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
• Neurons


  • Cell body - which contains a single nucleus
  • Dendrite - a cytoplasmic extension from the cell body, that usually receives information from other neurons and transmits the information to the cell body
  • Axon - a single long cell process that leaves the cell body at the axon hillock and conducts sensory signals to the CNS and motor signals away from the CNS
• Structural Types of Neurons

  • Multipolar neurons - have many dendrites and a single axon. Most of the neurons within the CNS and nearly all motor neurons are multipolar
  • Bipolar neurons - have two processes: one dendrite and one axon. Bipolar neurons are located in some sensory organs, such as in the retina of the eye and in the nasal cavity
  • Pseudo-unipolar neurons - have a single process extending from the cell body, which divides into two processes a short distance from the cell body. One process extends to the periphery, and the other extends to the CNS. The two extensions function as a single axon with small, dendrite-like sensory receptors at the periphery
• Types of Neurons Figure 8.4
• Glial Cells


  • Astrocytes - serve as the major supporting cells in the CNS. Astrocytes 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, those neurons are termed, myelinated
  • 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
• Nodes of Ranvier


  • Gaps in the myelin sheath that occur about every millimeter
  • Ion movement can occur at the nodes of Ranvier
  • 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


  • Lack the myelin sheaths
  • Rest in indentations of the oligodendrocytes in the CNS and the Schwann cells in the PNS
  • A typical small nerve, which consists of axons of multiple neurons, usually contains more unmyelinated axons than myelinated axons
• 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 Potentials and Action Potentials

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


  • Leak channels - always open, ions can "leak" across the membrane down their concentration gradient
  • Gated channels - generally closed, but can be opened due to voltage or chemicals
• Leak Channels


  • There are 50 to 100 times more K+ leak channels than Na+ leak channels, so the resting membrane has much greater permeability to K+ than to Na+, contributing the most to the resting membrane potential
• Gated Channels


  • Opened by specific signals
  • Chemically gated channels are opened by neurotransmitters or other chemicals
  • Voltage-gated channels are opened by a change in membrane potential
  • When opened, 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
  • Actively transports K+ into the cell and Na+ out of the cell
  • 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, and the presence of many negatively charged molecules, such as proteins, inside the cell
• 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, and the presence of negatively charged molecules inside the cell and leak protein channels more permeable to K+ than Na+
• Maintaining the resting membrane potential

  1. Na+ tends to diffuse into the cell and K+ tends to diffuse out

  2. 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

  Closed during rest (resting membrane potential)