• Created by: Hindleyc
  • Created on: 27-01-19 09:44
What is the human CNS
Very complex structure and contains 10^12 nuerones
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What do many nerves branch out from
The CNS carry impulses to and from organs
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What are the 2 regions in the CNS
Grey matter which consists of cell bodies and synapses and White matter which consists of the long axon of the neurones filled with cytoplasm
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What do neurones have
Same basic structure but diff types of nerve cell are specialised for their particular functions
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Cell body
Contains nucleus and other organelles
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Bring impulse to cell body enable to connect using neurotransmitters- projections
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Takes Impulse away from cell body - long
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Myelin sheath
Secreted by Schwann cells- fatty layer surrounding axon speeding up rate of electrical impulse
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What does a neurone consist of
Cell body containing nucleus with one or more long thin structures called processes that are extensions of the cytoplasm surrounded by a plasma membrane
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What do the processes called dendrons do
Conduct nerve impulses towards the cell bodying have very find processes called dendrites
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What are the processes called that carry nerve impulse away from the cell body
Axons - receive impulse by dendrites - other neurones. axon away from cell body
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What are the axon of many neurones surrounded by
Schwann cells which form (secrete) a myelin sheath. Do this because as they grow the Schwann cell twist around the axon several times
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Function of myelin sheath
Increase speed of conduction of the nerve impulse, electrically insulate the axons from each other
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What are the junctions between adjacent Schwann cells called
Nodes of ranvier
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What do neurones link together at
Junctions called synapses that occur mainly in the CNS - few when first born
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What can 1 single neurone have
Many synapses with other neurones
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What can sysnapse be
Junctions with other neurones or effectors
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What are they
The only way in which impulses can pass from one neurone to the next
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What is there at this junction
Gap of about 20nm
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What is transmission across the gap via
Chemical substances
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What does a nerve consist of
Bundle of neurones
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Length of fibres in a sensory neurone
Long dendrites and short axon
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Cell body and dendrite are outside of the spinal cord ; cell body located in a dorsal root ganglion
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Function of sensory neurone
Conduct nerve impulse to the spinal cord
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Length of fibres on interneurone
Short dentrites and short or long axon
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Entirely within the spinal cord or CNS
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Interconnect the sensory neurone with appropriate motor neurone
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Motor neurone length
Short dentrite and long axon
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Dendrites and cell body located in the spinal cord; axon outside of the spinal cord
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Conduct impulse to an effector (muscle or gland)
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Whats a reflex arc
Simple pathway that transmits information in a very straight forward way and rapid way from a receptor to and effector
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Stimulus receptor S N coordinator(I N) M N effector and response
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Why are reflex actions rapid
Direct link b/w receptor and effector
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What do simple reflex actions allow the body to make
Automatic involuntary adjustments to changes in the external environment
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What do they also help control
The internal environment
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What do they not have to be
Learnt- nerve pathways are built into the N system under genetic control
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What do they control
Simple responses needed for survival and avoiding danger
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Simplest form of response in the nervous system
Reflex action
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What is it
Rapid automatic response to a stimulus which isn't under the voluntary control of the brain- involuntary action
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What does the same stimulus produce
Same response every time
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What is the nervous pathway taken by nerve impulses in a reflex action called
Reflex arc
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What is the information about the stimulus picked up by
A receptor
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In some reflex arcs what is there no
Interneurone- impulse passes directly from sensory to motor N
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What do reflex arcs usually invole
3 neurones- sensory inter and motor
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eg of withdrawal reflex
***** finger on pin- spinal reflex meaning reflex archaises thru spinal cord rather than brain
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As we later become aware of pain after we have moved foot shows
Reflex arcs are connected through synapses to other parts of the Nervous system
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What is there a one way system of through the spinal cord
Nerve fibres
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Where are all nerve cell bodies
CNS spinal cord
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Card 2


What do many nerves branch out from


The CNS carry impulses to and from organs

Card 3


What are the 2 regions in the CNS


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Card 4


What do neurones have


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Card 5


Cell body


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