~Chapter 14 - Lecture Section 14.1 Flashcards
___ Perception is part of the broader category of Somatosensory processing.
Cutaneous
What is Cutaneous Perception?
Processing of touch and pain sensations from receptors in the skin
What is Proprioception?
“Body sense”, processing of input from skin, muscles, tendons, and vestibular systems to create a perception of the body, and where it is in the environment. Can be used for posture and movement
What is Kinesthesis?
A sense of movement of the body and limbs
What sense is one of the most ancient and important of all the senses?
Touch
All ___ are deaf, this includes ___, ___, and ___.
Cephalopods // Octopi // Squid // Cuttlefish
___ and ___ have poor hearing.
Snakes // Armadillos
In no group of animals is the sense of ___ optional, sense of ___ is well-developed across all different kinds of animals.
touch // touch
What are the Evolutionary 4 F’s?
Fighting, Fleeing, Feeding, and Fornicating
Why has Cutaneous Perception been difficult to study?
- Developing a precisely controllable stimulus
- There is a limitation in the Electrophysiological techniques. Its fairly hard to characterize the receptors themselves because of Touch Artifacts, where, when you’re recording from an area, if you move and wiggle the electrode it creates interference, and so the fact that you are touching the skin, even if the electrode is placed fairly far away from the site of recording, you get movement artifacts.
- Finding appropriate animal models to study touch info in. Humans are fairly unique mammals in that we have mostly hairless skin, and so there are specializations in humans that don’t exist in other mammals.
What is the heaviest organ in the body?
The Skin
Is the skin the largest organ in the body?
No. The Villi and Alveoli in the digestive and respiratory system have larger surface areas.
What is the function of the Epidermis and Dermis?
They work together to prevent bacteria, chemical agents and dirt from entering our bodies. They also preserve bodily fluids by decreasing evaporation.
What is the Epidermis composed of?
Dead cells
The Dermis is made up of ___.
Live cells
The Dermis houses specialized receptors for ___.
Cutaneous perception
The specialized receptors for touch are referred to as ___.
Mechanoreceptors
What are the 4 Mechanoreceptors?
Merkel Receptor, Meissner Corpuscle, Ruffini Cylinder, Pacinian Corpuscle
The names of the Mechanoreceptors are of ___ and ___ origin.
Italian // German
The Merkel Receptor is associated with ___ fibres.
SA1
The Meissner Corpuscle is associated with ___ fibres
RA1
The Ruffini Cylinder is associated with ___ fibres.
SA2
The Pacinian Corpuscle is associated with ___ fibres.
RA2
Mechanoreceptors have Mechanosensitive transducers which transform ___ into ___. Somewhat similar to the Mechanosensitive channels in the ___.
physical movement // neural activity // Cochlea
Transducers reside in the ___ of ___.
unmyelinated endings // afferent fibres
The unmyelinated ending of a Transducer is studded with ___.
Mechanosensitive ion channels
What does “SA” mean?
“Slowly adapting”. This means that, if you press on a Merkel Receptor, as long as the pressure is present, it will continuously fire action potentials until the stimulus is discontinued.
What is the frequency response of a Merkel Receptor?
0.3-3Hz
Where is the Merkel Receptor located?
Shallow location, on the Dermis/Epidermis border.
What is the order of depth of the Mechanoreceptors from most superficial to deepest?
Merkel Receptor → Meissner Corpuscle → Ruffini Cylinder → Pacinian Corpuscle
What is the size of a Merkel Receptor?
1 branch = 0.5mm
Whole RF = 2-5mm
What does “RA” mean?
“Rapidly adapting”. This means that these neurons only respond to changes in a pressure stimulus.
The Meissner Corpuscle will only give a burst of action potentials when the pressure is ___ and when the pressure is ___.
initiated // relieved
What is the frequency response of the Meissner Corpuscle?
3-40Hz
What is the location of the Meissner Corpuscle?
Shallow location in the Superficial Dermis
What is the size of the Meissner Corpuscle?
3-5mm
What is the frequency response of the Ruffini Cylinder?
15-400Hz
What is the size of a Ruffini Cylinder?
Large in size, 10-30mm
What is the location of the Ruffini Cylinder?
Deep location in the Mid-Dermis
What is the Frequency response of a Pacinian Corpuscle?
10-500Hz
What is the location of the Pacinian Corpuscle?
Deep location in Subcutaneous fat
It only responds to Transient Pressure Events, where a change in the stimulus is signalled by a burst of action potentials.
What is the size of a Pacinian Corpuscle?
Large in size. Entire finger or whole hand.
The Pacinian Corpuscle only responds to ___, where a change in the stimulus is signalled by a burst of action potentials.
Transient Pressure Events
There is a relationship between the ___ of the receptor types and the ___.
location // receptive field size
The more shallow a receptor is, the ___ the receptive field, and the deeper, the ___ the receptive field.
smaller // larger
Each Mechanoreceptor has evolved to detect ___ touch stimulus.
behaviorally relevant
What are the 3 things that dictate the response properties of each receptor?
- The physical ultrastructure of the receptor ending
- The Ion channels they express on the unmyelinated ends of the afferent fibers
- The physical location of the receptors is important.
The 4 Mechanoreceptors all have different structures which likely contribute to their ___.
function
The 4 Mechanoreceptors occur most frequently on ___.
Glabrous Skin
What is Glabrous Skin?
Glabrous skin is smooth, hairless skin that occurs on your hands and your face most predominantly
Other skin, which is referred to as “hairy skin”, on humans and other mammals, is covered in thick fur, and has different kinds of receptors.
The location of the different receptors indicates that they probably do ___.
specialized jobs
The 4 Mechanoreceptors are very important for interacting with objects with your ___ and ___. Related to ___ and ___.
hands // face // grasping objects // eating
Touch stimuli are further processed in the ___ and ___.
Thalamus // Cortex
There are 2 pathways from the skin to the ___, one for ___ information, and other for ___ information.
Cortex // touch // pain
The ___ is made up of large fibers that carry information about touch and Proprioception.
Medial Lemniscal Pathway
What is the journey of the Medial Lemniscal Pathway?
There are fibre endings → the cell bodies are located the Dorsal Root Ganglion → those axons will travel from the skin to the spinal cord → there they Synapse on the Gracile and Cuneate nuclei → then Decussate in the Medulla before reaching the Thalamus, which is the Ventral Posterior Lateral nucleus, which the controls input to the Somatosensory Cortex.
The ___ consists of small fibers which carry temperature and pain signals.
Spinothalamic Pathway
What is the journey of the Spinothalamic Pathway?
Their cell bodies are located in the Dorsal Root Ganglion → the axons of these fibres go from the skin all the way through to the spinal cord where they Synapse at the Dorsal Horn and the Substansial Gelatinosa → then they Decussate/cross over the Contralateral side before they travel up to the Thalamus, the Ventral Posterior Lateral nucleus, from the Thalamus, that pain info then travel to Somatosensory Cortex.
Like the Visual and Auditory system, there is ___ representation, so your ___ finger is represented in the ___ Somatosensory Cortex.
Contralateral // Left // Right
The Somatosensory Cortex is located at the most ___ part of the ___.
Anterior // Parietal Lobe
Fibers from both pathways ___ before reaching the ___.
decussate // Thalamus
Most Fibers synapse in the ___ or ___ portions of the ___.
medial // lateral // Ventral Posterior Lateral Nucleus
What is Somatotopic mapping?
Where neighbours on your skin are represented by neighbouring neurons in the Thalamus and Cortex. This Somatotopic organization that creates a map in the brain that looks like a little body sometimes called a Homunculus.
There are ___ representations of the body in one piece of Cortex, and then also there are Somatotopic maps that are repeated across the Somatosensory Cortex.
multiple
There are several maps in the ___, ___, and Somatotopic maps in other ___.
Somatosensory Receiving Area (S1) // Secondary somatosensory area (S2) // Somatosensory areas
Why do Somatotopic maps/Homunculi not have regular human proportions?
This is because there is something similar to a Magnification Factor like we covered in vision, the Cortical representation of the different parts of the body are related to the receptive field size, such that, parts of the skin that are covered with very small and numerous receptive fields tend to take up a larger portion of the Cortex.
The Cortical representation of the different parts of the body are related to the ___, such that, parts of the skin that are covered with very small and numerous receptive fields tend to take up a ___ portion of the Cortex.
receptive field size // larger
Each neuron with a receptive field takes up some unit of space in the Cortex, all the neurons are basically the ___.
same size
Areas of the body with numerous small receptive fields end up having a very ___ representation in the Cortex.
large
___, ___, and ___ have a very large representation in the Cortex.
Genitals // Hands // Lips
Areas of the body with fewer, but larger receptive fields have ___ representation in the Cortex.
less
The ___ have a small representation in the Cortex.
forearms
Plasticity in the Cortical representation of touch (Primary, Somatosensory receiving area, and Secondary Somatosensory receiving area) changes in these areas, and can be induced by increasing the ___ of a stimulus.
behavioural relevance
When using electrodes to study the Somatotopic Maps in Primates what did researchers find?
When the monkey realizes it has to use its fingertip in order to detect the stimulation and get the reward, the representation of the finger blows up and becomes larger. The Cortex is flexible, and it can rewired its processing to better accommodate the behaviourally relevant stimuli.
___ rewires even in adults, while in the ___, much of the plasticity that was studied, ends up being locked in during development, such that it is much less plastic in teenage and adult years.
Somatosensory Cortex // Visual system
One of the functions of the Cortex is to flexibly deal with ___.
behaviourally relevant stimuli
