1. Chapter 13 Spinal Cord, Nerves and Reflexes
Spinal cord is the information highway between brain and body
The spinal cord is protected by:
a. the vertebral column
b. meninges
c. cerebrospinal fluid

2. Anatomy of the Spinal Cord
1. Spinal cord begins as a continuation of the medulla oblongata and terminates at about the L1 vertebra.
Thick as a finger
2. Cervical and lumbar enlargements serve as points of origin for nerves to the extremities
31 pairs of spinal nerves
3. Distal end is tapered and called the cauda equina (horse’s_____)

3. Meninges of the Spinal Cord
The meninges are three fibrous coverings that enclose the spinal cord and brain
a. innermost layer is the pia mater
b. middle layer is the arachnoid
c. outermost layer is the dura mater
There is a “PAD” around the spinal cord
Inflammation of the meninges is known as meningitis.

4. Meninges of Vertebra & Spinal Cord
____________

5. Spinal Tap/ Epidural
Placing a needle in the subarachnoid space is called a spinal tap (lumbar puncture)
Used to diagnose pathologies and to introduce drugs.
Headache is a frequent side effect, WHY?
Spinal tap must be given below L1, Why?
An Epidural is typically used for anesthesia

6. WHAT’S THE MATTER? KINDS OF MATTER:
1. White Matter- myelinated (Why white?)
2. Gray Matter- unmyelinated (Why gray?)
3. ______ (Alma Mater)
BCC

7. MORE ON MATTER Spinal cord: Brain:
Gray matter forms an H-shaped inner core
Surrounded by white matter
Brain:
A thin outer shell of gray matter covers the cerebral hemispheres
THE SPINE IS GRAY INSIDE, WHITE OUTSIDE, THE BRAIN IS OPPOSITE

8. Cross-Sectional Anatomy of the Spinal Cord
Gray matter is shaped like the letter “H” or a butterfly and surrounded by white matter divided into 3 columns
Gray matter = neuron cell bodies
White matter = myelinated axons
Gray matter is divided into horns (posterior, anterior and lateral).
The posterior horn is the area of the posts

9. Gray Matter in the Spinal Cord
Pair of dorsal or posterior horns
totally sensory
Pair of ventral or anterior horns
totally motor fibers
Connected by gray commissure

10. Spinal Tracts
Ascending tracts come from the periphery to head up and are called __________, _________
Descending tracts head down and to the periphery are called ________, _________
Decussation means that the fibers cross
Contralateral means origin and destination are on opposite sides while ipsilateral means on same side
Sensory, afferent
motor, efferent

11. The Motor and Sensory Brains
The Grand prix (Pronounced: “grand pre”) is a motor car race

12. Sensory Homunculus
Demonstrates that the area of the cortex dedicated to the sensations of various body parts is proportional to how sensitive that part of the body is.

13. Motor Homunculus http://faculty. washington. edu/chudler/flash/fgames

14. Noisy Neighbors
Neurons that control your right arm and right leg dwell near each other in the _______ gyrus on the left side of your brain.
Experiment 1: Polish the desk with a clockwise circling motion of your right hand. Now start your right foot circling clockwise.
When neurons controlling your arm and leg are near each other they work well together.
Experiment 2: Now reverse the rotation direction of your right foot.
Tough to do, why? When neurons near each other are called on to do different work they disturb each other.
Precentral gyrus

15. Neighbors Across Town
Your left arm and left leg are “across town” in the _____ precentral gyrus from your right and left arm and leg.
Experiment 3: Using you left arm to buff the top of your desk in a clockwise direction. This time rotate your right leg counterclockwise.
This should pose no problem because the control centers for the two limbs are found on opposite sides of the brain, so they don’t bother each other.
right

16. 2 SENSORY TRACTS 1. Spinothalamic tract 2. Posterior (Dorsal) Columns
These travel UP the spinal cord

17. Spinothalamic Tract Pain and temperature
Decussation of the second order neuron occurs in spinal cord

18. Dorsal Columns Vibration, proprioception
Two Dorsal columns on each side of the spine:
1. Fasciculus gracile
carry signals from the leg
(remember: gracilis muscle of the leg)
2. Fasciculus cuneatus
carry signals from the arm
Decussation of in
medulla
Third neuron in thalamus carries signal to: ___ ___ of the brain
Postcentral gyrus

19. PROPRIOCEPTION Awareness of your body in space
****** STAND UP ******

20. 2 Motor Tracts Called the Pyramidal Tracts:
1. Anterior (Ventral) Corticospinal
2. Lateral Corticospinal
These travel DOWN the spinal cord

21. Corticospinal Tract Coordinates limb movements
Two neuron pathway start in the:
upper motor
neuron in _____ _____ of the brain
Precentral gyrus

22. Crossing the Tracts Remember that the medulla has two “L”s
Decussates in MEDULLA
Decussates in SPINE
DorsaL Column Tracts X
Spinothalamic Tract
LateraL Corticospinal
Anterior Corticospinal

23. The Spinal Nerves 31 pairs of spinal nerves:
a. 8 pairs of cervical nerves (C1-C8)
b. 12 pairs of thoracic nerves (T1-T12)
c. 5 pairs of lumbar nerves (L1-L5)
d. 5 pairs of sacral nerves, (S1-S5)
e. 1 pair of coccygeal nerves
Spinal nerves exit superior to their vertebrae for C1-C7 nerves only. C8 nerve-coccyx nerves exits inferior to their vertebrae

24. Spinal Nerves (Cont.)
Roots: points of attachment for each spinal nerve to a segment of the spinal cord
Posterior, or dorsal (sensory), root contains sensory nerve fibers, conducts nerve impulses into the spinal cord
The ganglion contains the cells bodies of the sensory neurons
Anterior, or ventral (motor), root contains motor neuron axons and conducts impulses from the cord
Cell bodies are located in the gray matter

25. Branches of a Spinal Nerve
After passing through its intervertebral foramen (IVF), a spinal nerve divides into a dorsal and ventral branch called rami
Spinal nerve branches, except for T2-T12, form a network of nerves called a plexus

26. Nerve Plexus Two UP: Cervical plexus, C1 to C5
supplies neck and phrenic nerve to the diaphragm
Brachial plexus, C5 to C8 and T1
supplies upper arm and shoulder, multiple nerves
Two DOWN:
Lumbar plexus, L1 to L4
supplies anterior thigh & genitalia
Femoral nerve
Sacral plexus, L4- S4
supplies butt & lower leg
Sciatic nerve

27. Cervical Plexus- Clinical
Damage to the cervical plexus can effect the diaphragm muscle.
Damage to the spinal cord in the origin of the phrenic nerves (C3-C5) causes respiratory arrest.
Breathing stops because the phrenic nerves no longer send impulses to the diaphragm.
Classic anatomy: “C3, 4 and 5 keeps the diaphragm alive.”

28. The Cervical Plexus, C1 to C5

29. Brachial Plexus Nerves of the upper extremities:
Axillary nerve to deltoid and teres minors and arm pit
Musculocutaneous nerve to flexors of arm and forearm and cutaneous sensation of forearm
Median nerve to anterior forearm, palm and first 3 ½ fingers (thumb, index finger, middle finger and lateral half of ring finger)
Ulnar nerve of anteriomedial forearm, palm and last 1 ½ fingers (medial half of ring finger, small finger)
Radial nerve to the posterior forearm and dorsal surface of hand

30. The Brachial Plexus, C5 to T1

31. Brachial Plexus- Clinical
Injury to the brachial plexus:
Crutch palsy (Axillary nerves),
Wrist drop (Radial nerve)
Carpal tunnel syndrome (Median nerve)
Decreased sensation, thumb and wrist and pain
Tunnel of Guyon (Ulnar nerve)
decreased adduction, abduction of fingers, and flexing wrist, and sensation over little finger

32. The Lumbar Plexus, L1 to L4

33. Lumbar Plexus- Clinical
Injury to the femoral nerve
An inability to extend the leg
loss of sensation in the skin over the anteromedial aspect of the thigh.

34. The Sacral Plexus, L4- S4

35. Sacral Plexus- Clinical
The largest nerve in the body arises from the sacral plexus called the sciatic nerve.
A large as your small finger
Injury to the sciatic nerve results in pain from the buttock down the back of the leg, foot drop, an inability to dorsiflex the foot, and loss of sensation over the leg and foot.
Sciatica: Inflammation of the sciatic nerve
A few causes include: herniated (slipped) intervertebral disc, sacroiliac subluxation, piriformis syndrome

36. Dermatomes Dermatome = skin sensation
All spinal nerves except C1 innervate segments of the skin
Helps diagnosis nerve problems
Shingles: acute infection of the peripheral nerves by the herpes zoster virus
The virus goes from the posterior horn and down the sensory nerves causing pain and skin blisters.

37. Reflex Arc Simplest type of neural pathway
1. receptor
2. sensory neuron
3. motor neuron
4. effector
Example: The flexor (withdrawal) reflex is ipsilateral and is a protective withdrawal reflex that moves a limb to avoid pain
Brain is NOT involved in a reflex

38. The Muscle Spindle
Tendon
Stretch receptors that monitor the length of skeletal muscles (biceps, triceps, petellar and achilles reflexes)
Golgi Tendon organs are stretch receptors in the tendon of a muscle.

39. Reflexes- Clinical
Reflexes are used to diagnose disorders and locating injured tissue.
Absent = usually not pathological
Absent unilaterally = damage may be somewhere along a nerve pathway on that side.
Hyperreflexia = Brain abnormality
Clinically important reflexes:
1) Biceps (C5), Triceps (C7)
2) Petellar (L4), Achilles reflex (S1)
3) Babinski sign (Pathological reflex

40. Upper/ Lower Motor Neuron Disease
Paralysis
Upper motor neuron= spastic
Lower motor neuron= flaccid
UMN / LMN
UMN= Brain
LMN= peripheral nerves
UMN
LMN
Reflexes
Hyperactive
Absent
Atrophy
Present
Fasciculation
Tone
Increased
Decreased

41. CNS Nerve Injury
In the CNS, injury to the brain or spinal cord can be permanent.
Injury is followed by spinal shock
A loss of reflex activity called areflexia results.
Anti-inflammatory drugs given at time of trauma may decrease swelling
Spinal cord injury may result in paralysis which may be classified as:
monoplegia (one limb), diplegia (two limbs), paraplegia (both lower limbs)*, hemiplegia (one side), or quadriplegia (all limbs).
*Para = Beside; near; alongside

42. Polio and ALS
Diseases that cause destruction of motor neurons and result in skeletal muscle atrophy
Poliomyelitis is caused by poliovirus spread by contaminated water from fecal matter
weakness progresses to paralysis and possible respiratory arrest
Amyotrophic lateral sclerosis
sclerosis of spinal cord
paralysis and muscle atrophy

43. Spina Bifida Vera Congenital defect Failure of vertebral arch to close
Causes a lack of covering for the spinal cord
Mothers can reduce risk by taking folic acid supplement before pregnancy
Spina Bifida occulta is a benign anamaly

44. Syphilis Sexually transmitted disease Three stages
Causes degeneration of the dorsal column
Symptoms will be loss of _______ and _______
(Dorsal column signs)
Vibration and proprioception