somatosensory system Flashcards
mechanoreceptors
sensitive to bending, stretching, pressure, or vibration
what are the 4 specialized nerve endings
- merkel’s disk
- meissner’s corpuscle
- pacinian corpuscle
- ruffini ending
what are the 4 qualities of a stimulus that are endoded by our sensory system
- modality
- location
- intensity
- duration
what are the 5 sensory modalities
- vision
- hearing
- touch
- taste
- smell
each with submodalities
awareness of ____ ____ depends on spatial distribution of activated receptors
spatial aspects
what is intensity signaled by
signaled by firing rate
what is duration signaled by
signaled by time course of response
what is the receptive field of a receptor
the space within the receptive sheet in which the sensory receptor is located and in which it transduces stimuli
RF of mechanoreptor
certain area of skin where it can transduce pressure or vibration
what is the gradient of sensitivity within the receptive field
highest in the center and progressively lower toward the periphery
the frequency of action potentials is proportional to the ____ of the stimulus
intensity
neurons tell us something about stimulus ____ and ____
location and intensity
what is duration
adaptation to prolonged stimulation
meissner’s corpuscle adaptation and receptive field size
rapid; small
pacinian corpuscle adaptation and receptive field size
rapid; large
merkel’s disk adaptation and receptive field size
slow, small
ruffini’s ending adaptation and receptive field size
slow, large
most 2nd order neurons have ____ ____ in their RFs which enhances spatial resolution
surround inhibition
spatial resolution: two-point discrimination
best for body regions with the highest innervation density and amount of cortical area devoted to them: e.g. fingers and lips
spinal segments
spinal nerves within the divisions of the spinal cord
what does each spinal segment provide
sensory innervation to a particular region of the skin
dermatome
the area of skin and deeper tissues innervated by a single dorsal root
DC-ML first neuron
large myelinated axons of dorsal roots that carry proprioception and touch modalities into the cord
touch, vibration, conscious proprioception information ascends through:
- dorsal columns (spinal cord)
- dorsal column nuclei (medulla)
- medial lemniscus (brainstem)
- ventral posterior nucleus (VPL, thalamus)
- primary somatosensory cortex, S1
nociceptors
- mediate transduction of pain
- activated by stimuli that could cause tissue damage
- free nerve endings
thermal receptors
- mediate transduction of cold, cool, warm and hot
- free nerve endings
spinothalamic tract first neuron
- small diameter axons of dorsal roots that carry pain and temperature modalities into the cord
- they all synapse with sensory neurons in the dorsal horn
what synapses in the substantia gelatinosa of dorsal horn
A and C afferents
decussate and travel up the cord in the ____ tract to the thalamus, VPL, and then to S1
spinothalamic
the trigeminothalamic tract (dorsal trigeminal tract)
- touch, vibration
- CN V, from face to main sensory nucleus of V
the trigeminothalamic tract (ventral trigeminal tract)
- pain, temperature
- spinal trigeminal tract
- spinal trigeminal nucleus
somatotopic map in S1 of contralateral body
neighboring receptors in skin send information to neighboring cells in VPL/VPM which send information to neighboring cells in S1
damage to somatosensory cortex results in:
contralateral sensory deficits
somatotopic map of facial vibrissae in mouse SI
- sensory signals from each vibrissa follicle go to one cluster of SI neurons called a “barrel”
- barrel cortex in SI
areas 3b and 1
cutaneuous stimuli
areas 3a and 2
proprioceptive stimuli from muscles and joints
functional columns in neocortex
- found within the somatopic map
- neurons with same modality from pia to white matter
- slowly adapting neurons
- rapidly adapting neurons
the posterior parietal cortex
- involved in somatic sensation
- analysis of “where” things are from visual inputs
agnosia
inability to recognize objects
astereognosia
loss of stereognosis: the ability to perceive the form of an object by using the sense of touch
neglect syndrome
part of body or part of world is ignored
parietal neglect in dogs
- don’t eat half the bowl of food
- run into things on neglected side
- circling
