1. The Spinal Cord and Spinal Nerves
Bio 137 Anatomy & Physiology I

2. Spinal Cord Protection
Bones
Spinal cavity (Vertebral Column)
Meninges – below bony coverings
Dura mater
Arachnoid mater
Pia mater
Cerebrospinal Fluid

3. Meninges of the Spinal Cord

4. Spinal Cord Meninges: Dura Mater
Dura mater continues into vertebral canal as a sheath that surrounds the spinal cord
The dura mater of the spinal cord is not directly attached to the bone of the vertebra
An epidural space is found between the dural sheath and bony walls of vertebrae
This space is filled with loose connective tissue, vessels and fat
Provides a cushion for the cord

5. Meninges of Brain & Cord

6. CSF Circulation
CSF circulates in lateral ventricles to 3rd and 4th ventricles of brain and to central canal of spinal cord
CSF is also found in subarachnoid spaces

7. External Cord Anatomy
The spinal cord begins as a continuation of the medulla oblongata (the most inferior portion of the brain stem)
Extends from the
foramen magnum of
the occipital bone
Terminates as the
conus medullaris
between L1 - L2.

8. External Cord Anatomy
The spinal cord has two enlargements, one in the cervical area from C4–T1, and another in the lumbar area between
T9–T12.
The cervical enlargement
correlates with the sensory
input and motor output to the
upper extremities.
The lumbar enlargement handles
motor output and sensory input
to and from the legs.

9. External Cord Anatomy
Arising from the conus medullaris is the filum terminale, an extension of the pia mater that extends inferiorly and
blends with the arachnoid
and dura to anchor the spinal
cord to the coccyx.
The cauda equina or “horses
tail” are the roots of the
lower spinal nerves that angle
down alongside the filum terminale.

10. Spinal nerves below conus medullaris descend and form cauda equina

11. PNS: Spinal Nerves 31 segments of the spinal cord All are Mixed nerves
Each gives rise to a pair of spinal nerves, which branch to various body parts
All are Mixed nerves
8 cervical (numbered C1 to C8)
12 thoracic (T1 to T12)
5 lumbar (L1 to L5)
5 sacral (S1 to S5)
1 coccygeal (Co)
Please keep in mind that these numbers refer to the spinal nerves

12. Lumbar Puncture
A needle inserted into the subarachnoid space for the purpose of withdrawing CSF (for diagnosis or to reduce pressure) or to introduce a drug or contrast agent is called a lumbar puncture.
CSF is often collected to diagnose meningitis or some other disease of the CNS.
Agents injected into the subarachnoid space include drugs such as antibiotics, chemotherapeutic agents, or analgesics, or contrast media for radiographic procedures.
The pressure of CSF in the SAS can also be measured during a lumbar puncture.

13. Lumbar Puncture
The site used for most lumbar punctures is between the 3rd and 4th (or 4th and 5th) lumbar vertebrae - below the termination of the actual cord in the region of the cauda equina. With the needle in the SAS, CSF can be sampled.
Anesthetics can also
be given in this way,
but using 1/10 the
dose required for
epidural anesthesia.

14. Spinal Cord Structure
Cross Section

15. Cross Section of Spinal Cord
Anterior median fissure and Posterior median sulcus divide cord into left and right halves

16. Spinal Cord Cross Section
White matter surrounds ‘butterfly’ of gray matter
WHITE MATTER
GRAY MATTER
Posterior horns
Lateral horns
Anterior horns
Gray commissure
Surrounds central canal
Composed of Interneuronal cell bodies and some motor neuron cell bodies
Posterior column (funiculi)
Lateral column
Anterior column
Composed of bundles of myelinated axons that comprise major nerve pathways called nerve tracts

17. Spinal Cord Model (cross-section)

18. Spinal Cord Structures
Dorsal Root Ganglion
Cell bodies of sensory neurons (unipolar)
Dorsal Root
Axons of sensory neurons
Ventral Root
Axons of motor neurons
Fusion of dorsal root & ventral root forms a spinal nerve

19. Spinal Cord Model (cross-section) Photo from

20. Internal Cord Anatomy
A tract is a bundle of neuronal axons that are all located in a specific area of the cord and all traveling to the same place (higher or lower in the brain or cord).
Sensory (Ascending) Tracts
Sensory impulses from body to brain
Motor (Descending) Tracts
Motor impulses from brain to body

21. Sensory Tract

22. Motor Tract

23. Spinal Cord Injury
If damage is to ascending tracts, lose sensory function below injury
If descending tracts are damaged, lose motor function below injury

24. Reflexes A reflex is a fast, involuntary response to a stimulus.
In a spinal reflex the integration takes place in the spinal cord, not the brain.

25. Reflexes
A reflex arc is a pathway that a nerve impulse follows to produce a reflex.
Components of a reflex arc:
Sensory receptor and a sensory neuron
Integrating center inside the cord
A motor neuron
An effector
Usually some sort of
muscle or a gland which
makes something move
or secrete (“involuntarily”).

26. Reflex Arc

27. Withdrawal Reflex At least a 3-neuron pathway
Protective, prevents or limits tissue damage

28. Knee-Jerk Reflex
2-neuron pathway that maintains an upright position

29. Spinal Nerves: Nerve Plexus
Spinal nerves exit out intervertebral foramina and immediately branch
Anterior rami (branches) of spinal nerves (except T2-T11) combine to form a nerve plexus
Fibers (anterior branches) of various spinal nerves are sorted and recombined to feed an area of the body
Particular body part receives ‘nerves’ consisting of nerve fibers from different starting points of origin in cord

30. Nerve Plexuses
The cervical plexus, formed by the anterior rami of C1-C5, serves the head, neck, and diaphragm.
The phrenic nerves arise from the cervical plexus to supply the major muscle of
respiration (“C3,4,5 keep
the diaphragm alive”).

31. Brachial Plexus Formed by anterior branches C5-C8 and T1
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Formed by anterior branches C5-C8 and T1
Lies deep within shoulders
There are five (5) branches
Supply muscles of the arms and hands and some shoulder, chest and back muscles C5
Ventral rami: C5, C6, C7, C8, T1
Trunks: upper, middle, lower C6 C7
Anterior divisions C8
Posterior divisions C5
Dorsal
scapular n. T1 C6
Suprascapular n. C7
Axillary n.
Lateral pectoral n. C8
Humerus
Medial pectoral n.
Lower subscapular n.
Thoracodorsal n. T1
Musculocutaneous n.
Median n.
Median n.
Ulnar n.
Axillary n.
Musculo-
cutaneous n.
Radial n.
(a)
Ulnar n.
Radial n.
Ulna
Radius
(b)

32. Nerve Plexuses
Some of the major nerves that arise from the brachial plexuses are the:
musculocutaneous nerve
axillary nerve
radial nerve
median nerve
ulnar nerve
long thoracic nerve

33. Nerve Plexuses
The ulnar nerve is the largest unprotected (by muscle or bone) nerve in the human body. It emerges from the medial and lateral cords of the brachial plexus to supply the medial half of the hand. Striking the medial epicondyle of the humerus where the nerve is exposed is referred to as bumping one’s “funny bone”.
Damage to the nerve leads to abnormal sensations
in the 4–5th fingers and an inability to abduct
or adduct the little and ring fingers.

34. Nerve Plexuses
The lumbar plexus is formed by the anterior rami of L1-L4 to supply the anterolateral abdominal wall, external genitalia, and part of the lower limbs.
The femoral and obturator nerves
come from the lumbar plexus.

35. Nerve Plexuses
The sacral plexus is formed by the anterior rami of L4-L5 and S1-S4. It supplies the buttocks, perineum, and part of the
lower limbs.
It gives rise to the largest
nerve in the body, the
sciatic nerve.

36. Nerve Plexuses
The coccygeal plexus is formed by the anterior rami of S4-S5 and the coccygeal nerves. It is a small plexus from which the anococcygeal nerve exits to supply a small area of skin in the coccygeal region.

37. Spinal Cord versus spinal nerve injuries
Which is worse?
Why?