The Brain and Behavior

1. The Brain and Behavior PART III

2. Chemical Control of the Brain and Behavior Chapter 15

3. Point to Point Communication • The brain uses precise and specific pathways to communicate. • Synaptic Transmission is Tightly Confined in Time and Space. • Neurons communicate with only one or a small subset of neurons. • Transmission is rapid • Minute quantities of neurotransmitters are used. • Transmitters are quickly destroyed or taken up.

4. The Nervous System also Communicates Over Great Distances and Time. • Hormonal communication • Secretes chemicals into the blood stream to affect the entire body. • Networks of neurons in ANS • Simultaneously controls responses in many internal organs. • Diffuse modulatory systems extend their reach with widely divergent axonal projections. • Each modulatory system uses a specific neurotransmitter or set of neurotransmitters. • Use metabotropic postsynaptic receptors to prolong their action. • Regulate arousal, mood, motivation, sexual behavior, emotion, sleep, etc.

5. Point to Point Communication Hormonal Communication Interconnected neurons of the ANS Diffuse modulatory systems

6. Hypothalamus &Pituitary • Hypothalamus is located below the thalamus and forms the walls of the third ventrical. • It can be divided into several nuclei using cytoachitectonics. • Each nucleus has a very specific function. • The pituitary is connected to the base of the hypothamlamus.

7. The Secretory Hypothalamus • Integrates somatic and visceral responses in accordance with the needs of the brain. • A tiny lesion in the hypothalamus can be lethal • Homeostasis – the hypothalamus maintains the body’s internal environment in a narrow physiologic range. • Temperature, blood volume and pressure, osmolarity, pH, and oxygen levels are all regulated by hormonal mechanisms.

8. Structure and Connections of the Hypothalamus • Three zones: Lateral, Medial, Periventricular • Connections are extensive (discussed later). • Periventricular is most highly connected to the pituitary. • Controls: • Circadian rhythms • ANS to viscera.

9. Posterior Pituitary • Neurohormones are produced in the magnocelluar hypothalamus and released at the pituitary • Oxytocin • Released to initiate uterine contraction or milk letdown. • Can be triggered by somatic, visual or auditory stimuli or inhibited by stress. • Antidiuretic Hormone (vasopressin) • Regulated blood volume, pressure and osmolarity

10. ADH • The Subfornical organ detects Angiotensin II and activates the release of ADH and initiates thirst responses. • ADH acts at the level of the kidney to decrease urine production and thus increase blood volume.

11. Anterior Pituitary • Parvocellular neurosecretory cells release tropic factors that cause the production of hormones in the anterior pituitary • Hormones include: • Follicle Stimulating Hormon • Luteinizing Hormone • Thyroid Stimulating Hormone • Adrenocorticotropic hormone • Growth Hormone • Prolactin

13. The Autonomic Nervous System • The autonomic nervous system works independently to initiate typically multiple, widespread and relatively slow responses to our environment. • Sympathetic N.S. – fight or flight response. • Increase in heart rate, blood pressure, glucose mobilization, sweating, etc. • Parasympathetic – decreases heart rate, blood pressure, increases digestion, etc.

14. Organization of Neural Outputs of the CNS • CNS uses a monosynaptic pathway • ANS uses a disynaptic pathway. • Cell bodies of ANS located in Ganglion • Preganglionic neurons lead to postganglionic neurons.

15. PNS vs ANS • Operate in parallel but pathways and neurotransmitters are distinct. • Sympathetic • Emerge from T1-L3 • Preganglionic neuron is short. • Parasympathetic • Cranial nerves, cervical and sacral origin. • Long preganglionic and shot postganglioic neuron. • Each system innervates a wide variety of tissues. • Actions tend to be reciprocal.

16. Enteric Division • Lines the digestive system • Consists of the myenteric (Aurbach’s) plexus and the submucosal (Meissner’s) plexus. • Controls the transport and digestion of food. • Has sensory and ANS components. • Monitors tension and stretch of digestive system and works independently to control movement, digestive enzyme secretion, and mucous production.

17. Central Control of ANS • Hypothalamus is the main regulator of the ANS • It coordinates information from the body and other parts of the brain and provides a coordinated set of both neuronal and hormonal outputs • The periventricular nucleus (PVN) is central to control of the ANS • The nucleus of the solitary tract (located in the medulla) is also important in the control of autonomic function. • Controls output to other autonomic brain stem nuclei including those necessary for cardiac and respiratory function.

18. Neurotransmitter and Pharmacology of Autonomic Function • Preganglionic Neurotransmitters • Acetylcholine (ACh) binds to fast nicotinic receptors that initiate EPSP or slower muscarinic (G-Protein coupled ) receptors. • NPY and VIP Triggers slow responses that can last several minutes. (Effects are mostly modulatory) • Postganglionic • Parasympathetic • ACh that bind muscarinic receptors. • Very localized • Activated by either mAChR agonists or NE antagonists propranolol. • Sympathetic • Norepinepherine • Wide spread throughout body. • Activated by either NE agonists or mAChR antagonists (atropine). • Adrenal medulla releases NE and EPI and acts like a nonspecific postganglionic cell.

19. The Diffuse Modulatory Systems • Messages that must be widely broadcast through the brain use diffuse modulatory systems. • The brain uses many of these mechanisms each requiring a specific neurotranmitter. • Connections are widely dispersed throughout the brain. • Modulatory system affect wide areas to make them more or less excitable or more or less synchronously active etc. • Like volume, treble and bass controls – don’t change lyrics or melody but do change how they are preceived. • Important in motor control, memory, mood, motivation, and metabolic state. • Heavily involved in many psychiatric disorders.

20. Anatomy and Functions of the Diffuse Modulatory Systems. • Core of each system has a small number of neurons. • Neurons of the diffuse system arise from this central core (usually found in brain stem) • Each neuron has tremendous affect because it can connect to as many as 100,000 neurons. • Neurotransmitters are released into the extracellular fluid and can diffuse to many neurons.

21. The Noradrenergic Locus Coeruleus • Makes some of the most diffuse connections in the brain. • “Involved” in regulation of attention, arousal, sleep wake cycles, learning and memory, anxiety, pain, mood and brain metabolism • Activated by new, unexpected, nonpainful sensory stimuli. • General arousal to interesting events in the outside world. • Functions generally to increase brain responsiveness, speeding information processing.

22. Serotonergic Raphe Nuclei • Caudal innervate spinal cord and modulate pain-related sensation • Rostral innervate brain. • Fire most during wakefulness. • Part of reticular activating system • Involved in sleep wake cycles and stages of sleep. • Important in control of mood and emotional behaviors (Ch 21).

23. Dopaminergic Substantia Nigra and Ventral Tegmental Area. • Neurons project from Substantia nigra to striatum. • Control voluntary movements • Degeneration results in Parkinson’s disease. • VTA projects to frontal cortex and limbic system • Reward system that reinforces adaptive behaviors.

24. Cholinergic Basal Forebrain and Brain Stem Comlexes • General function not completley understood. • First cells to die in the course of Alzheimer’s disease. • Implicated in arousal, sleep wake cycles, learning and memory