physiology exam 2 Flashcards
sensory system
part of NS consisting of sensory receptors that receive stimuli, neural pathways to conduct info, and brain to process info
may or may not lead to lead to conscious awareness of stimuli
(DONT notice BP changes)
sensation
stimulus info reaches consciousness
perception
awareness of sensation
sensation ex
feel pain
sensory processing
Transduction of stimulus energy into graded potentials and then APs in afferent neurons
Pattern of APs is a code that provides info about stimulus such as location, intensity and input type
Communicate with the brain to process info
May determine reflexive efferent responses, perception, memory storage, assignment of emotional significance
sensory receptors
at peripheral ends of afferent neurons change this info into graded potentials that can initiate APs to travel to CNS
adequate stimulus
type of stimulus which a particular receptor responds in normal functioning
a receptor may respond at low threshold to other stimuli
receptor
2 kinds
1. sensory receptor at peripheral end of afferent neurons trigger graded potentials to initiate APs
2. plasma membrane proteins that binds chemical messengers and trigger signal
mechanoreceptors
respond to mechanical stimulus like pressure or stretch
- resp. for touch and muscle tension
stimuli alter the permeability of ion channels on receptor membrane, changing membrane potential Vm
thermoreceptors
detect cold warmth sensations
photoreceptors
respond to wave length
chemoreceptors
respond to binding of chemicals to membrane
smell and taste
nociceptors
sense pain due to tissue damage
can be activated by variety of stimuli (heat, chemical, mechanical)
sensory transduction
process a stimuli is transformed into electrical response
Regardless of OG form the signal that activates sensory receptors, the info must be translated into graded potentials or APs
- involves open/closing of ion channels
- gating of channels allows a change in ion flux across receptor membrane and produces graded potential called receptor potential
afferent neuron receptor potential for sensory transduction
receptor membrane region where initial ion channel changes does NOT generate APs
- local current flows a short distance. along axon to voltage gated ion channels and can generate APs
- usually 1st node of ranvier if myelinated
receptor potential
like graded potentials, response to intensities and diminishes as it travels
receptor potential when receptor membrane is on a separate cell
receptor potential releases NT
- NT diffuses across cleft ~ receptor/afferent neuron and binds receptor protein on afferent neuron
- junction is a synapse
- NT binds binding site generates graded potential in afferent neuron
- analogous to EPSP (or IPSP)
true of all graded potentials
magnitude of receptor potential or graded potential decreases with dist. from origin
graded to AP
if intensity of depolarization at 1st excitable node of ranvier in afferent neuron is large enough to bring membrane to threshold, APs are generated and propagate along afferent
as long as receptor potential keeps afferent neuron depolarized to level at/above threshold, APs fire and propagate
magnitude of receptor potential
determines frequency of APs,
does NOT determine amplitude of APs
factor control magnitude of receptor potential
stimulus strength, rate of change of stimulus strength, temporal summation of successive receptor potentials and
adaptation
adaptation
decrease in receptor sensitivity which results in decrease in AP freq. in afferent neuron despite continuous presence of stimulus
slowly adapting receptors
tonic
maintain persistent or slowly decaying receptor potential during a constant stimulus
initiating APs in afferent neurons for duration of stimulus
tonic receptors
slowly adapting receptors
maintain persistent or slowly decaying receptor potential during a constant stimulus
initiating APs in afferent neurons for duration of stimulus
rapidly adapting receptors
phasic receptors
generate receptor potential and APs at onset of stimulus but quickly cease responding
adaptation may be so quick that only 1 AP is generated
some receptors may only initiate APs at onset of stimulus or w/ burst at beginning of stimulus
phasic receptors
rapidly adapting receptors
generate receptor potential and APs at onset of stimulus but quickly cease responding
adaptation may be so quick that only 1 AP is generated
coding
conversion of stimulus energy into signal that conveys relevant sensory info to CNS
- begins at receptive neurons in PNS
relevant info:
- type of input
- intensity
-location of body
sensory unit
single afferent neurons with receptor endings
- the peripheral end of an afferent neuron has many branches, each with a receptor
receptive field
area of body that leads to activity in particular afferent neuron when stimulated
usually overlap other afferent neurons receptive fields so multiple sensory units activate
stimulus type
modality - temp, sound, pressure, taste
given receptors are particularly sensitive to 1 modality bc of single transduction mechs and ion channels in membrane
modality
stimulus type - temp, sound, pressure
receptive fields overlap
a single stimulus can simultaneously give rise to sensations of different modalities
EX: ice = touch and cold
stimulus intensity
APs all same amplitude
FREQ. of APs
increased stimulus strength = larger receptor potential = more frequent APs
as stimulus strength increases, adj. receptors are activated = summation of local currents
stronger stimuli affect larger area and can activate other afferent neurons
recruitment
activating receptors on additional adj. afferent neurons given strong stimulus
stimulus location
coded by site of stimulated receptor
APs from each receptor travel unique pathways to specific regions of CNS assoc. w/ specific modalities and locations = labeled lines
labeled lines
APs from each stimulated receptor travel unique pathways to specific regions of CNS assoc. w/ specific modalities and locations
acuity
precision of locate/discerning stimuli from adj. one depends on convergence of neural input
greater convergence = less acuity
factors affecting acuity:
1. size of receptive field
2. density of sensory units
3. amount of overlap in nearby receptive fields
neuron w/ small receptive field can be located most precisely but receptive field overlap can help with localization of stimuli
acuity example
2 pt discrimination
easy to distinguish stimuli applied to skin on lips were sensory units are small and numerous
hard on back w/ few sensory units that are large and spaced
importance of receptive field overlap
afferent neurons respond most vigorously to stimuli applied directly at center of its receptive field bc there is greatest receptor density
decreased response at periphery
firing freq. of afferent neuron related to stimuli strength
receptor endings of different afferent neurons overlap, a stimulus will trigger activity in 1+ sensory unit.
high freq. EX
moderately intense stimulus was applied at center of receptive field OR
strong stimulus was applied at periphery
Therefore, neither intensity nor the location of stimulus can be detected w/ single afferent neuron.
lateral inhibition
enables localization of stimulus site
info from receptors at edge of stimulus is INHIBITED compared to info from afferent neurons at the center
afferent neurons in center have higher firing freq.
- reduces # of APs
lateral inhibition EX
press in a pencil on skin
- can localize point precisely
lateral inhibition removes info from peripheral regions
lateral inhibition importance
in retina for visual acuity
central control of afferent info
all signals subject to mods at synapses along pathways before reaching CNS
lateral inhibition reduces incoming info
RETICULAR FORMATION & CEREBRAL CORTEX control input of afferent info via descending pathways
inhibitory control by synapses or via interneurons that affect other neurons in pathway
afferent sensory pathways
formed by chains of 3+ neurons connected by synapses
chains travel in bundles carrying info into CNS
called ASCENDING PATHWAYS up to brain
central processes of afferent neurons
synapse on interneurons
diverge or converge on second order neurons and so on til info coded in APs reaches cerebral cortex
second order neurons
interneurons upon which afferent neurons synapse
go on to synapse on 3rd order… up to cerebral cortex
(coded in APs)
ending of ascending pathways
pass brainstem and thalamus to cerebral cortex
- cross to side of CNS opposite the location of sensory receptors
somatic receptors
carry info from skin/bone/tendons, etc to somatosensory cortex in parietal love posterior to central sulcus
central sulcus
separates pariental and frontal loves
somatosensory cortex
parietal lobe, posterior to central sulcus
visual cortex
occipital lobe
auditory cortex
temporal lobe
gustatory cortex
tastebuds, adj. to somatosensory cortex in parietal lobe
olfactory cortex
under frontal/temporal loves
end point of processing afferent info
cerebral cortex
integration
Golgi tendon organs
monitor muscle tension
tendons connect muscle to bone
nonspecific ascending pathways
activated by diff. types of sensory units
nonspecific neuron is polymodal neuron
end points: brainstem reticular formation and thalamus –> cerebral cortex
cortical association areas
adj. areas to primary sensory area
process info further
from primary sensory areas
factors affecting perception
- sensory receptor mechs (adaptation)
- emotions, personality, experience
- not all sensory info gives rise to conscious sensation - much info is canceled out
- we lack suitable receptors for many types of stimuli
- damaged neural networks may give faulty perceptions - phantom limb
- drugs
- mental illness - hallucinations
cortical assoc. area
region of cerebral cortex where info from primary sensory cortical areas is relayed for further processing
somatic sensation
Sensation from the skin, skeletal muscles, bones, tendons, and joints is initiated by specific somatic receptors
touch and pressure
mechanoreceptors stimulation
linked to networks of collagen fibers within fluid filled capsule
networks transmit mechanical tension to ion channels in neuron endings, activate them
slowly adapting receptors = pressure sensation
rapidly adapting = touch, move, vibrations
Merkel’s corpuscle
lowly adapting mechanoreceptor, touch and pressure
Pacinian corpuscles
rapidly adapting mechanoreceptor, vibration and deep pressure
Ruffini corpuscle
slowly adapting mechanoreceptor, skin stretch
posture and movement
muscle spindle stretch receptors and Golgi tendon organs
mechanoreceptors in muscle and tendon
Golgi tendon organs monitor muscle tension
also, Vision and the vestibular organs
kinesthesia = sense of movement at joint.
muscle spindle stretch receptors and Golgi tendon organs
mechanoreceptors for posture and movement
Golgi tendon organs monitor muscle tension
temperature
info transmitted along small diameter afferent neurons with little/no myelination
thermoreceptor neurons originate as free neuron endings
temp sensors are ion channels in plasma membrane of axon terminals belonging to TRP transient receptor potential proteins
isoforms of TRP channels have gates that open for diff temps
when active/open, allow nonspecific flux of cations dominated by depolarizing inward flux of Na and Ca2+
transient receptor potential proteins
channels; actual temperature sensors are ion channels in the plasma membranes of the axon terminals
Different isoforms of TRP channels have gates that open in differ- ent temperature ranges
activate/open allows nonspecific inward flux of cations = depolarizing
TRP protein channels for TEMP
act as temp sensors
1. temps open gates of channel
2. allow nonspecific influx, dominated by Ca and Na+ = depolarizing
3. results in receptor potential initiating AP in afferent neuron
4. AP travels labeled line to brain to be perceived
some TRPs can be opened by chem ligands
- explains why capsaicin chem is perceived as hot and menthol as cool
pain and itch
nociceptors are free axon terminals of small diameter afferent neurons with little/no myelination
bind to ligand gated ion channels on nociceptor plasma membrane
- glutamate and substance P neuropeptide are NTs releases a synapse on ascending neurons
pain and itch NTs
glutamate and substance P neuropeptide are synapsed by nociceptor endings on ascending neurons
referred pain
incoming nociceptive afferents activate interneurons, where sensation of pain is experienced at site other than injured/diseased tissue
EX: heart attack
referred pain EX
heart attack
experience paining chest and arms
exciting the somatic afferent fibers activate receptors
hyperalgesia
changes in nociceptors or ion channels result in increased sensitivity to painful stimuli
inhibiting pain
- analgesia - selective suppression of pain w/out effects on consciousness or other sensations
- stimulation produced analgesia inhibits pain pathways by electrical stimulation to CNS
- endogenous opioids
stimulation produced analgesia
inhibits pain pathways by electrical stimulation to CNS
descending pathways from the brain inhibit transmission of info from nociceptors
some neurons in inhibitory pathway release endogenous opioids which inhibit propagation of input through higher order levels of pain system
endogenous opioids mediates placebo
acupuncture and placebo
acupuncture
activate afferent neurons leading to carinal cord/midbrain that release endogenous opioids and NTs for pain relief
TENS transcutaneous electrical nerve stimulation
painful site itself/nerves leading from it are stimulated by electrodes placed on skin surface
stimulation of non pain, low threshold afferent fibers leads to inhibition of neurons in pain pathway
itch
somatic sensation w/ pain signaling pathway
can be mechanically activated to chemically mediated (anti/histamine)
neural pathway of somatosensory system
- enter CNS, afferent nerve fibers from somatic receptors synapse on neurons of ascending pathways to somatosensory cortex via brainstem and thalamus
- synaps eon interneurons
- …
2 somatosensory pathways
- anterolateral pathway - spinothalamic
- dorsal column pathway
anterolateral pathway
of somatosensory pathway
spinothalamic
1. 1st synapse ~ neurons in gray matter of spinal cord
2. 2nd neuron crosses to OPPOSITE side and ascents to thalamus
processes PAIN AND TEMP.
Which pathway processes pain?
somatosensory - anterolateral
Which pathway processes temp?
somatosensory - anterolateral
dorsal column pathway
of somatosensory process
1. section of white matter the sensory receptor neurons project
2. neurons do NOT immediately cross or synapse
they ascend the same side and make 1st synapse in brainstem
secondary neuron crosses in brainstem and ascends
2nd synapse is thalamus, projections sent to somatosensory cortex
compare anterolateral and dorsal column pathway
BOTH: somatosensory, 2nd synapse is thalamus
both cross at diff times
DIFF: dorsal - ascend on the same side of the cord and make the first synapse in the brainstem
anterolateral - makes its first synapse in the gray matter of spinal cord. This second neuron immediately crosses to the opposite side and ascends to thalamus
somatosensory cortex end off pathway
endings of axons of specific somatic pathways are grouped by peripheral location of receptors that gave input
areas of body that are most densely innervated have largest area of somatosensory cortex
- overlap
- sizes change with sensory experience
dynamic nature of somatosensory cortex
sizes change with sensory experience
ex: phantom limb - reorganization. cortical areas formerly responsible for a missing limb are “rewired” to respond to sensory inputs originating in the face
afferent neurons
neurons carry information from sensory receptors towards CNS
visible light
400-750nm
the eye overview
3 layers, fluid filled, 2 chambers
1. sclera outer layer, white and tough connective tissue, muscles connect
also forms cornea - clear and dense
2. choroid under sclera - colored and absorbs light at back of the eye (uvea)
choroid contains iris (regulates pupil), ciliary muscle, zonular fibers = suspensory ligament
3. retina
sclera
outer layer of eye
tough, fibrous white connective tissue that muscles attach to
forms clear dense cornea
cornea
part of white sclera, dense and clear
covers iris and allows light to enter
can help focus image on retina
choroid
middle layer of eye under sclera
absorbs light at back of the eye
mainly blood vessels
iris, ciliary muscle, zonular fibers = suspensory ligament
iris
part of choroid layer
colored
regulates pupil diameter
2 layers of smooth muscle innervated by autonomic nerves
dilate: stim sympathetic nerves, cause radial muscle fibers to contract
constrict: stim parasympathetic fibers
integrate din midbrain
pupil
regulated by iris smooth muscles
anterior opening allows light in
lens
behind the iris
crytalline
controlled by activity go ciliary muscle and tension of zonular fibers that determine shape and focusing power
cells of lens lack ability to replicate except at surface
with age, central part of lens becomes denser/stiff with cells
retina
formed as part of brain in embryo
forms inner posterior surface of eye
contains neurons and photoreceptors
macula lutea - yellow spot , relatively free of blood vessels; processes image
fovea centralis - in macula, high density of cones = high visual acuity
optic disc = nasal side of retina, neurons carry info from photoreceptors exit the eye as optic nerve
2 chambers of eye
support
aqueous humor - anterior chamber of eye between iris and cornea
vitreous - posterior chamber of eye between lens and retina; viscous
refraction
bending light to focus image on retina
lens refracts light inward, converges back into a point on retina
retina better at focusing light
adjustments in lens shape
accommodation
controlled by ciliary muscle and tension it applies to zonular fibers which Utah to ciliary muscles to lens
accommodation
adjustments in lens shape
kinesthesia
sense of movement of a joint
receptors for posture and movement
mechanoreceptors in skin, muscle, etc
- muscle-spindle stretch receptors
- golgi tendon organs (musc tension)
- vision and vestibular organs
thermoreceptors
transmit temp info
skinny NON-myelinated afferent neurons are FREE NEURONS ENDINGS (no capsular ending)
temp sensor is ion channel in plasma membrane belonging to transient receptor potential proteins TRP proteins
