Yezi Cho
A sheep brain was dissected to learn its function through the observation a typical mammalian brain anatomy.
Initially, the sheep brain was surrounded by a layer of tissue, which was removed using a scalpel.
The surface of the brain is mostly observed as the cortex which surrounds the cerebrum, which has a folded appearance. This structure allows the brain to increase its surface area, containing more neurons.
Figure 1. Frontal section of the brain
The cortex contains grey matter, which is connected to white matter located in the inner part of the brain. White matter is composed of millions of bundles of axons that connect neurons of the brain. In the spinal cord, grey matter is surrounded by white matter.
Figure 2. Meninges (Cleveland Clinic, 2021)
The brain and spinal cord is covered by meninges, which consists of three layers: dura mater, arachnoid mater, and pia mater. The dura mater is a thick and tough outer layer, consisting of the periosteum and dura. The arachnoid is a thin layer that covers the brain. Between the dura and arachnoid is the subdural space. The pia mater, which is closest to the brain, contains blood vessels. The space between the arachnoid and pia is the subarachnoid space, where the cerebrospinal fluid (CSF) flows. CSF also surrounds the spinal cord and brain, protecting the brain and spinal cord.
The forceps show the lateral ventricles located under the corpus.
The thalamus and hypothalamus are located between the lateral ventricles and pons. The main function of the thalamus is to relay motor and sensory signals before they are sent to the cerebral cortex for interpretation. It is also associated with sleep, consciousness and memory. The hypothalamus maintains homeostasis, controlling the autonomic system and releasing hormones.
The spinal cord, which is part of the central nervous system, is connected to the brain as such. The central nervous system (CNS) refers to the brain and spinal cord, while the peripheral nervous system (PNS) is composed by spinal nerves that branch from the spinal cord, along with cranial nerves that branch from the brain.
The lateral side of the brain.
A mid-sagittal cross section of the brain was made.
The right hemisphere and left hemispheres are connected by the corpus callosum, which is made up of fiber bundles. The corpus callosum transmits messages from each hemisphere.
Figure 3. The cerebrum, cerebellum, and brainstem (Mayfield Clinic, 2018)
The brain is composed of the cerebrum, cerebellum, and brainstem.
1.
The cerebrum consists of the left and right hemispheres, composing the majority of the brain. Each hemisphere controls the opposite side of the body. The right hemisphere is in charge of creativity and art, while the left hemisphere is in charge of speech, writing, and mathematical skills.
Figure 4. The frontal, parietal, occipital, and temporal lobes that compose the cerebrum (Mayfield Clinic, 2018)
The frontal lobe controls emotion, voluntary body movement, and cognitive skills. The parietal lobe manages sensory perception (taste, hearing, sight, touch, smell), interpreting signals from parts of the body. The occipital lobe is associated with vision. The temporal lobe is associated with auditory interpretation and memory, recognizing language.
2.
The cerebellum, which is located under the cerebrum, coordinates muscle movement and balance.
3.
The brainstem connects the cerebrum and cerebellum to the spinal cord, controlling automatic functions such as breathing, maintaining body temperature, heart rate, managing the circadian rhythm, etc.
Figure 5. The brainstem
The brainstem includes the midbrain, pons, and medulla. The midbrain (mesencephalon) is composed of neuron clusters and neural pathways, controlling various functions. The pons connects the midbrain and the medulla. The medulla connects the brain to the spinal cord, managing automatic processes.
Figure 6. Midsagittal view (WebMD, 2000)
The midsagittal cut reveals the cerebrum, pons, cerebellum, hypothalamus, pituitary gland, and other major structures of the brain. The pituitary gland produces and regulates the release of hormones that controls metabolism and growth.
A coronal cut was made.
The coronal view of the brain reveals the lateral ventricle (first and second ventricles) and third ventricle. The ventricles produce cerebrospinal fluids. The third ventricle is connected to the fourth ventricle, where the CSF flows through and reaches the spinal cord.
Figure 7. Coronal view (WebMD, 2000)
Additionally, inside the cranium, 12 pairs of cranial nerves (I olfactory nerve, II optic nerve, III oculomotor nerve, IV trochlear nerve, V trigeminal nerve, VI abducens, VII facial, VIII vestibulocochlear, IX glossopharyngeal, X vagus, XI accessory, XII hypoglossal) convey motor and sensory signals from the head and neck - two of which originate from the cerebrum and the rest which originate from the brainstem.
Figure 8. Cranial nerves (Medical News Today, 2013)
After observing the structures, the specimen was disposed in accordance to disposal guidelines.
References
human brain. (2018). Mayfieldclinic.com. https://mayfieldclinic.com/pe-anatbrain.htm
Brain Anatomy and How the Brain Works. (2021, July 14). Hopkinsmedicine.org. https://www.hopkinsmedicine.org/health/conditions-and-diseases/anatomy-of-the-brain
Anand. (2023, June 30). Brain Anatomy: Overview, Gross Anatomy: Cerebrum, Gross Anatomy: Cortex. Medscape.com; Medscape. https://emedicine.medscape.com/article/1898830-overview?form=fpf
Johnson, S. (2019, October 10). What are the 12 cranial nerves? Medicalnewstoday.com; Medical News Today. https://www.medicalnewstoday.com/articles/326621#diagram
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