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Chapter13 15(one section)
The document discusses the anatomy and function of the spinal cord and spinal nerves. It begins by describing the gross anatomy of the spinal cord, including the 31 pairs of spinal nerves and their numbering. It then discusses the functional organization of the spinal cord gray matter into dorsal, lateral, and ventral horns that contain sensory and motor nuclei. The document also describes the monosynaptic and polysynaptic reflex arcs in the spinal cord that underlie reflexes like the stretch reflex. It concludes by discussing spinal nerve structure and the dermatomal distribution of cutaneous innervation.
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Chapter13 15(one section)
- 1. Miscellaneous http://faculty.plattsburgh.edu/donald.slish/DA. html The above linkwill show drugs and impact at synapse
- 2. Chapter13a OrganizationoftheNervousSystem Kathleen Cercone PT,PhD http://www.mmi.mcgill.ca/mmimediasampler/default.htm Go down, will see what we talked about last class
- 3. © 2015 PearsonEducation, Inc.© 2015 Pearson Education, Inc. You can view The relationship of the spinal nerve and the vertebrae that they exit under or above Cervical, C1 spinal nerve, above the vertebrae C8 is below C7 T1 now under T1 To right: The conus medullaris, horses tail and the spinal nerve from the spinal cord must travel to exit under the vertebrae is belongs under
- 4. In Ch. 13,we focus on the spinal cord—we will deal with cranial nerves later • sensory receptors / neurons (Chap. 15) • spinal cord and spinal nerves (Chap. 13) motor neurons / NMJs (Chap. 10) • spinal reflex arcs (Chap. 13)
- 6. A. Functional Organization Spinalreflexes: What is a reflex? • sensory receptors / neurons (Chap. 15) • spinal cord and spinal nerves (Chap. 13) motor neurons / NMJs (Chap. 10) • spinal reflex arcs (Chap. 13)
- 11. A.GrossAnatomyoftheSpinalCord Spinal Nerve Numbering •31 pairs, corresponding to spinal nerve origins • 8 cervical: – nerve C1 – C7 above vertebra they are named for – nerve C8 below C7 and above T1) • 12 thoracic, 5 lumbar (below vertebra they are named for) • 5 sacral, 1 coccygeal
- 12. 13-2SpinalCord 31 Spinal CordSegments Based on vertebrae where spinal nerves originate Positions of spinal segment and vertebrae change with age Cervical nerves Named for inferior vertebra All other nerves Named for superior vertebra
- 15. Subarachnoid space Contains cerebrospinalfluid (CSF) that acts as shock absorber and diffusion medium Lumbar puncture (spinal tap) withdraws CSF
- 16.
- 19. An anterior viewof the cervical spinal cord showing the meninges, supporting ligaments, and the roots of the spinal nerves Denticulate ligaments Blood vessels within the subarachnoid space Spinal cord Anterior median fissure Pia mater Dorsal root Ventral root, formed by several “rootlets” from one cervical segment Arachnoid mater (reflected) Dura mater (reflected) Supporting ligaments: Prevent lateral movement of spinal cord Denticulate ligaments; Extend from pia mater through arachnoid to dura mater
- 20. © 2013 PearsonEducation, Inc. This cross section through the cervical region of the spinal cord shows some prominent features and the arrangement of gray matter and white matter. C3 Dorsal root Dorsal root ganglion Central canal Spinal nerve Ventral root Posterior median sulcus White matter Gray matter Anterior median fissure
- 25. b Figure13-5TheSectionalOrganizationoftheSpinalCord. Dorsal root ganglion Lateral white column Posteriorgray horn Lateral gray horn Anterior gray horn Anterior white column Posterior white column Posterior median sulcus Posterior gray commissure Somatic Visceral Somatic Visceral Ventral root Sensory nuclei Motor nuclei The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. Functional Organization of Gray Matter Posterior median sulcus Anterior gray commissure Anterior white commissure Anterior median fissure Posterior gray commissure Dura mater Arachnoid mater (broken) Central canal Anterior gray commissure Anterior median fissure Pia mater ANTERIOR POSTERIOR Structural Organization of Gray Matter The projections of gray matter toward the outer surface of the spinal cord are called horns. Posterior gray horn Lateral gray horn Dorsal root Anterior gray horn Dorsal root ganglion Ventral root A micrograph of a transverse section through the spinal cord, showing major landmarks in and surrounding the cord. The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns. a
- 28. Different levels alongthe spinal cord join together to form the spinal nerve. The nerve is a mixed nerve as it has afferent and efferent fibers, sensory, motor fibers join together as 1 spinal nerve
- 31. Spinal nerve 1. Dorsalramus 2. Ventral ramus 3. Spinal Nerve 4. Afferent 5. Efferent
- 32. © 2015 PearsonEducation, Inc.© 2015 Pearson Education, Inc.
- 33. Neuron Pathways and NucleiLocations White matter in spinal cord: 1. posterior white columns 2. anterior white columns; 3. lateral white columns 4. anterior white commissure – axons crossing to opposite side of spinal cord
- 38. Most of thespinal nerves are associated with specific dermatomes (an area of skin innervated by all the cutaneous neurons of a certain spinal or cranial nerve).
- 41. Sensation Our bodies areconstantly exposed to sensory information called stimuli. Sensation is a conscious or unconscious awareness of external or internal stimuli. – information about conditions inside or outside the body Perception is the conscious awareness and interpretation of sensations. the conscious awareness and interpretation of a sensation
- 45. Sensory Transduction translatesthe sensory stimulus to an action potential
- 48. Free nerve endingsaRoot hair plexusb c d e Tactile discs Tactile corpuscle Lamellated corpuscle Hair Tactile disc Tactile corpuscle Free nerve ending Ruffini corpuscle Sensory nerve Lamellated corpuscle Root hair plexus Root hair plexus f Ruffini corpuscle Tactile corpuscle Sensory nerve fiber Dermis Dendrites Capsule Epidermis Tactile corpuscle Merkel cell Nerve terminal (dendrite) Tactile disc Afferent nerve fiber Dermis Dendritic process Accessory cells (specialized fibroblasts) Concentric layers (lamellae) of collagen fibers separated by fluid Lamellated corpuscle (cross section) LM × 330 LM × 125 These are tactile receptors in the Skin
- 49. ReflexesandNeuralCircuits Neuronal pools Functional groupsof interconnected neurons Most cases are interneurons in CNS May involve several regions of brain May involve neurons in one specific location in brain or spinal cord Estimated number of pools ~100s to 1000s Patterns of neuronal interactions suggest functional classifications Neural circuit (“wiring diagram”) Simple circuits in PNS and spinal cord control reflexes Preprogrammed responses to specific stimuli
- 50. Work like a“team” in a business
- 52. Arrival of stimulus and activationof receptor Activation of a sensory neuron Dorsal root Sensation relayed to the brain by axon collaterals Spinal cord Receptor Stimulus Effector Response by a peripheral effector Activation of a motor neuron Ventral root REFLEX ARC KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated) Information processing in the CNS 3 2 4 5 1 Steps in reflex: • muscle spindle detects stretch of muscle • sensory neuron is activated • sensory neuron signals across a synapse in the spinal cord to a motor neuron • motor neuron is activated • motor neuron signals across a NMJ to skeletal muscle fibers Some reflexes are inborn, such as pulling your hand away from a hot surface before you even feel that it is hot
- 54.
- 55. Response REFLEX ARC Stimulus Stretch Receptor (muscle spindle) Effector Spinal cord Sensory neuron (stimulated) Motorneuron (stimulated) KEY http://www.sumanasinc.com/webcontent/animations/conte nt/reflexarcs2.html http://www2.sunysuffolk.edu/pickenc/Reflex%20Arc.swf
- 56. 13-7SpinalReflexes Muscle Spindles The receptorsin stretch reflexes Bundles of small, specialized intrafusal muscle fibers (receptors) Innervated by sensory and motor neurons Surrounded by extrafusal muscle fibers (effectors) Which maintain tone and contract muscle reflex arc: intrafusal fibers → sensory neuron extrafusal fibers ← motor neuron
- 57. Intrafusal muscle fibersof a muscle spindle Specialized fibers with a central sensory region has myofibrils in terminal regions only innervated by 2 types of neurons: 1.sensory neurons: detect stretch of the sensory region 2. gamma motor neurons: adjust tone by controlling the terminal regions
- 58. Sensory (stretch) receptor Monosynapticreflex: Direct communication between sensory and motor neuron Polysynaptic reflex: Interneuron facilitates sensory-motor communication Sensory receptor Sensory neuron Interneuron Motor neuron Spinal cord Sensory neuron Motor neuron Effector organ Effector organ Monosynaptic and Polysynaptic Reflexes
- 59. Painful stimulus Flexors stimulated Extensors inhibited Distribution within grayhorns to other segments of the spinal cord Withdrawal reflex—polysynaptic reflex arc Painful stimulus causes transmission of sensory information to the spinal cord. Interneurons receive the sensory information and stimulate the motor neurons to direct flexor muscles to contract in response. Simultaneously, antagonistic extensor muscles are inhibited so that the traumatized body part may be quickly withdrawn from the harmful stimulation.
- 60. The crossed extensorreflex, which involves a contralateral reflex arc To motor neurons in other segments of the spinal cord Painful stimulus Extensors stimulated Flexors inhibited Extensors inhibited Flexors stimulated Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated) Motor neuron (inhibited) Inhibitory interneuron Step on tack Flexor reflex pulls injured foot away a. Flexor muscles stimulated b. Extensor muscles inhibited Crossed extensor reflex straightens uninjured leg and supports shifting weight Activated by collaterals of excitatory and inhibitory interneurons Extensor muscles stimulated Flexor muscles inhibited
- 62. b Figure13-17TheBabinskiReflexes. The plantar reflex (negativeBabinski reflex), a curling of the toes, is seen in healthy adults. The Babinski sign (positive Babinski reflex) occurs in the absence of descending inhibition. It is normal in infants, but pathological in adults. a
- 63. 13-2Spinal Cord The Interlayer Spaces of Arachnoid Mater CerebrospinalFluid (CSF) Carries dissolved gases, nutrients, and wastes Lumbar puncture or spinal tap withdraws CSF
- 64. Spinalnervestructureanddistribution Shingles: Viral infection ofdorsal root ganglia Caused by varicella-zoster virus Same herpes virus as chickenpox Produces painful rash and blisters on dermatome served by infected nerves Those who have had chickenpox are more at risk Virus can remain dormant within anterior gray horns Unknown trigger for reactivation
Editor's Notes
- #3 Did you ever wonder why spinal cord injuries can have such widespread effects on the body?
- #5 The spinal cord and spinal nerves and homeostasis The spinal cord and spinal nerves contribute to homeostasis by providing quick, reflexive responses to many stimuli. The spinal cord is the pathway for sensory input to the brain and motor output from the brain. About 100 million neurons and even more neuroglia compose the spinal cord, the part of the central nervous system that extends from the brain. The spinal cord and its associated spinal nerves contain neural circuits that control some of your most rapid reactions to environmental changes. If you pick up something hot, the grasping muscles may relax and you may drop the hot object even before you are consciously aware of the extreme heat or pain. This is an example of a spinal cord reflex—a quick, automatic response to certain kinds of stimuli that involves neurons only in the spinal nerves and spinal cord. Besides processing reflexes, the gray matter of the spinal cord also is a site for integration (summing) of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs), which you learned about in Chapter 12. These graded potentials arise as neurotransmitter molecules interact with their receptors at synapses in the spinal cord. The white matter of the spinal cord contains a dozen major sensory and motor tracts, which function as the “highways” along which sensory input travels to the brain and motor output travels from the brain to skeletal muscles and other effectors. Recall that the spinal cord is continuous with the brain and that together they make up the central nervous system (CNS)
- #13 The various spinal cord segments vary in size, shape, relative amounts of gray and white matter, and distribution and shape of gray matter. For example, the amount of gray matter is largest in the cervical and lumbar segments of the spinal cord because these segments are responsible for sensory and motor innervation of the limbs. In addition, more sensory and motor tracts are present in the upper segments of the spinal cord than in the lower segments. Therefore, the amount of white matter decreases from cervical to sacral segments of the spinal cord. There are two major reasons for this variation in spinal cord white matter: (1) As the spinal cord ascends from sacral to cervical segments, more ascending axons are added to spinal cord white matter to form more sensory tracts. (2) As the spinal cord descends from cervical to sacral segments, the motor tracts decrease in thickness as more descending axons leave the motor tracts to synapse with neurons in the gray matter of the spinal cord
- #14 After emerging from spinal cord, each spinal nerve divides into dorsal and ventral rami - rami contain both, efferent motor and afferent sensory fibers - smaller dorsal rami serve the skin and muscles of the posterior body trunk - larger ventral rami of spinal nerves T2 - T12 pass anteriorly as intercostal nerves; supply muscles of the intercostal spaces, the skin and muscles of the anterior and lateral trunk; Ventral rami of all other spinal nerves form complex nerve networks called plexi; serve the motor and sensory needs of the upper and lower limbs. 4 major nerve plexi are found, which are: 1. Cervical plexus 2. Brachial plexus 3. Lumbar plexus 4. Sacral plexus
- #16 Subarachnoid space: location of the subarachnoid trabeculae filled with cerebrospinal fluid (CSF) Shock absorber and diffusion medium for dissolved gases, nutrients, chemical messengers, and wastes spinal tap = sampling of CSF from subarachnoid space
- #17 Three layers Dura mater (dura, hard) Outermost covering Contains dense collagen fibers oriented longitudinally prevents longitudinal movement coccygeal ligament = blended fibers of dura mater and filum terminale Has narrow subdural space separating from arachnoid mater Subdural space Between arachnoid mater and dura mater Subarachnoid space Between arachnoid mater and pia mater Contains collagen/elastin fiber network (arachnoid trabeculae) Filled with cerebrospinal fluid (CSF)
- #20 Figure 12.2.3 The spinal cord is surrounded by the meninges, which consist of the dura mater, arachnoid mater, and pia mater Structures of the Spinal Cord Paired denticulate ligaments Extend from pia mater to dura mater Stabilize side-to-side movement Blood vessels Along surface of spinal pia mater Within subarachnoid space Pia mater: meshwork of elastic and collagen fibers attached to neural tissue of spinal cord denticulate ligaments – extend laterally to dura mater; prevent lateral movement Structures of the Spinal Cord Paired denticulate ligaments Extend from pia mater to dura mater Stabilize side-to-side movement Blood vessels Along surface of spinal pia mater Within subarachnoid space Pia mater: meshwork of elastic and collagen fibers attached to neural tissue of spinal cord denticulate ligaments – extend laterally to dura mater; prevent lateral movement
- #22 gray commissures: axons crossing to opposite side of spinal cord (important for many reflexes—e.g. if you step on a tack with your right foot, your left foot needs to stabilize as you jerk up the right foot)
- #23 White matter is divided into columns Columns contain TRACTS; composed of axons of similar structural and functional characteristics Specific tracts convey either sensory or motor commands All axons in a tract relay information in the same direction ASCENDING TRACTS relay sensory information toward the brain DESCENDING TRACTS relay motor information into the spinal cord Gray matter is organized into nuclei – neuron cell bodies Sensory nuclei receive and relay sensory information Motor nuclei send out commands to peripheral effectors, skeletal muscles
- #26 Gray Matter: Centrally located in spinal cord Sectioned shape resembles butterfly Subdivided into: Anterior Horns Lateral Horns Posterior Horns Gray Commissure The posterior gray horns contain axons of sensory neurons, and cell bodies and axons of interneurons. Nuclei: functional groups of cell bodies in gray matter of the brain and spinal cord two types in spinal cord: sensory nuclei motor nuclei
- #30 Root – inside vertebral canal a. dorsal sensory root with a ganglion b. ventral motor 2. Mixed spinal nerve 3. Rami a. dorsal - mixed to skin and muscles of back b. ventral - mixed “spinal nerve” to ventrolateral body surfaces and limbs c. white ramus communicans motor ANS d. gray ramus communicans motor ANS Spinal nerves are associated with the spinal cord and, like all nerves of the peripheral nervous system (PNS), are parallel bundles of axons and their associated neuroglial cells wrapped in several layers of connective tissue. Spinal nerves connect the CNS to sensory receptors, muscles, and glands in all parts of the body. The 31 pairs of spinal nerves are named and numbered according to the region and level of the vertebral column from which they emerge. Not all spinal cord segments are aligned with their corresponding vertebrae. Recall that the spinal cord ends near the level of the superior border of the second lumbar vertebra (L2), and that the roots of the lumbar, sacral, and coccygeal nerves descend at an angle to reach their respective foramina before emerging from the vertebral column. This arrangement constitutes the cauda equina.
- #34 A short distance after passing through its intervertebral foramen, a spinal nerve divides into several branches. These branches are known as rami (RĀ-mī = branches). The posterior (dorsal) ramus (RĀ-mus; singular form) serves the deep muscles and skin of the posterior surface of the trunk. The anterior (ventral) ramus serves the muscles and structures of the upper and lower limbs and the skin of the lateral and anterior surfaces of the trunk. In addition to posterior and anterior rami, spinal nerves also give off a meningeal branch (me-NIN-jē′-al). This branch reenters the vertebral cavity through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges. Other branches of a spinal nerve are the rami communicantes (kō-mū-ni-KAN-tēz), components of the autonomic nervous system
- #37 Move to next slide just point out that this is in the book and is the same as mine Information transmitted through dorsal and ventral rami of spinal nerves: somatic sensations from exteroceptors and proprioceptors visceral sensations from interoceptors somatic motor commands to skeletal muscles visceral motor commands to smooth muscle and glands
- #39 A dermatome is a specific segment of skin supplied by a single spinal nerve. All spinal nerves except C1 innervate a segment of skin. The dermatome map follows a segmental pattern along the body Dermatomes The skin over the entire body is supplied by somatic sensory neurons that carry nerve impulses from the skin into the spinal cord and brain. Each spinal nerve contains sensory neurons that serve a specific, predictable segment of the body. One of the cranial nerves, the trigeminal (V) nerve, serves most of the skin of the face and scalp. The area of the skin that provides sensory input to the CNS via one pair of spinal nerves or the trigeminal (V) nerve is called a dermatome (DER-ma-tōm; derma- = skin; -tome = thin segment) . The nerve supply in adjacent dermatomes overlaps somewhat. Knowing which spinal cord segments supply each dermatome makes it possible to locate damaged regions of the spinal cord. If the skin in a particular region is stimulated but the sensation is not perceived, the nerves supplying that dermatome are probably damaged. In regions where the overlap is considerable, little loss of sensation may result if only one of the nerves supplying the dermatome is damaged. Information about the innervation patterns of spinal nerves can also be used therapeutically. Cutting posterior roots or infusing local anesthetics can block pain either permanently or transiently. Because dermatomes overlap, deliberate production of a region of complete anesthesia may require that at least three adjacent spinal nerves be cut or blocked by an anesthetic drug.
- #42 Our bodies are constantly exposed to sensory information called stimuli. Our conscious awareness to these stimuli is called sensation. Stimuli are detected by receptors in our body. There are two classes of receptors: general senses receptors—temperature, pain, touch, stretch, and pressure special senses receptors—gustation, olfaction vision, equilibrium, and audition
- #49 On a microscopic level, sensory receptors may be one of the following: (1) free nerve endings of first-order sensory neurons, (2) encapsulated nerve endings of first-order sensory neurons, or (3) separate cells that synapse with first-order sensory neurons. C. By contrast, sensory receptors that are separate cells produce graded potentials termed receptor potentials. Receptor potentials trigger release of neurotransmitter through exocytosis of synaptic vesicles . The neurotransmitter molecules liberated from synaptic vesicles diffuse across the synaptic cleft and produce a postsynaptic potential (PSP) in the first-order neuron. In turn, the PSPs may trigger one or more nerve impulses, which propagate along the axon into the CNS. The amplitude of both generator potentials and receptor potentials varies with the intensity of the stimulus, with an intense stimulus producing a large potential and a weak stimulus eliciting a small one. Similarly, large generator potentials or receptor potentials trigger nerve impulses at high frequencies in the first-order neuron, in contrast to small generator potentials or receptor potentials, which trigger nerve impulses at lower frequencies.
- #53 A reflex is a fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus. Some reflexes are inborn, such as pulling your hand away from a hot surface before you even feel that it is hot. Other reflexes are learned or acquired. For instance, you learn many reflexes while acquiring driving expertise. Slamming on the brakes in an emergency is one example. When integration takes place in the spinal cord gray matter, the reflex is a spinal reflex. An example is the familiar patellar reflex (knee jerk). If integration occurs in the brain stem rather than the spinal cord, the reflex is called a cranial reflex. An example is the tracking movements of your eyes as you read this sentence. You are probably most aware of somatic reflexes, which involve contraction of skeletal muscles. Equally important, however, are the autonomic (visceral) reflexes, which generally are not consciously perceived. They involve responses of smooth muscle, cardiac muscle, and glands.
- #56 Because reflexes are normally so predictable, they provide useful information about the health of the nervous system and can greatly aid diagnosis of disease. Damage or disease anywhere along its reflex arc can cause a reflex to be absent or abnormal. For example, tapping the patellar ligament normally causes reflex extension of the knee joint. Absence of the patellar reflex could indicate damage of the sensory or motor neurons, or a spinal cord injury in the lumbar region. Somatic reflexes generally can be tested simply by tapping or stroking the body surface.
- #57 In addition to the large-diameter motor neurons that innervate typical skeletal muscle fibers, smaller-diameter motor neurons innervate smaller, specialized muscle fibers within the muscle spindles themselves. The brain regulates muscle spindle sensitivity through pathways to these smaller motor neurons. This regulation ensures proper muscle spindle signaling over a wide range of muscle lengths during voluntary and reflex contractions. By adjusting how vigorously a muscle spindle responds to stretching, the brain sets an overall level of muscle tone, which is the small degree of contraction present while the muscle is at rest. Because the stimulus for the stretch reflex is stretching of muscle, this reflex helps avert injury by preventing overstretching of muscles. Although the stretch reflex pathway itself is monosynaptic (just two neurons and one synapse), a polysynaptic reflex arc to the antagonistic muscles operates at the same time. This arc involves three neurons and two synapses. An axon collateral (branch) from the muscle spindle sensory neuron also synapses with an inhibitory interneuron in the integrating center. In turn, the interneuron synapses with and inhibits a motor neuron that normally excites the antagonistic muscles . Thus, when the stretched muscle contracts during a stretch reflex, antagonistic muscles that oppose the contraction relax. This type of arrangement, in which the components of a neural circuit simultaneously cause contraction of one muscle and relaxation of its antagonists, is termed reciprocal innervation (rē-SIP-ro′-kal in′-er-VĀ-shun). Reciprocal innervation prevents conflict between opposing muscles and is vital in coordinating body movements.
- #58 Muscle spindles: contain muscle fibers which are both receptors & effectors for stretch reflexes intrafusal muscle fibers (receptors- sensory) extrafusal muscle fibers (effectors- motor)
- #61 Figure 12.11.2 Withdrawal reflexes and crossed extensor reflexes are polysynaptic reflexes
- #62 Figure 12.11.3 Withdrawal reflexes and crossed extensor reflexes are polysynaptic reflexes
- #63 The Babinski Reflexes Normal in infants May indicate CNS damage in adults • Babinski sign (ba-BIN-skē). This reflex results from gentle stroking of the lateral outer margin of the sole. The great toe extends, with or without a lateral fanning of the other toes. This phenomenon normally occurs in children under 1½ years of age and is due to incomplete myelination of fibers in the corticospinal tract. A positive Babinski sign after age 1½ is abnormal and indicates an interruption of the corticospinal tract as the result of a lesion of the tract, usually in the upper portion. The normal response after age 1½ is the plantar flexion reflex, or negative Babinski—a curling under of all the toes
- #64 Subarachnoid space: location of the subarachnoid trabeculae filled with cerebrospinal fluid (CSF) Shock absorber and diffusion medium for dissolved gases, nutrients, chemical messengers, and wastes spinal tap = sampling of CSF from subarachnoid space