CH 14, Spinal Cord and Spinal Nerves

Nerves

Collection of thousands of axons of neurons

Ganglion

Collection of cells bodies of neurons in PNS

Inferior end of spinal cord

Conus medullaris

Spinal cord spans from….

Medulla oblongata to inferior border of L1 vertebrae

Cervical enlargment

Neurons → upper extremity

Lumbosacral enlargment

Neurons → lower extremity

Spinal cord white matter is

myelinated axons

What do myelinated axons do, and where do we find them

they relay nerve signals, and in the white matter of the spinal cord

Spinal cord grey matter

Dendrites and cell bodies of neurons

The grey matter of the spinal cord is the

process center

Posterior median

sulcus

Anterior median

fissure

Dorsal/Posterior root ganglion

cell bodies of sensory neurons

Dorsal/Posterior root

Axons of sensory neurons

Ventral/Anterior root

Axons of motor neurons

Spinal nerves

merger of ventral and dorsal roots, mixed nerves

Cervical region

C1-C8

Thoracic Region

T1-T12

Lumbar region

L1-L5

Sacral Region

S1-S5

Coccygeal Region

Co1

How many vertebrae in the Cervical region

8

How many vertebrae in the Thoracic Region

12

How many vertebrae in the Lumbar region

5

How many vertebrae in the Sacral Region

5

How many vertebrae in the Coccygeal Region

1

Cauda equina

Nerve roots of inferior spinal nerves L2-Co1

Posterior ramus

small branch, innervates muscles and skin of back

Anterior ramus

Splits into multiple other branches, many involved plexuses

Rami communicantes

Small branches of autonomic fibers

Spinal nerve → sympathetic trunk ganglion

Sympathetic trunk ganglia

ganglia of sympathetic neurons

Dermatomes

part of skin with only one spinal nerve

What are dermatomes involved in

referred visceral pain

pain from one organ is mistakenly

referred to a dermatome

What spinal nerve roots contribute to the intercostal nerves?

Ventral rami of T2–T11

What areas do the intercostal nerves innervate?

Muscles of the ribs, anterolateral thorax, and abdominal wall

What is a nerve plexus?

A network of interweaving ventral rami of spinal nerves

Where are nerve plexuses found?

In the cervical, brachial, lumbar, and sacral regions

What do nerve plexuses primarily serve?

The limbs

What does each nerve contain?

Axons from several ventral rami

How is each limb muscle supplied with nerves?

By more than one spinal nerve

What forms the cervical plexus?

Ventral rami of C1 - C4

What does the phrenic nerve innervate?

Diaphragm

What spinal nerves form the cervical plexus?

Ventral rami of C1–C4

What important nerve comes from the cervical plexus?

Phrenic nerve

What does the phrenic nerve innervate?

The diaphragm

What spinal nerves form the brachial plexus?

Ventral rami of C5–T1 (often also C4 and T2)

How many major nerves innervate the upper limb from the brachial plexus?

Five

What muscle does the axillary nerve innervate?

Deltoid

The five nerves that innervate the upper limb

Musculocutaneous n

Median n

Axillary n

Radial n

Ulnar n

What muscle does the musculocutaneous nerve innervate?

Biceps brachii, brachialis

What nerve passes through the carpal tunnel?

Median nerve

What does the median nerve innervate?

Some flexors of the wrist and fingers

What does the ulnar nerve innervate?

Some anterior forearm muscles

What does the radial nerve innervate?

Triceps brachii, brachioradialis, and extensors of the wrist and fingers

What spinal nerves form the lumbar plexus?

Ventral rami of L1–L4

What does the lumbar plexus innervate?

The thigh, abdominal wall, and psoas muscle

What does the femoral nerve innervate?

Quadriceps femoris and sartorius

What does the obturator nerve innervate?

Adductor group and gracilis

What spinal nerves form the sacral plexus?

Ventral rami of L4–S4

What does the sacral plexus serve?

The buttock, lower limb, pelvic structures, and perineum

What is the longest and thickest nerve of the body?

Sciatic nerve

Where does the sciatic nerve split?

Superior to the popliteal fossa

What two nerves does the sciatic nerve split into?

Tibial nerve and fibular nerve

What muscles are innervated by the tibial nerve?

Biceps femoris long head, semimembranosus, semitendinosus, soleus, gastrocnemius

What muscles are innervated by the fibular nerve?

Short head of biceps femoris and tibialis anterior

What is the major nerve of the cervical plexus?

Phrenic nerve

What muscle does it innervate?

Diaphragm

List the ventral rami that make up the brachial plexus

C5–T1 (often also C4 and T2)

List the rami that make up the lumbar plexus

L1–L4

List the nerves that make up the sacral plexus

L4–S4

What is “rami”

branches of a spinal nerve

What structures protect the spinal cord?

Bone (vertebrae), meninges, and cerebrospinal fluid (CSF)

What are meninges?

Connective tissue membranes covering the brain and spinal cord

What is the filum terminale?

A thin strand of pia mater that anchors the conus medullaris to the coccyx

Put the spinal cord structures in order from superficial to deep:

Vertebrae
Epidural space
Dura mater
Subdural space
Arachnoid mater
Subarachnoid space
Pia mater

Deepest structure in the spinal cord?

Pia mater

Most superficial structure in the spinal cord?

Vertebrae

Where are lateral horns found in the spinal cord?

Only in segments T1–L2

What do lateral horns contain?

Cell bodies of autonomic motor neurons

What do autonomic motor nuclei innervate?

Smooth muscle, heart, and glands

What do the posterior/dorsal horns of the spinal cord contain?

Axons of sensory neurons and cell bodies of interneurons

What type of nuclei are found in the dorsal horns?

Sensory nuclei

What do somatic sensory nuclei receive signals from?

Skin, muscles, and joints

What do visceral sensory nuclei receive signals from?

Blood, vessels, and viscera

What is the gray commissure?

Gray matter with unmyelinated axons that connect the left and right gray matter

What structure runs through the center of the gray commissure?

Central canal

What are tracts in the spinal cord?

Bundles of axons in white matter

What do ascending tracts carry?

Sensory signals from receptors to the spinal cord to the brain

What do descending tracts carry?

Motor signals from the brain to the spinal cord to effectors

What type of information does the posterior funiculus carry?

Sensory/ascending

What type of information does the lateral funiculus carry?

Sensory/ascending and motor/descending

What type of information does the anterior funiculus carry?

Mostly motor/descending

What are three characteristics of conduction pathways?

They are paired, most decussate (cross over), and each is made of a chain of two or more neurons

What does decussation in conduction pathways result in?

Contralateral control (opposite side of the body)

Where are axons located in conduction pathways?

In spinal cord tracts (white matter)

Where are cell bodies located in conduction pathways?

Ganglia, spinal cord gray horns, and brain gray matter

What do somatosensory pathways carry signals for?

Proprioception, touch, temperature, pressure, and pain

Where do somatosensory pathways start?

At a sensory receptor

How many neurons are in somatosensory pathways?

Up to 3 neuron chain