Nervous system

• The nervous system gathers information, processes the information and elicits a corresponding response or reaction to stimulus
• Two main division of Nervous system

  • CNS
  • PNS
• Central Nervous system is composed of the brain and spinal cord.


  The brain is the control center while spinal cord connects the brain to the other nerves of the body.
• Peripheral nervous system is composed of nerves that branch out from the brain and spinal cord to specific body parts. It further divided into somatic and autonomic nervous system.


  The somatic nervous system controls voluntary body movement while autonomic nervous system controls involuntary movement.
• The basic structural unit of Nervous system is neurons.
• 4 basic parts of neuron:

  • Dendrites
  • Soma
  • Axon
  • Axon terminal
• Dendrites are several projections which extends outward from the cell body to receive chemical signals from the axon terminals of another neuron.
• Soma or the cell body contains the nucleus and most of organelles.
• Axon a single projection from the soma which carries the impulse to the axon terminal. 


  Maybe envelope by myelin sheath for faster conduction of impulse.
• Myelin Sheath is a fatty white substance that surround the axon of some nerve cells, forming an electrically insulating layers. It is essential for the proper functioning of the Nervous system.
• A neurons transmits electrical signals called action potential or an impulse across the system and let's a body part respond accordingly.
• Impulse is a sudden change in the electrical potential of the cell membrane.
• 3 interconnected functions of the nervous system are:

  • Sensory receptors
  • Integration
  • Effector


  With corresponding 3 types of neurons

  • Sensory neuron
  • Interneuron
  • Motor neuron
• •Sensory neurons convey sensory input

  •Interneurons perform integration, the interpretation of the sensory signals.

  •Motor neurons carries out motor input

  •Effector performs body's response to motor input.
• Sensory pathways have 4 basic functions in common:

  • Sensory reception
  • Transduction
  • Transmission
  • Integration
• • Sensory reception detection of stimuli by sensory receptors.
  • Sensory receptors interact directly with stimuli both outside and inside of the body.
  • Sensory transduction is the conversion of stimulus energy into a change in the membrane potential of a sensory receptors.
  • This change in the membrane potential is called a receptor potential.
• Receptors is afferent neuron.
• After energy has been transduced into a receptor potential, some sensory cells generate the transmission of action potential to the CNS.
• Perceptions are the brains construction of stimuli
• Types of sensory receptors:

  • MECHANORECEPTORS
  • CHEMORECEPTORS
  • ELECTROMAGNETIC RECEPTORS
  • THERMORECEPTORS
  • PAIN RECEPTORS
• Mechanoreceptors sense physical deformation caused by stimuli such as pressure, stretch, motion and sound.
• Chemoreceptors transmits information about the total solute concentration of a solution. 


  When a stimulus molecules binds to a chemoreceptors, it becomes more or less Permeable to ions.
• Electromagnetic receptors detect electromagnetic energy such as light, electricity and magnetism.
• Thermoreceptors which responds to heat or cold, helps regulate body temperature.
• Pain receptors or nociceptors are a class of naked dendrites in the epidermis. They respond to excess heat, pressure or chemicals released from damage or inflamed tissues.
• Tropism is a directional growth of a plant or part of a plant in response to a external stimulus.
• Stimulus is an action that causes change or response
• Response is the reaction or action to a stimulus.
• Negative response is when the growth of a plant is away from the stimulus.


  Positive response is when the growth of a plant is towards the stimulus.
• Types of tropism

  • Hydrotropism
  • Thermotropism
  • Gravitropism
  • Thigmotropism
  • Phototropism
  • Heliotropism
• Hydrotropism:

  Stimulus: water

  Response: A plants root grow towards the source of water.

  Response type: Positive response.
• Thermotropism:

  Stimulus: temperature

  Response: A plants grows in the direction or away from the source of cold or heat.

  Response type: Both negative or positive.
• Gravitropism:

  Stimulus: Gravity

  Reaction:

  • Positive: The roots grow downward with the gravity.
  • Negative: The stalk grow upward against the gravity.
• Thigmotropism

  Stimulus: Touch

  Response: The leaves( or part of a plant that are sensitive to touch) move or coil away from the touch or trigger some action.
• Phototropism

  Stimulus: Light

  Response: A plants grows in the direction of the unidirectional light( it only comes one direction).

  Response type: Positive
• Heliotropism

  Stimulus: Sunlight

  Response: The plants grows or turn their face in the direction of a sun.

  Response type: Positive response.