Neurons

The Structure of a Neuron

1 Neurons

a.     have specialized cell structures that enable them to transmit nerve impulse.

b.     Have different types but all have 4 common features:

                                               i.     Dentrites

1.     short, branching terminals that receive nerve impulses from other neurons and relay the impulse to the cell body.

2.     Numerous and highly branched

                                              ii.     Cell body

1.     contains nucleus and site of cell’s metabolic reactions

2.     processes input from the dendrites

3.     if input is large, CB relays to axon

                                            iii.     Axon

1.     Conducts impulses away from the cell body

2.     Different lengths

                                            iv.     Branching ends

1.     Branches into many fibers

2.     Communicate with adjacent neurons, glands, muscles by releasing chemical signals into the space between it and the receptors.

c.      Some neurons- myelin sheath

                                               i.     Fatty insulating layer

                                              ii.     Gives axons a glistening white appearance

                                            iii.     Protects neurons and speeds the rate of nerve impulse transmission

                                            iv.     Composed of Schwann cells

Classifying Neurons

      I.         Three types of neurons (Structure)

a.     Multipolar

                                               i.     Several dendrites, single axon, found in brain and spinal cord

b.     Bipolar

                                               i.     Single dendrite, single axon, found in inner ear, retina, olfactory are of brain

c.      Unipolar

                                               i.     Singles process that extends from the cell body, dendrite and axon are fused, found in peripheral nervous system

    II.         Three types of neurons (function)

a.     Sensory neurons (Sensory input)

                                               i.     Receive stimuli(ex. Skin) and nerve impulse

                                              ii.     Transmits impulses to central nervous system

b.     Interneurons

                                               i.     Found within central nervous system

                                              ii.     Link between sensory and motor

                                            iii.     Process and integrate incoming sensory information

c.      Motor neurons

                                               i.     Transmit information from the central nervous system to effectors (Ex.Muscles, glands, and other organs that respond to impulses from motor neurons)

Sensory input(collect information) > Integration > Motor output (effectors)

The Reflex Arc

      I.         Reflexes- sudden, involuntary responses to stimuli (ex. Blinking, vomiting, jerking hand from hot object)

    II.         Reflex arcs

a.     simple connections of neurons that explain reflexive behaviours.

b.     Usually involve three neurons

c.      Can be very rapid(Example, pressure of cactus needle)