Chapter 13: The Spinal Cord and Spinal Nerves. Copyright 2009, John Wiley & Sons, Inc. Spinal Cord Anatomy Protective and stabilizing structures: Vertebral

Chapter 13: The Spinal Cord and Spinal Nerves

Copyright 2009, John Wiley & Sons, Inc.

Spinal Cord Anatomy

Protective and stabilizing structures: Vertebral column Meninges – continuous around spinal cord and

brain cerebrospinal fluid denticulate ligament


Spinal Cord Anatomy

Meninges – 3 layers1. Dura mater

most superficial dense irregular connective tissue Ends at second sacral vertebra Cushion of fat and connective tissue in epidural space Subdural space filled with interstitial fluid

2. Arachnoid mater Spider web arrangement of delicate collage and elastic Subarachnoid space filled with cerebrospinal fluid (CSF)

3. Pia mater Thin delicate ct adheres to spinal cord and brain Extensive blood supply

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External Anatomy of the Spinal Cord Two enlargements: cervical and lumbar Conus medullaris Filum terminale Cauda equina Posterior (dorsal root) & anterior(ventral) root Posterior (dorsal root) ganglion Spinal nerve


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Internal Anatomy of the Spinal Cord Partially divide spinal cord into right and left

Anterior median fissure Posterior median sulcus

Gray matter Divided into horns Anterior, posterior & lateral gray horns

White matter Columns Anterior, posterior & lateral white columns

Central canal


Internal Anatomy of the Spinal CordLook for (see next slide)

1. Gray commissure

2. Central canal

3. Anterior, posterior and lateral gray horns

4. Anterior, posterior and lateral white columns


Internal Anatomy of Spinal Cord

White columns

Ascending tracts – sensory information Examples: Spinothalamic, spinocortical

Descending tracts – motor impulses Examples: Corticospinal, vestibulospinal


Sensory and Motor Tracts

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

The white matter contains both sensory and motor tracts


Spinal Nerves 31 pairs mixed nerves

Cervical (C1-C8) Thoracic (T1-T12) Lumbar (L1-L5) Sacral (S1-S5) Coccygeal


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Spinal Nerves Spinal nerves are mixed with motor and sensory

axons Spinal nerves connect to each segment of spinal

cord by two roots posterior or dorsal – sensory Anterior or ventral – motor

Branches of spinal nerves Posterior ramus Anterior ramus Meningeal branch Rami communicantes


Spinal Nerves

Distribution of Spinal Nerves

Plexus Anterior rami of spinal nerves, except T2-T12,

form networks of nerves Emerging from a plexus are nerves bearing

names that typically describe the general regions they supply or route they follow


Cervical Plexus


anterior rami of C1 -C5 Muscles and skin of

head, neck, upper shoulder

Phrenic nerve formed by cranial nerve XII and cervical plexus innervates diaphragm

Brachial plexus

anterior rami of C5 – C8 & T1.

Supplies the shoulders and upper limbs.


Brachial plexus

Major nerves Axillary Musculocutaneous Radial Median Ulnar


Lumbar Plexus

L1 – L4 Supplies the antero-

lateral abdominal wall, external genitals, and part of the lower limbs

Femoral & obturator nerves


Sacral Plexus

L4 – L5 and S1 – S4. buttocks, perineum,

and lower limbs Sciatic – largest nerve

in the body


Coccygeal Plexus

S4 – S5 and the coccygeal nerves

skin in the coccygeal region


T2 – T12

Anterior rami do not form plexus Intercostal / thoracic nerves Distributed directly to structures they supply

in intercostal spaces

Dermatome

Dermatome is the area of the skin that provides sensory input to the CNS via one pair of spinal nerves or the trigeminal nerve


Spinal Cord Functions

White matter tracts represent “highways” for nerve impulse propagation

Sensory input toward brain and motor output to skeletal muscles and effector organs / tissues

Sensory – two main routes Posterior column Spinothalamic tract

Motor – two main routes Direct pathways Indirect pathways

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Spinal Cord Functions

Integrating center for spinal reflexes Integration occurs in gray matter Reflex

Fast, automatic, and predictable involuntary response to a stimulus

May occur as muscle contractions or glandular secretions Occurs in response to changes in environment May be spinal or cranial and somatic or autonomic

(visceral) When the integration takes place in the spinal cord it is a

spinal reflex

Reflex Arc The pathway followed by nerve impulses

that produce a reflex is a reflex arc A reflex arc components:

1. sensory receptor

2. sensory neuron

3. integrating center

4. motor neuron

5. effector


1 SENSORY RECEPTOR(responds to a stimulusby producing a generatoror receptor potential)

1SENSORY NEURON(axon conducts impulses from receptor to integrating center)

SENSORY RECEPTOR(responds to a stimulusby producing a generatoror receptor potential)

2 1SENSORY NEURON(axon conducts impulses from receptor to integrating center)


INTEGRATING CENTER(one or more regions within the CNSthat relay impulses from sensory tomotor neurons)

Interneuron

2

3




MOTOR NEURON(axon conducts impulses fromintegrating center to effector)

Interneuron

2

3

4




MOTOR NEURON(axon conducts impulses fromintegrating center to effector)

EFFECTOR(muscle or gland thatresponds to motornerve impulses)

Interneuron

2

3

4 5

Reflex Arc

Somatic Spinal Reflexes

1. Stretch (monosynaptic)

2. Tendon (polysynaptic)

3. Flexor / withdrawal (polysynaptic)

4. Crossed extensor (polysynaptic)

Stretch Reflex Stretching stimulates muscle spindles Impulse along somatic sensory neuron through posterior root into

spinal cord Activation of motor neuron in anterior gray horn through

integrating center Strong enough stimulus activates impulses out motor neuron

through anterior root stimulating muscle Monosynaptic (2 neuron) Reciprocal innervation – components of neural circuit

simultaneously cause contraction of on muscle and relaxation of antagonists

Ipsilateral maintaining muscle tone Patellar reflex

Stretch Reflex

Tendon Reflex

Polysynaptic – more than one synapse and more than two different neurons involved

Golgi tendon organ is sensory organ Sensory neuron synapses with two interneurons Inhibitory interneuron relaxes effector Stimulatory neuron contracts antagonist Ipsilateral preventing damage to muscles and

tendons when muscle force become too extreme

Tendon Reflex

Flexor (withdrawal) Reflex

Ipsilateral and polysynaptic Inter-segmental reflex arc Reciprocal innervation Single sensory neuron activates several

motor neurons Stimulates more than one effector

Flexor (withdrawal) Reflex

Crossed Extensor Reflex

Contralateral reflex arc Polysynaptic Synchronizes the extension of contralateral

limb with withdrawal (flexion) of stimulated limb

Reciprocal innervation

Crossed Extensor Reflex

Reflexes and Diagnosis

1. Patellar reflex Absent in damage to sensory or motor nerves or

integrating center in 2nd, 3rd, 4th lumbar Absent in chronic DM and neurosyphilis Exaggerated in disease or injury involving certain

descending motor tracts from brain


2. Achilles reflex – plantar flexion through contraction of gastrocnemius and soleus

Absence indicates damage nerves of posterior leg or neurons of lumbo-sacral region

DM, neurosyphilis, alcoholism, subarachnoid hemorrhage

Exaggerated Cervical cord compression or lesion of motor tracts of

1st and 2nd sacral segments


3. Babinski sign – gentle stroking of the lateral outer margin of the sole

Great toe dorsiflexes / extends with fanning of other toes

Normal in children under 1 ½ due to incomplete myelination corticospinal tract

Abnormal after 1 ½ indicating interruption of corticospinal tract

Negative Babinski – normal response is plantar felxion – curling under of toes


4. Abdominal reflex – contraction of muscles that compress abdominal wall in response to stroking side of abdomen

Causes contraction moving umbilicus toward stimulus

Absence indicates lesions of corticospinal tract Multiple sclerosis

5. Absence of normal pupillary light reflex – associated with brain injury or damage


End of Chapter 13

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Chapter 13: The Spinal Cord and Spinal Nerves. Copyright 2009, John Wiley & Sons, Inc. Spinal Cord Anatomy Protective and stabilizing structures: Vertebral