Week 3 - finished Flashcards
Define sensation
The perception of our relationship to our environment
What are the 4 sensory modalities?
Pain
Temperature
Touch
Proprioception
How is the perception of touch elicited?
By the mechanical stimulation of the body surface
What is proprioception? How is the perception of it elicited?
It is information about joint angles, position and the orientation of our body in space.
It is elicited by the mechanical displacement of joints, overlying skin and muscle.
How is the perception of pain elicited?
By noxious or tissue damaging stimuli
How is the perception of temperature elicited?
By warm or cold stimuli acting on receptors specific to either hot or cold
What are the 4 types of mechanoreceptors in glabrous skin?
Merkles receptors
Meisners corpuscles
Pacinian corpuscles
Ruffini’s corpuscles
Which of the mechanoreceptors are type 1 receptors and where are they found?
These are Merkles receptors and Meisners corpuscles and they are found at the function of the dermis and the epidermis.
Which of the mechanoreceptors are type 2 receptors and where are they found?
There are Pacinian and Ruffini’s corpuscles and they are found deep in the dermis.
Define a receptive field
The area of skin sensitised by each type of receptor
With type 1 and type 2 receptors, which of these groups have a role in determining fine touch and fine discrimination
Type 1
Describe the division of mechanoreceptors into their response to constant stimuli
Meisners corpuscles and Pacinian corpuscles can be put into the category of rapidly adapting receptors, as they are the first to respond upon contact but are quickly silenced and may possibly fire again upon removal of stimulus.
Merkles receptors and Ruffini’s corpuscles are known as slow adapting receptors and they will continue to fire as long as stimulus is maintained.
What is the role of fast adapting receptors in sensation?
They gather information on temporal changes in stimulus.
They play a large role in the perception of texture
What is the role or slow adapting receptors in sensation?
Often provides isomorphic representation of the surface chatarcteristics of the stimuli.
Below what temperature do cold thermoreceptors increase their rate of firing?
Below 32 degrees
Above what temperature do hot thermoreceptors increase their rate of firing?
Above 32 degrees
At approx what temperature do hot thermoreceptors shut down and are replaced by signals from nociceptors?
At approx 45 degrees
At approx what temperature do cold thermoreceptors shut down and are replaced by signals from nociceptors?
Below 10 degrees.
What 3 primary locations is position sense information gathered?
- joint capsules (mechanoreceptors within the joint)
- muscles acting over the joints (mechanoreceptors withing muscle)
- the skin overlying both (cutaneous receptors)
What do the mechanoreceptors within the joint capsule do in relation to position sense?
They record extreme joint angles, and are rarely used to sense smaller joint movements.
What do the cutaneous receptors do in relation to position sense?
They respond to compression and distension of the skin overlying moving joints
What do the mechanoreceptors within the muscle do in relation to position sense?
Muscle spindle are our primary input into perception of joint location and are sensitive to even the most minute changes in muscle length.
What factors is conduction velocity dependant on?
Fibre diameter
Degree of myelination
Is the propagation speed of a nerve impulse related to stimulus strength?
No
How much faster can a large myelinated AB axon conduct signals than a smaller unmyelinated C fibre?
Up to 200 times
What are the largest fibre types? Describe them
A fibres
(5-20 microns & 130 m/sec)
myelinated somatic sensory & motor to skeletal muscle
What are the middle sized fibre type? Describe them
B Fibres
(2-3 microns & 15 m/sec)
myelinated visceral sensory & autonomic preganglionic
What are the smallest size of fibre type? Describe them
C fibers
(.5-1.5 microns & 2 m/sec)
unmyelinated sensory & autonomic motor
What is nociception?
Information transmitted about actual of potential tissue damage
What is pain?
Pain is the perception of an adverse or unpleasant sensation
What are the 3 classes of nociceptors?
Mechanical
Thermal
Polymodal
How are mechanical nociceptors activated?
They’re activated by strong mechanical forces on tissue
What kind of threshold do mechanical nociceptors have?
Fairly high so they require a lot of input
What are mechanical nociceptors particularly sensitive to?
Sharp stimuli
What are the 2 types of thermal nociceptor?
Cold and hot
They react to extremes in temperature
Where are polymodal nociceptors found?
Found in the skin and deeper tissues
How are polymodal nociceptors activated?
Activated by mechanical, thermal and chemical stimuli
Where does the DCML decussate?
In the medulla, via the internal arcuate fibres
What sensations does the DCML system carry
Light touch
Proprioception
Vibration
Where do the first order neurons for the DCML synapse with the second order neuron?
In either the gracile or cuneate nucleus, depending on if its above T6 (cuneate nucleus) or below T6 (gracile nucleus)
Where do the terminal/third order neurons of the DCML project to once they have arisen and synapsed with the second order neuron in the thalamus? What do they travel via?
They project to the primary somatosensory cortex via the internal capsule
What does DCML stand for?
Dorsal column medial lemnisci
What does ALS stand for?
Anterolateral system
What are the 3 tracts of the ALS?
Spinothalamic
Spinomesencephalic
Spinoreticular
What sensory information does ALS carry?
Crude touch
Pain
Temperature
Where does the ALS decussate?
In the cord at the level it enters
What does the ALS decussate via?
The anterior white commissure
Where does the first order neuron synapse with the second order neuron in the ALS system?
In the dorsal horn
Where is the primary somatosensory cortex?
Post-central gyrus
Where is the secondary somatosensory cortex?
Within the lateral sulcus and PPC (posterior parietal cortex?)
Can the secondary somatosensory cortex process any information independent from the primary somatosensory cortex?
No
Where does the secondary somatosensory cortex receive its input from?
The primary cortex and the thalamus
How is the primary somatosensory cortex arranged?
Somatotopically
What is the posterior parietal cortex?
Sensory information from the different areas of the primary somatosensory cortex, visual and other cortices are brought together here to allow the different sensory systems to function as an overall unit
This in part allows for identification or recognition of familiar objects with very little thought so we can selectively test this region with stereognosis
What divides the posterior parietal cortex and what is it divided into?
It is divided into superior and inferior parietal lobules by the intraparietal sulcus.
What is function of the superior lobule of the posterior parietal cortex?
The superior lobule is essential for the completion of self image and lesions of this region may lead to disorders in the recognition or visualisation of the contralateral side of the body.
What is the function of the inferior lobule of the posterior parietal cortex?
The inferior lobule integrates diverse sensory information for speech and perception and is more concerned with creating a complete perception of our environment.
What CN functions to supply somatosensory information to the head and neck? Is this system dependant on the rest of the body’s somatic sensory system
Trigeminal nerve
No it is analogous to the somatic sensory systems
Where do the primary afferent fibres of the trigeminal nerve synapse?
They synapse at the CN nuclei in the brainstem
What are the 3 CN nuclei that the trigeminal nerve synapses with for sensation?
The principle sensory nucleus
The mesencephalic nucleus
The spinal nucleus
What type of sensory information does the principle sensory nucleus receive and what sensory system is it part of?
It receives the perception of touch and is part of the trigeminal nerve.
What type of sensory information does the mesencephalic receive and what sensory system is it part of?
It receives proprioceptive input from the musculature and periodontal membranes and is part of the trigeminal nerve
What type of sensory information does the spinal nucleus receive and what sensory system is it part of?
It receives information of pain and temperature and is part of the trigeminal nerve.
Where do the second order neurons from the trigeminal nucleus ascend from and where do they decussate? Where does the second order neuron terminate and where does the 3rd order neuron arise and terminate?
The first order neurons synapse with the second order neurons in the CN nuclei in the brainstem. From here they ascend and decussate in the brainstem before terminating in the ventral posteromedial nucleus of the thalamus.
From here the 3rd order neuron arises and projects to the lateral portion of the somatosensory cortex where it terminates.
