Physiology - Somatic Sensation Flashcards
List the functions of the sensory system.
Acquire information about environment (external and internal)
Convert into AP (transduction: change physical stimulus into AP)
Communicate info around body
Process info
Give it meaning - stimulates responses
Name the 3 sensory subtypes.
Somatic: from body e.g. touch/pain
Visceral: from internal organs e.g. BP
Special senses; from specific organs e.g. hearing/vision/taste
Name and describe the two types of somatic sensation.
Discriminative sensation: touch, vibration, muscle length and tension, proprioception (joint position sense)
Affective sensation: pain, erotic touch and warm/cold
List the different types of sensory receptors.
Mechano Chemo Thermo Photo Nociceptors
What does the sensation we feel depend on?
Coding depends on which receptors are stimulated (i.e. modality specific)
What we feel depends on which receptors are stimulated
No receptors = no feeling
What is the function of receptors?
Transduce the physical stimulus into an AP
Describe the structure of a sensory neuron.
Specialized ending of a sensory neuron (receptor is part of the nerve)
Specialized cell associated with a sensory neuron
How do we increase the intensity of the sensation we feel?
Increase the frequency of activation of the receptors (activate receptors more often)
Activate more receptors
What is the relationship between intensity of sensation and stimulus?
Intensity is directly proportional to the log of the stimulus energy.
10 x stimulus = 2 x intensity of sensation
What is the exception to the relationship of intensity and stimulus?
Pain - pain sensation has a linear relationship to its stimulus
What is a receptive field?
One sensory neuron usually associated with more than one receptor.
Each neuron has a receptive field
What is the importance of small receptive fields?
Improve localization and discrimination
What is surround inhibition?
Receptive fields overlap
Touching one field activates another field
By having the surround inhibition, inhibitory signals are sent to the other fields
Strength of signal decreases, but output is discrete
No surround inhibition results in the spreading out of information and no discrimination
What is sensory adaptation?
Some types of receptors adapt to a constant stimulus with decreases neuronal output. E.g. light touch - cannot feel clothes on skin
Speed of adaptation varies
What determines the conduction of APs?
Size and myelination of sensory axons
Big - conduct quickly
Small - conduct slower
Describe the general direction of pathways of communication
Peripheral nerves/dorsal horn –> spinal cord pathways to thalamus –> thalamus to cortex
What is important to note about the communication pathways?
Cross over - right body is controlled by left brain and vice versa
Name the two ascending tracts.
Dorsal column (medial lemniscal pathway) Anterolateral/Spinothalamic
What is another name for the dorsal column?
Medial lemniscal pathway
What info is conveyed in the dorsal column?
TVP - touch, vibration, proprioception
What is the speed of the dorsal column pathway?
Fast
Describe the pathway of the dorsal column.
Crosses at medulla
UP and ACROSS
Ascends ipsilaterally
Dorsal horn - dorsal column - cuneate and gracile nuclei - arcuate fasciculus - ventroposterolateral (thalamus) - primary somatosensory cortex
Describe the pathway of unconscious proprioception from the lower body.
Lower body - clarke’s nucleus - spinocerebellar tract - gracile nucleus and branches to cerebellum
Describe the pathway of unconscious proprioception from the upper body.
Upper body - cuneate nucleus - branches to cerebellum
What info does the anterolateral/spinothalamic pathway carry?
Pain, temperature (affective sensation)
What is the speed of the spinothalamic pathway.
Slow
Describe the pathway of the anterolateral/spinothalamic.
ACROSS and UP
Crosses at level of entry to spinal cord
Ascends contralaterally
Dorsal root - dorsal horn - cross in anterior commissure - anterolateral tract - VPL - primary somatosensory cortex + branches to brainstem and cortex and cingulate gyrus (arousal/emotion)
Where does processing occur?
Primary somatosensory cortex (post central gyrus) - parietal lobe
Describe how the type, intensity and location of sensation is determined.
Type - type of receptors activated
Intensity - number/frequency of receptor activation
Location - cortical mapping (somatotopy)
How many areas is the somatosensory cortex divided into?
4 functional areas
3a + 3b –> 1+ 2
