Autonomics 1 Flashcards
Describe general autonomic organization
In many ways, the autonomic nervous system parallels and interacts with the somatic nervous system.
– Specific stimuli activate specific central processors, leading to specific responses.
– Visceral responses (e.g., sweating) are less subject to voluntary regulation than are somatic responses (e.g., shivering).
Describe central autonomic control overview
Control of visceral efferents, comprised of the sympathetic and parasympathetic divisions of the autonomic nervous system (ANS), involves several areas of the Central Nervous System (CNS), including the forebrain and the brainstem. The hypothalamus is a central relay for the ANS and a key site for the integration of autonomic function, endocrine function and motivated behavior. Note, however, the critical role of inputs to the lateral horns of the spinal cord as central autonomic processors.
Describe neuronal afferent input
Special visceral afferents (taste) run in cranial nerves CN VII (facial), CN IX (glossopharyngeus) and CN X (vagus) and enter the brainstem and synapse in the nucleus of the solitary tract (solitary nucleus). Second order neurons located in the solitary nucleus send their axons (ipsilaterally) to the ventromedial nucleus of the thalamus. Third order neurons located in the thalamus send their axons to the primary gustatory cortex in the insula.
General visceral afferents (for example pain fibers) are also carried in these cranial nerves VII, IX and X, and synapse in the solitary nucleus. Second order neurons synapse in the hypothalamus and the parabrachial nucleus, and third order neurons synapse in the amygdala
What’s importance of the insular cortex to the forebrain autonomic control?
The insular cortex receives visceral pain sensations, temperature sensations, and taste sensations via the thalamus. It integrates these interoceptive inputs with emotions (see future lecture on Emotions) and it controls autonomic output via the hypothalamus.
What’s the importance of anterior cingulate cortex to the forebrain autonomic control?
The anterior cingulate cortex forms the anterior portion of the limbic lobe. It controls autonomic output via its connections with the insula, the prefrontal cortex, amygdala, hypothalamus and brainstem.
What is the importance of the amygdala of the forebrain autonomic control?
The amygdala is a central element of the emotional system (see future lecture on Emotions). It contributes to the regulation of the stress response and is essential in fear and fear-related responses. It receives direct input from olfactory system (see lecture on Chemical Senses) and other visceral input from the solitary nucleus. Its output fibers project to the hypothalamus (via the stria terminalis) and to the brainstem (including periaqueductal grey and reticular formation).
What is the autonomic input via circumventricular organs ?
Circumventricular organs of the forebrain, including the subfornical organ and the organum vasculosum of the lamina terminalis, lack a blood-brain barrier. These organs are able respond to changes in electrolyte balance and other blood compounds. Projections originating in these circumventricular organs provide input to the hypothalamus, where they regulate hypothalamic output, for example the secretion of anti-diuretic hormone (ADH, or vasopressin)
What are the circumventricular organs?
- around 3rd and 4th ventricles
- in contact with blood (highly permeable capillaries, no BBB)
- chemosensory and secretory organs
• chemosensory:
– Area postrema
• projects to NTS and activates the vomiting reflex
• mediates nausea with increased CSF pressure, fever, toxins in blood
– Subfornicalorgan(SFO)
• osmoregulation, blood pressure regulation, energy homeostasis
• neurons respond to blood tonicity changes
• also senses blood glucose levels, important role in energy balance
– Oragnum Vasculosum of the Lamina Terminalis (OVLT)
• key role in osmoregulation
• angiotensin receptors sense circulating angiotensin levels
• non-selective cation channels convey sensitivity to blood tonicity
What are the secretory circumventricular organs?
• Subcommissural organ
– secretion of the glycoprotein SCO-spondin, which aggregates in 3rd ventricle to
create Reissner’s fibers (RF)
– role in osmoregulation, loss of RF causes congenital hydrocephalus
• Posterior pituitary
– Oxytocin and vasopressin (ADH), more detail later in this lecture
• Median eminence
– in the inferior portion of the hypothalamus and is ventral to the third ventricle
– transport of neurohormones between the CSF and the peripheral blood
– e.g. anterior pituitary projections of GnRH neurons end at median eminence, allowing for its release into the portal blood system
• Pineal gland
– sleep-wake cycle regulation: melatonin production and release into
bloodstream
– melatonin production ceases when retina receives light, coordinated via suprachiasmatic nucleus (SCN, ‘circadian pacemaker’)
What is the significance of the hypothalamus?
The hypothalamus is the central control unit of life, governing five basic processes:
- Blood pressure and electrolyte composition
- Body temperature
- Energy metabolism
- Reproduction
- Emergency responses
This is achieved by an integration of the three major output pathways from the hypothalamus, which modulate:
• Autonomic function
• Endocrine function
• Motivated behavior
What is homeostasis?
Despite wide environmental variation, the hypothalamus tightly regulates physiological parameters, thereby establishing homeostasis. For example, habitable environments vary enormously in temperature, yet body temperature varies only slightly around 37 degrees Celsius.
What hypothalamic structures can be viewed from a saggital view?
Sagittal View Key structures to identify include: • Anterior commissure • Lamina terminalis • Optic chiasm • Mammillary body • Hypothalamic sulcus
In the sagittal view we differentiate between anterior and posterior hypothalamic functionality
What hypothalamic structures can be seen at coronal view?
The hypothalamus forms the lower anterior portion of the diencephalon, a small area surrounding the third ventricle. In the coronal view, we differentiate between three hypothalamic zones:
• Periventricular zone adjacent to the third ventricle
• Medial zone, which contains most of the distinct nuclei of the hypothalamus
• Lateral zone, which contains less defined nuclei but also many fiber tracts either
passing through or connecting the hypothalamus with other areas of the brain
Summarize hypothalamic functions
Basic Life Processes – Blood pressure and fluid balance – Body temperature – Energy metabolism – Reproduction – Emergency responses
• Integration of
– Autonomic control
– Endocrine control
– Motivated behavior
What were Harvey Cushing statements on the hypothalamus?
“Here in this well- concealed spot, almost to be covered by a thumb- nail, lies the very main spring of primitive existence - vegetative, emotional, reproductive - on which, with more or less success, man has come to superimpose a cortex of inhibition.”
