NERVOUS SYSTEM

• Nervous System


  • The communication system, receiving signals from and sending commands to different areas of the body
  • Helps coordinate the body functions to maintain homeostasis
• Functions of the Nervous System

  • Receiving Sensory Input
  • Integrating Information
  • Controlling Muscles and Glands
  • Maintaining Homeostasis
  • Establishing and Maintaining Mental Cavity
• Divisions of the Nervous System

  • Central Nervous System
  • Peripheral Nervous System
• Central Nervous System


  • Interprets incoming action potential
  • Initiates action potentials that are conducted through the motor divisions: response
• Divisions of the Central Nervous System

  • Somatic
  • Autonomic
• Peripheral Nervous System


  • The communication link between the CNS and various parts of the body
  • Carries information about the different tissues of the body to the CNS
  • Delivers command from the CNS to other body tissues that alter body activities
• Divisions of the Peripheral Nervous System


  • Sensory Division
  • Motor Division
• Sensory Division


  • Afferent division
  • Conducts action potentials from sensory receptors to the CNS
  • Sensory Neurons: Action potentials from the periphery to the CNS
• Motor Division


  • Efferent division
  • Conducts action potentials from the CNS to effector organs
  • Motor Neurons: Action potentials from the CNS toward the periphery
• Motor Division

  • Somatic: Transmits action potentials from CNS to skeletal muscle
  • Autonomic: Transmit action potentials from the CNS to Cardiac muscle, smooth muscle, and glands
• Enteric Nervous System


  • Has both sensory and motor neurons contained wholly within the digestive tract
  • Function without input from CNS or other parts of the PNS
  • Integrated with the CNS by sensory neurons and ANS motor neurons
• Neurons


  • Nerve cells
  • Receive stimuli
  • Conduct action potentials
  • Transmit signals to other neurons or effector organs
• Parts of a Neuron

  • Cell Body
  • Axons
  • Dendrites
• Types of Neurons

  • Multipolar Neurons
  • Bipolar Neurons
• Multipolar Neurons


  • With many dendrites and a single axon
  • Most of the neurons within the CNS and all motor neurons
• Bipolar Neurons


  • With two processes: One dendrite and one axon
  • Sensory organs: retina of the eyes and nasal cavity
• Glial Cells


  • Neuroglia
  • Supportive cells of the CNS and PNS
  • Do not conduct action potentials
  • Enhance neuron function
  • Maintain normal conditions within nervous tissue
  • More numerous than neurons
  • Most retain the ability to divide
• Types of Glial Cells

  • Astrocytes
  • Ependymal Cells
  • Microglia
  • Oligodendrocytes
  • Schwann Cells
  • Satellite Cells
• Astrocytes


  • Major supporting cells in the CNS
  • Stimulate or inhibit the signaling activity of nearby neurons
  • Form a permeability barrier (blood brain barrier) between the blood and CNS
  • Limit damage to neural tissue
• Ependymal Cells


  • Line fluid filled cavities within the CNS
  • Produce cerebrospinal fluid through the CNS
• Microglia


  • Act as immune cells of the CNS
  • Help protect the brain by removing bacteria and cell debris
• Oligodendrocytes


  Provide an insulating material that surrounds axons
• Schwann Cells


  Provide insulating material around axons
• Satellite Cells


  • Found around the cell bodies of certain neurons of the PNS
  • Provide support and nutrition to the neurons
  • Protect the neurons from heavy-metals poisons (mercury and lead)
• Myelin Sheaths


  • Specialized layers that wrap around the axons of some neurons
  • Formed by the cell processes of oligodendrocytes in the CNS and Schwann cells in the PNS
  • Excellent insulator that prevents almost all ion movement across the cell membrane
• Nodes of Ranvier


  • Gaps in the myelin sheath
  • Ion movement occurs
• Gray Matter


  • Consists of groups of neuron cell bodies and their dendrites
  • There is very little myelin
  • CNS- Cortex
  • PNS- Ganglion
• White Matter


  • Consists of bundles of parallel axons with their myelin sheaths
  • CNS: Consists of bundles of parallel axons with their myelin sheaths
  • PNS:Consists of bundles of axons and associated connective tissue that forms nerves
• Resting Membrane Potential


  • Voltage difference in an unstimulated (or resting) cell that can be measured across the cell membrane
  • Generated primarily by the uneven distribution of K+, Na+ and negatively charged proteins across the cell membrane
• Resting Membrane Potential

  Na+ channels and most but not all, K+ channels are closed. The outside of the cell membrane is positively charged compared to the inside.
• Depolarization


  Na+ channels open. K+ channels begin to open. Depolarization results because the inward movement of Na+ makes the inside of the membrane positive.
• Repolarization


  Na+ channels close and additional K+ channels open. Na+ movement into the cell stops, and K+ movement out of the cell increases, causing repolarization.
• In a resting cell, there is a higher concentration of K+ (purple circles) inside the cell membrane and a higher concentration of Na+ (pink circles) outside the cell membrane. Because the membrane is not permeable to negatively charged proteins (green) they are isolated to the inside of the cell membrane.
• There are more K+ leak channels than Na+ leak channels. In the resting cell, only the leak channels are opened; the gated channels (not shown) are closed. Because of the ion concentration differences across the membrane, K+ diffuses out of the cell down its concentration gradient and Na+ diffuses into the cell down its concentration gradient. The tendency for K+ to diffuse out of the cell is opposed by the tendency of the positively charged K+ to be attracted back into the cell by the negative charge inside the cell.
• The sodium-potassium pump helps maintain the differential levels of Na+ and K+ by pumping three Na+ out of the cell in exchange for two K+ into the cell. The pump is driven by ATP hydrolysis. The resting membrane potential is established when the movement of K+ out of the cell is equal to the movement of K+ into the cell.
• Neuron Communication


  • Generation of action potentials
  • Action potential propagation along the cell membrane
  • Communication with target cell at the synapse
• Converging Pathways


  • Two or more neurons synapse with the same postsynaptic neuron
  • Allows information transmitted in more than one neuronal pathway to converge into a single pathway
• Diverging Pathways


  • Axon from one neuron divides and synapses with more than one other postsynaptic neuron
  • Allows information transmitted in one neuronal pathway to diverge into two or more pathways
• Brain


  Housed within the skull
• Spinal Cord


  • Housed in the vertebral column
  • Extends from the foramen magnum at the base of the skull to the second lumbar vertebra
  • Spinal nerves communicate between the spinal cord and the body
  • Inferior end of the spinal cord and spinal nerves that exit resemble a horse's tail and are collectively called the caudaequina
  • Superficial white matter portion: consists of myelinated axons