Nervous system

• Peripheral Nervous System


  Consists of cranial nerves and spinal nerves
• Nervous system


  Among the 11 body systems, it and the endocrine system play the most important roles in maintaining homeostasis
• Cranial nerves


  • 12 pairs
  • Attached to undersurface of brain
• Neurology


  The branch of medical science that deals with the normal functioning and disorders of the nervous system
• Spinal nerves


  • 31 pairs
  • Attached to spinal cord
• Nervous system


  • Very complex structure and composed of many organs that all look similar and can only be differentiated using tools such as the microscope or electrophysiology
  • Within the brain, many different and separate regions are responsible for many different and separate functions
  • The ability to balance like an acrobat combines functions throughout 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
• Somatic Nervous System (voluntary)


  • Receptors to CNS
  • CNS to muscles
• Functions of the Nervous System

  • Detecting stimuli (sensory function)
  • Analysing, integrating, and storing sensory information (integrative function)
  • Responding to integrative decisions (motor function)
• Autonomic Nervous System (involuntary)


  • Regulates bodies involuntary responses
  • Relays information to internal organs
• Divisions of Autonomic Nervous System

  • Sympathetic nervous system (stress)
  • Parasympathetic nervous system (at rest)
• It 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)
• Spinal Nerves


  • Receptors to CNS
  • CNS to effectors
• Stimulus


  A change from homeostasis or a particular event in the environment
• Structure of Spinal Nerve

  Layers of protective connective tissue coverings: Epineurium, Perineurium, Endoneurium
• Cranial Nerves


  • 12 pairs
  • Designated with roman numerals
  • Names
• The senses


  • Taste
  • Smell
  • Touch
  • Sight
  • Hearing
• Cranial Nerves


  Emerge from nose (I), eyes (II), brain stem (III-XII), inner ear (VIII), spinal cord (XI)
• Stimuli


  • Chemical substances
  • Physical or mechanical stimuli
  • Light stimuli
  • Perception of sound
• Types of Cranial Nerves

  • Sensory nerves (I, II, VIII)
  • Motor nerves (III, IV, VI, XI, XII)
  • Mixed nerves (V, VII, IX, X)
• Response


  Movement of muscles, such as withdrawing a hand from a hot stove
• Functions of Cranial Nerves

  • I. Olfactory: Smell
  • II. Optic: Visual fields and ability to see
  • III. Oculomotor: Eye movements; eyelid opening
  • IV. Trochlear: Eye movements
  • V. Trigeminal: Facial sensation
  • VI. Abducens: Eye movements
  • VII. Facial: Eyelid closing; facial expression; taste sensation
  • VIII. Auditory/vestibular: Hearing; sense of balance
  • IX. Glossopharyngeal: Taste sensation; swallowing
  • X. Vagus: Swallowing; taste sensation
  • XI. Accessory: Control of neck and shoulder muscles
  • XII. Hypoglossal: Tongue movement
• Types of muscle tissue influenced by the nervous system

  • Skeletal muscle
  • Cardiac muscle
  • Smooth muscle
• Autonomic Nervous System (ANS)


  • Regulates smooth muscle, cardiac muscle, and certain glands
  • Regulated mainly by hypothalamus and brain stem
• Responses


  • Voluntary or conscious (contraction of skeletal muscle)
  • Involuntary (contraction of smooth muscles, regulation of cardiac muscle, activation of glands)
• Somatic Nervous System (SNS)

  • Contains both sensory and motor neurones
  • Sensory neurones receive input from receptors for the special senses and somatic senses
  • Motor neurones convey impulses to striated muscles
• Integration


  Stimuli that are received by sensory structures are communicated to the nervous system where that information is processed
• Autonomic motor neurons


  • Regulate activities of cardiac and smooth muscle, and glands, by both excitation and inhibition
• Divisions of the Nervous System

  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
• Branches of Autonomic Nervous System

  • Sympathetic division
  • Parasympathetic division
• Neurons


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


  Most organs receive impulses from both sympathetic and parasympathetic neurons
• Neuroglia


  Support, nourish, and protect the neurons and maintain homeostasis in the interstitial fluid that bathes neurons
• Sympathetic division


  • Also called the thoracolumbar division
  • Outflow of sympathetic nerve impulses comes from the thoracic and lumbar segments of the spinal cord
• Parts of the Neuron

  • Dendrite
  • Cell Body with nucleus
  • Axon
  • Schwann Cells
  • Myelin sheath
  • Node of Ranvier
• Sympathetic preganglionic neuron


  1. Cell bodies in the 12 thoracic and the first two lumbar segments of the spinal cord

  2. A single sympathetic preganglionic axon may synapse with 20 or more postganglionic neurons (located outside of the spinal cord)

  3. Sympathetic responses can affect organs throughout the body almost simultaneously
• Types of Neurons


  • Sensory neurons
  • Motor neurons
  • Interneurons
• Paths of sympathetic preganglionic neuron axon

  1. Synapse with postganglionic neurons in the sympathetic trunk ganglion it first reaches

  2. Ascend or descend to a higher or lower sympathetic trunk ganglion before synapsing with postganglionic neurons

  3. Continue, without synapsing, through the sympathetic trunk ganglion to end and synapse with postganglionic neurons there

  4. Terminate in the adrenal medulla
• Neuroglia in the CNS

  • Astrocytes
  • Oligodendrocytes
  • Microglia
  • Ependymal cells
• Functions of Sympathetic Nervous System

  • Maintains homeostasis through actions like sweating to dissipate heat, or by altering cardiac output based on position and activity level
  • Stimulation of the body's fight-or-flight response: increase in heart rate, bronchial dilation, increase in cardiac output, dilation of pupils