Perception and Sensorimotor Control 2 Flashcards
Otolith Organs structure allow them to sense static and translational head movements. How?
Otolithic membrane mass relative to endolymph & physical uncoupling from macula = hair bundle displacement occurs transiently in response to translational head movements (e.g. - head tilting)
Otolith Orientation enables them to transmit information about linear forces acting in every direction that the head moves. How?
the utricle (horizontal movement) and the saccule (vertical movement) combine to effectively gauge the linear forces acting on the head at any instant in time, in three directions
Vestibular nerves arise from bipolar neurones. What does this mean? (3 points)
- cell bodies reside in the vestibular nerve ganglion
- distal processes innervate semi-lunar canals & otolith organs, while the central processes project via the vestibular portion of the vestibulocochlear nerve to the vestibular nuclei
- large amounts of canal-otolith convergence is found in the vestibular nuclei –> enables the unambiguous encoding of head orientation & movement in the environment
central projections of the vestibular system have 2 reflex classes. what are they?
- those responsible for maintaining equilibrium and gaze during movement
- those responsible for maintaining posture
what does the ‘vestibulo-occular reflex’ (VOR) do?
the vestibulo-occular reflex produces eye movements that counter head movements, allowing a fixed gaze
what occurs in the otolith organs when the head tilts backwards? (2 things)
- inertia of otolith organs push gelatinous membrane down & makes hairs deflect
- sterocellia deflected towards kinocilium –> inc^ firing rate
(opposite when head tilts forwards)
what is reflex suppression and reflex potentiation?
reflex suppression: raises the threshold for reflex excitation
reflex potentiation: lowers the threshold for reflex excitation
state what it is meant by the key term - muscle synergy
muscle synergy: a group of muscles connected by neural circuitry and act following a coordinated pattern
state 2 additional facts about the implications of muscle synergy
- reduces possible degrees of freedom & make movement control easier
- reflexes can work in a feedback control fashion –> the voluntary controller sets the desired value of the controlled variable & reflexes are used to activate the muscles needed to maintain/follow it
what type of afferents convey pain and temperature?
smaller afferents
what is the function of the receptive field?
receptive field is a function of the branching characteristics of the afferent within the skin; smaller arborizations result in smaller receptive fields
the receptive fields in areas of dense innervation (e.g. - lips) are relatively small compared to those in the forearm that are innervated by a smaller amount of fibres
what is the effect of different receptive field sizes?
- regional diff in receptive field size and innervation density limit spatial accuracy with which tactile stimuli can be sensed
fingers = 2 mm
bicep = 40 mm
talk about haptics
- active touching (haptics) involves interpretation of complex spatiotemporal patterns of stimuli that are likely to activate many classes of mechanoreceptors
- manipulating an object with your hand can often provide enough information to identify an object (stereogmosis)
what are Merkel Cell Afferents?
Merkel Cell Afferents are slow adapting fibres which make up 25% of the mechanosensory in the hand (especially in fingertips)
what do merkel cell afferents respond to?
information from the epidermis
what are Merkel Cell-Neurite Complexes
merkel cell-neurite complexes lie in the tips of the primal epiderma ridges on finger surfaces
what else do Merkel Cells do?
- play a key role in modulating the activity of their afferent axons by releasing neuropeptides on the neutrites at unctions which resemble synapses
what is the spatial resolution of Merkel Cells?
0.5 mm (highest of all sensory afferents)
What are Merkel Cells receptive to?
points, edges, & curvature –> idead for analysis info on shape and texture
what do Meissner Afferents express?
Piezo2 Channels
what are Meissner Afferents?
- rrepid adapting fibres innervating skin more densely than merkel cells (40%)
where are Meissner Afferents located?
in the Demal Papillae (adjacent to primary ridges and closest to skin surface)
what is the structure of Meissner Afferents? (2 points)
- contain flattened lamellar & nerve terminals both suspended from basal epidermis via collagen fibres
- capsule centre contains 2-6 afferent nerves which terminate between & around lamellar cells, contributing to transient responses of these afferents
what do Meissner Afferents detect?
with identification of the skin, the dynamic tension transduced by the collagen fibres provides the transient mechanical force that deforms the corpuscle and triggers generator potentials (rapid-responders - on/off quickly)
