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Back
I.
II.
Landmarks: These are used as reference points for establishing the location of
internal structures or for anthropological measurements. Hence, the use of landmarks
is important when studying topographical (regional) anatomy.
A. usually they're bony structures that can be palpated but they may also be soft tissue
structures that can be visualized such as the sternocleiodomastoid muscle, nipple,
or umbilicus
B. as you gain knowledge in gross anatomy, locate landmarks on yourself or others
1. it is important that you know what structures are present in the area of interest
so that an accurate diagnosis can be concluded from your physical exam
2. whenever a new region of anatomy is studied, be aware of the landmarks that
are presented and review the ones you have already learned
C. landmarks for studying the back
1. mastoid process on the skull
2. external occipital protuberance of the skull
3. superior nuchal line on the skull
4. ligamentum nuchae
5. spine of C7 (vertebrae prominens)
6. iliac crest on the hip bone
7. posterior superior iliac spine on the hip bone
8. lateral third of the clavicle
9. scapula
a. vertebral and axillary borders
b. superior and inferior angles
c. acromion process
d. spine
Skin
A. the skin on the dorsal side (back) is thicker than the skin ventrally (front)
B. skin in most areas has the majority of its collagen fibers oriented in one direction
1. if a round probe penetrates the skin, it will result in a slit-like opening
2. cleavage (Langer's) lines are parallel to the dominant pattern of collagen fibers
3. surgical incisions along cleavage lines tend to leave smaller and stronger scars
C. nerves
1. dermatome - the specific area of skin supplied by a single spinal nerve
a. named for its corresponding spinal nerve
b. spinal nerve innervations overlap
c. not all vertebral levels supply the skin on the back
(1) C1 spinal nerve is not cutaneous hence, it has no dermatome pattern
2. areas on each side of the dorsal midline are supplied by dorsal primary rami
3. C7 & 8 dorsal primary rami have minimal or no cutaneous branches in the back
4. L4 & 5 dorsal primary rami do not have primary cutaneous rami
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III.
Fascia
A. superficial fascia: panniculus adiposus
1. its the fatty layer of connective tissue deep to the skin
2. in some areas it may be very thick with the amount on the back being thinner
3. the distribution of fat in this layer is partly determined by sex hormones
B. deep fascia
1. dense, organized sheets of connective tissue that binds together or "invests"
the deep structures
2. it encloses all of the structures deep to the superficial fascia
3. the most prominent deep fascia of the back is the thoracolumbar fascia
a. consists of anterior and posterior lamellae (encloses deep back muscles)
IV.
Vertebrae
A. vertebral parts
1. anteriorly - body - supports the weight
2. posteriorly - vertebral arch protects the spinal cord and composed of
a. pedicles - two short, thick processes that project dorsally from the cranial
part of the body at the junction of its dorsal and lateral surfaces
(1) they connect the transverse processes to the body
(2) constricted in middle forming superior and inferior vertebral notches
(a) with articulation of vertebrae the notches form vertebral foramina
b. laminae - two broad plates directed dorsally and medially from the pedicles
(1) fuse in the midline to complete the vertebral arch
(2) provide a base for the spinous processes in the midline
(3) their cranial and caudal borders are attachments for the ligamenta flava
c. processes - there are seven
(1) spinous process - single
(a) attached in the midline at the junction of the two lamina
(b) serves as attachment for muscles and ligaments
(2) transverse processes - one on each side
(a) project laterally from the junction of the lamina and pedicles
(b) lie between the superior and inferior articular processes
(c) serve as attachments for muscles and ligaments
(3) superior and inferior articular processes - paired on each side at the
junction of the laminae and pedicles - surfaces have hyaline cartilage
(a) two superior articular processes
i. project cranially
ii. their articular surfaces are directed more or less dorsally
(b) inferior articular processes
i. project caudally
ii. their articular surfaces are directed more or less ventrally
V.
Nervous System
A. central nervous system (CNS) - consists of the brain and spinal cord
B. peripheral nervous system (PNS) consists of the cranial, spinal nerves,
and the autonomic nervous system (ANS)
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1. 31 pairs of spinal nerves
a. 8 cervical (C1 - 8)
b. 12 thoracic (T1 - 12)
c. 5 lumbar (L1 - 5)
d. 5 sacral (S1 - 5)
e. 1 coccygeal
2. the 3rd through 11th thoracic nerves are considered typical; the rest are modified
C. spinal nerve development
1. ventral roots
a. outgrowths of axons from neuroblasts in the basal lamina
2 dorsal roots
a. formed by the ingrowths of fibers from cell bodies in dorsal root ganglia
3. in the adult, sequential segmentation can best be seen in the thoracic region
a. thoracic wall is made up of parallel segmentation that is better
represented after the formation of the vertebrae from the embryonic
sclerotomes whose caudal half had condensed and proliferated into the
cranial half of the subadjacent sclerotome
(1) represented here are the vertebrae, ribs, intercostal muscles and vessels
(a) here, the structures are referred to as typical
(b) in contrast to the thoracic nerves, other areas of the body have lost
their segmental patterns and are considered atypical
D. spinal nerves
1. dorsal (posterior) and ventral (anterior) roots
a. attach to the spinal cord
b. consist of axons carrying nerve impulses in or out of the spinal cord
2. dorsal (posterior) root - afferent and sensory
a. transmits impulses into spinal cord
b. their cell bodies are in the dorsal root ganglia
c. the distal fibers of the sensory axon (physiologic dendrite) are specialized
sensory organs for detecting sensory stimuli
d. the induced nerve impulses are transmitted into the spinal cord and are
then routed to various sites to synapse with second order neurons either
in the spinal cord or caudal medulla
3. ventral (anterior) root - efferent and motor
a. most fibers in the ventral root carry impulses to skeletal muscles
b. cell bodies for motor neurons are in anterior horn of the spinal cord
(1) a single neuron and the muscle fibers it innervates is a motor unit
d. only the ventral roots from T1 - L2 contain preganglionic fibers for the
sympathetic autonomic nervous system
(1) before the effector organ (such as smooth muscle or sweat gland) is
stimulated, the sympathetic nerves running with the peripheral motor
nerves will have already synapsed in the sympathetic spinal ganglia
(2) hence, there are two sympathetic neurons from the spinal cord to the
effector organs they make active
(a) preganglionic neuron - the first neuron with its cell body in the
intermediolateral gray column of the spinal cord
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(b) postganglionic neuron - the second neuron with its cell body in the
sympathetic trunk or a collateral ganglia
4. spinal nerve proper - formed by the ventral and dorsal spinal roots at all levels
a. contain motor and sensory fibers at all levels and additionally
(1) there are preganglionic nerve fibers only in T1 - L2
(2) only the spinal nerves of S2 - S4 contain preganglionic sacral
parasympathetic nerve fibers (from corresponding ventral roots)
b. in less than a centimeter from its commencement, the spinal nerve
divides into dorsal (posterior) and ventral (anterior) primary rami
(1) both rami contain the same kinds of nerve fibers as their respective
spinal nerve proper in regards to motor and sensory fibers
(2) all ventral and dorsal rami have postganglionic sympathetic fibers
and so do all of the other non-typical peripheral nerves in the body
5. dorsal (posterior) ramus for the typical spinal nerve
a. innervates the deep muscles of the back and the overlying skin
b. receives sensory stimuli from all the tissues in its posterior segment
(1) it divides into a medial and lateral branch of which only one will
become cutaneous: medial br. C4 - T6 and for lateral br. T7 - L3
6. ventral (anterior) primary ramus - for the typical spinal nerve
a. passes towards the front of the body for motor and sensory functions
b. receives sensory stimuli from the tissues in its anterior segment
(1) at the side of the body (for the thoracic spinal nerves) it gives off
a lateral cutaneous branch
(2) at the front of the body (for the thoracic spinal nerves) it gives off
an anterior cutaneous branch
c. after and close to the origin of the ventral primary ramus, two
communicating rami emerge at the T1 - L2 vertebral levels
(1) white communicating ramus - carries autonomic fibers to the
sympathetic trunk
(a) fibers with a preponderance of myelin that are mainly
preganglionic fibers
(b) some fibers are visceral afferents from organs
(2) gray communicating ramus - carries postganglionic fibers to be
distributed to the body via the anterior and posterior primary rami
d. some spinal nerves may team up together to form plexuses
(1) cervical plexus: anterior primary ramus of C1 - C4
(2) brachial plexus: anterior primary rami of C5 - T1
(3) lumbar plexus: anterior primary rami of L1 - L4
(4) sacral plexus: anterior primary rami of L4 - S4
VI.
Muscles
A. there are over 650 muscles in the human body
B. superficial muscles of the back have their origin an the axial skeleton and
their insertion on the pectoral girdle or humerus: primarily serve the upper limb
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1. the pectoral girdle is composed of the scapulae and clavicles
2. trapezius muscle
a. the most superficial muscle of the back
b. origin is from the superior nuchal line, external occipital protuberance,
ligamentum nuchae, and the spinous processes of C7 - T12
c. the uppermost fibers insert on the lateral third of the clavicle, acromion
process, and spine of the scapula: the lower fibers insert at the medial
end of the spine of the scapula
d. the upper fibers elevate the shoulders, the middle fibers retract the
shoulders toward the vertebral column, the lower fibers draw the
shoulder downward, and the upper and lower fibers together rotate the
scapula to allow for full abduction of the arm
e. the upper fibers also draw the head to the same side, turns the face to the
opposite side when only one side contracts and when both sides contract
the head is drawn directly dorsalward
f. innervation: spinal accessory nerve (Cr.N. XI) and C3 & C4 nerves
g. the principal blood supply: superficial (cervical) branch of the
transverse cervical artery or the superficial cervical artery if it comes
directly off the thyrocervical trunk (both superficial arteries correspond)
2. latissimus dorsi muscle
a. origin: posterior lamella of the thoracolumbar fascia (lumbar aponeurosis)
and the spinous processes of T7 down to the lumbar and sacral spinous
processes and posterior part of the crest of the ilium plus lower 3 or 4 ribs
b. as part of origin, but not as important as the ones described above, is a fibrous
attachment to the inferior angle of the scapula
c. thoracolumbar fascia - Basically, the origin for the aponeurosis of the
transversus abdominis muscle seeking to attach to vertebrae is blocked by the
lateral border of the sacrospinalis muscle (erector spinae). So, it splits into
a deep sheet (going anterior) and a superficial sheet (going posterior) relative
to the sacrospinalis muscle. The anterior lamellae attach to transverse
processes and the posterior lamellae attach spinous processes of vertebrae.
Hence, the dorsal (posterior) lamellae of the thoracolumbar fascia separates
the superficial back muscles from the deep back muscles.
d. the tendon of insertion is about an inch wide and inserts into the bottom of
intertubercular groove (sulcus) of the humerus
e. extends, adducts and medially rotates the humerus in the shoulder joint
f. innervation: thoracodorsal (middle subscapular) nerve (C6, 7, & 8)
g. blood supply: thoracodorsal vessels
3. levator scapulae muscle
a. arises from the transverse processes of the upper four cervical vertebrae
b. inserts on the vertebral border of the scapula, above the spine
c. elevates the scapula and tends to draw it medially
d. innervation: branches of C3 & 4 of the cervical plexus and the dorsal
scapular nerve (C5)
e. blood supply: dorsal (descending) scapular artery
4. rhomboideus major and minor muscles
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a. rhomboideus major: positioned below and parallel to the minor muscle
(1) arises from the spinous processes of T2 - 5
(2) inserts on the vertebral border of the scapula, below the spine
b. rhomboideus minor: positioned above and parallel to the major muscle
(1) arises from the lower part of the ligamentum nuchae, spine of C7 & T1
(2) inserts in the vertebral border of the scapular at the root its spine
c. innervation: dorsal scapular nerve (C5) - (both muscles)
d. blood supply: dorsal (descending) scapular vessels
e. adduct (draw medially to the spinal column) the scapulae toward each other
5. serratus posterior superior and inferior muscles
a. serratus posterior superior - is attached to a thin and broad aponeurosis that
(1) arises from the caudal ligamentum nuchae and spines of C7 - T2 or T3
(2) after declining downward and lateralward, it inserts into the superior
borders of the 2nd through 5th ribs, just a little beyond their angles
(3) innervation: ventral primary divisions of first four thoracic nerves
(4) action: raises the ribs to which it is attached on forced inspiration
b. serratus posterior inferior - is attached to a thin aponeurosis that
(1) arises from T11 - L2 or L3
(2) after inclining upward and lateralward it inserts into the inferior borders
of the last four ribs, just beyond their angles
(3) innervation: ventral primary divisions of the 9th -12th thoracic nerves
(4) action: pulls the ribs it is attached downward on forced expiration
C. triangle of auscultation: if the scapula is drawn ventrally by folding the arms
over the chest and the trunk bent forward, parts of the 6th and 7th ribs and their
interspaces become subcutaneous
1. its boundaries are
a. lateral - scapula
b. medial - trapezius muscle
c. inferior - latissimus dorsi muscle
D. deep muscles of the back - located between the anterior and posterior lamellae
of the thoracolumbar fascia; all of the following are deep muscles
1. innervation: posterior primary rami of the spinal nerves
2. they act on the spinal column
3. splenius capitis muscle
a. arises from the caudal half of the ligamentum nuchae and C7 - T4
b. inserts on the occipital bone just inferior to the lateral third of the
superior nuchal line and into the mastoid process of the temporal bone
4. splenius cervicis muscle
a. arises by a narrow tendinous band from the spinous process of T3 - 6.
b. inserts into the posterior tubercles of the transverse processes of the
upper two or three cervical vertebrae
c. action of the splenius capitis and cervicis muscles: Individually they
draw the head and neck dorsally and laterally so that the face turns to the
same side. Together, both sides extend the head and neck.
d. innervation: the lateral branches of the dorsal primary divisions of the
middle to lower cervical nerves for both muscles
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5. Erector spinae (Sacrospinalis) muscles - splits into three columns and has
prolongations from the lumbar region into the thoracic and cervical regions
a. medially, the erector spinae arises from a tendon that is attached to the
middle crest of the sacrum, spinous process of the lumbar, and T11 & 12
b. going laterally, the erector spinae arise from the lateral crests of the
sacrum, sacrotuberous and sacroiliac ligaments, and back part of the
iliac crests
6. iliocostalis muscle (the lateral column) has the following three parts
a. iliocostalis lumborum
(1) arises as described above for the erector spinae
(2) inserts by six or seven flat tendons into the inferior angles of the last
six or seven ribs
b. iliocostalis thoracis
(1) arises from the upper borders of the angles of the lower six ribs
medial to the insertion of the iliocostalis lumborum cited above
(2) inserts into the cranial borders of the angles of the first six ribs and
transverse process of C7
c. iliocostalis cervicis
(1) arises from the angles of ribs 3, 4, 5, and 6
(2) inserts into the posterior tubercles of the transverse processes of the
C4 - C6 vertebrae
(a) action of the iliocostalis muscles - they extend the vertebral
column and bend it to one side
(b) innervation: for the iliocostalis muscles are branches of the
dorsal primary rami of the spinal nerves
7. longissimus muscle (the intermediate column) also with three parts
a. longissimus thoracis
(1) arises as described above for the erector spinae, but is medial to the
iliocostalis muscle's origination
(2) inserts into the tips of the transverse process of all the thoracic
vertebrae and onto the area between the tubercles and angles of the
lower nine or ten ribs
b. longissimus cervicis
(1) arises from the transverse processes of the upper four or five
thoracic vertebrae, medial to the longissimus thoracis
(2) inserts into the posterior tubercles of the transverse processes of the
vertebrae C2 - C6
(a) action: for the longissimus thoracis and cervicis muscles
is to extend the vertebral column and bend it to one side
(b) innervation: branches of the spinal dorsal primary rami
c. longissimus capitis
(1) arises from the transverse processes of the upper four or five
thoracic vertebrae with the longissimus cervicis but medial to it
& the articular processes of the last three or four cervical vertebrae
(2) inserts in the posterior margin of the mastoid process, deep to the
splenius capitis and sternocleidomastoid muscles
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(a) action of the longissimus capitis is to extend the head if both
sides are acting together and if one side is acting alone, then it
will turn the head and face to the same side
(b) innervation: branches of the dorsal primary rami of the middle
and lower cervical nerves
8. spinalis muscle (the medial column) and this too, has three parts
a. spinalis thoracis
(1) arises from the spinous processes of T 9 - L2 and is medial to the
longissimus thoracis muscle
(2) insertion is into the spinous processes of the upper thoracic
vertebrae, with the number varying four to eight
b. spinalis cervicis - an inconsistent muscle
(1) arises from the caudal part of the ligamentum nuchae, the spinous
process of C7, and sometimes T1 and T2.
(2) insertion into the spinous process of C2 and sometimes C3 & 4
c. spinalis capitis - is usually inseparable from the semispinalis capitis,
which will be described in the transversospinalis muscle group next
d. action of the three spinalis muscles is to extend the vertebral column
e. innervation: branches of the spinal dorsal primary rami
9. transversospinalis muscles are not erector spinae muscles - there seven
muscles in this group
a. semispinalis thoracis muscles span about six vertebral levels
(1) arise from the transverse processes of T6 - 10 vertebrae
(2) insert into the spinous processes of C6 - T4
b. semispinalis cervicis muscles span about six vertebral levels
(1) arise from transverse process of the first five or six thoracic vertebrae
(2) insert into the spinous processes of C1 - 5
c. action: both the semispinalis thoracis and cervicis muscles extend the
vertebral column and rotate it toward the opposite side
d. innervation: branches of the primary dorsal rami
e. semispinalis capitis muscles (spinalis capitis) span about six vertebral
levels
(1) arise from the tips of the transverse processes of C7 - T6 or 7 and
also from the articular processes of C4 - 6
(2) insert between the superior and inferior nuchal lines of the occipital
bone, deep to the origin of the trapezius muscle
(a) action: extends the head and rotates it toward the opposite side
(b) innervation: branches of the spinal dorsal primary rami
f. multifidus muscles span about three to five vertebrae from the sacrum to
the axis
(1) arise from the posterior superior iliac spine and sacroiliac ligaments,
the mamillary processes of the lumbar spine, transverse processes of
the thoracic vertebrae, and articular processes of C4 - 7
(2) insert into the spinous process of a vertebra superiorly from the last
lumbar up to the axis
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(a) action: extends the vertebral column and rotates it to the opposite
side
(b) innervation: branches of the spinal dorsal primary rami
g. rotatores - deep to the multifidus and span one or two vertebra
(1) arise from a transverse process of one vertebra
(2) insert at the base of one spinous process above
(a) action: extend the vertebral column and rotate it to the opposite
side
(b) innervation: branches of the dorsal primary rami
h. interspinalis are short paired muscles between the spinous process of
contiguous vertebrae with one being on each side of the interspinal
ligament
(1) in the cervical region: distinct with the first pair between C2 and C3
(2) in the thoracic region: between T1 & 2 and caudally, between T11 &
T12
(3) in the lumbar region: four pairs between the lumbar vertebrae
(a) action: extend the vertebral column
(b) innervation: branches of the spinal dorsal primary rami
i. intertransversarii - between the vertebral transverse processes
(1) in the cervical region: best developed and passing from the anterior
and posterior tubercles of a vertebra to those of the next vertebra
below
(a) a ventral primary division of a cervical nerve runs between each
pair of anterior and posterior intertransversarii
(b) the first pair are between the atlas and atlas; the last between C7 &
T1
(2) in the thoracic region: they are present between the transverse
processes of the last three thoracic vertebrae and T12 & L1
(3) in the lumbar region: present between each pair of transverse
processes
(a) one intertransversarii passes between adjacent lumbar transverse
processes - intertransversarii lateralis
(b) another passes from the mammillary process of one vertebra to the
accessory process of the next vertebra below - intertransversarii
medialis
(c) action: all of the intertransversarii bend the vertebral column
laterally
(d) innervation: the anterior, posterior, and lateral
intertransversarii are supplied by the spinal ventral primary
rami; the medial intertransversarii are supplied by the spinal
dorsal primary rami
E. The suboccipital triangle is a space related to the occipital bone and the
first two cervical vertebrae, bounded by muscles and containing the
vertebral artery.
1. first cervical vertebra (atlas) - C1
a. superior articular facets articulate with the occipital condyles
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2.
3.
4.
5.
b. the vertebral foramen lies below the foramen magnum
c. the atlas has no body
d. it has a posterior tubercle instead of a spinous process
second cervical vertebra (axis) - C2
a. the embryological body of C1 is fused to it and is called the dens
or odontoid process
muscles that bound the suboccipital triangle
a. inferior oblique - arises from the spine of C2 and inserts on the
transverse process of C1
(1) action: rotates the atlas, turning face to the same side
b. superior oblique - arises from the transverse process of C1 and
inserts on the occipital bone
(1) action: extends the head and bends it laterally
c. rectus capitis posterior minor - arises from the posterior tubercle of
C1 and inserts on the occipital bone
(1) action: extends the head
d. rectus capitis posterior major - arises from the spinous process of
C2 and inserts on the occipital bone
(1) extends the head and rotates it to the same side
e. all of the above four muscles are innervated by a branch of the dorsal
primary ramus of the suboccipital nerve - C1 nerve root level
vertebral artery passes through the transverse foramen of C6 up to C1
a. passes posteriorly and medially to the superior articular process to lay
in a groove in the posterior arch of C1 and then turns anteriorly and
superiorly to pass through the foramen magnum
b. on the posterior arch of the atlas it is seen through the suboccipital
triangle
c. dorsal (posterior) primary ramus of C1 (suboccipital nerve) passes
beneath the artery (between the artery and posterior arch of C1) to
innervate the suboccipital muscles
d. ventral (anterior) primary ramus continues laterally to pass
immediately posterior to the vertebral artery as it leaves the transverse
foramen
the suboccipital triangle is covered by the trapezius, splenius capitis, and
semispinalis capitis muscles
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