Visceral Afferent Pathways Flashcards
when does the fasciculus cuneatus transition to the fasciclus gracilis?
T6
visceral afferent nucleus
-sensory nucleus in the SC that handles visceral reflexes
visceral afferent fibers
- Rs are naked nerve endings in the walls of blood vessels and viscera
- sensitive to touch, ischemia, but insensitive to cutting and burning
- most visceral pain fibers enter the SC along its entire length via spinal Ns
- most visceral reflex fibers enter the SC at the cranial and sacral levels
primary neurons in the spinal visceral sensory pathways
- cell bodies are pseudo unipolar neurons in the spinal ganglia
- central processes bifurcate after entering the SC and ascend in the fasciculus proprius
- most fibers terminate in the VISCERAL AFFERENT NUCLEUS at sacral levels S2-4
visceral somatic reflex pathway
- one connection of the visceral afferent nucleus
- fibers from VAN may project the effects of visceral stimuli upon the alpha and gamma motor neurons
- interneurons in the intermediate gray and fibers in the fasciculus proprius are key links to diversity and pattern of responses
- alpha motor neurons control extrafusal M spindles and gamma motor neurons control intrafusal M spindles
- M spasm or inc M tone (hypertonia) may result
visceral visceral reflex pathways
- one connection of the VAN
- fibers from the VAN may project the effects of visceral stimuli to the intermediolateral cell column for a sympathetic response OR to the PS nuclei in brainstem or sacral cord
- PS nuclei are mostly dorsal motor nucleus of vagus and sacral autonomic nucleus
- interneurons in the intermediate gray and fibers in the fasciculus proprius are key links to diversity and pattern of responses
spinoreticulothalamic pathway
- one connection of the VAN
- some info from VAN may enter the adjacent fasciculus proprius, and diffusely, bilaterally ascend to the brainstem reticular formation or the hypothalamus as part of the spinoreticulothalamic pathway
- this pathway is an ascending visceral afferent pathway conveying diffuse, poorly localized persistent pain (C type fibers)
- stimulus may be sharp pain if enough Rs and CNS neurons
- spinoreticular fibers terminate in nuclei of brainstem reticular formation and are involved in arousal, alertness, and activating the ascending reticular activating system (ARAS)
- some fibers may reach the centromedian nucleus of the thalamus and hypothalamus where there is sensory, motor, hormonal, and behavioral responses thru its connection to reticular formation
referred pain
- visceral pain may be interpreted as originating from somatic areas distant from source
- cause:
- visceral afferents may send collaterals to areas of the dorsal horn that are associate with the spinothalamic somatic pain pathways in the substantia gelatinosa–>incoming visceral and somatic pain info intermingles and ascends to thalamus in spinothalamic system where at the level of the cortex it is interpreted as being somatic
- stimulation of visceral afferent fibers may trigger a viscero somatic reflex and the vasomotor spasm and ischemia may stimulate somatic afferent fibers
- cerebral cortex is highly conditioned in infancy to perceive and integrate somatic sensory info, so visceral pain can be misinterpreted as part of somatic stimuli b/c o greater cortical awareness
corticoreticulospinal pathway
- formed by fibers for the promotor and prefrontal cortex that descend adjacent to the corticospinal tract and bilaterally terminate in pontine and medullary reticular nuclei
- pontine reticular nuclei–influence automatic, involuntary mvmts of axial and limb musculature via the medial reticulospinal tracts
- medullary reticular nuclei project descending influences to all levels of the SC via the lateral reticulospinal tract
- both have same influence on posture and locomotion, but lateral reticulospinal tract is likely link b/w reticular formation and sympathetic and PS nuclei of SC
cranial visceral afferent (GVA) pathways
- cranial ganglia and regions innervated by GVA fibers
- GVA sensory ganglia are comprised of pseudo unipolar neurons assoc with CNs VII, IX
solitary-superior salivatory reflex
solitary nucleus–>superior salivatory nucleus–>preganglionic PS fibers–>sphenopalatine ganglion–>lacrimal gland
solitary nucleus–>superior salivatory nucleus–>preganglionic PS fibers–>submandibular ganglion–>submandibular and sublingual glands
-response: inc lacrimation and salivation
solitary-inferior salivatory reflex
solitary nucleus–>inferior salivatory nucleus–>preganglionic PS fibers–>otic ganglion–>parotid gland
-response: inc salivation
solitary dorsal motor nucleus (X) reflex
solitary nucleus–>dorsal motor nucleus of X–>preganglionic PS fibers–>ganglia in the larynx, pharynx, thorax, abdomen–>small glands in larynx, pharynx, thorax, abdomen
- response: inc secretion
- huge input on body–post. tongue to transverse colon
- impacts GERD–LES
solitary nucleus ambiguus reflex
solitary nucleus–>interneurons in the reticular formation–>nucleus ambiguus–>Ms of larynx and pharynx
-response: deglutition
carotid body reflex
- stimulus: inc CO2
- sinocarotid N–vagus N
- nucleus tract of solitarius
- reticular formation
- phrenic nucleus
- diaphragm
- response: inc ventilation
carotid sinus reflex
- stimulus: inc BP
- sinocarotid N–vagus N
- nucleus tract of solitarius
- reticular formation
- dorsal motor nucleus
- cardiac branches of vagus
- response: dec cardiac contraction
gag reflex
- stimulus: touching pharyngeal mucosa
- glossopharyngeal N (IX)
- nucleus tract of solitarius
- reticular formation
- nucleus ambiguus
- pharyngeal branch of vagus (X)
- response: gagging
laryngeal expiration reflex (LER)
- stimulus: to laryngeal mucosa
- internal branch of SLN (X)
- nucleus tractus solitarius and adjacent LER pattern generator
- reticular formation
- nucleus ambiguus–>RLN–>glottal control–>response: expiratory cough epoch to clear airway
- medial motor cell column–>thoracoabdominal Ns relaxes diaphragm–>external abdominal oblique M contracts as a girdle effect–>closure of abdominal and pelvic sphincters–>response: expiratory “coughs”
cough
- inhalation followed by an expiratory cough similar to a voluntary cough
- not typical of airway protective cough which is the laryngeal expiration reflex which is a series of 3-5 expiratory coughs without inhalation
- LER is the essential component in a neurologically protected upper airway
- closure of the LES, internal urethral sphincter, external urethral sphincter, anal sphincter, and inguinal canal must be synchronized with the inc in intra-abdominal pressure during the LER cough speech
bladder reflex
- M in bladder is under PS control of S2-4
- some sympathetic fibers relax the bladder
- external sphincter is innervated by GSE fibers
- as the bladder fills with urine, stretch Rs in the bladder wall are activated
- pseudounipolar sensory neurons in the peripheral Ns send impulses thru the dorsal root to the visceral afferent nucleus
- interneurons convey stimulus to sacral autonomic nucleus at S2-4
- efferent fibers stimulate the Ms of the bladder to contract and void the bladder
bladder reflex pathway
stimulus: inc volume which activates stretch Rs in the bladder wall–>afferent neurons at S2-4–>VAN at S2-4 with input from the lateral reticulospinal tract–>sacral autonomic nucleus at S2-4–>efferent neurons at S2-4–>response is voiding the bladder
atonic bladder
- due to lesions of dorsal roots of S2-4 or dorsal funiculi
- results in a flaccid bladder and inc bladder capacity
- voluntary voiding is possible but incomplete
- seen in tabes dorsalis
reflex bladder
- transection of the SC above S2 interrupts the lateral reticulospinal tract to the sacral autonomic nucleus
- pt is unable to voluntarily void his bladder (there is urinary retention)
- after spinal shock, the bladder relax may return without voluntary control and the pt will have automatic reflex boiling or a reflex bladder
taste and salivation reflex pathway
- stimulus: food or fluid
- taste buds–>facial or glossopharyngeal N
- nucleus tractus solitarius
- inferior salivatory nucleus–>otic ganglion–>GVE p to the parotid gland
- superior salivatory nucleus–>sphenopalatine ganglion–>GVE p to the submandibular and sublingual glands
- response: salivation
