THE NERVOUS SYSTEM
- Created by: Katy **
- Created on: 16-04-16 13:47
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- THE NERVOUS SYSTEM
- REFLEX ARC
- reflex arc = response to a change in environment; it is rapid, involuntary & protective
- refractory period = prevents a backward travel of impulse (area around the impulse is hyperpolarised) to prevent any further action potentials being propagated
- overcome pathway by ascending nervous fibres to direct the impulse to the brain
- A Reflex Arc
- NEURONES
- neurones = antagonistic, highly specialised cells that generate & transmit the impulse signal
- sensory neurones relay the impulse from the organs to the Central Nervous System
- relay neurones relay the impulse from the sensory neurone to the motor neurone
- motor neurones relay the impulse from the Central Nervous System to the effector (muscle or gland)
- dendrites = LARGE surface area & carry the impulse to the cell body
- axon = carry the impulse from the cell body to the synapse
- ganglion = cell body in the axon
- Schwann cells (myelin sheath) around the neurone insulate & help with impulse transmission
- node of Ranvier allow for the impulse to jump from node to node
- NERVE NETS OF HYDRA
- simple nervous systems
- invertebrate phyla (jelly fish, coral)
- chemical synapse
- epithelial receptors
- contractile effector cells
- complex nervous system
- more complex hydra nets
- more diverse behaviours
- more complex hydra nets
- Comparison between Simple & Complex Hydra Nets
- simple nervous systems
- NERVE IMPULSE
- use a microelectrode to measure
- resting potential = -70mV lower in neurone than outside
- The Nerve Impulse Initiation
- ACTION POTENTIAL
- action potential = results in a change in membrane permeability to ions
- phospholipids will isolate the impulse
- threshold potential = minimum mV of impulse needed to initiate an action potential
- propagation = an action potential will cause sodium channels on adjacent neurone to open
- An Action Potential
- SYNAPSE
- synapse = a junction between neurones which slow down the impulse
- The Synaptic Transmission
- a stronger stimulus will cause an increase in action potential frequency
- speed of impulse is effected by
- myelin sheaths
- increases speed as impulse can jump from node to node
- wider axon diameter
- increases speed as less phospholipid contact
- higher temperature
- increases speed as increase in energy & faster
- myelin sheaths
- function
- convey action potential between neurones, unidirectional
- filters out low-level stimuli for protection
- summation = added effect of more than one action potential
- spacial summation = action potentials from many neurones
- temporal summation = many action potentials from one neurone
- excitatory synapses = sodium ions cause polarisation
- inhibitory synapses = chloride ions cause depolarisation
- neurotransmitters
- noradrenaline will increase heart rate
- acetylcholine will decrease heart rate
- THE EFFECT OF DRUGS
- agonist = mimic to increase metabolism
- mimic neurotransmitters
- block enzymes
- release neurotransmitters
- e.g. cocaine
- antagonist = block to slow down metabolism
- block neuroreceptor
- e.g. curare
- agonist = mimic to increase metabolism
- PHOTOPERIODISM
- plants have a slow response rate as the co-ordination is caused by chemicals
- photoperiodism = response to light by leaves
- photochrome = photoreceptors with will absorb light & change light pigments
- when light, 660Pr is converted in 730Pfr (which is unstable)
- when dark 730Pfr is converted into 660Pr
- a normal day will have no effect on flowering
- on a long-day light will influence flowering
- on a short-day dark will induce flowering
- REFLEX ARC
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