Sensory Flashcards
Major divisions of the nervous system - afferent
Sensory input:
-cell bodies out of CNS
-cranial nerves (somatic, visual, olfactory, taste, auditory, vestibular)
-spinal nerves (somatic sensation - touch temp and pain) visceral senstation (info from internal organs)
Major divisions of the nervous system - efferent
Motor output:
-Cell bodies out of CNS
-Cranial nerves
-Somatic efferent (innervates skeletal muscle, motor neurons - solely excitatory)
-Autonomic efferent (innervates interneurons, smooth and cardiac muscle - both excitatory and inhibitory)
-Enteric
Division od the spinal cord (top to bottom)
Cervical nerves (upper limbs and neck)
Thoracic “ (upper trunk)
Lumbar “ (lower body)
Sacral “ (digestion and genitals)
Coccygeal “
How many cranial nerves are there?
12
What is a brain edema? result?
Increased intercranial pressure pushes the brain out of the base of the skull (brain swelling)
Compresses the brain stem and the cranial nerves (affects puppillary response
Describe the early development of the nervous system + timeline
Ovum (fertilized egg) - ball of cells - blastocysts - formation of cavities - neural plate (over 3 weeks)
Development of the neural tube + timeframe
Neural plate is compose of 3 things: ectoderm (also known as the neural plate), mesoderm and endoderm
Ectoderm folds up to form the neural groove - closes up to form neural tube
Mesoderm becomes dura
Neural tube becomes CNS
Neural crest becomes PNS
Over week 3 and 4
What develops in the neural tub ine week 4? What is the overall morphology?
Vesicles develop : become the forebrain, midbrain, hindbrain and then a tail (with cavity)
What does the neural tube become?
CNS
Over development what does the forebrain become
Cerebral hemispheres, thalamus
Over development what does the midbrain become
Remains as the midbrain
Over development what does the hindbrain become
Pons, cerebellum, medulla
Over development what does the tail&cavity of the neural tube become
Spinal cord, with the cavity forming the ventricles and the central canal
Ventricles - what, where, what do they contain?
Openings within the brain, containing 150mL of cerebral spinal fluid.
Formation of the cerebrospinal fluid? Where, rate + how is it circulated
Within the choroid plexus
Rate of 500ml/day
Passive
Functions of cerebrospinal fluid?
1) Supports and cushions the CNS (brain) - buyoancy of CSF is the same as CNS
2) Provides nourishment
3)Removal of metabolic waste by the arachnoid villi
Composition of cerebrospinal fluid
Sterile, colorless fluid containing glucose
Circulation of CSF within the CNS?
Formed in choroid plexus in two latera ventricules
Into third ventricule via choroid plexus, down cerebral aqueduct (midbrain) into the fourth ventricule.
Exit process of CSF?
Fgrom the fourth ventricule, passes through 2 foramens of Luksha and one of Magendie (located in the central canal - midbrain) to enter the subarachnoid space
Encounters the arachnoid villi, drains back into the venous blood supply via a cavity in dural sinus
What are the 3 meninges? (def + names)
The three layers of the CNS (protects brain + spinal cord)
Dura matter (1st)
Arachnoid membrane (2nd)
Pia matter (3rd)
Layers from outside into the brain
Skin
Bone
Dura matter
Arachnoid membrane
Subarachnoid space (CSF flow + blood vessel + trabeculae)
Pia matter
Grey matter
White matter
What is the dural sinus? Role + location
Cavity lining central midline of head + opening of dura
CSF return to venous blood supply
Located after the arachnoid villi between the left and righ hemisphere, within the Dura
How does the brain access its glucose requirement?
Glucose is metabolized by neurons, and is transported in by the blood (15% of blood supply)
There is essentially no glycogen (glucose storage in the brain)
How does the blood get from the heart to the brain?
Heart splits into
-aorta (body - 85% of blood)
-carotid artery (brain) into external carotid artery (outside of skull) and internal carotid artery (base of the brain)
-the vertebral artery (x2) join into basilar artery
All joins into the circle of willis into brain
What is the blood brain barrier (BBB)?
Morphology
-semipermeable membrane that protects the brain from harmful substances in the blood while allowing essential nutrients to reach the brain
-capillary wall
-Foot process of astrocytes and endothelial cells (with tight junctions)
What does the BBB allow for passage of?
Water, CO2, O2, lipid soluble substances
Ions
Active transport of glucose and some a.a.
What are astrocytes?
Role
Non neuronal cells in the CNS
Support neurons
maintain homeostasis by ion (neurotransmitter) debris collection
contribute to the blood-brain barrier (BBB) by inducing tight junctions
structural support
What are the two components of the perception of the external world?
Sensation: awareness of sensory stimulation
Perception: the understanding of a sesnsations meaning
“perception of the neural activity that is produced by sensory stimulation”
What is the law of specific nerve energies?
Regardless of how a sensory receptor is activated, the sensation felt corresponds to that of which the receptor is specialized
(e.g: rub your eyes and you will see light)
What is the law of projection?
Regardless of where in the brain you stimulate a sensory pathway, teh sensation is always felt at the sensory receptors location (e.g. phantom limb pain)
What are sensory inputs represented by?
Labeled line code: the brain “knows the modality (type) of stimulus and the location of every sensory afferent
(this is the summary of the specific nerve energies and projections)
What is the general process for sensory receptors to produce afferents?
1) adequate stimulus energy (external energy activates receptors) (specificity)
2) hits receptor membrane
3) transduction occurs to convert stimulus energy into
4) ion channel activation sends action potentials by
5) afferents to the CNS
How is stimulus energy converted to afferent activity?
Stimulus of energy depolarizes receptor membrane , causing action potential (increase in stimulus energy increases number of action potentials) which propagate down sensory receptor, causing release of neurotransmitter
Three types of afferent response?
Non adapting |||||||||
Slowly adapting ||| | | | |
Rapidly adapting || | |||
(on-response, off-response)
What is the receptive field?
The region in space that activates a sensory receptor or neuron
What is a population code?
produced by overlap of receptive fields
(method in which the brain uses the activity of many neurons to encode and process information, with each neuron having a receptive field)
What is stimulus acuity?
Ability to differentiate one stimulus from another
(how close can two pins be before you think there is only one)
Relationship between stimulus acuity and RF size?
Small RF = high acuity
Large RF = low acuity
What sharpens sensory acuity? Term + definition
Lateral inhibition = neural process that occurs when an excited neuron reduces the activity of its neighboring neurons (inhibitory interneurons)
Where has the highest and lowest sensory acuity?
Fingers and lips have highest
Legs and feet have lowest acuity
What shapes sensory input?
Bottom up and top down mechanisms
“descending pathways modulate sensory inputs”
presynaptic inhibition by inhibitory neurons coming down from the CNS
What does the somatosensory system do?
processing tactile recognition, body perception, and motor actions
Receptor classes of the somatosensory system?
Mechanoreceptors
chemoreceptors
thermoreceptors
nociceptors (harmful stimuli)
4 mechanceptors types of the somatosensory system?
and whats the other polymodal component
Meissner’s corpuscle
Merkels disk
pacinian corpuscle
ruffini endings
+ free nerve endings
Physiology, type of receptor and role of: Meissners corpuscule
FLuid filled structure enclosing the nerve terminal
Rapidly adapting
Light stroking and fluttering
Physiology, type of receptor and role of: Merkels disk
Smal epithelial cells surrounding nerve terminal
Slowly adapting
Pressure and texture
Physiology, type of receptor and role of: free nerve endings
Unencapsulated dendrites of sensory neurons
Thermoceptors, mechanoreceptors, nociceptors
Polymodal
Physiology, type of receptor and role of: pacinian corpuscle
Large concentric capsules of connective tissue around nerve terminal
Rapidly adapting
Strong vibrations
Physiology, type of receptor and role of: ruffini endings
Nerve endings wrap around spindle like structures
Slowly adapting
Stretch and bending of the skin (shape of an object)
What is proprioception? What part of the body is responsible for it
sense of static position and movement of limbs and body
muscle spindles
What activates the mechanoreceptors?
Stretching of cytoskeletal strands pulling ion channels open
What activates the two types of thermoreceptors?
ion channels respond to temp ranges
cold afferents: 0-35 activated by menthol
hot afferents: 35-50 activated by capsaicin and ethanol
What receptor type does extreme temp activate
pain receptors (nociceptors
Nociceptors: what/where, respond to
Enhanced or suppressed?
Free nerve endings containing ion channels
Mechanical deformation, excessive temp, chemicals (things capable of causing damage)
Highly modulated, both enhanced and supressed
What activates visceral pain receptors?
Inflammation
Describe the initial pain response steps of nociceptors (4)
1- stimulus energy from injury
2- activation of nociceptors causes action potentials
3- subtance P gets released into the spinal cord
4- sends impulse to the brain
Bottom up mechanisms (2) enhancing nociceptors? why?
-enhancement of surrounding nociceptors by injured tissue and afferent feedback onto mast cells
-dilation of nearby blood vessels (swelling - increases sensitivity)
increases pain and swelling to prevent usage of limb during the healing process
Where is somatosensory input sent to?
The somatosensory cortex, located behind the motor cortex and central sulcus
What is reffered pain?
How does it happen?
pain that is felt in a part of the body that is different from where the pain originates
visceral and somatic pain afferent commonly synapse on the same neurons in the spinal cord so the perception of pain can activate the pain afferent of another location
**shared secondary neurons
Whats the link between pain and presynaptic inhibition?
Presynaptic pathways can reduce pain in the body : descending pathways will release opiate neurotransmitters, preventing the release of substance P in the spinal cord.
Pathway of light through the eye
cornea -> pupils -> lens -> vitreous humor -> retina (location of photoreceptors) -> optic nerve
Purpose of the optic nerve?
Axons emerging from the retina transporting info to the brain
The optic disk is the ______
blind spot
The fovea centralis is the location of ______ , meaning it has the ___________
highest visual acuity ; smallest receptive fields
Role of the lens?
Refracts light to one point (bending from one medium to another)
What are the two components of the eye refracting light?
Which of the two has more impact, which changes shape
The lens and the cornea
The cornea refracts light more than the lens
The lens can change shape, allowing for change in focus
What accomodation does the lens have based on object position? How?
If the object is far , the lens flattens out
If the object is close, the lens becomes more round
The ciliary muscles control the lens shape
Myopia? Corrected by?
Bad far eyesight, corrected by concave lens
Nearsightedness
Hyperopic? Corrected by?
Bad close vision, corrected by convexe lens
Farsightedness
Astigmstism?
The lens or the cornea are not spherical
Presbyopia?
The lens gets stiff and is unable to accomodate for near vision
Cataract?
Change in lens colour
Where in the eye are photoreceptors located? Why? What are the two type?
At the back of the retina, next to the retinal pigment epithelium.
For biochemical reasons
Rods and cones
Describe the organization of the retina?
Vitreous humor -> ganglion cells -> … -> photoreceptors -> retinal pigment epithelium
What is special about the retina organization at the fovea centralis? Why?
The retinal circuitry is shifted out of the way to prevent distortion of the light on its away to the photoreceptors
Role of the ganglion cells?
(Optical system)
Converges the input from all the photoreceptors, becomes the optic nerve
Describe the process occuring when photons hit the photoreceptors
not within the photoreceptors but after
Transduction occurs (stimulus is converted, causing the closing of ion channels) causing:
Change in neurotransmitter release
Processing and convergence of action potentials
Output from ganglion cell, becomes the optic nerve
Describe the physiology of the rod, as well as what photons hitting the rod do to the ion channels
Outer segment (pointed towards retinal pigment epithelium): catches photons via stacked discs.
Inner segment holds ion channels: open in the dark, closed when hit with photons
How does phototransduction work?
- Light hits opsin molecule
- Activation of G-protein cascade
- Converts cGMP to GMP
- cGMP gated sodium channels close - action potential cannot be generated.
What is the effect of light on photoreceptors?
Hyperpolarization
Rod properties? (5)
High sensitivity, used in night vision
More rhodopsin to capture more light
High amplification (one photo affects many Na+ channels)
Slow response time
More sensitivity to captured light
Cone properties? (5)
Low sensitivity, day vision
Less opsin
Lower amplification (effect of photon on Na+)
Faster response time
Most sensitve to direct axial rays
Properties of rod system (2)
Low acuity, highyl convergent, not present in fovea
Achromatic (one type of opsin - rhodopsin
Properties of cone system (2)
High acuity,highly concentrated in fovea
Chromatic (3 types of opsin, responsible for colour vision)
Explain dark adaptation
Birght light to dark light
Cones deactivate, causing temporary blindness until
Rods previously inactivated by teh high quantity of photons hiting the rhodopsin gradually activate
Explain light adaptation
Dark light to bright light
Cones are inactive in the dark (not enough light for opsin to activate)
Bright light saturates rods, temporary blindness occurs until cones take over
(i think rods still contribute after the initial saturation)
What happens during phototransduction during light and dark adaptation?
Light breaks the bond between opsin (protein) and the retinene (chromophore) by hyperpolarizing the photoreceptors. Is it then put back together by the retinal pigment epithelium
Why is there a delay during light to dark or dark to light adaptation?
It takes a while to put the opsin and chromophore back together
What is the role of the retina?
Reports the relative intensity of light by detecting the differnce in the # of detected photons (via the photoreceptors within it)
What are the types of visual receptive fields and what causes them to fire action potentials?
They are center surround receptive fields:
-excitatory center, inhibitory surroundings (activated by light hitting just teh center, inhibited by light hitting just the surroundings, uniform light has no effect as there is no contrast
-inhibitory center , excitatory surroundings (opposite effects, uniform light is the same)
What is chromatic sensitivity and what is it determined by?
the ability to see chromatic colors - opsin molecules (blue cones, green cones, red cones)
How do we see brightness and colour?
Retinal ganglion cell have colour opponent receptive fields - the output of the retina encodes relative values of brightness and colour (B-Y) (R-G)
What does the amplitude of the sound wavelength dictate?
The loudness
What does the frequency of the sound wavelength dictate?
The pitch
What is a decibel?
A unit used to measure the relative loudness of sounds
sound pressure / reference pressure
What amplifies the sound within the ear?
Skeletal muscles - malleus, incus, stapes
Path of sound energy through the ear
Tympanyum -> malleus -> incus -> stapes
oval window
Scala vestibuli -> helicotrema -> scala tympani (filled with fluid that decompresses out the)
round window
What effect does the sound energy have?
Creates motion in the basilar membrane (lining the cochlear duct - also known as the scala media) between the scala vestibuli and the scala tympani.
Motion is frequency dependent
How does sound energy become neuronal energy?
Causes motion in the basilar membrane, which is converted to neuronal energy in the organ of Corti (located within the cochlear duct, sitting on the basilar membrane)
Name of the three flui-filled compartments of the ear?
Scala vestibuli, cochlear duct (or scala media) and the scala tympani)
eEffect of basilar membran deflection (up&down motion)
Produces shearing of hair cell stereocilia - this triggers the transduction process
What helps to amplify the movement of the basilar membrane? THEORY
Hair cell electromotility (almost acts like a muscle)
Properties of stereocilia ion channels?
How are action potentials triggered?
-Ion channels are located on the end
-Tip links connect each stereocilia, allowing for organization by height
-Ion channels are gated by these tip links
-Movement of stereocilia pulls the channels open, allowing the entry of K+ into the cells
**due to this link of sound energy to mechanical energy, they are considered to be mechanoreceptors
-The cell being depolarized alloweds for entry of Ca2+ into the cell, causing neurotransmitter release onto afferent neurons
Which movement allows for the opening of the K+ channels on the stereocilia?
Movement of small to large
Tinnitus? Two types + where it originates from
Transiet (<24h): usually due to loud noise, excessive mechanical stress of stereocilia causes tip links to break, but they’ll grow back
Chronic: predominantly cause by loud noise, originates in the inner ear, nerve or central pathways.
What are the three vestibular organs (+ category)
Semicircular canals (angular acceleration)
Utricule (horizontal) & saccule (vertical) (linear acceleration)
What is the vestibular ocular reflex?
reflex that stabilizes the eyes during head movements
What are semicircular canals and explain their vestibular role
Fluid filled cavities in the ear: Movement of the head causes the cupula, and thus the stereocilia to be bent on the ampular (inner edge of the bump in the semicircular canal), pulling open ion channels to activate vestibular system and maintain balance and orientation
What are utricule and saccules and explain their vestibular role
utricule and saccules are fluid filled compartments in the ear containing otoliths, connected to stereocilia. Movement caused the otoliths to lag, bending stereocilia. Vestibular system is activated
How many taste buds does an individual have?
~10,000
Explain the morphology of the taste bud by the flow of chemicals causing you to taste things
Contained in the papillae (bumps on the tongue), the chemicals dissolved in saliva (food or wtv) enter the taste pore, into the taste cell, taste bud and then into the taste afferent
How many taste transductions are there?
5 - umami, salty, sour, bitter, sweet
Explain transduction for: umami
Activation of glutamate receptors causes G-protein cascade
Explain transduction for: salty
Dissolved sodium causes transduction - Na+ flows through ion channels
Explain transduction for: sour
High acid content (dissolved H+ ions) causes H+ flow in,, Na+ flow in and K+ out
Explain transduction for: bitter
Blocks K+ leak channels, activates various g protein cascades
Explain transduction for: sweet
Triggers G-protein cascades
How does olfactory signal transduction work?
1) odorant binds to oderant receptors
2) G-protein activation
3) Opening of ion channels
Where does the olfactory pathway lead to? In what way does it differ from all other sensory pathways?
It runs straight to the limbic system (link of smell to emotional response)
Skips the thalamus
