Peripheral Nervous System - PARA 1002 PDF

Peripheral Nervous System PARA 1002 1 Nerves of the PNS Recall: the PNS comprises the pathways to and from the CNS 31 pairs of spinal nerves emerge from the spin...

Peripheral Nervous System PARA 1002 1 Nerves of the PNS Recall: the PNS comprises the pathways to and from the CNS 31 pairs of spinal nerves emerge from the spinal cord 12 pairs of cranial nerves emerge from the brain The spinal and cranial nerves branch to form the remainder of the nerves in the body PARA 1002 2 1  The Spinal Nerves Spinal nerves do not have descriptive names but are named according to where they emerge from the VC – 8 cervical nerve pairs (C1 – C8) – 12 thoracic nerve pairs (T1 – T12) – 5 lumbar nerve pairs (L1 – L5) – 5 sacral nerve pairs (S1 – S5) – 1 coccygeal nerve pair Spinal cord terminates at approximately L1, so the lumbar, sacral and coccygeal nerve pairs all descend from this point to the point of emergence PARA 1002 3 The Spinal Nerves Dorsal root Rami Spinal Nerve Ventral root All Spinal nerves are MIXED nerves, formed by a – dorsal root (sensory) – ventral root (motor) PARA 1002 4 2  The Spinal Nerves As spinal nerves emerge from the spinal cavity, they form large branches or rami (ramus) Dorsal Ramus: Splits into smaller somatic sensory and motor nerves that innervate muscles and skin of posterior head, neck, trunk Ventral Ramus: Much more complex Motor and sensory fibres innervate muscles and glands in extremities and lateral/ventral portions of neck and trunk Autonomic fibres split and merge with ganglia of the sympathetic chain PARA 1002 5 Nerve Plexuses Complex networks of nerves formed by the ventral rami of most spinal nerves (except T2 – T12) Fibres from several rami form “braids” of fibres that emerge as one nerve that will supply a particular body region Nerves are named based on particular destination Branches from adjacent spinal nerves can be combined to reduce the number of nerves required for a particular area Are there advantages to this? Specific plexuses: Cervical Plexus, Brachial Plexus, Lumbar Plexus, Sacral Plexus, Coccygeal Plexus PARA 1002 6 3  Nerve Plexuses Cervical Plexus Deep in the neck Innervates skin and muscle of the neck, upper shoulders and part of the head Brachial Plexus Deep in the shoulders Innervates lower part of the shoulder and entire arm Lumbar Plexus Lumbar region of the back Innervates the thigh and leg Sacral and Coccygeal Plexus Sacral lies in pelvic cavity and innervates skin of the leg, post. thigh muscles and leg/foot muscles (includes sciatic) Small coccygeal plexus innervates floor of pelvic cavity PARA 1002 7 PARA 1002 8 4  Cervical Plexus Ventral rami of C1-C4 and part of C5 Innervates skin and muscles of neck, part of the head and shoulders Fibres from C3,C4,C5 form the phrenic nerve – Innervates diaphragm – C3,4,5 “keeps the diaphragm alive” PARA 1002 9 Referred Pain Distribution C 3,4,5 sensory stimuli from diaphragm often interpreted as pain over shoulder and lower neck PARA 1002 10 5  Brachial Plexus (C5 - T1) Innervates lower part of the shoulder and entire arm Deep in the shoulders (see Table 14-5) PARA 1002 11 Nerves of Brachial Plexus Radial (C5 – C8, T1) Musculocutaneous (C5 – C7) Ulnar (C8 & T1) Median (C8 & T1), (C5 – C7) PARA 1002 12 6  Brachial Plexus Injuries PARA 1002 13 Nerve Injury PARA 1002 14 7  Lumbar Plexus Ventral rami of L1-L4 Innervates lower abdomen, anterior and medial side of lower limb - sensory Anterior and medial thigh - motor PARA 1002 15 Sacral Plexus Lies in the pelvic cavity Innervates skin of the leg, posterior thigh muscles and leg/foot muscles (includes sciatic) PARA 1002 16 8  Dermatomes Dermatomes: There is a “mapable” relationship between the spinal origin of each spinal nerve and the associated sensory region of the body This can be illustrated diagrammatically keeping in mind that there is actually a degree of overlap How could a “map” be useful diagnostically? Shingles? PARA 1002 17 Shingles Herpes Zoster - affecting the sensory nerve distribution L1 of lumbar plexus Ophthalmic division of Trigeminal Nerve PARA 1002 18 9  Myotomes Myotomes: Refers to a muscle or muscle group innervated by a given spinal nerve (some muscles are innervated by more than one) Not as easy to “map” graphically… PARA 1002 19 Cranial Nerves 12 pairs arising from the undersurface of the brain and brainstem Identified by both numbers (order in which they connect) and names (based on distribution or function) Cranial nerves are bundles of axon that may be: sensory, motor (may have a few sensory) or mixed Detailed classification and function for additional personal referencecan be found in textbook or additional resources PARA 1002 20 10  Cranial Nerves PARA 1002 21 Cranial Nerves On Old Olympus’s Towering Top A Fat Vicious Goat Vandalized A Hat Oh, Oh, Oh, To Touch And Feel Very Good Velvet, AH! PARA 1002 22 11  Olfactory Nerve (CN I) Sensory nerve Olfactory epithelium ethmoid olfactory bulb olfactory tract 1 Olfactory cortex Anosmia – partial or total loss of smell PARA 1002 23 Optic Nerve (CN II) Sensory nerve Retina optic foramen optic chiasm optic tract thalamus visual cortex PARA 1002 24 12  Oculomotor Nerve (CN III) Motor nerve Midbrain orbit eye Innervates 4 of 6 extrinsic muscles of eye: medial rectus superior rectus inferior oblique inferior rectus Levator palpebrae (eyelid) PARA 1002 25 Trochlear Nerve (CN IV) Mainly motor Midbrain orbit eye Innervates superior oblique muscle Turns eye inferior and lateral Trauma results in double vision and inability to turn eye down and out PARA 1002 26 13  Trigeminal (CN V) Mixed nerve Two roots: sensory and motor Sensory: Ophthalmic, maxillary, mandibular divisions (V1, V2, V3) – Sensations from face, nasal cavities, lacrimal gland, palate Motor: mandibular division – All muscles of mastication (chewing): masseter, temporalis, pterygoids, anterior belly digastric PARA 1002 27 Trigeminal (CN V) Sensory V1 -opthalamic V2 -maxillary V3 -mandibular Motor Three divisions: V1, V2, V3 PARA 1002 28 14  Abducens (CN VI) Mainly motor Pons orbit eye Innervates lateral rectus muscle Rotates eye laterally (abducts) PARA 1002 29 Facial Nerve (CN VII) Mixed nerve Innervates glands Motor component innervates all muscles of facial expression Sensory input from anterior 2/3 tongue Five major branches: Temporal, Zygomatic, Buccal, Mandibular, Cervical PARA 1002 30 15  Facial Nerve Distribution Autonomic innervation: salivary glands, lacrimal glands Taste - Anterior 2/3 Muscles facial expression PARA 1002 31 Vestibulocochlear (CN VIII) Sensory nerve Two major branches merge before entering pons Vestibular – associated with equilibrium/balance Cochlear – sense of hearing, input from spiral organ PARA 1002 32 16  Glossopharyngeal (CN IX) Mixed nerve *Proprioception from a superior pharyngeal muscle Motor: Innervates tongue and pharynx, involved in swallowing and gag reflex Parasympathetic fibres to parotid salivary glands Sensory: taste from posterior 1/3 of tongue PARA 1002 33 Vagus Nerve (CN X) Mixed nerve Innervates visceral organs of thorax and abdomen Longest cranial nerve Motor to vocal cords and pharynx Parasympathetic fibres to abdominal viscera and thoracic organs (breathing and heart rate) Sensory feedback related to blood pressure (carotid and aortic bodies) and respiration (chemoreceptors) PARA 1002 34 17  Vagus Nerve Pharynx Larynx Thorax Abdomen PARA 1002 35 Accessory Nerve (CN XI) Motor nerve Uniquely formed by union of cranial and a spinal roots Innervates pharynx, larynx; involved in swallowing Innervates trapezius, sternocleidomastoid; involved in moving head/neck/shoulder Damage to spinal root interferes with shoulder shrugging (trapezius), and causes head to turn toward injury (sternocleidomastoid) PARA 1002 36 18  Hypoglossal Nerve (CN XII) Motor nerve Innervates intrinsic and extrinsic muscles of tongue Involved in mastication, swallowing and speech “Stick out your tongue and say Ahh” PARA 1002 37 Cranial Nerve Function Some Say Marry Money But My Brother Says Big Bucks Matter Most PARA 1002 38 19  Common Cranial Nerve Injury CN #6 (Abducens) – paralysis of abductor muscle of eye causing eye to turn in CN #8 (Vestibulocochlear) – deafness CN #7 (Facial) – loss of facial expression and drooping of corner of the mouth – “Bell’s Palsy” PARA 1002 39 Bell’s Palsy Paralysis of facial muscles on one side May appear or disappear spontaneously May be related to HSV PARA 1002 40 20  Somatic Motor Nervous System These “voluntary” motor pathways innervate the somatic effectors (skeletal muscles) They follow the final common path principle mentioned previously The actual stimulation of the effector cells by the final somatic motor neuron is accomplished by the neurotransmitter acetylcholine (neuromuscular junction) The function of several peripheral motor pathways involves the action of reflex arcs PARA 1002 41 Somatic Reflexes A reflex involves a “predictable” response to a particular stimulus (consciously or unconsciously) Reflex Arc = signal conduction route to and from CNS that does not necessarily involve “higher integration” They may be two-neuron, three-neuron, or multi-neuron reflexes based on the involvement of interneurons and multiple synapses Reflex arc centred on the brain is a cranial reflex; if centred on the spinal cord, it is a spinal reflex Somatic reflexes specifically stimulate contraction of skeletal muscle –vs- autonomic (visceral) reflexes that stimulate smooth or cardiac muscles or glands PARA 1002 42 21  Clinically Important Somatic Reflexes Knee Jerk Reflex (patellar) Ankle Jerk Reflex Babinski Sign? Corneal Reflex Abdominal Reflex PARA 1002 43 Withdrawal Reflex (Pain) PARA 1002 44 22  PARA 1002 45 23