Title: The nervous system 1 14 November 2018 Learning question: Can you describe the structure and function of the eye? Homework: study!

Learning Objectives Candidates should be able to: outline the organisation of the central nervous system and peripheral nervous system; (b) describe, with the aid of diagrams and photographs, the structure of the eye and outline the functions of its parts; (c) describe, with the aid of diagrams and electronmicrographs, the structure of the retina (including rods, cones, bipolar cells and ganglion cells); (d) describe, with the aid of diagrams, how a sensory receptor converts a stimulus into nerve impulses with reference to the rod cell in the retina;

Key words Rods Cones Retina Bibolar cell Ganglion Lamellae Synapses Rhodopsin Iodopsin Fovea centralis Macula Blind spot Amacrine cells Dendrites Axons

The structure of the eye

Cells in the eyes

Cells in the eyes Rods Cones Bipolar cells ganglion Good in dim light for night vision – do not detect colour Good in day light – detect colour Cells that form synapses with either rods or cones A type of neuron located near the inner surface of the retina . It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina amacrine cells.

Retina Light energy converted to action potentials that travel from the optic nerve to the brain Light has to travel through the lens, to the ganglion, amacrine and bipolar cells before it reaches rods and cones Only then are action potentials initiated and information sent to brain

Rods and Cones Make a table or list to show the similarities and differences between rod and cone cells.

Rods Cones Long cells with outer segment specialised for receiving light Shorter and broader cells. More tapered Formed from many discs, enclosed in membrane bound sac Membranes (lamellae) form a continuous folded surface Membranes contain the pigment visual purple Once a cone pigment is bleached, it takes 6 minutes to regenerate the pigment Inner segment forms synapses with other cells in retina Inner segment contains nucleus and mitochondria – proteins formed here. Passed to outer segment Inner segment contains nucleus and mitochondria – proteins formed here. Passed to outer segment Only contains pigment rhodopsin Contains 3 types of pigment, sensitive to different wavelengths of light; iodopsin Able to work at low light intensity because cells respond to a single photon of light Do not detect colour Detect colour

Macula and Fovea The macula contains the highest concentration of cones Fovea centralis at the centre of the macula only contains cones and no rods The area where there are no cones or rods carries information via neurones to optic nerve and then to the brain Light rays focused on this area are not transduced and the brain receives no information. This is known as the blind spot.

Bipolar cells Bipolar cells have two processes from central body Process nearest rods and cones are short and branch into many endings that form synapses with either Single cone cell Many rod cells

Ganglion cells Many dendrites that form synapses with bipolar cells This is where an action potential is first generated in the retina Amacrine cells have processes that spread horizontally. Their job is to connect bipolar cell axons with ganglion cell dendrites

Now complete questions 1 – 4 (a) (i) Using the letters, B, C, D or E, identify the following cells in Fig. 3.1. The light sensitive region of the eye is the retina. Fig. 3.1, below, shows a computer generated picture of cells in the human retina. Now complete questions 1 – 4 on page 217