Nervous System

Question 1

nervous system

Answer 1

detect stimuli, process information, initiate response

Question 2

CNS

Answer 2

Central Nervous System = brain + spinal cord

Question 3

PNS

Answer 3

Peripheral Nervous System = pairs of nerves from brain and spinal cord that contain sensory + motor neurones

Question 4

basic nervous control mechanism

Answer 4

stimulus
receptors 
(sensory neurones)
CNS
(motor neurones)
effector (muscle/gland)
response

Question 5

reflex actions

Answer 5

rapid, involuntary, protective response to a stimulus

Question 6

spinal cord

Answer 6

grey matter - mostly full of cell bodies/nuclei of neurones, stain darkly
white matter - mostly axons and myelin sheaths of neurones, axons dont stain darkly and myelin sheaths only stain lightly

Question 7

hydra

Answer 7

no CNS
sense receptors respond to limited number of stimuli
small number of effectors
nerve net

Question 8

human

Answer 8

CNS
sense receptors respond to wide range of stimuli
large number of efectors

Question 9

neurones

Answer 9

nerve cells (motor, sensory, relay)

Question 10

sensory neurones

Answer 10

bring impulses from receptors into CNS

Question 11

relay neurones

Answer 11

receive impulses from receptors in CNS

Question 12

motor neurones

Answer 12

carry impulses from CNS to effector organs

Question 13

function of cell body

Answer 13

dendrites receive nerve impulses, transmit along axon, contain nucleus + ribosomes for protein synthesis, contain mitochondria for ATP synthesis

Question 14

function of nucleus

Answer 14

DNA transcription

Question 15

function of dendrites

Answer 15

receive impulse from other neurones, carry impulse to cell body

Question 16

function of axon

Answer 16

transmits impulses away from cell body

Question 17

function of axon terminals

Answer 17

form synapses with other neurones

Question 18

function of myelin sheath

Answer 18

electrical insulator speeds up nerve impulse transmission, protects axon

Question 19

function of Schwann cells

Answer 19

wrap around axon to form myelin sheath

Question 20

function of nodes of ranvier

Answer 20

intervals between myelin sheath speed up nerve impulse transmission (impulses jump node to node = saltatory conduction)

Question 21

function of synaptic end bulb

Answer 21

swelling where neurotransmitter is synthesised

Question 22

resting potential definition

Answer 22

electrical potential difference found across membrane of resting neurone
membrane polarized -70mV, inside of membrane negative with respect to outside

Question 23

resting potential

Answer 23

Na+/K+ pumps, energy from ATP - 3Na+ out, 2K+ in per ATP hydrolysed
differential permeability of membrane to Na+ + K+ ions - some K+ channels open for K+ to diffuse out but most Na+ channels shut to prevent Na+ diffusing in
negative ions (anions) of large proteins + organic phosphates remain in cytoplasm

Question 24

action potential description

Answer 24

change in electrical charge which occurs across axon membrane when stimulated
membrane depolarised +40mV

Question 25

action potential

Answer 25

energy of stimulus above 'threshold' level causes sudden opening of some Na+ channels, voltage change makes many voltage-gated Na+ channels open, rapid influx of Na+ into axon depolarised membrane +40mV action potential established, Na+ channels close voltage-gated K+ channels open, K+ diffuse out rapidly, membrane repolarises potential difference overshoots below resting to -75mV (hyperpolarisation) - more K+ out than Na+ in refractory period - K+/Na+ pump restores ionic balance to resting where voltage-gated Na+ channels open producing new action potential (ensures impulse is unidirectional)

Question 26

all or nothing principle

Answer 26

applies to threshold potential nervous impulse either initiated or not (too small, no action potential) will always reach +40mV further increase in stimulus won't increase size of action potential but give more frequent action potentials

Question 27

factors that affect speed of nerve impulse

Answer 27

myelination - myelin insulates axon preventing depolarisation, nodes of ranvier have voltage gated ion channels for depolarisation, node to node (saltatory conduction) diameter - bigger diameter temperature - higher temp (more kinetic energy Na+/K+ diffuse more quickly)

Question 28

synapse

Answer 28

gap between neurones | transmits nerve impulses between neurones in one direction only

Question 29

synapse between neurone + muscle

Answer 29

neuromuscular junction

Question 30

transmission across most synapses is

Answer 30

chemical rather than electrical

Question 31

synapse labels

Answer 31

axon, pre-synaptic membrane, synaptic knob, calcium ions, mitochondrion, synaptic vesicle, neurotransmitters, Na+ ,synaptic cleft, acetylcholine receptor with ion channel, post-synaptic membrane, dendrite, myelin sheath

Question 32

process of synaptic transmission

Answer 32

action potential arrives at axon terminal depolorising pre-synaptic membrane Ca2+ channels open, Ca2+ ions rush into synaptic knob/axon terminal synaptic vesicles containing neurotransmitter (acetylcholine) fuse with pre-synaptic membrane acetylcholine released by exocytosis into synaptic cleft acetylcholine diffuses across synaptic cleft and binds to receptors on post-synaptic membrane Na+ channels in post-synaptic membrane open, Na+ ions enter + depolarise membrane depolarisation above threshold generates action potential in post-synaptic, nerve impulse transmits along axon acetylcholine broken down by acetyl cholinesterase in synaptic cleft, products (ethanoic acid + choline) diffuse back into axon terminal, ATP re-synthesises + packages acetylcholine into synaptic vesicles

Question 33

preventing merging of impulses

Answer 33

neurotransmitter reabsorbed so it can't bind to receptor molecules on post-synaptic acetyl cholinesterase catalyses hydrolysis of acetylcholine to form ethanoic acid + choline in synaptic cleft Ca2+ actively transported out of synaptic knob so no more exocytosis of acetylcholine can occur

Question 34

psychoactive drugs

Answer 34

e.g. cannabis + cocaine affect synapses THC in cannabis can increase/decrease release of neurotransmitters cocaine blocks re-uptake of proteins excitatory drugs (cocaine) increase post-synaptic transmission inhibitory drugs (cannabis) decrease transmission

Question 35

excitatory drugs

Answer 35

stimulate nervous system by creating more action potentials in post-synaptic membranes mimics neurotransmitters when binding to receptors on post-synaptic neurone drug blocks uptake of neurotransmitter in synaptic knob drug inhibits enzyme involved in breakdown of neurotransmitter

Question 36

inhibitory drugs

Answer 36

inhibit nervous system by creating fewer action potentials in post-synaptic membranes prevents release of neurotransmitter from pre-synaptic knob prevents entry of Ca2+ into pre-synaptic knob binds with receptors on post-synaptic membrane blocking normal transmitter binding

Question 37

organophosphorous (OP) insecticides

Answer 37

act as acetyl cholinesterase inhibitors in cholinergic synapse, insecticide combines with acetyl cholinesterase so it can't breakdown acetylcholine acetylcholine remains in synaptic cleft and on post-synaptic membrane causing repeated stimulation of post-synaptic neurone if at neuromuscular junction, repeated stimulation causes repeated contractions of muscle to occur