• Forebrain, brainstem, and spinal cord function together to:
• (1) Integrate sensory inputs (heart rate, BP, lung inflation, gastric acidity) from visceral tissues
• (2) Generate or modulate rhythmic behaviors (respiratory, sleep-wake cycle)
• (3) Regulate autonomic function in order to maintain homeostasis
• These structures also receive input from cortical structures: limbic cortex (e.g. amygdala, cingulate gyrus) which is involved in regulation of emotional states. Interconnections provide the framework for the autonomic system.
• The Autonomic system receives its commands from all levels of the neuro axis.

Three levels of modulation of autonomic outflow – i.e. descending influences on autonomic function

• (1) Cortex: Determines behavioral state which, in turn, influences autonomic status
• Neo-Cortex: larger part of cerebral cortex; 6 layers
• Limbic Cortex
• Sympathetic preganglionic fibers innervate the same pathways that motor pathways are involved in (e.g. dilatation of blood vessels around a muscle before its contraction – the cortex is preparing the muscle for a change in behavioral state or anxiety)
• (2) Hypothalamus; integrates visceral and hormonal autonomic responses
• Controls 2 neuronal pathways: direct sensory input (BP, osmolality), hormonal (circulation)
• Coordinates neural and neuroendocrine responses:
• Neural: hypothalamus Þ intermediolateral column Þ peripheral nerve
• Neuroendocrine: hypothalamus Þ pituitary gland Þ ACTH Þ acts on peripheral tissues
• (3) Brainstem and spinal cord; Pattern generation and reflex circuits
• Visceral motor neurons – BP (symp tone to vasculature) and respiration (via nucleus tractus solitarious)
• Pattern generator networks (crying, suckling) sympathetic tone is modulated by sensory input in a reflexive manner
• Reflex circuits – homeostatic
• Sensory inputs to autonomic circuits
• Sensory input: primary sensory neurons; 10% of dorsal root ganglions are visceral sensory neurons (mostly cranial sensory ganglion); largest are vagal (vagal sensory nodose ganglion) and glossophayrngeal nerves (petrosal ganglion) which provide input from the visceral system to nucleus solitarius (7 geniculate, 9, 10).
• Unlike somatosensory, visceral sensory does not go up to the cortex. They are involved in reflex circuits in the brainstem
• 

• Immune system is also regulated by the autonomic nervous system
• Cytokines affect the central nervous system. The brain has receptors for cytokines. Immune system cells have receptors for neurotransmitters, therefore immune system and nervous system are integrated NOT separate.
• How do cytokines cross the Blood Brain Barrier? Area Postrema – small elevated area in the lateral wall of the inferior recess of the 4^th ventricle where an opening in the BBB exists. (located in areas of the brain responsible for autonomic function) near dorsal motor root of vagus near solitarius tract (cardiac glycosides sensory inputs coming through the blood, emetic response when toxins are ingested)