Nervous System Flashcards
Order of reaction
Stimulus Detector Coordinator Effector Response
The nervous system
Consists of the nervous system and peripheral nervous system
What are the 2 components of the peripheral nervous system
Somatic - brain and spinal cord - motor and sensory neurone
Autonomic - involuntary
Neurones
Sensory- carry impulses from receptors to CNS
Relay or connector with the CNS that receive impulses from sensory into the motor neurone
Motor neurone - transmit impulses from CNS to effectors
Differences between nerve nets and nervous systems
Nerve nets 1 type of simple neurone Unmyelinated Short, branched neurones Impulse transmitted in both directions Slow impulse transmission
3 types of neurone Myelinated Long unbranched neurones 1 direction Fast
Nervous impulse
At resting potential -70 MV
impermeable to Na and K
use intrinsic protein to move across membrane
Gates
Na hates allow Na to pass in
K gates allow K out
Most K are open, most Na gates are closed
Resting potential negative because they’re are fewer positive ions inside the than there are outside
Action potential
At resting potential, k gates open and na gates are closed = negative charge
Energy of stimulus causes Na gates to open, Na ions flood in down their conc gradient - depolarising the neurone
As more Na enter, more gates open so ever more Na ions rush in - positive feedback
When potential reaches +40mv neurone is depolarised, Na gates close and K gates open
K ions flood out resulting in more k gates opening and more k ions leaving the neurone - repolarisation
Too many k ions leave and causes to drop to -80 Mv hyperpolarisation
Factors affecting speed
Myelination - speeds it up
Diameter of axon - transmission speed increases with axon diameter due to less leakage of ions
Temp - increases with temp, rate of diffusion increases
Synapse - transmission
Impulses arrives
Calcium channels open - diffuses rapidly to the pre synaptic knob
Vesicles containing neurotransmitter acetylcholine migrate to and fuse with the pre-synaptic knob membrane
Contents of the vesicle are released into the synaptic cleft by exocytosis
Acetylcholine diffuse across the cleft and bind to the receptors on the post synaptic membrane = Na channels open
Na rush into the post synaptic neurone depolarising of post synaptic membrane = action potential
Acetylcholine splits into ethanoic acid and choline releasing them from the receptor and sodium channels close, products diffuse back
Reabsorbed in the ps knob
ATP used to reform into acetylcholine
Repeated depolarisation prevented by
Hydrolysis of acetylcholine
Reabsorption of ethanoic acid and choline back into pre- synaptic knob
Active transport of calcium ions
Insufficient acetylcholine is released, not enough Na channels open
Drugs
Excitatory - more action potentials
Sedative - less
Many drugs mimic action of neurotransmitters, but unlike acetylcholine nicotine is removed by acetylcholinesterase
Over time less acetylcholine produced
People addicted
