Chapter 12 Spinal Cord and Spinal Nerves BIOL-3301

Spinal Cord

Integrates incoming information and produces responses through reflex mechanisms

Cervical
Thoracic
Lumbar
Sacral

Segments of the Spinal Cord

31 pairs

How many pairs of spinal nerves are there?

Cervical enlargement

inferior to the cervical region, location of nerve fibers to the upper limbs

Lumbosacral enlargement

inferior to the thoracic, lumbar, and superior sacral regions, location of nerve fibers supplying lower limbs

Conus medullaris

inferior conelike region of the spinal cord

Cauda equina

roots of spinal nerves extending inferior to the lumbosacral enlargement and conus medullaris

Dura mater
Arachnoid mater
Pia mater

Three layers of meninges of spinal cord

Epidural space
Subdural space
Subarachnoid space

Associated spaces of the spinal cord

Dura mater

-Most superficial/thickest membrane
-Contains thecal sac

Arachnoid mater

Thin, wispy middle layer

Pia mater

Deepest layer and bound tightly to the surface of the spinal cord

Epidural space

-Space between wall of vertebral canal and the dura mater of spinal cord
-Contains spinal nerve roots, blood vessels, areolar connective tissue, adipose tissue

Subdural space

-between dura mater and arachnoid mater
-Contains small amount of serous fluid

Subarachnoid space

-between arachnoid mater and pia mater
-Contains weblike strands of the arachnoid mater, blood vessels, and cerebrospinal fluid (CSF)

Denticulate ligaments

connective tissue septa extending from the lateral sides of the spinal cord to the dura mater

Filum terminale

Connective tissue strand anchoring the conus medullaris and thecal sac to the first coccygeal vertebra

Thecal sac

sac surrounds the spinal cord formed by the dura mater

Anterior median fissue

partially separate the two halves of the spinal cord

Posterior median sulcus

partially separate the two halves of the spinal cord

White commisure

connect the two halves of the spinal cord

Ventral column
Lateral column
Dorsal column

Three columns of White matter

Dorsal horn
Lateral horn
Ventral horn

Three horns of Gray matter

Dorsal horn

contains cell bodies of interneurons

lateral horn

contains cell bodies of autonomic neurons

Ventral horn

contains cell bodies of somatic motor neurons

Gray commisure

connect the two halves of the spinal cord

Central canal

opening that contains CSF located in the center of gray commisure

Ventral root

Contains axons of motor neurons (somatic and autonomic)

Dorsal root

Carries sensory axons

Spinal nerve roots

pass through the subarachnoid space and pierce the arachnoid mater and dura mater

Reflex

Autonomic response to stimulus

Autonomic reflexes

responsible for maintaining relatively constant blood pressure, blood carbon dioxide levels, water intake

Somatic reflexes

maintain posture, remove body from painful stimuli, keep body from suddenly falling or moving due to external force

Reflex arc

Nural pathway that controls a reflex and the basic functional unit of the nervous system

Sensory receptor
Sensory neurons
Integration center
Motor neurons
Effector organs

Five components of reflex arc

Complexity
Development
Effector
Location of integration center

Reflexes classified based on...

Stretch reflex

Simplest reflex; contraction of muscles in response to stretching of that same muscle

Muscle spindle

sensory receptor for the reflex

Alpha motor neuron

motor neurons that causes the muscle to contract

gamma motor neuron

innervate the ends of muscle spindle fibers

Golgi Tendon reflex

prevents contracting muscles from applying excess tension to tendons

Withdrawal reflex

Flexor reflex that functions to remove a limb or another body part away from a painful stimulus

reciprocal innervation

-allows opposing muscles to reinforce the efficiency of the withdrawal reflex
-allows coordination contraction of flexor muscles and relaxation of the opposing extensor muscles

Crossed Extensor reflex

Occurs on the opposite side of the body from the stimulus
Causes the opposite response in the other limb

Endoneurium
Perineurium
Epineurium

Three layers of connective tissue

Endoneurium

delicate connective tissue layer surrounding each axon and its Schwann cell sheath

Perineurium

heavier connective tissue layer that surround groups of axons

Epineurium

dense connective tissue layer surrounding the nerve, continuous with the dura mater

8 pairs

# of pairs of spinal nerves that exit in cervical region

12 pairs

# of pairs of spinal nerves that exit in the thoracic region

5 pairs

# of pairs of spinal nerves that exit in the lumbar region

5 pairs

# of pairs of spinal nerves that exit in the sacral region

1 pair

# of pairs of spinal nerves that exit in the coccygeal region

Dermatone

area of the skin supplied with sensory innervation by a pair of spinal nerves

Dermatomal Map

distribution of sensory distribution of each spinal nerve to the skin

Ramus

major branch of spinal nerve

Dorsal ramus

-present for each spinal nerve
-Innervate most of the deep muscles of the dorsal trunk responsible for moving the vertebral column
-Innervate connective tissue and skin near midline of the back

Ventral ramus

-present for each spinal nerve
-Forms five major plexuses
-Form intercostal nerves, innervates the intercostal muscles and skin over thorax

Communicating rami

found from thoracic and upper lumbar spinal cord regions, carry axons associated with the sympathetic division of the ANS

Plexus

Intermingling of nerves

Roots

ventral rami of different spinal nerves joint to form a plexus

Cervical plexus

ventral rami of spinal nerves C1-C4; innervates superficial neck structures; small plexus

Brachial plexus

ventral rami of spinal nerves C5-T1

Lumbar plexus

ventral rami of spinal nerves L1-L4

Sacral plexus

ventral rami of L4-S4

Coccygeal plexus

ventral rami of S5 and coccygeal nerve; supplies motor innervation to muscles of pelvic floor

Ansa cervicalis

loop between C1 and C3, nerves to infrahyoid muscle branch from here

Phrenic nerve

originates from C3-C5 spinal nerves; descends along the side of the neck and mediastinum to diaphragm and regulates the contraction of diaphragm

Axillary nerve
Radial nerve
Musculocutaneous nerve
Ulnar nerve
Median nerve

Brachial plexus nerves

Axillary nerve

innervates deltoid and teres minor muscle and provides sensory innervation to the shoulder joint

Radial nerve

Innervates all extensor muscles of upper limb, supinator muscle, and brachioradialis
Sensory distribution to posterior portion of upper limb and posterior surface of hand

Musculocutaneous nerve

innervates anterior muscles of the arm and sensory to part of the forearm

Ulnar nerve

Innervates two forearm muscles and intrinsic hand muscles except thumb; sensory to ulnar side of hand; easily damaged nerve (funny bone)

Median nerve

Innervates almost all flexor muscles of forearm and most hand muscles; cutaneous sensory distribution to radial portion of palm of hand; passes through carpal tunnel

Obturator nerve
Femoral nerve
Tibial nerve
Common fibular nerve

Four major nerves of lumbosacral plexus

Obturator nerve

innervates the muscles of medial thigh that adducts thigh; cutaneous sensory distribution to medial side of the thigh

Femoral nerve

innervates iliopsoas and sartorius muscles and the quadriceps femoris group; sensory distribution to anterior/lateral thigh and medial leg and foot

Tibial/ Common Fibular nerve

-Bound together within connective tissue sheath for the length of the thigh
-Form sciatic nerve
-Largest nerve in body
-passes through greater sciatic notch and descends in the posterior thigh to the popliteal fossa and separates

Tibial nerve

Innervates most of the posterior thigh and leg muscles
-Branches to medial and lateral planter nerves and sural nerve

Common Fibular nerve

Divides into deep fibular and superficial fibular nerve