Anatomy Lecture 6/5 and 6/6

A continuation of the posterior longitudinal ligament connecting atlas to occipital bone along anterior margin of foramen magnum.

The ligament that forms a collar around the atlas maintaining the median atlantodental joint. Rupture - injury of spinal cord by dens.

Extends from dens to occipital condyles. Limits rotation and lateral bending of head to opposite side. A hyperflexion injury could cause a fracture of the dens and a tear of the alar ligament.

Attach - spinous process of C7. Purpose - Resist flexion of head that results from the center of gravity being anterior to the atlantooccipital joints. Also to position special sense organs located in the skull optimally in response to stimuli.

Superficial: Splenius group
Intermediate: Erector spine group
Deep: Semispinalis group, Intertransversarii, Interspinales
Actions: Resist/restrict flexion and contralateral bending. Stabilization.

Rectus capitis minor and major, Obliquus capitis superior and inferior.

Bounded by the rectus capitis major medially, obliquus capitis superior laterally, obliquus capitis inferior inferior. Within triangle: sub-occipital nerve (dorsal rami C1), vertebral artery, posterior arch of atlas.

Contraction of the dura mater due to the closeness to the spinal cord.

posterior atlanto-occipita membrane *ossifications of the portions of the membranes are not uncommon in the elderly, creating bony tunnels which may reduce flow through the arteries.

spinal cord, brain stem and cerebellum

rigid and extended head posture, often leading to chronic headaches

Central Nervous System - comprised brain and spinal cord.

a bundle of axons in the CNS

a bundle of axons in the PNS

a collection of nerve cell bodies in the CNS

a collection of nerve cell bodies in the PNS

Peripheral Nervous System - comprised of the spinal nerves and 12 pairs of cranial nerves

body wall and extremities

somatic motor (efferent) fibers, somatomotor fibers stimulate voluntary and reflex contraction of skeletal muscle

somatic sensory (afferent) fibers, somatosensory fibers transmit to the CNS two things: 1) touch, pain, pressure and temperature from body wall 2) proprioception from tendons and joints

viscera - internal organs

Descends from the caudal portion of the brain stem (medulla obligate) through the foramen magnum and through the vertebral canal and terminates in the conus medullar is around L1/L2

Thecal

Cervical (gives rise to nerves of the brachial plexus) and lumbo-sacral (gives rise to the lumbosacral plexus)

formed by the roots of the lower lumbar, sacral and coccygeal spinal nerves starting around L1/L2

A projection of pia mater, descends from the tip of the conus thru the sacral hiatus to the coccyx

S1 - S2 level

pia mater, (subarachnoid space), arachnoid mater, dura mater, epidural fat in epidural space

A network of valveless veins running the length of the trunk. An important route for the spread of infection and metastases as bell as emboli to the endocranium. Communicates freely between the veins of the body wall and the dural venous sinuses that drain the brain and endocranium.

projects laterally at each intervertebral level to encompass roots of the spinal nerves

Weblike structure surrounding spinal cord, the pressure of the CSF in the subarachnoid space keeps the dura and arachnoid apposed.

Found between emerging nerves, they penetrate the arachnoid, attach to dura and help stabilize the cord.

The chord plexus within the ventricles of the brain. CSF is a clear colorless liquid, low in protein and cellular content and functions as a liquid cushion for the CNS within the skull and spine.

Circulates along the length of the subarachnoid space (dura and arachnoid covering the brain are continuous at the foramen magnum with the dura and arachnoid covering the cord) before being absorbed into the network of venous dural sinuses in the skull.

Anterior and posterior spinal arteries. Also, radicular and segmental medullary arteries (these enter through the vertebral canal through the IV foramina).

connections of vessels, contribute to collateral pathways to tissue

Dorsal horn --> dorsal (posterior) root which are somatic afferent fibers that carry info from periphery to CNS
Ventral horn --> ventral (anterior) root comprised of somatic efferent fibers carrying info from CNS to periphery

Dorsal roots and ventral roots combine to make a mixed spinal nerve, this nerve splits into mixed dorsal and ventral rami. *There is a difference between the word root and rami!

Located on the dorsal root in the IV foramen just proximal to the mixed spinal nerve.

The anterolateral body wall, hypaxial muscles and extremities.

The skin of the back and posterior scalp, facet joints, posterior ligaments of the spine and epaxial (intrinsic) back muscles.

Cervical / upper thoracic: one level higher.
Middle thoracic: two levels higher.
Lumbar, sacral, coccygeal: all adjacent to the T11 and L1 vertebrae.

3 month fetus: segments adjacent to vertebrae. 2nd - 3rd trimesters: spine is growing more rapidly than cord creating the difference in length.

The herniation will usually compress the nerve roots of spinal nerves emerging through the next IV foramen down. It also may effect multiple discs!

Caused by acute or chronic mechanical trauma or inflammation. May initiate impulses in sensory (pain, parasthesia) or motor (spasm, twitching) fibers.

May result from trauma or neuropathy. Motor symptoms - paralysis or paresis (weakness). Sensory symptoms - anesthesia or hyperesthesia (diminished feeling)

CNV the trigeminal nerve.

The specific area of the skin supplied by the somatic afferents in the pair of spinal nerves arising from each spinal cord segment. Dermatomes overlap so if a nerve is damaged anesthesia does not occur.

Exteroceptors (cutaneous receptors) in the skin to the CNS.

They are sensitive to a particular form of physical energy, or stimulus, which it traduces into electrochemical energy or an action potential.

Mechanoreceptors - deformation/displacement
Thermoreceptors - temperature
Nociceptors - stimuli that damage tissue
All of these receptors are continuous with peripheral processes of pseudo unipolar sensory neurons whose cell bodies are located in the dorsal root ganglia.

A collection of pseudounipolar sensory neurons located on the dorsal root in an IV foramen, just proximal to the mixed nerve. This is where inputs enter the spinal cord but they are segregated by modality.

Lower motor neurons located in the brainstem or spinal cord. Ventral roots convey axons of these lower motor neurons whose cell bodies are located in the ventral horns of the spinal grey to the mixed spinal nerves.

muscle fiber

motor unit - a lower motor neuron and all the muscle fibers which it supplies. With any given muscle, the fibers belonging to a single motor unit are distributed over a wide territory and intermingle with fibers of other motor units. A muscle fiber is innervated by a single alpha motor neuron yet each neuron may innervate many fibers.

scapula and clavicle, maximize stability

It develops early via intramembranous ossification. It is the earliest postcranial bone to initiate ossification and the only bony connection b/t upper limb and axial skeleton.

acromioclavicular joint and glenohumeral joint

The glenoid fossa, a shallow oval articular surface, deepened by a cartilaginous labrum. SLAP tears occur in the labrum may result in poor throwing mechanics - these won't heal because of poor vascularization.

Incongruity of bony articular surfaces (little contact) and the thin, lax articular capsule. Price = instability (dislocation and subluxation).

The muscles and tendons of the rotator cuff because the glenohumeral ligaments are weak.

Lateral: broad and flat, articulates with scapula, trapezoid line, conoid tubercle.
Middle: curved
Medial: Round, articulates with manubrium of sternum.

Sinous shape.
Changing cross-sectional shape of middle.
Early ossification.
Bone's role a strut b/t arm and axial skeleton.
Subcutaneous location.

Sternocledomastoid pulls medial portion up. Pectoralis major pulls humorous medially. Gravity pulls humorous down.

scapulothoracic
glenohumeral
acromioclavicular
sternoclavicular
subacromial space

Close to critical or vital structures.

trapezoid and conoid

Made up of 15 - 20 lobes each opening separately onto the nipple through a lactiferous duct. The lymphatic drainage is directed toward the axillary nodes.

Extend from the pectorals major fascia, through the mammary layer, to the deep surface of the skin. Breast carcinomas commonly invade these ligaments to cause their contracture, which may dimple the skin.

The serratus anterior muscle is weakened or paralyzed by a destructive lesion of the long thoracic nerve. Resulting from trauma to the lateral thorax or mastectomy.

Elevation - upper trapezius and levator scapulae
Depression - pectoralis minor, latissimus dorsi, lower trapezius

Protraction - serratus anterior and pectoralis minor
Retraction - rhomboids and middle trapezius

Arm abduction and flexion, produced by force couples.

Upper trapezius, lower trapezius, and serratus anterior

Levator scapulae, rhomboids, latissimus dorsi and pectoralis minor.

Suprapinatus
Infraspinatus
Teres Minor
Subscapularis
The SITS muscles move the arm at the glenohumeral joint.

subscapularis, latissimus dorsi, teres major

supraspinatus, subscapularis, infraspiatus, teres minor *note that the rotator cuff is incomplete inferiorly!

Teres minor, Infaspinatus, Supraspinatus (on greater tubercle), Intertubercular groove, subscapularis (on lesser tubercle)

Avulsion fracture, occur commonly in middle aged people following a fall on the point of the shoulder. However stable fractures with no displacement are most common requiring minimal external fixation and exercise.

Beyond first 20 degrees.

Spurt - initiates abduction of arm at glenohumeral joint.
Static - resists pull of gravity on upper limb.

suprascapular

Teres major and minor, medial humoral shaft, long head of triceps.

It's where you usually get shots!

Teres major and minor and long head of biceps brachii. Circumflex scapular artery and axillary nerve.

triangular interval, formed with long head of biceps and teres major. The artery and vein course along the radial (spiral) groove vulnerable to lesion with a midshaft humoral fracture.

Splits around two pairs of large cervical muscles the trapezius and sternocleidomastoid

posterior cervical - scm, trap, clavicle, investing layer of fascia,
Anterior cervical - scm, mandible

occipital triangle above the inferior belly of the omohyoid (floor = splenius capitis, levitator scapulae, scalene group) and the subclavian triangle below the inferior belly of the omohyoid

lesser occipital - C2
great auricular - C2, C3
transverse cervical - C2, C3
supraclavicular - C3, C4

the point where the nerves arising from the cervical plexus meet, nerves blocked may cause shoulder drop

arises from C3, C4, C5 innervates diaphragm and adjacent membranes of thorax (pleura)

surrounds cervical spine and the anterior and posterior muscles which attach to it

-formed by the anterior scalene, middle scalene, and the first rib
-transmits the subclavian artery and brachial plexus

Subject to compression with hypertrophy or pathology of the scalenes, compression called scalene interval or thoracic outlet syndrome.