Nervous System Flashcards
nervous system
detect stimuli, process information, initiate response
CNS
Central Nervous System = brain + spinal cord
PNS
Peripheral Nervous System = pairs of nerves from brain and spinal cord that contain sensory + motor neurones
basic nervous control mechanism
stimulus receptors (sensory neurones) CNS (motor neurones) effector (muscle/gland) response
reflex actions
rapid, involuntary, protective response to a stimulus
spinal cord
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
hydra
no CNS
sense receptors respond to limited number of stimuli
small number of effectors
nerve net
human
CNS
sense receptors respond to wide range of stimuli
large number of efectors
neurones
nerve cells (motor, sensory, relay)
sensory neurones
bring impulses from receptors into CNS
relay neurones
receive impulses from receptors in CNS
motor neurones
carry impulses from CNS to effector organs
function of cell body
dendrites receive nerve impulses, transmit along axon, contain nucleus + ribosomes for protein synthesis, contain mitochondria for ATP synthesis
function of nucleus
DNA transcription
function of dendrites
receive impulse from other neurones, carry impulse to cell body
function of axon
transmits impulses away from cell body
function of axon terminals
form synapses with other neurones
function of myelin sheath
electrical insulator speeds up nerve impulse transmission, protects axon
function of Schwann cells
wrap around axon to form myelin sheath
function of nodes of ranvier
intervals between myelin sheath speed up nerve impulse transmission (impulses jump node to node = saltatory conduction)
function of synaptic end bulb
swelling where neurotransmitter is synthesised
resting potential definition
electrical potential difference found across membrane of resting neurone
membrane polarized -70mV, inside of membrane negative with respect to outside
resting potential
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
action potential description
change in electrical charge which occurs across axon membrane when stimulated
membrane depolarised +40mV
action potential
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)
all or nothing principle
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
factors that affect speed of nerve impulse
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)
synapse
gap between neurones
transmits nerve impulses between neurones in one direction only
synapse between neurone + muscle
neuromuscular junction
transmission across most synapses is
chemical rather than electrical
synapse labels
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
process of synaptic transmission
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
preventing merging of impulses
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
psychoactive drugs
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
excitatory drugs
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
inhibitory drugs
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
organophosphorous (OP) insecticides
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
