Senses

Unit Student Learning Outcomes (CSLO)

  • Describe the anatomy, role and function of the nervous system (CSLO 1, 3).
  • Describe potential disruptions of the nervous system and its potential impact on the human body (CSLO 4).
  • Describe the role of the nervous system and its impact on other body systems (CSLO 2, 4).
  • Recognize the interrelationships of the nervous system related to common pathophysiology utilizing nursing judgment (CSLO 4).
  • Identify major senses of the body, and associated structures and describe their functions. (CSLO 1, 3)

Key Terms

  • Ceruminous gland
  • Cones
  • Conjunctiva
  • Gustatory cells
  • Iris
  • Lacrimal gland
  • Lens
  • Ossicles
  • Proprioception
  • Receptor
  • Rod
  • Semicircular canals
  • Tactile corpuscles
  • Vitreous body

Sensory System: Overview

  • The sensory system provides awareness of our external and internal environments.
  • Sensors detect environmental change (stimulus).
  • Sensory (afferent) neurons carry sensor information to the central nervous system (CNS).
  • The CNS interprets the information, resulting in a sensation.

General Senses

  • There are 55 general senses: Proprioception, Pain, Touch, Temperature, and Pressure.
  • Proprioception: perception of one’s own body position; used in activities such as walking, running, and muscle coordination.
  • Pain: nociception; protective mechanism signaling potential tissue damage.
  • Touch: tactile sensation including texture, pressure, and surface features.
  • Temperature: sensation of heat and cold;
    • Heat/pain responses relate to thermal receptors and protective reflexes.
  • Pressure: perception of force per unit area, related to mechanical deformation of tissues.

Special Senses

  • There are 55 special senses: Smell (olfaction), Taste (gustation), Sight (vision), Hearing (audition), Balance (vestibular sense).
  • Each has dedicated sensory organs and pathways for perception and CNS processing.

Vision: Sense of Sight – Eye Structures

  • Sclera: white of the eye; provides shape and protection.
  • Choroid: vascular layer supplying blood to the eye.
  • Retina: sensory layer containing photoreceptors (rods and cones).
  • Lens: focuses light by changing shape (accommodation).
  • Cornea: outer, transparent curved surface that begins light refraction.
  • Pupil: opening in the iris that regulates light entry.

Vision: Sense of Sight – Accessory Structures

  • Eyebrows
  • Eyelids
  • Conjunctiva
  • Eyelashes
  • Lacrimal gland: produces tears for lubrication and cleansing of the eye.

Cavities of the Eyeball

  • Posterior cavity (between lens and retina): contains vitreous humor; maintains eyeball shape and provides optical support.
  • Anterior cavity (between lens and cornea): contains aqueous humor; maintains corneal curvature and nourishes avascular structures.

Refraction

  • Refraction: bending of light rays to focus on the retina.
  • Lens is the primary refracting structure.
  • The focal point is on the retina.

How Seeing Occurs

  • Pathway of light: Cornea → Aqueous humor → Pupil → Lens → Vitreous humor → Rods and cones.
  • Pathway of nerve impulses: Rods and cones → CN II (optic nerve) → Occipital lobe (visual cortex).

Sense of Hearing: Three Parts of the Ear

  • External ear: structures located exterior to the tympanic membrane.
  • Middle ear: from tympanic membrane to the oval window; contains ossicles.
  • Inner ear: located beyond the oval window; contains cochlea and vestibular apparatus.

How Hearing Occurs

  • Pathway of vibrations: Sound waves → Tympanic membrane → Ossicles → Oval window → Cochlea.
  • Pathway of nerve impulses: Cochlea → CN VIII (cochlear branch) → Temporal lobe (auditory cortex).

Proprioception

  • Proprioception is the perception of one’s own body position.
  • Key activities include walking, running, and muscle coordination.