Study Notes on Sense Organs and General and Special Senses

General Senses

• Visceral Sensations

  • Types include:
  • Hunger
  • Thirst
  • Hollow-organ fullness
  • Characteristics:
  • Miscellaneous category of interior body sensations
  • Vague and poorly localized
  • Originates in GI tract and urinary system

• Touch

  • Definition: Tactile sense
  • Sensation of something in contact with the surface of the body
  • Different touch and pressure receptors produce sensations of:
    • Light contact
    • Deep pressure
    • Vibration
    • Hair movement

• Temperature

  • Types of temperature receptors:
  • Superficial receptors located in the skin detect changes in skin temperature.
  • Central receptors in the hypothalamus monitor the temperature of the blood, indicating core temperature.

• Pain (Nociception)

  • Pain receptors known as nociceptors:
  • Widely distributed inside and on the surface of the body
  • Absent in the brain
  • Can be simple nerve endings or specialized structures to detect mechanical forces, temperature, etc.
  • Purpose: Protect the body from damage.

• Pain Processes during Nociception

  • Stages involved:
  • Transduction: Conversion of painful stimulus to a nerve impulse.
  • Transmission: Movement of nerve impulse to the spinal cord.
  • Modulation: Detection in the spinal cord for severity of the stimulus.
  • Perception: Reaction of the brain receiving the nervous impulse.

• Classification of Pain

  • Superficial: Pain from the skin and cutaneous layers.
  • Deep: Pain from muscles and joints.
  • Visceral: Pain from internal organs.
  • Acute: Sharp, intense, and/or immediate pain.
  • Chronic: Dull, aching, and/or long-term pain.

• Proprioception

  • Definition: Subconscious awareness of body position.
  • Includes:
  • Movements of limbs
  • Positions of joints
  • State of contraction of muscles
  • Tension exerted on tendons and ligaments

Special Senses

• Taste (Gustatory Sense)

  • Definition: Detection of chemical substances by receptors in the mouth (papillae on the tongue, lining of the mouth, and pharynx).

• Smell (Olfactory Sense)

  • Chemical sense, similar to taste.
  • More important in nonhuman animals.
  • Olfactory cells located in epithelial patches in nasal passages; odor molecules dissolve in mucus.

• Hearing (Auditory Sense)

  • Definition: Mechanical sense that converts vibrations of air molecules into nerve impulses interpreted as sound by the brain.
  • Organ of hearing: The ear, with structures located primarily within the temporal bones of the skull.

• Hearing Mechanics

  • External Ear: Pinna collects sound waves; leads to the L-shaped external auditory canal.
  • Tympanic Membrane (Eardrum): Thin connective tissue membrane that vibrates in response to sound.
  • Middle Ear: Contains 3 ossicles (malleus, incus, stapes) that amplify sound vibrations from the tympanic membrane to the cochlea.
  • Eustachian Tube/Auditory Tube: Connects middle ear with the pharynx to equalize air pressure.
  • Inner Ear: Contains the cochlea, which houses the organ of Corti, the receptor organ for hearing.
  • Organ of Corti: Consists of hair cells and supporting cells; vibrations from sound waves stimulate the hair cells, generating nerve impulses sent to the brain.

• Equilibrium

  • Definition: Mechanical sense that maintains balance by tracking head position and movements.
  • Receptors located in the inner ear, specifically the vestibule (between the cochlea and semicircular canals) and semicircular canals.
  • Information required from the eyes and proprioceptors around the body.
  • Vestibule: Includes saclike spaces (utricle and saccule) with macula containing hair cells and otoliths.
  • Semicircular Canals: Fluid-filled structures that detect motion; ampulla contains the crista ampullaris and cupula, where sensory hairs respond to motion, generating nerve impulses.

• Vision

  • Components of the eye primarily function to form accurate visual images rather than just detecting them.
  • Photoreceptors: Located in the retina, responsible for generating visual nerve impulses.
  • Eyeball Layers:
  • Outer Fibrous Layer: Cornea (transparent, admits light) and sclera (white part of the eye).
  • Middle Vascular Layer (Uvea): Includes choroid, iris (controls light entry), and ciliary body (adjusts lens shape).
  • Inner Nervous Layer: Retina, containing rods (sensitive to light) and cones (sensitive to color).

• Compartment Structure of the Eyeball

  • Aqueous Compartment: Anterior segment filled with aqueous humor produced by the ciliary body.
  • Subdivided into anterior chamber and posterior chamber.
  • Vitreous Compartment: Contains vitreous humor, gelatinous fluid filling the back of the eye.

• Lens of the Eye

  • Soft, translucent, and biconvex structure that aids in focusing images on the retina through accommodation (changing shape to focus on near or distant vision).

• Retina

  • Multilayered structure responsible for processing visual information, lines most of the vitreous compartment, includes:
  • Pigment layer
  • Photoreceptor layer
  • Bipolar cell layer
  • Ganglion cell layer (conveys impulses to the optic nerve).

• Formation of a Visual Image

  • Four refractive components: cornea, aqueous humor, lens, and vitreous humor help in forming a clear image on the retina which is inverted by the brain for proper perception.

• Extraocular Structures

  • Conjunctiva: Thin, transparent membrane covering front of the eyeball and lining eyelids.
  • Eyelids: Upper and lower folds protecting and covering the eyes, lined with conjunctiva.
  • Eyelashes: Modified cilia on upper eyelid, preventing debris from entering the eye.
  • Lacrimal Apparatus: Structures that produce and drain tears; consists of lacrimal glands, puncta, and nasolacrimal duct.
  • Tears: Composed of three layers (inner mucous, middle, and outer oily) maintaining moisture and protecting the eye surface.
  • Eye Muscles: Small skeletal muscles that attach to the sclera, allowing for movement of the eye.