Final Flashcards
3 parts of the cerebral hemispheres
Cortex (surface)
white matter (nerve tracts)
deep structure (basal ganglia, anygdala and hippocampus)
commissures
in the hemispheres
Commissure are nerve bundles
the largest is the corpus callosum
Topographic organization in the brain
each area of the cortex is organized topographically
ipsilateral/contralateral organization in the brain
most of the brain is organized conralaterally, but the cerebellum is organized ipsilaterally.
physical structure of the cortex
Most of cortex is 6-layered with large pyramidal cells - Betz Cells - whose axons make up the major output
Brodmann areas
52 regions of the brain
neocortex, archicortex and paleo cortex
where is the hippocampus?
where is the cingulate cortex?
are phylogenetically older areas of the brain.
Have less layers of cells (3, 4/5)
90% of human brain is the newer neocortex
archicortex contains the hippocampus
cingulate cortex is part of the paleocortex
The cortexes and their functions
- Occiptal - vision
- parietal - somatosensory
- temporal - hearing, language, speech
- frontal - motor and general planning
Association areas of the brain
large areas, particularly in the frontal and parietal lobes that are assumed to be for higher function
overrepresentation in the somatosensory cortex
Some areas in the somatosensory cortex that are important for touch sensation are overrepresented on the topographic map of the cortex
these areas have higher two point discrimination
Phantom limbs
- When part of the body is lost, it’s corresponding region of the sensory homunculous still exists
- plasticity leads to other parts of the body connecting with this region, so sensation in those regions may lead to sensation on the phantom limb
- May be painful/unpleasant
*
Common causes of prolongued pain (6)
- Shingles = postherpetic neuralgia. Reactivation of zoster virus can leave pain for months or years
- Tic Douloureux = trigeminal neuraliga. Intense facial pain. Due to pressure on the trigeminal by vascular or neuroplastic changes
- Cancer pain - tissue damage activates silent nociceptors
- Spinal nerve root compression - eg herniated disk
- fibromyalgia - widespread pain in muscles, joints, bones without known cause. More in women
- Complex regional pain syndrome - usually an entire arm or leg.
Central pain:
Damage to anterolateral disk
Damage to thalamus
Damage to the anterolateal system can cause central pain. Particularly on the spinothalamic and spinoreticular fibres.
Damage to thalamus itself can lead to central pain.
Central pain can be intense and can involve half of the body. Often resistant to analgesics.
Effect of distraction on pain
Many people don’t feel pain in urgent activites
Dstraction reduces percieved pain
Responses to pain: somatic reflexes
due to spinal cord connections
Flexor and crossed extensor reflexes - cutaneous pain in an extremity causes limb withdrawal and contralateral limb extension
scratch reflex - cutaneous pain on the body causes limb to remove the source of irritation.
Responses to pain
- autonomic responses
- emotional responses
- learning and memory
hypothalamus and brainstem
- Increased heart rate, respiration rate and blood pressure
- Nausea, vomiting, sweating, dilated pupils
cingulate cortex and limbic system
- anxiety, fear
hippocampal connections
- Important to learn to avoid pain, but people can learn to expect pain, which increases perception of pain (wind up phenomenon)
EEG
what is it
records
wave types
used clinically for
contaminated by
electroencephalogram
- small ascillating voltage recorded from the scalp.
- Mainly measures post synaptic potentials produces by thalamic signals to the cortex
- Alpha rhythms when we are relaxed, awake, eyes closed
- Beta rhythms when open eyes, alert, even in dark. Smaller and faster than alpha.
- Used clinically because epileptiform (abnormal) EEG shows off electrical activity in the brain and can be used for diagnosis of epilepsy, coma level and brain death, measurement of anaesthesia effects, detection of psychotropic drugs
- EEG can be contaminated by eye movements, tongue movements, EKG
REM sleep
when
waves look like
cycling
amount of REM
physical symptoms of REM
At the end of the first sleep cycle, the person doesn’t wake up, instead they enter into REM
REM looks similar to normal/awake/alert EEG
after a short time anodhter cycle through stages 1-4 occurs
Amount of REM increases with each cycle
REM is usually 4 times per night about 20-25% of the total sleep time
When dreaming occurs; muscles relaxed, eyes frequently active, twitches of muscles
Parasomnias
- Somnambulism
- Night terrors
- rhythmic movement disorder
- REM behaviour disorder
- Restless leg syndrome
- Somnambulism - sleepwalking and sleeptalking but not dreaming. Can’t see; often injured
- Night terrors - screaming, sweating, frightened, more than nightmare
- rhythmic movement disorder - rocking, head-rolling
- REM behaviour disorder - acting out dreams, can cause injury to sleeper or companions
- Restless leg syndrome - involuntary leg movements; genetic links
treatment for severe sleep disorder symptoms
tranquilizers - benzodiazepines
NT release during sleep and wakefulness
During wake/alert state, neurons that release norepinephrine and serotonin are active
During awake or in REM sleep, neurons that release acetyl choline are active
sleep wake cycle driven by
Circadian rhythm - a clock mechanism inherent to the brain and triggered by night/day cycle
sleep/wake cycle influenced by several areas of the brain
- superchiasmatic nucleus
- hypothalamus
- reticular system
coma
means a person cannot be aroused
result of many causes (injury, disease, drugs)
consciousness
includes
brain regions
paying attention
includes self awareness, thought, decision making, feeling, planning, imagining
structures involved in consciousness are not well know. Parts of cerebral cortex: thalamus, basal ganglia are essential
the ability to pay attention is enhanced by sensory information
right parietal damage
leads to loss of awareness of the left visual field and body parts on the left side.
The opposite occurs for left parietal damage
hemi-spatial neglect
apraxia
difficulty performing complex motor tasts due to premotor cortex, corpus callosum, parietal cortex damage
schizophrenia
type of disorder
causes
includes
treatment
a disorder of consciousness
Due to a variety of causes including genetic predisposition
delusions, hallucinations, often paranoia
helped by dopamine antagonists
general mood disorder treatment
treatment for bipolar disorder
Drug therapies for mood disorder usually increase serotonin or norepinephrine by limiting reuptake or degredation
- most popular increase serotonin - prozac
Lithium effective for damping mood swings in bipolar disroder. Mechanism probably involves second messenger systems
Frontal lobe
functions
size
age of maturity
types of neurons
result of damage
Impulse control, judgement, language, working memory, motor control, sexual behaviour, socialization, spontaneity, planning, coordination
- Executive functions: recognizing future consequences of actions, choosing between good, bad and better actions, suppressing unacceptable social responses, determining similarities and differences between things or events
developed later in evolution. Enormous in humans and relatively high in apes.
reach full maturity around age 25
rich in dopamine sensitive neurons
Damage leads to: impulsiveness, impaired planning of complex action sequences, persistence when change would be more appropriate
limbic system:
what does it mean
includes
major functions
function of the amygdala/result of damage
- LImbic means edge/border so its contents are the inner edge of the cingulate cortex
- Includes amygdala and hippocampus and thalamus (thalamus and front lobe are often included)
- Major function is emotion, control of hypothalamus, learning/memory
- Amygdala important for expressing emotion and interpreting emotion in others
- Stimulation produces sensations of fear/apprehension
- Amygdala is selectively activated by expressive faces
- Damage leads to inability to detect emotion in others
Papez circuit
originally thought to be mainly concerned with emotion
now considered to be important for memory
important cerebellar inputs
Hypothalamus
where is it
important for
involved in controlling (long list)
Small structure under the thalamus
Connected to pituitary gland
Important for homeostatic control - receives inputs from many sensory structures throughout the body and compares them to optimal set points
involved in controlling: anterior pituitary gland, blood pressure, water balance, eating and drinking, reproduction, circadian rhythm, body temperature, emotional expression, general autonomic functions
Thermoregulation
Pyrogens change the hypothalamis set point causing fever
Central heat receptors in hypothalamus detect changes
Shivering activaes muscles - piloerection (raised hairs)
Too much heat - sweating and blood flow to surface of skin to cool off
Two major classes of memory
Declarative: factual information (phone numbers, faces).
Procedural: how to do things like skating/riding a bike
forming declarative and procedural memories
limit to memory
damage to hippocampus
lateral specialization of hippocampus
Hippocampus is critical for forming long-term declarative memories
Cerebellum is involved in forming procedural memories
Seems to be no limit to the amount of declarative memory
Damage to hippocampus prevents storage of long-term memory, but does not erase existing memory
Lateral specialization of hippocampus:
- left = verbal memory, learning
- right = spatial memory
Cellular basis of memory
- Memory involves synaptic strength
- changes in amount of NT released with AP
- changes in size of PSP produced by a fixed amount of NT
- 2 models
- Long term potentiation and long term depression.
- Synaptic connections become stronger or weaker after appropriate stimuli and remain unchanged for days or weeks
- changes in 2nd messenger systems are particularly important
- Growth of postsynaptic reions or neurons or the delivery of additional receptor molecules to the postsynaptic membrane
Cerebral hemisphere specialization and dominance
corpus callossum cut studies show
specializatation of left and right
sominance
- Studies with a corpus callossum cut show that the two hemispheres can operate relatively independently and disagree about what to do
- Alien hand syndrome - one hand acts indpendently of conscious thought
- Language concentrated in left - speaking, writing and understanding language
- Left tends to dominate brain activity
- right hemisphere specializes in spatial functions: perspectives of 3D objects, recognizing faces, mathematical skill, but can understand simple language too
hemisphere that recognizes an object
Implications in split brain
Objects in the right visual field will be perceived by the left brain only and vice versa.
A split brain patient’s hemispheres can’t communicate so when a word or image appears in the left, the info goes to the right brain and the patient can’t name it, though they can draw it.
Broca’s and Wernicke’s areas
describe. Result of damage to each
connected by. Damage to this
Broca’s area = creation of speech, using respiratory muscles, vocal chords, mouth (left hemisphere)
- damage causes expressive aphasia
Wernicke’s area = Language comprehension, musical tone comprehension, non-verbal sounds
- Damage causes trouble understanding spoken or written speech. People may produce fluent but meaningless speech
The two areas are connected by the arcuate fasciulus - damage to it causes difficulty repeating words: conduction aphasia
- You would have to hear the word, understand it and then have it repeated in Broca’s area
language: damage to central areas
leads to more difficulties in language comprehension - central aphasias
Sclera
Aqueous humour
vitreous humour
lens
cornea
choroid
fovea
Sclera - the white over the whole eye
Aqueous humour - under the cornea
vitreous humour - filling up most of eye
lens - the disk at the front of eye
cornea - protective layer over the pupil and lens
choroid - dark structure behind the retina. Dark in humans because all light is absorbed. Not for nocturnal animals
fovea - depression at the back of retina. fine focus
Cornea
transparent, convex structure
Non-vascular
many nerve endings - trigeminal nerve (so very sensitive to touch)
Light coming in has to be bent - 2/3 of total focusing power
Pupil
what is it
why black
size controled by
increases depth of focus as
analogous to
- Hole at the centre of the iris.
- Appears black because all light entering the eye is absorbed
- Size controled by radial and circular eye muscles
- Pupil increases depth of focus as it becomes smaller due to pinhole effect
- light from one part of object only reaches one part of the eye (due to pinhole)
- directly analogous to a camera aperture - more depth of focus with more available light
pinhole effect
LIght from one part of an object only reaches one part of the eye due to the pinhole
Distance of object from pinhole doesn’t matter - still get a sharp image/depth of focus
smaller pupil = better focusing on back of eye
Iris
colour
muscle control
- Has pigmented cells containing several types of melanin, another pigment is lipofuscin
- Number and position of pigment cells leads to eye colour
- Iris has blood vessels so haemoglobin in blood contributes to colour
- Eye colour is difficult to predict even if genetics are known
- Two groups of muscles: sphinchter/circular muscles constrict the pupil and radial muscles dilate the pupil.
- Iris muscles controlled by autonomic system: sympathetic drive radial (dilate), parasympathetic drive circular
pupillary light reflex
Light falling in eye causes reflex activation of circular muscle.
Light detected by retina - signal goes from eye to pretectal area of midbrain and then back to ciliary ganglion of parasympathetic
Lens
what does it do
how does it do it
far-sighted
Adjusts focus
Distant vision - thin, stretched by zonule fibres
Near vision - circular ciliary muscles contract, allowing lens to relax
Only activates focusing power on far things. As we age, the lens gets rigid and won’t relax as easily so near vision is compromised (far sighted)
accomodation and vergence
As an object moves farther and closer, the lens must change shape - accomodation - to maintain focus
For a close object, eyes converge (turn in). Degree of convergence is used by brain to determine how far or close the object is. - binocular depth cue
cataracts
Clouding of the lens due to protein changes
mostly age-related
lens colour also changes
Surgical removal is common procedure - lens replaces with a prosthetic implant. Restores vision, but accomodation is lost because the lens has fixed depth focus
Aqueous and vitreous humours
Lens seperates the eye into two chambers. Aqueous humour fillst he front and the vitreous humour fills the back
Vitreous humour occupies 2/3 of eye and is a jelly like consistency and transparent.
Vitreous humour naturally shrinks with age and tends to seperate from the retina giving the appearance of floaters are the vitreous pulls away causing visual phenomena
Glaucoma
- Aqueous humour is clear, filling the frount of the eye
- Produces by the epithelium of cilary body; flows through pupillary space and exits through Schlemm’s channel
- Carries nutrients to the cells of the lens and cornea
- Conduction and drainage of aqueous humour controls intraocular pressure (IOP)
- Glaucoma is a common eye disease that is associated with elevated IOP, though some glaucoma patients have normal IOP levels
- Causes damage to optic nerve
- Produces loss of peripheral vision (visual world starts to shrink), but is not usually noticed until there is already signficant damage
- Surgery to make additional hols is done if Schlemm channel is blocked
Retina
choroid absorbs most of the light
the macula (darker area) contains the fovea, where accurate vision occurs.
Blod vessels avoid the macula/fovea so as not to interfere with vision
the blind spot is the area of the visual field correspondng to the optic disk - no retina there but the brain can fill in missing info for colours, lines, patterns (each eye has diff blind spot so they fill in for each other)
optic disk
where the optic nerve and the blood vessels leave and enter the eye
Light
A photon is a single quantum of light with energy -hc/wavelength
Natural light intensity range from brightest to darkest is 10^15, human functional intensity is about 10^12 with time for adaption
Human short term functional intensity about 10^3
Longer wavelengths = lower energy. A lot of animals can see beyond 400 nm but we can’t
Retinal cells
ganglion cells
amacrine cells
bipolar cells
horizontal cells
rods and cones
retinal cells distribution
- rods and cones > bipolar cells > ganglion cells
- amacrine cells connect bipolar cells
- horizontal cells connect rods and cones
- Foveola - mashed with cones. Each cone to a ganglion cell
- Fovea - depression in macula; mainly cones, fewer as you move away
- periphery - outside macula; manily rods, few cones; up to 250 rods per ganglion cell
Rods structure
- Rhodopsin is a light sensitive molecule on disks (photopigment/visual pigment)
- Disks are made by invagination of epithelium. Made hourly and progress down the rod, eventually being degraded at end
- First few rods are clear invaginations, and then they move down and separate
cones structure
- much less in eye than cones
- Disks are all invaginated from the epithelium and remain that way. Cone shaped
- In some animals (not humans), you find oil droplets full of brightly coloured pigments
retinitis pigmentosa
a group of at least 70 different genetic diseases in which the retina degrades
some cause rod/cone degeneration, some due to failure of pigment epithelium to degrade disks, causing accumulation of debris
Rhodopsin structure
Rhodopsin is made up of opsin and retinal
- Retinal absorbs light (in UV too)
- Opsin has 7 TM helices, determines the wavelength of absorption of light and has retinal in it
- Retinal is derived from vitamin A - has a highly conserved molecular structure
- Retinal is surrounded by amino acids (opsins) that shift vibration frequencies of double bonds in retinal, giving different light absorption wavelengths
- OPsins shift the retinal absorption into the visible wavelength - depending on what the opsin is, we see a diff shift int he visible region
- Humans have 4 opsins: red, gree, blue cones, plus rods (mainly green)
Transduction in rods
- Light hits rhodopsin, causing it to change to meterhodopsin
- Metarhodopsin has a chemical cascade that reduces cGMP concentration
- cGMP normally holds the Na channels open when there is darkeness - dark current
- Light lowers cGMP and closes Na channel, so that receptor potentials are hyperpolarizing
Ion current in rods
- cGMP opens Ca/Na channel that is primary sodium selective but some Ca gets in too.
- In light, cGMP is downregulated and this channel is closed
- Na and Ca levels are dealt with bu the Na/Ca exchanger and the Na/K pump to keep Ca levels low
- Ca is important for adaption process
Light adaption
- With dtrong light, the amount of rhodopsin available falls to about 1% of normal. This reduces sensitivity but cannot account entirely for major adaption to light.
- Ca important for light adaption
- Adaptopn much faster to light than to dark
- Rods adapt more than cones, but cones adapt more quickly
Temporal resolution of fovea
critical fusion frequency
Critical fusion frequency = the frequency at which a flashing image beinfs to look continuous (used for movies)
Horizontal cells important for
collecting information from surrounding area
processing in retinal cells
transduction in rods/cone and bipolar cells
amacrine cells
retinal processing favors in different light
- These first two layers of retinal cells don’t use APs
- The distance is so small that graded potentials can propogate without much loss
- 2 types of bipolar cell responses - due to different synaptic receptors to the same transmitter (glutamate)
- amacrine cells perform a great deal of processing before visual signals leave retina via optic nerve
- Retinal processing favors fine discrimination in bright light and maximum sensitivity in dull light
- visual receptive fields are split into centre and surround - each with different effects on the cell.
receptive field
is usually the area on the retina where light causes a change in activityin the neuron
light falling on other parts of the retina has no effect
neuron may be far from the receptive field (in visual cortex)
receptive field split into centre and surround
Retinal ganglion cell responses: centre and surround
Surround is the ‘off region’ - fires less in light and demonstrates an ‘off burst’ when light is turned off
centre is the ‘on region’ - fires less in darkness, ‘on burst’ when light is turned on
If both are illuminated together, little to no response on ganglion cell
dark adaption can make both areas excitatory in darkness
light outside of these regions has no effect on the neuron
primate fovea centre are less than 0.1 mm - larger in cats
Intrinsically photosensitive retinal ganglion cell
function
structure
transduction mechanism
connected to
- ganglion cells that can detect light without rod or cone input.
- Stillconnected to bipolar and amacrine cells that respond to rod and cone inputs
- large dendritic areas containing melanopsin - blue-sensitive photopigment
- different transduction mechanism - IP3, not cGMP
- slow responses - measure average ight level
- connected to superchiasmatic nucleus - important for light/dark cycle behaviour
- Involved in release of melatonin from pineal gland
- Can contribute to conscious vision, though probably low acuity
overlap of ganglion cell receptive fields
half have ‘on’ centre, ‘off’ surround, the outher hald have the opposite
ganglion recpetive fields overlap on the retina
Alignment of different receptive fields is probably to help detect light/dark edges
two levels of crossing over in vision
Light crosses over in the eyes, so nasal visual fields go to temporal retinas and temporal visual fields go to nasal retinas
Axons from nasal retinas cross at optic chiasm
retinal topographic organization
Topographic at each level, but distorted in favour of fovea
distorted because there are so many retinal ganglion cells in the fovea
points that are next to each other on the retina, tend to have axons leaving together
lateral geniculate
lateral geniculate nucleus of the thalamus
inputs fromt he two eyes are still separated here
receptive field is similar to that of ganglion cell with on/off centre/surround
Damage to optic chiasm
retain central nasal vision, but you see a narrower world
subcortical retinal ganglion pathways
paths leaving the retina that don’t end up at top of midbrain like most others.
to superior colliculous and pretectal area (brainstem)
superior colliculus
subcortical visual destination
superior colliculous has topographic map and matching maps of auditory and other sensory modalities
- recieves input from cerebrum
- controls saccadic eye movement
- contributes to blindsight - can’t consciousless see, but aware of surrounding
pretectal area
subcortical visual destination
pupillary reflex - light entering eyes is used to determine diameter of pupil
overrepresentation of fovea in the cortex
macula sparing
fovea is overrepresented in the thalamus and cortex - even has dual blood supply to areas in the cortex representing fovea
damage to cortex usually results in loss of vision in the corresponding visual field.
Loss of peripheral vision is common, but some maintain vision from the fovea because it is represented in such a large portion of the cortex
Simple cortical neurons
Have receptive fields with centre/surround organization, but distorted to respond better to lines
complex cortical neurons
- more numerous than simple cortical neurons, larger receptive fields, respond better to bars or edges of a particular orientation
- use convergence from simple cells
- we seem to analyze the visual world based mostly on lines.
- Cortex organized into groups of cells responding to different orientations of lines
- more complex shape = more complex cells repsonding
columnar organization
at any point in a vertical column, the cells have a similar type of receptive field orientation.
ocular dominance
Many cells respond to inputs from either eye, but there is ocular dominance - a strong response to one eye for each column
colour receptors in humans
red, green and blue
opsin mutations
has complex molecular biology
two important genes for opsins on X chromosome so red/green blindness if common in men
some people lack colours (like green), other have mixed up hybrids due to deletions and duplications
Colour in retinal ganglion cells
result of damage
M and P cells.
M cells are not colour sensitive
P cells (80%) are composed of red/green opponents, and blue/yellow opponents
damage to colour pathways can selectively remove colour sensations from part of visual field leaving only black and white vision in that area
human frequency sound range
sound location
20-20,000 Hz
Higher Hz = shorter wavelength
location of sound mainly detected by time delay between the sound arriveing at each of the two ears
sound location impossible at low frequencies
closer ears means you need higher frequencies to do sound location
Eustation tube
problems with pressure
COnnected to the back of the throat, but entrance is clsoed except for in yawning and swallowing
middle ear is normally at atmospheric pressure, so this is problematic when going up in planes. You need to open you eustachian tube to normalize pressure. Conscious action.
trasduction of sound in middle ear
eardrum > malleus > incus > stapes > oval window
middle ear transmits sound from air to water because coclea is filled with endolymph
when sound hits air/water interface, about 99% is reflected
contraction of muscles reduces sound transmission
- acoustic reflex: lous sound causes muscle contraction
audiometry
the measurement of auditory system function. Measure minimum sound pressure for detection at different frequencies
hearing loss is usually due to damage to middle ear or the cochlea
presbycusis is loss of hearing (especially high frequencies) with age
weber test tests bone conduction through middle ear. Knock head, shoul hear equally in both ears
rinne test - compares sound and air conduction in one ear. Place tuning fork next to mastoid bone and tell patient to tell you when they stop hearing it. When they do, hold it outside pinna and ask if they can hear it. They should because air conduction is longer than bone conduction
wave travel in cochlea
waves grow in amplitude as they travel down basilar membrane.
Gap at end of basilar membrane called helicotrema
travelling wave has an enveloped maximum displacement that changes with frequency
peak or the envelope moves down the basilar membrane has we go from high to low frequency
auditory neuron thresholds
basilar membrane pushes hair cells against he tectorial membrane
hair cells transduce movement and synpase onto auditory neurons
threshold intensity changes with each frequency specialization.
Each neuron responds becast the frequency it was meant for. Depending on its position on the basilar membrane, that is where that preferred frequency envelope is at max displacement
helicotrema likes low frequency, by stapes is high frequency
Inner and outer hair cells
3 rows outer hair cells
1 row inner hair cells
inner hair cells transduce movement into graded membrane potential changes. Have no axons, but synapse onto neurons that send APs along axons into auditory nerve
outer hair cells contract with depolarization, as well as transduce movement. Contract with music.
cochlear amplification
cochlea has great sensitivity that depends on local amplification mechanism
can tell that it amplifies because the ear itself often makes sounds
outer hair cells may give feedback to amlify guiet sounds and negative feedback to reduce loud sounds
organization or auditory cortex
damage
electrication stimulation
Organization if tonotopic at each level - large and complex map of sound frequency in human cortex
damage to cortex causes more deafness in contralateral ear, but not complete deafness because of complex crossing over
electrical stimulation of cortex gives sensation of sounds
organ of corti
on basilar membrane
stimulated by vibrations and sends nerve impulses via hair cells
hair cell potentials (1)
hair cells use graded potentials to synapse onto neurons
Membranous labyrinth includes
includes membranes lining bony labyrinth
sensory nerves leaving vestibular system
leave each of the canals and the big chambers.
join to form the vestibular nerve - 8th cranial nerve
functions of vestibular system
control of eye, head and body positions
spatial sensation
ditinguish between velocity, force and angular movement
vestibular system experience of acceleration due to gravity
detects acceleration, not velocity. If you sit on a plane and it’s not accelerating you don’t feel movement
Cannot distinguish between gravity and acceleration upward - so you just feel heavy when going up an escalator
Otolith organs
Stones in the ear
density 3:1 endolymph
detect linear acceleration by moving to fall and sitmulating hair cells in saccule and utricle.
hairs in utricle and saccule bend preferentially
In utricle, horizontal respons inward
In saccule, vertical respons where hairs bend away from the striolla
detecting angular acceleration
Inside the ampulla is the cupulla, that bends in response to pressure, moving hair cells one way or the other depending on which way the endolymph is trying to move.
any movement that causes the endolymph to move relative to the canal will bring about a circular motion response.
ampulla response to acceleration in firing
ampulla fires all the time, fires more when accelerating and less when decelerating
vestibular neural connection
very fast connections to cerebellum and vetibular nucleus or spinal cord
cranial nerves 3, 4, 6
saccades
quick changes in fixation point ar normal and continual
if the eye is artificially fixed, the image washes out.
saccadic and tracking vision
contributions to normal vision
ouchi illusion
vestibular-ocular reflex
normally, vision includes a mixture of saccadic and tracking movements. Tracking if an opbject of interest that moving across the visual field or subject moves relative to visual world
Ouchi illusion - horizontal sacades make the disk appear to move and vertical make background apear to move so disk looks floating
vestibular-ocular reflex - in angular acceleration, subject will make slow tracking movements and when their fixation point is out of view, there is fast saccades to track that object again
vestibular nystagmus
rotation of the head (even in dark) results in repeated slow tracking movements in opposite direction
displays plasticity - can change amplitude and direction if the eyes are fitted with prism glasses
pros and cons of vestibular-ocular reflexes
It is possible to control eye and head position based on other senses, especially vision but vestibular control is fast and works in the dark
however, anything that disturbs vestibular function, also causes problems with eye position
caloric nystagmus
Irrigate one ear with water - leads to nystagmus - strong sensationof rotation, nausea
only clinical way to test each ear
mainly effects horizontal semicircular canal (closest to ear)
vestibulo-postural reflexes
Connections from vestibular nuclei to spinal cord produce postural reflexes in body and neck
these refelxes produce rotation of of head relative to body movements that tend to keep the visual world stationary
ability here varies with species. Owls are very good
linear acceleration contributes to reflexs - cat dropped on back with flip to feet
Menier’s syndrome
symptoms
causes
one side
both sides
in children
nystagmus, dizziness, nausea, postural problems, deafness and tinnitus (ringing in ear)
caused by genetic mutation, infection, blood supply problems, elevated fluid pressure
Destruction of labyrinth causes extreme nystagmus for several weeks followed by faily complete recovery
loss of both labyrinths causes mild symptoms.
Difference causes the problem, loss isn’t as bad.
children born without vestibular function are pretty normal, but learn to stand and walk more slowly
define taste
gustation is the sensation evoked by stimulation of taste receptors by water soluble chemicals
olfaction
is the sensation that results from the detection of odorous substances aerosolized in the environment
capsaicin
stimulated ion channels in somatosensory nerve fibres, so not a gustatory stimulus.
however, it may stimulate interactions between somatosensory trigeminal nerve fibres in the tongue and taste buds, thus moderating taste
different tast sensations
umami, salty, butter, sour, sweet
mostly GPCRs
tast buds
found all over the oral cavity, but most obvious on tongue.
50-100 tase receptor cells in each bud
apical end covered with microvilli that extend into the pore that is open to the external milieu
3-14 afferent nerve fibres per bud. One fibre may innervate more than one bud
taste buds on three types of papillae: cirvumvallate papillae, foliate papillae, fungiform papillae
all taste qualities are detected on all regions of the tongue, though sensitivity to different tasts may vary by region
tast receptor cells (4)
Type 1 - support cell. Maybe involved in salt taste
Type 2 - releast ATP that acts as NT. Have G protein coupled receptors for bitter, sweet and umami
Type 3 - detect suor taste
B - basal cell
Bitter receptors
T2R
7 TM domains
detect poison as too bitter
sweet receptors
umami receptors
2 GPCRs: T1R2 + T1R3
2 GPCRs: T1R1 + T1R3
Sour taste transduction
- Protons flow into the taste cells via proton channels
- depolarization and acidification of the cell
- Na channels open and K channels close
- further depolarization
- Ca influx and GABA + serotonin released
weak (organic) acid are membrane permeable - skip a step but same effects
same cells repond to carbonation
salt transduction
Na and other cations may be perceived as salty
Low sal concentrations are attractive, high are aversive.
Low salt activates Na ion channels of the ENaC family
Salty tasting ENaC channels are blocked by amiloride in rodesnts, but humans are less sensitive to amiloride
salt transduction can occur at any taste cell
Innervation of the esophagus, pharynx and tongue
Three cranial nerves:
- 7 - facial innervates must of fungiform papillae
- 9 - takes information from back of tongue
- 10 - vagus, takes info from pharynx
adaption in gustatory pathway
adaption occurs easily at every step of conduction.
We don’t sense the same chemical for very long
Olfaction
olfactory sensory neurons and ORs
- Systen is very sensitive - we can detect about 1 part per billion of methylmercaptan
- Can discriminate more than a trillion odors
- Millions of olfactory neurons that are continually replaced by differentiation of stem cells in olfactory mucosa
- 350-400 different odorant receptor molecule - all GPCRS
- Each olfactory sensory neuron has one functional OR gene
- Each OR has detects a small number of odors to a general odor
- Each olfactory sensory neurons/OR typically respones to a variety of odors so the smell identity is encoded by a combo of OR/OSN responses
- Women are more sensitive than men
Process of olfaction
- Oderant molecule bind to receptors on no-motile cilia
- Olfactory sensory neurons depolarize and fire APs
- Sensory info is relayed to glomeruli
- Information is transmitted to higher regions of the brain
olfactory transduction
Similar to other G protein signalling cascades
leads to opening of cyclic nucleoside gated channels that are permeable to Ca and Na, leads to depolarization and opening of Ca activated Cl channels
Cl efflux and further depolarization and generation of APs
Olfactory bulb
Olfactory sensory neurons with the same type of receptor molecule project their acons into the same olfactory glomeruli
They synapse with mitral and tifted cells
Olfactory bulb also recieves input from several CNS areas via centrifugal fibres
Periglomerular interneurons synapse with centrifugal fibres and with mitral and tufted cells. Likely an inhibitory feedback loop
neural connections of the olfactory system
Olfactory bulb projects directly to olfactory cortex, not via thalamus as other sensory systems do
Olfactory bulb is part of the telencephalon - can be considered the primary olfactory cortex
piriform cortex
is the largest olfactory cortical area in humas.
activated by all olfactory stimuli but habituates rapidly
other olfactory projections
parts of amygdala involved. Affective response to smell and alfactory hedonics
hippocampus contributes to learning and behaviour
no known topographical organisation of olfactory bulb onto olfactory cortex
anosmia
inability to smell
many caues: anatomical, CNA tomour in cribiform plate, olfactory nerve damage
early sign of parkinsins that can precede motor symptoms, and in other neurological diseases too.
olfaction decreases with age
hypernosmia
enhanced sensitivity to smell - especially in pregnancy
olfactory hallucination
central origin
Epilepsy, psychiatric aneurism
loss of sense of taste
caused by smoking, xerostomia, hyperviscosity of saliva, systic fibrosis, brain damage, tumours, drugs
carotid body chemoreceptors
give information to carotid body and aortic body about chemical composition of blod
innervated by the glossopharynegeal nerve (9)
carotid sinus is a baroceptor
alpha rhythms
relaxed, awake, eyes closed.
busy wave
beta rhythm
opening eyes, being alert, even in dark.
Smaller and faster wave
structure of a taste bud
- 50-100 tase receptor cells in each bud
- apical end covered with microvilli that extend into the pore that is open to the external milieu
- 3-14 afferent nerve fibres per bud. One fibre may innervate more than one bud
- taste buds on three types of papillae: cirvumvallate papillae, foliate papillae, fungiform papillae
