Week 5: Sensory System & Hearing Flashcards
What is a receptor or generator potential?
A graded change in membrane potential in a receptor cell in response to a stimulus.
What differentiates generator potentials from receptor potentials?
Generator potentials occur in nerve endings; receptor potentials occur in specialized sensory cells.
What are the three types of sensory output connections?
Type 1: direct afferent fiber endings; Type 2: chemical synapse to afferent fibers; Type 3: via an intermediate neuron.
What is adaptation in sensory systems?
A decline in receptor response despite continuous stimulus, enabling dynamic stimulus detection.
What do rapidly adapting receptors encode?
Rate of change in a stimulus (dynamic characteristics).
What do slowly adapting receptors encode?
Stimulus intensity and duration (static characteristics).
What is a receptive field (RF)?
The area of the receptor surface that influences the activity of a sensory neuron.
Why do neurons with small RFs offer better discrimination?
Because they detect stimuli in a smaller, more localized area, enabling fine spatial resolution.
What is somatotopy?
Ordered spatial mapping of sensory inputs from body surfaces maintained throughout the CNS.
What fibers carry discriminative sensation?
Aβ fibers for touch; Aα fibers for proprioception.
What pathway carries discriminative information?
Dorsal Column-Medial Lemniscus pathway (DCML).
What sensory information travels via the spinothalamic tract?
Pain, temperature, and crude touch.
Where does crossover occur in DCML vs spinothalamic tracts?
DCML: in the medulla; Spinothalamic: at the spinal cord entry level.
What thalamic nuclei receive DCML vs spinothalamic inputs?
DCML → Ventral Posterior (VP); Spinothalamic → Intralaminar and Ventromedial (VM).
What do areas 3a and 3b of the somatosensory cortex process?
3a: proprioception; 3b: fine touch, vibration, and pressure.
What is cortical magnification in somatosensory mapping?
Functionally important body parts occupy larger areas of the cortex.
What defines a small receptive field neuron?
It responds to stimulation in a confined area, enabling fine discrimination.
What is the function of the outer ear?
To collect and funnel sound waves into the auditory canal.
What is the function of the ossicles in the middle ear?
To amplify vibrations from the tympanic membrane to the oval window.
What is the attenuation reflex?
Reflex contraction of middle ear muscles to protect the cochlea from loud sounds.
Which fluids fill the cochlear chambers?
Perilymph (vestibuli/tympani) and endolymph (media).
What does the basilar membrane do?
Vibrates in response to sound, initiating hair cell stimulation.
How is sound frequency encoded in the cochlea?
High frequencies → base; low frequencies → apex, due to stiffness gradient.
What happens when hair cell stereocilia bend?
Mechanically gated K+ channels open → depolarization → Ca2+ influx → neurotransmitter release.
What nerve transmits auditory signals to the brain?
The cochlear branch of cranial nerve VIII (vestibulocochlear nerve).
What is the organ of Corti?
Structure in the cochlea where hair cells transduce mechanical sound vibrations into receptor potentials.
What is the role of inner vs outer hair cells?
Inner hair cells send most auditory info; outer hair cells amplify sound-induced vibrations.
What causes the depolarization in cochlear hair cells?
Influx of potassium from endolymph when stereocilia bend.
What is the round window’s function in the cochlea?
Allows fluid displacement and wave propagation through cochlear chambers.
What are otolith organs and their function?
Utricle and saccule; detect linear acceleration and head tilt.
What are otoconia (otolith stones)?
Calcium carbonate crystals that provide inertia for detecting head movement.
What fluid surrounds vestibular hair cells?
Endolymph, which triggers stereocilia deflection during movement.
What is the cupula?
A gelatinous cap in semicircular canals that bends with fluid motion to activate hair cells.
What movement do semicircular canals detect?
Rotational or angular acceleration of the head.
What movement do the utricle and saccule detect?
Linear acceleration and static head position (tilt).
What is the function of stereocilia in vestibular hair cells?
Bend to open mechanosensitive channels for ion flow and signal transduction.
What ion influx causes vestibular hair cell depolarization?
Potassium influx through stretch-activated channels in endolymph.
What does the vestibulo-ocular reflex (VOR) do?
Stabilizes gaze during head movement by moving eyes in opposite direction.
What nerve carries vestibular information?
The vestibular branch of cranial nerve VIII.
What are the four classes of nociceptors?
Thermal, mechanical, mechanical-thermal, and polymodal.
What nerve fibers carry nociceptive signals?
Aδ fibers (fast pain) and C fibers (slow, dull pain).
What receptor transduces heat and capsaicin?
TRPV1 ion channel.
What is hyperalgesia?
Increased sensitivity to pain following tissue damage.
What is referred pain?
Pain perceived at a location other than the source of the stimulus.
What is the role of Golgi tendon organs?
Monitor muscle tension to prevent damage from excessive force.
What is the role of muscle spindles?
Detect muscle stretch and prevent overstretching.
Which afferents carry proprioceptive signals?
Aα fibers (Type 1a and 1b).
What does the term ‘receptor surface’ refer to?
The specific location where sensory receptors detect stimuli.
What is the function of mechanoreceptors?
Detect physical stimuli like pressure, vibration, and touch.
What is the cochlea’s shape and function?
Snail-shaped; transforms sound waves into electrical signals.
What structural property of the basilar membrane enables frequency detection?
Varies in width and stiffness along its length (base to apex).
What happens to endolymph during head rotation?
Pushes the cupula and deflects stereocilia to initiate transduction.
What is the significance of potassium in endolymph?
High [K+] allows depolarization when mechanically-gated channels open.
What are spiral ganglia?
Contain the cell bodies of neurons that transmit auditory signals to the brain.
What does the stapes do during hearing?
Pushes on the oval window, initiating fluid movement in the cochlea.
What are the smallest skeletal muscles in the human body?
Tensor tympani and stapedius (involved in the attenuation reflex).
What is vestibular inertia?
Lag of otoconia during movement, allowing detection of acceleration/deceleration.
What reflex allows stable vision while walking or turning?
Vestibulo-ocular reflex (VOR).
