Chapter 15: Chemical Control of Behavior

Chapter 15

Point-to-point signaling (pattern)

Restricted synaptic activation of target cells with brief duration.

Secretory neurons (pattern)

Neurons that release hormones directly into the bloodstream to affect target cells.

Autonomous nervous system (ANS) (pattern)

A system with networks of interconnected neurons that activate tissues all over the body.

Diffuse modulatory systems (pattern)

Systems that extend their reach with divergent axonal projections releasing neurotransmitters into an area.

Hypothalamus (function)

integrates somatic and visceral responses per the needs of the brain

Homeostasis

Regulatory process within the body that maintains an optimal internal environment; controlled by the hypothalamus (ex: shivering)

Four F’s of the Hypothalamus

fighting, fleeing, feeding, and fornicating

Allostasis

The body's response to abnormalities by changing its internal environment briefly; controlled by the hypothalamus

Hypothalamus Mechanisms for Regulation

endocrine, autonomic, and behavioral

Functional Zones of the Hypothalamus

lateral, medial, and periventricular (surrounding the third ventricle)

Periventricular Zone

receives input from the lateral and medial zones, as well as, the brain stem and telencephalon

Three Groups of Cells Within the Periventricular Nucleus

suprachiasmatic nucleus, ANS cells, and neurosecretory neurons

Suprachiasmatic nucleus (SCN)

Group of cells that synchronizes circadian rhythms by receiving information from the retina.

Pituitary gland

Acts as the “mouthpiece” for the hypothalamus, controlling various hormonal functions; separated into anterior and posterior lobes

Magnocellular neurosecretory cells

Cells that extend into the posterior lobe of the pituitary, releasing oxytocin and vasopressin.

Oxytocin

A peptide hormone known as the 'love hormone', released during intimate behaviors, lactation, and childbirth (positive feedback)

Vasopressin

Also known as antidiuretic hormone (ADH), regulates blood volume and salt concentration (negative feedback)

Negative feedback loop

Process where the result of a system reduces the output or activity of that system

Posterior Pituitary Pathway (for regulating blood volume)

• low blood pressure is sensed by the cardiovascular system or the hypothalamus

• hypothalamus:

  • posterior pituitary releases ADH

• cardiovascular system

  • conversion of angiotensinogen to angiotensin

  • → subfornical organ → periventricular hypothalamus → ADH

  • → subfornical organ → lateral hypothalamus → overwhelming thirst

  • → kidney → water retention

  • → blood vessels → vasoconstriction

Anterior Pituitary Gland Hormones

• FSH and LH (testes and ovaries)

• TSH (thyroid)

• ACTH (adrenal cortex)

• GH (mammary glands)

• Prolactin (melanocytes)

Parvocellular neurosecretory cells

cells that secrete hypophysiotropic hormone into the hypothalamic-pituitary portal circulation

Hypophysiotropic hormones

hormones that travel to receptors (via the median eminence) for stimulation or inhibition of anterior pituitary hormone release

Adrenal Cortex

a part of the adrenal gland, produces cortisol which is regulated via parvocellular neurosecretory cells in the hypothalamus

HPA Axis

(hypothalamus, pituitary, adrenal cortex) release cortisol

• a stressful stimulus is sensed

• neurons from the hypothalamus release corticotropin-releasing factor (CRF) into the portal circulation

• CRF stimulates the release of adrenocorticotropic hormone from the posterior pituitary to the adrenal cortex

• the adrenal cortex releases cortisol

Autonomic Nervous System

balances excitation and inhibition to achieve widely coordinated and graded control via the periventricular zone of the hypothalamus; automatically

Sympathetic division of the ANS

Part of the ANS that increases heart rate and blood pressure while depressing digestive reserves.

Parasympathetic division of the ANS

Part of the ANS that slows heart rate and blood pressure while increasing digestive function.

Somatic vs, Autonomic

somatic

• innervates and commands skeletal muscle fibers

• cell bodies are in the CNS in the ventral horn or brain stem

• monosynaptic

autonomic

• innervates and commands tissue and organs

• cell bodies are in the autonomic ganglia

• disynaptic (pre- and postganglionic neurons)

Preganglionic neurons

Neurons that drive postganglionic neurons, with cell bodies located in the spinal cord and brain stem.

Postganglionic neurons

Neurons in the autonomic ganglia that innervate and command tissue and organs.

Acetylcholine (ACh)

The neurotransmitter released by preganglionic neurons of the ANS, as well as the parasympathetic postganglionic neuron (local effect)

Norepinephrine (NE)

the neurotransmitter released by postganglionic sympathetic neurons (widespread effect)

Preganglionic axons (sympathetic vs. parasympathetic)

sympathetic

• emerge from the thoracic and lumbar segments of the spinal cord

• lie within the intermediolateral gray matter of the spinal cord

• axons go through the ventral root to synapse on neurons in the ganglia of the sympathetic chain (which lies next to the spinal cord)

  • the adrenal gland is an exception

parasympathetic

• emerge from the brain stem and sacral segments of the spinal cord

• axons go up to or directly innervate target tissue

some tissue are innervated by both divisions, others by just one division

Glands, Smooth Muscle, and Cardiac Muscle the ANS Innervates/Regulates

• secretory glands (salivary, sweat, tear, and various mucus-producing glands)

• heart and blood vessels

• bronchi of the lungs

• digestive and metabolic functions of the liver, gastrointestinal tract, and pancreas

• functions of the kidney, urinary bladder, large intestine, and rectum

• sexual responses of the genitals and reproductive organs

• immune system

The Balance of the Two Divisions of the ANS

• the divisions function inversely: when one is high, the other is low

• the sympathetic division frenetically mobilizes the body for a short-term emergency

• the parasympathetic division works calmly for the long-term good

Enteric Division (location)

lies within the lining of the esophagus, stomach, intestines, pancreas, and gallbladder; consists of 500 million neurons; sensory neurons monitor levels in these organs

Networks of the Enteric Division

the myenteric plexus and submucous plexus; they control many of the physiological processes involved in the transport and digestion of food

Nucleus of the Solitary Tract

located in the medulla and connected with the hypothalamus, integrates sensory info from the internal organs and coordinates output to the autonomic brain stem nuclei

Nicotinic receptors

Ionotropic receptors that respond to acetylcholine, causing EPSPs in postganglionic cells.

Muscarinic receptors

G protein-couples receptors that affect ion channels, causing slow EPSPs and IPSPs

Neuroactive peptides

Peptides that interact with metabotropic receptors, producing small EPSPs (neuropeptide Y and vasoactive intestinal polypeptide)

Parasympathomimetic drugs

drugs that promote the muscarinic action of ACh of inhibit the actions of NE (propranolol)

Sympathomimetic drugs

drugs that promote the action of NE of inhibit the muscarinic actions of ACh (atropine)

Epinephrine

A hormone released by the adrenal medulla due to activation by the hypothalamus.

Diffuse Modulatory Systems Common Principles

• a small set of neurons

• arise form the central core of the brain, most of them from the brain stem

• each neuron can influence many others across the brain

• synapses release transmitter molecules into the extracellular fluid so they can diffuse to many neurons

Locus coeruleus (blue spot)

• A small group of neurons in the pons that use norepinephrine (NE) for various functions.

• axons innervate the cerebral cortex, thalamus, hypothalamus, olfactory bulb, cerebellum, midbrain, and spinal cord

• functions: regulation of attention, arousal, sleep-wake cycles, learning and memory, anxiety and pain, mood, and brain metabolism

• activation: new, unexpected, nonpainful sensory stimuli

Raphe nuclei

• Neurons that release serotonin (5-HT) and are involved in sleep-wake cycles and mood regulation

• axons innervate the cerebral cortex, thalamus, hypothalamus, cerebellum, basal ganglia, temporal lobe, and spinal cord

• functions: together with the noradrenergic system, comprise the ascending reticular activating system

• activation: wakefulness, arousal, and activeness

Substantia nigra

• A brain structure that facilitates the initiation of voluntary movements via DA; degeneration leads to Parkinson’s disease.

• axons project to the striatum (caudate nucleus and putamen)

Ventral tegmental area

• innervates circumscribed regions of the telencephalon (frontal cortex and parts of the limbic system)

Mesocorticolimbic dopamine system

Dopaminergic projection from the midbrain involved in the reward pathway.

Basal forebrain complex

• Collection of nuclei at the core of the telencephalon involved in learning and memory, and sleep-wake cycles.

• medial septal nuclei innervate the hippocampus

• the basal nucleus of Meynert innervates the neocortex

Brainstem (pontomesencephalotegmental) complex

• located in the pons and midbrain tegmentum

• function: regulates excitability of thalamic sensory relay nuclei

Hallucinogens

Drugs like LSD that may inhibit firing of raphe neurons by acting on serotonin receptors.

Stimulants

Drugs such as cocaine and amphetamine that block catecholamine uptake to prolong DA and NE signaling.