Intro to Nervous System

NS Function

• Sensory input
• Integration
• Motor output

Division

• CNS: spinal cord, brain
• PNS: 31 spinal & 12 cranial nerve
• sensory
• somatic sensory
• visceral motor 
• motor
• somatic motor: voluntary = SNS 
• visceral motor: involuntary = ANS
• Sympathetic NS: fight or flight - increase heart rate 
• PSNS: rest 
• ENS = GI 

Nervous Tissue 

• neurons
• excitable
• highly specialized
• basic functional unit 
• structural unit
• extreme longevity
• no divide 
• exceptionally high metabolic rate 
• cannot survive more than few min w/o O2
• large, complex cells
• produce AP 
• component:
• cell body = perikaryon = soma
•  5-120 um diameter
• single spherical nucleus 
• cytoplasm no centriole 
• nucleolus 
• chromatophilic (Nissl) bodies = rER + ribosome 
• neurofibrils = cytoskeleton 
• microtubule
• lipofuscin in aging neuron 黄褐granule 
• process
• dendrite = receive info & carry to soma 
• axon 
• away neuron = efferent 
• fatter axon, faster impulse travel 
• preganglionic fiber = axons from CNS to ganglion
• postganglionic fiber = ganglion to effector 
• myelin sheath/neurilemma
• axon hillock 头
• axon terminal 尾
• initial segment 最靠近头
• trigger zone = nerve impulse arise at junction of axon hillock & initial segment 
• axoplasm
• axolemma
• axon collateral = side branches of axon 
• functional region
• receptive
• conducting 
• secretory 
• tracts in CNS, nerves in PNS
• structural classification
• anaxonic 
• multipolar = multiple process
• 99%
• major in CNS
• motor neuron 
• bipolar = 2 process
• special sensory organ
• sensory neuron
• pseudo/unipolar
• ganglia of PNS
• most sensory neuron in PNS
• functional classification
• sensory neuron
• motor neuron
• upper in brain, lower in PNS
• interneuron
• multipolar 
• pyramidal cell = large neuron in primary motor cortex of cerebrum
• purkinje cell = cerebellum 
• distribution of sensory info & coordination of motor 
• more complex response, more interneuron involved
• other class
• based on axon length
• Golgi type 1/projection neuron - long axon = pyramidal cell
• Golgi type 2/local circuit - short axon = stellate cell
• based on neurotransmitter
• Ach = cholinergic
• enkephalin = enkephalinergic
• histamine = histaminergic 
• neuroglia = supp cell 
• CNS
• astrocyte 
• largest
• most abundant 
• protoplasmic (gray matter, short branches), fibrous (white matter, unbranch) 
• nourish neuron
• maintain ionic concentration 
• take up accumulation of neurotransmitter
• aid neuronal growth
• synapse formation in developing neural tissue - learning & memory 
• maintain BBB
• create 3D framework for CNS
• repair damage neural tissue 
• provide rapid-transit for nutrient transport, gas exchange 
• control blood flow volume thro capillaries
• microglial
• smallest
• least abundant 
• thorny process
• phagocyte - macrophage 
• ependymal
• cilia 
• CSF
• oligodendrocyte 
• myelin sheath 
• PNS
• Schwann cell
• myelin sheath - single axon 
• repair damage axon
• satellite cell 
• flat 
• structural supp 

Myelin Sheath = 70-80% lipid & protein 

• prevent leakage of electrical current from axon
• increase speed of impulse conduction
• makes impulse propagation more energy efficient 

Myelinated

• PNS
• myelination
• conduct AP 15-150x faster 

Unmyelinated 

• ANS, SNS 

Nodes of Ranvier = gaps btwn myelin sheath

Myelination differences btwn PNS & CNS

• presence of neurolemma = CNS no neurolemma
• no of axons myelinated by a single glial cell = Schwann encircle a portion of a single axon, oligodendrocyte multiple process
• timing = PNS @ early fetal, CNS @ brain

Neuroeffector junction

• neuromuscular
• neuroglandular = neuron control secretory cell

Axonal transport 

• slow
• one direction = away from cell body
• movement at 1-5mm/d
• cytoskeletal proteins & other proteins
• fast 
• moves organelles & materials along surface of microtubule
• vesicle & membrane-bound organelle
• at 200-400mm/d
• transport in anterograde前 or retrograde后