1. Spinal Cord & Spinal Nerves
Chapter 12
Spinal Cord & Spinal Nerves
AP1 Chapter 12

2. Chapter 12 Outline Spinal Cord (SC) Reflexes
Interaction with SC reflexes
Structure of peripheral nerves
Spinal Nerves
AP1 Chapter 12

3. Chapter 12: SC & spinal nerves
CNS
PNS
Structure:
Brain
Spinal Cord
Fxn:
Receives sensory info
Integrates & evaluates the input it receives
Stores some information
Initiates rxns
Structure
Nerves & ganglia outside of the CNS
Ganglia: accumulation of cell bodies in the PNS
Fxn:
Collects information from numerous sources inside & outside the body & relays it through axons of sensory neurons to the CNS
Axons of the motor neurons of the PNS carry info from the CNS out to the body regulating the structures
AP1 Chapter 12

4. I. Spinal Cord (CNS!) CNS division
Major communication link between the brain & the PNS inferior to the head.
Participates in the integration of info & prod’s responses thru reflex mechanisms
AP1 Chapter 12

5. I. Spinal Cord: General Structure
Fig 12.1 pg 412
SC: extends from the foramen magnum to L2
Segments: cervical, thoracic, lumbar, & sacral
SC gives rise to 31 pairs of spinal nerves that exit the vertebral column thru intervertebral foramen or the sacral foramina
2 regions of enlargement
Cervical enlargement
Loc where axons that supply the upper limbs enter & leave the SC
Lumbosacral enlargement
Loc where axons supplying the lower limbs enter or leave SC
Conus medullaris: SC tapers into a cone-like region
Cauda equina: numerous roots extending inferiorly from LS enlargement that resemble a horse’s tail
31-Pairs- Elevator has the floors it stops on but it has hallways going both right and left out of the doors.

6. I. SC: Meninges of the SC Meninges: CT coverings around brain & SC
Dura Mater:“tough mother”
Most superficial & thickest
DM forms a “sac”  thecal sac surrounds SC. Attaches to the rim of the foramen magnum  C2
Epidural Space: layer of fat between the DM & the Vertebral Foramen (cushion)
Arachnoid Mater: “Spider web like”
middle membrane very thin & wispy
Subdural space: small amount of serous fluid
Pia Mater: “Affectionate”
inner most bound very tightly to surface of SC
Subarachnoid space: contains web-like strands of arachnoid mater+ blood vessels, & cerebrospinal fluid (CSF)
Fig 12.2
Pg 413

7. I. SC: Meninges of the SC SC is held in place by 2 things:
Denticulate ligaments
CT septa extending from the lateral sides of the SC to the DM
Filum terminale
CT strand that anchors the conus medullaris & thecal sac to the 1st coccygeal vertebra, limiting superior movement
AP1 Chapter 12

8. I. SC: Cross section of the SC
Figure 12.3 pg 414
Anterior Median Fissure
Posterior Median Sulcus
White matter
Columns/Funiculi: Anterior (Ventral), posterior (Dorsal), lateral
Each column is divided into Tracts/Faciculi/Pathways
Gray Matter:
Horns: Posterior, Anterior, Lateral (only in areas associated w/ANS)
Commissures (Gray & White)
Central Canal
Ventral Root
Dorsal Root
Dorsal Root Ganglion

9. Cross Section of the Spinal Cord
AP1 Chapter 12

10. I. SC: Cross section of the SC
White matter
Columns are divided into tracts
“Blue” ascending tracts that carry info from the body to the brain.
“Pink” descending tracts that carry info from the brain to the body.
Axons within a given tract carry basically the same type of info (even if there is overlap).
Fig 12.3 pg 415
AP1 Chapter 12

11. Spinal Nerves Origin Spinal Nerves MIXED Ventral Roots
Dorsal Root Ganglion
Multiple Ventral Rootlets
Dorsal Roots
Autonomic
Neuron
Somatic Motor
(Efferent) Neurons
Multiple Dorsal Rootlets
Sensory (Afferent)
Neurons
Spinal Nerves Origin
Cell bodies are in the lateral (autonomic) or anterior (multipolar somatic motor) gray horns
Can either go to an interneuron in the Posterior gray horn OR pass into WM & ascend or descend in the SC

12. II. Reflexes
AP1 Chapter 12

13. II. Reflexes
Basic Structural Unit
NS Neuron
Basic Functional Unit
NS Reflex Arc
Smallest, simplest portion capable of receiving a stimulus & prod’ing a response
Can be used as a tool to learn about NS fxn
Reflex: an automatic response to a stimulus prod’d by a reflex arc. It occurs w/o conscious thought
Somatic Reflexes (pain)
Autonomic Reflexes (blood pH)
Monosynaptic Reflex (SNMN)
Polysynaptic Reflex (SN IN MN)
AP1 Chapter 12

14. 5 basic components of a reflex arc
Sensory receptor
Sensory neuron
Interneuron
Motor Neuron
Effector Organ
II. Reflexes
Fig 12.5
Page 416
AP1 Chapter 12

15. II. Reflexes 3 major SC reflexes include: Stretch Reflex
Golgi tendon reflex
Withdrawal Reflex
AP1 Chapter 12

16. A. Stretch Reflex: Simplest Reflex
Reflex in which muscles contract in response to stretching force applied to them. (Knee jerk/Posture)
Sensory Receptor Muscle Spindle (MS*)
When the mallet hits the patellar ligament it stretches the Quadricepts, the sensory receptor (MS*) conduct AP’s to the SC where they directly synapse to  a Motor Neurons
a motor neuron stimulation  AP to muscle Contraction initiated to resist stretch (muscle contracting is the one being stretched)
Monosynaptic Reflex:
**There is no interneuron involvement**
AP1 Chapter 12

17. A. Stretch Reflex: Simplest Reflex
Perception of muscle stretch
Figure 12.6 page 417

18. B. Golgi Tendon Reflex “Golgi Tendon Organs” GTO
“sensory receptor”
Encapsulated nerve endings that have their “axon terminals” embedded in the collagen fibers in tendons attached to muscles.
When a great amount of tension is applied to the tendon the sensory neurons of the GTO are stimulated AP carried to SC and an Inhibitory Interneuron wh/ are stimulated to release inhibitory NT’s  These NT’s inhibit the a motor neurons of the associated muscle causing relaxation.
**Purpose??** To protect both muscles & tendons from XSV tension causing damage
AP1 Chapter 12

19. B. Golgi Tendon Reflex
Figure 12.7 page 418
AP1 Chapter 12

20. 1. Reciprocal Innervation
C. Withdrawal/Flexor Reflex Removal of a body part from a painful stimulus
2. Crossed Extensor
1. Reciprocal Innervation
While one leg is pulling away from the painful stimulus, the other “non-injured” limb is extending to transfer the weight.
While an agonist is contracting automatic relaxation of the antagonist occurs
AP1 Chapter 12

21. C. Withdrawal/Flexure Reflex
Sensory Receptors Pain receptors (PR)
PR carry AP’s thru the dorsal root to the SC where they synapse with excitatory interneurons  which synapse with a motor neurons  stimulate (usually flexure) muscles to remove the limb from the painful stimulus
**Collateral branches of sensory neurons synapse w/ ascending fibers to the brain conscious awareness of pain!!**
AP1 Chapter 12

22. C. Withdrawal/Flexor Reflex
Figure 12.8 page 419
AP1 Chapter 12

23. C. Withdrawal/Flexure Reflex: 1. Reciprocal Innervation
Reinforces the Withdrawal Reflex’s efficiency.
As the pain receptors carry the AP to the SC they split.
½ goes to the agonist muscle to bend the leg away from the painful stimulus
½ goes to collateral branches of the pain receptors  Collateral branches synapse with inhibitory interneurons (Reciprocal innervation) Inhibitory interneurons synapse with the a motor neurons of the antagonist muscles can cause them to relax, THUS not opposing the action of the agonist.
**Last thing that is needed is fighting muscles**
AP1 Chapter 12

24. C. Withdrawal/Flexure Reflex: 1. Reciprocal Innervation
Figure 12.9 page 419
AP1 Chapter 12

25. C. Withdrawal/Flexure Reflex: 2. Crossed Extensor Reflex
During flexion of one limb caused by the withdrawal reflex, the opposite limb is stimulated to extend
As the pain receptors carry the AP to the SC they split.
½ goes to the agonist muscle to bend the leg away from the painful stimulus
Collateral branches of the pain receptors synapse with excitatory interneurons that cross thru the white commissure of the SC to activate a motor neurons in the opposite leg cause the muscles in the opposite leg to contract & support the body weight during the withdrawal reflex.
AP1 Chapter 12

26. C. Withdrawal/Flexure Reflex: 2. Crossed Extensor Reflex
AP1 Chapter 12

27. III. Interactions with SC Reflexes
AP1 Chapter 12

28. III. Interactions with SC Reflexes
Page 421
Reflexes do not operate as isolated entities w/in the NS b/c of divergent & convergent pathways.
Pain: Withdrawal reflex, reciprocal reflex, crossed extensor reflex, & signal to the brain for pain perception
NT’s can be inhibitory or stimulatory & can D sensitivity via EPSP or IPSP mechanisms
AP1 Chapter 12

29. IV. Structure of Peripheral Nerves
AP1 Chapter 12

30. IV. Structure of Peripheral Nerves
Peripheral Nerves: consist of axons, Schwann cells, & CT.
Endoneurium:
Delicate CT layer that surrounds each axon & its Schwann cell Sheath
Perineurium
Heavier CT layer that surrounds groups of axons to form fascicles
Epineurium
Outer most DCT layer that binds the nerve fascicles together to form the nerve
Epineurium of the PNS is continuous with the Dura Mater of the CNS
Page 421
AP1 Chapter 12

31. V. Spinal Nerves (PNS!)
AP1 Chapter 12

32. V. Spinal Nerves 31 pairs 25 exit thru the intervertebral foramina
Fig pg 422
31 pairs
25 exit thru the intervertebral foramina
1st pair exits between the skull & C1
S1-5 exit thru the sacral foramina
Cervical Nerves
C1-C8
Thoracic Nerves
T1-T12
Lumbar Nerves
L1-L5
Sacral Nerves
S1-S5
Coccygeal Nerves C0
Letter: indicative of where nerve emerges
#: indicative of location w/in each region (smallest # is most superior)

33. V. Spinal Nerves: Dermatome
Nerves arising from each region of the SC & vertebral column supply specific regions of the body.
Each spinal nerve has a specific cutaneous sensory distribution
Dermatomal Map
Sensory cutaneous distribution of spinal nerves
Dermatome
Area of the skin supplied w/sensory innervation by a pair of spinal nerves
Figure page 423
AP1 Chapter 12

34. V. Spinal Nerves: Nerves & fxns of SC
Head & diaphragm mvmt
C1-C4
Neck & shoulder mvmt
C4-C6
Upper limb mvmt
C6-T1
Rib mvmt in breathing, vertebral column mvmt, & tone in postural back muscles
T1-T12
Hip mvmt
T11-L2
Lower limb mvmt
L2-S3
Figure page 423
AP1 Chapter 12

35. V. Spinal Nerves: Ramus “branch”
Fig 12.15
Pg 424
V. Spinal Nerves: Ramus “branch”
These are branches that come off of the spinal nerves
Up to 3 branches may come off of the spinal nerve
Dorsal Ramus (Rami)
Ventral Ramus (Rami)
Communicating Ramus (Rami)
Only found from the thoracic to upper lumbar

36. Classification of Rami
Back
Front
Communicating Rami
Carry axons associated with the Sympathetic Nervous System of the Autonomic Nervous System
Dorsal Rami
Innervate:
Most deep back muscles of the dorsal trunk responsible mvmt of the vertebral column
The CT and skin near the midline of the back
Ventral Rami
Distributed in 2 ways:
Thoracic Region
Plexuses
AP1 Chapter 12

37. Ventral Rami Distributed in 2 ways:
Thoracic Region
Form intercostal nerves wh/extend along the inferior margin of the rib & innervate the intercostal muscles & skin over the thorax
Plexuses
Nerves that are organized as braids produced by intermingling of the nerves
Thus the nerves from a plexus usually have axons from >1 spinal nerve & are from >1 level of the SC
AP1 Chapter 12

38. Ventral Rami: Plexuses
Cervical Plexus
C1-C4
Brachial Plexus
C5-T1
Lumbar Plexus
L1-L4
Sacral Plexus
L4-S4
Coccygeal Plexus
S5-Co
Fig 12.13
Pg 422
Fig 12.6
Pg 426
Ventral Rami: Plexuses

39. Cervical Plexus (Origin C1-C4)
Branches innervate superficial neck muscles (mvmt) & skin of neck & posterior portion of the head (sensory)
Ansa cervicalis (C1&C3 making loop)
Phrenic Branches
(C3C5) derived from both cervical & brachial plexus
Descend along neck to enter thorax sides of mediastinum Diaphragm  Contraction  breathing control
AP1 Chapter 12

40. Brachial Plexus (Origin C5-T1)
5 rami (red) join to form 3 trunks (blue) Separate into 3 divisions (purple & green) Join to create 3 cords (orange) split to becomes the 5 major branches of the upper limb.
Axillary nerve
Radial nerve
Musculocutaneous nerve
Median nerve
Ulnar nerve
AP1 Chapter 12

41. Brachial Plexus: Axillary nerve
Motor Fxn:
Lateral rotation of the arm
Abducts the arm (moves away from trunk)
Sensory (Cutaneous) Fxn:
Inferior Lateral Shoulder
AP1 Chapter 12

42. Brachial Plexus: Radial nerve
Motor Fxn:
Extends & flexes elbow
Extends, adducts, & abducts wrist
Supinates forearm & hand
Extends fingers
Abducts & extends thumb
Sensory Fxn
Posterior forearm & arm
Lateral 2/3 of the dorsum of the hand
AP1 Chapter 12

43. Brachial Plexus: Musculocutaneous nerve
Motor Fxn:
Flexes shoulder & elbow
Supinates forearm & hand
Sensory Fxn
Lateral surface of the forearm
AP1 Chapter 12

44. Brachial Plexus: Ulnar Nerve
Motor Fxn:
Flexes wrist, fingers, metacarpophalangeal joints
Extends the interphalangeal joints
Controls pinkie mvmt
Adducts wrist & thumb
Sensory Fxn
Medial 1/3 of the hand, pinkie, & medial ring finger
AP1 Chapter 12

45. Brachial Plexus: Median Nerve
Motor Fxn:
Pronates forearm & hand
Abducts wrist
Controls thumb mvmt
Flexes wrist & fingers
Sensory Fxn:
Lateral 2/3 of the palm & hand, thumb & index & middle fingers
Lateral ½ of the ring finger
Dorsal tips of all aforementioned fingers
AP1 Chapter 12

46. Brachial Plexus: Other
Motor:
scapula & arm control
Sensory
Innervation of the medial arm & forearm
AP1 Chapter 12

47. Lumbar & Sacral Plexus (a.k.a. lumbosacral Plexus)
4 major nerves that enter the lower limb
Obturator Nerve
Innervates medial thigh
Femoral Nerve
Innervates anterior thigh
Tibial Nerve
Innervates posterior thigh, leg, & foot
Common Fibular Nerve
Innervates posterior thigh, anterior & lateral leg, and foot
Other
Supply lower back, hip, & lower abdomen
AP1 Chapter 12

48. Lumbosacral Plexus: Obturator Nerve
Motor:
Rotates the thigh medially
Adducts thigh
Flexes knee
Sensory:
Superior medial portion of the thigh
AP1 Chapter 12

49. Lumbosacral Plexus: Femoral Nerve
Motor:
Flexes hip & knee
Extends the knee
Sensory:
Anterior & lateral thigh
Medial leg & foot (sephnous branch)
AP1 Chapter 12

50. Lumbosacral Plexus: Tibial Nerve
Motor:
Extends hip
Flexes knee & toes
Plantar flexes foot
Adducts thigh
Sensory:
Tibial nerve None
Branches:
Medial & lateral Plantar nerves
Motor: flex & adduct toes
Sensory: sole of the foot
Sural Nerve (not shown)
Motor: None
Sensory: Lateral & posterior 1/3 of leg & lateral foot
AP1 Chapter 12

51. Lumbosacral Plexus: Common fibular nerve
Motor:
Extends the hip
Flexes knee
Sensory:
Lateral surface of the knee
Branches
Deep fibular nerve
Motor: dorsiflexion of the foot & extension of the toes
Sensory: Big & second toe
Superficial fibular nerve
Motor: Plantar flexs & everts the foot
Sensory: Dorsal Anterior 1/3 of the leg & dorsum
AP1 Chapter 12

52. Lumbosacral Plexus: Other
Motor:
Gluteal nerves: act on femur & affect hip
Pudendal nerves: act on abdomen
Sensory:
Innervate the skin of the suprapubic area, external genitalia, superior medial thigh, & posterior thigh.
Pudendal nerves: vital role in sexual stimulation & response
AP1 Chapter 12

53. Coccygeal Plexus Motor: Sensory:
Innervation to muscles of the pelvic floor
Sensory:
Skin of the coccyx
AP1 Chapter 12