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87 Cards in this Set

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Describe the concept of a threshold for an action potential

A cell must achieve a threshold in cellular depolarization in order to evoke a neural AP.

Describe the concepts of threshold/AP regarding sensory cells

Most sensory cells do not fire AP, the simply increase or decrease the level of NT on the sensory nerve




Exception: Olfaction and some cutaneous senses

While most sensory cells do not fire AP, there are some exceptions. What are they?

Olfaction and some cutaneous senses

Describe Tonic Receptors

Tonic receptors are "slow adapting", or do not adapt at all. They detect sustained stimuli

Describe Phasic Receptors

Phasic receptors are fast adapting. They dectect on/off stimuli

Explain the law of specific nerve energies

During adequate stimulus, the stimulation of a sensory nerve fiber produces only one sensation (pain, cold, light...etc).




However, in circumstances where there is abnormal stimulation, such as being punched in the eye, a person may experience paradoxical sensations (light)





How are the receptors of sensory systems classified

They are classified based upon their normal or adequate stimulus

Mechanoreceptors

touch, proprioception, hearing, balance, and cardiovascular regulation

Chemoreceptors

taste and smell

pain receptors

pain

thermoreceptors

temperature

Photoreceptors

Light

Explain receptive field

This is the specific area in which a sensory neuron will sense stimuli




For example,


Cutaneous receptors sense stimuli only in the immediate area (one small area of skin)

Visual ganglion cells respond to stimuli in one region of space. What is the term used for this specific region of space?

Receptive field

If the two points of a compass lie within the receptive field of one sensory neuron, how many points would a person feel touching them?

1

If the individual points of a compass lie within the receptive fields of two different sensory neurons, how many points would a person feel touching them?

2

Which part of the body has the greatest and least number of neuron receptors per unit of skin.

The first finger has the greatest amount of neuron receptors/unit of skin, with neuron receptors that are only 2mm apart from each other.




The upper arm has the least amount of neuron receptors/unit of skin, with neuron receptors that lie 47 mm apart.




Sensor acuity!!!

Describe lateral inhibition

Thestimulation of a sensor not only excites the neuron associated with itsreceptive field, but inhibits neurons representing surrounding receptivefields.




This phenomenon leads to sharpened discrimination (sharpened localization of the response).

What are the 5 different types of Cutaneous Sensations?

Touch, Heat, Cold, Pressure, and Pain

What are the two anatomical classes of cutaneous sensors

Encapsulated and Free nerve Endings

What are Encapsulated cutaneous sensors responsible for?

Touch and Pressure




(In general, fast adapting)

Give 2 examples of cutaneous sensors

Pacinian (Vibration) and Meissner's (Touch) Corpuscles

What is the function of cutaneous receptors that are free nerve endings?

To detect touch, pressure, heat, cold, and pain.




(In general are slow adapting)

Give two examples of cutaneous receptors that are free nerve endings.

Dendrites around hair follicles (hair movement) and free nerve endings in the skin (pain and temperature)

What important players can be found in the superficial layers? Are they fast or slow adapting?

–Meissner’s Corpuscle (fast adapting akaphasic)–Merkel disk (slow adapting)

What important players can be found in the deep layers? Are they fast or slow adapting?

–Pacinian Corpuscle (fast adapting)


–Rufini endings (slow adapting)

What are these 4 structures

What are these 4 structures

–Meissner’s Corpuscle (fast adapting aka phasic) –Merkel disk (slow adapting)


–Pacinian Corpuscle (fast adapting)


–Rufini endings (slow adapting)

Molecular sensors of cutaneous sensory nerve

Not much is known about these. Although suspected to be ion channels. TRP is latest one discovered in regards to sensing temperature.




"Last Frontier"

Explain the neural pathway for proprioception and touch.

dorsal root ganglion cell runs ipsilateral,then innervates and crosses at medulla oblongata




(Ascend the spinal cord to the base of the brainstem before crossing)

Explain the neural pathway for temperature and pain

dorsalroot ganglion, innervates at dorsal horn, crosses then ascends lateral spinothalamictract to thalamus.




(cross as soon as entering the spinal cord e.g. left foot goes to right spinal cord)

Phantom Limb

afterremoval of limb; due to activated nerve endings? CNS?

What type of wave form is a sound wave

Sinusoidal Wave

What structures belong to the external outer ear?

Pinna, Concha, Tympanic Membrane

What structure is the boundary between the outer and middle ear?

Tympanic Membrane

A (Concha)


B (Pinna)


C (Tympanic Membrane)

What is the function of the Pinna and Concha?

1. The pinna and head casts a shadow to give an intensity difference for spatial resolution, however this only works at high frequency tones where the wavelength is less than the width of the head.




2.Pinna and Concha act as a resonator, however this only works between 2,000 and 5,000 Hz (perfect for language) and can increase the intensity by ~10dB.

What are the structures of the middle ear?

Malleus, Incus, and Stapes

A. Malleus


B. Incus


C. Stapes

What is the function of the bones of the middle ear?

1. Amplify sound via transfer from a low to a high impedance medium (Tympanic membrane to oval window) and via lever action of the bones.




2. To prevent damage from loud noises by regulation of the tensor tympani and stapidius, which contract when there are loud noises to decrease the response.

What part of the middle ear connects to the oval window?

Stapes

What serves as an opening to the Cochlea?

Oval window (superior)


Round window (inferior)




These two holes open to two different parts of the Cochlea

What are the structures of the internal ear?

Cochlea

When the cochlea is cut open what do you see?

That it is composed of 3 compartments: Scala vestibule, Scala tympani, and Scala media

A. Scala Tympani


B. Scala Vestibuli


C. Scala Media

What is the name of the internal ear structure that sits in the Scala Media?

Organ of Corti


This is the Organ of Corti




A (1 row of inner hair cells), B (Tectorial Membrane), C (3 rows of outer hair cells), D (Basilar Membrane)

What is the sensory cell of the auditory system?

The Hair Cell

What is the name of the structure that the arrow is pointing to? What is unique about it?

What is the name of the structure that the arrow is pointing to? What is unique about it?

The kinocilium. It disappears in humans shortly after birth.

What is the function of the tip links?

They attach the stereocilia together

What stimulates the hair cell?



The stereocilia stimulate the hair cell.





Explain the overall process of the stimulation of the hair cell.

The Basilar membrane vibrates (has upwards and downwards phases) causing the hair cells to brush up against the tectorial membrane aka shearing forces. These shearing forces stimulate the stereocilia, which ultimately stimulate the hair cell.

What are the molecular sensors in the Auditory system?

K+ channels




(the hair cells are depolarized by potassium, NOT SODIUM!)

Do hair cells fire AP?

No, hair cells oscillate their membrane potential in response to stimuli




The K+ channels have a basal activity that can increase or decrease depending upon the direction of the shearing force.

What is important about the shearing force?

Depending upon it's direction, the hair cell is either stimulated to decrease basal activity, or increase basal activity.

What is the importance of the K+ channels being leaky??

There will be some activity when the hair cells are at rest. This allows the hair cells to hyperpolarize or depolarize depending upon the stimuli.




(It also gives the sinusoidal curve at LOW FREQUENCIES.)

Explain where K+ levels are highest and lowest within the Organ of Corti

K+ is highest where the stereocilia are (endolymph), but low where the cell body is (perilymph).

What is strange about hair cell activation?

K+ both depolarizes and repolarizes the cell

Explain the order of cellular stimulation of the Hair Cell

A shearing force in a specific direction stimulates the stereocilia, opening K+ channels. Since K+ is higher in the endolymph, K+ rushes into the hair cell, depolarizing the cell. Depolarization causes Ca2+ channels to open and Ca 2+ rushes in. The influx of Ca2+ causes vesicular release and this NT release into the synaptic cleft. Ca2+ influx also opens Ca2+ gated K+ channels. K+ rushes out of the cell body down it's concentration gradient (K+ is low in the perilymph).

Briefly explain the neural pathway of the auditory system.

Cochlear nerve innervates cochlear nuclei. Immediately after, many of the fibers cross.




Key point: Sound from the two ears is integrated and processed very early.

A patient has a lesion in the nervous system that is located post-cochlear nucleus. What do you expect the patient to have as a result of this lesion?

Overall depression in hearing or sound processing.

What is sound?

The compression and rarefaction of air pressure.

Explain compression in regards to the mechanics of the ear

A compression wave hits the tympanic membrane. This causes the stapes to push against the oval window, which then causes compression in the scala vestibuli. The compression wave travels to the end of the cochlea via the hellicotrema (a hole at the end connecting the scala vestibule with the scala tympani) and ultimately pushes against the round window.

Explain rarefaction in regards to the mechanics of the ear

Once compression wave hits round window, rarefaction sets a flow in the opposite direction (from round window to oval window). The rarefaction wave pushes on the opposite side of the tympanic membrane, causing the stapes to "pull".

Ultimately, what do the compression and rarefaction waves cause?

The flow of the sound wave creates resonance (Vibration of the basilar membrane).

Define the term tonotopic mapping (or "place" or "label-line" coding.

The Basilar Membrane thickens and widens as it gets further away from the oval window, thus different pitches vibrate this membrane in different regions. The tonotopic map is a map of the pitches and where they vibrate the membrane. Hi frequency is encoded at the base, low frequency at the apex.




Works best at high frequencies

What is the frequency range where human hearing is the most sensitive.

1,000-5,000 Hz




(Human speech is in this range)

What is the basis of a cochlear implant ?

Utilizes the normal tonotopic map to encode the sound into a pattern the system can utilize






Does not simply amplify the sound, but bypasses hair cells to directlystimulate the nerve cells

Which of the hair cells are the primary sensors?

Inner hair cells, 95% of the afferent fibers are to the inner hair cells.




Outer hair cells have many efferent connections and apparently adjust the mechanical properties of the local regions.

Explain Otoacoustical Emissions (OAE)

Asensitive microphone at the eardrum can monitor a response after brieflypresenting a tone (or can sometimes occur spontaneously). This phenomenon is known as OAE.

What is phase locking/volley theory?

Frequency information can be conveyed via the rate of action potentials. Neurons can fire about 1000 impulses/sec. The refractory periods between action potentials allows a 1:1 ration between the sound wave and neuronal firing. This could be a way of encoding at LOW FREQUENCIES. (Volley Theory)

Explain phase shift

The ear that is closer to the sound will reach the peak of the wave slightly sooner than the ear further away. Only works at low frequencies.

What Cues Used in Spatial and FrequencyEncoding work best at low frequencies?

Spatial localization: Phase shift


Frequency Encoding: Volley Theory

What Cues Used in Spatial and FrequencyEncoding work best at high frequencies?

Spatial localization: Intensity (shadowing)


Frequency Encoding: Tonotopic map

The vestibular apparatus lies in what part of the ear?

Inner ear

What are the structures of the Vestibular Apparatus?

Otolith organs (utricle and saccule) and the Semicircular canals (anterior, posterior, and lateral)

What kind of motion do the otolith organs detect?

Linear acceleration

What kind of motion do the semicircular canals detect?

Angular forces






Otolith


Top: Utricle


Bottom: Saccule

What covers the otolithic membrane?

Calcium carbonate (otoliths)

Otolithic membrane and otoliths

What are the cista ampullaris?

Elevated structures in the semicircular canals that are the location of the hair cells.

What is the cupula?

Where the hair cells of the semicircular canal are embedded

A (cupula), B (cista ampullaris), C (hair cells)

Describe the hair cells of the semicircular canals

Epithelial cells with sterocilia and one kinocillium that are connected by tip links.

Describe the neural pathway involved in the Vestibular Apparatus

Vestibular nuclei in the brain stem send information to the cerebellum. The vestibular apparatus also sends information to the cerebellum. The cerebellum then adjusts movements and sends the information back to the brainstem. The brainstem then integrates this information with information from the eyes and propropceptive sensors, then innervates the occularmotor center (control of eyes) and spinal cord (control of movement).

Nystagmus

Activation of the system independent of stimuli causes eye movements (to and fro).






(Semicircular canals are being stimulated while head is not in motion)

Vertigo

Loss of equilibrium