Lecture 14: Autonomic nervous system 2 Flashcards
Why does the CNS need information from the periphery?
to report on the state of the internal environment, i.e., specialised sensors, visceral sensory nerves (visceral afferents)
Why does the CNS need circuits?
to interpret signals, decide on the most suitable outcome, activate the appropriate sympathetic or parasympathetic nerves with the correct sequence and timing and integrate with behavior and higher order functions
What do the sensory and integrative CNS centres involved in autonomic function have key roles in?
many complex functions, e.g. stress, pain, sickness, behaviors
What are the divisions of the nucleus of the solitary tract in the medulla?
there is a rostral gustatory division and a caudal visceral sensory division
What is the role of the caudal part of the nucleus of the solitary tract in the medulla?
receives sensory input (from sensors and sensory nerves) that provide information about various tissues and the environment
What is the role of the nucleus tractus solitarius (NTS)?
major integrative centre for autonomic function
How is information from the NTS distributed?
provides feedback to reflexes that control organ/tissue function and provide information to higher centres to drive more complex responses (coordinated behaviour: visceral, somatic, endocrine; emotion)
What information does the hypothalamus receive?
sensory inputs (e.g. visceral afferents, visual, olfactory) contextual information from other brain regions hormonal signals (access via circumventricular organs)
What does the hypothalamus integrate with?
higher cortical and limbic systems (emotion, fear, anxiety, motivation, etc.)
What are examples of outcomes of the hypothalamus?
feeding / water balance
thermoregulation
circadian rhythms / sexual function
coordinated activation of the fight-or-flight response
How does the hypothalamus work?
compares situation to biological set points, then adjusts behavior, autonomic and endocrine function
What are the primary issues of spinal cord injury?
partial or complete loss of ascending and descending connections with the brain, therefore no way of sensing or responding properly to changes in the environment or the body’s needs
What are the secondary issues of spinal cord injury?
spinal and peripheral nerve circuits can remodel or degenerate
unregulated organs can undergo changes, including altered trophic signaling to peripheral nerves
What is the overall impact of spinal cord injury?
not simply subtractive but adds new problems due to neural and non- neural changes
What are examples of problems caused by spinal cord injury?
cardiovascular dysregulation, bladder and bowel problems, sexual dysfunction and disrupted thermoregulation
When does autonomic dysreflexia occur?
occurs when spinal cord injury at or above spinal level T6
What is autonomic dysreflexia?
acute hypertensive episode triggered by peripheral signals such as bladder/bowel distension, urinary tract infection, nociceptor activity -> stroke, seizure, death
What is the mechanism of autonomic dysreflexia?
sensory activity triggers vasoconstrictor reflex e.g. brain detects rise in BP but it cannot control it
-> BP cannot be counterbalanced as normal by brain regulation of sympathetic and parasympathetic pathways
What is visceral pain?
pain originating from internal organs
What is most of our current understanding of pain mechanisms and therapies based on?
biology of somatic pain (skin, skeletal muscle, bone, joint), especially the biology of somatic sensory neurons and their communication with the spinal cord
How is the neurobiology of visceral sensory neurons very different from somatic neurons?
most visceral sensory activity is not perceived
visceral nociceptors have more extensive branching
visceral sensory activity can elicit unique sensations (e.g. bloating, nausea)
How is visceral pain perceived?
visceral pain is perceived as diffuse, imprecisely localised or
referred
How are nociceptors different in organs? What is the implication of this?
respond to more diverse stimuli
send different types of messages
can be involved in normal autonomic reflexes
therefore, many visceral pain states are accompanied by over-activity of autonomic nerves
What is the challenge of treating visceral pain?
to devise therapies that reduce visceral pain without disrupting the normal autonomic reflexes
What is bioelectronic medicine?
swapping drugs with devices (modulation of visceral nerves)
What is the goal of bioelectronic medicine?
to regulate activity of neural pathway relevant to specific organ/disease function (‘neuromodulation’)
What are the requirements for bioelectronic medicine?
detailed maps of visceral nerve circuits, computational models of visceral nerve function and devices suitable for attaching to moving organs or visceral nerves
