Chapter 10 Flashcards
Puberty brings about many changes in the human body.
- Both genders get a growth spurt during puberty, & the 2ndary sex characteristics begin to develop.
- Males= the growth of body and facial hair, deepening of the voice, & the development of the genitals.
- Females= the growth of body hair, the onset of their menstrual cycle, & the development of breasts & broader hips.
- All of these developments r timed & controlled by hormones
A hormone is
a chemical made by cells in one part of the body that regulate the processes of cells in another part of the body
- are prduced by the endocrine system
- act as chemical messengers, enabling 1 part of the body to give instructions to another part
- Some cells even self-regulate, producing chemicals to stimulate their own cellular processes
Local regulators are
chemicals like hormones but act on nearby cells, rather than cells some distance away.
Hormones r secreted by…
the cells, tissues, & organs that compose the endocrine system
The endocrine system does what?
Regulates & coordinates organ functions like growth, development, reproduction, behavior, energy metabolism, & water balance. (like the nervous system)
The nervous system & Endocrine system
- Both systems regulate & coordinate body functions.
- r structurally, chemically, & functionally related, but they control organ & tissue functions in diff ways
–> Nervous system: Sends fast electrical signals for rapid responses to the external environment.
–> Endocrine system: Uses slower, longer-acting hormonal responses to control organ and tissue functions. - Nervous system regulates the release of most hormones, ultimately controlling the endocrine system.
Endocrine glands are
ductless secretory organs that secrete their hormones
directly into the blood or extracellular fluid.
–> (In contrast, exocrine glands, like the sweat & salivary glands, release their secretions into ducts that lead outside the body or into the body cavities)
- Hormones circulate throughout the body in blood & other fluids.–> As a result, most body cells r constantly exposed to a wide variety of hormones but only target cells will respond to a specific hormone cuz only they have receptor proteins that recognize & bind to that type of hormone
- Hormones r cleared from the body at a steady
rate by enzymatic breakdown in their target cells, in the blood, or in organs such as the liver or kidneys. –> The breakdown products are reused or excreted
There are more than ____known hormones and local regulators in humans. How do they compare to hormones and regulators in other animals?
60
- Many r identical or very similar in structure & function to the hormones in other animals, tho many animals have hormones not found in humans.
Hormones are identified by their _____________________.
chemical structure
There are 2 main types of Hormones:
- protein hormones, which are water soluble,
- steroid hormones, which are lipid soluble.
- Most hormones fall into one of these two types
A protein hormone is
a hormone composed of chains of amino acids that is water soluble; usually acts on cell membrane receptors
- amino acid chains= 3 amino acids to more than 200
- released into the blood or extracellular fluid by the cells in the endocrine glands where they are made.
- usually hydrophilic: they have an affinity for water & diffuse well through the blood & intercellular fluids
- 1 group of protein hormones= the growth factors, regulates the division & differentiation of many types of cells in the body
A steroid hormone is
a hormone composed of cholesterol that is not very water soluble; usually passes through the cell membrane & acts on receptors inside the cell
- not very soluble in blood but they can pass easily through the lipid bilayer of cellular membranes
–> Combine with hydrophilic carrier proteins to form water-soluble complexes, enabling diffusion into blood & other fluids.
- When it contacts a cell, it is released from its carrier protein.
- passes through the plasma membrane of the target cell & then binds to internal receptors in the nucleus or cytosol.
- Steroid hormones include aldosterone, cortisol, & the sex hormones. –> all natural
Some steroid hormones have very similar structures but produce very diff effects. Give an example
- ex, testosterone & estradiol, 2 major sex hormones that r responsible for the development of male & female characteristics, respectively, differ only in the presence or absence of a single methyl group
Prohormones
- Many hormones r secreted in an inactive or less active form called prohormones
- Prohormones r converted to active forms by target cells or enzymes in blood or tissues.
- Protein hormones are commonly synthesized as prohormones, which r then converted to the active form in the source cell –> some cases, further conversion occurs once the hormone has been secreted
- Ex, Angiotensinogen, secreted by the liver, is an inactive precursor. –> Cleaved by enzyme to an inactive form of angiotensin, which is activated by angiotensin-converting enzyme (ACE) to regulate blood pressure by increasing it. –> ACE inhibitors r used to manage high blood pressure.
Hormones are usually secreted in relatively ________________, but a process of amplification magnifies their effect. Explain
small amounts
- Once a receptor cell activates a few proteins, these
proteins activate other proteins, each of which activates other proteins, and so on.
- This chain reaction amplifies the effect of the small amount of hormone initially received.
Pathways for Water-Soluble Hormones
- Hormones use 2 main mechanisms to control cellular activities.
- The 1st mechanism governs water-soluble protein hormones (protein hormones), which cannot easily cross membranes
- bind to receptor molecules in the cell membrane, causing the receptor molecule to change shape.
- This activates a signal, which passes into the cell
- This signal can lead to internal changes in the cell, such as releasing enzymes that modify proteins by adding or removing phosphate groups.
- The signal may act only in the cytosol or affect the nucleus, as with many protein hormones such as growth factors
- Ex of the surface receptor mechanism is the protein hormone glucagon. –> When glucagon binds to surface receptors on liver cells, it triggers a series of reactions.
–> These reactions lead to the addition of phosphate groups, which activate the enzyme that governs the breakdown of stored glycogen into glucose.
glucagon is
a hormone produced by alpha cells in the pancreas that raises the blood glucose level by promoting the breakdown of glycogen in the liver
Pathways for Lipid-Soluble Hormones
The 2nd main mechanism involves hormones binding to receptors inside a cell –> used by most steroid hormones
- Steroid hormones=lipid based= lipid soluble= they pass easily through the plasma membrane.
- attach to receptors in the cytosol or nucleus of a cell.
- The hormone-receptor complex then binds to a control sequence on a specific gene, turning the gene’s action on or off.
- Activation & deactivation of the gene changes the
amount of protein that it synthesizes, which changes the cellular activity
- Ex,steroid hormone aldosterone.
-Secreted by adrenal glands when bp is low. - Travels through membranes & binds to receptors in kidney, sweat gland, & colon cells.
- The receptor acts as a transcription factor, synthesizing proteins that increase sodium reabsorption.
- Increased sodium leads to water retention, raising blood pressure.
The two mechanisms used by hormones are not mutually exclusive. Explain.
A single target cell may have receptors for several hormones & respond differently to each hormone.
- Ex, the liver cells of vertebrates have receptors for the pancreatic hormones insulin & glucagon.
- Insulin increases the uptake of glucose & its conversion to glycogen, which decreases the blood glucose level.
- Glucagon stimulates the breakdown of glycogen into glucose, which increases the blood glucose level.
particular hormones can interact with diff types of receptors in or on a range of target cells. Elaborate
- Diff responses r then triggered in each target cell
cuz the receptors trigger diff signal pathways. - As well, the response to a hormone may differ among species.
- Ex, melatonin, a protein hormone derived from tryptophan, is important in regulating daily & annual cycles in most animals. –> But, it also plays a role in regulating the salt glands of marine birds.
In summary, the mechanisms by which hormones work have 4 major features:
1) Only the cells that contain surface or internal receptors for the hormones respond to the hormones.
2) Once bound to their receptors, hormones produce a response by turning cellular processes on or off. They do this by altering the proteins that r functioning in or produced by the cell
3) Hormones are effective in very small concentrations cuz of the amplification that occurs in both the surface and internal receptor mechanisms.
4) The response to a hormone differs among target organs and among species.
Hormones as Part of Feedback Mechanisms
- Most hormones r regulated by negative feedback mechanisms.
- In a -ve feedback mechanism, a chemical that is affected at the end of the action pathway of a hormone controls the further action of the hormone by inhibiting an earlier chemical reaction.
- A response in a feedback loop may be the production of a substance or a decrease in the production of a substance
- Ex, hypothalamus releases thyroid-releasing hormone (TRH), which initiates a pair of hormone releases by the pituitary and thyroid glands.
- As the concof the thyroid hormone in the blood increases, it inhibits an earlier step in the pathway, the secretion of thyroid-stimulating hormone (TSH) by the pituitary gland.
Regulation of Body Processes by Hormones
- Some glands make multiple hormones, & many body processes r influenced by multiple hormones simultaneously.
- Glucose, fatty acids, and ions (e.g., Ca²⁺, K⁺, Na⁺) levels r regulated by hormones from different glands.
- Functions such as metabolism, digestion, growth, sexual development, & stress responses rely on multiple hormones.
- many systems= negative feedback loops adjust the level of secretion of hormones that act in opposing ways.–>maintains homeostasis in the body.
–> Consider regulation of fuel molecules, like glucose, fatty acids, &amino acids, in the blood. Between meals, 5 diff hormone systems, involving the digestive
tract, pancreas, nervous system, & pituitary & adrenal glands, all act together in a coordinated fashion to keep the body’s fuel levels in balance.
Many other important hormones are secreted
by other organs, such as…
the heart, liver, kidneys, and intestines, & have diff primary functions.
The hypothalamus is
the region of the brain that releases hormones to control the pituitary gland, which, in turn, controls
other endocrine glands
- It is a region of the brain & thus part of the nervous system.
- Neurons (nerve cells) in the hypothalamus make a special type of hormone= neurohormones.
A neurohormone is
a hormone produced by neurons, such as in the hypothalamus, that controls the production of other
hormones in the pituitary gland
- The neurohormones travel along the length of the nerve cells, diffuse into the bloodstream, & then travel through the blood into the pituitary
-2 types of neurohormones made by hypothalamus: releasing hormones & inhibiting hormones
–> either stimulate or inhibit the release of specific hormones that r made in the anterior pituitary gland.
- The hormones secreted by the endocrine cells inside the anterior pituitary gland r then released into bloodstream to reach their target tissues, where they control many other endocrine glands & some bodily processes directly
The hypothalamus itself is controlled by input from other parts of the nervous system. Elaborate.
- Some neurons connect directly to the hypothalamus from sensory receptors that monitor lood for changes in body chemistry or temp.
- Input to the hypothalamus also comes from numerous connections from control centres elsewhere in the brain.
- -ve feedback systems help to control how the hypothalamus releases its hormones
The pituitary gland is
a two-lobed gland located within the cranium, just below the brain that produces hormones that control the other endocrine glands
- It has 2 major lobes: the anterior lobe & posterior lobe
- Neurohormones travel through a portal vein connecting the capillaries in the hypothalamus to those in the anterior pituitary gland.
- The portal vein=a critical link between the nervous & endocrine system, as most blood entering the anterior pituitary must first pass through the hypothalamus, allowing the neurohormones to go from hypothalumus to anterior pituitary gland
The pituitary gland is referred to as the _______________ because…
- “master gland”
- it produces hormones that control most of the other endocrine glands
- anterior pituitary secretes several major hormones into the bloodstream, some that drive hormone secretion in other glands.
- posterior pituitary gland stores & releases 2 important hormones, 1 of which helps to control
bp.
Anterior pituitary gland overview
- endocrine system= largely controlled by the anterior pituitary hormones, which, in turn, r controlled by the releasing or inhibiting hormones that come from the
hypothalamus. - The anterior pituitary secretes 8 major hormones into the bloodstream: prolactin, growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, melanocyte-stimulating hormone, endorphins
Anterior Pituitary Gland: PRL
- Full form: Prolactin
- influences reproductive activities & parental care in vertebrates.
- In mammals: stimulates the development of the secretory cells of the mammary glands during late pregnancy, & milk synthesis after birth
- Stimulation of the mammary glands & the nipples, which occurs during suckling, leads to the release
of PRL. - In all vertebrates, it has a role in promoting both maternal & paternal behaviour
- found in non-mammalian vertebrates, where it has a variety of functions. –> Ex, In fish, it is one of the hormones that controls H20 balance.
Anterior Pituitary Gland: GH
- Full form: Growth Hormones
- Stimulates cell division, protein synthesis, and bone growth in children & adolescents, causing overall body growth.
- stimulates protein synthesis & cell division in adults.
- GH binds to target tissues like muscle, triggering release of insulin-like growth factor (IGF),a protein hormone that directly stimulates the growth processes
- controls # of major metabolic processes in mammals: conversion of glycogen–>glucose, fats–>fatty acids to regulate their levels in the blood.
-stimulates body cells to take up fatty & amino acids & limits the rate at which muscle cells can take up glucose. –> helps to maintain the availability of glucose & fatty acids to tissues & organs between meals, which is particularly important for the brain.
Growth Hormone defiencies & overproduction
- In humans, deficiencies in GH secretion during childhood produce pituitary dwarfs, who remain
small in stature - Overproduction of GH during childhood or adolescence, usually cuz of tumour of the anterior pituitary, makes pituitary giants, who may grow up to 2.7 m in height
Tropic Hormones
are hormones secreted by the anterior pituitary gland that control endocrine glands elsewhere in the body.
- the tropic hormones secreted by anterior pituitary gland r Thyroid-stimulating hormone (TSH), Adrenocorticotropic hormone (ACTH),
Follicle-stimulating hormone (FSH), Luteinizing hormone (LH)
Anterior Pituitary Gland: TSH
- Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to grow in size & secrete thyroid hormones
Anterior Pituitary Gland: ACTH
- Adrenocorticotropic hormone (ACTH) triggers hormone secretion by cells in the adrenal cortex.
Anterior Pituitary Gland: FSH
Follicle-stimulating hormone (FSH) affects egg development in females and sperm production in males.
- also stimulates the secretion of sex hormones in female mammals.
Anterior Pituitary Gland: LH
Luteinizing hormone (LH) regulates part of the menstrual cycle in human females and the secretion of sex hormones in males.
- FSH & LH r grouped together as gonadotropins cuz they regulate the activities of the gonads
Anterior Pituitary Gland: MSH
Melanocyte-stimulating hormone (MSH) named cuz of effect on melanocytes, skin cells that contain black pigment melanin
- Increased MSH secretion darkens the skin in fish, amphibians, reptiles, & humans–> less noticeably in humans.
- MSH secretion increases in pregnant women –> combined with elevated estrogen levels, increases skin pigmentation –> effects= reversed after child birth
Anterior Pituitary Gland: Endorphins
protein hormones made by hypothalamus & the pituitary gland
- released by the intermediate lobe of the pituitary gland.
- humans= the intermediate lobe isn’t well developed, comprising only a thin layer of cells between the anterior & posterior lobes.
- In the nervous system, endorphins act as
neurotransmitters in pathways that control pain, thereby inhibiting the perception of pain. –> Hence, endorphins are aka “natural painkillers.”
The posterior lobe of the pituitary gland stores and releases 2 important hormones…
antidiuretic hormone & oxytocin, into the bloodstream
- produced in the cells of the hypothalamus
- r transferred to the posterior pituitary gland along nerve cells that reach from the hypothalamus into the posterior pituitary –> stores the hormones & releases them into the bloodstream when appropriate nerves from the hypothalamus r stimulated.
Antidiuretic hormone
- aka ADH
- Stimulates kidney cells to reabsorb more water from urine, increasing blood volume.
- released when hypothalamus sensory receptor cells detect increase in the blood Na+ conc after salty meal or when the body is dehydrated
- also released when severe blood loss or drop in bp.
- Inhibited by: Ethanol & caffeine, causing increased urine volume.
- Stimulated by: Nicotine & emotional stress, causing H20 retention.
- Stress relief & the return to normal ADH secretion often results in increased urination.
- ADH helps maintain bp by reducing H20 loss & causing blood vessels in some tissues to constrict
ADH & Kidneys
- enables the kidneys to maintain a homeostatic balance of extracellular fluid in the body
- about 85% of H20 filtered into nephrons is reabsorbed in the proximal convoluted tubule.
- remainder is absorbed in the distal convoluted tubule only if ADH is present
- ADH causes the upper part of distal convoluted tubule to be permeable to water. The high conc
of NaCl in the interstitial fluid causes water to move, by osmosis, out of the upper part of the distal tubule & the collecting duct into the interstitial fluid. - It is the control of this volume of water (15 %) in the kidneys that balances the conc of the body fluids.
- Hormones like ADH r also secreted in fish, amphibians, reptiles, & birds. –> In amphibians, they increase amount of water that enters the body through skin & from the urinary bladder.
Oxytocin
- stimulates the release of milk from the mammary
glands of a mother. –> stimulation of the nipples in suckling sends neuronal signals to the hypothalamus & leads to the release of oxytocin. - released oxytocin stimulates more oxytocin secretion by a positive feedback mechanism
- causes the smooth muscle cells surrounding the mammary glands to contract, forcibly expelling the milk through the nipples
- entire cycle, from onset of suckling to milk ejection, takes < 1min in mammals.
- also plays a key role in childbirth by stimulating the contraction of the muscles of the uterus
- In males, it’s secreted into the seminal fluid by the testes.
- When seminal fluid is ejaculated into the vagina, oxytocin stimulates contractions of the uterus, which aid the movement of sperm through the female reproductive tract
The Thyroid gland
located in the front of the throat in humans & is shaped like a bow tie.
- secretes the same hormones in all vertebrates
- The thyroid hormones have an extraordinarily wide range of effects
- The primary thyroid hormone, thyroxine, is aka T4 cuz it contains 4 iodine atoms –> A supply of iodine in the diet is needed to make all of these hormones.
PRINT PAGE 478 DIAGRAM
When there is not enough iodine to make thyroxine…
- the negative feedback loop fails and the thyroid is continually stimulated by TSH from the pituitary gland
- The overstimulated thyroid swells and results in a condition called a goiter, which can result in a noticeable swelling on the neck
- To ensure that people get enough iodine in their diet to produce thyroxine & prevent goiter, iodine
is added to table salt in many places in the world, including Canada.
is the thyroid hormone T4 a steroid hormone?
NO, but it is lipid soluble and can pass through the cell membrane.
- Once inside, T4 loses an iodine atom & is converted into T3.
- T3 enters the nucleus & combines with nuclear receptors. –> There, it alters gene expression, bringing about many of its effects –> increases the metabolic rate; essential for normal body growth
Thyroid hormones are vital to… Elaborate.
….growth, development, maturation, & metabolism
in all vertebrates.
-They interact with growth hormone for their effects on growth & development
- also increase the sensitivity of many body cells to
the effects of epinephrine & norepinephrine: hormones released by the adrenal medulla as part of the fight-or-flight response.
- In amphibians, rising conc of thyroid hormones trigger metamorphosis or a change in body form from tadpole to adult .
- also contribute to seasonal moulting, leading to changes in the plumage of birds & the coat colour of mammals.
Calcitonin
A Protein hormone secreted by specialized thyroid cells as the principal source; also made in lungs & intestines.
-discovered in fish by Dr. Harold Copp, a professor
at the University of British Columbia
- lowers the level of Ca2+ in the blood by inhibiting the ongoing release of calcium from bones.
- Stimulated by high blood Ca²⁺ levels & inhibited by low blood Ca²⁺ levels.
The parathyroid glands
- found only in amphibians, reptiles, birds, & mammals.
- Mammals have 4 parathyroid glands, 2 on each side of the posterior surface of the thyroid gland.
- Each parathyroid= spherical structure about pea size.
- The only hormone they make= parathyroid hormone (PTH), is secreted in response to a fall in the Ca2+ level in the blood
- The PTH pathway= negative feedback loop.
- PTH stimulates bone cells to dissolve the mineral matter of bone tissues, releasing both Ca2+ & P3- ions into blood.
- The released Ca2+ is available for enzyme activation, conduction of nerve signals across synapses, muscle contraction, blood clotting, & other uses.
- Although fish do not have a parathyroid gland, they make PTH & have PTH receptors. However, the origin of the hormone & its precise function remain uncertain.
PTH & Kidney
PTH stimulates enzymes in the kidneys to convert vitamin D, a steroid-like molecule, into calcitriol, its fully active form in the body.
- The activated vitamin D increases the absorption of Ca2+ & phosphates from ingested food by promoting
the synthesis of a calcium-binding protein in the intestines.
- It also increases the release of Ca2+ from bones in response to PTH.
PTH underproduction causes the….
the Ca2+ conc in the blood to fall steadily, disturbing nerve and muscle function.
- As a result, the muscles twitch & contract uncontrollably, & convulsions & cramps occur. –> Without treatment, the condition is usually fatal cuz the severe muscular contractions interfere with breathing
Overproduction of PTH results in…
the loss of so much calcium from the bones that
they become thin and fragile.
- This condition is known as osteoporosis. At the same
time, the elevated Ca2+ conc in the blood causes calcium deposits to form in soft tissues, especially in the lungs, arteries, & kidneys (where the deposits
form kidney stones)
The adrenal glands
- ( ad= “near” and renes=“kidneys”)
- mammal adrenal glands of have 2 distinct regions.
- 1) The central region, aka adrenal medulla, contains highly modified neurosecretory neurons.
-2) The tissue surrounding the adrenal medulla, aka the adrenal cortex, contains non-neural endocrine cells. - The 2 regions secrete hormones with entirely diff functions.
The adrenal medulla secretes
- secretes 2 adrenal hormones: epinephrine & norepinephrine
–> r chem that can act as hormones or neurotransmitters (chemicals that transmit nerve signals) –> They bind to receptors in the plasma membrane of their target cells. - Norepinephrine is also released as a neurotransmitter by some neurons of the nervous system
- they are secreted when the body encounters stresses like excitement, danger (fight-or-flight situations), anger, fear, infection, injury, and even anxiety
The adrenal cortex secretes
several hormones, like aldosterone & cortisol
- Aldosterone= main hormone of mineralocorticoids, is involved in osmoregulation & control of bp.
- Cortisol= main hormone of glucocorticoid hormones that help to regulate blood glucose levels & promote
fats & protein breakdown as alternative fuels when the glucose supply is low
Function of Epinephrine
-prepares the body for handling stress or physical activity
- It causes the heart rate to increase and glycogen & fats to break down, releasing glucose & fatty acids into the blood as fuel molecules
- In the heart, skeletal muscles, & lungs, the blood vessels dilate to increase blood flow. –> Elsewhere, the blood vessels constrict.
- This raises bp, reduces blood flow to the intestines & kidneys, & stops smooth muscle contractions, thus reducing water loss & slowing down the digestive system.
- Airways in lungs dilate, increasing air flow.
- The effects of norepinephrine on heart rate, bp, & blood flow to the heart muscle r similar to those of epinephrine.
The effects of epinephrine are what make it a life-saving drug. Elaborate
- life-saving for someone who is experiencing a severe allergic reaction called anaphylaxis.
- A person who has an extreme allergy can go into shock & die from an anaphylactic reaction.
- Epinephrine counters anaphylaxis. –> Its effects are immediate, opening airways and raising bp. People with severe allergies often carry a pen-shaped epinephrine auto-injector that they can use in an emergency
The pineal gland is
an endocrine gland located in or on the brain of vertebrates that secretes the hormone melatonin to
regulate daily biological rhythms
- Melatonin is a neurohormone secreted by the pineal gland, primarily during periods of darkness. –> as light hitting the eyes generates signals that inhibit melatonin secretion.
- Melatonin targets hypothalamus to synchronize the biological clock with daily light-dark cycles, maintaining biorhythms.
- The nightly release of melatonin may help to synchronize the biological clock with daily cycles of light & darkness. –> Jet lag occurs as the biological clock adjusts to a new time zone, reflects time that is required for melatonin secretion to reset a traveller’s daily biological clock to match the period of daylight in a new time zone
- Melatonin is found throughout animal kingdom, as well as in many plants & fungi.
- In invertebrates, it helps control diurnal (daily) rhythms
location of pineal gland
- mammals= near the brain centre
- birds & reptiles= the surface of the brain, just under the skull, & is directly sensitive to light.
- Some of earliest vertebrates had a light-sensitive organ at the top of the head (a third eye), & some lizards retain an eyelike structure in this location.
- In most vertebrates, the third eye became modified into a pineal gland, which may retain some degree of photosensitivity
- In mammals, it is too deeply buried in the brain to be affected directly by light.
- Nonetheless, specialized photoreceptors in the
eyes make connections to the pineal gland.
Overview of the Invertebrate Endocrine System- Insect Growth & Development Hormones: Ecdysone
- A steroid hormone that signals moulting (shedding of the exoskeleton). –> A new exoskeleton (the hard body covering) is laid down beneath the old exoskeleton, which is then shed.
- Secreted by glands responding to a neurohormone produced in the brain.
Overview of the Invertebrate Endocrine System- Insect Growth & Development Hormones: Juvenile hormone
- Controls metamorphosis –> its presence maintains the larval stage.
–> when absence, , the next moult is metamorphic, making a pupa (if applicable) & then an adult. - In adults, it stimulates reproductive processes like egg development.
- Regulated by inhibitory & stimulatory protein hormones from the brain.
Overview of the Invertebrate Endocrine System-Hormones in Crustaceans:
Moult-Inhibiting Hormone:
- Suppresses ecdysone secretion during periods between moults.
- Inhibition of this hormone triggers moulting.
Ecdysone
- Initiates exoskeleton replacement during moulting.
Metamorphosis and Reproduction:
- governed by a hormone
that is different from, but structurally related to, juvenile hormone
Like most processes of the endocrine system, blood sugar level regulation normally occurs _________________
automatically
-Since all of the body’s cells use glucose as fuel, the regulation of the blood glucose level is crucial to maintaining homeostasis.
Many people have a problem with their blood glucose monitoring system, a condition called___________________. Elaborate
diabetes mellitus
- in 2000, there were 2 million diagnosed diabetes cases in Canada, with >60,000 new cases annually.
- Diabetics have abnormally fluctuating blood glucose level, changing their metabolism & leading to some
serious health risks & long-term problems.
- Diabetics face health risks & must monitor & control their blood glucose levels consistently.
- Advances in technology, including electronic glucose monitors and insulin delivery devices (syringes, pens, pumps), assist diabetics in managing their condition.
- Modern medical research has significantly improved treatments for diabetes & other endocrine disorders,
Pancreas Function
- The pancreas makes 2 main blood sugar-regulating hormones: insulin & glucagon, –>made in specialized endocrine cells= the islets of Langerhans.
- most of the pancreas functions as an exocrine gland secreting digestive enzymes
- about 2% of its cells r endocrine cells forming the islets.
Role of Insulin & glucagon: Insulin
Insulin & glucagon regulate the ability of most tissues in the body to metabolize fuel substances.
INSULIN
- secreted by beta cells in the islets in response to a rise in blood glucose, such as after a meal.
- Insulin lowers blood glucose by instructing target cells ( mainly skeletal muscles, liver cells, & adipose tissue) to uptake glucose.
- Insulin prevents the liver from breaking down glycogen into glucose
- also promotes fatty acid uptake & storage in in adipose tissue while inhibiting fat breakdown.
- lowers amino acid levels by promoting protein synthesis from amino acids, while inhibiting the breakdown of proteins into amino acids.
Role of Insulin & glucagon: Glucagon
- secreted by alpha cells in the islets & opposes insulin by raising blood glucose levels
- Stimulates glycogen breakdown into glucose in the liver.
- Promotes fat breakdown into fatty acids & protein breakdown into amino acids.
- Facilitates glucose synthesis from amino acids & non-carbs, particularly during fasting.
Is secretion of insulin & glucagon regulated by insulin & glucagon regulated by + or - feedback mechanisms
negative feedback mech.
- Alpha & beta cells in the pancreas adjust hormone secretion based on glucose concs in their cytosol.
- High Blood Glucose=Beta cells increase insulin production, & alpha cells decrease glucagon production to lower glucose levels.
- Low Blood Glucose= Alpha cells increase glucagon production, & beta cells decrease insulin production to raise glucose levels.
The adrenal glands also play a role in controlling blood sugar. Elaborate
- The adrenal cortex secretes steroid hormones= glucocorticoids
- main glucocorticoid=cortisol
- glucocorticoids help raise blood glucose levels using 3 major mechanisms
1) they stimulate the synthesis of glucose from
non-carb sources, such as fats and proteins
2) they reduce glucose uptake by body cells, except those in central nervous system –> favouring of glucose uptake in the central nervous system keeps the brain well supplied with glucose between meals & during periods of extended fasting
3) they promote the breakdown of fats & proteins, releasing fatty acids & amino acids into the blood as alternative fuels when the glucose supply is low.
The secretion of glucocorticoids is ultimately under the control of the __________________
hypothalamus
- low glucose conc in blood, or elevated level of epinephrine secreted by the adrenal medulla in response to stress, is detected in the hypothalamus.
- This leads to the secretion of adrenocorticotropic hormone (ACTH) by the anterior pituitary.
- ACTH then promotes the secretion of glucocorticoids by the adrenal cortex.
Despite the body’s different mechanisms for maintaining glucose homeostasis, the level of glucose in the blood is not completely constant. Elaborate
- It varies throughout the day, largely due to meals & sleep.
- there is typicaly an overall slow decrease during the night, with spikes bringing the level of glucose up after each meal during the day
- ## conc of insulin in the blood is much lower than the conc of glucose, but, as this graph shows, it rises & falls with the glucose level.
Hyperglycemia
- A blood glucose level that is too high can cause a condition= hyperglycemia
- Symptoms of hyperglycemia include thirst, frequent urination, sugar in urine, vision problems, fatigue, & weight loss.
Hypoglycemia
A blood glucose level that is too low can cause a condition= hypoglycemia
- Symptoms of hypoglycemia include nervousness, shaking, cold sweats, hunger, headaches, & weakness
Diabetes mellitus is
- a disease characterized by a high blood glucose level caused by problems with insulin production and/or
action - Diabetes afflicts about 6 % of world
- Untreated diabetes can lead to complications such as vision loss, kidney failure, hypertension, and cardiovascular issues.
there are 3 classic symptoms of diabetes
- Frequent Urination: Caused by excess glucose in the kidneys pulling water from the blood via osmosis in the nephrons.
- Increased Thirst: Results from the need to replace water lost through excessive urination.
- Increased Appetite: Occurs because body cells can’t efficiently use glucose for energy, leading to breakdown of fats & proteins for fuel.
- Blurred vision, lethargy, nausea, vomiting, abdominal pain, and weight loss (if additional food is not consumed).
Diabetes is classified into 3 diff types: List Them
- type 1
- type 2
- gestational diabetes.
Type 1 diabetes
- Results from the degeneration of beta cells in the pancreas, leading to no insulin production.
- Typically begins in infancy or childhood, earning it the name “juvenile diabetes” or “insulin-dependent diabetes.” –> people with type 1 diabetes r usually diagnosed in childhood
- Requires frequent blood glucose monitoring.
- Treated with daily insulin administration, either through injections or an insulin pump
Type 2 diabetes
- Results from reduced insulin production and/or the inability of insulin to bind properly to its receptors.
- Typically develops in adulthood & is strongly linked to obesity.
- Accounts for about 90% of all diabetes cases.
- Over 80% of type 2 diabetics have a family history of the condition.
- cuz type 2 diabetics can still make insulin, treatment often involves controlling diet & exercise to restore a normal level of insulin production. –> Focuses on lifestyle changes, including a healthy diet, weight management, & increased physical activity.
- Oral medications may be used to boost insulin production or improve binding of insulin to its receptors.
Gestational diabetes
- occurs in about 2 to 10 % of pregnant women, due to a high blood glucose level that develops during pregnancy.
- It’s usually a temporary condition, but it can increase the risk that both mother & child may develop diabetes later in life
The latest external insulin pumps can both….
monitor the blood glucose level continuously & deliver insulin by a tube through the abdomen.
When was insulin discovered?
(A journal report as it may have been written by
Frederick Banting and Charles Best)
- in the 1920s
READ ARTICLE 10.4
the term “steroid” refers to
a class of lipids that includes cholesterol & hormones derived from cholesterol, which act on receptors inside cells.
Natural Steroid Hormones
Steroid hormones act on specific target tissues= tissues with the right steroid receptor molecules in cytosol of their cells.
- Steroid hormones derived from cholesterol & easily pass through the cell membrane to attach to the receptor molecules inside a cell–> The hormone-receptor complex enters nucleus & binds to specific regulatory sequences adjacent to the genes whose expression is controlled by the hormone.
- This binding starts transcription, & the proteins r made rapidly.
- Target genes have a specific DNA sequence, called a steroid hormone response element, that binds to the hormone-receptor complex. –> All genes regulated by a particular steroid hormone share the same response element for that hormone.
- Ex, Glucocorticoids activate gene transcription through glucocorticoid response elements.
testosterone is
- a natural steroid hormone
the main male sex hormone, which stimulates and controls the development of male secondary sexual
characteristics –> ex, helps to build muscle mass - Binds to receptors inside the cell nucleus to regulate metabolic genes that build the protein used in muscle development.
- Testosterone levels naturally increase during puberty in males, leading to muscle mass growth.
- increase in muscle mass can be induced by taking more testosterone
In females, the ____________ & the ________________
are steroid sex hormones that trigger…
estrogens, progestins
… female sexual development & control the female reproductive cycle
A Synthetic hormone is
a hormone designed to mimic the actions of natural hormones.
- Ex, Anabolic Steroids= A group of synthetic hormones that replicate many of testosterone’s muscle-building effects.
Synthetic steroids for medical purposes
- Treat organ transplant patients by suppressing the immune system to reduce organ rejection.
- Manage inflammatory disorders (e.g., arthritis, asthma) & autoimmune disorders (e.g., lupus) cuz they can reduce pain and inflammation –> r found in many prescription asthma inhalers.
- are considered safe and effective when used as prescribed, but should only be used under doctor supervision
Unfair Advantages in Sports: Anabolic Steroids & EPO
Anabolic Steroids:
- Synthetic steroids mimic testosterone, aiding in muscle mass development.
- Useful primarily in sports where muscle mass is critical.
Erythropoietin (EPO):
- A protein hormone that stimulates red blood cell production.
- Increases oxygen-carrying capacity, improving endurance and energy levels.
- Beneficial in aerobic sports where endurance is key.
Side effects of Anabolic Steroids
- have a variety of well-known negative effects, like acne, bad breath, high bp, liver disease, & cancer.
- In men= can reduce testes size & enlarge breasts.
- In women,= can cause irregular menstrual cycles & the growth of facial hair
Some performance-enhancing drugs have a mood-altering effect. Elaborate
- anabolic steroids increase levels of aggressiveness. –> This, aka “roid rage,” can lead a person to uncharacteristically violent or dangerous actions.
- Other drugs cause anxiety, depression, paranoia, or addiction.
Despite all the risks, there have been many high-profile cases of professional & Olympic athletes using performance-enhancing drugs.
- Canadian sprinter Ben Johnson lost his 1988 Olympic gold medal due to banned substances.
- Baseball player Mark McGwire admitted to using steroids during his record-setting 1998 season.
- University of Waterloo Warriors football team faced a year-long suspension in 2010 for doping violations, with some players banned for 2 years.
- Detecting banned substances is difficult, but methods r improving –> Organizations like the International Olympic Committee regularly update banned substance lists & monitor masking agents.
The World Anti-Doping Agency
- aka WADA
- Established in 1999 in Switzerland, led by the International Olympic Committee (IOC).
- Former Canadian lawyer Richard (Dick) Pound served as a WADA president.
- Coordinates global efforts to combat doping across all sports.
- Requires athletes to be available for random testing 1 hour daily.
- Sophisticated labs can distinguish between natural & synthetic. –> Ex, can distinguish EPO made by body & injected synthetic EPO used as a performance enhancer.
The complex ________________ & (to a lesser extent) __________________of bees mediate specific behaviours triggered by information from the environment. Elaborate.
nervous system, endocrine system
- ex, bees r able to find food & communicate with other bees to share information about the location of food.
Bees: vision, smell, & navigation
- Bees see a broader spectrum of light, including ultraviolet light, which we can’t see.
- They r attracted to flowers that emit more ultraviolet light, such as white, bright yellow, blue, or purple flowers.
- Visual characteristics of flowers are the primary attractants for bees.
- Odour acts as a secondary stimulus, helping bees locate their floral targets more precisely
- Bees navigate back to their hive using the Sun, Earth’s magnetic field, and visual landmarks.
A neuron is
a specialized nerve cell that is the functional unit of the nervous system.
- allows an organism to receive & respond to both internal & external stimuli. –> is capable of
conducting nerve impulses
Neural signalling is
(communication by neurons)
- the process by which an animal responds appropriately to stimuli.
- It involves four main components: reception, transmission, integration, & response.
The components of Neural Signalling
- Reception: Detection of stimuli by neurons or sensory receptors (e.g., those in eyes, skin).
- Transmission: Transfer of messages along neurons to other neurons, muscles, or glands.
- Integration: Sorting, interpreting multiple neural messages, & determining the response.
- Response: The resulting action or output following neural message integration.
Neural signalling involves 3 functional classes of neuron
- Afferent Neurons (Sensory Neurons): Transmit stimuli from their sensory receptors to interneurons in the central nervous system.
- Interneurons: local circuit neurons of the central nervous system which integrate the information to formulate an appropriate response.
- found primarily in the brain and spinal cord.
- humans & some other primates: about 99 % of the neurons r interneurons.
- Efferent neurons (motor neurons): a neuron that carries impulses from the central nervous system (interneurons)to skeletal muscles and glands (effectors)
The information-processing steps in the nervous system can be summarized as..
(1) stimulus reception by sensory receptors on afferent neurons
(2) message transmission by afferent neurons to interneurons
(3) integration of neural messages in interneurons
(4) response by the transmission of neural messages by efferent neurons to effectors, where appropriate action occurs.
Structure of Neurons
- vary widely in shape & size but all neurons have an enlarged cell body & 2 types of extensions or processes
- Cell Body: Enlarged region containing the nucleus & most organelles; synthesizes proteins, carbs, & lipids.
- Specialized projections from the cell body conduct electrical signals, which r made by ions flowing down conc gradients, through channels in the plasma membrane of neuron
- Dendrites: Highly branched, tree-like projections of cytosol that receive signals & transmit them to the cell body.
- Axons: are elongated projections of cytosol that conducts signals away from the cell body to other neurons or effectors. –> each neuron usually has 1 axon that arises from a junction with the cell body
called an axon hillock. - Axon Hillock: Junction where the axon arises from the cell body.
- Axon Terminals: Button-like swellings at the axon’s tip that connect with other neurons or effectors for signal transmission. –> The more terminals in contact with a neuron, the greater its capacity to integrate incoming information.
Nerves
- Axons r often very long & thin projections from the cell body.
- Usually, many axons r bundled together to form nerve fibres of various sizes, aka “nerves”
- These nerves branch extensively to relay signals throughout the periphery of the entire body
neuronal circuit
- typical neuronal circuit= an afferent neuron, 1 or > interneurons, & an efferent neuron.
- Interneurons may receive input from several axons & may connect to other interneurons & several efferent neurons.
- In this way, circuits of neurons combine into networks that interconnect the different parts of the
nervous system. - Connections between the axon terminals of 1 neuron & the dendrites or cell body of a 2nd neuron form the basic elements of a neuronal circuit
A Glial cell is
- Not all cells in nervous system= neurons.
a cell that does not conduct electrical signals but provide nutrition & support to neurons. - Schwann cells: a type of glial cell –>form tightly wrapped layers of plasma membrane around axons = myelin sheaths. –> myelin sheaths act as electrical insulators due to their high lipid content
- gaps between Schwann cells= nodes of Ranvier, expose the axon membrane directly to extracellular fluids.
- This arrangement of insulated stretches of axons, punctuated by uninsulated gaps, speeds the rate at which electrical impulses move along the axons
What cells are responsible for brain cancer?
Glial cells
- Unlike most neurons, glial cells have capacity to divide throughout the life of an animal.
- This capacity allows glial tissues to replace damaged or dead cells.
- also makes them the source of nearly all brain tumours, which occur cuz of lack of glial cell division regulation
The nervous system of most invertebrates and vertebrates is made up of ____ functional subsystems. Elaborate
2
- Interneurons form central nervous system (CNS):
composed of the brain & spinal cord
- The peripheral nervous system (PNS) is the subsystem that communicates with the central nervous system.
Divisions of the PNS: - Afferent System: Transmits sensory input from receptors to the CNS (“carrying toward”).
- Efferent System: Sends signals from the CNS to muscles and glands (“carrying away”).
- whole system is similar to the collection of neighbourhoods in a large city & the transportation systems that connect these neighbourhoods
Afferent system is
the component of the peripheral nervous system that receives input through receptors & transmits the
input to the central nervous system
efferent system is
the component of the peripheral nervous system that carries signals away to the effectors (muscles & glands)
Efferent system subdivisions
- Somatic System: communicates with skeletal muscles; primarily voluntary, but some actions (e.g., reflexes, shivering, posture) r involuntary.
- Autonomic System: communicates with smooth muscles & glands. controls mainly involuntary processes like digestion, blood circulation, gland secretion, & smooth muscle contractions
somatic system is
a subdivision of the efferent system (within the PNS);
composed of efferent (motor) neurons that carry signals to skeletal muscles in response to external stimuli
autonomic system is
subdivision of the efferent system (within the PNS); regulates the internal environment
The autonomic system subdivisions
Sympathetic Division: dominates during stress, danger, excitement, or physical activity. Effects include:
–> Increase heartbeat force & rate
–> raise bp by vasoconstriction
–> dilate air passages in the lungs
–>Induces sweating & pupil dilation.
Parasympathetic Division: Dominates during relaxation & low stress. Effects include:
–> Reduction of sympathetic responses (e.g., slower heartbeat, lower bp).
–>Promotion of maintenance activities like digestion.
- These divisions r always active & have opposing effects on the organs that they affect, thereby enabling precise control.
sympathetic division is
1of 2 subdivisions of the autonomic nervous system; increases E consumption & prepares the body for action
parasympathetic division is
1 of 2 subdivisions of the autonomic nervous
system; stimulates body activities that acquire & conserve energy
What happens when you touch a hot stove?
- There is an instantaneous, involuntary response to harmful stimuli
- Thermal E is detected by skin pain receptors & thermoreceptors, which stimulate an afferent neuron
- it transmits the impulse to at least 2 interneurons in the spinal cord, which relay the impulse to an efferent
neuron (a motor neuron) that coordinates the rapid withdrawal of hand & perhaps an involuntary scream of pain - Reflex actions bypass conscious processing to minimize injury by providing a quicker response.
- This situation is an ex of a neural circuit, which has 5 components: the receptor, the afferent neuron, the interneuron, the efferent neuron, & the effector.
The reflex arc
- the simplest neural circuit.
- it’s a circuit that does not require the coordinating effort of the brain.
-ex of the reflex arc is the withdrawal reflex that occurs when ur finger touches a hot object - Interneurons connected to the reflex circuits also send signals to the brain, making u aware of the stimulus that caused the reflex.
why do u feel pain a few seconds after u withdraw ur hand from the stove?
- Interneurons connected to the reflex circuits also send signals to the brain, making u aware of the stimulus that caused the reflex.
- This delay in feeling the pain is the extra time required for the impulses to travel from the neurons of the reflex to the brain
The philosopher Alcmeon of Croton
- Theories about transmission of info through nervous system go date back to ancient Greece
- Alcmeon of Croton (540–500 BCE) discussed presence of pores & channels in the brain & sensory organs
Luigi Galvani
- doctor & physiologist at Italy’s University of Bologna
- 1781: discovered that the muscles of a dead frog would twitch when touched with diff metals or
an electric current - In hypothesis of “animal electricity,” proposed that electric forces generated in muscles travelled from the nerves to the muscles & were responsible for muscle contractions & movements.
- While we now know that his hypothesis was only partially correct, his work sparked an increased interest in neurology
Emil DuBois-Reymond
(1848) developed instruments to detect electrical transmission in nerves & muscles at the University of
Berlin
Willem Einthoven
By 1906
- A Dutch physiologist who refined a machine that
could detect electric impulses in the heart muscle, a methodology that is now the basis of the electrocardiogram (ECG).
Hans Berger
In 1929, Hans Berger, a German psychiatrist,
measured electric currents during brain activity by placing electrodes on a patient’s skull.
One of Canada’s first neurologists was _______________________. Elaborate
Sir William Osler (1849–1919).
- published almost 200 works about neurological disorders, often drawing details from autopsies he had performed
Differences Between Electrical & Neural Transmission:
- Nerve impulses travel slower than electric current due to resistance in the neuron’s cell body cytosol
- Neural impulses maintain strength over distance, unlike electric currents.
- Nerves use internal energy to generate current, unlike electric currents that rely on external sources.
Julius Bernstein
Around 1900, German physiologist who proposed the idea that nerve impulses r the result of ions moving through the nerve cell membrane.
- 2 researchers in Columbia University, K.S. Cole & H.J. Curtis, provided evidence for Bernstein’s theory using an electrode applied to the large neuron of a squid.
- When the nerve became excited, the electrical potential across the membrane rose rapidly
from about –70 mV at rest to about +40 mV
A synapse is
a site where a neuron makes a connection with either another neuron or an effector, such as a muscle fibre or gland.
COMPONENTS
- Presynaptic Cell: Neuron transmitting the signal, with its axon terminal on one side of the synapse.
-Postsynaptic Cell: Neuron or effector receiving the signal, with a dendrite or cell body on the other side of the synapse
-Depending on the kind of neuron, communication across a synapse may occur either chemically
or electrically
Chemical synapse
- more common
- a chemical messenger called a neurotransmitter
is released by an axon terminal at the synapse. - The plasma membranes of the presynaptic & postsynaptic cells r separated by a narrow gap, about 25 nm wide= the synaptic cleft
A chemical synapse is
a synapse in which a neurotransmitter moves from
a presynaptic cell to a postsynaptic cell through the synaptic cleft
A neurotransmitter is
a chemical that is released from vesicles into synapses to facilitate nerve signal transmission (in chemical synapses only, pretty sure)
A synaptic cleft is
the tiny gap between presynaptic & postsynaptic cells in a chemical synapse, across which the neurotransmitter diffuses
Electrical Synapse
- plasma membranes of presynaptic & postsynaptic cells r in direct contact, allowing current to flow directly from one neuron to the next
- When an electric impulse arrives at the axon terminal, a gap junction allows ions to flow directly between the two cells, providing unbroken transmission of the electrical signal.
- Electrical synapses allow rapid transmission & synchronous activity in a group of neurons.
Charge Separation in Cells
-All animal cells maintain a separation of charges: “+” outside & “-“ inside the plasma membrane.
-This creates a voltage (electrical potential diff) across the plasma membrane= the membrane potential.
–> caused by the uneven distribution of Na+& K+
inside & outside the cell.
- Selectively permeable ion channels allow specific ions to move across the membrane. –> Some ion channels r closed in their resting state, & only open in response to a change in voltage. –> Other ion channels open upon the binding of a specific substance
In most cells, the membrane potential remains _______, but…
stable
…but neurons & muscle cells, respond to electrical, chemical, mechanical, & other stimuli, causing their membrane potential to change rapidly.
–> Cells with this property r called excitable.
- Excitability, made by a sudden flow of ions across the plasma membrane, is the basis for nerve impulse generation
membrane potential is
the electrical potential of a membrane, which is caused by an imbalance of charges on either side
of the membrane
An ion channel is
a protein embedded in the plasma membrane that allows ions to pass through it
Resting Membrane Potential
- A specialized ion channel, the Na⁺/K⁺ active transport pump, uses ATP energy to pump 3 Na⁺ ions out of the cell for every 2 K⁺ ions pumped in. –> This generates a higher Na⁺ concentration outside the cell and a higher K⁺ concentration inside the cell. –> explains the net “+” charge outside the cell.
-Inside the cell, other anions contribute to a net “-“ charge. - typical neuron at rest has a steady “-“ membrane potential of about –70 mV = the resting potential.
- A cell with a resting potential other than 0 V (that is, a cell with some separation of charge on either side of its membrane) like this one is called polarized.
- The pump maintains the ion imbalance &, along with intracellular anions, establishes the polarized state of the neuron.
Action Potential is
the voltage diff across a nerve cell membrane when the nerve is excited
When a neuron conducts an electric impulse, there is an abrupt and temporary change in membrane potential. –> This is called an action potential.
- An action potential begins as a stimulus that causes +charges from outside the neuron to flow inward, making the interior side of the membrane less -.
Phases of action potential
Phase 1 - Depolarization Begins:
- Incoming + ions raise the membrane potential from its resting state, making it less - (depolarization).
- If the threshold potential (about –50 to –55 mV in a typical neuron) is reached, Na⁺ channels open.
Phase 2 - Above Threshold:
- Na⁺ channels fully open, and Na⁺ flows inward along its conc gradient.
- The action potential then fires, causing the membrane potential to increase sharply.
- In <1 ms, the action potential rises so high that the
inside of the plasma membrane becomes + cuz of the influx of + ions
Phase 3 - Peak Action Potential:
- the action potential reaches its peak, momentarily
reaching a value of +30 mV or >.
- Interior of the neuron is relatively +.
- The Na+ channels close & become inactive, & the K+
channels open & allow K+ to exit
Phase 4 - Repolarization:
- K⁺ exits the cell along its conc gradient, causing the membrane potential to decrease rapidly (repolarization).
Phase 5 - Undershoot:
- the voltage-gated K+ channels begin to close slowly.
-Slow closure of K⁺ channels causes the membrane potential to briefly drop below the resting potential (undershoot).
- When the potential is below the resting value, the membrane is said to be hyperpolarized.
Phase 6 - Stabilization:
- The membrane potential returns to its resting value (–70 mV) as all ion channels reset, preparing the neuron for a new action potential.
- The entire change, from the initiation of the action potential to the return to the resting potential, takes less than 5 ms in the fastest neurons.
Threshold Potential is
the potential at which an action potential is generated
by a neuron
An action potential takes the ________ basic form in all neurons. However, diff types of neurons exhibit diffs in…
same
…the value of the resting potential & the peak of the action potential, & in the time required to return to the resting potential.
Many stimuli cause some degree of depolarization of a neuron, but an action potential is produced only if…
the stimulus is strong enough to cause the depolarization to reach the threshold.
- This is referred to as the all-or-nothing principle.
- Once triggered, the changes in membrane potential take place independently of the strength of the stimulus.
Once an action potential is initiated at the ___________ of a neuron, it passes along…
dendrite end
…the surface of a nerve or muscle cell as an automatic wave of depolarization.
- It travels away from the stimulation point, without requiring further triggers. –>this = propagation of the action potential.
Refractory Period is
Beginning at the peak of an action potential, the membrane enters a resting period of a few milliseconds= refractory period
- During this time, the threshold required for generation of an action potential is much > normal.
- The refractory period lasts until the membrane has stabilized at the resting potential.
- It keeps impulses travelling in a one-way direction in the neurons. –> This is cuz, once ion channels r opened to their activated state, they need time to reset to their original position before they can open again
- thus, only downstream ion channels r able to open, ensuring the one-way movement of the action potential along the axon toward the axon terminals
Does the magnitude of an action potential stay the same or decrease as it travels along an axon?
it stays the same, even where the axon branches at its tips.
- Thus, the propagation of an action potential resembles a fuse that burns with the same intensity along its length & along any branches once it is lit.
- but unlike a fuse, an axon is not spent.
- It can fire another action potential of the same intensity within a few milliseconds after the first has
passed through.
is the intensity of a stimulus is reflected in their magnitudes or frequencies?
Frequencies
- The all-or-nothing characteristic of the action potential means that the intensity of a stimulus is reflected in the frequency of action potentials rather than in their magnitudes –> cuz once triggered, the magnitude (size) of the action potential is always the same in a given neuron, regardless of stimulus strength.
- The greater the stimulus, the faster the action potentials, up to a rate determined by the physical
limitations of the neuron (typically 10–100 per second)
- The rate of conduction increases with the diameter of the axon. –> large axons can conduct impulses as rapidly as 25 m/s, but they take up a large amount of space
Conduction by hopping
- In jawed vertebrates, action potentials “hop” along axons rather than traveling continuously, increasing conduction speed.
- this relies on the gaps in the insulating myelin sheath that surrounds many axons known as the nodes of Ranvier, that expos the axon membrane to extracellular fluids
- Na+ & K+ channels, crowded into the nodes, allow action potentials to develop at these positions, jumping rapidly from 1 node to the next.
-inward movement of Na+ ions causes depolarization, but the excess +ions can’t leave the axon through the membrane regions covered by the myelin sheath.–> Instead, they diffuse rapidly to the next node (due to coc gradient i think), where they cause depolarization, inducing an action potential at that node. - Myelinated axons can transmit impulses at speeds up to 130 m/s, significantly faster than the 1 m/s seen in unmyelinated axons of the same diameter.
Importance of conduction by hopping
allows thousands to millions of fast-transmitting axons to be packed into a relatively small diameter
- ex, the optic nerve in humans, leads from the eye to the brain, is only 3 mm in diameter but is packed with
>1million axons.
- If these axons were unmyelinated, each would have to be about 100x as thick to conduct impulses at the same velocity. –> This would make an optic nerve of about 300 mm in diameter
Multiple Sclerosis
A disease where the immune system attacks & progressively destroys myelin sheaths, replacing them with hardened scar tissue.
-loss of myelin slows or blocks action potential transmission, leading to symptoms like numbness, muscle weakness, poor coordination, & paralysis.
- tho clear genetic factors are involved, research shows that environment may also play a role. –> the risk of the disease increases with the distance from the equator. –> in Canada= 2.4 people per 1000
Are action potentials transmitted across electrical synapses or chemical?
electrical synapses
- they cannot jump across the synaptic cleft in a chemical synapse.
- The time required for the release, diffusion, & binding of neurotransmitters across a chemical synapse delays transmission, whereas the transmission of impulses across an electrical synapse is almost instantaneous.
Conduction across Chemical Synapses Overview
- The vast majority of vertebrate neurons communicate by means of neurotransmitters.
–> communication through chemical synapses allows neurons to receive input from 100s-1000s of axon terminals at the same time.
Conduction across Chemical Synapses: Process
Neurotransmitters are stored in synaptic vesicles in the cytosol of the axon terminal.
- Ca2+ ions r actively pumped out of the cell to maintain > conc outside; action potentials open Ca2+ channels, allowing Ca2+ to enter the cytosol.
- rise in Ca2+ conc triggers a protein that causes synaptic vesicles to fuse with the plasma membrane, releasing neurotransmitters into the synaptic cleft via exocytosis.
- Neurotransmitters diffuse across the synaptic cleft & bind to receptors on the postsynaptic cell, opening gated ion channels –>allowing ions to flow into the dendrite or cell body of postsynaptic neuron
- Some neurotransmitters have stimulatory effects, whereas others have inhibitory effects. Most neurotransmitters work by opening or closing
membrane-embedded ion channels that conduct Na+
or K+ across the postsynaptic membrane. Some regulate Cl– ions –> IF CLOSES CHANNELS, DOES THAT MEAN THAT SIGNAL STOPS TRAVELLING? - If the postsynaptic neuron becomes depolarized to the point of threshold, it will generate a new action potential that travels along its axon to reach a synapse with the next neuron or effector in the circuit
A chemical synapse is more than a simple on/off switch. Elaborate
- Many factors can influence the generation of a new electrical impulse in the postsynaptic cell, including neurotransmitters that inhibit that cell rather than
stimulate it. - The balance of stimulatory and inhibitory effects in chemical synapses contributes to the integration of incoming information in a receiving neuron.
Nearly ____ diff substances are known or suspected to be neurotransmitters.
100
- Most r relatively small molecules that diffuse rapidly across the synaptic cleft .
- Some axon terminals release only one type of neurotransmitter, whereas others release several types
Acetylcholine
- One of the best-known neurotransmitters
- In humans, acetylcholine triggers muscle contraction, stimulates hormone secretion, & is involved in wakefulness, attentiveness, memory, learning, anger, aggression, & sexuality.
- Acetylcholine-releasing neurons in the brain degenerate in Alzheimer’s disease, leading to memory, speech, & perceptual decline.
Acetylcholine is targeted by many natural and artificial poisons. Elaborate
CURARE
- a plant extract that is used as an arrow poison by some Indigenous peoples of South America
- Blocks muscle contractions & causes paralysis by competing with acetylcholine for binding sites at muscle synapses.
NICOTINE
- the drug released from smoking tobacco
- binds to acetylcholine receptors, but it acts as a stimulant by turning the receptors on rather than off .
Other substances can block the operation of these neurotransmitters. Elaborate
Tetanus Toxin: Released by bacterium Clostridium tetani, blocks neurotransmitters in synapses controlling muscle contractions.
- Causes severe muscle contractions, leading to painful body arching and clenched teeth, known as lockjaw.
- If it affects respiratory muscles, it can lead to quick death.
- The disease is preventable through vaccination with inactivated tetanus toxin.
Neurotransmitters:Endorphins
- Neurotransmitters that are released during pleasurable experiences (like eating or sex) or physical stress (like childbirth or exercise)
- These neurotransmitters have the opiate-like property of reducing pain & inducing euphoria, well known to exercise enthusiasts as a pleasant by-product of their physical efforts
Octopamine
a neurotransmitter involved in insect-feeding activities.
- recently been linked to bee waggle-dance behaviour & is also associated with firefly flashing
general diff between CNS & PNS
- The CNS consists of the brain and spinal cord, and the PNS consists of the nerves that connect the brain and spinal cord to the rest of the body
- The CNS manages body activities by integrating incoming sensory information from the PNS into compensating responses
- PNS links the body’s periphery to the central nervous system (CNS).
____________ have the most complex nervous system
of all animals. Elaborate
Humans
- complexity of our brain is what distinguishes us from other animals and allows complex behaviours, including language & the ability to develop culture and civilization
- but we have the same basic brain regions that are found in simpler vertebrates.
- most significant changes in human brain evolution occurred in the region associated with reason, intellect, memory, language, & personality.
- Our reasoning ability, rather than the acuity of our senses, is what makes the human brain unique
Nervous system evolutionary history
- Vertebrates likely evolved from larval forms of primitive chordates.–> . In chordates, the nervous
system is formed dorsally as a hollow neural tube with the anterior forming the brain & the rest becoming the spinal cord. - During development in vertebrates, central cavity of the neural tube becomes fluid-filled ventricles of the brain & the narrow central canal of the spinal cord.
The organization of the brain is exceedingly complex. One way to understand its complexity is to examine its development from the embryonic neural tube. Elaborate
- general vertebrate brain midway through embryonic development, shows the principal regions found in all vertebrate brains.
- Early in development, the anterior part of the neural tube enlarges into 3 distinct regions.
–>Forebrain: Initially linked to olfaction (sense of smell).
–>Midbrain: Was primarily associated with vision.
–> Hindbrain: was mainly associated with balance
The brain & Spinal cord’s protection
- r both surrounded & protected by, 3 layers of
connective tissue= the meninges & the cerebrospinal fluid. - cerebrospinal fluid circulates through the central canal of the spinal cord, through ventricles of the brain, & between 2 of the meninges–>cushions the brain & spinal cord from jarring movements & impacts, nourishes them, & protects them from toxic substances
meninges are
3 layers of connective tissue that surround & protect the brain & spinal cord
cerebrospinal fluid is
circulating fluid that surrounds the membranes of the brain & spinal cord; provides neural connection to
the endocrine system
Spinal Cord
- Extends from the brain through a canal in the vertebrae.
- carries impulses between the brain & the PNS &
contains the interneuron circuits that control motor reflexes. - Consists of a butterfly-shaped core of grey matter (nerve cell bodies & dendrites) surrounded by white matter (axons, many myelinated).
-Pairs of spinal nerves connect to the spinal cord through spaces between vertebrae.
Afferent (incoming) axons:
- Enter through the dorsal root.
- Synapse with interneurons in grey matter, which send signals upward to the brain through the white matter.
Efferent (outgoing) axons:
- Pass from interneurons of the brain down the spinal cord.
- synapse with dendrites & cell bodies of efferent neurons in the grey matter
- Axons from efferent neurons exit the spinal cord via the ventral root of spinal nerves.
- Efferent nerves in the ventral root carry info from the spinal cord to the peripheral muscles, organs, & glands.
Grey Matter is
the tissue of the brain & spinal cord where the cell bodies & dendrites of neurons r located
white matter is
the tissue of the brain & spinal cord, composed primarily of axons of neurons; in the spinal cord, it surrounds the grey matter
Brain
- the major center for receiving, integrating, storing, & retrieving info
- its interneuron networks generate responses that provide basis for our voluntary movements, consciousness, behaviour, emotions, learning, reasoning, language, & memory, as well as many other complex activities.
- The 3 major divisions of the embryonic brain (forebrain, midbrain, & hindbrain i think) give rise to the structures of the adult brain
- Like spinal cord, each brain structure has grey & white matter & is surrounded by meninges & circulating cerebrospinal fluid
The hindbrain of vertebrates develops into the ________________ & _______________
medulla oblongata (aka medulla), the cerebellum
MEDULLA
- Controls involuntary functions like breathing, digestion, heart rate, & bp.
CEREBELLUM
- plays major role in motor responses (voluntary movements of the skeletal muscles) & is responsible for balance & fine motor control.
- In higher mammals, a mass of fibres that connects the cerebellum to higher centres in the brain is so prominent that it’s called= pons (bridge)–> Connects the cerebellum to higher brain centers –> part of the brainstem, which links the forebrain to the spinal cord.
- 10 pairs of nerves originate from the brain stem to serve the head, neck, and body trunk areas.
The brain stem is
a stalk-like structure formed by the medulla
and the pons, along with the midbrain that connects the forebrain to the spinal cord
medulla oblongata is
the hindbrain region that connects the spinal cord to the cerebellum; important in autonomic nerve control
cerebellum is
the hindbrain region that is involved in muscle movement and balance
pons is
the brain region that transfers nerve signals between the cerebellum & the medulla
Cerebrum is
the brain region that is involved in motor activities & sensory info
- The forebrain, which makes up most brain mass in humans, forms the cerebrum.
- The cerebrum is the most developed part of the brain.
- It controls most of the sensory and motor activities
Evolutionary trends of the brain include the increasing prominence of the cerebrum. Elaborate
–> Beginning with reptiles, the cerebrum increased in size relative to the rest of the brain.
- In mammals, folds appeared, increasing the amount of brain surface area within a particular volume
- The total mass of the brain relative to the size of the
animal increased as well, permitting animals to undertake more complex tasks
Cerebral Cortex
is a thin layer of grey matter in which numerous unmyelinated neurons r found which makes up the surface layer of the cerebrum
- carries out all of the higher brain functions
Cerebrum Structure:
- divided into right & left cerebral hemispheres.
- It is corrugated by fissures & folds that increase the SA of the cerebral cortex & divide the brain into the frontal, parietal, temporal, & occipital lobes
- This structure reflects 2 of the evolutionary tendencies in the brains of mammals: the corrugation of the hemispheres and the development of
a layer of grey matter on the periphery
Can the right & left cerebral hemispheres function separately?
YES
- Each cerebral hemisphere has its own communication lines within itself, with the CNS, & the body.
- The left hemisphere primarily responds to sensory signals from and controls movements on the right side of the body. –> The right hemisphere does the same for the left side of the body.
- This opposite control is due to the crossing of afferent (incoming) and efferent (outgoing) nerve signals from left to right within the spinal cord or brain stem.
- The corpus callosum, a thick bundle of axons, connects the two hemispheres and coordinates their functions.
Sensory regions of the cerebral cortex
- Areas of the cortex process sensory information, including touch, pain, temperature, pressure, hearing, vision, smell, & taste.
- Primary somatosensory area: Located in the parietal lobes in each hemisphere; registers touch, pain, temp, & pressure.
- Other sensory regions of the cerebral cortex help with hearing, vision, smell, and taste.
- Primary motor area of cerebral cortex runs in a band across the frontal lobe, just in front of primary somatosensory area; controls voluntary movements.
- larger regions in the primary somatosensory & motor areas r dedicated to body parts requiring more sensory precision or motor control (e.g., lips, fingers). Smaller regions represent less sensitive or less mobile areas (e.g., arms, legs).
- The size diffs create a “distorted” body map, reflecting functional importance rather than acc proportions.
-Greater representation corresponds to higher precision of touch or movement, such as in the lips, tongue, & fingers.
Cerebellum
has a folded structure that increases its relative size; it’s connected 2 the pons but is functionally & structurally distinct from the brain stem.
- tho great connection to other brain parts, it receives input from muscles, joints, balance receptors in the inner ear, & touch, vision, & hearing receptors.
- sensory input conveys details about body position, movement direction, & muscle contraction/relaxation.
- cerebellum integrates this input & compares it with signals from the cerebrum that control voluntary body movements.
- Output from cerebellum to cerebrum, brain stem, & spinal cord modify body movements, ensuring balance & precise targeting in space.
The thalamus is
the brain region that interprets sensory input & signals the cerebrum
-Acts as a sensory switchboard, relaying sensory information to the cerebral cortex. It also regulates wakefulness, drowsiness, and sleep
The hypothalamus is
-a relatively small cone-shaped area that occurs in all vertebrates
- Regulates homeostatic functions like body temp (e.g., triggering shivering or sweating) & osmotic balance by monitoring blood composition.
- Plays a key role in the endocrine system by making hormones & controlling pituitary gland hormone release.
Basal nuclei
are grey-matter centers surrounding the thalamus on both sides that moderate voluntary movements directed by motor centers in the cerebrum
- Damage to the basal nuclei disrupts movement planning & fine-tuning, causing stiffness, rigidity, or hand tremors (e.g., Parkinson’s disease).
Blood–Brain Barrier is
a barrier formed by tight junctions between endothelial cells in the capillaries in the brain that blocks the movement of most substances into the
brain via the bloodstream
Prevents most substances in the blood from entering cerebrospinal fluid, offering brain & spinal cord protection against viruses, bacteria, & toxins.
- Maintains a stable environment for neurotransmission, shielding cerebrospinal fluid from blood fluctuations due to meals & other factors.
- While it blocks most immune cells, T-cells can cross during an immune response.
Some area of brain called _______________________ are not behind the blood-brain barrier. Elaborate
the circumventricular organs
- Ex, the part of hypothalamus involved in communication with pituitary gland, the blood vessels do not have tight junctions, allowing direct exposure to the bloodstream.
- Ex, the pineal gland, which secretes melatonin
directly into the bloodstream, is also not protected by the blood–brain barrier.
Substances that Cross the BBB:
- Lipid-soluble molecules like oxygen, carbon dioxide, alcohol, caffeine, nicotine, & anesthetics diffuse across cell membranes.
- Glucose, a critical energy source for brain cells, is transported via selective transport proteins.
Imaging the Living Brain
-The skull encases the brain, making direct observation difficult.
-Modern imaging technologies allow indirect observation of the living brain without physically entering skull.
- Much learned about functions of various brain regions by studying patients with brain damage caused by strokes, infections, tumours, & other conditions.
- Key techs include:
- Functional Magnetic Resonance Imaging (fMRI): Detects brain activity through blood flow changes.
- 3-D Ultrasound: Offers imaging of brain structures.
- Positron Emission Tomography (PET): Tracks metabolic activity in brain regions.
- they record a subject’s brain activity during various mental & physical tasks by detecting minute increases in blood flow or metabolic activity in specific regions
Higher functions of human brain
-Abstract thought, reasoning, personality, spatial recognition, and artistic/musical ability involve coordinated participation of many regions in the cerebral cortex.
- Some functions are equally distributed between hemispheres, while others are concentrated in 1.
-Most functions require integrated activity of both hemispheres.
- “Left-brained” & “right-brained” labels are loose descriptors & do not reflect a strict division of abilities.
- Left hemisphere controls the right side of the body, & vice versa.
Equally Distributed Functions:
Recognizing faces, consciousness, sense of time, and recognizing emotions.
Left Hemisphere Specializations:
- Spoken and written language.
- Abstract reasoning.
- Precise mathematical calculations.
Right Hemisphere Specializations:
- Non-verbal conceptualizing & intuitive thinking.
- Musical & artistic abilities.
- Spatial recognition (e.g., puzzles) & mathematical estimates via spatial representation.
