Mechanoreception Flashcards
Tactile receptors
Proprioceptors
Baroreceptors
Tactile receptors:
- Exteroceptors
- Detect touch, pressure, vibration on body surface
- Invertebrates and vertebrates
Proprioceptors:
- Monitor position of body
- Invertebrates and vertebrates
Baroreceptors:
- Interoceptors
- Detect pressure changes and quickly adapt (Uses free nerve endings that branch w/ elastic tissues)
Phasic vs Tonic receptors
Phasic: Fire once when activated and deactivated
Tonic: Firing as long as stimulus persists
Trichoid sensilla
Campaniform sensilla
(External mechanoreceptors in insects)
Trichoid sensilla:
- Tactile hairs (setae)
- Dendrite of neuron attach near base of hair
- Clusters found behind head, on legs, near joints
Campaniform sensilla:
- Dome-shaped organs acting as proprioceptors
- Throughout body, mainly legs base of wings, sutures where two plates of exoskeleton meet
Scolipudium
Chordotonal organs
Scolopale and cap cells
Tympanal organs
(internal mechanoreceptors in insects)
Scolipudium:
- Internal surface if cuticle, at every joint
- Proprioception
Chordotonal organs:
- Grouped scolipidium
- Main unit is scolopidium
Scolopale and cap cells:
- Accessory cells of scolopidium
- Scolopale envelop sensory neurons
- Cap anchors sensory neurons
Tympanal organs:
- Scolipidia can be modified into tympanal organ for sound detection
Vertebrate tactile receptors:
- Root hair plexus
- Merkel disks
- Ruffini corpuscle
- Pacinian corpuscle
- Free nerve endings
Root hair plexus:
- Free nerve ending wrapped around hair follicles to monitor hair distortions from mechanical stimuli
- Adapt rapidly; ideal for detecting initial contact and subsequent movements
Merkel disks:
- Where epidermis meets dermis
- Find touch and pressure receptors (small receptive fields)
- Sensitive tonic receptors
Ruffini corpuscle:
- Deep pressure, pulsing, high-frequency vibrating stimuli
- Fast adapting (surrounded by modified schwann cells containing liquid that detect stimuli)
Pacinian corpuscle:
- Pressure, stretching of skin, joint movement
- Found in reticular (deep) dermis
- Tonic receptors w/ little adaptation
- Work w/ proprioceptors
Free nerve endings:
- Mediate nociception (pain)
- A fibres myelinated, C fibres unmyelinated
- Skin, muscle, joint capsule, bone and major organs
- Identify w/ cutaneous Schwann cells
Vertebrate proprioceptors:
Muscle spindles
Golgi tendon organs
Joint capsule receptors
Muscle spindles:
- Surface of muscle
- Monitor muscle length
Golgi tendon organs:
- Junction between skeletal muscle and tendon (stimulated by tension)
- Monitor external tension during muscle contraction
Joint capsule receptors:
- Free nerve, in capsules that enclose joints
- Detect pressure, tension, movement at joint
Tympanal organs
Statocysts (Macula and cristae)
(Hearing and equilibrium organs in invertebrates)
Tympanal organs:
- Thin region of cuticle over an air soace
- Sound waves cause it to vibrate
- Found all over bodies
Statocysts:
- Hollow, fluid filled cavities
- Lined w/ mechanosensory ciliated sensory neurons
- Contain statoliths that roll around
In octopus:
- 1 macula (linear acceleration/forward motion)
- 3 cristae (angular acceleration/turning)
Invertebrate hearing:
Modified trichoid sensilla
Subgenual organ
Johnston’s organ
Tympanal organ
Modified trichoid sensilla:
- Sound waves bend them to send signal to bipolar neuron
Subgenual organ:
- Detects vibrations carried thru ground
- Modified chordotonal organ in legs
Johnston’s organ:
- Detects sound waves in air by bending fine hairs in antenna
Tympanal organ:
- Thin region of cuticle (tympanum)
- Sound waves cause it to vibrate and stimulate chordotonal organ inside
Hair cells
- Kinocilium
- Stereocilia
- Tip links
(Vertebrate hearing and balance)
Kinocilium: One long
Stereocilia: Several short
- Connected w/ tip links
More K+ on outside of cell
@ Rest: Mechanically gated cation channels always open, partially depolarized
Stereocilia towards kinocilium: More K+ channels open, depolarized
Stereocilia bent away kinocilium: Hyperpolarized, low AP firing
Neuromasts
Lateral line ststem
(Fish hearing and orientation)
Neuromasts:
- Cup-shaped sensory organs
- Hair cell w/ cupula (viscous gel that causes hair to move)
- Detect water movement
Lateral line system:
- Array of neuromasts within pits or tubes along side of body
Vestibular apparatus
(Vertebrate hearing)
Vestibular apparatus:
- 3 semicircular cabals w/ enlarged region at one end (ampulla) and 2 sacklike swellings (utricle and saccule)
- All contain hair cells responding to movement
- Lagena: Extension of saccule
Otolith
(Utricle and saccule)
Respond to linear acceleration forces
- Stereocilia and kinocilia have otolith membranes
Macula in utricle -> Horizontal movements and tilting head side to side
Macula in saccule -> Vertical movement
Crista
(ampulla)
Senses rotational acceleration
Each crista has supporting cells and hair cells extending into ampullary cupula (gel-like mass)
Cochlea
- Perilymph, endolymph, organ of corti
- Inner and outer hair cells
(Verebrate hearing)
Inner hair cells:
- Detect sound
Outer hair cells:
- Amplify sounds
- Change in shape of hair bundle causes membrane depolarization and dislodges Cl-
- Causes prestin to change shape and shorten length of outer hair cell
Steps of sound transduction
(Vertebrate)
1) Outer and middle ear detect sound
2) Oval window vibrates from pressure
3) Waves in perilymph of vestibular duct
4) Basilar membrane vibrates
5) Stereocilia on inner hair cells bend
6) Depolarization of hair cell
- Glutamate release causing neuron excitation
Basilar membrane
- Stiff and flexible ends -> What frequency do they vibrate?
Stiff - High freq (closest to oval window of cochlea)
Flexible - Low freq (middle of cochlea)
Tonotopic map
Sound frequency is mapped to specific brain region
1) Cochlea signals to brainstem
2) Midbrain
3) Thalamus
4) Auditory complex
How does the brain use info on time lags and differences in time intensity for sound location?
Whichever ear detects sound first, sound is from that side
If sound is louder in certain ear, sound located on that side
3 regions of vertebrate ear:
Outer
Middle
Inner
Outer:
- Receives and channels sound
Middle:
- Amplifies sound
Inner:
- Sorts sounds by tone and converts them into impulses (cochlea)
- Senses rotational movements (semicircular canals, ampulla)
- Senses position and linear acceleration (utricle and saccule)
