chapter 15- nervous coordination and muscles Flashcards
compare hormonal and nervous system
h:communication by hormones, n:communication by nerve impulses
h:slow transmission n:fast transmission
h: transmission by blood system n: transmission by neurones
h: effects are longer lasting than n
structure of a motor neurone
cell body-associated with the production of proteins including neurotransmitters
dendrons- extensions of the cell body which divide into dendrites that carry nerve impulses towards the cell body
axon- single long fibre that carries nerve impulses away from the cell body
Schwann cells- surround the axon providing electrical insulation
myelin sheath- forms a covering to the axon- APs cannot be produced here
nodes of ranvier- gaps between Schwann cells where there is no myelin sheath. APs can be generated here
how is the resting membrane potential maintained.
sodium potassium pump
potassium ions actively transported in and sodium ions actively transported out
3 sodium ions transported out for every 2 potassium actively transported in
how is an action potential produced
- at resting potential some voltage gated sodium ion channels are closed
- energy of stimulus is detected by receptors causing some channels to open and sodium ions diffuse into axon down electrochemical gradient causing resting membrane potential to become more positive
- more sodium ion channels open so more sodium ions diffuse into axon. Positive feedback
- once membrane action potential reaches around +40 the sodium ion channels close and potassium ion channels open
- potassium ions diffuse out of the axon which causes repolarisation of the axon
- the outward diffusion of these potassium ions causes a potential overshoot of the electrical gradient with the inside of the axon being more negative than usual (hyper polarisation)
- gates on potassium ion channels close and the sodium potassium pump re-establishes the resting membrane potential
define an action potential
a wave of depolarisation followed by a wave of depolarisation, travelling along a neurone
passage of an action potential along a myelinated neurone
myelin prevents APs from forming
action potential jump from node to node in a process called saltatory conduction
APs travel along neurone faster than in unmyelinated neurone as depolarisation doesn’t have to occur along the whole length of the neurone
how does axon diameter affect the speed of the action potential
the greater the diameter, the faster the speed of conductance. This is due to less leakage of ions
how does temperature affect the speed of action potentials
As temp increases the diffusion of ions increases so speed of nerve impulse increases. This is because the energy for active transport comes from respiration . Respiration happens more rapidly at higher temperatures because enzymes function more rapidly
all or nothing principle
when threshold has been reached an action potential will be genrated of the same size
below threshold value means no action potential
how can an organism distinguish between different stimulus intensities
larger stimulus = greater frequency of impulses
by having different neurones with different threshold values
what is the refractory period
period after an action potential when inward movement of sodium ions is prevented because the voltage gated channels are closed. During this time it is impossible for another action potential to be generated
what are the purposes of the refractory period
- ensures that action potentials are propagated in one direction only. APs cannot move in refractory direction so only move forwards
- produces discrete impulses. an action potential cannot be formed immediately behind the first one so action potentials are separated from one another
- limits the number of action potentials that can pass along an axon in a given time as they are separated from one another so limits the strength of stimulus that can be detected
what is spatial summation
number of different pre-synaptic neurones together release enough neurotransmitter to exceed the threshold value of the post synaptic neurone to produce a new action potential
what is temporal summation
a single pre-synaptic neurone releases neurotransmitter many times over a very short period. If the concentration of neurotransmitter exceeds the threshold value of the post- synaptic neurone then a new action potential is produced
how do inhibitory synapses work
- presynaptic neurone releases a neurotransmitter that binds to chloride ion protein channels
- chloride ion protein channels open
- chloride ions diffuse into post synaptic neurone by facilitated diffusion
- binding on the neurotransmitter causes potassium ion channels to open
- potassium ions move out of the post-synaptic neurone into the synapse
- this makes the inside of the post-synaptic membrane more negative and the outside more positive
why do these synapses make it less likely that a new action potential will be produced
membrane potential increases
larger influx of sodium ions needed to produce an action potential
describe the process of transmission across a cholinergic synapse
- AP at presynaptic knob causes calcium ion channels to open and calcium ions enter the pre-synaptic knob by FD
- Causes synaptic vesicles to fuse with pre-synaptic membrane, releasing acetyl choline into synaptic cleft
- Diffuses across cleft and binds to receptors on sodium ion channels on post-synaptic membrane, causing channels to open and sodium ions diffuse into post-synaptic neurone
- this creates a new action potential in the post-synaptic neurone
- acetylcholine is hydrolysed into choline and ethanoic acid which diffuse back across the synaptic cleft into pre-synaptic neurone. This prevents it from generating a new action potential
- ATP used to recombine choline and ethanoic acid
microscopic structure of skeletal muscle
actin- thinner
myosin-thicker
I bands appear lighter as thick and thin filaments do not overlap
A bands appear darker as thick and thin filaments overlap in this region
at the centre of the A band is the H zone which is a lighter region
At the centre of each I band is the Z line
slow twitch fibres
-contract slowly and produce less powerful contractions but over a longer period than fast twitch
- large store of myoglobin that stores oxygen
- a large supply of blood vessels that deliver oxygen and glucose for aerobic respiration
- numerous mitochondria to produce ATP
fast twitch fibres
- contract more rapidly and more powerful contractions for shorter periods of time than slow twitch
- thicker and more numerous myosin filaments
- high conc of glycogen
- respire anaerobically which provides ATP rapidly
- store of phosphocreatine which can rapidly generate ATP from ADP in anaerobic conditions so provide energy for muscle contraction
similarities between neuromuscular junctions and synapses
- have neurotransmitters that are transported by diffusion
- have receptors that on binding with neurotransmitters cause and influx of sodium ions
- use a sodium-potassium pump to depolarise the axon
- use enzymes to break down the neurotransmitter
differences between neuromuscular junctions and synapses
NMJ: only links neurones to muscles S: links neurones to neurones or neurones to other effector organs
NMJ: only motor neurones involved
S: motor and sensory neurones involved
NMJ:action potential ends here
S: new action potential produced in another neurone
changes that occur to sarcomere when muscle contracts
I band decreases
Z line moves closer together
H zone decreases
A band stays the same
evidence for sliding filament theory
A band stays the same
Length of a band is the length of myosin filaments
myosin filaments have not become shorter so filaments themselves can’t be shortening
