Proprioception Case File

Proprioception Case File

EUGENE C.TOY, MD, RAHUL JANDIAL, MD, PhD, EVAN YALE SNYDER, MD, PhD, MARTIN T. PAUKERT, MD

CASE 18

An 18-year-old female, who is wheel-chair bound, states that since she was a 9-year-old girl, she began to suffer from an irregular, staggering gait with frequent falls. Over the next several years, her upper extremity coordination deteriorates. She later develops weakness during her teenage years. Physical examination reveals abnormal eye movements, slow and poorly coordinated movements of all her extremities, and severe weakness of her legs. She has deficits in position sense, vibratory sense, pain, and tactile discrimination. Her deep tendon reflexes are absent. Hypertrophic cardiomyopathy was reported, and she is subsequently diagnosed with Friedreich ataxia.

• What is the mechanism of this disease pathology?
• Which pathways are involved?
• What are the sensory modalities lost with each pathway?

ANSWERS TO CASE 18: PROPRIOCEPTION

Summary: An 18 year old female has progressive ataxia, lower extremity weakness, loss of coordination of extremities and eye movements. Examination reveals loss of position sense, vibratory sense, pain and tactile discrimination. She is diagnosed with Friedreich ataxia.

• Mechanism: The degeneration of nerve tissue in the spinal cord and of nerves that control muscle movement in the arms and legs is the ataxia encountered in Friedreich ataxia. What results is the thinning of the spinal cord, and the loss of myelin sheaths in many neurons. The leading theory about the pathogenesis of the disease implicates an overaccumulation of iron in mitochondria, leading to cellular damage and death by the production of free radicals in neurons of the central nervous system (CNS) and peripheral nervous system (PNS).
• Involved pathways: This disorder leads to progressive degeneration of the dorsal root ganglia with secondary degeneration of the dorsal and ventral spinocerebellar tracts, medial lemniscal system, spinothalamic tract, and lateral cervical system. The corticospinal pathways are also affected.
• Sensory modalities lost: The dorsal and ventral spinocerebellar tract conveys proprioceptive, sense of balance and self, information from the body to the cerebellum. The medial lemniscal system conveys somatic, specialized touch, pressure, vibration, and joint receptors, and proprioceptive information from the body to the cerebral cortex. The spinothalamic tract conveys somatosensory information including nociception (pain), temperature, itch, and crude touch to the thalamus. The corticospinal tract conveys motor information from the cerebral cortex of the brain to the spinal cord in response to information generated from all different sensory pathways.

CLINICAL CORRELATION

Friedreich ataxia is the most common of the recessively hereditary ataxias. This disorder is characterized by a degeneration of neurons which begins in the periphery, with ultimate loss of neurons and a secondary scarring process, also known as gliosis. Large myelinated axons in peripheral nerves are affected progressively with age and duration of the disease. Unmyelinated fibers in sensory roots and peripheral sensory nerves are spared. The posterior columns, corticospinal, ventral, and lateral spinocerebellar tracts are all affected by demyelination. The dorsal root ganglia shrink and eventually show disappearance of neurons. The posterior column degeneration accounts for the loss of position and vibration senses and the sensory ataxia. Absent tendon reflexes in the legs occur as a result of loss of afferent fibers from muscle spindle receptors. The progressive degeneration of the corticospinal pathway leads to limb weakness. While research in this area is progressing, there is currently no effective treatment available.

APPROACH TO PROPRIOCEPTION

Objectives

1. Be familiar with the CNS pathways that convey proprioceptive information.
2. Understand the clinical symptoms that result from a lesion to the dorsal column pathways.

Definitions

Kinesthesia: The sense of movement.

Astereognosis: Loss or impairment of the ability to recognize common objects by touching or handling them without visual input.

Romberg test: A test in which the patient stands with feet placed closely together and eyes closed. A positive test results if the body sways abnormally or there is loss of balance, indicating a deficiency in conscious recognition of muscle and joint position.

Golgi tendon organ: A proprioceptive sensory receptor located in muscle fibers and tendons.

Medial lemniscal system: The pathway carrying proprioceptive information to the cerebral cortex involving position sense, kinesthesia, and tactile discrimination.

DISCUSSION

Two sets of sensory pathways in the spinal cord provide important information to the brain regarding muscle action, joint position, and the objects with which a person is in contact. One of these sets of pathways projects to the cerebellum, where the information is processed for the coordination of movement, but not for conscious perception. These pathways include the dorsal and ventral spinocerebellar tracts, the cuneocerebellar tract, and the rostral spinocerebellar tract. The second set of pathways consists of three tracts that project to the cerebral cortex by way of the thalamus. This information is perceived consciously. These are the spinal lemniscus, the spinothalamic tract, and the lateral cervical system. Both sets of sensory receptors receive information from mechanoreceptors.

Mechanoreceptors located in the muscles, joints, and skin mediate the various separate and integrated sensations of proprioception, touch, and tactile discrimination. Mechanoreceptors consist of Golgi tendon organs, pacinian corpuscles, Meissner corpuscles, Ruffini corpuscles, Merkel complexes, and free nerve endings in muscles, tendons, ligaments, joint capsules, and skin. Information about static limb position is carried mainly through muscle spindle afferents. Kinesthetic information is mediated by a combination of joint receptor afferents and receptors in the skin, muscles, and joints.

Pacinian corpuscles, found in the skin and connective tissue, detect vibration. Meissner corpuscles detect superficial phasic touch. The movement of hairs is detected by free nerve endings in hair follicles and also conveys a sense of touch. Contrastingly, Ruffini corpuscles detect skin stretch. Merkel’s complexes are specialized epithelial cells that detect fine touch information. Most of the mechanoreceptors are innervated by large-diameter myelinated fibers. The free nerve endings are exceptions; as their cell bodies are located in the dorsal root ganglia, and their central processes enter the medial side of the dorsal root zone. These nerve endings detect pain and temperature. Afferent fibers from mechanoreceptors enter the spinal cord and distribute either to the interneurons and motoneurons in the ventral horn, the neurons in the dorsal and intermediate gray areas where ascending pathways originate, or to the neurons of the dorsal column nuclei in the medulla (see Table 18-1).

The ventral and dorsal spinocerebellar tracts carry proprioceptive and other somatosensory stimuli from the lower limbs to the cerebellum. Proprioceptive sensation is the perception of the relative position of the parts of the body. Unlike the other sensory systems that allow us to perceive the world outside our body, proprioception provides feedback information about the body itself. It consists of both static limb position and kinesthesia, or the sensation of motion. Some proprioceptive fiber collaterals from Golgi tendon organs synapse with neurons in the intermediate gray area and the base of the posterior horn of the spinal cord. At the lumbar and sacral levels of the spinal cord, these neurons give rise to the primarily crossed ventral spinocerebellar tract. This is the most peripheral tract in the ventral margin of the lateral funiculus.

The nucleus dorsalis, or Clarke nucleus, is located at the base of the posterior horn in spinal segments T1 through L2. This column of neurons receives afferents from muscle spindles, cutaneous touch receptors, and joint receptors. The axons of these neurons ascend rostrally and ipsilaterally as the dorsal spinocerebellar tract just posterior to the ventral spinocerebellar tract in the lateral funiculus. While the proprioceptive afferents traveling from dorsal roots T1 to L2 synapse in the nucleus dorsalis at the level where they enter the spinal cord, the corresponding afferents from dorsal roots L3 through S5 ascend first in the fasciculus gracilis of the dorsal funiculus to reach the nucleus dorsalis. They synapse there at levels L1 and L2, which becomes the most caudal level of the dorsal spinocerebellar tract.

The cuneocerebellar tract and the rostral spinocerebellar tract carry information from mechanoreceptors in the upper extremities to the cerebellum. Afferent fibers from C2 to T5 travel rostrally in the dorsal funiculus in the fasciculus cuneatus before synapsing on neurons in the accessory cuneate nucleus in the lower medulla. This is the upper extremity counterpart of the nucleus dorsalis and gives rise to the ipsilateral cuneocerebellar tract or dorsal arcuate fibers. This tract also mediated information from muscle spindles, cutaneous touch receptors, and joint receptors.

The rostral spinocerebellar tract is the upper-extremity tract that corresponds to the ventral spinocerebellar tract. It originates in the cervical enlargement of the intermediate zone of the spinal cord gray area. After projecting to the cerebellum, the tract synapses with fibers of the ventral spinocerebellar tract.

All of the ascending fibers from the dorsal spinocerebellar, cuneocerebellar, and rostral spinocerebellar pathways enter the cerebellum through the inferior cerebellar peduncle. The ventral spinocerebellar tract, however, travels through the pons prior to entering the cerebellum through the superior cerebellar peduncle. These four tracts terminate primarily in the midline vermis and intermediate zone of the cerebellum ipsilateral to the cells of origin. There is also a significant projection to the anterior lobe and posterior lobe of the cerebellum that contributes to standing and walking.

Proprioceptive information regarding position sense, kinesthesia, and tactile discrimination are carried to the cerebral cortex by afferent fibers from muscle spindles, Golgi tendon organs, and mechanoreceptors in joints and skin by way of the medial lemniscal system. This information contributes to conscious position as well as movement sense. The posterior funiculus consists of two large bundles of fibers called fasciculi. Fibers from the leg ascend as the fasciculus gracilis adjacent to the dorsal median septum. Fibers from the arm ascend lateral to the leg fibers as the fasciculus cuneatus. The fibers of the posterior funiculus maintain somatotopic organization in relation to one another. The fasciculus cuneatus terminates in the lower medulla in the nucleus cuneatus. Similarly, the fasciculus gracilis terminates in the nucleus gracilis, also in the lower medulla. These tracts are frequently referred to as the dorsal column pathways. A portion of the fibers of the medial lemniscal system travel with the lateral cervical system in the dorsal part of the lateral funiculus. The dorsolateral pathway can also be used to describe the entire lemniscal pathway of the spinal cord.

The cells of the dorsal column nuclei give rise to the internal arcuate fibers which cross to the contralateral side of the medulla in the decussation of the medial lemniscus. From here they ascend as the medial lemniscus to the thalamus and terminate in the ventral posterolateral nucleus (VPL). The somatotopic organization of the fibers is maintained in both the medial lemniscus and VPL. Thalamocortical fibers from the VPL continue on to the postcentral gyrus of the parietal lobe and terminate in the primary somatosensory cortex. This cortex maintains a topographic representation of the body that is similar to that of the parallel motor strip on the opposite side of the central sulcus.

The spinal lemniscus system mediates the sense of limb position and movement, the sense of steady joint angles, the sense of motion produced by active muscular contraction or passive movement, the sense of tension exerted by contracting muscles, and the sense of effort. Cortical processing is necessary for the conscious recognition of body and limb posture. The lemniscal pathways also provide important information regarding the place, intensity, and temporal and spatial patterns of neural activity evoked by mechanical stimulation of the skin. This same pathway to the cortex, therefore, is necessary for discriminative tactile sensation and vibration sense.

The lateral cervical system responds to light mechanical stimulation of the skin on the ipsilateral side of the body. This system is an alternate pathway to the information conveyed in the posterior column system, and its relevance in humans is not fully understood. The peripheral nerve fibers synapse in the dorsal horn throughout the length of the spinal cord. Heavily myelinated axons from second-order neurons arise in this lamina and ascend ipsilaterally in the dorsal corner of the lateral funiculus to terminate in the lateral cervical nucleus. Projections from this nucleus cross the spinal cord in the ventral white commissure to join the contralateral medial lemniscus and proceed with it to terminate in the thalamus. Information from here is projected to the somatic sensory areas of the cerebral cortex.

A bilateral interruption of the dorsolateral pathway in the spinal cord will result in complete loss of proprioceptive sensation. A lesion in this location will produce deficits in position sense, vibration sense, and tactile discrimination. A unilateral injury of a dorsolateral pathway will create ipsilateral symptoms. Lesions within the gracile and cuneate nuclei, the medial lemniscus, the thalamus, and the postcentral gyrus will create varying degrees of similar symptoms. A lesion of the lemniscal pathway preserve simple touch, pain, and temperature, but will disrupt proprioceptive sensation and result in the following symptoms: inability to recognize limb position, astereognosis or loss of ability to recognize common objects by touching them with the eyes closed, loss of two-point discrimination, loss of vibratory sense, a positive Romberg sign. In the Romberg test a patient stands with feet close together. The amount of sway is noted with the eyes open. The patient then closes the eyes and an abnormal increase in sway or loss of balance without visual input results in a positive sign. The visual system is able to partly compensate for the deficiency in recognition of muscle and joint positions, allowing patients with dorsolateral pathway lesions to maintain balance with their eyes open.

COMPREHENSION QUESTIONS

[18.1] A 63-year-old woman comes into your office for a routine physical examination. She notes that she has some occasional tingling in her feet and toes. You perform a complete neurological examination and find that she has reduced vibration sense in her great toe and at her ankle on both sides. Through which structure does the tract carrying this information to the brain pass?

A. Ventral horn of the spinal cord

B. Lateral funiculus

C. Medial lemniscus

D. Lateral lemniscus

[18.2] A 23-year-old man is brought into the emergency department by EMS, restrained and screaming that he feels bugs crawling all over his skin. A friend who is accompanying him reports that he has recently begun using cocaine quite heavily. The physician examines the patient and notes that there are in fact no bugs crawling on him, despite his claims. If there actually were bugs on him, which of the following sensory organs would most likely be responsible for the crawling sensation?

A. Meissner corpuscle

B. Pacinian corpuscle

C. Golgi tendon organ

D. Muscle spindle

[18.3] A 16-year-old female is brought into the emergency department following a motor vehicle collision in which she was ejected from the vehicle. She has a shard of metal sticking out of her back right in the midline at the level of T7. A CT scan of the back is obtained and on the CT the tip of the shard appears in the spinal canal, possibly in the area of the dorsal columns, slightly more to the left than the right. If the shard has injured the right dorsal column at T7, which of the following sensory defects would be expected?

A. Loss of proprioception in the left leg

B. Loss of proprioception in the right leg

C. Loss of pain sensation in the left leg

D. Loss of pain sensation in the right leg

Answers

[18.1] C. The sensation in question here, vibration, is transmitted via the dorsal column/medial lemniscal pathway. The sensation is detected by a pacinian corpuscle, which is innervated by a sensory neuron whose body is in the dorsal root ganglion. This neuron’s axon enters the cord via the dorsal horn, ascends the posterior column of the spinal cord all the way to the lower medulla where it synapses in the gracile nucleus (because it was from the lower body). From there the second-order neuron sends its axons across the midline to ascend in the contralateral medial lemniscus all the way to the ventral posterolateral nucleus (VPL) of the thalamus. From the thalamus the information is relayed to the sensory cortex where it is processed. In addition to vibration, discriminative touch and joint proprioception follow the same pathway. The lateral lemniscus is a tract in the brainstem involved in the relay of auditory information.

[18.2] A. The sensory organ responsible for registering light touch is the Meissner corpuscle. The pacinian corpuscle is responsible for registering vibration, the Golgi tendon organ measures muscle tension, and the muscle spindle registers muscle fiber length. All of these organs are part of the dorsal column/medial lemniscal system, and are innervated by large diameter–myelinated nerve fibers.

[18.3] B. In this scenario, the patient would lose proprioception in the right leg. The dorsal columns transmit the signals for discriminative touch, vibration, and proprioception. A lesion to one of these columns will cause a loss of all of these sensations below the level of the lesion on the ipsilateral side. The sensation loss will be ipsilateral because the fibers of the pathway do not decussate until after they have synapsed in the nuclei gracilis and cuneatus in the lower medulla.

NEUROSCIENCE PEARLS ❖ Proprioceptive information is carried from mechanoreceptors located in the muscles, joints, and skin. ❖ The medial lemniscal pathway is located in the dorsolateral region of the spinal cord and carries position, movement, touch, pressure, and vibratory information. ❖ Injuries to the lemniscal pathway can result in inability to recognize limb position, astereognosis, and a positive Romberg sign.

REFERENCES

Buck LB. The bodily senses. In: Kandel ER, et al, ed. Principles of Neural Science. 4th ed. New York: McGraw-Hill; 2000. 

Martin JH. The somatic sensory system. Neuroanatomy, Text and Atlas. 2nd ed. Stamford, CT: Appleton and Lange; 1996. 

Ropper AH, et al. Degenerative diseases of the nervous system. In: Adam and Victor’s Principles of Neurology. 8th ed. New York: McGraw-Hill; 2005.

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