Exam 3 Flashcards
Parts of the vestibular system (5 sense organs in the inner ear)
3 Semicircular canals
-Anterior, Posterior, Horizontal
2 Otolith organs
-Saccule, Utricle
What is the movement and the semicircular canals responsible for Pitch
=nodding your head “yes”
-Anterior and Posterior canal
What is the movement and the semicircular canals responsible for Yaw
=shaking your head “no”
-Horizontal canal
What is the movement and the semicircular canals responsible for Roll
=touching your ear to your shoulders
-Anterior and Posterior canal
How do semicircular canals transduce head movement into a neural signal?
Firing rates increase or decrease depending on the AMPLITUDE of the rotation and the DIRECTION
-Amplitude coding
-Direction Coding
Amplitude Coding
(Semicircular canals)
= each pair of semicircular canals works in a push-pull arrangement
□ Movement in one direction increase the rate of firing on one side by hyperpolarizes the other
Direction Coding
(Semicircular canals)
= each semicircular canal transduces the component of head acceleration perpendicular to its plane
-the brain combines these signals to sense direction
Amplitude Coding
(Otolith organs)
= when larger accelerations move the otoconia more, leading to greater deflection of the hair cells and larger neural signals
-Size of accelerations = size of neural signals
□ Populations of hair cells on each macula have their stereocilia organized in different directions
□ This causes hair cells in one region of the utricle macula to be sensitive to forward/ backward acceleration and hair cells in another region to be sensitive to side-to-side acceleration (same is true for saccule and vertical acceleration)
Direction Coding
(Otolith organs)
= occurs from the orientation of the otoliths
-Saccule
-Utricle
□ Populations of hair cells on each macula have their stereocilia organized in different directions
□ This causes hair cells in one region of the utricle macula to be sensitive to forward/ backward acceleration and hair cells in another region to be sensitive to side-to-side acceleration (same is true for saccule and vertical acceleration)
What is the function of the Saccule?
= vertical
ex: riding in an elevator, jumping up and down in a potato sac race
What is the function of the Utricle?
= horizontal
ex: accelerating in a car
Bar stool illusion
- When rotating at a constant velocity there is little or no hair cell movement, because endolymph and cupula are moving together
- When you stop the cupula stops moving quickly but the endolymph has a momentum- deflecting the hair cells in the opposite direction
Visual-Vestibular Integration
= self-motion perception requires a combination of visual and vestibular signals (and maybe somatosensory and proprioceptive cues)
□ Vestibular system can put the brakes on visually induced vection (perception of self-movement)
□ The Vestibular system can also trick the visual system with deadly consequences- somatogravic illusion
Somatogravic illusion
= rapid forward acceleration makes you feel like you-re pitching up, compelling you to lower the aircraft’s nose
What is the Vestibulo-ocular reflex?
=allows eye rotations that help compensate for angular rotations of the head
-Eyes counter rotate in response to head motion sensed by vestibular system
-ex: ability to read a road sign while driving
What brain regions are involved in the Vestibulo-ocular reflex?
Pons (Afferent neurons carry information to the abducens nucleus
-> Vestibular nuclei
-> Midbrain (oculomotor nuclei)
Vestibulo-spinal response
= a family of reflexes that adjust for correct body posture when the ground shifts
□ Vestibular system synapses on vestibular nuclei, where the primary afferent neurons synapse on descending interneurons that carry information through the lateral and medial vestibulo-spinal tracts
□ Interneurons which synapse on motor efferent neurons
□ Motor efferent neurons activate muscles that control balance
□ How far these neurons carry information down the spinal
What brain regions are involved in the Vestibulo-spinal reflex?
Vestibular afferent neurons
-> one of the vestibular nuclei (some project to the cerebellum)
-> carry information via vestibulo-spinal tracts downward through the brainstem and spinal cord
-> until synapse on efferent neurons that activate the muscles that control balance
Why isn’t their a vestibular cortex?
Hypothesis/theory that the information is not useful in other things and gets integrated with other things rather than being useful enough to be on its own
What are the 5 Vestibular problems mentioned in class?
-BPPV (Benign Paraoxysmal Positional Vertigo)
-Acoustic Neuroma
-Meniere’s Syndrome
-Motion Sickness
-Mal de Debarquement Syndrome
What is the cause of BPPV (Benign Paraoxysmal Positional Vertigo)?
□ Caused when otoconia become dislodged from the utricle and migrate to the semicircular canals
-These otoconia interfere with normal fluid motion and send false signals to the brain
□ Most common cause of vertigo (false sense of spinning)
What is the cause of Acoustic Neuroma?
□ Nonmalignant tumor that develops on the vestibulo-cochlear nerve
□ When a tumor develops on the vestibular cochlear nerve
□ As it grows it compresses / damages the nerve causing hearing loss, tinnituss, dizziness or loss of balance
What is the cause of Meniere’s Syndrome?
= people who have dizziness so severe that they have to sit down
□ Afflicts 1/500 people and occurs in mid-adulthood
□ Exact cause is unknown. But may be due to an abnormally large amount of endolymph in the inner ear
What is the cause of Motion Sickness?
□ Usually caused by a disagreement between the motion and orientation signals provided by the semicircular canals and vision (argument between the systems)
□ ex: being below on a ship, the rocking stimulates the semicircular canals but there is no change in the relative motion (since you and the boat are both moving)
What is the cause of Mal de Debarquement Syndrome?
□ “Sickness of Disembarkment”- Illusion of movement felt as an after effect of traveling on a ship
□ Usually only lasts 24 hours but can last years
□ Thought to be caused by the brain adapting to this unfamiliar movement but having a hard time readapting; But still unclear
Touch
sensations caused by the mechanical displacement of the skin
Tactile
touch and perception of temperature, pain, itchiness, pleasantness, and internal sensation of limbs in space
Proprioception
sensory input from your internal body (e.g. stomach)
Somatosensation
tactile and proprioception
What are the 5 tactile receptors?
-Meissner Corpuscle (FA I)
-Merkel cell neurite complexes (SA I)
-Pacinian corpuscles (FA II)
-Ruffini endings (SA II)
-Hair follicle receptor
What is the function of Meissner Corpuscle and is it fast or slow adapting?
Fast adapting
○ Specialized encapsulated nerve endings
○ Concentrated in thick hairless skin (particular finger pads)
○ Relay light touch and low frequency vibration sensations
○ Sensitive to “skin slip” like when you start to drop the item you are holding
Fast adapting
What is the function of Merkel cell neurite complexes and is it fast or slow adapting?
Slow adapting
○ Oval-shaped mechanoreceptors
○ Abundant in highly sensitive areas like the fingertips
○ Essential for light touch
○ Sensitive to texture or form perception
○ ex: reading braille
What is the function of Pacinian corpuscles and is it fast or slow adapting?
Fast adapting
○ Larger and fewer in number
○ Very responsive to vibration and pressure
○ Sensitive to fine texture perception and vibration
○ ex: tell the difference between rough and smooth sandpaper, when an object you are holding and it hits something
What is the function of Ruffini endings and is it fast or slow adapting?
Slow adapting
○ Spindle shaped receptors
○ Found on hairless skin on the fingertips
○ Important for finger position when picking up objects
ex: playing the piano
Hair follicle receptor
Hair plexus forms a network around a hair follicle
-found on parts of your body with hair
-when the hair moves, it sends nerve impulses to your brain
-important for touch on hairy skin
What is the function of kinesthetic receptors?
- Sense limb placement and movement
-Additional mechanoreceptors that are located within muscles, tendons, and joints
The somatosensory pathways- from axons of tactile receptors to somatosensory cortex
-Somatosensory Nerve Trunks
-Dorsal Horn of the Spinal Cord
-Dorsal Column-medial lemniscus pathway & Spinothalamic pathway
-Somatosensory Cortex
Somatopically
= point for point correspondence with an area of the body
○ Stimulation of the skin are spatially represented in S1
○ Homunculus= a maplike representation of the regions of the body in the brain
What is phantom limb pain and how is it thought to occur?
= severe pain in the phantom limb can occur
* fMRI scans during phantom limb pain show activity in S1 corresponding to the region that was associated with the limb
* After amputation, the brain loses input from the missing limb and adjusts to this detachment in unpredictable ways… sometimes sending pain signals
* The neurons that were devoted to that area are still in the brain, now firing action potentials and it perceives it as pain in that area
○ Neurons not responding to any input, trying to find input
What stimulus they respond to Pleasant touch fibers?
=A new class of mechanoreceptors that respond to stroking that people find enjoyable
* Classified as “pleasant” or “emotional” touch
What are the specifics about the type of fiber in Pleasant touch fibers?
- A class of unmyelinated (i.e. slow) peripheral C fibers known as CT afferents (C tactile)
What is the function of Thermoreceptors
= temperature sensing
○ Located in both the epidermal and dermis; free nerve endings
○ Inform the brain about skin temperature
What are the types of fibers in thermoreceptors ?
○ Warmth fibers- respond when skin gets hotter
○ Cold fibers- respond when skin gets cold
§ Respond when touch something below
§ 30x more cold than warm fibers; easier to sense cold
○ Neither fibers respond while the skin temperature remains between 86-96F
What is the function of Nociceptors?
○ Receptors that also have bare nerve endings and respond to various types of tissue damage
Stimuli include injury, extreme hot or cold, as well as chemical stimuli
What is the ascending pain signaling pathway and how is pain perceived?
> Spinothalamic pathway
○ Nocioreceptor (free nerve ending
§ Pain occurs (ex: finger)
§ Amount of information passed = amount of pain there is
§ Primary afferent nociceptive sensory neurons send noxious stimulus information to spinal cord (dorsal horn); sends signal
○ Dorsal Horn of the Spinal Cord
○ Hindbrain
○ Thalamus
§ Relays information to cortex
○ Somatosensory Cortex
§ Where perception happens; subjective experience of pain occurs
What is the descending pain signaling pathway and how is pain modulated?
○ Deescending pathway modifies pain transmission of the ascending pathway
○ Involves 3 limbic regions
§ Amygdala-
□ fear/emotional
□ Carry information motivational state/ environment
§ => PAG
□ Periaquectual gray (PAG)
□ Modulates ascending pain information indirectly in the->
§ => Hindbrain
□ Descending modulates ascending
□ Hindbrain stops the passage of information (making the amount received after the Hindbrain to the Thalamus and Somatosensory Cortex less)
Gate Control Theory
○ Pain transmission in the spinal cord
○ blocks signals by inhibiting this pathway
§ Pain signal can be blocked/reduced by inhibiting the ascending pathway
§ This reduces the pain signal to the cortex and decreases the subjective feeling of pain
How do Opioids modulate our pathway?
They high jack the system
○ Bind in the PAG and shutting down the pain at the Hindbrain
○ Chemically related and interact with opioid receptors on nerve cells in the body and brain
