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
what is spatial summation?
many different neurones collectively trigger a new action potential by combining the neurotransmitter the release to exceed threshold
what is temporal summation?
a single neurone releases neurotransmitter many times over a short period which add up to enough to exceed threshold
how to inhibitory synapses function?
presynaptic neurone releases a neurotransmitter that binds to chloride ion protein channels on postsynaptic membrane
causes chloride channels to open
chloride ions move into postsynaptic neurone
binding of neurotransmitter causes opening of potassium channels
potassium ions move out of neurone
negatively charged chloride ions moving in and positively charged potassium ions moving out makes it more negative so its harder to reach threshold
what is a cholinergic synapse?
neurotransmitter is acetylcholine
what are the three types of muscle in the body?
cardiac muscle: in the heart
smooth muscle: walls of blood vessels and gut
skeletal muscle: attached to bone and acts under voluntary control
general structure of skeletal muscle
made up of many myofibrils which are collectively very powerful
separate cells fused together into muscle fibres, they share nuclei and cytoplasm, calles sarcoplasm, large conc of mitochondria and ER
what are the main types of protein that make up myofibrils?
actin: thinner and consists of two strands twisted around one another
myosin: thicker and consists of long rod-shaped tails with bulbous heads
microscopic structure of myofibril
I bands: lighter because filaments don’t overlap, only actin
A bands: darker because actin and myosin overlap
H-zone: only myosin, but no heads
Z line: end of each sarcomere
how do skeletal muscles occur?
antagonistic pairs which pull in opposite directions, when one is contracted the other is relaxed
why do muscle occur in antagonistic pairs?
muscles can only pull, can only move in one direction
evidence for the sliding filament mechanism
when a muscle contracts:
I-band becomes narrower
Z-lines move closer together (sarcomere shortens)
H-zone becomes narrower
evidence for the sliding filament mechanism
when a muscle contracts:
I-band becomes narrower
Z-lines move closer together (sarcomere shortens)
H-zone becomes narrower
what is tropomyosin?
long thin threads that are wound around actin filaments
the sliding filament mechanism
1) tropomyosin prevents myosin head from attaching to binding site on actin
2) calcium ions released from ER cause tropomyosin to change shape, uncovering binding sites
3) myosin head forms cross bridges with actin
4) head pulls actin over myosin, ‘power stroke’, ADP molecule released
5) new ATP attaches to myosin head, causing it to detach
6) hydrolysis of ATP to ADP provides energy for head to ‘re-cock’
7) myosin head reattaches to binding site further along actin
what happens during muscle relaxation?
calcium ions are actively transported back into endoplasmic reticulum using energy from hydrolysis of ATP
reabsorption of calcium ions allows tropomyosin to block actin filament again
myosin heads unable to bind to actin so can’t contract
what are the two types of skeletal muscle?
slow-twitch fibres
fast-twitch fibres
what is myoglobin?
respiratory protein found in slow-twitch fibres that has a high affinity for oxygen (stores oxygen)
comparison of slow-twitch and fast-twitch fibres
slow-twitch darker colour, high conc of myoglobin, fast-twitch lighter colour, low conc of myoglobin
slow-twitch used for endurance activity, contracts slowly and fatigues slowly, fast-twitch used for rapid bursts of activity, contracts quickly and fatigues quickly
slow-twitch uses aerobic respiration, high density of mitochondria, fast-twitch uses anaerobic respiration, low density of mitochondria
comparison of cholinergic synapse and neuromuscular junction
both unidirectional
neuromuscular only excitatory, cholinergic excitatory or inhibitory
neuromuscular connects motor neurone to muscles, cholinergic connects two neurones
neuromuscular is end point for action potential, cholinergic new action potential generated in next neurone
