Nervous system

• Among the 11 body systems, the nervous system and the endocrine system play the most important roles in maintaining homeostasis
• Neurology


  The branch of medical science that deals with the normal functioning and disorders of the nervous system
• The central and peripheral divisions coordinate control of the body using the senses of balance, body position, and touch on the soles of the feet
• Functions of the Nervous System

  • Detecting stimuli (sensory function)
  • Analysing, integrating, and storing sensory information (integrative function)
  • Responding to integrative decisions (motor function)
• The nervous system controls and coordinates all essential functions of the body including all other body systems allowing the body to maintain homeostasis or its delicate balance
• Sensation


  Receiving information about the environment to gain input about what is happening outside the body (or, sometimes, within the body)
• The senses


  • taste
  • smell
  • touch
  • sight
  • hearing
• The stimuli


  • chemical substances
  • physical or mechanical stimuli
  • light stimuli
  • perception of sound
• Response


  Movement of muscles, such as withdrawing a hand from a hot stove
• Types of muscle tissue influenced by the nervous system

  • Skeletal muscle
  • Cardiac muscle
  • Smooth muscle
• Responses


  • Control of glands
  • Production and secretion of sweat by the eccrine and merocrine sweat glands
• Responses


  • Voluntary or conscious (contraction of skeletal muscle)
  • Involuntary (contraction of smooth muscles, regulation of cardiac muscle, activation of glands)
• Integration


  Stimuli that are received by sensory structures are communicated to the nervous system where that information is processed
• Stimuli integrates with other stimuli, memories of previous stimuli, or the state of a person at a particular time, leading to the specific response that will be generated
• Divisions of the Nervous System

  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
• Types of cells in the nervous system

  • Neurons
  • Neuroglia
• Neurons


  Cells specialized for nerve impulse conduction and provide most of functions of the nervous system, such as sensing, thinking, remembering, controlling muscle activity
• Neuroglia


  Support, nourish, and protect the neurons and maintain homeostasis in the interstitial fluid that bathes neurons
• Parts of the Neuron

  • Dendrite
  • Cell Body with nucleus
  • Axon
  • Schwann Cells
  • Myelin sheath
  • Node of Ranvier
• Types of Neurons


  • Sensory neurons
  • Motor neurons
  • Interneurons
• Neuroglia in the CNS

  • Astrocytes
  • Oligodendrocytes
  • Microglia
  • Ependymal cells
• Neuroglia in the PNS

  • Schwann cells
  • Satellite cells
• Myelination


  Myelinating glia wrap several layers of cell membrane around the cell membrane of an axon segment
• Neuroglia in the CNS and PNS secrete cerebrospinal fluid (CSF)
• White matter


  Composed primarily of myelinated axons
• Gray matter


  Contains neuronal cell bodies, dendrites, and axon terminals of neurons, unmyelinated axons, and neuroglia
• In the spinal cord, gray matter forms an H-shaped inner core that is surrounded by white matter. In the brain, a thin, superficial shell of gray matter covers the cerebrum and cerebellum
• Nucleus


  A localized center of function with the cell bodies of several neurons
• Ganglion


  A cluster of neuronal cell bodies located in the PNS
• Nerve


  A bundle of axons located in the PNS
• Tract


  A bundle of axons located in the CNS
• Stimulus


  A change in the environment with sufficient strength to initiate a response
• Excitability


  The ability of a neuron to respond to the stimulus and convert it into a nerve impulse
• The stimulus is either strong enough to start an impulse or nothing happens (All or Nothing Rule)
• Impulses are always the same strength along a given neuron and they are self-propagation - once it starts it continues to the end of the neuron in only one direction - from dendrite to cell body to axon
• Synapse


  Small gap or space between the axon of one neuron and the dendrite of another, using neurotransmitters to start the impulse in the second neuron or an effector
• Neurotransmitters


  Chemicals in the junction which allow impulses to be started in the second neuron
• Action potentials


  Brief changes in the distribution of electrical charge across the cell surface membrane
• Resting potential


  The inside of the axon always has a slightly negative electrical potential compared to outside the axon, due to an unequal distribution of ions on either side of the plasma membrane and a higher membrane permeability to K+ than to Na+
• Steps of Action Potential

  1. Sodium channel proteins in the axon membrane open

  2. Sodium ions pass into the axon down the electrochemical gradient

  3. This reduces the potential difference across the axon membrane as the inside of the axon becomes less negative - a process known as depolarisation

  4. This triggers voltage-gated sodium channels to open, allowing more sodium ions to enter and causing more depolarisation

  5. If the potential difference reaches around -50mV (known as the threshold value), many more channels open and many more sodium ions enter causing the inside of the axon to reach a potential of around +30mV