Somatic Sensation (The Bodily Senses) • Exteroception (perception of external events) – Touch (active and passive) – Thermal senses (heat and cold) – Pain (external or internal events that damage or harm the body) • Proprioception (sense of oneself) – Movements of the limbs – Posture of the body • Interoception (function of organ systems)
Somatic Sensation (The Bodily Senses). Exteroception (perception of external events) Touch (active and passive) Thermal senses (heat and cold) Pain (external or internal events that damage or harm the body) Proprioception (sense of oneself) Movements of the limbs Posture of the body - PowerPoint PPT Presentation
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Somatic Sensation (The Bodily Senses)
• Exteroception (perception of external events)– Touch (active and passive)
– Thermal senses (heat and cold)
– Pain (external or internal events that damage or harm the body)
• Proprioception (sense of oneself)– Movements of the limbs
• Transduce stimulus energy into electrical signals
• Encode depolarization as a spike train
• Transmit encoded information to spinal cord or brainstem
Common properties of DRG neurons
• Sensory transduction occurs in the nerve endings, not in the DRG or trigeminal cell bodies
• Sensory modality determined by the receptor class expressed in the nerve terminals
• Distal axons of DRGs form the peripheral nerves
• Each peripheral nerve innervates a specific body region
Common properties of DRG neurons
• Damage to a peripheral nerve produces deficits in more than one sensory modality in a specific body region
• Proximal branch of DRG neuron transmits somatosensory information to the spinal cord and brainstem from specific body region
Dorsal root ganglion neurons differ in:
• Receptor morphology and sensitivity• Diverse sensations mediated • Body region innervated• Axon conduction velocity and fiber diameter• Analysis of type(s) of sensory deficits and
localization to specific body region(s) are important diagnostic tools
• Spinal and brainstem termination sites• Ascending pathways to higher brain centers • Sensitivity to neurotrophins during development
Fiber diameter profile for different modalities
The Sense of Touch
Jusepe de Ribera c. 1615-16
Norton Simon Museum Pasadena CA
The sense of touch • Touch is the special sense by which contact with the body is
perceived in the conscious mind
• Touch allows us to recognize objects held in the hand and use them as tools
• Touch enables the blind to perceive the three dimensional form of objects, and to read Braille with their fingers
• Tactile information guides the skilled movements of the surgeon, the sculptor, the musician, the pitcher, or the chef
The sense of touch is mediated by skin indentation
Mechanoreceptors mediate the sense of touch • Mechanoreceptors in the skin provide information to the
brain about the size, shape, weight, and texture of objects • They allow us to perceive whether objects appear hard or
soft, large or small, heavy or light in weight, smooth or rough in texture
• Tactile acuity is highest on the glabrous skin of the hand
• The hand contains ~150,000 mechanoreceptors innervated by ~25,000 myelinated nerve fibers traveling in the median, ulnar and superficial radial nerves