Sensory Receptors 2 Flashcards
What are the differences in receptive field sizes which reflect the differing roles of pacinian corpuscles and meissners corpuscles
Pacinian corpuscles
vibration and pressure
Receptive field are on the middle finger half pinky and half of the hand covering a large continuous area
Meissners corpuscles
Sensitivity to light touch
Receptive field across thumb and other aspect of hand
2 point discrimination
Not very strong in torso
Very strong in finger tip
Due to variation of different receptors
What provides redundancy or back up in the two point discrimation system
Sensory neurones have field of sensitivity that overlap
Size of receptive field?
The smaller the receptive field the better the lines discrimination between stimuli is
What is high linear discrimination
The ability to sense to stimulation points - 2 point discrimination
Why don’t all parts of body have high linear discrimination
High linear discrimation needs more sensory fibres and neurones to over the area with small receptive fields
There is no requirement for some areas of the body such as the torso to have that discrimination and the extra neurones would present a space problem in the spinal cord
Saving space in the spinal cord via less neurones as?
No requirement for certain areas of the body to have high linear discriminatory power which cuts down on neurones
Multiple sane modality sensory neurones with overlapping fields all projecting to a single ascending neuron which again saves space in the spinal cord
Signal convergence?
Sensory neurones can converge on a single secondary neurone
For instance 3 primary neurones overlap to form one large receptive field, and these primary sensory neurones are all sent to and converge on 1 secondary neurone (one Input) which is transferred to the CNS
The failure of one neurone is backed up by the other two
How can we enhance contrast?
Using lateral inhibition
What is contrast enhancement?
When one primary sensory neurone is activated by stimulus and all 3 in the vicinity have a proportional response. It then inhibits neighbouring secondary neurones from firing from their secondary sensory neurone causing an enhanced contrast (makes signal easier to perceive)
Advantages and limitations of sensory receptors
Sensory receptors are good at detecting changes in space or with time and often work using comparisons
However are poor at determining the absolute levels of stimulus intensity
What is the pathway to the brain for sensory information?
Primary afferent - first order neuron - terminates in spinal cord/ brain stem
Second order neurone- projects to the thalamus
Third order neuron- projects to the brain
Where does sensory info go in the brain
Passes through thalamus and onto primary sensory cortex
This is located in a strip posterior to the post central sulcus of the brain
How is sensory information projected in the brain
In a topographical manor to this area with areas of higher discrimation having a larger proportion of he space
Loss of sensation in specific areas can be used?
To determine where neuronal lesions lie this is where maps of sensory dermatomes come in
Arrangement of spinal nerve pairs in body
Cervical nerves are head and upper limb
Thoracic is torso
Lumbar is hips and anterior aspect of dull leg
Sacral is bottom and posterior aspect of full leg
What is shingles and where can it lie dormant
Shingles caused by herpes zoster virus which causes chicken pox in children
Virus can remain dominant in dorsal root ganglion for many years n it’s retroviral form (L4/L5)
What’s the point of adaptation
Helps filter out ongoing signals and emphasis others
What does the size of receptor do
Determines degree of detail sent to the CNS
Smaller better than larger
How are smaller receptive fields represented in the primary sensory cortex
Sensory homunculus
Areas with smaller receptive fields are represented as disproportionately large areas
How can the dermatome pattern be mapped
Using patients with spinal injury or those with shingles
