Animal Responses to Stimuli (Exam 3)

What are the 4 main differences between the endocrine and the nervous system?

The endocrine system is analog, chemical, pervasive, and slow. The nervous system is electrical, digital, local, and fast. 

Why is the nervous system generally faster than the endocrine system?

Nervous signals are electrical and travel quickly down myelinated axon sheaths whereas the chemical signals of the endocrine system travel through blood.

What are the main differences between protein and steroid hormones?

Protein hormones are water soluble, travel directly through the blood stream, bind to membrane receptors, often include secondary messengers, and have effects on enzymes (quicker reaction). Steroid hormones are lipid soluble, travel by attaching to transport proteins, travel through the membrane and bind to receptors inside of the cell, bind to DNA and transcription factors, making new proteins (slower process)

What is the advantage of secondary receptors and signal transduction pathways?

Signal amplification

How does epinephrine increase blood glucose levels?

It binds to a membrane receptor, activating a G protein which takes ATP and turns it into cAMP through adenylyl cyclase which acts a second messenger to protein kinase A which increases the activity of glycogen phosphorylase (an enzyme that breaks down glycogen) increasing levels of glucose 

What 2 steroid hormones are made in the adrenal cortex?

Cortisol and aldosterone

What 3 steroid hormones are made in the gonads?

testosterone, estrogen (estrodiol), and progesterone

What are the main 7 endocrine glands?

hypothalamus, pituitary gland, thyroid gland, adrenal glands, pancreas, ovaries, testes

Why is the pituitary gland considered the “master” endocrine gland?

It secretes hormones that control the rest of the other systems 

What are tropic hormones?

Specific hormones secreted from the pituitary gland that control the release of other hormones across the body 

Where is oxytocin secreted from, what is its destination and what is its function?

secreted from the pituitary gland, goes to mammary glands and uterine muscles, stimulates uterine contractions during childbirth & milk ejection during breast feeding

Where is thyroid-stimulating hormone (TSH) secreted from, where is its destination and what is its function?

secreted from the pituitary gland, goes to the thyroid, stimulates the release of thyroxine

Where is adrenocorticotropic hormone (ACTH) secreted from, where is its destination, and what is its function?

secreted from the pituitary gland, goes to the adrenal gland, stimulates the release of cortisol 

Where is prolactin released from, where is its destination, and what is its function?

secreted from the pituitary gland, goes to mammary glands, promotes lactation and breast development

Where is melanocyte-stimulating hormone (MSH) released from, where is its destination, and what is its function? 

Secreted from the pituitary gland, goes to melanocytes, stimulates the release of melanin

Where are growth hormones (GH) secreted from, where is its destination, and what is its function?

secreted from the pituitary gland, goes to liver, bones, and other tissues, stimulates growth 

What does thyroxine do?

secreted from thy thyroid gland, acts like a steroid, regulates overall rate of cell activity (metabolic rate), thermal and weight balance and energy levels

What happens when a person has too little (hypothyroidism) or too much (hyperthyroidism) thyroxine?

Hypo: low metabolic rate, cold, weight gain

Hyper: high metabolic rate, fever, weight loss 

What does insulin do?

secreted by the pancreas when blood glucose is high (GLP protein stimulates pancreas after food intake), reduces blood sugar through increasing activation of glucose transporters in the cell membranes which take glucose out of the blood stream

What does glucagon do?

secreted by the pancreas when blood glucose is low, increases blood sugar by promoting the breakdown of glycogen 

What is insulin and glucagon’s relationship?

they work in opposition of eachother, doing the opposite and combating the effects of one another to regulate blood glucose concentration (antagonistic hormones)

What is anti-diuretic hormone (ADH)?

released by the posterior pituitary gland when the blood is too salty, increases water absorption in the kidneys (anti-pee hormone) also makes you thirsty

What is aldosterone?

released by the adrenal cortex when there is a loss of blood volume causing the kidney to reabsorb more Na+ which causes an increase in water volume to the kidney, increasing blood volume

What is goiter?

A thyroid disorder due to an iodine deficiency where thyroxine can’t be made preventing any negative feedback from occurring creating an excess of thyroid stimulating hormone where the thyroid gland swells 

What is diabetes?

disorder where cells are unable to absorb glucose from the blood into cells, causing cells to burn fats/proteins as fuel, excess sugar binds up proteins, resulting in vascular disease and blindness 

What is the difference between type I and II diabetes?

Type I: autoimmune disease where the body produces antibodies against insulin producing cells (treated with insulin injections)

Type II: Cells produce insulin but the signal transduction pathways don’t respond to the insulin and don’t pull the glucose out of the blood stream (treated with medication)

How does ozempic work?

works against diabetes by binding to GLP-1 receptors (protein that increases insulin secretion after a meal) to boost insulin secretion. It also reduces appetite through GLP receptors in the brain and stomach

What is the difference between ADH and aldosterone in their action at the cellular level?

ADH is a protein hormone and works (similarly to insulin) by attaching to transporters on the cell membrane, causing increased water reabsorption through a signaling cascade that makes more water channels merge with the outer membrane causing increased water intake. Aldosterone on the other hand is a lipid hormone and works by binding to intracellular receptors, altering gene activity and causing the transcription and formation of new sodium channel to transport the Na+ into the cell. ADH works faster than aldosterone. 

What does alcohol do to ADH?

Inhibits the release of ADH, becoming an anti-anti-pee hormone, making you conserve water less, and pee more

What do ADH and aldosterone show us?

the difference in cellular action of lipid and protein hormones 

Why are homeostatic hormones called “hormones of reaction”?

they are released by the body in response to a stimulus or change in the internal environment. They react  

Why are reproductive and stress hormones referred to as “hormones of anticipation”?

they are released and act all the time instead of responding to a stimulus or change in the body

What do gonadotropin releasing hormones do?

secreted by the hypothalamus when sex hormone levels are low, target the pituitary gland to release gonadotropic hormones (LH & FSH)

What do luteinizing hormone (LH) do?

released by the pituitary gland, causes steroid secretion (progesterone & testosterone: leydig cells) and helps with secondary sex characteristics 

What do follicle stimulating hormones (FSH) do?

released by the pituitary gland, goes to the gonads (males: sertoli cells, female:oocytes), promotes gamete maturation

Describe the Ovarian and Uterine cycle in females

GnRH is released by the hypothalamus causing the pituitary to release FSH and LH which stimulate the follicle to grow. As the follicle grows it releases estrodiol in increasing amount until a peak is reached that causes a large surge in LH. This LH surge triggers ovulation where the corpus luteum grows, releasing lots of progesterone and estrodiol which promotes the thickeing of the endometrium. The presence of these hormones causes negative feedback to the hypothalamus so GnRH isn’t released anymore. Eventually the corpus luteum begins to degenerate, causing levels of progesterone and estrodiol to drop. The very low levels of estradiol causes the endrometrium to shed and the cycle starts over.

What function does estrogen have in both males and females?

required for gamete maturation in both sexes along with brain development and metabolic health

Where are estrogen receptors located in the body?

reproductive organs, hypothalamus, pituitary gland, adrenal glands, brain, spinal cord, heart, bones, muscles, prostate

What organs besides ovaries produce estrogen?

adrenal glands, fat cells, placenta

How is estrogen and Alzheimers disease related?

the decline in estrogen levels after menopause is linked to an increased risk of developing the disease as a woman 

How does the timing of estrogen treatment influence its effect on brain function?

early initiation during perimenopause or early menopause showing benefits for cognition and memory, while starting late in postmenopause may be ineffective and potentially harmful

How do birth control pills work?

increase levels of estrogen and progesterone, preventing release of FSH and LH so ovulation cannot occur, preventing pregnancy

How do abortion pills work?

Progesterone receptors are blocked so the endometrium walls cannot thicken and the embryo cannot survive

What are the functions of the sympathetic and parasympathetic nervous systems?

Parasympathetic: rest and digest, sympathetic: fight or flight 

What does epinepherine do?

secreted by the adrenal gland due to acute stress, activates the sympathetic NS, inducing the fight or flight responses (increased blood glucose, pressure, breathing rate, metabolic rate)

What does cortisol do?

secreted by the adrenal gland in response to long term stress, mobilizies internal fuel breakdown, regulates sleep-wake cycle

How are cortisol levels normally reduced after the stress goes away?

negative feedback loops, presence of cortisol inhibits CRF in the hypothalamus

What are the adverse effects of chronically high cortisol levels?

muscle wasting, reproductive inhibition, immunosuppression

What are the two special features of neurons?

they are highly interconnected and electrically active

What is the distribution of ions and charges across the membnrane at resting potential?

Inside: high levels K+, low levels Na+, negative charge

Outside: low levels K+, high levels Na+, positive charge

How are the chemical/electrical gradients created in the neuron at resting potential?

K+ is permeable and leaks out of the cell more than Na+ leaks in, the sodium potassium pump pumps 2 K+ in and 3 Na+ out

How does the flow of ions across the membrane generate an action potential?

Ion hold charges and when they flow across membranes they change the overall charge of the membrane, creating an action potential

What happens in the membrane when the action potential threshold is reached?

Sodium channels open creating a rush of Na into the cell, depolarizing (making positive) the membrane

Why is the action potential considered a digital signal?

It is all or nothing, either it fires at its full potential or it doesn’t fire at all

How is variety of intensity of signals controled by the nervous system?

More intensity is shown by a greater rate and number of action potentials instead of the strength of the action potential itself

How do action potentials propagate down the axon?

The signal is generated at the axon hillock and propagates down the axon to the axon terminal, jumping between nodes of ranvier

What is the myelin sheath and what is its effect on the propagation of action potentials?

Insulates an axon and increases the speed of action potentials

Summarize an action potential

1. Resting potential: negative charge inside. All channels are closed

2. Depolarization: stimulus triggers some Na channels to open, if membrane potential reaches threshold, more Na channels open causing them to rush into the cell, making the inside positive

3. Depolarization: Na channels inactivate, K channels open and K rushes out of cell making inside of membrane negative again

4. Hyperpolarization: membrane potential breifly becomes more negative than resting as K channels close

How do action potentials affect other neurons?

synaptic transmission

How do excitatory and inhibitory neurotransmitters work differently at the synapse?

Excitatory neurotransmitters cause depolarization (Na+ channels), increasing the likelihood of an action potentials instead whereas inhibitory neurotransmitters cause hyperpolarization (K+ and Cl- channels), decreasing the likelihood of an action potential

Why is a single action potential in the sending neuron unable to cause an action potential in the receiving neuron?

The resulting depolarization is too small to reach the threshold for firing

How does Botox affect neurotransmission?

Blocks the release of acetylcholine

How does cobra toxin affect neurotransmission?

Blocks acetylcholine receptors

What is the role of acetylcholine in the synapse?

Stimulates the opening of Na+ channels, allowing action potentials to occur

What is Sarin gas’s affect on neurotransmission?

Inhibits the enzyme that breaks down ACh

What is temporal summation of action potentials?

The addition of signals from a single neuron firing multiple times in quick succession

What is spatial summation in action potentials?

Addition of signals from multiple different neurons firing at nearly the same time

Why is summation so crucial in the nervous system?

In order for signals to be strong enough to reach the action potential threshold

What is sensory transduction?

The process of converting a stimulus into an electrical change in a cell

What is the sensory transduction path of taste?

Sugar molecule, hits sensory receptor cells in the taste bud, which activates a signal transduction pathway, opens/closes ion channels, changing the receptor potential, stimulating neurotransmitter release in the sensory receptor cell which sends signals to a sensory neuron, creating an action potentials instead that is sent to the brain to show when sugar is present

What is the difference between modality and stimulus quality?

Modality regrets to the type of sense or distinct class of sensation (sight, sound or touch), while stimulus quality describes the specific characteristics of a stimulus within that modality (color of a light, pitch of a sound)

How is stimulus quality conveyed to the brain?

It is conveyed to the brain through specialized receptors that detect different chemical and physical properties and send the signals along dedicated neural pathways to specific brain regions. Ex. Sweet tastes is detected by sugar receptors whereas sour tastes is detected by ion channels that respond to acids

How is stimulus intensity conveyed to the brain?

Weak stimulus comes across with little neurotransmitter relase and low action potential frequency, strong stimulus comes with a lot of neurotransmitter release and high action potential frequency. Also determined by the frequency of an action potential

What is the function of the lens?

Thick bulge of cells behind the iris that bulges and flattens in order to reflect light onto the correct spot on the retina. Thicker when looking st something close, flatter when looking at something far

What is the function of rhodopsin?

Protien within rods that is sensitive to light and changes its shape, opening/closing ion channels, allowing for action potentials to generate

What is the difference between rods and cones?

Rods: very light sensitive, no color, periphery vision

Cones: less light sensitive, color vision, concentrated in the fovea

What is the molecular difference between the blue, red, and green cones?

Containers different ops in types that are most sensitive to a different color

How have opsin molecules evolved within terrestrial vertebrates?

Loss of 2 types of opsin in mammal evolution, then gained one in primates

What is the big picture of sensory transduction?

100 million sensory receptor cells each with their own sensitivity that can each stimulate action potentials that vary in frequencies help transducer the world into things we can perceive

What is special about the human eye that allows us to see in high resoution?

We have the most densely packed retina with 125 million photoreceptors

How do animals see better at night?

The back of their retina is lined with a reflective surface called a tapetum that amplifies the amount of light coming into the eye allowing nocturnal vision

How do animals see better in the water?

Water reflects light everywhere so a much stronger lens is needed to bend the light to allow it to focus on the retina

How are longer wavelengths of light detected by animals (infrared in snakes)?

I fared receptors in snakes detect the body heat (infrared radiation) emitted by warm blooded animals in the “pit organ” which contained highly sensitive nerve endings that have the ability to convert heat into electrical signals allowing a “thermal image” of an organism to be formed in the brain

What are the function of electroreceptors in sharks, and electric fish?

They detect weak electric fields from other animals

What is the difference between the central and peripheral nervous system?

Central: brain and spinal cord, makes decisions

Peripheral: nerves and receptors, transmits signals

What is a motor unit?

The smallest functional unit of the muscular system, consisting of a motor neuron and the muscle fibers that are innervated by it

What is the anatomy of a muscle from largest to smallest?

Muscle → bundle of muscle fibers → single muscle fiber (cell) → myofibril → sarcomere → thick filaments (myosin) and thin filaments (actin)

How can a muscle generate such large movements even though it only shortens 2-5% of its length?

Muscles insert near the join so small muscle movements can cause large bone movements. Anatomical structure

Describe the process of muscle contraction

In a relaxed muscle the actin and myosin fibers are separated, when the muscle contracts, the myosin head attaches to myosin binding sites on the actin fiber creating a cross bridge, the myosin head to pull the actin towards the center of the sarcomere, ATP is used to detach

What is rigor mortis?

Stiffening of the joints and muscles of the body a few hours after death due to a depletion of ATP

How is actin and myosin interactions regulated?

Tropomyosin blocks myosin binding sites and only exposes them when troponin complexes bind with Ca2+ ions that come from inside of the muscle cell (sarcoplasmic reticulum)

Why is it important to reputable calcium from the cytoplasm of a muscle cell?

So the muscles can relax

How is the digital to analog conversion accomplished by the nueromuscular system?

Occurs at the nueromuscular junction. Action potential from the neuron is translated into neurotransmitter release into the synaptic cleft to the muscle cell

What happens to the force of contraction when action potential frequency increases?

Force of contraction increases. More Ca2+ release = less tropomyosin blocking = more actin/myosin interaction = more force

What two ways can the strength of a contraction increase?

Through increasing action potential frequencies, or increasing the number of motor units firing

How does the neurotransmitter at the nueromuscular junction (ACh) cause a muscle cell to depolarize?

It open sodium channels allowing Na+ to rush into the muscle cell creating a local depolarization which can trigger voltage gated sodium channels to open, causing a full action potential