© 2018 Pearson Education, Inc.

Module 12.1: The spinal cord can function independently from the brain
In this figure, because “Muscles” are listed on the top line, some students may incorrectly think it is saying that the brain controls all muscles. Be sure they realize both cranial and spinal nerves act on muscles, glands, and adipose tissue. © 2018 Pearson Education, Inc.

Module 12.1: The brain and spinal cord
Both the brain and the spinal cord: Receive sensory input from receptors Contain reflex centers Send motor output to effectors Reflex Rapid, automatic response triggered by specific stimuli Spinal reflexes Controlled in the spinal cord Function without input from the brain © 2018 Pearson Education, Inc.

Module 12.2: The spinal cord has 31 segments with 31 pairs of nerves
Spinal cord structure: cross section Outer white matter Inner gray matter with central canal White matter Gray matter Ask students to compare organization of white/gray matter in spinal cord to that of brain. © 2018 Pearson Education, Inc.

Module 12.2: Spinal cord structure
Adult length ~ 45 cm (18 in.) Max. width ~ 14 mm (0.55 in.) Ends at L1–L2 Spinal cord has 31 segments: 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal The figure is complex, and many students may struggle to grasp the concepts outlined here. One way to address this is to have them focus on each bullet point as you describe them. © 2018 Pearson Education, Inc.

Conus medullaris: cone-shaped end of spinal cord at L1–L2 Filum terminale (“terminal thread”) Strand of fibrous tissue from tip of conus medullaris to S2 Provides longitudinal support to spinal cord The figure is complex; point out the structures as you refer to them. Explain that the spinal cord stops growing sooner than the vertebral column, so lower spinal nerve roots elongate and travel as a cluster until each reaches the appropriate level of the vertebral column from which it emerges. This cluster of anterior and posterior roots forms the cauda equina. © 2018 Pearson Education, Inc.

Cauda equina (cauda, tail + equinus, horse) Extended anterior and posterior roots of spinal segments L2 to S5 and filum terminale Name comes from resemblance to a horse’s tail The figure is complex; point out the structures as you refer to them. Explain that the spinal cord stops growing sooner than the vertebral column, so lower spinal nerve roots elongate and travel as a cluster until each reaches the appropriate level of the vertebral column from which it emerges. This cluster of anterior and posterior roots forms the cauda equina. © 2018 Pearson Education, Inc.

Naming spinal nerves 31 pairs of spinal nerves arise from 31 spinal cord segments Designated by the region and number: C1 runs above 1st cervical vertebra C8 below 7th cervical vertebra All others named for vertebrae above Example: T1 is below 1st thoracic vertebra In the image, be sure students see that it is a lateral view. Because structures are color-coded by region rather than by structure, point out the bodies and spinous processes of the vertebrae and the spinal cord within the vertebral canal. © 2018 Pearson Education, Inc.

Cross-sectional spinal cord anatomy White matter—superficial; myelinated & unmyelinated axons Gray matter—deep; forms an H, or butterfly shape Mostly neuron cell bodies, neuroglia, unmyelinated axons Central canal—contains cerebrospinal fluid Remind students that white matter gets its appearance from myelin and ask what part of the neuron has myelin. This helps students relate structure to function. © 2018 Pearson Education, Inc.

Spinal nerve—axons of sensory and motor neurons Anterior root contains axons of motor neurons Posterior root contains axons of sensory neurons Posterior root ganglion (spinal ganglion) contains cell bodies of sensory neurons in posterior root Pointing to the components on the image as you describe them helps students follow. You can reinforce the directionality of the roots by tracking them in the correct direction as you describe them—posterior root in, anterior root out. Or, ask students to tell you which way the signals travel in each. © 2018 Pearson Education, Inc.

Module 12.3: Describe the three meningeal layers that surround the spinal cord
Spinal meninges 3 specialized membranes surrounding spinal cord and continuous with the cranial meninges Dura mater—outermost layer Arachnoid mater— middle layer Pia mater—innermost layer Functions Physical stability Shock absorption Carry blood supply (oxygen and nutrients) © 2018 Pearson Education, Inc.

Dura mater (dura, hard + mater, mother)
Module 12.3: Meninges Dura mater (dura, hard + mater, mother) Outermost covering Tough, fibrous Dense collagen fibers oriented along the longitudinal axis of the spinal cord © 2018 Pearson Education, Inc.

Arachnoid mater (arachne, spider + mater, mother)
Module 12.3: Meninges Arachnoid mater (arachne, spider + mater, mother) Middle meningeal layer Includes arachnoid membrane—layer of simple squamous epithelium Subarachnoid space— between arachnoid membrane and pia mater © 2018 Pearson Education, Inc.

Pia mater (pia, delicate + mater, mother)
Module 12.3: Meninges Pia mater (pia, delicate + mater, mother) Innermost meningeal layer Meshwork of elastic and collagen fibers Anchored to neural tissue © 2018 Pearson Education, Inc.

Spaces associated with meninges
Module 12.3: Meninges Spaces associated with meninges Subarachnoid space Contains arachnoid trabeculae—collagen and elastic fibers; anchor arachnoid mater to pia mater Contains cerebrospinal fluid (CSF)—shock absorber; diffusion of gases, nutrients, etc. Blood vessels for spinal cord are located here Epidural space Between dura mater and vertebrae Areolar tissue, blood vessels, and adipose tissue Consider reviewing CSF production and circulation. Might point out that epidural injections for anesthesia are administered into the epidural space. © 2018 Pearson Education, Inc.

Cross-sectional view of the spinal cord, showing the meninges and associated spaces
© 2018 Pearson Education, Inc.

Supporting ligaments maintain position of spinal cord
Module 12.3: Meninges Supporting ligaments maintain position of spinal cord Denticulate ligaments extend from pia mater through arachnoid mater to dura mater; prevent lateral movement Dural connections at foramen magnum and coccygeal ligaments at sacrum prevent superior–inferior movements Consider asking students why it is important to stabilize the cord, such as while jogging. © 2018 Pearson Education, Inc.

Lumbar puncture, or spinal tap
Module 12.3: Meninges Lumbar puncture, or spinal tap Withdraw sample of cerebrospinal fluid Needle inserted into subarachnoid space, lumbar region, below conus medullaris to avoid spinal cord Sagittal view of the lumbar spine, showing proper placement of a lumbar puncture needle. Point out the actual needle in the image at right—students may overlook it, mistaking the dark line for one of the label lines. X-ray of the lumbar vertebrae, showing the cauda equina © 2018 Pearson Education, Inc.

Structural organization of gray matter
Module 12.4: Gray matter integrates sensory and motor functions, and white matter carries information Structural organization of gray matter Posterior gray horn—somatic and visceral sensory nuclei Lateral gray horn—only in thoracic and lumbar segments; contains visceral motor nuclei Anterior gray horn—somatic motor nuclei Ask students to explain how they can tell anterior from posterior in a cross-sectional image such as this. This helps them focus better on the information presented in the image and improves their orientation. © 2018 Pearson Education, Inc.

Module 12.4: White and gray matter
Functional organization of gray matter Nuclei Functional groups of neuron cell bodies in gray matter of spinal cord Sensory nuclei receive and relay sensory information Motor nuclei issue motor commands to effectors Gray commissures (commissura, a joining) Contain axons that cross from side to side in spinal cord Located posterior and anterior to the central canal; named by this position Some students get confused by the term nuclei, confusing these with individual cell nuclei. Be sure students know the spinal cord is bilaterally symmetrical. The image is showing different information on each side for simplicity. © 2018 Pearson Education, Inc.

A cross-sectional view of the spinal cord
Note that sensory nuclei are located posteriorly, and motor nuclei are anterior. Be sure students see the red arrows—helps reinforce the directionality of the roots. © 2018 Pearson Education, Inc.

Structural organization of white matter Three columns on each side of spinal cord Posterior white column between posterior gray horns and posterior median sulcus Lateral white column between anterior and posterior columns Anterior white column between anterior gray horns Anterior white commissure Interconnects anterior white columns; axons cross side to side Another good opportunity to have students associate myelin with white matter—helps them remember white matter is mostly axons transmitting impulses to other areas. © 2018 Pearson Education, Inc.

White matter is organized in tracts Bundles of axons in CNS (similar to a nerve in PNS) Ascending tracts carry sensory information In posterior columns Descending tracts carry motor commands In anterior columns Ask students to think about ascending and descending tracts—should be able to understand why ascending are sensory and descending are motor. © 2018 Pearson Education, Inc.

Structural and functional organization of the white matter in the spinal cord
Consider pulling up an image of the sensory and motor homunculi and correlating those images with the specific areas of the spinal cord to help students better understand mapping. Point out that the colored areas in the lower right represent the organization of tracts in the anterior white column—they are not labeled the same as those of the posterior column, and the label for the anterior column is on the left side. © 2018 Pearson Education, Inc.

The posterior and anterior rami and rami communicantes of a spinal nerve
This image may seem complex for some students. Be sure they see the difference between a root and a ramus. Also have them say how they determine anterior and posterior in this image—the addition of the sympathetic ganglion may confuse some students who look for the posterior root ganglion for orientation. © 2018 Pearson Education, Inc.

Module 12.5: Spinal nerve organization
Dermatome A specific bilateral area of skin supplied by pair of spinal nerves C1 usually lacks a sensory branch; when present it supplies scalp with C2/C3 Face monitored by CN V Dermatome boundaries overlap Consider poking on some area of your body surface and having students determine the correct dermatome from the image. © 2018 Pearson Education, Inc.

Module 12.5: Spinal nerve organization
Shingles Varicella-zoster virus (VZV)—herpes virus; causes chickenpox and shingles Attacks neurons in posterior roots and sensory ganglia Painful rash/blisters along dermatome of affected nerve History of chickenpox increases risk of shingles—virus lies dormant; unknown trigger reactivates Single bout or recurrent Shingles vaccine now available Correlate the curvilinear pattern of shingles in this image with the pattern of dermatomes in the previous slide. © 2018 Pearson Education, Inc.

The path of sensory information in spinal nerves and the spinal cord
Point out that the arrows in the figure indicate the direction in which neural information is traveling. Consider reviewing the types of receptors mentioned here. © 2018 Pearson Education, Inc.

Module 12.6: Sensory and motor distribution
Motor commands—originate in motor nuclei Anterior root—axons of somatic and visceral motor neurons Spinal nerve forms at junction of anterior and poster roots Posterior ramus—somatic/visceral motor fibers to skin/skeletal muscles of back Anterior ramus—ventrolateral body surface, body wall, limbs © 2018 Pearson Education, Inc.

Module 12.6: Sensory and motor distribution
Motor commands—originate in motor nuclei (continued) White ramus communicans—short branch with preganglionic visceral motor fibers to sympathetic ganglia (white—myelinated) Gray ramus communicans—postganglionic fibers to glands/smooth muscle (gray— unmyelinated) Sympathetic nerve—pre-/postganglionic fibers to thoracic cavity © 2018 Pearson Education, Inc.

The path of motor information in spinal nerves and the spinal cord
Ask students what differences they see in the motor pathway compared to sensory pathway—should notice starting point is in cord and fibers exit via the anterior root. © 2018 Pearson Education, Inc.

Nerve plexus (plexus, braid)
Module 12.7: Spinal nerves form nerve plexuses that innervate the skin and skeletal muscles Nerve plexus (plexus, braid) Complex, interwoven nerve network Formed during development Anterior rami of adjacent spinal nerves blend fibers to form plexuses 4 major nerve plexuses Cervical plexus—neck and diaphragm Brachial plexus—pectoral girdle, upper limb Lumbar plexus—pelvic girdle, lower limb Sacral plexus—pelvic girdle, lower limb © 2018 Pearson Education, Inc.

The major nerve plexuses
Point out in the image that most of the thoracic spinal nerves don’t form plexuses. Ask students why. The ribs articulate with the vertebrae between these spinal nerves, and these nerves form the intercostal nerves. © 2018 Pearson Education, Inc.

Module 12.8: The cervical plexus innervates the muscles of the neck and diaphragm
From anterior rami of spinal nerves C1–C5 Branches innervate skin/muscles of neck Extends into thoracic cavity Phrenic nerve Formed by C3–C5 Provides entire nerve supply to the diaphragm (breathing) © 2018 Pearson Education, Inc.

Module 12.8: The cervical plexus
This figure shows two of the cranial nerves. Be sure your students don’t mistakenly think their depiction here means that they are part of the cervical plexus. © 2018 Pearson Education, Inc.

Module 12.9: The brachial plexus innervates the pectoral girdle and upper limbs
Innervates pectoral girdle, upper back, upper limbs Anterior rami of C5–T1, form trunks; trunks split into divisions; divisions combine to form cords Most nerves of brachial plexus come off cords; a few originate at the trunks © 2018 Pearson Education, Inc.

Major brachial plexus nerves
Module 12.9: The brachial plexus innervates the pectoral girdle and upper limbs Major brachial plexus nerves Musculocutaneous nerve Median nerve Ulnar nerve Axillary nerve Radial nerve Have students focus on the names of the nerves to see what they can figure out about their locations—helps break the common habit of just memorizing terms. © 2018 Pearson Education, Inc.

Module 12.9: The brachial plexus

Nerves of the brachial plexus
1. There is a lot of information in this image. Walk students through the components so they know how to interpret it. 2. Using the radial or median nerves, consider showing students all spinal nerves that contribute fibers to their formation. Discuss the value of this mixing of fibers from different levels. © 2018 Pearson Education, Inc.

Module 12.9: The brachial plexus
The brachial plexus (continued) Cutaneous nerve distribution to wrist/hand is clinically important Nerve damage can be precisely localized by testing sensory function of the hand Motor damage can also be assessed by checking for motor deficits. Look for images of “claw hand” or “median nerve injury ape hand” and show the deformities to see if students can figure out which nerve is damaged. © 2018 Pearson Education, Inc.

Lumbar and sacral plexuses
Module 12.10: The lumbar and sacral plexuses innervate the skin and skeletal muscles of the trunk and lower limbs Lumbar and sacral plexuses From lumbar and sacral segments of spinal cord Innervate lower trunk, pelvic girdle, lower limbs The lumbar plexus Formed from spinal nerves T12–L4 Lumbosacral trunk—L4 branches contribute to sacral plexus The sacral plexus Formed from spinal nerves L4–S4 Contains the sciatic nerve—largest/longest nerve in body You might point out that these two plexuses are sometimes referred to together as the lumbosacral plexus. Remind students that the spinal cord ends at L1–L2, so most of the nerves in these plexuses are part of the cauda equina. © 2018 Pearson Education, Inc.

Nerves of the lumbar and sacral plexuses
Be sure students realize they are seeing an anterior and a posterior views. Consider using this slide to ask students why the sciatic nerve can cause so many problems for people. It supplies the posterior thigh and almost everything below the knee—sensory and motor. © 2018 Pearson Education, Inc.

Module 12.10: Lumbar and sacral plexus
Sensory innervation of foot Nerves supplying foot and ankle: Saphenous nerve Sural nerve Common fibular nerve Tibial nerve As in hand, mapping sensory perception can determine damage to specific peripheral nerves. © 2018 Pearson Education, Inc.

Module 12.11: CNS neurons are grouped into neuronal pools, which form neural circuits
Functional groups of interconnected neurons May involve neurons in several regions of the brain May involve neurons in one specific CNS location Number of pools estimated between a few hundred and a few thousand Pattern of interaction reflects function of the pool Most complex processing occurs in brain Simplest circuits are in PNS and spinal cord; control automatic responses of reflexes © 2018 Pearson Education, Inc.

Module 12.12: Reflexes are vital to homeostasis
Rapid, automatic responses to specific stimuli Preserve homeostasis through rapid adjustments in organ/organ system function Little variability in response 5 components of a reflex arc Stimulation of a receptor Activation of a sensory neuron Information processing in the CNS Activation of a motor neuron Response of a peripheral effector Consider having students list as many reflexes as they can think of. Additional Resources: SmartArt Module 12.12—The reflex arc. © 2018 Pearson Education, Inc.

The steps of a simple reflex arc
This image provides the whole reflex arc but it can be overwhelming to students. The following slides present each step individually. © 2018 Pearson Education, Inc.

Steps in a simple reflex arc
Module 12.12: Reflexes Steps in a simple reflex arc Activation of a receptor by a stimulus Receptor can be specialized cell or dendrites of a sensory neuron; detect physical or chemical changes Example: Lean on tack, stimulates pain receptors This is an opportunity to review different types of receptors. © 2018 Pearson Education, Inc.

Module 12.12: Reflexes Activation of a sensory neuron
Stimulation of dendrites produces graded polarization Generates action potentials in sensory neurons; signal enters spinal cord through posterior root Remind students that subthreshold stimuli will not elicit a reflex response because an action potential will not be generated in the sensory neuron. © 2018 Pearson Education, Inc.

Module 12.12: Reflexes Information processing in the CNS
Sensory neuron releases neurotransmitter, causes excitatory postsynaptic potentials (EPSPs) at interneuron Signals integrated with others arriving at same time. Not all reflex arcs use an interneuron, as will be discussed with the patellar reflex. © 2018 Pearson Education, Inc.

Module 12.12: Reflexes Activation of a motor neuron
Interneuron stimulates motor neurons that carry action potentials to periphery Simultaneously, collaterals from interneuron may send pain sensations to other areas in CNS This explains why we sometimes respond to a painful stimulus before we are consciously aware of the pain—the reflex arc may be completed at the spinal level and the effector activated before the incoming signals reach the conscious levels of the brain. © 2018 Pearson Education, Inc.

Module 12.12: Reflexes Response of a peripheral effector
Motor neuron(s) release neurotransmitters at axon terminals; stimulates effector to respond Example: skeletal muscle contraction to pull away from tack © 2018 Pearson Education, Inc.

Module 12.13: The stretch reflex is a monosynaptic reflex involving muscle spindles
Best known monosynaptic reflex Automatically regulates skeletal muscle length Stimulus: increasing muscle length Sensory neuron triggers immediate motor response (contraction of stretched muscle) Example: Patellar (knee-jerk) reflex Point out that stretch reflexes are very common in internal organs and blood vessels, so they will hear about them a lot while studying other organ systems. Consider using a rubber band as a prop—stretch it and release one end—it snaps back. That’s essentially what muscles do in a stretch reflex. © 2018 Pearson Education, Inc.

Module 12.13: The stretch reflex
Steps in the patellar reflex Stimulation of a receptor Tapping patellar ligament stretches fibers in quadriceps femoris muscle © 2018 Pearson Education, Inc.

Activation of a sensory neuron Distortion of stretch receptors stimulates sensory neurons Sensory neurons enter spinal cord; synapse directly with motor neurons of the motor units in stretched muscle © 2018 Pearson Education, Inc.

Information processing in CNS Occurs at cell body of the motor neuron—no interneuron Sufficient stimulation activates the motor neuron The lack of an interneuron speeds up this reflex—one less synapse that has to be traversed. © 2018 Pearson Education, Inc.

Muscle spindles = Sensory receptors for stretch reflex Made of intrafusal muscle fibers—bundles of small, specialized skeletal muscle fibers; supplied by both sensory and motor neurons Surrounded by muscle fibers that maintain resting muscle tone and can contract whole muscle Gamma motor neuron innervates each muscle spindle Alters tension in intrafusal fibers; allows CNS to increase/decrease muscle tone © 2018 Pearson Education, Inc.

Structure of a muscle spindle
Consider comparing the intrafusal fibers to the children’s toy, a Slinky, or a spring. This gives students a visual image of what happens when a muscle is stretched or compressed. © 2018 Pearson Education, Inc.

Module 12.14: Withdrawal reflexes and crossed extensor reflexes are polysynaptic reflexes
Move away from stimulus Strongest triggered by painful stimuli Sometimes initiated by stimulus from touch or pressure receptors Versatile because sensory neurons activate many pools of interneurons Distribution and strength of response depend on intensity and location of stimulus For the latter point, have students consider their reaction time if they put their hand under a faucet and the water is too hot, compared to if they lift a metal pan out of the oven and forget to use an oven mitt or pot holder. The latter is more painful and will elicit a faster response. © 2018 Pearson Education, Inc.

Module 12.14: Polysynaptic reflexes
Flexor reflex Type of withdrawal reflex Affects muscles of a limb Example: Pain stimulus of grabbing a hot pan Pain receptors stimulated Sensory neurons activate interneurons in spinal cord Interneurons stimulate motor neurons in anterior gray horns resulting in: Contraction of flexor muscles—withdraws hand from stimulus Reciprocal inhibition—keeps extensors relaxed (blocks opposition) Reciprocal inhibition can confuse students. Revisit the concept of muscle tone and how antagonists resist movement by prime movers, allowing a more controlled movement. Reciprocal inhibition inhibits the antagonists, allowing the reflex action to occur mostly unchecked and thus much more quickly. © 2018 Pearson Education, Inc.

Steps in a flexor reflex

Crossed extensor reflexes Stretch reflexes and withdrawal reflexes use ipsilateral reflex arcs (ipsi, same) Sensory stimulus and motor responses are on the same side of the body Crossed extensor reflexes involve contralateral reflex arcs (contra, opposite) An additional motor response occurs on side opposite the stimulus © 2018 Pearson Education, Inc.

Crossed extensor reflexes (continued) Coordinated with flexor reflex Flexion of affected side accompanied by extension of opposite side Example: Step on something sharp Before flexor reflex lifts injured foot, crossed extensor reflex straightens opposite limb to receive body weight Then flexor reflex can lift foot Have students think through the events that occur if you step on something sharp so they will realize the need for the crossed extensor reflex simultaneously with the flexor reflex. Demonstrate by standing and acting like you step on a bee. From that pose, ask what you have to do next. You are weight-bearing on the painful stimulus, but before you can withdraw you have to shift your weight to the other side. When you act it out in this way, students see the importance of the chronology—you must extend the opposite leg to shift your weight off the injured foot before you can lift the foot. © 2018 Pearson Education, Inc.

Crossed extensor reflexes (continued) Stimulus elicits flexor reflex to pull affected foot away Interneurons stimulate flexors/inhibit extensors Crossed extensor reflex occurs simultaneously Collaterals of excitatory and inhibitory interneurons cross spinal cord to motor neurons in unaffected leg Excitatory interneurons stimulate extensors Inhibitory interneurons relax the flexor muscles Opposite leg straightens (crossed extension) to support shift in weight These are maintained by reverberating circuits © 2018 Pearson Education, Inc.

The crossed-extensor reflex

Module 12.15: Reflex assessment
Reflexes assessed during physical exams Biceps reflex, triceps reflex, ankle-jerk reflex Stretch reflexes Each controlled by specific segments of spinal cord Reflex responses provide information about status of the corresponding spinal segments Reflex hammers are fairly inexpensive—if you have them, have students test these reflexes on each other, if mutually agreeable. © 2018 Pearson Education, Inc.

Babinski reflex Stroking foot on lateral side of sole triggers extension of hallux (big toe) and spreading of other toes Normal in infant—occurs due to lack of inhibition by descending motor fibers Response disappears as descending pathways develop © 2018 Pearson Education, Inc.

Abdominal reflex Light stroking of skin produces reflexive twitch in abdominal muscles; moves navel toward stimulus Depends on facilitation of descending tracts Absence may indicate damage to descending tracts © 2018 Pearson Education, Inc.

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