Visceral Afferent Pathways

Question 1

when does the fasciculus cuneatus transition to the fasciclus gracilis?

Answer 1

T6

Question 2

visceral afferent nucleus

Answer 2

-sensory nucleus in the SC that handles visceral reflexes

Question 3

visceral afferent fibers

Answer 3

• 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

Question 4

primary neurons in the spinal visceral sensory pathways

Answer 4

• 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

Question 5

visceral somatic reflex pathway

Answer 5

• 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

Question 6

visceral visceral reflex pathways

Answer 6

• 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

Question 7

spinoreticulothalamic pathway

Answer 7

• 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

Question 8

referred pain

Answer 8

• 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

Question 9

corticoreticulospinal pathway

Answer 9

• 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
  
  1. pontine reticular nuclei–influence automatic, involuntary mvmts of axial and limb musculature via the medial reticulospinal tracts
  2. 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

Question 10

cranial visceral afferent (GVA) pathways

Answer 10

• cranial ganglia and regions innervated by GVA fibers

- GVA sensory ganglia are comprised of pseudo unipolar neurons assoc with CNs VII, IX

Question 11

solitary-superior salivatory reflex

Answer 11

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

Question 12

solitary-inferior salivatory reflex

Answer 12

solitary nucleus–>inferior salivatory nucleus–>preganglionic PS fibers–>otic ganglion–>parotid gland

-response: inc salivation

Question 13

solitary dorsal motor nucleus (X) reflex

Answer 13

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

Question 14

solitary nucleus ambiguus reflex

Answer 14

solitary nucleus–>interneurons in the reticular formation–>nucleus ambiguus–>Ms of larynx and pharynx

-response: deglutition

Question 15

carotid body reflex

Answer 15

• stimulus: inc CO2
• sinocarotid N–vagus N
• nucleus tract of solitarius
• reticular formation
• phrenic nucleus
• diaphragm
• response: inc ventilation

Question 16

carotid sinus reflex

Answer 16

• stimulus: inc BP
• sinocarotid N–vagus N
• nucleus tract of solitarius
• reticular formation
• dorsal motor nucleus
• cardiac branches of vagus
• response: dec cardiac contraction

Question 17

gag reflex

Answer 17

• stimulus: touching pharyngeal mucosa
• glossopharyngeal N (IX)
• nucleus tract of solitarius
• reticular formation
• nucleus ambiguus
• pharyngeal branch of vagus (X)
• response: gagging

Question 18

laryngeal expiration reflex (LER)

Answer 18

• stimulus: to laryngeal mucosa
• internal branch of SLN (X)
• nucleus tractus solitarius and adjacent LER pattern generator
• reticular formation
  
  1. nucleus ambiguus–>RLN–>glottal control–>response: expiratory cough epoch to clear airway
  2. 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”

Question 19

cough

Answer 19

• 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

Question 20

bladder reflex

Answer 20

• 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

Question 21

bladder reflex pathway

Answer 21

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

Question 22

atonic bladder

Answer 22

• 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

Question 23

reflex bladder

Answer 23

• 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

Question 24

taste and salivation reflex pathway

Answer 24

• stimulus: food or fluid
• taste buds–>facial or glossopharyngeal N
• nucleus tractus solitarius
  
  1. inferior salivatory nucleus–>otic ganglion–>GVE p to the parotid gland
  2. superior salivatory nucleus–>sphenopalatine ganglion–>GVE p to the submandibular and sublingual glands
• response: salivation