Reflexes Flashcards
Reflex
simple relatively stereotyped action elicited by a sensory stimulus
Reflex arc
the neural pathway that underlies a reflex
somatic reflex examples
stretch, golgi tendon, withdrawal, crossed extensor
autonomic reflex examples
respiration, temperature, blood pressure
Sherrington suggested that complex behavior could be explained as a result of
chaining different reflexes together
5 components generally found in reflex arc
- a sensor to detect stimuli
- an afferent pathway
- an integrative center
- an efferent pathway
- an effector
reflexes mediated by
neurons in nervous system
monosynaptic reflex
involves only a single sensory neuron and a motoneuron (one synapse between two neurons hence monosynaptic)
stretch reflex neurotransmitters
excitatory sensory NT: glutamate
excitatory motor NT: acetylcholine
effect of stretch reflex
once muscle stretched muscle fiber = contracted to help maintain standard stretch of that muscle; stretch reflex is for proprioception it lets you maintain posture
all skeletal muscle innervation is
excitatory
stretch reflex signs of afferent and efferents
stretch in muscle detected spindle afferent (which detects stretch) produces action potential that will terminate on motor neuron in spinal cord
spindle afferent- if activation of spindle neuron depolarizes motor neuron it has excitatory effect on motor neuron
spindle efferent- motor neuron activated by afferent synapsing on it (all skeletal muscle innervation is excitatory) -> muscle excitation -> contraction
inhibitory reflex arc to inhibit flexor
spindle afferent excitatory synapse -> inhibitory interneuron activated -> inhibitory effect on flexor motor neuron (because motor neuron synapse on muscle excitatory interneuron works by preventing firing of motor neuron)
interneuron can have
excitatory or inhibitory effects on post-synaptic cells they contact
withdrawal reflex (arm as example) signs
one reflex arc to excite flexor (bicep)
nociceptive afferent -> excitatory synapse on interneuron -> interneuron excitatory synapse on flexor motor neuron -> contraction of flexors
one reflex arc to inhibit extensor (triceps)
nociceptive afferent -> excitatory synapse on inhibitory interneuron -> inhibitory synapse interneuron on extensor motor neuron -> inhibit excitatory synapse on motor neuron
baroreceptor reflex function
helps to maintain blood pressure (homeostasis)
homeostasis
aims to provide cells in body with constant environment (O2, pH, blood supply, glucose, temperature, other critical parameters, blood pressure)
- maintains consistancy
- negative feedback loops’
- redundancy
baroreceptor reflex sensory
baroreceptor: Mechanosensitive channel on aortic and carotid arches:
Baroreceptors are modified stretch receptor these are located in carotid artery and aortic arch (carotid sinus and aortic arch bot distend under pressure) bc walls of vessels stretch in response to vasodilation
- baroreceptors are myelinated sensory nerve fibers which have specialized endings which detect changes in degree of stretch
baroreceptor composed of
subunits called degenerins which are sensitive to stretch because connect to both cytoskeleton and exterior surface via variety of adaptor protiens, these function to connect inside of cell to outside with a channel between
- the 2 sides of channel get pulled apart by pressure and lets ions through
sympathetic and parasympathetic systems
always active and always on
- basal rate= tone which allows for regulation in either up or down direction
baroreceptor reflex afferents
- afferents from aortic arch project via vagus nerve
- afferents from carotid sinus project via glossopharyngeal nerve
- both go to medulla?
baroreceptor reflex integration center
information from barrorreceptors is received by nucleus of solitary tract (nucleus tracts solitarius ie NTS) located in the medulla
- NTS integrate signals from sensory afferents, input from higher cortical areas and thalamic regions to generate an output
baroreceptor afferents are generally
glutamatergic
receptors we know are present in NTS
AMPA and NMDA don’t know too much else
autonomic regulation involves modulating
the basal rate of continuously active parasympathetic and sympathetic systems known as tone
if blood pressure is up we want to
lower it so want to reduce blood flow so inhibit blood flow by increasing parasympathetic signals to heart and blood vessels and decrease sympathetic signals to heart and blood vessels
how does baroreceptor reflex modulate ANS tone
NTS integrates info from baroreceptors output -> medullary nuclei:
excitatory output -> CVLM -> inhibitory neurons in CVLM -> RVLM -> controls sympathetic vascular tone and heart rate
NTS also projects to -> NA and DMNX -> control parasympathetic outflow to heart
CVLM
RVLM
NA
DMNX
Caudal ventrolateral medulla
Rostral ventrolateral medulla
Nucleus ambiguous
Dorsal motor nucleus aka parasympathetic nucleus of CN X
baroreceptor efferents
sympathetic and parasympathetic branches of nervous system
baroreceptor effetors/ outpts
change in sympathetic and parasympathetic outflow purpose of reflex is to maintain homeostasis
what happens when there is rapid rise in arterial pressure
- carotid and aortic vessel walls stretch -> activate baroreceptors -> excitatory stimulation neurons in NTS -> excite inhibitory internueons in CVLM -> inhibit vasomotor neurons in RVLM and inhibit sympathetic outflow to heart from RVLM -> vasodilation and reduction in heart rate
also: - carotid and aortic vessel walls stretch -> activate baroreceptors -> excitatory stimulation neurons in NTS -> excitatory connections to NA and DMNX -> promotion parasympathetic outflow to heart -> bradycardia and vasodilation -> drop in arterial pressure
RVLM
unless inhibited by NTS neurons neurons in RVLM produce tonic output that promotes vasoconstriction (symp tone)
- inihibiting RVLM promotes vasodilation
NA and DMNX affect
these areas are cardioinhibitory excitation of these areas promotes parasympathetic outflow to heart resulting bradycardia and vasodilation leads to drop in arterial pressure
baroreceptors ideal should be able to sense
stretch and also quality of that stretch to integrating center
strong stimulus evokes
stronger reflexive response
how does baroreceptor reflex produce quantitative stretch information
- firing rate of baroreceptor neuron changes exponentially with small increase or decrease in pressure within given range pressure differences; small change in pressure can cause baroreceptor to fire more frequently or less frequently
- baroreceptors tuned to monitor small changes away from given set point (maintain arterial pressure v close to given setpoint)
small increase in arterial pressure
results in dramatically increase baroreceptor firing leading eventually to drop in pressure by increased parasympathetic outflow and decreased sympathetic outflow which in turn -> lowering firing frequency of baroreceptor to match drop in pressure
small decrease in arterial pressure
baroreceptor fires are dramatically lower rate producing associated increase in sympathetic outflow to boost pressure
sympathetic affect on blood pressure
increases blood pressure
parasympathetic affect on blood pressure
decreases blood pressure
baroreceptor reflex during exercise
activation of baroreceptor reflex will occur at higher arterial pressure because baroreceptor reflex is reset to be activated at different pressure
baroreceptor reset get input from
- central command
- presser reflex
baroreceptor reflex setpoint change
- occurs at level or baroreceptor itself as well as at level of integrating center in medulla
- NTS receives input from higher cortical areas including hypothalamus so central command from other areas of brain can modulate input to NTS and its subsequent output -> rapid alterations in effectiveness and range of reflex this is why brain can modulate and modify reflexes
startle reflex
leads to higher heart rate and blood pressure bc brain anticipates need to appropriate action and raises tone of symp nervous system and resets in process baroreceptor reflex
recelfex response due to
sensory activation but also in case of baroreceptor modified by feedback form muscles
- feedback and feedforward mechanisms operate to control and modify baroreceptor reflex
baroreceptor reflex in diseased animals
- baroreceptor reflex can adapt to long-term changes in physiology of animal
- in hypertensive patients baroreceptor reflex setpoint shifted right reflecting higher, longterm blood pressure in these animals (reflecting baroreceptor role in regulating short-term, moment to moment changes)
- baroreceptor response also flattens so it is not as sensitive and need greater differences in pressure to trigger the reflex
- exercise can imporve sensitivty of reflex in hypertensive patient showing impact of physiology on reflex
crossed extensor response
in leg that steps on noxious stimuli
excitatory interneuron activated -> flexor contraction
inhibitory interneuron activated -> inhibition extensor
Opposite leg
extensor excited and flexor inhibited by interneurons crossing midline off body
locomotion decrebreate animals
animals can walk when placed on treadmill (these animals are not getting forebrain input for locomotion)
if treadmill increases in speed animal can adjust from walk to trot to gallop ect.
- this indicates that complex behavior such as locomotion can be explained by series of reflexes interconnected with one another
decerebrate animals
transection in mid-brain separating input from cortex to the limbs
how are rhythmic motor behaviors observed or produced in absence of sensory stimuli
in part these are controlled by central pattern generators
examples of rhythmic motor behavior
- walking
- running
- swimming
- respiration
- vomitting
- shivering
goal of each CPG
generate rhythmic pattern of firing that -> motor response
CPGs for locomotion
located in spinal cord not within brain; there is at least one for each limb; locomotory CPGs interconnected with one antoher
how does CPG function 2 theoretic ways
- Pacemaker neurons can drive interneuron that drives motor output
- interneurons reciprocally inhibit one another
pacemaker neurons driving interneurons that drive motor output
pacemaker neuron (one that oscillates its firing patterns) could drive interneuron that drives motor output; motor circuitry would not be activated without pacemaker activation
interneurons reciprocally inhibit one another
- excitatory interneuron activates contraction of extensor motoneuron also excites inhibitory interneuron
- activation inhibitory interneuron inhibitors excitatory interneuron that activates flexor motor neuron preventing flexor contraction
- must have way to release excitatory interneuron controlling flexor from inhibition (do with wide variety of mechanisms)
excitatory interneuron controlling flexor released from inhibition
it excites flexor motoneuron and excited inhibitory interneuron which inhibits excitatory interneuron that activates extensor resulting in opposite response (flexor activation and extensor inhibition_
- eventually the excitatory interneuron will escape inhibition and cycle will repeat
CPGs can be
- triggered (locomotion) or constitutive (respiration)
- their functions can be modified (can hold breath, can stop walking to avoid obstacle)
CPG function affected by both
sensory input and central command
respiratory CPG sensory inputs
- sensors that measure partial pressure of oxygen in blood
- sensors that measure partial pressure of Co2 (plays greater role than partial pressure O2 sensors)
- mechanosensors in lung, nose, gut, heart, elsewhere
- firing can also be affected by central command
central command CPG respiratory
- hypothalamus (during pain)
- cortex (when you want to sing ect.)
output of CPG respiratory
to appropriate muscle groups, also interacts with other CPGs like those for V+ and swallowing
locomotion CPGs involves what sensory inputs
vision proprioception ect.
CPGs have large number of
modulatory inputs
oscillating rhythmic behavior can be accomplished in absence of
sensory stimuli but integration of sensory stimuli and cortical control with motor circuits of CPG are necessary for normal rhythmic activity
what demonstrates complexity that can underlie control of spinal reflexes
existence of CPGs and integration of external information by cortex
