The Senses Flashcards
What is transduction?
The process where receptors will convert sensory information into neural signals
What is the sensory process?
- Sensory organs collect the signal
- Sensory receptors convert the energy of the stimuli into neural signals
- The signal is transmitted to sensory brain areas
- The brain processes the signal
Where does transduction begin?
At the sensory receptor
How are sensory systems specialised?
To detect environmental stimuli
What is the step of receptor potentials?
Between the arrival of energy at the receptor cell and the initiation of an action potential
What does the thalamus do?
Relays sensory impulses from receptors to various parts of the body to the cerebral cortex
What does the pupil do?
Allows an opening for light to reach the retina
What does the iris do?
Vary the size of the pupil
What is the pupil and iris covered by?
Cornea
What is the optic nerve?
A nerve that carries axons from the retina, exits the back of the eye and passes through the orbit to reach the brain
What is the optic disk?
Where the optic nerve exits the retina
Why can’t the sensation of light occur at the optic disk?
Lack of photoreceptors
What happens when the eye captures light?
It focuses it on the visual receptors?
What do photoreceptors do?
Convert light energy into neural impulses which are sent to the brain
What does photoreceptors influence?
The membrane potential of bipolar cells
What are the two types of photoreceptors?
Rods and cones
What are the four types of neurones in the retina?
Ganglion cell, bipolar cell, amacrine cell, horizontal cell
What do ganglion cells do?
Fire action potentials to propagate to the optic nerve and then to the brain
What do amacrine cells do?
Input from bipolar cells and influence ganglion, bipolar and other amacrine cells
What do horizontal cells do?
Receive input from photoreceptors to influence bipolar cells and photoreceptors
What are the layers of the retina?
Photoreceptor layer, the intermediate layer, the ganglion cell layer
What vision does the rods and cones provide?
Rods- grey scale and cones- colour
What happens in the photoreceptor layer?
Phototransduction
What occurs when there is darkness in the photoreceptor layer?
The Na+ ion channel open from cGMP and the photoreceptor is depolarised from the influx of sodium which creates a dark current
What does the dark current from phototransduction lead to?
A continuous release of glutamate
What is light absorb by in phototransduction?
A pigment in the rods and cones, rhodopsin
What happens when there is light in the photoreceptor layer during phototransduction?
The photopigment changes shape, G-proteins are activated from the exchange of GTP for GDP which activates PDE. cGMP is removed and the NA+ channels to signal to decrease glutamate release
What occurs in the intermediate layer of the retina?
Bipolar, amacrine and horizontal cells will transfer information from rods and cones to retinal ganglion cells
What cell is the output from the retina?
Ganglion cells in the ganglion cell layer which fire action potentials to reach the visual brain areas
What is the vision pathway?
Eye, retina, lateral geniculate nucleus, primary visual cortex (V1), secondary visual cortex
What is the lateral geniculate nucleus a part of?
The thalamus
What does the lateral geniculate nucleus do?
A primary centre for the processing of visual information and receives feedback from the cortex and the eye
What is the primary function of the primary visual cortex?
To process visual information
What does the primary visual cortex project to?
Higher visual areas in the cortex
What does the primary visual cortex compute?
Orientation, spatial frequency, motion,
colour, depth
What organisation does the primary visual cortex have?
Topographic
What does secondary cortical areas do?
Feed forward and feedback connections to the primary visual cortex
What is somatosensation responsible for?
Perceiving and interpreting various sensations related to the body’s physical state and the external environment such as touch and pain
What are the 4 receptors for touch?
Merkel cells, Meissner’s corpuscles, Pacinian corpuscles, Ruffini endings
What do Merkel cells process?
Light, touch and shape
What do Meissner’s corpscules process?
Light, touch and low frequency vibrations
What do Pacinian corpuscles process?
Deep pressure and high frequency vibrations
What do Ruffini endings process?
Skin stretch and pressure
Which mechanoreceptors have large receptive fields?
Pacinian corpscules and Ruffini’s endings
Which mechanoreceptors have small receptive fields?
Meissner’s corpscule and Merkel cells
Which mechanoreceptors are rapidly adapting?
Meissner’s corpscule and Pacinian corpscule
Which mechanoreceptors are slow adapting?
Merkel cells and Ruffini’s endings
What are receptive fields
Region of space in which a sensory receptor responds to a stimulus
What do different parts of the body have?
Different numbers of receptors and different receptive fields
High density of mechanoreceptors=?
Smaller and numerous receptive fields and fine tactile discrimation
Low density of mechanoreceptors=?
Large and less densely packed receptive fields with less precise touch discrimination
What is a dermatome?
Area of skin that is mainly supplied by a single spinal nerve
What is the touch pathway?
Mechanoreceptors, dorsal column, thalamus, primary somatosensory cortex, secondary somatosensory cortex, associative areas (parietal lobe)
What is somatotopic organisation?
When each part of the skin surface is represented by a specific region of the somatosensory cortex
What does a homunculus show?
Represents the body based on proportion of the brain areas dedicated to processing tactile signals (Mouth and tongue being large due to taste perhaps)
What is pain defined as?
“Unpleasant sensory or emotional experience
associated with actual or potential tissue damage”
How is pain detected?
Nociceptors
What are the two types of nociceptors?
A fiber and C fiber
What is the characteristics and what does A fiber transmit?
Transmits sharp prickly pain
Thin, myelinated and fast
What is the characteristics and what does C fiber transmit?
Dull aching pain
Thin unmyelinated slow
What is the pain pathway?
Nociceptors on the skin, dorsal column, thalamus, primary somatosensory cortex, secondary somatosensory cortex, anterior cingulate+insula+amygdala
What does the somatosensory cortex S1 and S2 do?
Mediates the perception of location, intensity and quality of the painful stimuli
What does the amygdala. anterior cingulate cortex and the insular cortex do in the pain pathway?
Mediate the perception of fear, anxiety and unpleasantness associated with painful stimuli
What are waves produced by sound characterised by?
Frequency and amplitude
What is frequency?
The speed of the vibration
What happens to the pitch when there is a shorter wavelength cycle?
A higher pitch
What happens to the pitch when there is a longer wavelength cycle?
A lower pitch
What does amplitude mean?
The size of the vibrations
What does the greater amplitude correspond to?
A louder sound
What does a lower amplitude correspond to?
A softer sound
What occurs when there are vibrations from sound waves?
- The hair cells of the stereocilia bend
- Ca+ channels open for calcium to flow and vesicles release neurotransmitters
- An action potential is generated
- Hair cells convert mechanical energy into action potential
- The action potential is transmitted to the brain via the auditory nerve
What is the hearing pathway?
Cochlea, cochlear nerve, olivary nucleus in the brainstem, inferior colliculus, median geniculate nucleus in the thalamus, auditory cortex
Where is sound processsed?
In the primary auditory cortex
Where is the primary auditory cortex?
In the superior temporal lobe
How is the primary auditory cortex organised?
Tonotopically where different frequencies are represented in different locations
Where are complex features of sound processed?
In higher auditory areas
What is the vestibular system important for?
Balance, movement, gaze orientation, angular acceleration
What is angular acceleration?
Head rotation
What are semi-circular canals?
A component of the vestibular labyrinth filled with a jelly like liquid
What is the semi-circular canals continuous with?
The cochlea
What happens when there is movement of the head?
- Liquid moves
- Liquid bends the vestibular hair cells
- The bending of the vestibular hair causes a generation of action potentials
What do otolith organs (otoliths) sense?
Linear acceleration
What do otoliths consist of?
Hair cells in a jelly like substance and covered with heavy calcium carbonate crystals
What occurs during linear acceleration?
The crystals pull the jelly like substance down, so the stereocilia bends and depolarisation occurs
What is the vestibular pathway?
Vestibular receptors, brainstem, cerebellum, thalamus, vestibular areas
What does the vestibular network include?
Somatosensory cortex, premotor cortex, anterior insula, posterior parietal cortex, temporoparietal junction, hippocampus
