Chapter 18 The Spinal Cord

1
Chapter 18The Spinal Cord Spinal Nerves

• Together with brain forms the CNS
• Functions
• spinal cord reflexes
• integration (summation of inhibitory and
  excitatory) nerve impulses
• highway for upward and downward travel of sensory
  and motor information

2
Spinal Cord Protection
By the vertebral column, meninges, cerebrospinal
fluid, and vertebral ligaments.
3
Structures Covering the Spinal Cord

• Vertebrae
• Epidural space filled with fat
• Dura mater
• dense irregular CT tube
• Subdural space filled with interstitial fluid
• Arachnoid spider web of collagen fibers
• Subarachnoid space CSF
• Pia mater
• thin layer covers BV
• denticulate ligs hold in place

4
(No Transcript)
5
External Anatomy of Spinal Cord

• Flattened cylinder
• 16-18 Inches long 3/4 inch diameter
• In adult ends at L2
• In newborn ends at L4
• Growth of cord stops at age 5
• Cervical enlargement
• upper limbs
• Lumbar enlargement
• lower limbs

6
(No Transcript)
7
Inferior End of Spinal Cord

• Conus medullaris
• Filum terminale
• cone-shaped end of spinal cord
• thread-like extension of pia mater
• stabilizes spinal cord in canal
• Caudae equinae (horses tail)
• dorsal ventral roots of lowest spinal nerves
• Spinal segment
• area of cord from which each pair of spinal
  nerves arises

8
Spinal Cord Spinal Nerves

• Spinal nerves begin as roots
• Dorsal or posterior root is incoming sensory
  fibers
• dorsal root ganglion (swelling) cell bodies of
  sensory nerves
• Ventral or anterior root is outgoing motor fibers

9
Gray Matter of the Spinal Cord

• Gray matter is shaped like the letter H or a
  butterfly
• contains neuron cell bodies, unmyelinated axons
  dendrites
• paired dorsal and ventral gray horns
• lateral horns only present in thoracic spinal
  cord
• gray commissure crosses the midline
• Central canal continuous with 4th ventricle of
  brain

10
White Matter of the Spinal Cord

• White matter covers gray matter
• Anterior median fissure deeper than Posterior
  median sulcus
• Anterior, Lateral and Posterior White Columns
  contain axons that form ascending descending
  tracts

11
(No Transcript)
12
Tracts of the Spinal Cord

• Function of tracts
• highway for sensory motor information
• sensory tracts ascend
• motor tracts descend
• Naming of tracts
• indicates position direction of signal
• example anterior spinothalamic tract
• impulses travel from spinal cord towards brain
  (thalamus)
• found in anterior part of spinal cord

13
Location of Tracts inside Cord

• Motor tracts Sensory tracts
• pyramidal tract (corticospinal) ---spinothalamic
  tract
• extrapyramidal tract ---posterior column
• 
  ---spinocerebellar

14
Function of Spinal Tracts

• Spinothalamic tract
• pain, temperature, deep pressure crude touch
• Posterior columns
• proprioception, discriminative touch, two-point
  discrimination, pressure and vibration
• Direct pathways (corticospinal corticobulbar)
• precise, voluntary movements
• Indirect pathways (rubrospinal, vestibulospinal)
• programming automatic movements, posture muscle
  tone, equilibrium coordination of visual
  reflexes

15
Spinal Reflexes

• Automatic response to change in environment
• Integration center for spinal reflexes is gray
  matter of spinal cord
• Examples
• somatic reflexes result in skeletal muscle
  contraction
• autonomic (visceral) reflexes involve smooth
  cardiac muscle and glands.
• heart rate, respiration, digestion, urination,
  etc
• Note cranial reflexes involve cranial nerves

16
Reflex Arc

• Specific nerve impulse pathway
• 5 components of reflex arc
• receptor
• sensory neuron
• integrating center
• motor neuron
• effector
• 4 important somatic spinal reflexes
• stretch, tendon, flexor(withdrawal) crossed
  extensor reflexes

17
Stretch Reflex (patellar reflex)

• Monosynaptic,ipsilateral reflex arc
• Prevents injury from over stretching because
  muscle contracts when it is stretched
• Events of stretch reflex
• muscle spindle signals stretch of muscle
• motor neuron activated muscle contracts
• Brain sets muscle spindle sensitivity as it sets
  muscle tone (degree of muscle contraction at
  rest)
• Reciprocal innervation (polysynaptic-
  interneuron)
• antagonistic muscles relax as part of reflex

18
Illustration of the Stretch Reflex
19
Flexor (withdrawal) Reflex

• Step on tack (pain fibers send signal to spinal
  cord
• Interneurons branch to different spinal cord
  segments
• Motor fibers in several segments are activated
• More than one muscle group activated to lift foot
  off of tack

20
Crossed Extensor Reflex

• Lifting left foot requires extension of right leg
  to maintain ones balance
• Pain signals cross to opposite spinal cord
• Contralateral extensor muscles are stimulated by
  interneurons to hold up the body weight
• Reciprocal innervation - when extensors contract
  flexors relax, etc

21
Spinal Nerves

• 31 Pairs of spinal nerves
• Named numbered by the cord level of their
  origin
• 8 pairs of cervical nerves (C1 to C8)
• 12 pairs of thoracic nerves (T1 to T12)
• 5 pairs of lumbar nerves (L1 to L5)
• 5 pairs of sacral nerves (S1 to S5)
• 1 pair of coccygeal nerves
• Mixed sensory motor nerves

22
Connective Tissue Coverings

• Endoneurium wrapping of each nerve fibers
• Perineurium surrounds group of nerve fibers
  forming a fascicle
• Epineurium covering of entire nerve
• dura mater blends into it at intervertebral
  foramen

23
Endoneurium Perineurium Epineurium
24
Branching of Spinal Nerve

• Spinal nerves formed from dorsal ventral roots
• Spinal nerves branch into dorsal ventral rami
• dorsal rami supply skin muscles of back
• ventral rami form plexus supply anterior trunk
  limbs
• meningeal branches supply meninges, vertebrae
  BV

25
A Nerve Plexus

• Joining of ventral rami of spinal nerves to form
  nerve networks or plexuses
• Found in neck, arm, low back sacral regions
• No plexus in thoracic region
• intercostal nn. innervate intercostal spaces
• T7 to T12 supply abdominal wall as well

26
Cervical Plexus

• Ventral rami of spinal nerves (C1 to C5)
• Supplies parts of head, neck shoulders
• Phrenic nerve (C3-C5) keeps diaphragm alive
• Damage to cord above C3 causes respiratory arrest

27
Phrenic Nerve
28
Brachial Plexus

• Ventral rami from C5 to T1
• Supplies shoulder upper limb
• Passes superior to 1st rib under clavicle
• Axillary n. deltoid teres m.
• Musculocutaneous n. elbow flexors
• Radial n. shoulder elbow extensors
• Median ulnar nn. flexors of wrist hand

29
Branches off Brachial Plexus
30
(No Transcript)
31
Clinical Correlations

• Erb-Duchene palsy
• waiters tip position
• fall on shoulder
• Radial nerve injury
• improper deltoid injectionor tight cast
• wrist drop
• Median nerve injury
• numb palm fingers inability to pronate flex
  fingers
• Ulnar nerve injury (clawhand)
• inability to adduct/abduct fingers, atrophy of
  interosseus
• Long thoracic nerve injury (winged scapula)
• paralysis of serratus anterior, cant abduct
  above horizontal

32
Lumbar Plexus

• Ventral rami of L1 to L4
• Supplies abdominal wall, external genitals
  anterior/medial thigh
• Injury to femoral nerve causes inability to
  extend leg loss of sensation in thigh
• Injury to obturator nerve causes paralysis of
  thigh adductors

33
Branches of Lumbar Plexus

• Notice Femoral and Obturator nerves
• Found anterior and medial to hip joint

34
Sciatic Nerve Branches

• Notice Common Peroneal nerve and Tibial nerve
  behind the knee
• Notice Sciatica pain extends from the buttock
  down the leg to the foot
• may be sign of herniated disc

35
(No Transcript)
36
Sacral Plexus

• Ventral rami of L4-L5 S1-S4
• Anterior to the sacrum
• Supplies buttocks, perineum part of lower limb
• Sciatic nerve L4 to S3 supplies post thigh
  all below knee
• Peroneal nerve injury produces foot drop or
  numbness
• Tibial nerve injury produces calcaneovalgus (loss
  of function on anterior leg dorsum of foot)

37
Branches of Sacral Plexus

• Notice Sciatic nerve origins