Chapter 10 - The Senses

General senses

Touch, pressure, temperature, pain. Widely distributed and structurally simple.

Special senses

Vision, hearing, smell, taste, balance. Have complex specialized sensory organs in the head.

Chemoreceptors

Sensory receptors sensitive to changes in chemical concentration

Pain receptors

Sensory receptors that detect tissue damage

Thermoreceptors

Sensory receptors that respond to temperature differences

Mechanoreceptors

Sensory receptors that respond to changes in pressure or movement

Photoreceptors

Sensory receptors that respond to light and are found in the eye

Sensation

This occurs when receptors are stimulated and sends impulses to the brain

Perception

This occurs when there is conscious awareness of stimuli

Projection

This is what the brain uses to send the sensation back to its point of origin, so the person can pinpoint the area of stimulation

Sensory adaptation

The ability of the nervous system to become less responsive to a maintained stimulus, results from receptors becoming unresponsive or inhibition along CNS pathway.

Free nerve endings

These are of sensory nerve fibers in the epithelial tissues and are associated with itching and other sensations

Tactile (Meissner’s) corpuscles

Flattened connective tissue sheaths surrounding two or more nerve fibers; respond to motion of objects that contact the skin; abundant in hairless areas.

Lamellated (Pacinian) corpuscles

Large structures of connective tissue fibers and cells and they detect deep pressure, common in deep dermis and subcutaneous layer.

2 groups of free nerve endings in skin’s thermoreceptors

Warm receptors: 25 - 45C

Cold receptors: 10 - 20C

Below or above those ranges would stimulate pain receptors, causing burning or freezing sensations.

Proprioception

Sense of body position and location in space

Proprioceptors in skeletal muscles

Muscle spindles: Bundles of special skeletal muscle fibers within skeletal muscle, with fibers of sensory neurons wrapped around muscle fibers. Monitors state of muscle contraction.

Golgi tendon organs: Found near a tendon, near point of attachment with muscle. Detects amount a tendon stretches during muscle contraction.

Nociceptors (pain receptors)