Chapter 6 Other Sensory Systems Module 6.1: Audition Module 6.2: The Mechanical Senses Module 6.3 The Chemical Senses

Audition: The Sense of Hearing Physical stimulus: sound waves Sound waves are periodic compressions of air, water or other media. Sound waves are “transduced” into action potentials sent to the brain.

Audition Amplitude refers to the height and subsequent intensity of the sound wave. Loudness refers to the perception of the sound wave. Amplitude is one factor.

Audition Frequency refers to the number of compressions per second and is measured in hertz. Related to the pitch (high to low) of a sound.

Anatomy of the Ear The ear is divided into 3 parts: Outer ear Middle ear Inner ear

Neuroanatomy Handout #5: The Auditory System The outer ear includes: pinna (pl: pinnae) (A): focus sound waves into middle ear help locate the source of a sound external auditory canal (B): pathway to middle ear

Neuroanatomy Handout #5: The Auditory System The middle ear includes: Tympanic membrane (C) (eardrum) vibrates when struck by sound waves 3 middle ear bones transmit information to the inner ear: malleus (D) incus (E) stapes (F)

Neuroanatomy Handout #5: The Auditory System The Inner Ear The inner ear includes: Oval window (G): a second membrane, like the eardrum Semicircular canals (H): part of the vestibular system, involved in balance and equilibrium

Neuroanatomy Handout #5: The Auditory System Cochlea (I): a snail shaped structure containing three fluid-filled tunnels auditory receptors (hair cells) Hair cells: auditory receptors (A,B) frogs (C) cat (D) lizard

Neuroanatomy Handout #5: The Auditory System Organ of Corti (K) Hair cells and two surrounding membranes in the cochlea

The Organ of Corti Hair cells (K1): auditory receptor cells Supporting cells (K2): attached to flexible basilar membrane (L) Tectorial membrane (J) is more rigid and runs along other end of hair cells

Audition Auditory nerve (M) exits the inner ear and carries information about sound to the auditory cortex

Theories of Pitch Perception Frequency theory - the basilar membrane vibrates in synchrony with the sound and causes auditory nerve axons to produce action potentials at the same frequency (explains low frequency range). Place theory - each area along the basilar membrane is tuned to a specific frequency of sound wave (explains higher range).

Theories of Pitch Perception Volley principle states that the auditory nerve can have volleys of impulses (up to 5000 per second) even though no individual axon approaches that frequency by itself. There is power in numbers…

Audition Which part of the brain helps process information about hearing? Primary auditory cortex located in the superior temporal cortex Each hemisphere receives most of its information from the opposite ear.

Audition The primary auditory cortex provides a tonotopic map cells are responsive to preferred tones Damage can lead to deficits processing auditory info: loss of ability to identify a song or voice It does not result in a loss of hearing

Hearing Loss About 99% of hearing impaired people have at least some response to loud noises. Two categories of hearing impairment include: Conductive or middle ear deafness Nerve deafness

Hearing Loss Conductive or middle ear deafness: Bones of middle ear fail to transmit sound waves properly to cochlea Caused by disease, infections, or tumerous bone growth near the middle ear. Can be corrected by surgery or hearing aids that amplify the stimulus.

Hearing Loss Nerve or inner-ear deafness: Results from damage to cochlea, hair cells or auditory nerve Can be confined to one part of the cochlea people can lose certain frequencies Can be inherited or caused by prenatal problems or early childhood disorders

Audition Tinnitus: frequent or constant ringing in the ears Experienced by many people with nerve deafness Sometimes occurs after damage to cochlea

Sounds that cause hearing loss Heavy city traffic = 90 decibels Car horn = 110 decibels Headphones = 120 decibels (common volume) Jackhammer = 130 decibels Rock band at close range = 140 decibels Rocket launching = 180 decibels

The Mechanical Senses Mechanical senses respond to pressure, bending, or other distortions of a receptor. Mechanical senses include: Audition (discussed in Module 6.1) Vestibular sensation (balance/equilibrium) Touch Pain Other body sensations (sense of kinesthesis, or movement, discussed in movement chapter)

The Mechanical Senses The vestibular sense refers to the system that detects the position and the movement of the head. Directs compensatory movements of the eye and helps to maintain balance.

The Mechanical Senses Vestibular organ: in inner ear, adjacent to cochlea, consists of: two otolith organs calcium carbonate particles (otoliths) activate hair cells when head tilts three semicircular canals oriented in three different planes filled with jellylike substance that activates hair cells when the head moves

The Mechanical Senses Which part of the brain helps process information about our vestibular sense? Angular gyrus integrates balance and movement info with other sensations Located at border between parietal and temporal cortex

The Mechanical Senses Somatosensory system refers to sensation of the body and its movements: Involves mechanoreceptors: discriminative touch deep pressure pain Itch tickle position and movement of joints Involves thermoreceptors: warm cold

The Mechanical Senses Touch receptors can be: simple bare neurons (pain, warm, cold) elaborated neuron ending (pressure) bare ending surrounded by non-neural cells that modify its function (pressure)

The Mechanical Senses Pacinian corpuscle: type of touch receptor that detects sudden displacement or high-frequency vibrations on skin Mechanical pressure bends membrane increases flow of sodium ions and triggers an action potential

The Mechanical Senses Pain depends on many axon types, neurotransmitters, and brain areas. Mild pain triggers the release of glutamate. Strong pain triggers the release of glutamate and several neuropeptides (including substance P and CGRP (calcitonin gene-related peptide). Substance P results in the increased intensity of pain.

The Mechanical Senses Emotional pain can activate the same neural pathways as physical pain

The Mechanical Senses Itch occurs with damage and healing in the nervous system Can signal individual to remove foreign object from skin Histamines (chemical messengers) are released by individual and cause itchy feeling

The Mechanical Senses Which part of the brain helps process information about touch? Somatosensory cortex of parietal lobe Info from touch receptors in head enters CNS through cranial nerves Info from receptors below head enters spinal cord and travels through spinal nerves to brain

The Mechanical Senses 31 spinal nerves each has a sensory component and a motor component connects to a limited area of the body Dermatome: the skin area connected to a single sensory spinal nerve

The Chemical Senses: Taste Taste refers to the stimulation of taste buds by chemicals. Our perception of flavor is the combination of both taste and smell. Taste and smell axons converge in the endopiriform cortex.

The Chemical Senses: Taste Taste receptors modified skin cells excitable membranes release neurotransmitters and excite neighboring neurons replaced every 10 to 14 days

The Chemical Senses: Taste Papilla(e): structure(s) on surface of tongue that contain up to 10 taste buds Each taste bud contains approx. 50 receptors Most taste buds are located along the outside of the tongue in humans.

The Chemical Senses: Taste Western societies have traditionally described sweet, sour, salty and bitter tastes as the “primary” tastes and four types of receptors. Evidence suggests a fifth type of glutamate receptor that detects savory taste (umami).

The Chemical Senses: Taste Various areas of the brain are responsible for processing different taste information. Somatosensory cortex responds to the touch aspect of taste The insula is the primary taste cortex.

The Chemical Senses: Smell Olfaction: detection and recognition of chemicals that contact membranes inside the nose Olfactory cells: receptor cells for smell Olfactory epithelium: membrane in rear of nasal passage Contains olfactory cells

The Chemical Senses: Smell Neural processing: Axons from olfactory receptors carry information to the olfactory bulb in the brain. The olfactory bulb sends axons to many areas of the cerebral cortex. Coding in the brain is determined by which part of the olfactory bulb is excited.

The Chemical Senses: The VNO Pheromones: chemicals released by an animal that affects the behavior of others of the same species Vomeronasal organ (VNO): set of receptors located near the olfactory receptors that are sensitive to pheromones The VNO and pheromones are important for most mammals, but less so for humans It is tiny in human adults and has no receptors. Humans unconsciously respond to some pheromones through receptors in the olfactory mucosa. Example: synchronization of menstrual cycles

Integration of the Senses Synesthesia is the experience of one sense in response to stimulation of a different sense. Suggests some axons from one area have branches to other cortical regions. Video clip, “Seeing Life in Colors: Crosswired Senses” (3m): http://www.youtube.com/watch?v=KApieSGlyBk&feature=related Optional documentary, “The Boy with the Incredible Brain” (48m): https://www.youtube.com/watch?v=_N7eV7wXm-w