The auditory and samatosensory systems Flashcards
in what range can human’s perceive sound?
30- 20,000 Hertz
Amplitude (loudness)
is determined by the degree to which air molecules are pushed together and pulled apart; more vigorous vibrations of an object cause larger amplitude sound waves, which in turn leads to more intense sounds
Frequency (pitch)
pitch is determined by the frequency of the sound waves produced by a vibrating object; the more sound waves per second the higher pitched the sound
Complexity (timbre)
timbre (sound quality) is determined by the complexity of the sound waves; the more little peaks and troughs in the waveform the more complex the sound. A completely smooth sinusoidal waveform is a pure tone
Outer ear
consist of the outer fleshy pinna, the auditory canal and the tympanic membrane (ear drum). The tympanic membrane vibrates with the soundwaves that enter the auditory canal, and this signal is transmitted on to the middle ear
Middle ear
consists of 3 tiny bones called the ossicles. The malleus (hammer) is connected to the tympanic membrane. It transmits vibrations via the incus (anvil) to the stapes (stirrup), which is connected to a structure called the cochlea
Inner ear (cochlea)
The cochlea contains the receptors for analysing sound. the cochlea is a bony structure, but it has two small membranes that form windows on its fluid filled interior
oval window
the stapes is connected to the oval window. Soundwaves that cause the stapes to move in and out move the fluid over the receptors in the cochlea
round window
allows the fluid to move within the cochlea
Basilar membrane
a sheet of tissue that contains the auditory receptors. The basilar membrane sits in the middle of the cochlea, and runs all the way from its base to its apex
Organ of corti
composed of the basilar membrane as its base, receptors in the middle called hair cells, and a rigid shelf over the top called the tectorial membrane
Hair cells and stereocilia
on top of the hair cells are tiny filaments called stereocilia. bending of the stereocilia of hair cells is what produces receptor potentials that convert sound into neural signals
Auditory nerve
the axons of thousands of spiral ganglion cells. The axons of auditory nerve neurons form synapses with neurons in the medulla
95% of all axons of the auditory nerve form synapses with the inner hair cells, and just 5% do so with outer hair cells. therefore it is the inner hair cells that are crucial for hearing. It is believed that outer hair cells modulate the effects of sound waves on the inner hair cells
place coding of frequency (basilar membrane)
sounds of different frequencies cause different regions of the basilar membrane to flex back and forth. Higher frequencies produce greater displacements as the basal end and lower frequencies produce more displacement at its apex
Binaural processing
The signals from the auditory nerve of each ear are transmitted to both cerebral hemispheres. Binaural processing is essential for localising sounds in space
Primary auditory cortex
the primary auditory cortex is located in a region of the temporal lobe called the superior temporal gyrus. Much of this cortical region is buried inside the deep fold of the lateral fissure, and is therefore not visible from a lateral view of the brain
Tonotopic organisation of the primary auditory cortex
lower frequencies represented more anteriorly and higher frequencies more prosteriorly
The samatosensory system
responsible for representing what is happening to the outer surface of the body and inside it
The samatosensory system incorporated
cutaneous senses: those pertaining to touch
kinaesthesia: information about the positions of limbs
organic sense: information about the state of internal organs
cutaneous senses
respond to many different aspects of a stimuli that impinge directly or indirectly on the skin: pressure, vibration, heating, cooling and noxious stimuli that damage the skin and cause pain
receptors (hairy skin)
Ruffini corpuscles: respond to indentation of the skin
Pacinian corpuscles: respond to rapid vibrations. These are relatively large receptors (up to 1mm in diameter), made up of many onion like layers wrapped around the dendrite of a single axon
Free nerve endings: located near the outer layer of the ski, detect painful stimuli and changes in temperature. Free nerve endings are also found around hair folicles, and are responsible for detecting movement of the hairs
receptors (glaborous skin)
in addition to other skin receptors:
Meissner’s corpuscles: respond to taps and low-frequency vibrations.
Merkel’s disks: respond to indentation of the skin.
The cell bodies of neurons whose dendrites are present in the skin are located in the dorsal root ganglia of the spinal cord.
Somatosensory receptive fields
easier to discriminate between two points when the receptive field in small than when it is large. e.g. threshold for discriminating between two points on the index finger is 2 or 3 mm, whereas our threshold on the back is more than 40 mm
Code of temperature
temperature is encoded by free nerve endings in the skin
Pain - types of nociceptor
pain sensation is also encoded by free nerve endings
- High threshold mechanoreceptors: encode striking, stretching or pinching
- Capsaicin receptors: respond to extreme heat, acid and capsaicin
- ATP receptors: respond when a muscle is damaged or blood supply is interrupted (these fibres are most likely responsible for the pain associated with muscle injury and migraine
the axons from pain receptors have their cell bodies in the dorsal root ganglia of the spinal cord
Somatosensory homunculus
the amount of somatosensory cortex devoted to representing different parts of the skin i based on sensitivity
Phantom limbs
are the sensations that arise from a limb that is no longer present. Occasionally phantom limbs may ‘migrate’ so that it is felt as a part of another region of the skin this is due to brain plasticity
