Human Anatomy

1. © 2012 Pearson Education, Inc.
14
The Nervous System:
The Spinal Cord and
Spinal Nerves
PowerPoint®
Lecture Presentations prepared by
Steven Bassett
Southeast Community College
Lincoln, Nebraska

2. © 2012 Pearson Education, Inc.
Introduction
• The Central Nervous System (CNS)
consists of:
• The spinal cord
• Integrates and processes information
• Can function with the brain
• Can function independently of the brain
• The brain
• Integrates and processes information
• Can function with the spinal cord
• Can function independently of the spinal cord

3. © 2012 Pearson Education, Inc.
Gross Anatomy of the Spinal Cord
• Features of the Spinal Cord
• 45 cm in length
• Passes through the foramen magnum
• Extends from the brain to L1
• Consists of:
• Cervical region
• Thoracic region
• Lumbar region
• Sacral region
• Coccygeal region

4. © 2012 Pearson Education, Inc.
Figure 14.1a Gross Anatomy of the Spinal Cord
Cervical spinal
nerves
Thoracic
spinal
nerves
Lumbar
spinal
nerves
Sacral spinal
nerves
Coccygeal
nerve (Co1)
Filum terminale
(in coccygeal ligament)
Cauda equina
Inferior
tip of
spinal cord
Conus
medullaris
Lumbosacral
enlargement
Posterior
median sulcus
Cervical
enlargement
C1
C2
C3
C4
C5
C6
C7
C8
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
L3
L4
L5
S1
S2
S3
S4
S5
Superficial anatomy and orientation of the adult spinal cord. The
numbers to the left identify the spinal nerves and indicate where
the nerve roots leave the vertebral canal. The spinal cord, however,
extends from the brain only to the level of vertebrae L1–L2.

5. © 2012 Pearson Education, Inc.
Gross Anatomy of the Spinal Cord
• Features of the Spinal Cord
• Transverse view
• White matter
• Gray matter
• Central canal
• Dorsal root and ventral root: merge to form a spinal
nerve
• Dorsal root is sensory: axons extend from the
soma within the dorsal root ganglion
• Ventral root is motor

6. © 2012 Pearson Education, Inc.
Figure 14.1d Gross Anatomy of the Spinal Cord
Inferior views of cross sections
through representative
segments of the spinal cord
showing the arrangement of
gray and white matter
Posterior median sulcus
White matter
Gray
matter
Anterior median fissure
Dorsal root
Spinal
nerve
Ventral
root
Dorsal root
ganglion
Central
canal
C3
T3
L1
S2

7. © 2012 Pearson Education, Inc.
Gross Anatomy of the Spinal Cord
• Features of the Spinal Nerves
• Consist of:
• Sensory nerves (afferent nerves): transmit
impulses toward the spinal cord
• Motor nerves (efferent nerves): transmit impulses
away from the spinal cord

8. © 2012 Pearson Education, Inc.
Spinal Meninges
Spinal meninges are specialized membranes that provide protection,
physical stability, and shock absorption.
Three meningeal layers:
 The dura mater— tough and thickest, fibrous outermost layer
 The arachnoid mater— middle layer. Contains meshwork of elastic
fibers called arachnoid trabeculae.
 The Pia mater— innermost layer
Meningeal spaces:
 Epidural space: the space just outside the dura mater
 Subdural space: the space between dura and arachnoid layers.
 Subarachnoid space: the space between arachnoid and pia layers.
It contains CSF (Cerebro Spinal Fluid). This is space is used in
spinal tap to obtain CSF.

9. © 2012 Pearson Education, Inc.
Figure 14.2c The Spinal Cord and Spinal Meninges
Posterior view of the spinal cord showing the
meningeal layers, superficial landmarks, and
distribution of gray and white matter
White matter
Ventral root
Dorsal root
Pia mater
Arachnoid mater
Gray matter
Spinal nerve
Dorsal root
ganglion
Dura mater

10. © 2012 Pearson Education, Inc.
Sectional Anatomy of the Spinal Cord
• Gray matter
• Central canal
• Consists of somas (cell bodies) surrounding
the central canal
• White matter
• Consists of axons
• Nerves are organized into tracts or columns
• Located outside the gray matter area

11. © 2012 Pearson Education, Inc.
Sectional Anatomy of the Spinal Cord
Organization of Gray Matter
 Surrounds the central canal and contains cell bodies of neurons
and glial cells. This is the H shape mass in the center of spinal
cord.
 Groups of nuclei (sensory or motor) with specific functions
 Posterior gray horns contain somatic and visceral sensory
nuclei; this is the destination of dorsal root.
 Anterior gray horns contain somatic motor nuclei. This is the
origin of ventral root.
 Lateral gray horns contain visceral motor neurons.
 Gray commissures contain the axons of interneurons that cross
from one side of the cord to the other.

12. © 2012 Pearson Education, Inc.
Figure 14.4b Sectional Organization of the Spinal Cord
The left half of this sectional view shows important anatomical landmarks; the right half indicates
the functional organization of the gray matter in the anterior, lateral, and posterior gray horns.
Posterior
gray horn
Posterior gray
commissure
Lateral
gray horn
Anterior
gray horn
Anterior gray
commissure
Anterior median
fissure
To ventral
root
Posterior median sulcus
From dorsal root
Sensory
nuclei
Motor
nuclei
Somatic
Somatic
Visceral
Visceral

13. © 2012 Pearson Education, Inc.
Sectional Anatomy of the Spinal Cord
Organization of White Matter
 Divided into 6 columns, which contain tracts
 Ascending tracts relay information from spinal
cord to brain
 Descending tracts carry information from brain to
spinal cord
 The spinal nerves that extend distal to the
conus medularis are collectively referred to as
the cauda equina.

14. © 2012 Pearson Education, Inc.
Figure 14.4c Sectional Organization of the Spinal Cord
The left half of this sectional view shows the major columns of white matter. The right half
indicates the anatomical organization of sensory tracts in the posterior white column for
comparison with the organization of motor nuclei in the anterior gray horn. Note that both
sensory and motor components of the spinal cord have a definite regional organization.
Posterior white
column (funiculus)
Anterior white
column (funiculus)
Anterior white
commissure
Flexors
Extensors
Lateral
white
column
(funiculus)
Leg
Hip
Trunk
Arm
Hand
Forearm
Arm
Shoulder
Trunk

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Spinal Nerves
• There are 31 pairs of spinal nerves
• 8 cervical nerves
• 12 thoracic nerves
• 5 lumbar nerves
• 5 sacral nerves
• 1 coccygeal nerve

16. © 2012 Pearson Education, Inc.
Figure 14.1a Gross Anatomy of the Spinal Cord
Cervical spinal
nerves
Thoracic
spinal
nerves
Lumbar
spinal
nerves
Sacral spinal
nerves
Coccygeal
nerve (Co1)
Filum terminale
(in coccygeal ligament)
Cauda equina
Inferior
tip of
spinal cord
Conus
medullaris
Lumbosacral
enlargement
Posterior
median sulcus
Cervical
enlargement
C1
C2
C3
C4
C5
C6
C7
C8
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
L3
L4
L5
S1
S2
S3
S4
S5
Superficial anatomy and orientation of the adult spinal cord. The
numbers to the left identify the spinal nerves and indicate where
the nerve roots leave the vertebral canal. The spinal cord, however,
extends from the brain only to the level of vertebrae L1–L2.

17. © 2012 Pearson Education, Inc.
Spinal Nerves
• The covering of the nerve fibers from
inside out is:
• Endoneurium: covers the nerve fiber.
• Perineurium: covers a bundle of nerve fibers
( Fascicle)
• Epinerium: covers a group of fascicles.

18. © 2012 Pearson Education, Inc.
Figure 14.5a Anatomy of a Peripheral Nerve
A typical peripheral
nerve and its connective
tissue wrappings
Connective Tissue
Layers
Blood vessels
Fascicle
Schwann cell
Myelinated
axon
Epineurium covering
peripheral nerve
Perineurium (around
one fascicle)
Endoneurium

19. © 2012 Pearson Education, Inc.
Figure 14.6a Peripheral Distribution of Spinal Nerves
Motor Commands
KEY
Postganglionic fibers
to smooth muscles,
glands, etc., of back
To skeletal
muscles of back
To skeletal
muscles of body
wall, limbs
Postganglionic fibers to
smooth muscles, glands,
etc., of body wall, limbs
Postganglionic fibers
to smooth muscles,
glands, visceral organs
in thoracic cavity
Preganglionic fibers to
sympathetic ganglia
innervating abdomino-
pelvic viscera
Somatic motor
commands
Visceral motor
commands
Rami
communicantes
Gray ramus
(postganglionic)
White ramus
(preganglionic)
Sympathetic nerve
Sympathetic ganglion
Spinal nerve
Ventral ramus
Dorsal ramus
Dorsal root ganglion
Dorsal
root
Visceral
motor
Somatic
motor
Ventral
root
The distribution of motor neurons in the spinal cord and motor fibers within the spinal
nerve and its branches. Although the gray ramus is typically proximal to the white ramus,
this simplified diagrammatic view makes it easier to follow the relationships between
preganglionic and postganglionic fibers.

20. © 2012 Pearson Education, Inc.
Figure 14.6b Peripheral Distribution of Spinal Nerves
Sensory Information
KEY
From interoceptors
of visceral organs
From interoceptors
of back
From exteroceptors,
proprioceptors of back
From exteroceptors,
proprioceptors of
body wall, limbs
From interoceptors
of body wall, limbs
Somatic
sensations
Visceral
sensations
Ventral ramus
Rami
communicantes
Dorsal
root
ganglion
Dorsal
root
Somatic
sensory
Visceral
sensory
Ventral
root
A comparable view detailing the distribution of sensory neurons and sensory fibers
Dorsal ramus

21. © 2012 Pearson Education, Inc.
Nerve Plexuses
• There are four nerve plexuses
• Cervical plexus
• Brachial plexus
• Lumbar plexus
• Sacral plexus
• Sometimes the lumbar and sacral are combined to
form the lumbosacral plexus

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Important brachial plexus nerves
• Musculocutaneous N.:
• mainly for flexors of the arm like brachialis and brachioradialis.
• Radial N.:
• mainly the extensors of the arm like triceps brachii and
ancuneous.
• Ulnar N.:
• sense and motor of 5th
and half of 4th
finger and associated area
of the hand.
• Median N.:
• sense and motor of the rest of the hand and fingers.

23. © 2012 Pearson Education, Inc.
Important lumbosacral plexus
nerves
• Sciatic nerve:
• posterior muscles of the thigh.
• the largest nerve of the body.
• Femoral nerve:
• Anterior muscles of the thigh.
• Obturator nerve:
• Adductors of the thigh.

24. © 2012 Pearson Education, Inc.
Figure 14.8 Peripheral Nerves and Nerve Plexuses
Lesser occipital nerve
Great auricular nerve
Transverse cervical nerve
Supraclavicular nerve
Phrenic nerve
Axillary nerve
Musculocutaneous
nerve
Thoracic nerves
Radial nerve
Ulnar nerve
Median nerve
Iliohypogastric
nerve
Ilioinguinal
nerve
Genitofemoral
nerve
Femoral nerve
Obturator nerve
Superior
Inferior
Gluteal
nerves
Pudendal nerve
Sciatic nerve
Lateral femoral cutaneous nerve
Saphenous nerve
Common fibular nerve
Tibial nerve
Medial sural cutaneous nerve
Cervical
plexus
Brachial
plexus
Lumbar
plexus
Sacral
plexus
C1
C2
C3
C4
C5
C6
C7
C8
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
L3
L4
L5
S1
S2
S3
S4
S5
Co1

25. © 2012 Pearson Education, Inc.
Figure 14.9 The Cervical Plexus
Great auricular nerve
Geniohyoid muscle
Transverse
cervical nerve
Thyrohyoid muscle
Ansa cervicalis
Omohyoid muscle
Phrenic nerve
Sternohyoid muscle
Sternothyroid muscle
Cranial
nerves
Accessory
nerve (N XI)
Hypoglossal
nerve (N XII)
Lesser occipital
nerve
Nerve roots of
cervical plexus
Supraclavicular
nerves
Clavicle
C1
C2
C3
C4
C5

26. © 2012 Pearson Education, Inc.
Figure 14.10b The Brachial Plexus
Anterior view of the brachial plexus and upper limb
showing the peripheral distribution of major nerves
Anterior
Distribution of
cutaneous nerves
Median nerve
Ulnar nerve
Radial nerve
Palmar digital nerves
Superficial branch of ulnar nerve
Deep branch of ulnar nerve
Anterior interosseous nerve
Median nerve
Ulnar nerve
Deep radial nerve
Radial
nerve
Median nerve
Ulnar nerve
Superficial branch
of radial nerve
Lateral antebrachial
cutaneous nerve
Musculocutaneous
nerve
BRACHIAL
PLEXUS
Dorsal scapular nerve
Suprascapular nerve
Superior trunk
Middle trunk
Inferior trunk
C4
C5
C6
C7
C8
T1

27. © 2012 Pearson Education, Inc.
Figure 14.10a The Brachial Plexus
Radial nerve
Ulnar nerve
Thoracodorsal
nerve
Long thoracic
nerve
INFERIOR
TRUNK
MIDDLE
TRUNK BRACHIAL
PLEXUS
The trunks and cords of the brachial
plexus
KEY
Lateral cord
Posterior cord
Medial cord
C5
C6
C7
C8
T1
Median nerve
Medial antebrachial
cutaneous nerve
Posterior brachial
cutaneous nerve
Musculocutaneous
nerve
Axillary nerve
Subscapular nerves
Medial pectoral nerve
Lateral pectoral nerve
Suprascapular nerve
SUPERIOR TRUNK
Nerve to
subclavius muscle
Dorsal scapular
nerve
First
rib
Roots (ventral rami)
Trunks
Divisions
Cords
Peripheral nerves

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Figure 14.12a The Lumbar and Sacral Plexuses, Part I
The lumbar plexus, anterior view
Lumbosacral
trunk
LUMBAR
PLEXUS
T12
L1
L2
L3
L4
L5
Femoral branch
Genital branch
Femoral nerve
Obturator nerve
Branches of
genitofemoral
nerve
Lateral femoral
cutaneous nerve
Genitofemoral nerve
Ilioinguinal nerve
Iliohypogastric nerve
T12 subcostal nerve

29. © 2012 Pearson Education, Inc.
Figure 14.12c The Lumbar and Sacral Plexuses, Part I
The lumbar and sacral
plexuses, anterior view
Subcostal nerve
Iliohypogastric nerve
Ilioinguinal nerve
Genitofemoral nerve
Lateral femoral
cutaneous nerve
Femoral 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
Obturator nerve
Sural
nerve
Sural
nerve
Saphenous
nerve
Saphenous
nerve
Saphenous
nerve
Sural
nerve
Tibial
nerve
Tibial
nerve
Fibular
nerve
Fibular
nerve

30. © 2012 Pearson Education, Inc.
Reflexes
 A reflex is an immediate involuntary response to
a specific stimulus.
The neural “writing” of a single reflex is referred to
as a reflex arc.
 Reflexes are classified according to:
 Their development (innate and acquired)
 The site where information processing occurs (spinal
and cranial)
 The nature of resulting motor response (somatic and
visceral or autonomic)
 The complexity of the neural circuit (monosynaptic and
polysynaptic)

31. © 2012 Pearson Education, Inc.
Figure 14.14 A Reflex Arc
Arrival of stimulus and
activation of receptor
Response by effector
Activation of a
sensory neuron
Activation of a
motor neuron
Information processing
in CNS
Stimulus
Effector
Receptor
REFLEX
ARC
Ventral
root
Dorsal
root
Sensation
relayed to
the brain by
collateral
KEY
Sensory neuron
(stimulated)
Excitatory
interneuron
Motor neuron
(stimulated)

32. © 2012 Pearson Education, Inc.
Figure 14.15 The Classification of Reflexes
Reflexes
development response
can be classified by
complexity of circuit processing site
• Processing in
the spinal cord
• Processing in
the brain
• One synapse
• Multiple synapses
(two to several hundred)
• Genetically
determined
• Learned • Control actions of smooth and
cardiac muscles, glands
• Control skeletal muscle contractions
• Include superficial and stretch reflexes
Innate Reflexes
Acquired Reflexes
Somatic Reflexes
Visceral (Autonomic) Reflexes
Spinal Reflexes
Cranial Reflexes
Monosynaptic
Polysynaptic

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Reflexes
• Spinal reflexes can be:
• Monosynaptic
• Involves a single segment of the spinal cord
• Polysynaptic
• Integrates motor output from several spinal
segments

34. © 2012 Pearson Education, Inc.
Figure 14.16 Neural Organization and Simple Reflexes
CENTRAL
NERVOUS
SYSTEM
CENTRAL
NERVOUS
SYSTEM
Motor
neuron
Ganglion
Sensory
neuron
Sensory
receptor
(muscle
spindle)
Skeletal muscle
Circuit 1
A monosynaptic reflex circuit involves a peripheral
sensory neuron and a central motor neuron. In this
example, stimulation of the receptor will lead to a
reflexive contraction in a skeletal muscle.
A polysynaptic reflex circuit involves a sensory neuron,
interneurons, and motor neurons. In this example, the
stimulation of the receptor leads to the coordinated
contractions of two different skeletal muscles.
Skeletal muscle 1
Skeletal muscle 2
Motor
neurons
Circuit 2
Interneurons
Ganglion
Sensory
neuron
Sensory
receptor

35. © 2012 Pearson Education, Inc.
Figure 14.17b Stretch Reflexes
KEY
Motor neuron
(stimulated)
Sensory neuron
(stimulated)
The patellar reflex is controlled by muscle spindles in the quadriceps group. The
stimulus is a reflex hammer striking the muscle tendon, stretching the spindle
fibers. This results in a sudden increase in the activity of the sensory neurons,
which synapse on spinal motor neurons. The response occurs upon the activation
of motor units in the quadriceps group, which produces an immediate increase in
muscle tone and a reflexive kick.
Spinal cord
Stimulus
Stretch
Contraction
Effector
Receptor
(muscle
spindle)
REFLEX
ARC
Response

36. © 2012 Pearson Education, Inc.
Terminology
• Hemiplegia:
• loss of sensation and motor fonction of one
side of the body.
• Paraplegia:
• loss of sensation and motor function of lower
limbs.
• Quadriplegia:
• loss of sensation and motor function of upper
and lower limbs.