Chapter 13 Spinal Cord PDF

Introduction Thousands of Americans are paralyzed by spinal cord injury every year The spinal cord is the “information highway” that connects the brain with the lower body In this chapter we will study the spinal...

Introduction Thousands of Americans are paralyzed by spinal cord injury every year The spinal cord is the “information highway” that connects the brain with the lower body In this chapter we will study the spinal cord and spinal nerves ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Functions of the Spinal Cord Conduction—nerve fibers conduct sensory and motor information up and down the spinal cord Neural integration—spinal neurons receive input from multiple sources, integrate it, and execute appropriate output (e.g., bladder control) Locomotion—spinal cord contains central pattern generators: groups of neurons that coordinate repetitive sequences of contractions for walking Reflexes—involuntary responses to stimuli that are vital to posture, coordination and protection ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Surface Anatomy 1 Spinal cord—cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull – Occupies the upper two-thirds of vertebral canal – Inferior margin ends at L1 or slightly beyond – Averages 1.8 cm thick and 45 cm long – Gives rise to 31 pairs of spinal nerves – Segment: part of the spinal cord supplied by each pair of spinal nerves ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Surface Anatomy 2 Longitudinal grooves on anterior and posterior sides - Anterior median fissure and posterior median sulcus Spinal cord divided into the cervical, thoracic, lumbar, and sacral regions Two areas of the cord are thicker than elsewhere - Cervical enlargement—nerves to upper limb - Lumbar enlargement—nerves to pelvic region and lower limbs Medullary cone (conus medullaris): cord tapers to a point inferior to lumbar enlargement Cauda equina: bundle of nerve roots that occupy the vertebral canal from L2 to S5 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Spinal Cord, Posterior Copyright © McGraw-Hill Education. Permission required for reproduction or display. Aspect Figure 13.1 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Meninges of the Spinal Cord 1 Meninges—three fibrous membranes that enclose the brain and spinal cord – They separate soft tissue of central nervous system from bones of cranium and vertebral canal – From superficial to deep: dura mater, arachnoid mater, and pia mater – Dural sheath surrounds spinal cord and is separated from vertebrae by epidural space – Arachnoid membrane adheres to dura and is separated from pia by fibers spanning the subarachnoid space that is filled with cerebrospinal fluid (CSF) Lumbar puncture (spinal tap) takes sample of CSF – Pia is delicate membrane that follows contours of spinal cord and continues inferiorly as a fibrous terminal filum that fuses with dura to form coccygeal ligament ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Meninges of the Spinal Cord 2 Copyright © McGraw-Hill Education. Permission required for reproduction or display. (a) Spinal cord and vertebra (cervical) Figure 13.2a ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Meninges of the Spinal Cord 3 Copyright © McGraw-Hill Education. Permission required for reproduction or display. (b) Spinal cord and meninges (thoracic) Figure 13.2b ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Spina Bifida Spina bifida—congenital defect in which one or more vertebrae fail to form a complete vertebral arch for enclosure of the spinal cord – In 1 baby out of 1,000 – Common in lumbosacral region – Most serious form: spina bifida cystica Folic acid (a B vitamin now added to flour) is part of a healthy diet for all women of childbearing age – it reduces risk of spina bifida – Defect occurs during the first 4 weeks of development, so folic acid supplements for mothers must begin 3 months before conception ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Spina Bifida Cystica Copyright © McGraw-Hill Education. Permission required for reproduction or display. © Biophoto Associates/Science Source Figure 13.3 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Cross-Sectional Anatomy 1 shaped like a Central area of gray matter butterfly and surrounded by white matter in three columns Gray matter—neuron cell bodies with little myelin – Site of information processing, synaptic integration White matter—abundantly myelinated axons – Carry signals from one part of the CNS to another ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Cross-Sectional Anatomy 2 Copyright © McGraw-Hill Education. Permission required for reproduction or display. (b) Spinal cord and meninges (c) Lumbar spinal c: © Ed Reschke/Getty (thoracic) cord Images Figure 13.2b,c ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Gray Matter Spinal cord has a central core of gray matter that looks butterfly- or H-shaped in cross section – Pair of posterior (dorsal) horns – Posterior (dorsal) root of spinal nerve carries only sensory fibers – Pair of thicker anterior (ventral) horns – Anterior (ventral) root of spinal nerve carries only motor fibers – Gray commissure connects right and left sides Has central canal lined with ependymal cells and filled with CSF – Lateral horn: visible from T2 through L1 Contains neurons of sympathetic nervous system ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  White Matter White matter of the spinal cord surrounds the gray matter Consists of bundles of axons that course up and down the cord providing communication between different levels of the CNS Columns or funiculi—three pairs of these white matter bundles – Posterior (dorsal), lateral, and anterior (ventral) columns on each side Tracts or fasciculi—subdivisions of each column ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Spinal Tracts Fibers in a given tract have similar origin, destination and function Ascending tracts—carry sensory information up Descending tracts—carry motor information down Decussation—crossing of the midline that occurs in many tracts so that brain senses and controls contralateral side of body Contralateral—when the origin and destination of a tract are on opposite sides of the body Ipsilateral—when the origin and destination of a tract are on the same side of the body; does not decussate ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Tracts of the Spinal Cord Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.4 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Figure 12.30 Major ascending (sensory) and descending (motor) tracts of the spinal cord, cross-sectional view. Ascending tracts Descending tracts Ventral white Dorsal Fasciculus gracilis commissure white Fasciculus cuneatus Lateral column reticulospinal tract Dorsal Lateral spinocerebellar tract corticospinal tract Ventral Rubrospinal tract spinocerebellar tract Medial Lateral spinothalamic reticulospinal tract tract Ventral corticospinal tract Ventral spinothalamic tract Vestibulospinal tract Tectospinal tract ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Dorsal root Dorsal horn (interneurons) (sensory) Dorsal root ganglion SS VS Somatic sensory neuron VM Visceral sensory neuron SM Visceral motor neuron Somatic motor neuron Spinal nerve Ventral horn Ventral root (motor neurons) (motor) SS Interneurons receiving input from somatic sensory neurons VS Interneurons receiving input from visceral sensory neurons VM Visceral motor (autonomic) neurons SM Somatic motor neurons ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Ascending Tracts Ascending tracts carry sensory signals up the spinal cord Sensory signals travel across three neurons from origin (receptors) to destinations in the sensory areas of the brain – First-order neurons: detect stimulus and transmit signal to spinal cord or brainstem – Second-order neurons: continues to the thalamus at the upper end of the brainstem – Third-order neurons: carries the signal the rest of the way to the sensory region of the cerebral cortex Gracile fasciculus Cuneate fasciculus Spinothalamic tract Spinoreticular tract Posterior (dorsal) and anterior (ventral) spinocerebellar tracts ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Gracile Fasciculus Gracile fasciculus carries signals from midthoracic and lower parts of body Below T6, it composes the entire posterior column – At T6 and above, it is accompanied by cuneate fasciculus Consists of first-order nerve fibers traveling up the ipsilateral side of the spinal cord Terminates at gracile nucleus of medulla oblongata Carries signals for vibration, visceral pain, deep and discriminative touch, and proprioception from lower limbs and lower trunk Proprioception—nonvisual sense of the position and movements of the body ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Cuneate Fasciculus At T6 and above, cuneate fasciculus occupies lateral portion of posterior column (pushes gracile fasciculus medially) It contains first order neurons carrying the same type of sensory signals as the gracile fasciculus – Its signals are from upper limb and chest Fibers end in cuneate nucleus of ipsilateral medulla oblongata Second order neurons of gracile and cuneate nuclei decussate and form the medial lemniscus—a tract leading to thalamus Third-order neurons go from thalamus to cerebral cortex, carrying signals to cerebral hemisphere – Due to crossing of 2nd order neurons, the left hemisphere processes stimuli from right side of body, and vice versa ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Figure 12.31a Pathways of selected ascending spinal cord tracts. (2 of 2) Dorsal Medial lemniscus (tract) spinocerebellar (axons of second-order neurons) tract (axons of Nucleus gracilis second-order neurons) Nucleus cuneatus Medulla oblongata Fasciculus cuneatus (axon of first-order sensory neuron) Joint stretch receptor Axon of (proprioceptor) first-order Cervical spinal cord neuron Muscle Fasciculus gracilis spindle (axon of first-order sensory neuron) (proprioceptor) Lumbar spinal cord Touch receptor Spinocerebellar pathway Dorsal column–medial lemniscal pathway ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Figure 12.31a Pathways of selected ascending spinal cord tracts. (1 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons Spinocerebellar pathway Dorsal column–medial lemniscal pathway ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Some Ascending Pathways of the CNS Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.5 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Spinothalamic Tract Spinothalamic tract is part of the anterolateral system that passes up the anterior and lateral columns of the spinal cord It carries signals for pain, pressure, temperature, light touch, tickle, and itch The tract is made up of axons of second-order neurons – First-order neurons end in posterior horn of spinal cord – Second-order neurons start in posterior horn, then decussate and form the spinothalamic tract – Third-order neurons continue from there to cerebral cortex Due to cross of second-order neurons, signals are sent to cerebral hemisphere that is contralateral to site of stimulus ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Figure 12.31b Pathways of selected ascending spinal cord tracts. (2 of 2) Lateral spinothalamic tract (axons of second-order neurons) Medulla oblongata Pain receptors Cervical spinal cord Axons of first-order neurons Temperature Lumbar spinal cord receptors Spinothalamic pathway ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Figure 12.31b Pathways of selected ascending spinal cord tracts. (1 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons Spinothalamic pathway ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Spinoreticular Tract Spinoreticular tract travels up anterolateral system Carries pain signals resulting from tissue injury It is made up of axons of second-order neurons – First-order neurons enter posterior horn and immediately synapse with second-order neurons – Second-order neurons decussate to opposite anterolateral system Ascend the cord and end in reticular formation: loosely organized core of gray matter in the medulla and pons – Third-order neurons continue from the pons to the thalamus – Fourth-order neurons complete the path to the cerebral ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Spinocerebellar Tracts Anterior and posterior spinocerebellar tracts travel through lateral column Carry proprioceptive signals from limbs and trunk up to the cerebellum They are made up of axons of second-order neurons – First-order neurons originate in the muscles and tendons and end in posterior horn of the spinal cord – Second-order nerves ascend spinocerebellar tracts and end in cerebellum providing it with feedback needed to coordinate movements – Posterior spinocerebellar tract stays ipsilateral – Anterior spinocerebellar tracts cross over and travel up contralateral side, but cross back to end in ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Descending Tracts 1 Descending tracts—carry motor signals down brainstem and spinal cord Involve two motor neurons – Upper motor neuron originates in cerebral cortex or brainstem and terminates on a lower motor neuron – Lower motor neuron neurosoma is in brainstem or spinal cord Axon of lower motor neuron leads to muscle or other target organ ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Corticospinal Tracts Corticospinal tracts carry signals from cerebral cortex for precise, finely coordinated movements Pyramids—ridges on anterior surface of medulla oblongata formed from fibers of this system Most fibers decussate in lower medulla forming the lateral corticospinal tract on contralateral side of spinal cord Some fibers form the anterior (ventral) corticospinal tract that descends in the ipsilateral side of spinal cord and decussates inferiorly (like lateral tract, they ultimately control contralateral muscles) ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Two Descending Pathways of the CNS Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.6 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Figure 12.32a Three descending pathways by which the brain influences movement. (1 of 2) Pyramidal cells (upper motor neurons) Primary motor cortex Internal capsule Cerebrum Midbrain Cerebral peduncle Cerebellum Pons Pyramidal (lateral and ventral corticospinal) pathways ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Figure 12.32a Three descending pathways by which the brain influences movement. (2 of 2) Ventral corticospinal tract Medulla oblongata Pyramids Decussation of pyramids Lateral corticospinal tract Cervical spinal cord Skeletal muscle Lumbar spinal cord Somatic motor neurons (lower motor neurons) Pyramidal (lateral and ventral corticospinal) pathways ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Descending Tracts 2 Tectospinal tract—begins in midbrain region (tectum) – Crosses to contralateral side of midbrain – Reflex turning of head in response to sights and sounds Lateral and medial reticulospinal tracts – Originate in the reticular formation of brainstem – Control muscles of upper and lower limbs, especially those for posture and balance – Contain descending analgesic pathways Reduce the transmission of pain signals to brain Lateral and medial vestibulospinal tracts – Begin in brainstem vestibular nuclei – Receive impulses for balance from inner ear – Control extensor muscles of limbs for balance control ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education. ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Poliomyelitis and ALS 1 Both diseases cause destruction of motor neurons leading to skeletal muscle atrophy from lack of innervation Poliomyelitis – Caused by the poliovirus – Destroys motor neurons in brainstem and anterior horn of spinal cord – Signs of polio include muscle pain, weakness, and loss of some reflexes Followed by paralysis, muscular atrophy, and respiratory arrest – Virus spreads by fecal contamination of water ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Poliomyelitis and ALS 2 Amyotrophic lateral sclerosis (ALS) or Lou Gehrig disease – Destruction of motor neurons and muscular atrophy – Also sclerosis (scarring) of lateral regions of the spinal cord – Astrocytes fail to reabsorb the neurotransmitter glutamate from the tissue fluid Accumulates to toxic levels – Early signs: muscular weakness; difficulty speaking, swallowing, and using hands – Sensory and intellectual functions remain unaffected ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Anatomy of a Nerve Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.8a ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Dorsal root Dorsal horn (interneurons) (sensory) Dorsal root ganglion SS VS Somatic sensory neuron VM Visceral sensory neuron SM Visceral motor neuron Somatic motor neuron Spinal nerve Ventral horn Ventral root (motor neurons) (motor) SS Interneurons receiving input from somatic sensory neurons VS Interneurons receiving input from visceral sensory neurons VM Visceral motor (autonomic) neurons SM Somatic motor neurons ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  General Anatomy of Nerves and Ganglia 1 with the rest of Spinal cord communicates the body by way of spinal nerves Nerve—a cord-like organ composed of numerous nerve fibers (axons) bound together by connective tissue – Mixed nerves contain both afferent (sensory) and efferent (motor) fibers ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  General Anatomy of Nerves and Ganglia Sensory (afferent) nerves 3 – Carry signals from sensory receptors to the CNS Motor (efferent) nerves – Carry signals from CNS to muscles and glands Mixed nerves – Consists of both afferent and efferent fibers Both sensory and motor fibers can also be described as: – Somatic or visceral – ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  General Anatomy of Nerves and Ganglia Ganglion—cluster 4 of neurosomas outside the CNS – Enveloped in an endoneurium continuous with that of the nerve Among neurosomas are bundles of nerve fibers leading into and out of the ganglion Posterior root ganglion associated with spinal nerves ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Anatomy of a Ganglion Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.9 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Spinal Nerves 31 pairs of spinal nerves (mixed nerves) – 8 cervical (C1–C8) First cervical nerve exits between skull and atlas Others exit at intervertebral foramina – 12 thoracic (T1–T12) – 5 lumbar (L1–L5) – 5 sacral (S1–S5) – 1 coccygeal (Co1) ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Proximal Branches Each spinal nerve is formed from two roots (proximal branches) – Posterior (dorsal) root is sensory input to spinal cord Posterior (dorsal) root ganglion—contains the neurosomas of sensory neurons carrying signals to the spinal cord Six to eight rootlets enter posterior horn of cord – Anterior (ventral) root is motor output out of spinal cord Six to eight rootlets leave spinal cord and converge to form anterior root – Cauda equina: formed from roots arising from ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Spinal Nerve Roots and Plexuses Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.10 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Nerve Plexuses 1 Anterior rami branch and anastomose repeatedly to form five nerve plexuses – Cervical plexus in the neck, C1 to C5 Supplies neck and phrenic nerve to the diaphragm – Brachial plexus near the shoulder, C5 to T1 Supplies upper limb and some of shoulder and neck Median nerve—carpal tunnel syndrome – Lumbar plexus in the lower back, L1 to L4 Supplies abdominal wall, anterior thigh, and genitalia – Sacral plexus in the pelvis, L4, L5, and S1 to S4 Supplies remainder of lower trunk and lower limb – Coccygeal plexus, S4, S5, and Co1 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Nerve Plexuses 2 Somatosensory function—carry sensory signals from bones, joints, muscles, and skin – Proprioception: brain receives information about body position and movements from nerve endings in muscles, tendons, and joints Motor function—primarily to stimulate muscle contraction ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Cervical Plexus Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.14 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Brachial Plexus 1 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.15 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Brachial Plexus 2 Copyright © McGraw-Hill Education. Permission required for reproduction or display. © McGraw-Hill Education/Photo and Dissection by Christine Eckel Figure 13.16 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Lumbar Plexus Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.17 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Sacral and Coccygeal Plexuses Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.18 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Nerve Injuries Radial nerve injury – Passes through axilla – Crutch paralysis – Wrist drop Sciatic nerve injury – Sciatica: sharp pain that travels from gluteal region along the posterior side of the thigh and leg to ankle – 90% of cases result from herniated intervertebral disc or osteoporosis of lower spine ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Cutaneous Innervation and Dermatome—aDermatomes specific area of skin that conveys sensory input to a spinal nerve Dermatome map—a diagram of the cutaneous regions innervated by each spinal nerve Dermatomes overlap their edges as much as 50% – Necessary to anesthetize three successive spinal nerves to produce a total loss of sensation in one dermatome ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  A Dermatome Map Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.19 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Nature of Reflexes 1 Reflexes—quick, involuntary, stereotyped reactions of glands or muscle to stimulation – Reflexes require stimulation Not spontaneous actions, but responses to sensory input – Reflexes are quick Involve few, if any, interneurons and minimum synaptic delay – Reflexes are involuntary Occur without intent and are difficult to suppress – Reflexes are stereotyped Occur essentially the same way every time ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Nature of Reflexes Reflexes include glandular2secretion and contraction of all three types of muscle Somatic reflexes—reflexes involving the somatic nervous system innervating skeletal muscle ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Nature of Reflexes Pathway of a somatic reflex arc3 – Somatic receptors In skin, muscles, or tendons – Afferent nerve fibers Carry information from receptors to posterior horn of spinal cord or to the brainstem – Integrating center A point of synaptic contact between neurons in gray matter of cord or brainstem Determines whether efferent neurons issue signal to muscles – Efferent nerve fibers Carry motor impulses to muscles – Effectors The muscles that carry out the response ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  A Representative Reflex Arc Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 13.20 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Muscle Spindle Muscle spindle—stretch1receptors embedded in skeletal muscles Proprioceptors—specialized sense organs to monitor position and movement of body parts Muscle spindles inform the brain of muscle length and body movement Enables brain to send motor commands back to the muscles that control coordinated movement, corrective reflexes, muscle tone, and posture ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  A Muscle Spindle and Its Copyright © McGraw-Hill Education. Permission required for Innervation reproduction or display. Figure 13.21 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.