AP1, Lab 8

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HOW A T.E.N.S. UNIT BLOCKS PAIN TENS = Transcutaneous Electrical Nerve Stimulation � Every day, ordinary afferent sensory impulses enter the spinal cord at the posterior horns of the gray matter. Here they must pass through synapses before traveling up to the brain via ascending tracts of the spinal cord. Pain messages follow the same pathway. � Applying continuous or repetitive stimulation through the skin of an appropriate area using TENS ‘annoys’ the brain with a flood of sensory input. In response, the brain increases the frequency of impulses down the spinal cord to create IPSPs to “block” both the incoming messages from the skin as well as the pain messages. � Electrical stimulation of nerves using TENS also stimulates the release of endorphins so that fewer pain generating impulses reach the brain, so pain is not felt or at least is felt less. REFERRED PAIN � A painful sensation felt in a region of the body that is not the origin of the stimuli. � Usually, it’s a painful sensation of visceral origin felt in a somatic region of the body that is not the origin of the stimuli. Examples: 1. Heart attack – the origin of the impulses is the heart muscle but the pain is often felt in the upper chest, left side of the mandible, and on the medial surface of L arm. 2. Gallbladder and Liver – often felt at the top of the R shoulder. 3. Kidney and Ureters – often felt in the lower back. � Happens because the visceral and somatic sensory neurons converge on the same ascending tracts of the spinal cord. When messages arrive on these tracts the brain can’t always distinguish between the two points of origin. PHANTOM PAIN � The sensation of pain experienced in a body part you no longer have – a missing foot, leg, arm, etc. � The brain receives no sensory information from the missing limb to inhibit pain sensations. If an action potential is initiated anywhere along the neuronal pathway from the severed limb, the idea of pain will be projected back to the missing limb even though the limb is not there. Revised 5-3-2012 8
Dissection of Cow Brain with Dura Mater � Use images from the dissection manuals in lab and your knowledge of the brain to identify the following. Recall the functions of those with an *. � Your group will be evaluated on the quality of your dissection. FOLLOW INSTRUCTIONS CAREFULLY. 1. Glove up – your choice of latex or polyethylene. 2. Safety – practice caution with the knives and other implements. 3. Housekeeping (Your mother does not work here, kindly clean up after yourself) – Don’t put pieces of tissue in the sink. If you notice, there is no garbage disposal. At the end of lab, we will put brains back in the bag. Don’t get “slime” on the brain models. When you are finished, wash everything and return it where you found it. 4. Open your bag and rinse away as much preservative as possible. Observe the dull white DURA MATER covering the surface of the brain. 5. The two, large fatty masses dangling from the anterior and inferior surface are the tissues that were behind the eyes. Find the two OPTIC NERVES in these and then cut the fatty mass off. 6. Use scissors to cut away the superior 90% of the DURA MATER. Leave the bottom portion intact as it will contain the pituitary gland. The ARACHNOID LAYER will come off with the dura mater leaving only the PIA MATER on the surface of the brain. 7. Observe the LONGITUDINAL and TRANSVERSE FISSURES containing DURAL SINUSES as you remove the dura mater. What occurs at your dural sinuses? _______________ 1. Identify the following externally visible structures while the brain is still whole. No cutting necessary. CEREBRUM L and R CEREBRAL HEMISPHERES Various SULCI & GYRI OLFACTORY BULBS and OLFACTORY TRACTS. This is CRANIAL NERVE #1 carrying sensory messages to the brain for the sense of smell. Observe the delicate PIA MATER anchoring blood vessels to the cerebrum mostly in the sulci. These vessels are dark brown/black in color. CEREBELLUM OPTIC NERVES and OPTIC CHIASMA. Cut the optic nerves (cranial nerve #2) and other motor nerves as far out as you can clearly see them to get rid of those dangling lumps of fatty tissue that were located behind the eyes. Pituitary gland - usually appears as a nodule or “lump” approximately ¼ inch in diameter on the ventral side of the brain.) TRIGEMINAL NERVES - The lateral edges of the dura mater containing the pituitary gland also contain the large trigeminal nerves (cranial nerve #5). Cut the nerves near the dura mater to leave stumps on the lateral walls of the pons. Remove the dura mater containing any branches of this nerve but do not remove the pituitary gland. Revised 5-3-2012 9
Page 1 and 2: AP1, Lab 8 - Central Nervous System
Page 3 and 4: 12 pairs of cranial nerves are asso
Page 5 and 6: Vestibulocochlear Nerve (VIII): Sen
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AP1, Lab 8

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