Chemical Control of Behavior

Homeostasis  Keeping the internal environment of the body the same (constant) regardless of changes externally.  Communication is accomplished by three systems: Central nervous system (hypothalamus) Brain stem (diffuse modulatory systems) Autonomic and diffuse enteric (visceral) systems of the peripheral nervous system.

Purpose of Homeostasis  Maintains internal temperature.  Maintains blood sugar level.  Maintains balance of essential salts and minerals.  Maintains fluids (level of hydration) in cells and intracellular.

Central Regulation (CNS)  Hypothalamus – integrates visceral functioning: Activates the autonomic nervous system Regulates hormones secreted from the pituitary gland and thereby controls the endocrine system.

Three Parts of Hypothalamus  Periventricular Zone – regulates temperature, salt concentration, levels of hormones.  Medial Zone – produces vasopressin and oxytocin in posterior pituitary.  Lateral Zone – permits cortex and limbic system to over-ride hypothalamic activity, manages long-term regulation.

Medulla Oblongata  Responsible for monitoring: Spontaneous respiratory movement (breathing) Blood pressure Cardiac rhythm  “Brain death” occurs with loss of hypothalamic and medullary control over respiration, lack of EEG waves.

Endocrine System  Endocrine organs include: Pituitary gland Adrenal Cortex Gonads (ovaries and testes) Thyroid and parathyroid Adrenal cortex Islet cells of pancreas Secretary cells that line intestinal tract

Autonomic Nervous System  Two parts: Sympathetic Parasympathetic  Includes sensor and effector components. Sensors monitor internal functioning. Effectors activate or inhibit target structures such as blood vessels or glands.

What Do Sensors Monitor?  Chemical variations in blood composition.  Tension changes in the vascular system (blood vessels).  Distension of the intestines, bladder and gall bladder.

Where Sensor Neurons Go  Sensor neurons from the viscera (visceral afferent nerves) go: To the spinal cord From spinal cord to ganglia in the sympathetic and parasympathetic systems. Postganglionic fibers go to the targets.  ACh is the neurotransmitter for neurons from spinal cord to ganglia.

Parts of the Autonomic System  Different in function.  Preganglionic fibers emerge from different spots in the spinal cord.  Ganglia are in different places: Close to organs for parasympathetic Close to spinal cord for sympathetic  Postganglionic effectors use different neurotransmitters (NE vs ACh)

Sympathetic  Mobilizes body for “fight or flight” response.  In addition to direct NE to targets, adrenal medulla secretes NE in bloodstream to sympathetic targets.  Nicotine in cigarettes activates sympathetic nervous system.

Parasympathetic  Initiates rest and recuperation.  Activation comes from the brainstem.  Vagus nerve carries sensor and effector information from heart, lungs and intestines.  Preganglionic axons are very long.  Postganglionic fibers use ACh not NE – receptors are muscarinic (blocked by atropine) not nicotinic.

Coordination of the Systems  Systems are complementary.  Both are active to some extent at the same time – not alternating.  What happens during anger? Sympathetic arousal increases blood pressure. Medulla detects that arousal and activates the parasympathetic to keep blood pressure within normal limits. Hypertension occurs with deficient feedback.

Diffuse Enteric System  A third major division of the autonomic nervous system.  Neural control unit between the autonomic postganglionic nerves and the gastrointestinal system.  Contractions of muscles propels food through digestive system (peristalsis).

Diffuse Modulatory Systems  A small set of diffuse modulatory neurons arise from the brain stem.  Each neuron has an axon that can influence more than 100,000 postsynaptic neurons spread widely across the brain.  Their synapses release neurotransmitter into the extracellular fluid, not into a confined synaptic cleft.

Origins of Diffuse Neurons  Origins vary depending on the neurotransmitter involved: NE system – locus coeruleus (waking, arousal, attention, memory, anxiety, pain, mood). 5-HT serotonin system – raphe nuclei (wakefulness, mood, emotional behavior). DA system – substantia nigra & ventral tegmentum (reward). ACh system – basal forebrain (unknown)

Effects of Drugs  Many abused drugs act directly on the modulatory systems.  Hallucinogens such as LSD – agonist for serotonin, decreasing activity of raphe nuclei.  Stimulants (cocaine, amphetamine) – affect DA and NE systems, causing increased alertness, self-confidence, euphoria. Mimic effects of sympathetic ANS activation.

Drug Effects (Cont.)  Stimulants block catecholamine reuptake and stimulate release of DA (dopamine), intensifying effects of DA and NE. This causes the stimulant effect.  Because cocaine and amphetamine affect the reward systems, drug-seeking behaviors are reinforced leading to addiction or psychological dependence.