Sensory loss

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Many types of sense loss occur due to a dysfunctional sensation process, whether it be ineffective receptors, nerve damage, or cerebral impairment. Unlike agnosia, these impairments are due to damages prior to the perception process.

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Vision loss

Degrees of vision loss vary dramatically, although the ICD-9 released in 1979 categorized them into three tiers: normal vision, low vision, and blindness. Two significant causes of vision loss due to sensory failures include media opacity and optic nerve diseases, although hypoxia and retinal disease can also lead to blindness. Most causes of vision loss can cause varying degrees of damage, from total blindness to a negligible effect. Media opacity occurs in the presence of opacities in the eye tissues or fluid, distorting and/or blocking the image prior to contact with the photoreceptor cells. Vision loss often results despite correctly functioning retinal receptors. Optic nerve diseases such as optic neuritis or retrobulbar neuritis lead to dysfunction in the afferent nerve pathway once the signal has been correctly transmitted from retinal photoreceptors.

Partial or total vision loss may affect every single area of a person's life. Though loss of eyesight may occur naturally with age, trauma to the eye or exposure to hazardous conditions may also cause this serious condition. Workers in virtually any field may be at risk of sustaining eye injuries through trauma or exposure. A traumatic eye injury occurs when the eye itself sustains some form of trauma, whether a penetrating injury such as a laceration or a non-penetrating injury such as an impact. Because the eye is a delicate and complex organ, even a slight injury may have a temporary or permanent effect on eyesight.

Hearing loss

Similarly to vision loss, hearing loss can vary from full or partial inability to detect some or all frequencies of sound which can typically be heard by members of their species. For humans, this range is approximately 20 Hz to 20 kHz at ~6.5 dB, although a 10 dB correction is often allowed for the elderly. [1] Primary causes of hearing loss due to an impaired sensory system include long-term exposure to environmental noise, which can damage the mechanoreceptors responsible for receiving sound vibrations, as well as multiple diseases, such as CMV or meningitis, which damage the cochlea and auditory nerve, respectively. [2]

Hearing loss may be gradual or sudden. Hearing loss may be very mild, resulting in minor difficulties with conversation, or as severe as complete deafness. The speed with which hearing loss occurs may give clues as to the cause. If hearing loss is sudden, it may be from trauma or a problem with blood circulation. A gradual onset is suggestive of other causes such as aging or a tumor. Associated neurological problems, such as tinnitus or vertigo, may indicate a problem with the nerves in the ear or brain. Hearing loss may be unilateral or bilateral. Unilateral hearing loss is most often associated with conductive causes, trauma, and acoustic neuromas. Pain in the ear is associated with ear infections, trauma, and obstruction in the canal.

Anosmia

Anosmia is the inability to perceive odor, or in other words a lack of functioning olfaction. Many patients may experience unilateral or bilateral anosmia.

A temporary loss of smell can be caused by a blocked nose or infection. In contrast, a permanent loss of smell may be caused by death of olfactory receptor neurons in the nose or by brain injury in which there is damage to the olfactory nerve or damage to brain areas that process smell. The lack of the sense of smell at birth, usually due to genetic factors, is referred to as congenital anosmia.

The diagnosis of anosmia as well as the degree of impairment can now be tested much more efficiently and effectively than ever before thanks to "smell testing kits" that have been made available as well as screening tests which use materials that most clinics would readily have. [3]

Many cases of congenital anosmia remain unreported and undiagnosed. Since the disorder is present from birth the individual may have little or no understanding of the sense of smell, hence are unaware of the deficit. [4]

Somatosensory loss

The somatosensory system is a complex sensory system made up of a number of different receptors, including thermoreceptors, nociceptors, mechanoreceptors and chemoreceptors. It also comprises essential processing centres, or sensory modalities, such as proprioception, touch, temperature, and nociception. The sensory receptors cover the skin and epithelia, skeletal muscles, bones and joints, internal organs, and the cardiovascular system.

While touch (also called tactile or tactual perception) is considered one of the five traditional senses, the impression of touch is formed from several modalities. In medicine, the colloquial term "touch" is usually replaced with "somatic senses" to better reflect the variety of mechanisms involved.

Insensitivity to somatosensory stimuli, such as heat, cold, touch, and pain, are most commonly a result of a more general physical impairment associated with paralysis. Damage to the spinal cord or other major nerve fiber may lead to a termination of both afferent and efferent signals to varying areas of the body, causing both a loss of touch and a loss of motor coordination. Other types of somatosensory loss include hereditary sensory and autonomic neuropathy, which consists of ineffective afferent neurons with fully functioning efferent neurons; essentially, motor movement without somatosensation. [5] Sensory loss can occur due to a minor nick or lesion on the spinal cord which creates a problem within the neurosystem. This can lead to loss of smell, taste, touch, sight, and hearing. In most cases it often leads to issues with touch. Sometimes people cannot feel touch at all while other times a light finger tap feels like someone has punched them. There are medications and therapies[ example needed ] that can help control the symptoms of sensory loss and deprivation.

Ageusia

Ageusia is the loss of taste, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami (meaning "pleasant/savory taste"). It is sometimes confused with anosmia (a loss of the sense of smell). Because the tongue can only indicate texture and differentiate between sweet, sour, bitter, salty, and umami, most of what is perceived as the sense of taste is actually derived from smell. True ageusia is relatively rare compared to hypogeusia (a partial loss of taste) and dysgeusia (a distortion or alteration of taste).

Tissue damage to the nerves that support the tongue can cause ageusia, especially damage to the lingual nerve and the glossopharyngeal nerve. The lingual nerve passes taste for the front two-thirds of the tongue and the glossopharyngeal nerve passes taste for the back third of the tongue. The lingual nerve can also be damaged during otologic surgery, causing a feeling of metal taste.

Taste loss can vary from true ageusia, a complete loss of taste, to hypogeusia, a partial loss of taste, to dysgeusia, a distortion or alteration of taste. The primary cause of ageusia involves damage to the lingual nerve, which receives the stimuli from taste buds for the front two-thirds of the tongue, or the glossopharyngeal nerve, which acts similarly for the back third. Damage may be due to neurological disorders, such as Bell’s palsy or multiple sclerosis, as well as infectious diseases such as meningoencephalopathy. Other causes include a vitamin B deficiency, as well as taste bud death due to acidic/spicy foods, radiation, and/or tobacco use. [6]

Dual sensory loss and psychological impact

Dual sensory loss is the simultaneous loss of two senses. Research has shown that 6% of non-institutionalized older adults had a dual sensory impairment, and 70% of severely visually impaired older adults additionally suffered from significant hearing loss. [7] Vision and hearing loss both interfere with the interpretation and comprehension of speech. People with sensory loss often have problems communicating. Personal, situational and environmental factors can also become prohibitive barriers to communication.

Poor communication frequently results in poor psychosocial functioning. Older adults with sensory loss often find it difficult to adapt to their sensory loss, becoming depressed, anxious, lethargic, and dissatisfied. Thus, sensory loss, the inability to communicate, and poor psychosocial functioning reduces quality of life and well-being. [7]

See also

Related Research Articles

<span class="mw-page-title-main">Cranial nerves</span> Nerves that emerge directly from the brain and the brainstem

Cranial nerves are the nerves that emerge directly from the brain, of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck, including the special senses of vision, taste, smell, and hearing.

<span class="mw-page-title-main">Olfactory nerve</span> Cranial nerve I, for smelling

The olfactory nerve, also known as the first cranial nerve, cranial nerve I, or simply CN I, is a cranial nerve that contains sensory nerve fibers relating to the sense of smell.

<span class="mw-page-title-main">Trigeminal nerve</span> Cranial nerve responsible for the faces senses and motor functions

In neuroanatomy, the trigeminal nerve (lit. triplet nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial 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, from Latin tri- 'three', and -geminus 'twin') 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.

<span class="mw-page-title-main">Glossopharyngeal nerve</span> Cranial nerve IX, for the tongue and pharynx

The glossopharyngeal nerve, also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior to the vagus nerve. Being a mixed nerve (sensorimotor), it carries afferent sensory and efferent motor information. The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, whereas the sensory division originates from the cranial neural crest.

<span class="mw-page-title-main">Sensory nervous system</span> Part of the nervous system

The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons, neural pathways, and parts of the brain involved in sensory perception and interoception. Commonly recognized sensory systems are those for vision, hearing, touch, taste, smell, balance and visceral sensation. Sense organs are transducers that convert data from the outer physical world to the realm of the mind where people interpret the information, creating their perception of the world around them.

<span class="mw-page-title-main">Somatic nervous system</span> Part of the peripheral nervous system

The somatic nervous system (SNS) is made up of nerves that link the brain and spinal cord to voluntary or skeletal muscles that are under conscious control as well as to skin sensory receptors. Specialized nerve fiber ends called sensory receptors are responsible for detecting information within and outside of the body.

<span class="mw-page-title-main">Afferent nerve fiber</span> Axonal projections that arrive at a particular brain region

Afferent nerve fibers are axons of sensory neurons that carry sensory information from sensory receptors to the central nervous system. Many afferent projections arrive at a particular brain region.

Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation. All sensory modalities work together to heighten stimuli sensation when necessary.

<span class="mw-page-title-main">Olfactory system</span> Sensory system used for smelling

The olfactory system or sense of smell is the sensory system used for smelling (olfaction). Olfaction is one of the special senses, that have directly associated specific organs. Most mammals and reptiles have a main olfactory system and an accessory olfactory system. The main olfactory system detects airborne substances, while the accessory system senses fluid-phase stimuli.

<span class="mw-page-title-main">Sensory neuron</span> Nerve cell that converts environmental stimuli into corresponding internal stimuli

Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded receptor potentials. This process is called sensory transduction. The cell bodies of the sensory neurons are located in the dorsal ganglia of the spinal cord.

Neuralgia is pain in the distribution of a nerve or nerves, as in intercostal neuralgia, trigeminal neuralgia, and glossopharyngeal neuralgia.

Ageusia is the loss of taste functions of the tongue, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami. It is sometimes confused with anosmia – a loss of the sense of smell. Because the tongue can only indicate texture and differentiate between sweet, sour, bitter, salty, and umami, most of what is perceived as the sense of taste is actually derived from smell. True ageusia is relatively rare compared to hypogeusia – a partial loss of taste – and dysgeusia – a distortion or alteration of taste.

In medicine and anatomy, the special senses are the senses that have specialized organs devoted to them:

<span class="mw-page-title-main">Lingual nerve</span> Human nerve relaying sense to the tongue

The lingual nerve carries sensory innervation from the anterior two-thirds of the tongue. It contains fibres from both the mandibular division of the trigeminal nerve (CN V3) and from the facial nerve (CN VII). The fibres from the trigeminal nerve are for touch, pain and temperature (general sensation), and the ones from the facial nerve are for taste (special sensation).

<span class="mw-page-title-main">Cranial nerve examination</span> Type of neurological examination

The cranial nerve exam is a type of neurological examination. It is used to identify problems with the cranial nerves by physical examination. It has nine components. Each test is designed to assess the status of one or more of the twelve cranial nerves (I-XII). These components correspond to testing the sense of smell (I), visual fields and acuity (II), eye movements and pupils, sensory function of face (V), strength of facial (VII) and shoulder girdle muscles (XI), hearing and balance, taste, pharyngeal movement and reflex, tongue movements (XII).

Dysosmia is a disorder described as any qualitative alteration or distortion of the perception of smell. Qualitative alterations differ from quantitative alterations, which include anosmia and hyposmia. Dysosmia can be classified as either parosmia or phantosmia. Parosmia is a distortion in the perception of an odorant. Odorants smell different from what one remembers. Phantosmia is the perception of an odor when no odorant is present. The cause of dysosmia still remains a theory. It is typically considered a neurological disorder and clinical associations with the disorder have been made. Most cases are described as idiopathic and the main antecedents related to parosmia are URTIs, head trauma, and nasal and paranasal sinus disease. Dysosmia tends to go away on its own but there are options for treatment for patients that want immediate relief.

<span class="mw-page-title-main">Gustatory nucleus</span> Rostral part of the solitary nucleus located in the medulla

The gustatory nucleus is the rostral part of the solitary nucleus located in the medulla. The gustatory nucleus is associated with the sense of taste and has two sections, the rostral and lateral regions. A close association between the gustatory nucleus and visceral information exists for this function in the gustatory system, assisting in homeostasis - via the identification of food that might be possibly poisonous or harmful for the body. There are many gustatory nuclei in the brain stem. Each of these nuclei corresponds to three cranial nerves, the facial nerve (VII), the glossopharyngeal nerve (IX), and the vagus nerve (X) and GABA is the primary inhibitory neurotransmitter involved in its functionality. All visceral afferents in the vagus and glossopharyngeal nerves first arrive in the nucleus of the solitary tract and information from the gustatory system can then be relayed to the thalamus and cortex.

Hereditary sensory and autonomic neuropathy (HSAN) or hereditary sensory neuropathy (HSN) is a condition used to describe any of the types of this disease which inhibit sensation.

A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of stimuli. Although, in some cultures, five human senses were traditionally identified as such, many more are now recognized. Senses used by non-human organisms are even greater in variety and number. During sensation, sense organs collect various stimuli for transduction, meaning transformation into a form that can be understood by the brain. Sensation and perception are fundamental to nearly every aspect of an organism's cognition, behavior and thought.

The following outline is provided as an overview of and topical guide to the human brain:

References

  1. ↑ Hawkins, S. (2010). "Phonological features, auditory objects, and illusions". Journal of Phonetics. 38 (1): 60–89. doi:10.1016/j.wocn.2009.02.001.
  2. ↑ Bizley, J. K.; Walker, K. M. M. (2010). "Sensitivity and Selectivity of Neurons in Auditory Cortex to the Pitch, Timbre, and Location of Sounds". Neuroscientist. 16 (4): 453–469. doi:10.1177/1073858410371009. PMID   20530254. S2CID   5931412.
  3. ↑ Craig JC (1999). "Grating orientation as a measure of tactile spatial acuity". Somatosensory & Motor Research . 16 (3): 197–206. doi:10.1080/08990229970456. PMID   10527368.
  4. ↑ Stevens, Joseph C.; Alvarez-Reeves, Marty; Dipietro, Loretta; Mack, Gary W.; Green, Barry G. (September 2003). "Decline of tactile acuity in aging: a study of body site, blood flow, and lifetime habits of smoking and physical activity". Somatosensory & Motor Research. 20 (3–4): 271–279. doi:10.1080/08990220310001622997. PMID   14675966. S2CID   19729552.
  5. ↑ Li, X. (1976). "Acute Central Cord Syndrome Injury Mechanisms and Stress Features". Spine. 35 (19): E955–E964. doi:10.1097/brs.0b013e3181c94cb8. PMID   20543769. S2CID   36635584.
  6. ↑ Macaluso, E. (2010). "Orienting of spatial attention and the interplay between the senses. [Review]". Cortex. 46 (3): 282–297. doi:10.1016/j.cortex.2009.05.010. PMID   19540475. S2CID   2762445.
  7. 1 2 Heine, C.; Browning, C. J. (2002-01-01). "Communication and psychosocial consequences of sensory loss in older adults: overview and rehabilitation directions". Disability and Rehabilitation. 24 (15): 763–773. doi:10.1080/09638280210129162. ISSN   0963-8288. PMID   12437862. S2CID   32915734.
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