Sensation

Introduction

According to Jones (2011)[1] sensation is complex consisting of several modalities including our four special senses including Vision, Hearing, Smell and Taste and our Somatosensory Senses including tactile - light touch and pressure, proprioception, temperature and pain. Sensation plays a huge role in how we perceive our environment, impacts on our control of movement, maintaining arousal and provides warning of potential danger[1]. The evaluation of sensation, or any sensory modality for that mattter, is highly dependent on the ability and desire of the patient to cooperate. Sensation belongs to the patient (i.e., is subjective) and the examiner must therefore depend almost entirely on their reliability. Sensory changes that are unassociated with any other abnormalities (i.e., motor, reflex, cranial, hemispheric dysfunctions) must be considered weak evidence of disease unless a pattern of loss in a classical sensory pattern is elicited e.g. in a typical pattern of peripheral nerve or nerve root distribution. Therefore, one of the principle goals of the sensory exam is to identify meaningful patterns of sensory loss. Basic testing should sample the major functional subdivisions of the sensory systems. The patient's eyes should be closed throughout the sensory examination.

Sensory Receptor Nerve Fibre Sensory Pathway
Light Touch

Meissner's Corpuscle

Merkel's Discs

Aβ Fibers Spinothalamic
Pressure

Pacinian Corposcles

Aβ Fibers
Pain / Pin Prick

Free Nerve Endings

Aδ Fibers (Nociceptors of Neospinothalamic Tract)
C Fibers (Nociceptors of Paleospinothalamic Tract)
Temperature

Thermoreceptors

Aδ Fibers (Cold Receptors)
C Fibers (Warmth Receptors)
Vibration

Meissner's Corpuscle

Pacinian Corposcles

Aβ Fibers Dorsal Column
Proprioception

Muscle Spindle

Ruffini Endings

Aβ Fibers
Touch Localization

Meissner's Corpuscle

Merkel's Discs

Aβ Fibers
Stereognosis Hemispheric
Graphesthesia

Light Touch

Light touch allows us to be aware of tactile stimuli and has a role in warning us of impending damage.

Pain / Pin Prick

Pain provides a mean to alert the body that tissue damage has occurred, although pain can be elicited without tissue damage..

Two Point Discrimination

Two point discrimination is the ability to identify two objects in contact with the skin as two discount points, rather than 1.


Proprioception 

Proprioception is the sense of the relative position of body segments in relation to other body segments. Unlike the six exteroceptive senses (sight, taste, smell, touch, hearing and Balance) by which we perceive the outside world, and interoceptive senses, by which we perceive the pain and the stretching of internal organs, proprioception is a third distinct sensory modality that provides feedback solely on the status of the body internally. It is the sense that indicates whether the body is moving with the appropriate effort and where the various segments of the body are located in relation to each other. Read more about Proprioception.

Temperature

Temperature, like pain provides a mean to alert the body to potential tissue damage

Vibration

The appreciation of vibration, a form of pressure sense; most acute when a vibrating tuning fork is applied over a bony prominence.It should also be remembered that vibration sense is diminished in the older person.

Vision

Vision plays an important role in balance and movement, therefore any deficits may have a huge impact on functional activities. As many as 40% of individuals with Stroke will present with visual deficits post-Stroke.
Eyesight in the Older Person

Hearing

The sense of hearing is of paramount importance in spoken communication, and hearing loss can lead to porblems with communication, decreased awareness of environmental clues and even social isolation.
Hearing in the Older Person

References

  1. 1.0 1.1 Jones K. Neurological Assessment: A Clinician's Guide. Elsevier Health Sciences; 2011 Nov 29.