Lecture 6- the senses Flashcards
What is transduction
The process by which receptors convert sensory stimuli to neural signals/ action potentials.
What does the thalamus do?
It relays sensory impulses from receptors to the body to the cerebral cortex.
Summary of the vision system pathway
Light enters through the cornea through the pupil. And an image is produced onto the retina. The retina contains photoreceptors which convert light into signals.
Photoreceptors then send signals to bipolar cells, then to ganglion cells which send them into the optic nerve to carry information to the brain.
Photoreceptor layer of the retina
Have rods (grey-scale) and cones (colour vision- either red green or blue).
When there is light the cGMP molecule opens Na channels. Na depolarises the photoreceptor creating a dark current. The dark current leads to release of the neurotransmitter glutamate.
When there is light it is absorbed by Rhodopsin enzyme which causes g-protein to activate PDE which brakes down cGMP causing Na ion channel to close. So there is no dark current
Intermediate layer of the retina
Contains Bipolar, amacrine and horizontal cells which transfer information from rods and cones to retinal ganglion cells.
Ganglion cells layer of the retina
Output action potentials to meet the brain through the optic nerve.
Vision pathway summary (after retina)
Optic nerves from each eye meet at the Optic Chiasm where nerve fibres cross to opposite sides of the brain.
Info is processed in the thalamus .
In the V1/ striate cortex the occipital lobe processes information about the orientation, colour depth and spatial frequency. It has topographic organisation.
Then travels to the secondary visual cortex which feeds back and forward to V1. It has higher level processing (object recognition and where it is )
Different types of mechanoreceptors
Merkel cells: light touch and shape
Meissner’s corpuscles: light touch and low-frequency vibrations.
Pacinian corpuscles: deep pressure and high- frequency vibrations.
Ruffini endings: skin stretch and pressure.
Different parts of the body have different number of receptors and receptive fields (fingertips have larger receptive fields and are more densely packed)
Sensory pathway summary
Receptor’s electrical signal travels along a sensory nerve fibre to the dorsal column in the spinal cord.
Passes through the thalamus
To the primary sensory cortex. This has somatotopic organisation and Homunculus which is the representation of the body based off the parts of the brain dedicated to processing signals from those areas. Lots of cortical areas are dedicated to processing info from hands and fingers.
Then to secondary cortex
To any associative areas.
Pain pathway summary
Pain detected by nociceptors.
2 types: A fibres (detect immediate pain quickly and myelinated.) C fibres (detect dull and aching pain, slow and unmyelinated)
S1 and S2 perceive the intensity and quality of the painful stimuli.
Other areas (amygdala ACC and insular cortex) meditate fear perception and any anxiety/ fear connected to the limbic system.
Frequency/ pitch VS amplitude
Frequency/ pitch is the speed of vibrations (how many waves)
Amplitude (size of vibration)
Hearing pathway summary
Soundwave vibrations call receptors hair cells to ben.
Bending causes opening of Ca channels.
Ca entering signals vesicles to bind to hearing cells and release neurotransmitters.
Action potential is transmitted to the brain via the auditory nerve (chemical synapse)
Action potential travels through the thalamus to the auditory cortex.
A1 is tonotopically organised.
Higher auditory areas process complex features like recognition of what the sound is.
A1 processes only speed and frequency
What is the vestibular system
Detects rotation, head rotation, balance and gaze orientation.
Vestibular system- Three semi-circular canals
located in the inner ear. At right angles to each other.
They are filled with liquid. Contain a structure called Ampulla which contains hair cells embedded in a mass called cupula. When we move so does this mass.
Movement causes bending of hair cells.
Generating action potentials
(The anterior, posterior and horizontal)
The utricle and saccule in the Vestibular system
Detect moving forward, sudden stops and moving up or down.
Contain hair cells which are covered by a layer of calcium carbonate crystals called otoliths which sense linear acceleration as they move in the same direction as our movement.
Linear acceleration causes crystals to bull the substance downwards, bending hair cells and leading to depolarisation.
