Regulation

Transmission of an Impulse A resting neuron (not transmitting

an impulse) has the following electrical charge Outside is positive (+) Inside is negative (-)

The cell membrane is said to be electrically polarized b/c of the difference in charges inside & out

Polarization is caused by different concentrations of sodium (Na+) & potassium (K+)

Some of the polarization is due to the selective permeability of the cell membrane to Na+ & K+

Most of it is due to the active transport of Na+ & K+

The nerve cell membrane pumps Na+ out of the cell & K+ into the cell through active transport

Na+/K+ Pump At rest, a neuron is permeable to K+ but not

Na+, therefore the K+ that was pumped in can diffuse out leaving more (+) outside than inside (-)

During an Impulse

Stimulation/stimulus at receptor or from one neuron to another

The permeability of membrane to Na+ ↑

Since there is more Na+ outside, some diffuses in

This reverses the polarization of membrane… Inside becomes (+) Outside becomes (-)

After an Impulse

Original polarity returns Membrane no longer

permeable to Na+

Refractory period Brief period (3/1000

seconds) during which neuron cannot be stimulated again after passage of impulse

Rate of Impulse Conduction

Depends on two factors:Size of nerve fiber (larger = faster)Whether or not it has myelin

w/o = slow w/ = fast

www.biologymad.com/nervoussystem/nerveimpulses.htm

Transmission at the Synapse

The nerve impulse doesn’t cross the synapse! Instead, neurotransmitters (NT) are secreted

into the synapse and begin the impulse at the next neuron (b/c they change the permeability to Na)

Each impulse caused the release of a certain amount of NT (stronger impulse = more NT)

In order for an impulse to start in the post-synaptic neuron, it needs to reach its threshold (all or none)

The synaptic knobs contain synaptic vesicles that hold & release NT

Once a NT has finished transmitting the signal, it must be removed from gap to clear the way for new signals Enzymes remove/break down NT or they’re

reabsorbed into pre-synaptic knob/terminal branch

Acetylcholine (Ach) is excitatory; causes muscles to contract

Muscles would stay contracted until acetyl cholinesterase (Ach-ase) hydrolyzes Ach

http://www.mind.ilstu.edu/flash/synapse_1.swf

Affects of Drugs on Signal Conduction

Nerve gases inhibit Ach-ase producing spasms/paralysis of respiratory muscles therefore DEATH

Stimulants (caffeine): increase synaptic transmission; cause sleeplessness & nervousness

Depressants (barbituates): decrease body activities by blocking formation of norepinephrine (excitatory NT)

Anesthetics (ex. Novocaine): “nerve-conduction block”; decrease permeability of nerve

membrane to Na+, prevents their influx (no change in polarization) therefore stops propagation of impulse along axon or synapse & you don’t feel the pain!

Neurotransmitters (NT)

There are over 60 chemicals used as NT Acetylcholine: excitatory (inhibitory in

parasympathetic NS); lack of it may cause Alzheimer’s

Dopamine Involved in emotional behavior & motor

control Too much = schizophrenia Too little = shaking & wild movements;

lack causes Parkinson’s Amphetamines activate dopamine

receptors & cause psychotic rxns Anti-psychotic drugs block the action of

dopamine

NT continued

Serotonin Controls sleep (inhibitory) Regulates emotional responses Too little = depression Anti-depressants block the re-uptake of

serotonin into pre-synaptic neuron Glutamate: main excitatory NT in brain GABA: main inhibitory NT in brain Glycine: inhibitory

Amino Acids

Neuromodulators

Small proteins a.k.a. neuropeptides Produce changes that are longer lasting

than NT Examples

Vasopressin: increase blood pressure Somatostatin: inhibits release of hormones Oxytocin: induces labor Enkephalins: released by axons descending

from brain; inhibit passage of pain info Endorphins: released by neurons in brainstem;

block perception of pain

Chemical Control: The Endocrine System

Mechanisms

Works by action of hormones in plants & animals

(auxins & gibberellins in plants) Hormones are chemical messengers

that coordinate processes within organisms (transmit messages from one part of organism to the other)

Comparison w/ Nerve Control

Slower response time because chemical must be transported

Nerves are faster! Chemical response lasts longer

(duration) Both use chemicals (NT &

hormones)

Chemical control in plants

Characteristics of plant hormones No specific organs which produce

hormones Hormones are produced in growing

areas such as the tips of roots & stems, also buds & seeds

Auxins influence cell division, elongation &

differentiation unequal distribution of auxins = tropism (an

unequal growth response) tropisms can be cause by:

light (phototropism) gravity (geotropism) water (hydrotropism) touch (thigmotropism)

http://plantsinmotion.bio.indiana.edu/plantmotion/movements/nastic/mimosa/strongmimosa.html

Gibberellins Growth hormones; reproductive Promote flowering, fruit & seed

development

Chemical Control in Animals & Humans

Differs from plants b/c animals have glands that produce hormones

Endocrine glands ductless hormones absorbed by circulatory system &

carried to target tissue Exocrine glands

have tubes for passage Ex. sweat, tear, salivary & digestive glands

Roles of Animal Hormones

Control metabolic activities such as:

Metamorphosis (insects & amphibians)

Reproduction Growth Metabolic rate Glucose levels

Humans & other animals

Human Endocrine System

Composed of endocrine glands & their hormones

Hormones are secreted by glands into the bloodstream

Affect other tissues & organs (target tissue)

Hormones are either protein or steroid (lipid) in nature

Organization of the Endocrine System

Hypothalamus Connected to pituitary gland Controls release of hormones from

pituitary Major link b/t nervous & endocrine

systems Receives messages from nervous

system & stimulates pituitary gland Thought to control emotions

Pituitary: “Master gland” Has anterior (front) & posterior (back)

lobeAnterior lobe hormones: a. TSH (thyroid stimulating hormone)

stimulates thyroid to secrete thyroxin

b. ACTH (adrenocorticotropic hormone) stimulates production & release of

hormones called cortin from the cortex layer of the adrenal glands

used in the treatment of arthritis, asthma & allergies

c. GH (growth hormone) controls growth of long bones (by

affecting the metabolism of carbohydrates, protein & fat)

d. FSH (follicle stimulating hormone) stimulates follicles in ovaries to

develop eggs in men, controls development of sperm

in testes e. LH (lutenizing hormone)

causes release of egg from ovary & the production of the corpus luteum (female)

controls production of sex hormones (estrogen & testosterone)

f. Prolactin stimulates secretion of milk in women

after giving birth

Posterior Lobe Hormones a. Oxytocin

stimulates contraction of muscles in the uterus during childbirth

b. Vasopressin (ADH: anti-diuretic hormone)

controls reabsorption of H2O by nephrons in kidney

increase permeability of kidney tubules to H2O (so more H2O returned to blood)

Thyroid In throat, below larynx Secretes thyroxin

(contains iodine) Thyroxin regulates rate

of metabolism & is essential for normal mental development

Regulated by TSH from pituitary

pinealhypothalamuspituitarythyroidparathyroidthymus

adrenalpancreasovariestestes

Thyroid Disorders

Goiter Enlargement of thyroid due to lack of

iodine in diet (prevalent in underdeveloped countries)

Hyperthyroidism Overactive, too much thyroxin

Hypothyroidism Underactive, too little thyroxin

Endocrine disorder slide show

Parathyroid 4 small glands embedded in thyroid Secrete parathormone which

regulates Ca2+ and phosphate metabolism (ADP, ATP)

Needed for nerve function, blood clotting and strong teeth & bones

Adrenal On top of each kidney Each has 2 layers: cortex & medulla

Adrenal medulla (inner) Hormones Adrenaline (epinephrine) 80% Noradrenaline (norepinephrine) 20% Have the same effects as those

produced by nervous system (NT) but these effects last longer

secreted in response to sudden stresses (fear, anger, pain)

“Fight or Flight” response created when Both hormones constrict blood

vessels Epinephrine: increases metabolism,

release of glucose by liver, heart rate, blood pressure, breathing rate & sweating

Adrenal cortex (outer) Hormones stimulated by pituitary’s ACTH known as corticosteroids (derived from

cholesterol) Cortisol (hydrocortisone): affects

metabolism Cortisone: can be made synthetically, it

can treat arthritis, inflammation & allergies

Aldosterone: helps maintain normal mineral balance in the blood

female bodybuilder female bodybuilder2 malesteroid-bodybuilder003.jpg man whose arm exploded

Pancreas Exocrine & endocrine gland

Exocrine (ducts) secrete digestive enzymes into small

intestine Endocrine (ductless)

contain small clusters (islets) of hormone secreting cells called “Islets of Langerhans”

scattered throughout the pancreas

Two types of cells in Pancreas Alpha cells (α): secrete glucagon Beta cells (β): secrete insulin

antagonistic: work opposite of each other in carbohydrate metabolism

eat a meal glucose level in blood ↑ β cells release insulin which promotes passage

of glucose into liver cells blood sugar ↓ to “normal” (cells use glucose

for energy or store as glycogen in the liver) between meals,

blood glucose is ↓ α-cells release glucagon liver converts it’s glycogen to glucose glucose enters bloodstream & blood glucose

levels return to “normal”

Disorders Diabetes

when the Islets of Langerhans fail to produce enough insulin

not enough glucose enters liver cells therefore blood sugar level rises, excess sugar is excreted in urine

Type II: non-insulin dependent (controlled by diet); usually occurs after age 60

Type I: usually occurs early in life; insulin

& diet dependent

Gonads (sex glands) Produce hormones that control sexual

development Female glands: ovaries; produce egg

cells Male glands: testes; produce sperm

cells Egg & sperm are called gametes

Ovaries produce 2 hormones

estrogen: stimulates development of female reproduction system & secondary sex characteristics (breasts, wider hips)

progesterone: acts w/ estrogen to regulate menstrual cycle

Testes produce hormones called androgens

(ex. Testosterone) stimulates development of male

reproduction system & secondary sex characteristics (facial hair, deep voice)

anabolic steroids are derived/synthesized from testosterone!

Thymus In upper chest, near

the heart Produces hormone

thymosin Large in infants,

shrinks in teens (produces lymphocytes)

No major function in adults

Pineal Gland Base of the brain Produces melatonin

and influences pigment cells

May also inhibit sexual development

Also involved in sleep/wake cycles

Regulation of Hormone Secretion

Feedback Glands secrete hormones as a result of a nerve

impulse or other chemicals stimulating the glands

Most work by negative feedback Ex. Thermostat

Low temp. → turns furnace on High temp. → turns furnace off

When one change opposes original change ↑A → ↑B → ↓A until A reaches homeostasis

Some work by positive feedback Amplifies original change/ when one change

reinforces original change ↑A → ↑B → ↑A → ↑B