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55 terms

Chapter 12 - Nervous Tissue

Exam IV, nervous tissue, CNS
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Nervous System
Second system in body that controls other systems, very fast acting with a short duration; produces neurotransmitters, local response
Central Nervous System (CNS)
Made up of brain, spinal cord; association neurons
Peripheral Nervous System (PNS)
Everything (aside from brain & spinal cord), composed of nerves & ganglia; sensory division & motor division
Sensory Division
Portion of PNS that takes info to CNS from various receptors, afferent; contains afferent neurons; somatic sensory division & visceral sensory division
Somatic Sensory Division, PNS
Carries signal from receptors in the skin, muscles, bones, & joints (muscles)
Visceral Sensory Division, PNS
Carries signals mainly from the viscera of the thoracic & abdominal covities, such as the heart, lungs, stomach, & urinary bladder (organs)
Motor Division, PNS
Portion that carries info away from CNS to target (muscle, gland, etc.) that carry out the body's responses, efferent
Somatic Motor Division, PNS
Carries signals to skeletal muscles, voluntary control
Visceral Motor Division, PNS
(AKA Autonomic Nervous System) carries signals to glands, cardiac muscle, & smooth muscle, involuntary control

Sympathetic & parasympathetic divisions (+ enteric)
Sympathetic Division, ANS
Arouses body for action -- as in accelerating the heartbeat & increasing respiratory airflow -- but inhibits digestion
Parasympathetic Division, ANS
Tends to have a calming effect -- slowing the heartbeat -- but stimulates digestion
Afferent
Fibers that take information to the CNS
Efferent
Fibers taking information away from the CNS (exit)
Structure of a Neuron
Body (soma) and processes including dendrites & axons
Body (Soma)
Contains most organelle in normal cell, except the centrosome (neurons do not replicate), neurons do NOT regenerate
Nissl Bodies
Dark staining areas, clusters of Rough ER, ribosomes; unique to neurons & aide in tissue identification
Axon Hillock
Funnel like portion of soma, action potentials originate from here
Processes
Dendrites & axons
Dendrite
Receive info (electrical change) and take it to the soma; branching, tapered (non-uniform diameter)
Axon
Take information away from the cell body; if branching is present it is call ____ collateral, uniform diameter, terminal aborization, ____lemma
Terminal Aborization
Ending of branching of axon, synaptic knobs - tips of the small branches from round stubby structures
Synapse
Connection between two neurons, example: neuromuscular junction (contains synaptic vesicles, synaptic cleft, etc.)
Unipolar Neuron
(AKA pseudounipolar neuron) neuron with one process, mostly sensory neurons

Developmentally = bipolar
Eventually branches merged to form one
Bipolar Neuron
Neuron has two processes (axon & dendrite), found in sensory organs (nasal mucosa for smell, retina for sight, etc.)
Multipolar Neuron
Neuron has multiple processes (dendrites), most common type, located in CNS
Neuronglial Cells
Cells that assist the neuron, AKA supporting cells, four types:
1. Oligodendrocyte
2. Ependymal
3. Microglial
4. Astrocyte
Oligodendrocyte
Multiple processes that wrap several times around axons (hold axons), myelination (formation of myelin sheath) with nodes of ranvior
Node of Ranvior
Gaps between the myelin sheath
Ependymal Cell
Cell which lines the cavities of the CNS, help CSF formation & movement
Microglial Cell
Small cells derived from white blood cell colony, migrate from PNS to CNS before there was a blood brain barrier, BBB prevents cells & substance from crossing over; small macrophages (get rid of foreign agent or dead/dying cells)
Astrocyte
Have numerous processes, wrap around blood vessels, neurons, axons, dendrites

Functions:
1 - Physical support
2 - form BBB by wrapping blood vessels
3 - Maintenance of extracellular environment
4 - Development of proper connection between neurons, release various nerve growth factors, promote synapse formation
5 - Formation of scar tissue = astrocytosis, sclerosis
6 - Nutrition of neurons
Schwann Cell
Located in PNS, wrap around axons of neurons, help myelination like oligodendrocytes

One entire cell wraps around one axon
Area which is deep = myelin sheath
Area which is superficial = neurolemma
More NoR peripherally
**Still present around unmyelinated cells but not wrapping around a single axon
Schwann Cell Conduction Speed
Dependent upon the axon thickness & myelination type (A, B, or C)
Type A Myelination
Thick & heavy myelination; conduct up to 20 m/s (fastest)
Type B Myelination
Medium to small myelination; conduct up to 3 to 15 m/s (mild to moderate)
Type C Myelination
Thin unmyelinated; conduct up to 2 m/s (slowest)
Satellite Cell
Wraps around the soma, functions to insulate & provide nutrition to the soma
Synapse
Neuron to neuron connection
Electrical Synapse
Between cells that contain gap junctions
Chemical Synapse
Uses neurotransmitters to transmit graded potential
Axodendritic Synapse
Axon connected to dendrite
Dendodendritic
Dendrite connected to dendrite
Axoaxonic
Axon connected to axon
Axosomatic
Axon connected to soma (cell body)
Synaptic Knob Action Potential Travel
1. Arrival of AP at axon terminal, opens Ca channels on synaptic knob
2. Causes exocytosis of a few neurotransmitter vesicles (ACh), dumps neurotransmitter into synaptic cleft (ACh)
3. Vesicle is recycled to dump more ACh, opens ligand gated channel
4. AP travels down the cell membrane
Neurotransmitters
Acetylcholine, amino acids, monoamines, neuropeptides
Acetylcholine (ACh)
Neuromuscular junctions, most synapses of autonomic nervous system, retina, & many parts of the brain; excites skeletal muscle, inhibits cardiac muscle, & has excitatory or inhibitory effects on smooth muscle and glands depending on location
Amino Acids
Examples: glutamate (glutamic acid), aspartate (aspartic acid), glycine, GABA
Monoamines (Biogenic Amines)
Include catecholamines: norepinephrine, epinephrine, dopamine

Others: serotonin, histamine
Neuropeptides
Chains of amino acids; substance P, enkephalins, beta-endorphin, cholecystokinin (CCK)
Post Synaptic Potentials
IPSP & EPSP
Inhibitory Post Synaptic Potential (IPSP)
Hyperpolarizing - will take the membrane potential further away from the threshold
Excitatory Post Synaptic Potential
Depolarizing - help create action potentials
Temporal Summation of Impulses
One neuron firing
Spatial Summation of Impulses
Multiple neurons firing