Neuron

 

Functional classification of neurons

Sensory neurons

These are provided with receptors

There are two types of sensory receptors- exteroceptors and interoceptors. Exteroceptors are placed externally, while interoceptors are internal and within organs.

Exteroceptors

  • Ruffini’s end organs
  • Krause end bulb
  • Meckel’s disc
  • Golgi-Mazzoni bodies
  • Free nerve endings.

All these are involved in touch and deep pressure (i.e. mechanoceptors), except free nerve endings, which carry pain impulses. Pain fibers are usually non-medullated and so the conduction is slow. They have a function structure in which there ganglions are placed in the dorsal root containing cell bodies which provide peripheral and central fibers. Peripheral fiber is attached to the sensory receptors while the central fiber enters the spinal cord or brain in the head region.

Motor neurons

These are divided into autonomic neurons and somatic neurons

Autonomic neurons usually have two fibers in their pathways.

1.                  Presynaptic (or preganglionic) neurons, which run from the central nervous system to the autonomic ganglia

2.                   Postsynaptic (or postganglionic)neuron, which runs from the ganglion to the effector cell. Most of them belong to one of the following categories

  • ·        Vasomotor (blood vessels)

  • ·        Sudomotor (sweat glands)

  • ·        Myomotor (smooth muscle)

  • ·        Secretomotor (glands)

  • ·        Pilomotor (hair on skin)

Somatic motor nerves usually have only one neuron in their path. They run from the central nervous system to the effector organ, which is usually skeletal or striated muscle forming so called myoneural (neuromuscular) junction. At this junction neurotransmitters are also required to depolarize the muscular membrane in order to cause contraction of the muscle.

 

 

 

 

 

 

 

 

 

 

 

       

Spinal nerve and mature spinal cord: 1 posterior horn 2 intermediolateral horn 3 ventral horn 4 prevertebral sympathetic ganglion 5 dorsal root ganglion 6 dorsal ramus 7 spinal nerve 8 white ramus communicans 9 gray ramus communicans 10 interneuron 11 lateral cutaneous nerve 12 anterior cutaneous branch 13 sensory root 14 motor root  

 

 

 

 

 

 

 

 

 

 

 

 


 

 

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