Central Nervous Lab

We will explore the central nervous system and delve into the intricate structures of the cerebrum, diencephalon, cerebellum, brain stem, cranial nerves, and spinal cord. Additionally, you will have the unique opportunity to perform a brain dissection from a fetal pig, enhancing your understanding of these structures in a hands-on manner.

The central nervous system, composed of the brain and spinal cord, is a complex network of interconnected structures responsible for controlling and coordinating our body's functions. By studying the different regions of the brain, we can gain insight into how our senses, thoughts, movements, and emotions are processed and regulated.

Our exploration begins with the cerebrum, the largest and most intricate part of the brain. This region plays a crucial role in higher cognitive functions such as memory, language, perception, and conscious thought. By identifying the various lobes and sulci, you will gain a deeper understanding of how different areas of the cerebrum contribute to our daily experiences and behaviors.

We will investigate the diencephalon, a small but vital region located deep within the brain. Here, you will explore structures such as the thalamus and hypothalamus, which are responsible for relaying sensory information, regulating homeostasis, and controlling the endocrine system. Understanding the diencephalon's functions will provide insight into our sleep-wake cycles, hormone regulation, and emotional responses.

We will examine the cerebellum, located at the posterior part of the brain. Despite its relatively small size, the cerebellum plays a crucial role in coordinating movement, maintaining balance, and motor learning. By identifying its distinctive structures, you will develop an appreciation for the cerebellum's intricate role in our everyday physical activities.

We will then delve into the brain stem, a critical pathway connecting the brain to the spinal cord. The brain stem houses important structures such as the midbrain, pons, and medulla oblongata, which control vital functions like breathing, heart rate, and consciousness. Identifying these structures will deepen your understanding of the brain's fundamental control mechanisms.

We will examine the cranial nerves, which emerge from the brain and are responsible for transmitting sensory and motor information to and from different parts of the body. You will learn to identify these cranial nerves and understand their specific functions in sensory perception, motor control, and visceral activities.

We will embark on the brain dissection from a fetal pig, providing you with a hands-on experience to consolidate your knowledge. This dissection will allow you to explore the external and internal structures of the brain, reinforcing your understanding of the different regions and their interconnections. It will also serve as an opportunity to appreciate the anatomical similarities between human and porcine brains.

As the principal organ of the nervous system, the brain regulates many processes needed to maintain the dynamic internal balance of homeostasis. In this activity, you will be guided through the dissection and close examination of an adult mammalian brain. Although there are some differences between the specimen provided and a human brain, the structures and their relative locations are highly similar.

Objectives

·         To identify and locate the structures of the cerebrum, diencephalon, cerebellum, brain stem, cranial nerves, and spinal cord.

·         To understand the functions and roles of the different regions within the cerebrum, diencephalon, cerebellum, brain stem, cranial nerves, and spinal cord.

·         To appreciate the anatomical relationships and interconnections between these structures within the central nervous system.

·         To develop proficiency in anatomical terminology related to neuroanatomy.

·         To reinforce theoretical knowledge through a hands-on brain dissection from a fetal pig, thereby enhancing understanding of the structures studied.

·         To compare and contrast the similarities and differences between the human and porcine brain structures.

·         To practice proper laboratory techniques, including safety precautions and ethical handling of specimens.

·         To promote critical thinking and problem-solving skills through active engagement in the dissection process.

·         To cultivate a deeper appreciation for the complexity and significance of the central nervous system in regulating bodily functions, sensory perception, and cognitive processes.

Materials

·         Dissection kit

·         Fetal Pig

·         Large Dissecting tray

·         Camera

Brain Dissection

1.       Examine the dura mater, the white layer of connective tissue enveloping the brain. Pull on it gently with your forceps to examine its tough texture. Gently remove the dura by separating it from underlying structures with the wooden probe, taking care to leave all nerves intact. You may notice some web like material clinging to the surface of the brain. This is arachnoid space.

2.       Take a photo of a superior view of the brain. Then begin studying the external features of the intact mammalian brain.

a.   The most prominent features are the right and left hemispheres of the cerebrum. Note the sulci and gyri of the cerebral cortex. The two cerebral hemispheres are separated from one another by the medial longitudinal fissure.

b.   Identify the lobes of the cerebrum: frontal, parietal, temporal, and occipital.

c.        Posterior to the cerebrum, observe the smaller cerebellum.

3.       Position the brain inferior-side up, and take a photo. For orientation, locate the cerebrum and cerebellum.

a.   Locate the large, anteriorly situated pair of olfactory bulbs. These receive input from each olfactory nerve (I). Note their relationship to the pyriform lobe, which receives and processes olfactory information.

b.   Looking from an anterior to posterior direction, locate the optic nerves (II), optic chiasm, and optic tracts. (Note that only stumps of the optic nerves will be present.)

c.        Find the hypothalamus, located just posterior to the optic chiasm and anterior to the brain stem. (Although the pituitary is usually detached from the inferior portion of the hypothalamus when the brain is removed from the cranial cavity, occasionally this small gland or a fragment of it will remain. If so, gently remove the pituitary and set it aside.)

d.   Locate the brain stem. The medulla is the portion of the brain stem that is continuous with the spinal cord. The pons is located between the medulla and the midbrain, which is the most superior region of the brain stem. Note the pyramidal tracts of the medulla and the cerebral peduncles of the midbrain. Together, these structures link the cerebral cortex with the brain stem and spinal cord.

e.   Observe the oculomotor (III) and trochlear (IV) nerves. The oculomotor nerves should be visible as they emerge from the posterior region of the midbrain. The trochlear nerves (IV) are very small and emerge from the junction of the midbrain and the pons.

f.         Identify the trigeminal nerves (V), abducens nerves (VI), and facial nerves (VII), all of which emerge from the pons.

g.   Locate the junction of the pons and medulla. Here, you should see the emergence of the vestibulocochlear nerve (VIII).

h.   Examine the medulla from anterior to posterior, noting the locations of the glossopharyngeal (IX), vagus (X), spinal accessory (XI), and hypoglossal (XII) nerves.

4.       Position the brain superior-side up, and gently spread the cerebrum and cerebellum apart, so that the midbrain is exposed.

a.   Locate the corpora quadrigemina—the four mound-shaped structures projecting from the superior surface of the midbrain. The larger pair are the superior colliculi, and the smaller ones are the inferior colliculi.

b.   Anterior to the superior colliculi, note the pineal body.

5.       Position the brain superior-side up, and use the scalpel to cut the entire brain longitudinally along the medial longitudinal fissure. The incision will separate the brain into equal right and left halves.

6.       Take a photo of a medial view of the brain.

7.       locate and identify the following structures:

a.   The corpus callosum is the tract that links the right and left cerebral hemispheres. Along with the septum pellucidum, it comprises the boundaries of the right and left lateral ventricles.

b.   The thalamus lies inferior to the corpus callosum; the third ventricle lies between its two halves.

c.        The hypothalamus is inferior to the thalamus.

d.   The arbor vitae are the white matter network within the cerebellum. Note that the outer layer of the cerebellum consists of gray matter.

e.   The fourth ventricle lies between the cerebellum and the brain stem.

f.         From anterior to posterior, the brain stem consists of the midbrain with the corpora quadrigemina, including the superior colliculi; pons; and medulla. Recall that the medulla is continuous with the spinal cord.

g.       The pineal body lies between the thalamus and the superior colliculi.

Draw the brain below and label all of its parts.

Review Questions

1.       What is the role of the cerebellum in the Central Nervous System (CNS)?
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2.       How do the spinal cord and the brainstem differ in their function in the CNS?
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3.       How does damage to the primary motor cortex affect movement in the body?
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4.       Compare and contrast the functions of the thalamus and the hypothalamus in the CNS.
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5.       How does the CNS integrate information from multiple sensory modalities to create a cohesive perception of the external world?
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6.       How does the concept of neuroplasticity affect our understanding of the effects of injury and rehabilitation on the CNS?
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7.       What is the role of the corpus callosum in the CNS?
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8.       How do the sympathetic and parasympathetic nervous systems differ in their function in the CNS?
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9.       How does damage to the occipital lobe affect visual processing in the CNS?
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10.    Compare and contrast the functions of the prefrontal cortex and the limbic system in the CNS.
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