WEEK 8 LECTURE + TUTORIAL Flashcards
Auditory and Somatosenses + Inner Ear (26 cards)
The three sections of the human ear
- Outer ear
- Middle ear
- Inner ear
*They all play a different role in our ability to perceive and hear sound
Outer Ear
-Protects the middle and inner ear
-The ear canal, or auditory canal (pinna), is a tube that runs from the outer ear to the eardrum (tympanic membrane) which then vibrates when the sound hits it
-Pinna causes spectral modification, provides location cues
-Ear canal amplifies frequencies between 1.5 and 6 Khz
-When the tympanic membrane is damaged by trauma, infection or an autoimmune attack, hearing is impaired, especially low frequencies
Middle Ear
-Increases efficiency of sound transfer into the cochlea- independence matching
-Acts as a translator to the inner ear
-Area Effect: Greater pressure is exerted at the oval window than at the tympanic membrane
-Lever Effect: Ossicles act as a lever, amplifying the force exerted on the tympanic membrane
Inner Ear
-composed of two sections, the cochlea and vestibular system
Cochlea:
Three fluid filled canals
-Scala vestibula (upper)
-Scala media (middle)
-Scala tympani (lower)
Receptive organ
-Basilar membrane
-Hair cells
-Tectorial membrane
Organ of Corti
-3500 inner hair cells arranged in a row
12000 outer hair cells arranged in 3-5 rows
-Transform sound vibrations into electrical neurotransmissions
Auditory Nerve
-Contains 30000 afferent nerve fibres that are tonotopically organised (different fibres correspond to different frequencies
-Fibres innervating IHC responding to low frequencies are near the centre of the nerve
-Fibres innervating IHC responding to high frequencies are near the periphery of the nerve
Auditory Pathway
-Organ of corti
auditory nerve
-Cochlear nucleus
medulla
-Superior olivary
complex medulla
-Inferior colliculus
midbrain
-Medial geniculate
midbrain
-Auditory cortex
Temporal lobe
Auditory Cortex
Hierarchal Arrangement
Core Region
-Contains the primary auditory cortex
Belt Region
-first level of auditory association cortex
Parabelt region
-Highest level of auditory association cortex
2 Processing Streams
- Ventral Stream: Helps us understand what we are hearing
Anterior para belt > anterior temporal lobe
the WHAT pathway - Dorsal Stream: Helps us understand where we heard that from
Posterior para belt > posterior parietal cortex
the WHERE pathway
Perception of Loudness
-Corresponds to physical dimension of amplitude of sound waves
-Loudness signalled by the rate of firing
-Our brains perception of loudness corresponds to the physical dimensions of sounds waves (i.e., the amplitude and difference between peaks and troughs)
-Loudness in a neurological sense is signalled by the rate of firing – louder noise = more firing
Perception of pitch
- corresponds to physical dimension of frequency
Signalled by:1. Place coding: Different neurons fire depending on the location on the basilar membrane
2.Rate (Temporal) coding: Information carried by the timing of the AP fired
Vestibular system
components, functions
- Vestibular sacs
-Semi-circular canals
-Each containing hair cells
Functions: - Balance
-Eye movements for image stability
-Maintenance of head position
What is the somatosensory system
- A subset of the sensory nervous system
Skin Anatomy
-Consists of epidermis, dermis and subcutaneous tissue
-Variable appearance of skin: mucous membrane, hairy or glabrous
Contains a variety of morphologically diverse sensory receptors:
-Encapsulated somatosensory receptors
- Ruffini corpuscles
- Meissner’s corpuscles
- Merkel’s disks
- Free nerve endings
Touch Receptors
Respond to vibration in the skin and changes in pressure against it
-Movement of dendrites of mechanoreceptors
-Opening of ion channels: influx/efflux of ions
-Receptor potential (change in membrane potential)
-Use large myelinated fibres
Merkels Disks
Location, Responds to, Responsible for
Location: Hairy and glabrous skin
Responds to: indentation of skin
Responsible for: Detecting pressure; static discrimination of shapes and edges
Ruffini corpuscles
Location, Responds to, Responsible for
Location: Hairy and glabrous skin
Responds to: Stretching of skin
Responsible for: Maintaining grip to avoid slippage
Meissner’s corpuscles
Location, Responds to, Responsible for
Location: Glabrous skin
Responds to: Low freq vibration and light touch
Responsible for: Detecting surface roughness when textured objects move across the skin
Pacinian corpuscles
Location, responds to, responsible for
Location: Hairy and Glabrous skin
Responds to: High frequency vibration
Responsible for: Discrimination of fine surfaces, textures or moving stimuli
Perception of touch depends on
- Density of mechanoreceptors
Receptive field size
Two types of thermoreceptors
- Warm receptors
-Located deeply in the skin
-Uses unmyelinated C fibres - Cold receptors
-Located beneath the epidermis
-Uses unmyelinated C fibres, and lightly myelinated Ao Fibres
Types of nociceptors/ free nerve endings/ pain receptors
1.Mechanical nociceptors:
-Sensitive to strong pressure
2.Thermal nociceptors
-Sensitive to burning heat and extreme cold
3.Chemical nociceptors
-Sensitive to histamine
4.Polymodal nociceptors
- Respond to mechanical, thermal and chemical stimuli
Pain Perception
-Sensory component (perception of pain intensity) involving pathway to S1 and S2
-Immediate emotional component (unpleasantness of stimulus) involving pathways including the insular cortex and anterior cingulate cortex
-Long-term emotional component in case of chronic pain involving pathways to the prefrontal cortex
Psychological factors influencing pain:
-Previous experience
-Perceived self-efficacy or helplessness
-Attention
-Anxiety/ Depression
Critical Conditions which effect the inner ear
-Labyrinthitis: Inner ear infection
-Tinnitus: Perception of sound without an external source
-Benign paroxysmal positional vertigo (BPPV): disorder of the inner ear with symptoms including dizziness, vertigo, nausea
