Understanding the Nervous System - WJEC A Level Biology 3.8

Key Point: The reflex arc bypasses your brain for super-quick responses, going straight through your spinal cord from sensory to motor neurones via relay neurones.

Key Point: The lack of directional control in nerve nets shows why having specialised neurone types and a CNS gives us such precise responses.

Key Point: The specific positioning of cell bodies in different regions ensures signals flow in the right direction for effective reflexes.

Key Point: The refractory period ensures action potentials only travel in one direction and prevents the neurone from being over-stimulated.

Key Point: The all-or-nothing principle prevents minor stimuli from overwhelming your nervous system while ensuring important signals always get through clearly.

Key Point: Myelinated neurones with large diameters in warm conditions transmit impulses fastest - which is why your major motor and sensory pathways are heavily myelinated.