Exam 2 week 8 ppt 1 Intro to Somatic Sensory System Flashcards
Somatic Receptors:
In general, the type of environmental energy that a specific receptor responds to is _______ and ________; some receptors are _________.
•In general, the type of environmental energy that a specific receptor responds to is unique and unimodal; some receptors are polymodal
Four common ways to classify somatic receptors
- –By structure
- –By the source of the stimulus
- –By the type of stimulus energy
- –By the rate of adaption
Two ways to classify Somatic Receptors by sturcture
- –Unencapsulated (free and diffuse) nerve endings - just covered by endoneurium
- –Encapsulated receptors- surrounded by supporting connective tissue
three ways to classify Somatic Receptors by the source of stimulus
- –Exteroreceptors – respond to external environment
- –Interoreceptors – respond to internal environment
- –Proprioceptors – deep somatosensory response
4 ways to classify Somatic Receptors by the type of stimulus energy
- •Mechanoreceptors – respond to mechanical deformation
- •Thermoreceptors – respond to temperature gradients across the skin
- •Nociceptors – respond to tissue-damaging stimuli
- •Chemoreceptors – respond to chemical constituents
Quck Reveiw of Receptor Potentials
•Receptors
- –Generator (receptor) potential
- Transduction of mechanical stimulus to action potentials
- Coding of stimulus
Remember we have sensory receptors with receptor potentials with the conversion of the mechanical, thermal or chemical stimulus into an electrical depolarization. This electrical depolarization, the receptor or generator potential, is then converted into action potentials and there is a coding of the characteristics of the stimulus.
2 ways to classify Somatic Receptors by the rate of receptor adaption
- •Slowly adapting
- –Respond throughout stimulus
- •Rapidly adapting
- –Respond only at beginning and end of stimulus
Receptors are commonly classified rate of adaptation
Slowly adapting – Receptor responds throughout stimulus
Rapidly adapting – Receptor responds only at beginning and end of stimulus
This illustration shows the stimulus, generator potential and action potential firing pattern with each type of receptor
What are receptor Fields?
•Area of receptive surface to which a receptor responds when that area is stimulated
- –Varies by receptor type
- –Varies by most sensitive & least sensitive areas
Receptors also have receptor fields. The receptor field is the Area of receptive surface to which a receptor responds when that area is stimulated. The size of the receptor field varies by receptor type and by most sensitive & least sensitive areas of the skin
What is Sensory Acuity determined by?
•Determined by receptor field size & density
- –Smaller receptor field – higher acuity
- –Higher receptor density – higher acuity
Sensory acuity is determined by receptor field size & receptor density. Smaller receptor field & Higher receptor density give rise to higher sensory acuity of the receptive surface. As was noted earlier the skin of the face and hands have the highest receptor density and smallest receptor fields so have the highest sensory acuity.
Sensory Acuity: smaller recoptor field goes with (higher or lower) accuity?
higher acuity
Sensory Acuity: higher receptor density goes with (higher or lower) accuity?
higher acuity
What are the three categories of specific receptors that are part of the symatasensory system?
(each have several types within each category)
- §11 types of cutaneous receptors
- (notes of the powerpoint says 7-9)
- §4 types of joint receptors
- §2 types of muscle receptors
–Specialized sensory end-organs – mechanoreceptors: how may types of cutaneous receptors are there?
11
(notes under powerpoint say 7-9)
–Specialized sensory end-organs – mechanoreceptors: how may types of joint receptors are there?
4
–Specialized sensory end-organs – mechanoreceptors: how may types of muscle receptors are there?
2
explain an overvew of the typical somatosensory pathway
•Three neuron pathway to cortex
- –Primary afferent neurons
- –Prethalamic relay
- §2nd order
- §Decussation
- §Ascending tract
- –Thalamic relay - 3°
- –Cerebral cortex
The somatosensory pathway is characterized as a Three neuron pathway to cortex with Primary afferent neurons arising from the sensory receptor. Then there is the Prethalamic relay neuron which is the 2nd order neuron in the pathway and the one whose axon decussates to the opposite side. This secondary neuron ends on the Thalamic relay neuron which is the tertiary nueuron in the pathway to the Cerebral cortex
describe the primary afferent neurons in the somatosensory pathway
•Also called first-order fibers
- –Specialized receptor – peripheral process – afferent axon
- –Cell body in the dorsal root ganglion (DRG)
- –Central process (efferent axon) enters CNS synapsing relay nucleus
The primary afferent neuron, Also called first-order fibers, have the following characteristics:
They begin with the Specialized receptor
They are the afferent axon of the peripheral nervous system
Their Cell body is in the dorsal root ganglion (DRG)
Their Central process (efferent axon) enters CNS synapsing relay nucleus
Somatosensory Pathway:
details about the prethalamic relay
secodnary neuron
& decussation
•Relay nucleus
- –Dorsal horn spinal cord
- –Dorsal column nuclei caudal medulla
- –Trigeminal nuclei
- §Nucleus of spinal trigeminal tract
- §Chief sensory nucleus
•Axons decussate to ascend to thalamus
Relay or Secondary Neuron is characterized in the following ways:
Has its cell body in a central nervous system nucleus – examples are dorsal horn neurons for spinothalamic pathway, dorsal column nuclei of the caudal medulla for the dorsal column-medial lemniscus pathway and the spinal trigeminal nucleus for the cutaneous afferents of the trigeminal nerve. All axons decussate and ascend to the thalamus
Prethalamic Relay and Decussation: Why is the level of decussation important?
•Level decussation important
- –Lesion caudal – ispilateral signs/symptoms
- –Lesion rostral – contralateral signs/ symptoms
- –Lesion at decussation –bilateral signs/symptoms
The Level decussation is important because it will often tell you where a lesion in the pathway is:
Lesion caudal to the decussation the signs/symptomswill be ispilateral to the lesion
Lesion rostral to the decussation the signs/ symptoms will be contralateral
Lesion at decussation the signs/symptoms may be bilateral
somatosensory pathway; Thalamic Relay and Cerebral Cortex:
describe the third order pathway
- •3 degree neurons or 3 neuron pathway
- •Located in ventral posterolateral (VPL) & ventral posteromedial (VPM) nuclei of thalamus
- •Thalamocortical projection fibers ascend to the cerebral cortex in the internal capsule
The thalamic relay neurons are the third order or tertiary neurons of the pathway and they are contralateral to the site of stimulus. For somatosensory pathways these neurons are located in ventral posterolateral (VPL) & ventral posteromedial (VPM) nuclei of thalamu. The Thalamocortical projection fibers ascend to the cerebral cortex in the anterior limb of the internal capsule up to the primary somatosensory cortex
