Neural system

• Coordination


  The process through which two or more organs interact and complement the functions of one another
• Neural system and endocrine system


  Jointly coordinate and integrate all the activities of the organs so that they function in a synchronised fashion
• Neural system

  • Provides an organised network of point-to-point connections for a quick coordination
  • Endocrine system provides chemical integration through hormones
• The neural system of all animals is composed of highly specialised cells called neurons which can detect, receive and transmit different kinds of stimuli
• Parts of the human neural system

  • Central neural system (CNS)
  • Peripheral neural system (PNS)
• Central neural system (CNS)


  Includes the brain and the spinal cord and is the site of information processing and control
• Peripheral neural system (PNS)


  Comprises all the nerves of the body associated with the CNS (brain and spinal cord)
• Nerve fibres of the PNS

  • Afferent fibres
  • Efferent fibres
• Afferent nerve fibres


  Transmit impulses from tissues/organs to the CNS
• Efferent nerve fibres


  Transmit regulatory impulses from the CNS to the concerned peripheral tissues/organs
• Divisions of the PNS

  • Somatic neural system
  • Autonomic neural system
• Somatic neural system

  Relays impulses from the CNS to skeletal muscles
• Autonomic neural system


  Transmits impulses from the CNS to the involuntary organs and smooth muscles of the body
• Divisions of the autonomic neural system


  • Sympathetic neural system
  • Parasympathetic neural system
• Visceral nervous system


  Part of the peripheral nervous system that comprises the whole complex of nerves, fibres, ganglia, and plexuses by which impulses travel from the central nervous system to the viscera and from the viscera to the central nervous system
• Neuron

  A microscopic structure composed of three major parts: cell body, dendrites and axon
• Types of neurons based on number of axon and dendrites

  • Multipolar
  • Bipolar
  • Unipolar
• Myelinated nerve fibres


  Enveloped with Schwann cells, which form a myelin sheath around the axon
• Unmyelinated nerve fibre


  Enclosed by a Schwann cell that does not form a myelin sheath around the axon
• Resting potential


  The electrical potential difference across the resting plasma membrane
• Generation and conduction of nerve impulse

  1. Stimulus applied at a site on the polarised membrane

  2. Membrane at that site becomes freely permeable to Na+

  3. Rapid influx of Na+ leads to reversal of polarity and generation of action potential (nerve impulse)

  4. Impulse conducted along the axon by repeated depolarisation and repolarisation
• Synapse


  Junction formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called synaptic cleft
• Types of synapses

  • Electrical synapses
  • Chemical synapses
• Transmission of impulses at chemical synapses

  1. Neurotransmitters released from synaptic vesicles in the axon terminal

  2. Neurotransmitters bind to receptors on post-synaptic membrane

  3. This opens ion channels and generates a new potential in the post-synaptic neuron
• Brain


  The central information processing organ of the body, acts as the 'command and control system'
• Major parts of the brain

  • Forebrain
  • Midbrain
  • Hindbrain
• The brain is well protected by the skull and covered by cranial meninges
• Potential in the post-synaptic neuron

  The new potential developed may be either excitatory or inhibitory
• Central Neural System

  • The brain is the central information processing organ of our body, and acts as the 'command and control system'
  • It controls the voluntary movements, balance of the body, functioning of vital involuntary organs, thermoregulation, hunger and thirst, circadian rhythms, activities of several endocrine glands and human behaviour
  • It is also the site for processing of vision, hearing, speech, memory, intelligence, emotions and thoughts
• Brain

  • Well protected by the skull
  • Covered by cranial meninges consisting of dura mater, arachnoid and pia mater
• Major parts of the brain

  • Forebrain
  • Midbrain
  • Hindbrain
• Forebrain

  • Consists of cerebrum, thalamus and hypothalamus
  • Cerebrum forms the major part of the human brain
  • Cerebral hemispheres connected by corpus callosum
  • Cerebral cortex is the layer of cells covering the cerebral hemisphere
  • Cerebral cortex contains motor areas, sensory areas and association areas
  • Cerebral white matter is the inner part of the cerebral hemisphere
• Thalamus


  • Major coordinating centre for sensory and motor signaling
• Hypothalamus


  • Contains centres which control body temperature, urge for eating and drinking
  • Contains neurosecretory cells which secrete hormones
• Limbic system


  • Involved in the regulation of sexual behaviour, expression of emotional reactions, and motivation
• Midbrain


  • Located between the forebrain and hindbrain
  • Contains the corpora quadrigemina
• Hindbrain


  • Comprises pons, cerebellum and medulla
  • Pons consists of fibre tracts that interconnect different regions of the brain
  • Cerebellum has a convoluted surface to provide space for more neurons
  • Medulla contains centres which control respiration, cardiovascular reflexes and gastric secretions
• Brain stem

  • Consists of midbrain, pons and medulla oblongata
  • Forms the connections between the brain and spinal cord
• Reflex action

  A sudden withdrawal of a body part in response to a peripheral nervous stimulation, occurring involuntarily without conscious effort or thought
• Reflex arc

  • Comprises at least one afferent neuron (receptor) and one efferent (effector or excitor) neuron arranged in a series