Ch. 12 Flashcards
vestibular organs
the set of five sense organs located in each inner ear that sense head motion and head orientation with respect to gravity
- sense of equilibrium
- located in the inner ear right next to the cochlea
- three semicircular canals that sense rotational motion and two otolith organs that sense gravity and linear acceleration
spatial orientation
a sense consisting of three interacting modalities: perception of linear motion, angular motion, and tilt
- sensory foundation for it is the vestibular system
vestibular system
the vestibular organs as well as the vestibular neurons in cranial nerve VIII and the central neurons that contribute to the functional roles that the vestibular system participates in
- contributes to clear vision when we move
- helps us maintain balance when we stand
vertigo
a sensation of rotation or spinning
vestibulo-ocular reflex (VOR)
a short-latency reflex that helps stabilize vision by counterrotating the eyes when the vestibular system senses head movement
balance
the neural processes of postural control by which weight is evenly distributed, enabling us to remain upright and stable
- sensory foundation for it is kinesthesia
kinesthesia
perception of the position and movement of our limbs in space
active sensing
sensing that includes self-generated probing of the environment
efferent commands
information flowing outward from the central nervous system to the periphery
- ex. motor commands that regulate muscle contraction
afferent signals
information flowing inward to the central nervous system from sensors in the periphery
graviception
the physiological structures and processes that sense the relative orientation of gravity with respect to the organism
- tilt sensation
Relative to the vestibular organs of all other vertebrates, the human vertical canals are relatively large
Larger canals contribute to higher sensitivity, which is believed to yield enhanced head and eye stabilization when we run
angular motion
rotational motion like the rotation of a spinning top or swinging saloon doors that rotate back and forth
linear motion
translational motion like the predominant movement of a train car or bobblehead doll
tilt
to attain a sloped position like that of the Leaning Tower of Pisa
transduce
to convert from one form of energy to another (e.g., from light to neural electrical energy, or from mechanical energy to neural electrical energy)
for vestibular sensation, perceiving rotation, translation, and tilt requires that three different stimuli be transduced:
angular acceleration, linear acceleration, and gravity
angular acceleration, linear acceleration, and gravity are sensed by two types of vestibular sense organs
semicircular canals and otolith organs
semicircular canal
any of three toroidal tubes in the vestibular system that sense angular motion
angular acceleration
the rate of change of angular velocity
otolith organ
either of two mechanical structure (utricle and saccule) in the vestibular system that sense both linear acceleration and gravity
- predominant contribution to sense of head tile and sense of linear motion
linear acceleration
the rate of change of linear velocity
sense of angular motion
the perceptual modality that senses rotation
sense of linear motion
the perception modality that senses translation
sense of tilt
the perceptual modality that sense head inclination with respect to gravity
sensory conflict
sensory discrepancies that arise when sensory systems provide conflicting information
- ex. vision may indicate that you are stationary while the vestibular system tells you that you are moving
each of the three spatial orientation modalities includes two qualities
amplitude and direction
amplitude
in reference to vestibular sensation, the size (increase or decrease) of a head movement (with angular velocity, linear acceleration, tilt, etc.)
direction
the line one moves along (or faces), with reference to the point or region one is moving toward (or facing)
three directions for sense of linear motion
- Stepping forward or backward along the x-axis
- Sliding from right to left along the y-axis
- Translating up or down along the z-axis
three directions define sense of angular motion (the head can rotate in three independent ways)
- Roll angular velocity
Ex. cartwheels or lying on your back with your nose at the center of a merry-go-round - Pitch angular velocity
Ex. when you nod “yes” - Yaw angular velocity
Ex. when you shake your head “no”
velocity
the speed and direction in which something moves
otolith organs and semicircular canals respond to…
changes in velocity, called acceleration
acceleration
a change in velocity
hair cell
any cell that has stereocilia for transducing mechanical movement in the inner ear into neural activity sent to the brain; some hair cells also receive inputs from the brain
- act as mechanoreceptors in each of the five vestibular organs
mechanoreceptor
a sensory receptor that responds to mechanical stimulation (pressure, vibration, or movement)
hair cells as mechanical transducers
- Head motion causes hair cell stereocilia to deflect
- Stereocilia deflection causes a change in the hair cell voltage, which alters neurotransmitter release, which, in turn, evokes action potentials in those vestibular-nerve fibers that have one or more synapses on the hair cell
- These afferent neurons carry the action potentials to the brain
- In the absence of stimulation, vestibular hair cells have a negative voltage and release neurotransmitters at a constant rate
receptor potential
a change in voltage across the membrane of a sensory receptor cell (in the vestibular system, a hair cell) in response to stimulation
three semicircular canals
horizontal, anterior, and posterior
ampulla
an expansion of each semicircular-canal duct that includes that canal’s cupula, crista, and hair cells, where transduction occurs
crista
any of the specialized detectors of angular motion located in each semicircular canal in a swelling called the ampulla
the three semicircular canals are maximally sensitive to…
rotations in different planes, thus yielding direction coding for head rotation
how amplitudes is coded in the semicircular canals
- In the absence of any rotation, many afferent neurons form the semicircular canals respond with a nearly constant rate of action potentials
- The relatively high spontaneous firing rate of vestibular afferent neurons allows these neurons to decrease the firing rate for rotations in one direction and increase the firing rate for rotations in the opposite direction
how direction is coded in the semicircular canals
The three semicircular canals are maximally sensitive to rotations in different planes; the result is direction coding of head rotations
oscillatory
referring to back-and-forth movement that has a constant rhythm
sinusoidal
referring to any oscillation, such as a sound wave or rotational motion, whose waveform is that of a sine curve; the period of a sinusoidal oscillation is the time that it takes for one full back-and-forth cycle of the motion to occur; the frequency of a sinusoidal oscillation is defined as the numeral 1 divided by the period
Fourier Analysis
a mathematical procedure by which any signal— in this case, motion trajectories as a function of time— can be separated into component sine waves at different frequencies
two structures in the otolith organs
utricle and saccule
utricle
one of the two otolith organs; a saclike structure that contains the utricular macula
- consists of a small, oval-shaped, fluid-filled sac that is about 3 mm long in the longest direction and includes an area called the macula
saccule
one of the two otolith organs; a saclike structure that contains the saccular macula
- consists of a small, oval-shaped, fluid-filled sac that is about 3 mm long in the longest direction and includes an area called the macula
macula
any of the specialized detectors of linear acceleration and gravity found in each otolith organ
otoconia
tiny calcium carbonate stones in the ear that provide inertial mass for the otolith organs, enabling them to sense gravity and linear acceleration
- denser than the surrounding fluid so that they are pulled by both gravitational force and inertial force due to linear acceleration
- resulting displacement of the otoconia drags the gelatinous layer, thereby moving the hair cell stereocilia, leading to changes in the hair cell receptor potential, which in turn causes changes in the rate of action potentials in the afferent neurons
how amplitude is coded in the otolith organs
- movement of stereocilia
- larger accelerations move the otoconia more –> leads to greater deflection of the hair cell bundles, which causes larger changes in the hair cell receptor potentials
how direction is coded in the otolith organs
- in part from the otolith organs’ anatomical orientation
- utricle will be sensitive primarily to any Earth-horizontal linear acceleration
- saccule will be sensitive to vertical linear acceleration
- variations in the orientation of hair cells
three different techniques frequently used to investigate spatial orientation perception
thresholds, magnitude estimation, and matching
magnitude estimation study
participants might be asked to give verbal reports of how much they tilted, rotated, or translated, using physical units like the number of degrees they rotated
matching task
participants might be asked to align a visual line with perceived Earth-vertical
velocity storage
prolongation of a rotational response by the brain beyond the duration of the rotational signal provided to the brain by the semicircular canals, typically yielding responses that are nearer the actual rotational motion than the signal provided by the canals
dizziness and imbalance experienced when we stop rotating are due to…
an illusion of self-rotation caused by the semicircular-canal response
dizziness
a commonly used lay term that nonspecifically indicates any form of perceived spatial disorientation, with or without instability
imbalance
ack of balance; unsteadiness; nearly falling over
multisensory integration
the process of combining different sensory signals; typically, combining several signals yields more accurate and/or more precise information that can be obtained from individual sensory signals
vection
an illusory sense of self-motion caused by moving visual cues when one is not, in fact, actually moving
crucial contributions of vision to sense of self-rotation
Signals related to vision converge with the semicircular-canal signals in the vestibular nuclei, which is the first place in the brain that vestibular information reaches
sensory reafference
change in afference caused by self-generated activity; for the vestibular system, vestibular afference evoked by an active self-generated head motion would yield sensory reafference
- in order to avoid responding to sensory inputs that arise from self-generated actions, the sensory system needs to know what the motor system has done
efference copy
a neural copy of an efferent command sent from the central nervous system to the periphery
- One example pertinent to spatial orientation is a copy of the efferent command sent to muscles; this muscle efferent copy transmits information about expected motion resulting from the anticipated muscle activation
predicted sensory activity
brain’s estimate of sensory reafference is subtracted from the sensory afferent signal to eliminate reafferent information
balance system
the sensory systems, neural processes, and muscles that contribute to postural control
autonomic nervous system
the part of the nervous system that is responsible for regulating many involuntary actions and that innervates glands, heart, digestive system, etc.
motion sickness
Typically results when there is a disagreement between the motion and orientation signals provided by the semicircular canals, otolith organs, and vision
one hypothesis for motion sickness
it is a defense against some classes of poisons
spatial disorientation
any impairment of spatial orientation; more specifically, any impairment of our sense of linear motion, angular motion, or tilt
vestibulo-spinal reflexes
provides us with balance; without it, we would be unable to stand in the dark
vestibular thalamocortical pathways
neurons from the vestibular nuclei carry vestibular information to the thalamus, where that information is processed and relayed to the cortex; cortex also projects back to the vestibular nuclei (feedback)
Mal De Debarquement syndrome
- after travelers disembark a ship after an extended trip, symptoms that usually only last a few hours continue to last
- symptoms of spatial disorientation, imbalance, and rocking last a month or more after they disembark
- in extreme cases, the symptoms can last for years and can be very debilitating
Meniere’s syndrome
- Suddenly experiencing dizziness, imbalance, and spatial disorientation so severe that one has to lie down or they will fall down
- Severe motion sickness ensues and leads to repeated vomiting
- these symptoms can occur suddenly and more or less unexpectedly at any time
- Other symptoms include tinnitus (an illusory ringing sound), hearing loss, and a feeling of pain or fullness in the ear
- Treatments include medications to lower pressure in the inner ear, implanted devices that provide transtympanic micropressure pulses, and sometimes procedures that destroy the vestibular apparatus
