Topic 4: Sensory Systems Flashcards
Which 3 sensory systems support movement?
- Vision
- Vestibular
- Somatosensory
Visual Pathway
Retina, thalamus, primary visual cortex
How do neurons in the visual system create perception of the world?
- based on electromagnetic radiation
- eyes detect visible light (400-700nm)
Primary visual cortex
First area of the cortex to receive visual information
- Brodmann’s area 17 in the occipital lobe
- AKA V1
- begins mapping and processing visual info
- Splits info into two main pathways
Dorsal stream of visual processing
Information passed toward parietal lobe which specializes in processing of visual motions
- NAVIGATING: perceiving the direction and speed of objects helps us navigate safely
- DIRECTING EYE MOVEMENTS: sense motion and quickly react to it
- MOTION PERCEPTION: interpretation of moving objects
Ventral stream of visual processing
Information passed towards the temporal lobe - specilized processing of vision other than motion
- Object perception and facial recognition
The vestibular system
- Balance, equilibrium and posture
- Based on the motion of hair cells
- Made up of otolith organs and semicircular canals
Otolith Organs and components
Measures acceleration and tilt
- MACULA: epithelium filled pouch with hair cells
- KINOCILIUM: Tallest, most important cilia
- OTOCONIA (ear stones): Calcium carbonate crystals
How do the otolith organs work?
- Baseline nerve impulse generated in vestibular fiber
- DEPOLARITATION: when hairs bend toward the kinocilium, the hair cell depolarizes, exciting the nerve fiber, which generates more frequent AP
- HYPERPOLARIZATION: when hair beds away from the kinocilium, the hair cell hyperpolarizes, inhibiting the nerve fiber, and decreasing AP frequency
Macular orientation
Array of orientations within organ
- Saccular macula - vertically oriented
- Utricular macula - horizontally oriented
Allows measure of all possible linear movements
Semicircular Canals
Measures head rotation (angular acceleration)
- three canals on each side helping sense all possible head rotation angles
- CRISTA AMPULLARIS: cupula (bubble) full of cilia found within an ampulla (bulge)
- Endolymph reacts slowly to quick rotations which deflects the cupula
- paired on opposite side of head acting in push-pull activation of vestibular axons
Purpose of central vestibular pathways
Pathways of vestibular information and reflexes to control head, body, eye movement
Central vestibular pathway
- Otolith organs + semicircular canals
- Vestibulocochlear nerve
- Bipolar neurons - Vestibular nuclei
- Dorsolateral regions of medulla
- integrate with other information (visual/motor) - Send out information above and below
Where does the vestibular pathway send information to
- Cerebellum
- Vestibular sensations needed for coordinating movements - Thalamus (VP nucleus)
- Then projects to postcentral gyrus
- Info received by the cortex maintains a representation of the body in space - Extraocular Motor Neurons
- Reflexive eye movements
- Primary goal is to maintain gaze - Limbs
- Reflexive limbs movement
- primary goal is to keep body upright - Neck and Trunk
- Reflexive neck/trunk movements
- Primary goal is to keep head upright
Vestibulo-ocular reflex
- Function: to fixate line of sight on visual target during head movement
- Mechanism: senses rotations of head, commands compensatory movement of eyes in opposite direction
How are horizontal eye movements mediated?
Mediated by vestibular connections
- When head rotation occurs, fluid in the semicircular canals moves in the opposite direction
- Results in positive stimulation to canal that the head is moving towards and negative stimulation to the canal that the head is moving away from
- causes eye movement to move in the opposite direction to head movement by activating muscles on the side of the eye that the movement goes towards
Vestibular Changes with age
Peripheral changes likely to occur first
OTOLITH ORGANS
- Loss of cilia
- alterations in otoconia (shape and size)
SEMICIRCULAR CANALS
- Loss of cilia, to greater extent than otolith organs
- Greater impact in VOR and fall risk
Central changes likely to occur later (after 60 years of age)
VESTIBULAR NUCLEI
- slow loss of neurons
CEREBELLUM
- slow loss or change in connectivity
Together, this leads to a reduction in sensory information necessary to control head, eyes and body and maintain balance
- when combined with changes to other sensory structures (vision, touch, proprioception) and loss of muscle strength it leads to an increased fall risk
What are the 4 common vestibular pathologies?
- Benign Paroxysmal Position vertigo
- Vestibular Neuronitis
- Labyrinthitis
- Meniere’s Disease
Benign Paroxysmal Positional Vertigo (BPPV)
- Benign = harmless in long-term
- Paroxysmal = sudden onset/recurrence of symptoms
- vertigo = Sensation of spinning/dizziness
CAUSED BY: - Ear stones (otoconia) migrating into semi-circular canals
- Disrupting the cupula located in ampulla
TREATMENT: - Often resolves on own
- specific head maneuvers can reposition debris out
Vestibular Neuronitis
CAUSED BY:
- Inflammation of the vestibular nerve
SYMPTOMS:
- sudden vertigo that can last several days
- Does not affect hearing
TREATMENT:
- anti-nausea medication until inflammation reduces
- Steroids to reduce inflammation
- Physical therapy/activity can help the body compensate
Labyrinthitis
CAUSED BY:
- inflammation of the entire inner ear due to infection
SYMPTOMS:
- Sudden vertigo that can last for several days
- does affect hearing
TREATMENT:
- Treat infection
- Anti-nausea medication until inflammation reduces
- physical therapy/activity can help the body compensate
Meniere’s Disease
CAUSED BY:
- Excessive fluid build up in inner ear
- unknown why this occurs
SYMPTOMS:
- sudden episodes of: tinnitus, hearing loss, and/or vertigo
- Each episode can last minutes to hours
- May occur in clusters, then subside for years
TREATMENT:
- No cure; managing symptoms
- can lead to permanent hearing loss, but rare
Mechanoreceptors in skin
- Most somatosensory receptors are mechanoreceptors which are receptive to physical distortion
- 4 primary receptors in skin: pacinian corpuscles, meissner’s corpuscles, ruffini endings, merkel’s disks
- Vary in terms of receptive field and adaptation rate
Pacinian Corpuscles
- Largest and deepest mechanoreceptor in skin
- Get compressed and detect pressure and vibration
- large receptive field
- rapid adapting: react quickly to initial contact, but not sustained contact
- best at detecting finer textures and high frequency vibrations
Meissner’s Corpuscles
- Small receptors in upper dermis; common in fingers
- detect fine touch and pressure
- small receptive field
- rapid adapting
- best at detecting heavier textures and lower frequency vibrations
Ruffini Endings
- Large receptors in dermis layer
- detect stretch and deformation
- large receptive field
- slow adapting
- react to sustained deformations
- best at detecting grip and position