🐅Animal Physiology Unit 4 – Sensory Systems and Perception

Key Sensory Systems Overview

• Sensory systems allow animals to detect and respond to stimuli in their environment
• Major sensory modalities include vision, audition, olfaction, gustation, and somatosensation
• Sensory information is transduced by specialized receptors into electrical signals
• Neural processing integrates and interprets sensory information to create perceptions
• Sensory systems vary across species based on evolutionary adaptations to different environments
• Sensory input guides behaviors essential for survival and reproduction (foraging, predator avoidance, mate selection)
• Sensory systems exhibit plasticity and can be modified by experience and learning

Sensory Receptors and Transduction

• Sensory receptors are specialized cells or structures that detect specific stimuli
• Transduction converts physical or chemical stimuli into electrical signals in sensory neurons
• Receptor potential is a graded potential generated by the activation of sensory receptors
• Ion channels in receptor cell membranes open or close in response to stimuli, altering membrane potential
• Sensory receptors exhibit adaptation, decreasing sensitivity to sustained stimuli over time
• Sensory receptors have different thresholds for detecting stimuli, determining sensitivity
• Sensory receptors can be classified as mechanoreceptors, chemoreceptors, photoreceptors, or thermoreceptors based on the type of stimuli they detect

Neural Processing of Sensory Information

• Sensory neurons transmit electrical signals from receptors to the central nervous system
• Afferent pathways carry sensory information from the periphery to the brain
• Sensory information is processed hierarchically in the nervous system, from simple to complex features
• Thalamus acts as a relay station for most sensory information before reaching the cerebral cortex
• Sensory cortices (visual, auditory, somatosensory) process and integrate sensory information
• Sensory information is encoded by the firing rate and pattern of action potentials in sensory neurons
• Lateral inhibition enhances contrast and sharpens sensory representations
• Top-down processes, such as attention and expectation, modulate sensory processing

Vision and Visual Perception

• Vision is the ability to detect and interpret light stimuli
• Eyes contain photoreceptors (rods and cones) that transduce light into electrical signals
• Rods are sensitive to low light levels and provide scotopic vision, while cones are responsible for color vision and high acuity
• Retina contains layers of neurons that perform initial processing of visual information
• Optic nerve carries visual information from the retina to the brain
• Primary visual cortex (V1) processes basic features such as edges, orientation, and motion
• Higher visual areas (V2, V4, MT) process more complex features and integrate information
• Binocular vision allows depth perception through stereopsis
• Visual perception involves the interpretation of visual information based on prior knowledge and experience

Audition and Sound Localization

• Audition is the sense of hearing, detecting pressure waves in the environment
• Outer ear collects and funnels sound waves to the middle ear
• Middle ear contains ossicles that amplify and transmit vibrations to the inner ear
• Inner ear contains the cochlea, which transduces vibrations into electrical signals using hair cells
• Auditory nerve carries signals from the cochlea to the brainstem and auditory cortex
• Tonotopic organization in the cochlea and auditory cortex maps sound frequencies
• Sound localization relies on binaural cues, such as interaural time and level differences
• Auditory scene analysis allows the segregation and grouping of sound sources in complex environments

Chemical Senses: Olfaction and Gustation

• Olfaction is the sense of smell, detecting airborne chemical stimuli
• Olfactory receptors are located in the nasal epithelium and bind to specific odorant molecules
• Olfactory bulb is the primary processing center for olfactory information
• Olfactory cortex processes and integrates olfactory information with other sensory modalities
• Pheromones are chemical signals used for communication between individuals of the same species
• Gustation is the sense of taste, detecting dissolved chemicals in the mouth
• Taste receptors are located in taste buds on the tongue and palate
• Five basic taste qualities: sweet, salty, sour, bitter, and umami
• Taste information is transmitted to the gustatory cortex via cranial nerves
• Flavor perception involves the integration of taste, smell, and somatosensory information

Somatosensation and Proprioception

• Somatosensation includes touch, pressure, temperature, and pain sensations
• Mechanoreceptors in the skin detect mechanical stimuli (Merkel cells, Meissner's corpuscles, Pacinian corpuscles)
• Thermoreceptors detect changes in temperature (cold and warm receptors)
• Nociceptors detect noxious stimuli that can cause tissue damage
• Somatosensory cortex contains a somatotopic map of the body's surface
• Proprioception is the sense of body position and movement
• Proprioceptors (muscle spindles, Golgi tendon organs) detect muscle length and tension
• Vestibular system detects head position and acceleration, contributing to balance and spatial orientation

Comparative Sensory Adaptations

• Sensory systems have evolved to meet the specific needs of different species in their environments
• Nocturnal animals (owls, bats) have enhanced auditory and olfactory systems for navigation and prey detection
• Aquatic animals (fish, sharks) have specialized lateral line systems for detecting water movement and pressure changes
• Electroreception allows some fish (electric eels, sharks) to detect electric fields in the water
• Echolocation in bats and dolphins uses high-frequency sound waves for navigation and foraging
• Infrared detection in some snakes (pit vipers) allows them to locate warm-blooded prey
• Polarized light detection in some insects (bees) aids in navigation and communication
• Magnetoreception in migratory birds and sea turtles helps in long-distance navigation