Sensory Perception Flashcards
What are the steps to sensation?
- Stimulation
- Transduction
- Conduction
- Perception
Stimulation
Application of stimulus
Transduction
Induction of AP (if strong enough depolarization)
Increased stimulus strength above threshold leads to increase AP
Conduction
Relay of info through a sensory pathway to specific region of CNS
1st, 2nd and 3rd order neuron
1st, 2nd and 3rd order neuron
- From stimulation point to CNS
- From entry into CNS to thalamus
- From thalamus to perception site
Perception
Detection of environmental change by the CNS
Adequate stimulus
Sensors most sensitive to one particular stimulus modality
Phasic receptors
Exhibits sensory adaptation (response of sensors to constant stimulation)
Decrease with constant stimulus
Ex: don’t feel a shirt after a while
Tonic receptors
Exhibit little adaptation
Maintain constant firing rate as long as stimulus is applied
Sensory system (receptor types)
Touch (mechanoreceptor)
Temperature (thermoreceptor)
Pain (nociceptors)
Body position (proprioceptors)
Photoreceptors
Osmoreceptors
Chemoreceptors
What re the receptors of the skin?
Free nerve endings for heat, cold, and pain:
Expanded dendritic endings
Encapsulated endings
Bundled receptors
Expanded dendritic endings
Ruffini endings and Merkel’s disks (touch)
Encapsulated endings
Meissener’s corpuscles, krause’s corpuscles, pacinian corpuscles (touch and pressure)
Bundled receptors
Spindle fibers, golgi tendon organs
Tactile sensory input
Responds to pressure and movement of skin
Specialized receptors that respond to particular types of inputs
Pacinian
Heavy pressure and rapid vibration (300 hz)
Meissener’s
Light pressure
Slow vibration (50 Hz)
Acuity
Ability to discriminate size and shape of an object in the environment
When is acuity increased?
With increase in receptor density and decrease in receptive field size
Receptive field
The region of the skin in which a stimulus evokes a response in a sing,e sensory neuron
Discrimination depends on the density of receptors
Thermoreception
Responds to not painful temperatures
Warm and cold thermoreceptors
Where are thermosensitive neurons present?
Skin, hypothalamus and spinal cord
Proprioception
Internal awareness of body position in relation to the environment
What are the 2 types of proprioceptors?
- Muscle spindle and golgi tendon organs found in skeletal muscle
- Mechanoreceptors found in CT, ligaments and joint capsules
Myelinated sensory functions
Muscle spindle- primary (slowest condition velocity)
Muscle tendon
Hair receptors (slowest CV)
Vibration (pacinian corpuscle)
High discrimination touch
Deep pressure touch
Picking pain
Cold
Warm
Unmyelinated motor function
Cold
Warm
Acting pain
Tickle (fastest condition velocity)
Crude touch and pressure
Nociceptors
Respond to painful stimulus
Carried by non-myelinated C fiber sensory neurons
Painful heat, acids, mechanical damage all activate non-specific cation channels
What substances are released from damaged cells?
ATP
Bradykinin
Substance P
How is transduction of warm temperatures carried out?
By several types of TRPV cation channels
TRPV1
Receptor that’s activated by the vanilloid class of compounds (capsaicin, spicy food ingredient)
Segmental pain modulation
Pain control when there’s not too much damage, the body will take care of it automatically
Body will inhibit the pain receptor
Descending pain modulation
Pain in the brain
1. C fiber (dorsal horn)
2. Medulla (Nucleus raphe magnus and nucleus paragigantocellularis
3. Periaqueductal gray
Referred pain
Feel pain in a part of the body that is fairly remote from the tissue causing the pain
Due to lack of precision in the central organization of pain pathways
Ex; heart attack, feeling pain in left shoulder)
Dorsal column-medial lemniscal pathway
Propioceptors or mechanoceptors
Crosses over @ the medulla and will synapse at the dorsal column nuceli (2nd order neuron)
Spinothalamic tract
Nociceptors or thermoreceptors
Crosses over @ the SC (synapse @ first order neuron)
Spinocerebellar tracts
Prorioceptive to cerebellum
Ipsillateral
Keeps track of movement
Spinoreticular tract
Conveys deep and chronic pain
