Nervous System and Hormones

Nervous System and Hormones

Nervous System Basics

  • The nervous system is made up of the brain, spinal cord, and peripheral nerves; it controls and coordinates body functions.
  • Neurons (nerve cells) are the basic units of the nervous system. They transmit electrical impulses from one part of the body to another.
  • Each neuron comprises a cell body, dendrites (receive stimuli), and an axon (transfers impulses).
  • An impulse is an electrical signal transmitted along neurons.
  • Neurons communicate with each other at junctions called synapses through chemical messengers known as neurotransmitters.

Reflex Actions and Reflex Arc

  • A reflex action is an automatic response to certain stimuli, bypassing the brain.
  • The reflex arc is the pathway taken by the nerve impulses during a reflex action, from receptor to effector.
  • Key components: receptor (responds to stimulus), sensory neuron (transfers impulses to CNS), motor neuron (carries impulses from CNS to effector), effector (produces response).

Endocrine System and Hormones

  • The endocrine system is composed of glands that secrete hormones. Key glands include the pituitary, thyroid, adrenal, and pancreas.
  • Hormones are chemical messengers that travel through the bloodstream to target organs.
  • Hormones regulate various body functions like growth, metabolism, and reproduction.
  • Hormonal responses are slower and longer-lasting than nervous responses.


  • Homeostasis is the maintenance of a constant internal environment in the body.
  • Temperature, water, glucose, and carbon dioxide levels are controlled by homeostasis.
  • Negative feedback mechanisms are used to rectify changes - if levels are too high or low, corrective measures are triggered to bring them back to normal.
  • High blood glucose levels trigger the release of insulin from the pancreas, which helps cells absorb glucose and lowers blood glucose levels.
  • Low blood glucose levels cause the pancreas to release glucagon, which causes the liver to convert stored glycogen back into glucose, raising blood glucose levels.

Hormonal Control of the Menstrual Cycle

  • The menstrual cycle is controlled by hormones released by the pituitary gland and the ovaries.
  • Follicle-stimulating hormone (FSH) stimulates follicle development, and with it, oestrogen production.
  • Oestrogen causes the lining of the uterus to thicken and stimulates the release of luteinising hormone (LH).
  • LH triggers ovulation - the release of the egg from the ovary.
  • After ovulation, the remains of the follicle in the ovary form the corpus luteum, which secretes progesterone.
  • Progesterone further thickens the uterine lining, preparing it for possible pregnancy. If pregnancy does not occur, progesterone levels fall, and the cycle starts again.

Remember: Understanding the roles and functions of different parts of the nervous and endocrine systems, as well as the hormones involved in various processes, is crucial.