Classification of Sensory Receptors

Classification of Sensory Receptors

• Sensory receptors are categorized based on energy transduced into five types: thermoreceptors, pain receptors, mechanoreceptors, chemoreceptors, and electromagnetic receptors.
• Receptors can be classified by sensory modality (type of stimulus), receptor mechanism (metabotropic or ionotropic), and location (exteroceptors or interoceptors).

Types of Sensory Receptors

• Metabotropic Receptors: Engage G proteins for a slower response upon stimulation.
• Ionotropic Receptors: Directly open ion channels, providing a fast response.
• Exteroceptors: Located externally and detect stimuli like sound and light.
• Interoceptors: Found internally, sensing changes such as pH and osmotic concentration.

Auditory System

• The vertebrate acoustico-lateralis system integrates hearing and equilibrium functions.
• Sound transmission begins in the exterior ear and involves the tympanic membrane and ossicles (malleus, incus, stapes).
• The stapes vibrates against the cochlea, generating pressure waves in cochlear fluid, leading to the activation of hair cells.

Organ of Corti

• Contains hair cells that respond to sound wave amplitude (volume) and frequency (pitch).
• Different regions of the basilar membrane are tuned to specific frequencies, allowing pitch discrimination.

Hearing Process

• Sound waves cause tympanic membrane vibrations, translated through ossicles to the cochlea.
• Pressure waves alter the basilar membrane, stimulating hair cells, which relay auditory information to the brain.

Gravity and Body Orientation

• The vestibular system consists of semicircular canals and otolith organs (saccule and utricle) to maintain balance and detect head position.
• Semicircular canals respond to angular head movements; otoliths help detect linear acceleration.

Visual System

• The vertebrate eye is structured with components for light entry (cornea), focusing (lens), and photoreception (retina).
• Rods are responsible for night vision, while cones facilitate color vision and high acuity.
• Phototransduction occurs when light converts retinal shapes, prompting signal transmission to the brain.

Color Vision in Humans

• Humans possess three types of cones sensitive to different wavelengths, facilitating color perception through contrasting signals.
• Color vision is determined by the ratios of red, green, and blue cones, allowing for wide spectrum recognition.

Plant Light Detection

• Plants utilize photoreceptors, such as phytochromes and cryptochromes, to monitor light presence, direction, intensity, and wavelength.
• Photoperiodism influences flowering based on light duration—short-day, long-day, and day-neutral plants follow distinct flowering cues.

Gravitropism in Plants

• Roots exhibit positive gravitropism while shoots show negative gravitropism through the settling of statoliths.
• The gravitational response influences auxin distribution in plants, regulating growth direction based on gravity's pull.