Control and coordination

• Coordination in organisms can involve all systems in the body, from whole organisms to microscopic structures like the nephron in a kidney
• Coordination can be achieved through electrical impulses in the nervous system or through hormones in the endocrine system, both leading to responses
• The nervous system coordinates systems and regulates body functions by sending electrical impulses along nerves
• The human nervous system consists of the central nervous system (CNS) - brain and spinal cord, and the peripheral nervous system (PNS) - nerves outside the CNS
• Nerve cells (neurones) in the CNS and PNS include motor neurones, sensory neurones, and relay neurones
• Synapses are junctions between neurones where impulses pass from one neurone to another
• Motor neurones carry impulses from the CNS to muscles and glands, sensory neurones carry impulses from sense organs to the CNS, and relay neurones make connections within the CNS
• At a synapse, neurotransmitter molecules are released and bind with receptor proteins in the membrane of the next neurone to stimulate a new impulse
• Synapses control the direction of impulses and slightly slow down the speed of nerve impulses
• A reflex action is a rapid and automatic response to a stimulus, like blinking when something touches the eye
• A reflex arc is the nervous pathway for reflexes, like the knee-jerk reflex, involving a sensory neurone, a synapse, and a motor neurone
• The knee-jerk reflex involves tapping a tendon, stimulating a stretch receptor, sending sensory impulses to the spinal cord, and contracting the thigh muscle to jerk the leg forward
• The brain is not needed for a spinal reflex to occur
• Responses like blinking, coughing, and iris contraction have their reflex arcs in the brain
• Bright light stimulates light-sensitive cells in the retina
• Nerve impulses from the retina travel through the optic nerve to the brain
• In a simple reflex arc, the correct order is:

  • Impulse travels in sensory fibre
  • Receptor organ stimulated
  • Impulse crosses synapse
  • Impulse travels in motor fibre
  • Effector organ stimulated
• Sense organs can convert one form of energy to another
• Receptors send nerve impulses to the brain when responding to a stimulus
• The eye can transfer light energy into electrical energy
• The ears transfer sound vibrations into nerve impulses
• Stimuli can be mechanical, chemical, or light, but are all transferred into electrical energy in nerves
• • Suspensory ligament: links muscles to the lens and controls lens shape
  • Fovea: central part of the retina with concentrated cone cells
• The eye structure includes:

  • Sclera: tough, white outer coating
  • Cornea: clear front part of the sclera
  • Conjunctiva: thin epithelium lining eyelids and front of sclera
  • Aqueous humour: clear liquid behind the lens
  • Vitreous humour: jelly-like liquid behind the lens
  • Lens: transparent structure that can change shape
  • Iris: coloured ring controlling light entering the pupil
  • Pupil: hole in the centre of the iris
  • Retina: light-sensitive layer sending nerve impulses to the brain
  • Optic nerve: transmits impulses from the retina to the brain
  • Ciliary muscles: control lens thickness
• Cone cells in the retina detect coloured light
• Tear glands produce tear fluid to keep the eye moist and wash away particles
• Functions of eye parts:

  • Cornea: refracts light entering the eye
  • Iris: controls pupil size
  • Lens: refracts light onto the retina
  • Retina: light-sensitive layer with rods and cones
  • Optic nerve: transmits impulses to the brain
  • Ciliary muscles: control lens shape
  • Suspensory ligaments: control lens shape
  • Fovea: concentrated cone cells for coloured light detection
• Light from an object forms a focused image on the retina
• The pupil reflex adjusts pupil size based on light intensity
• In low light, the pupil enlarges to allow more light in
• In bright light, the pupil constricts to limit light entering the eye
• The eye can accommodate for near and distant objects by changing lens shape
• Ciliary muscles control lens shape for focusing on near or distant objects
• Hormones
• A hormone is a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs
• Hormones are released into the bloodstream from special glands called endocrine glands
• Hormones circulate around the body in the blood and eventually reach their target organs
• Hormones speed up, slow down or alter the activity of target organs
• Hormones only remain temporarily in the blood, changed by the liver into inactive compounds and excreted by the kidneys
• Endocrine glands release hormones directly into the blood circulation