Week 7 Notes Flashcards
Neuromodulatory pathways
pathways that do not carry specific sensory info or motor commands
neurons in neuromodulatory pathway serving fxs such as
- regulating baseline level of activity in broader regions of nervous system
- gaiting flow of information w/ in nervous system
- regulating cognitive fxs l
regulating baseline level of activity in broader regions of nervous system to control
arousal, sleep wake cycling, and vigilance
gaiting flow of information within nervous system determines
ex. which info is attended to, reaches consciousness and/or generates a behavioral response
regulate cognitive fxns such as
mood, motivation, memory
en passant terminals
some of the neurons of in neuromodulatory system use these terminals to release neurotransmitter to neuropil to broadly affect regional neurons rather than forming conventional synapses w/ specific neuron populations
en passant terminals act on
- target cells through G-protein coupled receptors not ligand gated ion channels-> more enduring effects in pathway
Neuromodulatory systems
- The Ascending Reticular Activating System (ARAS): Chollinergic Pathway
- Monoaminergic systems
Monoaminergic systems
- Noradrenergic system
- Seratonergic System
- Histaminergic system
- dopaminergic system
ARAS system main location
- major component is group of ARAS is group cholinergic neurons in reticular formation near pons/ midbrain junction
Cholinergic
release acetylcholine as major neurotransmitter
Other neurons contributing to ARAS (other than cholinergic neurons in reticular formation)
- Ascending monoaminergic neurons from pons, medulla, and hypothalamus also contribute to ARAS
input to ARAS
- ascending sensory pathways (especially non-specific nociceptive pathways)
- visual input
- auditory input
Information coming in ARAS can
alert brain that potentially threatening or important event occurred w/o regard for details of sensory stimulus
Where does more processed information reaching ARAS neurons come from
- projections from cerebral cortex
- projections from limbic structures
- this is why thinking of stressful things can stress you out
cholinergic neurons project to
- intralaminar nuclei (in medial thalamus)
- specific cholinergic basal nuclei
cholinergic neurons to basal nuclei
- further project diffusely to and stimulate cerebral cortex
ascending cholinergic neurons reach basal nuclei via
pathway through lateral thalamus
monoaminergic pathways from locus coeruleus, raphe nuclei, and tuberomammillary nuclei
- utilize norepinephrine, serotonin, and histamine as neurotransmitters play role in ascending activation of cerebrum by projections to forebrain
ARAS functions in
sleep wake cycle and alertness
Lesions that interrupt ARAS pathway are located in
- brainstem (midbrain)
- lateral hypothalamus
- intralaminar nuclei of thalamus
anticholinergic drugs
- if cross CNS barrier can affect state of alertness and -> seizures and respiratory depression
monoaminergic systems
- brainstem nuclei w/ diffuse projections to many regions of CNS use monoamine neurotransmitters to modulate activity in cognitive, behavioral, and autonomic pathways
monoaminergic system modulates
behavioral processes including:
- arousal
- attention
- sleep/wake cycling
- emotions
- motivation
- motor fxns
- processing of nociceptive information
noradernergic system which neurotransmitters?
epinephrine and norepinephrine
Noradrenergic system neuron location
- locus coeruleus (pons)
- lateral tegmentum of pons and medulla
noradrenergic system projections
- makes diffuse projections to most regions of CNS
ascending projections of noradernergic system
- transverse lateral hypothalamus
- generally excitatory and form component of ARAS
noradernergic system projections to spinal cord
generally reduce transmission of nociceptive information
seratonergic system neurotransmitter
seratonin
seratonergic system neurons location
- Raphe Nuclei (runs throughout cd brainstem near midline)
Seratonergic system projections
- makes diffuse projections to many regions CNS
- projects to forebrain, brainstem, spinal cord
Ascending projections seratonergic system forebrain
- play role in wake/ sleep cycling
- mood
- motivation
- emotions
projections to brainstem and spinal cord seratonergic system
- play role in respiratory fx
- reduce transmission of nociceptive information in spinal cord circuits
abnormal levels in seratonergic system
- implicated psychiatric dx and are targets of common behavioral medication
histaminergic system neurotransmitter
histamine
histaminergic system neuron location
hypothalamic nuclei
histaminergic system projections
- virtually all regions of brain and spinal cord
histaminergic system mediates
- arousal and attention
- modulates activity in vestibular system
- may influence brain blood flow
histaminergic antagonists that cross blood- CNS barrier
- diphenhydramine
- causes drowsiness as side effect
- can be used to control motion sickness by blocking vestibular pathways
dopaminergic system neurotransmitter
dopamine
dopaminergic system neurons location
ventral midbrain tegmentum (ex. substantia nigra)
dopaminergic system projections
- less diffuse
- more specifically organized than other monoamine pathways
dopaminergic system involved in control of
- voluntary movement
- cognitive processes such as reward-based learning
why do midbrain and hypothalamic lesions cause most extreme deficits in terms of consciousness and arousal
b/c pathways = v focal in those lesions; midbrain lesions knock out cholinergic neurons knocking out ARAS -> depression/ unconsciousness (lesion rostral to midbrain can do same)
- lesion in hypothalamus can knock out things gong to basal nuclei so knocks all communication out same with intralaminar nuclei
- with cortex can knock out a little not knocking out the entire pathway
Hierarchy in control of homeostasis
lowest: - spinal cord
- cd brainstem
- hypothalamus
highest: - cerebral cortex and limbic structures
homeostasis
mechanisms that maintain w/ in narrow physiological range the constancy and composition of bodily fluids, body temp, blood pressure, and other physiological variables
ultimate control center for homeostatic regulation
- hypothalamus but this gets influence from cerebral cortex and basal nuclei
spinal cord homeostasis input
- receives visceral afferent input via spinal nerve
- input can be used to mediate local reflexes or relayed to brain (Nucleus of solitary tract) -> further processing
spinal cord homeostasis output
- visceral efferent neurons controlled by local visceral or somatic afferent input or by descending pathways from autonomic centers in brainstem and hypothalamus
cd brainstem homeostasis fx VA and VEs
fxs like spinal cord with VA and VE and local reflex loops these travel in CNs rather than spinal nerves
brainstem reticular formation
- contains neurocircuitiry that regulates and coordinates autonomic and homeostatic activity in brainstem and spinal cord
- these circuits often called “regulatory centers” but these are not always well defined
regulatory centers fx
- maintaining vital fxs like blood pressure, respiration, micturition
severe brainstem damage
can have life-threatening physiologic consequences
hypothalamus homeostatic fx
- master coordinator of homeostasis, coordinating autonomic, endocrine, and somatic activity
hypothalamus projections to
-brainstem and spinal cord permits control of somatic and visceral LMNs
hypothalamus output
- via hypophysis, permits control of endocrine systems
cerebral cortex and limbic structures
- brain regions underlie recognition of sensory stimuli, memories of experiences and their consequences and spontaneous thought processes
limbic system an influence homeostasis via
projections to hypothalamus and brainstem
cd brainstem contribution to homeostasis
- autonomic reflexes
- brainstem homeostatic regulatory centers
autonomic reflexes
include PLR and baroreceptor reflex
brainstem homeostatic regulatory centers
- medullary cardiovascular center
- swallowing center
- respiratory center
- vomiting center
- micturition center
baroreceptor reflex afferents
- afferents in aortic arch and carotid sinus
- relay blood pressure info via CN IX and X
baroreceptor reflex center
in medulla includes:
- nucleus of solitary tract
- PN X
- Nucleus ambiguus
VE pathway to heart
travels via CN X and sympathetic pathway
regulatory center
- includes more basic reflex centers but will integrate input from variety of sources to generate more broadly useful output via multiple pathways
- many for physiological homeostasis in cd brainstem generate autonomic output
what other pathways play critical role in homeostasis
- somatic efferent pathways also play crucial role in many aspects of homeostasis such as
- breathing
- swallowing
- V+
- micturition
medullary cardiovascular system includes
regions medulla that regulate vascular tone, heart rate, cardiac contractility to maintain appropriate cardiac output and distribution of blood
medullary cardiovascular system input
- baroreceptors in aorta, carotid bifurfactoin and other blood vessels (CN IX, X)
- Chemoreceptors sense O2, CO2, H+
- Circulating hormones bind at circumventricular organs
- Hypothalamus and Amygdala- modify blood pressure in response to stress
medullary cardiovascular system output
- via PN CN X
- Nucleus Ambiguous
- Descending projections ot sump preganglionic neurons in spinal cord
effect medullary cardiovascular system output
changes in peripheral vascular tone, heart rate, and force of contractility depending on cardiovascular demands
swallowing center afferents
- CNs V, IX, X (sensory of food bolus in mouth, pharynx, esophagus)
swallowing center efferents
V, VII, IX, X, XII
swallowing center neurocircuitiry
coordinates sequence of pharyngeal and esophageal relaxation and contraction, closure of glottis, raising soft palate, movements of tongue, cheeks, and jaw to accomplish swallowing in response to stimulus of food bolus in mouth and pharynx
Respiratory center location
pons and medulla
respiratory center input from
- neurons w/ in respiratory center stimulated by increased levels CO2 and hydrogen ions in blood
- Peripheral chemoreceptors sense O2, CO2, H+
- Receptors via CN X
- reticular activating system
- hypothalamus
- cerebral cortex
Receptors via CN X respiratory center input
pulmonary stretch receptors, airway receptors
reticular activating system and respiratory center input
more alert = faster response
hypothalamus respiratory center
modify resp rate to control body temp or in response to pain, stress, or fear
cerebral cortex respiratory center
mediates voluntary control of respiration by projections to respiratory control center and also directly to phrenic LMNs
respiratory center processing
- occurs in Nucleus of solitary tract
- occurs in other nuclei w/ in reticular formation
UMNs in respiratory center project to
- phrenic motor neuron pool (MNP) in spinal cord segments C5, C6,C7 to control diaphragm
- accessory respiratory muscles
- muscles involved in breathing (pharyngeal, laryngeal, tongue, facial, and abdominal muscles)
brainstem or cervical spinal cord lesions can severely damage
the respiratory center or its descending projections to spinal cord can lead to abnormal breathing patterns or respiratory paralysis respectively; these lesions must be severe to cause respiratory paralysis
Vomiting center afferents
- area postrema
- CN X
- Vestibular nuclei
- cortex
area postreama and vomiting center
- a circumventricular organ that plays role in chemically induced emesis by detecting circulating toxins or drugs like opiates
CN X and vomitting center
GI distention or chemical irritation can trigger vomiting
vestibular nuclei and vominting center
motion sickness
cortex and vomiting center
psychological component of nausea, HUMANS
CNs which contribute to V+
V, VII, IX, X, XII (+ LMNs to skeletal muscles)
opening mouth
CN V and VII
anti peristalsis in duodenum, stomach, esophagus, relaxation fo GIT sphincters
CN X
salvation
CN VII and IX
pharyngeal muscle coordination, raising soft palate to occlude nasal cavity, closure of glottis
CN IX and X (nucleus ambiguus)
movement of tongue
CN XII
contraction of abdominal wall and diaphragm, followed by suppression of respiration
LMNs to abdominal wall and diaphragm
clinical application of vomitting center
- different neurotransmitters used by different afferents knowing which pathway causing V+ lets you know which to treat
respiratory center used when
- swimming hold breath
- about to start dong something exertion and start breathing harder with anticipatory need for O2 (forebrain)
- sleep (hypothalamus to respiratory center)
- vocalization
c1-c5 lesion -> tetraplegia and loss of nociception
respiration can be next to go this is v bad
brainstem lesion affecting respiration
lesion big enough to effect respiration then it is big enough to cause other signs
2 paths to forebrain using cholinergic neruons
- intralaminar nuclei -> cerebral cortex (usually activating)
- Lateral hypothalamus -> Basal nuclei -> cerebral cortex
narcolepsy
loss oc consciousness in anims
cataplexy
lack of tone in collapsing
Suprachiasmatic nuclus and ARAS
suprachiasmatic nucleus -> pineal gland -> hypothalamus -> ARAS
major players in ARAS
Locus cueruleus and substantial nigra? bc they get input from somatosensory pathway and special senses, generally excite
neuromodulatory pathways important points
- don’t carry specific info
- dont make neuron fire but can increase or decrease fifing
- influence how info processed in CNS
- role in level of arousal / attention / sleep wake
