Spine Health & Spinal Hygiene

El Paso, TX. Chiropractor, Dr. Alexander Jimenez continues the discussion on the anatomy of nerve fibers, receptors, spinal tracts and brain pathway/s. As the spinal nerve nears the spinal cord, it splits into the dorsal and ventral roots. The dorsal root only contains the axons of sensory neurons. While the ventral roots contain only the axons of motor neurons. Some of the branches synapse with local neurons in the dorsal root ganglion, posterior (dorsal) horn, and even the anterior (ventral) horn, at the spine where they enter.

Other branches travel short distances up or down the spine to interact with neurons at other levels of the spinal cord. A branch can also turn into the posterior (dorsal) column white matter to connect with the brain. Spinal nerve systems that connect to the brain are contralateral, in that the right side of the body is connected to the left side of the brain and the left side of the body is connected to the right side of the brain.

Cranial nerves convey specific sense information from the head and neck directly to the brain. Whereas spinal information is contralateral, cranial nerve systems are for the most part ipsilateral, meaning that a cranial nerve on the right side of the head is connected to the right side of the brain. Some cranial nerves contain only sensory axons. Other cranial nerves have both sensory and motor axons, including the trigeminal, facial and glossopharyngeal. General senses of somatosensation for the face travel through the trigeminal system.

PATHWAYS

THE POSTERIOR COLUMN– MEDIAL LEMNISCUS SYSTEM CONVEYS INFORMATION ABOUT TOUCH AND LIMB POSITION

POSTERIOR COLUMN MEDIAL LEMNISCAL PATHWAY

• The term posterior column refers to the entire contents of a posterior funiculus, exclusive of its share of the propriospinal tract. The posterior columns consist mainly of ascending collaterals of large myelinated primary afferents carrying impulses from various kinds of mechanoreceptors (although substantial numbers of second-order fibers and unmyelinated fibers are also included). This has traditionally been considered the major pathway by which information from low-threshold cutaneous, joint, and muscle receptors reaches the cerebral cortex.

2-Minute Neuroscience: Touch & The Dorsal Columns-Medial Lemniscus

DAMAGE TO THE POSTERIOR COLUMN–MEDIAL LEMNISCUS SYSTEM CAUSES IMPAIRMENT OF PROPRIOCEPTION AND DISCRIMINATIVE TACTILE FUNCTIONS

“As might be expected from the types of afferents contained in the posterior columns, this pathway carries information important for the conscious appreciation of touch, pressure, and vibration and of joint position and movement. However, because input from cutaneous receptors also reaches the cortex by other routes, damage to the posterior columns causes impairment, but not abolition, of tactile perception. Complex discrimination tasks are more severely affected than is the simple detection of stimuli. Other functions, such as proprioception and kinesthesia, are classically considered to be totally lost after posterior column destruction. The result is a distinctive type of ataxia (incoordination of movement); the brain is unable to direct motor activity properly without sensory feedback about the current position of parts of the body. This ataxia is particularly pronounced when the patient’s eyes are closed, preventing visual compensation.”

Given the role of the posterior column, the patient should be screened for any abnormalities regarding their sense of fine touch, vibration, barognosis, graphesthesia, stereognosis, kinaesthesia, two-point discrimination and conscious proprioception:

• A common way of testing for fine touch is to ask the patient to recognize common objects placed within a cloth using their touch.
• Vibration sense can be tested using a low pitched C128 tuning fork placed along a bony prominence of the desired corresponding spinal level(s) to be tested.
• Barognosis refers to the ability to determine the approximate weight of an object.
• Graphesthesia refers to the ability to recognize writing on the skin by touch. The practitioner can draw out a letter on the patients skin as a way of testing.
• Kinaesthesia refers to ones own sense of body motion (excluding equilibrium which is controlled in part by the inner ear) and is commonly tested using the subject’s ability to detect an externally imposed passive movement, or the ability to reposition a joint to a predetermined position.
• Proprioception is often assessed using the Rombergs test. This examination is based on the notion that a person requires at least two of the three following senses to maintain balance while standing: proprioception; vestibular function and vision. A patient who has a defect within their proprioceptive mechanism can still maintain balance by using vestibular function and vision. In the Romberg test, the patient is stood up and asked to close their eyes. A loss of balance is interpreted as a positive Romberg sign.

THE SPINOTHALAMIC TRACT CONVEYS INFORMATION ABOUT PAIN AND TEMPERATURE

A GOOD BRAIN CAN MODULATE PAIN

SPINOTHALAMIC TRACT

• Pain is a complex sensation, in that a noxious stimulus leads not only to the perception of where it occurred but also to things such as a rapid increase in level of attention, emotional reactions, autonomic responses, and a greater likelihood that the event and its circumstances will be remembered. Corresponding to this complexity, multiple pathways convey nociceptive information rostrally from the spinal cord. One of them (the spinothalamic tract) is analogous to the posterior column–medial lemniscus pathway.

SPINOTHALAMIC TRACTS

Two main parts of the Spinothalamic Tract (STT)

• Lateral Spinothalamic Tract
• Transmission of pain and temperature
• Anterior Spinothalamic Tract
• Transmission of crude touch and firm pressure 

DAMAGE TO THE ANTEROLATERAL SYSTEM CAUSES DIMINUTION OF PAIN AND TEMPERATURE SENSATIONS

Examination:

Given the role of the spinothalamic tract, the patient should be screened for any abnormalities regarding their sense of touch, pain, temperature, and pressure sensation.

Screening for such abnormalities is commonly done using gentle pin pricks and cotton wool, to contrast between sharp and soft, following cutaneous sensory nerve root distributions. Hot and cold discrimination can be ascertained using the cold metal arm of a tuning fork, and a warm palm or heated object.

2 Minute Neuroscience: Pain & The Anterolateral System 

HAUSER ET AL. FIBROMYALGIA, 2015

• “Pain processing and its modulation: Activation of peripheral pain receptors (also called nociceptors) by noxious stimuli generates signals that travel to the dorsal horn of the spinal cord via the dorsal root ganglion. From the dorsal horn, the signals are carried along the ascending pain pathway or the spinothalamic tract to the thalamus and the cortex. Pain can be controlled by nociception- inhibiting and nociception-facilitating neurons. Descending signals originating in the supraspinal centers can modulate activity in the dorsal horn by controlling spinal pain transmission. CNS, central nervous system.”

SPINAL INFORMATION REACHES THE CEREBELLUM BOTH DIRECTLY AND INDIRECTLY

The spinal cord is an important source of information used by the cerebellum in the coordination of movement. This information reaches the cerebellar cortex and nuclei both directly, by way of spinocerebellar tracts, and indirectly, by way of relays in brainstem nuclei. A number of spinocerebellar tracts have been described, some representing the upper extremity and others the lower extremity. Only three have been well characterized.

Ascending Tracts | Spinocerebellar Tract

DESCENDING PATHWAYS INFLUENCE THE ACTIVITY OF LOWER MOTOR NEURONS

By RYAN CEDERMARK, DC DACNB RN BSN MSN

El Paso, TX. Chiropractor, Dr. Alexander Jimenez discusses the anatomy of nerve fibers, receptors, spinal tracts and brain pathways. Regions of the Central Nervous System (CNS) coordinate various somatic processes using sensory inputs and motor outputs of peripheral nerves. Important areas of the CNS that play a role in somatic processes are separated in the spinal cord brain stem. Sensory pathways that carry peripheral sensations to the brain are referred to an ascending pathway, or tract. Various sensory modalities follow specific pathways through the CNS. Somatosensory stimuli activate receptors in the skin, muscles, tendons, and joints throughout the entire body. The somatosensory pathways are divided into two separate systems based on the location of the receptor neurons. Somatosensory stimuli from below the neck run along the sensory pathways of the spinal cord, and the somatosensory stimuli from the head and neck travel through cranial nerves.

ANATOMY OF RECEPTORS, NERVE FIBERS, SPINAL CORD TRACTS AND BRAINSTEM PATHWAYS

RECEPTORS AND RECEPTOR BASED THERAPY

NEURONS NEED THREE THINGS TO SURVIVE!

FUNCTIONAL NEUROLOGY KEY CONCEPTS

The cell needs three things to survive.

• Oxygen, glucose and stimulation.
• Stimulation = Chiropractic, exercise, etc.
• Stimulation leads to neuronal growth
• Neuronal growth leads to plasticity
• Subluxations alter the frequency of firing of neurons
• Activation of one side will stimulate ipsilateral cerebellum and contralateral cortex (usually)
• Proper stimulation CAN reduce pain.

CHIROPRACTIC IS RECEPTOR-BASED THERAPY

INTRODUCTION

• The ongoing activity and output of the CNS are greatly influenced, and sometimes more or less determined, by incoming sensory information.
• The basis of this incoming sensory information is an array of sensory receptors, cells that detect various stimuli and produce receptor potentials in response, often with astonishing effectiveness.
• The health of the neuron, however, plays a huge role in how neurons can produce receptor potentials, the endurance of the neuron and the ability to create plasticity.
• ”Neurons that fire together, wire together.” Hebbian Theory

TYPES OF RECEPTORS

• Chemoreceptors
• Smell, taste, interoceptors
• Thermoreceptors
• Temperature
• Mechanoreceptors
• Cutaneous receptors for touch, auditory, vestibular, proprioceptors
• Nociceptors
• Pain

PARTS OF RECEPTORS

Although their morphologies vary widely, all receptors have three general parts:

1. Receptive Area
2. Area Rich In Mitochondria

• Health of the neurons within the receptors will determine its response to stimulation

3. Synaptic Area To Pass Messages To The CNS

RECEPTIVE FIELDS

• These are particular areas in the periphery where application of an adequate stimulus causes the receptors to respond.
• Neurons in successive levels of sensory pathways (second- order neurons, thalamic and cortical neurons-also have receptive fields, although they may be considerably more elaborate than those of the receptors.

TRANSDUCTION

Sensory receptors use ionotropic and metabotropic mechanisms to produce receptor potentials

• Sensory receptors transduce some physical stimulus into an electrical signal – a receptor potential – that the nervous system can understand.
• Sensory receptors are similar to postsynaptic membranes as their adequate stimuli are analogous to neurotransmitters. 

THE DIAMETER OF A NERVE FIBER IS CORRELATED WITH ITS FUNCTION

BIGGER = FASTER

Larger fibers conduct action potentials faster than do smaller fibers.

• Aα fibers are the largest and most rapidly conducting myelinated fibers.
• The slowest conducting fibers of the body are the C fibers

RECEPTORS IN MUSCLES AND JOINTS DETECT MUSCLE STATUS AND LIMB POSITION

MUSCLE SPINDLES

Muscle spindles (Fig. 9-14) are long, thin stretch receptors scattered throughout virtually every striated muscle in the body.

• These muscle spindles sense muscle length and proprioception (“one’s own” perception).
• They are quite simple in principle, consisting of a few small muscle fibers with a capsule surrounding the middle third of the fibers.
• These fibers are called intrafusal muscle fibers (fusus is Latin for “spindle,” so intrafusal means “inside the spindle”), incontrast to the ordinary extrafusal muscle fibers (“outside the spindle”).
• The ends of the intrafusal fibers are attached to extrafusal fibers, so whenever the muscle is stretched, the intrafusal fibers are also stretched.
• The central region of each intrafusal fiber has few myofilaments and is noncontractile, but it does have one or more sensory endings applied to it.
• When the muscle is stretched, the central part of the intrafusal fiber is stretched, mechanically sensitive channels are distorted, the resulting receptor potential spreads to a nearby trigger zone, and a train of impulses ensues at each sensory ending.

GOLGI TENDON ORGANS

• Golgi tendon organs are spindle-shaped receptors found at the 
• junctions between muscles and tendons. They are similar to Ruffini endings in their basic organization, consisting of interwoven collagen bundles surrounded by a thin capsule (Fig. 9-16).
• Large sensory fibers enter the capsule and branch into fine processes that are inserted among the collagen bundles. Tension on the capsule along its long axis squeezes these fine processes, and the resulting distortion stimulates them.
• If tension is generated in a tendon by making its attached muscle contract, tendon organs are found to be much more sensitive and can actually respond to the contraction of just a few muscle fibers.
• Thus Golgi tendon organs very specifically monitor the tension generated by muscle contraction and come into play whe
• n fine adjustments in muscle tension need to be made (e.g., when handling a raw egg).
• Thus the mode of action of Golgi tendon organs is quite different from that of muscle spindles (Fig. 9-17). If a muscle contracts isometrically, tension is generated across its tendons, and the tendon organs signal this; however, the muscle spindles signal nothing because muscle length has not changed (assuming that the activity of the gamma motor neurons remains unchanged).
• In contrast, a relaxed muscle can be stretched easily, and the muscle spindles fire; the tendon organs, however, experience little tension and remain silent. A muscle, by virtue of these two types of receptors, can have its length and tension monitored simultaneously.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4668288/

https://www.ncbi.nlm.nih.gov/pubmed/23709641

By RYAN CEDERMARK, DC DACNB RN BSN MSN