PSY10007 Week 4 Modules - Sensation and Perception
Concise Version
Studying Sensation and Perception
Lecture Outlines and Learning Objectives:
Each lecture has an outline with learning objectives to set the stage.
Videos introduce key ideas but don't cover everything.
Learning objectives provide a framework for studying.
Textbook also has learning objectives.
Suggested Study Method:
Read the lesson outline and check learning objectives.
Watch the videos.
Read and reread the text, making notes each time.
Focus on finding connections between ideas to build a "web of knowledge".
Why Study Sensation and Perception?
Gathering Information:
Sensation and perception are how we gather and interpret information about our environment.
It's our only contact with reality.
Importance:
Essential for basic knowledge of the world and how our brains work.
Practical Applications:
Clinical settings: Understanding normal perception helps in understanding clinical conditions.
Working with young or old individuals: Understanding normal development and aging aids in working with these populations.
Crossover with Other Disciplines:
Computational approaches: Computer modeling is used to understand perception, especially vision.
Inspiration for Machines: Understanding animal/human sensation and perception can be used to design better machines and robots.
Sensation vs. Perception:
Sensation: Concrete physiological process of turning environmental stimuli into neural messages.
Perception: Abstract psychological process of interpreting signals into experiences or knowledge.
Perception occurs in the brain.
Taste Example:
Taste buds transduce chemicals into nerve impulses, but the experience of taste happens when the brain processes these signals.
Rewiring taste buds to the auditory cortex would result in auditory experiences when eating.
Adaptation:
If a stimulus doesn't change, the sense becomes less responsive over time.
Adaptive value: Prevents constant awareness of unimportant, unchanging stimuli (e.g., clothes, air flowing in the nose).
General Structure of Sensory Systems
Common Structure: All sensory systems have a similar structure and subsystems with similar functions.
Stimulus:
Energy (light, sound), mechanical pressure, or chemicals (food, airborne molecules).
Accessory Structures:
Anatomical features that modify the signal.
Example: The eye's lens focuses light; the iris controls light amount.
Receptors:
Specialized cells that transduce the stimulus into a neural signal.
Example: Photoreceptors in the eyes.
Sensory Nerves:
Carry the signal to the central nervous system.
Neural Code:
Special format for transmitted signals.
Spatial codes: Location of stimulation corresponds to a place in space (e.g., in the eye).
Temporal codes: Nerve firing rate or pattern.
Thalamus:
Most signals are routed through the thalamus.
Relay Station: Often called the brain's relay station.
Cortical Regions:
Signals are processed in specific areas of the cortex.
Olfaction Exception:
Smell signals go directly from the nose to a frontal brain area before going elsewhere.
Visual and Auditory Senses
General Pattern: Vision and audition follow the same general plan:
Accessory structures,
Specialized receptors that transduce the stimulus,
Neural codes related to higher brain areas for processing.
Vision
Stimulus:
Vision: Electromagnetic radiation (light) with wavelengths of 400 to 750 nanometers.
Wavelength correlates with the psychological experience of color.
Intensity correlates with the psychological experience of brightness.
Accessory Structures of the Eye (Outside In):
Cornea: Clear outer covering.
Aqueous Humor: Clear fluid that supplies oxygen and nutrients to the cornea and lens.
Iris: Shutter that controls light amount.
Pupil: Hole in the center of the iris.
Lens: Crystalline structure that focuses light onto the back of the eye. It flattens for distant objects and squeezes up for nearby objects; this process is called accommodation.
Presbyopia (old eyes): Loss of accommodation ability with age, requiring glasses for reading.
Vitreous Humor: Clear fluid filling the main body of the eye.
Retina: Back wall of the eye where sensory transduction occurs.
Special receptor cells: Rods and cones (named for their shapes).
Cones: Predominate at the center of vision (fovea - region of highest visual acuity), sensitive to fine detail and color.
Rods: Mostly in the periphery, not color sensitive, wired for motion detection.
Layers of cells:
Rods and Cones.
Bipolar Cells.
Retinal Ganglion Cells- Light has to travel through these to reach the rods and cones.
When light strikes a rod or cone, it bleaches changing the membrane potentia.
Many photoreceptors are connected to a bipolar cell forming the graded potential across it.
Many bipolar cells feed into a single retinal ganglion cell. Once excited, it generates and action potential sending an impulse down a nerve cell to the brain for further processing.
Data compression. 120 million rods and cones compressed to only 1 million nerve cells that leave the eye
Neural Pathway:
Optic Nerve: Carries the signal from the eye.
Optic Chiasm: Nerves cross over from one side of the brain to the other.
Lateral Geniculate Nucleus (LGN) of the Thalamus: Relay station for vision; has a retinotopic map.
Superior Colliculus: Involved in orienting and motion, helps eyes track objects and catch attention.
Primary Visual Cortex (V1 or Striate Cortex): Early cortical area for higher visual processing.
Contains edge detectors for detecting edges or lines.
About a quarter of the V1 area deals with fovea, the other three quaters deals with the rest of the eye.
Signal Spreads: Signal then spreads across the cortex.
What Pathway (Temporal Area): Deals with object recognition.
Where Pathway (Parietal and Occipital Lobes): Deals with locations in space.
Specialized Brain Areas: The brain has specialized areas that solve specific functions like processing color, motion, etc.
Audition
Stimulus:
Vibrations of air molecules (compression and rarefaction).
Amplitude: Correlates with the psychological experience of loudness.
Measured using a logarithmic scale in decibels (dB).
0 dB: Quietest sound an average human can hear.
Frequency: Number of times a waveform repeats per second.
Measured in hertz (Hz).
Typical range: 20 Hz to 20 kHz (but varies with age).
Low frequency = low pitch.
Most speech sounds are between 100 - 300 Hz.
Timbre:
Complex shape of waveforms gives sound its characteristic quality
Accessory Apparatus and Information Flow:
Outer Ear: Pinna and ear canal.
Head: an accessory structure because it separates the ears. Sounds arrive at the two ears at different times and bend around the head providing information about where the sound is coming from.
Pinna: Shields sound from behind, focusing sound energy.
Middle Ear:
Eardrum (Tympanic Membrane): Collects vibrations.
Malleus, Incus, Stapes: Three little bones that act as a lever system for impedance matching.
Taking the vibrations in air and transforms them into fluid vibrations in the inner ear.
Inner Ear:
Cochlea: Snail-like structure.
vestibular canal
tympanic canal
basilar membrane- floor of the cochlear structure.
organ of Corti-Inside the basilar membrane, sound waves travel through the structure causing bending in hair cells.
Hair cells are the transducers that turn vibrations into neural impulses- like the rods and cones.
There are 15,000 hair cells on each cochlea.
Inner hair cells: (3,500) control eeverything we concsioulsy hear.
Outer hair cells-lie along the outside.
Neural Codes:
Details to be studied in the textbook.
Temporal codes: Intensity coded by rate of firing of neurons.
Frequency coded by place on the basilar membrane and firing rate.
Neural Pathway:
Nerve cells project from the cochlea to the auditory nerve and then to the medulla.
Most predictions go to the other side of the brain.
Structures: inferior colliculus onto the temporal areas of the cortex.
Brain Processing: Particular aspects of sound processing happen in pockets of the temporal lobe.
A lot of cortex devoted to resolving pitch, particularly speech sounds, concentrated in the temporal lobes.
Loudness and Pitch: Detailed information in the textbook, discussed in class.
Timbre: More complex topic discussed in other units.
Taste (Gustation)
Type of Sense: Chemical sense; detects chemicals dissolved in saliva.
Function:
Helps us regulate intake of certain nutrients such as sugar and salt
Facilitates eating by helping avoid poisonous or bad-tasting substances.Accessory Structures: Mouth and papillae (bumps on the tongue); move food around the mouth.
Transduction:
Taste buds (about 10,000) inside the papillae and in the roof of the mouth/throat.
Each papilla contains about 50-150 taste receptors.
Taste buds age and are replaced every 10-15 days.
Receptors:
Chemicals dissolved in saliva penetrate the pores on the pupillae and other part of the mouth and stimulate the specialized receptors
Four different kinds of receptors:
* Sweet and bitter (specially shaped binding sites).
* Salty and sour (ion channel based).Additional Tastes
* Umami (savory, e.g., mushrooms, MSG).
* Astringent (e.g., tannins in tea and wine).Fat Receptors: Growing evidence of fat receptors; less conscious experience.
Pain Receptors: Eating chili causes pain, detected as heat (capsaicin).
Neural Pathways:
Travels to the medulla in the pons and then into the brain stem.
Thalamus and Gestatory Cortex (postcentral gyrus of the parietal lobe): Processing of conscious taste identification.
Limbic System (non-conscious): Rapid emotional and behavioral responses.
Smell (Olfaction)
Type of Sense: Chemical sense.
Function: Detects foods, animals, fires, etc., in the environment.
Use smell to tell if food is edible or poisonous
There's evidence of pheromones being released where women menstrual cycles synchronize.Accessory Structure: Nose; channels air to the receptor site.
Receptor Site: Olfactory epithelium at the roof of the nose.
1000s of little receptor hair cells with dendrites imbedded in a mucus. The odourants that are soluble in the mucus get detected by these dendrites.Neural Pathway:
Olfactory Epithelium to the Olfactory Bulb to the Primary Olfactory Cortex in the Frontal Lobe.
Smell does NOT go to the thalamus!
Then to the Thalamus and Limbic System for other more recognition and emotional components of smell.
Smell Perception
*Animals can use smell to regulate or influence behavior.
*Unlike other senses, smells are very hard to label.
*Smells can also get to the olfactory epithelium via the back of the mouth.
*Taste is heavily influenced by back of the mouth smell called retronasal-olfaction.Receptor Types: Many different receptor cells that respond to specific odorant molecules.
Humans have about 10,000,000 olfactory neurons.
Number of receptor types is very large (thousands).
Cutaneous and Proprioceptive Sensors
Cutaneous Sensors (Somatosensory System)
Multiple senses: Pressure, motion, vibration, temperature, pain.
Physiology: Not as well understood as other senses.
Accessory Structure: Less clear; cells located all over the body.
Large number of kinds of touch receptors (free nerve endings, Pacinian corpuscle, etc.).
Emerging area of research; specifics not well understood.
Temperature Receptors:
Warm receptors: Increase firing as heat is applied.
Cold detectors: Fire more as the area gets colder.
Interesting illusion extreme heat will also cause the cold receptors to fire. If you take two or three or four small objects, some of which are warm, some are cold then this simultaneous warm cold sensation will trick you into experiencing extreme pain.
Touch Receptor Distribution: Not evenly distributed around the body.
Homunculus: Distorted mannequin depicting the proportion of nerves, receptors, and brain area.
Fingers have the most receptors, followed by the face, then the back.
Two-Point Threshold: Spacing needed to perceive two separate points; tests sensor distribution.
Neural Codes:
Temporal: More pressure, heat, or vibration = more rapid/intense firing.
Spatial: Part of the body corresponds to a spatial map in the brain.
Proprioception
Body Position: Where your body is in space and how you currently have your limbs positioned is figured out by two systems.
Kinesthetic sense
Vestibular system
Kinesthetic Sense
Functionposition of your body parts.
Proprioceptors: Special receptors in the muscles and joints.
Nervous system Signals travel up through the spinal cord, then through the thalamus and to the somatosensory cortex.
They send information to your brain about how flexed or how stretched a muscle is and what the angle of a joint is, how a particular limb is bent.Coordination Another projection goes to the cerebellum to help coordinate activity.
Vestibular Sense
Deals with balance and the position of your head
Located near the cochlea, in the inner ear *Key Receptors
Semicircular canals: Fluid filled tubes with hairs; motion or change in motion of your head stimulates the hairs causing to flex and stimulate signal to the brain.
Vestibular sacs: Little bags lined with hair that contains tiny stones(otolith) allowing you to turn your head which moves the stones around providing the signal of which way the head is tilted.
Works due to gravity.
Detailed Version
Studying Sensation and Perception
Lecture Outlines and Learning Objectives:
Each lecture has an outline with learning objectives to set the stage for the topics to be covered. These objectives clearly state what you should know or be able to do after each lecture.
Videos introduce key ideas, providing visual and auditory explanations, but they don't cover every single detail. They serve as an initial guide.
Learning objectives offer a structured framework for studying. Align your studying with these objectives to ensure you grasp the essential concepts.
The textbook also has learning objectives, often providing a more comprehensive and detailed overview. Use these to deepen your understanding.
Suggested Study Method:
Read the lesson outline and check the learning objectives before diving into the material. This will help you focus on what's important.
Watch the videos to get an initial understanding of the topics. Take notes on the key concepts and any questions that arise.
Read and reread the text, making notes each time. The first reading should give you an overview, while subsequent readings should focus on details and connections.
Focus on finding connections between ideas to build a "web of knowledge." Relate new information to what you already know to create a more cohesive understanding.
Why Study Sensation and Perception?
Gathering Information:
Sensation and perception are how we gather and interpret information about our environment. They are fundamental to our understanding of the world.
It's our only contact with reality. All our experiences and interactions are mediated through our sensory systems.
Importance:
Essential for a basic knowledge of the world and how our brains work. Understanding sensation and perception provides insights into cognitive processes and neural mechanisms.
Practical Applications:
Clinical settings: Understanding normal perception helps in understanding clinical conditions. This knowledge is crucial for diagnosing and treating sensory disorders.
Working with young or old individuals: Understanding normal development and aging aids in working with these populations. Perception changes throughout the lifespan, and this understanding helps in providing appropriate care.
Crossover with Other Disciplines:
Computational approaches: Computer modeling is used to understand perception, especially vision. These models help simulate and explain how the brain processes sensory information.
Inspiration for Machines: Understanding animal/human sensation and perception can be used to design better machines and robots. Biomimicry in engineering often draws from sensory mechanisms in living organisms.
Sensation vs. Perception:
Sensation: The concrete physiological process of turning environmental stimuli into neural messages. This involves the activation of sensory receptors and the transmission of signals to the brain.
Perception: The abstract psychological process of interpreting signals into experiences or knowledge. Perception is subjective and influenced by prior knowledge, expectations, and context.
Perception occurs in the brain through complex neural processes.
Taste Example:
Taste buds transduce chemicals into nerve impulses, but the experience of taste happens when the brain processes these signals. The brain integrates information from taste receptors with other sensory inputs (e.g., smell, texture) to create the overall taste experience.
Rewiring taste buds to the auditory cortex would result in auditory experiences when eating. This thought experiment illustrates the brain's plasticity and how sensory information is interpreted based on the receiving cortical area.
Adaptation:
If a stimulus doesn't change, the sense becomes less responsive over time. Sensory adaptation helps us focus on changes in our environment rather than constant, unchanging stimuli.
Adaptive value: Prevents constant awareness of unimportant, unchanging stimuli (e.g., clothes, air flowing in the nose). This allows us to attend to more critical and potentially threatening stimuli.
General Structure of Sensory Systems
Common Structure: All sensory systems have a similar structure and subsystems with similar functions, including receptors, neural pathways, and cortical processing areas.
Stimulus:
Energy (light, sound), mechanical pressure, or chemicals (food, airborne molecules) that trigger sensory receptors.
Accessory Structures:
Anatomical features that modify the signal before it reaches the receptors. These structures enhance or focus the stimulus.
Example: The eye's lens focuses light; the iris controls light amount. These structures optimize the incoming light for clear vision.
Receptors:
Specialized cells that transduce the stimulus into a neural signal. These cells convert energy or chemicals into electrical signals that the nervous system can process.
Example: Photoreceptors in the eyes (rods and cones).
Sensory Nerves:
Carry the signal from the receptors to the central nervous system.
Neural Code:
Special format for transmitted signals.
Spatial codes: Location of stimulation corresponds to a place in space (e.g., in the eye, different locations on the retina correspond to different parts of the visual field).
Temporal codes: Nerve firing rate or pattern, which encodes information about the intensity and duration of the stimulus.
Thalamus:
Most signals are routed through the thalamus, which acts as a central relay station.
Relay Station: Often called the brain's relay station. The thalamus filters and directs sensory information to the appropriate cortical areas.
Cortical Regions:
Signals are processed in specific areas of the cortex, allowing for higher-level analysis and interpretation.
Olfaction Exception:
Smell signals go directly from the nose to a frontal brain area before going elsewhere. This direct pathway may be related to the strong emotional and memory associations with smell.
Visual and Auditory Senses
General Pattern: Vision and audition follow the same general plan:
Accessory structures to modify the incoming stimulus.
Specialized receptors that transduce the stimulus into neural signals.
Neural codes that transmit information to higher brain areas for processing.
Vision
Stimulus:
Vision: Electromagnetic radiation (light) with wavelengths of 400 to 750 nanometers. This range represents the visible spectrum.
Wavelength correlates with the psychological experience of color. Different wavelengths are perceived as different colors.
Intensity correlates with the psychological experience of brightness. Higher intensity light is perceived as brighter.
Accessory Structures of the Eye (Outside In):
Cornea: Clear outer covering that helps focus light as it enters the eye.
Aqueous Humor: Clear fluid that supplies oxygen and nutrients to the cornea and lens. It also maintains the shape of the anterior chamber of the eye.
Iris: Shutter that controls the amount of light entering the eye by adjusting the size of the pupil.
Pupil: Hole in the center of the iris through which light passes.
Lens: Crystalline structure that focuses light onto the back of the eye. It changes shape to focus on objects at different distances; this process is called accommodation.
Presbyopia (old eyes): Loss of accommodation ability with age, requiring glasses for reading. The lens becomes less flexible, making it harder to focus on near objects.
Vitreous Humor: Clear fluid filling the main body of the eye, helping to maintain its shape.
Retina: Back wall of the eye where sensory transduction occurs. It contains several layers of cells, including photoreceptors.
Special receptor cells: Rods and cones (named for their shapes).
Cones: Predominate at the center of vision (fovea - region of highest visual acuity), sensitive to fine detail and color. Cones function best in bright light.
Rods: Mostly in the periphery, not color sensitive, wired for motion detection. Rods are more sensitive to light and function better in dim conditions.
Layers of cells:
Rods and Cones: The photoreceptors that transduce light into electrical signals.
Bipolar Cells: Intermediate neurons that receive input from the photoreceptors and transmit it to the ganglion cells.
Retinal Ganglion Cells: Neurons whose axons form the optic nerve, carrying visual information to the brain. Light has to travel through these to reach the rods and cones.
When light strikes a rod or cone, it bleaches, changing the membrane potential. This initiates the process of phototransduction.
Many photoreceptors are connected to a bipolar cell, forming the graded potential across it. This allows for signal summation and amplification.
Many bipolar cells feed into a single retinal ganglion cell. Once excited, it generates an action potential, sending an impulse down a nerve cell to the brain for further processing. This convergence of signals results in data compression.
Data compression: 120 million rods and cones are compressed to only 1 million nerve cells that leave the eye, allowing efficient transmission of visual information.
Neural Pathway:
Optic Nerve: Carries the signal from the eye to the brain.
Optic Chiasm: Nerves cross over from one side of the brain to the other, allowing information from each visual field to be processed by the contralateral hemisphere.
Lateral Geniculate Nucleus (LGN) of the Thalamus: Relay station for vision; has a retinotopic map, meaning that adjacent points on the retina are represented by adjacent neurons in the LGN.
Superior Colliculus: Involved in orienting and motion, helps eyes track objects and catch attention. This midbrain structure is important for visual reflexes.
Primary Visual Cortex (V1 or Striate Cortex): Early cortical area for higher visual processing.
Contains edge detectors for detecting edges or lines. These neurons are sensitive to specific orientations of lines and edges.
About a quarter of the V1 area deals with the fovea; the other three-quarters deals with the rest of the eye. This reflects the high visual acuity of the fovea.
Signal Spreads: The signal then spreads across the cortex to various specialized areas.
What Pathway (Temporal Area): Deals with object recognition, identifying what objects are.
Where Pathway (Parietal and Occipital Lobes): Deals with locations in space, determining where objects are located.
Specialized Brain Areas: The brain has specialized areas that solve specific functions like processing color, motion, etc., allowing for efficient and specialized visual processing.
Audition
Stimulus:
Vibrations of air molecules (compression and rarefaction) that propagate as sound waves.
Amplitude: Correlates with the psychological experience of loudness. Higher amplitude waves are perceived as louder.
Measured using a logarithmic scale in decibels (dB).
0 dB: The quietest sound an average human can hear (threshold of hearing).
Frequency: The number of times a waveform repeats per second.
Measured in hertz (Hz).
Typical range: 20 Hz to 20 kHz (but varies with age). As we age, our ability to hear high-frequency sounds decreases.
Low frequency = low pitch. Lower frequencies are perceived as lower pitches.
Most speech sounds are between 100 - 300 Hz, which is the range our auditory system is most sensitive to.
Timbre:
The complex shape of waveforms gives sound its characteristic quality, allowing us to distinguish between different instruments or voices.
Accessory Apparatus and Information Flow:
Outer Ear: Pinna and ear canal.
Head: an accessory structure because it separates the ears. Sounds arrive at the two ears at different times and bend around the head, providing information about where the sound is coming from. This is known as interaural time difference and interaural level difference.
Pinna: Shields sound from behind, focusing sound energy into the ear canal, and helps in sound localization.
Middle Ear:
Eardrum (Tympanic Membrane): Collects vibrations from the air.
Malleus, Incus, Stapes: Three little bones (ossicles) that act as a lever system for impedance matching.
Taking the vibrations in the air and transforms them into fluid vibrations in the inner ear. This amplification is necessary because it takes more energy to vibrate fluid than air.
Inner Ear:
Cochlea: Snail-like structure containing the sensory receptors for hearing.
vestibular canal
tympanic canal
basilar membrane: The floor of the cochlear structure. It vibrates in response to sound waves.
organ of Corti: Located inside the basilar membrane, contains hair cells that transduce mechanical vibrations into neural signals. Sound waves travel through the structure, causing bending in hair cells.
Hair cells are the transducers that turn vibrations into neural impulses, similar to rods and cones in the eye.
There are about 15,000 hair cells on each cochlea.
Inner hair cells: (3,500) primarily responsible for our conscious perception of sound.
Outer hair cells: Lie along the outside; amplify and refine the vibrations, enhancing the sensitivity of the inner hair cells.
Neural Codes:
Details to be studied in the textbook.
Temporal codes: Intensity coded by the rate of firing of neurons. Louder sounds result in higher firing rates.
Frequency coded by the place on the basilar membrane that is most stimulated and by the firing rate of auditory nerve fibers. Different locations on the basilar membrane vibrate maximally in response to different frequencies.
Neural Pathway:
Nerve cells project from the cochlea to the auditory nerve and then to the medulla in the brainstem.
Most projections go to the other side of the brain, allowing for contralateral processing of auditory information.
Structures: Inferior colliculus (midbrain structure) to the medial geniculate nucleus (MGN) of the thalamus and onto the temporal areas of the cortex.
Brain Processing: Particular aspects of sound processing happen in pockets of the temporal lobe. Different areas are specialized for processing different aspects of sound.
A lot of cortex is devoted to resolving pitch, particularly speech sounds, concentrated in the temporal lobes. This area is crucial for understanding spoken language.
Loudness and Pitch: Detailed information in the textbook, discussed in class.
Timbre: A more complex topic discussed in other units.
Taste (Gustation)
Type of Sense: Chemical sense; detects chemicals dissolved in saliva.
Function:
Helps us regulate the intake of certain nutrients such as sugar and salt, which are essential for bodily functions.
Facilitates eating by helping to avoid poisonous or bad-tasting substances; this is a crucial survival mechanism.Accessory Structures: Mouth and papillae (bumps on the tongue); these structures move food around the mouth, facilitating the interaction between food and taste receptors.
Transduction:
Taste buds (about 10,000) are located inside the papillae and in the roof of the mouth/throat. These contain specialized receptor cells.
Each papilla contains about 50-150 taste receptors.
Taste buds age and are replaced every 10-15 days, ensuring a continuous ability to detect tastes.Receptors:
Chemicals dissolved in saliva penetrate the pores on the papillae and stimulate the specialized receptors.
Four different kinds of receptors:Sweet and bitter (specially shaped binding sites). These receptors bind to specific molecules, triggering a neural signal.
Salty and sour (ion channel based). These receptors respond to the presence of specific ions, such as sodium (salty) or hydrogen (sour).
Additional Tastes
Umami (savory, e.g., mushrooms, MSG). This taste is elicited by glutamate, an amino acid.
Astringent (e.g., tannins in tea and wine). Astringency is more of a tactile sensation than a taste, causing a puckering or drying sensation in the mouth.
Fat Receptors: Growing evidence of fat receptors; less conscious experience. These receptors may contribute to our preference for fatty foods.
Pain Receptors: Eating chili causes pain, detected as heat (capsaicin). Capsaicin activates pain receptors that are sensitive to heat.
Neural Pathways:
Travels to the medulla in the pons and then into the brain stem. This relays information to higher brain regions.
Thalamus and Gustatory Cortex (postcentral gyrus of the parietal lobe): Processing of conscious taste identification. This allows us to identify and discriminate different tastes.
Limbic System (non-conscious): Rapid emotional and behavioral responses. Taste stimuli can trigger emotional responses and influence feeding behavior.<!-- -->
Smell (Olfaction)
Type of Sense: Chemical sense; detects airborne molecules.
Function:
Detects foods, animals, fires, etc., in the environment; this is crucial for survival.
Use smell to tell if food is edible or poisonous, preventing the ingestion of harmful substances.
There's evidence of pheromones being released, where women's menstrual cycles synchronize. Pheromones can influence behavior and physiology.Accessory Structure: Nose; channels air to the receptor site, optimizing the detection of odorants.
Receptor Site: Olfactory epithelium at the roof of the nose.
1000s of little receptor hair cells with dendrites imbedded in mucus. Odorants that are soluble in the mucus get detected by these dendrites.Neural Pathway:
Olfactory Epithelium to the Olfactory Bulb to the Primary Olfactory Cortex in the Frontal Lobe. This is a direct pathway to the cortex without going through the thalamus.
Smell does NOT go to the thalamus!
Then to the Thalamus and Limbic System for other more recognition and emotional components of smell. This allows for integration with other sensory information and emotional processing.<!-- -->Smell Perception
Animals can use smell to regulate or influence behavior. Pheromones, for example, play a key role in animal communication.
Unlike other senses, smells are very hard to label. This may be due to the lack of direct access to the thalamus.
Smells can also get to the olfactory epithelium via the back of the mouth. This is retronasal olfaction, which contributes significantly to the perception of flavor.
Taste is heavily influenced by back of the mouth smell called retronasal olfaction. The combination of taste and retronasal olfaction creates the overall perception of flavor.
Receptor Types: Many different receptor cells that respond to specific odorant molecules.
Humans have about 10,000,000 olfactory neurons, allowing for the detection of a wide range of odors.
The number of receptor types is very large (thousands), with each receptor responding to a specific set of odorants.
Cutaneous and Proprioceptive Sensors
Cutaneous Sensors (Somatosensory System)
Multiple senses: Pressure, motion, vibration, temperature, pain. These senses, when combined, give us a rich perception of our body and its interaction with the environment.
Physiology: Not as well understood as other senses, but research is continually advancing our understanding.
Accessory Structure: Less clear; cells located all over the body, each with specialized functions.
Large number of kinds of touch receptors (free nerve endings, Pacinian corpuscle, etc.). These receptors respond to different types of mechanical stimulation.
Emerging area of research; specifics not well understood but under active investigation.Temperature Receptors:
Warm receptors: Increase firing as heat is applied. These receptors are sensitive to increases in temperature.
Cold detectors: Fire more as the area gets colder. These receptors are sensitive to decreases in temperature.Interesting illusion: Extreme heat will also cause the cold receptors to fire. If you take two or three or four small objects, some of which are warm and some are cold, then this simultaneous warm cold sensation will trick you into experiencing extreme pain due to the activation of both warm and cold receptors.
Touch Receptor Distribution: Not evenly distributed around the body, with some areas having a higher density of receptors than others.
Homunculus: A distorted mannequin depicting the proportion of nerves, receptors, and brain area dedicated to different body parts. Areas with more sensory receptors are represented as larger on the homunculus.
Fingers have the most receptors, followed by the face, then the back. This distribution reflects the importance of these areas for tactile discrimination.Two-Point Threshold: The spacing needed to perceive two separate points; tests sensor distribution. This measures the tactile acuity in different areas of the body.
Neural Codes:
Temporal: More pressure, heat, or vibration = more rapid/intense firing. The frequency and intensity of nerve firing encode the strength of the stimulus.
Spatial: Part of the body corresponds to a spatial map in the brain (somatotopic map). This allows us to localize tactile sensations to specific body parts.
Proprioception
Body Position: Where your body is in space and how you currently have your limbs positioned is figured out by two systems.
Kinesthetic sense: Provides information about the movement and position of body parts.
Vestibular system: Deals with balance and spatial orientation.
Kinesthetic Sense
Function: Provides awareness of the position and movement of body parts.
Proprioceptors: Special receptors in the muscles and joints that detect stretch and tension.
Nervous system: Signals travel up through the spinal cord, then through the thalamus and to the somatosensory cortex. This pathway conveys conscious awareness of body position and movement.
They send information to your brain about how flexed or how stretched a muscle is and what the angle of a joint is, and how a particular limb is bent, providing detailed feedback about body posture.
Coordination: Another projection goes to the cerebellum to help coordinate activity. The cerebellum integrates this information to fine-tune movements and maintain balance.
Vestibular Sense
Deals with balance and the position of your head in space.
Located near the cochlea in the inner ear. Key Receptors:
Semicircular canals: Fluid-filled tubes with hairs. Motion or change in motion of your head stimulates the hairs, causing them to flex and stimulate a signal to the brain. These canals detect rotational movements of the head.
Vestibular sacs: Little bags lined with hair that contain tiny stones (otoliths), allowing you to turn your head, which moves the stones around, providing a signal of which way the head is tilted.
Works