NERVOUS

• Nervous System

  • most complex
  • composed of neurons (nerve cells) and Neuroglia/Glial (supporting cellß
• somites

  • determines the path where neural crest cells go
• irritability

  • react to various stimuli
  • "react"
• conductivity

  • transmit impulses
  • "transmit"
• CNS - brain (cerebrum, cerebellum) and spinal cord
• PNS - cranial nerves, spinal nerves, ganglia
• Ganglia: masses or groups of neuronal bodies or soma, pericarion of nerve cell, grouped to form ganglion
• Plexuses: elongated processes that emanate from the neuronal body called axons, grouped into plexuses (made of axonal fibers), extensive network found in the CNS
• Nerve or neuronal fiber: groups of axons which made up nerve fibers
• Enteric plexuses: GI intestine (location; "eneteri- or entero-")
• Functional Division:

  1. Sensory (Afferent) - periphery to CNS, has receptors
  2. Motor (Efferent) - CNS to body, motor info to effectors
• Somatic sensory:

  • receive sensory info from skin, special senses, joints
• Visceral Sensory

  • receive sensory info from viscera
• somatic motor

  • voluntary
  • innervate skeletal muscle
• autonomic motor

  • involuntary
  • innervates cardiac, smooth muscles
  • parasympathetic, sympathetic, enteric nervous system
• parasympathetic - rest and digest
• sympathetic - fight or flight
• enteric nervous system - brain of the gut
• neurulation - development of neurons
• neural plate = neural folds + neural groove
• somite - structure important in determining migratory paths or the pathway of the neural crest cells
• odontoblast - found in teeth, forms dentine
• neurons:

  • functional unit
  • permanent cell: cannot divide
  • large cell
  • transmit, receive signals
• neuroglia/glial cells

  • smaller
  • abundant
  • six types
  • capable of mitosis
  • for defense
• parts of neuron

  1. cell body/perikaryon/soma
  2. dendrites
  3. axons
• cell body/perikaryon/soma

  • trophic center
  • owls eye or fish eye nucleus
  • prominent cluster of RER = nissl bodies/tigroid substance
• absence of nissl bodies = neuronal injury ; chromatolysis
• nerve processes/fiber

  • largest volume in cell cytoplasm
• dendrites

  • little trees
  • signal reception, processing site of neurons
  • short, tapering, highly branched
  • cytoplasm lacks golgi
  • synapse found in dendritic spines
  • presence of spines - crucial for neural plasticity
• Axon

  • from cell body
  • long cylindrical projection
  • toward another neuron
  • has mitochondria and microtubules
• axon hillock - attachment site, pyramidal or triangular, axon originates
• axon collateral - branches along length of axon, found in interneurons and motor neurons
• axolemma - membrane

  axoplasm - contents of axolemma
• telodendria - branches found at the ends of axons
• boutons - end of telodendria
• axon terminal/axon boutons

  • end of axon and its collaterals
• classification of neurons accrdg to no. of processes

  1. multipolar: dendrites, cell body, axon
  2. bipolar: dendrite, cell body, axon
  3. unipolar: dendrite, axon, cell body
  4. anaxonic: no axon
• multipolar neurons:

  • several dendrites, one axon
  • CNS interneurons, all motor neurons
• bipolar neurons:

  • one main dendrite, one axon
  • retina of eye, inner ear, olfactory area
• unipolar neurons:

  • dendrites and one axon are fused
  • spinal and cranial ganglia