4.1.2 NERVES

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What does the nervous system consist of?
neurons and glial (supporting cells)
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What are sensory receptors?
transducers - convert different forms of energy into nerve impulses
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Give some examples of sensory receptors
light sensitive cells in the retina// olfactory cells in the retina detect presence of volatile chemicals// tastebuds detect presence of soluble chems/ pressure receptors
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What do sensory neurons do?
transmit impulses from receptors to the CNS
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What does the Central nervous system consist of?
brain and spinal cord
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What do motor neurones do?
transmit impulses from the CNS to effectors, such as muscles and glands
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Describe the structure of motor neurones
a cell body at end with a large nucleus with lots of rough ER and golgi / many short dendrites that carry impulses to body/ long axon that carries impulse
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Why do motor neurones have such large nuclei?
lots of Rough ER and golgi to synthesise proteins involved in impulse transmission
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How is a potential difference established across a membrane?
result of an unequal distribution of ions// more anions being within the cell// Sodium-potassium pump actively transports 3Na+ ions out for every 2K+ in// axon contains organic ions which the mem is impermeable to (to Na+)
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When not conducting an impulse, what is the value of the resting potential?
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How to neurones transmit nerve impulses over one distances?
uses reversals of the potential difference to 'boost' current flow
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what is the difference between sodium and potassium channel proteins?
sodium channel proteins are much more sensitive to changes in pd
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Where do action potentials occur?
along all unmyelinated neurones
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What is meant by a myelinated neurone?
sensory and motor neurones are protected by schwann cells, makes up myelin which acts as an insulator// here AP transmission must occur in the Nodes of Ranvier
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What is a myelin sheath?
insulating layer of fatty material which Na and K ions cannot pass through
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How is an action potential transmitted in myelinated neurones?
myelin contains voltage gated K and Na ion channels// the action potential jumps from one node of ranvier to the next// myelinated neurones have a much faster transmission time than unmyelinated
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What is a signal?
many successive impulses form a group called a volley - a group of volleys is a signal
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What is the refractory period?
the time that must elapse after an initial stimulus has been set up an AP before a second stimulus can set up a second AP
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describe the difference between refractory periods in myelinated and non-myelinated neurones
myelinated neurones the RF period is much smaller than that of a non// this allows a wide range of responses to be controlled
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What is a threshold potential?
the p.d. across a membrane which if met or exceeded will trigger an AP
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What is a generator potential?
caused by a slight depolarisation in the membrane from a small stimuli
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what is an action potential?
depolarisation of the Smem where the inside is more positive than the outside, transmitted along a neurone
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What is a resting potential?
the state of a neurone when it is not transmitting an AP// but is still actively transporting Na+ and K+ ions to maintain the p.d. of around -60mv
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What is the transmission of an action potential called on myelinated neurones>
saltatory conduction - jumps from one to the next
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Where are non-myelinated neurones used in the body?
coordinated body functions over short distances - less need for rapid transmission i.e. digestive system
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what happens if a stimulus is too small?
threshold frequency will not be met - no AP
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How can you determine the intensity of a stimulus?
by the frequency of the APs arriving - more APs generated
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What is a Cholinergic synapse?
junction between two or more neurones// acetylcholine is the neurotransmitter
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What is the function of a synapse?
allows neurones to communicate with each other
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What is a presynaptic neurone?
ends in a synaptic knob // specialised bulge in a neurone
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Describe the function and characteristics of the presynaptic neurone
contains many mitochondria for ATP // smooth ER /// vesicles containing acetylcholine // voltage gated Ca2+ ions in the presynaptic mem
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What is the purpose of a postsynaptic neurone?
found on a neurone or effector - to either transmit another AP or bring about a response
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Describe the characteristics of the postsynaptic neurone
specialist Na+ ion channels // channels with receptor to Ach, open when binds // only on postsynaptic to APs can only be in one direction
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What is the purpose of several presynaptic neurones converging to one postsynaptic neurone?
signals from different parts of the nervous system converge for one response // danger
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What is the purpose of one presynaptic neurone diverging to several postsynaptic neurones?
produces several responses // i.e. in a reflex when one neurone informs effector and the other the brain
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How are low level signal filtered out?
several generator potentials required for an AP// if only a few arrive at the synapse less likely to be transmitted because its likely to be unimportant
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What is summation?
persistent low level signals are amplified by adding together the many postsynaptic generator potentials to produce one full AP
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What is acclimatisation?
synapse may run out of Ach if there is repeated stimulation // prevents potentially damaging an effector my overstimulation // persistent background noise not responded to after time
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How do synapses and the brain work together?
synapses create specific pathways so that the brain knows where an AP originated
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Card 2


What are sensory receptors?


transducers - convert different forms of energy into nerve impulses

Card 3


Give some examples of sensory receptors


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Card 4


What do sensory neurons do?


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Card 5


What does the Central nervous system consist of?


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