Somatic Sensation Flashcards
Outline somatic senses
Mechanoreceptors
Nociceptors
Thermoreceptors
Chemoreceptors
List the stimuli for mechanoreceptors
Touch
Pressure
Vibration
Proprioception
What is the stimuli for nociceptors
Pain
Outline special senses
Vision
Hearing
Balance
Taste
Smell
Why are special senses referred to as special
Have localises special organ structures associated with their reception
What class of neurons are involved in sensory information
Unipolar - single process that branches
How many neurons in dorsal/posterior column pathway
Three neurons between sensory receptor and post central gurus
Outline neuron 1 of the dorsal/posterior column pathway
Cell body in dorsal rot ganglion (unipolar)
Peripheral fibre from sensory receptor in skin
Central fibre (output zone) ascends toward brain in dorsal columns white matter
Makes synapse on neuron 2 in medulla oblongata
Outline neuron 2 in dorsal/posterior column pathway
Cell body in medulla oblongata
Axon crosses to opposite side and ascends
Makes synapse on neuron 3 in thalamus
Outline neuron 3 in dorsal/posterior column pathway
Cell body in thalamus
Axon ascends to somatosensory cortex
Makes synapse on cell body of somatosensory cortex neuron
Hence perception of stimulus, e.g. touch
What stimulates mechanoreceptors and what do nerve endings contain
Physical forces that distort the plasma membrane
Nerve endings contain mechanically gated ion channels
What influences the sensitivity of compression sensing lamellar corpuscles
More superficial = more sensitive
More deep = less sensitivity
What is glamorous skin
Hairless skin
What stimulates nociceptors
Noxious stimuli - responding to signals generated by tissue damage - trigger perception of pain
Where are nociceptors absent from
Absent from the brain
Outline the nerve endings of nociceptors
Usually free nerve endings
What are the 3 main stimuli that nociceptors respond to
Thermal
Mechanical
chemical
What is the relation between a receptor potential and an action potential
Presence of stimulus opens ion channels, creating receptor potential
If receptor potential reaches threshold, and action potential is initiated at sensory receptor
What is single transduction
Process of converting stimulus of one form (e.g. touch) into another (change in membrane potential) is called signal transduction
What is a receptive field
Endings of any single receptor spread over a restricted area
What dictates the receiving of a stimulus in terms of receptive field
Sensory neuron only stimulated when stimulus present within area receptors are located (receptive field)
What is the relationship between receptive field size and perceived stimulus localisation
Large receptive field provides poor localisation of the stimulus, and small fields provide good localisation
What is a tonic receptor
Continually active to reflect background level of stimulation. AP frequency is proportional to stimulus level (eg skeletal muscle position)
Slow adapting
What is a physic receptor
Normally silent
Brief responce to change e.g. touch and temperature
Fast adapting
What are the 4 types of information encoded in sensory stimuli
Modality - type of receptor activated
Intensity - stimulus strength, encoded by frequency of AP firing
Duration - time period over which stimulus exists/ AP are active
Location - place in body where receptors are activated
Why do the regions of the tongue, lip, face etc occupy relatively larger areas of the somatosensory cortex
They have greater numbers of receptors with small receptor fields, in turn providing high reception fidelity, and having more physical synapses in the brain
Area of receptor fields proportional to area take up in brain
