Ch.7 Pt. 2 Flashcards
(41 cards)
What 3 separate and Interacting systems are the Somatosensory System made up of?
- Exteroceptive: External Stimuli
- Proprioceptive: Body Position
- Interoceptive: Body conditionds (temp, blood pressure)
What are the 3 parts of the Exteropcetive System?
- Mechanical Stimuli (touch)
- Mediated by 4 key receptors - Thermaal Stimuli (temp)
- Noicipetion (pain)
- 2 and 3 are not really distinct in the cellular sense
What are the 3 layers the skin is comprised of?
- Epidermis -> outermost layer (thinnest)
- Dermis -> middle layer (rich in nerve fibers, blood vesicles
- Hypodermis - innermost layer - provides an anchor for muscles
Mechanoreceptors of the skin: What are the 5 Receptors for touch (5)
- Merkels Disk (dermis) pressure
- Meissners Corpuscle (dermis) light touch
- Hair follicle receptor (dermis)
- Pacinian Corpuscle (hypodermis) vibration
- Ruffinis Ending (hypodermic) stretch
Adaptation:
You do not feel your clothes against you skin unless you bring it to your attention (due to adaptation)
(Adaptation in the somatosensory system) What are the two types of receptors?
- Tonic Receptors- Show little adaptation, in response to continuous stimuli they show little to no change in AP rate
- Phasic Receptors: show adaptation - in response to continuous stimulation they rapidly decrease AP firing rate
Why do we have adaptation?
Tuned to detect amplify CHANGE in the environment
- Change is more likely to signify meaningful events
Suppression:
Pretty much telling receptors to quiet down
What are the 2 Mechanisms of Suppression?
- Accessory Structures - closing the eyelids deuces light information reaching the eyes
- Top down Processing - CNS modulation of sensory information. The cortex and thalamus can suppress some sources of information and amplify others
How Mechanoreceptors Work: (Pacinian Corpuscles as example)
- Stimuli to the corpuscle (like vibration) produce a graded potential proportional to the intensity of the stimulus
- If the graded potential is sufficient and AP fires
More in depth on How Mechanoreceptors work with pacinian corpuscles as example
- Mechanostimulation deforms the corpuscle
- Deformation stretches the tip of the axon
- Stretching opens mechanically gated ion channels
- Stretch sufficient enough cations enter and AP fires
If the corpuscle is removed this cells does not show an adaptation response - continuous vibration elicits a continuous response
.
Meissners Corpuscle (touch)
- Fewer than Merkels Discs and have less spatial resolution
- Respond to changes in stimuli between skin and surface
- Provide info about texture
- Adapt quickly to continued stimuli
Merkels Discs (touch)
- Receptive fields have an inhibitory surround (increases spatial resolution)
- Receptive to edges and isolated points on a surface (braille)
- Adapt slowly to continuous stimulations
Ruffini’s Ending (stretch)
- Very few of them - they have large receptive fields
- Detect streching in the skin when we move our fingers or limbs
- Adapt slowly to continued stimuli
Pacinian Corpuscle (vibration)
- Detect Vibration - when skin moves across texture on a surface
- They respond quickly (fast acting) to appropriate stimuli
- They adapt quickly in response to continued stimuli
What are Dermatomes?
” Bands” of skin that send their sensory information to different dorsal roots of the spinal cord. Each dermatome is the section of skin that is innervated by a given dorsal root
What are the 4 Types of Dermatomes? (from the brain downward)
- Cervical
- Thoracic
- Lumbar
- Sacral
Ascending Sensory Circuit (Dorsal-Column-Medial-Lemniscus system)
- Tends to carry info about touch and perception
- First synapse in the dorsal column nuclei of the medulla
- Information does not intersect until within the brain at the dorsal column nuclei
- Goes from the spinal cord to the hindbrain to the forebrain
Cortical Areas of Somatosensation:
Primary Somatossensory Cortex (SI): more sensitive more cortex, input largely contralteral
SII: maily input from SI: soma topic; input from both sides of the body
- Much of the output from SI and SII goes to the association cortex in the posterior parietal lobe
Somatotopic Map In the Cortex:
Organized like the primary somatosensory cortex, according to a map of the surface of the body
- Often called the sensory homunculus
Effects of Damage to the Primary Somatosensory Cortex
Effects of damage to the primary somatosensory cortex are often mild
- Likely due to numerous parallel pathways
Somatosensory Agnosias
- Asterognesia: inability to recognize objects by touch, pure cases are rare: other sensory deficits are usually present
- Asomatognosia: the failure to recognize parts of ones own body (eg: the case of the man who fell out of bed)
The highest level of the sensory hierarchy is made up of areas of association cortex in the ________ and _______ _____ _____
prefrontal and posterior parietal cortex
