BIOL 1000 Chapter 38: Sense Organs

Specialized sensory cells that detect various stimuli.

Sensory organs are complex receptors made up of multiple cell and tissue types.

Sensory neurons convey information to the central nervous system about internal and external environments.

Sensing the Internal Environment

Temperature: Monitored by thermoreceptors.

Blood Chemistry: Includes pH levels, glucose concentration, etc.

Pain: Detected by nociceptors for harmful stimuli.

Muscle Contraction: Noted by proprioceptors that inform brain of body position and movement.

Blood Pressure: Monitored by baroreceptors.

Touch: Detected by mechanoreceptors in the skin.

Sensing the External Environment

Chemoreceptors

Detect chemicals from the environment.

Taste

There are five main types of taste receptors:

Sweet

Sour

Salty

Bitter

Umami

Taste Buds:

Located primarily on the tongue, on the walls of papillae.

Open at a taste pore and contain supporting and taste cells.

Smell (Olfaction)

Olfactory Cells:

Specialized modified neurons found within the nasal epithelium.

Vision

Photoreceptors: Sensitive to light, primarily rods and cones located in the retina.

Rods: Detect grayscale light.

Cones: Responsible for color detection.

Pupil: Opening in the iris that regulates light entry.

Fovea Centralis: Densely packed with cones, providing sharpest vision.

Blind Spot: Area devoid of rods and cones where the optic nerve exits.

Sensing Sounds

Mechanoreceptors

Detect vibrations and sound waves.

Hearing Process:

Sound waves hit the eardrum (tympanic membrane), creating vibrations.

Three ossicles (malleus, incus, stapes) amplify these vibrations.

Cochlea:

A snail-shaped fluid-filled chamber containing sound receptors (hair cells with stereocilia).

Sensing Balance

Mechanoreceptors in the Ear

Rotational Equilibrium:

Semicircular Canals: Detect motion in three dimensions, with hair cells in the ampulla responding to head rotation.

Gravitational Equilibrium:

Utricle and Saccule: Two membranous sacs in the vestibule that detect straight-line head movement by responding to the sagging of the otolithic membrane due to otolith displacement.

The utricle is sensitive to back and forth movements; the saccule responds to up and down movements.

Senses in Other Organisms

Lateral Line System: Found in fish; detects water currents and pressure waves, assisting in locating prey and predators.

Echolocation: Used by certain mammals (e.g., bats, whales) to navigate by emitting sounds and interpreting the returning sound waves.

Heat Detection: Certain species like pit vipers can detect infrared heat to locate prey.

Electricity Detection: The duck-billed platypus and some fish can sense electrical fields generated by the movements of their prey.

Magnetism: Many species including eels, sharks, and birds utilize Earth's magnetic fields for navigation.