Content Summary:
Sensory physiology deals with the way our bodies perceive and interact with the environment. These perceptions are taken in by many different types of receptors that transduce energy from the environment into nerve impulses that are delivered to the brain. Senses covered in this chapter are: cutaneous sensations, taste and smell, the vestibular apparatus and equilibrium, the ears and hearing and the eyes and vision.

Summary #1
Sensory receptors are grouped into the type of stimulus energy they transduce such as:
  • chemoreceptors-sense chemical stimuli in the environment or the blood
    • taste buds, olfactory epithelium, aortic and carotid bodies
  • photoreceptors-senses light
    • rods and cones in the retina of the eye
  • thermoreceptors-respond to heat and cold
  • mechanoreceptors_stimulated by mechanical deformation of the receptor cell membrane
    • touch and pressure receptors in the skin, hair cells within the inner ear
  • nociceptors_pain receptors
  • proprioceptors_sense body position, allow fine control of skeletal movements
    • muscle spindles, golgi tendon organs, joint receptors
  • cutaneous receptors-sense anything on the skin
    • touch and pressure receptors, heat and cold receptors, pain receptors
Phasic receptors respond with a burst of activity when stimulated but then decrease their firing rate.
Tonic receptors maintain their higher firing rate the entire time they are stimulated.

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Summary #2

The minimum distance at which two points of touch can be perceived as separate is called the two-point touch threshold. A two-point touch threshold test measures the distance between the two points of a pair of calipers to ascertain the size of the receptive field. Cutaneous receptive fields are areas that change the firing rate of a neuron when stimulated. The health professional lightly touches the person's skin with both points of the calipers and measures the distance between them. Different receptive fields have different thresholds. This test measures the tactile acuity of touch perception and is used to determine how intact the CNS may be. Lack of two-point sensitivity may mean damage to the CNS. Reading Braille is an example of using tactile acuity as the symbols are formed by raised dots on a surface that are separated by 2.5 mm of each other. This is slightly greater than the fingertip two-point threshold of 2 mm.


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Summary #3
Accommodation is the ability of eyes to keep an image focused on the retina as the distance changes. This process involves contraction of the ciliary muscle, which is similar to a sphincter muscle, that allows the aperture to widen or narrow. Relaxation of the ciliary muscle makes the aperture widen, puts tension on the zonular fibers of the suspensory ligament, pulls the lens taut and makes it flatten. Relaxation occurs when the eye is viewing an object 20 feet or more from the eye. When the eye views object closer than 20 feet, the muscles of the ciliary body contract which narrows the aperture, reduces tension on the zonular fibers and the lens becomes more rounded and convex. Accommodation can be measured by a near-point-of-vision test. The near point is the minimum distance at which an object is brought into focus by the eyes. As people age, this distance increases and a condition called presbyopia develops. Presbyopia results when the zonular fibers and lens are pulled taut even when the ciliary muscle contracts. Those with presbyopia may need glasses that magnify in order to read small print or see small objects.



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Application:
A working knowledge of how our senses perceive and interact with the environment is important for any health care practitioner. My patients will have issues with their sensory receptors, otherwise they would not be coming to see me :) The most common sensory issues that an OTA would treat would be patients with deficits in proprioceptors, cutaneous receptors, nociceptors, mechanoreceptors and photoreceptors. All of my OTA studies have focused on deficits in these areas. My job would be to help desensitize, offer sensory education, pain education, proprioceptive activities, and vision edcuation and adaptation to name just a few. These are all needed for patients to perform their ADL as well as possible.

Personally, I have had cataract surgery on both of my eyes over two years ago. I opted to have the Crystalens put in and it is a decision that I am very happy with as I rarely have to wear glasses. I was shocked when I was told that I had cataracts in both eyes, and I was able to live with them for a few years through adaptation. My vision got to a point where it was time to have them replaced. Yes, I was young, but the ophthalmologist said his youngest patient was a teenager and his oldes was in their 80's, so I was right in between:)


Essential Questions:
1. Sound waves in the air within the external auditory meatus are transduced into the movements of the basilar membrane in these steps:
  1. Sounds waves are funneled from the pinna into the external auditory meatus
  2. The external auditory meatus channels sounds waves to the tympanic membrane
  3. The malleus is attached to the tympanic membrane and transmits the sound waves to the incus
  4. Sounds waves travel from the incus to the stapes
  5. The stapes is attached to the oval window which vibrates when the sound waves reach it
  6. Vibrations displace perilymph fluid within the scala vestibuli
  7. Fluid from the scala vestibuli is transmittled through the vestibular membrane and the basilar membrane.
  8. Displacement of the basilar membrane causes pitch discrimination

2. Pathway of light from the external environment to the brain:
  1. Light comes into the cornea
  2. It travels to the anterior chamber
  3. It travels to the pupil, the lens and to the posterior chamber
  4. It travels to the retina
  5. It travels to the optic nerve, to the optic chasm, and to the optic tract
  6. It travels to the brain via the thalamus, brain stem and the occipital lobe



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References: Anatomy & Physiology by Stanley E Gunstream, Julie Kalahar,MS,OTR/L