1. The Spinal Cord & Spinal Nerves Lecture Outline
Chapter 13
The Spinal Cord & Spinal Nerves
Lecture Outline

2. INTRODUCTION
The spinal cord and spinal nerves mediate reactions to environmental changes.
The spinal cord has several functions.
It processes reflexes.
It is the site for integration of EPSPs and IPSPs that arise locally or are triggered by nerve impulses from the periphery and brain.
It is a conduction pathway for sensory and motor nerve impulses.
The size of the vertebral canal varies in different regions of the vertebral column and affects spinal cord injuries.
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3. Chapter 13 The Spinal Cord & Spinal Nerves
Together with brain forms the CNS
Functions
spinal cord reflexes
integration (summation of inhibitory and excitatory) nerve impulses
highway for upward and downward travel of sensory and motor information
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4. SPINAL CORD ANATOMY
The spinal cord is protected by two connective tissue coverings, the meninges and vertebra, and a cushion of cerebrospinal fluid.
The vertebral column provides a bony covering of the spinal cord (Figure 13.1c).
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5. Spinal Cord Protection
By the vertebral column, meninges, cerebrospinal fluid, and vertebral ligaments.
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6. Meninges
The meninges are three coverings that run continuously around the spinal cord and brain (Figures 13.1a, 14.4a).
The outermost layer is the dura mater.
The middle layer is the arachnoid.
The innermost meninx is the pia mater, a thin, transparent connective tissue layer that adheres to the surface of the spinal cord and brain
Denticulate ligaments are thickenings of the pia mater that suspend the spinal cord in the middle of its dural sheath.
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7. Structures Covering the Spinal Cord
Vertebrae
Epidural space filled with fat
Dura mater
dense irregular CT tube
Subdural space filled with interstitial fluid
Arachnoid = spider web of collagen fibers
Subarachnoid space = CSF
Pia mater
thin layer covers BV
denticulate ligs hold in place
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8. Structures Covering the Spinal Cord
Vertebrae
Epidural space filled with fat
Dura mater
dense irregular CT tube
Subdural space filled with interstitial fluid
Arachnoid = spider web of collagen fibers
Subarachnoid space = CSF
Pia mater
thin layer covers BV
denticulate ligs hold in place
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9. Applications
The subarachnoid space is between the arachnoid mater and pia mater and contains cerebrospinal fluid (CSF).
Inflammation of the meninges is known as meningitis.
Removal of cerebrospinal fluid from the subarachnoid space is called a spinal tap (lumbar puncture). This procedure is used to diagnose pathologies and to introduce antibiotics, contrast media, anesthetics, and chemotherapeutic drugs.
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10. External Anatomy of the Spinal Cord
The spinal cord begins as a continuation of the medulla oblongata and terminates at about the second lumbar vertebra in an adult (Figure 13.2).
It contains cervical and lumbar enlargements that serve as points of origin for nerves to the extremities.
The tapered portion of the spinal cord is the conus medullaris, from which arise the filum terminale and cauda equina.
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11. External Anatomy of Spinal Cord
Flattened cylinder
16-18 Inches long & 3/4 inch diameter
In adult ends at L2
In newborn ends at L4
Growth of cord stops at age 5
Cervical enlargement
upper limbs
Lumbar enlargement
lower limbs
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12. Inferior End of Spinal Cord
Conus medullaris
cone-shaped end of spinal cord
Filum terminale
thread-like extension of pia mater
stabilizes spinal cord in canal
Caudae equinae (horse’s tail)
dorsal & ventral roots of lowest spinal nerves
Spinal segment
area of cord from which each pair of spinal nerves arises
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13. Spinal tap or Lumbar Puncture
Technique
long needle into subarachnoid space
safe from L3 to L5
Purpose
sampling CSF for diagnosis
injection of antibiotics, anesthetics or chemotherapy
measurement of CSF pressure
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14. Spinal nerves
The 31 pairs of spinal nerves are named and numbered according to the region and level of the spinal cord from which they emerge (Figure 13.2).
8 pairs of cervical nerves,
12 pairs of thoracic nerves,
5 pairs of lumbar nerves,
5 pairs of sacral nerves, and
1 pair of coccygeal nerves.
Spinal nerves are the paths of communication between the spinal cord and most of the body.
Roots are the two points of attachment that connect each spinal nerve to a segment of the spinal cord (Figure 13.3a).
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15. Spinal Cord & Spinal Nerves
Spinal nerves begin as roots
Dorsal or posterior root is incoming sensory fibers
dorsal root ganglion (swelling) = cell bodies of sensory nerves
Ventral or anterior root is outgoing motor fibers
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16. Internal Anatomy of the Spinal Cord
The anterior median fissure and the posterior median sulcus penetrate the white matter of the spinal cord and divide it into right and left sides (Figure 13.3b).
The gray matter of the spinal cord is shaped like the letter H or a butterfly and is surround by white matter.
The gray matter consists primarily of cell bodies of neurons and neuroglia and unmyelinated axons and dendrites of association and motor neurons.
The gray commissure forms the cross bar of the H-shaped gray matter.
The white matter consists of bundles of myelinated axons of motor and sensory neurons.
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17. Gray Matter of the Spinal Cord
Gray matter is shaped like the letter H or a butterfly
contains neuron cell bodies, unmyelinated axons & dendrites
paired dorsal and ventral gray horns
lateral horns only present in thoracic spinal cord
gray commissure crosses the midline
Central canal is continuous with 4th ventricle of brain
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18. Internal Anatomy of the Spinal Cord
Anterior to the gray commissure is the anterior white commissure, which connects the white matter of the right and left sides of the spinal cord.
The gray matter is divided into horns, which contain cell bodies of neurons.
The white matter is divided into columns.
Each column contains distinct bundles of nerve axons that have a common origin or destination and carry similar information.
These bundles are called tracts.
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19. White Matter of the Spinal Cord
White matter covers gray matter
Anterior median fissure deeper than Posterior median sulcus
Anterior, Lateral and Posterior White Columns contain axons that form ascending & descending tracts
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20. Principles of Human Anatomy and Physiology, 11e

21. SPINAL CORD PHYSIOLOGY
The spinal cord has two principal functions.
The white matter tracts are highways for nerve impulse conduction to and from the brain.
The gray matter receives and integrates incoming and outgoing information.
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22. Sensory and Motor Tracts
Figure shows the principal sensory and motor tracts in the spinal cord. These tracts are discussed in detail in Chapter 16 summarized in tables 16.3 and 16.4.
Sensory (ascending) tracts conduct nerve impulses toward the brain.
the lateral and anterior spinothalamic tracts and the posterior column tract.
Motor (descending) tracts conduct impulses down the cord.
Direct pathways include lateral and anterior corticospinal and corticobulbar tracts.
Indirect pathways include rubrospinal, tectospinal, and vestibulospinal tracts.
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23. Tracts of the Spinal Cord
Function of tracts - highways for sensory & motor information
sensory tracts ascend
motor tracts descend
Naming of tracts
indicates position & direction of signal
example = anterior spinothalamic tract
impulses travel from spinal cord towards brain (thalamus)
found in anterior part of spinal cord
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24. Location of Tracts inside Cord
Motor tracts Sensory tracts
pyramidal tract (corticospinal) ---spinothalamic tract
extrapyramidal tract ---posterior column
---spinocerebellar
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25. Function of Spinal Tracts
Spinothalamic tract
pain, temperature, deep pressure & crude touch
Posterior columns
proprioception, discriminative touch, two-point discrimination, pressure and vibration
Direct pathways (corticospinal & corticobulbar)
precise, voluntary movements
Indirect pathways (rubrospinal, vestibulospinal)
programming automatic movements, posture & muscle tone, equilibrium & coordination of visual reflexes
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26. Reflexes and Reflex Arcs
The spinal cord serves as an integrating center for spinal reflexes. This occurs in the gray matter.
A reflex is a fast, predictable, automatic response to changes in the environment that helps to maintain homeostasis.
Reflexes may be spinal, cranial, somatic, or autonomic.
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27. Reflex Arc Specific nerve impulse pathway 5 components of reflex arc
receptor
sensory neuron
integrating center
motor neuron
effector
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28. Reflex Arc
A reflex arc is the simplest type of pathway; pathways are specific neuronal circuits and thus include at least one synapse.
Reflexes help to maintain homeostasis by permitting the body to make exceedingly rapid adjustments to homeostatic imbalances.
Somatic spinal reflexes include the stretch reflex, tendon reflex, flexor (withdrawal) reflex, and crossed extensor reflex; all exhibit reciprocal innervation.
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29. Stretch Reflex (patellar reflex)
It operates as a feedback mechanism to control muscle length by causing muscle contraction.
Prevents injury from over stretching because muscle contracts when it is stretched
Monosynaptic,ipsilateral reflex arc
Events of stretch reflex
muscle spindle signals stretch of muscle
motor neuron activated & muscle contracts
Brain sets muscle spindle sensitivity as it sets muscle tone (degree of muscle contraction at rest)
Reciprocal innervation (polysynaptic- interneuron)
antagonistic muscles relax as part of reflex
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30. Illustration of the Stretch Reflex
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31. Tendon Reflex
It operates as a feedback mechanism to control muscle tension by causing muscle relaxation when muscle force becomes too extreme.
ipsilateral polysynaptic reflex
Golgi tendon organs are in tendon
activated by stretching of tendon
inhibitory neuron is stimulated (polysynaptic)
motor neuron is hyperpolarized and muscle relaxes
Both tendon & muscle are protected
Reciprocal innervation (polysynaptic)
causes contraction of ipsilateral muscle group
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32. Illustration of Tendon Reflex
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33. Flexor and Crossed Extensor Reflexes
The flexor (withdrawal) reflex is ipsilateral and is a protective withdrawal reflex that moves a limb to avoid pain (Figure 13.16).
This reflex results in contraction of flexor muscles to move a limb to avoid injury or pain.
The crossed extensor reflex, which is contralateral, helps to maintain balance during the flexor reflex.
This is a balance-maintaining reflex that causes a synchronized extension of the joints of one limb and flexion of the joints in the opposite limb (Figure 13.17).
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34. Flexor (withdrawal) Reflex
Step on tack (pain fibers send signal to spinal cord
Interneurons branch to different spinal cord segments
Motor fibers in several segments are activated
More than one muscle group activated to lift foot off of tack
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35. Crossed Extensor Reflex
Lifting left foot requires extension of right leg to maintain one’s balance
Pain signals cross to opposite spinal cord
Contralateral extensor muscles are stimulated by interneurons to hold up the body weight
Reciprocal innervation - when extensors contract flexors relax, etc
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36. Clinical Considerations
Checking a patient’s reflexes may help to detect disorders/injury
Plantar flexion reflex -- stroke the lateral margin of the sole
normal response is curling under the toes
abnormal response or response of children under 18 months is called Babinski sign (upward fanning of toes due to incomplete myelination in child)
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37. SPINAL NERVES
Spinal nerves connect the CNS to sensory receptors, muscles, and glands and are part of the peripheral nervous system.
The 31 pairs of spinal nerves are named and numbered according to the region and level of the spinal cord from which they emerge (Figure 13.2).
Roots of the lower lumbar, sacral, and coccygeal nerves are not in line with their corresponding vertebrae and thus form the cauda equina (Figure 13.2).
Spinal nerves connect to the cord via an anterior and a posterior root (Figure 13.3a). Since the posterior root contains sensory axons and the anterior root contains motor axons, a spinal nerve is a mixed nerve.
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38. Spinal Nerves 31 Pairs of spinal nerves
Named & numbered by the cord level of their origin
8 pairs of cervical nerves (C1 to C8)
12 pairs of thoracic nerves (T1 to T12)
5 pairs of lumbar nerves (L1 to L5)
5 pairs of sacral nerves (S1 to S5)
1 pair of coccygeal nerves
Mixed sensory & motor nerves
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39. Connective Tissue Covering of Spinal Nerves
Spinal nerve axons are grouped within connective tissue sheathes (Figure 13.4a).
A fiber is a single axon within an endoneurium.
A fascicle is a bundle of fibers within a perineurium.
A nerve is a bundle of fascicles within an epineurium.
Numerous blood vessels are within the coverings.
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40. Connective Tissue Coverings
Endoneurium = wrapping of each nerve fibers
Perineurium = surrounds group of nerve fibers forming a fascicle
Epineurium = covering of entire nerve
dura mater blends into it at intervertebral foramen
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41. Endoneurium – Perineurium -- Epineurium
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42. Branching of Spinal Nerve
Spinal nerves formed from dorsal & ventral roots
Spinal nerves branch into dorsal & ventral rami
dorsal rami supply skin & muscles of back
ventral rami form plexus supply anterior trunk & limbs
meningeal branches supply meninges, vertebrae & BV
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43. A Nerve Plexus
Joining of ventral rami of spinal nerves to form nerve networks or plexuses
Found in neck, arm, low back & sacral regions
No plexus in thoracic region
intercostal nn. innervate intercostal spaces
T7 to T12 supply abdominal wall as well
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44. Plexuses
The cervical plexus supplies the skin and muscles of the head, neck, and upper part of the shoulders; connects with some cranial nerves; and supplies the diaphragm (Figure 13.6, Exhibit 13.1).
Damage to the spinal cord above the origin of the phrenic nerves (C3-C5) causes respiratory arrest.
Breathing stops because the phrenic nerves no longer send impulses to the diaphragm.
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45. Cervical Plexus Ventral rami of spinal nerves (C1 to C5)
Supplies parts of head, neck & shoulders
Phrenic nerve (C3-C5) keeps diaphragm alive
Damage to cord above C3 causes respiratory arrest
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46. Phrenic Nerve
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47. Plexuses
The brachial plexus constitutes the nerve supply for the upper extremities and a number of neck and shoulder muscles (Figures 13.7a and b, Exhibit 13.2).
A number of nerve disorders may result from injury to the brachial plexus.
Erb-Duchene palsy or waiter’s tip palsy
Klumphe’s palsy
wrist drop
carpal tunnel syndrome
claw hand
winged scapula
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48. Brachial Plexus Ventral rami from C5 to T1
Supplies shoulder & upper limb
Passes superior to 1st rib & under clavicle
Axillary n. = deltoid & teres m.
Musculocutaneous n. = elbow flexors
Radial n. = shoulder & elbow extensors
Median & ulnar nn. = flexors of wrist & hand
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49. Branches off Brachial Plexus
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50. Plexuses
The lumbar plexus supplies the anterolateral abdominal wall, external genitals, and part of the lower extremities (Figure 13.9a and b, Exhibit 13.3).
The largest nerve arising from the lumbar plexus is the femoral nerve.
Injury to the femoral nerve is indicated by an inability to extend the leg and by loss of sensation in the skin over the anteromedial aspect of the thigh.
Obturator nerve injury is a common complication of childbirth and results in paralysis of the adductor muscles of the leg and loss of sensation over the medial aspect of the thigh.
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51. Lumbar Plexus Ventral rami of L1 to L4
Supplies abdominal wall, external genitals & anterior/medial thigh
Injury to femoral nerve causes inability to extend leg & loss of sensation in thigh
Injury to obturator nerve causes paralysis of thigh adductors
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52. Branches of Lumbar Plexus
Notice: Femoral and Obturator nerves
Found anterior and medial to hip joint
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53. Plexuses
The sacral plexus supplies the buttocks, perineum, and part of the lower extremities (Figure 13.10, Exhibit 13.4).
The largest nerve arising from the sacral plexus (and the largest nerve in the body) is the sciatic nerve.
Injury to the sciatic nerve (common peroneal portion) and its branches results in sciatica, pain that extends from the buttock down the back of the leg.
Sciatic nerve injury can occur due to a herniated (slipped) disc, dislocated hip, osteoarthritis of the lumbosacral spine, pressure from the uterus during pregnancy, or an improperly administered gluteal injection.
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54. Sacral Plexus Ventral rami of L4-L5 & S1-S4 Anterior to the sacrum
Supplies buttocks, perineum & part of lower limb
Sciatic nerve = L4 to S3 supplies post thigh & all below knee
Peroneal nerve injury produces foot drop or numbness
Tibial nerve injury produces calcaneovalgus (loss of function on anterior leg & dorsum of foot)
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55. Branches of Sacral Plexus
Notice: Sciatic nerve origins
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56. Sciatic Nerve Branches
Notice: Common Peroneal nerve and Tibial nerve behind the knee
Notice: Sciatica pain extends from the buttock down the leg to the foot
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57. Dermatomes
The skin over the entire body is supplied by spinal nerves that carry somatic sensory nerves impulses into the spinal cord.
All spinal nerves except C1 innervate specific, constant segments of the skin; the skin segments are called dermatomes (Figure 13.11).
Knowledge of dermatomes helps a physician to determine which segment of the spinal cord or which spinal nerve is malfunctioning.
Skin on face supplied by Cranial Nerve V
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58. Dermatomes
Damaged regions of the spinal cord can be distinguished by patterns of numbness over a dermatome region
Infusing local anesthetics or cutting roots must be done over 3 adjacent spinal nerves.
Spinal cord transection
injury that severs the cord loss of sensation& motor control below the injury
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59. Disorders Neuritis inflammation of nerves
caused by injury, vitamin deficiency or poison
Shingles
infection of peripheral nerve by chicken pox virus
causes pain, skin discoloration, line of skin blisters
Poliomyelitis
viral infection causing motor neuron death and possible death from cardiac failure or respiratory arrest
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60. Clinical Correlations
Erb-Duchene palsy
waiter’s tip position
fall on shoulder
Radial nerve injury
improper deltoid
injection or tight cast
wrist drop
Median nerve injury
numb palm & fingers; inability to pronate & flex fingers
Ulnar nerve injury (clawhand)
inability to adduct/abduct fingers, atrophy of interosseus
Long thoracic nerve injury (winged scapula)
paralysis of serratus anterior, can’t abduct above horizontal
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61. end
Principles of Human Anatomy and Physiology, 11e