Download General Sensory Reception

GENERAL SENSORY
RECEPTION
The Sensory System
• 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
• Vision
• Hearing
• Taste
• Smell
• Equilibrium
Special Senses – External Stimuli
Somatic Senses – Internal Stimuli
• 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
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
• Free nerve endings
• Cold receptors
• Warm receptors
• Pain receptors
• Sensory coding:
– Intensity
– Duration
Pain perception
sharp and well localized, transmitted by
myelinated axons
• Fast pain:
dull aching sensation, not well localized,
transmitted by unmyelinated axons
• Slow pain:
• 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
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