Neural Control and Coordination

SYNOPSIS

• Human Nervous System
  
  
• Neurons and their Types
  
  

  Types of Neurons
  Basis their function	Basis the number of nerve processes
  Sensory neurons Association neurons Motor neurons	Unipolar neuron Bipolar neuron Multi-polar neuron

  
  
  
  
• Types of Axons
  
  

  Myelinated Axons	Non-myelinated Axons
  Schwann cell covering the axons forms the myelin sheath.	Schwann cell covering the axons does not form the myelin sheath.
  They contain nodes of Ranvier.	They are continuous.
  Found in the spinal and cranial nerves.	Found in ANS and somatic nervous system.

• Conduction of Nerve Impulse

• Involuntary actions in response to external or internal stimuli are termed reflex actions.
• The path travelled by the impulse during a reflex action is called a reflex arc.
  
  
  
  Stimulus → Receptor in the sense organ → Afferent (sensory) nerve fibre → CNS (spinal cord) → Efferent (motor) nerve fibre → Muscle/gland → Response
  
  
• Function of Parts of the Human Brain
  
  

  Cerebrum	Centre of intelligence, memory, consciousness, will power and voluntary actions
  Thalamus	Relays motor and sensory impulses to the cerebrum
  Hypothalamus	Contains the centres which control body temperature, blood pressure and homeostasis
  Midbrain	Controls the movement of the head and eye
  Cerebellum	Coordinates muscular activity and the balance of the body
  Pons varolii	Coordinates between the two lobes of the cerebellum
  Medulla oblongata	Controls the activities of the internal organs, heartbeat and breathing

  
  
• Mechanism of Vision

• Light rays reflected from the object enter the eyes through transparent structures.
• The light energy produces chemical changes in rods and cones which send the nerve impulse. 
• This nerve impulse is sent to the cerebrum through the optic nerve. The cerebrum gives the sensation of sight.
• Photosensitive compounds like opsin and retinal generate potential differences in photoreceptor cells.
• The brain interprets the inverted image on the retina, and the object is seen upright.

• Mechanism of Hearing

• The pinna collects sound waves and conducts them through the external auditory canal. They finally strike the eardrum and the vibration is set.
• The Eustachian tube equalises the air pressure on either side of the eardrum allowing it to vibrate freely.
• The vibrating eardrum sets the three ear ossicles into vibration. The vibration of the first two ossicles, i.e. malleus and incus, magnifies the vibration in the stapes.
• The stapes transmits the vibration to the membrane of the oval window which sets the fluid in the cochlea into vibration.
• The vibrating movement in the fluid stimulates hair-like processes of sense cells of the cochlea and the impulses are transmitted to the brain via the auditory nerve.