Sensory
Biol. 211 Anatomy & Physiology 1
Tony Serino, Ph.D.
Biology Department
Misericordia University
Sensation –state of awareness of external and internal conditions of the
body
• Four conditions for sensation:– 1. Adequate stimulus– 2. Adequate receptor (transducer)– 3. Conduction– 4. Translation (interpretation)
Characteristics of Sensation
• Modality –ability to interpret nerve impulses differently
• Projection –referral of sensation to point of origin
• Adaptation –decrease in sensitivity of receptors to continued stimulation
– Phasic (fast)– Tonic (slow)– Some receptors never adapt (pain, cold, etc.)
• Afterimage –persistence of sensation after stimulus ceases
Classification of Receptors• Type of Sensory Information Relayed
– Exteroreceptors, Enteroreceptors, Proprioceptors
• Type of Stimulus Transduced– Mechanoreceptors, Thermoreceptors, Chemoreceptors,
and Nociceptors
• Complexity of Receptor– Simple structure (usually single cell) –most general senses
– Complex structure (many cells) –special senses
Receptor Physiology• Stimulation of a receptor leads to the generation of a
receptor (generator) potential in its membrane.
• These are usually excitatory, and are similar to the EPSPs found in neurons
• If the receptor potential reaches the threshold potential for the sensory neuron; it fires an AP into the CNS
• Strength of the stimulus is therefore encoded by the number of AP generated
• Sensations may be sharpened through Lateral Inhibition
General Senses
• Cutaneous –skin receptors
• Proprioception –sense of body position
• Nociception –pain perception (chemoreceptors that perceive locally secreted warning hormones (prostaglandins))
Muscle sensors
Muscle spindles (Intrafusal fibers:-senses degree of length of muscle fibers and the rate of change in length
Golgi Tendon organs –sense tension within tendon
(Canal of Schlemm)
Aqueous Humor Flow
Glaucoma results frominadequate drainage ofAqueous Humor leading to increase pressure in the eye.
Astigmatism and Presbyopia
• Astigmatism –results from imperfections in the resolving structures in the eye (lens and/or cornea)
• Presbyopia is the loss of near vision with age; resulting from a decrease in elasticity of the lens.
Frequency Perception
• Different frequency (pitch) of sound stimulates different areas of cochlear duct
• The overall area stimulated relates to the sound intensity