Mechanisms of Sensory Systems and Somatosensory Receptor Physiology Flashcards
____________refers to the detection of the elements and energies in our internal and external environment.
Sensation
Sensation requires the conversion of ___________ into signals that can be recognized by our __________.
Environmental signals; CNS
______________ is the interpretation of the significance, meaning or quality of sensory information.
Perception
What factors play a role in perception?
Learning
Memory
Context
Physiological state
*Perception can vary widely between individuals
What is sensory physiology?
The study of the mechanisms guiding the transduction of a stimulus into action potentials that travel to the brain resulting in sensation (conscious or unconscious).
What are the three types of sensory systems? What does each system produce and convey?
Somatosensory Systems
- Convey: impulses from skin, skeletal muscles, and joints
- Produce: sensations of temperature, touch, pressure, itch, pain, and muscle tension
Visceral Sensory Systems
- Convey: impulses from visceral organs
- Produce: sensations of stretch, pressure, pain
Special Sensory Systems
- convey: impulses from special sense organs (ears, eyes, nose, tongue)
- Produce: sensations of light, sound, taste, smell, head motion & equilibrium/balance
Which type of sensory system is involved in subconscious detection?
Visceral sensory systems process subconscious detection of osmolarity, pH, O2, and CO2.
Distinguish between general and special senses
General senses are detected by sensory receptors that are scattered throughout the body.
Special senses are detected by receptors localized to special sensory organs (located in the head)
What are the general senses?
Temperature
Touch
Pressure
Pain
Proprioception
What are the special senses?
Sight
Sound
Taste
Smell
Balance
What are the steps of the afferent pathway?
Sensory receptors-> Primary afferent neuron-> Secondary sensory neuron-> Thalamus-> Brain
What are the steps of the efferent pathway?
Brain-> Effector
Of the basic types of neurons, which type is not found in humans?
Unipolar
What are the functions of transducers?
- Specialized to detect environmental energy (stimuli)
- Convert stimulus energy into changes in transmembrane electical potential of the sensory (afferent) neuron
- Trigger action potentials (in the primary afferent neuron) that are transmitted to secondary and tertiary afferent neurons and travel to the brain
Where do transducers initially trigger action potentials?
In the primary afferent neuron
Type of receptor that responds to stimuli arising from outside the body. Where is this receptor type found and what does it produce?
Exteroceptors
Location: in skin and special sensory organs
Produce : sensations of light, sound, smell, taste, touch, temperature
Type of receptor that responds to stimuli arising in internal viscera and blood vessels. What is this receptor type sensitive to and what does it produce?
Interoceptors
›Sensitive to chemicals, pH, tissue stretch, and temperature
›Produce sensations of distension or pain; many do not lead to sensations
Interoceptors are also known as________________
Visceroceptors
Type of receptor that responds to stimuli arising in skeletal muscles, tendons, joints, ligaments, and connective tissue. What is this receptor type sensitive to and what does it produce?
Proprioceptors
›Sensitive to contraction, stretch, movement
›Produces sensations of body movements and special position
What are the 5 main types of receptors? What type of stimulus does each type respond to?
Mechanoreceptors
- Respond to mechanical forces
- Touch, pressure, vibration, stretch, tension
Thermoreceptors
- Respond to temperature changes
- Heat, cold
Photoreceptors
- Respond to wavelength of light
Chemoreceptors
- Respond to chemicals
- Osmolality, pH, CO2, O2, organic molecules, airborne molecules
Nociceptors (polymodal)
- Respond to potentially damaging stimuli
General senses
Location of cell body
Neuronal structure
Location of cell body: Dorsal root ganglia or cranial nerve ganglia
Neuronal structure: Pseudounipolar
Special senses
Location of cell body
Neuronal structure
Location of cell body: In special sense organs
Neuronal structure: Bipolar
What are the different structures of sensory receptors? What are characteristics of each?
Simple
- Naked nerve endings
- Encapsulated naked nerve endings
Complex
- Specialized receptor cells
- produce neurotransmitters
- Primary afferent neuron is a separate cell from the receptor cell
What are the steps of stimulus transduction in simple receptors?
- Stimulus is detected by receptor
- Alters membrane permeability to ions
- Activate second messender systems which then lead to altered membrane permeability to ions
- Change in graded potential
- Graded potential triggers action potentials in afferent neurons
- Action potentials are propagated
For sensation, generator potential must reach threshold at ___________.
Trigger zone
What are the steps of stimulus transduction in special sensory cells (complex)?
- Stimululus detected by receptor cell
- Change in graded potential in receptor cell
- Receptor cell releases neurotransmitter
- Neurotransmitters genreate graded potentials in primary sensory neuron
- Graded potential triggers APs in primary afferent neuron
What are the receptors from the organs listed below?
Eyes
Tongue
Nose
Otolith organ
Organ of corti
- Eyes (retina): rods and cones
- Tongue: Taste buds
- Nose: Olfactory cells
- Otolith organs: hair cells
- Organ of corti: hair cells
Accessory organs direct and transfer input _________.
Energy
What is the role of the pinna?
The pinna, also known as the outer ear, amplifies and directs sound waves into the auditory canal
What is the role of the tempanic membrane?
The tempanic membrane, also known as the eardrum, amplifies sound waves
What is the role of the cornea and lens of eye?
Focus entry of light onto the retina of the eye
What is the role of the hair cells on body?
Transmits light touch and movement
Sensory systems mediate what four attributes of a stimulus
- Modality
- Form of energy to which the receptor responds
- Intesity
- # of receptors activated
- Frequency of APs
- Duration
- Duration of action potentials
- APs at onset and again at the cessation of a stimulus
- Location
What are the different modalities to which a receptor can respond?
- Mechanical (touch, pressure, vibration, stretch, acceleration)
- Thermodynamic (heat, cold)
- Electromagnetic (light)
- Chemical (oxygen, pH, odorants, glucose and other organic molecules)
- Damaging Intensities (tissue damage or potentially damaging levels of other stimulus modalities)
____________ is the specific sub-modality (specific range of modality) to which a receptor is most sensitive.
Adequate stimulus
Very low levels of the adequate stimulus affects the __________ potential.
Receptor
What is the labeled line principle?
Excitation of sensory receptor and sensory neuron elicits only one sub-modality of sensation
- This localizes the stimulus and identifies the type of stimulus
Premises:
- Individual receptors preferentially transduce information about an adequate stimulus
- Individual primary afferent fibers carry information from a single type of receptor
NOTE: Stimulation anywhere along the sensory pathways from a sensory receptor to the specialized sensory cortex will only result in one particular sensation
Which areas of the brain process skeletal muscle movement?
Primary motor cortex
Motor association area (premotor cortex)
Which areas of the brain process sensory information from skin, musculoskeletal system, viscera, and taste buds?
Primary somatic sensory cortex
Parietal lobe
Sensory association area
Which areas of the brain process sensory information from vision?
Visual association area
Occipital lobe
Visual cortex
Which areas of the brain process sensory information from hearing?
Auditory association area
Auditory cortex
Temporal lobe
Which areas of the brain process sensory information from taste?
Temporal lobe
Gustatory cortex
Which areas of the brain process sensory information from smell?
Temporal lobe
Olfactory cortex
Which areas of the brain coordinates information from other association areas, and controls some behaviors?
Frontal lobe
Prefrontal association area
What determines the frequency of APs?
- Directly related to the receptor potential
- Modified by inhibitory or stimulatory inputs
- Modified by adaptation
Sensation of the duration of an AP is modified by it’s ability to ____________.
Adapt
_______________ is the decreased sensitivity to a sustained stimulus.
Adaptation
- Receptor membranes become less responsive
- Receptor potential decreases
- Action potentials decline in frequency
- Dictated by the receptor structure
What ion channel activity causes a receptor potential to decrease?
- Inactivation of Na+ or Ca2+ channels
- Activation of K+ channels
_______________ adapt slowly or not at all.
Tonic receptors
- Usually coupled to small diameter, unmyelinated fibers
Which type of receptors are tonic receptors?
Nociceptors
Proprioceptors
Thermoreceptors
Crude Touch
___________ are fast adapting and signal at the beginning and end of stimulus.
Phasic receptors
- Usually coupled to large, myelinated fibers
Which type of stimuli activate phasic receptors?
Pressure
Fine Touch
Smell
Absolute threshold
- Minimum stimulation needed to detect a particular stimulus
- Usually defined as the stimulus needed for detection 50% of the time
Difference Threshold
- Minimum difference between two stimuli that a subject can detect 50% of the time
- Just noticeable difference (JND)
- Increases with magnitude
What is the relationship between stimulus intensity and receptor potential at stimulus intensities less than 1.5?
Exponential
What is the relationship between stimulus intensity and receptor potential at stimulus intensities between 1.5 to 3?
Linear
What is the relationship between stimulus intensity and receptor potential at stimulus intensities between 3 and 4.5?
Logarithmic
What is the relationship between stimulus intensity and receptor potential at stimulus intensities greater than 4.5?
Horizontal
Weber’s Law
States that the amount of change in stimulus intensity that is needed for the change to be detectable is proportional to the initial intesity of the stimulus
ΔI/I= K
*NOTE: The constant K varies according to stimulus modality
What are examples of skin mechanoreceptors? What does each receptor detect?
Hair follicle receptor
- Light touch
- Moving touch
Pacinian corpuscles
- Deep pressure
- Vibration
Meissner’s corpuscles
- Fine touch
Merkel receptors
- Pressure & texture
Ruffini endings
- Skin stretch
- Deep pressure
Hair Follicle Receptor
Location
Accessory organ
Receptor
Receptive Field
Adaptation
Fiber type
Location: Deep dermis
Accessory organ: Hair follicle
Receptor: Free nerve endings tightly coiled around hair follicle
Receptive Field: Small
Adaption: Rapid
Fiber Type: Aβ & Aδ
What is the transduction mechanism for hair follicle receptors?
- Hair is deflected
- Motion of hair follicle against nerve endings triggers opening of mechanosensitive ion channels
- Ion channels are opened
- Ion channels are quickly blocked by collagen fibers
Pacinian Corpuscle
Location
Accessory organ
Receptor
Receptive Field
Adaptation
Fiber type
Location:
- Deep dermis hairy and glabrous (hairless) skin
- Joint capsules (proprioceptor)
Accessory organ
- Concentric lamellae of flattened cells
- Supported by collageneous tissue
- Spaces between lamellae are filled with fluid
Receptor:
- Bare nerve terminals
- Occupies center of corpuscle
Receptive Field: Large
Adaptation : Rapid
Fiber type: Aβ
What is the transduction mechanism for Pacinian Corpuscle?
- Applied pressure is transmitted to the nerve terminal derfoming it
- Mechanically gated Na+ channels are opened, depolarizing the membrane
- AP are generated along the fiber
- Fluid between lamellae is quickly dispersed, relieving the pressure on the terminal
- Membrane potential returns to resting level
- Removal of the probe again deforms nerve terminal resulting in depolarization
Meissner’s Corpuscle
Location
Accessory organ
Receptor
Receptive Field
Adaptation
Fiber type
Location:
- Beneath the epidermis
- Fingers, palm of the hand, plantar surface of the foot (glabrous skin)
Accessory organ
- Stacks of horizontally flattened epithelial cells enclosed in a connective tissue sheath
Receptor:
- Bare nerve terminals arborizes among the epithelial cells
Receptive Field: Small
Adaptation: Rapid
Fiber type: Aβ
Merkel’s Cells
Location
Receptor
Transduction
Receptive Field
Adaptation
Location:
- Below the epidermis
- Lips, Finger tips (glabrous skin)
Receptor:
- Large epithelial cell in close contact with a sensory neuron terminal
Transduction: Merkel’s cell releases neurotransmitter
Receptive Field: Small
Adaptation: Slowly adapting
Fiber type
Rufini’s ending
Location
Accessory organ
Receptor
Receptive Field
Adaptation
Fiber type
Location:
- Deep dermis layer of both hairy and glabrous skin
Receptor:
- Endings of sensory neuron encapsulated within bundles of collagen fibrils that are connected with similar fibrils of the dermis
Receptive Field: Large
Adaptation: Slow
Fiber type: Aβ
