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Neuroanatomy of Cranial Nerves

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1 Neuroanatomy of Cranial Nerves

2 Information processing/Interneurons
Overview CNS Brain and Spinal Cord Information processing/Interneurons PNS Nerves Sensory/Afferent Motor/Efferent Examples of each Recall that we have anatomically, PNS, CNS is specifically brain and spinal cord. On the sensory side, receptors, these fibers are all called afferent, going towards the central nervous system, can divide sensations into two main categories, special sensories are defined as vision, hearing, equilibrium, taste and smell, those are the special senses. General senses can be coming from outside world, touch, temp, pain, pressure. Same thing could be coming from internal structures, not usually as clearly defined in the brain or localized, c an feel pain and signals you are not aware of, visceral afferent. Also mention that on the somatic side have proprioceptors, which are the muscle spindles in the muscles, golgi tendon organs and so forth, monitoring positions of joints and muscles, body positions, all is general sensory, afferent. On the efferent side, motor commands coming out of the central nervous system basically, somatic motor, motor to skeletal muscles, visceral motor is motor to smooth muscles and glands, can put cardiac muscle in there, to pace maker and so forth, that whole category is autonomic nervous system, generally involuntary, somatic motor is generally voluntary, but really muscle type that is responsible for that. Functional component of phrenic is GSE, somatic motor, not GVE. General Sensory (Somatic and Visceral) Special Sensory Somatic Motor Visceral Motor (ANS) EFFECTORS RECEPTORS

3 Functional Components of Nerves
General sensory Somatic sensory (GSA) Visceral sensory (GVA) Special sensory (SSA, SVA) Somatic motor (GSE) Branchial motor (SVE) to skeletal muscles derived from branchial arches Somatic motor (GSE) to skeletal muscles derived from other sources Visceral motor (GVE) to smooth muscle and glands General somatic afferent Functional components of nerves. What we mean by that, what type of fibers are traveling in a given nerve. Put pin in nerve and ask for functional component. Depending on if at beginning of nerve different answer than out at branches. Say we had a pin in the infraorbital nerve, and said what are the functional components at this point, would say its GSA, general sensory, at that point, infraorbital, that nerve, all fibers in there are general sensory, to skin in that area. Divide this into four categories in this course. General sensory includes somatic and visceral sensory, not specifying that. If you are going to use the letters, know what the letters stand for! GSA General somatic afferent, also GVA, general visceral afferent. G or S, general or special, second has to do with somatic or visceral, and third is either A or E, afferent, sensory, or efferent, motor. Special sensory, doesn’t matter if its special somatic of visceral. Vision and hearing, and equlib are somatic afferents, bringing the outside world in, taste and smell counted as special visceral afferent because taste and smell related to digestion, but no need to know that. On the somatic motor side, motor to skeletal muscle, that’s all I’m expecting that you know, but realize that that is subdivided into branchial motor, specifically has to do with the fibers of neurons innervating muscles derived from branchial arches. From arch 2, muscles of facial expression, those would be branchial motor, SVE, special visceral efferent, but somatic motor is good enough, neurons innervating skeletal muscle. Liebgott does mention branchial motor though. Somatic motor is all other skeletal muscle.

4 Cranial Nerves Carry 1-4 functional components General sensory
Special sensory Somatic motor Visceral motor Martini et al Cranial nerves all come off of the brain as opposed to spinal nerve, similar in many ways. Main difference is that cranial nerves carry one to four of possible functional components, some are all the same all nerve fibers doing the same thing others are mixed. What is the typical spinal nerve? Three functional components, general sensory, somatic motor and visceral motor for spinal nerves, the additional one with cranial nerves is that some carry special senses, only carried in cranial nerves. Tomorrow’s lecture is brain and cranial nerves, will learn about cranial nerves as they come off of base of brain.

5 What to Know About Cranial Nerves
Name and Number Origin from brain Functional components Location of cell bodies Nucleus Ganglion Foramen of exit from cranial cavity Distribution: branches, targets, and functions Testing and lesions What else is there to know, but not for midterm! Just be thinking ultimately at the end of the course, what to know about each cranial nerve. First thing is the name and the number, the numbers are roman numerals, prefer that system, although I wont mark you off. Names, get a good handle on the names and numbers, various pneumonics, but sooner rather than later know them. For the midterm, know the origin from the brain, tomorrow’s lecture, what part of the brain does it come off of. Ultimately want to know the functional components by each cranial nerve, talk about that more today, another thing today, know the locations of the cell bodies of the neurons in that cranial nerve. Already expected to know foramen through which the cranial nerve exits the cranial cavity. That means not only recognize that opening in a boney skull but recognize them in the cadaver as they go under the meninges. Ultimately know the branches of each of the cranial nerves, target, what's being innervated and the functions of individual branches. Quite a few of the cranial nerves don’t have a lot of branches, a few have a lot like trigeminal and facial. Need to know those specific branches, ultimately expect you to be able to test cranial nerves to see if they are functional. Should have idea of what a lesion to a CN what the symptoms would be. If you want to test facial nerve, smile, close eye, etc. As course goes on, be giving you questions where we describe some symptoms related to damage to a CN, expect you to know which CN that is. At this point, know names numbers, where they come off brain, where they exit through cranial cavity. Going to start talking about the functional components.

6 Cell Bodies of Cranial Nerves
General sensory neurons – in a sensory ganglion (no synapses, pseudounipolar) Special sensory neurons – in a sensory ganglion or in the sensory organ Somatic motor neurons – in a nucleus Visceral motor neurons– Preganglionic – in a nucleus Postganglionic – in an autonomic ganglion (synapses) Where are the cell bodies of the neurons in the cranial nerves? General rule is that for general sensory neuron, the cell bodies are in a sensory ganglion, what is the name of that for the spinal cord? Dorsal root ganglion, for CN we also have sensory ganglion but not every one has one only those with general sensory, biggest ganglion is the trigeminal ganglion because the trigeminal nerve has a large distribution of general sensory neurons. The cell bodies would be in the trigeminal ganglion, pseudounipolar neurons. Sensory neuron in a peripheral nerve has a receptor out somewhere, pesuedounipolar cell body in ganglion, then goes into the CNS and synapse on another neuron there, and that goes on. What would you call the collection of cell bodies in the CNS where it synapses? A nucleus Peripheral nerve has cell body in a sensory ganglion, but then there is a synapse in a sensory nucleus. Special sensory neurons, same set up basically, couple of exceptions because cell bodies for special sensory for vision are in retina, and for olfaction in olfactory epithelium, but for taste and hearing in sensory ganglion. For motor side, somatic motor neurons cell bodies are in CNS, go out to synapse on skeletal muscle. Collection of cell bodies of motor neurons for CN are a nucleus. For each cranial nerve with a motor component, eventually learn name of motor nucleus. Most of the time the name is motor nucleus of the For the visceral motor neurons, essentially being motor, first cell body in the CNS in a nucleus, and then there is a synapse on a second neuron that goes to the target, so smooth muscle or gland. In this case, first preganglionic neurons, cell bodies in a nucleus in CNS, and post ganglion is in a ganglion.

7 General Sensory Pathways
Neurons Primary/peripheral Secondary Tertiary (cell body in thalamus) Spinal nerve and cranial nerve, same thing, receptor in the skin or proprioception, cell body in sensory ganglion, then go in to CNS and synapse on secondary neuron who’s cell body is in a nucleus, that would project up to synapse on a tertiary neuron with cell body in thalamus, thalamus is area of the brain where all of the sensory neurons synapse, all sensations except smell, but every other thing, all relay through the thalamus, synapse there, then tertiary neuron goes to sensory cortex, should be familiar with already. L 1-23

8 Voluntary Motor Pathway
AKA Pyramidal system Upper motor neurons Lower motor neurons Typical voluntary motor pathway, aka pyramidal system, because fibers all pass through pyramid of medulla. Primary neuron cell body in motor cortex, that descends through tract down, if its going to spinal chord, then goes to corticospinal tract, to brain stem nucleus then corticobulbar, but wont ask you that, synapse on cell body in the CN nucleus, and motor fibers out in cranial nerve. There are multiple motor pathways, extrapyramidal pathways. But basic point L Fig 1-23

9 VIII Vestibulocochlear IX Glossopharyngeal X Vagus XI Spinal accessory
I Olfactory II Optic III Oculomotor IV Trochlear V Trigeminal VI Abducens VII Facial VIII Vestibulocochlear IX Glossopharyngeal X Vagus XI Spinal accessory XII Hypoglossal Don’t just memorize this picture, only divides into sensory and motor. As cranial nerves come off of brain from front to back, 1 to 12, helps to identify. Oculomotor, eye, motor moves the eye. Moving the eye is one but there are two other cranial nerves that have to do with moving the eye, Trochlear, innervates one muscle. Abducens, innervates the one muscle that abducts the eye, makes it look to the side. Trigeminal, why that? Three divisions, main branches. V1 2 3, V refers to roman numeral 5. VII facial, muscles of facial expression. Vestibulocochlear, vestibular apparatus, equilibrium and cochlear, hearing. Glossopharyngeal, tongue and pharynx. Vagus, root of that is wanderer, vagabond? Spinal accessory, because it arises from spinal chord, CN because it came up through foramen magnum, when out through cranial base, through jugular foramen, coming out of cranial foramina it’s a cranial nerve, but nothing special. Hypoglossal, named because it comes in under the tongue.

10 Special Sensory CN I – Olfactory (olfaction) CN II – Optic (vision)
CN VIII – Vestibulocochlear (hearing, equilibrium) CN’s VII, IX, X - taste Grouping CN into categories, start thinking about them in their categories by function. CN that carry special sensory components, three of them, olfactory optic and Vestibulocochlear carry only special sensory fibers. Whole nerve is functioning is in special sensation. Other special sense, taste, fibers for taste in three cranial nerves, , learn ultimately, that 7 9 and 10 carry all four functional components, when they come out of the brain, have neurons for all four of the possible functional components.

11 General Sensory CN V – Trigeminal
Sensory neuron cell bodies in trigeminal ganglion Other cranial nerves with general sensory fibers – CN’s VII, IX, and X General sensory, cell bodies in a sensory ganglion like trigeminal. Biggest is trigeminal, responsible for a lot of general sensation, face and deeper structures, including everything in orbit, nasal cavity, oral cavity, all the teeth, all trigeminal sensation. Ophthalmic division totally general sensory, when it leaves the ganglion only general sensory, likewise the maxillary, only general sensory, mandibular has general sensory and also some somatic motor. Other CN with general sensory are , amount in 7 is small, general sensory to a bit of skin in external auditory meatus. Herpes zoster, lives in sensory ganglion, becomes active, comes down the nerve to area served by those fibers, herpes zoster of facial manifested by vesicle in that external auditory meatus for 7.

12 Somatic Motor CN’s III, IV and VI ocular muscles
CN XI SCM and trapezius CN XII tongue muscles CN V3 (arch I) muscles of mastication, etc. CN VII (arch II) m’s of facial expression, etc. CN IX (arch III) stylopharyngeus CN X (arches IV, VI) m’s of soft palate, pharynx, and larynx Put muscles into groups, always exceptions, but general rule, easier to remember. Oculomotor, Trochlear and Abducens supply ocular muscles, voluntarily move eye. Cranial 11, only somatic motor to two muscles, SCM and Trapezius, CN 12, hypoglossal, only tongue muscles. Next four are arch derived branchial motor, V3, mandibular division of trigeminal, muscles of mastication, basically supplies muscles that attach to the mandible or were associated with first arch. Two muscles that are supplied by mandibular division of trigeminal, Mylohyoid and anterior belly of digastric both attaching to mandible. Posterior belly of digastric and Stylohyoid are innervated by facial because they were derived from second arch. CN 9 has some somatic motor to one muscle, only one muscle derived from 3rd branchial arch, don’t need to know stylopharyngeus yet. CN 10 takes care for skeletal muscle those derived from arches 4 and 6, includes muscle of soft palate, pharynx and larynx. Already know the Vagus’s branches to the larynx, two, one to fourth arch and one to 6th arch. First one is superior laryngeal, branches into internal and external and the other was the recurrent, branches of the vagus to the larynx, for the muscles.

13 Visceral Motor (Parasympathetic)
CN’s III, VII, IX, X Ganglia: Targets: Postganglionic parasympathetics tend to follow branches of the trigeminal nerve. Visceral motor fibers, autonomic nervous system divided into sympathetic and parasympathetic, both visceral motor, similar targets, smooth muscle, glands, but origins are different. Parasympathetic from craniosacral, cranio part now, some cranial nerves carry preganglionic parasympathetic fibers, four of them. Shown here, CN Oculomotor, facial 7 9 and 10 carry everything, for parasympathetics, , carry preganglionic parasympathetic fibers, rule is that they have to synapse somewhere, in ganglion, then post ganglion to the target. You will learn names of ganglia not now though. Targets in the head, smooth muscle and glands, parotid gland, salivary glands, lacrimal gland, glands in nose, smooth muscle such as iris, constricts pupil, cilliary muscle changing shape of lens, will learn later. One general rule that we will learn is that post ganglionic parasympathetic coming out of ganglia follow branches of trigeminal nerve because its going almost everywhere in the head most of these parasympathetic ganglia are closely related to some branch of the trigeminal ganglia. L 1-25

14 Sympathetics to the Head
Origin: Ganglia: Targets: Postganglionic sympathetics follow branches of carotid arteries (in a perivascular plexus) Sympathetics originate coricolumbar, no sympathetic as part of cranial nerves, all come out of spinal cord. Ganglia in sympathetic trunk, to get ot head, preganglionic come up in sympathetic trunk, and synapse in cervical ganglion, for head in superior cervical ganglion, and post ganglionic travel to the head on the walls of blood vessels, on the branches of carotid, internal, external, get to all of the structures in the head that need sympathetics. What needs sympathetics? Smooth muscle in eye, salivary glands, sweat glands and blood vessel walls. Relative to quiz, specific answer for questions about sweat glands in neck, notice the superior cervical ganglion, gray communicating rami coming off to join spinal, 4 come off of superior cervical ganglion, what cervical spinal nerves innervate skin of neck, supraclavicular, what spinal nerves C1 – C4, superior cervical ganglion would be the most specific answer, in practical, if we put in, most specific answer you can give. L 1-26

15 CN’s Carrying All Four Functional Components

16 Branches of Cranial Nerves May Serve Different Functions
Concept of branches of cranial nerves, different functions. Just because the cranial nerve, when it comes out of the brain may have a number of functional components, they don’t all go to every target, each nerve fiber, neuron has a target. For example, mandibular division of trigeminal, when it comes through, general sensory neurons and somatic motor neurons in it, so the mandibular division of trigeminal exiting through foramen ovale, see different branches. Some of the branches will carry motor fibers, for example, branches to temporalis muscle, those have somatic motor, other branches like long buccal, carrying general sensory, looks like its innervating buccinator, but what supplies buccinator? Facial nerve, so you need to know eventually, the concept is that when nerves branch, not all of the branches have all of the functions in them, some of the motor neurons go to muscles and sensory continue to mucus membrane or skin. What about that branch going through mental foramen, that is the mental nerve, what functional components at that point in the nerve? General sensory, supplying skin, mucus membrane, and before that supplies teeth. One other thing, this parasympathetic ganglion here, Submandibular ganglion, hanging off of branch of trigeminal nerve, what you have to do is follow it back up and realize its not a branch of the trigeminal, some other nerve joins it, later find out that sometimes, branch of facial nerve joining branch of trigeminal and running together!. Focus each time when you learn a nerve what the functions of that specific nerve are. V3 Netter Plate 42

17 References Regional anatomy – Liebgott Chapter 7
Systemic anatomy – Liebgott Chapter 8 Images – Netter Plates

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