Homeostasis and Survival

• Survival and reproduction are key objectives for living organisms.
• Both cells and organisms are in a constant battle against entropy, necessitating a consistent energy source.
• Cells function optimally within specific physiological parameters, making homeostasis crucial for survival.
• Homeostasis involves maintaining stable body temperature, blood pH, and substrate concentrations.
• Hormonal responses and the autonomic nervous system predominantly manage homeostatic requirements.
• The autonomic nervous system (ANS) regulates smooth muscle, cardiac muscle, and glands via afferent and efferent nerve signals
• Behavioral responses are triggered by environmental challenges, like seeking warmth.
• The hypothalamus is essential in homeostatic responses by managing autonomic activity, hormone secretion, and behavior.
• The limbic system, including especially the hypothalamus, uses risk assessment to help determine behavior.
• Recognition and memory of risky or favorable situations are key to survival.
• Successful reproduction involves both autonomic/hormonal changes and specific behaviors.
• The limbic system helps regulate behavior by assessing particular situations’ risks and benefits.
• The drive to eat might be suppressed temporarily if the social context is inappropriate.
• A cold animal may risk moving to a warmer area if predators are present.

Maintenance of Homeostasis

• Visceral sensory and motor functions possess pathways and connections paralleling somatic functions.
• Visceral functions are affected by circuits involving cerebral cortex, basal ganglia, and cerebellum
• The CNS receives visceral condition information, like body chemistry and organ tension.
• Visceral receptor types include long receptors with peripheral sensory endings and short receptors in the periphery.
• The hypothalmus has neurons directly sensitive to internal temperature or blood chemistry.
• Some afferents from thoracic, abdominal, and pelvic areas go through spinal nerves along with sympathetic and parasympathetic nerve signals.
• Signals related to visceral damage use the anterolateral pathway that also transmits skin nociception signals.
• Referred pain occurs when internal organ disorders cause pain in other body areas as signals from cutaneous and visceral damage converge.
• The vagus and glossopharyngeal nerves carry primary afferents from viscera and blood vessels to the brainstem.
• Visceral sensory information integrates in the nucleus of the solitary tract in the brainstem.
• The VPM nucleus passes solitary tract information to the insula’s visceral sensory cortex.
• Discomfort, well-being, moods, and emotions correlate to the cortical network point of entry.
• Areas near the insula get information from pleasant gentle stroking of the skin, temperature and pain.

Visceral Efferents

• Unlike skeletal muscle innervation, neurons innervating smooth muscle, glands, and cardiac muscle exist outside the CNS in autonomic ganglia.
• The enteric nervous system in the gastrointestinal tract walls is a sensory, motor, and interneuron network.
• Peristalsis, unlike coordinated muscle contractions, can occur independently of the CNS.
• Sympathetic and parasympathetic ANS divisions have preganglionic neurons with thinly myelinated axons exiting via spinal ventral roots or cranial nerves.
• Unmyelinated postganglionic axons from autonomic ganglion cells innervate visceral structures.
• Acetylcholine is the preganglionic neurotransmitter for sympathetic and parasympathetic neurons
• Postganglionic parasympathetic fibers use acetylcholine muscarinic while postganglionic sympathetic rely on norepinephrine.

Sympathetic System

• Postganglionic sympathetic fibers reach essentially all of the body part
• Sympathetic chain ganglia near the spinal cord serve the head, neck, chest, skeletal muscle blood vessels, and cutaneous targets.
• The spinal cord houses all preganglionic sympathetic neurons
• Preganglionic sympathetic neurons produce a lateral column in the intermediate gray matter, extending from T1 to L2/L3.
• Upper thoracic controls sympathic innervation controls innervation of the upper extremity
• Thoracic segments of lower extremities control abdominal and pelvic organs
• Thinly myelinated axons from preganglionic sympathetic neurons exit spinal nerves traveling between the T1 and L3 segment.
• Splanchnic nerves connect prevertebral ganglia after preganglionic fibers transit the sympathetic chain.
• Splanchic nerve fibers terminate in the adrenal medulla, neural crest derivatives acting as modified sympathetic ganglion cells releasing epinephrine and norepinephrine.
• The splanchnic area release epinephrine because unmyelinated postganglionic fibers travel through gray communicating rami.
• All spinal nerves have gray rami since the sympathetic chain is the length of the cord

Parasympathetic System

• Parasympathetic fibers originate from ganglia near innervated organs, and are unmyelinated and short
• Their distribution is restricted to the head, neck, and body cavities, not reaching the limbs or body surface.
• Preganglionic Parasympathetic Neurons are Located both in the Spinal Cord and Brainstem
• Lateral gray matter sections (S2-S4) go to ganglia near the distal colon, bladder, and reproductive organs.
• The vagus nerve contains thinly myelinated axons from the dorsal motor nucleus in the rostral medulla
• Small clusters for salivary and lacrimal glands are near and use the glossopharyngeal and facial nerves
• The oculomotor nerve extends to the ciliary ganglion for pupillary sphincter and ciliary muscle innervation.

Coordinated Autonomic Function

• The sympathetic nervous system prepares the body for "fight or flight."
• The parasympathetic nervous system favors "rest and digest."
• Specific activation is appropriate for bladder control and vasodilation for example
• These patterns involve connections that run parallel with those that control the skeletal system

Autonomic Reflexes and Central Pattern Generators

• Simple background reflexes depend on autonomic efferents, visceral afferents, and interneurons in the intermediate gray matter of the nucleus of the solitary tract
• Complex patterns incorporate all kinds of afferent in combination and spinal nerves
• Central pattern generators implement patterns made out of a sub set of combinations of autonomic parts
• Medulla and pons neurons coordinate sympathetic response to blood pressure with the solitary nucleus

Bladder Control and Micturition

• The bladder alternates between storing and eliminating urine as a muscular container.
• We have control over storage and elimination by using parts of our Somatic and visceral system
• Storage occurs while under low pressure, as pressure to the bladder must be lower than an external outlet
• Parasympathetic activation occurs from S2-S4 and the signal constricts the internal muscles
• The external urethra constricts due to a collection of slow- twitch fibers around the organ
• Detrusor muscles relax under a slight inhibitor from signals in the sympathetic system

Pharmacology related note

• Some cholinergic muscarine (M3) antiagonists can relax the muscles of an over active bladder

Efferent Innervation of the Bladder Musculature

• Sacral parasympathetics activate the detrusor muscle in the bladder wall, increasing the intravesical pressure.
• Motor neurons of Onuf's nucleus in the S2 anterior horn activate the external urethral sphincter, increasing outflow resistance.

Vesicovesical Reflex

• The vesicovesical reflex activates the detrusor’s parasympathetic output from stimulus in the bladder.
• Sympathetic control of the bladder involves the activation of B-receptors to relaxes detrusor wall while inhibiting parasympathetic nerves, sacral nerve
• The bladder is inhibited by symphathetic and contracted by parasympathetic at the same time

Hypothalamus

• The body operates by using the Hypothalamus chief operator to orchestrate, homeostasis reproduction, and stress
• The structure is a tiny spot compared to the rest of the brain
• Subdivisions are broken up into zones of Nucleis and patterns of connection same with the Thalamus
• Axons can pass to other autonomic sites via periventricular zones

Afferents to the Hypothalamus

• The hypothalamus monitors internal conditions
• Signals Arrive to the organ by sensory and direct communication in the blood stream
• Some in the preoptic nuclei are temp related
• Circumentricular organs in the ventricular walls use hormones and concentration
• Blood volume is received by in the solitary track
• Photosensitive ganglion cells connect to the suprachiasmatic nucleus

Efferents from the Hypothalamus

• Outputs include Limibic structures, autonomic output, and pituitary gland
• Nuclei connect via medial forebrain bundling
• Hormones are controlled by two parts the posterior and Anterior

Regulation of Function by the Hypothalamus

• Set points maintain records of variables
• Set points regulate function with stimuli and efferents
• More or less thyrotropin releases into portal for regulation
• Temperature is maintained due to parts in both the A and P with neurons, shivering is done by signals through forebrain bundle

Limbic System

• Stimuli and situations with Homeostatic importance cause drives, emotional reactions, action
• Osmolality triggers the release of Vassopresin
• The Limibic system works together by using emotions (cortical stimuli to autonmic reactions
• Structures serve as a bridge including the hypothalamus
• Cortical reactions extend to daily life with a bunch of emotion and autonomic functions

Conditoned fear

• Connections connect to a part deep in the Limbic portion called the Amygdala with an unpleasent reaction
• Auditory comes quick to tell about danger
• Damage to this place effects recall in reactions but not damage from damage