39641904
Descripción
Fichas por Darcey Griffiths, actualizado hace 3 meses
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Creado por Darcey Griffiths
hace 5 meses
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| Pregunta | Respuesta |
| Stimulus meaning | a detectable change in the internal or external environment of an organism that produces a response in that organism. |
| How a stimulus works | Sensory receptors give an organism its senses. There are specialised sensory cells eg pressure sensors in the skin and in complex sense organs eg ear and eye. |
| More on sensory receptors | Sensory receptors are transducers as they detect energy in one form and convert it into electrical energy. These electrical impulses travels along neurones and are called nervous impulses. They initiate a response in an effector, which may be a muscle or a gland. |
| Stimulus= visible light | Sensory receptor location: retina Sense: sight |
| Stimulus: sound | Sensory receptor location: inner ear Sense: hearing |
| stimulus: pressure | Sensory receptor location: dermis of the skin Sense: touch |
| Stimulus: heavy pressure | Sensory receptor location: deeper in dermis of the skin Sense: pain |
| Stimulus: chemical pt1 | Sensory receptor location: nose Sense: smell |
| Stimulus: chemical pt2 | Sensory receptor location: tongue Sense: taste |
| Stimulus: temperature | Sensory receptor location: dermis of skin Sense: temperature |
| Stimulus: gravity | Sensory receptor location: middle ear Sense: balance |
| The nervous system has 2 parts- part 1- CNS | The central nervous system= brain and spinal cord CNS processes information provided by a stimulus. Both the brain and spinal cord are surrounded by tough membranes-collectively called meninges |
| CNS- spinal cord description | white matter contains nerve fibres surrounded by myelin which is fatty and looks Grey matter has much less myelin- is largely nerve fibres of relay neurones and cell bodies of relay and motor neurones |
| The nervous system has 2 parts- part 1- PNS | comprises: -somatic nervous system eg pairs of nerves that originate in the brain or the spinal cord and their branches |
| PNS pt 2 | These nerves contain the fibres of sensory neurones which carry impulses of receptors to the CNS and motor neurones which carries impulses away from CNS to effectors Also has autonomic nervous system provides unconscious control of the functions of internal organs eg heartbeat, digestion |
| The reflex arc | Simplest type of nervous response to stimulus= reflex arc Neural pathway taken by nervous impulse of reflex action eg withdrawal effect-instantly withdraw hand |
| Reflex action | Rapid, automatic response from nervous impulses initiated by a stimulus. Decision making areas of brain not involved/ involuntary. Reflex action= generally protective. |
| Elements of reflex arc | stimulus--- receptor---sensory neurone--- relay neurone in CNS---- motor neurone---effector---- response can be identified as any reflex action. |
| put diagram of reflex arc | h |
| reflex arc example | stimulus- heat sensory receptor- temp and pain receptors in the skin sensory neurone-sends impulse up the arm to the spinal cord CNS-relay neurone in spinal cord transmits an impulse from sensory neurone to a motor neurone Motor neurone- sends impulse to an effector- in this case a muscle Response- arm muscles contract and hand is removed from heat source |
| Reflex arc- example pupil reflex | stimulus- light sensory receptor- photosensitive cells in retina sensory neurone- optic nerve CNS-brain Motor neurone- carries impulse to muscles of iris response- iris muscles relax/ contract- altering pupil diameter |
| do diagram of spinal column-neurones | h |
| nerve nets-evolution | animals in the phyla that appear early on fossil record dont have nervous systems Those that appeared later have radical symmetry/ nervous system=nerve net eg phylum cnidaria-includes jellyfish those that appeared even later have bilateral symmetry and have CNS eg chordates |
| Nerve net is the simplest type of nervous system- it's a diffused (distributed) network of cells that groups into a ganglia but doesn't form a brain | Nerve net is the simplest type of nervous system- it's a diffused (distributed) network of cells that groups into a ganglia but doesn't form a brain |
| nerve net- cell types | Ganglion cells- provide connections in several directions Sensory cells- detect stimuli eg light, sound, touch, temperature |
| Hydra nerve net | Hydra is in phylum cnidaria nerve net- has a simple pattern,is easy to manipulate in exps, regenerates rapidly eg when replacing lost tentacle so- model organism for studying nerve nets |
| hydra- nerve net- ectoderm | Hydras nerve net is in its ectoderm-(outer 2 layers of body wall)- Nerve net allows hydra to sense light- physical contact and chemicals- so it can contract, perform locomotion, hunt and feed. Without a brain has complex movement/ behaviour- larger stimulus stimulates more cells-causes larger response |
| compare hydra to human | nervous system type- nerve net/ CNS NO. cell types in nervous system- 2/many Regeneration of neurones- Rapid/ slow if at all Myelin Sheath-Absent/present onduction speed- Slow approx 5m/s to Fast up to 120m/s |
| Neurones-description | Specialized cells adapted to rapidly carry nervous impulses from one body part to another- 3 types of neurones. |
| 3 types of neurones | sensory- carries impulses from sense receptors or organs into CNS Motor-Carry impulses from CNS to effector organs eg muscles/ glands- Motor neurones has one axon and multiple short dendrons Relay, connector or association- receive impulses from sensory neurones or other relay neurones and transmit them to motor or other relay neurones |
| Cell body/ centron function | contains a nucleus and granular cytoplasm |
| Cytoplasm function | Granular-- contains many ribosomes |
| Nucleus function | Holds DNA |
| Nissl granules | Cytoplasmic granules comprising ribosomes grouped on ER |
| Dendrite function | Thin fibre carrying impulses towards the cell body -carries action potentials to surrounding cells |
| Axon function | Thin fibre carrying impulses away from cell body, a cell body only has one axon. |
| Schwann cells function | Glial cells that surround and support nerve fibres. In vertebrate embryos, they wrap around the developing axons many times and withdraw their cytoplasm, leaving a multi latyered phospholipid myelin sheath- lipid- doesn’t allow charged ions to pass through it |
| Myelin sheath function | electrical insulator- speeds up transmission of impulses |
| Nodes of Ranvier function | 1 um gaps in myelin sheath, where adjacent Schwann cells meet and where the axon membrane is exposed- allows impulses to be transferred rapidly |
| synaptic knob function | swelling at end of axon in which neurotransmitter is synthesised |
| Axon ending/ terminal function | Secretes neurotransmitter which transmits impulse to adjacent neurone |
| nervous impulse- resting potential | Neurone= an excitable cell- means it can change its resting potential resting potential- When a neuron is not conducting an impulse there’s a difference between electrical charge (potential difference) on the inside and outside of the neurone (across the membrane) known as resting potential |
| nervous impulse- potential difference | Potential difference across a cell membrane = 70 mv- membrane is more negative inside so resting potential is -70 mv- potential difference across cell membrane means it's polarised |
| reason for resting potential 1 | Inside of the cell has a higher concentration of K+ ions and a lower concentration of Na+ ions compared to outside- Uneven distribution of ions causes a chemical and electrical gradient- together- electrochemical gradient-some of the channels that allow K+ in are open and most that allow Na+ in are closed- makes axon membrane 100 times more permeable to K+ ions- diffuse out faster than Na+ diffuses in |
| What are sodium- potassium exchange pumps | Trans membrane proteins with ATPase activity transport K+ and Na+ ions against conc gradient by active transport- maintains conc and uneven distribution of ions across membranes. |
| reason for resting potential 2 | This is achieved by active transport: the sodium-potassium pump pumps 3 Na+ out of the axoplasm and only 2 K+ in. Also the axon membrane is highly permeable to K+ and they leak out by facilitated diffusion through open channels. This outward movement of positive ions means the outside of the axon membrane is positive relative to the inside. The membrane is polarised. The ATP needed to maintain a resting potential is produced by the numerous mitochondria present in the axoplasm of the axon. |
| Reason for resting potential-3 | Voltage gated sodium channels- in axon membrane- doesn't open when Na+ wants to come back in but lets K+ out |
| Other reasons for resting potential | some of the channels allow K+ out in the membrane but not Na+ in- membrane is 100x more permeable to K+ |
| Action Potential Definition | (The rapid rise and fall of electrical potential across a nerve cell membrane as a nervous impulse passes) If stimulation is strong enough signal travels along entire length of axon in phenomenon called action potential - increase in voltage or depolarisation is due to neurone membrane becoming more permeable to Na+- once AP is generated moves along like a Mexican wave- when you reach threshold of -55mv action potential occurs |
| The action potential | In an excitable cell, the potential across the membrane can alter. A nervous impulse is the transmission of a change in potential along a nerve fibre associated with the movement of sodium ions- voltage change is very small but can be picked up with by a pair of microelectrodes fed to an oscilloscope |
| Oscilloscope function | A membrane potential is the difference in charge between one side of a membrane and the other, sometimes described as the potential difference, An oscilloscope is a type of electronic test instrument that graphically displays voltage across membrane changes with time. Measures magnitude and speed of impulse transmission and helps us analyse patterns of impulses generated in different parts of the nervous system in different situations The display produced is like a graph with time in milliseconds on the x-axis and the membrane potential in millivolts on the y-axis |
| conclusions drawn using oscilloscope | Neurones transmit electrical impulsesalong cell surface membrane surrounding axon- put microelectrode inside axon and one in bathing solution to find: There’s some Na+ gates that are always open but some that only open when a certain voltage is reached- a stimulus can open some of these gates- sometimes big enough stimulus to open enough gates to reach the -55mv threshold as more Na+ ions move in Once you reach threshold even more sodium ion channels open- get more Na+ in- peak at +40 mv |
| conclusions drawn using oscilloscope pt 2 | At point of peak some sodium channels close but potassium ones are open- diffuses out- repolorisation- causes even more K+ to diffuse out- causes overshoot called hyperpolarization-goes below resting potential up to -80mv- sodium potassium pumps pumps K+ ions out and allows Na+ in- restores ion back to resting potential |
| Depolarisation definition | A temporary reversal of potential across the membrane of a neurone so the inside becomes less negative than the outside as an action potential is transmitted |
| How action potential travels along axon | Na+ ions move along axon due to their locally high concentration-move to lower concentration. In doing this they depolarise the adjacent section of the memrane-opens more voltage gated sodium channels in those regions- mopre sodium ions floods in- depolarises axon at this point - sodium ions then diffuse further down the axon |
| Absolute refractory period | Site of initial action potential- sodium channels- are inactivated- can't open again until resting potential has been re-established so new action potential can be initiated this is the absolute refractory period-lasts around 1ms-ensures nervous impulse travels in 1 direction |
| Relative refractory period | for next 3-4ms during hyperpolarisation if an impulse is strong enough a new action potential may pass - occurs while sodium and potassium pumps are restoring resting potential. |
| Properties of nerves/impulses- 'All or nothing' | If the intensity of a stimulus is below a certain threshold value- no action potential is initiated- When action potential is initiated is always the same size +40 mv- remains that same size as it is propagated along the axon- no energy lost in transmission- increase in stimulus intensity doesn't = greater action potential- frequency of action potentials increases instead. |
| All or nothing law effect | An action potential is a rapid sequence of changes in the voltage across a membrane. Any stimulus that brings depolarization to -55mv will peak at same max voltage- bigger stimulus causes greater frequency of action potentials= the change of voltage from -70mv to + 40mv across the membrane Allows the action potential to act as a filter, prevents minor stimuli from setting up nervous impulses- so brain isn't overloaded with info |
| Factors affecting speed of conduction of nerve impulse- temp | Temp- ions move faster at high temperatures than lower temps- more kinetic energy- birds/ animals (warm blooded) transmit nervous impulses more quickly- faster responses |
| Factors affecting speed of conduction of nerve impulse-Diameter of axon | Greater diameter of axon- greater volume in relation to the area of the membrane- more sodium ions can flow through the axon, so impulses travel faster- |
| Factors affecting speed of conduction of nerve impulse-Diameter of axon pt 2 | human non-myelinated axons= 0.2-1.5 um diameter- such dimensions= very slow action potential transmission especially at low temperatures- some marine habitats evolved in very low temps so to compensate squid has giant axons up to 1mm diameter- earthworm- even though warm blooded has large axons for evolved escape responses |
| Factors affecting speed of conduction of nerve impulse- myelination | Speeds up rate of rate of transmission- sodium ions flow through the axon- but myelinated nerve fibre only depolarises where resistance is low (at nodes of ranvier)-whole process of depolarization, repolarization, hyperpolarization and refractory period happens at each node goes all along a motor neurones axon until a synapse is reached |
| Factors affecting speed of conduction of nerve impulse- myelination pt 2 | voltage gated ion channels only occur at these nodes - (spaces that are unmyelinated)- this is where sodium ions enter- consequence= action potential jumps from node to node along axon- this is saltatory conduction- nodes of ranvier= 1mm- transmission is rapid compared to unmyelinated- unmyelinated axons have voltage-gated sodium channels along the entire length of the membrane. In contrast, myelinated axons have voltage-gated sodium channels only in the nodal spaces. |
| 2 parts of the nervous system | The human nervous system consists of the: Central nervous system (CNS) – the brain and the spinal cord Peripheral nervous system (PNS) – all of the nerves in the body It allows us to make sense of our surroundings and respond to them and to coordinate and regulate body functions |
| Nerves | Information is sent through the nervous system as nerve impulses – electrical signals that pass along nerve cells known as neurones A bundle of neurones is known as a nerve Neurones coordinate the activities of sensory receptors (eg. those in the eye), decision-making centres in the central nervous system, and effectors such as muscles and glands |
| Basic pattern of spinal nerves- dorsal and ventral root | Spinal nerves are an integral part of the peripheral nervous system (PNS). They are the structures through which the central nervous system (CNS)- receives sensory information from the periphery, and through which the activity of the trunk and the limbs is regulated- Also transmit the motor commands from CNS to muscles of the periphery- composed of both motor, sensory fibres and autonomic fibres They begin as nerve roots that emerge from a segment of the spinal cord at a specific level. Each spinal cord segment has four roots: an anterior(ventral) and posterior (dorsal) root on both right and left sides. |
| Voltage gated channels | Ions can’t move across the membrane at will- need a protein embedded in membrane- most ions move through ion channels via passive diffusion- some are always open- some require a signal to tell them to open or close- eg voltage gated channels |
| Terms- simple | When a neuron is not conducting an impulse there’s a difference between electrical charge on the inside and outside of the neurone- known as resting potential |
| Refractory period- general | Very shortly (about 1 ms) after an action potential has been generated in a section of the axon membrane, all the sodium ion voltage-gated channel proteins in this section close. This stops any further sodium ions from diffusing into the axon Potassium ion voltage-gated channels open, allowing the diffusion of potassium ions out down their concentration gradient- returns the potential difference to normal (repolarisation) Once the resting potential is close to being reestablished, the potassium ion voltage-gated channel proteins close and the sodium ion channel proteins in this section become responsive to depolarisation again Until this occurs, this section of the membrane is in recovery period-unresponsive |
| Ventral root | The ventral root contains efferent nerve fibres-carry stimuli away from the CNS towards their target structures. The cell bodies of the ventral root neurons are located in the central grey matter of the spinal cord. Motor neurons controlling skeletal muscle, as well as preganglionic autonomic neurons are located in the anterior roots. |
| Dorsal root | The dorsal root contains afferent nerve fibres, which return sensory information from the trunk and limbs to the CNS. The cell bodies of dorsal root neurons are located in structure called the spinal/dorsal root ganglion. The anterior and posterior roots join to form the spinal nerve proper, containing a mixture of sensory, motor, and autonomic fibers. |
| What you see on an oscilloscope | If there is a resting potential=a straight, horizontal line on the display screen at a level of -70 mV Action potential= a spike, rising up to a maximum voltage between +30 and +40 mV The rising phase of the spike =depolarisation The falling phase of the spike shows =repolarisation often there's a gradual rise in membrane potential just before the membrane rapidly depolarises Before threshold potential is reached, only a small number of sodium channels in the membrane are open, so the membrane depolarises slowly, but when the threshold is reached many more sodium channels open |
| What you see on an oscilloscope pt 2 | Instead of repolarisation causing the membrane potential to return immediately to the normal resting potential of -70 mv, the trace often shows a short period of hyperpolarisation This is when the membrane potential briefly becomes more negative than resting potential |
| Role of synapse | a very small gap, known as the synaptic cleft, separates them The ends of the two neurones, along with the synaptic cleft, form a synapse This stimulates the postsynaptic neurone to generate an electrical impulse that then travels down the axon of the postsynaptic neurone A cholinergic synapse is one that uses the neurotransmitter acetylcholine. Y |
| Impact of drugs pt 1 | Many drugs impact the nervous system by altering the events that occur at synapses Drugs can increase transmission of impulses at a synapse and so increase frequency of APs at post synaptic (stimulants) by: Causing more neurotransmitter to be produced in the synaptic knob Causing more neurotransmitter to be released at the presynaptic membrane Imitating the effect of a neurotransmitter by binding to and activating receptors on the postsynaptic membrane Preventing the breakdown of neurotransmitters by enzymes Preventing the reuptake of neurotransmitters by the presynaptic cell |
| Impact of drugs pt 2 | Drugs can decrease transmission of impulses at a synapse (sedatives) by Preventing production of neurotransmitter in the presynaptic knob Preventing the release of neurotransmitter at the presynaptic membrane Enabling neurotransmitter to gradually leak out of the presynaptic knob so there is little left when an action potential arrives The neurotransmitter that leaks out of the cell is destroyed by enzymes Binding to receptors on the postsynaptic membrane and so preventing neurotransmitters from binding |
| Nicotine | Nicotine is the addictive chemical found in tobacco Nicotine affects synapses in more than one way It mimics acetylcholine Nicotine binds to a type of acetylcholine receptor on the postsynaptic neurone known as a nicotinic receptor The binding of nicotine to nicotinic receptors initiates an action potential in the postsynaptic neurone After stimulation by nicotine these receptors become unresponsive to other stimulation While it is normal for receptors to be briefly unresponsive to further stimulation after being activated, nicotine causes a prolonged period of unresponsiveness |
| Nicotine- how you become addicted | It stimulates release of dopamine Dopamine is released from the pleasure centres in the brain in response to nicotine The release of dopamine is thought to reinforce rewarding behaviours, in this case smoking Unlike acetylcholine- nicotine isn’t removed by hydrolysis- continues to initiate impulses- may become habituated- nervous system only functions normally when nicotine is present- as drug tolerance is developed if you don’t take nicotine impulses aren’t transmitted normally- unpleasant withdrawal symptoms are experienced |
| Organophosphate | Organophosphate Drugs may inhibit breakdown of neurotransmitters- OPs inhibit acetylcholinesterase so acetylcholine isn’t hydrolysed- remains in synaptic cleft- causes repeated firing of postsynaptic neurone- OPs are esters of phosphoric acid- A chemical substance made when an acid and an alcohol combine and water is removed. - alcohol added to acid to make ester- can be inhaled/ absorbed/ ingested |
| Organophosphates- effects | -when long term health can be damaged when OPs are used insecticides eg malathion, dichlorvos, herbicides eg glyphosate, nerve gases eg sarin Nerve gases inhibit acetylcholinesterase- at neuromuscular function junction generating repeated uncontrollable contraction of muscles- occurs in antagonistic muscles where it can break bones These chemicals stop a key enzyme in the nervous system called cholinesterase from working, |
| Psychoactive drugs | Primarily affect different neurotransmitters or their receptors- affects firing of neurones- alters brain function and so: perception, mood, consciousness and behaviour- can be therapeutic- Ritalin, Prozac etc or recreational- nicotine, alcohol, canabbis, cocaine, amphetamines, ecstacy and heroin- may be pleasant -euphoria and help with alertness or recall- so many are abused |
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