Bear: Neuroscience: Exploring the Brain 3e

Chapter 15: Chemical Control of the Brain and Behavior

• Three Components of the Nervous System That Have Great Influences on Behavior – Secretory hypothalamus (all over the body) – Autonomic nervous system (all over the body) – Diffuse modulatory systems (all over the brain)

• Detailed level – Each system performs different functions

• General level – All work to maintain brain homeostasis

Synaptic Connections

Point-to-point or NOT • Mechanism to restrict synaptic communication • Brief transmission • Presynaptic “autoreceptors”

hypothalamus ANS Organs, glands,

Diffuse (ascending)

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The Secretory Hypothalamus • Function – Different for hypothalamus and dorsal thalamus

• Hypothalamus defect – Fatal disruption to body function

• Dorsal thalamus defect – Blind spot, lack of feeling

The Secretory Hypothalamus • Homeostasis – react to environment – Regulatory process: Regulates body temperature and blood composition levels

– Hypothalamus commands in cold weather – Shiver, goosebumps, turn blue

– Hypothalamus commands in hot weather • Turn red, sweat

• ALSO oxygen, glucose, salt, blood pressure, etc.

thalamus 3rd V

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The Secretory Hypothalamus • Structure and Connections of the Hypothalamus (peri includes SCN)

Suprachiasmatic nucleus

Optic Chiasm Infundibulum Connects hypothalamus To pituitary Mammillary bodies Link hippocampus to hypothalamus

Can neurons be “glands”? • Pathways to the Pituitary – POSTERIOR • MAGNOCELLULAR CELLS – Two neurohormones

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peptides – Oxytocin • Lactation, suppress hypothalamic function

– Vasopressin (ADH) – Antidiuretic hormone • Regulate blood volume and salt concentration

The Secretory Hypothalamus • Hypothalamic Control of the Posterior Pituitary • kidneys and brain Communicate Renin enzyme produced by kidneys

No BBB Also Area postremia

Anti diuretic hormone Blood volume Salt

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The Secretory Hypothalamus • Hypothalamic Control of the Anterior

Pituitary (gland, not brain?) – Anterior lobe

• Controlled by parvocellular neurosecretory cells – Secrete hormone » Bind to specific receptors on pituitary cells » Receptor activation: Pituitary cells secrete or stop secreting hormones

Parvocellular to anterior (gland) to adrenal, gonads, thyroid, etc.

Adrenal glands: Adrenal cortex and adrenal medulla STRESS – CORTISOL (STEROID hormone) Moblize energy reserves Suppress immune system

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Hypothalamus secretes CRH (corticotropin-releasing hormone) into pituitary Pituitary releases ACTH (adreno-corticotropic hormone) Into blood Stimulates Cortisol release

PTSD? • • • • •

STEROIDS CROSS BBB Enter nucleus and alter gene expression Some stress is helpful MORE calcium ions into cell Excitotoxicity?

• Lots of cortisol receptors in hippocampus • Dendrites wither, cells die

Sexual Orientation, Sexual Identity, and Brain Organization • Homosexual males - Large suprachiasmatic nucleus (SCN) while INAH of hypothalamus is smaller. • Interstitial nucleus of anterior hypothalamus • Transexuals may have difference in BNST • X linked ? Sexually DIMORPHIC

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Studied in male rats with lesions to medial preoptic area of hypothalamus (larger in males than in females) Post lesion would not mate with females. Note that in homosexual male humans, no difference in size •The amygdala influences motivation – with lesions here males would mate, but only when females were provided

Queer Science Simon Levay, visual system, 1996

Post mortem studies show hypothalamus INAH-smaller (somewhat similar to females, but not exactly ) Environmental? Cells are born during development – prenatal? Reported in press as “missing cells” Think about controls Levay wrote SF book about “converting” based on hypothalamic cell implants

same sex sexual behavior

• adaptive?? • non-humans??

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Lower motor neurons in ANS are in ganglia DIsynaptic pathway

The Autonomic Nervous System PERIVENTRICULAR ZONE

• Divisions of autonomic nervous system (ANS) – Sympathetic division • Increased heart rate and blood pressure • Depressed digestive function • Mobilized glucose reserves

– Parasympathetic division • Slower heart rate, fall in pressure • Increased digestive functions • Stop sweating

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The Autonomic Nervous System • ANS Circuits versus Somatic Motor System – ANS • Actions multiple, widespread, slow • Wide coordinated and graded control • Commands all tissue and organ except skeletal muscle • Outside CNS • Disynaptic pathway

The Autonomic Nervous System • ANS Circuits versus Somatic Motor System Somatic • • • • •

Rapid and accurate Only peripheral targets Commands only skeletal muscle Within CNS Monosynaptic pathway

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The Autonomic Nervous System • Sympathetic and Parasympathetic Divisions Sympathetic 4Fs Fight Flight Fright F (sex) Short term OK (long -unhealthy)

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The Autonomic Nervous System The Enteric Division – a brain in your gut – Location: Lining of esophagus, stomach, intestines, pancreas, and gallbladder

– Function: Control physiological processes involved in transport, digestion of food – Inputs: From brain via axons of the sympathetic and parasympathetic divisions

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The Autonomic Nervous System • Central Control of the ANS – Connections for autonomic control • Nucleus of solitary tract (medulla)

– Function of solitary nucleus • Integrates sensory information from internal organs and coordinates output

ganglion

ganglion

ACh is transmitter here – but muscarinic (not nicotinic) System conserves energy

Epinephrine is transmitter here (adrenergic - adrenaline) System mobilizes energy

Neurotransmission in the Autonomic Nervous System (CNS coordinates autonomic) sympathetic, parasympathetic (and diffuse enteric) • Most large organs are “dually innervated” • Not one or the other – rather an integration. typically as one increases, one decreases

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Fight or flight sympathetic •Pupils dilate for more light •Heart rate increases – increased blood supply •Blood shifts away from skin to the brain and muscles •Digestion slows down •Respiratory rate increases •Liver and fat cells furnish more glucose and insulin production slows down. Brain does not need insulin to utilize glucose, so the BRAIN gets

more

glucose

Rest and recuperation Parasympathetic •Pupils constrict. •Heart rate decreases. •Digestion increases. •Respiratory rate decreases.

•Insulin production goes up. •Brain gets less glucose. (Thanksgiving)

Sympathetic –fight or flight - post ganglion neurons use Epinephrine (adrenergic - adrenaline)

Parasympathetic – rest and digest both cholinergic synapses

post ganglion receptors are muscarine receptors, not nicotinic Parasympathetic Activated by muscarine (muscarinic Ach receptors) and blocked by atropine (absinthe, “Belladonna”, deadly nightshade) to dilate pupils, activate sympathetic or block parasympathetic

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excite or inhibit depends on receptors on post synaptic cells in the organs Response is not similar permits same drug to do two things

Epinephrine receptors on heart excite; on gut inhibit (diet pills)

ACh receptors on heart inhibit; on gut excite

The Diffuse Modulatory Systems of the Brain • Anatomy and Functions – Different structure and function, common principles • • • •

Small set of neurons at core Arise from central core of brain One neuron influences others Synapses release transmitter molecules into extracellular fluid

The Diffuse Modulatory Systems of the Brain • The Nonadrenergic Locus Coeruleus – Path: LOTS! – Function: Regulation of attention, arousal, sleepwake cycles, learning and memory, anxiety and pain, mood, brain metabolism – Activation: New, unexpected, nonpainful sensory stimuli

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The Diffuse Modulatory Systems of the Brain • The Serotonergic Raphe Nuclei

The Diffuse Modulatory Systems of the Brain • Dopaminergic Cells – Substantia Nigra • Projects axons to the striatum • Facilitates the initiation of voluntary movements

– Ventral tegmental area – Mesocorticolimbic dopamine system: Dopaminergic projection from midbrain

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The Diffuse Modulatory Systems of the Brain • Cholinergic Systems – Basal forebrain complex • Telencephalon, basal ganglia • Function: Unknown, participates in learning and memory

– Pontomesencephalotegmental complex • Releases ACh • Function: Regulates excitability of thalamic sensory relay nuclei

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The Diffuse Modulatory Systems of the Brain • Drugs and the Diffuse Modulatory Systems – Psychoactive drugs: Act on CNS – Many drugs of abuse act on modulatory systems • Noradrenergic • Dopaminergic • Serotonergic

The Diffuse Modulatory Systems of the Brain • Hallucinogens – LSD discovery: Accidentally by Swiss chemist Albert Hofmann – LSD chemical structure: Close to serotonin, potent agonist – Effect: Dreamlike state, mixing of perceptions – cortical areas

The Diffuse Modulatory Systems of the Brain • Stimulants

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• Three Components of the Nervous System That Have Great Influences – Secretory hypothalamus (all over the body) – Autonomic nervous system (all over the body) – Diffuse modulatory systems (all over the brain)

• Detailed level – Each system performs different functions

• General level – All work to maintain brain homeostasis

• What Stimulates an Emotion? Which comes first – the physiological changes ? or the emotions? Are changes what we interpret as emotions? (sweating, rapid heartbeat)?

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People with spinal cord injury have less knowledge about their PNS –

they also have a decrease in emotions

Upper cord damage results in very limited emotional intensity

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