CNS/sensory 2 - blood/sensory Flashcards
what is usually the only substrate metabolized by brain
glucose
what is very little in the brain
Glycogen
what does brain need
continuous supply of glucose and oxygen (to metabolize glucose constantly)
brain does not store glucose so it needs constant supply
does glucose transport into brain require insulin
no
what happens when diabetes
if too much insulin = affect formation of nervous system
makes them act drunk - too much insulin = causes glucose to be absorbed by tissues = not enough for brain
can get a candy and eat sugar to bring glucose back
how much blood does brain receive
15% of total blood
but 2% of total mass
blood hog
body will do everything it can to keep glucose flowing to brain - breaks down muscle/fat
what happens if blood supply interruption
loss of consciousness
a few mins = neuronal death - stroke - neurons die
describe flow of blood supply to brain
common carotid artery - branch off aorta
vertebral artery - carry blood to brain (and vertebrae/brain stem)
internal carotid artery = base of brain
external carotid artery = outside head, arterial blood to outside surface of head
what is basilar artery - brain blood supply
2 vertebral arteries join and form basilar artery
what is circle of willis
basilar artery + 2 internal carotid arteries join at base of brain
forms loop
what does circle of willis act as
- safety factor
- allows blood to be shunted from one side to other side like if arteries are not doing well = other side compensates
describe CSF and blood circulation
CSF
heart to choroid plexus –> (ventricles) subarachnoid space –> (arachnoid villi) dural sinus –> venous system –> heart
blood
from heart –> vertebral and carotid arteries –>
(basilar artery) circle of willis (also carotid arteries go straight to circle of willis) –> brain –> venous system –> heart
what is blood brain barrier
capillary wall
what does blood brain barrier do
regulates brain internal composition
what moves easy through blood brain barrier
water
carbon dioxide
oxygen
lipid soluble substances
what is weakly transported in blood brain barrier
na
k
cl
what will not cross blood brain barrier
plasma proteins
large organic molecules
how is glucose and some amino acids transported in blood brain barrier
active transport of glucose
some amino acids
or passively diffuse
what does capillary of blood brain barrier have
tight junctions between endothelial cells
endothelial cells line capillary
in other parts of body = gap junctions, allows things to easily flow out but not good for brain, very careful about what is allowed into ECF of brain
describe foot processes of astrocytes of blood brain barrier
- glial cell
- when attached to capillaries = induce tight junctions between endothelial cells
if treating disease what must you consider about blood brain barrier
must make sure it can cross barrier
describe effect of caffeine on brain
very lipid soluble
flies across blood brain barrier
describe effect of alcohol in brain
alcohol can cross
describe effect of drugs in brain
certain drugs like heroins, opiods
morphine does not cross but when converted to heroin = crosses blood brain barrier and then in brain enzymes convert heroin back to morphine but then morphine cannot get out
what is an astrocyte
network of glial cells that maintain structure of brain and extracellular environment around neurons in brain
name and describe 5 functions of astrocytes
- phagocytosis of debris (collect debris or garbage floating around and keep things working well)
- glutamate (takes up excess neurotransmitters)
- K+ (regulate concentration of ions)
- provide structural support
- induce tight junctions
what is sensation
awareness of sensory stimulation
what is perception
Understanding of a sensations meaning
what do we perceive
we do not perceive energy of sensory stimulus directly
only perceive neural activity that is produced by sensory stimulation
like ear = sound is changes in pressure = do not perceive that but do perceive changes in neural activity coming from auditory afferent
what is law of specific nerve energies
No matter how a sensory receptor is activated, it always produces the sensation it is designed to transduce
doorbell only plays one sound no matter how you press,will ring the same
give ex of law of specific nerve energies
rub eyes hard and see light
intraocular pressure
neuron activate by mechanical energy
what is law of projection
No matter where a sensory signal is activated in the brain, your brain always “feels” the sensation at the original location of the sensory receptor.
give 1st ex of law of projection
penfield electrically stimulated somatic sensory cortex of patients and patients perceived somatic sensation in body
Penfield stimulated a part of the brain connected to the foot, and the patient felt like their foot was touched, even though it wasn’t.
sensation felt at location of original receptor, no matter where signal
give 2nd ex of law of projection
phantom limb pain
somatosensation
axons severed but afferents do not die since cell bodies are in dorsal root ganglion
as amputation heals afferents try to regrow and sprout and connect to things
then activated by movement or somatosensory stimuli that would not normally cause pain
perception = hurting body part that isnt there, due to the 2 laws
what is modality
general class of a stimulus
brain knows
what are sensory inputs represented by
labeled line code
what is labelled line
brain knows modality and location of every sensory afferent
see laws
what is an exception to labelled line code
pain - referred pain
miswiring of painful stimuli and labeled line code breaks down a bit
describe sensory receptors
proteins designed to respond to specific stimulus energy
in specialized membranes
- can be part of axon
- sends info to brain
- a receptor cell
Think of sensory receptors like different types of sensors on a smartphone:
Camera sensor → Detects light (like photoreceptors in your eyes).
Microphone → Detects sound (like auditory receptors in your ears).
Touchscreen → Detects pressure (like mechanoreceptors in your skin).
sensory receptors convert signals from outside into electrical messages
describe what happens - sensory receptor pathway
adequate stimulus - specificity
1: stimulus energy (message sent)
2: receptor membrane (body receives message)
3: transduction (body converts message (stim.) into electrical signal)
4: ion channel activation (activate from signal)
5: afferent - to cns
describe transduction
stimulus energy converted to neural activity by opening or closing of ion channels
describe receptors - neurons/cells
specialized intermediate neurons or cells that encode stimulus and transmit to other neurons and send ap to brain
name an ex of receptor cell
retina = more than one
circuitry in eye that initially processes visual input and then info sent via afferent from eye to brain via optic nerve
describe how stimulus energy is converted to afferent activity
- stimulus energy
- receptor potential - membrane depolarization
- action potential - if reaches threshold to produce AP
- propagation of action potentials
- release of neurotransmitter
describe stimulus intensity and afferent response
diff amounts of stimulus energy encoded by afferent activity in 3 ways
name 3 ways stimulus intensity is told by afferent response
- magnitude of receptor potential
- magnitude of neurotransmitter release
- frequency of action of potentials
proportional to frequency of aps
what do majority of afferents show
adaptation
allows up to be sensitive to changes in sensory input
describe non adapting afferent response
- encodes stimulus intensity and slow changes
- not change frequency of ap
describe slowly adapting afferent response
- fast change = initiate stimulus
- some stimulus intensity and moderate stimulus changes
describe rapidly adapting afferent response
- ap frequency changes but stimulus does not change on response and off response
fast stimulus changes
what is more important to know about a stimulus
more important to know when things are changing
what is receptive field
region in space that activates a sensory receptor or neuron
describe response across receptive field
graded response
not uniform
issue since brain only listens to afferent info
brain does not know if light stimulus or strong at edge of receptive field
middle is highest afferent response - lowers toward edges
describe receptive fields overlapping
one somatosensory response produce effects in overlapping receptive fields
produce population code - pinpoint where it is located
what is acuity
ability to differentiate one stimulus from another
linked to size of receptive field
describe acuity and receptor field size
small RF = high acuity (like lips)
large RF = low acuity (like back)
poke with 2 points = further apart but feel one = low acuity
what does lateral inhibition do
sharpens sensory acuity
describe lateral inhibition - generally
- interneurons inhbit neurons around it
- stimulus in center of receptive field = largest inhibitory effect
what do descending pathways modulate
sensory inputs
what is sensory info shaped by
top down
bottom up mechanism
what can brain do - sensory info shaped by
brain can inhibit neurons and turn off neurons carrying info up spinal cord = descending top down modulation
give ex of top down mechanisms
- attention mechanisms pain highly modulated by state of brain
- descending pathway that modulates sensory input can shut off pain
- which does happen
- synapses have opiate receptors = why morphine works
give example of bottom up processing
lateral inhibition - occurs all by itself as sensory into going to brain
