the nervous system.

introduction.

functions

• to collect information about the external and internal environment
• to process and integrate the information; relating to previous response/experiences
• to initiate response appropriate to the stimulus, thereby coordinating the organism's activity

organisation of the vertebrate nervous system

1. central nervous system (CNS) - brain and spinal cord
2. peripheral nervous system (PNS) - PNS made up of nerves and ganglia that carry signals into and out of CNS

the nature of the nerve impluse - series of electrical charges being passed along nerves

the resting potential

• under normal resting condition (neurone not stimulated), the inside of axon (axoplasm) is negatively charged w.r.t the outside (surrounding tissue fluid) due to the difference in chemical composition of potassium ions (K+), sodium ions (Na+), chloride ions (Cl-) and proteins
• potential diff. of about -65mV to -70mV is the resting potential of the axon
• [K+](inside) > [K+](outside) ; [Na+](inside) < [Na+](outside) , hence electrochemical gradient exist where [positive charges](inside) < [positive charges](outside)

what causes and maintain potential difference? (sodium-potassium gradient)

• sodium-potassium (Na-K) pump - transmembrane protein carrier/pump that transports Na+ out and K+ in. unequal transport; 3 Na+ out -- 2 K+ in
• selective permeability of memb to K+ than to Na+ - ions enter/leave cells by facilitated diffusion through specific transmembrane protein molecules; memb 20-25x more permeasble to K+ than to Na+, hence K+ ions tend to diffuse out
• = net effect is greater concentration of +ve ions outside the axon - membrane is polarised

action potential