Neurology · MU Sofia

3. Sensation: anatomy and physiology of superficial and deep sensibility

Explains sensation as a classification into superficial (exteroceptive) and deep (proprioceptive) modalities, then walks through the spinothalamic pathway for pain, temperature and crude touch and the posterior column–medial lemniscus pathway for vibration and position sense. Cortical discriminative functions such as stereognosis and graphesthesia follow. A summary table links each system to its lesion result, and clinical signs such as sensory ataxia and a positive Romberg sign are noted.

Inside: 1 section · 3 labelled pictures · 1 table · 15 flashcards · 2 min

Topic 3 of 88 in the MU Sofia syllabus for Neurology (Medicine, Year 4). The free AceMed note covers it in 1 section, about 318 words (2 min of reading), with 15 flashcards.

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  1. Sensation - anatomy, physiology of the superficial and deep sensibility

Sensation - anatomy, physiology of the superficial and deep sensibility

Definition: Sensation is the ability to perceive and interpret stimuli from the external and internal environment. It requires:

  • Intact receptors. Peripheral nerves. Ascending sensory pathways. Thalamus. Sensory cortex (postcentral gyrus)

Classification of Sensibility

1. Superficial Sensibility (Exteroceptive): Arises from skin and mucous membranes

  • Modalities: Pain. Temperature. Crude (non-discriminative) touch

2. Deep Sensibility (Proprioceptive): Arises from muscles, tendons, joints, and deep tissues

  • Modalities: Joint position sense. Movement sense (kinesthesia). Vibration sense. Deep pressure

A. Superficial Sensibility Pathway

Receptors

  • Free nerve endings → pain, temperature
  • Mechanoreceptors → crude touch

Spinothalamic Tract (Anterolateral System)

1. First-order neuron: Cell body: dorsal root ganglion. Enters spinal cord via dorsal root

2. Second-order neuron

  • Location: posterior horn of spinal cord
  • Decussates within 1–2 spinal segments
  • Ascends in:
  • Lateral spinothalamic tract → pain & temperature
  • Anterior spinothalamic tract → crude touch

3. Third-order neuron

  • Thalamus: ventral posterolateral (VPL) nucleus
  • Projects to: Primary sensory cortex (postcentral gyrus, Brodmann 3,1,2)

Clinical Importance

  • Lesion in spinal cord → contralateral loss of pain and temperature below lesion
  • Due to early crossing of fibers

B. Deep Sensibility Pathway

Receptors: Muscle spindles. Golgi tendon organs. Joint receptors. Pacinian corpuscles (vibration)

Posterior Column–Medial Lemniscus System

1. First-order neuron

  • Cell body: dorsal root ganglion
  • Ascends ipsilaterally in posterior columns: Fasciculus gracilis → lower limb. Fasciculus cuneatus → upper limb

2. Second-order neuron

  • Nuclei in medulla: Nucleus gracilis. Nucleus cuneatus. Fibers decussate in medulla. Form medial lemniscus

3. Third-order neuron: Thalamus (VPL nucleus). Projects to primary somatosensory cortex

Functions (Deep Sensibility): Vibration sense. Proprioception (position sense). Kinesthesia (movement sense). Fine/discriminative touch

Clinical Importance

  • Lesion causes: Loss of vibration sense. Loss of position sense. Sensory ataxia. Positive Romberg sign

C. Cortical Sensory Functions: Require intact superficial + deep sensation

1. Stereognosis: Identification of objects by touch (eyes closed)

2. Graphesthesia: Recognition of written symbols on skin

3. Two-point discrimination: Ability to distinguish two close points

4. Barognosis: Ability to perceive weight differences

Key Clinical Correlation

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