Topic Nervous Control / Homeostasis Essay - Main Points!

Q) Distinguish between endocrine system and nervous system

Main points
Key idea:	Nature & mode of transmission
Endocrine sys: · Info transmitted chemically · Hormones secreted directly into bloodstream, transported throughout body, regulate activities of target cells upon arrival Nervous sys: · Info transmitted electrically · Nerve impulses travel along nerve axons to a particular destination in body · But transmission of information a/x a synapse occurs chemically (i.e. neurotransmitter)
Key idea:	Nature of the signal molecule
Endocrine sys: · Many types of hormones present (each affecting specific tissues) Nervous sys: · Fewer types of signal mol (e.g. acetylcholine, noradrenaline)
Key idea:	Nature of response
Endocrine sys: · Graded response as strength of cellular response may be due to amount of hormone secreted by endocrine gland · Strength of cellular response subjected to regulation of activities of relay mol along signal transduction pathways in target cells (i.e. ‘cross-talk’ b/w diff signal transduction pathways) Nervous sys: · Action potential follows all-or-nothing principle · If stimulus is strong enough to achieve threshold potential, an AP of a fixed magnitude will be achieved
Key idea:	Speed and duration of effect
Endocrine sys: · Speed is generally slow but long lasting effect (e.g. growth and development). Nervous sys: · Rapid but generally short-lived (e.g. withdrawal from a hot object).
Key idea:	Location of effect
Endocrine sys: · Generally widespread as blood able to transport hormones to target tissues or organs   Ref to which may be located far fr each other and fr source of the hormone Nervous sys: · As nerve impulses travel along nerve axons to a part destination in body, effect is localized (e.g. contraction of a particular muscle gp in one part of the body)
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations e.g. AP – action potential) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)

Topic Nervous Control Essay - Main Points!

Q) Give possible reasons for the unidirectional transmission of impulse across a synapse

Main points
Key idea:	Synaptic transmission is unidirectional
·  Reasons : (i) Nerve impulses travel only in one direction along axon of pre-synaptic neurone due to refractory period (ii) Ca2+ channels & vesicles containing neurotransmitters only found in synaptic knob of pre-synaptic neurone but absent in post-synaptic neurone ; hence, neurotransmitters can only diffuse a/x synaptic cleft in one direction (iii) Receptors only found on post-synaptic side of synapse
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)

Topic Nervous Control Essay - Main Points!

Q) Describe synaptic transmission

Main points
Key idea:	What is a synapse
· A junction b/w two neurons or b/w a neuron and and effector (muscle or gland) for the purpose of transfering information
Key idea:	Role of Ca2+
· Initially, little amount of Ca2+ in synaptic knob · Arrival of an action potential (AP) depolarizes pre-synaptic membr, Ca2+ channels open, influx of Ca2+ into synaptic knob, synaptic vesicles fuse with pre-synaptic membr, release neurotransmitters (e.g. acetylcholine) into synaptic cleft · Neurotransmitters diffuse a/x synaptic cleft, bind to receptor-linked ion channels on postsynaptic membr · Ion channels open, influx of Na2+ into post-synaptic neurone, depolarizes post-synaptic membr, generates AP if threshold value is reached
Key idea:	Breakdown and synthesis of acetylcholine
· Acetylcholinesterase breaks down acetylcholine into choline + acetate · Return to synaptic knob, re-form acetylcholine + re-packed into synaptic vesicles · Removal of acetylcholine causes postsynaptic membr to repolarize
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Deplorization of post-synaptic membrane is weak; requires temporal or spatial summation of excitatory potentials (v) The transmission of a nerve impulse across a synapse is slower than the transmission of a nerve impulse (propagation of action potential) along the axon. Compare and contrast between these two types of transmission

Topic Nervous Control Essay - Main Points!

Q) Describe how nerve impulse travels along the axon of a myelinated neurone

Main points
Key idea:	Explain resting potential (-70mV) of neurone
· Resting potential -70mV · Axoplasm of neurone more –ve charged than tissue fluid · Reasons : (i) Na/K pumps - actively transport 3 Na+ out, 2 K+ into cell per ATP hydrolyzed (ii) membr more permeable to 2 K+ than Na+
Key idea:	Generation of action potential at Node of Ranvier
· Action potential (AP) generated only at a node of Ranvier as other areas of neurone are insulated by myelin sheath · AP - rapid change in potential diff a/x axon membr · 3 stages – depolarization, repolarization and hyperpolarization.
Key idea:	Na+ channels during depolorization
· Na+ channels open, influx of Na+, down conc gradient, into axoplasm · Membr potential becomes less -ve until threshold potential (e.g. -55mV) · More Na+ channels open, greater influx of Na+ · Membr potential changes from -70 to +40mV (i.e. depolarization)
Key idea:	Influx of Na+ at node of Ranvier depolarizes next node of Ranvier
· Inside of neurone at point of stimulus is more +ve charged than outside · But, next node of Ranvier still at resting potential · Creates a local electrical circuit, allows Na+ to diffuse to next node causing Na+ channels open, influx of Na+ ; hence deplorization, new AP generated · Another new local electrical circuit is established b/w newly depolarized portion of axon and next node · Hence, AP ‘jumps’ from one node to another (i.e. saltatory conduction)
Key idea:	Unidirectional movement of nerve impulse along axon
· At original point of impulse, Na+ channels close, K+ channels open, efflux of K+, down its conc gradient, out of the neurone ·  Restores resting potential as membr potential changes fr +40mV back to -70mV · K+ channels slow in closing, membr potential turns more -ve than -70mV (hyperpolarization) before resting potential is restored · Ref to refractory period where no new AP can be generated in response to a new stimulus · Result: unidirectional movement of nerve impulse
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) The transmission of the action potential can be described as a wave of depolarization transmitted in one direction over infinite distance of the neurone with no change in speed and amplitude