Chapter 12 - Nervous Tissue

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Exam IV, nervous tissue, CNS

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

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