Kines Axial Skeleton Muscles

Based on Figure 10-16, which muscle has the greatest moment arm for (a) flexion and (b) lateral flexion at L3?

Rectus abdominis for flexion and obliquus externus abdominis for lateral flexion.

What are the deepest of the transversospinal

Rotatores

Linea Alba

thickening & crisscross as the sheaths cross midline Mechanical link, strengthens

Rotatores are most developed where?

thoracic

Rectus Abdominis: 1) what way does it run? 2) what is it intersected with?

1) longitudial 2) fibrous bands - tendinous intersections

Muscles of Deep Layer of the Back

1. Erector Spinae 2. Transversospinal Group 3. Short Segmental Group

Transverse Abdominis (TA) 1) where is it located? 2) what does it increase?

1) Attachments to thoracolumbar fascia, deepest, "corset m." 2) abdominal pressure

Action of abdominal m.

1) Trunk Flexion 2) Trunk Rotation

What is the primary difference between a dorsal ramus of a spinal nerve root and a dorsal nerve root?

A dorsal ramus of a spinal nerve is a mixed nerve (containing both sensory and motor fibers) that innervates tissues associated with the back. A dorsal nerve root is set of sensory fibers that enter the spinal cord at a specific spinal nerve root level.

Assume a person has a complete spinal cord injury at the level of T8. Based on your knowledge of muscle innervation, predict which muscles of the trunk would be unaffected and which would be partially or completely paralyzed. Consider only the abdominal muscles, multifidi, and erector spinae in your response.

Assuming no innervation below the T8 vertebral level, you would generally expect the following: (a) The multifidi would show essentially normal strength above T8 and complete paralysis below T8. (b) The erector spinae would show normal to near normal strength above T8 and complete paralysis below T8. (Weakness may persist in some muscle fibers above T8 because of the reduced stabilization of the more [paralyzed] inferior parts of the muscle.) (c) Only the most superior fibers of selected abdominal muscles would remain innervated. Paralysis of the muscle group would be nearly complete. From a practical perspective, however, as a group, the abdominal muscles would likely be considered nonfunctional. Clinical scenarios often vary due to partial or asymmetric trauma to the spinal cord, a combined injury to the exiting spinal nerve roots, and the natural variability in muscle innervation.

As indicated in Figure 10-29, why is the axial rotation function of the rectus capitis posterior major muscle limited to the atlanto-axial joint only?

Axial rotation is not considered a degree of freedom at the atlanto-occipital joint.

Justify why an isolated strong contraction of the semispinalis thoracis would likely produce contralateral axial rotation, whereas a strong isolated contraction of the longissimus cervicis or capitis would likely produce ipsilateral axial rotation. Use Figures 10-7 and 10-9 as a reference for answering this question.

Based on fiber direction, the resultant force produced by each muscle in question could be trigonometrically resolved into horizontal and vertical components. Although considerably less than the muscle's vertical force component, the horizontal force component would produce some magnitude of axial rotation torque. Assuming a strong contraction directed from a cranial-to-caudal direction, each muscle would produce either a contralateral or an ipsilateral rotation. A contraction of the left semispinalis thoracis, for example, would pull the spinous processes to the left, causing the body (front) of the vertebrae to rotate to the right. Furthermore, contraction of the left longissimus capitis, for example, would pull the left mastoid process of the temporal bone to the right (toward the midline), causing the front of the cranium to rotate to the left. From the anatomic position, the line of force of these muscles for horizontal plane rotation is slight to moderate. By observing Figures 10-7 and 10-9, appreciate that the line of force of each muscle is more favorable for axial rotation if the contraction starts from a position that is opposite to the muscles' rotation action.

Cervical plexus

C1-C4

Recurrent Meningeal Nerves

C1-S4 (interbody joints, primarily posterior annulus, PLL)

Brachial plexus

C5-T1

At the level of the third lumbar vertebra, which connective tissues form the anterior rectus sheath (of the abdominal wall)?

Connective tissues that are associated with the obliquus externus abdominis and the obliquus internus abdominis.

largest & most superficial abdominal

External oblique

As a group, the trunk extensor muscles produce greater maximal-effort torque than the trunk flexor muscles (abdominals). Cite two factors that can account for this difference in strength.

First, the cross-sectional area of the trunk extensor exceeds that of the abdominal muscles. Second, as a group, the average fiber direction of the trunk extensor is more vertically oriented than the abdominal muscles.

Why are the superficial and intermediate muscles of the posterior back classified as "extrinsic" muscles? Describe how the specific innervation of these muscles is associated with this classification.

From an embryologic perspective, the deep muscles of the posterior back have retained their original location near the neuraxis. For this reason these muscles are classified as "intrinsic" muscles of the back. In contrast, the superficial and intermediate muscles of the back have migrated from their original location within the limb buds to their final location in the back region. These muscles are embryologically associated with the extremities and therefore classified as "extrinsic" muscles of the back. Extrinsic muscles of the back are innervated by nerves that branch for the ventral ramus of spinal nerves.

With the aid of a plastic skeleton model or other visual resource, describe the rotational (horizontal plane) action of the right scalenus anterior muscle from (A) the anatomic position, (B) a position of full rotation to the right, and (C) a position of full rotation to the left.

From the anatomic position, contraction of the right scalenus anterior would rotate C3-6 vertebrae a short angular distance to the right, likely only about 5-10 degrees. At about this position, the line of force of the muscle would pass directly through the vertical axis of rotation of the cervical region, thereby losing effective leverage for continued rotation. b) From a position of full rotation to the right, contraction of the right anterior scalane would rotate C3-6 vertebrae to the left, back toward the anatomic position. c) rom a position of full rotation to the left, contraction of the right anterior scalane would rotate C3-6 vertebrae to the right, back toward the anatomic position. Answers B and C reinforce an important global kinesiologic point. When the cervical spine is rotated well outside the anatomic position, the scalenus anterior has the ability to return the cervical spine back toward the anatomic position. Restricting an analysis of the axial rotation potential of this muscle (and other scalenes) strictly from the anatomic position limits one's appreciation of the muscle's full potential actions within this plane. This point also applies to other muscles in the body.

What produces rotationary torque in multifidi?

High angle of insertion to spinous process

Iliopsoas muscles

Iliacus & Psoas Major

Describe the similarities and differences in the structure of the multifidi and the semispinales muscles.

In general, the multifidi and most of the semispinales muscles attach between transverse and spinous processes. The specific attachments of these muscles differ, however, in at least two ways: (a) the semispinales cross 6-8 intervertebral junctions, whereas the multifidi span only 2-4; (b) the multifidi are most developed in the lumbar region, the semispinales in the cranial region.

Short Segmental Group

Interspinalis & intertransversarus

Lumbar plexus

L1-L4

Sacral plexus:

L4-S4

Which of the major trunk muscles would experience the most significant stretch (elongation) after a motion of full trunk extension, right lateral flexion, and right axial rotation?

Left internal oblique muscle.

Thoracolumbar Fascia / Lumbodorsal fascia attachments

Medial Sacral Crests • Spinous processes lower thoracic & all of lumbar • Supraspinous Ligaments lower thoracic & lumbar • Iliac Crests • Sacrotuberous & Sacroiliac Ligaments • Gluteus Maximus • Multifidi

Help with coordinated movements of C-spine & head with visual & sensory input

Short Segmental Group

Intercostal Nerves

T1-12

List structures that receive sensory innervation from the recurrent meningeal nerve. What nerves provide sensory innervation to the capsule of the apophyseal joints?

The recurrent branch of the meningeal nerve is a segmental nerve that is responsible for carrying sensation from the meninges of the spinal cord, posterior longitudinal ligament, and more superficial regions of the annulus fibrosis. Sensory innervation from the capsule of the apophyseal joint is supplied by afferent fibers within dorsal rami of local spinal nerves.

List three muscles that attach to anterior tubercles and three that attach to posterior tubercles of transverse processes of cervical vertebrae. What important structure passes between these muscle attachments?

The scalenus anterior, longus colli, and longus capitis attach to anterior tubercles of cervical transverse processes. The scalenus medius, splenius cervicis, and longissimus cervicis attach to posterior tubercles of cervical transverse processes. The brachial plexus passes between these two sets of muscles.

Semispinalis muscles

Thoracis, cervicis, & capitis (deep to trap)

"common tendon"

Thoracolumbar Fascia / Lumbodorsal fascia

________________gives sensation to ligaments of posterior vertebra, apophyseal joints, and dorsal SI ligaments

dorsal ramus

As described in the chapter, the Valsalva maneuver is often used as a way to increase pneumatic-based stability within the lumbopelvic region when lifting or performing other activities. List three muscle groups within the axial skeleton that are directly involved with this activity, and describe the common mechanical principle by which they, acting in concert, increase stability within the region.

Three muscle groups directly involved in the Valsalva maneuver are the diaphragm, deep abdominal muscles, and the pelvic floor muscles. Coordinated contraction of the muscles reduces intra-abdominal volume (abdominal muscles pulling in, diaphragm pulling down, and pelvic floor muscles pulling up), thereby increasing pressure within this sealed cavity.

__________________Located deep to erector spinae. What type of motions do they produce? (axial, bilateral, extension)

Transversospinal Muscles axial: fine controlled movements bilateral: extension unilateral: lateral flexion or contralateral rotation

T/F: erector spinae attach to a common tendon

True

Describe the most likely craniocervical posture resulting from (a) unilateral and (b) bilateral spasm (or shortening) in the sternocleidomastoid muscle(s).

Unilateral shortening of the sternocleidomastoid typically results in varying amounts of flexion (especially in the lower region), lateral flexion, and contralateral rotation of the craniocervical region. Bilateral shortening of the sternocleidomastoid typically results in a protracted posture of the craniocervical region: slight flexion of the mid- and lower craniocervical region with slight extension of the upper craniocervical region.

Describe how an overshortened (contracted) iliacus muscle can cause an increased lumbar lordosis while a person is standing. What effect could this posture have on the stress at the lumbosacral junction?

While in a standing position, a contracted iliacus muscle rotates the ilium (pelvis) anteriorly toward the femur. Assuming the trunk is maintained upright, this movement is typically described as an excessive anterior tilt of the pelvis. The lumbar spine is forced to rotate into extension, which increases its lordosis. Excessive lumbar lordosis is likely associated with an increased sacrohorizontal angle and an increased anterior shear force at the L5-S1 junction.

Ventral ramus innervation:

anterolateral trunk, neck and extremities

Horizontal force =

axial rotation

T/f: Dorsal ramus gives segmental innervation of_____________. Also contributes to dermatome sensation.

back

The Intermediate Layer plays a role in:

breathing & rib movement for thoracic expansion.

30-45% of extension torque of head is from_________.

cervicis and capitis

What are bilateral actions of erector spinae?

extension (Also pelvic tilt)

Is abdominal flexion or extension greater? Why?

extension is greater Extensors high function with carrying loads in front Extensors counteract gravity

________________nearly perpendicular fibers to EO.

internal oblique

Vertical force =

lateral flexion & flexion

What are unilateral actions of erector spinae?

lateral flexion, some ipsilateral rotation

Short Segmental Group are___________level torque producers.

low

Multifidi are most developed where?

lumbar region

Dorsal ramus innervation:

post. trunk and neck

___________________ afferent axons (sensory)

posterior root

Superficial Layer: Consider dual action or ______________due to origin.

reverse action

Ventral ramus: Each either forms Plexus or has single_____________.

segmental intervation

Why is rotation force minimal in transversalis group?

short muscle length

___________________________determines effectiveness or potential to produce particular action

spacial orientation

One of multifidi's major functions

stabilization

T/F: Dorsal ramus has branches from every spinal nerve

true

______________________ efferent axons (movement)

ventral root

Why do abdominal extensors have greater force?

• Extensors have greater mass • Extensors have vertical orientation of mm fibers (note that flexors do have better leverage)