15.9: Senses

• 15.9A: Mechanoreceptors

  This page explains the role of mechanoreceptors in animals, which detect mechanical stimuli like touch, pressure, and motion, triggering nerve impulses. It highlights different types such as Pacinian corpuscles for pressure, Meissner corpuscles for skin movement, and Merkel cells for light touch. It also discusses proprioception's importance in body position and coordination.

• 15.9B: Hearing

  This page explains the process of hearing, which involves mechanical vibrations traveling from the outer ear to the brain through various structures. It also discusses causes of deafness, including noise exposure and genetic factors, and highlights the inner ear's role in balance and spatial orientation. Additionally, the use of echolocation by bats for navigation is mentioned.

• 15.9C: Vision

  This page explains the structure and function of the human eye, detailing its three tissue layers: the sclera, choroid, and retina. It describes how the lens adjusts focus and how the retina's rods and cones process light, with rods enabling basic vision and cones responsible for sharpness and color detection.

• 15.9D: Processing Visual Information

  This page discusses research by Stephen W. Kuffler and Nobel laureates David H. Hubel and Torsten N. Wiesel, focusing on how ganglion and LGN cells react to light. Ganglion cells vary their firing rates based on light location on the retina, while LGN cells are affected by cortical connections. In the visual cortex, cells respond to light edges, suggesting a convergence of inputs that filters information to recognize features. Hubel and Wiesel's work culminated in a Nobel Prize in 1981.

• 15.9E: Vision in Arthropods

  This page discusses arthropod compound eyes, composed of numerous ommatidia that create a mosaic image. While they excel at motion detection, their resolution is lower than that of vertebrate eyes. Certain insects, such as honeybees, can perceive colors and ultraviolet light, which helps in pollination and navigation. Modifications in pigment improve sensitivity in low light. Overall, despite some limitations, compound eyes provide distinct advantages in motion detection and light sensitivity.

• 15.9F: Heat, Cold, and Pain Receptors

  This page explains how specific sensory neurons and their receptors detect heat, cold, and pain, detailing the roles of Aδ, C, and Aβ fibers in transmitting pain signals. It discusses various ion channels involved in temperature response and categorizes pain types—nociceptive, neuropathic, and visceral. Treatments like NSAIDs and opioids are examined, focusing on their mechanisms, effectiveness, and risks associated with opioid addiction and tolerance.

• 15.9G: Taste

  This page explores the taste system, detailing five primary taste sensations—salty, sour, sweet, bitter, and umami. It explains that taste buds contain various cells responsive to these tastes, with specific receptors activating sensory neurons through distinct mechanisms: ion channels for salty, proton detection for sour, and G-protein-coupled receptors for sweet and bitter.

• 15.9H: Olfaction - The Sense of Smell

  This page explains that human smell involves sensory receptors in the olfactory epithelium, where odorant molecules interact with receptors on sensory neuron cilia. This interaction activates a signaling pathway that generates action potentials, allowing the brain to identify odors. Each olfactory neuron expresses one receptor gene, enabling the detection of up to a trillion distinct scents through combinatorial receptor activation patterns.

• 15.9I: Electric Organs and Electroreceptors

  This page discusses how electric eels use electrocytes to generate high-voltage discharges of up to 600 volts to stun prey. The process involves a nerve impulse that causes sodium ions to flow, allowing current to flow similarly to a series circuit. Eels initially emit low-voltage signals to provoke a response from prey, followed by high-voltage bursts to immobilize them. Additionally, other fish with weaker electric organs employ electric signals for navigation and communication.

• 15.9J: Magnetoreceptors

  This page discusses how various animals, like birds, sea turtles, and honeybees, can adapt their behavior based on the Earth's magnetic field. Examples include homing pigeons getting disoriented by magnets and woodmice affected by reversed fields. Research shows thrush nightingales gain weight when exposed to specific magnetic conditions. While receptors such as magnetite and cryptochrome may play a role, their mechanisms are still unclear.