STI Unit 4: Neuromechanical Aspects

Question 1

What are the four major categories of receptors in the body?

Answer 1

• Mechanoreceptors
• Nociceptors
• Thermoreceptors
• Chemoreceptors

All of these receptors influence or are influenced by movement, temperature, physiology, and/or pathology. Also, all receptors influence movement and movement control, and they all influence, directly or indirectly, cardiovascular and respiratory physiology.

Question 2

What are Mechanoreceptors?

Answer 2

They are peripheral sensory receptors of mechanical events

• They transduce mechanical energy into nerve impulses, which are then transmitted to the central nervous system via their afferent neuron axons. They are located throughout the musculoskeletal system, the vascular tree, and the skin.

Question 3

What are the 3 Mechanoreceptors in muscle and joints that signal the stationary position of the limb and the speed of direction of the limb movement?

Answer 3

• Muscle Spindle Receptors: Specialized stretch receptors in muscle
• Golgi Tendon Organs: Receptors in the tendon that sense contractile force or effort exerted by a group of muscle fibers
• Receptors located in joint capsules that sense flexion or extensoin of the joint

Question 4

Mechanoreceptors

What is Meissner’s Corpuscles?

Answer 4

Specialized structures located in glabrous (hairless) skin of mammels (e.g., palms, soles of feet, lips)

• They adapt rapidly in response to mechanical stimuli, such as skin indentation

Question 5

Mechanoreceptors

Meissner’s corpuscles has 2 characteristics, what are they?

Answer 5

• They are mechanically coupled with the surrounding subcutaneous tissues by thin strands of connective tissue. These strands promote the transmission of adequate stimulating force to several surrounding corpuscles for a given pinpoint stimulus area
• The Receptive Field for meissner’s corpuscles are very small. They can be thought of as an isolated area of skin that receives stimulation and the area that perceives a stimulus

Meissner’s corpuscles are invaluable to the manual practitioner

Question 6

What are Pacinian Corpuscles?

Answer 6

Located in both hairless and hairy skin. They have also been found in the fibrous periosteum near ligamentous attachments and in the anterior/posterior horns of the knee meniscus. Although very sensitive in sensing stimuli, they are poor at localizing it.

Question 7

Mechanoreceptors

What are Ruffini Corpuscles?

Answer 7

These are found in subcutaneous tissue beneath both hairy and glabrous skin. Also found in superficial layers of fibrous joint capsules and other connective tissue surrounding joints.
- Their intertwining with the connective tissue is functional, because they are stimulated by the displacement of the collagen fibers surrounding them.
- They are slowly adapting receptors and have a very large receptive field (unlike meissners which is fast with small field)

Question 8

Mechanoreceptors

With Ruffinin Corpuscles, what is the Major Advantage of slow adapting receptors?

Answer 8

Because of functional significance: they do not “turn off” following a stimulus but continue to fire with a consistently applied stimulus, they contribute to steady-state positions sense and tactile sensations

Question 9

Mechanoreceptors

What are Merkel Receptors?

Answer 9

There are the most peripheral of all the sensory receptors

• Located in the epidermis of glabrous skin. The receptors synapse with epithelial cells, this synapse or connection, of epithelial cells directly with the merkle receptors results in an action potential for the neurons serving the receptors with any mechanical stimulus to its related epithelial cells
• Like Ruffini they are slow adapting, however unlike ruffini they have small receptor fields
• The endings can respond to very small stimuli and localize well with their small fields along with their capacity to continue to send “tonic” signals to the CNS without a change in stimuli intensity

Question 10

Mechanoreceptors

What are Muscle Spindles?

Answer 10

This tranduces change in length of the musle
- Located in striated (skeletal) muscle

Question 11

Mechanoreceptors

What are the 3 categories of Muscle Spindles?

Answer 11

• Dynamic Nuclear Bag Fibers: These tranduce information about rapid changes in length and the rate of change of length. They are most heavily concentrated in phasic muscles.
• Static Nuclear Bag Spindles: These tranduce more tonic information about spindle information
• Nuclear chain fibers: These tranduce information about slower changes in length and are more concentrated in tonic/postural muscles

Question 12

Mechanoreceptors

What are the characteristics of Muscle Spindles?

Answer 12

They consist of:

• A group of special muscle fibers (intrafusal fibers), which are located in the spindle
• Sensory axons that terminate as a spiral ending around the intrafusal fibes
• Motor axons (gamma efferent fibers) which adjust the sensitivity of muscle spindles

Question 13

Mechanoreceptors

With Muscle Spindles, what are Primary Endings?

Answer 13

This consist of branches of a Group 1a afferent axon
- They terminate on all three types of intrafusal fibers in the muscle spindle
- They exhibit a property known as velocity sensitivity, where they incresae their firing rate with a sudden and rapid change in length
- Conseqeuently, they respond viforously with increased firing rates when stimulated briefly, such as with a tap or vibration, also they are very sensitive to changes in length

Question 14

Mechanoreceptors

With Muscle Spindles, what are Secondary Endings?

Answer 14

Group 2 afferents branch into secondary endings, which innervate the static nuclear bad fibes and the nuclear chain fibers in a spiral fashion, like the primary endings
- They exhibit a fairly steady firing rate in either the presence of the absence of movement
- These slowly adapting receptors are, therfore, ideal for signaling the length of muscle without the need for movement to increase their sensitivity

Question 15

Mechanoreceptors

What are Golgi Tendon Organs?

Answer 15

These transduce information about tension and are located in musculotendinous junctional zones
- GTOs are free nerve endings with specialized nodes on their branches that respond to the mechanical deformation from collagen fibers placed on stretch
- They are extremly sensitive to changes in tension on the connective tissue in which they are located

Question 16

Mechanoreceptors

With Joint Receptors, What are Type 1 Receptors?

Answer 16

Ruffini Endings

• They tend to be more heavily concentrated in the proximal extremity joint capsules and are slowly adapting
• Their proximal concentration makes then ideally suited to provide postural information about static positions given the fact that proximal stability is necessary to allow distal movement

Question 17

Mechanoreceptors

With Joint Receptors, what are Type 2 Receptors?

Answer 17

Pacinian Corpuscles

• These are located in the deeper layers of the joint capsule and the fat pad
• Tend to be concentrated near the boney attachments of the joint capsule
• Pacinian corpuscles are virtually silent in inactive joints are are activated with the onset and cessation of movement. This behavior is consistent with their rapidly adapting characteristic as seen in their skin counterparts

Question 18

Mechanoreceptors

With Joint Receptors, what are Type 3 Receptors?

Answer 18

Golgi-Mazzoni Endings (anatomically similar to GTOs)

• These are located among the collagen fibers of the extrinsic and intrinsic ligament of larger joints
• Along with their similarity to GTOs comes a similar functional characteristic. They are most active in their firing patterns of extremes of positions in flexion/extension or other motions that stress the ligaments

Question 19

Mechanoreceptors

With Joint Receptors, what are Type 4 Receptors?

Answer 19

These are primarly free nerve endings

• They are located in the fibrous joint capsule, fat pads, ligaments, and walls of blood vessels
• They tend to be unmyelinated are are high-threshold, nonadapting pain receptors

Question 20

Mechanoreceptors

Where are Group 3 and 4 Muscle Afferents located?

Answer 20

• Group 3 are located in the interstitial spaces of skeletal muscle, either close to or within the adventitia or arterioles and venuels
• Group 4 are found in the adventitia of small veins and even in the lymphatic system

Question 21

Mechanoreceptors

Group 3 and Group 4 Muscle Afferents have been studied and are said to have a power effect on what 2 systems on the body?

Answer 21

Ventilation and Circulation

Question 22

Mechanoreceptors

On the Sensory Side of Ventilation and Circulation, to what stimuli do Group 3 and 4 Muscle Afferent respond to?

Answer 22

Mechanical, Chemical and Thermal stimuli

Question 23

Mechanoreceptors

Would Non-noxious probing stimulate Group 3 or Group 4 receptors?

Answer 23

They will stimulate group 3 receptors, with noxious probing generating explosive burst of impulses from many more group 3 receptors

Question 24

Mechanoreceptors

Would Noxious probing stimulate Group 3 or Group 4 receptors?

Answer 24

They will stimulate group 4, and then after only a few burst of impulses will occur

Question 25

# Mechanoreceptors How do Group 3 Muscle receptors respond to Muscular Contraction?

Answer 25

Half of the Group 3 receptors respond immediately with a vigorous increase iin afferent discharge during muscular contraction. The remaining half tend to respond as the exercise session progresses - This finding indicates that about half of the receptors may be more chemically sensitive rather than mechanically sensitive

Question 26

What are Nociceptors?

Answer 26

Nerve fibers that are selectively responsive to stimuli that may potentially damage tissue or to stimuli from actual tissue damage

Question 27

What are the 3 major categories of Nociceptors?

Answer 27

Mechanical, Thermal, and Polymodal - Mechanical and Theramal Stimuli are transmitted via A-Delta Fibers and Polymodal Stimuli via C-Fibers

Question 28

What is the Muscle Stretch Reflex?

Answer 28

*aka Deep Tendon Reflex* - This is a monosynaptic reflex with input from the primary and secondary endings in the muscle spindle with the major portion of the stimulus coming from the primary ending. - The Stimulus to the primary endings in the form of a sudden lengthening of the muscle, is conducted by the Group 1a afferent. This results in transmission of a motor impulse to the stimulated muscle and contraction of the muscle

Question 29

What is the difference between Muscle Stretch Reflex and GTOs?

Answer 29

- MSR is monosynaptioc connection and is conducted by the Group 1a Afferent - GTOs are more complex, the afferent input from the GTOs synapse on the Group 1b inhibitory interneurons and they receive input from multiple sources before synapsing themselves with the motor axons of either the agonist or the antagonist muscle

Question 30

What are the 3 levels to Electrogenic Muscle Tone?

Answer 30

- Resting Tone - Electrogenic Spasm: This is involunatary contraction and associated with measurement EMG activity from that muscle - Voluntary Muscular Contraction

Question 31

What are the 2 components of Viscoelastic Muscle Tone?

Answer 31

- Elastic Component: this requires a steady force to produce a deformation of the substance, which in this case is myofascial connective tissue. - Viscoelastic component: The GAGs, actin, and myosin all contribute to the viscoelasticity of myofascial tissue. Unlike elasticity, the stiffness of viscoelasticity is velocity dependent.

Question 32

What is Thixotropy?

Answer 32

Thixotropy describes a state of stiffness of a fluid that is dependent on the history of movement. - Thixotropy is thought to explain the phenomenon of palpable "muscle spasms" that are found on examination of patients with myofascial trigger points.

Question 33

What is the benefit Iliac Crest Release Technique?

Answer 33

This technique addresses restriction of the thoracolumbar fascia and the muscular and ligamentous attachments.

Question 34

What are the benefits for the Diaphragmatic Technique?

Answer 34

- For correcting restrictions in the diaphragm and inferior border of the rib cage - Good for patients who have difficulty with postrual re-education - Progression from a gentle stretching of superficial and middle layers in supine and Sidelying positions to deeper layers that have the patient in a seated position and use the patient's breathing to increase depth - ST restrictions in the diaphragm can lead to or be a result of multiple postural problems such as forward head posture, protracted shoulders, or general slumped posture in sitting

Question 35

What may happen if a patients have increased FHP? | FHP: Forward head posture

Answer 35

- Can lead to the ribs and sternum to move inferioly and posteriorly - This leads to shortening of the CT in the abdomen and thorax - IF the diaphragm does not contract and expand properly the secondary respiratory muscles become more active

Question 36

How does the Diaphragmatic Technique effect the somatosensory system?

Answer 36

- Decreased tissue length can lead to increased activity froom the tension receptors (GTOs, RE, PC) - Increased tension on the GTOs of the central tendon of the diaphragm has been shown to inhibit the external intercostal mms and the diaphragm - The inhibatory signals over time result in reduced lung volume and the CT would remodel to the new length