04.28.2016 Sheep Brain Dissection

Today we dissected a sheep's brain to help us learn about the structures and functions of a human brain.

the superior side of the brain

the inferior side of the brain with the meninges (protective covering) still attached -- it is the white stuff

the outside of the brain, labeled (white = anterior; green = posterior; yellow = cerebrum; black = cerebellum; red = brainstem)

a drawing of the outside of the brain

a table showing the different parts of the outside of the brain and their functions

First, we observed the brain from the outside and identified the anterior (front), posterior (back), and the cerebrum, cerebellum, and brain stem. The brain stem is connects the rest of the brain to the spinal cord and is involved in involuntary activities such as breathing and the heartbeat. The cerebellum is responsible for motor control and coordination, and the cerebrum is responsible for voluntary actions, senses, reasoning, and other higher functions.

cross-section of the brain showing the internal structures

a table showing the different parts of the inside of the brain and their functions

the inside of the brain, labeled (on the left hemisphere: red = medulla oblongata; blue = pons; black = midbrain; yellow = hypothalamus; white = thalamus; green = optic nerve // on the right hemisphere: red = corpus callosum)

a drawing of the inside of the brain

Next, we cut the brain in half longitudinally to expose the inside. We were then able to identify the thalamus, hypothalamus, optic nerve, medulla oblongata, pons, midbrain, and corpus callosum. The thalamus is the "router" of the brain which filters and sends sensory information coming in to the appropriate parts of the brain. The hypothalamus is responsible for maintaining homeostasis and for regulating hormone release. The optic nerve carries visual sensory information from the eyes to the brain. The medulla oblongata, the pons, and the midbrain together make up the brain stem -- the medulla oblongata is responsible for involuntary functions like breathing; the pons is plays a part in senses and motor control; the midbrain also plays a part in senses and motor control. The corpus callosum connects the left and right hemispheres of the brain and allows them to communicate with each other.

cross-section of the cerebrum showing the white and grey matter

a drawing of the cross-section of the cerebrum with the grey and white matter labeled

Finally, we cut the cerebrum in half to study the grey and white matter. White matter is made mostly of axons coated in myelin (an insulating sheath made mostly of fatty tissue that speeds up neural impulses), while grey matter is made mostly of neuron cell bodies and unmyelinated axons.

From this lab, I was able to see the parts of the brain as they really are, not like the brightly-colored pictures one can find in textbooks. The parts of the brain are not as clear-cut as the diagrams in the textbook; for example, there is no clear division between the thalamus and the hypothalamus.