4.Sensations and Receptors
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Transcript of 4.Sensations and Receptors
Sensations and Receptors
By
Dr. D. Fisher
SENSATION• 4 events must occur for a sensation to take place:
1. Sensory receptors or sense organs must respond to stimulus (Stimulus is capable of activating specific sensory neurons Specific to that stimulus)
1. Information is then transduced into nerve impulses
1. Sensory neurons conduct nerve impulses to CNS by first-order neurons translation
1. A region of CNS must translate nerve impulses into sensation (mostly in cerebral cortex)
CLASSIFICATION OF RECEPTORS
• Sensory receptors have selectivity (i.e. they respond vigorously to one particular type of stimulus OR weakly or not at all others)
• Different classifications of peripheral sensory receptors
CLASSIFICATION OF RECEPTORS
• Simple receptors – associated w/ general (or somatic) senses Vs. Complex receptors – associated w/ special senses
• Location: near or at surface of body, deep w/in blood vessels, viscera, or musculoskeletal organs
• Type of Stimulus Detected: mechanical pressure or stretching, temperature changes, light intensity, chemical changes, damage to tissues
• Adaptation (i.e. change in sensitivity to long lasting stimuli)
• Structure – encapsulated vs. free nerve endings
LOCATION
• Exteroceptors external stimuli
• Interoceptors internal stimuli
• Proprioceptors position & movement stimuli
TYPE OF STIMULUS
Receptor Type Modality
• Mechanoreceptor mechanical
• Thermoreceptor temperature
• Photoreceptor light
• Chemoreceptor chemical
• Nociceptors pain/tissue damage
STRUCTURE
• Unencapsulated dendritic endings– Free or naked nerve endings – Abundant in epithelial tissue and connective
tissue underlying epithelia
• Encapsulated – Nerve fibers enclosed in capsule of
connective tissue– Widely shaped, sized, and found throughout
the body
CUTANEOUS RECEPTORS• Tactile sensation (i.e. touch,
pressure, vibration, itch, tickle)• Thermal sensations (cold & warmth)
• Cutaneous receptors densely populate tip of tongue & lips, but few are found on back of neck
• Dendrites of cutaneous receptors may or may not be enclosed in capsule of epithelial or connective tissue
• Nerve impulses of cutaneous receptors are transmitted along somatic afferent neuron in spinal cord or cranial nerves thru thalamus to somatosensory are of parietal lobe of cerebral cortex
CUTANEOUS RECEPTORS
• End organ of Ruffini crude touch
• Merkel discs discriminative touch
• Root hair plexus hair movement
CUTANEOUS RECEPTOR(FREE NERVE ENDINGS)
• Itch & tickle
• Thermoreceptors Heat loss & gain
• Nociceptors pain
NOCICEPTORS• Free nerve endings• Tonic receptors• Detect pain or tissue damage• Somatic or visceral pain
• Referred pain is a phenomenon in which pain is felt in a surface area far from a stimulated organ (brain freeze or pain in arm during heart attack)
• Phantom pain (phantom limb sensation) is phenomenon in which pain is felt in an amputated (nonexistent, phantom) limb may feel itch on toes or fingers/actual pain of lost part
PROPRIOCEPTORS
• Position or movement of body
• Tonic
• Somatosensory area of cerebrum
• Cerebellum via spinocerebellar tracts
• Muscle spindle fibers
• Golgi tendon organs
• Joint kinesthetic receptors
TOUCH
Types of classification
1. Capsulated/ Non-capsulated
2. Fast adapting/ slow adapting-myelin wrapping amount
3. Superficial/ deep layer
Merkel= Slow adapting, superficial layer, non-capsulated
Meissner= Fast adapting, superficial layer, capsulated
Pacinian= Fast adapting, Deep layer, capsulated
Ruffini= Slow adapting, Deep layer, non-capsulated
Nociceptors= Non-capsulated
Thermal= Non capsulated
ADAPTATION TO STIMULI
• Phasic rapidly adapting role in signaling changes in intensity
• Tonic adapt slowly or not at all role in signaling information regarding steady state
Effects of Stimulus Strength on AP transmission
MUSCEL SPINDLE FIBERS
• Monitor changes in length of skeletal muscle
• Degree of muscle stretch
• Aid in coordination & efficiency of muscle contraction
TENDON ORGANS (GOLGI TENDON ORGANS)
• Junction of tendon & muscle
• Monitors force of muscle contraction
• Detect tension applied to tendon
• Protects tendon & muscle from excessive tension
JOINT KINESTHETIC RECEPOTRS
• Located in articular capsules & synovial joints
• Acceleration & deceleration of joint movement
• Pressure in joint
• Excessive joint strain