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Human Anatomy, First Edition McKinley & O'Loughlin Chapter 16 Lecture Outline: Spinal Cord and Spinal Nerves The Spinal Cord Provides a vital link between the brain ... – PowerPoint PPT presentation

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Title: Human Anatomy, First Edition McKinley


1
Human Anatomy, First EditionMcKinley
O'Loughlin
  • Chapter 16 Lecture Outline
  • Spinal Cord and Spinal Nerves

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The Spinal Cord
  • Provides a vital link between the brain and the
    rest of the body.
  • Exhibits some functional independence from the
    brain.
  • The spinal cord and its attached spinal nerves
    serve two important functions.
  • pathway for sensory and motor impulses
  • responsible for reflexes

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Structure of the Spinal Cord
  • A typical adult spinal cord ranges between 42 and
    45 centimeters (cm) (16 to 18 inches) in length.
  • Viewed in cross section, it is roughly
    cylindrical, but slightly flattened both
    posteriorly and anteriorly.
  • Its external surface has two longitudinal
    depressions.
  • the posterior (or dorsal) median sulcus, dips
    internally on the posterior surface
  • the anterior (or ventral) median fissure, is
    observed on its anterior surface

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Regions of the Spinal Cord
  • The cervical region is the superior-most region
    of the spinal cord.
  • continuous with the medulla oblongata
  • contains neurons whose axons form the cervical
    spinal nerves
  • The thoracic region lies inferior to the cervical
    region.
  • attached to this region are the thoracic spinal
    nerves
  • The lumbar region is a shorter segment of the
    spinal cord that
  • contains the neurons for the lumbar spinal nerves
  • The sacral region lies inferior to the lumbar
    region and
  • contains the neurons for the sacral spinal nerves
  • The coccygeal region is the most inferior tip
    of the spinal cord.
  • one pair of coccygeal spinal nerves arises from
    this region.

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Structure of the Spinal Cord
  • The spinal cord is shorter than the vertebral
    canal that houses it.
  • The tapering inferior end of the spinal cord is
    called the conus medullaris and it marks the
    official end of the spinal cord proper.
  • Inferior to this point, nerve roots (groups of
    axons collectively called the cauda equina)
    project inferiorly from the spinal cord.
  • Within the cauda equina is the filum terminale, a
    thin strand of pia mater that helps anchor the
    conus medullaris to the coccyx.

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Structure of the Spinal Cord
  • The spinal cord is associated with 31 pairs of
    spinal nerves that connect the CNS to muscles,
    receptors, and glands.
  • Each side of the spinal cord contains 8 cervical
    nerves (called C1C8), 12 thoracic nerves
    (T1T12), 5 lumbar nerves (L1L5), 5 sacral
    nerves (S1S5), and 1 coccygeal nerve (Co).

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Arrangement and Functions of the Spinal Meninges
  • Are continuous with the cranial meninges.
  • Structures that encircle the spinal cord, listed
    from outermost to innermost are
  • vertebra
  • epidural space
  • dura mater
  • subdural space
  • arachnoid
  • subarachnoid space
  • pia mater

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Location and Distribution of Gray Matter
  • In the spinal cord, IT is centrally located.
  • Its shape resembles a letter H or a butterfly.
  • The gray matter may be subdivided into the
    following components
  • anterior horns
  • lateral horns
  • posterior horns
  • the gray commissure

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Location and Distribution of White Matter
  • The white matter of the spinal cord is external
    to the gray matter.
  • White matter on each side of the cord is also
    partitioned into three regions.
  • A posterior funiculus lies between the posterior
    gray horns on the posterior side of the cord and
    the posterior median sulcus.
  • The white matter region on each lateral side of
    the spinal cord is the lateral funiculus.
  • The anterior funiculus is composed of tracts of
    white matter that occupy the space on each
    anterior side of the cord between the anterior
    gray horns and the anterior median fissure.
  • The anterior funiculi are interconnected by the
    white commissure.

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Spinal Nerves
  • 31 pairs of spinal nerves connect the central
    nervous system to muscles, glands, and receptors
  • Each spinal nerve is formed from the union of
    thousands of motor and sensory axons.
  • Motor axons originate from the spinal cord.
  • Each anterior root and its corresponding
    posterior root unite within the intervertebral
    foramen to become a spinal nerve.
  • Contain both motor axons and sensory axons.
  • Each spinal nerve is associated with the vertebra
    of the same number.

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Dermatomes
  • A specific segment of skin supplied by a single
    spinal nerve.
  • All spinal nerves except for C1 innervate a
    segment of skin, and so each of these nerves is
    associated with a dermatome.
  • The skin of the body may be divided into sensory
    segments that collectively make up a dermatome
    map.

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Intercostal Nerves
  • Anterior rami of spinal nerves T1T11.
  • Travel in the intercostal space sandwiched
    between two adjacent ribs.

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Nerve Plexuses
  • A network of interweaving anterior rami of spinal
    nerves.
  • Anterior rami of most spinal nerves form nerve
    plexuses on both the right and left sides of the
    body.
  • Nerve plexuses then split into multiple named
    nerves that innervate various body structures.
  • Principal plexuses are the cervical plexuses,
    brachial plexuses, lumbar plexuses, and sacral
    plexuses.

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Reflexes
  • Rapid, automatic, involuntary reactions of
    muscles or glands to a stimulus.
  • All reflexes have similar properties.
  • a stimulus is required to initiate a response to
    sensory input
  • a rapid response requires that few neurons be
    involved and synaptic delay be minimal
  • an automatic response occurs the same way every
    time
  • An involuntary response requires no intent or
    pre-awareness of the reflex activity.
  • Reflexes are usually not suppressed.
  • Awareness of the stimulus occurs after the reflex
    action has been completed, in time to correct or
    avoid a potentially dangerous situation.

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Components of a Reflex Arc
  • The neural wiring of a single reflex.
  • Always begins at a receptor in the PNS.
  • Communicates with the CNS.
  • Ends at a peripheral effector (muscle or gland)
    cell.

40
Ipsilateral and Contralateral Reflex Arcs
  • Ipsilateral is when both the receptor and
    effector organs of the reflex are on the same
    side of the spinal cord.
  • for example, an ipsilateral effect occurs when
    the muscles in your left arm contract to pull
    your left hand away from a hot object
  • Contralateral is when the sensory impulses from a
    receptor organ cross over through the spinal cord
    to activate effector organs in the opposite limb.
  • for example, contralateral effect occurs when you
    step on a sharp object with your left foot and
    then contract the muscles in your right leg to
    maintain balance as you withdraw your left leg
    from the damaging object

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Monosynaptic Reflexes
  • The simplest of all reflexes.
  • Interneurons are not involved in processing this
    reflex.
  • The patellar (knee-jerk) reflex is a monosynaptic
    reflex that physicians use to assess the
    functioning of the spinal cord.
  • By tapping the patellar ligament with a reflex
    hammer, the muscle spindles in the quadriceps
    muscles are stretched.
  • Produces a noticeable kick of the leg.

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Polysynaptic Reflexes
  • Have more complex neural pathways that exhibit a
    number of synapses involving interneurons within
    the reflex arc.
  • Because this reflex arc has more components,
    there is a more prolonged delay between stimulus
    and response.

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Stretch Reflexes
  • Monosynaptic reflex that monitors and regulates
    skeletal muscle length.
  • When a stimulus results in the stretching of a
    muscle, that muscle reflexively contracts.
  • The patellar (knee-jerk) reflex is an example of
    a stretch reflex.
  • The stimulus (the tap on the patellar tendon)
    initiates contraction of the quadriceps femoris
    muscle and extension of the knee joint.

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Golgi Tendon Reflex
  • Prevents skeletal muscles from tensing
    excessively.
  • Golgi tendon organs are nerve endings located
    within tendons near a muscletendon junction.
  • activation of the Golgi tendon organ signal
    interneurons in the spinal cord, which in turn
    inhibit the actions of the motor neurons
  • The associated muscle is allowed to relax, thus
    protecting the muscle and tendon from excessive
    tension damage.

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Reflex Testing in a Clinical Setting
  • Reflexes can be used to test specific muscle
    groups and specific spinal nerves or segments of
    the spinal cord.
  • Consistently abnormal reflex response may
    indicate damage to the nervous system or muscles.
  • A reflex response may be normal, hypoactive, or
    hyperactive.

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Spinal Cord Development
  • The central nervous system forms from the
    embryonic neural tube.
  • Cranial and spinal nerves form from neural crest
    cells that have split off from the developing
    neural tube.
  • The cranial (superior) part of the neural tube
    expands and develops into the brain.
  • The caudal (inferior) part of the neural tube
    forms the spinal cord.

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