Sheep Brain Dissection

Transcription

1 Sheep Brain Dissection s%29/sheep+organs/preserved+sheep+dissection.do Michigan State University Neuroscience Program Brain Bee Enrichment Workshop October 6, 2012 Material and information from this handout was adapted from the following sources: Barnard College: Neuroscience: Exploring the Brain, Bear et al., 2007 The Sheep Brain: A Basic Guide, Cooley & Vanderwolf, 1979 BrainFacts.org

2 Introduction to anatomical terms Dorsal (Latin: dorsum = back): the top of the brain Ventral (Latin: venter = belly): the underside of the brain Anterior: front of the brain Posterior: back of the brain Coronal cuts: parallel to the anterior/posterior axis Horizontal cuts: parallel to the dorsal/ventral axis Medial: towards the midline Lateral: towards the side Sagittal cuts: parallel to the medial/lateral axis

3 Surface structures of the brain There are many structures of the brain that can be identified on the surface of the brain. Locate the structures below (illustrated on the following page) and try to identify the functions of such areas. **Be sure to ask your volunteer to help you if you need help associating functions to different brain areas. Sulcus (plural: sulci); the hills Gyrus (plural: gyri); the valleys Medial longitudinal fissure Central sulcus (aka Sylvian fissure) Cerebrum Match the following structures with their functions: Structures Cerebellum Medulla Pons Functions Controls respiration, blood glucose levels, and heart rhythms Receives sensory info & sends it to the brain, but also receives motor info from the brain and sends it to the limbs Involved in motor learning and timing of movements Spinal cord Includes tracts that conduct signals from the cerebrum down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus Olfactory bulbs What is the function of the olfactory bulbs? Compare the size of the olfactory bulbs in a sheep relative to the total brain size compared to the olfactory bulbs in a human brain. What could account for the size differences in the olfactory bulbs when comparing different species?

4 Parietal Lobe Temporal Lobe Primary Motor Cortex Occipital Lobe Primary Sensory Cortex Frontal Lobe

5 The cerebral cortex can be divided into 4 lobes. Identify each of these lobes and associate the different functions listed below with the correct lobe of the brain (each lobe many have multiple functions from the list). A. Processing auditory information B. Initiating and coordinating motor movements C. Processing sensory information D. Problem solving and planning E. Visual processing F. Attention and Language G. Personality H. Short-term memory and learned emotional responses Frontal lobe A portion of the frontal lobe is defined as the primary motor cortex. Locate this structure on the sheep brain. What is the role of the motor cortex? Parietal lobe A portion of the parietal lobe is defined as the primary sensory cortex What would happen if we were to electrically stimulate this area in a sheep that was alive? The entire surface of the body is represented in the primary sensory cortex. Interestingly, some parts of the body have more cortical space that others. The figure below (right) is known as the homunculus and illustrates what the body would look like based on the amount of cortical space devoted to each body region (larger body regions have more cortical space). What parts of the body do think are more sensitive to touch based on this figure? Occipital lobe Temporal lobe

6 Ventral view of the brain Mammals have 12 pairs of cranial nerves. Some of these nerves are sensory nerves, other are motor nerves, and some are both sensory and motor (mixed). Locate these 12 nerves on your sheep brain, match each function with its associated nerve, and circle whether each nerve is sensory, motor, or both. A. Controls muscles of the tongue B. Control muscles of the neck and shoulder C. Vision D. Eye movements; pupillary constriction E. Eye movements F. Eye movements G. Smell H. Sensations of the skin, muscles and teeth; controls biting and chewing I. Mediates visceral sensations; Innervates larynx, pharynx, gastrointestinal and cardiovascular systems J. Hearing and sense of balance K. Taste and motor movements of the throat L. Taste, movements of the face, winking, smiling, secretion of tears I. Olfactory Nerve What would happen if we were to damage the olfactory nerve in a living sheep? (Sensory/Motor/Mixed) II. Optic Nerve You may notice that each optic nerve (containing axons of ganglion cells from a single eye) converge at the optic chiasm. What is happening here? (Sensory/Motor/ Mixed) III. Oculomotor Nerve Based on the naming of this nerve, what do you think the function is? (Sensory/Motor/ Mixed) IV. Trochlear Nerve (Sensory/Motor/ Mixed) V. Trigeminal Nerve (Sensory/Motor/ Mixed) VI. VII. Abducens Nerve (Sensory/Motor/ Mixed) Facial Nerve (Sensory/Motor/ Mixed) VIII. Vestibulo-cochlear (Auditory) Nerve (Sensory/Motor/ Mixed) IX. Glossopharyngeal Nerve (Sensory/Motor/ Mixed) X. Vagus Nerve (Sensory/Motor/ Mixed) XI. XII. Spinal Accessory Nerve (Sensory/Motor/ Mixed) Hypoglossal Nerve (Sensory/Motor/ Mixed)

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8 White versus gray matter You may notice that some areas of the brain are white (e.g. optic nerve; white matter), while others are a darker color (more ivory or gray; gray matter). What could account for these differences? Think about the different components of a neuron (see diagram below) and how this may influence the color differences you see. Also, many of the white structures you see are nerves. What part of the neuron makes up nerves? Diseases of the nervous system: Multiple sclerosis (MS) MS is an autoimmune disorder that is caused by the body s own immune system attacking the myelin sheath of axons. Why is the loss of myelin a problem? Two common areas that are damaged in MS are the optic tract and the cerebellum. What kinds of symptoms may patients with MS have based on this information?

9 Midline view of the brain We will now be making the first cut to observe some medial structures of the brain. Place the brain in the dissection pan and cut down the longitudinal fissure, the sulcus that marks the separation of the left and right cerebral hemispheres. Try to make a single smooth cut down the middle. Margaret Bell, MSU Identify the structures in bold and match them with their associated function (listed below) A. Little brain ; balance and motor learning B. Relay station of the brain; relays sensory, spatial, and motor information to the cortex C. Consists of the superior and inferior colliculi (receive visual and auditory information); Contains nuclei that regulate reward mechanisms and mood D. Receives sensory information and sends it to the brain, but also receives motor information from the brain and sends it to the limbs E. Bridge ; Connects midbrain to the medulla F. Connects the left and right hemisphere G. Links the nervous system to the endocrine system; controls body temperature, hunger, thirst, fatigue, sleep, & circadian rhythms H. Autonomic functions such as respiration, heart rate, blood pressure I. Endocrine gland; main site of melatonin production Corpus callosum If this structure was cut in a living sheep, what wouldn t be able to take place? Thalamus Hypothalamus Pineal body

10 Midbrain Pons Medulla Spinal cord Cerebellum The ventricular system (Lateral ventricle, Third ventricle, Cerebral aqueduct, Fourth ventricle) The brain contains multiple cavities or chambers filled with cerebrospinal fluid (CSF). What do you think is the purpose of this fluid in the brain? Besides filling the ventricles, CSF also surrounds the brain. Why might this be beneficial?

11 Coronal Sections Now put the two halves of the brain together to make three coronal cuts (shown below) and locate the labeled structures. Cut #1 - Through the anterior portion of the corpus callosum Cut #1 Lateral Ventricle The caudate nucleus and putamen are part of the basal ganglia. What is the primary function of the basal ganglia? What neurodegenerative disease is associated with a loss of dopamine neurons that project to the basal ganglia?

12 Cut #2 Through the thalamus and hypothalamus Cut #2 What is the function of the hippocampus? What is the name of a neurodegenerative disease that effects this structure? Cut #3 Through the caudal end of the cerebrum (anterior to the cerebellum), through the superior colliculus and in between the midbrain and the pons Cut #3

13 Hippocampal formation and dorsal brainstem Observe the sheep brain that has had the cerebellum and the caudal portion of the cerebral cortex removed. Find the structures labeled in the figure below.