Chapter 1 Organization of the Nervous System

Hypothalamus

Outline

• Function of the Hypothalamus

• Regulation of Body Temperature

• Autonomic Nervous System

I. Function of the Hypothalamus

• Reference– Adina Michael-Titus, et al. System of the Body – The

Nervous System. 2nd version, Elsevier Limited, 2011. P19 – 20

– 姚泰主编， 8年制及 1年制临床医学等专用生理学，第二版，人民卫生出版社， 2010年。 P 483 – 485。

Tu :19.17

 Hypothalamus

Hypothalamic Functions

• Food Intake• Water Balance• Sleep/wake cycle• Emotions and behavior• Circadian• Endocrine Functions• Body Temperature• Autonomic Nervous System

Food Intake

• Ventromedial and Paraventricular Nuclei are satiety centers– Lesion causes obesity– Through disrupting satiety input to the periventricular nucleus

• Lateral HT is feeding center – Stimulation cause food and water intake– Lesion causes starvation behavior– Through damage the medial forebrain bundle, leading to neglect syndrome – no

motivation to eat

Water Balance

• Thirst center in the hypothalamus (supraotic nucleus) is stimulated by:– Cellular dehydration– Decreased salivary production– Increased blood osmotic pressure– Decreased blood volume

• Thirst center response– Release vasopressin– Cause sensation of thirst

Sleep/Wake Cycle:

suprachiasmatic nuc is biological clock

preoptic nuc can initiate sleep

lat HT can change cortical arousal

post HT lesion can cause coma or impaired arousal

Emotions and Behavior

Ventromedial lesions can cause viciousness/rage

Posterior HT stimulates sympathetic functions

Anterior HT stimulates parasympathetic functions

Mamillary nuclei recent memory

Almost all land animals coordinate their

behavior according to circadian rhythms

Suprachiasmatic Nuclei (SCN)

Circadian

Circadian Rhythms of Physiological Functions

Endocrine Function

• Regulation of Adenohypophysis

• Secretion of Hormones (Vasopressin and Oxytocin)

Functions of the Hypothalamus

• Food intake

• Water balance

• Sleep/wake cycle

• Emotions and behavior

• Circadian

• Endocrine Function

• Body temperature

• Autonomic Nervous System

II Energy metabolism and body temperature

Reference

• Arthur C. Guyton, John E. Hall. Textbook of Medical Physiology, 11th edition, Elsevier Science, 2006. P 881-900

• 姚泰主编， 8年制及 7年制临床医学等专用生理学，第二版，人民卫生出版社， 2010年。 P 483 – 485。

Section 1 Energy Metabolism

materialsynthesis

materialbreakdown

releaseenergy

requireenergy

materialmetabolism

energy metabolism

Metabolism

Anabolism Catabolism

Energy storage, liberation, transfer and utilization

Energy balance

Energy input = energy output

heatFood heat heat ATP cellular functions heat

metabolismFood heat

Metabolic Rate

• The amount of energy liberated from a living organism per unit of time

• Expressed in terms of the rate of heat liberation during the chemical reactions

Measurement of the metabolic rate

• Direct calorimetry• Indirect calorimetry

– Caloric value / thermal equivalent of food– Oxygen consumption / thermal equivalent of

oxygen （ 1 L）– Respiratory quotient （ CO2 / O2）

Factors that affect the metabolic rate

• Exercise - increase in metabolic rate• Ingestion of food - Increase metabolic rate

– The specific dynamic action of protein

• Emotional state• Environmental temperature

– 20-30 °C have stable metabolic rate– < 20 or >30°C , metabolic rate is increased

• Other factors (sleep, sex, age, etc.)

Component of Energy Expenditure

Basal metabolic rate (BMR)

• minimum level of energy required to exist– a person is at basal condition (complete rest)

• useful for diagnosing the diseases:– Hyperthyroidism, hypothyroidism

Basal conditions

• Fasted for at least 12 hours• After a night of restful sleep• No strenuous activity is performed for at least 1

hour before the test• All psychic and physical factors that cause

excitement must be eliminated• The temperature 25 – 30 °C • No physical activity is permitted during the test

Section 2 Body temperature

Skin and Core Temperature

• Skin temperature– the temperature of the skin and tissues immediately underlying

the skin. rises and falls with the temperature of the surroundings

• Core temperature – the temperature of the deep tissues of the body – the “core” of

the body. – remains almost constant, varying not more than 1 °C

• Rectal T: 36.9-37.9 °C • Oral T: 36.7-37.7 °C • Axillary T: 36.0-37.4 °C

Range of Body TemperatureRange of Body Temperature

Factors affecting normal temperature

• Circadian rhythm– In the early morning, the body T is the lowest.

– In late afternoon or early evening, it is the highest.

• Age– Newborn child > adult > old person

• Sex– Women > man 0.3 °C

• Muscular activity• Other factors: emotion, eating, change in climate

Heat Production

• BMR of all the cells• Extra metabolism caused by

– muscle activity

– hormone (thyroxine, growth hormone and testosterone)

– the effect of epinephrine,

– norepinephrine and sympathetic stimulation on the cells

– increased chemical activity in the cells themselves

Heat Loss

• The major organ to loss heat is the skin• Blood flow to the skin from the body core provides heat transfer

Methods of heat loss from the skin to the surroundings

Effect of Environment air Temperatureon Conductance of Heat from the Body

•1) Insensible perspiration

•2) Sweating•Innervated mainly by

sympathetic cholinergic nerve

(acetylcholine)

•Caused by nervous reflex

•Mechanism of sweat secretion

• Primary secretion• • reabsorption

• Sweat (urea, lactic acid, K+ )

Evaporation

Regulation of the body temperature

• Behavioral control of the body temperature

• Autonomic control of the body temperature

Feedback mechanisms of regulation of the body temperature

• Temperature receptor– Peripheral temperature receptor

• Locations: skin, mucous,, abdominal viscera• Types: cold receptor and warmth receptor• cold receptor > warmth receptor

– Central temperature receptor• Locations: spinal cord, preoptic and anterior hypothalamic area of the

hypothalamus (PO/AH)• Types: heat-sensitive neurons and cold-sensitive neurons

• Temperature-regulating center– 1) The thermoregulating center is mainly in the hypothalamus– 2) The PO/AH area is the basic thermostatic temperature

controlling center

Feedback mechanisms of regulation of the body temperature

• Efferent pathways: Control of the heat loss and heat production

– Control of the skin vascular tone and sweating by sympathetic nerve system

– Changes of the muscular tension by somatic motor nerve system

– Control of the metabolic rate by altering the function of endocrine system, mainly the hormone secretion of the thyroid glands or adrenal medulla

“Set-point”

37 °C

PO/AH area

T > 37 °C

Production < loss

T < 37 °C

Production > loss

Fever

III Autonomic Nervous System

• Reference– Adina Michael-Titus, et al. System of the Body – The

Nervous System. 2nd version, Elsevier Limited, 2011. P24 – 28

– 姚泰主编， 8年制及 7年制临床医学等专用生理学，第二版，人民卫生出版社， 2010年。 P 478 – 482

Section 1. Basic of the ANS

• Including – parasympathetic– sympathetic– enteric divisions

• Coordinates cardiovascular, respiratory, digestive, excretory and reproductive systems

• The enteric system– an independent nervous system responsible for

regulation of digestive functions.

Somatic and Autonomic Nervous System

Somatic and Autonomic Nervous System

Somatic• Skeletal muscle• Conscious and

unconscious movement• Skeletal muscle

contracts• One synapse• Acetylcholine

Autonomic• Smooth and cardiac

muscle and glands• Unconscious regulation• Target tissues

stimulated or inhibited• Two synapses• Acetycholine by

preganglionic neurons and ACh or norepinephrine by postganglionic neurons

• Preganglionic cell bodies in lateral horns of spinal cord T1-L2

Sympathetic Division

Parasympathetic Division

• Preganglionic cell bodies in nuclei of brainstem or lateral parts of spinal cord gray matter from S2-S4– Preganglionic axons from

brain pass to ganglia through cranial nerves

– Preganglionic axons from sacral region pass through pelvic nerves to ganglia

Preganglionic axons pass to terminal ganglia within wall of or near organ innervated

Parasympathetic and sympathetic

nerve distribution

2. Neurotransmitters and Neuroreceptors

• Acetylcholine and Norepinephrine

• All preganglionic neurons are cholinergic

• Parasympathetic post ganglionic neurons are cholinergic

• Sympathetic post ganglionic neurons are adrenergic except

• Sympathetics innervating sweat glands, blood vessels in skeletal muscle, and piloerection muscles are cholinergic

Neurotransmitters

ACh AChSweatglands

Striatedmuscle

AChSOMATIC NERVOUS SYSTEM

HeartSm. mus.Glands

ACh AChParasympathetic

AChE, NE

Ad. M.

HeartSm. mus.Glands

ACh NE

AUTONOMIC NERVOUS SYSTEM

Sympathetic

Section 3 Function of the Sympathetic and Parasympathetic Nerve

SNS

• Sympathetic nervous system prototypically “fight” or “flight”.

• Associated with increased

energy expenditure

cardiopulmonary adjustments for intense activity,

blood flow adjustments for maximum energy expenditure.

SNS - Fight & Flight Reaction

You’re walking alone at night and all the sudden you hear an unfamiliar noise near by… In a matter of seconds,

your heart rate increases dramatically, blood vessels in your skeletal muscles dilate, blood vessels in the visceral muscles constrict, digestion is ceased, your liver ramps up glucose release, your pupils dilate, salivary production decreases, sweat increases.

Parasympathetic Nervous System

• If that noise turns out to be the result of wind, then the body is returned to “pre-noise” state.

• This is the job of the parasympathetic nervous system.

Autonomic Nervous System• Parasympathicus• Wind down,

relaxation, digestion• Dominated by

Acetylcholine

• Sympathicus • Fight & Flight

Reaction• Dominated by

Noradrenaline (Adrenaline)

• Fear, exercise, rage

Interactions of the ANS

• Most visceral organs are innervated by both types of nerves.

• Most blood vessels are innervated only by sympathetic nerves.

• PS activity dominates the heart and GI tract.• Activation of the sympathetic division causes wide spread,

long-lasting mobilization of the fight-or-flight response. • PS effects are highly localized and short lived.