Receptors and Sensations Notes

Sensory Receptors

  • Detect changes in the external environment.

  • Send impulses to the CNS to act on the info gathered.

  • Two Types:

    • Somatic: Associated with pain, touch, temperature, and pressure. Located within the skin and deep tissue.

    • Special Senses: Associated with smell, taste, hearing, and vision. Located within the specialized organs (tongue, lip, finger tip)

  • Categorized based on type of sensitivities.

    • Chemoreceptors: Respond to the chemical concentration variations.

    • Nocicreceptors (pain): Responds to tissue damage.

    • Thermoreceptors: Respond to temperature change.

    • Mechanoreceptors: Responds to pressure or movement changes.

    • Photoreceptors: Responds to the changes in light.

Sensation, Projection, and Adaption

  • All impulses that leave the sensory neurons are alike. Sensation depends on the portion of the brain that receives the sensory impulse.

  • Projector is the feeling that seems to come from the stimulated receptor. This is caused by the cerevral cavity.

  • Receptors that are continuously stimulated eventually adapt. Once this occurs the receptor can only be stimulated by a strong stimulus.

Somatic Senses

1. Touch and Pressure Senses

  • Based on three kinds of receptors:

  1. Sensory Nerve Fibers: Located in epithelial tissue.

  2. Meissner Corpuscles: Located in connective tissue, especially in hairless areas. Detects light touch.

  3. Pacinian Corpuscles: Located in subcutaneous, tissue, tendons, and ligaments. Detects heavy pressure.

2. Temperature Senses

  • Dependent on two types of nerve endings.

  1. Warm Receptors: Sensitive to temps between TPF and 113°F. Above that temperature stimulates pain receptors (burning).

  2. Cold Receptors: Sensitive to temperatures between 50°F and 68°F. Below that temperature stimulates the pain receptors.

  • Both types adapt fast.

Sense of Pain

Skin Pain

  • Distributed throughout the skin and internal tissue.

  • Protects the body because tissue damage stimulates them.

  • Poorly adaptable, which is why you can be in pain for a while.

  • Not sure exactly how they are stimulated.

Visceral Pain

  • In the organs it is the pain receptor that produce any sort of sensation.

  • Sometimes pain comes from another body part other than the organ being stimulated. This is referred pain. Ex. Heart can be felt in arm.

Pain Nerve Fiber

  • Nerve fibers conducting impulses away.

  • Two types:

  1. Acute Pain Fibers: Thin and myelinated. Produces a sharp pain. Pain seldom continues after the pain-producing stimulation ceases.

  2. Chronic Pain Fibers: Thin and unmyelinated. Produces a dull pain.

Pain Triggering Event

  • Triggers both acute and chronic fibers.

  • Pain impulses in the head travel to the brain on the cranial nerves.

  • Other impulses reach the brain via the spinal nerves.

  • Pain fibers terminate at the reticular formation.

Pain Regulation

  • Pain awareness happens when the impulse reaches the thalamus.

  • Cerebral cortex determines the pain intensity, source, and mediates the response.

  • Movement of the impulses back to the spinal cord is regulated by the midbrain, pons, and medulla oblongata.

  • Impulses are sent to certain nerve fibers to release biochemical to block pain.

  • Inhibitors: Enkephins, serotonin, endorphins