16) Nerve structure and Function

• Organisation of the nervous system:

   - The nervous system can be divided into the central (CNS) and peripheral nervous system (PNS)
• The nervous system has 3 components:

  1. Sensory (afferent)
  2. Integrative (central)
  3. Motor (efferent) 

  ⤷ Motor component can be divided into somatic and autonomic 
• Somatic: Voluntary movement (Skeletal muscles) 

  Autonomic: Involuntary (Smooth muscle, glands) 
• Neuroglia cells consist of four cell types

  1. Astrocytes
  2. Oligodendrocytes 
  3. Microglia
  4. Ependymal
• The nervous system is made up of neuronal and non-neuronal cells (Neuroglia)
• 1. Astroglia (star) - Attach to blood vessels in CNS and form the blood-brain barrier between blood and cerebrospinal fluid
• Oligodendroglia (tree) Form Myelin sheaths (Similar to shwann cells in PNS) 
• Microglia - Scattered throughout the CNS to protect against infection by producing many cytokines (macrophages)
• Ependymal - Columnar epithelial cells that line fluid spaces
• Structure of a neurone: 

   - Myelin sheath made of lipoprotein cover the axon

   - 1µm gaps between (nodes of ranvier) 

   -  In the CNS, Myelin sheath is formed by olidendroglia and in the PNS is formed by Schwann cells
• The reflex arc:

  Sensory receptor ⟶ Sensory (afferent) neurone ⟶ synapse ⟶ efferent (motor) neurone ⟶ effector organ 
• Structure of a peripheral nerve:

  in the CNS, Axons are protected by vertebral and cranial bones

  ⤷ Outside of the CNS they run in the PNS along major blood vessels  

   - On myelin sheaths axons are protected by connective tissues
• Peripheral nerves are bundles of axons that connect the CNS to the rest of the body, allowing sensory perception, motor control, and coordination of bodily function
• Axoplasmic Transport is the movement of materials within the axon of the neurone!

   - This occurs along the axons cytoplasm (axoplasm) 
• Factors that influence resting potential:

  1. the semi-permeable nature of the cell membrane
  2. The unequal distribution of ions between the inside and outside of the cell
  3. Presence of ion pumps for active transport
  4. Presence of ion channels on the cell membrane
• The cell membrane is selectively semi-permeable and only allow some ions to diffuse across

  ⤷ K+ channels are open even during resiting state
• The movement of ions across the cell membrane is influenced by the an electrochemical gradient
• a cell’s activity is influenced by secondary messengers such as cAMP, DAG and hormones (eg: thyroid hormones)
• When a significant influx of Na+ arrives at a neurone beyond a threshold, it changes membrane potential and triggers an action potential down an axon
• During resting state:

  • 3Na+ are being Actively pumped out of a neurone whilst 2K+ are simultaneously being pumped into the neuron
• Synapses are Junctions between neurones or effectors.

  There two types of synapses

  • Chemical (location and neurotransmitter)
  • Electrical (rectifying and non rectifying)