A&P Ch. 14 Nerve Part 2 PPT PDF

Chapter 14 – Spinal Nerves PNS Part II: Major Nerves, Reflexes https://www.youtube.com/watch?v=Nn2RHLWST-k https://www.youtube.com/watch?v=HiuXfbwND9s https://www.youtube.com/watch?v=0sqCIzuotWo https://www.youtube.com/watch?v=rHYk1sYsge0  Spinal Nerves:...

Chapter 14 – Spinal Nerves PNS Part II: Major Nerves, Reflexes https://www.youtube.com/watch?v=Nn2RHLWST-k https://www.youtube.com/watch?v=HiuXfbwND9s https://www.youtube.com/watch?v=0sqCIzuotWo https://www.youtube.com/watch?v=rHYk1sYsge0  Spinal Nerves: Nerve Plexuses Nerve plexus – Network of interweaving anterior rami of spinal nerves – Anterior rami of most spinal nerves form plexuses on both right and left sides – Main plexuses cervical plexuses brachial plexuses lumbar plexuses sacral plexuses  Plexuses and Nerves Cervical Plexus Brachial Plexus Lumbar Plexus Sacral Plexus Plexus – “Braids”, no such thing as Plexi.  Cervical Plexus Phrenic Nerve – C3, C4 (mostly) and C5 – Through neck and thorax – To the diaphragm – Sensory and motor to the diaphragm Phrenic Nerve  Cervical Plexus (Figure 14.15) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anterior rami Cervical plexus branches Other nerves (not part of cervical plexus) C1 Atlas Hypoglossal nerve (XII) Accessory nerve (XI) C2 Segmental branches Axis C3 Lesser occipital nerve Great auricular nerve Transverse cervical nerve C4 Superior root Ansa cervicalis Inferior root C5 Branch to brachial plexus Supraclavicular nerves Phrenic nerve  Brachial Plexus Medial, Ulnar and Radial Nerves Both sides of body C8 through T1 Brachial Plexus  Axillary n. Brachial Plexus Median n. Musculocutaneous n. Superior, Middle, and Inferior Radial n. Trunks of Brachial Plexus Ulnar n. Brachial Plexus - Median Nerve  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Clavicle Lateral cord Posterior cord Medial cord Axillary nerve Scapula Musculocutaneous nerve Humerus Brachial Plexus Radial nerve (Figure Ulnar Median nerve nerve 14.16c) Superficial branch of radial nerve Deep branch Ulna of radial nerve Ulnar nerve Median nerve Radius Recurrent branch Deep branch of median of ulnar nerve nerve Superficial branch of ulnar nerve Digital branch Digital branch of median of ulnar nerve nerve (c) Right upper limb, anterior view  Spinal Nerves: Brachial Plexus Clinical View: Brachial Plexus Injuries – Minor injuries treated with rest – More severe injuries may require nerve grafts – Axillary nerve injury can be compressed within axilla can be damaged if surgical neck of humerus broken difficulty abducting the arm and anesthesia along superolateral skin  Spinal Nerves: Brachial Plexus Clinical View: Brachial Plexus Injuries (continued) – Radial nerve injury during humeral shaft fractures or injuries to lateral elbow results in paralysis of extensor muscles of forearm, wrist, fingers results in anesthesia along posterior arm, forearm, part of hand – Posterior cord injury may be injured by improper use of crutches includes axillary and radial nerves  Spinal Nerves: Brachial Plexus Clinical View: Brachial Plexus Injuries (continued) – Median nerve injury may be compressed in carpal tunnel syndrome results in paralysis of thenar muscles, lateral lumbricals results in anesthesia along part of hand – Ulnar nerve injury may be injured by fractures or dislocations of elbow most intrinsic hand muscles paralyzed sensory loss on medial hand  Lumbar Plexus Pelvis, anterior of leg Obturator nerve Femoral nerve – down front of leg. Lumbar Plexus Femoral n. Obturator n. Lumbosacral trunk  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Femoral nerve Lateral femoral cutaneous nerve Obturator nerve Lumbar Plexus (Figure 14.17c) Saphenous nerve (continuation of femoral nerve) (c) Right lower limb, anterior view  Sacral Plexus Down back of leg, foot. Sacral Nerve. – Greater Sciatic Notch. Sacral Plexus Common Sciatic n. Tibial n. Fibular n. Superficial Deep Fibular n. Fibular n. Tibial n. Fibular n.21  Spinal Nerves: Sacral Plexuses Sacral plexus nerves – Sciatic nerve largest and longest nerve in body formed from portions of anterior and posterior sacral plexus projects from pelvis through greater sciatic notch extends into posterior region of thigh composed of tibial division and common fibular division  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anterior rami Posterior divisions Anterior divisions L4 L5 Sacral Plexus (Figure S1 14.18a) Superior gluteal nerve Inferior gluteal nerve S2 Nerve to piriformis S3 Common fibular division Sciatic S4 nerve Tibial division Posterior femoral cutaneous nerve Pudendal nerve (a) Anterior view  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Superior gluteal nerve Inferior gluteal nerve Pudendal nerve Sciatic nerve Posterior femoral cutaneous nerve Sacral Plexus (Figure 14.18c) Common fibular nerve Tibial nerve Lateral sural cutaneous nerve Sural nerve Medial plantar Lateral plantar nerve nerve (c) Right lower limb, posterior view  Spinal Nerves: Sacral Plexus Clinical View: Sacral Plexus Injuries – Superior or inferior gluteal nerves can be injured by poorly placed gluteal injection – Sciatica injury to sciatic nerve characterized by extreme pain down posterior thigh and leg may be caused by herniated intervertebral disc – Common fibular nerve prone to injury due to fracture of neck or compression from cast may cause paralysis of anterior and lateral leg muscles person unable to dorsiflex and evert the foot  Reflexes: Characteristics Reflex properties – Rapid, pre-programmed, involuntary reactions of muscles or glands e.g., touch burner on stove automatically remove hand from stimulus survival mechanism enables quick response without waiting for brain to process – Stimulus required to initiate response  Reflexes: Characteristics Reflex properties (continued) – Rapid response few neurons involved and minimal synaptic delay – Pre-programmed response occurs same way every time – Involuntary response requires no conscious intent awareness occurring after completion of reflex act  Reflexes: Components of a Reflex Arc Reflex arc – Neural “wiring” of a single reflex – Begins at a receptor in PNS – Communicates with CNS – Ends at a peripheral effector (muscle or gland) – Varying number of intermediate steps  Reflexes: Components of a Reflex Arc Five steps of reflex arc 1) Stimulus activates a receptor. e.g., temperature, pressure 2) Nerve signal travels through sensory neuron to the CNS. in spinal cord 3) Information from the nerve signal is processed by interneurons. more complex reflexes with a number of interneurons integrate sensory signals and transmit information to motor neuron simplest reflexes without interneurons  Reflexes: Components of a Reflex Arc Five steps of reflex arc (continued) 4) The motor neuron transmits a nerve signal to an effector. transmits signal through anterior root to gland or muscle 5) The effector responds to the nerve signal from the motor neuron. peripheral target organ responding to nerve signal response intended to counteract original stimulus  Simple Reflex Arcs (Figure 14.19) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Stimulus activates 2 Nerve signal is propogated through receptor. sensory neuron to the spinal cord. Skin 3 Nerve signal is processed in the integration center by interneurons. Interneuron Spinal cord 4 Nerve signal is propogated by motor neuron to effector. 5 Effector responds.  Reflexes: Components of a Reflex Arc Reflex types – Ipsilateral reflex arcs both receptor and effector organs on same side of spinal cord e.g., remove hand from hot stimulus on same side – Contralateral reflex arcs sensory impulses from receptor on opposite sides of spinal cord e.g., step on object with left foot contract right leg to maintain balance (as withdraw left leg)  Reflexes: Components of a Reflex Arc Reflex types (continued) – Monosynaptic reflexes simplest of all reflexes sensory axons directly synapsing on motor neurons very minor synaptic delay e.g., patellar reflex – tap patellar ligament with a reflex hammer – muscle spindles in quadriceps stretched – causes a reflexive contraction, noticeable leg kick  Reflexes: Components of a Reflex Arc Reflex types (continued) – Polysynaptic reflexes more complex neural pathways more prolonged synaptic delay before response e.g., withdrawal reflex initiated by painful stimulus – sensory input transmitted to spinal cord – received by interneurons – stimulate motor neurons to flex muscles in limb – hand pulled away from painful stimulus  Monosynaptic and Polysynaptic Reflexes (Figure 14.20) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Monosynaptic reflex Polysynaptic reflex Direct communication between Interneuron facilitates sensory and motor neuron sensory-motor communication Sensory (stretch) receptor (e.g., stretch reflex) (e.g., withdrawal reflex) Spinal cord Sensory receptor Sensory Sensory neuron neuron Interneuron Effector organ Effector organ Motor neuron Motor neuron  Reflexes: Spinal Reflexes Stretch reflex – Monosynaptic reflex – Regulates skeletal muscle length – Reflexive muscle contraction after stretching of a muscle  Stretch Reflex (Figure 14.21) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Excitatory Inhibitory 2 Muscle stretch stimulates sensory Spinal cord nerve signals to travel to the CNS. Sensory neuron α motor nerve Intrafusal Interneuron endings to muscle fiber γ motor neuron extrafusal to muscle spindle muscle fibers γ motor nerve endings to muscle spindle Extrafusal Muscle muscle fiber spindle α motor neurons to Sensory nerve extrafusal muscle fibers endings 3 Sensory neuron synapses on α 4 α motor neurons transmit motor neurons. 1 Muscle spindle nerve signals to extrafusal detects stretch. muscle fibers, resulting in contraction of the muscles (in response to being stretched). 5 Interneurons synapse with α motor neurons to antagonist muscles, inhibiting muscle contraction (reciprocal inhibition).  Reflexes: Spinal Reflexes Golgi tendon reflex – Prevents muscles from contracting excessively – Polysynaptic reflex – Results in muscle lengthening – Prevents damage to tendons or muscles – Occurring in response to tension at Golgi tendon organ composed of sensory nerve endings within a tendon or near muscle-tendon junction  Reflexes: Spinal Reflexes Golgi tendon reflex (continued) – Reciprocal activation stimulation of alpha motor neurons of antagonistic muscles e.g., Golgi tendon organ activated in quadriceps relaxation of quadriceps femoris due to Golgi tendon reflex hamstrings stimulated to contract via reciprocal activation occurs via interneurons in spinal cord – Golgi tendon reflex and stretch reflex stretch reflex may be nullified by Golgi tendon reflex – under extreme tension  Reflexes: Spinal Reflexes Crossed-extensor reflex – Often in conjunction with withdrawal reflex – Reflex path sensory transmission to spinal cord synapse with interneurons in stretch and crossed-extensor reflex synapse with motor neurons on antagonistic muscle in opposite limb e.g., step on sharp object with right lower limb cross-extensor reflex stimulating left quadriceps femoris to contract left limb stays extended  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Withdrawal reflex Excitatory Crossed-extensor reflex Inhibitory Spinal cord 2 Sensory nerve signal 3b Other interneurons cross to the opposite side detected by and stimulate motor neurons to extensors on interneurons. other side of body, resulting in extensor contraction and support of body weight. Interneurons Sensory Motor neuron neuron to flexors Withdrawal 3a Interneurons stimulate motor neurons Motor neuron to extensors and Crossed- to flexors, resulting in withdrawal of limb from painful stimulus. Extensor Quadriceps femoris Reflexes (Figure 14.23) Hamstrings Quadriceps femoris Hamstrings 1 Painful stimulus detected by sensory neurons during withdrawal reflex.  Cross extensor Reflex videos http://www.youtube.com/watch? v=hwYewR_HK24 52 seconds http://www.youtube.com/watch? v=MAI4KLjCbek 52 seconds also  Reflexes: Reflex Testing in a Clinical Setting Reflex variations – Can be important diagnostic tool – Used to test specific muscle groups and spinal nerves – Some variation normal – Consistently abnormal reflex may signal damage to nervous system or muscles  Reflexes: Reflex Testing in a Clinical Setting Reflex variations (continued) – Hypoactive reflex reflex diminished or absent may indicate damage to – segment of spinal cord – muscle disease – damage to neuromuscular junction  Reflexes: Reflex Testing in a Clinical Setting Reflex variations (continued) – Hyperactive reflex abnormally strong response may indicate damage in brain or spinal cord clonus, rhythmic oscillations between flexion and extension – may especially indicate damage See Table 14.9: Some Clinically Important Reflexes