NERVOUS SYSTEM

• Nervous System


  • Communication and coordination system in the body
  • Seat of intellect and reasoning
  • Communicates with the endocrine system
  • Electrochemical signals

  
• Divisions of the Nervous System

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

  
• Central Nervous System (CNS)


  Brain and spinal cord
• Peripheral Nervous System (PNS)


  • Nerves
  • Named because it is in the periphery - meaning beyond the brain and spinal cord
• Components of the Autonomic Nervous System

  • Sympathetic System (fight or flight)
  • Parasympathetic System (rest and digest)

  
• Neuron


  Transmits messages from one cell to another
• Neurons


  • Nucleus, cytoplasm, and cell membrane
  • Dendrites - to cell body
  • Axons (only one per cell) - away from cell body
  • Neurilemma or myelin sheath

  
• Types of Neurons


  • Multipolar neurons
  • Bipolar cells
• CNS Glial Cells


  • Astrocytes
  • Oligodendrocytes - makes myelin sheath (1:many)
  • Microglia
  • Ependymal cell - spinal fluid

  
• PNS Glial Cells

  • Satellite cells
  • Schwann cell - makes myelin sheath (1:1)

  
• Myelin Sheath

  Lipid-rich sheath that surrounds the axon and facilitates the transmission of electrical signals along the axon

  
• Synapse


  1. Synaptic transmission begins with action potential conduction to the axon terminal

  2. Depolarization of the axon terminal opens voltage-gated Ca2+ channels

  3. Vesicles respond by fusing with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft

  4. Neurotransmitters bind with receptors on the postsynaptic cell that are ligand-gated ions, causing a change in membrane potential

  5. After inactivation, neurotransmitters are re-absorbed into the presynaptic terminal and stored in vesicles until the next action potential arrives
• Neurotransmitters


  Chemical substances that make it possible for messages to cross the synapse to a target receptor
• Myasthenia gravis is an [EXAM] related to neurotransmitters
• Brain


  • Weighs about 1,400 grams or 3 pounds
  • 100 billion neurons
  • Meninges and cerebrospinal fluid
  • Without oxygen, brain damage occurs within 4-8 minutes
  • Bleeding: banana shape (bleeding outside dura), lemon shape (bleeding inside dura)
• Cerebrum


  • Largest part of the brain
  • Weighs about 2 pounds
  • Cerebral cortex (gray matter)
  • Two hemispheres and longitudinal fissure
  • Right hemisphere - left side, Left hemisphere - right side
  • Decussate around brain stem (90% of axons switch to other side)
  • Fissures (deeper) and sulci (shallow)
  • Gyri or elevation or convolutions (elevated ridges between the sulci)
  • A large component of the CNS in humans
  • Corpus callosum - provides the major pathway for communication between the two hemispheres or cortex

  
• Lobes of the Cerebrum

  • Frontal lobe - thinking, reasoning, speech
  • Parietal lobe - touch
  • Temporal lobe - like thumb, aka temple
  • Occipital lobe - vision

  
• Broca's Area


  Speech production
• Wernicke's Area


  Speech comprehension
• Diencephalon


  • Located between the cerebrum and the midbrain
  • Thalamus - relay station for incoming and outgoing nerve impulses
  • Hypothalamus - considered to be the brain of the brain, releases hormones that control endocrine system, autonomic nervous control, cardiovascular control, temperature, appetite control, water balance, manufacture of oxytocin, gastrointestinal control, emotional state, sleep control, mind-over-body experiences

  
• Cerebellum


  • Located behind the pons and below the cerebrum
  • Right and left cerebellar hemispheres connected by vermis
  • Gray matter on the outside and white matter on the inside
  • Communicates with the rest of the CNS by three pairs of tracts called peduncles
  • Functions: maintenance of balance, maintenance of muscle tone, coordination of muscle movements

  
• Brain Stem Components


  • Midbrain
  • Pons
  • Medulla Oblongata

  
• Memory


  • Storage of old and new information
  • Role of the hippocampus of the limbic system
  • Short- or long-term memory
• Coverings of the Brain

  • Dura mater
  • Arachnoid mater
  • Pia mater
• Ventricles of the Brain

  • Four-lined cavities filled with cerebrospinal fluid
  • Choroid plexus helps with the production of cerebral spinal fluid
  • 1st and 2nd (right and left lateral ventricles)
  • 3rd and 4th (3rd is connected to the two lateral ventricles via the interventricular foramen, 3rd and 4th are connected via a narrow canal called the cerebral aqueduct)

  
• Cerebrospinal Fluid (CSF)


  • Formed inside the four ventricles
  • Transports nutrients to and removes metabolic waste products from the brain cells
  • Blood-brain barrier - selectively permeable, consist of choroid plexus capillaries
  • Lumbar puncture

  
• Spinal Cord


  • Begins at foramen magnum of the occipital bone
  • Ends at the second lumbar vertebrae
  • 31 pairs of spinal nerves
  • Protected by meninges and other tissues
  • White and gray matter
  • Functions: carry messages from the sensory neurons to the brain for interpretation, then carry the response back through the motor neurons to muscles and glands
  • Divided into regions that correspond to the regions of the vertebral column: Cervical, Thoracic, Lumbar, Sacral

  
• Components of the Peripheral Nervous System

  • Afferent peripheral system - conveys information from the periphery back to the brain and spinal cord
  • Efferent peripheral system - Somatic (from brain and spinal cord to skeletal muscle), Autonomic (from brain and spinal cord to smooth muscle)

  
• Somatic Nervous System


  Responds to changes in the external environment
• Autonomic Nervous System


  • Sympathetic: fight or flight response (norepinephrine)
  • Parasympathetic: rest and digest response (acetylcholine)
• Sympathetic System


  • Consists primarily of two cords, beginning at the base of the brain and proceeding down both sides of the spinal column
  • Nerves extend to all vital organs
  • Fight-or-flight system
• Parasympathetic System


  • Vagus nerve
  • Pelvic nerves
  • Counteracts effects of the sympathetic nervous system
  • Brings the body back to homeostasis
• Cranial and Spinal Nerves

  • 12 pairs of cranial nerves - originate from the brain and brain stem
  • 31 pairs of spinal nerves - direct connection to the spinal cord, plexus, largest spinal nerve: sciatic

  
• Reflex Arc


  1. Stimulus

  2. Receptors

  3. Response