Download The Spinal Cord and Spinal Nerves

Dr. Michael P. Gillespie
 Kyphosis – exaggeration of the thoracic curve
 Lordosis – an exaggeration of the lumbar curve or
cervical curve
 Lumbar spine stenosis – narrowing of the spinal
canal
 Scoliosis – lateral bending of the vertebral column
 Bony vertebrae
 Meninges
 Cerebrospinal fluid (produced in the brain)
 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.
 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.
 Connective tissue coverings that encircle the spinal
cord and brain.
 Spinal meninges.
 Cranial 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.
 Cervical enlargement – nerves to and from the upper
limbs
 Lumbar enlargement – nerves to and from the lower
limbs
 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
 Cauda equina “horse’s 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
 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.
 Anterior median fissure.
 Posterior median sulcus.
 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.
 White columns.
 Sensory (ascending) tracts.
 Motor (descending) tracts.
 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.
 The name of the tract often indicates its position in
the white matter and where it begins and ends.
 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.
 Direct pathways – convey precise voluntary
movements.
 Lateral corticospinal.
 Anterior corticospinal.
 Corticobulbar.
 Indirect pathways – govern automatic movements (I.E.
Reflexes).
 Rubrospinal.
 Tectospinal.
 Vestibulospinal.
 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.
 Reflex arc (reflex circuit) - the pathway followed by
nerve impulses.
 Sensory receptor.
 Distal end of a sensory neuron.
 Responds to a stimulus.
 Sensory neuron.
 Nerves terminate in the brain stem or spinal cord.
 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.
 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.
 Reflexes are normally predictable.
 They can provide information about the health of the
nervous system.
 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.
 Stretch reflex
 Tendon reflex
 Flexor (withdrawal) reflex
 Crossed (extensor) 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.
 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.
 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.
 Helps you maintain balance.
 Contralateral reflex arc.
 Reciprocal innervation occurs.
 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.
 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.
 Endoneurium – surrounds individual axons.
 Perineurium - surrounds bundles of axons called
fascicles.
 Epineurium – surrounds the entire nerve.
 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.
 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.
 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.”
 The brachial plexus provides the entire nerve supply of
the shoulders and upper limbs.
 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.
 Known as “waiter’s tip position”.
 Results from forceful pulling away of the head from
the shoulder.
 Caused by improper intramuscular injections into the
deltoid or when the cast is applied too tightly around
the mid-humerus.
 Indicated by wrist drop.
 Numbness, tingling, and pain in the palm and fingers.
 Inability to pronate the forearm.
 Weak wrist flexion.
 Inability to abduct or adduct the fingers.
 Atrophy of the interosseous mm of the hand.
 “Clawhand”.
 Loss of sensation over the little finger.
 Paralysis of the serratus anterior mm.
 The scapula protrudes.
 “Winged scapula”.
 The lumbar plexus supplies the anterolateral
abdominal wall, external genitals, and part of the
lower limbs.
 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.
 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.
 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.
 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.
 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.