NERVOUS SYSTEM

• Nervous System


  Highly specialized cells that are capable of transmitting information rapidly between different parts of the body
• Divisions of the Nervous System

  • Central nervous system
  • Peripheral nervous system
• Cell types in nervous system

  • Neurons (functional, signal conducting cells)
  • Neuroglia (supporting cells)
• Neuron


  Basic cellular unit of the nervous system
• Neuron


  • The shape of the neuron is decided by their function and location within the nervous system
  • The characteristic components are cell body, axon, dendrites
• Cell Body or Soma


  The expanded portion of the cell containing the nucleus and the apparatus necessary to sustain the metabolic activities of the cell
• Dendrites


  Processes of the cell membrane that radiate from the cell body and are responsible for receiving information and transmitting it to the cell body
• Axon


  A longitudinal, tubular extension of the cell membrane and cytoplasm that transmits information away from the cell body
• Myelination


  A process of wrapping individual neurons in a sheath of lipid to provide protection, insulation, and increase the speed of conduction of electrical impulses
• Myelination


  • In the peripheral nervous system, myelination is brought out by Schwann cells
  • In the central nervous system, myelination is brought out by oligodendrocytes
• Glial Cells


  Cells that hold the neurons of the central nervous system together, outnumbering neurons by about 10 to 1
• Types of Glial Cells in CNS

  • Oligodendrocytes
  • Microglia
  • Ependymal cells
  • Astrocytes
• Astrocytes


  Protoplasmic astrocytes are present in the grey matter and fibrous astrocytes in the white matter, functioning to hold cell bodies and axons in place, and regulate the exchange of chemicals between themselves and blood vessels
• Ependymal Cells


  Epithelial cells forming a cellular barrier between nervous system and the fluid in its cavities
• Synapse


  A specialized structure involved in communication between separate neurons, where one neuron transmits information to another neuron or to a muscle or gland cell by releasing chemicals called neurotransmitters
• Synaptic Transmission


  1. Action potential travels down an axon to the terminal buttons

  2. Voltage-gated Ca2+ channels open, allowing Ca2+ ions to flood into the terminal button

  3. This stimulates synaptic vesicles packed with neurotransmitter to fuse with the membrane of the terminal button

  4. The neurotransmitter diffuses across the cleft to the postsynaptic membrane

  5. The neurotransmitter binds to specific receptor sites on the postsynaptic membrane, causing localised depolarisation of the membrane
• Sensory Receptors


  Specialized neurons or epithelial cells that respond to specific or generalized stimuli
• Types of Sensory Receptors

  • Mechanoreceptors (hearing, balance, stretching)
  • Photoreceptors (light)
  • Chemoreceptors (smell, taste, internal sensors)
  • Thermoreceptors (changes in temperature)
  • Electroreceptors (detect electrical currents)
• Sensations


  Action potentials that reach the brain via sensory neurons
• Perceptions


  The brain's interpretation of sensations
• Sensory Reception


  The detection of the energy of a stimulus by receptors in sensory cells
• Types of Sensory Receptors

  • Exteroreceptors (detect stimuli outside the body)
  • Interoreceptors (detect stimuli within the body)
• Sensory Receptors


  • Convert stimuli into membrane potentials and transmit signals to the nervous system
• Functions of Sensory Receptors

  • Transduction (conversion of stimulus energy into membrane potential)
  • Amplification (strengthening of a weak stimulus)
  • Transmission (conducting impulses to CNS)
  • Integration (processing of information)
• Central Nervous System (CNS)


  The command center of the body that interprets incoming sensory information and sends out instructions on how the body should react, consisting of the spinal cord and brain
• Cerebrum


  The largest part of the brain that controls higher mental functions
• Cerebrum


  • Divided into left and right cerebral hemispheres
  • Outer layer is the gray matter (neuron cell bodies)
  • Inner layer is the white matter (long axons)
• Lobes of the Cerebrum

  • Frontal lobe
  • Parietal lobe
  • Temporal lobe
  • Occipital lobe
• Functions of the Cerebral Cortex

  • Mental activities (memory, intelligence, thinking, reasoning)
  • Sensory perception (pain, temperature, touch, sight, hearing, taste, smell)
  • Motor function (initiation and control of skeletal muscle contraction)
  • Retrieving stored information
• Frontal Lobe


  Involved in reasoning, planning, parts of speech, movement, emotions, problem solving, expression of intellect and personality
• Motor Area


  The precentral (motor) area in the frontal lobe that is responsible for the contraction of skeletal muscles, with the body represented upside down
• Premotor Area


  Immediately anterior to the motor strip, with a controlling influence over the motor area and responsible for manual dexterity
• Broca's Area


  Found on the inferior frontal gyrus, dominant in the left hemisphere in right-handed people, involved in speech production
• Prefrontal Cortex


  The most anterior part of the frontal lobe, involved in complex cognitive processes like behavior, character, reasoning and judgment
• Parietal Lobe


  The forward parts receive information about temperature, taste, touch, position of body and limbs, and movement from the rest of the body
• Motor cortex


  • Those in the highest part control the trunk, those in the middle part control the limbs, and those in the lowest part control the head, neck, face and fingers
  • The sizes of the areas of cortex representing different parts of the body are proportional to the complexity of movement of the body part and not its size. i.e., in comparison with the trunk, the hand, foot, tongue and lips are represented by large cortical areas
• Premotor area/Supplemental motor area

  Immediately anterior to the motor strip, have a controlling influence over the motor area and are responsible for the manual dexterity, but do not program the motor commands for speech as these are generated in Broca's area
• Broca's Area


  Found on the inferior frontal gyrus in the hemisphere that is dominant for language, dominant in the left hemisphere in right handed people and vice versa
• Prefrontal cortex


  The most anterior part of the frontal lobe, involved in complex cognitive processes like behavior, character or intellectual trait, reasoning and judgment
• Primary sensory areas


  The forward parts of these lobes, just behind the motor areas, receive information about temperature, taste, touch, position of body and limbs and movement from the rest of the body