15 nervous coordination Flashcards
what are the two main forms of coordination in animals?
the nervous system
the hormonal system
what is the nervous system?
uses nerve cells to pass electrical impulses along their length, rapid but responses are short lived and restricted to a localised region of the body
what is the hormonal system?
produces chemicals that are transported in the blood plasma to their target cells, slower less specific form of communication but results are long lasting and widespread
what are neurones?
specialised cells adapted to rapidly carrying nerve impulses
what are the structural components of a neurone?
cell body - contains nucleus and other organelles
axon - carries impulses away from cell body
dendrites/dendrons - carry impulses towards cell body
myelin sheath - made of Schwann cells, protects and insulates
nodes of ranvier - constrictions between Schwann cells where no myelin sheath
what is the resting potential in humans?
-65mV
inside membrane negative outside positive
what is resting potential?
electrochemical gradient between the inside and the outside of the axon, sodium ions outside, potassium ions inside
what maintains resting potential?
active transport - sodium potassium pump, for each ATP molecule 3 Na+ pumped out and 2Na+ pump in
unequal facilitated diffusion - more leaky potassium channels than sodium channels so potassium diffuses out faster than sodium diffuses in
what is an action potential?
the nerve impulse, a rapid reversal of the resting potential
what are the main stages of an action potential?
depolarisation
repolerisation
hyperpolarisation
return to resting potential
what occurs during depolarisation?
some voltage gated sodium channels open causing more to open allowing sodium ions to diffuse in
positively charged so trigger a reversal in the potential difference
what occurs during repolarisation?
once an action potential of +40mV is reached sodium channels close and potassium channels open
positively charged potassium ions diffuse out
what occurs during hyper polarisation?
diffusion of potassium ions causes a temporary overshoot
are resting and action potentials active or passive processes?
resting potential - active
action potential - passive
why is an action potential self-propagating?
the depolarisation of one region of an axon will immediately cause the depolarisation of the next region
what is the role of the myelin sheath?
electrical insulation
physically protect
speed up transmission of nerve impulse
what is saltatory conduction?
when nerve impulse jumps from one node to the next
what factors affect the speed of conductance of a nerve impulse?
saltatory conduction along myelinated neurones
wider axon diameter, less leakage of ions
temperature, high increases enzyme activity, too high denatures them
what is the all or nothing principle?
if the potential generated reaches the threshold value an action potential is generated
if the generator potential is not large enough there is no action potential
all action potentials are the same size
what is the refractory period?
after an action potential is created there is a period when sodium voltage gated channels are closed making it impossible to create an action potential
what are the purposes of the refractory period?
ensures that action potentials are propagated in one direction only
produces discrete impulses, separates action potentials from each other
limits the number of action potentials
what is a synapse?
the point where one neurone communicates with another or with an effector
what are the structural components of a synapse?
presynaptic membrane postsynaptic membrane synaptic knob synaptic cleft vesicles
what are key features of synapses?
unidirectional - impulse can only pass one way
inhibitory - some synapses make it less likely a new action potential will be created
summation - combine to generate an impulse
