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Chapter 13 The Spinal Cord & Spinal Nerves Lecture Outline

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Chapter 13 The Spinal Cord & Spinal Nerves Lecture Outline INTRODUCTION The spinal cord and spinal nerves mediate reactions to environmental changes. – PowerPoint PPT presentation

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Title: Chapter 13 The Spinal Cord & Spinal Nerves Lecture Outline


1
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.

3
Chapter 13The 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

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).

5
Spinal Cord Protection
By the vertebral column, meninges, cerebrospinal
fluid, and vertebral ligaments.
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.

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

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

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.

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.

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

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 (horses tail)
  • dorsal ventral roots of lowest spinal nerves
  • Spinal segment
  • area of cord from which each pair of spinal
    nerves arises

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

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).

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

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.

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

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.

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

20
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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.

22
Sensory and Motor Tracts
  • Figure 13.12 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.

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

24
Location of Tracts inside Cord
  • Motor tracts Sensory tracts
  • pyramidal tract (corticospinal) ---spinothalamic
    tract
  • extrapyramidal tract ---posterior column

  • ---spinocerebellar

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

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.

27
Reflex Arc
  • Specific nerve impulse pathway
  • 5 components of reflex arc
  • receptor
  • sensory neuron
  • integrating center
  • motor neuron
  • effector

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.

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

30
Illustration of the Stretch Reflex
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

32
Illustration of Tendon Reflex
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).

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

35
Crossed Extensor Reflex
  • Lifting left foot requires extension of right leg
    to maintain ones 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

36
Clinical Considerations
  • Checking a patients 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)

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.

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

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.

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

41
Endoneurium Perineurium -- Epineurium
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

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

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.

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

46
Phrenic Nerve
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 waiters tip palsy
  • Klumphes palsy
  • wrist drop
  • carpal tunnel syndrome
  • claw hand
  • winged scapula

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

49
Branches off Brachial Plexus
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.

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

52
Branches of Lumbar Plexus
  • Notice Femoral and Obturator nerves
  • Found anterior and medial to hip joint

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.

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)

55
Branches of Sacral Plexus
  • Notice Sciatic nerve origins

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

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

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

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

60
Clinical Correlations
  • Erb-Duchene palsy
  • waiters tip position
  • fall on shoulder
  • Radial nerve injury
  • improper deltoid
  • injectionor 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, cant abduct
    above horizontal

61
  • end
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