2 - Somatosensory system 1 Flashcards
What are the somatic senses?
- Pain
- Temperature
- Pressure
- Stretch
- 2-point discrimination
- Vibration
Which receptors detect pain?
Nociceptors
Which receptors detect temperature?
Thermoreceptors
Which receptors detect pressure on skin?
Pacinian corpuscles
Which receptors detect stretch?
Ruffini nerve endings
What is meant by a tonic receptor? Give an example:
Slow adapting, continue to fire APs as long as stimulus continues
- Nociceptors
- Muscle spindle
- Golgi tendon
What is meant by a phasic receptor? Give an example:
Fast adapting, freq of APs decrease over time even if stimulus is unchanged
All mechanoreceptors:
- Pacinian corpuscle
- Baroreceptors
What type of receptors are fast adapting? What does this mean?
Phasic receptors
Freq. of APs decrease over time even if stimulus is unchanged = we can adapt to certain sensory stimuli
ie Pacinian corpuscles
What type of receptors are slow adapting? What does this mean?
Tonic receptors
Freq. of APs continues as long as stimulus continues = we cannot adapt to certain stimuli ie pain
ie Nociceptors
What is the 1st law of the somatosensory system?
1st order neurone is receptor, and has cell body in dorsal root ganglion of spinal cord
What is the 2nd law of the somatosensory system?
2nd order neurone crosses the midline and passes up to thalamus
What is the 3rd Law of the somatosensory system?
3rd order neurone passes from thalamus to sensory cortex via corona radiata
Which order neurone in the somatosensory system is the receptor?
1st order neurone
Which order neurone in the somatosensory system crosses the midline? Where does this neurone end-synapse?
2nd order neurone
Thalamus
Which order neurone in the somatosensory system delivers sensory information to the cortex?
3rd order neurone
Receptors of the somatosensory system have cell bodies…
in the dorsal root ganglion of spinal cord
What factors affect the acuity of a somatic receptor?
- Receptive field
- Density of receptors
- Lateral inhibition
In which parts of the body do somatic receptors have high acuity? (^density, low receptive field)
- Hands
- Face
What is the relationship between acuity and receptive field?
Acuity is inversely proportional to the size of the receptive field
- ^ acuity if small receptive field
What is meant by lateral inhibition?
The primary neurone which is MOST stimulated by the stimulus can inhibit lateral neurones, allowing localisation of the stimulus
How do inhibitory neurones help us localise a stimulus?
Lateral inhibition
The primary neurone which is MOST stimulated by the stimulus can inhibit lateral neurones, allowing localisation of the stimulus
Why is there a large representation of the face and hands on the cortical homunculus?
Representation of each body part is proportional to the density of receptors in that region
^density receptor on face/hands = ^representation
Which areas of the body are represented on the medial aspect of the cortical homunculus?
Lower limb + genitals
Which areas of the body are represented on the upper lateral aspect of the cortical homunculus?
Trunk + Upper limb
Which areas of the body are represented on the lower lateral aspect of the cortical homunculus?
Face
Describe the area of the brain responsible for the motor function of swallowing:
Lower lateral aspect of the pre-central gyrus (primary motor cortex)
- Frontal lobe
Describe the area of the brain responsible for the motor function to bend the knee:
Medial aspect of pre-central gyrus (primary motor cortex)
- Frontal lobe
Describe the area of the brain responsible for detecting a change in pressure on the feet:
Medial aspect of the post-central gyrus (primary somatosensory cortex)
- Parietal lobe
Describe the area of the brain responsible for detecting a change in temperature in the hands:
Middle lateral aspect of the post-central gyrus (primary somatosensory cortex)
- Parietal lobe
Describe the area of the primary motor cortex:
Pre-central gyrus, frontal lobe
