecting a sheep brain because they are somewhat similar to a human brain, which is what I intend on learning about. After each definition is my report on the dissection of specifically the sheep brain.
----------------Human and Sheep Brain Differences----------------Quote:
Western Oregon University highlights the similarities between a human and a sheep brain:
The human brain is rounded, whereas the sheep’s brain is elongated in shape
The sheep’s brain has a more developed olfactory bulb, giving them a sharper sense of smell
The human brain has a larger frontal lobe than the sheep’s brain (‘seat of consciousness’)
http://www.wou.edu/~lemastm/Teaching/BI335/Laboratory%2001%20-%20Brain%20Anatomy.pdf
----------------Meninges: dura mater, arachnoid mater, pia mater----------------The brain and the spinal chord are protected by bone and wrapped in three protective membranes known as the
Meninges. The outer
menynx is named
dura mater. It is a tough and thick membrane. Within the dura mater is the
archanoid mater. The inner most membrane is named
pia mater. Between the dura mater and pia mater exists a spaced called the
subarachnoid space wherein exists a spongy material called the
trabecula, which is a tissue that helps move
cerebrospinal fluid (CSF).
The length of the spinal cord is filled with CSF and the brain also holds CSF in four
ventricles, which are cavities in the brain. CSF provides the brain with protection from mechanical injuries by supporting and cushioning the brain. Patients who have had CNS drained from their heads suffer from headaches whenever jerk or jolt their head.
CSF is constantly produced by
charoid plexuses, which are small blood vessels that, from the pia mater, make entry into the four ventricles. The excess CSF makes an exit when it is absorbed in the subarachnoid space by blood filled spaces, which flow through the dura mater and and drain into jugular veins in the neck.
-Pathology-Whenever the flow of CSF from the lateral ventricles is blocked (perhaps by a tumor), the build-up of CSF causes the ventricles and the brain to expand. This pathology is named
hydrocephalus ("water head"). Hydrocephalus is treated by dealing with the obstructing object and draining excess fluid from the enlarged ventricles.
-Locating the Meninges on a Sheep Brain-The brain I received had the meninges already removed and so I cannot provide a picture. Normally the meninges appear as a white film surrounding the brain.
----------------The Ventral Surface----------------

1. Pons
2. Medulla
3. Spinal cord
4. Pituitary gland
5. Olafactory Bulb
6. Optic Nerve
7. Optic Chiasm
8. Optic Tract
9. Longitudinal Fissure
10. periamygdaloid cortex
11. Rhinal fissure(1) Pons.......(2) Medulla........(3) Spinal Cord.......(4) Pituitary Gland........(5) Olfactory Bulbs........The olafactory bulbs are located rostrally and on the inferior side of the brain.
The olafactory bulbs (OB) receives input from
olafactory receptor neurons (ORN), which are located in the nasal passage. Activation of ORNS send electric signals to glomeruli, which are located on the olafactory bulb.
10,000 ORNs send electric signals to one or two glomeruli on the OB.
Christiane Linster and coworkers studied the OB by using a technique called the 2-Deoxyglucose Technique. This technique involves injecting the radioactive 2-deoxyglucose(2DG) molecule an animal (rat) and then exposing it to different chemicals. Neurons take up 2-deoxyglucose and from that one can measure levels of radioactivity of a particular structure - such as the (OB). Linster studied pairs of molecules that have the same chemical formula, but which a section on the molecule is rotated to a different position. Linster made two forms of carvone and two forms limonene. The rats were exposed to these odors. It was found that the OB was activated differently to the two forms of carvone, but similarly to the two forms of limonene. Behavioral testing of the rats showed that the rats could indeed tell the difference between the two forms of carvone, but not the limonene. Thus activation in the OB is related to the function of olafactory mechanisms and perceived odor.Other experiments have been done that show the length of molecules activate particular ORNS and particular areas of the OB. Such information supports the idea that certain molecules have different recognition profiles.
-Pathways-From the OB signals are then sent to the piriform cortex and the amygdala, and then on to the orbitofrontal cortex.
-Locating the Olafactory Bulbs on a Sheep brain-(6)Optic Nerves.......The eyes have optic nerves that channel into the brain. Sensory information from the world travels through the optic nerves. The optic nerves channel underneath the brain and can be seen on a cadaver brain by simply observing the underneath of the brain. Typically the severed optic tracts should be located medially and should look like a "X" on the brain.
-Locating the Optic Nerves on a Sheep Brain-(7) Optic Chiasm.......(8) Optic Tract.......(9) Longitudinal Fissure........(10) Periamygdaloid Cortex.......(11) Rhinal Fissure .......----------------Lobes----------------
1. Longitudinal Fissure
2. Frontal Lobe
3. Ansate Sulcus
4. Temporal Lobe
5. Occipital Lobe
6. Parietal lobe
7. Cerebellum
8. Spinal cord-----------------------CUTS-----------------------
----------------Examination of the Mid Sagittal Cut----------------My mid Sagittal cut consisted of cutting the brain directly along Rhinal fissure.

1. Lateral Ventrical
2. Cerebral Aqueduct
3. Septum Pellucidum
4. Fornix
5. Cingulate Gyrus
6. Tegmentum
7. Fourth Ventrical
8. Third Ventrical----------------Coronal Frontal Cuts----------------I made my coronal cuts as illustrated in the following picture.

Corpus Collosum
Basal Ganglia: caudet nucleus, putamen, globus pallidus
Anterior Commissure
-----------------------References-----------------------(2010). Anatomy and Pathology (5th edition). Skokie, IL: Anatomical Chart Company.
Goldstein B. E. (2010). Sensation and Perception Eight Edition. Wadsworth, CA: Cengage Learning.
Pinel J. P. J. (1993). Biopsychology: second edition. Needham Heights, MA: Allyn & Bacon.
https://www.msu.edu/~brains/brains/sheep/index.htmlhttp://psych.hanover.edu/classes/neuropsychology/Syllabus/Labs/DISSECTION.pdf http://www.wou.edu/~lemastm/Teaching/BI335/Laboratory%2001%20-%20Brain%20Anatomy.pdfhttp://portal.psy.uoguelph.ca/faculty/peters/labmanual/PrintSheepBrain.htmlhttp://www.wou.edu/~lemastm/Teaching/BI335/Laboratory%2001%20-%20Brain%20Anatomy.pdfhttp://www.exploratorium.edu/memory/braindissection/