PSL - CNS and senses up until Lec 4 Flashcards
what make up the CNS vs the PNS
the CNS is made up of brain and spinal cord while the PNS is made of everything outside the CNS as it includes all neurons and parts of neurons outside CNS
how is the PNS further divided into
PNS is divided into the somatic nervous system which controls volunatry action using skeletal muscle and then the autonomic nervous sytem which maintain the viseral functions like heart rate and breathing
what is the enteric nervous system
it is part of autonomic nervous system which is controlled by digestion and movement of gut as it gets input from spinal cord but cna also work independentaly
What are the ventricles in the brain and what are they filled with
thereare 4 ventricles: 2 lateral vnetricals-one in each hemisphere-, third ventricle, fourth ventricle which are connected to spinal cord through central canal
all are filled with CSF
order the following from one with most number of neurons to least: CNS, enteric nervous system, and PNS
CNS has the most as the brain by itself contain around 86 billion and then the spinal cord has another 1 billion
PNS which has around less than 1 billion
ENS which has around 100-600 millions
What are glia cells
found in both CNS and PNS to protect and support neurons
how are the white and grey matters of teh CNS different
grey matter- have nerve cell bodies, unmyelinated axons, nd dendritis, the cell bodies are arranged in layers or in clusters called nuclei
white matter- consist of myelinated axons running in bundles called tracts
What are clusterrs of neurons called in PNS and what are bundles of axons called in PNS
cluster of neurons= ganglia
bundle of axons= nerves
how many segments does the CNS have and what do these segments consist of
there are 31 segments and each has pair of spinal nerves which consist of dorsal root and ventral root
How much energy does the brain utilizes
the brain make up around 2% of body’s mass but gets 15% of blood pumped by heart and consumes half of body’s glucose
even though that sounds like brain is using too much, thta is nothing compared to amount of energy other computers need that try to mimic teh brain
How does the CNS save energy
by limiting the communication of neurons since neurons communicate by sending AP down their axons, these AP takes lot of energy and energy supply to CNS support low rate of firing as it permits only 4% of neruons to fir in the cortex which is one spike every 6 sec
so communication is expensive and CNS has to use it sparingly
what is the difference between the dorsal root and ventral roots of the segment in spinal cord
dorsal root- carries afferent signal which is an incoming sensory signal and the dorsal root ganglion has cell bodies of neurons carrying these signals
ventral root- caries the efferent signal which is an outgoing one from CNS to body which also includes motor signals
dorsal= toward the back, ventral= toward the belly
where can the grey matter be found and where are the dorsal and ventral horns
the grey matter is in teh middle of spinal cord and has butterfly shape where it has ventrical and dorsal horn on each side
wht are the two nuclei in the grey matter
sensory nuclei- in dorsal horn because the signal arrive on dorsal root as somatic sensory nuclei get signal from skin and visceral sensory nuclei get signal from viscera , there is one somatic on eth right dorsal horn and one viseral one the left dorsal horn
efferent nuclei- are ventral, the autonomic efferent nuclei on the right ventral horn sends command to gland and smooth muscle and the somatic motor nuclei in leftventral horn send command to skeletal muscle
what are the 3 types of tracts that the white matter consist of
ascending tracts- carry sensory signal to brain, are mainly dorsal since sensory signal arrive at dorsal horn
descending tracts- are ones carrying signal from brain as they are mainly ventral, where the outgoing signal leave CNS
propriospinal tracts- stay in the spinal cord
How does the knee crack reflex happen when the physician hit the knee with rubber hammer
the hammer stretch’s a ligament below the kneecap and the snesory fibers carry this stretch news to dorsal horn and the sensory fibres send a branch up to teh brain but aslo excites neurons in ventral horn so those send signal out to the leg muscles to contract and counter the stretch so teh spinal cord ends up responding to stimuli without consulting the brain
\What are teh major six divisions of the brain
the cerebrum, cerebellum, pons, medulla, diencephalon, midbrain
What does teh cerebral grey matter include
an outer layer called cortex, limbic sysrtem, and basal ganglia to help control movement
What make up the brain stem and what are some of the main functions of the brain stem
brain stem consist of the medulla, pons, and midbrain and it is the main central center for any autonomic functions and reflexes like breathing, swallowing, vomitting, and regulating blood pressure
what cranial nerves arise from brain stem
cranial nerves III-X, XII,
What connects the 2 hemispheres
the corpus callosum whoch is large bundle of myelinated sheath
what are cranial nerves
the ones that enter and leave teh brain rather than the spinal cord, the information arrive or leave brain to go otr come from peripheray
What are the functions of the parts that make up teh diencephalon
thalamus- process information going to and from cerebral cortex
hypothalamus- regultes behavioural and endocrine and autonomic homeostasis ]
pituitary and pineal glands secrete hormones
what consist teh diencephalon
the thalamus, hypothalamus, pituitary, and pineal
What is cerebral lateralization
the idea of teh 2 hemisphere’s functions differing where the left hemisphere is more language and math while the right hemisphere is more spatial analysis
what are teh 4 lobes of the brain
frontal, temporal, occipital, and parietal
what is cingulate gyrus
part of limic system which is found in each hemisphere
what is the limic system
an evolutionary old group of brain regions which are the cingulate gyrus, amyglada, and hippocampus
it is concerned with motivation, emotion, and memory
What are the senses we are conscious of and which aren’t we conscious of
the consious sense are: 5 spatial sense where each has its own organ and are vision, hearing, equilibrium-sense motion, taste and smell , there are also 4 somatic senses which we are conscious of: touch, temperature, proprioception, and nocicption and are somatic because they share one sense organ which is teh skin
the unconscious senses are ones like blood pressure, lung inflation, blood glucose concentration, internal body temp, pH, etc
what do teh cells that have receptores to precieve stimuli do
these cells will convert stimuli into electrical signal and this conversion is called transduction
what are these receptor cells that are transducting the stimuli into electrical signal
these cells can be neurons like in vision or non neuronal epithelial cells like in hearing and even if they are neuronal, they may or may not fire an AP
the receptor cell is converting the stimuli into an electrical signal, what does that do to the rest of teh cell
this electrical signal is a graded change in membrane called receptor potential and depending on the change, it amy cause release of neurotransmitters to affect the neuron and if teh receptor is neuron, it can fire AP
does that mean receptor cells can only respond to the energy they are most responsive to
no, if the other stimuli are powerful, then the receptor cell will also be responsive to them
What is adequate stimulus
each type of receptor cell have it which is form of energy the receptor is most responsive to
how is receptor’s senstivity determined
by their receptor threshold which is teh weakest stimuli that will cause response and some photoreceptores can detect single photon of light while others might cause response only if there is at least 10 photons of light
how are receptors classified
according to their adequate stimuli:
chemoreceptores- respond to specific molecules/ions
mechanoreceptores- respond to mechanical energy like pressure, vibration, sound, gravity
thermoreceptores- respond to temp
photoreceptores- respond yo light
how is perceptual threshold different from receptor threshold
perceptual threshold is the weakest stimuli that will cause conscious perception in organism
What is stimulus modality
sensory neurons don’t just carry electrical and energy signals throughout the process, they also carry other aspects of the stimulus like its modality, which just means what is the type of stimulus, is it light/sound/touch/ect and sensory systems can indicate that by labelled lines which means modality is revealed by which axons carry signal( the neurons activated are in which pathway, like photoreceptores activity means it is a light stimulus)
What is teh idea od convergence
since many neurons are involved in sensory system, there are primary neurons which are the receptor cells or cells immediatly downstream of them, and those will synapse ontp secondary neurons, those secondary neurons may synapse into teritary ones and so on, but at any stage of synapse, amny presynaptic neurons will contact any one of post synaptic cell, so postsynaptic cell willhave convergence of signal from more than one presynpatoc cell and this allows higher up neurons to combine data from any receptor
How do neurons also represent intensity
intensity is teh strength of teh stimuli and neurons can also represent that in two ways:
1- population coding which means stronger stimuli will have more neurons activated
2- frequency conding where stronger stimuli can cause neurons to fire at faster rate
these two ways can also be combined like strong stimuli increasing fire rates and causing more neurons to be active
What does it mean when cells have dynamics
that means their activities don’t depend on stimuli only but also on how the stimuli is changing over time
What are the three different dynamic in cell
phasic cell- cell responding breifly to any change and then ceasing firing
tonic cells- cell maintaining their activities when stimulus doesn’t change so they carry info for signalling at present levels
phasic tonic- react to change but doesn;t return all the way to zero firing when stimmulus is constant so they carry information about the steady level
What type of dynamic do retinal cells have
phasic as they report change in your visual world when somthing moves, but if everything is constant, then there is nothing reporting
Why are phasic signalling more efficient
because tehy make communication more efficient since it is reporting temporal changes which are changes through time
What are spatial changes
another efficinet way of reporting changes but it is changes between neighbouring regions of space, also known as contrast where there is strong contrast in edges
What is lateral inhibition
it is when cells inhibit their neighbors or inhibit cells their neighbor’s excite and this can help sensory systems accentuate edges
do all sensory pathways run through thalamus for higher processing nd then go to their prospective regions
no, most pathways run though thalamus but olfactory pathwyas dont and equilibrium pathways project mainly to cerebellum
What does it mean by brain making inferences
since the brain has to guess most of the time about the things around it, it can be fooled and mistrust coinsidences to mean something else
What is lens
it is a transparent disk that focuses light and suspended by ligmants called zonules, it also divides the eye into 2 chambers: antyerior chamber is the one in front of the lens which is filled with aqueous humor and behind the lens is the vitrous chamber which is filled with the vitrous body(clear jelly that help maintain eyeball’s shape)
What is the cornea
transparent buldge at front of the eye which is continous with the white of the eye (sclera- outer wall of teh eyeball) AND LIGHT ENTERS EYE THOUGH THE CORNEA
What is retina and how does light go through teh eye
retina is inner lining of the eye that contains teh photoreceptores and the cornea with the lens focus the light on retina
the light passes from cornea to lens throufh hole in iris called pupil
How does the pupil adjust with light
pupil can change size: in bright light it constrict to reduce the light reaching lens and in teh dark it dilate 20 times bigger to let more light in
what controlls the pupil size changes
the smooth muscles in iris where in bright light the parasympathatic signal from brain contracts the ring shaped pupilary constrictor muscle shrinking the pupil and in teh dark it is the sympathatic signalling from brain that contract the radial pupilary dilator muscle of teh iris dilating pupil
What does it mean by pupil helping focus light
small pupil ensures that each point on retina recieve light from just one direction in space and that is what focusing mean
How is depth of field controlled by pupil
when pupil constrict, we have full depth of field as everything seen is equally in focus and when pupil is dilated, we have shallow depth of field as only object near one specific distance are oin focus
Why does bending of the light occur in refraction
because light hits medium with different refreactive indecs like the one between air and collagen of the corneas
What is the structure of teh lens
it is a mesh of long cells without nuclei, packed with clear proteins called crystallins and zipped together in concentric layers for flexibility and have no blood supply but absorb nutrients from aqueous humour
How is the problem of using pupil alone to focus light fixed
using refraction which is light bends when it enters medium with different refractive index
Is lens a concave or conves shaped
lens is convex shaped which is fatter in middle and thinner at edges to make light rays converge to focal point
What structures of teh eye are responsible for the refraction of light
cornea is repsonsible for 2/3 of the refraction due to its different refractive indeces and 1/3 of refraction is due to the lens which changes shape to adjust focus
How does rounding the lens affect light rays
rounding the lens will bend the light more and so has closer focal point and to have clear vision, the focal point must fall on retina
How does angle at which the light rays hit teh medium of different indeces affect refraction
it depend on angle at which light rays hit interface between media which it the angle at which it hits lens surface and the angle depend on shape of teh lens and directions of light ray
it it strikes lens at right angles, then it doesn’t bend at all
What will happen if teh object get closer but the lens doesn’t change shape
if object draw closer and the lens doesn’t get rounder then the focus fall behind the retina, teh focal point isn’t on retina so vision is blurry
How does ciliary muscle get affected by signals from nervous system to change shpae of the lens
parasympathetic input from brain contract teh ring shaped ciliary muscle reducing tension in zonules and make lens rounder so light rays bend more and focal points move forward
sympathatic input will relx ciliary muscle making lens flatter for far vision
what is accomodation
rounding lens fro near vision and the closest point a person can focus is called near point accomodation
What is the issue with hyperopia and how is it fixed
this is also known as far sightedness where focal point fall behind retina so cna see object far but not close one because focal point falls behind retina
solved with convex lens because the lens of the eye isn’t beinding enough light rays so extra convex help out with bending the light rays for the eyes
What is presbyopia
when with advance aging the lens stiffens and hinders accommodation
what is the issue behind myopia and how is it fixed
also known as near sightened where the focal point falls in front of retina so can see close things but not far ones and solved with concave lenswhich causes light rays to disperse so they counteract the too much bending of light rays by the eye’s lens by spreading rays out slightly
What are photoreceptores
they are in retina and are light sensitive neurons that convert light into electrical energy in cells and this conversion is called phototransduction
what is fova’s role
use fovea for detailed vision, 5 degrees away from its centre
What are the two types of photoreceptores in the retina and how are they different
they are teh cones and rods, cones are around 6 million and rods are 120 millions and are neurons but don’t fire AP, they respond with membrane graded potentials
how are photoreceptores distributed in retina
they are distributed non uniformily where they are mosly dense packed in macula which is a central disk that have central pit called fova
what is the structure of the cones and rods
they both share similiar structure:
outer segment- membrane folds into disk like layers which contain the visual pigment that respond to light
inner segment- where teh nucleus and organells are for protein synthesis and in basal layer have synapse that release glutamate
how do photoreceptores detect light
using membrane bound visual pigments, these pigemnts change shape when l;ight hit them starting chemical cascade that hyperpolarize the cell which reduces the release of glutamate
what is teh type of pigment in cones and rodes
cones have rhodospin and there are 3 types of cones with each having its own type of pigemnnt
what is the characteristics of the blind spot
there are no receptores in it and that hole is where axons carrying visual information exit eyeball to form optic nerve
How are the cones and rods different when it comes to light detection/sensitivity
cones are for bright light while rods are for bdim light that is because cones are less sensitive than rods and are responsible for vision in bright light and for distinguishing colours but they don’t operate in dim light so the ones that will take their place in dim light will be the rods that cna detect single photons but operate only in low light as their rhodopsin is broken down in daylight so they don’t sense light
how is the distribution between rods and cones in the eye
the fovea contains mainly cones while the peripheral retina contains mainly rods and that is one of the reasons why the peripheral retina is more sensitive to light than fovea
what makes up the three layers of neuron in retina and how is convergence utilized in there
the photoreceptores make up teh first layer that will synapse onto bipolar cells which make the second layer and those bipolar cells will synapse onto ganglion cells which make up the third layer
as the synapse go from photoreceptores to ganglion, convergence is used so that the 126 million photoreceptores are condensed into 1 million ganglion cells as
up to 45 photoreceptores converge onto one bipolar cell and then 2 bipolar cells converge onto one ganglion cells in peripheral retina and least in fovea where one bipolar synapse onto one ganglion
how does the receptive field for bipolar cells look like
every neuron in visual system has receptive field also called visual field which is region of retina where light affect the cell’s activity and bipolar cells have a center surround fields with round center regions and doughnut shaped surround
what are the two types of bipolar cell receptive fields
on center and off center
on center= excited by light in center of their fields and inhibited by light in surround so they respond when light spot fill their center and surround is dark
off center cells= inhibted by lught in center and excited by light in surround so they respond when dark spot fills their center and surround is light
when do bipolar cells react the strongest
when lighting is not unifrom so there is contrast and that is because when light is uniform, bith types of bipolar cells (on and off center) are nonresponsive because the effect of center and surround cancel so cell is at its resting level of activity and evcen when bipolar cells respond, they respond with graded membrane potential
How do ganglion cells contrast and compare with other layers of cells in retina
they get synapsed by bipolar cells biut unlike photoreceptores and bipolar cells, they do fire AP but like polar cells they mostly have center surround receptive fields and these fields are also on and off center so they best respond to contrast
how does ganglion cell being positioned in different part of retina, either in fovea or peripheray affect their receptive fields
ganglion cell near fovea gets input from only few photoreceptores and are mostly cones and they are less sensitive to light but has better spatial resolution since they are getting input from less densly packed cones while in peripheray, the ganglion cell is very sensitive to light but poor at resporting spatial detail because it is getting info from wide number of rods
What are the three classes of ganglion cells based on how their signals is used in brain
magnocellular ganglion cells (Mcells) which provide info that is used by brain to infer movement of object and these cells are phasic
parvocellular ganglion cells (Pcells) provide info used to infer form and fine details
melanopsin ganglion cells, make up 1% of ganglion cells, are photoreceptores with their own pigemnt called melanopsin and tbhey project to suprachiasmatic nucleus
how is optic nerve formed
each of the million ganglion cellls in each retina send their axon out the back of eye through blind spot and these fibres from each eye form their own optic nerve aka as cranial nerve II
what is optic chiasm
when each of the optic nerve reached this point called optic chiasm, half of its fibres cross to the other side and fibres from nasal half of each retina cross
Why do the fibres cross
that is because in the eye, the right of the scene projects onto half side of each retina which is the nasal side of right retina and temporal side of left retina so because nasal fibres cross, all information from right hemifield come together in left cerebral hemisphere and vice versa
how does info from chiasm then travels
the info move from chiams to thalamus and then to cortex as teh nerve bundle emerges from chiasm are now called optic tracts which ends in 2 lateral geniculate nuclei in thalamus which projects via the optic radiation to primary visual cortex snd together the 2 LGN have aroudn 2 million neurons while V1 have around 300 million in occipital lobe
how is the arrangement of cells in retina related to the neurons in brain
many areas in the brain are organized retinotopicallu as neurons close to each other in brain get info from close together parts of retina but it doesn’t preserve area, even though fovea is small area opf retina, it projects to large area in V1 and other cortical regions and LGN and those large proportions of visual cells in brain receive and process data from foveal photoreceptores and one of reasons fovea get such a large space in brain is because it has many photoreceptores, bipolars, ganglion cells, etc.
