Somatic Sensation Flashcards
What are the different types of senses that sensory neurons can pick up?
Somatic (detected by receptors in the skin, muscles and joints) and Visceral (detected by receptors in the internal organs)
What does transduction mean?
To convert or change from one form to another
Sensory transduction is converting a sensory stimulus into an action potential.
How does the brain interpret action potentials from sensory neurons?
- Modality: type of stimulus detected by a specific type of receptor
- Duration: time period over which action potentials fire in afferent neurons
- Intensity: rate (frequency) of action potential firing in afferent neurons
- Location: location of receptors within the body. The somatosensory cortex has a map of the locations from which it receives action potentials
Modality of stimulus: what are the four types of sensory receptors?
- Thermoreceptor - temperature
- Chemoreceptor - chemicals
- Mechanoreceptor (3 types)
- Tactile receptors: skin touch
- Proprioceptor: limp position related to torso/trunk
- Baroreceptor: pressure
- Nociceptor: Pain
How do thermoreceptors work?
Thermoreceptors:
- are nerve endings with temperature-gated ion channels
- respond to different temperatures and changes in temperature
- are phasic (fast-adapting)
Transduction of temperature stimuli:
- Temperature stimuli open temperature gated Na+ ion channels
- Allowing Na+ to enter and depolarise the membrane
- If threshold is reached in the thermoreceptor, an AP will fire and propagate to the brain.
How do chemoreceptors work?
Chemoreceptors:
- are specialised receptor cells with chemically-gated ion channels
- respond to different chemical concentrations
Transduction of chemical stimuli:
- Chemical stimuli open chemically gated Na+ ion channels
- Allowing Na+ to enter and depolarise the membrane
- If threshold is reached in the chemoreceptor, an AP will fire and propagate to the brain.
How do mechanoreceptors work?
Mechanoreceptors:
- are nerve endings with mechanically gated ion channels
- respond to physical forces that distort the plasma membrane (deformation)
Transduction of mechanical stimuli:
- Mechanical stimuli deforms the membrane, causing mechanically gated Na+ ion channels to open
- Allowing Na+ to enter and depolarise the membrane
- If threshold is reached in the mechanoreceptor, an AP will fire and propagate to the brain.
Describe the three types of mechanoreceptors
Tactile receptors:
- respond to light touch, pressure, vibration and/or stretch of skin
- some are tonic (slow-adapting)
- some are phasic (fast-adapting)
Proprioceptors:
- respond to stretch/tension in receptors
- Inform about limb position in relation to trunk/torso
- are tonic (slow-adapting)
- it is required to move in a complex and coordinated way without aid of your visual system
Baroreceptors:
- direct pressure in/stretch of tubes
How do Nociceptors work?
Nociceptors:
- are nerve endings that respond to noxious stimuli (hurtful/harmful) typically caused by tissue damage
- have either temperature-gated, chemically-gated or mechanically-gated ion channels responding to extreme stimuli
- are tonic (slow-adapting)
Transduction of noxious stimuli:
- Noxious stimuli cause ion channels to open, allowing Na+ to enter and depolarise the membrane
- If threshold is reached in the nociceptor, an action potential will fire and propagate to the brain
Duration of stimulus: Tonic (slow-adapting) vs Phasic (fast-adapting) Receptors
Tonic Receptors:
- Continually active to reflect background levels of stimulation
- Ap frequency changes when stimulus intensity changes
- slowly adapting
Phasic Receptors:
- Normally silent (no APs)
- Send APs with change but stop quickly (in not painful)
- Fast adapting
What are the advantages of adapting?
- Tonic (slow adapting) we want to get rid of the thing (that is causing pain or harming us) so we feel pain continually
- Phasic (fast adapting) it would drive us crazy to feel everything all the time (overstimulation) so we feel it initially and then adapt quickly so the feeling can be less (if its not important/causing us harm)
This system means we can pay more attention to the important stuff
What affects the intensity of the stimulus?
- the brain interprets stimulus intensity based on the number of action potentials arriving from different neurons (eg. no APs = no sensation, lots of APs = more intense sensation)
- below threshold there is no response in afferent neuron (so no sensation), increasing stimulus increases action potential frequency. - stronger stimuli can also activate more receptors, and action potentials in more sensory axons.
How does the location of stimulus help the brain interpret action potentials from sensory neurons?
- Receptive fields: the area with receptive endings for a single sensory neuron
- size and density of receptive fields affect discriminatory touch (sensitivity) and ability to localise a stimulus
- Large and more widely spaced receptive fields provide: less sensitivity and less accurate localisation
- Small and densely packed receptive fields provide: more sensitivity and more accurate localisation
Describe the somatosensory cortex map
- Somatic sensory neurons send signals from different parts of the body
- Up axons within the dorsal column pathway
- to the somatosensory cortex of the brain
- creating a somatotopic map
How is the somatosensory cortex map laid out (proportions wise)
- Areas of skin with larger receptive fields (eg. trunk/torso/limbs) have less representation in the brain because there are fewer neurons involved.
- Areas with smaller receptive fields (eg. hands and lips) have more representation the brain because there are more neurons involved.
