Behavioural Neuroscience Flashcards
Action potentials
- electrical signal that occurs when neurons are excited
- -A very rapid reversal (depolarisation) of the membrane potential of an axon is called an action potential.
- occur due to opening of voltage gated ion channels
Changes in air pressure from sound waves
We hear sounds when objects vibrate, which in turn causes air molecules to compress and rarefy (become more dispersed) leading to waves that travel away from the object at around 1,100 km/h.
-as it move away, the air pressured is reduced, we then receive these signal
Physical and perceptual dimensions
of sound waves
amplitude(intensity) of sound wave affect loudness (how tall it is)
frequency of a sound wave pitch (how many oscillations)
Accumulation of amplitude and frequency affect the timber (simple or compolex)
Middle ears
-Middle ear: consists of three tiny bones called 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 (snail), which is part of the inner ear.
Inner ears
-Inner ear: consists of the cochlea, which contains the receptors for analysing sounds. The cochlea is a bony structure, but it has two small membranes that form windows on its fluid-filled interior. The stapes is connected to the oval window. Sound waves that cause the stapes to move in and out move the fluid over receptors inside the cochlea. Because the cochlea is a closed structure, another membrane is needed to allow the fluid to move: this membrane is called the round window.
The cochlea
contains the basilar membrane runs along the length of the cochlear
The cochlea converts mechanical movement of the ossicles into fluid movement along the basilar membrane
Movement of stirrup against the oval window
The round window deforms to allow the movement
Transduction of auditory information in hair cells
cillia are linked toghter by tip link
these tip link also control K and Ca ion channels
-bend tot he left ( no signal, to the right 100% signal)
Spiral ganglion cells and the auditory nerve
- When the stereocilia are moved ion channels are opened which in turn cause receptor potentials in the hair cells. The hair cells secrete a neurotransmitter that triggers action potentials in neurons called spiral ganglion cells. The axons of many thousands of spiral ganglion cells are grouped together to form the auditory nerve
- The axons of auditory nerve neurons form synapses with neurons in the medulla (part of the brainstem), which in turn send their axons to other parts of the brain for further processing
Place coding of frequency
along the basilar membrane
- higher frequencies produce greater displacements of the basilar membrane toward its basal end, and lower frequencies produce more displacement at its apex
- Different frequencies of sound are therefore coded by the particular spiral ganglion cells that are active along the basilar membrane, and this information is transmitted via the auditory nerve to the brainstem and other parts of the brain
Characteristic frequency of
hair cells
- a hair cell have a specific frequency that it respond to
Pathway to auditory cortex
Auditory nerve-> Conclear Nuclei ->Superior olivary nucleus -> Inferior Conclius -> Medial geniculate nucleus -> Auditory Cortex
Tonotopic organisation of 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.
Just as the basilar membrane represents different frequencies along its length, so the primary auditory cortex is organised as a tonotopic map, with lower frequencies represented more anteriorly and higher frequencies more posteriorly.
Cochlear implants – based on knowledge of place coding
- Some people are deaf because of damage to hair cells
- electrodes inserted along the basilar membrane
- Stimulation causes spiral ganglion cells to generate actionpotentials
Cochlear implant challenges
- a large number of electrodes to reproduce sound well
- fast sound processors required to determine how much of each frequency is in the sound
- Especially with a large number of electrodes
- Not optimised for music
- Our brain loses the capacity to make sense of novel input as we age
Experience of someone with a
cochlear implant
- Helen lost her hearing at 2 from meningitis
- one of the first people to receive a cochlear implant
- Still has difficulty after successful implant
- Keep in mind the technology has improved
- people able to perceive sound more accurately
- some children learn to sing in tune and can acquire local accents
Extracellular microelectrode
recording
Normally, neural tissue is transparent, but if we inject dye into the cell bodies, we can actually see the cell bodies of these neurons and the processes the dendrites and axons.
we can see also in this microscope image. There’s a fine wire that’s been lowered close to one of these neurons, and this electrode, when it’s hooked up to an amplifier, can actually pick up small electrical changes.
They are associated with the activity in these individual neurons. And on the basis of this technique, it’s possible to understand how neurons at different stages of processing are transforming the signals that originate in the ear and that eventually how those signals will enable us to understand sounds in the world around us.
The electromagnetic spectrum
Our eyes detect the presence and pattern of light reflected off objects in the world. We are sensitive to a very narrow range of wavelengths in the electromagnetic spectrum, known as the visible spectrum. The visible spectrum extends from 380 nm to 760 nm.
Our ability to see these particular wavelengths depends on the fact that this wavelength of energy interacts with structures.
The photoreceptors in our eyes and enables enables them to convert those wavelengths into a neural signal.
-Its the brain that make us see color
The human eye
- Inside the skull the eye is held by a muscle know as extra ocular muscles. also help with pointing the eye to different direction (allow focus of attention)
- light from object will come through the cornea and the lens, and passing through the vitreous centre part of the eye. all of which are transparent
- the back of the eye is a sturcture called retina where photoreceptor (cell that convert light to neural signal) exist
The retina and fovea
- region of highly packed photoreceptor are called fovea, image have highest resolution
- light from lower visual will be process by upper retina and vice versa
- there is a region where ganglion of neuron bundle up to connect the eye with the brain, this region is the blind spot and there is no picture here
Cells of the retina
- Light must pass through ganglion cell and bipolar cell before reaching photoreceptor (all are relatively transparent)
- in photoreceptors, and then it’s converted into neural signal. The signals from these photoreceptors then go through bipolar cells out to gangling cells.
- lateral cell, horizontal cell (make multiple connection with photoreceptor) and amacrine cell (make multiple connection with the ganglion cell) exist in the bipolar layer which allow signal procession.
Transduction of light into
electrical signals in the retina
- stimulus cause the photo pigment lamellae of the receptor cell to become hyperpolarise (more negative) which cause the bipolar cell to depolarise
- enough depolarisation of bipolar cell lead to action potential to be generated by the ganglion cell toward the brain
Three cone types with different spectral sensitivities
there are three types of cones, each containing a photopigment that is sensitive to a different range of wavelengths within the visible spectrum.
1) Short-wavelength (S) cones – peak sensitivity at 440 nm (blue light)
2) Medium-wavelength (M) cones – peak sensitivity at 530 nm (green light)
3) Long - wavelength (L) cones – peak sensitivity at 560 nm (red light)
rod cell 496nm activate at dim light
Ishihara colour plates test for colour deficiencies (blindness)
• Deuteranopia • the green cones are absent • Protanopia • the red cones are absent 1 out of 12 men and 1 out of 200 female are red-green colour blind
Cone combination in the fovea
and periphery
in the central part of the of our vision, where we have most sensitivity, we actually have a closer coupling between the number of photo receptors and the number of ganglion cells.
As we move further away from the phobia, we find that we have a lower density of photoreceptors. But we also have more than one photo receptor, ultimately contributing to a single ganglion cells.
-leading to diference in spacial resolution