GENERAL PSYCHOLOGY (PSYC
290) UNIT 3 LECTURE NOTES, A+ GRADED
AND VERIFIED ATHABASCA UNIVERSITY
, Sensory Systems
9.1 Overview of Sensation
Sensation: the conscious or subconscious awareness of changes in the external or internal
environment
- Sensation that reaches the spinal cord results in mechanical movements (flexor reflex
that moves limb away from a painful stimulus)
- Sensation that reaches the brain stem results in complex reflexes (change in heart rate
or breathing rate)
- Sensation that reaches the cerebral cortex can be precisely located and identified → you
are consciously aware (one the 5 senses → touch, taste, smell, hearing, or visual)
Perception: the conscious awareness and interpretation of sensations and is primarily a function
of the cerebral cortex
- If sensory information does not go to the cerebral cortex, you will have no perception of it
- Ex. blood pressure → receptors on blood vessels send the sensory information to
the cardiovascular center in the medulla oblongata, not the cerebral cortex →
blood pressure is not consciously perceived
The Process of Sensation Involves Four Events
Sensory information is converted into the “language” of the nervous system (electrical signals →
action/graded potentials) through the process of sensation:
1. Stimulation of the Sensory Receptor
Sensory Receptor = a structure of the nervous system that is associated with a sensory
(afferent) neuron → responds to one particular type of stimulus
Stimulus = a change in the external or internal environment that can activate the sensory
receptor
2. Transduction of the Stimulus
Transduction = the process of a sensory receptor converting the energy in the stimulus into a
graded potential (a change in membrane potential that causes the membrane to become either
depolarized or hyperpolarized)
3. Generation of Action Potentials
If a graded potential in a sensory neuron reaches threshold, it triggers one or more action
potentials, which then propagates into the CNS
4. Integration of Sensory Input
The information is integrated/processed as sensory input is relayed from one synapse to
another in the CNS → information is either modified, allowed to continue as is, or filtered out
(depending on how important the information is)
- The most important information is integrated into the cerebral cortex (conscious)
,There Are Different Types of Sensory Receptors
Sensory receptors are classified into five major groups according to their adequate stimulus:
- Adequate Stimulus = the type of stimulus to which a sensory receptor responds best
1. Mechanoreceptors
Sensitive to mechanical stimuli such as deformation, stretching, or bending of cells
- Provides sensation of touch, pressure, vibration, proprioception (muscle and joint
position), and hearing equilibrium
- Monitors the stretching of blood vessels and internal organs
2. Thermoreceptors
Detects change in temperature
3. Photoreceptors
Detects change in light that strikes the retina of the eye
4. Chemoreceptors
Detects chemicals in the mouth (taste), nose (smell), and bodily fluids
5. Nociceptors (noci = harmful)
Responds to painful stimuli resulting from physical or chemical damage to tissues
Different sensory receptor structures:
1. Peripheral Endings (dendrites) of Sensory Neurons
a. Encapsulated Nerve Endings → surrounded by a connective tissue capsule →
enhances the sensitivity of the receptor
- Ex. receptors for pressure, vibration, and some touch sensations
b. Free Nerve Endings → bare (not encapsulated)
- Ex. receptors for pain, thermal, itch, tickle, and some touch sensations
, 2. Seperate Cells that Synapse with Sensory Neurons
- Receptors for most special senses (taste, sight, hearing, smell):
- Gustatory receptor cells in taste buds
- Photoreceptor cells in the retina of the eye for vision
- Hair cells for hearing and equilibrium in the inner ear
- Olfactory receptors for smell are not separate cells → located in olfactory
cilia (hairlike structures) that project from the dendrite of an olfactory
receptor cell
Receptor Potential = the graded potential that that forms in a sensory receptor as a response to
a stimulus (transduction)
- Stimulus opens/closes ion channels in the membrane of the sensory receptor (either
directly or indirectly by activating a second messenger pathway)
- In most cases, cation channels open → Na+ and Ca2+ enter the sensory
receptor → depolarization
- Visual system: cation channels close in response to light stimulus →
photoreceptors are hyperpolarized
Peripheral Endings: if the receptor potential is large enough to reach threshold, it triggers one
or more action potentials in the axon of the sensory neuron → AP propagates along the axon
into the CNS
Seperate Cells: the receptor potential triggers release of neurotransmitter through exocytosis of
synaptic vesicles → the neurotransmitter molecule liberated from the synaptic vesicle diffuses
across the synaptic cleft and produce postsynaptic potential (PSP) → a type of graded potential
→ if threshold is reached, the PSP will trigger one or more action potentials → AP propagates
along the axon into the CNS
290) UNIT 3 LECTURE NOTES, A+ GRADED
AND VERIFIED ATHABASCA UNIVERSITY
, Sensory Systems
9.1 Overview of Sensation
Sensation: the conscious or subconscious awareness of changes in the external or internal
environment
- Sensation that reaches the spinal cord results in mechanical movements (flexor reflex
that moves limb away from a painful stimulus)
- Sensation that reaches the brain stem results in complex reflexes (change in heart rate
or breathing rate)
- Sensation that reaches the cerebral cortex can be precisely located and identified → you
are consciously aware (one the 5 senses → touch, taste, smell, hearing, or visual)
Perception: the conscious awareness and interpretation of sensations and is primarily a function
of the cerebral cortex
- If sensory information does not go to the cerebral cortex, you will have no perception of it
- Ex. blood pressure → receptors on blood vessels send the sensory information to
the cardiovascular center in the medulla oblongata, not the cerebral cortex →
blood pressure is not consciously perceived
The Process of Sensation Involves Four Events
Sensory information is converted into the “language” of the nervous system (electrical signals →
action/graded potentials) through the process of sensation:
1. Stimulation of the Sensory Receptor
Sensory Receptor = a structure of the nervous system that is associated with a sensory
(afferent) neuron → responds to one particular type of stimulus
Stimulus = a change in the external or internal environment that can activate the sensory
receptor
2. Transduction of the Stimulus
Transduction = the process of a sensory receptor converting the energy in the stimulus into a
graded potential (a change in membrane potential that causes the membrane to become either
depolarized or hyperpolarized)
3. Generation of Action Potentials
If a graded potential in a sensory neuron reaches threshold, it triggers one or more action
potentials, which then propagates into the CNS
4. Integration of Sensory Input
The information is integrated/processed as sensory input is relayed from one synapse to
another in the CNS → information is either modified, allowed to continue as is, or filtered out
(depending on how important the information is)
- The most important information is integrated into the cerebral cortex (conscious)
,There Are Different Types of Sensory Receptors
Sensory receptors are classified into five major groups according to their adequate stimulus:
- Adequate Stimulus = the type of stimulus to which a sensory receptor responds best
1. Mechanoreceptors
Sensitive to mechanical stimuli such as deformation, stretching, or bending of cells
- Provides sensation of touch, pressure, vibration, proprioception (muscle and joint
position), and hearing equilibrium
- Monitors the stretching of blood vessels and internal organs
2. Thermoreceptors
Detects change in temperature
3. Photoreceptors
Detects change in light that strikes the retina of the eye
4. Chemoreceptors
Detects chemicals in the mouth (taste), nose (smell), and bodily fluids
5. Nociceptors (noci = harmful)
Responds to painful stimuli resulting from physical or chemical damage to tissues
Different sensory receptor structures:
1. Peripheral Endings (dendrites) of Sensory Neurons
a. Encapsulated Nerve Endings → surrounded by a connective tissue capsule →
enhances the sensitivity of the receptor
- Ex. receptors for pressure, vibration, and some touch sensations
b. Free Nerve Endings → bare (not encapsulated)
- Ex. receptors for pain, thermal, itch, tickle, and some touch sensations
, 2. Seperate Cells that Synapse with Sensory Neurons
- Receptors for most special senses (taste, sight, hearing, smell):
- Gustatory receptor cells in taste buds
- Photoreceptor cells in the retina of the eye for vision
- Hair cells for hearing and equilibrium in the inner ear
- Olfactory receptors for smell are not separate cells → located in olfactory
cilia (hairlike structures) that project from the dendrite of an olfactory
receptor cell
Receptor Potential = the graded potential that that forms in a sensory receptor as a response to
a stimulus (transduction)
- Stimulus opens/closes ion channels in the membrane of the sensory receptor (either
directly or indirectly by activating a second messenger pathway)
- In most cases, cation channels open → Na+ and Ca2+ enter the sensory
receptor → depolarization
- Visual system: cation channels close in response to light stimulus →
photoreceptors are hyperpolarized
Peripheral Endings: if the receptor potential is large enough to reach threshold, it triggers one
or more action potentials in the axon of the sensory neuron → AP propagates along the axon
into the CNS
Seperate Cells: the receptor potential triggers release of neurotransmitter through exocytosis of
synaptic vesicles → the neurotransmitter molecule liberated from the synaptic vesicle diffuses
across the synaptic cleft and produce postsynaptic potential (PSP) → a type of graded potential
→ if threshold is reached, the PSP will trigger one or more action potentials → AP propagates
along the axon into the CNS
