Lecture 18: Viscerosensory Afferents Flashcards
What do visceral afferent neurons interface between?
visceral organs and the brain
What are the two visceral afferent pathways?
cranial visceral afferents and spinal visceral afferents
What is role of spinal visceral afferents?
send information to the brain about what is perceived in terms of the state of the internal organs
What is role of cranial visceral afferents?
send information to the brain about the function of the internal organs
Where are the cell bodies of spinal visceral afferents?
in the dorsal root ganglion
Approximately what percentage of inputs to the spinal cord are spinal viscerosensory afferents?
10%
Where do spinal visceral afferents terminate?
first terminate in the dorsal horn of the spinal cord
Where do spinal visceral ascending pathways lead to?
the thalamus, hypothalamus, pons/midbrain, rostral medulla and caudal medulla
What is the role of spinal visceral afferents?
visceral non-painful sensations, visceral discomfort and pain, referred pain, local organ feedback and shaping emotional state
What are all visceral organs innervated by?
either or both of the spinal and cranial visceral sensory neurons
What do spinal and visceral sensory neurons sense?
mechanical and chemical (and temperature) stimuli
Where do cranial visceral afferents first terminate?
in the solitary tract nucleus of the brainstem
What is the role of cranial visceral afferents?
visceral non-painful sensations, shaping emotional state relating to the body (interoception) and organ regulation, organ reflexes, neuroendocrine regulation
Where can the cell bodies for cranial visceral afferents be found?
nodose / inferior ganglion of the vagus
petrosal ganglion
jugular / superior ganglion of the vagus
What is the structure of a reflex?
sensor -> integration -> effector
What do cranial visceral afferents drive?
the autonomic nervous system
Where do cranial visceral sensory neurons input?
to the brainstem
What do cranial visceral sensory neurons sense?
mechanical and chemical stimuli
What is a major physiological role of cranial visceral sensory neurons?
to initiate autonomic reflexes (to alter organ function)
What initiates the baroreceptor reflex?
pumping of blood into the aortic arch activates aortic arch receptors which stimulate the vagus nerve
also blood entering the right and left interior carotid arteries activate carotid sinus receptors which stimulate the carotid sinus nerve which leads to nerve IX
What is the baroreceptor reflex?
control of autonomic activity to the heart which provides a rapid means of adjusting cardiac output to match arterial blood pressure
What is an important characteristic of baroreceptors?
always active (asleep or awake), phasic
How many baroreceptors are unmyelinated?
90% of baroreceptors are unmyelinated “C-fiber”
What are characteristics of myelinated baroreceptors?
high sensitivity and high fidelity
What are characteristics of unmyelinated baroreceptors?
low sensitivity and low fidelity
What are the two classes of baroreceptor afferent neuron?
A fibres and C fibres
Are A fibres myelinated or unmyelinated?
Are C fibres myelinated or unmyelinated?
A fibres are myelinated
C fibres are unmyelinated
What are the characteristics of A fibres?
active at resting blood pressure and fine-tune autonomic function
10%
What are the characteristics of C fibres?
activated at elevated blood pressure
90%
What do neurons of the baroreceptor reflex sense?
mechanical stimuli (vessel stretch)
