The Spinal Cord and Spinal Nerves

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The Spinal Cord and Spinal Nerves

• Dr. Michael P. Gillespie

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Protective Structures

• Bony vertebrae
• Meninges
• Cerebrospinal fluid (produced in the brain)

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Vertebral Column

• The spinal cord is located within the vertebral
  canal of the vertebral column.
• The vertebral foramina form the canal.
• The vertebrae form a shelter for the cord.
• The vertebral ligaments, meninges and CSF also
  provide protection.

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Functions of the Spinal Cord and Spinal Nerves

• White matter contains the sensory and motor
  tracts (highways).
• Gray matter site for integration (summing) of
  action potentials.
• Spinal nerves connect the CNS to sensory
  receptors, muscles, and glands.

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Meninges

• Connective tissue coverings that encircle the
  spinal cord and brain.
• Spinal meninges.
• Cranial meninges.

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Meninges

• 3 spinal meninges.
• Dura mater (most superficial).
• Epidural space between dura mater and wall of
  vertebral canal.
• Arachnoid mater (middle layer) spider web
  arrangement.
• Subdural space between dura and arachnoid.
• Pia mater (innermost layer).
• Subarachnoid space between arachnoid and pia
  contains CSF.
• Denticulate ligaments extend from pia and fuse
  with arachnoid.

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External Anatomy of the Spinal Cord

• Cervical enlargement nerves to and from the
  upper limbs
• Lumbar enlargement nerves to and from the lower
  limbs

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External Anatomy of the Spinal Cord

• Conus medullaris the spinal cord tapers to a
  conical portion
• Filum terminale an extension of the pia mater
  that anchors the spinal cord to the coccyx

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External Anatomy of the Spinal Cord

• Cauda equina horses tail
• Spinal nerves paths of communication between
  the cord and the nerves innervating specific
  regions of the body
• Posterior (dorsal) root
• Sensory nerve axons
• Posterior (dorsal) root ganglion swelling
  cell bodies
• Anterior (ventral) root
• Motor nerve axons

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Spinal Tap

• Spinal tap (lumbar puncture).
• Local anesthetic is given and a long needle is
  inserted into the subarachnoid space.
• Uses.
• Withdraw CSF for diagnosis.
• Introduce antiobiotics, contrast media,
  anesthetics.
• Introduce chemotherapy.
• Measure CSF pressure.

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Internal Anatomy of the Spinal Cord

• Anterior median fissure.
• Posterior median sulcus.

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Internal Anatomy of the Spinal Cord

• Gray commissure form the crossbar of the H.
• Anterior (ventral) gray horns cell bodies of
  somatic motor neurons and motor nuclei.
• Posterior (dorsal) gray horns - cell bodies of
  somatic and autonomic sensory nuclei.
• Lateral gray horns cell bodies of autonomic
  motor neurons that regulate smooth muscle,
  cardiac muscle and glands.
• Central canal in the center of the gray
  commissure.

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Internal Anatomy of the Spinal Cord

• White columns.
• Sensory (ascending) tracts.
• Motor (descending) tracts.

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Spinal Cord Physiology

• 2 principle functions.
• Nerve impulse propagation white matter tracts.
• Sensory impulses flow toward the brain.
• Motor impulses flow from the brain.
• Information integration gray matter.

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Sensory Motor Tracts

• The name of the tract often indicates its
  position in the white matter and where it begins
  and ends.

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Sensory Tracts

• Lateral and anterior spinothalamic tracts.
• Convey impulses for pain, warmth, tickling,
  itching, deep pressure, and a crude sense of
  touch (poorly localized).
• Posterior columns.
• Convey impulses for proprioception,
  discriminative touch, 2 point discrimination,
  light pressure sensations, and vibrations.

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Motor Tracts

• Direct pathways convey precise voluntary
  movements.
• Lateral corticospinal.
• Anterior corticospinal.
• Corticobulbar.

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Motor Tracts

• Indirect pathways govern automatic movements
  (I.E. Reflexes).
• Rubrospinal.
• Tectospinal.
• Vestibulospinal.

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Reflexes and Reflex Arcs

• Reflex a fast, unplanned sequence of actions
  that occurs in response to a particular stimulus.
• Location of integration.
• Spinal reflex.
• Cranial reflex integration in brain stem.
• Types of reflexes.
• Somatic reflexes contraction of skeletal
  muscles.
• Autonomic (visceral) reflexes responses of
  smooth muscle, cardiac muscle, and glands.

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Reflex Arc

• Reflex arc (reflex circuit) - the pathway
  followed by nerve impulses.

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Five Functional Components of a Reflex Arc

• Sensory receptor.
• Distal end of a sensory neuron.
• Responds to a stimulus.
• Sensory neuron.
• Nerves terminate in the brain stem or spinal cord.

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Five Functional Components of a Reflex Arc

• Integrating center.
• Monosynaptic reflex arc - A synapse between a
  sensory neuron and a motor neuron.
• Polysynaptic reflex arc one or more
  interneurons and a motor neuron.

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Five Functional Components of a Reflex Arc

• Motor neuron.
• Effector.
• The part of the body that responds to the motor
  nerve impulse.
• Somatic reflex the effector is a skeletal
  muscle.
• Autonomic reflex the effector is smooth muscle,
  cardiac muscle or a gland.

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Reflexes

• Reflexes are normally predictable.
• They can provide information about the health of
  the nervous system.

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Reflexes

• Damage or disease anywhere along the reflex arc
  can cause the reflex to be absent or abnormal.
• Somatic reflexes can be tested by tapping or
  stroking the body surface.
• Autonomic reflexes cannot be tested easily
  because the visceral receptors are deep inside
  the body.

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Four Important Somatic Spinal Reflexes

• Stretch reflex
• Tendon reflex
• Flexor (withdrawal) reflex
• Crossed (extensor) reflex

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Stretch Reflex

• A stretch reflex causes contraction of a skeletal
  muscle in response to stretching of the muscle.
• Monosynaptic reflex arc.
• Ipsilateral reflex.
• This reflex helps avert injury by preventing
  overstretching of a muscle.
• Reciprocal inhibition when the stretched muscle
  contracts, the antagonistic muscle(s) relax.

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Tendon Reflex

• The tendon reflex controls muscle tension by
  causing muscle relaxation before muscle forces
  become so great that they tear tendons.
• Ipsilateral reflex.
• Sensory receptors tendon (Golgi tendon) organs.

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Flexor (Withdrawal Reflex)

• Causes withdrawal from a painful stimulus.
• This reflex causes contraction of the flexor
  muscles with causes withdrawal from a painful
  stimulus.
• Ipsilateral reflex.
• Several motor units at different levels of the
  spinal cord are recruited intersegmental reflex
  arc.
• Reciprocal innervation occurs.

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Crossed Extensor Reflex

• Helps you maintain balance.
• Contralateral reflex arc.
• Reciprocal innervation occurs.

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Plantar Flexion Reflex

• The plantar flexion reflex is elicited by
  stroking the lateral outer margin of the sole.
• The normal response is curling under of the toes.
• Babinski sign the great toe extends this
  indicates damage to the descending motor
  pathways.
• The babinski sign is normal in children under 18
  months due to incomplete myelination of the
  axons.

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Spinal Nerves

• The spinal nerve has two connections to the cord
  a posterior root and an anterior root.
• The posterior and anterior roots unite to form a
  spinal nerve at the intervertebral foramen.
• The posterior root contains sensory axons and the
  anterior root contains motor axons Therefore,
  the spinal nerve is a mixed nerve.

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Connective Tissue Coverings of Spinal Nerves

• Endoneurium surrounds individual axons.
• Perineurium - surrounds bundles of axons called
  fascicles.
• Epineurium surrounds the entire nerve.

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Branches

• After passing through the IVF, the spinal nerve
  forms rami (branches).
• Posterior (dorsal) ramus.
• Anterior (ventral) ramus.
• Meningeal branch.
• Rami communicantes serves the autonomic nervous
  system.

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Plexuses

• A network of axons.
• Principle plexuses
• Cervical plexus.
• Brachial plexus.
• Lumbar plexus.
• Sacral plexus.
• Coccygeal plexus.
• The nerves have branches named for the structures
  they innervate.

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Cervical Plexus

• The cervical plexus supplies the skin and muscles
  of the head, neck, and superior part of the
  shoulders and chest.
• The phrenic nerves arise from the cervical plexus
  and innervates the diaphragm.
• C3, 4 5 keep the diaphragm alive.

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Brachial Plexus

• The brachial plexus provides the entire nerve
  supply of the shoulders and upper limbs.

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Brachial Plexus

• Major nerves
• Axillary nerve supplies deltoid and teres minor
  mm.
• Musculocutaneous nerve supplies arm flexors.
• Radial nerve supplies posterior arm and forearm
  mm.
• Median nerve supplies anterior forearm mm and
  some hand mm.
• Ulnar nerve supplies anteromedial mm of the
  forearm and most of the hand muscles.

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Erb-Duchenne Palsy

• Known as waiters tip position.
• Results from forceful pulling away of the head
  from the shoulder.

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Radial Nerve Injury

• Caused by improper intramuscular injections into
  the deltoid or when the cast is applied too
  tightly around the mid-humerus.
• Indicated by wrist drop.

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Median Nerve Injury

• Numbness, tingling, and pain in the palm and
  fingers.
• Inability to pronate the forearm.
• Weak wrist flexion.

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Ulnar Nerve Injury

• Inability to abduct or adduct the fingers.
• Atrophy of the interosseous mm of the hand.
• Clawhand.
• Loss of sensation over the little finger.

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Ulnar Nerve Palsy
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Long Thoracic Nerve Injury

• Paralysis of the serratus anterior mm.
• The scapula protrudes.
• Winged scapula.

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Long Thoracic Nerve Injury
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Lumbar Plexus

• The lumbar plexus supplies the anterolateral
  abdominal wall, external genitals, and part of
  the lower limbs.

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Lumbar Plexus Injuries

• Femoral nerve injury.
• Can be caused by a stab or gunshot wounds.
• Inability to extend the leg and lost sensation.
• Obturator nerve injury.
• Complication of childbirth.
• Paralysis of the adductor muscles of the leg and
  loss of sensation.

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Sacral and Coccygeal Plexuses

• The sacral plexus supplies the buttocks, perineum
  and lower limbs.
• The sciatic nerve originates here.
• The coccygeal plexus supplies a small patch of
  skin in the coccygeal region.

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Sciatic Nerve Injury

• Injury to the sciatic nerve causes sciatica
  pain the extends from the buttock, down the
  posterolateral aspect of the leg and to the foot.
• Damage to the fibular nerve can cause
• Footdrop.
• Equinovarus inverted foot.
• Calcaneovalgus injury of the tibial portion of
  the sciatic nerve resulting in dorsiflexion.

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Dermatomes

• Specific segments of skin that are innervated by
  specific spinal segments or specific cranial
  nerves.
• The nerve supply in adjacent segments overlaps
  somewhat.
• Knowing which spinal segments supply each
  dermatome allows us to determine the location of
  nerve damage.

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Terminolgy

• Meningitis inflammation of the meninges.
• Nerve block loss of sensation in a region due
  to injection of a local anesthetic.
• Neuralgia pain along the course of a sensory
  nerve.
• Neuritis inflammation of the nerves.
• Paresthesia abnormal sensation.