Sheep´s brain dissection- biodeluna


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Sheep´s brain dissection guide.
2011-12 Biology - level 3º ESO.
Zaragoza - Spain

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Sheep´s brain dissection- biodeluna

  1. 1. Sheep´s brain dissectionFirst examine the exterior of the entire brain. The meninges are the protective coverings, whichenclose the brain and spinal cord.You may be able to see one or two of the three layers of themeninges, the dura mater, the arachnoid layer, and the pia mater.Next locate the area referred to as the brain stem (medulla + pons + midbrain). Find also the rootwhere the pituitary gland or hypophysis was (or if youa are lucky it is still) attached to your brain.Find the medulla (oblongata) which is an elongation below the pons. The medulla is locatedright under the cerebellum. In this the nerves cross over so the left hemisphere controls the rightside of the body and vice versa. This area of the brain controls the vital functions like heartbeatand respiration (breathing).The pons is next to the medulla. It serves as a bridge between the medulla and the upperbrainstem, and it relays messages between the cerebrum and the cerebellum.The pituitary gland or hypophysis, which produces important hormones, is a pea size sac-likearea that attaches to the brain between the pons and the optic chiasm. This may or may not bepresent on yourspecimen.Examine the ventral surface of the sheep brain where you can find a pair of olfactory bulbs, oneunder each lobe of the frontal cortex. Several important parts of the visual system are visible in theventral view of the brain. Muscles, other nerves and fatty tissue may surround the optic nerve onyour specimen. After inspection of these, use a scalpel to cut away this muscle tissue, leaving asmuch of the optic nerve as possible protruding from the ventral side of the brain. Notice that asthe optic nerves from the right and left eyes proceed towards the center of the brain, they meet inthe optic chiasm (named for the Greek letter chi, C, which it resembles). In the optic chiasm,there is a partial crossover of fibers carrying visual information. Any time fibers in a tract or nervecross the midline of the brain it is called a decussation.
  2. 2. The cerebrum is divided into approximately symmetric hemispheres.The corpus callosum is a bundle of white fibers that connects the two hemispheres of the brain,providing coordination between the two.Now find the four lobes of the cerebrum: frontal, parietal, temporal, and occipital.Examination of the Mid-Saggital Cut.Use a scalpel (or sharp, thin knife) to slice through the brain along the center line, starting at thecerebrum and going down through the cerebellum, spinal cord, medulla, and pons.Now you can see the cerebellum. To some it resembles a tree or bush and is called as a resultthe arbor vitae (the tree of life).Look closely at the inside of the cerebellum to notice the pattern of grey and white matter. Youshould see a branching "tree" of lighter tissue surrounded by darker tissue. The branches arewhite matter, which is made up of nerve axons. The darker tissue is gray matter, which is acollection of nerve cell bodies. You can see gray and white matter in the cerebrum, too, if you cutinto a portion of it.This dissection guide was elaborated thanks to the resources from:  