Peripheral Nervous System Text and Lecture Summary PDF

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Peripheral Nervous System Text and Lecture Summary. Good to use for studying and refreshing for tests or NCLEX...

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Peripheral Nervous System – Ch 13 Peripheral nervous system (PNS) – links CNS to body and to external environment - Sensory Division- afferent neurons that detect various sensory stimuli and bring them into the CNS - Motor Division- efferent neurons that carry out the motor functions of the nervous system *Both divisions are then classified further based on which organs the neurons contact *Many nerves contain both sensory and motor neurons = MIXED NEURONS *Some sensory neurons contain only sensory neurons *All motor neurons contain small population of sensory neurons so there are NO PURE MOTOR NERVE, but can be predominantly motor nerves (PNS) Sensory Division: 1.Somatic Sensory Division: -neurons that detect sensory stimuli from the skin and musculoskeletal system. -neurons that respond to general senses (touch, temp, pain) -neurons that respond to senses originating in the body (muscle stretch and chemical concentration) -contains special neurons that respond to special senses (sight, hearing, equilibrium, taste, smell) 2.Visceral Sensory Division: -neurons that relay sensory stimuli from the abdominopelvic & thoracic cavities -neurons that detect internal changes (BP, degree of an organs stretch) Motor Division 1.Somatic Motor Division: -responsible for the body’s voluntary motor functions -made up of LMN, lower motor neurons (or somatic motor neurons) -directly contact skeletal muscle fibers and trigger contraction when stimulated by UMN, upper motor neurons in the CNS 2.Visceral Motor Division/Autonomic Nervous System -maintaining homeostasis -control of the body’s involuntary motor functions -innervate cardiac muscle cells, smooth muscle cells, and secretory cells of gland -The ANS has 2 divisions: sympathetic (fight/flight)and parasympathetic(rest/digest) Integration of the Systems

Sensory neurons – Stimuli sensory neuron Cerebral cortex Interpretation, integration  Motor response: – Impulse spinal cord synapse LMN muscles contraction Numbe Name Exit Type Function (F) & Info (I) r F-Smell (nerve endings contain chemoreceptors that depolarize in Cribriform 1 (VI) Olfactory Sensory response to chemicals in air we plate breathe) I-1% degeneration rate/year F-Vision (transmits visual stimuli in AP form when light hits photoreceptors) I-Optic pathway begins at retina, 2 (VII) Optic Optic chiasm Sensory passes through optic pathway, ends in optic chiasm where some axons switch sides to reach destinations in brain F-4/6 extrinsic eye mm (inferior oblique, and superior, medial, inferior recti) And 1 skeletal m Superior Motor levator palpebrae superioris. 3 (VIII) Oculomotor orbital fissure F-pupillary sphincter F-Moves eyeball, opens eye, constricts pupil, changes lens shape F-1/6 extrinsic eye mm (Superior oblique) F-Intorsion, Depression, Abduction Moves eye medially &inferiorly Superior Motor I-longest intercranial nerve, very 4 (IV) Trochlear orbital fissure small & fragile. Not uncommon for head injuries to damage CNIV. I-Known as Tramps Nerve or SO4 5 (V)

Trigeminal: Ophthalmic

Maxillary

Mandibular

F-Senses Scalp, forehead and nose, Superior Sensory supply eye structure and nasal orbital fissure mucosa. F- Senses Cheeks, lower eye lid, F. rotundum Sensory nasal mucosa, upper lip, upper teeth and palate. (middle of face) F-Senses anterior 2/3 tongue, skin Sensory F. ovale over mandible and lower teeth. &Motor F- Motor - muscles of mastication.

Numbe Name r

6 (VI)

Abducens

7 (VII)

Facial

8 (VIII)

9 (IX)

10(X)

Exit

Function (F) & Info (I)

Destination-Lateral rectus muscle of the eye Superior Motor F- abducts eyeball (this muscle orbital fissure (GSM) abducts the gaze when it turns the eye laterally) F- sensation to part of ext. ear. F-taste from ant. 2/3 tongue, hard and soft palate, lacrimal, submandibular, sublingual glands Internal and mucous glands of mouth and Sensory acoustic nose. &Motor meatus > F-muscles of facial expression stylomastoid f. I-Motor facial root splits into 5 Branches : temporal, zygomatic, buccal, mandibular, cervical

Internal Vestibulocochle acoustic ar meatus

Jugular f. Glossopharynge (Tongue & al Throat)

Vagus “The Travelling Nerve”

Type

Jugular f.

F-Hearing and balance I-Start out as 2 separate nerves , (vestibular for orientation in space and cochlear for hearing Sensory soundwaves), which fuse together after temporal bone. Then the separate axons reach to some same and some separate areas.

F- Senses post. 1/3 tongue, ext. ear, and middle ear cavity, carotid body and sinus. F-taste from post. 1/3 tongue. Sensory F- Parasympathetic neurons trigger &Motor salvation from parotid gland. F- Motor-swallowing (stylopharyngeus) Sensory F- senses ext. ear, larynx and &Motor pharynx, thoracic & abdominal viscera. F- detect blood CO2 concentration F- taste from epiglottis region of tongue. F- smooth muscles of

Numbe Name r

Exit

Type

Function (F) & Info (I) pharynx, larynx and most of the GIT I- contract during speaking and swallowing (Voicebox)

11 (XI)

Spinal accessory

Jugular f.

Hypoglossal Hypoglossal 12 (XII) “Muscles of the canal Tongue”

Cranial Nerves I - XII  CN I – Olfactory n  CNII–Optic n.  CN III – Oculomotor n.  CN IV – Trochlear n.  CN V – Trigeminal n.  CN VI – Abducens n.  CN VII – Facial n.  CN VIII – Vestibulocochlear n.  CN IX – Glossopharyngeal n.  CNX– Vagus n.  CN XI – Spinal accessory n.  CN XII – Hypoglossal n.

Motor

Motor (GSM)

F-Cranial component innervates certain muscles of larynx for speech F-Spine component innervates mm that move head & shoulders (trapezius and sternocleidomastoid) F-Intrinsic and extrinsic tongue muscles (except the palatoglossus). I-Dysarthria if damaged F-allows us to articulate I- No role in taste

Sensory, Motor, Both S S M M B M B S B B M M

Cranial Nerves attach to the brain and mainly innervate structures of head and neck.

Olfact-smell Opt-vision Aud-hear Oculo-eye Hypo=below Glosso-tongue Tri-three

Pharynx-throat

Special Considerations Anosmia(an-without os-smell)(CNI) -CNI damages loose ability to smell -bilateral/unilateral -Etiologies: common cold, trauma, normal aging, degenerative dementias -tumors (meningioma) Anopia(an-without, opia-sight)(CNII) 1. Ipsilateral blindness – Total blindness in affected eye 2. Bitemporal hemianopia  - Bipolar hemianopia - loose vision in temporal fields of both eyes (peripheral vision) -Tunnel vision -some information/stimuli can get through -Pituitary Adenoma- tumor of pituitary glands compress optic chiasm Papilledema(CNII) -a serious medical condition where the optic nerve at the back of the eye becomes swollen -Symptoms can include visual disturbances, headaches, and nausea & Swollen optic disc -occurs when there is a buildup of pressure in or around the brain -caused by any tumors, blockages or more, which causes the optic nerve to swell Third Nerve Palsy(CNIII) - causes a completely closed eyelid and deviation of the eye outward (Divergent Squint) and downward. - eye cannot move inward or up -Diplopia -double vision -Dilatation of pupil (pupil is typically enlarged) -Levator superioris opens eye, when damaged leads to ptosis -Ptosis (falling/dropping of eyelid) -Loss of accommodation reflex -Loss of light reflexes When CNVI damaged - paralysis of superior oblique m

- diplopia Lesions (CNV) -When all of CNV branches damaged can lead to mouth closed tightly -decreased sensation of tongue anterior 2/3 -More frequently it will be separate branches damaged, test different regions individually Trigeminal Neuralgia (Tic Douloureaux) (CNV) -Periodic severe stabbing pain -Painful -Unpredictable intervals -Pharmacological or surgery is often to sever a nerve. -Not very common but very serious, not sure of cause -Medications cannot do very much Inferior Alveolar Nerve Block (CNV) - a common procedure in dentistry -insertion of a needle near the mandibular foramen in order to deposit a solution of local anesthetic near to the nerve before it enters the foramen -a region where the inferior alveolar vein and artery are also present Abducen Nerve Palsy (6 Nerve Palsey) (CNVI) - CNVI is damaged or doesn't work right -Medial strabismus (convergent squint or lazy eye) -Diplopia -when one muscle pair is weakened the other pair has greater pull (greater muscle tone) -ex) medial rectus has greater pull when lateral rectus is damaged, the eyeball will be directed medially, causing diplopia Facial Paralysis (CNVII) -Facial mm. paralysis -Loss of taste sensation -↓ salivation -↓ lacrimation -Hyperacusis -Side paralyzed is side with nerve damage when making facial expressions Lesions (CNVIII) 1.Cochlear n. lesions – Tinnitus = jingling/to ring (Latin) – Deafness – Acoustic neuromas – intracranial tumors 2.Vestibular n. lesions – Disequilibrium – Vertigo = dizziness (Latin), OR to turn (French) – Nystagmus (persistent involuntary mvmt of eye) Peripheral Nerves : Spinal Nerves -all the nerves that come from and to the spine and brain -“one way streets” -originate from spinal cord

-innervate below head & neck -matter in which way they enter/exit - mixed nn - -sensory nn - -spinal nn -Anterior Root- carries motor signals from CNS to skeletal muscles & gland cells -Posterior Root- carries sensory signals from PNS to spinal cord -Each spinal nerve is formed by the combination of nerve fibers from the dorsal roots (AFFERENT)and ventral roots (EFFERENT) of the spinal cord. -DAVE = Dorsal Afferent, Ventral Efferent -Rootlets come together to form roots 1)dorsal roots carry afferent sensory axons, while the ventral roots carry efferent motor axons. 2)spinal nerve emerges from the spinal column through an opening (intervertebral foramen) between adjacent vertebrae…Except for the first spinal nerve pair, which emerges between the occipital bone and the atlas 3)All spinal nerves carry both (motor/sensory) once they bundle together 4)Then diverge into an Anterior Ramus and a Posterior Ramus -Ramus (pleural) Rami (singular) Ramus= branch - Anterior Ramus is largest and travels to anterior side of body and upper and lower limbs -Posterior Ramus travels to anterior side of body and muscles on posterior side -Another small branch stems from anterior ramus called “rami communcantes”, they contain visceral motor or automatic neurons of the sympathetic NS. They are NOT mixed nerves and only contain motor neurons. 31 pairs of spinal nerves 8 pairs of cervical nerves – 12 pairs of thoracic nerves – 5 pairs of lumbar and 5 sacral nerves – 1 pair of coccygeal nerves

Spinal Nerves & Plexuses -Plexus = braid -The anterior rami of the cervical, lumbar and sacral nerves merge to form complicated networks of nerves called nerve plexuses. -Due to nerve plexuses the muscles supplied by a single branch of plexuses usually contain two or more spinal nerves -Advantage: if one spinal nerve is damaged, it won’t completely cut off sensation or motor to the part of the body it innervates.

-C1 spinal nerve comes off spinal cord and emerges between skull and C1 vertebra, unlike other Cervical nerves that run superiorly (C2-C7). -C8 emerges inferior to pedicle of CV VII. -Nerves T1 to Co emerge inferior to pedicles of their respective vertebrae.

Cervical Plexuses C1-C4 -plexus of the anterior rami of the first four cervical spinal nerves which arise from C1 to C4 cervical segment in the neck. -Phrenic Nerve is main nerve that drives respiration. -Remember:C3, 4, 5 keep you alive. Main spinal nerve for Phrenic nerve is C4, but receive some innervation from C5 (C5 is not a part of Cervical plexus)

Brachial Plexuses C5-T1 -formed by the anterior rami of the lower four cervical nerves and first thoracic nerve (C5, C6, C7, C8, and T1). -extends from the spinal cord, through the cervicoaxillary canal in the neck, over the first rib, and into the armpit.

*white glints show anterior divisions, no glints show posterior

Terminal Branches (Nerves) of Brachial Plexus Musculocutaneous n. • Lateral cord -Coracobrachialis m. (landmark) (actually pierces) -Biceps brachii m. – Brachialis m. -Flexion & Extension -skin over lateral forearm - The sideways “M” shape signals the 3 nerves that innervate 3 mm of the anterior brachium (all upper extremity)

Median n. -Mm of anterior compartment of forearm (Exceptions) -Skin over palm -Does not innervate brachium -Runs down middle of arm -Innervates all mm of anterior forearm except 1.5 mm -Continues through carpal tunnel then into hand to innervate mm of thenar, lumbricals and cutaneous sensory ___________________ Ulnar n. -medial epicondyle/olecranon (funny bone) -1.5 in forearm (the median exception) -Lumbrical 3&4 -Dorsal and palmar interossei mm. -Innervates part of the of anterior forearm -Flexor carpi ulnaris and ½ of flexor digitorum (both median & ulnar innervate flexor digitorum)

Radial n. -Triceps brachii m. -Brachioradialis m. -Supinator m. -Extensor carpi radialis longus m. -Extensor carpi radialis brevis m. -Extensor digitorum m. -Extensor carpi ulnaris m. -Anconeus m. -innervatea all of mm of post. aspect of brachium & forearm, skin over post. thumb, digits 2 and 3 and ¼ of digit 4

Axillary n. -Surgical neck of humerus

-Teres minor m. -Deltoid m. & skin -serves structures near axillary

Upper Brachial Plexus Injuries -Upper Trunk (C5, C6 ect) -Mechanism of Action: during birth or accident -separating head & shoulder, -Erb-Duchene palsy -“Waiter’s tip” -at rest: abducted, internally rotated, elbow extended -due to no oppositional pull Lower Brachial Plexus Injuries -Lower Trunk -Stress/Pull on T1 -Klumpke’s Palsy “Claw hand” -usually cant treat itself (unless roots Pulled out ,then no trxt) Saturday Night Paralysis -Radial Nerve Damage (ex-ill; fitting crutches, compression on nerve) -Wrist drop -Posterior aspect of upper limb inability to extend wrist Long Thoracic N. (Winged Scapula) -Contributions from C5,6,7 -serratus anterior m. (innervated by long thoracic n.) -Mechanism of injury: Radical mastectomy during surgery, severe injury, -Medial border of scapula comes off of thorax

Thoracic Spinal nn. T1-T12 -Thoracic spinal nerves do not form plexuses (except T1) -Each posterior ramus innervates deep back muscles -Each anterior ramus travels between two ribs as an intercostal nerve

-costal groove on true ribs in interior aspect of rib

Lumbar Plexus L1-L4 -Arise from L1, L2, L3, and superior part of L4 *Femoral n: motor to the quadriceps femoris, iliopsoas, sartorius mm -sensory to anterior thigh, medial thigh, medial leg and foot -largest n. from post. division -supplies psoas and iliacus mm *Obturator n: motor to the thigh adductors and gracilis muscle -sensory to superomedial thigh

Sacral Plexus L4-S4 -Sciatic n: sensory to hip joint -Pudendal n: motor to mm of pelvic floor,

external anal sphincter, external urethral sphincter -sensory to skin over external genitalia -Superior gluteal n: motor to gluteus medius, minimus, and tensor fasciae latae mm -Inferior gluteal n: motor to gluteus maximus m. -Tibial n: motor to hamstring mm, post leg mm, plantar foot mm - sensory to knee joint, ankle joint, skin of post and lateral leg(via sural n) and skin of planta and surface of foot -Common Peroneal/Fibular n: -motor to lateral leg mm (superficial branch) -motor to anterior leg mm, and 2 foot mm (deep branch) -sensory to knee joint, skin of anterior and distal leg and dorcum of foot Foot Drop*(common peroneal n. injury) -when compressed / damaged -foot slides / slaps behind when walking Role of PNS in Sensation Sensory Transduction -Sensory transduction is the process of converting that sensory signal to an electrical signal in the sensory neuron. -The process of reception is dependent on the stimuli itself, the type of receptor, receptor specificity, and the receptive field, which can vary depending on the receptor type. -neurons communicate by AP -resting potential -70 mmV -Na on outside, K on inside -Once AP starts, it is all or none -@-55 mmV the threshold for AP to start 1) Before any stimuli arrives the ion channels in the axolemma of the somatic sensory neuron are closed 2) When a stimulus such as pressure is applied, mechanically gated Na + channels open and Na+ enter the axoplasm, generating a receptor potential 3) If enough Na+ enter that the membrane potential reaches threshold, voltage gated Na+ channels open. This triggers an AP, which will be propagated along the axon to the spinal cord.

Receptor: many kinds, sense change, can be classified Rapidly adapting receptors – respond rapidly with high intensity to stimuli – stop sending signals after certain time period (adaptation) – receptors detect initiation of stimuli but ignore ongoing stimuli Slowly adapting receptors – respond to stimuli with constant action potentials – don’t diminish over time Sensory Receptors Exteroceptors – detect stimuli originating from outside body (ex-texture, temp, odour) Interoceptors – detect stimuli originating from within body itself (ex-BP, chemical concentration) Mechanoreceptors (mechanically gated ion channels) -Mechanoreceptors–interoceptors or exteroceptors (MSK, skin, other organs) – depolarize in response to anything that mechanically deforms tissue where receptors are found (including internal such as stretch/pressure change or external such as light touch/vibration)

Proprioceptors – in MSK system (not skin), detect movement and position of joint or body part

Hair follicle receptors – free nerve endings around base of hair follicles, stimuli is hair bending Thermoreceptors–exteroceptors – most slowly adapting receptors – separate receptors detect hot and cold Chemoreceptors – can be either interoceptors or exteroceptors – depolarize in response to binding to specific chemicals (in body fluids or in air, ex-taste, smell) Photoreceptors – special sensory exteroceptors found only in eye – depolarize in response to light Nociceptors – usually slowly adapting exteroceptors – depolarize in response to noxious stimuli (pain) Sensory Action Potential Transmission -Speed depends on axon diameter & thickness of myelin sheath (insulation) -Fastest = large diameter EX-Proprioceptive EX-Touch -Slowest = small diameter EX-Pain EX-Temperature Receptive Field -2 Point discrimination Test -More Neurons with smaller receptive fields is best for better discrimination -Less neurons having to cover a larger area (large reception field) will have larger discrimination threshold

Dermatomes -Derma=skin, -tome=section -Skin mapped according to spinal nerve supplying somatic sensation -May help identify source of referred pain -Referred Pain- pain that originates in an organ is perceived as cutaneous pain -nerves are close together so they spread sensation to areas near -Ex- Heart attackleft arm & anterior chest wall -Shingles: follow dermatomes, respond better to earliest trxt, can migrate to neighbouring ganglia & affect their dermatomes

Role of the PNS in Movement CNS  PNS Upper motor neurons – neurons of primary motor cortex make decision to move and initiate that movement – not in contact with muscle fiber Lower motor neurons – receive messages from upper motor neurons – in contact with skeletal muscle fibers – release acetylcholine onto muscle fibers to initiate contraction -Motor neuron pools – groups of lower motor neurons that innervate same muscle – Large motor neurons (alpha) – stimulate skeletal muscle fibers to contract – Smaller motor neurons (gamma) – innervate intrafusal fibers, part of specialized stretch receptors Control of Movement by Nervous System 1) CNS: UMN in premotor cortex select a motor program 2) CNS: The basal nuclei enable the thalamus to stimulate UMN of primary motor cortex 3) CNSPNS: UMN stimulate LMN 4) PNS: LMN stimulate a skeletal mm to contract ...