1. Lecture

2. An Introduction to the Spinal Cord, Spinal Nerves and Spinal Reflexes
Spinal reflexes are rapid, automatic nerve responses triggered by specific stimuli
They are controlled by the spinal cord; they are not controlled by the brain

3. What is part of the CNS? What is part of the PNS?
An Overview of the CNS and PNS
The Brain (CNS)
Motor output over cranial nerves
(PNS)
Sensory input over cranial nerves
Effectors
Reflex centers in brain
Sensory receptors
Muscles
The Spinal Cord (CNS)
Glands
Sensory input over spinal nerves
Motor output over spinal nerves (PNS)
Reflex centers in spinal cord
Sensory receptors
Adipose tissue
What is part of the CNS? What is part of the PNS? 3

4. Spinal Cord Structure and Function
Gross Anatomy of the Spinal Cord
The cord is about 18 inches (45 cm) long and a 1/2 inch (14 mm) wide
It ends between the first and second lumbar vertebrae (L1 and L2)
It has bilateral symmetry (grooves divide the spinal cord into left and right sides)
Posterior median sulcus – on posterior side
Anterior median fissure – on anterior side
Cord enlargements are caused by the amount of gray matter in the segment, and the involvement with sensory and motor nerves of the limbs
The cervical enlargement serves nerves of the shoulders and upper limbs
The lumbar & sacral enlargements serve nerves of the pelvis and lower limbs

5. There are 30 vertebrae with 31 pairs of spinal nerves in the PNS
There are 30 vertebrae with 31 pairs of spinal nerves in the PNS. Spinal nerves are based on the vertebrae where the spinal nerves originate
Cervical nerves are named for the vertebra superior to the nerve’s exit (except for the 8th nerve; it is inferior).
All other nerves are named for the vertebra inferior to the nerve’s exit
The first pair of spinal nerves pass between the skull and C1. The rest pass through the intervertebral foramina

6. Mention that Cranial section has 7 bones and 8 nerves
Cranial - superior radiation of nerves
Thoracic - inferior radiation of nerves
C7, T12, L5, S5, C1 = 30 bones
C8, T12, L5, S5, C1 = 31 nerves
HaHa!

7. On the the distal end of the cord…
The Conus medullaris is the tapered terminus of the cord (connective tissue), located below the lumbar enlargement (L1-L2)
The Filum terminale is a thin thread of fibrous tissue (pia mater) at the end of the conus medullaris. It helps anchor the conus medullaris to the coccyx (attaches to coccygeal ligament)
The Cauda equina are nerve roots extending inferiorly below the conus medullaris (L2-S5) that innervates the pelvic organs and lower limbs

8. Roots are the two branches of spinal nerves
The ventral root (anterior side) contains axons of motor neurons (efferents)
The dorsal root (posterior side) contains axons of sensory neurons (afferents)
Dorsal root ganglion contains many cell bodies of sensory neurons
Spinal nerves are on each side of the spine; the dorsal and ventral roots join to form a spinal nerve
Mixed Nerves carry both afferent (sensory) and efferent (motor) fibers

9. The Spinal Meninges
The spinal meninges are specialized membranes that isolate the spinal cord from their surroundings
They protect the spinal cord, provide continuity within the CNS (brain and spinal cord) and channel the vasculature (blood supply)
Meningitis is a deadly viral or bacterial infection of these tissues (inflammation and damage will kill the nervous system!)

10. There are three meningeal layers of the spinal cord
The dura mater is the dense, outer layer, composed of collagen. It is contiguous with the cranial dura mater, and serves as a longitudinal anchor, terminating with the filum terminale (coccygeal ligament – shown in previous slide)
The arachnoid mater is the middle, avascular layer
The pia mater is the delicate, inner vascular layer, composed of elastin. Dendiculate ligaments are a latitudinal anchor (next slides)

11. The epidural space is between the dura mater and the walls of the vertebral body. It contains blood vessels, loose connective and adipose tissue; this is the site of epidural injection of anesthetic – commonly, it is done wrong (damage)!
The subdural space is between the dura mater and the arachnoid mater (little or no space)
The subarachnoid space is between the arachnoid mater and pia mater. It is filled with cerebrospinal fluid (CSF) that carries dissolved gases, nutrients and wastes; this is the site of lumbar puncture (spinal tap) to withdraw CSF for diagnostic purposes (L3 to L5) – this is a very delicate procedure!

12. Paired denticulate ligaments are found along the length of the spinal cord
They extend from the pia mater to the dura mater
They help to laterally suspend and anchor the spinal cord

13. Gray Matter and White Matter
Spinal tissue is structurally divided into two types of matter
Inside gray matter (shaped like H) is the location of cell bodies and unmyelinated axons. There is a greater amount of gray matter in the spinal cord segments serving the limbs. It also has projections (horns)
Outside white matter is the location of myelinated axons organized in ascending and descending columns (funiculi)

14. of white matter. The right half indicates the
Posterior white column
Posterior gray horn
Lateral white column
Lateral gray horn
Dorsal root ganglion
Anterior gray horn
Anterior white column a
The left half of this sectional view shows important anatomical landmarks, including the three columns
of white matter. The right half indicates the
functional organization of the nuclei in the anterior, lateral, and posterior gray horns.

15. Structural Organization of Gray Matter
POSTERIOR
Structural Organization of Gray Matter
Posterior median sulcus
The projections of gray matter toward the outer surface of the spinal cord are called horns.
Posterior gray horn
Lateral gray horn
Dorsal root
Anterior gray horn
Dorsal root ganglion
Ventral root
ANTERIOR
A micrograph of a section through the spinal cord, showing major landmarks in and surrounding the cord. 15

16. Gray Matter is Functionally Organized in Anatomical Horns
Posterior gray horns contain somatic and visceral sensory nuclei
Anterior gray horns contain somatic motor nuclei
Lateral gray horns are in thoracic and lumbar segments; they contain visceral motor nuclei
Commissures are axons that cross laterally from one side of the cord to the other before reaching gray matter (anterior and posterior sides)

17. We can pinpoint damage in the spinal cord
to functional deficits which are observed…

18. Functional Organization of White Matter
White matter is organized in tracts (fasciculi); these are bundles of myelinated axons that relay information
Ascending tracts carry information to the brain
Descending tracts carry motor commands to spinal cord

19. Spinal Nerves and Plexuses
Anatomy of Spinal Nerves
Every spinal cord segment is connected to a pair of spinal nerves
Every spinal nerve is surrounded by three connective tissue layers that support structures and contain blood vessels

20. Three Connective Tissue Layers of Spinal Nerves
Epineurium
Outer layer
Dense network of collagen fibers
Perineurium
Middle layer
Divides the nerve into fascicles (axon bundles)
Endoneurium
Inner layer
Surrounds Schwann cells that envelope individual axons in the fascicle
Is continuous onto peripheral nerves
Hmmm, looks a lot like muscle tissue, eh?

21. Perineurium (around one fascicle) (around myelin sheath)
Blood vessels
Perineurium (around one fascicle)
Endoneurium
(around myelin sheath) 21

22. Peripheral Distribution of Spinal Nerves
Spinal nerves form lateral to intervertebral foramen, where dorsal and ventral roots unite, and then branch, to form pathways leading to and from their destination
There are two classified branches; sensory or motor

23. Somatic sensory nuclei Visceral sensory nuclei
From interoceptors of back
From exteroceptors, proprioceptors of back
The dorsal root of each spinal nerve carries sensory information to the spinal cord.
The dorsal ramus carries sensory information from the skin and skeletal muscles of the back.
Somatic sensory nuclei
The ventral ramus carries sensory information from the ventrolateral body surface, structures in the body wall, and the limbs.
Dorsal root ganglion
From exteroceptors, proprioceptors of body wall, limbs
From interoceptors of body wall, limbs
Rami communicantes
Visceral sensory nuclei
Ventral root 
Somatic sensations 
Visceral sensations
The sympathetic nerve carries sensory information from the visceral organs.
From interoceptors of visceral organs 23

24. Motor 24 To skeletal muscles of back
Postganglionic fibers to smooth muscles, glands, etc., of back
The spinal nerve forms just lateral to the intervertebral foramen, where the dorsal and ventral roots unite.
The dorsal ramus contains somatic motor and visceral motor fibers that innervate the skin and skeletal muscles of the back.
Dorsal root ganglion
Dorsal root
The axons in the relatively large ventral ramus supply the ventrolateral body surface, structures in the body wall, and the limbs.
The ventral root of each spinal nerve contains the axons of somatic motor and visceral motor neurons.
To skeletal muscles of body wall, limbs
Visceral motor nuclei
Somatic motor nuclei
Rami communicantes
Postganglionic fibers to smooth muscles, glands, etc., of body wall, limbs 
Somatic motor commands
Sympathetic ganglion 
Visceral motor commands
The white ramus is the first branch from the spinal nerve and carries visceral motor fibers to a nearby sympathetic ganglion. Because these preganglionic axons are myelinated, this branch has a light color and is therefore known as the white ramus.
Postganglionic fibers to smooth muscles, glands, visceral organs in thoracic cavity
A sympathetic nerve contains preganglionic and postganglionic fibers innervating structures in the thoracic cavity.
The gray ramus contains postganglionic fibers that innervate glands and smooth muscles in the body wall or limbs. These fibers are unmyelinated and have a dark gray color.
Preganglionic fibers to sympathetic ganglia innervating abdominopelvic viscera 24

25. C2C3
N V
A specific bilateral region of the skin surface monitored by a single pair of spinal nerves is known as a dermatome (The pair of spinal nerves are sensory and motor)
Shingles is caused by a herpes virus that attacks dorsal roots of spinal nerves and cranial ganglia
C2C3 C2 C3 C3 C4 T2 C4 C5 T3 T1 T2 T4 T5 T3 C5 T6 T4 T7 T5 T8 T6 T9 T2 T2 T7
T10 T8
T11
T12 T9 L1 C6
T10 L2
T11 L4 L3 T1 C6
T12 L5 C7 L1 S L2 4 S S2 3 C8 C8 T1 L3 L1 C7 S5 S1 L5 L4 L2 S2 L5 L3 S1 L4
ANTERIOR
POSTERIOR 25

26. If you ever had chicken pox, beware
If you ever had chicken pox, beware! The virus that caused it is within you and can express itself (unknown why) at a later stage in life 
It follows a dermatome pattern of expression

27. Nerve Plexuses
Nerve plexuses (trunks) are a complex, interwoven network of nerve fibers
They are formed from blended fibers of ventral rami of adjacent spinal nerves
The trunks form cords that control the skeletal muscles of the neck and limbs (arms and legs)

28. There are four major Plexuses of Ventral Rami
Cervical plexus (C1 – C5)
Brachial plexus (C4 – T2)
Lumbar plexus (T12 – L4)
Sacral plexus (L4 – S4)

29. Lesser occipital nerve C2 Great auricular nerve C3
Cervical plexus C3
Transverse cervical nerve C4 C5
Supraclavicular nerve C6 C7
Phrenic nerve
Brachial plexus C8 T1 T2 T3
Axillary nerve T4 T5 T6 T7
Musculocutaneous nerve T8 T9
Thoracic nerves
T10
T11 29

30. Iliohypogastric nerve S2 S3 S4 Ilioinguinal nerve
Radial nerve
Lumbar plexus L2
Ulnar nerve L3
Median nerve L4 L5
Sacral plexus S1
Iliohypogastric nerve S2 S3 S4
Ilioinguinal nerve S5
Co1
Lateral femoral cutaneous nerve
Genitofemoral nerve
Femoral nerve
Obturator nerve
Superior
Gluteal nerves
Inferior
Pudendal nerve
Saphenous nerve
Sciatic nerve 30

31. Extra Stuff…

32. The Cervical Plexus Includes ventral rami of spinal nerves C1–C5
It innervates the neck, thoracic cavity and diaphragmatic muscles
Major nerves:
Phrenic n. (diaphragm mvt)
Great auricular n. (ear mvt)
Cervical n. (neck mvt)

33. Redundant slide… Cranial Nerves Nerve Roots of Cervical Plexus
Accessory nerve (XI)
Hypoglossal nerve (XII)
Lesser occipital nerve
Nerve Roots of Cervical Plexus C1 C2 C3 C4 C5
Supraclavicular nerves
Clavicle 33

34. The Brachial Plexus Includes ventral rami of spinal nerves C4–T2
It innervates the pectoral girdle and upper limbs
Nerves that form the brachial plexus originate from:
Superior, middle, and inferior trunks; these are large bundles of axons from several spinal nerves
Lateral, medial, and posterior cords; these are smaller branches that originate at trunks

35. Major nerves of the Brachial Plexus
Musculocutaneous (lateral cord) and Ulnar n. (medial cord) flexes the arm
Median n. (lateral and medial cords) flexes and pronates the arm
Radial n. (posterior cord) elongates and supinates the arm

36. Major nerves of the Brachial Plexus
Pectoral n. pectoralis
Thoracic n. serratus anterior
Subclavius n. subclavius

37. Major nerves of the Brachial Plexus
Axillary n. deltoid and teres minor
Thoracodorsal n. latissimus dorsi
Subscapular n. subscapular and teres major
Suprascapular n. supraspinatus and infraspinatus
Dorsal Scapular n. rhomboid and levator scapulae

38. The Lumbar Plexus Includes ventral rami of the spinal nerves T12–L4
Iliohypogastric nerve
Ilioinguinal nerve
Genitofemoral nerve
The Lumbar Plexus
Includes ventral rami of the spinal nerves T12–L4
Major nerves:
Genitofemoral n. skin of genitals
Lateral femoral cutaneous n. skin of upper pelvic area
Femoral n. flex the thigh and hip
Sciatic n. flex the knee
Fibular n’s (from Sciatic branch) flex the knee (to walk)
Lateral femoral cutaneous nerve
Femoral nerve
Obturator nerve
Superior gluteal nerve
Inferior gluteal nerve
Pudendal nerve
Posterior femoral cutaneous nerve (cut)
Sciatic nerve
Saphenous nerve
Common fibular nerve
Superficial fibular nerve
Deep fibular nerve
Nerves of the lumbar and sacral plexuses, anterior view

39. The Sacral Plexus Includes ventral rami of spinal nerves L4–S4
Superior gluteal nerve
Inferior gluteal nerve
The Sacral Plexus
Includes ventral rami of spinal nerves L4–S4
Major nerves:
Pudendal n. controls urinary and anal sphincters (control urination and defacation)
Sciatic n.
Two branches of the sciatic nerve
Fibular n. flex the knee (to walk)
Tibial n. flex the knee, extend the ankle, extend the toes (to walk)
Pudendal nerve
Posterior femoral cutaneous nerve
Sciatic nerve
Tibial nerve
Common fibular nerve
Sural nerve
Nerves of the sacral plexus, posterior view

40. Cutaneous distribution of the nerves in the foot and ankle
Saphenous nerve
Sural nerve
Sural nerve
Saphenous nerve
Sural nerve
Fibular nerve
Tibial nerve
Sural nerve
Saphenous nerve
Fibular nerve
Tibial nerve
Cutaneous distribution of the nerves in the foot and ankle 40