Topic 8 - Coordination, Response and Gene Technology

Neurones carry electrical impulses. A cell body maintains the cell, an axon conducts the impulse and axon terminals connect with other cells; myelin insulates some axons so impulses jump between nodes of Ranvier.

Sensory neurones carry information from receptors to the CNS, relay neurones connect within the CNS, and motor neurones carry signals to muscles or glands. Their structures reflect these routes.

A myelinated axon can transmit faster because depolarisation occurs at nodes rather than along every section of membrane.

A nerve is a bundle of neurones, not one giant neurone. Do not infer function from myelination alone without identifying the pathway.

The basic pathway is stimulus → receptor → sensory neurone → CNS → motor neurone → effector. The CNS integrates information and the effector produces a response through muscle contraction or gland secretion.

Bright light activates retinal receptors; impulses reach the CNS and motor neurones stimulate circular iris muscles so the pupil constricts. In low light, radial muscles contract and the pupil dilates.

Antagonistic effectors allow opposite outcomes, while a rapid neural pathway limits exposure to harmful conditions.

A receptor detects a change but does not itself perform the response. Keep sensory input, CNS coordination and effector action distinct.

A reflex arc routes a stimulus from receptor through a sensory neurone and relay neurone in the CNS to a motor neurone and effector. The response is rapid and protective, reducing delay from conscious decision-making.

Synapses determine direction and integration, while antagonistic muscles can create the final movement. The brain can receive information about the stimulus even though the immediate arc is local.

Touching a hot surface activates pain receptors; flexor muscles contract and opposing extensors relax before the person consciously interprets the pain.

A reflex is not an absence of the brain and not every rapid movement is a simple spinal reflex. State receptor, CNS relay, effector and response.

When membrane depolarisation reaches threshold, voltage-gated sodium channels open and sodium ions enter. Potassium ions then leave to repolarise the membrane; the signal propagates as neighbouring sections reach threshold.

The all-or-nothing action potential is regenerated along the axon, so its amplitude does not fade with distance. Refractory periods help maintain one-way transmission.

A stronger stimulus is represented by more frequent action potentials, not a larger action potential, once threshold has been crossed.

Threshold is not a graded “bigger signal”, and ion movement is not the same as the whole impulse physically travelling as one sodium wave.

In a myelinated axon, the sheath insulates the membrane between nodes of Ranvier. Depolarisation is regenerated at the nodes, so the impulse appears to jump along the axon by saltatory conduction.

The insulation reduces ion leakage and increases conduction speed compared with a non-myelinated axon, where the membrane is activated continuously.

Damage to myelin can slow or disrupt signalling even when the axon and its cell body remain present, because the normal node-to-node pattern is lost.

Saltatory conduction does not mean the impulse skips the cytoplasm entirely, and a nerve is a bundle of axons rather than one myelinated cell.

An action potential opens calcium channels in the presynaptic knob. Calcium triggers vesicles to release neurotransmitter, which diffuses across the cleft and binds receptors on the postsynaptic membrane, opening ion channels.

Transmission is one-way because release and receptors are on opposite sides. Summation of repeated or converging inputs can bring the postsynaptic membrane to threshold.

At the pupil pathway, receptor impulses reach the CNS and motor neurones activate antagonistic iris muscles; synapses ensure the signal is routed rather than reflected backward.

Neurotransmitter does not electrically jump the cleft, and binding is not enough unless the postsynaptic effect reaches threshold.

A drug can increase or decrease synaptic transmission by changing neurotransmitter production, release, receptor binding, breakdown or reuptake. Its effect depends on the specific step and target.

Blocking serotonin reuptake leaves more transmitter in the cleft, whereas a receptor antagonist prevents the normal transmitter from activating the postsynaptic cell.

The same principle can produce therapeutic or harmful effects: L-dopa is converted to dopamine for Parkinson’s symptoms, while recreational drugs can disrupt mood and neural control.

A drug’s effect is not simply “more neurotransmitter = better”. Identify the receptor, transmitter and direction of change before predicting behaviour.

Rod cells are photoreceptors specialised for low-light detection. Absorbed light changes the photopigment and alters ion-channel activity, which changes neurotransmitter release onto the next neurone.

Rods are sensitive but do not provide colour discrimination; their convergence improves sensitivity while reducing spatial resolution. The retina therefore transforms light into a pattern of neural signals.

In dim light, rods can detect movement at the edge of vision, whereas bright-light colour and fine detail depend more on cone pathways.

A rod cell does not send light itself and “more rods” does not guarantee sharper vision. Keep photoreceptor transduction separate from CNS interpretation.

Habituation occurs when repeated harmless stimulation produces a smaller response. The animal saves energy because fewer calcium ions enter the presynaptic neurone, less neurotransmitter is released and the postsynaptic cell is less likely to reach threshold.

A snail may take less time to re-emerge after repeated gentle touches. If the sound or touch becomes stronger, the response can return because the stimulus is no longer identical.

The change is in synaptic transmission, not a loss of all sensory ability. The animal can still respond when the stimulus becomes relevant.

Habituation is not fatigue, permanent damage or forgetting every similar stimulus. Control stimulus intensity and use a consistent endpoint when measuring it.

The central nervous system (CNS) is the brain and spinal cord; the peripheral nervous system (PNS) carries information between the CNS and receptors or effectors. Sensory and motor pathways connect the two.

This division separates integration from transmission. A receptor detects a stimulus, the CNS coordinates a response, and motor neurones carry the output to muscles or glands.

A skin receptor sends an impulse through a sensory neurone in the PNS to the spinal cord; a motor pathway then activates an effector.

The PNS is not only voluntary movement, and the CNS is not simply a cable. Identify the direction and function of each pathway.

Phytochrome exists as inactive Pr and active Pfr. Red light converts Pr to Pfr; far-red light converts Pfr back to Pr. The balance changes with day and night length and can switch flowering genes on or off.

In a long-day plant, short nights leave more Pfr, which activates gene expression leading to flowering. A far-red pulse can reverse the conversion and alter the response.

The pigment is a reversible sensor: the plant responds to the light history and duration of darkness, not simply to daytime brightness.

“Long-day” describes short-night flowering, and Pr/Pfr are pigment states rather than hormones. Keep light wavelength, pigment form and gene expression distinct.

During germination, gibberellin signalling stimulates aleurone cells to produce amylase. Amylase hydrolyses starch in the endosperm to soluble sugars that the embryo can respire and use for growth.

Compare germinating and non-germinating grains or vary a condition while controlling temperature, water and time. Measure reducing sugar or iodine-starch change with suitable repeats and controls.

A grain with active amylase loses the blue-black iodine colour as starch falls and gains soluble sugar; that sugar supports respiration rather than being “new starch”.

Iodine detects starch, not amylase directly, and a colour change needs a controlled comparison. Do not infer enzyme activity from germination alone.

Nervous control uses rapid electrical impulses and targeted neurotransmitter release; hormonal control uses chemicals carried in blood, usually with slower onset and longer-lasting, broader effects. Both use receptors, coordination centres and effectors.

A reflex can move a hand away quickly, while adrenaline or thyroxine changes metabolism across several tissues. The best system depends on speed, duration and distribution.

The systems can interact: neural signals can trigger hormone release, and hormones can alter the sensitivity or activity of nervous tissues.

Hormones do not always act slowly and nerves do not always produce a brief response. Compare route, target, timing and persistence rather than memorising a single slogan.

Brain regions specialise in tasks such as sensory processing, movement, coordination, memory and endocrine control, but behaviour emerges from networks rather than one isolated “on/off” centre.

A motor area can initiate movement while the cerebellum coordinates timing and the brainstem regulates vital functions; damage to one region can be partly compensated by connected circuits.

Functional evidence from lesions, imaging and stimulation must be interpreted with anatomy and task demands together.

A labelled brain map is not proof that one region alone causes a behaviour. Avoid deterministic localisation when the evidence shows distributed processing.

Brain imaging methods answer different questions: structural scans show anatomy, while functional methods track activity or blood flow during a task. The interpretation depends on timing, resolution and the comparison condition.

A region that is more active during a task may be involved without being the only cause. Converging evidence from lesions, stimulation and behaviour strengthens a localisation claim.

If a motor task increases activity in a cortical area compared with a matched rest condition, the result supports involvement; it does not prove that the area alone controls movement.

Correlation between activity and a task is not proof of a single function, and an image is not a diagnosis without clinical context.

Some disorders are associated with altered neurotransmitter levels or signalling. Parkinson’s involves reduced dopamine from lost neurones; antidepressant drugs can increase serotonin or noradrenaline signalling.

A drug may mimic a transmitter, supply a precursor, block breakdown or inhibit reuptake. These mechanisms change synaptic transmission, but symptoms usually involve networks and multiple contributing factors.

L-dopa is converted into dopamine in the brain, while an SSRI reduces serotonin reuptake so more remains in the synaptic cleft.

“Low neurotransmitter causes the disorder” is stronger than the evidence usually supports. Distinguish an association, a treatment mechanism and a complete explanation.

A desired gene is isolated, amplified and joined to a plasmid vector using restriction enzymes and ligase. The recombinant plasmid enters a microorganism, which is cultured in a fermenter to make the protein for purification.

Microbes grow rapidly and express the inserted gene at scale. The final product must still be isolated, purified and checked for safety and function.

A bacterial plasmid carrying the human insulin gene allows cultured bacteria to produce insulin, which is purified rather than administered with the whole bacterial culture.

A vector carries DNA but does not guarantee correct expression or a safe product. Separate gene insertion, culture, purification and quality control.

Recombinant DNA is formed when DNA from different sources is joined. A restriction enzyme cuts the desired gene and vector, complementary ends pair, and DNA ligase seals the sugar-phosphate backbone.

PCR can amplify the target before insertion, while a plasmid provides replication or expression signals in the host. The construct must be introduced into cells and selected or screened.

A gene coding for insulin can be joined to a bacterial plasmid; the plasmid is then transferred into bacteria where the gene may be expressed.

Cutting DNA is not the same as expressing it. A recombinant construct needs a compatible host, promoter and verification before useful protein is produced.

A recombinant plasmid or vector must enter a suitable host cell. Selection or screening distinguishes cells that received the construct, after which expression and product quality can be tested.

Transformation is only the entry step: culture conditions, selectable markers, gene orientation and host machinery affect whether the target protein is made.

A bacterial colony carrying the plasmid may grow on selective medium, but protein assays are still needed to show that the inserted gene is expressed correctly.

Antibiotic resistance as a marker does not prove therapeutic protein production, and a vector is not itself the finished medicine.

A microarray uses labelled nucleic acids from samples to measure which genes are expressed relative to a reference. Complementary binding at spots produces a pattern that can be compared between tissues or conditions.

The result is a relative expression profile, not a direct measurement of every protein or a guaranteed cause. Controls, normalisation and probe specificity determine how confidently differences can be interpreted.

A gene spot with stronger signal in diseased tissue suggests higher transcript abundance, but follow-up experiments are needed to test whether the gene drives the phenotype.

A microarray signal is not automatically protein activity, and a difference in expression is not proof of causation.

Bioinformatics uses databases and computational tools to compare DNA, RNA or protein sequences, predict relationships and identify patterns. The output depends on the input sequence, reference database and comparison method.

Check alignment quality, sequence length, conserved regions and the scoring or statistical assumptions before interpreting a match.

A high sequence similarity can support common ancestry or a shared function, while a low-quality or partial sequence may produce a misleading result.

A database hit is not proof of function or causation. Distinguish similarity, homology, prediction and experimental confirmation.

Genetic modification can add a useful characteristic, such as producing a medicine or resisting a pest. Its value depends on effectiveness, containment, ecological effects, ownership, welfare and who receives the benefit.

Benefits may include reliable therapeutic protein production or reduced losses; risks include unintended gene flow, resistance, ecological disruption and ethical objections to animal or food applications.

A GM microorganism making insulin is contained and purified, whereas a GM crop releasing a trait into wild relatives raises a different monitoring problem.

“GM” is not automatically safe or harmful. Judge the specific organism, gene, environment and evidence rather than using a blanket claim.