The Spinal Cord and Spinal Nerves - PowerPoint PPT Presentation


PPT – The Spinal Cord and Spinal Nerves PowerPoint presentation | free to view - id: 1626c8-ZDc1Z


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation

The Spinal Cord and Spinal Nerves


Caudae equinae (horse's tail) dorsal and ventral roots of lowest spinal nerves. Spinal segment ... Step on tack (pain fibers send signal to spinal cord) ... – PowerPoint PPT presentation

Number of Views:228
Avg rating:3.0/5.0
Slides: 25
Provided by: diete70
Tags: cord | horse | nerves | spinal | tack


Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: The Spinal Cord and Spinal Nerves

Chapter 13
The Spinal Cord and Spinal Nerves
  • 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
    (excitatory) and IPSPs (inhibitory) 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.

External (Gross) Anatomy of Spinal Cord
  • Flattened cylinder
  • Continuation of the medulla oblongata
  • 42 to 45 cm (16-18 inches) long and 2cm (.75
    inch) in diameter
  • Cervical enlargement
  • upper limbs
  • Lumbar enlargement
  • lower limbs
  • 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 and ventral roots of lowest spinal nerves
  • Spinal segment
  • area of cord from which each pair of spinal
    nerves arises

Structures Covering and Protecting the Spinal Cord
  • Vertebrae
  • The vertebral column provides a bony covering of
    the spinal cord.
  • Epidural space filled with fat
  • The meninges are three coverings that run
    continuously around the spinal cord and brain
  • Dura mater (outer layer)
  • dense irregular connective tissue tube
  • Subdural space filled with interstitial fluid
  • Arachnoid (middle layer)
  • - spider web of collagen fibers
  • Subarachnoid space filled with cerebrospinal
  • Pia mater (inner layer)
  • thin layer covers blood vessels
  • denticulate ligiments hold in place
  • Spinal cord-fixed in place
  • Anchored -superiorly to the brain
  • -laterally to the denticulate ligaments
  • inferiorly to the coccyx

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.
  • 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.

Spinal Cord and Spinal Nerves
  • Spinal nerves begin as roots
  • Dorsal or posterior root entry for sensory fibers
  • dorsal root ganglion (swelling) cell bodies of
    sensory nerves
  • Ventral or anterior root site of outgoing motor

Internal Anatomy Gray Matter 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
  • 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.
  • paired dorsal and ventral gray horns
  • lateral horns only present in thoracic spinal
  • gray commissure crosses the midline
  • Central canal is continuous with fourth ventricle
    of brain

Internal Anatomy White Matter of the Spinal Cord
  • White matter covers gray matter
  • The white matter consists of bundles of
    myelinated axons of motor and sensory 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.
  • Anterior median fissure deeper than Posterior
    median sulcus
  • Anterior, Lateral and Posterior White Columns
    contain axons that form ascending and descending

  • The spinal cord has two principal functions.
  • The white matter tracts are pathways for nerve
    impulse conduction to and from the brain.
  • The gray matter receives and integrates incoming
    and outgoing information.

Sensory and Motor Tracts
  • 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.
  • Naming of tracts
  • indicates position and direction of signal
  • example anterior spinothalamic tract
  • impulses travel from spinal cord towards brain
  • found in anterior part of spinal cord

Functions of Spinal Tracts
  • Spinothalamic tract
  • pain, temperature, deep pressure and crude touch
  • Posterior columns
  • proprioception, discriminative touch, two-point
    discrimination, pressure and vibration
  • Direct pathways (corticospinal and corticobulbar)
  • precise, voluntary movements
  • Indirect pathways (rubrospinal, vestibulospinal)
  • programs automatic movements, posture and muscle
    tone, equilibrium and coordination of visual

Reflexes and the Reflex Arc
  • The spinal cord serves as an integrating center
    for spinal reflexes. This occurs in the gray
  • 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
  • Specific nerve impulse pathway
  • 5 components of reflex arc
  • receptor
  • sensory neuron
  • integrating center
  • motor neuron
  • effector
  • Somatic spinal reflexes include the stretch
    reflex, tendon reflex, flexor (withdrawal)
    reflex, and crossed extensor reflex all exhibit
    reciprocal innervation.

Stretch (Patellar Reflex) 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 and muscle contracts
  • Brain sets muscle spindle sensitivity as it sets
    muscle tone (degree of muscle contraction at
  • Reciprocal innervation (polysynaptic-
  • antagonistic muscles relax as part of reflex

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 and muscle are protected
  • Reciprocal innervation (polysynaptic)
  • causes contraction of ipsilateral muscle group

Flexor and Crossed Extensor Reflexes
  • The flexor (withdrawal) reflex is ipsilateral and
    is a protective withdrawal reflex that moves a
    limb to avoid pain.
  • 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

Flexor (withdrawal) Reflex
  • Step on tack (pain fibers send signal to spinal
  • Interneurons branch to different spinal cord
  • Motor fibers in several segments are activated
  • More than one muscle group activated to lift foot
    off of tack

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.

Clinical Considerations
  • Reflexes-
  • diagnosis of nervous system disorders or damaged
  • Superfiscial reflexes
  • withdrawal reflexes-tactile or noxious stimuli
  • corneal reflex abdominal reflex gag reflex
    pharyngeal reflex.
  • Deep tendon reflexes (stretch stimulus to a
  • integrity or function of reflex arc and spinal
  • patellar reflex(knee jerk) Achilles reflex
    (ankle jerk) abdominal reflex.

  • 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
  • Knowledge of dermatomes helps determine which
    segment of the spinal cord or which spinal nerve
    is malfunctioning.
  • Skin on face supplied by Cranial Nerve V

Connective Tissue Coverings of Spinal Nerves
  • 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
  • Numerous blood vessels are within the coverings

Spinal Nerves
  • Spinal nerves connect the CNS to sensory
    receptors, muscles, and glands and are part of
    the peripheral nervous system.
  • 31 Pairs of spinal nerves
  • Named and numbered by the cord level of their
  • 8 pairs of cervical nerves (C1 to C8)
  • 12 pairs of thoracic nerves (T1 to T12) (T2-12
    do not enter into plexuses)
  • 5 pairs of lumbar nerves (L1 to L5)
  • 5 pairs of sacral nerves (S1 to S5)
  • 1 pair of coccygeal nerves
  • Mixed sensory and motor nerves

Branching of Spinal Nerves
  • Spinal nerves formed from dorsal and ventral
  • Spinal nerves branch into dorsal and ventral rami
  • dorsal rami supply skin and muscles of back
  • ventral rami form plexus supply anterior trunk
    and limbs
  • meningeal branches supply meninges, vertebrae and
    blood vessels
  • rami-communicantes branches associated with the
    autonomic nervous system

A Nerve Plexus
  • Joining of ventral rami of spinal nerves to form
    nerve networks or plexuses
  • Found in neck, arm, low back and sacral regions
  • No plexus (T2-T12) in thoracic region
  • intercostal nerves
  • innervate intercostal spaces
  • T7 to T12 supply abdominal wall as well

  • Neuritis
  • inflammation of nerves
  • caused by injury, vitamin deficiency or poison
  • sciatica injury to the sciatic nerve and its
    branches results in sciatica, pain that extends
    from the buttock down the back of the leg