Nervous system

• Stimulus is a change in the environment that causes a reaction
• A response is an organism’s reaction to a stimulus
• Sensitivity is the ability of an organism to detect and response to changes in the environment
• Nervous system is a specialised network of tissues that detect, process and coordinate responses to stimulus
• Nervous system consists of the brain, spinal cord and nerves
• Nervous system allows organisms to detect changes in their surrounding via receptors
• Involuntary actions — not controlled consciously
• Nervous system enables the coordination of different parts of the body to carry out different actions
• Voluntary actions — controlled consciously
• CNS is known as Central nervous system
• PNS is known as Peripheral nervous system
• CNS consists of brain and spinal cord
• PNS consists of cranial nerves, which are found in the brain and spinal nerves
• Spinal nerves consists both sensory and motor nerve fibres
• Nerves are a bundle of nerve fibres of neurones
• neurones are nerve cells
• nerve fibres are extended strand of cytoplasm from cell body
• Neurones consists of a cell body, an axon and a dendron
• sensory neurone: receptors consists of dendrites —> dendron —> circular cell body —> axon —> axon terminals
• a cell body contains cytoplasm and a nucleus
• motor neurone: dendrites merge into dendrons —> irregular cell body —> axon —> axon terminals
• dendron (longer ) — nerve impulses are carried towards the cell body
• axons (shorter ) — nerve impulses are carried away from the cell body
• myelin sheath is a layer of fatty substance
• node of ranvier is the area without myelin sheath
• Synapse is a junction or connection between two neurones
• white matter is located in the inner brain and outer spinal cord
• white matter includes mainly myelinated nerve fibres of neurones
• function of white matter:

  1. it coordinates between parts of the brain and the spinal cord
  2. IN THE SPINAL CORD, it helps to transmit info from different parts of the body to the brain, and from the brain to the spinal cord
• grey matter locates in the outer brain and the inner spinal cord
• Function of grey matter

  1. IN BRAIN, muscle control , sensory perception and decision making
  2. IN SPINAL CORD , muscle movement , sensory functions
• spinal cords include the dorsal root and ventral root
• dorsal root only contains the sensory neurone and the dorsal root ganglion
• ventral root only contains the motor neurone
• possible pathways of voluntary actions:

  1. sensory neurone —> relay neurone in CNS —> brain
  2. Brain —> relay neurone —> motor neurone —> effector
• possible pathways for reflex arc: sensory neurone —> relay neurone —> motor neurone
• reflex actions is an immediate response to a specific stimulus without conscious control.
• reflex actions are involuntary
• reflex arc is the shortest pathway of nerve impulses from the receptor to the effector
• spinal reflex is controlled by the spinal cord