Wednesday, February 11, 2009 Lecture

After our test over the CNS, the lecture consisted of learning about the remaining cranial nerves and then an introduction into the peripheral nervous system. 3 important terms that pertain to our senses include: smell=olfaction, hearing=auditory, taste=gustation. The cranial nerves are ordered by roman numerals from the anterior to the posterior part of the base of the brain. They include: I olfactory, II optic, III oculomotor, IV trochlear, V Trigeminal, VI Abducens, VII Facial, VIII Vestibulocochlear, IX Glossopharyngeal, X Vagus, XI Accessory, XII Hypoglossal. We learnt the entry and exit points of each nerve through the skull, as well as the function of the nerve. It is important to note that sensory nerves are afferent nerves (toward the brain) and motor nerves are efferent (away from the brain). There are also mixed cranial nerves that have sensory, motor, and/or autonomic functions. If cranial nerves are mixed and have autonomic fibers, they are always parasympathetic axons. Our brief introduction to the Autonomic Nervous System described the parts of the neuron that lead from the CNS to the target. (Nerves from the ventral horns of the spinal cord deal with motor impulses.) Between the CNS and the target there are always TWO NEURONS. There is a ganglion (bundle of fibers) that stretches to the target cell. The first neuron is the preganglionic neuron and the second is the postganglionic neuron. The parasympathetic system has 3 types of targets: smooth muscle, cardiac muscle, and glands. There are also two types of receptors on the dendrites of the neurons. 1) nicotinic receptors: which increase the level of activity, cause target to be excited, and 2)muscarinic: cause an inhibatory effect on target. The first neuron from the CNS always releases the excitatory neurotransmitter acetylcholine ACh, therefore the dendrites on the postganglionic must be nicotinic. The action potential from the postganglionic neuron will then determine the effect on the target.
The majority of people today have to get their wisdom teeth (third molars) extracted to avoid their teeth from becoming impacted. If you have had your wisdom teeth taken out you know that your jaw and lips are numb for quite some time following the procedure. I researched the nerves involved in the extraction of wisdom teeth and found that they numb the lingual nerve, which branches off of the mandibular nerve of the trigeminal nerve (cranial nerve V3). This nerve provides sensation for the lower lip, teeth and gums. The maxillary branch (V2) of the Trigeminal (V) nerve provides sensation to the superior lip, teeth, and gums. To quote a site which explained the procedure of numbing nerves, "In regional anesthesia, a numbing medication is injected around the nerves that transmit pain signals from the area involved in the surgery. The procedure “blocks” the nerves, ensuring that you will not feel pain during or immediately after surgery."