Young, John Zachary


John Zachary Young (1907–1997) was a British zoologist and anatomist, pioneer of the experimental study of the cellular bases of learning and memory and of British brain science. He discovered the giant axon of the squid, which was to become the most successful experimental model for the study of the nerve impulse mechanism and of the physicochemical properties of neuron membranes. His work on learning and memory in Octopus vulgaris represents one of the earliest attempts of employing simple experimental systems in the study of complex mental functions.

Keywords: brain; learning and memory; invertebrate models; neuroscience; medical education

Figure 1.

Transverse section of a pallial nerve of Loligo forbesii (squid). The larger circles (g.f.a and g.f.2a–c) are the giant fibres, surrounded by a bundle of smaller ones (smaller circles, unmarked). Reproduced from Young (), plate 45, Figure 38. © Royal Society Publishing.

Figure 2.

Arrangement of the giant fibre system, connecting the central nervous system of the squid to the mantle, and controlling the contraction of the muscles of the mantle and funnel. The whole system is controlled by two large cells in the lobus magnocellularis, just beneath the oesophagus (g.c.1 in the image). These cells are activated by impulses from sensory centres (eyes, statocyst and skin) and from the higher ‘brain’ centres. Their axons fuse completely in a first‐order giant fibre (interaxonic bridge marked with b) in their proceeding away from the lobe and towards the stellate ganglion (st.g.), where they make synaptic contact with the proceedings of several smaller neurons (second‐order giant cells – g.c.2). In the stellate ganglion, the second‐order fibres make many synapses with the axons of the third‐order giant cells (g.c.3), whose axons fuse in syncitia and finally reach the mantle muscle. The scheme is complicated by a number of intermediary connexions with other nerve cells controlling the funnel, to guarantee the maximum of integration and speed in the contraction of the mantle and in the ejection of streams of water from the funnel. Given that a squid has to respond as a whole to stimuli coming from either side, the fusion of the axons allows for a quicker response. Moreover, given that in the squid, like in all invertebrates, nerve fibres are not coated in an isolating myelin sheath (which increases conduction speed), the unusual dimension of the axons guarantees very fast transmission of the impulse. All this allows the animal to perform very sudden movements, although not finely graded ones. Diagram taken from Young (), p. 469, Figure 2. © Royal Society Publishing.

Figure 3.

J.Z. Young recording his second BBC Reith Lecture (1950). The Reith Lectures were instituted in 1948 to honour the first director general of the Corporation, Sir John Reith, and “to advance public understanding and debate about significant issues of contemporary interest”. © Young family.



Boycott BB and Young JZ (1955) A memory system in Octopus vulgaris Lamarck. Proceedings of the Royal Society B 143: 449–480.

Young JZ (1939) Fused neurons and synaptic contacts in the giant nerve fibres of cephalopods. Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences 229(564): 465–503.

Further Reading

Boycott BB (1998) John Zachary Young. Biographical Memoirs of the Fellows of the Royal Society of London 44: 485–509.

Bullock TH and Quarton GC (1965) Simple systems for the study of learning mechanisms. Neurosciences Research Program Bulletin 4(2): 106–233.

Rose S (1993) The Making of Memory: From Molecules to Mind. New York: Bantam Books.

Sanders GD (1975) The cephalopods. In: Corning WC, Dyal JA and Willows AOD (eds) Invertebrate Learning, p. 139–145. New York: Plenum Press.

Young JZ (1950) The Life of Vertebrates. Oxford: Clarendon Press.

Young JZ (1964) A Model of the Brain. Oxford: Clarendon Press.

Young JZ (1971) An Introduction to the Study of Man. Oxford: Clarendon Press.

Young JZ (1975) John Z. Young. In: Squire L (ed.) History of Neuroscience in Autobiography, p. 554–586. Washington DC: The Society for Neuroscience.

Young JZ (1975) Sources of discovery in neuroscience. In: Worden F, Swazey JP and Adelman G (eds) The Neurosciences: Paths of Discovery, p. 15–46. Cambridge, Massachusetts and London: MIT Press.

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De Sio, Fabio(Jan 2014) Young, John Zachary. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0023950]