Audition, Body Senses, and Chemical Senses

• Auditory


  Relating to the sense of hearing

  
• Hearing/Audition


  The three primary functions are: to detect sounds, to determine the location of their sources, and to recognize the identity of these sources
• Hearing


  • We can understand speech, recognize a person's emotion from his/her voice, appreciate music, detect the approach of a vehicle or another person, or recognize an animal's call
• We can recognize not only what the source of the sound is but also where it is located
• Sound Waves


  Produced by objects that vibrate and set molecules of air into motion, causing waves that travel away from the object
• Three Perceptual dimensions of sound

  • Pitch
  • Loudness
  • Timbre
• Pitch


  An auditory stimulus determined by the frequency of vibration
• Loudness


  A function of intensity, the degree to which the compressions and expansions of air differ from each other
• More vigorous vibrations of an object produce more intense sound waves and hence louder ones
• Timbre


  Provides information about the nature of the particular sound
• Outer Ear


  The medical term is the auricle or pinna, made up of cartilage and skin that funnels sound through the ear canal to the tympanic membrane

  
• Middle Ear


  • Contains three small bones (ossicles) that transmit sound waves to the inner ear
  • Contains the Eustachian tube that links the middle ear with the back of the nose and helps equalize pressure

  
• Inner Ear


  • Contains the cochlea with the nerves for hearing
  • Contains the vestibule and semicircular canals with receptors for balance

  
• Auditory hair cells


  Vibrations caused by sound waves bend the stereocilia on these hair cells, converting mechanical energy into electrical energy transmitted to the central nervous system via the auditory nerve
• Two types of auditory receptors

  • Inner auditory hair cells
  • Outer auditory hair cells

  
• Auditory pathway


  Conveys auditory information from the cochlear hair cells in the inner ear to the central nervous system via the vestibulocochlear nerve

  
• Components of the auditory pathway

  • Primary (lemniscal) pathway - main pathway to primary auditory cortex
  • Non-lemniscal pathway - mediates unconscious perception like attention, emotional response, and auditory reflexes
• Pitch perception


  The perceptual dimension of pitch corresponds to the physical dimension of frequency, with place coding on the basilar membrane
• Cochlear implant


  Provides evidence for place coding of pitch in the human cochlea
• Loudness perception


  Louder sounds produce more intense vibrations of the eardrum and ossicles, causing more intense shearing force on the auditory hair cell cilia
• Timbre perception


  We hear sounds with a rich mixture of frequencies, allowing us to distinguish different timbres
• Vestibular system


  Functions to maintain balance and head orientation, and adjust eye movements to compensate for head movements
• Vestibular apparatus


  • Contains vestibular sacs that respond to gravity and inform the brain about head orientation
  • Contains semicircular canals that respond to angular acceleration and head rotation
• Vestibular pathway


  Allows sensory information from the inner ear to reach multiple destinations in the body and produce simultaneous outputs

  
• Somatosenses


  Provide information about what is happening on the surface of the body and inside it
• Somatosensory submodalities


  • Cutaneous senses (touch, temperature, pain)
  • Proprioception and kinesthesia (body position and movement)
  • Organic senses (internal sensations)
• Cutaneous senses


  Respond to stimuli like pressure, vibration, heating, cooling, and pain
• Kinesthesia


  Awareness of body movement, arising from receptors in muscles, joints, and skin
• Organic senses


  Detect internal sensations like stomachaches or pleasurable feelings, influenced by factors like food or drink
• Skin


  • A complex and vital organ that protects the body, participates in thermoregulation, and contains various receptors
• Categories of cutaneous receptors

  • Merkel's disks (form and roughness detection)
  • Ruffini corpuscles (static force and skin stretching detection)
  • Meissner's corpuscles (edge contour detection)
  • Pacinian corpuscles (vibration detection)
  • Hair follicle endings (hair movement detection)
  • Free nerve endings (thermal, noxious, and pleasurable touch detection)
• Touch perception


  Tactile stimuli are detected by mechanoreceptors, allowing analysis of shapes and textures
• Temperature perception


  Feelings of warmth and coolness are relative, detected by free nerve ending thermal receptors located at different depths in the skin
• Categories of mammalian thermal receptors

  • TRPV2 (noxious heat)
  • TRPV1, capsaicin (heat)
  • TRPV3 (warmth)
  • TRPV4 (warmth)
  • TRPM8, menthol (coolness)
• Pain perception


  A complex sensation controlled by mechanisms in the brain, accomplished by networks of free nerve endings that respond to intense pressure, extreme temperatures, acids, and chemicals
• Itch


  An unpleasant sensation caused by skin irritation, reduced by scratching due to pain suppressing itch
• Somatosensory pathways


  Somatosensory axons enter the central nervous system via spinal and cranial nerves, ascend through the dorsal columns and spinothalamic tract to the thalamus, and project to the primary and secondary somatosensory cortex
• Somatosensory cortex

  • Arranged in columns and divided into multiple maps of the body surface
• Somatosensory pathways


  1. Axons from spinal cord to nuclei in lower medulla

  2. Axons cross brain and ascend through medial lemniscus to ventral posterior nuclei of thalamus

  3. Axons of these neurons cross to other side of spinal cord and ascend through spinothalamic tract to ventral posterior nuclei of thalamus
• Somatosensory cortex


  • Primary and secondary regions are arranged in columns and divided into multiple maps of the surface
  • Primary visual cortex contains columns of cells, each of which responds to particular features, such as orientation, ocular dominance, or spatial frequency
  • Within these columns are blobs that contain cells that respond to particular colors