Week 5: Sensory System & Hearing

Question 1

What is a receptor or generator potential?

Answer 1

A graded change in membrane potential in a receptor cell in response to a stimulus.

Question 2

What differentiates generator potentials from receptor potentials?

Answer 2

Generator potentials occur in nerve endings; receptor potentials occur in specialized sensory cells.

Question 3

What are the three types of sensory output connections?

Answer 3

Type 1: direct afferent fiber endings; Type 2: chemical synapse to afferent fibers; Type 3: via an intermediate neuron.

Question 4

What is adaptation in sensory systems?

Answer 4

A decline in receptor response despite continuous stimulus, enabling dynamic stimulus detection.

Question 5

What do rapidly adapting receptors encode?

Answer 5

Rate of change in a stimulus (dynamic characteristics).

Question 6

What do slowly adapting receptors encode?

Answer 6

Stimulus intensity and duration (static characteristics).

Question 7

What is a receptive field (RF)?

Answer 7

The area of the receptor surface that influences the activity of a sensory neuron.

Question 8

Why do neurons with small RFs offer better discrimination?

Answer 8

Because they detect stimuli in a smaller, more localized area, enabling fine spatial resolution.

Question 9

What is somatotopy?

Answer 9

Ordered spatial mapping of sensory inputs from body surfaces maintained throughout the CNS.

Question 10

What fibers carry discriminative sensation?

Answer 10

Aβ fibers for touch; Aα fibers for proprioception.

Question 11

What pathway carries discriminative information?

Answer 11

Dorsal Column-Medial Lemniscus pathway (DCML).

Question 12

What sensory information travels via the spinothalamic tract?

Answer 12

Pain, temperature, and crude touch.

Question 13

Where does crossover occur in DCML vs spinothalamic tracts?

Answer 13

DCML: in the medulla; Spinothalamic: at the spinal cord entry level.

Question 14

What thalamic nuclei receive DCML vs spinothalamic inputs?

Answer 14

DCML → Ventral Posterior (VP); Spinothalamic → Intralaminar and Ventromedial (VM).

Question 15

What do areas 3a and 3b of the somatosensory cortex process?

Answer 15

3a: proprioception; 3b: fine touch, vibration, and pressure.

Question 16

What is cortical magnification in somatosensory mapping?

Answer 16

Functionally important body parts occupy larger areas of the cortex.

Question 17

What defines a small receptive field neuron?

Answer 17

It responds to stimulation in a confined area, enabling fine discrimination.

Question 18

What is the function of the outer ear?

Answer 18

To collect and funnel sound waves into the auditory canal.

Question 19

What is the function of the ossicles in the middle ear?

Answer 19

To amplify vibrations from the tympanic membrane to the oval window.

Question 20

What is the attenuation reflex?

Answer 20

Reflex contraction of middle ear muscles to protect the cochlea from loud sounds.

Question 21

Which fluids fill the cochlear chambers?

Answer 21

Perilymph (vestibuli/tympani) and endolymph (media).

Question 22

What does the basilar membrane do?

Answer 22

Vibrates in response to sound, initiating hair cell stimulation.

Question 23

How is sound frequency encoded in the cochlea?

Answer 23

High frequencies → base; low frequencies → apex, due to stiffness gradient.

Question 24

What happens when hair cell stereocilia bend?

Answer 24

Mechanically gated K+ channels open → depolarization → Ca2+ influx → neurotransmitter release.

Question 25

What nerve transmits auditory signals to the brain?

Answer 25

The cochlear branch of cranial nerve VIII (vestibulocochlear nerve).

Question 26

What is the organ of Corti?

Answer 26

Structure in the cochlea where hair cells transduce mechanical sound vibrations into receptor potentials.

Question 27

What is the role of inner vs outer hair cells?

Answer 27

Inner hair cells send most auditory info; outer hair cells amplify sound-induced vibrations.

Question 28

What causes the depolarization in cochlear hair cells?

Answer 28

Influx of potassium from endolymph when stereocilia bend.

Question 29

What is the round window's function in the cochlea?

Answer 29

Allows fluid displacement and wave propagation through cochlear chambers.

Question 30

What are otolith organs and their function?

Answer 30

Utricle and saccule; detect linear acceleration and head tilt.

Question 31

What are otoconia (otolith stones)?

Answer 31

Calcium carbonate crystals that provide inertia for detecting head movement.

Question 32

What fluid surrounds vestibular hair cells?

Answer 32

Endolymph, which triggers stereocilia deflection during movement.

Question 33

What is the cupula?

Answer 33

A gelatinous cap in semicircular canals that bends with fluid motion to activate hair cells.

Question 34

What movement do semicircular canals detect?

Answer 34

Rotational or angular acceleration of the head.

Question 35

What movement do the utricle and saccule detect?

Answer 35

Linear acceleration and static head position (tilt).

Question 36

What is the function of stereocilia in vestibular hair cells?

Answer 36

Bend to open mechanosensitive channels for ion flow and signal transduction.

Question 37

What ion influx causes vestibular hair cell depolarization?

Answer 37

Potassium influx through stretch-activated channels in endolymph.

Question 38

What does the vestibulo-ocular reflex (VOR) do?

Answer 38

Stabilizes gaze during head movement by moving eyes in opposite direction.

Question 39

What nerve carries vestibular information?

Answer 39

The vestibular branch of cranial nerve VIII.

Question 40

What are the four classes of nociceptors?

Answer 40

Thermal, mechanical, mechanical-thermal, and polymodal.

Question 41

What nerve fibers carry nociceptive signals?

Answer 41

Aδ fibers (fast pain) and C fibers (slow, dull pain).

Question 42

What receptor transduces heat and capsaicin?

Answer 42

TRPV1 ion channel.

Question 43

What is hyperalgesia?

Answer 43

Increased sensitivity to pain following tissue damage.

Question 44

What is referred pain?

Answer 44

Pain perceived at a location other than the source of the stimulus.

Question 45

What is the role of Golgi tendon organs?

Answer 45

Monitor muscle tension to prevent damage from excessive force.

Question 46

What is the role of muscle spindles?

Answer 46

Detect muscle stretch and prevent overstretching.

Question 47

Which afferents carry proprioceptive signals?

Answer 47

Aα fibers (Type 1a and 1b).

Question 48

What does the term 'receptor surface' refer to?

Answer 48

The specific location where sensory receptors detect stimuli.

Question 49

What is the function of mechanoreceptors?

Answer 49

Detect physical stimuli like pressure, vibration, and touch.

Question 50

What is the cochlea's shape and function?

Answer 50

Snail-shaped; transforms sound waves into electrical signals.

Question 51

What structural property of the basilar membrane enables frequency detection?

Answer 51

Varies in width and stiffness along its length (base to apex).

Question 52

What happens to endolymph during head rotation?

Answer 52

Pushes the cupula and deflects stereocilia to initiate transduction.

Question 53

What is the significance of potassium in endolymph?

Answer 53

High [K+] allows depolarization when mechanically-gated channels open.

Question 54

What are spiral ganglia?

Answer 54

Contain the cell bodies of neurons that transmit auditory signals to the brain.

Question 55

What does the stapes do during hearing?

Answer 55

Pushes on the oval window, initiating fluid movement in the cochlea.

Question 56

What are the smallest skeletal muscles in the human body?

Answer 56

Tensor tympani and stapedius (involved in the attenuation reflex).

Question 57

What is vestibular inertia?

Answer 57

Lag of otoconia during movement, allowing detection of acceleration/deceleration.

Question 58

What reflex allows stable vision while walking or turning?

Answer 58

Vestibulo-ocular reflex (VOR).