Senses and Perception Flashcards
What are sensory systems?
- structures containing receptors and interneurons that are specialised for detecting/processing particular types of stimuli
- these can be sensory organs (eye, ear) or body systems (touch)
What are the different sensory systems and their modalities?
- mechanical: touch, pain, hearing, vestibular, joint, muscle
- visual: seeing
- thermal: cold, warmth
- chemical: smell, taste, common chemical, vomeronasal
- electrical: electroreception
Why do sensory receptors need specialised structures to detect stimuli?
- sensory receptor neurons are specialised neurons that detect internal and external stimuli of sensory modality
- input zone contains accessory structures, receptor molecules and/or specialised ion channels (instead of dendrites)
- transforming stimulus energy into neural signals that are transmitted to sensory interneurons
- receptors are either spiking or non-spiking neurons
What is the definition of transduction and what are the receptor types and their associated stimulus energy?
- receptor cell transforms stimulus energy into neural signal
- mechanoreceptors: mechanical (pressure, vibration, stretch, sound)
- photoreceptors: electromagnetic (light)
- thermoreceptors: heat (temperature)
- chemoreceptors: chemical (airborne molecules, surface molecules)
- nociceptors: mechnical, thermal, chemical, uni/polymodal
What are the signal transmissions in sensory systems?
- taste receptors and sensory interneurons in the tongue
- photoreceptor and sensory interneurons in the eye
- hair cells and sensory interneurons in the ear
- pacinian corpuscle in the skin
- olfactory receptor in the nose
What are reflex arcs?
- basic neural circuits, synapse is in the spinal cord
- often complex (polysynaptic: with several interneurons)
- knee-jerk reflex is very fast, connects the sensory neuron directly to the motor neuron
How do sensory neurons connect to one or more circuits?
- sensory neurons (receptor neuron and interneurons): afferent neurons
- motoneurons: efferent neurons that innervate the effector muscle
- motoneuron can either receive input directly from receptor or can be mediated by an interneuron (comes between receptor and motoneuron, other interneurons can connect and give input before the motoneuron)
What distinguishes receptor neurons from interneurons?
- accessory structures, receptor molecules, found in reflex arcs, special type of transduction
- receptor neurons lack ability to generate action potentials and only transmits graded potentials to the output zone
What is the hierarchy of how sensory signals are transmitted?
- hierarchy of processing steps: information is filtered, combined or enhanced as it passes from one layer to the next
- each layer has networks compared of input and output neurons, as well as interneurons
- sensory pathways need serial layers and parallel streams in order to decode, recombine and store different types of information of varying complexity
- from top of hierarchy to bottom: association cortex, secondary sensory cortex, primary sensory cortex, primary sensory cortex, thalamic nuclei, receptors
What is the connectivity of the brain?
- identified anatomically or functionally
- serial connections: bottom-up processing (sensory organ to primary cortex) with top-down control
- parallel streams: e.g. signals diverge into different networks
- cross-connections: e.g. modulation, inhibition, synchronisation
How do the mechanoreceptors pathways to the brain differ?
- each type have distinct pathway to the brain so different qualities of skin stimulation can be communicated to distinct places in brain
- skin is sensitive to mechanical stimulation
- touch and pain: diverse receptors in the skin and body
- posture control: propioreceptors in the body
- hearing: hair cells in inner ears
- balance control: vestibular receptors in the vestibular apparatus
What are the similarities and differences in the function/morphology of skin receptors?
-skin receptors: differs in receptive field sizes, axons for both are located in dorsal root ganglia of the spinal cord, some have encapsulated nerve endings while others have dorsal root, they also differ in the stimulations that they respond to
How do mechanoreceptors differ in their sensitivity?
- small receptive fields: have free nerve endings, Merkel’s disc and Meissner’s corpuscle sense innervate the surface of the skin and are sensitive to stimuli in small areas of the skin
- wide/large receptive fields: Pacinian corpuscles and Ruffini’s endings innervate deeper layers of the skin and are sensitive to larger areas
Which receptors transmit signals from skin to spinal cord?
- Pacinian corpuscle is a unipolar cell that extends one branch of it’s axon to skin and other to spinal cord
- afferent projections form the dorsal root nerve and the cell bodies are part of the dorsal root ganglion
What happens at mechanically-gated ion channels?
- vibration/pressure on skin deforms the corpuscle and stretches the tip of the axon opening the channel
- action potentials generated by influx of sodium ions, if strong enough they’ll travel down axon towards the spinal cord
- response will be low for weak stimulus
- when stimulus is strong (allowing for depolarisation) the response has higher amplitude allowing for action potential to occur
