General Concepts for Head and Neck Anatomy

General concepts for Head and Neck Anatomy Nervous Tissue • • Controls and integrates all body activities within limits that maintain life Three basic functions 1. sensing changes with sensory receptors 2. interpreting and remembering those changes 3. reacting to those changes with effectors (motor function) 2 Cranial nerves 12 pairs Spinal nerves 31 pairs The PNS is divided into : 1- Somatic nervous system (SNS) 2- Autonomic nervous system (ANS) Sensory (Afferent) vs. Motor (Efferent) sensory (afferent) nerve (pseudo-) unipolar neurons conducting impulses from sensory organs to the CNS e.g., skin motor (efferent) nerve multipolar neurons conducting impulses from the CNS to effector organs (muscles & glands) e.g., muscle Organization Sensory Integration Motor SNS (Motor) SNS (Sensory) Brain ANS (Sensory) Spinal cord ANS (Motor) 6 Neurons • Dendrites: carry nerve impulses toward cell body • Axon: carries impulses away from cell body • Synapses: site of communication between neurons using chemical neurotransmitters • Myelin & myelin sheath: lipoprotein covering that increases axonal conduction velocity dendrites cell body axon with myelin sheath synapses 1. Multipolar neurons ➢ Usually have several dendrites and one axon ➢ Motor neurons 2. Bipolar neurons ➢ Have one main dendrite and one axon ➢ The retina of the eye 3. Unipolar neurons (pseudounipolar neurons) ➢ Sensory neurons Sensory (Afferent) vs. Motor (Efferent) sensory (afferent) nerve (pseudo-) unipolar neurons conducting impulses from sensory organs to the CNS e.g., skin motor (efferent) nerve multipolar neurons conducting impulses from the CNS to effector organs (muscles & glands) e.g., muscle Clusters of Neuronal Cell Bodies 1. 2. Transverse section of spinal cord Ganglion (plural is ganglia) a cluster of neuronal cell bodies located in the PNS. Nucleus (plural is nuclei) : a cluster of neuronal cell bodies located in the CNS. Bundles of Axons A nerve: is a bundle of axons that is located in the PNS. ➢Cranial nerves connect the brain to the periphery ➢ Spinal nerves connect the spinal cord to the periphery A tract: is a bundle of axons located in the CNS. Coronal section of brain Bundles of Axons dorsal root ventral root spinal nerve Structure of Spinal Nerves: Somatic Pathways dorsal root dorsal ramus Sensory ganglion spinal nerve somatic sensory nerve ventral ramus ventral root Mixed Spinal Nerve somatic motor nerve Structure of Spinal Nerves: Dorsal & Ventral Rami dorsal root dorsal ramus Sensory ganglion spinal nerve Territory of Dorsal Rami (everything else, but head, innervated by ventral rami) somatic sensory nerve ventral ramus somatic motor nerve Autonomic nervous system • ANS is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control • Visceral motor innervates nonskeletal (non-somatic) muscles • Composed of a special group of neurons serving: – Cardiac muscle (the heart) – Smooth muscle (walls of viscera and blood vessels) – Glands glands smooth muscle cardiac muscle 14 Divisions of the autonomic nervous system • Parasympathetic division • Sympathetic division Serve most of the same organs but cause opposing or antagonistic effects Parasysmpathetic: routine maintenance “rest &digest” Sympathetic: mobilization & increased metabolism “fight, flight or fright” or “fight, flight or freeze” 15 Basic anatomical difference between the motor pathways of the voluntary somatic nervous system (to skeletal muscles) and those of the autonomic nervous system • Somatic division: – Cell bodies of motor neurons reside in CNS (brain or spinal cord) – Their axons (sheathed in spinal nerves) extend all the way to their skeletal muscles • Autonomic system: chains of two motor neurons – 1st = preganglionic neuron (cell body in brain or cord) – 2nd = postgangionic neuron (cell body in ganglion outside CNS) 16 • Axon of 1st (preganglionic) neuron leaves CNS to synapse with the 2nd (ganglionic) neuron • Axon of 2nd (postganglionic) neuron extends to the organ it serves This dorsal root ganglion is sensory This autonomic ganglion is motor Autonomic Somatic Diagram contrasts somatic and autonomic 17 Ganglia • Ganglia Are Masses Of Neuronal Cell bodies, Usually Defined As Being Outside The Central Nervous System. They Seem To Act As Coordinating Way Stations. • Two type Ganglia: • 1. Sensory. 2. Autonomic 18 Sensory ganglion Sensory ganglia do not receive synapses 19 Autonomic ganglion Autonomic ganglia do contain synapses 20 Autonomic Nervous System Similarities between Sympathetic & Parasympathetic • Both are efferent (motor) systems: “visceromotor” • Both involve regulation of the “internal” environment generally outside of our conscious control: “autonomous” • Both involve 2 neurons that synapse in a peripheral ganglion • Innervate glands, smooth muscle, cardiac muscle glands CNS ganglion smooth muscle preganglionic neuron postganglionic neuron cardiac muscle Autonomic Nervous System Differences between Sympathetic & Parasympathetic Relative Lengths of Neurons Sympathetic CNS target ganglion short preganglionic neuron long postganglionic neuron Parasympathetic ganglion CNS long preganglionic neuron target short postganglionic neuron Autonomic Nervous System Differences between Sympathetic & Parasympathetic Location of Preganglionic Cell Bodies Sympathetic Parasympathetic Thoracolumbar Craniosacral T1 – L2 levels of the spinal cord Brain: CN III, VII, IX, X Spinal cord: S2 – S4 vasomotor secretomotor Structure of Spinal Nerves: Somatic Pathways dorsal root dorsal ramus Sensory ganglion spinal nerve ventral ramus ventral root Mixed Spinal Nerve Structure of spinal nerves: Sympathetic pathways dorsal ramus spinal nerve ventral ramus gray ramus communicans sympathetic ganglion white ramus communicans Sympathetic ganglia are the ganglia of the sympathetic nervous system They are located close to and on either side of the spinal cord in long chains Spans from the base of the skull to the coccyx There are usually 22-23 pairs of paravertebral sympathetic ganglia: 3 in the cervical region (cervical ganglia) 11 in the thoracic region 4 in the lumbar region 4-5 in the sacral region 1 unpaired coccygeal ganglion Preganglionic nerves from the spinal cord synapse at one of the chain ganglia, and the postganglionic fiber extends to an effector Sympathetic Innervation to the Head and Neck Located anterior to the C1-4 vertebrae. The sympathetic fibers synapse with this ganglion, with post ganglionic fibers hitch-hike along arteries in the head and neck (and their branches) in order to reach their target organs. Sympathetic Innervation to the Head and Neck ✓ The oculomotor, facial, glossopharyngeal and vagus nerves carry the parasympathetic fibers out of the brain. ✓ Then, the parasympathetic fibers synapse in a peripheral parasympathetic ganglion Parasympathetic ganglia lie near or within the organs they innervate ✓ From the ganglia, post-ganglionic parasympathetic fibres continue to the organs in the head and neck, providing parasympathetic innervation. Parasympathetic ganglia in the head and neck: 1- Ciliary ganglion (sphincter pupillae, ciliary muscle) 3rd 2- Pterygopalatine ganglion (lacrimal gland, glands of nasal cavity) 7th 3- Submandibular ganglion (submandibular and sublingual glands) 7th 4- Otic ganglion (parotid gland) 9th Cranial nerves The numbering of the cranial nerves is based on the order in which they emerge from the brain, front to back Foramina of skull and cranial nerves passing through 1. Olfactory nerve Component: sensory Function: smell Origin: Olfactory receptor nerve cells Opening of the Skull: Openings in cribriform plate of ethmoid 2. Optic nerve Component: sensory Function: vision Origin: Back of the eyeball Opening of the Skull: Optic canal 3. Oculomotor nerve Contains parasympathetic Component: motor Function: ▪ Turns eyeball upward, downward and medially, upward and laterally ▪ Raises upper eyelid ▪ Constricts pupil ▪ Accommodates the eye Opening of the Skull: Superior orbital fissure 4. Trochlear nerve Component: motor Function: Turns eyeball downward and laterally Opening of the Skull: Superior orbital fissure Superior oblique 6. Abducent nerve Component: motor Function: Turns eyeball laterally Opening of the Skull: Superior orbital fissure Lateral rectus Ophthalmic nerve 5. Trigeminal Nerve Component: mixed (motor and sensory) Function: General sensation from the face, supplies muscles of mastication Large sensory root Maxillary nerve Mandibular nerve Small motor root V1. Ophthalmic Nerve Component: sensory Function: sensation from: cornea, skin of forehead, scalp, eyelids and nose, mucous membranes of paranasal sinuses and nasal cavity Opening of the Skull: Superior orbital fissure V2. Maxillary Nerve Component: sensory Function: sensation from: skin over maxilla, upper lip, teeth of the upper jaw, mucous membrane of the nose, the maxillary sinus and palate Opening of the Skull: Foramen rotundum Trigeminal Nerve 1 2 3 V3. Mandibular Nerve Component: sensory and motor Function: sensation from: skin of cheek, over mandible and side of head, teeth of lower jaw and TMJ, mucous membrane of mouth and anterior part of tongue Motor to: Muscles of mastication, Mylohyoid, Anterior belly of digastric, Tensor veli palatine, Tensor tympani Opening of the Skull: Foramen ovale Contains parasympathetic 7. Facial Nerve Component: mixed (sensory and motor) Function: taste sensation from the anterior 2/3 of the tongue General sensation from a small area around the concha of the auricle, EAM Motor to: muscles of the face and scalp, stapedius, posterior belly of digastric, stylohyoid Parasympathetic to: Sublingual and submandibular glands, lacrimal gland Opening of the Skull: Internal acoustic meatus, facial canal, stylomastoid foramen 8. Vestibulocochlear Nerve Component: sensory Origin: Vestisbular: utricle , saccule, semicircular canals Cochlear: Organ of Corti Function: balance and hearing Opening of the Skull: Internal acoustic meatus 9. Glossopharyngeal Nerve Contains parasympathetic Component: mixed (sensory and motor) Function: General sensation and taste from post. 1/3 of the tongue and oropharynx, carotid sinus and carotid body Motor to: stylopharyngeus Parasympathetic to: Parotid gland Opening of the Skull: Jugular foramen 10. Vagus Nerve Contains parasympathetic Component: mixed (sensory and motor) Function: Motor: Constrictor muscles of pharynx and intrinsic muscles of larynx; involuntary muscle of trachea and bronchi, heart, alimentary tract from pharynx to splenic flexure of colon; liver and pancreas Sensory: Taste sensation from epiglottis and vallecula and afferent fibers from structures named above, General sensation from skin of EAM Opening of the Skull: Jugular foramen 11. Accessory Nerve Component: motor Function: Cranial root: Pharyngeal plexus (Muscles of soft palate, pharynx, and larynx) Spinal root: motor to Sternocleidomastoid and trapezius Opening of the Skull: Jugular foramen 12. Hypoglossal Nerve Component: motor Function: Motor to muscles of the tongue Opening of the Skull: Hypoglossal canal Hypoglossal Nerve The cranial nerves emerge from the brain and are transmitted through foramina and fissures in the base of the skull. All the nerves are distributed in the head and neck except the vagus, which also supplies structures in the thorax and abdomen. Olfactory Optic Oculomotor/ Trochlear/ Abducent/ Ophthalmic Maxillary Mandibular Facial / Vestibulocochlear Glossopharyngeal/ Vagus/ Accessory The olfactory, optic, and vestibulocochlear nerves are entirely sensory; the oculomotor, trochlear, abducent, accessory, and hypoglossal nerves are entirely motor; and the remaining nerves are mixed Hypoglossal Pure sensory: Olfactory Optic Vestibulocochlear Pure motor: Oculomotor Trochlear Abducent Accessory hypoglossal Mixed (motor and sensory): Trigeminal Facial Glossopharyngeal Vagus Contains parasympathetic (secretomotor): Oculomotor Facial Glossopharyngeal Vagus