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Pathophysiology · Chapter 28. Standard forms of pathology of the nervous system

Sensory disorders

Sensory disorders are typical pathological conditions in which the body's ability to adequately perceive stimuli is impaired. They are classified according to three main criteria: type, intensity, and adequacy of sensations.

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CriteriaType, intensity, and adequacy of sensation.
SynesthesiaA single stimulus evokes sensations in multiple sensory modalities.
Levels of lesionReceptor, pathway, central.
ParesthesiaSensations occur without an external stimulus.
3 min readFor medical studentsUpdated 09/24/2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesReviewed by medical editor: Aulov A. A., general practitioner · 09/24/2026

Hypoesthesia and anesthesia

Depending on the scale of sensory pathway damage, there are two main forms of decreased or lost sensitivity:

  1. Total form. Occurs with extensive damage (nerve roots, medial lemniscus, internal capsule, postcentral gyrus). The patient completely loses the ability to perceive all types of stimuli.
  2. Partial form. Develops when the posterior horns, spinal cord columns, or parts of the medulla oblongata are affected. Only specific types of sensitivity suffer (e.g., pain or tactile).

Specific partial disorders include astereognosis (inability to recognize an object by touch) and topoanesthesia (loss of ability to determine where a stimulus was applied).

Mechanisms and etiology

Decreased sensitivity can develop due to dysfunction of the receptors themselves, a reduction in their number on cell membranes, as well as blockade of signal conduction (e.g., in diabetic polyneuropathy or lead poisoning). In some cases, the central perception apparatus (thalamus, cortex) is affected.

The main causes include:

  • Nerve tissue injuries.
  • Strokes and circulatory disorders.
  • Degenerative diseases (syringomyelia).
  • CNS tumors.
  • Encephalitis and developmental anomalies of pathways.
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Hyperesthesia and dysesthesia

Hyperesthesia (hyper — over, aisthesis — feeling) is an excessive reaction to a stimulus. It can be receptor-based (e.g., in burns or herpes) and central (in neuroses, when the excitability of the cortex and hippocampus is increased).

Dysesthesia is an inadequate perception of a stimulus. Its main variants are:

  • Thermalgia: warmth or cold are perceived as pain.
  • Polyesthesia: a single stimulus is perceived as several different ones (a prick feels like burning and pressure).
  • Allodynia: a non-painful stimulus causes pain.
  • Hyperpathy: excessive pain without clear localization, even from a light touch.
  • Paresthesia: "crawling ants" or numbness occurring without external impact (in ischemia or root lesions).

Levels of disorders

All disorders can be divided into three levels depending on the localization of the pathology:

  1. Receptor level. The threshold of sensitivity changes (hypo- or hypersensitization) or the number of receptors changes. Causes: hypoxia, hypothermia, sodium and potassium ion imbalance.
  2. Pathway level. Occurs when impulses are inhibited or blocked in nerve trunks and the spinal cord.
  3. Central level. The thalamic nuclei and cerebral cortex are affected, distorting the very formation of sensation.

Briefly: answers to topical questions

Which specific spinal cord pathways are responsible for conducting pain and temperature sensitivity?

The lateral spinothalamic tract is responsible for conducting pain and temperature sensitivity. In the spinal cord, the fibers of these types of sensitivity run anatomically inseparably close.

  • Spinothalamic tract (tractus spinothalamicus) is the main highway for pain and temperature sensitivity, located in the lateral funiculus (funiculus lateralis).

Tract fibers have a strict somatotopic organization: fibers from the legs are located laterally, while those from the trunk and arms are medial. Before ascending to the thalamus, the processes cross to the opposite side via the anterior commissure.

What types of synesthesia exist and how are they classified?

Synesthesia is classified as a disorder based on the inadequacy of sensation to the stimulus that caused it. In pathology, the following forms of synesthesia are distinguished, manifesting beyond the scope of the stimulus:

  • Segmental — occur within the innervation area of the corresponding spinal cord segment or cranial nerves (e.g., referred pain).
  • Pathway-based — perceived in the innervation zones of a specific nerve trunk (e.g., phantom pain).

Synesthesia also includes illusory perceptions, such as "colored hearing" and "colored olfaction", when stimulation of one sense organ causes sensations characteristic of other organs.

Class and exam questions

How does allodynia differ from hyperpathy?

In allodynia, a non-painful stimulus causes pain. In hyperpathy, pain is excessive and combined with the loss of ability to accurately determine the site of impact.

What is a dissociated sensory loss?

This is a condition occurring with a lesion of the posterior horns of the spinal cord, where pain and temperature sensitivity are lost while deep sensitivity is preserved.

What is the characteristic of Brown-Séquard syndrome?

It develops with a hemisection of the spinal cord. Pain and temperature sensitivity disappear on the side opposite to the injury, below the level of the lesion.

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What else to study on this topic

  • Mechanisms of pain syndrome formation
  • Features of the segmental type of sensory disturbance
  • Signaling and pathogenic significance of pain
  • Pathogenesis of receptor and central hyperesthesia

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Other topics in "Chapter 28. Standard forms of pathology of the nervous system"

Neuron damageClassification of nervous system disordersPathological hyperactivation of the nervous systemEfferent nervous system disordersCentral paralysis and paresisExtrapiramidal disordersAtaxiaPathophysiology of painNeurodystrophic processNeurosesSubject and tasks of pathophysiology
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