Stereognosis

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Stereognosis (also known as haptic perception or tactile gnosis) is the ability to perceive and recognize the form of an object in the absence of visual and auditory information, by using tactile information to provide cues from texture, size, spatial properties, and temperature, etc. [1] In humans, this sense, along with tactile spatial acuity, vibration perception, texture discrimination and proprioception, is mediated by the dorsal column-medial lemniscus pathway of the central nervous system. Stereognosis tests determine whether or not the parietal lobe of the brain is intact. [2] Typically, these tests involved having the patient identify common objects (e.g. keys, comb, safety pins) placed in their hand without any visual cues. [3] Stereognosis is a higher cerebral associative cortical function. [4] : 71 

Astereognosis is the failure to identify or recognize objects by palpation in the absence of visual or auditory information, even though tactile, proprioceptive, and thermal sensations may be unaffected. [5] It may be caused by disease of the sensory cortex or posterior columns. [6] People suffering from Alzheimer's disease show a reduction in stereognosis. [7] Astereognosis can be caused by damage to the posterior association areas of the parietal, temporal, or occipital lobes, or the postcentral gyrus of either hemisphere. [5] For other types of dementia, stereognosis does not appear to decline.

Mechanism of neural pathway

The dorsal column medial lemniscus pathway is responsible for relaying sensory information regarding proprioception, vibration, and fine touch. [8] First order neurons carry sensory information from proprioceptive and tactile receptors to the medulla oblongata where they synapse in either the medullary gracilus or cuneate nuclei. Information carried from regions above spinal level T6 synapse at the cuneate nuclei, while information carried from T6 and below synapse at the gracilus nuclei. At this point, second order neurons decussate and relay information through the contralateral medial lemniscus to the thalamus. At the thalamus, second order neurons synapse with third order neurons, which continue through the internal capsule to the primary sensory cortex of the post central gyrus where the tract terminates. [8] Stereognosis determines whether or not this tract is properly functioning. [9]

An individual who cannot properly identify an object using stereognosis, could suffer from lesions in nerve roots, peripheral nerves, the spinal cord, thalamus, or primary sensory cortex. [10] Because the dorsal column medial lemniscus pathway travels through and relays information to these areas, a lack of proper sensation indicates a problem with this neural sensory tract. Administered tests and recognition of pattern sensory loss can identify lesions in particular nerves or areas. [10]

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Pronator quadratus is a square-shaped muscle on the distal forearm that acts to pronate the hand.

Brainstem Posterior part of the brain, adjoining and structurally continuous

The brainstem is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is continuous with the thalamus of the diencephalon through the tentorial notch, and sometimes the diencephalon is included in the brainstem.

Trigeminal nerve Cranial nerve responsible for sensory perception and motor functions of the face

The trigeminal nerve (the fifth cranial nerve, or simply CN V) is a nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves. Its name ("trigeminal" = tri-, or three, and - geminus, or twin: thrice-twinned) derives from each of the two nerves (one on each side of the pons) having three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory (or "cutaneous") functions. Adding to the complexity of this nerve is that autonomic nerve fibers as well as special sensory fibers (taste) are contained within it.

Spinothalamic tract Sensory pathway from the skin to the thalamus

The spinothalamic tract is a sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the somatosensory cortex of the postcentral gyrus.

Dorsal column–medial lemniscus pathway

The dorsal column–medial lemniscus pathway (DCML) is a sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception (position) from the skin and joints. It transmits information from the body to the primary somatosensory cortex in the postcentral gyrus of the parietal lobe of the brain. The pathway receives information from sensory receptors throughout the body, and carries this in nerve tracts in the white matter of the dorsal columns of the spinal cord to the medulla, where it is continued in the medial lemniscus, on to the thalamus and relayed from there through the internal capsule and transmitted to the somatosensory cortex. The name dorsal-column medial lemniscus comes from the two structures that carry the sensory information: the dorsal columns of the spinal cord, and the medial lemniscus in the brainstem.

Medial lemniscus

The medial lemniscus, also known as Reil's band or Reil's ribbon, is a large ascending bundle of heavily myelinated axons that decussate in the brainstem, specifically in the medulla oblongata. The medial lemniscus is formed by the crossings of the internal arcuate fibers. The internal arcuate fibers are composed of axons of nucleus gracilis and nucleus cuneatus. The axons of the nucleus gracilis and nucleus cuneatus in the medial lemniscus have cell bodies that lie contralaterally.

Primary somatosensory cortex

The primary somatosensory cortex is located in the postcentral gyrus, and is part of the somatosensory system. It was initially defined from surface stimulation studies of Wilder Penfield, and parallel surface potential studies of Bard, Woolsey, and Marshall. Although initially defined to be roughly the same as Brodmann areas 3, 1 and 2, more recent work by Kaas has suggested that for homogeny with other sensory fields only area 3 should be referred to as "primary somatosensory cortex", as it receives the bulk of the thalamocortical projections from the sensory input fields.

Spinocerebellar tract

The spinocerebellar tract is a nerve tract originating in the spinal cord and terminating in the same side (ipsilateral) of the cerebellum.

Posterior thoracic nucleus

The posterior thoracic nucleus, is a group of interneurons found in the medial part of lamina VII, also known as the intermediate zone, of the spinal cord. It is mainly located from the cervical vertebra C7 to lumbar L3-L4 levels and is an important structure for proprioception of the lower limb.

Internal arcuate fibers

The internal arcuate fibers or internal arcuate tract are the axons of second-order sensory neurons that compose the gracile and cuneate nuclei of the medulla oblongata. These second-order neurons begin in the gracile and cuneate nuclei in the medulla. They receive input from first-order sensory neurons, which provide sensation to many areas of the body and have cell bodies in the dorsal root ganglia of the dorsal root of the spinal nerves. Upon decussation from one side of the medulla to the other, also known as the sensory decussation, they are then called the medial lemniscus.

Dorsal column nuclei

In neuroanatomy, the dorsal column nuclei are a pair of nuclei in the dorsal columns in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are present at the junction between the spinal cord and the medulla oblongata. Both nuclei contain second-order neurons of the dorsal column-medial lemniscus pathway, which carries fine touch and proprioceptive information from the body to the brain. Each nucleus has an associated nerve tract, the gracile fasciculus and the cuneate fasciculus.

Sensory decussation

The sensory decussation or decussation of the lemnisci is a decussation or crossover of axons from the gracile nucleus and cuneate nucleus, which are responsible for fine touch, vibration, proprioception and two-point discrimination of the body. The fibres of this decussation are called the internal arcuate fibres and are found at the superior aspect of the closed medulla superior to the motor decussation. It is part of the second neuron in the posterior column–medial lemniscus pathway.

Cutaneous innervation refers to the area of the skin which is supplied by a specific cutaneous nerve.

The ventral trigeminal tract, ventral trigeminothalamic tract, anterior trigeminal tract, or anterior trigeminothalamic tract, is a tract composed of second order neuronal axons. These fibers carry sensory information about discriminative and crude touch, conscious proprioception, pain, and temperature from the head, face, and oral cavity. The ventral trigeminal tract connects the two major components of the brainstem trigeminal complex – the principal, or main sensory nucleus and the spinal trigeminal nucleus, to the ventral posteromedial nucleus of the thalamus.

The trigeminal lemniscus, also called the trigeminothalamic tract, is composed of the ventral trigeminal tract, and the dorsal trigeminal tract – nerve tracts that convey tactile, pain, and temperature impulses from the skin of the face, the mucous membranes of the nasal and oral cavities, and the eye, as well as proprioceptive information from the facial and masticatory muscles.

Pallesthesia, or vibratory sensation, is the ability to perceive vibration. This sensation, often conducted through skin and bone, is usually generated by mechanoreceptors such as Pacinian corpuscles, Merkel disk receptors, and tactile corpuscles. All of these receptors stimulate an action potential in afferent nerves found in various layers of the skin and body. The afferent neuron travels to the spinal column and then to the brain where the information is processed. Damage to the peripheral nervous system or central nervous system can result in a decline or loss of pallesthesia.

The dorsal trigeminal tract, dorsal trigeminothalamic tract, or posterior trigeminothalamic tract, is composed of second-order neuronal axons. These fibers carry sensory information about discriminative touch and conscious proprioception in the oral cavity from the principal nucleus of the trigeminal nerve to the ventral posteromedial (VPM) nucleus of the thalamus.

Somatosensory system Widely distributed parts of the sensory nervous system

The somatosensory system is a part of the sensory nervous system that is associated with the sense of touch, but includes parallel receptors and nerve pathways for the sensations of temperature, body position and movement, and pain. This complex system of sensory neurons, and neural pathways responds to changes at the surface of, or inside, the body. The axons of sensory neurons connect with, or respond to, various receptor cells. These sensory receptor cells are activated by different stimuli such as heat and nociception, giving a functional name to the responding sensory neuron, such as a thermoreceptor which carries information about temperature changes. Other receptor types include mechanoreceptors, chemoreceptors, and nociceptors which send signals along a sensory nerve to the spinal cord, where the signals may be processed by other sensory neurons, and then relayed to the brain for further processing. Sensory receptors are found all over the body including the skin, epithelial tissues, muscles, bones and joints, internal organs, and the cardiovascular system.

Spinal cord Long, tubular central nervous system structure in the vertebral column

The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord, which contains cerebrospinal fluid. The brain and spinal cord together make up the central nervous system (CNS). In humans, the spinal cord begins at the occipital bone, passing through the foramen magnum and entering the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae, where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) long in adult men and around 43 cm (17 in) long in adult women. The diameter of the spinal cord ranges from 13 mm in the cervical and lumbar regions to 6.4 mm in the thoracic area.

References

  1. ↑ Yekutiel, M., Jariwala, M., & Stretch, P. (1994). Sensory deficit in the hands of children with cerebral palsy: a new look at assessment and prevalence. Dev Med Child Neurol, 36:61-24.
  2. ↑ Silvestri: Saunders Comprehensive Review for the NCLEX-RN Exam
  3. ↑ Unsworth, C.A. (2007). Cognitive and Perceptual Dysfunction. In S.B. O'Sullivan & T.J. Schmitz (Eds.), Physical Rehabilitation, 5th ed. (pp. 1180-1181). Philadelphia: F.A. Davis Company.
  4. ↑ Blumenfield, Hal (2002). Neuroanatomy Through Clinical Cases. Sunderland, MA: Sinauer. ISBN   0-87893-060-4.
  5. 1 2 Mauguiere, F., Desmedt, J.E., & Courjon, J. (1983). Astereognosis and dissociated loss of frontal or parietal components of somatosensory evoked potentials in hemispheric lesions. Brain, 106:271-311.
  6. ↑ Bickley, Lynn; Szilagui, Peter (2007). Bates' Guide to Physical Examination and History Taking (9th ed.). Lippincott Williams & Wilkins. ISBN   0-7817-6718-0.
  7. ↑ F. J. Huff; J. T. Becker; S. H. Belle; R. D. Nebes; A. L. Holland; F. Boller (1987). "Cognitive deficits and clinical diagnosis of Alzheimer's disease". Neurology. 37 (1119): 1119–24. doi:10.1212/wnl.37.7.1119. PMID   3601078.
  8. 1 2 "The Ascending Tracts." Teach Me Anatomy. Teachmeanatomy.info, 1 Sept. 2016. Web.
  9. ↑ Irving, John B. "Stereognosis." RES MEDICA: Journal of the Royal Medical Society 6.2 (1968): 23-27. Journals.ed.ac.uk. Res Medica. Web.
  10. 1 2 Blumenfeld, Hal, MD, PhD. "Cortical Sensation, Including Extinction." Neuroanatomy through Clinical Cases. Hal Blumenfeld, n.d. Web.


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