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level: Responding to the Environment 1

Questions and Answers List

level questions: Responding to the Environment 1

QuestionAnswer
the role of acetylcholinethe neurotransmitter used in the parasympathetic nervous system
myelin sheathproduced by schwaan cells acts as an electric insulator
what is a neuron?nerve cells it conducts nerve impulses 3 types of neurons: sensory, motor and relay
sensory neuron functionneuron that transmits impulses from receptors to relay neurons in the CNS
motor neuron functiona neuron that transmits impulses from the CNS to the effectors
relay neurons functionfound in the CNS connects the sensory to the motor neurons
sensory neuron structureone long dendron and one short axon cell body in the middle of the neuron
motor neuron structureone long axon and many short dendrites cell body at the end of the axon
relay neuron structuremany short dendrites one axon with many axon terminals unmyelinated
axonsan extension that transmits nerve impulses away from the cell body
dendrites/dendronsan extension from a neuron that carries nerve impulses to the cell body
define effectorsa muscle or gland that produces a response to a stimulus
what is an action potential?a large rapid change in potential difference across a membrane
define potential differencethe voltage across a membrane
what is a resting potential?the potential difference across the membrane when the neurone is at rest the outside is more positively charged than the inside so the membrane is polarised resting potential is at about -70mV
define stimulusa change in internal or external conditions of an organisms environment which brings about a response
CNScentral nervous system made of the brain and spinal cord
myelinationa layer of fatty substance produced by Schwan cells to form the myelin sheath acts as an electric insulator around axons and dendrites
nodes of Ranvierthe gaps between the myelin sheaths
Schwan cellscells that form the myelin sheath around nerve cells
saltatory conductionthe mechanism by which speed of the action potential increases by jumping between the nodes of Ranvier
structure of the eyeiris, pupil, fovea, retina, optic nerve, rod cells and cone cells, circular and radial muscles, blind spot
function of the iriscoloured part of the eye controls the amount of light that enters the eye using the circular and radial muscles
function of the pupilalso controls the amount of light that enters the eye it involuntarily constricts in bright light and widens in dim light
function of the foveawhere most cone cells are found
function of the retinawhere the photoreceptor cells - cone and rod cells - are found creates electrical impulses that are sent to the optic nerve
what does the optic nerve do?carries nerve impulses from the retina to the brain to interpret as images
rod cellsdominant in dim light 1 type found only in the retina can detect all visible wavelengths low visual acuity most abundant photoreceptor has rhodopsin senses only black and white and movement
cone cellsdominant in bright light 3 types concentrated at the fovea high visual acuity has iodopsin senses colour
blind spotthis is where all the axons of the neurones collect together and leave the eye forming the optic nerve there are no photoreceptors here
circular and radial musclescircular muscles contract to constrict the pupil and make it smaller radial muscles contract to dilate the pupil and make it bigger
how does the pupil constrict?occurs in the presence of bright light photoreceptors in the retina detect the light stimulus an action potential is generated in the bipolar neurones then the optic nerve the action potential travels along the sensory neurone to the brain the brain transmitts an action potential along the oculomotor neurones to the circular muscles in the iris they contract and the pupil constricts, getting smaller
how does the pupil dilate?occurs in dim light photoreceptors in the retina detect the light stimulus an action potential is generated in the bipolar neurone then the optic nerve the action potential travels along the sensory neurones to the brain the brain transmitts an action potential along the oculomotor neurone to the radial muscles in the iris they contract and the pupil dilates, getting wider
5 steps for generating an action potentialresting potential threshold met depolarization repolarization hyperpolarization
how it the resting potential established?the sodium/potassium pump actively transports 3Na+ out of the axon for every 2K+ pumped in to the axon using ATP K+ diffuses back out of the cell down the chemical gradient through protein channels the K+ diffusion out of the cell is opposed by the electro gradient in the opposite direction - the K+ moving into the cell - so a resting potential of -70mV is achieved the membrane becomes less permeable to Na+ so less diffuses back into the cell
what happens when the threshold is met?the point when an action potential can be generated
what happens during depolarisation?the membrane is polarised at rest neurotransmitters arrive at the post synaptic membrane some voltage dependent Na+ channels open the membrane depolarises slightly to the threshold value of -50mV more voltage dependent Na+ channels open and Na+ floods in along their electrochemical concentration gradient the membrane reaches a potential difference of +40mV the membrane is depolarised as the inside is more positive than the outside
what happens during repolarisation?once the potential difference of the membrane has reached 40mV the Na+ channels close and the voltage dependent K+ channels open the membrane is now impermeable to Na+ K+ diffuse out of the axon down the concentration and electrochemical gradient The inside now becomes more negative than the outside so the membrane is polarised again
what happens during the refractory periods?absolute refractory period and relative refractory period periods of time where another action potential cannot take place in the absolute RP no action potential can be generated at all because the Na+ voltage dependent channels are closed so the membrane cannot be depolarised by the entry of Na+ in the relative RP there is a really low chance that an action potential can be generated
what are the names of the receptor cells in the eye?photoreceptors rod and cone cells
structure of synapsespresynaptic neurone synaptic cleft neurotransmitters voltage dependent Ca2+, Na+ and K+ channels
function of synapsesthe gap between two neurones or between a neurone and a muscle or gland controls the nerve pathways allowing flexibility of response integrates information from different neurones allowing a coordinate response
what are neurotransmitters?chemicals which diffuse across the synaptic cleft to stimulate other neurones or effectors they are made in the RER and Golgi like proteins examples include acetylcholine, glutamate or adrenaline
the role of acetylcholinethe neurotransmitter used in the parasympathetic nervous system
how does a synapse transmit an impulse?the action potential arrives the membrane the depolarises Ca2+ channels open and they enter the neurone the presence of Ca2+ causes the synaptic vesicles containing neurotransmitters to fuse with the presynaptic membrane the neurotransmitter are released by exocytosis into the synaptic cleft the neurotransmitters bind with the receptors on the postsynaptic membrane opening the cation channels (Na+) the postsynaptic membrane can now depolarise and initiate an action potential once released from the receptors they are broken down by enzymes found in the synaptic cleft and diffuse away or be taken in by the presynaptic neurone