Lecture 17

• Theme 2: Integrating and coordinating roles of the nervous system

  
• The myelin sheath in the CNS is made by Oligodendrocytes
• The part of neurotransmission that is carried out through a chemical signal is called Synapse
• Information that travels into the CNS is called Afferent
• The part of a neuron that makes the decision about whether to propagate an action potential in response to inputs is called Axon hillock
• Divisions of the nervous system: I. Based on direction of information flow

  1. Information comes IN through RECEPTORS

  2. AFFERENT SENSORY (IN)

  3. Integration/coordination

  4. EFFERENT MOTOR (OUT)

  5. ACTION, EFFECTORS respond to motor command
• Somatic


  The stuff we are aware of, have control over
• Autonomic


  The stuff we are not aware of, have no control over
• Divisions of the nervous system: II. Based on type of information transmitted

  1. SENSORY AFFERENT (IN)

  2. MOTOR EFFERENT (OUT)

  3. Integration/coordination

  4. ACTION, EFFECTORS respond to motor command
• Somatic efferent (motor) division

  • Two neurons between brain and effector:

  1. Upper motor neuron (cell body in brain, axon in spinal cord)

  2. Lower motor neuron (cell body in spinal cord, axon in spinal nerve)

  Effectors = skeletal muscle fibres
• Upper motor neuron


  • Cell body in brain, axon in spinal cord, axon is myelinated
• Lower motor neuron


  • Cell body in spinal cord, axon in spinal nerve, axon is myelinated
• Neuromuscular junction


  1. Pre-synaptic cell (lower motor neuron)

  2. Post-synaptic cell (effector, muscle)

  3. Neurotransmitter = Acetylcholine (ACh)
• Voluntary movement involves two neurons between brain and effector: upper motor neuron and lower motor neuron
• Autonomic nervous system


  • Involuntary control, two divisions: Sympathetic and Parasympathetic, effectors = smooth muscle, cardiac muscle, glands, adipose tissue, three neurons between brain and effector
• Autonomic nervous system: neuron organization

  1. Neuron #1 (cell body in CNS, axon in CNS)

  2. Neuron #2 (cell body in CNS, axon in PNS)

  3. Neuron #3 (cell body in PNS, axon in PNS)
• Pre-ganglionic neuron


  Neuron #2, cell body in CNS, axon extends in PNS, myelinated, synapse in autonomic ganglion, neurotransmitter = acetylcholine (ACh)
• Post-ganglionic neuron


  Neuron #3, cell body in PNS (autonomic ganglion), axon extends in PNS to effector organ, unmyelinated, synapse on effector organ, neurotransmitter = ACh or norepinephrine
• Neuron #2


  • Cell body in CNS
  • Axon extends in PNS
  • Myelinated
  • Synapse in Autonomic Ganglion
  • Pre-ganglionic neuron
• Neuron #3


  • Cell body in PNS, autonomic ganglion
  • Axon extends in PNS, to effector organ
  • Unmyelinated
  • Synapse on effector organ
  • Post-ganglionic neuron
• Neurotransmitter for Neuron #2 is acetylcholine (ACh)
• Neurotransmitter for Neuron #3 can be acetylcholine (ACh) or norepinephrine
• Divisions of the nervous system based on type of information transmitted

  • Sensory (afferent)
  • Motor (efferent)

  
• Sympathetic nervous system prepares the body for acute/stress responses ("fight or flight")
• Parasympathetic nervous system prepares the body for restful situations ("rest and digest")
• Sympathetic nervous system


  • Preganglionic neuron: Cell body in thoracolumbar levels of spinal cord, axon is short, synapse in sympathetic ganglion
  • Postganglionic neuron: Cell body in sympathetic ganglion, axon is long, unmyelinated
• Parasympathetic nervous system


  • Preganglionic neuron: Cell bodies in cranial (brainstem) and sacral (spinal cord) levels, axon is long, synapse in parasympathetic ganglia
  • Postganglionic neuron: Cell body in parasympathetic ganglia in or near the effector organs, axon is short
• Sympathetic preganglionic neurotransmitter is acetylcholine
• Sympathetic postganglionic neurotransmitter is mostly norepinephrine
• Parasympathetic preganglionic and postganglionic neurotransmitter is acetylcholine