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Block Three- Neurophysiology
Terms in this set (362)
What supplies blood to all four lobes? It's also the biggest, therefore commonly attacked during a stroke?
Middle cerebral artery
The parietal lobe
integrates sensory information from different modalities
The temporal lobe
auditory perception, semantics, memory (hippocampus)
The occipital lobe
visual processing (cortex)
Cranial nerve I
Cranial nerve II
Cranial nerve III
Oculomotor (eyelid & eyeball movements)
Cranial nerve IV
Trochlear (turns eyeballs down and laterally)
Cranial nerve V
Trigeminal (chewing, face and mouth pain and touch)
Cranial nerve VI
Abducen (turns eye laterally)
Cranial nerve VII
Facial (controls and most facial expressions, and secretes tears, salvia, taste)
Cranial nerve VIII
Cranial nerve IX
Glossopharyngeal (taste, sense carotid blood pressure)
Cranial nerve X
Cranial nerve XI
Spinal accessory (controls swallowing)
Cranial nerve XII
Hypoglossal (controls tongue)
separates frontal and parietal lobes
primary motor cortex
primary somatosensory cortex
In what order is the brain believed to have evolved?
1. Medulla Oblongata
What goes into the posterior horn of the spinal cord?
Sensory information (afferent neuron)
What leaves through the dorsal horn?
Motor neurons (efferent neurons)
What is the 3 divisions of the nervous system?
1. Sensory division
2. Integrative division
3. Motor division
What is the relay center of the brain?
What is the 3 major levels of CNS function?
1. Spinal cord level
2. Lower brain level
3. Higher brain or cortical level
What else does the spinal cord do? (other than being a signal carrier)
- walking circuits
- withdrawal circuits
- support against gravity circuits
- circuits for reflex control of organ function
What structures in the nervous system are considered in the lower brain level?
Medulla, Pons, Mesencephalon, Hypothalamus, Thalamus, Cerebellum, and Basal ganglia
What does the lower brain level control?
- arterial pressure
- feeding reflexes
- emotional patterns
The higher brain (cortical level) needs
help from the other levels
At what level do we 'live' at?
Higher brain or cortical level
main body of neuron
extends from soma to synaptic terminal (effector part of neuron)
projections from soma (sensory portion of neuron)
A- Bipolar cell
B- Pseudo-unipolar cell
C- Motor neuron of spinal cord
What is the resting membrane potential of neurons?
What ion controls the resting membrane potential of neurons?
What is electrotonic potential?
A graded potential ( a non-propaged local potential) that results from a local change in ionic conductance that when it spreads along a stretch of membrane, it becomes exponentially smaller (decrement)
What makes electrotonic potential different from action potentials?
- It's proportional to stimulus strength (graded)
- Not propagated but decremental with distance
- Exhibits summation
EPSP stands for
excitatory post synaptic potential
Which channels and ions can create an EPSP?
Cation channels (that conduct Na+, K+, Ca+2) or Na+ channels
What neurotransmitter is released with EPSP?
What are the chief excitatory transmitter in CNS? How?
glutamate- it opens cation channels
IPSP stands for?
Inhibitory post synaptic potential
How does spatial summation occur within EPSP?
A single presynaptic neuron lights up multiple spots via telodendria
Which channels and ions create IPSP?
K+ and/or Cl- ions
What neurotransmitter is released with IPSP?
What is the chief inhibitory transmitter in CNS? How?
GABA- it opens Cl- channels
Can excitation of a single presynaptic neuron on a dendrite induce an AP in the neuron?
No, just one isn't enough to reach threshold. You need multiple terminals to be excited simultaneously to create an EPSP
How long does a neurotransmitter open a membrane channel? How long do EPSP or IPSP last for?
Channels open for about 1 msec and EPSP/IPSP last about 15 msec
What is temporal summation?
One or more presynaptic neurons transmit impulses in rapid-fire order
EPSP are always... what is the change in membrane potential generated?
excitatory... +20 mV
IPSP are always... what is the change in membrane potential generated?
inhibitory... -5 mV
Facilitation occurs due to
events on presynaptic membrane
What is faciliation?
The increased transmitter release produced by an action potential that follows closely upon a preceding action potential
How does facilitation occur?
With prolonged elevation of presynaptic Ca+2 level following synaptic activity
Why does dendrites transmit electrotonic potentials instead of action potentials?
They have few voltage gated Na+ channels
About how long is the synaptic delay?
What are the three special characteristics of synaptic transmission?
1. Synaptic facilitation
2. Synaptic fatigue
3. Synaptic delay
What is synaptic fatigue?
Also called short term synaptic depression- happens when excitatory synapses are repetitively simulated at a rapid rate until rate of postsynaptic discharge becomes progressively less (protective mechanism for excessive neuronal activity)
What is the most common 2nd messenger mechanism?
G proteins (GPCR)
What are the two main types of neurotransmitters?
1. Small molecule that are rapidly acting
2. Neuropeptides that are slowly acting
Which small molecules are rapidly acting EXCITATORY transmitters?
Which small molecules are rapidly acting INHIBITORY transmitters?
Who has the highest cholesterol content?
A lot of the slow acting transmitters (neuropeptides) are
Neuropeptides are often co-released with
small molecule transmitters
What does acidosis do?
depresses neuronal activity
What alkalosis do?
increase neuronal excitability
Interruption of brain blood flow for how long causes unconsciousness?
5-10 seconds due to hypoxia
How does hyperventilation cause brain hypoxia?
1. Increased neuronal activity
2. Decreased CBF (vasoconstriction)
What happens with you have decreased CO2 levels in the brain?
Decreases even more (this can stimulate/help seizure activity)
What does mechanoreceptors detect?
What does thermoreceptors detect?
Changes in temperature
What does nociceptors dectect?
What does electromagnetic receptors detect?
What does chemoreceptors detect?
taste, smell, CO2, O2, etc.
How is sensation perceived?
It's determined by the characteristics of the receptor and the central connections of the axon connected to the receptor
What is the labeled-line principle?
A concept that each receptor responds to a limited range of stimuli and has a direct line to the brain
What are the 4 factors that generate receptor potentials?
1. Mechanical deformation- stretches the membrane that opens channels
2. Application of chemicals- opens channels
3. Change in temperature- alters membrane permeability
4. Electromagnetic radiation- changes membrane permeability to ions
Increased stimulus intensity causes increased receptor potential, which _____ AP frequency
Which receptor is the most rapidly adapting receptor in the body? What does it detect?
Pacinian corpuscle- it detects vibrations
Muscle spindles do no adapt which means
it has the same frequency even over a long period of time
Rate of adaptation varies with
type of receptor
Slowly adapting receptors are called
What does slowly adapting (tonic) receptors do?
Keeps the brain apprised of the status of the body with respect to its surroundings *
Rapidly adapting receptors are called
What does rapidly adapting (phasic) receptors do?
Predicting future position or condition of body, its very important for balance and movement
Which type of receptor has to be activated?
Rapidly adapting (phasic) receptors
What is a neuronal pool?
groups of neurons with special characteristics of organization (think of the brain as one giant neuronal pool)
What are the two types of divergence in neuronal pathways?
Amplifying and divergence in two tracts
What are the two types of convergence in neuronal pathways?
Convergence from a single source and convergence from multiple separate sources
Which type of convergence provides spatial summation?
Convergence from a single source
A lot of interneurons are _____ to prevent over-activity in the brain
What is reciprocal inhibition circuit?
Describes the process of muscles on one side of a joint relaxing to accommodate contraction on the other side of the joint. Since interneurons usually inhibitory it prevents the alpha motor neurons from firing- therefore reducing the contraction of the opposing muscle
What is reverberatory or oscillatory circuit?
Once an AP starts it can circle around and around 'forever' (due to positive feedback loop). Happens in the autonomic nervous system
How causes sudden cessation of reverberation in an oscillatory circuit?
fatigue of synaptic junctions
What is the mechanism of fatigue?
1. Transmitter depletion
2. Receptor inactivation
3. Abnormal ion concentration in axon
What does underactivity of synaptic sensitivity do?
Can lead to up-regulation of membrane receptors
What does overactivity of synaptic sensitivity do?
Can lead to down-regulation of membrane receptors (what happens to people addicted to painkillers)
What type of information transmission does ANS use to control vascular tone, gut tone, heart rate, etc.
Reverberatory circuits that do not fatigue
What are the two types of mechanoreceptors?
1. Tactile= touch, pressure, vibrations, tickle, itch
2. Proprioceptive= static position, rate of change
What are the 4 types of tactile receptors?
- Meissner corpuscles
- Pacinian corpuscle
- Ruffini corpuscle
Which tactile receptors have rapid adaptation?
Meissner Corpus and Pacinan corpuslce
Where are messiner corpus located?
Palms, sole of foot
Where are merkel discs located?
tip of epidermal ridge
Where are pacinan corpuscle located?
Dermis, deep tissues
Where are ruffini corpuscle?
What is the function of meissner corpus?
Motion detection and grip control
What is the function of merkel discs?
Form and texture perception
What is the function of pacinan corpuscle?
Transmitted vibration, tool use
What is the function of ruffini corpuscle?
Tangential forces, hand shape, motion detection
Pink- Messiner corpuscles
Green- Merkel discs
Blue- Pacinian corpuscle
Orange- Ruffini corpuscle
All tactile receptors are which type of nerve fibers?
What stimulates meissner corpus?
skin motion, low vibration
What stimulates merkel discs?
edges, points, corners, curves
What stimulates pacinan corpuscle?
What stimulates ruffini corpuscle?
What are the two types of free nerve endings?
Myelinated and unmyelinated
What type of adaptation does free nerve endings have?
What does free nerve endings detect?
pain, temperature (and itch in unmyelinated free nerve endings)
What are the two pathways for sensory afferents?
-dorsal column-medial lemniscal system
What is the dorsal column-medial lemniscal system?
- 3 neurons to sensory cortex
- decussates in medulla oblongata
- transmits touch, vibrations, position, fine pressure
- has rapid transmition with high degree of spatial fidelity
What is the anterolateral system?
- 3 neurons pathway
- immediately crosses over in the spinal cord
- transmits pain, thermal, crude touch, pressure, tickle, sexual sensations
- has low degree of spatial orientation
What are dermatome?
area of skin supplied by sensory neurons that arise from a spinal nerve ganglion
where viruses like to hang out
What does it mean that the somatosensory cortex has unequal representation of the body?
Things more important for survival have a higher representation in the body. Lips > face > thumb > hip > foot > genitals
What brodmann areas are associated with the primary somatosensory area?
What brodmann areas are associated with the somatosensory association areas?
What does the somatosensory association areas do?
Get the information from the primary somatosensory cortex and 'makes sense' of it all
What is hemineglect?
lesion of somatosensory area I that results in the patient being unaware of items to one side of space
What is asterognosis?
lesion of somatosensory area I that results in the patient being unable to recognize objects by touch
What is agraphesthesia?
lesions of somatosensory area I that results in the patient not being able to identify a letter/number being traced on the skin
Loss of the somatosensory association area results in
- inability to recognize complex objects
- neglect of contralateral world and even refusal to acknowledge ownership of contralateral body
How many layers are in the cellular organization of the cortex?
six (the higher the number the deeper into the cortex)
Vertical columns within the layers of the cerebral cortex detects
a different sensory spot on the body with a specific sensory modality
What is two-point discrimination?
The smallest distance between two points that can be differentiated by the somatic sensory system. It varies throughout the body due to differences in density of mechanoreceptors varies greatly
How does lateral inhibition improve two-point discrimination?
It's the capacity of an excited neuron to reduce activity of neighboring neurons, to improve degree of contrast (increases resolution)
What are the two types of pain?
fast and slow pain
Fast pain is also called
sharp pain (first pain)
How fast is fast pain?
.1 seconds after stimulus
Slow pain is also called
throbbing pain (second pain)
How fast is slow pain?
after 1 second or more after stimulus
Which pain is usually associated with bradykinin (tissue destruction)?
slow pain (second pain) (throbbing pain)
Pain perception is
the minimum amount of pain that evokes a report of pain
Pain tolerance threshold is
reached when the subject acts to stop the pain
Pain receptors ___ ___ ___ to the stimulus
do not adapt
What is the intensity of pain correlated with?
of tissue damage (not total amount of damage)
What causes ischemic pain?
-lactic acid buildup
What is bradykinin?
A peptide that promotes inflammation- it is the main cause of pain
What type of fiber transmits fast pain?
type A-delta fibers
What type of fiber transmits slow pain?
Type C fibers
What is the transmitters of slow pain?
Substance P (from type C fibers)
What is the transmitter of fast pain?
Glutamate (from A-delta fibers)
What tract does fast, sharp pain do?
Uses A-delta fiber in the neospinothalamic tract.
What happens in the neospinothalamic tract?
-Glutamate is excitatory transmitter of A-delta fibers
-The 2nd neuron immediately crosses when entering the spinal cord and then travels up anterolateral columns
What tract does slow, throbbing pain do?
Uses C-fibers in the paleospinothalamic tract
What happens in the paleospinothalamic tract?
-Substance P is excitatory transmitter of C pain fiber
-The 2nd neuron immediately crosses when entering the spinal cord and then travels up anterolateral columns BUT only 10-15% go up and terminate in the thalamus
Why can you not sleep when in pain? Especially throbbing pain?
Most signals terminate diffusely in reticular nuclei of medulla, pons, and mesencephalon. This is excitatory signal.
What is capsaicin?
It comes from chili peppers that deplete substance P from local nerve endings and relieves pain (think of orange is the new black)
The cortex is believed to determine the ______ of pain
How does the perception of pain change when you remove the somatic sensory areas of the cortex?
It does not change, pain impulses to loer areas can cause conscious perception of pain
What drug is used to counter the effects of opiate overdose?
What helps us fight pain all the time?
the endogenous analgesia system
How does narcan work?
In the endogenous analgesia system, it directly blocks the transmission of pain by hyperpolarizing the interneurons in the anterolateral system.
How does the placebo effect work with feeling pain?
You have slight control of the analgesia system of the brain and spinal cord in which you stimulate raphe nuclei to secrete serotonin that then stimulates enkephalin to go inhibit incoming type C and type A-delta pain fibers in the dorsal horn
How did the search of 'morphine receptors' start?
In the 1970s it was discovered you can inject morphine around 3rd ventricle it causes prolonged analgesia
Under extreme stress (an emergency)
major endogenous opiates are released to suppress the pain
What is the gate theory of pain?
Non-painful input closes the nerve "gates" to painful input, which prevents pain sensation form traveling up to CNS (cut your finger, first response to put pressure on)
Visceral tissues have few pain fibers so how do we feel the pain on a distant area of skin?
Intermingling of second order neurons in dorsal horn of the spinal cord (referred pain)
Where is heart pain referred to?
the neck, left shoulder/arm
Where is stomach pain referred to?
above the belly button
Where does pain fibers cross over compared to touch receptors?
Pain immediately crosses over in the spinal cord whereas touch receptors cross over at the base of brain
What is hyperalgesia?
Altered perception of pain (very sensitive) usually due to damage to nociceptors or peripheral nerves
What is tic douloureux?
disorder of trigeminal nerve (5th CN) that causes sudden onset of facial pain
What is Brown-Sequard syndrome?
Has two different types of symptoms:
What are the pain sensitive structures in the head?
-blood vessels of the dura
-middle meningeal artery
What is meningitis?
Inflammation of the meninges cause severe headache
How does a migraine occur?
Abnormal vascular phenomenon. Vasospasm followed by prolonged vasodilation, the vasodilation stretches covering of blood vessels
How do you have a headache when hungover?
irritation of meninges by alcohol breakdown products and additives
What allows you to automatically adjust your vision?
Zonule fibers and ciliary muscles
How is all fluid of the eye made?
By ciliary process
What does the optic nerve contain?
retinal ganglion cell axons and glial cells (about 1.5 million axons)
What is RI?
The refractive index= the ratio of speed of light in air versus speed of light in a substance
What does convex lens do?
Focuses light rays
What does concave lens do?
Diverges light rays
Why is it individuals with myopia see better when closer up to the object?
Because the focal point shifts back
What is diopter?
Power of a lens= how much a lens can cause focus
Where does 2/3 of the refractive power of the eye come from?
the anterior surface of the cornea
Where does 1/3 of the refractive power of the eye come from?
Lens- it's adjustable
What is the total refractive power of the eye?
What is accomodation?
The changing of the thickness of the lens, we automatically do this and this is necessary to focus image on the retina
What happens when you constrict ciliary muscles?
The lens becomes more round in order to increase the refractive power of the lens
What are the ciliary muscles under the control of?
Parasympathetic nervous system
What is prebyopia?
The inability to accommodate, caused by denaturation of proteins in lens, making lens less elastic
Who has the highest accommodation?
Children- it decreases with age
What is an astigmatism?
Unequal focusing of light rays due to an oblong shape of the cornea
What is normal vision called?
What is far sighted called? How is it corrected?
Hyperopia- a convex lens is used to decrease the focal length
What is near sighted called? How is it corrected?
Myopia- a concave lens is used to increase the focal length
What causes hyperopia?
A short eyeball
What causes myopia?
A long eyeball; you have no mechanism to focus distant objects on retina
As an object moves toward the eye, the rate of _____ stimulation increases, causing the ciliary muscles to _____, and the lens _____
As an object moves toward the eye, the rate of
stimulation increases, causing the ciliary muscles to
and the lens
What is the leading cause of blindness worldwide?
Cataracts- cloudy or opaque area of the lens caused by coagulation of lens proteins
What does 20/15 vision mean?
Someone can see at 20 feet what a person with 20/20 vision can only see at 15 feet
What is the aqueous humor?
The fluid chamber in front of the eye- it's free flowing
What is the vitreous humor?
The fluid chamber behind the lens; it's jelly-like
Where does fluid system of eye go?
Flows through the pupil into anterior chamber, then between cornea and iris, through the meshwork of trabeculae to enter the canal of schlemm which empties into aqueous veins and then into extraocular veins
How is the pressure of the eye determined?
By resistance to outflow of aqueous humor in canal of schlemm (air puff at the eye doctor)
What is the second leading cause of blindness worldwide?
Glaucoma- two types
-open angle glaucoma (most common)
-closed angle glaucoma
What is the appearance of all the cells in front of the retina?
Transparent so that light can pass
Where does the axons of ganglion cells go?
into optic nerve (makes up the optic nerve) (cranial nerve II)
How many rods, cones, and ganglion cells do we have?
100 million rods, 3 million cones, and 1.6 million ganglion cells
What has the highest visual acuity?
The fovea- the fovea centralis only contains cones
What is the ratio of cones to ganglion cells in the fovea?
Both rods and cones have ____ that undergo _____ that lead to vision
Both rods and cones have
that lead to vision
What is scotopic vision? What is responsible for it?
Night vision, rods produce
What is photopic vision? What is responsible for it?
Day vision, cones produce
Do rods or cones have higher acuity?
Cones because they have less convergent retinal pathways and concentrated in central fovea
trichromatic (red, blue, green)
The pigment layer of the retina is made up of? What is the purpose?
Melanin, so that light wont scatter
What vitamin is the pigment layer? Why?
Vitamin A, needed for phototransduction
What is the visual pigment in rods?
What is the visual pigment in cones?
Steps in visual phototransduction in rods?
1. Light comes in and hits 11-cis-retinol
2. 11-cis-retinol changes into 11-trans-retinol
3. 11-trans-retinol cannot fit inside the pocket within rhodopsin
4. Once 11-trans-retinol leaves, rhodopsin is now activated (now called metarhodopsin II)
5. Metarhodopsin II starts a 2nd messenger cascade
6. End result is hyperpolarization of the rod cell via closure of Na+/Ca+2 channels
What happens to 11-trans-retinol when it leaves the pocket inside of rhodopsin?
1st is travels to pigment layer where its recharged back into 11-cis-retinol. 11-cis-retinol now travels back to the rod and is conjugated to an opsin to form a
What is the visual pigment in ganglion cells?
What are the fat soluble vitamins?
D, E, A, K
Vitamin A is also called
Night blindness can occur in patients with GI absorption problem, why?
Vitamin A is fat soluble and is lost in feces, therefore no vitamin A means no retinol
What is the leading cause of preventable childhood blindness?
Vitamin A deficiency (up to 1/2 million children a year)
What is the resting membrane potential in the dark?
What is the resting membrane potential in the light?
What is happening with the flow of ions when its dark?
Na+ and Ca+2 are flowing into the rod/cone while K+ are flowed outwards
What is happening with the flow of ions when there is light?
When rhodopsin decomposes, Na+ and Ca+2 channels are closed so only K+ is leaving the cell= hyperpolarizes the cell to allow vision.
What are the steps that cause closure of Na+/ Ca+2 channels in phototransduction?
1. Light hits metarhopsin II
2. Activates transducin
3. Transduction activates cGMP phosphodiesterase
4. cGMP is destroyed
5. Lower cGMP closes Na+, Ca+2 channels
6. K+ still flows out
7. Membrane potential goes from -40mV to -70mV
Cone activation is _____ faster than rods
Cone activation is
faster than rods
Why does color blindness almost exclusively in males?
It's a genetic disorder that mostly passed along on X chromosome.
Lack of red cones is called
Lack of green cones is called
Lack of blue cones is called?
Deuteranomaly is when
Green wavelength goes from 533nm towards 564nm (red)
Protanomalous is when
Red wavelength goes from 564nm towards 533nm (blue)
All cells in the eye use _____ except for _____ that use APs
All cells in the eye use
that use APs
What does lateral inhibition do for the contrast border?
Sharpens it so that light can be more focused when coming into the eye
What are horizontal cells main function for the eye?
What is the optic disk?
The point where ganglion cell axons exit the eye to form the optic nerve (2nd cranial nerve). This creates a blind spot on the nasal side of the fovea.
What are the two functions of the lateral geniculate nucleus (LGN)?
1. Relay information to primary visual cortex
2. Gate control of information to primary visual cortex
What does and doesn't cross over in the optic chiasm?
-signals closest to temporal retina do not cross over
-signals from the nasal side cross over
Where does signals go after being in the optic chiasm?
Through lateral geniculate boy to the visual cortex via optic radiation
Relay function of the lateral geniculate nucleus (LGN)
It has 6 layers and each layer is responsible for one of the eyes in order for the information to not get mixed
Gate function of the lateral geniculate nucleus (LGN)
Has inhibitory input that controls the visual input that is allowed to pass into the cortex
The primary visual cortex lies in a
The fovea has several 100x more representation in the cortex compared to
peripheral portions of retina
Association areas do what?
Add clarity of what the signal means
What is the visual signal in the primary visual cortex is concerned with?
Mainly with contrasts in the visual scene
How is visual perception mediated?
By motion, depth/form, and color
Parasympathetic NS controls which part of the eye?
The ciliary muscles (focuses lens) and constricts the iris
Sympathetic NS controls which part of the eye?
Radial fibers of the iris and extraocular muscles, which opens the pupil
What part of the ANS controls accomodation of the eye?
Parasympathetic NS (exact mechanism is unknown)
What are the 4 hypothesis for parasympathetic control of accommodation?
1. Chromatic aberration
What is the pupillary light reflex?
Light hitting the retina causes a few impulses to pass from the optic nerve to pretectal nuclei to constrict the pupil
What is miosis?
When parasympathetic nerves excite pupillary sphincter muscles to constrict pupil
What is mydriasis?
Sympathetic nerves excite radial fibers of iris causing pupil dilation
What does atropine do?
Dilates the eye (by blocking parasympathetic effects by blocking muscarinic acetylcholine receptors)
What is binocular vision?
vision using two eyes with overlapping fields of view, allowing good perception of depth.
What is stereoscopic vision?
3D vision that occurs due to overlap of the eyes
What is retinitis pigmentosa?
Very common (about 1 in 4,000). Decreased peripheral vision (looking down a tube)
What is the function of the tympanic membrane?
Transmits vibration in the air to the cochlea (inner ear). It amplifies the signal about 17x
The tympanic membrane is connected to the
malleus, incus, stapes
What is the smallest skeletal muscle in the body?
stapedius (about 1 mm long)
What are the two muscles that attach to the ossicles?
stapedius and tensor tympani
What is the attenuation reflex?
A very loud noise causes both muscles in the ear to freeze the ossicles to prevent sound from reaching the cochlea (a protective mechanism)
How does humming help depress noise?
Through the stapedius reflex that lowers it about 20 decibel reduction in sound transmittion to the cochlea
Structure of cochlea
Filled with fluid and encased in bone
As long as you have a _____ then you can/will have_____
As long as you have a
then you can/will have
What does the basilar membrane within the cochlea do?
When sound comes in the stapes pushes against it, the round window pushes out to buffer pressure changes. This causes the fiber within to vibrate
What is the organ of corti?
receptor organ that generates nerve impulses, it has rows of stereocilia that generate APs in response to sound vibrations
Inner hair cells are what's thought to produce APs to have a sense of hearing when
the stereocilia is bent one way or another that depolarizes or hyperpolarizes the cells
What are the outer hair cells thought to control?
the sensitivity of the inner hair cells for different sound pitches
What is the place principle?
our perception of sound depends on where each component frequency produces vibrations along the basilar membrane
Babies and adults have the same sized
What are the only tastes we can taste?
sweet, sour, bitter, salty, umami
Where is the perception of sour?
On the side of the tongue
Where is the perception of salty?
Around the bottom edge of the tongue
Where is the perception of sweet and umami?
Both are on the bottom half of the tongue
Where is the perception of bitter?
the top half of the tongue
What is the threshold for sour perception?
What is the threshold for salty perception?
What is the threshold for sweet perception?
What is the threshold for umami perception?
What is the threshold for bitter perception?
.008mM or .0001mM
What are the most common type of taste bud, what does it sense?
Circumvallate papillae senses sour
What are the 3 types of tastebuds?
1. Circumvallate papillae
2. Foliate papillae
3. Fungiform papillae
How many receptors are on each taste bud?
What nerves innervate taste buds?
7, 9, 10
About how many days does it take for basal cells to give rise to taste cells?
about 12 days
Taste buds have
microvilli that is the place of transduction
Transduction of taste involves
G-protein coupled receptors and with voltage regulated Na+, K+, and Ca+2 channels
What is anosmia
No sense of smell
What is ageusia?
No sense of taste
What is the flow of odorants being sensed?
1. Up nares
2. Through olfactory epitheliumon cribriform plate
3. Through olfactory bulb
4. Through olfactory tract
5. Into brain
What are ORNs?
Olfactory receptor neurons- a true neuron (not usual)
What does bowmann's glands do?
Produce mucus that traps odorants
How long does it take basal cells to turn into ORNs?
About 45 days
How do you go from an odorant to an APs?
1. Odorant binds to receptor on cilia
2. G protein is activated
3. cAMP is formed
4. cAMP opens Na+ channels
5. Na+ comes into the cell and depolarizes it
How many more ORNs do bloodhounds have compared to humans?
What allows for many forms of anosmia to be termporary?
The constant regeneration of ORNs
What are the circuits that the spinal cords are responsible for?
-maintaining equilibrium (balance)
What comes in the dorsal (posterior) horn?
Sensory root (afferent)
What comes in the ventral (anterior) horn?
Motor root (efferent)
What are the two types of anterior motor neurons?
Alpha motoneurons and gamma motoneurons
Stimulation of alpha motoneurons excite
extrafusal muscle fibers (collectively called a motor unit) at the motor end plate
Stimulation of gamma motoneurons excite
intrafusal fibers within muscle spindle (a special type of sensory receptor)
Most neurons are?
Myelinated which allows them to have faster conductance velocity
Overview of interneurons:
- Most abundant
- Most signals from brain terminate on interneurons
What do propriospinal fibers do?
Sense the relative position of body parts and strength of effort used in movement (proprioception)
Extrafusal fibers make up
the bulk of muscle
Intrafusal fibers are encapsulated in sheaths to form
muscle spindles (runs in parallel with extrafusal fibers)
What does the muscle spindle sense?
Length and rate of change in length
What does the golgi tendon organ sense?
Tension and rate of change in tension
Muscle spindles provide what type of movement for large and small muscles?
For coarse movements in larger muscles and fine movements in smaller muscles (eyes, etc.)
What are the two types of intrafusal fibers within muscle spindles?
1. Nuclear bag- detects rate of length change
2. Nuclear chain- detects static changes in length
How many intrafusal fibers are in muscle spindles?
3 to 12
How does the muscle spindle work?
1. Stretch in muscle increases the length which stimulates 1a and II afferents
2. Type 1a fibers activate alpha motoneurons
3. Causes contraction and shortening of muscle (due to co-activation with gamma motoneurons)
4. Original stretch is opposed and muscle length is maintained
What would happen if you didn't have co-activation of alpha motoneurons and gamma motoneurons?
You would have no sensitivity to changes in length
How does static and dynamic response happen by?
-Static response is when the muscle spindle is stretched slowly
- Dynamic response is when the muscle spindle is stretched rapidly
Which afferents are responsible for static and dynamic responses?
1a afferent is responsible for dynamic response and 1a and II afferents are responsible for static response
How does the stretch reflex work?
1. Sudden tap causes stretch of muscle spindle
2. This stretch sends signals via 1a afferent to spindle cord
3. Excitation of alpha motoneuron
4. Sends a signal to contract and also send inhibitory signal to antagonist muscles to cause reflex
Which reflex is important for preventing jerkiness of body movements?
the stretch reflex
How does the patellar reflex work?
1. Strike knee with tendon hammer
2. Muscle spindle stretches in quadriceps
3. Type 1a afferent stimulates alpha motoneurons in L4
4. Hamstring relaxes via inhibitory neuron
5. Alpha motoneurons cause quadriceps to contract
6. Leg kicks
What is Westphal's sign?
Absence or decrease in patellar reflex
How can we change muscle length?
Via co-activation of alpha and gamma motoneurons that causes contraction of both muscle and ends of spindles
What does co-activation prevents what?
the spindle from being unloaded during contraction
When tension is high, the golgi tendon organ sends a signal by
What is the autogenic inhibition reflex?
A sudden muscle shut down when tension is too high (for protection)
How fast is information transmitted through the spinal cord to the brain?
What is the flexor withdrawal reflex?
A painful stimulus elicits an extensor reflex in opposite limb to lift the limb (step on a glass)
What is the blood supply for the whole brain?
cerebral blood flow
What is the anatomy of cerebral blood flow?
2 internal carotid and 2 vertebral arteries
Only 50% of people have a completed
circle of willis
CBF is what percentage of total cardiac output?
What does the brain use for energy?
glucose and glucose only (no fatty acids)
Glucose delivery to the brain does not depend on
Blood flow is higher to
Why is hypocapnia more important than hypoxia in CBF regulation?
Only in the brain does increased CO2 cause increased blood flow. CO2 undergoes bicarbonate reaction that releases more H+...... more H+ causes vasodilation
How does a lack of CO2 cause vasoconstriction?
Ions can not pass blood brain barrier but CO2 can easily diffuse through to brain tissue
What is hypocapnia?
What happens when brain activity goes up?
It also increases
What do 90% of synapses in the brain use as their transmitter?
Overview of astrocytes role in blood flow control:
- increased brain activity causes more glutamate to be in the brain
- excess glutamate comes in contact with an astrocyte
- triggers a Ca+2 wave
- increased Ca+2 releases prostaglandins
- PGs cause arterioles to dilate
- Results in increased blood flow
What happens to resistance and flow when pressure goes up in the brain?
Blood flow stays the same and resistance goes up
Cerebrospinal fluid is similar to
plasma (has the same osmolarity but less protein)
How much CSF is produced in a day?
What is the flow of CSF?
1. lateral ventricles
2. third ventricle
3. aqueduct of syluius
4. fourth ventricle
5. foremen of magendie
6. cisterna magna
7. subarachnoid space
Where is CSF produced?
By the choroid plexus and involves Cl- and Na+
How does subdural hematoma occur?
1.Hit to the head
2. You lose CSF out of arachnoid villi to relieve pressure
3. Sometimes that's not enough so ICP still increases (intracranial pressure)
4. ICP causes venous end of circulation to collapse
5. Increased pressure in capillaries
6. Brain tissue starts to swell
7. Pressure just keeps increasing due to positive feedback cycle
What is papilledema?
swelling of the optic disc due to ICP
What does the blood brain barrier have?
Special continuous epithelium cells that have tight junctions to not let anything through
What can transport through the BBB?
-small lipophilic molecules
What are the two types of strokes (cerebrovascular accident)?
What are the causes of ischemic strokes?
-Thrombosis (most common)
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