Brain+Dissection

Overview** A general set of instructions for dissecting mammal brains. With each type of brain, there will be differences in the size of the structure and brain regions, but the general structures and their relative location will be the same or every similar.
 * Brain Dissection Guide

Follow safety laboratory practices when performing any dissection. Wear safety glasses or goggles,gloves,and lab aprons when dissecting tray or pan to contain specimens and fluids. Be careful when using sharp insteruments such as scalpels,forceps,teasing needles,and scissors.
 * Safety**

1.Review the glossary provided at the end of the dissection guide. Refer to the Mammal Brain Section diagram to help you observe and identify external and internal structures.
 * Procedure**

2.Place the brain on a dissecting tray, dorsal side up.

3.Observe the dura mater, or outer meninges, if they are present and were not removed prior to preservation. The two remaining meninges, pia and arachnoid, form a thin covering which adheres oto the surface3 of the cerebrum. Use forceps to gently remove these layers.

4.Identify the cerebrum. On the cerebral surface, observe the grooves known as sulci. Also observe the ridges called gyri. Identify the medial longitudinal fissure, which separates the right and left hemispheres of the cerebral cortex.

5.Locate the four lobes of the cerebrum. At the anterior of the brain is the frontal lobe, which controls motor functions. Dorsal to this lobe is the parietal lobe, which receives and processes somatic sensory information. Inferior to the parietal lobe are the temporal lobes. The temporal lobes receive and process auditory sensations. The dorsal portion of the cerebrum makes up the occipital lobe, which receives and processes sensations from the eyes.

6.Locate the cerebellum, which is inferior to the occipital lobe of the cerebrum. The cerebellum has an outer cortex and is folded. It is incompletely divided by a dorsal central ridge called the vremis. The cerebellum has an outer cortex and is folded. It is completely divided by a dorsal cental ridge called the vermis. The cerebellum controls muscle coordination.

7.Place the brain on the dissecting tray, ventral surface up. Locate the following structures: medulla,pons,brain stem, and spinal cord.

8.The cranial nerves and pituitary were cut when the brain was removed from the skull.You should be able to identify the olfactory bulb, which lies below the frontal lobe of the cerebrum. Identify the optic chiasma. This x-shaped structure is formed by the crossover of the right and left optic nerves. The optic nerves have been removed, but portions of the optic chiasma are visible.

9.Place the brain on a dissecting tray,dorsal side up. Using your fingers,gently widen the medial longitudinal fissure. Insert a scalpel into the fissure and cut through the corpus callosum connecting the two cerbral hemispheres. Continue to cut out, dividing the cerebrum,cerebellum,and brain stem into two longitudinal halves.

10.Each hemisphere contains a lateral vwntricle, referred to as the first and second ventricles. The lateral ventricles can be located by removing the septum pellucidum. The septum pellucidum is a thin, transparent membrane located inferior to the corpus callosum on each hemisphere.

11.Locate the third and fourth ventricles. The fourth ventricle connects to the central canal of the spinal cord. It is also connected to the third ventricle by a cerebral aqueduct. Ewamine each ventricle and try to identify the chorid plexus, which produces cerebrospinal fluid.

12.With the cut side facing up, locate the following parts:thalamus,hypothalamus,pineal body,pons,and medulla.

13.Observe the cut surface of the cerebellum. In medial section, the white matter of the cerebellum forms a branched, treelike pattern called the arbor vitae. Try to identify this pattern.

14.Locate the midbrain region, located inferiorly between the thalamus and pons. This area contains important nerve tracts. Dorsal areas of the midbrain are concerned with responses to visual and auditory stimuli.

15.Make a cross section through a cerebral hemisphere just anterior to the thalamus. Examine the cross section and identify the inner white matter and outer gray matter.

16.Remove the cerebellum and the remainder of the cerebral hemisphere issecting away everything dorsal to the floor of the lateral ventricle. This will expose an infolding of the cerebral cortex, called the hippocamous. The hippocampus is involved with emotions and memory.

17.Remove the hippocampus to locate the remainder of the thalamus.

18.Once you have observed all the structures of the brain, dispose of the specimen in accordance with local guidelines and your teacher's instructions.