14.3 Reflex Arc

Nervous Organisation

  • Central nervous system (%%CNS%%): %%brain and spinal cord%%
  • Peripheral nervous system (%%PNS%%): %%pairs of nerves that originate from brain or spinal cord%%
  • %%Sensory%% neurone: carry nerve impulse from %%receptors to CNS%%
  • %%Motor%% neurone: carry nerve impulse from %%CNS to effector%%
  • %%Voluntary%% nervous system: carry %%nerve impulses body muscles%% and is under %%voluntary%% control
  • %%Autonomic%% nervous system: carries %%nerve impulses to glands, smooth muscle and cardiac muscle, involuntary%%

The Spinal Cord

  • %%Column of nervous tissue%% that runs down the back
  • Lies in %%vertebral column%% for protection
  • Emerging at intervals along spinal cord are %%pairs of neurones%%

 

Reflex Arc

  • Rapid, short lived response
  • I%%nvoluntary response to a sensory stimulus%% is a reflex
  • Reflex arcs only have %%3 neurones%%
  1. %%Stimulus%% - %%heat%% from hot object
  2. %%Receptor%% - %%temp. receptors%% on skin, generates %%nerve impulse in sensory neurone%%
  3. %%Sensory neurone%% - passes nerve %%impulse to spinal cord%%
  4. %%Coordinator%% - links %%sensory neurone to motor neurone%% in spinal cord
  5. %%Motor neurone%% - carries %%nerve impulse from spinal cord to arm%%
  6. %%Effector%% - %%muscle%% in arm, stimulated to %%contract%%
  7. %%Response%% - pull hand away from fire
  • Important as…
    • %%Involuntary%% so do %%not require brain to make decision%%, leaving it to %%carry out more complex impulses%%
    • %%Protects body%% from harm
    • %%Fast response as neurone pathway is short%%
    • %%No need for brain decision so action is rapi%%d