W3 PRINCIPLES

When the dorsal and ventral roots join in the IVF, what anatomical structure do they form?

The spinal nerve

How many pairs of spinal nerves does the spinal cord have?

31 pairs

The spinal nerve divides into what anatomical structures?

The anterior and posterior primary divisions (ventral & dorsal primary rami)

What fibres do the ventral rami carry?

Sensory and motor fibres

What structures does the ventral rami innervate?

• Muscles

• Joints

• Skin of lateral and ventral body walls and extremities

What structures does the dorsal rami innervate?

Skin and muscles of the back

Which option is correct?

a) Only the dorsal rami contains autonomic fibres

b) Only the ventral rami contains autonomic fibres

c) Both dorsal and ventral rami contain autonomic fibres

d) Both dorsal and ventral rami do not contain autonomic fibres

c) Both dorsal and ventral rami contain autonomic fibres

What does the anterior compartment of the spinal column contain?

• Prevertebral muscles

• Anterior longitudinal ligament

• Vertebral body

• IVD

• Anterior dura mater

What does the posterior compartment of the spinal column contain?

• Neural arch

• Posterior dura mater

• Facet joints and ligaments

• Ligamentum flavum

• Paraspinal muscles

Where do structures in the anterior compartment of the spinal column receive their innervation?

From the ventral ramus

Where do structures in the posterior compartment of the spinal column receive their innervation?

From the dorsal ramus

Why can most structures of the spinal column generate a sensory signal?

Due to being innervated

What are examples of structures within the spinal column that receive sensory innervation?

• Facet joints

• Ligaments

• Muscles

• IVD

• Meninges

What are the facet joints innervated by?

The dorsal ramus innervates the facet joints

What group fibres innervate the joint capsule?

Group II, III and IV fibres

What are the different receptor types in articular tissue of the facet joints?

• 3 types are encapsulated endings (mechanoreceptors)

• 1 type is unencapsulated (nociceptors)

What does a low density of receptors throughout the spine indicate?

Indicates that the receptive fields of the receptors is large

What does a larger receptive field indicate?

• The more sensitive is the primary afferent fibre to the stimulus

• The less able the primary afferent is able to localise the stimulus

What are the different classifications of joint receptors?

What innervates the ligamentum flavum (controversial)?

• Parts may be supplied by Group II and III fibres which may respond to mechanical movement in physiological range

• Sensory receptors thought to be rare

What nerve endings do the longitudinal ligaments contain?

Both free and encapsulated nerve endings

What stimuli can the longitudinal ligaments receive?

Both mechanical and noxious stimuli

What nerve endings do the supraspinous and interspinous ligaments contain?

The supraspinous and interspinous ligaments contain both free nerve endings and encapsulated endings

What stimuli can the supraspinous and interspinous ligaments receive?

Non-noxious and noxious stimuli

Is the outer or inner portions of the IVD innervated?

Outer portions→ 1/3 of annular fibres

What receptors are in the annular fibres of the IVD?

Mechanoreceptors and chemoreceptors→ Located near endplate region of IVD and anterolateral portions

Where do the costovertebral joints receive innervation from?

Articular branch from the ventral ramus

Describe the receptors found in the costovertebral joints and their level of activity

• Slowly adapting mechanoreceptors found in costovertebral joints

• They are active over entire range of rib cage movement during breathing

• Distension of joint increases rate of receptor discharge

• Other mechanorecptors are rapidly adapting→ only active during rib motion “shallow breathing”

What receptors are found in the paraspinal muscles?

• Muscle spindles

• Golgi tendon organs

• Pacinian corpuscles

• Group III mechanoreceptors

• Chemoreceptors

What are muscle spindles important mediators for?

Position and movement sense

What are muscle spindles very sensitive to?

Mechanical vibration

What is precise muscle spindle input of the paraspinal muscles essential for?

Accurate positioning of the pelvis and lumbosacral spine in a sitting posture

How may the spinal position sense of someone with nonspecific chronic low back pain alter to someone with no LBP?

There may be a difference in superficial multifidus activity during standing

• Unable to return to a ‘neutral spine’ position multiple times, studies showed greater error magnitude and variability

A porcine model was used to study whether muscular activation in the paraspinal muscles caused by nerve stimulation in the anulus fibrosus of a lumbar intervertebral disc could be altered by saline injection into the zygapophysial (facet) joint.

Stimulation of the nerves within the posterolateral anulus of the disc elicited reactions in the paraspinal muscles, namely the lumbar multifidus and longissimus. Introduction of physiologic saline into the zygapophysial joint resulted in a reduction in the motor unit action potential amplitude.

Introduction of physiologic saline into the zygapophysial joint reduced the stimulation pathway from the intervertebral disc to the paraspinal musculature.

What does the evidence suggesting the facet joints may have a regulating function imply?

It implies that the facet joints have the ability to control the intricate neuromuscular balance in the lumbar motion segment.

How may the therapeutic effect of the chiropractic adjustment occur?

Due to activation or silencing of sensory inflow from different spinal structures

• Removal of mechanical irritation

• Redistribution of stresses or strains on spinal structures

• Reduction of inflammation via changes in blood flow

• Activation of large diameter afferents in response to the adjustment (mechanical stimulus), inhibiting transmission of nociceptive afferents (gate control) or other pain modulating mechanisms

What is pain?

An unpleasant sensation experienced in order to stop and change what we are doing (behaviour). It is protective in nature

What is nociception?

Transmission of information about particular kinds of peripheral stimuli (mechanical, thermal, chemical) that are potentially harmful to the organism

Is the transmission and processing of nociceptive stimuli the same as pain?

No

Is pain an objective or subjective experience?

Subjective experience

Give an example for how pain is a subjective experience?

A stabbing sensation in the chest occurring spontaneously in a middle-aged man will produce considerably more pain than a similar sensation produced by a two-year child poking him on the chest wall with a stick

Are there pain receptors in the body?

No, only nociceptive receptors

What is the IASP definition of pain?

An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage

Is pain equal to tissue damage?

Pain is not equal to tissue damage

Explain how pain relies on context

• Sensory cues are evaluated by nervous system

• External cues taken into consideration (painful stimulus with red light hurts more than when paired with blue light)

What is an example of sensory pain?

Initial noxious stimulation of nociceptors such as a scratch on the hand

What are examples of emotional pain?

• Sense of loss

• Depression

• Anxiety

What is an example of actual pain?

Initial physical tissue damage

What is an example of potential pain?

Risk of damage or further/significant damage

Fill in the gap. The larger the diameter of the nerve, the faster the….

Conduction velocity

Fill in the gap. The size of the … determines the speed of propagation of the action potential

Axon

What do sensory nerves provide the brain with?

Information about the environment

How do receptors process information for the CNS?

Receptors transform mechanical, thermal or chemical stimuli into an electrical signal, which can then be interpreted by the CNS

What is the endpoint of the sensory nerve?

The receptor

What is the role of the receptor?

Generating an electrical potential that can be propagated along afferent nerves as an action potential

What are the 4 types of receptors?

• Mechanoreceptors

• Proprioceptors

• Theremoreceptors

• Nociceptors

What are nociceptors responsive to?

Noxious or potentially tissue damaging stimuli

What are mechanoreceptors responsive to?

Non-noxious mechanical stimuli including pressure, vibration and light touch

What are proprioceptors responsive to?

Changes in position and movement of muscles and joint

What are thermoreceptors responsive to?

Temperature

What 3 sub-types of nociceptors respond to a single modality?

• Mechanoreceptors

• Thermoreceptors

• Chemoreceptors

What sub-type of nociceptors respond to mechanical, thermal and chemical features of a noxious stimulus?

Polymodal receptors

What are nociceptors most sensitive to?

A higher range of stimulus intensities that are expected to cause tissue damage

What structures are dense populations of nociceptors found in?

• Skin

• Muscle

• Bone

• Joint capsules

• Viscera

• Blood vessels

• Meninges

• Peripheral nerve sheath

What structures are nociceptors not found in?

• Articular cartilage

• Synovial membranes

• Lung parenchyma

• Visceral pleura

• Pericardium

• Brain or spinal cord tissue

What are the two different types of nociceptive fibres?

• Small diameter thinly myelinated (A-Delta)→ well-localised sensations of sharp and prickling pain

• Small diameter unmyelinated (C-fibres)→ Poorly localised, dull, diffuse and persistent. Includes post-ganglionic fibres in the ANS and nerve fibres at the dorsal roots

What activates A-Delta fibres?

Noxious mechanical, chemical or thermal stimuli activates A-Delta fibres

What does excitation of A-Delta fibres cause?

Immediate sharp pain

What are A-Delta fibres responsible for?

Transmission of fast/first pain

What are C fibres responsible for?

Delayed onset or slow pain

Ryan stubs his toe on the chiro table in clinic in front of a patient. How awkward!! Explain how the different nociceptive fibres play a role in his injury.

• At time of injury, acute, sharp well localised pain is felt (activation of A-Delta fibres)

• This pain will subside within seconds

• Replaced by a deep, spreading pain, may also have a sickening quality (C fibres)

• There is now widespread tenderness and loss of function

• Physiologically, initial injury is associated with stimulation of both A-Delta and C fibres

• A fibres, first, then C fibres

• Nociceptors are unique as their sensitivity to stimuli increases after tissue damage

• Ongoing pain and tenderness partly due to C fibre activation and increased nociceptor sensitivity due to tissue damage (hyperalgesia)

What is the term for when nociceptor sensitivity to stimuli increases after tissue damage?

Hyperalgesia

What two types of hyperalgesia are there?

Primary and secondary hyperalgesia

Describe the peripheral sensitisation mechanism of hyperalgesia

• Noxious stimuli causes a response in the area of tissue damage

• An ‘inflammatory soup’ is released

• This sensitises nerve endings

• REWATCH THIS PART OF LECTURE

Describe the axon reflex mechanism of hyperalgesia.

• Elicited by stimulus that excites afferent neurons which without transmission to efferent neurons modify the activity of effector tissues

• Best known example is cutaneous flare response to irritation or injury

• Reddening (flaring due to vasodilation) spreading beyond the pin-point injury of the skin is the result of axon reflexes

• When some axon branches are activated by a irritant stimulus, nerve impulses travel centrally to the branching points where they pass backwards to other branches and back to the skin

• Periarteriolar branches of sensory neurons then can release vasoactive transmitters and cause arteriolar dilation

Diagram of hyperalgesia