L6 - Sensory systems Flashcards
What are mechanoreceptors innervated by?
Large myelinated axons with cell bodies in the dorsal root ganglia.
4 main nerve endings in skin, from deepest to most superficial
• Pacinian corpuscle (15%) - deep in dermis and hypodermis, rapidly adapting, most sensitive (lowest mechanical stimulation threshold) encapsulated ending surrounded by connective tissue that forms a sponge around the outside
-Vibration detectors with large receptive fields and stop firing after first activation, staying silent until stimulus is removed.
• Ruffini endings (20%) - slowly adapting receptors, in upper dermis, large receptive fields
-“Proprioceptive”
• Merkel cell complexes (25%) - slowly adapting receptors, tip of epidermal ridges, less sensitive, higher resolution, smallest receptive fields.
-Fires continuously throughout the stimulus as their axons have many branches
• Meissner corpuscles (40%) - rapidly adapting (but less rapidly and less sensitive than Pacinian corpuscles), small receptive fields
-Fires AP at the start and ends of the stimulus
Are mechanoreceptors neural cells?
No
What does CN5 aka ___ nerve innervate
Trigeminal. Skin of face and skull
What type of nerve endings are noiceptors?
High threshold free nerve endings
Which mechanoreceptor will tell you most about an object, if you were manipulating it?
Ruffini endings get activated from movement or stretch to skin as well as having a proprioceptive effect
When you have an object and touch it on something, which mechanoreceptor tells you the time of contact?
Pacinian corpuscle as they are vibration detectors
What is two point discrimination/threshold?
The smallest distance between two points that still results in the perception of two distinct stimuli is recorded as the patient’s two-point threshold.
Neuron pathway for mechanosensation
1) Medulla
2) Dorsal column nucleus
3) Thalamus (forebrain)
4) Cerebral cortex
The pathway from primary mechanoreceptive afferents to the cortex contains two synapses (in the brainstem and thalamus). Fibres cross in the brainstem so that the right side of the body is represented in the left side of the brain and vice-versa
Everything in front of central sulcus is used for ____
Everything behind it is for ___
Action - planning & movement
Perception (somatosensory areas)
3 features of cortical represenation
1) Topographic
2) Scaled
3) Plastic (can cut off hand and cortical representation will rearrange itself)
Which nerve endings have a higher innervation density (particularly where high tactile resolution is needed)?
Meissner and Merkel afferents
Slowly adapting receptors have what sort of responses vs rapidly adapting ones
Merkels and Ruffinis are slowly adapting receptors (dynamic plus static response); Meissners and Pacinians are rapidly adapting or fast adapting (dynamic response only).
The somatosensory cortex, on the postcentral gyrus, consists of Brodmann areas _______ The entire body surface is mapped onto the cortex in an ordered way. The map is distorted, with relatively more cortex devoted to parts of the body that require high spatial acuity (homunculus). Each Brodmann area has a complete map. Animals like the star-nosed mole have appropriately specialised somatosensory representations.
1, 2 , 3ab
