extra info

Question 1

what elements primarily form cells?

Answer 1

carbon
oxygen
hydrogen
nitrogen

Question 2

how are new cells created?

Answer 2

cell division

Question 3

how do cells become specialised?

Answer 3

they differentiate

Question 4

what are the two main cell types?

Answer 4

germ cells: consist of the sperm in the male and oocyte in the female (sex cells)

somatic cells: include all other cells in the body

Question 5

what are the types of somatic cells?

Answer 5

1. epithelial cell
2. blood cells (red/reythrocytes and white/leukocytes)
3. bone cell (osteoblasts)
4. fribroblast
5. muscle cells (skeletal and smooth)
6. nerve cells/neurons

Question 5

what are the germ cells?

Answer 5

sperm
ovum
*oocyte = immature gamete; called ovum once fertilised after fusion is is a zygote.

Question 6

epithelial cells

Answer 6

Epithelial tissue forms many of the linings and coverings in the body. Epithelial cells have many functions, including acting as a protective surface, secretory surface, or as an absorptive surface, regulating the movement of substances into and out of the body. Epithelial cells vary in shape depending on their function and location.

Question 7

blood cells

Answer 7

red blood cells/erythrocytes:
most common type of blood cell. these cells bind oxygen in the lungs and carry it to tissues throughout the body where it is exchanged for the waste product carbon dioxide.

white blood cells/leukocytes:
function by identifying, capturing, and eliminating invading pathogens/foreign particles. there are many types of white blood cell (e.g. neutrophils, basophils, manocytes and lymphocytes)

Question 8

bone cell

Answer 8

osteoblasts are bone-producing cells present in bone marrow and other connective tissues. they synthesise and secrete collagen fibers and other organic component which are used to build the extracellular matric of bone tissue and initiate calcification.

Question 9

fibroblast cell

Answer 9

large, flat, branching support cells present in most connective tissue. they secrete fibers including collagen and some of the ground substance component of the extracellular matrix. these are used to provide the structural framework for tissues. fibroblast cells also play an important part in skin wound healthin.

Question 10

muscle cells

Answer 10

skeletal:
found attached to the skeleton via tendons or thorugh a connective tissue sheet called an aponeuosis. skeletal muscle is under voluntary control and is able to contract, response to stimulation from the nervous system, stretch beyond its normal resting length and revert to its original resting length.

smooth:
found in the walls of internal organs, blood vessels and intrinsic (internal) muscles of the eye. smooth muscle tissue is involuntary. it helps to propel and expel liquid within and from the body, allows peristalisis that aids in digestion and helps to regulate the diameter of blood vessels.

Question 11

nerve cell/neurons

Answer 11

main functional cells of the nervous system have long extensions that are sensitive to external stimuli, allowing them to respond to and communicate information through electrical and chemical signals.

Question 12

ion channels

Answer 12

ions flow through the many ion channels in the plasma membrane down electrochemical gradients. a flow of electrical charge is created as each ion has an electrical charge. this can change the membrane potential of a neuron.

1. leakage channels
2. ligand-gates channels
3. mechanically gated channels
4. voltage gated channels

Question 13

leakage channels

Answer 13

(type of ion channel)
open and close randomly, independent of any stimuli.
the plasma membranes of neurons tend to exhibit a higher proportion of potassium ion leakage channels compared to sodium ion leakage channels. in addition, potassium ion leakage channels let more potassium though than sodium leakage chanels let sodium ions through. neuronal plasma membranes are therefore more permeable to K+ ions than they are to Na+.

Question 14

ligand-gated channels

Answer 14

(type of ion channel)
Open in response to the binding of specific chemical ligands, such as neurotransmitters and hormones, to ligand-binding domains that usually reside on the extracellular surface of the ligand-gated channel. binding of the ligand to the ligand-binding domains triggers a conformational change which opens the ligand-gated channel, permitting the passage of particular ions from one side of the membrane to the other.

Question 15

mechanically gated channels

Answer 15

(type of ion channel)
mechanically gated channels open in response to mechanical forced, such as vibration (sound waves), touch, pressure, or stretch, where forces in the lipid bilayer cause distortion of the channel: pulling it open, and permitting the flow of ions through it. some mechanically gated ion channels rely on links to extracellular or cytoplasmic proteins spanning the lipid bilayer. a change in tension in these proteins causes the channels to be pulled open.

e.g. auditory receptors in the ears, stretch receptors in the internal organs, and touch receptors in the skin.

Question 16

voltage-gated channels

Answer 16

(type of ion channel)
open in response to a change in membrane potential (voltage) across the plasma membrane of a neuron (e.g. depolarisation) and they play an important role in the generation and propagation of action potentials along a neuronal axon.

voltage-gated sodium channels have both an activation gate and an inactivation gate. at rest, the activation gate is closed and the inactivation gate is open. when stimulated, the activation gate opens, allowing the flow of Na+ though the channel. the inactivation gate then closes to stop the flow of Na+ ions and the channel becomes inactive. the voltage-gated Na+ channel may only be stimulated again once it has returned to its resting state.

voltage-gated potassium channels have only one gate, which opens to allow the flow of K+ ions through the channel and closes to stop the flow of K+ ions.

Question 17

explain resting membrane potential

Answer 17

the human body has the same proportion of positive and negative charges and in most areas, these charges are distributed evenly. However, there are area where one charge predominates causing the area involved to be either positively or negatively charged. when the opposite charges are separated, and because opposites attract, their separation causes potential energy, or voltage to be produced.

such an effect occurs at the plasma membrane, with a build up of negatively charges ions (anions) in the cytosol immediately inside the membrane and a build up of positively charged ions (cations) in the extracellular fluid immediately outside the membrane.
the separation of these opposite charges causes potential energy (voltage) to be produced and hence a resting membrane potential is established.
a greater difference in charge across the membrane will produce a larger membrane potential.

Question 18

cation vs anion

Answer 18

cation is a positively charged ion.

anion is a negatively charged ion.

Question 19

how is resting membrane potential measured?

Answer 19

measured in volts or milivolts using a voltmeter. as mentioned previously, voltage is always measured between two points, therefore the voltmeter is connected to a recording microelectrode, which is placed in the cytosol on the inside of the plasma membrane and a reference microelectrode which is placed in the extracellular fluid on the outside of the plasma membrane. the microelectrodes conduct electrical charges from these two points, on either side of the membrane, to the voltmeter which detects the difference in charge (voltage) across the plasma membrane.

Question 20

what does it mean if a cell is polarised?

Answer 20

all cells with an uneven charge distribution across their plasma membrane have a resting membrane potential and are said to be polarised.

neuronal resting membrane potential ranges from -40mV to -90mV with a typical value of -70mV. the negative value denotes a more negatively charged cytoplasmic side (inside) compared to the outside of the plasma membrane.

Question 21

what three factors contribute to creating a resting membrane potential?

Answer 21

1. movement of cations through leakage channels.
   The predominant cation in extracellular fluid is Na+ with cytosol rich on K+ and as previously stated neuronal plasma membranes contain more K+ leakage channels than Na+ leakage channels making the plasma membrane 75x more permeable to K+ ions than to Na+ ions. There is therefore a greater flow of K+ ions diffusing down their concentration gradient (out of the neuron) compared to the +ions.
   This causes the cytoplasmic side (inside) of the plasma membrane to become less positively charged and the extracellular side (outside) to become more positively charged.
   A difference in charge across the membrane is created and potential energy is produced contributing to the resting membrane potential.
2. trapped anions in the cytosol
   The cytosol is rich in negatively charged phosphate ions attached to large molecules such as ATP and cytoplasmic proteins. The inability of these large molecules to diffuse through the plasma membrane causes a build up of anions in the cytosol, along the inner surface of the plasma membrane. This amplifies the negative inside charge, contributing to the resting membrane potential.
3. Maintenance of resting membrane potential through Na+/K+ ATPases
   The plasma membrane exhibits sodium-potassium pumps (Na+/K+ ATPases) which actively pump three Na+ ions out of the cell in exchange for two K+ ion moving into the cell. Na+/K+ ATPases help to maintain the concentration gradients for K+ and Na+ by removing Na+ ions out of the cytosol as fast as they leak in. As Na+/K+ ATPases remove 3x more positive ions from the cell than they bring in, they help to maintain the negative charge inside the neuron thus helping to maintain the resting membrane potential.

Question 22

graded potentials

Answer 22

Depolarisation and hyperpolarisation are both terms used to describe deviations from the resting membrane potential. The plasma membrane is said to be polarised when it is in its resting state and depolarised when it is active.

depolarisation:
a change in membrane potential where the cytoplasmic side (inside) of the plasma membrane becomes less negatively charged (more positive) than at resting membrane potential, usually due to an influx (inflow) of positively charged ions (e.g. a change from -70mV to -40mV). The plasma membrane is thus said to become less polarised.

hyper polarisation:
a change in membrane potential where the cytoplasmic side of the plasma membrane becomes more negatively charged than at resting membrane potential, usually due to an efflux (outflow) of positively charged ions (e.g. a change from -70mV to -75mV) It can also be due to an influx of negatively charges ions such as Cl-. The plasma membrane is thus said to become more polarised.

Graded potentials are short-lived local changes in membrane potential, triggered by a stimulus, the strength of which determines the magnitude of change in membrane potential. A stimulus causes localised opening of mechanically gated, or ligand-gated ion channels, altering the flow of specific ions across the plasma membrane. This localised flow of current spreads out to adjacent segments of the plasma membrane, altering the charge distribution and polarisation of the plasma membrane.

Graded potentials occur mainly in the dendrites and cell body of a neuron and vary in amplitude, depending on the amount of ion channels opened and the duration of their opening. Graded potentials may be either depolarising or hyperpolarising.

hyper polarising graded potential:
a hyperpolarising graded potential is a short-lived local change in membrane potential, making the plasma membrane more polarised (increasing the negativity of the cytoplasmic side of the plasma membrane)

depolarising graded potential:
a depolarising graded potential is a short-lived local change in membrane potential, making the plasma membrane less polarised (decreasing the negativity of the cytoplasmic side of the plasma membrane)

As a graded potential travels along the plasma membrane, it either combines with another graded potential, becoming stronger, in a process known as summation, or it quickly loses intensity and dies out, in a process known as decremental conduction.

The summation of multiple depolarising graded potentials results in one large depolarising graded potential, while the summation of multiple hyperpolarising graded potential results in one hyperpolarising graded potential. If opposite graded potentials summate i.e. one hyperpolarising graded potential and one depolarising graded potential they cancel each other out, resulting in the disappearance of the graded potential all together.

Question 23

depolarisation

Answer 23

a change in membrane potential where the cytoplasmic side (inside) of the plasma membrane becomes less negatively charged (more positive) than at resting membrane potential, usually due to an influx (inflow) of positively charged ions (e.g. a change from -70mV to -40mV). The plasma membrane is thus said to become less polarised.

Question 24

hyper polarisation

Answer 24

a change in membrane potential where the cytoplasmic side of the plasma membrane becomes more negatively charged than at resting membrane potential, usually due to an efflux (outflow) of positively charged ions (e.g. a change from -70mV to -75mV) It can also be due to an influx of negatively charges ions such as Cl-. The plasma membrane is thus said to become more polarised.

Question 25

hyper polarising vs depolarising graded potential

Answer 25

hyper polarising graded potential: a hyperpolarising graded potential is a short-lived local change in membrane potential, making the plasma membrane more polarised (increasing the negativity of the cytoplasmic side of the plasma membrane) depolarising graded potential: a depolarising graded potential is a short-lived local change in membrane potential, making the plasma membrane less polarised (decreasing the negativity of the cytoplasmic side of the plasma membrane)

Question 26

summation vs decremental conduction

Answer 26

As a graded potential travels along the plasma membrane, it either combines with another graded potential, becoming stronger, in a process known as summation, or it quickly loses intensity and dies out, in a process known as decremental conduction.

Question 27

what triggers graded potentials?

Answer 27

Graded potentials are short-lived local changes in membrane potential, triggered by a stimulus, the strength of which determines the magnitude of change in membrane potential. A stimulus causes localised opening of mechanically gated, or ligand-gated ion channels, altering the flow of specific ions across the plasma membrane. This localised flow of current spreads out to adjacent segments of the plasma membrane, altering the charge distribution and polarisation of the plasma membrane.

Question 28

Generation of action potentials

Answer 28

Action potentials are triggered by depolarising graded potentials brought about by a stimulus. Stimuli occurring at dendritic nerve ending trigger the opening of mechanically gated or ligand-gated ion channels, which enables a local flow of ions across the plasma membrane, producing a graded potential. If a graded potential, or combination of graded potentials is strong enough to depolarise the plasma membrane from the resting membrane potential of about -70mV to the threshold potential of about -55mVm, an action potential will be triggered. However, if the membrane potential does not reach this threshold, an action potential will not be triggered. An action potential follows an 'all or nothing' principle, meaning it either occurs fully when a stimulus is strong enough to elicit a response, or it does not occur at all. When the threshold potential of the plasma membrane is reached, a stereotyped response occurs. Voltage-gated ion channels in the membrane open and close rapidly in a specific sequence, controlling the flow of ions across the plasma membrane. The movement of these ions causes a rapid increase then decrease in the membrane potential, known as an action potential. This action potential travels along the axon of the neuron as the axon membrane depolarises, then repolarises. Once it reaches the axon terminal, the action potential crosses to neighbouring neurons via a chemical synapse. An action potential occurs in three distinct phases: depolarising phase, repolarising phase, after-hyperpolarising phase: REST: at resting membrane potential, voltage-gated sodium channels are in their resting state (with the activation gate closed and the inactivation gate open), and voltage-gated potassium channels are closed. DEPOLARISATION: when a stimulus depolarises the cell membrane to a threshold potential, usually about -55mV this triggers the activation gates of voltage-gated sodium channels to open quickly, causing an influx of positive sodium ions down their concentration gradient, which results in further depolarisation. as more voltage-gated sodium channels open, positive ions build up on the inside of the plasma membrane and the potential difference across the plasma membrane increases. depolarisation reaches a maximum of about +30mV. the inactivation gates of voltage-gated sodium channels close 1 millisecond after they open, stopping the inward rush of positive sodium ions. REPOLARISATION: at +30mV, voltage-gated potassium channels open, leading to the repolarisation phase. during the repolarisation phase, an efflux of potassium ions and the suppression of sodium ion inflow cause the potential difference across the membrane to decrease. the plasma membrane repolarises back to a resting membrane potential of about -70mV. AFTER-HYPERPOLARISATION: During the after-hyperpolarisation phase, prolonged outflow of potassium ions causes the potential difference across the membrane to decrease further to about -90mV. The outflow of potassium ions is prolonged due to the slow closure of potassium gates. After the potassium gates close, the sodium-potassium pump and leakage channels restore resting concentrations of sodium and potassium ions, allowing the membrane to return to a resting state of -70mV. Following the onset of an action potential, there is a period during which a neuron cannot generate further action potentials in response to normal threshold stimuli. This is called the refractory period. There are two parts to the refractory period: the absolute refractory period, followed by the relative refractory period. Absolute refractory period= begins just as the action potential is triggered and extends until near the end of the repolarisation phase, when the voltage-gated sodium channels are inactivated. during the absolute refractory period, the plasma membrane is completely insensitive to another stimulus. inactivated voltage-gated sodium channels cannot be reponed by a stimulus until they return to their resting state, ensuring both the depolarisation and repolarisation phases are completed before another action potential can be triggered. large-diameter axons have a much shorter absolute refractory periods, allowing them to transmit more impulses per second. relative refractory period= follows straight on from the absolute refractory phase, beginning at the end of the repolarisation phase. during the relative refractory period, voltage-gated sodium channels return to their resting state and another action potential may be triggered. however only a very strong stimulus is capable of triggering an action potential during this period as voltage-gated potassium channels are still open, making it harder for a threshold depolarisation to be reached.

Question 29

relative vs absolute refractory period

Answer 29

Following the onset of an action potential, there is a period during which a neuron cannot generate further action potentials in response to normal threshold stimuli. This is called the refractory period. There are two parts to the refractory period: the absolute refractory period, followed by the relative refractory period. Absolute refractory period= begins just as the action potential is triggered and extends until near the end of the repolarisation phase, when the voltage-gated sodium channels are inactivated. during the absolute refractory period, the plasma membrane is completely insensitive to another stimulus. inactivated voltage-gated sodium channels cannot be reponed by a stimulus until they return to their resting state, ensuring both the depolarisation and repolarisation phases are completed before another action potential can be triggered. large-diameter axons have a much shorter absolute refractory periods, allowing them to transmit more impulses per second. relative refractory period= follows straight on from the absolute refractory phase, beginning at the end of the repolarisation phase. during the relative refractory period, voltage-gated sodium channels return to their resting state and another action potential may be triggered. however only a very strong stimulus is capable of triggering an action potential during this period as voltage-gated potassium channels are still open, making it harder for a threshold depolarisation to be reached.

Question 30

propagation of an action potential

Answer 30

In neurons, action potentials are generated at a trigger zone, they are then propagated towards the axon terminal. This propagation occurs either via continuous conduction or via saltatory conduction depending on the type of axon involved. continuous conduction: occurs along unmyelinated axons. During the generation of an action potential the axon membrane at the trigger zone is depolarised beyond threshold. this causes voltage-gated sodium channels to open, leading to a large influx of sodium ions into the axon. the sodium influx created a local region of positive charge on the inside of the axon membrane with respect to the outside. this established potential difference between the region of the axon which has depolarised and the adjacent regions which are still at resting potential. the potential difference results in local flow of current, in the form of ions, between these regions. the ionic current depolarises the adjacent region of the axon membrane to threshold, causing voltage-gated sodium channels to open and generating an action potential. therefore depolarisation of one region of the axon membrane leads to the depolarisation of the adjacent region and the action potential is propagated continuously along the membrane as a wave. although the local ionic currents caused by the influx of sodium ions flow in both directions, the action potential is only propagated towards the axon terminal. this is because after the depolarisation phase of the action potential, the voltage-gated sodium channels become inactive during the repolarisation phase. that region of the axon membrane therefore becomes refractory: it cannot fire another action potential until the voltage-gated sodium channels have returned to their resting state. saltatory conduction: unlike continuous conduction, saltatory conduction occurs along myelinated axons. Sections of these axons are surrounded by a myelin sheath, interspersed every 1 to 2 milimeters with short unmyelinated regions known as nodes of ranvier. The unmyelated sections of axon membrane lack voltage-gated channels, and therefore prevent the influx of sodium ions, and the generation of an action potential. The axon membrane at the nodes of ranvier however is rich in voltage-gated sodium channels. when an action potential is generated at the unmyelinated trigger zone, there is a large influx of sodium ions into the axon. This establishes a potential difference between the region of the axon which has depolarised and the adjacent regions which are still at resting potential. The difference established local flow of current in the form of ions, between these regions. However the myelin sheath and lack of voltage gated sodium channels prevent the depolarisation of the region of the the axon immediately adjacent to the trigger zone. As a result the ionic current flows to a node of Ranvier. At the node, the current causes the depolarisation of the membrane to the threshold, voltage-gated sodium channels open, and an action potential occurs. Therefore, as the action potential moves down the axon it appears to jump from node to node, as the ionic current flows between the nodes. As a result it travels much more rapidly than it would in an unmyelinated axon of the same diameter. As with continuous conduction, the action potential is only propagated towards the axon terminal. This is due to the inactivation of the voltage-gated sodium channels at the nodes of Ranvier during the repolarisation phase.

Question 31

comment on the speed of propagation

Answer 31

the speed at which an action potential is propagated during a neuronal axon is determined by myelination, axon diameter, and temperature. myelination: of neuronal axons enables faster propagation of action potentials along the plasma membrane due to saltatory conduction. axon diameter: the larger the diameter of a nerve fiber axon, the larger the surface area for an action potential to travel along and therefore the faster the rate of propagation.

Question 32

what are the three types of nerve fibre?

Answer 32

*each is capable of different speeds of propagation, determined by myelination and axon diameter. A myelinated; large diameter (5-20micrometers); 12 -130m/s propagation speed; conduct sensory information associated with touch, pressure, proprioception, temperature and pain, send motor impulses to skeletal muscles. B myelinated; medium diameter (2-3 micrometers); 15 m/s propagation speed; conduct sensory info from viscera to CNS, send autonomic motor impulses from CNS to autonomic ganglia of ANS C unmyelinated; small diameter (0.5-1.5 micrometer); 0.5-2 m/s propagation speed; conduct sensory info associated with pain, touch, pressure, heat and cold from the skin and visceral pain, send autonomic motor impulses from autonomic ganglia to the heart, glands, and smooth muscle of the organs.

Question 33

comment of stimulus intensity

Answer 33

the intensity of a stimulus being sensed is conveyed by both the number of sensory neurons activated and the frequency of the action potentials generated. a more intense stimulus will activate a larger number of sensory neurons and will initiate action potentials propagating along an axon at a higher frequency.

Question 34

cytoplasm

Answer 34

term used to describe everything that resides between the plasma membrane surrounding the cell and the nucleus. made up of many tiny organelles suspended in a fluid known as cytosol

Question 35

cytosol

Answer 35

intracellular fluid; accounts for over half the total volume of a cell. It stores metabolic substrates, allows chemical reactions to take place and suspends organelles. water; around 75-90% of cytosol is water, which acts as a solvent for many substances dissolved ions; concentrations of ions such as calcium, sodium, and potassium within the cytosol are different from those found in extracellular fluid: an important factor in osmoregulation and cell signalling. small suspended molecules; small molecules such as glucose, amino acids, and fatty acids are used as substrates in metabolism. large suspended molecules; cytosol contains significantly larger molecules, such as proteins and nucleic acids, than extracellular fluid. Enzymes form complexes that catalyse the chemical reaction involved in metabolism. storage masses; the cytosol contains large molecular masses that function as storage units, such as lipid droplets, which store triglyceride molecules, and glycogen granules which store glucose.

Question 36

nucleus

Answer 36

Commonly found in the centre of most cells. It is the control centre of the cell and contains most of the cell's genetic material encoded within DNA molecules. These DNA molecules are arranged and folded into chromosomes. The nucleus controls a cell's activities by regulating gene expression in response to signals acting upon it. All of the cell in the body have a nucleus except for red blood cells. Without a nucleus, red blood cells do not have the necessary codes and instructions for the synthesis of new proteins essential for reproduction and regeneration. As a result, red blood cells have short life cycles, living only for a few months before degrading. Cells with large cytoplasmic masses such as skeletal muscle cells have more than one nucleus to help cope with the regulation of their extensive cellular material. The nucleus is larger than all other organelles and is compartmentalised into regions that change during the cell cycle: 1. nuclear envelope the nuclear envelope forms a double membrane around the nucleus. It exhibits ribosomes on its outer surface and has nuclear pores spanning the inner and outer membrane. Inner membrane: the inner lipid bilayer. Outer membrane; outer lipid bilayer, continuous with rough endoplasmic reticulum. *Nuclear envelope separates nucleus from cytoplasm. Ribosomes: attached to surface of the outer membrane, link amino acids together to produce proteins. *protein synthesis Nuclear pores: transmembrane proteins that span the outer and inner membranes. Each pore consists of protein subunits arranged around a central channel 10x larger than that of an ion channel. *regulate the movement of substances across the nuclear envelope, between the cytoplasm surrounding the nucleus and the nucleoplasm within. Small molecules move across the nuclear envelope by simple diffusion, while larger molecules, such as proteins move by active transport. 2. nucleoplasm Nucleoplasm is a jelly-like fluid similar to the cytosol but contained within the nucleus. It contains ions, nutrients and other solutes. Nuclear elements suspended in the nucleoplasm include nucleoli and chromatin. NUCLEOLI: spherical bodies with no surrounding membrane, and are composed of DNA, RNA and protein. There are usually one or two nucleoli within a nucleus. They are particularly large in growing cells and active protein synthesis. **ribosomal subunits are assembles from ribosomal RNA within the nucleoli, they then pass out of the nucleus through the nuclear pores, before being joined together and commencing protein synthesis. CHROMATIN: structure resembles beads on a string and is comprised of long threads of DNA wrapped around nucleosomes, each of which is made of eight globular histone proteins. All cells prepare to divide, chromatin threads coil. condense and shorten to form chromosomes; a structure less likely to become damaged during cell division. **chromatin contains the cell's genetic material in the form of DNA, which when active, is transcribed into proteins. The function of chromatin is to determine which proteins the cell produces.