Chapter 13 Part A

All neural structures outside the brain
sensory receptors
peripheral nerves and associated ganglia
motor endings

survival depends upon sensation and perception
sensation: the awareness of changes in the internal and external environment
Perception: the conscious interpretation of those stimuli

Input comes from exteroceptors, proprioceptors, and interoceptors
Input is relayed toward the head, but is processed along the way

1. Receptors level - the sensor receptors
2. Circut level- ascending pathways
3. Perceptual level- neuronal circuits in the cerebral cortex

Receptors have specificity for stimulus energy
Stimulus must be applied in a receptive field
Transduction occurs
stimulus energy is converted into a graded potential called a receptor potential

stimulus
Receptor/generator potential in afferent neuron
action potential at first node of Ranvier

Stimulus
receptor potential in receptor cell
release of neurontransmitter
generator potential in first-order sensory neuron
action potentials (if threshold is reached)

Adaptation is a change in sensitivity in the presence of a constant stimulus

Receptor membranes become less responsive

Receptor potentials decline in frequency or stop
Phasic (fast-adapting) receptors signal the begining or end of a stimulus
eg: receptors for pressure, touch and smell

Tonic receptors adapt slowly or not at all
eg: nociceptors and most proprioceptors

Pathways of three neurons conduct sensory impulses upward to the appropriate brain regions
First-order neurons : conduct impulses from the receptor level to the second-order neurons in the CNS
Second-order neurons : transmit impulses to the thalamus or cerebellum
Third-order neurons : conduct impulses from the thalamus to the somatosensory cortex (perceptual level)

-Identification of the sensation depends on the specific location of the target neurons in the sensory cortex
-Aspects of sensory perception:
perceptual detection-ability to detect a stimulus
(requires summation of impulses)
Magnitude estimation- intensity is coded in the
frequency of impulses
Spatial discrimination - identifying the site or
pattern of stimulus (studied by the 2point
discrimination test)

Feature abstraction : identification of more complex aspects and several stimulus properties
Quality discrimination : the ability to identify submodalities of a sensation (eg: sweet or sour taste)
Pattern recognition : recognition o familliar or significant patterns in stimuli (eg: the melody in a piece of music)

Specialised to respond to changes in their environment (stimuli)
Activation results in graded potentials that trigger nerve impulses
Sensation (awareness of stimulus) and perception (interpretation of the meaning of the stimulus) occur in the brain

Based on:
Stimulus type
Location
Structural complexity

mechanoreceptors : respond to touch, pressure, vibration, stretch, and itch
Thermoreceptors: sensitive to changes in temperature
Photoreceptors: respond to light energy (re: retina)
Chemoreceptors: respond to chemicals (smell, taste, changes in blood chemistry)
Nociceptors: sensitive to pain-causing stimuli (eg: extreme heat or cold, excessive pressure, inflammatory chemicals)

1. Exteroceptors: resond to stimuli arising outside the body. Receptors in the skin for touch, pressure, pain, an temperature...most special sense organs
2. Interceptors (viseroceptors): respond to stimuli arising in internal viscera and blood vessels. Sensitive to chemical changes, tissue stretch, and temperature changes.
3. Proprioceptors: Respond to stetch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles. Inform the brain of one's movements.

1. Complex receptors (special sense organs) : Vision, hearing, equilibrium, smell, and taste
2. Simple receptors for general sense: tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense. Unencapsulated (free) or encapsulated dendritic endings.

Thermoreceptors
cold receptors (10-40*C); in superficial dermis
heat receptors (32-48*C); in deeper dermis
Nociceptors
respond to: pinching
chemicals from damaged tissue
temperatures outside the range of
thermoreceptors
capsaicin
Light touch receptors
tactile (Merkel) discs
hair folicle receptors

All are mechanoreceptors
Meissner's (tactile) corpuscles-discriminative touch
Pacinian (lamellated) corpuscles-deep pressure and vibration
Ruffini endings- deep continuous pressure
Muscle spindles - muscle stretch
Golgi tendon organs - stretch in tendons
joint kinestethitec receptors - stretch in articular
capsules