ANP 1106 Lecture 24: ANP1106 – Neurons
29 Apr 2018
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ANP1106 – Neurons
Organization of the Nervous System
- To adapt to environment we must perceive, plan action and execute
- 2 levels of integration:
o 1) Reflexes – simple mechanisms and well known
o 2) Voluntary actions – complex mechanisms and not well-known
- NS divided into
o CNS – includes brain and spinal cord, integrating and controlling
center
o PNS – part outside the CNS, includes nerves formed of axons that
extend from brain and spinal cord (spinal nerves, cranial nerves)
▪ 2 subdivisions:
• 1) Sensory or afferent division – afferent nerves that
convey impulses to the CNS
o Somatic sensory fibers – from skin, muscles
o Visceral sensory fibers – from organs
• 2) Motor or efferent division – nerves that convey from
CNS to effector organs
o Somatic NS – transmits efferent info from CNS to
muscles, voluntary
o Autonomic NS – transmits efferent info from CNS
to internal organs, involuntary
▪ Sympathetic
▪ Parasympathetic
Neuron: Ionotrophic Receptor
- In the presynaptic terminal, the AP triggers the opening of the Ca voltage-
gated channels, allows entry of calcium to serve as second messenger for the
release of neurotransmitters into synaptic cleft
o Artificially injecting Ca into terminal also triggers neurotransmitters
in the absence of AP
- Neurotransmitter in the synaptic cleft binds to the postsynaptic ionotropic
receptor of a ligand-gated channel and produces a synaptic potential
(excitatory or inhibitory) in postsynaptic neuron
o Ligand channels only found in soma and dendrites
o To terminate the neurotransmitter:
▪ 1) Enzymes in synaptic cleft
▪ 2) Endocytosis by presynaptic terminal
Neuron: Neurotransmitter Structure
- To be classified as a neurotransmitter (classified by chemical structure):
o 1) Must be released by presynaptic terminal after depolarizing action
potential stimulus received
o 2) Must have a postsynaptic receptor
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