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Questions and Answers
Which of the following are considered general senses?
Which of the following are considered general senses?
What characterizes un-encapsulated tactile receptors?
What characterizes un-encapsulated tactile receptors?
What is the primary function of nociceptors?
What is the primary function of nociceptors?
Which type of sensory receptor is classified as a proprioceptor?
Which type of sensory receptor is classified as a proprioceptor?
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Which receptor type is specifically associated with deep pressure and vibration?
Which receptor type is specifically associated with deep pressure and vibration?
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What type of receptors are responsible for detecting pain-causing stimuli?
What type of receptors are responsible for detecting pain-causing stimuli?
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Which receptors do not adapt readily and provide a sustained response?
Which receptors do not adapt readily and provide a sustained response?
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Which of the following is NOT a type of general sense receptor?
Which of the following is NOT a type of general sense receptor?
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Identify the correct example of a mechanoreceptor.
Identify the correct example of a mechanoreceptor.
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Which type of sensory receptor detects changes in temperature?
Which type of sensory receptor detects changes in temperature?
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Where are tactile (Meissner’s) corpuscles primarily located?
Where are tactile (Meissner’s) corpuscles primarily located?
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Which of the following best describes lamellar (Pacinian) corpuscles?
Which of the following best describes lamellar (Pacinian) corpuscles?
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What is the role of free nerve endings?
What is the role of free nerve endings?
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Which type of receptor would best respond to changes in blood chemistry?
Which type of receptor would best respond to changes in blood chemistry?
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What type of receptors are Merkel discs classified as?
What type of receptors are Merkel discs classified as?
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Which type of receptor is responsible for detecting stretch in skeletal muscle?
Which type of receptor is responsible for detecting stretch in skeletal muscle?
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What distinguishes Pacinian corpuscles from Meissner's corpuscles?
What distinguishes Pacinian corpuscles from Meissner's corpuscles?
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Which of the following types of receptors are classified as encapsulated tactile receptors?
Which of the following types of receptors are classified as encapsulated tactile receptors?
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Which type of receptor is primarily involved in detecting deep pressure and skin distortion?
Which type of receptor is primarily involved in detecting deep pressure and skin distortion?
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What sensation do nociceptors primarily detect?
What sensation do nociceptors primarily detect?
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Where are proprioceptors primarily located in the body?
Where are proprioceptors primarily located in the body?
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Which of the following accurately describes referred pain?
Which of the following accurately describes referred pain?
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What type of sensory receptors primarily respond to chemicals such as histamine?
What type of sensory receptors primarily respond to chemicals such as histamine?
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Which of the following describes the role of the somatosensory system?
Which of the following describes the role of the somatosensory system?
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Study Notes
Sensory Receptors
- Specialized to respond to changes in the environment (stimuli)
- Activation results in graded potentials that create nerve impulses.
- Awareness of stimulus (sensation) and interpretation of the stimulus (perception) occur in the brain.
General Function of Sensory Receptors
- Provide information about internal and external environments.
- Respond to specific types of stimuli.
- Transduce sensory energy into electrical energy.
- Receptors have resting membrane potentials and modality-gated channels that respond to their stimulus type (e.g., temperature, stretch, mechanical changes).
- Action potentials are sent to the central nervous system (CNS) for interpretation.
General Structure of Sensory Receptors
- Receptors convey signals to the CNS via sensory neurons.
- Receptive field: the area monitored by the endings of a sensory neuron.
- Smaller receptive fields allow more precise stimulus localization.
Sensory Receptor Classification
- Categorized by distribution, stimulus origin, and stimulus modality.
- General sense receptors are simple structures found throughout the body.
- Somatic sensory receptors are found in skin and mucous membranes; proprioceptors are in joints, muscles, and tendons.
- Visceral sensory receptors are in internal organs, monitoring stretch, chemical environment, temperature, and pain.
- Specialized receptors in complex sense organs (olfaction, gustation, vision, audition, equilibrium).
Receptor Classification by Stimulus Origin
- Exteroceptors detect stimuli from the external environment.
- Interoceptors detect stimuli from the internal environment (visceral).
- Proprioceptors detect body and limb movements.
Receptor Classification by Modality
- Mechanoreceptors: respond to touch, pressure, vibration, and stretch.
- Thermoreceptors: respond to changes in temperature.
- Photoreceptors: respond to light energy.
- Chemoreceptors: respond to chemicals (e.g., smell, taste, blood chemistry).
- Nociceptors: respond to pain-causing stimuli (extreme heat/cold, pressure, inflammatory chemicals).
Receptors (Modality, Location of Stimulus)
- Exteroceptors: detect external environment stimuli.
- Interoceptors: detect internal environment stimuli, typically visceral organs.
- Proprioceptors: detect body and limb movement, typically in joints, skeletal muscles, and tendons.
Sensory Information Provided by Sensory Receptors
- Sensation: a stimulus that is consciously perceived.
- Signals must reach the cerebral cortex for awareness.
- A lot of sensory input goes to other brain areas.
- Receptors provide modality, location, intensity, and duration of stimulus to the CNS.
Unencapsulated Tactile Receptors
- Dendritic endings of sensory neurons without protective coverings, commonly found in skin and mucous membranes.
- Respond mostly to temperature, pain and light touch.
- Thermoreceptors detect temperature changes.
- Nociceptors detect painful stimuli.
- Includes Merkel discs and root hair plexuses.
Encapsulated Tactile Receptors
- Neuron endings wrapped by connective tissue or glial cells.
- Found in dermis and mucus membranes.
- Krause bulbs: detect pressure and low-frequency vibration (tonic).
- Ruffini corpuscles: detect deep pressure and skin distortion (tonic).
- Meissner's corpuscles: detect light touch (phasic).
- Lamellated/Pacinian corpuscles: detect deep pressure and vibration (phasic).
Proprioceptors
- Specialized mechanoreceptors that provide sensory information regarding body position and movement.
- Tonic receptors.
- Types: Muscle Spindles, Golgi Tendon Organs, Joint Kinesthetic Receptors.
Referred Pain
- Signals from viscera (internal organs) are perceived as originating from skin, muscle, or other areas.
- Ascending tracts in the spinal cord.
- Somatosensory cortex can't determine the true source of pain.
General Organization of the Somatosensory System
- Part of the sensory system serving the body's surface and limbs.
- Receives inputs from exteroceptors, proprioceptors, and interoceptors.
- Input is relayed towards the head and processed through levels: Receptor, Circuit, Perceptual.
Transduction
- Conversion of stimulus energy into a graded potential.
- Generator potential vs. Receptor potential depends on whether the receptor region is part of the sensory neuron or a separate cell.
Olfaction (Sense of Smell)
- Detection of odorants (volatile molecules).
- Odorants dissolve in nasal mucus and stimulate chemoreceptors in the olfactory epithelium.
- Olfactory receptors detect different odorants, and supporting cells sustain receptors.
- Basal cells continually replace olfactory receptor cells.
Olfactory Structures
- Olfactory receptor neurons have cilia and axons.
- Olfactory hairs house chemoreceptors.
- Olfactory nerves project directly to the primary olfactory cortex.
Olfaction (Pathway)
- Olfactory receptors detect odorants
- Signals go directly to the olfactory bulb
- Then other brain regions, no thalamus relay.
Gustation (Sense of Taste)
- Detection of tastants (molecules).
- Sensory receptor cells (gustatory cells) located in taste buds within papillae on tongue.
Gustatory Papillae
- Filiform papillae: no taste buds; helps manipulate food.
- Fungiform papillae: tip and sides of the tongue.
- Foliate papillae: along posterior edges, reduced in adults.
- Vallate/Circumvallate papillae: largest, back of tongue, most taste buds.
Taste Buds Structures
- Gustatory cells with microvilli (taste hairs).
- Supporting cells sustain gustatory cells; basal cells regenerate them.
Gustation (Pathway)
- Tastants stimulate the gustatory cells.
- Signals are transmitted to the medulla oblonga.
- Then to the thalamus.
- Thalamic neurons project to gustatory cortex in the insula.
Vision
- 70% of body's receptors are in the eyes.
- Half of cerebral cortex is involved in visual processing.
Eye Accessory Structures
- Eyebrows, eyelids, eyelashes, conjunctiva, lacrimal glands.
Conjunctiva
- Membranous lining the eyelids and the front of the eye.
- Contains goblet cells to moisten the eye and blood vessels.
Lacrimal Apparatus
- Produces, drains tear fluid (lacrimal fluid).
Eye Structure
- The eye is a sphere with three tunics: fibrous, vascular, and neural.
- The fibrous tunic is the outer layer, with the sclera being the white of the eye.
- The cornea is the transparent front part of the eye.
- The vascular tunic, or uvea, is the middle layer.
- The choroid: extensive, posterior region; nourishes retina.
- The ciliary body: ciliary muscles and processes, connected to lens.
- The iris: controls pupil diameter.
- The retina: internal layer that contains photoreceptors (rods and cones).
- Pigmented layer: absorbs stray light and nourishes the photoreceptors
- Neural layer: receives light and converts it to nerve signals, contains photoreceptors (rods and cones), bipolar cells, ganglion cells, etc.
Lens
- Changes shape to focus light on retina.
Eye Humors
- Vitreous humor: located in the posterior cavity (behind the lens); helps maintain the eyeball shape.
- Aqueous humor: located in the anterior cavity (in front of the lens); nourishes the lens and cornea.
Internal Eye Structures
- Retina, optic disc, macula lutea, fovea centralis.
Phototransduction
- Process of converting light into electrical signals in the retina.
- Photoreceptors (rods and cones) have photopigments that change shape when light hits them.
Regions of the Retina
- Optic disc: blind spot; no photoreceptors.
- Macula lutea: highest concentration of cones (color vision).
- Fovea centralis: sharpest vision.
- Peripheral retina: primarily contains rods (night vision).
Clinical View: Functional Visual Impairments
- Emmetropia: Normal vision
- Hyperopia (farsightedness): eyeball too short
- Myopia (nearsightedness): eyeball too long
- Astigmatism: unequally curved refractive surfaces
- Presbyopia: age-related loss of lens flexibility.
Physiology of Vision: Refraction and Focusing of Light
- Refraction bends light.
- Lenses focus light onto the retina by changing convexity.
- Shape changes result in the focusing of light on the retina.
Ear
- External ear: auricle (pinna), external acoustic meatus (ear canal), tympanic membrane (eardrum).
- Middle ear: tympanic cavity, auditory ossicles (malleus, incus, stapes), auditory tube.
- Inner ear: bony labyrinth (cochlea, vestibule, semicircular canals), membranous labyrinth (cochlear duct, saccule, utricle, semicircular ducts), endolymph, perilymph.
Cochlea
- Houses the spiral organ of Corti, which contains hair cells (receptors) for hearing.
- Sound vibrations cause fluid movement, stimulating the hair cells.
- Hair cells release neurotransmitters to sensory neurons.
- Signals are sent to the brain via the cochlear branch of the vestibulocochlear nerve (CN VIII).
Hearing (Sound Perception)
- Sound is the perception of vibrating objects.
- Pitch is determined by frequency (Hertz) and loudness by amplitude (decibels).
- High frequencies are near the oval window, and low frequencies near the apex.
Central Nervous System Pathways for Hearing
- Signals from hair cells in the cochlea travel to the cochlear nuclei in the medulla.
- Some signals go directly to the inferior colliculus; others to the superior olivary nuclei.
- Signals are sent to the thalamus and then to the primary auditory cortex in the temporal lobe.
Deafness
- Any hearing loss.
- Types: Conductive (problems in external or middle ear), Sensorineural (malfunctions in the inner ear or cochlear nerve).
Equilibrium and Head Movement
- Awareness of head position (static equilibrium) and motion (dynamic equilibrium).
- Vestibular apparatus helps to keep balance.
- Detection includes static equilibrium and linear acceleration (utricle and saccule).
- Detects angular acceleration (semicircular canals).
Equilibrium Receptors
- Maculae of the utricle and saccule are receptors for static equilibrium and linear acceleration; these receptors are located within the vestibule (composed of hair cells and supporting cells).
- Hair cells have stereocilia and one kinocilium, while the gelatinous membrane that stereocilia project into has otoliths.
- Movement causes otolithic membrane to shift and bend stereocilia, causing a firing rate change on the vestibular part of CN VIII.
Crista Ampullaris
- The ampullae of the semicircular canals houses this receptor that is stimulated by angular acceleration.
- This region is composed of hair cells and supporting cells embedded within the gelatinous cupula
- Rotation of the head causes endolymph to push against the cupula, bending stereocilia, and signal direction.
Equilibrium (Pathways)
- Signals from the maculae and crista ampullaris are relayed to the vestibular nuclei (in the superior medulla) and cerebellum.
- The vestibular nuclei then coordinate eye movements, balance, and muscle tone.
- Information is relayed to the thalamus and then to the cerebral cortex for consciousness.
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