Biology Unit 1 - Structure and functions of cells and tissues Flashcards
what does cell theory state?
-all living things are made of cells
-cells are the basic units of life
-all cells come from the division of other cells
what are the parts of a light microscope?
-eyepiece lens = contains the ocular lens
-nosepiece = holds the high and low power objective lenses, can be rotated to change magnification
-objective lens = magnification ranges from 4x to 100x
-stage clips = holds the slide in place
-stage = supports the specimen being viewed
-light source = projects light upwards through the diaphragm, the specimen and the lenses
-base = supports the microscope
-diaphragm = regulates the amount of light on the specimen
-fine focus knob = moves the stage slightly to sharpen the image
-coarse focus knob = moves the stage up and down for focus
-arm = used to pick up the microscope when carried
how can a temporary microscope slide of human cheek cells be made?
- gently swab the inside of one of your cheeks using a cotton bud to rub off a few of the lining cells
- rub the swabbed cotton bud over a clean slide and then put the cotton bud in disinfectant
- add a few drops of methyl blue to the sample and then place a glass coverslip gently down on top of it
- put the slide on the stage of the microscope and then focus in on your cheek cells using the 4x lens ( they will just look like tiny blue dots )
- change to the 10x lens, focus and then change to 40x ( they should look like blue fried eggs )
- make a labelled drawing of one cell and label the cytoplasm, nucleus and cell membrane
how can a temporary microscope slide of onion epidermis cells be made?
- chop a small piece of onion on the chopping board / tile using a scalpel
- gently remove the single cell epidermal layer from the inside of the onion slice using forceps
- carefully cut a piece of epidermis about 5mm by 5mm using the scalpel and place it gently onto a clean glass slide
- add a few drops of iodine to the sample and then place a glass coverslip gently down on top of it
- put the slide on the stage of the microscope and then focus in on the cells using the 4x lens
- change to the 10x lens, focus and then estimate the number of cells across the field of view e.g. 4.5 cell lengths and 8.5 cell widths
- make a labelled drawing of one cell and label the cytoplasm, nucleus, cell membrane and cellulose cell wall
why does the specimen need to be thin?
-so that light or an electron beam can pass through it
why do samples need to be stained?
-stain binds to structures which helps to distinguish different features in the specimen
what is the purpose of a coverslip?
-to protect the specimen and the lens if they should touch
how do you convert between units: centimetre, millimetre, micrometre, nanometre?
-big → small = multiply, small → big = divide
-cm → mm = x 10
-mm → μm = x 1000
-μm → nm = x 1000
what is magnification?
-the number of times bigger an image appears compared to the size of the specimen
what is resolution?
-the smallest distance between two objects that can be distinguished
how is total magnification calculated?
-magnification of eyepiece lens x magnification of objective lens
how is image size ( I ) calculated?
-I = A x M
-image size ( I ) in any unit = actual size ( A ) in same unit as image size x magnification ( M )
what is a micrograph?
-a photograph or digital image taken through a microscope
compare the light microscope ( LM ) and electron microscope ( EM )
-both use a form of radiation to create an image, but LM uses visible light whereas EM uses x-rays
-LM uses a series of lenses and a light source to view an image whereas EM uses a beam of electrons which scatter over the specimen
-LM’s maximum magnification is around x1500 whereas EM’s is over x500,000
-LM’s maximum resolution is 200nm whereas EM’s is 0.1nm as electron beams have a much shorter wavelength than beams of light
-LM uses coloured stains ( e.g. iodine, methyl blue ) whereas EM uses electron-dense chemicals ( heavy metals e.g. lead, gold ) to stain a specimen
-LM costs around £300-10K so is avaliable for use to students whereas EM costs over £1M and requires a highly trained operator
-LM is small and portable whereas EM is large and requires a special room
-LM produces images in colour whereas EM produces images in black and white and requires a dead specimen in a vacuum as electron beams are deflected by air molecules
-LM is used to view living specimens whereas EM is used to view dead specimens in much more detail
how does the optical ( light ) microscope work?
-lenses focus rays of light and magnify the view of a thin slice of specimen
-different structures absorb different amounts and wavelengths of light
-reflected light is transmitted to the observer via the objective lens and eyepiece
how does the transmission electron microscope ( TEM ) work?
-pass a high energy beam of electrons through a thin slice of specimen
-more dense structures appear darker since they absorb more electrons
-focus image onto a fluorescent screen or photographic plate using magnetic lenses
how does the scanning electron microscope ( SEM ) work?
-focus a beam of electrons onto a specimen’s surface using electromagnetic lenses
-reflected electrons hit a collecting device and are amplified to produce an image on a fluorescent screen or photographic plate
compare the TEM and SEM
-both have a maximum magnification of around x500,000
-TEM’s maximum resolution is 0.5nm whereas SEM’s is 3-10nm
-TEM is used to view 2D images of internal structures and detail of cell organelles whereas SEM is used to view 3D images of surfaces
what are eukaryotic cells?
-multi-cellular organisms such as animals and plants
-they are complex cells with a nucleus and membrane-bound organelles
what are prokaryotic cells?
-single-celled organisms such as bacteria
-they are simple structures and do not have a nucleus or any membrane-bound organelles
what four structures do all cells contain?
-DNA
-cytoplasm
-ribosomes
-plasma membrane
what structures do all eukaryotic cells contain?
-nucleus
-nucleolus
-cytoplasm
-80S ribosomes
-plasma membrane
-vesicle
-centrioles ( except plant cells )
-lysosome
-Golgi apparatus
-mitochondria
-smooth endoplasmic reticulum
-rough endoplasmic reticulum
what is the structure and function of the nucleus?
-surrounded by a double membrane ( envelope ), with pores that allow molecules to enter and leave
-stores DNA, coordinates cell activities
what is the structure and function of the nucleolus?
-region of dense DNA, RNA and protein, found within the nucleus
-produces ribosomes
what is the structure and function of the cytoplasm?
-fluid that fills a cell
-many molecules dissolved in solution ( enzymes, sugars, amino acids, fatty acids )
-site of many metabolic processes
what is the structure and function of the ribosomes?
-composed of two subunits, may either be membrane-bound or free in the cytoplasm ( i.e. in prokaryotes )
-site of protein synthesis
what is the difference between ribosomes in eukaryotic and prokaryotic cells?
-80S ribosomes in eukaryotes are bigger than 70S ribosomes in prokaryotes
-S is a Svedberg, a measure of size by rate of sedimentation
what is the structure and function of the plasma membrane?
-protects cell from its surroundings
-regulates movement of substances in and out of cells
what is the structure and function of the vesicle?
-small, membrane-bound sac
-transports and stores substances in the cell
what is the structure and function of the centrioles?
-two hollow cylinders containing microtubules at right angles to each other
-makes the spindle in cell division
what is the structure and function of the lysosome?
-vesicles filled with digestive enzymes, bound by a membrane
-breakdown any of the cell’s waste e.g. old organelles, destroy disease-causing organisms ( pathogens ) that enter the cell
what is the structure and function of the Golgi apparatus?
-a series of flat, curved, fluid-filled sacs enclosed by a membrane and surrounded by vesicles
-processes proteins and lipids and packages them in vesicles for transport, produces lysosomes
what is the structure and function of the mitochondria?
-bound by a double outer membrane ( envelope ), inner membrane folded into finger-like projections called cristae to increase surface area
-central area contains a jelly called the matrix
-site of respiration and therefore ATP production
what is the structure and function of the smooth endoplasmic reticulum?
-a series of single, tubular, membrane-bound sacs, without ribosomes on the surface
-produces and processes lipids
what is the structure and function of the rough endoplasmic reticulum?
-a series of single, flattened, membrane-bound sacs, with large numbers of ribosomes on the surface
-site of protein synthesis and folding
what is the role of the RER and Golgi apparatus in transporting proteins?
-proteins are produced on the ribosomes of the RER, and are then folded and processed
-transported in vesicles to the Golgi body
-modified and repackaged to be transported around the cell, or to leave the cell by exocytosis
what other structures do plant cells contain?
-chloroplasts
-vacuole
-tonoplast
-cellulose cell wall
-amyloplast
-middle lamella
-plasmodesmata
-pits
what is the structure and function of the chloroplasts?
-contains chlorophyll ( green substance ) which absorbs light energy
-site of photosynthesis to convert solar energy to chemical energy
what is the structure and function of the vacuole?
-surrounded by a single phospholipid membrane called tonoplast
-stores cell sap, which contains mineral ions, water, enzymes, soluble pigments
what is the structure and function of the tonoplast?
-cytoplasmic membrane surrounding a vacuole, separating the vacuolar contents from the cell’s cytoplasm
-controls movement of molecules into and out of the vacuole
what is the structure and function of the cell wall?
-made of cellulose
-provides structure, support and protection for the cell, preventing bursting when water enters by osmosis
what is the structure and function of the amyloplast?
-plastid found only in plant cells
-produces, breaks down and stores starch
what is the structure and function of the middle lamella?
-cementing layer between the primary walls of adjacent cells
-sticks cells together
what is the structure and function of the plasmodesmata?
-tunnel from one cell to the next
-allows communication and the movement of molecules between cells
what is the structure and function of the pits?
-minute openings in the secondary cell wall of plant cells
-allows the flow of water and nutrients from one cell to another, linking water uptake in roots with transpiration in leaves
what structures do prokaryotic cells ( bacteria ) contain?
-nucleoid
-plasmids
-70S ribosomes
-capsule
-cell wall
-pili
-flagellum
-mesosomes
what is the structure and function of the nucleoid?
-irregularly-shaped region of cytoplasm
-contains the prokaryotic DNA
what is the structure and function of the plasmids?
-double-stranded DNA in a circular structure
-often contain additional genes that aid the bacterium’s survival, such as antibiotic resistance or toxin producing genes
-responsible for DNA replication, transferring DNA between bacteria and gene expression
what is the structure and function of the capsule?
-thick, slimy layer of polysaccharide that covers the cell wall
-prevents cell from drying out, protects cell from being engulfed by e.g. white blood cells, and helps adhesion to surfaces
what is the structure and function of the prokaryotic cell wall?
-forms a rigid outer covering over the cell, made of peptidoglycan ( long-chained molecule made up of a sugar and amino acids )
-provides strength, support and protection against damage
what is the structure and function of the pili?
-hair-like extentions on the surface of bacterial cells
-helps cells adhere to various surfaces, primarily each other
what is the structure and function of the flagellum?
-a long, thin projection attached to the cell wall
-rotates to move the cell
what is the structure and function of mesosomes?
-infolds of the plasma membrane
-provides a large surface area for the attachment of enzymes involved in respiration
what is the process of gram staining?
-stain culture with crystal violet, remove and rinse with water
-add iodine solution, remove after 1 minute and add alcohol
-counterstain with red safranin for 1 minute
-dry and examine sample under microscope
what is the structure of gram-positive bacterial cell walls?
-thick peptidoglycan cell wall that is insoluble in alcohol
-absorbs the crystal violet dye during the gram stain process and appears violet or blue under a microscope
what is the structure of gram-negative bacterial cell walls?
-thinner peptidoglycan cell wall surrounded by an outer lipopolysaccharide ( LPS ) membrane that is soluble in alcohol
-doesn’t retain the gram stain ( crystal violet ) when washed with alcohol and appears red under a microscope
why do gram-positive and gram-negative bacteria respond differently to certain antibiotics?
-gram-negative bacteria are more resistant to antibiotics such as penicillin which work by damaging the bacterial cell wall because they have an outer membrane which protects them from the antibiotic
what are specialised cells?
-cells that have developed unique features and structures which allow them to perform specific roles
-the process by which cells become specialised for a particular function from stem cells is known as differentiation
what are the functions of the specialised animal cells?
-sperm cells ( male gametes ) and egg cells ( female gametes ) = carry out fertilisation in organisms that reproduce sexually
-white blood cells = help the body fight infection and other diseases
-red blood cells ( erythrocytes ) = carry oxygen from the lungs to the tissues in different parts of the body
how are sperm cells adapted to their function?
-the haploid nucleus in the head contains half the normal number of chromosomes ( 23 ) so that the full number is restored at fertilisation
-the acrosome in the head contains digestive enzymes that can break down the outer layer of an egg cell so that the haploid nucleus can enter to fuse with the egg’s nucleus
-the mid region is packed with mitochondria to provide the energy from respiration for movement
-the undulipodium ( tail ) rotates to propel the sperm cell forwards so that it can move towards the egg
how are egg cells adapted to their function?
-the haploid nucleus contains half the chromosomes of a body cell ( 23 ) so that when the sperm’s nucleus fuses with the egg’s nucleus the full number is restored at fertilisation
-the corona radiata surrounds the egg cell and contains follicle cells which supply it with vital proteins
-the zona pellucida ( jelly layer ) surrounds the plasma membrane of the egg cell and helps to protect it
-the cortical granules ( specialised secretory vesicles ) contain a substance that helps to stop more than one sperm fertilising the egg
-the cytoplasm contains nutrients for the growth of the early embryo
what are the two types of white blood cell?
-neutrophils = phagocytic WBCs that engulf pathogens and then digest them ( non-specific response )
-lymphocytes = B and T cells ( WBCs ) that produce antibodies which respond to specific antigens on the surface of pathogens
compare the structures and functions of neutrophils and lymphocytes
-both make up the first line of defence within the body against foreign invaders
-both are made in the bone marrow and lymph nodes
-both contain nuclei / mitochondria / RER / ribosomes
-neutrophils provide a faster, non-specific response before lymphocytes provide a specific response
-neutrophils are more common and bigger than lymphocytes
-neutrophils have a lobed nucleus, and are flexible and mobile so they can squeeze between cells in the capillary wall and migrate to areas of infection
-neutrophils hold lysosomes in their cytoplasm that contain enzymes which help to digest and destroy pathogens that are ingested
-lymphocytes have a large nucleus and contain an immunological memory
-T lymphocytes send signals to B lymphocytes which makes the B cells produce antibodies
-the B cells proliferate ( reproduce rapidly ) so some of them make antibodies and some become memory lymphocytes
-the T cells destroy infected or cancerous cells
how are red blood cells adapted to their function?
-the cytoplasm contains haemoglobin which is the protein that binds to oxygen
-they have a thin membrane which decreases the diffusion distance for gas exchange
-they have no nucleus or other organelles so there is more space for haemoglobin, maximising the cell’s oxygen-carrying capacity so more oxygen can be transported around the body
-they are biconcave in shape which increases the surface area over which oxygen can be absorbed
-they are small and flexible so they can squeeze through narrow blood vessels
what are the functions of the specialised plant cells?
-palisade mesophyll cells = maximise light absorption for photosynthesis to produce glucose and oxygen
-root hair cells = absorb water ( by osmosis ) and mineral ions ( by active transport ) from the soil for photosynthesis and protein synthesis
how are palisade mesophyll cells adapted to their function?
-they are cylindrical shaped which enables them to pack tightly in the upper part of the leaf ( palisade layer ), increasing the surface area exposed to light which maximises light absorption
-they contain a large number of chloroplasts ( containing chlorophyll which absorbs light ) near to the edge of the cell so they can capture as much energy from light as possible
-the cytoskeleton can move the chloroplasts around in the cytoplasm to maintain photosynthesis in low light and protect chloroplasts in intense light
-the cellulose cell wall is thin and transparent which decreases the diffusion distance for gas exchange and allows sunlight to penetrate through to the chloroplasts
-they contain a large vacuole which helps to keep the cell and leaf structure rigid
how are root hair cells adapted to their function?
-the root hair is a fine protrusion from the cell out into the soil which increases the surface area in contact with the soil, increasing the rate of absorption of water and minerals
-the plasma membrane is thin and partially permeable to water which enables easier water absorption
-the cell membrane contains channels and carrier proteins which enable ions to cross the membrane into the cell
-the short diffusion distance across the thin cell wall increases the rate of diffusion
-they contain a large number of mitochondria which help supply energy for active transport of minerals from the soil into the cell, against the concentration gradient
-the permanent vacuole contains cell sap which is more concentrated than soil water, maintaining a water concentration gradient
what are tissues?
-collections of similar specialised cells, performing a specific function / set of functions
what are organs?
-collections of tissues performing specific physiological functions
what is epithelial tissue?
-a thin, continuous, protective layer of cells that line any surface that is in contact with the external environment and the surface of internal organs such as the lungs
-the lowest / bottom layer is attached to a basement membrane, which part of is secreted by the epithelial cells, for support and connection
what are the two types of epithelial tissue in the lungs?
-squamous epithelium
-columnar epithelium
what is the structure and function of simple squamous epithelial tissue?
-a single layer of flat, thin cells with each nucleus forming a lump in the centre
-to allow materials to pass through via diffusion and osmosis
where is simple squamous epithelial tissue found?
-walls of alveoli in lungs where oxygen ( diffuses from air into blood ) and carbon dioxide ( from blood into alveoli to be breathed out ) are exchanged
-blood capillaries around alveoli
what does chronic obstructive pulmonary disease ( COPD ) include?
-several lung conditions which are more common in smokers because substances in smoke damage the lungs
-the two main types are chronic bronchitis and emphysema
what is chronic bronchitis?
-where there is inflammation of the airways in lungs and thickening of squamous epithelium
-this causes excessive secretion of mucus, resulting in severe coughing to try and clear the mucus, and blocks the airways which makes breathing difficult
what is emphysema?
-usually develops because of long-term damage to the lungs from breathing in harmful substances such as cigarette smoke
-the membranes of the alveoli break apart and create abnormally large air spaces in the lungs, resulting in a decreased surface area for gas exchange to take place so less oxygen is able to enter the body and less carbon dioxide is able to leave
-also, destruction of the elastin of the alveoli cell membranes means alveoli don’t recoil which makes exhaling difficult
what is the structure and function of simple columnar epithelial tissue?
-a single layer of tall, thin cells with slightly oval nuclei and lots of mitochondria
-lots of cilia at the top on the outer surface which beat / waft back and forth to move surface mucus and trapped foreign bodies ( e.g. pathogens ) up and out of the respiratory system, preventing any inhaled particles causing infection
-may contain goblet cells in between which secrete mucus onto the outer surface of the epithelium to trap dust and bacteria
where is simple columnar epithelial tissue found?
-trachea and bronchi
-villi in small intestine
what is the structure and function of endothelial tissue?
-a single layer of flat, long cells which are orientated lengthways in the direction of blood flow
-to provide a smooth surface so that blood flows easily over them
where is endothelial tissue found?
-inside of blood vessels ( arteries, veins and capillaries )
what is the function of endothelium in the arteries and veins?
-reduces friction and allows for smooth flow of blood
-damaged endothelial cells release substances that cause blood vessels to constrict
-they both have an outer layer of connective and elastic tissue which is thicker in veins to prevent collapse of the blood vessel
-they also have a middle layer composed of smooth muscle, connective and elastic tissue which is thicker in arteries to maintain high blood pressure
what is the function of endothelium in the capillaries?
-only have a single layer to allow for easy exchange of nutrients and oxygen into the tissues and the removal of waste products
what is atherosclerosis?
-the disease process that leads to coronary disease and strokes ( cardiovascular diseases )
-fatty deposists produce plaques ( atheroma ) in the artery walls which reduce the lumen diameter and eventually block the artery completely or increase its chance of being blocked by a blood clot ( thrombosis )
-when plaques form, this has the potential to cause a rupture of the protective membrane over the plaque which can then lead to major problems such as a heart attack or stroke
what is the development of atherosclerosis?
-damage to endothelial tissue lining of artery ( e.g. by smoking, high blood pressure )
-low density lipoproteins ( LDL cholesterol ) accumulate in the artery wall
-inflammation results as white blood cells move into the artery wall
-build up of LDL cholesterol, white blood cells, calcium salts and fibres leading to plaque formation ( atheroma )
-narrowing of artery lumen, loss of elasticity restricts blood flow
-increased risk of blood clotting in the artery
how is smoking a risk factor for atherosclerosis?
-cigarette smoke contains many toxic chemicals which can lead to atherosclerosis
-the thickness of the blood increases which causes fatty deposits to build up on the walls of arteries and increases the risk of clotting
-smoking also increases blood pressure and heart rate which can cause damage to the endothelium
what is the structure of a skeletal muscle?
-attached to bones by tendons
-stiated / striped appearance due to the arrangement of contractile proteins ( actin and myosin ) inside the fibre
-made up of large bundles of muscle fibres which form a fascicle
-muscle fibres have lots of long, cylindrical organelles called myofibrils which are made up of repeated units of actin ( thin ) and myosin ( thick ) filaments called sarcomeres
-cell membrane of muscle fibre = sarcolemma
-cytoplasm = sarcoplasm
-endoplasmic reticulum = sarcoplasmic reticulum which stores and releases the calcium ions needed for contraction
-lots of mitochondria to provide the ATP needed for contraction
-contain many nuclei ( multinucleate ) which are pushed to the edge of the fibre by the contractile proteins inside
what does the sarcomere consist of?
-light / I bands = only thin ( actin ) filaments
-dark / A bands = the entire length of thick ( myosin ) filaments and the overlap with actin
-H zone = centre of A band which contains only thick ( myosin ) filaments so is slightly lighter
-Z line = border of sarcomere, the attachment site for actin filaments
-M line = middle of A band, the attachment site for myosin filaments
what is the structure of thin filaments?
-consists of the proteins actin, tropomyosin and troponin
-two actin molecules twist around each other to form a helical structure
-tropomyosin is wrapped around the actin
-troponin is attached to the tropomyosin along the actin fibre
what is the structure of thick filaments?
-made from many myosin molecules
-each myosin molecule is composed of a head and tail domain
-the head domain binds to the actin forming cross-links that change position to contract the sarcomere
-the tail domain provides an anchor for the rest of the molecule
what happens during muscle contraction?
-thin actin filaments are pulled along thick myosin filaments
-sarcomeres shorten ( increased overlap of actin and myosin filaments, Z lines move closer together )
-H zone and I band become narrower
-A band stays the same
what are the steps of the sliding filament theory?
-when a nerve impulse arrives at the neuromuscular junction, Ca^2+ are released from the sarcoplasmic reticulum into the sarcoplasm
-Ca^2+ bind to troponin which removes it from the myosin binding site and takes tropomyosin with it
-this exposes the myosin binding sites on the actin so myosin heads can form cross bridges with them
-the myosin head bends, pulling the actin past the myosin
-ATP at the end of the myosin head is hydrolysed into ADP and Pi which are released
-the cross-bridge is broken when ATP attaches to the myosin head which returns it to its original position
-more ATP is hydrolysed to ADP and Pi and a cross-bridge forms with the thin filament further along
-when the nervous stimulation ends, Ca^2+ are released from troponin and pumped out of the sarcoplasm
-the troponin and tropomyosin bind to the myosin heads and prevent any further contraction occurring until the next nervous stimulus
-T tubules are located in the sarcoplasm which help to conduct nerve impulses from the neuromuscular junction down into the muscle cell so that all cells in the muscle tissue can be stimulated to contract
what are the features of slow twitch muscles?
-slow, sustained contraction for long periods of exercise
-many mitochondria supply energy from aerobic respiration ( requires oxygen )
-lots of capillaries
-doesn’t tire easily
-large glycogen and glucose stores
-high levels of myoglobin providing high levels of oxygen stores
-high levels of respiratory enzymes
-people who have a higher proportion of slow twitch muscles are better at endurance events ( e.g. the marathon ) because they use aerobic respiration and can work for a long time without getting tired
what are the features of fast twitch muscles?
-rapid intense contractions in short bursts
-few mitochondria as energy for contraction comes from anaerobic respiration ( doesn’t require oxygen )
-few capillaries
-tires easily
-little stored oxygen and glucose
-people who have a higher proportion of fast twitch muscles can move quickly in short bursts ( e.g. sprinters ) because the muscles contract rapidly and strongly in short bursts using energy from anaerobic respiration
what are the divisions of the nervous system?
-central NS = brain + spinal cord
-peripheral NS = somatic NS + autonomic NS
-ANS = sympathetic NS ( fight or flight ) + parasympathetic NS ( rest and digest )
what is the difference between nerves and neurons?
-nerves = bundles of neurons
-neurons = specialised nerve cells that make up nerves and carry messages in the form of electrical signals ( known as action potentials ) along axons from one part of the body to another
what are the three types of neurons?
-sensory ( afferent ) = carry messages from sensory receptors in PNS to CNS, myelinated, long dendrites and short axons
-relay = connect sensory neurons to motor neurons or other relay neurons, non-myelinated, short dendrites and short axons
-motor ( efferent ) = carry messages from CNS to effectors in PNS such as muscles and glands, myelinated, short dendrites and long axons
what structures do neurons contain?
-nissl granule = responsible for protein synthesis
-cell body ( or soma ) = includes the nucleus which controls the cell’s activities and lots of RER which is associated with the production of proteins and neurotransmitters
-dendrites = carry nerve impulses from neighbouring neurons towards the cell body
-axon = single long fibre that carries nerve impulses away from the cell body down the length of the neuron
-myelin sheath = fatty covering that protects and insulates the axon, and speeds up electrical transmission
-Schwann cell = produces myelin sheath and surrounds the axon by wrapping around it many times
-nodes of Ranvier = gaps between adjacent Schwann cells where there is no myelin sheath which speed up the transmission of the impulse by allowing it to jump along the axon
-axon terminals = transmit messages to other cells ( neurons or effectors ) via neurotransmitters at synapses
compare myelinated and non-myelinated neurons
-myelinated neurons have myelin sheath and nodes of Ranvier ( saltatory conduction ), whereas non-myelinated neurons have neither ( continuous wave along axon )
-myelinated neurons are white in colour, whereas non-myelinated neurons are grey
-myelinated neurons transmit impulses very fast, whereas non-myelinated neurons transmit impulses slower
-myelinated neurons avoid loss of impulse during conduction, whereas non-myelinated neurons have a higher chance of loss of impulse due to having no insulating layer
how is an electrical impulse generated by a neuron?
-changes in the concentration of ions inside and outside the cell causes a potential difference ( PD ), called an action potential, which transmits an electrical signal between nerve cells
how is an action potential conducted along an axon?
-at rest, the inside of a neuron is negatively charged compared to the outside
-depolarisation = when a stimulus reaches a resting neuron, the Na+ gates in the cell membrane open and sodium ions diffuse into the neuron, generating a positive charge inside the cell and triggering an action potential if the PD ( voltage change ) reaches the threshold, and then the Na+ gates close
-repolarisation = the K+ gates open and potassium ions diffuse out of the neuron, returning the cell to its original negative charge, and then the K+ gates close
-hyperpolarisation = after an impulse has passed, a neuron cannot immediately fire another action potential ( to ensure that the impulse travels in one direction ) due to a refractory / recovery period where the cell is slightly more negative than at rest, which attracts potassium ions to move back into the cell through non-voltage gated channels, restoring the resting potential equilibrium ( -60 to -70 mV )
how does membrane permeability to sodium and potassium ions change during the conduction of an action potential?
-at rest = more permeable to potassium ions because more non-gated K+ channels are open than Na+ channels
-depolarisation = short-lived increase in Na+ permeability
-repolarisation = slower increase in K+ permeability
what is saltatory ( jumping ) conduction?
-in myelinated neurons, action potentials only occur where the axon is exposed at the nodes of Ranvier as those regions can depolarise
-therefore, the impulse jumps from node to node ( saltatory conduction ), which means that it can travel faster and a much longer distance
what is the pathway of blood through the heart?
-deoxygenated blood flows from the vena cava into the right atrium and then through the tricuspid valve into the right ventricle
-the blood then passes through the pulmonary valve into the pulmonary artery by which it travels to the lungs to be reoxygenated
-once oxygenated, the blood travels from the lungs through the pulmonary vein into the left atrium and then through the mitral valve into the left ventricle
-the blood then passes through the aortic valve into the aorta by which it travels to the rest of the body
what is the function of valves in the heart?
-to prevent the backflow of blood
what is an electrocardiogram ( ECG )?
-a simple, non-invasive test that records the heart’s electrical activity ( action potentials ) through repeated cardiac cycles
-ECG traces can help diagnose cardiovascular disease ( CVD ) because if disease disrupts the heart’s normal conduction pathways, there is a disruption of the expected ECG pattern ( i.e. 60 to 100 bmp at regular intervals )
-electrodes are placed on different parts of the body to detect electrical impulses and a machine amplifies the impulses during each heart beat and records them
what is the cardiac cycle?
-one cardiac cycle ( PQRST ) = one heartbeat
-P wave = atrial systole ( atria contract and push blood into ventricles ) due to atrial depolarisation as a result of an action potential created by the SAN ( sinoatrial node ) / pacemaker
-QRS complex = ventricular systole ( ventricles contract and push blood out through aorta and pulmonary artery ) due to ventricular depolarisation
-T wave = ventricular repolarisation during diastole ( chambers are relaxed and filling with blood )
what is a synapse?
-the junction between two neurons
-action potentials cannot pass across the synapse so transmitter substances are used
what is the process of synaptic transmission?
-an action potential arrives at the synaptic knob and causes the membrane to depolarise
-the Ca+ gates open and calcium ions enter the neuron, and then the Ca+ gates close
-calcium ions cause synaptic vesicles containing neurotransmitters to fuse with the presynaptic membrane, and neurotransmitter is released into the synaptic cleft through exocytosis ( which requires ATP )
-neurotransmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane
-the Na+ gates open and sodium ions flow through the channels
-the membrane depolarises and initiates an action potential
-when released, the neurotransmitter will be taken up across the presynaptic membrane ( whole or after being broken down ), or it can diffuse away and be broken down
what is acetylcholine and what happens to it in the synapse?
-acetylcholine was the first neurotransmitter to be discovered and it has many functions, including the stimulation of muscles
-acetylcholinesterase breaks down acetylcholine into acetyl and choline in the synaptic cleft
-Na+ channels close and the two parts are recycled and diffuse back across the synaptic cleft into the presynaptic membrane
how does an imbalance in dopamine contribute to Parkinson’s disease?
-dopamine is a neurotransmitter that is active in neurons in the frontal cortex, brain stem and spinal cord, and is associated with the control of movement and emotional responses
-Parkinson’s disease is associated with the death of a group of dopamine-secreting neurons in the brain, which results in the reduction of dopamine levels
-the symptoms include muscle tremors, stiffness of muscles, slowness of movement, poor balance, walking problems, difficulties with speech and breathing, and depression
how is Parkinson’s disease treated?
-most treatments aim to increase the concentration of dopamine in the brain
-dopamine cannot move into the brain from the bloodstream, but the molecule that is used to make dopamine can ( L-Dopa )
-L-Dopa can be turned into dopamine to help control the symptoms by increasing the amount of dopamine released by the presynaptic neuron so that normal levels of dopamine stimulate the postsynaptic neuron
how does an imbalance in serotonin contribute to depression?
-serotonin is a neurotransmitter linked to feelings of reward and pleasure
-a lack of serotonin is linked to clinical depression ( prolonged feelings of sadness, anxiety, hopelessness, loss of interest, restlessness, insomnia )
-ecstasy ( MDMA ) works by preventing the reuptake of serotonin, which results in the maintenance of a high concentration of serotonin in the synapse, bringing about the mood changes in the users
how is depression treated?
-prozac is an example of a serotonin selective reabsorption inhibitor ( SSRI ) which may be given to patients to reduce depression
-serotonin is not reabsorbed because the SSRI binds to reuptake proteins, which means that there is a high level of serotonin
-consequently, the increased level of serotonin in the synapses continues to bind to receptors in postsynaptic membranes, increasing the feelings of reward and pleasure
what types of effects can drugs have on synaptic transmisson?
-antagonist = the drug blocks the action of a transmitter on its receptors by preventing it from responding, e.g. atropine or curare
-agonist = the drug mimics the action of a transmitter on its receptors by binding to a receptor and activating it to produce some sort of response, e.g. nicotine or muscarine
how do drugs affect synapses?
-by affecting the synthesis or storage of the neurotransmitter
-by affecting the release of the neurotransmitter from the presynaptic membrane
-by affecting the interaction between the neurotransmitter and the receptors on the postsynaptic membrane
-by preventing the reuptake of the neurotransmitter back into the presynaptic membrane
-by inhibiting the enzymes involved in breaking down the neurotransmitter in the synaptic cleft
-may be excitatory which increases the likelihood of an action potential by binding to the receptors and opening sodium channels
-may be inhibitory which decreases the likelihood of an action potential by blocking the receptors on the postsynaptic membrane and preventing the neurotransmitters binding
