Nervous System

• Seeley's ESSENTIALS OF Anatomy & Physiology Tenth Edition Cinnamon Vanputte Jennifer Regan Andrew Russo See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. © 2019 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.
• Chapter 8 Nervous System Lecture Outline
• Nervous System Figure 8.1
• Nervous System Functions


  • Receiving sensory input
  • Integrating information
  • Controlling muscles and glands
  • Maintaining homeostasis
  • Establishing and maintaining mental activity
• Main Divisions of Nervous System

  • Central nervous system (CNS) - brain and spinal cord
  • Peripheral nervous system (PNS) - All the nervous tissue outside the CNS
  • Sensory division - Conducts action potentials from sensory receptors to the CNS
  • Motor division - Conducts action potentials to effector organs, such as muscles and glands
• Main Divisions of Nervous System

  • Somatic nervous system - Transmits action potentials from the CNS to skeletal muscles
  • Autonomic nervous system - Transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands
  • Enteric nervous system - A special nervous system found only in the digestive tract
• Organization of the Nervous System Figure 8.2
• Cells of the Nervous System

  • Neurons - receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs
  • Glial cells - supportive cells of the CNS and PNS, do not conduct action potentials but carry out different functions that enhance neuron function and maintain normal conditions within nervous tissue
• Neuron


  A nerve cell that has a cell body, dendrites, and an axon
• Structural Types of Neurons

  • Multipolar neurons - have many dendrites and a single axon
  • Bipolar neurons - have two processes: one dendrite and one axon
  • Pseudo-unipolar neurons - have a single process extending from the cell body, which divides into two processes as short distance from the cell body
• Types of Neurons Figure 8.4
• Glial Cells


  • Astrocytes - major supporting cells in the CNS, can stimulate or inhibit the signaling activity of nearby neurons and form the blood-brain barrier
  • Ependymal cells - line the cavities in the brain that contains cerebrospinal fluid
  • Microglial cells - act in an immune function in the CNS by removing bacteria and cell debris
  • Oligodendrocytes - provide myelin to neurons in the CNS
  • Schwann cells - provide myelin to neurons in the PNS
• Types of Glial Cells Figure 8.5
• Myelin sheath


  Specialized layers that wrap around the axons of some neurons, formed by oligodendrocytes in the CNS and Schwann cells in the PNS, an excellent insulator that prevents almost all ion movement across the cell membrane
• Myelin sheath


  • Gaps in the myelin sheath, called nodes of Ranvier, occur about every millimeter, where ion movement can occur
  • Myelination of an axon increases the speed and efficiency of action potential generation along the axon
  • Multiple sclerosis is a disease of the myelin sheath that causes loss of muscle function
• Unmyelinated axons


  Axons that lack the myelin sheaths, rest in indentations of the oligodendrocytes in the CNS and the Schwann cells in the PNS
• Myelinated and Unmyelinated Axons Figure 8.6
• Gray matter


  Consists of groups of neuron cell bodies and their dendrites, where there is very little myelin
• White matter


  Consists of bundles of parallel axons with their myelin sheaths, which are whitish in color
• Membrane Potentials


  • Resting membrane potentials
  • Action potentials
• Resting membrane potential


  Mainly due to differences in concentrations of ions across the membrane, membrane channels, and the sodium-potassium pump
• Leak channels


  Always open, allowing ions to "leak" across the membrane down their concentration gradient
• Gated channels


  Closed until opened by specific signals, either chemically gated or voltage-gated, can change the membrane potential and are responsible for the action potential
• Sodium-potassium pump


  Compensates for the constant leakage of ions through leak channels by actively transporting K+ into the cell and Na+ out of the cell, consuming 25% of all the ATP in a typical cell and 70% of the ATP in a neuron
• Resting membrane potential


  Exists because of the higher concentration of K+ on the inside of the cell membrane and the higher concentration of Na+ on the outside, as well as the presence of many negatively charged molecules such as proteins
• Gated channels


  Closed until opened by specific signals
• Types of gated channels

  • Chemically gated
  • Voltage-gated
• Chemically gated channels


  Opened by neurotransmitters or other chemicals
• Voltage-gated channels


  Opened by a change in membrane potential
• Gated channels can change the membrane potential and are responsible for the action potential
• Sodium-potassium pump


  Compensates for the constant leakage of ions through leak channels
• The sodium-potassium pump is required to maintain the greater concentration of Na+ outside the cell membrane and K+ inside</b>
• The sodium-potassium pump actively transports K+ into the cell and Na+ out of the cell
• The sodium-potassium pump consumes 25% of all the ATP in a typical cell and 70% of the ATP in a neuron
• Resting membrane potential


  Exists because of the higher concentration of K+ on the inside of the cell membrane and the higher concentration of Na+ on the outside, the presence of many negatively charged molecules inside the cell, and the presence of leak protein channels that are more permeable to K+ than Na+
• Na+ tends to diffuse into the cell and K+ tends to diffuse out


  The sodium-potassium pump recreates the Na+ and K+ ion gradient by pumping Na+ out of the cell and K+ into the cell
• Action potentials allow conductivity along nerve or muscle membrane, similar to electricity going along an electrical wire
• Voltage-gated Na+ and K+ channels

  Responsible for the action potential, closed during rest (resting membrane potential)
• Action potential generation


  1. Stimulus applied

  2. Na+ channels open briefly, Na+ diffuses quickly into cell

  3. Depolarization occurs

  4. If depolarization is large enough, threshold reached and Na+ channels open further

  5. Massive increase in membrane permeability to Na+

  6. Voltage-gated K+ channels open

  7. Repolarization occurs as K+ leaves cell

  8. Hyperpolarization occurs briefly
• Action potentials occur in an all-or-none fashion