Nervous Sysem

• Nervous Tissue


  Excitable characteristic that allows for generation of nerve impulses called Action Potentials
• Major Divisions of the Nervous System

  • Central Nervous System
  • Peripheral Nervous System
• Divisions of the Peripheral Nervous System

  • Autonomic Nervous System
  • Somatic Nervous System
• When studying for an exam, you reach for a beverage

  Your somatic nervous system is activated
• Enteric Nervous System (ENS)


  Division of the Peripheral Nervous System called the "brain of the gut"
• Enteric Nervous System


  • Involuntarily controls GI propulsion, and acid and hormonal secretions
  • Consists of over 100 million neurons in enteric plexuses that extend most of the length of the GI tract
• Functions of the Nervous System

  1. Sensory input

  2. Integration

  3. Motor output
• Sensory System (PNS)


  Input; sense changes in the internal and external environment through sensory receptors, sensory neurons serve this function
• Interpretation System (CNS)


  Process; interpret the sensory information, store some aspects, and make decisions, association or interneurons serve this function
• Motor Response (PNS)


  Output; respond to the stimuli by initiating the appropriate action in effectors (muscles and glands), motor neurons serve this function
• Sensory Function


  • Smell of coffee stimulates sensory receptors in nose
• Integrative Function


  • Olfactory information is subsequently relayed into brain where it is processed and the decision to drink the coffee is made
• Motor Function


  • Brain stimulates the contraction of specific muscles that allow you to grab a cup of Coffee and drink it
• Amyotrophic Lateral Sclerosis (ALS)
• In 90 to 95 percent of all ALS cases, the disease occurs apparently at random with no clearly associated risk factors
• Motor neurons throughout brain and spinal cord die and stop sending messages to skeletal muscles
• Muscles gradually weaken
• Respiratory failure due to weakened diaphragm and internal intercostal (muscles necessary for respiration)
• Sensory neurons and interneurons are not affected so awareness and reasoning do not deteriorate
• 2 Main Types of Nerve Cells

  • Neuron
  • Neuroglia (glial cells)
• Neuron

  Specialized cells of the nervous system that transmit signals throughout the body; "thinking" cells of brain, has property of electrical excitability (the ability to respond to a stimulus)
• The NS Contains Over 100 Billion Neurons
• Neuroglia

  Play a major role in support and nutrition of the brain, but they do not manipulate information, maintain the internal environment so that neurons can do their jobs
• Nerve cells cannot bring messages to muscles, to glands, or to other neurons by touching their axons to those other cells. Contact between a nerve cell and other tissues is not enough to send a message to those tissues. The neurotransmitters released at the synapse are responsible for transmitting the message.
• Dendrites

  Receiving end of neuron, short, highly branched structures that receive signals and conduct these impulses toward the cell body
• Cell Body/ Soma/ Perikaryon


  Nucleus surrounded by cytoplasm, contains organelles such as lysosomes, mitochondria, Golgi complexes, and Nissl bodies, Nissl bodies are the primary site of protein synthesis
• Axon


  Conducts Impulses AWAY from Cell Body to Other Cells
• Synapse


  Site of communication between two neurons or between a neuron and another effector cell, Synaptic cleft is the gap between the pre and post-synaptic cells
• Synaptic End Bulbs Contain

  • Synaptic vesicles - tiny membrane-enclosed sacs that store packets of neurotransmitters, may contain two or even three types of neurotransmitters, each with different effects on the postsynaptic cell
• Neurotransmitters


  Signaling molecules used at synapses to pass an excitatory or inhibitory signal from a neuron to its target cell
• Neuron Transport


  1. Slow axonal transport

  2. Fast axonal transport
• Fast Axonal Transport


  Moves material in both directions, Anterograde (forward) direction - moves organelles and synaptic vesicles from the cell body to the axon terminals, Retrograde (backward) direction - moves membrane vesicles and other cellular materials from the axon terminals to the cell body to be degraded or recycled
• Substances that enter the neuron at the axon terminals are also moved to the cell body by fast retrograde transport, including trophic chemicals such as nerve growth factor, as well as harmful agents such as tetanus toxin, botulinum toxin, and the viruses that cause rabies and polio.
• Structural Classification of Neurons

  • Based on the number of processes (axons or dendrites) extending from the cell body
  • Located throughout brain & spinal cord; all motor neurons; most common
  • Convey special senses of sight, smell, hearing, and balance (i.e. retina of eye, inner ear, olfactory)
  • Sensory neurons that convey touch and stretching information from extremities
• Classification of Neurons


  • Cerebellum
  • Cerebral Cortex
• Motor Neurons


  Convey signals from the CNS to muscles and glands
• Neuroglia


  Do not generate nerve impulses, glial cells function to serve, protect, and support neurons
• Gliomas are tumors derived from glial cells that grow in the CNS or PNS, they are highly malignant and grow rapidly
• Astrocytes


  • Star-shaped cells, encircle vessels and make up blood-brain barrier, provide nutrients for neurons, give structural support to nerve cells, regulate ion, nutrient, and dissolved gas concentration, absorb and recycle neurotransmitters
• Microglial Cells


  • Remove cell debris, wastes, and pathogens by phagocytosis, promote repair in the CNS