Transcript Somatic Sensations

General Sensory Reception
The Sensory System
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What are the senses ?
How sensory systems work
Body sensors and homeostatic maintenance
Sensing the external environment
Mechanisms and pathways to perception
General Properties of Sensory Systems
• Stimulus
– Internal
– External
– Energy source
• Receptors
– Sense organs
– Transducer
• Afferent pathway
• CNS integration
General Properties of Sensory Systems
Sensory Receptors
• Somatic
• Visceral
-- Chemoreceptors (taste,
smell)
-- Thermoreceptors
(temperature, pain)
-- Photoreceptors (vision)
-- Proprioreceptors (muscle
stretch)
--Mechanoreceptors (touch,
pain, audition, balance).
-- Chemoreceptors (chemicals
in blood, osmoreceptors)
-- Baroreceptors (bp)
Sensory Receptor Types
Special Senses – External Stimuli
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Vision
Hearing
Taste
Smell
Equilibrium
Special Senses – External Stimuli
Somatic Senses – Internal Stimuli
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Touch
Temperature
Pain
Itch
Proprioception
Pathway
Somatic Pathways
• Receptor
– Threshold
– Action potential
• Sensory neurons
– Primary – medulla
– Secondary – thalamus
– Tertiary – cortex
• Integration
– Receptive field
– Multiple levels
Somatic Pathways
Sensory Modality
• Location
– Lateral inhibition
– Receptive field
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Intensity
Duration
Tonic receptors
Phasic receptors
Adaptation
Sensory Modality
Figure 10-3: Two-point discrimination
Sensory Modality
The Somatosensory System
• Types of receptors
- Mechanoreceptors:
-- Proprioreceptors in tendons, ligaments
and muscles  body position
-- Touch receptors in the skin: free nerve endings, Merkel’s
disks and Meissner’s corpuscles (superficial touch), hair
follicles, Pacinian corpuscles and Ruffini’s ending
- Thermoreceptors: Warm receptors (30-45oC) and cold
receptors (20-35oC)
- Nociceptors: respond to noxious stimuli
Touch (pressure)
Skin touch receptors
Sensory
pathways
• The sensory pathways
convey the type and
location of the sensory
stimulus
• The type: because of the
type of receptor activated
• The location: because the
brain has a map of the
location of each receptor
Temperature
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Free nerve endings
Cold receptors
Warm receptors
Pain receptors
Sensory coding:
– Intensity
– Duration
Temperature
Pain perception
• Fast pain: sharp and well localized, transmitted by
myelinated axons
• Slow pain: dull aching sensation, not well localized,
transmitted by unmyelinated axons
• Visceral pain: not as well localized as pain originating
from the skin  pain impulses travel on secondary
axons dedicated to the somatic afferents  referred
pain
Pain and Itching
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Nociceptors
Reflexive path
Itch
Fast pain
Slow pain
Pain and Itching
All the Preceding Modalities
Culminate in the Propagation of
Action Potentials
Sensory transduction
• Receptors transform an
external signal into a
membrane potential
• Two types of receptor
cells:
- a nerve cell
- a specialized epithelial
cell
Two types of sensory receptors
Receptor adaptation
• Tonic receptors
-- slow acting, -- no adaptation:
continue to for impulses as long as
the stimulus is there
(e.g., proprioreceptors)
• Phasic receptors
-- quick acting, adapt: stop firing when
stimuli are constant (e.g., smell)
Sensory coding
• A receptor must convey the
type of information it is
sending  the kind of
receptor activated
determined the signal
recognition by the brain
• It must convey the intensity
of the stimulus  the
stronger the signals, the
more frequent will be the
APs
• It must send information
about the location and
receptive field,
characteristic of the
receptor
Referred pain
Figure 10.16a
Figure 10.16b
• What is Phantom pain?