neurones better

Questão	Responda
What is a stimulus	a detectable change in the internal or external environment of an organism that produces a response in that organism.
Neurones description	Specialized cells adapted to rapidly carry nervous impulses from one body part to another- 3 types of neurones. Categorised into 3 main groups- sensory relay and motor
Common features of neurons	All 3 have these common features: Cell body- contains organelles found in typical animal cell, Proteins and neurotransmitter chemicals made here Axons-Thin fibre carrying impulses away from cell body, a cell body only has one axon. Dendrons-Thin fibre carrying impulses towards the cell body -carries action potentials to surrounding cells
Common features pt2- schwann cells/myelin sheath	Schwann cells 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- electrical insulator- speeds up transmission of impulses
Common features pt 3- nodes of ranvier	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	The synaptic knob is a swelling which contains synaptic vesicles. The synaptic knob is the location where the nerve impulse is transmitted across the synpatic cleft. There are also lots of mitochondria in the synaptic knob. This is because lots of energy is needed to synthesise neurotransmitters.
Axon ending/terminal function/ other parts	Branched endings of axon that approach muscle fibre Secretes neurotransmitter which transmits impulse to adjacent neurone Cell body-contains a nucleus and granular cytoplasm Cytoplasm-Granular-- contains many ribosomes Nucleus- Holds DNA Nissl granules-Cytoplasmic granules comprising ribosomes grouped on ER
Sensory neurone	carries impulses from sense receptors or organs into CNS- long dendron- carries impulse from sensory receptor to cell body of neurone then an axon to carry impulse to next neurone (look at diagram to understand)
Relay neurone	Relay, connector or association- receive impulses from sensory neurones or other relay neurones and transmit them to motor or other relay neurones- multiple short axons and dendrons
Sensory receptor	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.
Sensory receptor-more	when a sensory receptor detects a stimulus- produces a nervous impulse- electrical impulses pass down neurone to CNS- does this by converting one form of energy into a nervous impulse- called a transducer
The nervous system has 2 parts	The human nervous system consists of the: Central nervous system (CNS) – the brain and the spinal cord Peripheral nervous system (PNS) – Pairs of nerves that originate from CNS and carry impulses into and out of the CNS It allows us to make sense of our surroundings and respond to them and to coordinate and regulate body functions
- 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- makes white matter look white Grey matter has much less myelin- is largely nerve fibres of relay neurones and cell bodies of relay and motor neurones
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.
Ventral	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	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.
PNS	comprises: -somatic nervous system eg pairs of nerves that originate in the brain or the spinal cord and their branches
PNS pt2	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
Nerves	nformation 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
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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
Reflex Action	Rapid, automatic response from nervous impulses initiated by a stimulus. Decision making areas of brain not involved/ involuntary. Reflex action= generally protective.
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
Elements of reflex arc	stimulus--- receptor---sensory neurone--- relay neurone in CNS---- motor neurone---effector---- response can be identified as any reflex action
Reflex arc- temp	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
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
Action Potential	(The rapid rise and fall of electrical potential across a nerve cell membrane as a nervous impulse passes) The change from -70 to +40 to -70 again at one node- means that node is polarised-depolarised-repolarised-hyperpolarised-polarised- when you get to depolarised bit (reaches +40mv- triggers next bit of axon to open gates)- causes nervous impulse
Difference between action potential and nervous impulse	AP- the process of the voltage change at one node- nervous impulse- the transmission of voltage change along entirety of axon
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	t 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
Absolute Refractory period	- 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
How action potential travels along axon	+40- sodium channels- are inactivated- can't open again until resting potential has been re-established- but that+40 triggers gates closest- so second site opens- triggers either side- but previous site has gates closed- can't be retriggered till resting potential is restored (time section can't be triggered= absolute refractory period)- travels one way down axon
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'	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 no energy lost in transmission- 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-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.
What you see on oscilloscope	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
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.
Synaptic transmission pt 1	Action potential arrives. When an action potential reaches the synaptic knob, the membrane of the pre-synaptic neurone changes permeability by opening voltage-dependent calcium channels. Calcium ions rush into the pre-synaptic neurone. Calcium ions diffuse into the synaptic knob down the concentration gradient. The synaptic vesicles fuse with the pre-synaptic membrane. The excess of calcium ions cause the vesicles to move towards and then fuse with the membrane, releasing acetylcholine (the contents of the vesicles) into the synaptic cleft. This process is exocytosis.
hSynaptic transmission pt2	Acetylcholine diffuses across the synaptic cleft. The neurotransmitters diffuse down the concentration gradient. Acetylcholine binds with receptors in the post-synaptic membrane. These receptors change shape, opening a channel to allow sodium ions to diffuse in. As the receptors are only present on the post-synaptic membrane, the impulse cannot travel back, so it is unidirectional. Sodium ions rush into the post-synaptic neurone. If enough sodium ions diffuse in, the action potential threshold is reached and this triggers depolarisation of the neurone. An action potential in the post-synaptic neurone is generated.
Impact of drugs pt1	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 pt2	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,
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-description	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
If sheath= unmylejated what happens to O2 consumption	Rate of consumption increases- saltatory conduction wouldn’t occur- membrane= not depolarised- AP’s along neurone- more Na+ and K+ pumps working- more active transort- more ATP needed- more aerobic respiration
Symptoms of you myelination gets damaged	Feel weak/ lack of feeling, slower reaction times
9 mark plan	Compare 7.1 to 7.2- describe both- takes impulse through spinal cord not brain- takes through white matter for sensory then grey for relay- motor takes impulse to muscle not pain centre in brain Anaesthetic A- prevents passage of sodium ions into neurons- prevents initial ap being set up- won’t depolarise other gates- pass impulse Anaesthetic B- stops calcium ions going in- no vescicles containing neurotransmitters move down- not released by exocytosis- doesn’t set up so in postsynaptic

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	Criado por Darcey Griffiths 3 meses atrás