CENTRAL ADJUSTING OF AVTONOMIC FUNCTIONS

Levels of ANS Control Figure 14.9

4 Influence of Brain on Autonomic Functions

1. Spinal cord  bladder and rectum reflex (micturition and defecation)  sexual reflex  the baroreceptor reflex  sweating of the skin Central Regulation of Visceral Function

Reflex control of micturition Bladder filling facilitated by tonic neural activity: sympathetics – inhibits bladder contraction sacral somatic motor nerves – contracts external sphincter Bladder filling activates Mechanoreceptors Voiding (micturition): threshold reached sympathetic and somatic motor neurons inhibited parasympathetic outflow to detrusor m. activated bladder smooth muscle contracts

Neural Control of Defecation. Filling of the rectum with feces stimulates stretch receptors, which transmit impulses to the spinal cord. A spinal reflex stimulates contractions of the rectum and relaxation of the internal anal sphincter. Defecation normally does not occur unless voluntary impulses relax the external anal sphincter.

2. Medulla oblongata  Vital (respiratory and cardiovascular) center:  Other autonomic reflexes: Swallow, cough, sneeze, gag, and vomit.

Tu : Hypothalamus

Hypothalamic Control Centers of the hypothalamus control: –Heart activity and blood pressure –Body temperature, water balance, and endocrine activity –Emotional stages (rage, pleasure) and biological drives (hunger, thirst, sex) –Reactions to fear and the “fight-or-flight ” system

2). Food intake:  ventromedial and paraventricular nuclei are satiety centers,  lesion causes obesity;  lateral HT (feeding center) stimulates food and water intake Hypothalamic Functions

3) Water balance  ADH (vasopressin)  Osmotic pressure in hypothalamus – Thirst - Drink Hypothalamus Functions

4) Sleep/wake cycle:  suprachiasmatic nuc is biological clock;  preoptic nuc. can initiate sleep;  lat HT can change cortical arousal;  post HT lesion can cause coma or impaired arousal

Hypothalamus Functions 5). Emotions and behavior:  ventromedial lesions can cause viciousness/rage  Posterior HT stimulates sympathetic functions  Anterior HT stimulates parasympathetic functions  Mamillary nuclei: recent memory

Circadian rhythms of physiological functions.

Central control of the Autonomic NS Amygdala: main limbic region for emotions -Stimulates sympathetic activity, especially previously learned fear-related behavior -Can be voluntary when decide to recall frightful experience - cerebral cortex acts through amygdala -Some people can regulate some autonomic activities by gaining extraordinary control over their emotions Hypothalamus: main integration center Reticular formation: most direct influence over autonomic function

Visceral Reflexes The visceral sensory neurons are the first link in the autonomic reflexes These neurons send information concerning chemical changes, stretch, and irritation of the viscera

Visceral Reflexes Visceral reflex arcs have essentially the same components as somatic reflex arcs –Receptor –Sensory neuron –Integration center –Motor neuron –Effector

Visceral Reflexes Visceral reflex arcs differ in that they have a two-neuron chain

Autonomic Reflexes

Visceral Reflexes Additional cutaneous areas to which visceral pain is referred

Autonomic reflexes a) viscero-visceral b) viscero-dermal (viscero-somatic) c) dermato-visceral (somato- visceral)

Eye Cornea Lens Ciliary muscle Iris

Blood vessels

Lungs and salivary glands

Gastrointestinal tract and liver

EXAMPLE: blood pressure falls sinus nerve activity falls sympathetic outflow increases to the: vasculature – vasoconstriction heart – increased cardiac output adrenal medulla – increased epinephrine release afferent input integrated in CNS centers impacts autonomic efferent outflow

Reflex control of GI function smell, taste of food and/or foods in the stomach LOCATION OF SENSORY STRUCTURES? central integration reflex parasympathetic efferent stimulation which leads to: increased motor activity (stomach, gallbladder and intestine) increased secretory activity (stomach and pancreas)

Fight or flight response This is a coordinated, massive increase in sympathetic outflow to all target organs in response to fear, stress, or exercise. Parasympathetic outflow ceases. The coordinated physiologic response is a survival mechanism which includes: Increased heart rate, cardiac output, and blood pressure Contraction of the spleen to mobilize blood cells Bronchial dilation Decreased GI activity Liberation of glucose into the bloodstream Inhibition of insulin secretion However, under normal non-stressful situations, autonomic efferent outflow is more discrete. Autonomic reflexes play an important role in regulating physiologic function.