Physiology Somatosensory system Flashcards
What are the 5 sensory modalities the somatosensory system mediates?
- fine discriminatory touch (mechanosensation)
- proprioception
- thermosensation
- nociception (pain)
- pruriception (itch)
What are 5 different types of fine discriminatory touch?
- light touch
- pressure
- vibration
- flutter
- stretch
What is another name for primary sensory afferent in the somatosensory pathway and is it PNS/CNS?
- 1st order neurone
- PNS
Where are the cell bodies of 1st order neurone in the somatosensory pathway? (2 options)
-dorsal root ganglia
OR
-cranial ganglia
What is another name for the projection neurones in somatosensory pathway and are they PNS/CNS?
- 2nd order neurone
- 3rd order neurone
- CNS
1st order neuron cell bodies are located in the cranial ganglia for innervation of which part of the body?
Anterior head
Where are the cell bodies of 2nd order neurone in the somatosensory pathway? (2 options)
-dorsal horn of spinal cord
OR
-brainstem nuclei
Where are the cell bodies for 3rd order neurones in the somatosensory pathway?
Thalamic nuclei
Where are the cell bodies for the neurones in the somatosensory cortex in the somatosensory pathway?
Parietal and posterior parietal cortex
The receptor potential caused by stimulus opening ion channels and depolarising cells is proportional to stimulus intensity. They have a linear relationship. True/false?
False - receptor potential is proportional to stimulus intensity but they have a non-linear relationship, more sloped in lower stimulus then starts to round out
The non-linear relationship between receptor potential and stimulus intensity means that the greatest sensitivity to change of receptor potential is at low stimulus strength. True/false?
True
What is the relationship between higher membrane potential (i.e. more depolarised) and the number of action potentials?
The higher the membrane potential, the more frequent the action potentials (receptor potentials)
What type of sensory receptor unit detects touch, pressure and vibration?
Skin mechanoreceptors (Different types for each one)
What type of sensory receptor unit detects proprioception?
Joint and muscle mechanoreceptors
What type of sensory receptor unit detects temperature?
Cold and warm thermoreceptors
What types of sensory receptor unit detects pain? (3)
-mechanical, thermal and polymodal nociceptors
What type of sensory receptor unit detects itch?
Itch receptors
What is the adequate stimulus in somatosensory pathway?
The type and intensity of energy that primary afferent neurons are tuned to respond to and that elicits the action potential
What are two types of receptors that have low threshold units and what stimuli do they respond to?
- low threshold mechanoreceptors -> fine discriminatory touch
- low threshold thermoreceptors -> cold through to hot
What are four types of receptors that have high threshold units?
- high threshold mechanoreceptors
- thermal nociceptors
- chemical nociceptors
- polymodal nociceptors
What is adaptation in terms of sensory units?
whether they change their firing rate in response to stimulus of changing intensity or fire continuously for whole stimulus
What is the difference between fast adapting (phasic) receptors and slowly adapting (tonic) receptors?
- Fast adapting receptors respond maximally but briefly to stimuli and their response decreases if stimulus is maintained
- slowly adapting receptors keep firing as long as stimuli is present
What type (very fast, fast or slow adapting) of sensory neurons provide info to CNS about position, degree of stretch or force?
Slowly adapting
What type (very fast, fast or slowly adapting) of sensory units detect changes in stimulus strength e.g. rate of movement?
Fast adapting
What type (very fast, fast or slowly adapting) of sensory unit responds only to very fast movement like rapid vibration?
Very fast adapting
Pacinian corpuscle is an example of what type of sensory unit adaption?
Very fast adapting
Which type of sensory unit adaption does not respond to ramp stimulus (gradually increasing) and only responds to step stimulus?
Very fast adapting
In what type of sensory unit adaptation is the number of impulses proportional to the rate of change of stimulus?
Fast adapting
Put these sensory receptors in order of conduction velocity from Group I to Group IV ( i.e. thickest - thinnest or fastest to slowest).
- Pain, temperature
- proprioceptors of skeletal muscle
- temperature, pain, itch
- mechanoreceptors of skin
- proprioceptors of skeletal muscle (thickest)
- mechanoreceptors of skin
- pain, temperature
- temperature, pain, itch
What is the receptor field?
The area that the free nerve ending to will respond to stimulus
Sensory acuity is his higher when receptor field is smaller and there is higher density innervation. True/false?
True
What is two-point discrimination?
Clinical test of tactile acuity
two areas far apart are pricked and the smallest separation at which two points of pain can be applied at same time and distinguished by patient as two different areas is their threshold distance
In the skin, free nerve endings of the C-fibres are low threshold units that sense vibration. True/false?
False
They are high threshold units that sense pain, heat and cold
What do Meissner’s corpuscles in the skin detect and are they present on hairy/non-hairy skin?
- Touch
- non-hairy skin
What do Merkel’s discs in the skin detect and are they present on hairy/non-hairy skin?
- Touch
- both hairy and non-hairy skin
What do Pacinian corpuscles in the skin detect?
Pressure
What do Krause end bulb receptors in the skin detect? (2)
- Touch
- cold
What do hair end organs receptors in the skin respond to?
Bending of hairs
What do Ruffini ending receptors in the skin respond to?
Dragging forces
In what ganglia does varicella zoster virus remain in latent state after chickenpox?
Dorsal root ganglia
In somatosensory cortex proprioception is interpreted in which Brodmann area?
3A
In somatosensory cortex cutaneous touch is interpreted in which Brodmann areas?
3b and 1
How many layers are there in the somatosensory cortex?
6
Damage to what part of the brain can cause hemispatial neglect syndrome?
Posterior parietal cortex
