Nerves 1.1

• General functions of the nervous system

  • Sensory function - receives incoming information (stimuli) from sensory receptors
  • Integrative function - Interprets & processes information to determine appropriate response (decision making process)
  • Effector function - produces outgoing signals to initiate response in muscles (skeletal, smooth, cardiac) or glands
• Primary subdivision of the nervous system

  Central nervous system (CNS): Brain & Spinal cord

  Peripheral nervous system (PNS): neural tissue outside CNS
• CNS


  • Contained within skull and vertebral column

  Integrative in function

  Responsible for simple reflexes, complex reflexes, and higher order functions (memory, learning, intelligence)
• PNS


  • Mostly outside of skull and vertebral column

  Includes cranial nerves and spinal nerves

  Location of cell bodies of nerves outside of CNS (sensory ganglia, peripheral ganglia, autonomic nervous system ganglia)
• Components of the PNS

  • Sensory organs (eyes, tongue, taste buds)

  Peripheral nerves

  Autonomic motor pathways
• Afferent division of peripheral nerves

  Brings sensory information from receptors
• Efferent division of peripheral nerves

  Carries motor commands to effectors
• Divisions of the efferent peripheral nervous system

  • Somatic nervous system to skeletal muscles

  Autonomic nervous system to cardiac muscle, smooth muscle, glands

  Sympathetic

  Parasympathetic
• Nerve cells (neurons)


  • Electrically active cells that process & conduct information in the form of electrical signals
• Neuroglia (glial cells)


  • Support cells
• Neuroglia cells in the PNS

  • Satellite cells

  Schwann cells
• Neuroglia cells in the CNS

  • Oligodendrocytes

  Astrocytes

  Microglia

  Ependymal cells
• Functional organization of the nervous system


  Collection of nerve cell processes (fibers) for transmission of information

  Collection of nerve cell bodies for processing of information
• White matter of the CNS

  • Fiber tracts, columns
• Grey matter of the CNS


  • Nerve cell bodies, nuclei, cortex
• Grey matter of the spinal cord

  • Posterior horns contain somatic and visceral sensory nuclei

  Anterior horns contain somatic motor control

  Lateral horns contain visceral (autonomic) motor neurons
• White matter of the spinal cord

  • Divided into columns (funiculi) containing ascending and descending tracts
• Spinal cord


  • Single continuous structure with 31 segments defined by spinal nerves

  Dorsal (posterior) root of spinal nerve is sensory (afferent)

  Ventral (anterior) root of spinal nerve is motor (efferent)

  Each spinal nerve receives sensory input from one dermatome (region of skin)
• Regions of the adult brain

  • Telencephalon (cerebrum or cerebral hemispheres)

  Diencephalon (thalamus & hypothalamus)

  Mesencephalon (midbrain)

  Metencephalon (pons & cerebellum)

  Myelencephalon (medulla oblongata)
• White matter of the brainstem

  • Contains projection fibers (ascending & descending tracts), association fibers, and commissural fibers
• Embryology of the brain and spinal cord

  • Develop from the cells in the walls of the developing hollow neural tube

  Ventricles of the brain and spinal canal develop from the hollow center of the developing neural tube
• Protective and support systems of the CNS

  • Vertebrae, ligaments, muscles

  Meninges

  Cerebrospinal fluid (CSF)

  Blood-brain barrier
• Meninges


  • specialized connective tissue layers
  • Dura mater, arachnoid, pia mater

  Provide physical stability and shock absorption

  Support blood vessels entering and exiting CNS tissue
• Spinal meninges


  • Surround spinal cord

  Anchor spinal cord from foramen magnum to coccyx

  Provide cushioning
• Cranial meninges


  • Continuous with spinal meninges

  Folds of dura mater help stabilize the position of the brain (contains sinuses that serve as veins)
• Cerebrospinal fluid (CSF)


  Produced in ventricles, circulates through subarachnoid space, exits into sinuses

  Transports nutrients, chemical messengers, and waste products

  Provides cushioning and buoyancy
• Blockage of CSF circulation causes pressure in ventricles, enlarging ventricles that can damage neural tissue (hydrocephalus- swelling with brain)
• Neuron classification


  • Motor (efferent)

  Sensory (afferent)

  Interneurons (association neurons)
• Neuroglia (glial cells)


  • Provide structural support, regulate the chemical environment, and assist with damage repair
• Schwann cells (PNS)


  • Ensheath axons and dendrites
• Oligodendrocytes (CNS)


  • Surround myelinated and unmyelinated CNS axons
• Astrocytes (CNS)


  • Largest and most numerous, provide structural support (scar tissue) and regulate the interstitial fluid
  • blood brain barrier
• Blood-brain barrier


  • Isolates neural tissue from general circulation, restricts migration of cells and diffusion of molecules out of brain capillaries
• Blood-CSF barrier


  • Restricts diffusion of CSF out of ventricles
  • Incomplete barrier in parts of the hypothalamus, pituitary gland, and pineal gland
• Damage repair mechanisms in the CNS

  
  

  Oligodendrocytes reabsorb myelin, astrocytes form scar tissue
• Damage repair mechanisms in the PNS

  • Schwann cells myelin pathway can guide regenerating axons, and sensory dendrites
• Disorders involving peripheral nerves and ganglia include herpes (latent infection of sensory neurons) and Hansen's disease (bacterial infection causing nerve damage)
• neuroglial cells surround and support both nerve cell bodies and processes
• damage to nerve cell soma = neuron death

  few if any germinative cells in adult brain
• glial cells (neuroglia) of the CNS: 


  microglia -phagocytic cells (remove debris, pathogens, etc)ependymal cells - lines chambers, produce CSF in chorid plexus regions