The Brain and Behavior PART III

Chemical Control of the Brain and Behavior Chapter 15

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.

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.

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

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.

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.

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.

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

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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