Physiology Term 1 Final Midterm (December 7) Flashcards
Define humoral immunity.
Immunity conferred by antibodies present in the blood plasma and other bodily fluids.
What do antibodies do?
Though they are produced by lymphocytes, antibodies circulate freely in the blood and lymph, where they bind primarily to extracellular targets—bacteria, bacterial toxins, and free viruses— inactivating them temporarily and marking them for destruction by phagocytes or complement.
Define cellular immunity.
Immunity conferred by activated T cells, which directly kill infected or cancerous body cells or cells of foreign grafts and release chemicals that regulate the immune response. Also called cell-mediated immunity.
What four key characteristics sets the adaptive immune system apart from the innate immune system?
- The adaptive immune system involves lymphoyctes called the T and B lymphocytes.
- It is specific
- It is systemic
- It has memory.
Define antigen.
Large organic molecules, usually a protein, stuck in a cell membrane which could be self or foreign.
Define MHC proteins.
Major histocompatibility complex. Molecules on the outer surface of the plasma membrane of all cells; help the immune system distinguish self from nonself. T cells recognize antigens only when combined with these proteins.
What marks a cell as “self” instead of non-self?
Self-antigens, particularly MHC proteins, mark a cell as self.
Which cells oversee humoral immunity?
B cells
Define T cells.
Non-antibody producing lymphocytes that constitute the cellular arm of adaptive immunity.
Define immunocompetence.
The ability of the body’s immune system to recognize (by binding) specific antigens; reflects the presence of plasma membrane-bound receptor.
Define self-tolerance.
Each lymphocyte must be relatively unresponsive to self-antigens so that it does not attack the body’s own cell.
Define antigen-presenting cell (APC)
A specialized cell (dendritic cell, macrophage, or B cell) that captures, processes, and presents antigens on its surface to T lymphocytes.
What two types of cells are involved in adaptive immunity?
T lymphocytes and B lymphocytes
Where are both T cells and B cells produced?
Bone marrow
Where do T cells mature?
thymus
Where do B cells mature?
Bone marrow. Then they go to the blood and lymph nodes.
What is the name of one of the important self-antigens contained on the cells?
MHC glycoprotein (major histocompatibility complex); also known as human leukocyte antigens - HLAs
What is the role of the MHC protein?
To present fragments of either your own proteins or foreign antigens.
What are the two main classes of glycoproteins?
Class 1 and Class 2.
Where are Class 1 found?
They are found on just about all cells in the body. (any cell with a nucleus)
Where are Class 2 found?
They are found on B cells, dendritic cells and macrophages.
How are B cells activated?
By an antibody challenge that usually happens in the spleen or the lymph node.
Describe what happens when a B cell comes into contact with an antigen.
Once it is bound onto the antigen, it is stimulated to start dividing. The cells it produces are known as clones. Keeps dividing and dividing and creating cells that identical to the parent cells.. After a while these clone cells start to differentiate and start to form plasma cells and occasionally a memory B cell.
Structurally, what do antibodies consist of?
Four looping polypeptide chains linked together by disulfide bonds.
Describe antibody class IgM
The first immunoglobulin class secreted by plasma cells during the primary response. Readily fixes and activates complement. Numerous binding sites make it a potent agglutination agent. (pentamer)
Describe antibody class IgA
Referred to as secretory IgA, is found in body secretions such as saliva, sweat, intestinal juice and milk. Helps stop pathogens from attaching to epithelial cell surfaces. (dimer)
Describe antibody class IgD
Found on B cell surface
Functions as a B cell antigen receptor (as does IgM) (monomer)
Describe antibody class IgG
Most abundant antibody in plasma, accounting for 75%-85% of circulating antibodies
Main antibody of both secondary and late primary responses
Readily fixes and activates complement
Crosses the placenta and confers passive immunity to the fetus. (monomer)
Describe antibody class IgE
Stem end binds to mast cells or basophils. Antigen binding to its receptor end triggers these cells to release histamine and other chemicals that mediate inflammation and an allergic reaction. (monomer)
What is the most common event in all antibody-antigen interactions?
Formation of antigen-antibody complexes.
List the defense mechanisms used by antibodies.
Neutralization, agglutination, precipitation and complement fixation.
What are the main functions of blood? Please give an example of each.
Transport (delivering oxygen from the lungs), regulation maintaining normal pH in body tissues), and protection. (preventing infection - antibodies, complements proteins and leukocytes drift in the blood).
What does ADP do as part of hemostasis?
A potent aggregating agent that causes more platelets to stick to the area and release their contents
Define antibody.
A protein molecule that is released by a plasma cell (a daughter cell of an activated B lymphocyte) and that binds specifically to an antigen; an immunoglobulin.
Define B-cells.
Also called B lymphocytes. Oversees humoral immunity; their descendants differentiate into antibody-producing plasma cells.
Define buffy coat.
Layer contains leukocytes (leuko = white), the white blood cells that act in various ways to protect the body, and platelets, cell fragments that help stop bleeding.
Define coagulation.
Process in which blood is transformed from a liquid to a gel; blood clotting.
Define diapedesis.
Passage of white blood cells through intact vessel walls into tissues.
Define erythropoeisis.
Refers to the production of red blood cells. Find them in flat bones like the pelvic girdle, sternum, skull or shoulder blades.
What is fibrin?
Fibrous insoluble protein formed during blood clotting.
What is fibrinogen?
A soluble blood protein that is converted to insoluble fibrin during blood clotting.
Define hematocrit. What is its normal value?
The percentage of total blood volume occupied by erythrocytes. It is normally about 45%.
List two protective functions of blood.
Blood can prevent blood loss by forming clots when a blood vessel is damaged. Blood can prevent infection because it contains antimicrobial proteins and white blood cells.
What is the chemical composition of plasma?
Blood plasma is a straw-colored, sticky fluid
Although it is mostly water (about 90%), plasma contains over 100 different dissolved solutes, including nutrients, gases, hormones, wastes and products of cell activity, proteins, and inorganic ions (electrolytes)
Electrolytes (Na+, Cl−, etc.) vastly outnumber the other solutes.
What are formed elements?
erythrocytes, leukocytes (white blood cells), and platelets
True/False: All formed elements are true cells?
False. 2 out of 3 are not (RBCs have no nucleus and platelets are fragments).
If you put blood in a centrifuge, what would the breakdown be?
RBCs (45%), Buffy coat (< 1%), plasma (55%)
How many molecules of oxygen can each hemoglobin molecule transport? What part of the hemoglobin binds the oxygen?
Each hemoglobin molecule can transport four O2. The heme portion of the hemoglobin binds the O2.
List the differential white blood cell count from most to least and outline their percentages.
Neutrophils (50-70%), Lymphocytes (25 - 45%), Monocytes (3-8%), Eosinophils (2-4%), Basophils (0.5 - 1 %) (think Never Let Monkeys Eat Bananas)
Define hemostasis.
Hemostasis is the prevention of blood loss by the three mechanisms of vascular spasm, the formation of a platelet plug and coagulation.
Define innate immunity.
Innate immunity refers to the type of immunity that does not have memory and that responds to a pathogen the same way every time - no specificity.
When infected by a virus a cell may respond by producing ____________.
Interferon
True or false, please correct if false: The chemical ADP causes vascular constriction.
False. It attracts more platelets to the forming platelet plug. Serotonin and thromboxane A2 cause vascular constriction in addition to attracting more platelets.
You have been infected by a bacterial infection; list all the innate mechanisms which will attempt to eliminate this.
Phagocytes and phagocytosis, natural killer cells, inflammation, antimicrobial proteins and fever.
(I didn’t include surface barriers as the question stated that I have been infected by a bacterial infection - so that mechanism failed)
Compare (2 similarities) and contrast (2 differences) the intrinsic and extrinsic blood clotting pathways (do not give details of all the factors involved)
2 similarities:
Both pathways are trying to produce prothrombin activator
Both pathways use clotting factors as well as the ion calcium
Crucial components in both pathways are negatively charged membranes.
2 differences:
The intrinsic pathway has more steps and is slower than the extrinsic pathway
The intrinsic pathway has the factors needed for clotting present within the blood while the extrinsic pathway requires tissue factor which is outside of blood.
How does histamine cause the 3 signs of inflammation?
Redness: Histamine causes vasodilation which leads to increased blood flow to the area. This results in redness.
Swelling (pain): Histamine increases vascular permeability, so plasma leaks into surrounding tissues causing the swelling. Swelling causes the pain.
Heat: Histamine causes vasodilation which leads to increased blood flow to the area. This results in redness.
Define myeloid cell
a stem cell that gives rise to all other formed elements
You have unfortunately been in a car accident and lost a large amount of blood. Explain in terms of homeostasis how the body will respond and why.
Your body will detect a drop in blood oxygen, which will put an imbalance in homeostasis. The kidney acts as the receptor and control centre in this case and releases erythropoietin. The erythropoietin will stimulate the red bone marrow (the effector) and the resulting enhanced erythropoiesis increases the RBC count. The blood can now carry more oxygen, thereby trying to return the body to homeostasis.
Relate structure to function for the erythrocyte
Anucleate biconcave disc allows for higher surface-to-volume ratio; this facilitates more gas diffusion. Additionally, it means that the no point within the cytoplasm is far from the surface.
Because erythrocytes lack mitochondria and generate ATP by anaerobic mechanisms, they do not consume any of the oxygen they carry, making them very efficient oxygen transporters
A blood sample taken from a patient indicates a large amount of eosinophils. How do you identify eosinophils and what might be the reason for the large numbers?
Eosinophil can be identified as it has a bilobed nucleus that has the appearance of earmuffs and red cytoplasmic granules. There may be large numbers because the patient has a parasitic worm.
A blood sample taken from a patient indicates a large amount of neutrophils. How do you identify neutrophils and what might be the reason for the large numbers?
Neutrophils can be identified by their multilobed nucleus and pale red and blue cytoplasmic granules. They are bacteria slayers so the large number may be due to the fact that the patient has a bacterial infection.
A blood sample taken from a patient indicates a large amount of basophils. How do you identify basophils and what might be the reason for the large numbers?
Basophils can be identified as it is similar to a mast cell and has a bilobed nucleus and purplish-black cytoplasmic granules. The granules are histamine containing. Someone may have an infection.
A blood sample taken from a patient indicates a large amount of monocytes. How do you identify monocytes and what might be the reason for the large numbers?
They are the largest leukocyte and have abundant pale-blue cytoplasm and a darkly staining purple nucleus, which is often U or kidney shaped. Because they can differentiate into highly mobile macrophages, the person may have a viral infection.
A blood sample taken from a patient indicates a large amount of lymphocyte. How do you identify lymphocytes and what might be the reason for the large numbers?
The nucleus is usually spherical but may be slightly indented, and it is surrounded by a thin rim of pale-blue cytoplasm.
How do cells of the innate immune system detect infection?
They have Toll Like Receptors (TLRs) either on the surface of their membranes or within the cell. These identify specific components of microorganisms that enter the body.
Why might fever be beneficial to the body in terms of the effect on microorganisms?
Most microorganisms work best at normal body temperature; increasing temperature decreases their replication rate.
How does interferon fight viruses?
Interferes with viral replication
Modulates inflammation
Activates immune cells
Explain how the leukocytes are produced.
Hematopoietic stems cells divide early on into myeloid stem cells and lymphoid stem cells. The myeloid stem cells divide into eosinophils, basophils and neutrophils (granulocytes) as well as monocytes (agranulocyte). The lymphoid cell divides into lymphocytes (agranulocyte). Lymphocytes are then divided until T and B lymphocytes.
Explain the difference between T and B lymphocyte production.
T cells mature in the thymus while B cells mature in the red bone marrow.
T cells differentiate when they come out of the thymus.
B and T cells then enter the lymph nodes
Define platelets
A formed element that is a fragment of a larger cell called a megakaryocyte. They play a major role in the formation of the platelet plug and in coagulation.
A hormone called _____________ regulates the formation of platelets.
thrombopoietin
Explain the three mechanisms involved in hemostasis.
Vascular spasm involves the vasoconstriction of the blood vessel. The smooth muscle contracts and restricts the flow of blood. Reduces blood loss for 20-30 minutes.
During platelet plug formation the site injury exposes collagen fibers, which enables the platelets to stick to the site of injury. Three chemicals are released (serotonin, ADP and thromboxane A2) that increase platelets sticking and vasoconstriction. This leads to the formation of a platelet plug that slows the loss of blood. Builds up the plug within one minute.
During coagulation, fibrin proteins form a mesh that traps red blood cells and platelets and forms the clot. Both the intrinsic and extrinsic paths can build the fibrin mesh.
What factors trigger vascular spasm?
Direct injury to vascular smooth muscle
Exposure to underlying collagen fibers
Metal or glass can activate it (a lot of negative charges will activate the pathways)
True or false: Capillaries are able to have vascular spasm.
False: They cannot because they don’t have smooth muscle.
What are the functions of the immune system?
Fights off pathogens and invaders Prevents the spread of damaging agents to nearby tissues Disposes of cell debris and pathogens Alerts the adaptive immune system Sets the stage for repair
What are four cardinal signs of inflammation?
Redness
Heat
Swelling
Pain
Describe the first line of defense for the innate immune system.
The first line of defense consists of surface barriers. The skin and mucosae are part of this line of defense. In addition to being a mechanical barrier, there are a number of chemicals that they use in their defense arsenal: Acid Enzymes Mucin Defensins Other chemicals (lipids in sweat)
List the mucous membranes involved in the first line of defense of the innate immune systems.
Respiratory - nose
Urinary
Reproductive
Digestive (mouth and anus)
Inflammation is good if it is _______ and ________.
localized, short-lived.
What cells produce inflammatory chemicals?
Mast cells produce inflammatory chemicals (histamine).
Define natural killer cell.
A defensive cell that can kill cancer cells and virus-infected body cells before the adaptive immune system is activated. It is non-specific (hence natural) and basically comes into contact with the cell it intends to kill and kills it by inducing apoptosis. They attack cells by detecting general abnormalities such as the lack of “self” cell-surface proteins called MHC.
What aspect of the skin makes it good at protection besides being a mechanical barrier?
pH, secretions and most especially, dendritic cells, which act as phagocytes. Also, keratin forms resistance.
Explain the various aspects of the mucous membrane line of defense.
Mucus: traps (respiratory and digestive tracts)
Urine: natural pH is acidic and inhibits bacterial growth
Gastric juices: acidic and protein digesting enzymes destroy pathogens
Lacrimal secretions/saliva: Cleanses and lubricates
Cilia: propels debris laden mucus away
Acid mantle of the vagina: inhibits bacteria and fungi growth
Nasal hairs: filters and traps
What type of movement is phagocytosis and name two cells that are good at it.
Endocytosis (engulfs or takes in) and macrophages (which arise from monocytes) and neutrophils are good at it. Dendritic cells are also fantastically good at phagocytosis.
Where are you likely to find a lot of macrophages?
Lungs
What steps are involved in the phagocytosis of a bacteria?
The macrophage sticks to the bacteria via a receptor
The bacteria is engulfed in a vesicles (formed by the fluid membrane of the macrophage)
The vesicle binds with a lysosome to make a phagosome
Inside the phagosome the pathogen is destroyed
Sometimes the remnants are put out of the cell by exocytosis
List the steps of phagocytic mobilization.
Leukocytosis: neutrophils enter blood from bone marrow
Margination: neutrophils cling to simple squamous epithelium
Diapedesis: Neutrophils flatten and squeeze out of capillaries
Chemotaxis. Neutrophils follow chemical trail.
What causes factor 12 to be activated?
Vessel endothelium ruptures, exposing underlying tissues such as collagen.
What are the positive effects of the inflammatory response?
Prevents infection from spreading to adjacent tissues - keeps it localized
Disposes of pathogens and dead tissue cells
Promote tissue repair
Release inflammatory chemicals to attract phagocytes to the area
Give a summary of how interferon works.
Infected cells can do little to save themselves, but some can secrete small proteins called interferons (IFNs) to help protect cells that have not yet been infected. The IFNs diffuse to nearby cells, which they stimulate to synthesize proteins that block further protein synthesis and degrade viral RNA. In this way, they “interfere” with viral replication.
Define complement system (of proteins).
The term complement system, or simply complement, refers to a group of at least 20 plasma proteins that normally circulate in the blood in an inactive state. These proteins include those numbered C1 through C9 plus several others that act as regulatory proteins and other factors.
The classical pathway involves antibodies, water-soluble protein molecules that the adaptive immune system produces to fight off foreign invaders. When antibodies bind to pathogens, they can also bind complement components. This double binding is the first step in this complement activation pathway.
Like the blood clotting cascade, complement activation by any of these pathways involves a cascade in which proteins are activated in an orderly sequence—each step catalyzing the next. The three pathways converge at C3, which is split into C3a and C3b. Splitting C3 initiates a common terminal pathway that enhances inflammation, promotes phagocytosis, and can cause cell lysis. Cell lysis begins when C3b binds to the target cell’s surface and triggers the insertion of a group of complement proteins called MAC (membrane attack complex) into the cell’s membrane. MAC forms and stabilizes a hole in the membrane that allows a massive influx of water, lysing the target cell.
Which cell in the adaptive immune system can identify foreign antigens themselves, B or T?
B cells
Once a B cell has identified a foreign antigen, what does it need to fully activate?
IL4 from T helper cells.
What is the origin of a plasma cell in humoral immunity and what is its job?
Origin is B-cell and its job is to produce antibodies.
Define agglutination.
Causes the foreign antigen to clump together.
Define neutralization.
Binds to bacterial toxin and neutralizes the effect.
Define enhancement of phagocytosis as a mechanism within the antibody tool kit.
Coats the invading bacteria, which helps cells such as macrophages identify the foreign cells.
When do the memory cells created by B cells come into use?
They do nothing until the person gets a second identical infection. They then leap to life and produce plasma cells and antibodies. The second wave is super fast - after about 24 hours antibodies are being produced.
What are the two main types of T-cells?
Helper T cells and cytotoxic t cells.
What are two similarities and two differences between helper T cells and cytotoxic T cells?
Similarities:
- Both types of cells require foreign antigen to be processed by your own cell to recognize it
- Both mature in the thymus
Differences
- Cytotoxic cells can identify all cells in the body (Class 1) and helper T cells can only identify certain cells such as B cells, dendritic cells and macrophages (APC)
- Helper T cells display a protein receptor called CD4 while cytotoxic t cells display a protein receptor called CD8
Define interleukin 2.
This stimulates T cell growth, both Helper T cells and cytotoxic cells. It helps to fully activate them.
Define interleukin 4.
This works on B cells helping to fully activate them.
Define macrophage inhibition factor.
This slows macrophages down so they remain in the area of the infection.
Define chemotaxins.
These lure neutrophils and macrophages to the area.
What are cytotoxic cells particularly good at dealing with?
Virus infected cells. These are our own body cells which then display self+foreign antigen.
What two types of proteins do cytotoxic T-cells divide into and what do they do?
One is called perforin and it acts in a similar way as a complement protein. It makes a hole in your own cell membrane. The second protein is granzyme enzymes that enter the whole and digest the contents of the cell.
What is the function of the suppressor/regulatory T cell?
They come into action at the end of an infection and they “turn off” or subdue the immune response.
What is meant by “integration,” and does it primarily occur in the CNS or the PNS?
Integration involves processing and interpreting sensory information, and making a decision about motor output. Integration occurs primarily in the CNS.
Which subdivision of the PNS is involved in (a) relaying the feeling of a “full stomach” after a meal, (b) contracting the muscles to lift your arm, and (c) increasing your heart rate?
(a) This “full stomach” feeling would be relayed by the sensory (afferent) division of the PNS (via its visceral afferent fibers).
(b) The somatic nervous system, which is part of the motor (efferent) division of the PNS, controls movement of skeletal muscle.
(c) The autonomic nervous system, which is part of the motor (efferent) division of the PNS, controls the heart rate.
Which type of neuroglia controls the extracellular fluid environment around neuron cell bodies in the CNS? In the PNS?
Astrocytes control the extracellular environment around neuron cell bodies in the CNS, whereas satellite cells perform this function in the PNS.
Which two types of neuroglia form insulating coverings called myelin sheaths?
Oligodendrocytes and Schwann cells form myelin sheaths in the CNS and PNS, respectively.
True or false? The human body is electrically neutral.
True
Which ion plays the major role in generating the resting membrane potential?
Potassium
What mechanism helps all sodium channels to open and reach threshold?
Positive feedback
What are the three phases that apply to a voltage gated sodium channel?
1: Closed ready to open, 2: Open and 3: Closed but inactivated
Why is potassium so important in the ECF?
It influences the resting membrane potential
What happens if you suffer from Hypokalemia?
There is not enough potassium in the ECF
Which is bigger, a graded potential or an action potential? Which travels farther? Which initiates the other?
Action potentials are larger than graded potentials and travel farther. Graded potentials generally initiate action potentials.
An action potential does not get smaller as it propagates along an axon. Why not?
An action potential is regenerated anew at each membrane patch.
Why does a myelinated axon conduct action potentials faster than a nonmyelinated axon?
Conduction of action potentials is faster in myelinated axons because myelin allows the axon membrane between myelin sheath gaps to change its voltage rapidly, and allows current to flow only at the widely spaced gaps.
If an axon receives two stimuli close together in time, only one AP occurs. Why?
If a second stimulus occurs before the end of the absolute refractory period, no AP can occur because sodium channels are still inactivated.
What are the functions of the endocrine system?
- reproduction
- growth and development
- maintenance of water, electrolyte, and nutrient balance of the blood
- regulation of cellular metabolism and energy balance
- mobilization of body defenses
What are three differences between the nervous and endocrine systems?
- Nervous system initiates responses rapidly while endocrine responds slowly
- nervous system has short duration responses and endocrine long-duration responses
- NS acts via neurotransmitters and action potentials and ES via hormones released into the blood
What are the main characteristics of endocrine glands?
- ductless glands
- produce hormones
- release hormones into the surrounding tissue fluid
- rich vascular and lymphatic drainage that receives their hormones
In the thymus, what tests must the T cells pass to survive?
They must recognize self MHC proteins and must not recognize self-antigens.
How do helper T cells help in humoral immunity?
The helper T cell binds to the self-non-self complex of a B cell that has encountered its antigen and is displaying it on MHC II on its surface. The T helper cell releases interleukins as co-stimulatory signals to complete B cell activation.
What are the major endocrine organs?
pineal, hypothalamus, pituitary gland, thyroid, parathyroid gland, thymus, adrenal glands, pancreas and gonads (ovary and testes)
Which glands are steroid producing?
gonads and adrenal
What are some characteristics of amino-acid based hormones?
- most common
- hydrophilic
- usually water soluble and can’t cross the plasma membrane
What are the two hormone classifications?
amino acid based and steroid based.
What are some characteristics of steroid based hormones?
- synthesized from cholesterol
- only adrenocortical and gonadal hormones are steroids
Name 3 changes that a hormone typically produces.
- Alters plasma membrane permeability
- Activates or deactivates enzymes
- Stimulates mitosis
What are the two mechanisms that hormones usually use?
Act on receptors in the plasma membrane or act on receptors inside the cell, which activate genes.
Which hormones act on receptors in the plasma membrane?
water-soluble hormones, which are all amino-acid based hormones except thyroid hormone
Which hormones act on receptors inside the cell?
Lipid-soluble hormones, which are steroid and thyroid hormones.
What is a second messenger?
Intracellular molecule generated by the binding of a chemical to a receptor protein; mediates intracellular responses to the chemical messenger.
List the steps involved in the cycle AMP second-messenger mechanism of water-soluble hormones.
- Hormone (1st messenger) binds to receptor in the cell membrane.
- Receptor activates G protein.
- G protein activates adenylate cyclase.
- Adenylate cyclase enzyme converts ATP to cAMP (2nd messenger).
- cAMP activates protein kinases.
- Activated protein kinases (phosphorylates) trigger responses of target cells)
T/F: amino acid hormones need a carrier protein in the blood?
False
T/F: Steroid hormones need a carrier in the blood?
True
Lipid soluble hormones act by entering the nucleus of the cell. What do they do within the nucleus?
They turn protein synthesis on or off.
Why can steroid hormones enter the cell?
Because they are small and non-polar.
Which steroid is slower, aldosterone or glucagon? And why?
Aldosterone is slower because not all components are there - it needs to make protein channels, etc.
What kind of hormone is aldosterone?
Lipid soluble (steroid); comes from adrenal glands
What kind of hormone is glucagon?
Water soluble hormone (amino acid based hormones); produced by alpha hormones in the pancreas.
Where is the main effect of glucagon?
In the liver on the hepatocytes. When the hepatocytes are activated by glucagon the enzyme glycogen phosphorylase will be activated and this breaks down glycogen and produces glucose.
Which is bigger, a graded potential or an action potential? Which travels farther? Which initiates the other?
Action potentials are larger than graded potentials and travel farther. Graded potentials generally initiate action potentials.
An action potential does not get smaller as it propagates along an axon. Why not?
An action potential is regenerated anew at each membrane patch.
Why does a myelinated axon conduct action potentials faster than a nonmyelinated axon?
Conduction of action potentials is faster in myelinated axons because myelin allows the axon membrane between myelin sheath gaps to change its voltage rapidly, and allows current to flow only at the widely spaced gaps.
If an axon receives two stimuli close together in time, only one AP occurs. Why?
If a second stimulus occurs before the end of the absolute refractory period, no AP can occur because sodium channels are still inactivated.
Why is potassium so important in the ECF?
It influences the resting membrane potential
What three channels are important relative to action potentials?
Leak channels, voltage-gates channels, chemical channels
Define synapse.
A junction that mediates information transfer from one neuron to the next or from a neuron to an effector cell—it’s where the action is. (e.g. axon to dendrite, axon to cell body, axon to muscle, axon to gland)
We learned that important ion channels in the walls of axons are voltage regulated. What regulates the protein channels found on the dendrite of the post synaptic cell to receive information crossing the synapse.
Chemicals -they are chemically regulated channels
After the dendrite has passed its information on the neurotransmitter such as acetylcholine is no longer needed. What three things can happen to the neurotransmitters when the are no longer needed?
1: they can be broken down by enzymes. 2: they can be taken back into the presynaptic cell or 3: they can just diffuse way from the synapse
Which ions flow through chemically gated channels to produce IPSPs? EPSPs?
IPSPs result from the flow of either K+ or Cl− through chemically gated channels. EPSPs result from the flow of both Na+ and K+ through chemically gated channels.
What is the difference between temporal summation and spatial summation?
Temporal summation is summation in time of graded potentials occurring in quick succession at the postsynaptic membrane. It can result from EPSPs arising from just one synapse. Spatial summation is summation in space—a postsynaptic neuron is stimulated by a large number of terminals at the same time.
Briefly list the steps involved with the amino acid based hormone glucagon.
Produced by pancreas>goes to liver>binds to receptor>activates G protein>G protein activates enzyme adenylate cyclase>converts ATP into cAMP>activate protein kinase>activates glycogen phosphorylase to break down glycogen into glucose
The main function of the endocrine system is to _____________________.
control metabolic functions.
Relative to extracellular fluid, the interior of a neuron has a negative charge because __________.
potassium diffuses out of the cell
The CNS can discriminate between strong and weak stimuli as strong stimuli __________.
increase the frequency of action potentials
Spatial summation occurs when __________.
multiple local potentials occur at different places on the same cell at the same time
In inhibitory synapses (IPSPs), the postsynaptic membrane become more permeable to _________________________.
potassium and chloride
The sodium-potassium ion pump will __________.
pump three sodium ions out of the cell for every two ions of potassium it brings into the cell
What is the inability of a neuron to respond to a second stimulus of equal strength to the first stimulus to which it has already responded?
The neuron is in the absolute refractory period.
What event or conditions would cause synaptic potentiation?
influx of Ca++
What is the primary difference between the somatic nervous system and the autonomic nervous system?
The somatic nervous system allows us to consciously control our skeletal muscles, and the autonomic nervous system controls activity that humans cannot consciously control, such as the pumping of the heart and the movement of food through the digestive tract.
What type of membrane ion channels open and close in response to changes in the membrane potential?
voltage-gated channels
True or false: An action potential is a phenomenon that either happens completely or doesn’t happen at all.
True
True or false: Chemical synapses transmit nerve impulses directly from one neuron to another.
False
The movement of which ion out of the cell through leakage channels establishes the negative membrane potential?
potassium
Which part of the action potential occurs when the voltage-gated Na+ channels are inactivating and voltage-gated K+ channels open?
repolarization
What two things produce a change in membrane potential?
(1) anything that alters ion concentrations on the two sides of the membrane, or (2) anything that changes membrane permeability to any ion.
Nervous tissue is made up of two principle cells including _______________ and ____________.
nerve cells and glial cells
List three unique characteristics of nerve cells.
they have extreme longevity, they are amitotic, they have very high cellular metabolic rate (cannot survive for more than a few minutes without oxygen.
What type of signals do dendrites receive?
These electrical signals are usually not action potentials (nerve impulses) but are short-distance signals called graded potentials.
True or false: A neuron never has more than a single axon.
True
What is the conducting region of the neuron?
the axon
What two types of signals can be produced by changes in the membrane potential?
graded potentials (short distances, variable strength, usually in dendrites or cell bodies) and action potentials (long-distance, same strength, axon)
What triggers a graded potential?
Graded potentials are triggered by some change (a stimulus) in the neuron’s environment that opens gated ion channels.
The direction an ion moves (into or out of the cell) is determined by the _________________________.
electrochemical gradient
What two components make up the electrochemical gradient?
- The concentration gradient. Ions move along chemical concentration gradients from an area of their higher concentration to an area of lower concentration.
- The electrical gradient. Ions move toward an area of opposite electrical charge.
What 2 factors generate resting membrane potential?
- differences in the ionic composition of the intracellular and extracellular fluids,
- differences in the plasma membrane’s permeability to those ions.
What two types of cells use membrane potentials?
neurons and muscle cells
Briefly describe the steps of an action potential.
- Resting membrane potential in place. Leak channel happening but voltage-gated channel closed.
- Through stimulus and positive feedback Na ions come in until it hits threshold (-50) and then Na rushes in. This period is depolarization and goes up to +30 mv.
- Na voltage gated channels are inactivated (absolute refractory period) and potassium voltage-gated channels open. This leads to repolarization and even a brief period of depolarization because K channels close more slowly. Once closed, the resting membrane potential value will be restored through the sodium-potassium pump.
True or false. Voltage-gated channel are specific and only allow one type of ion to move through it.
True
What type of feedback is key to creating an action potential?
positive feedback
Define threshold.
The minimum strength of stimulus required to create an action potential. Must be reached then all or none response happens.
Explain absolute refractory period.
The time period when it is impossible to create a second action potential. It begins when we hit threshold and all sodium gates are open. There are no more Na gates to open. At + 30 mv, the sodium channels close and lock (become inactivated).
How is relative refractory period different from absolute refractory period?
Relative refractory period follows the absolute refractory period. The sodium voltage gated channels have returned to their resting state and could reopen if there was a strong enough stimuli (would need to be exceptionally strong - stronger than the usual one).
How do nerves code for stimulus intensity?
Strong stimuli generate nerve impulses more often in a given time interval than do weak stimuli. Stimulus intensity is coded for by the number of impulses per second—that is, by the frequency of action potentials.
What 2 factors largely influence the rate of impulse propogation?
axon diameter and degree of myelination
List three differences between continuous conduction and saltatory conduction.
- Continuous conduction takes place in unmyelinated axons and saltatory in myelinated axons.
- Continuous conduction is slower and saltatory faster.
- in continuous conduction the voltage gated channels are immediately adjacent to each other while in saltatory they are located at the gaps between the myelin, allowing the current to be maintained and APs to only be triggered at the gaps.
True or false: Chemical regulated channels are specific the way that voltage-regulated channels are.
False. They are large enough that several different ions can move through at the same time.
List the steps associated with the synapse.
- P reaches the axon terminal. a causes calcium voltage gated channels to open.
- calcium ions flood in, activating SNARE protein, allows in synaptic vesicles to bind to the membrane and release neurotransmitters into the synaptic cleft.
- Neurotransmitter moves across the synaptic cleft and attaches to a post synaptic receptor protein (ligand or chemically gated channel protein).
- Ion gate opens and sodium and potassium can move through.
- a graded potential is created.
Compare and contrast graded potentials and action potentials.
- graded potentials happen at dendrites and cell bodies while action potentials happen in the axon.
- graded potentials travel short distances and action potentials long distances
- graded potentials use chemically regulated channels and AP use voltage gates channels
- graded potential amplitude varies based on stimulus while AP is always the same
- graded there is no positive feedback while it is significant in AP
- summation in graded; not in AP (all or none event)
