NEURAL TISSUE

I. Overview of Nervous System

1. CNS: central nervous system, brain and spinal cord, protected by bone, integrates, processes and coordinates information
2. PNS: peripheral nervous system, cranial and spinal nerves

1. sensory: afferent, receptors send information to CNS
a. somatic nervous system: from skin, fascia, joints
b. visceral nervous system: from internal organs
2. motor: efferent (exit), effectors, from CNS
a. somatic nervous system SNS: voluntary, impulse to skeletal muscles
b. autonomic nervous system ANS: automatic, involuntary, visceral, impulses to smooth muscles, heart, glands
1) sympathetic: accelerates heart rate "fight or flight"
2) parasympathetic: slows heart rate "rest and relaxation"

II. Neuroglia: support cells

1. ependymal cells: epithelial cells line cavities, produces and circulates cerebrospinal fluid
2. astrocytes: large star-shaped cells with many processes maintains blood-brain barrier, provides support, regulates ions, nutrients and gases, absorbs and recycles neurotransmitters, tissue repair
3. oligodendrocytes: form myelin sheath, provide structural support
a. gray matter: nucleus in brain or horn of spinal cord, integration
b. white matter: nerve conduction
4. microglia:microphage, removes dead tissue and foreign matter

1. satellite cells: surround neuron cell bodies in ganglia
2. Schwann cells: spiral wrapping of myelin, repairs axons
3. demyelination diseases
a. diptheria: bacterial infection, damages Schwann cells
b. Guillain-Barre: virus, progressive demyelination
c. multiple sclerosis: recurrent bouts of demyelination
d. Tay-Sachs disease: gradual deterioration of neurons due to buildup of wastes

III. Neurons

1. perikaryon: cytoplasm around nucleus
2. cytoskeleton: neurofilaments, neurotubules, neurofibrils
3. mitochondria and ribosomes
4. nissl bodies: rough ER, forms ganglion in PNS
5. in CNS cells lose centrioles, can't divide

1. collaterals: axon may branch
2. telodendria: fine branches, ends contain synaptic knobs that release neurotransmitters
3. rabies: virus moves by retrograde flow up axons to CNS

1. anaxonic: small, axons like dendrites, in CNS, sense organs
2. unipolar: 1 process from soma in PNS
3. bipolar: 2 processes, mostly in embryo
4. multipolar: 1 axon, several dendrites, most common

1. sensory neurons: afferent, unipolar, from receptor to CNS
a. receptors: receive sensory information
1) exteroceptors: from external environment
2) proprioceptors: tells position of muscles and joints
3) interoceptors: internal organs, deep pressure and pain
2. motor neurons: efferent, multipolar, from CNS to effector, muscle or gland
3. interneurons: in CNS only, association, multipolar, from one neuron to another

IV. Neural Physiology

1. chemical gradients
a. more Na+ and Cl- outside, more K- and Proteins- inside
b. diffusion: K+ moves outside faster than in; Na+ moves in faster than out
c. Na - K pump, pumps Na+ out, K+ in, takes ATP
2. electrical gradients:
a. membrane permeability to K+ is greater than Na+
b. just inside membrane (-) negative, outside (+) positive
c. resistance: cell membrane resists free movement of ions, can be changed by opening and closing gated channels
d. potential difference: created when + and - ions are separated by a membrane
e. + and - ions attract
f. current: movement or flow of electrical charges
1) when resistance is high, current is low
2) when resistance is low, current is high
3. electrochemical gradient: sum of electrical and chemical potential energy

1. all or none principle
2. threshold: small push to get it started
3. depolarization to threshold
a. Na channels open, Na+ rushes in
b. becomes + inside and - outside membrane
4. repolarization
a. Na gates close, K gates open, K+ goes out
b. becomes - inside and + outside again
5. refractory period: resting stage, return to normal
a. absolute: no action possible, Na channels back to normal
b. relative: needs stimulus greater than normal to stimulate, K channels return to normal

1. continuous in unmylenated axon: current flows along axon
2. saltatory in mylenated axon: jumps from 1 node to the next
3. larger axon diameter: lower resistance: goes faster

1. excitatory: acetylcholine, glutamate and aspartate
2. norepinephrine: sympathetic, maintains arousal, dreaming, regulates mood
3. epinephrine: brain stem, behavior, mood and emotions
4. dopamine: in brain, regulates emotional response and complex movements
5. serotonin: in brain, temperature regulation, sensory perception, sleep
6. blockers:
a. cholinesterase inhibitors: block breakdown of ACh
b. atropine: prevents ACh from binding to postsynaptic membrane
c. nicotine: binds to ACh receptor sites and stimulates postsynaptic membranes
7. summation: add effects of stimuli
a. temporal: more than 1 stimulation at 1 synapse
b. spatial: many sources for stimulation at 1 synapse
c. facilitation: getting to threshold and generating an impulse makes more impulses easier
8. adaptation: continuous stimulus lessens frequency of impulses with time
9. rate: greater depolarization, greater frequency of action potential generation

V. Factors that Affect Neural Function

1. divergence: 1 neuron goes to several
2. convergence: several neurons go to 1
3. serial processing: function in sequence
4. parallel processing: several neurons may process same information at once
5. reverberation: collateral axon stimulate presynaptic neurons