The Spinal Cord, Spinal
Nerves, and Reflexes
Exercise 19
Spinal Cord

Connects the PNS with the brain

Produces spinal reflexes

Passes down the foramen magnum and descends to
T12-L3

In children, spinal cord is as long as the spine

Two enlarged regions:

Cervical Enlargement: supplies nerves to upper
limbs

Lumbar Enlargement: supplies nerves to lower
limbs

Conus Medullaris: where the spinal cord ends

Cauda Equina (“horse’s tail”): group of spinal nerves
that branch from the end of the conus medullaris
Anatomy of the Spinal Cord
Sectional Anatomy

Cord is divided by deep anterior median fissure and surface posterior median sulcus

White Matter: contains many myelinated axons


Grey Matter: contains many glial cells and cell bodies


Divided into columns
Divided into “horns”

Posterior Gray Horn: carry sensory neurons in spinal cords

Anterior Gray Horn: carry somatic motor neurons to skeletal muscle

Lateral Gray Horn: occur in T1=L2 and consists of visceral motor neurons
Axons can cross opposite side of spinal cord at the crossbars called “commissures”
Spinal Meninges

Dura Mater – outer membrane, tough connective
tissue

Epidural space – contains adipose tissue to pad
the spinal cord

Arachnoid space

Subdural space – separates the dura mater from
the arachnoid

Subarachnoid space – contains the CSF to
protect and cushion the spinal cord

Pia Mater – thin, inner meningeal layer directly
over spinal cord; hold the blood vessels in place
What is meningitis?


Inflammation of the protective membranes of the brain and spinal cord
This inflammation can produce:

Fever

Headache

Seizures

Change in behavior

Even cause brain damage

Stroke or death
Spinal and Peripheral Nerves

12 pairs of cranial nerves

31 pairs of spinal nerves

8 cervical nerves – No ANS neurons

12 thoracic nerves

5 lumbar nerves – some ANS neurons

1 coccygeal nerve – no ANS neurons
Spinal Nerve Plexus

Plexus: groups of spinal nerves

Four regions

Cervical

Brachial

Lumbar

Sacral

**Thoracic  NOT part of any plexus but
make up the intercostal nerves that
innervate the intercostal and abdominal
muscles
Cervical Plexus

Supply the neck, shoulder, upper limb, and diaphragm (muscle used for
breathing)

Includes nerves from C1-C4 and parts of C5
Brachial Plexus

Innervates the shoulder, upper limb, some muscles of the trunk

Include nerves from C5-C8 and T1

Major nerves

Axillary nerve


Radial nerve


Controls flexor muscles (anterior) of the upper limb
Median nerve


Controls extensor (posterior) muscles of the upper limb
Muscolocutaneous nerve


Supplies deltoid, teres minor, skin of the shoulder
Innervates flexor muscles of the forearm and digits
Ulnar nerve

Innervates the flexor carpi ulnaris muscles of the forearm, and other muscles of the hand
Lumbosacral Plexus

Largest nerve network

Innervate the skin/muscles of the abdominal wall, genitalia, and thigh

Major nerves:

LUMBAR PLEXUS

Genitofemoral nerve


Lateral femoral cutaneous nerve


Innervates medial aspect of the skin of the thigh
Femoral nerve


Supplies the external genitalia and anterior/lateral skin of the thigh
Controls muscles of the anterior thigh and adductor muscles
SACRAL PLEXUS

Sciatic nerve


Supplies posterior thigh muscles
Pudendal nerve

Supplies the muscular floor of the pelvis, perineum and parts of external genitalia
Spinal Reflexes

Reflexes – automatic neural responses to certain stimuli

CNS has little involvement in these reflexes

Many type of reflexes

Reflex Arc – a stimulus does not to be recognized to elicit a
response to it
Reflexes

Cranial

Spinal

Somatic


Monosynaptic

Polysynaptic
Stretch aka “patellar”
Let’s try them!