The Senses Classification of Sense Organs Converting a Stimulus into a Sensation General Sense Organs

Sensory receptors vary Not just sense organs… Millions throughout the body in skin, internal organs, muscles Sensory receptors respond to: Touch Pressure Temperature Pain Located at the tips of sensory neuron dendrites

Importance of senses “Sense” changes in external and internal environments Required to maintain homeostasis, survival Initiate protective reflexes important for homeostasis

Classifying Sense Organs Special sense Large, complex organs Localized groupings of specialized receptors in areas (nasal mucosa, tongue) General sense Microscopic Widely distributed throughout the body

Classifying Receptors Classified according to: Types of stimuli that activate them Light (photoreceptors) Taste, smell – chemical (chemoreceptors) Physical damage/injury (pain receptors) Temperature (thermoreceptors) Mechanical (mechanoreceptors) Encapsulated or unencapsulated Whether they are covered by some sort of capsule or not

Converting a Stimulus into a Sensation All receptors must be able to sense or detect a stimulus in environment Stimulus must be changed into an electrical signal (nerve impulse) Generates a “receptor potential”

Receptor Potentials Must reach threshold to generate an action potential in the axonal portion of the neuron RP is a graded, decremental response (gradually diminishes) Strength of RP depends upon which ion the membrane becomes more permeable to (Na, K)

Signal transmitted over nervous system “pathway” to the brain

2 Types of Receptors Primary (1) Secondary (2) Receptor membrane is part of the afferent neuron (e.g. pain receptors, Pacinian corpuscles) Secondary (2) Receptor membrane is a specialized sensory cell Synapses with afferent neuron

General Sense Organs Found in almost every part of the body Concentrated in the skin Two-point discrimination Ability to distinguish one touch stimulus from two Clinically significant (lesions to parietal lobe impair it) Close in the fingertips (2-8 mm) Relatively close in palms (8-12 mm) Far over the back (40-60 mm)

Stimulation type varies Some leads to sensation of vibration Others lead to sensation of pressure, pain, temperature Proprioceptors Provide information about position/movement of different parts of body Length, extent of contraction of muscles (eye and depth perception)

“My leg fell asleep!” Temporary impairment of general sense receptors happens when blood flow is slowed Pressure of a crossed leg leads to… “Can’t feel legs!” “Can’t walk!” May not be able to tell where your legs are without looking at them Reactivation of sense organs leads to “tingling” Can also result from diabetes, cardiovascular disease, stroke, spinal cord/brain injury

Make a Flip Chart Read 10-1: General sense organs; make flip chart  with: 1. name 2. main location 3. general sense 4. picture of structure Chapter Review: 1, 2, 3