Flashcards in Biology Deck (147)
How does the motor end /neuromuscular junction depolarise the muscle fibre ?
When action potential arrives at the synapse they cause calcium ions to leak/enter into the synaptic knobs
Causes release of acetylcholine from the synaptic knobs
Attaches to receptions on sarcolemma
Making it permeable to sodium ions
Rush into fibre causing depolarisation
Explain briefly how part G depolarises the muscle fibre.
when action potentials arrive at the synapse they cause calcium ions to leak/enter into the synaptic knobs; (this) causes release of acetylcholine from the synaptic knobs;
this attaches to receptors on the sarcolemma;
making it permeable to sodium ions;
so that they rush into the fibre causing depolarisation;
State one function of each of the parts labelled Dendrite, Myelin sheath and Schwann Cell
A- receives action potentials from preceding/relay/intermediate/connector neurones;
B- insulates axon causing saltatory conduction;
C -secretes the myelin;
Distinguish between parts Grey matter (A) and White matter (B)
A consists of non-myelinated relay neurones running across the spinal cord; B consists of myelinated relay neurones running up and down the spinal cord;
What neurones carry impulses to muscles and glands
What neurones carry impulses from receptors to the central nervous system
In resting nerve fibre what is there a lower concentration of?
Low sodium levels is a result of what?
due to the actions of a sodium pump in its membrane
How is the resting potential described at rest in comparison with the outside?
Negative resting potential
When does depolarisation occur
Depolarisation occurs when the membrane permeability is changed by a stimulus allowing sodium ions to flood in
when will the depolarisation be propagated along the fibre?
If the depolarisation reaches a threshold value
In some fibres an insulating layer of myelin allows the depolarisation to jump between ..................................................
Impulses are propagated across synapses by release of .........................................
acetylcholine release is triggered by an inflow of ............................................ ions
How is a resting potential generated
axon membrane is impermeable to sodium ions but permeable to potassium ions;
sodium pumped out of axon to surrounding tissue fluid;
thus there is a lack of positive ions within the axon which tends to draw potassium ions in; this inflow of potassium is also supplemented by a weak potassium pump;
however, inflow of potassium ions cannot quite catch up with outflow of sodium ions;
and so inside stays negative with respect to outside;
ATP required to allow pumps to work;
Where are paccinian corpuscles found?
Where are beta cells found?
Islets of Langerhan
What are found in islets of langerhan
What do Beta cells do?
raise blood glucose level
What is the threshold stimulus
the smallest stimulus that is capable of setting up an action potential;
Describe what is happening when potential difference in increasing
stimulus makes axon membrane become permeable to sodium ions; these flood into the axon along the diffusion gradient;
thus polarity of membrane reverses to give action potential;
What happens when the potential difference begins to fall again?
too many positive ions are inside the axon at this stage;
membrane is now super permeable to potassium which floods out of axon along (electrical) gradient;
thus potential across membrane reverses back to resting value, (although correct ionic balance is not yet restored);
Describe how action potentials are propagated along the axon during nerve impulse transmission.
propogated by local currents;
electron flow occurs at margins of depolarised (+) and resting/repolarised (-) regions;
these currents make next bit of axon membrane permeable to sodium ions and so region of depolarisation spreads;
Why do synaptic knobs contain many mitochondria?
to provide energy for active absorption of acetate/choline into the knobs;
for combining acetate and choline/to make acetylcholine/synthesis of acetylcholine;
Briefly describe how the arrival of an impulse at the synapse causes depolarisation of the post-synaptic membrane.
calcium ions enter synaptic knobs;
and attract vesicles to the pre-synaptic membrane;
these fuse with the membrane and release acetylcholine;
this attaches to receptors on post synaptic membrane;
making it become permeable to sodium ions;
these rush into the muscle fibre along the concentration gradient;
this alters the potential across the sarcolemma/membrane resulting in an action potential;
(iii) How does the post-synaptic membrane become repolarised?
acetylcholine esterase enzyme is released as soon as the muscle is depolarised; this removes the acetylcholine from the receptors;
by hydrolysing/splitting it into acetate and choline;
thus membrane of muscle reverts to being impermeable to sodium ions;resting potential is restored;
How does an adrenergic synapse differ from a cholinergic synapse?
the transmitter substance is nor-adrenaline;the enzyme which removes it from the receptors is mono-amine oxidase;
(ii) Where are adrenergic synapses found in the body?
(ii) in the sympathetic nervous system;
(ii) Distinguish negative feedback control from positive feedback control.
negative feedback control is when a varying physiological value is returned to its mean value by the controlling mechanism (credit example. eg. sweating to reduce body temperature);
positive feedback control is when a physiological value is pushed above its mean value by the controlling
mechanism (credit example eg. increased uterine contractions in birth);