Third Test 160404 Flashcards
What are the characteristics of Sound (and how are they measured)?
- amplitude or intensity (measured in decibels, dB)
- frequency or pitch (Hz or kHz or cycles per second)
- phase (used for direction of sound)
What is decibel?
Decibels (dB) = 20 x log10 (p1/p2)
Where p1 and p2 are pressures in dyne/cm2
Define ‘pure tone’
Sound with only one component
Many sounds have regular set of components: eg f, 3f, 5f etc.
What is the ‘fundamental’ frequency?
The lowest frequency
What is ‘harmonics’?
Sound of higher integer multiples
List components of the outer ear
- pinna (auricle or flap)
- auditory canal
Why is the Pinna important?
For sound localization
List the components of the middle ear
- eardrum (tympanic membrane)
- ossicles (malleus, incus and stapes)
Why is the Eustachian (auditory) tube important?
It keeps air pressure equal on both sides of the eardrum
Sounds waves in outer vs inner ear
Outer: in air
Inner: in fluid
The impendance (resistance to compression) of water is much higher than that of air.
Hence without middle ear, 97% of energy would be reflected, but with it only 40% is (so we can hear better)
List the components of the inner ear
- cochlea
- vestibular apparatus
List events of sound reception in inner ear
- sound travels down auditory canal and hits middle ear, the stapes moves like a piston
- pressure wave transmitted through oval window of cochlea
- pressure wave moves basilar membrane - cilia bend on hair cells
- graded potential occurs with release of neurotransmitter
- basilar membrane vibrates, tectorial membrane as well but in a different direction - causes bending of hair cells
- sound to oval window
- wave travels down basilar membrane and reaches maximum height at some point
Describe function of the basilar membrane
Is a mechanical frequency analyzer:
- each location along the membrane is tuned to different frequency due to varying stiffness
- high frequency peak near base (oval window)
- low frequency peak near apex (helicotrema)
Describe the innervation of the organ of Corti
- afferent nerve fibers arise from nerve cell bodies within spiral ganglion
- 95% contact inner hair cells (each of which consists of the sole terminus for up to 10 axons)
- 5% contact the outer hair cells
What are the hair cells innervated by (in the ear)?
The cochlear (auditory) nerve (branch of 8th CN - vestibulocochlear nerve) With neuron cell bodies in the spiral ganglion
Describe the action of the cochlear nerve fibers
They fire in a phase-locked manner
I.e. Fire at peaks of wave
Where does the cochlear nerve project to?
To the dorsal and ventral cochlear nucleus in the medulla
- making tonotopic maps here
Where does the ventral cochlear nucleus project to?
Superior olivary nucleus
- inputs from both ears are correlated here and sound source is localized
- it’s here that there’s a response to inter-aural differences and phase differences
Where does the dorsal cochlear nucleus project to?
Superior olivary nucleus
- with information about the response to sound pattern (e.g. Frequency modulation
Where does the superior olivary nuclei project to?
(Via lateral lemmiscus) to inferior colliculus in midbrain
- cells respond to amplitude and frequency modulation, inter-aural amplitude and phase differences, direction of sound motion in space
Where does the inferior colliculus project to?
Medial geniculate in thalamus
Describe sound localization
Each neuron on the lateral superior olive receives inputs from both ears
- ear located on the same side provides excitatory input to dendrites
- ear located on the opposite side provides an inhibitory input
Describe sound localization based on amplitude
Sound source in front - excitatory and inhibition is equal
Sound to the side - excitatory and inhibition is unequal
Describe the traveling wave theory (by Georg Von Bekesy
- a sound impulse sends a wave along the basilar membrane.
- as the wave moves along the membrane it’s amplitude increases until it reaches a maximum, then falls off sharply until the wave dies out
- where the wave reaches its greatest amplitude is the point at which the frequency of the sound is detected by the ear
- high frequency = base of cochlea
- low frequency = apex
ERG: what does the a-wave measure?
The general physiological health of the photoreceptors in the outer retina
ERG: what does the b-waves measure?
The health of the inner layers of the retina
- The ON bipolar cells
- the muller cells
ERG: what does the c-wave measure?
The pigment epithelium
ERG: what does the d-wave measure?
The activity of the OFF bipolar cells
ERG: what does the oscillitatory potentials reflect?
The activity in amacrine cells
Define electrooculogram (EOG)
Electrophysiological test of function of the outer retina and retinal pigment epithelium
- records change in the electrical potential between the cornea and the ocular fundus during successive periods of dark and light adaptation
- diagnostic method of the human oculomotor system
Define BEST’s disease
Sight loss can be variable but it threatens central vision in one or both eyes
What is Fundus photography?
Photograph of interior surface of the eye, including
- retina
- optic disc
- macula
- posterior pole
What is fundus photography used for?
Monitoring progression of a disease
Diagnosis of a disease (in combination with retinal angiography)
Describe the properties of a fundus camera
Typical camera views 30 to 50 degrees of retinal area, with magnification 2.5x
Allows modification through zoom or auxiliary lenses from 15 degrees (5x magnification) to 140 degrees with wide angle lens (which minifies image by half)
Define sound
A temporal modulation of air pressure
How does the fundus camera work?
Observation light is focused via a series of lenses through a donut shaped aperture, then passes through a central aperture from an annulus, before passing through the camera objective lens and through cornea onto the retina.
Light reflected from retina passes through the un-illuminated hole in the donut formed by the illumination system.
Minimal reflections are captured in the image because the light paths of the two systems are independent.
When button is pressed to take a photo, a mirror interrupts the path of illumination system allowing light from flashbulb to pass into the eye.
A mirror also falls in front of the observation telescope, redirecting reflected light onto the capturing medium
What is fundus autoflourescensce used for?
Documenting metabolic changes at the level of retinal pigment epithelium, suggesting areas of high risk for visual function loss
What causes fundus autoflourescensce?
The light-sensing molecules (retinoids) in the photoreceptors are succeptible to damage and cross-linking. Photoreceptors shed their damaged outer segments which the RPE ingests through phagocytosis. The molecules are stored in liposomes and form lipofuscin (LF).
Age and disease can contribute to a buildup of LF in RPE. LF is made into fluorescence by 500-800 nm wavelengths, they then release a photon of light which is recorded
Define hyperfluorescence
Areas of excess lipofuscin accumulation during fundus autoflourescensce will appear hyperfluorescence
Define hypofluorescence
When RPE cells die or are absent, lipofuscin disappears, leading to hypofluorescence
What does fluorescein angiography do?
Evaluates blood vessels in the eyes with macular or retinal disease.
Used to asses the integrity of the retinal and choroidal vasculature.
Can be used to detect diabetic retinopathy, occlusions, edoema, and tumours
Describe procedure of fluorescein angiography
Test requires dilation of the pupils and a small injection of vegetable dye (through an IV needle into a vein in your arm)
A series of pictures are taken in the space of 15-20 mins.
For most patients: no side effects
Some will feel nauseated for a few minutes
What information does an a-scan ultrasonography give you?
Information regarding the density of the tissues
Describe procedure of ophthalmic ultrasonography
Uses high-frequency sound waves, transmitted from a probe into the eye.
As the wave strike intraocular structures, they’re reflected back and converted into an electric signal, which is reconstructed as an image and can be used to make a dynamic evaluation of the eye
Describe an a-scan ultrasonography
A thin, parallel sound beam is emitted, passes through the eye and images one small axis of tissue
- the echoes are represented as spikes arising from a baseline.
- the stronger the echo, the higher the spike
Describe a b-scan ultrasonography
An oscillating sound beam is emitted, passing through the eye and imaging a slice of tissue
- the echoes are represented as a multitude of dots that together form an image
- the stronger the echo, the brighter the dot
What information can a b-scan ultrasonography tell you?
It can help you differentiate a posterior detachment (a benign condition) from a more highly reflective retinal detachment (a blinding condition)
What is OCT?
An imaging technique that allows a detailed view of living structures within the eye, non-ivasively
How does OCT work?
Similar to ultrasound b-scan
Uses reflectivity of light instead of sound to produce detailed images (tomograms)
Low-coherent near-infrared light beam split into two
- one beam to a reference mirror, other to the imaged tissue
- back scattered light from both surfaces combine, interference occur and an image is generated
What does OCT stand for?
Ocular coherence tomography
What is the resolution of an OCT?
High resolution 1-10 um
Define sensation
A conscious or unconscious awareness of external or internal stimuli
What is sensory input?
Sensory impulses reach the CNS and become part of a large pool of sensory input
Each piece of incoming information is combined with other arriving and previously stored information
What is sensory modality
The property by which one sensation is distinguished from another
List different types of sensations
- touch
- pain
- temperature
- vibration
- hearing
- vision
Generally each type of sensory neuron can respond to only one type of stimulus
What are the two classes of sensory modalities?
General senses
Special senses
List examples of somatic senses
- tactile sensations (touch, pressure, vibration, itch and tickle)
- thermal sensations (warm and cold)
- pain sensations
- proprioception (awareness of limb and joint position in space)
Define visceral senses
Provide information about conditions within internal organs
Describe the process of sensation
- stimulation of receptor
- transduction (conversion) of stimulus into a graded potential (vary in amplitude and are not propagated)
- generation of impulses when graded potential reaches threshold
- integration of sensory input by the CNS
Name a few properties of sensory receptors
Demonstrate selectivity (respond to only one type of stimuli)
General sensory receptors (somatic)
- no structural specializations in free nerve endings, provide us with pain, tickle, itch, temperatures,
- some structural specializations in receptors for touch, pressure and vibration
Special sensory receptors (special sense)
- very complex structures - vision, hearing, taste and smell
List alternate classifications of sensory receptors
- structural identification
- type of response to a stimulus
- location of receptors and origin of stimuli
- type of stimuli they detect
Structural classification of sensory receptors
Free nerve endings
- bare dendrites
- pain, temperature, tickle, itch and light touch
Encapsulated nerve endings
- dendrites enclosed in connective tissue capsule
- pressure, vibration, and deep touch
Separate sensory cells
- specialized cells that respond to stimuli
- vision, taste, hearing, balance
Classification of sensory receptors by stimuli detected
Mechanoreceptors - detect pressure or stretch - touch, pressure, vibration, hearing, proprioception, equilibrium and blood pressure Thermoceptors detect temperature Nociceptors detect damage to tissues Photoreceptors detect light Chemoreceptors detect molecules - taste, smell and changes in body fluid chemistry
Classification of sensory receptors by response to stimuli
Generator potential
- free nerve endings, encapsulated nerve endings and olfactory receptors produce generator potentials
- when large enough, it generates a nerve impulse in a first-order neuron
Receptor potential
- vision, hearing, equilibrium and taste receptors produce receptor potentials
- receptor cells release neurotransmitter molecules on first-order neurons producing postsynaptic potentials
- PSP may trigger a nerve impulse
Amplitude of potentials vary with stimulus intensity
Classification of sensory receptors by location
Exteroceptors
- near surface of body
- receive external stimuli
- hearing, vision, smell, taste, touch, pressure, pain, vibration, and temperature
Interoceptors
- monitor internal environment (BV or viscera)
- not conscious except for pain or pressure
Proprioceptors
- muscle, tendon, joint, and internal ear
- senses body position and movement
Define tactile sensations
Touch, pressure, and vibration, plus itch and tickle
Receptors include:
-corpuscles of touch (Meissner’s corpuscles)
-hair root plexus was
-type I (Merkel’s discs)
-type II cutaneous (Ruffini’s corpuscles)
-mechanoreceptors
-lamellated (Pacinian) corpuscles
-free nerve endings
What is Meissner’s corpuscle?
- dendrites enclosed in CT in dermal papillae of hairless skin
- discriminative touch and vibration – rapidly adapting
- generate impulses mainly at onset of a touch
List two types of touch
Crude touch
Discriminative touch
Define crude touch
The ability to perceive that something has simply touched the skin
Define discriminative touch
(Fine touch) provides specific information about touch sensation such as location, shape, size, and texture of the source of stimulation
List two slowly adapting receptors for touch
Type I cutaneous mechanoreceptors (tactile or Merkel’s discs
Type II cutaneous mechanoreceptors (end organs or Ruffini)
Define Merkel’s disc
Flattened dendrites touching cells of stratum basale
Used in discriminative touch (25% of receptors in hands)
Define Ruffini’s corpuscle
Found deep in dermis of skin
Detect heavy touch, continuous touch and pressure
Define pressure (as a sensation)
Sustained sensation that is felt over a larger area than touch
- generally result from stimulation of tactile receptors in deeper tissues and are longer lasting and have less variation in intensity than touch sensations
- receptors for pressure are type II cutaneous
- like corpuscles of touch, lamellated corpuscles adapt rapidly
Define vibration as a sensation
Result from rapidly repetitive sensory signals from tactile receptors
- receptors are corpuscles of touch and lamellated corpuscles, which detect low frequency and high frequency vibrations, respectively
Define Pacinian corpuscle
- onion-like connective tissue capsule enclosing a dendrite
- found in subcutaneous tissues and certain viscera
- sensations of pressure or high-frequency vibration
What kind of receptors are tickle and itch receptors?
Free nerve endings
Itch and tickle sensations
- experienced when mild stimulation of the pain nerve endings occurs
- also specific nerve endings for itch sensation
- transmitted by group C unmyelinated nerve fibers
- histamine produces itch while pain signals suppress it
Define hair root plexus
Free nerve endings found around follicles, detects movement of hair
Define thermal sensations
- free nerve endings with 1mm diameter receptive fields on the skin surface
- cold receptors in stratum basale 10-40.5 degrees C
- warm receptors in dermis 32-47.8 degrees C
- both adapt rapidly at first, but continue to generate impulses at a low frequency
- pain is produced below 10 and over 40.5 degrees C
Define proprioceptive sensations
Receptors are located in skeletal muscles, tendons, in and around joints, and in the internal ear convey nerve impulses related to:
- muscle tone
- movement of body parts
- body position
This awareness of muscles, tendons, joints, and of balance or equilibrium is provided by the proprioceptive or kinesthetic sense.
Information is sent to cerebellum and cerebral cortex
Muscle spindles role in sensation
Stretching of the muscle stretches the muscle spindles sending sensory information back to the CNS
They monitor changes in muscle length
Brain regulates muscle tone by controlling gamma fibers
Golgi tendon organs
Found at junction of tendon and muscle
Consists of an encapsulated bundle of collagen fibers laced with sensory fibers
When tendon is overly stretched, sensory signals head for the CNS and resulting in the muscle’s relaxation
Joint receptors
Ruffini’s corpuscles
- found in joint capsule
- respond to pressure
Pacinian corpuscles
- found in connective tissue and around the joint
- respond to acceleration and deceleration of joints
What do somatosensory pathways do?
Send information from somatic receptors to the primary somatosensory area in the cerebral cortex
Pathways consist of three neurons (first order, second order and third order)
Axon collaterals of somatic sensory neurons simultaneously carry signals to the cerebellum and the reticular formation of the brain stem
Somatosensory pathways:
First order neuron
Conduct impulses to the CNS (brain stem or spinal cord)
- either spinal or cranial nerves
Somatosensory pathways:
Second order neurons
Conduct impulses from brain stem or spinal cord to thalamus
- cross over to opposite side of the body
Somatosensory pathways:
Third order neuron
Conducts impulses from thalamus to primary somatosensory cortex (postcentral gyrus of parietal lobe)
What impulses are conducted along the posterior column-medial lemniscus pathway to the cortex?
- fine touch
- stereognosis
- proprioception
- vibration sensations
Describe the anterolateral pathways to the cortex
- 3-neuron pathway
- carry mainly pain and temperature impulses
- relay sensations of tickle and itch and some tactile impulses
What are the major routes by which proprioceptive impulses reach the cerebellum?
Posterior spinocerebellar
Anterior spinocerebellar tracts
What are the impulses conducted by the cerebellum critical for?
Posture
Balance
Coordination of skilled movements
List three rapidly adapting receptors
Smell
Pressure
Touch
- specialized for detecting changes
List two slowly adapting sensory receptors
Pain
Body position
- nerve impulses continue as long as the stimulus persists - pain is not easily ignored
Define perception
The conscious awareness and interpretation of a sensation
- precise localization and identification
- memories of our perceptions are stored in the cortex
What are pain receptors?
(Nociceptors) are free endings that are located in nearly every body tissue (except the brain)
-adaptation is slight if it occurs at all
List different types of pain
Fast pain (acute) Slow pain (chronic) Somatic -Superficial -Deep Visceral Referred pain
Describe fast pain (acute)
- occurs rapidly after stimuli
- sharp pain like needle puncture or cut
- not felt in deeper tissues
- larger A nerve fibers
Describe slow pain (chronic)
- begins more slowly and increases in intensity
- aching or throbbing pain of toothache
- in both superficial and deeper tissues
- smaller C nerve fibers
Describe superficial pain
Somatic pain that arises from the stimulation of receptors in the skin
Describe deep pain
Somatic pain that arises from skeletal muscle, joints and tendons
Describe visceral pain
Usually felt in or just under the skin that overlies the stimulated organ
- localized damage (cutting) intestines may cause no pain, but diffuse visceral stimulation can be severe
(Eg distension of a bile duct from a gallstone, or of the urethral from a kidney stone)
Describe referred pain
When pain is felt in a surface area far from the stimulated organ
A version of visceral pain
E.g. Heart attack is felt in skin along left arm since both are supplied by spinal cord segment T1-T5
Examples of pain relief
- aspirin and ibuprofen block formation of prostaglandins that stimulate nociceptors
- novocaine blocks conduction of nerve impulses along pain fibers
- morphine lessen the perception of pain in the brain
What are the two chemical senses?
Olfaction (smell) and gustation (taste)
Define chemical senses
Interaction of molecules with receptor cells
Both smell and taste project to cerebral cortex and limbic system (evoke strong emotion)
Describe the anatomy of olfactory receptors
- bipolar neurons that are in the nasal epithelium in the superior portion of the nasal cavity
- first-order neurons of the olfactory pathway
- supporting cells are epithelial cells of the mucous membrane lining the nose
- basal stem cells produce new olfactory receptors
What three types of cells does the olfactory epithelium consist of?
Olfactory receptor
- bipolar neuron with cilia (olfactory hairs)
- there are 10-100 million of the in the nose that respond to odourant molecules
Supporting cells
- provide support and nourishment
Basal cells
- stem cells that replace olfactory receptors
How many different odours can the olfactory apparatus detect?
About 10,000
List the intracellular events that occur when we smell
- odourant binds to receptor of an olfactory hair
- initiates events through a G-protein and a 2nd messenger
- production of cAMP
- opening of Na+ channels
- inflow of Na+
- generator potentials
(- nerve impulses travel through 2 olfactory nerves - olfactory bulbs
- olfactory tract
- primary olfactory area in the temporal lobe of the cortex)
Olfactory supporting cells and glands are innervated by:
The facial (VII) nerve
- provides parasympathetic motor innervation to lacrimal glands and the mucous membranes in the nasal cavity
- this is why certain smells will make our nose run and cause us to produce tears
What is hyposmia?
A reduced ability to smell
- affects half of those over age 65
- affects 75% of those over age 80
Can be caused by neurological changes, drugs, or the effects of smoking
Where does conscious awareness of smell begin?
In the primary olfactory area of the temporal lobe
Where does identification of smell occur?
In the frontal lobe
Define adaption
Decreasing sensitivity
Comment on olfactory adaption
It is rapid
- 50% in 1 second
- complete in 1 minute
Low threshold - only a few molecules need to be present in order for us to feel the smell
What is vital in order for us too detect a taste?
The molecules must be dissolved
What different stimuli classes of taste is there?
Sour Sweet Bitter Salty Umami - protein-rich foods
List different aspects of flavour
Taste Aroma Temperature Texture Appearance of food
Define papillae
Specialized portions of the tongue associated with different types of taste buds
List the four major types of papillae
They're names after their shape: Vallate Fungiform Foliate Filiform
What papillae are taste buds associated with?
Vallate
Fungiform
Foliate
Describe filiform papillae
The most numerous papillae on the surface of the tongue
Have NO taste buds
Contain tactile receptors
Increase friction between tongue and food, making it easier to move food in the oral cavity
Describe vallate papillae
Largest
Least numerous
8-12 form a V-shaped row along the border between anterior and posterior parts of the tongue
Describe fungiform papillae
Scattered irregularly over entire superior surface of the tongue
Appear as small red dots among the more numerous filiform papillae
Mushroom shaped
Containing about 5 taste buds each
Describe foliate papillae
Distributed in folds on the sides of the tongue
Contain most sensitive taste buds
Most in young children, decrease with age
Located mostly posteriorly in adults
Define tastants
Chemicals that stimulate gustatory receptor cells
Once a tastant is dissolved in saliva, it can make contact with the plasma membrane of the gustatory hairs (= sites of taste transduction)
Result in receptor potential stimulating exocytosis of synaptic vesicles from the gustatory receptor cell
Neurotransmitters trigger nerve impulses in the first-order sensory neurons that synapse with gustatory receptor cells
How many gustatory receptors make up a taste bud?
About 50
What is the lifespan of a gustatory receptor cell?
About 10 days
Describe the anatomy of a taste bud
Consist of 50 receptor cells, surrounded by supporting cells
A single gustatory hair projects upward through the taste pore
Basal cells develop into new receptor cells every 10 days
How long does complete taste adaptation take?
1-5 minutes
List the cranial nerves in which first-order gustatory fibers are found
V
VII (facial) serves anterior 2/3 of tongue
IX (glossopharyngeal) serves posterior 1/3 of tongue
X (vagus) serves palate and epiglottis
Describe the gustatory pathway
Via cranial nerves to thalamus or limbic system and hypothalamus
To primary gustatory area on parietal lobe of cerebral cortex
- provides conscious perception of taste
List the motor control hierarchy
Cerebral cortex
Brain stem
Spinal cord (direct pathway)
Give a brief summary of the somatic motor system
Motor commands from brain travel down spinal cord
Signal relayed by motor neuron in ventral horn
Muscle contracts
Proprioceptors in muscles and joints send feedback to cord and brain
Ongoing motor command altered
