Histology - Nervous Tissue

Front 1

Nerve tissue derived from?

Back 1

Ectoderm, Outer layer of embryo

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Description of Afferent Neuron

Back 2

Receive and transmit info from environment to CNS

Front 3

Description of Efferent Neuron

Back 3

Receive and transmit info from the CNS to the periphery

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Somatic Nervous System

Back 4

Composed of neural elements associated with the body wall and extremities (skin, skeletal muscle, bones, joints)
Voluntary Functions

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Autonomic (Visceral) Nervous System

Back 5

Composed of neural elements associated with internal organs or viscera (cardiac muscle, smooth muscle, glandular epithelium)
Involuntary Functions

Front 6

Similarities in both ANS and SNS?

Back 6

Components lie in both CNS and PNS
Afferent and Efferent information is transmitted.

Front 7

How do Neurons respond to stimuli?

Back 7

By altering electrical potentails that exist between the inner and outer surfaces of their membranes

Front 8

Cell Body (aka?) - Structure

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AKA - Perikaryon
Contains nucleus and surrounding cytoplasm

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Cytoplasm - Structure

Back 9

Abundent RER (Nissl Substance) and plysomes
Well-developed Golgi complexes
Numerous mitochondria
Well-developed Cytoskeleton

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Nucleus - Structure

Back 10

Large, Spherical
Euchromatic w/prominent nucleolus

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Cell Body - Function

Back 11

Trophic center of cell
Receptive to stimuli

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Cortex/Nucleus

Back 12

Aggregate of neuronal cell bodies in CNS

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Ganglion

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Aggregate of neuronal cell bodies in PNS

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Dendrites - Structure

Back 14

Short, tapered, highly branched
Organelles similar to cell body, but no Golgi complexes
Dendritic spines are specializations located at synapses (more ion channels, greater AP)

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Dendrites - Function

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Signal reception
Transmit towards cell body

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Axons - Structure

Back 16

Long, cylindrical, don't branch profusely
Organelles similar to cell body, but NO RER or Polysomes, MORE mitochondria at terminal end

Front 17

Axon Hillock

Back 17

Pyrmaid shaped region where the axon emanates from cell body, devoid of Nissl
(Only way to differentiate from dendrite)

Front 18

Terminal Arborization

Back 18

Branched distal portion of axon
Each branch terminates on next cell in dilations, called Terminal Boutons

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Axons - Function

Back 19

Generate and conduct nerve impulses
Receptive to stimuli

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Motor (efferent) neurons

Back 20

Control effector organs

Front 21

Sensory (afferent) neurons

Back 21

Receive sensory stimuli

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Interneurons

Back 22

Connect other neurons
Most numerous

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Multipolar

Back 23

More than one dendrite and one axon
Most common, efferent and interneurons
(Motor neurons)

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Bipolar

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One dendrite and one axon
Developmental stage of most neurons
(special sense organs/retina)

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Pseudounipolar

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Single process that is close to the cell body and divides into two branches (central and peripheral)
Afferent
(Sensory neurons in dorsal root ganglion)

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Molecular Transport Systems (definitions and types)

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Transport of substances between cell body and processes, axons and dendrites
Three speeds (slow - .2-4mm/day, intermediate, fast - 20-400mm/day)
Anterograde, Retrograde

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Anterograde (Molecular Transport System)

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Carries materials (Organelles, macromolecules) from cell body to periphery

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Retrograde (Molecular Transport System)

Back 28

Carries material (Toxins, viruses) from periphery to cell body.

Front 29

Synapses - Ways to classify

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Sites of functional contact between neurons and effector cells
1) Morphology
2) Mechanism of Impulse Conduction

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Synapse based on morphology

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Axosomatic - Btw axon and cell body
Axodendritic - Btw axon and dendrite
Axoaxonic - Btw axon and another axon (least common)

Front 31

Synapse based on Mechanism of Impulse Conduction

Back 31

Electrical, Chemical

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Electrical Conduction

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Transmit ionic signals through Gap Junctions that cross the pre- and postsynaptic membranes --> conduct neuronal signals directly
Allow for rapid and synchronous firing of interconnected cells

Front 33

Chemical Conduction

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Use chemical messengers to transmit signal from axon terminal bouton (presynaptic cell), across thin extracellular space (synaptic cleft), to a region on another cell (postsynaptic cell) to generate a new signal
Consists of Chemical messengers, transmission, reception

Front 34

Chemical Conduction - Chemical Messengers

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Neurotransmitters - Bind to receptor proteins --> act on ion channels (direct or indirect)
Neuromodulators - Modify function of receptor

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Chemical Conduction - Transmission

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1) AP reaches terminal boutons of neurons
2) Voltage-gated Ca++ channels open
3) Ca++ influx causes synaptic vesicles to migrate to and fuse with presynaptic membrane
4) Synaptic vesicles release neurotransmitter into synaptic cleft
5) Neurotransmitter binds to receptors on postsynaptic membrane

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Chemical Conduction - Reception - Types

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Properties of receptors that recognize and bind to NT on postsynaptic cell determine the type of response
Excitatory/Inhibitory

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Impulse Conduction

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Generation of nerve impulse in postsynaptic neuron depends on summation of excitatory and inhibitory impulses reaching that neuron
Significant depolarization of postsynaptic membrane can cause V-gated Na++ to open, generating an impulse
Depolarization of one part of membrane sends E-stim to neighboring regions of membrane, repeating depolarization

Front 38

Neuron - Function

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Receive, transmit, and process stimuli
Release NT's and other informational molecules

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Glial Cells - Types

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Oligodendrocyte, Schwann Cell, Astrocyte, Ependymal Cell, Microglia

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Oligodendrocyte - Structure

Back 40

Large, ovoid with few radiating processes

Front 41

Oligodendrocyte - Function/Location

Back 41

Myelin Production
Ones that don't produce myelin are Satellite Cells associated with neuronal cell bodies
CNS

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Schwann Cell - Structure

Back 42

Irregular shape, associated with neurons

Front 43

Schwann Cell - Function/Location

Back 43

Myelin production
Ensheath axons - with or without myelin
Ones that do not ensheath axons are called Satellite Cells and are associated with neuronal cell bodies
PNS

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Astrocyte - Structure

Back 44

Stellate shape
Multiple radiating processes

Front 45

Astrocyte - Function/Location

Back 45

Structural support, Ionic homeostasis, NT uptake
REPAIR PROCESSES, BLOOD BRAIN BARRIER
CNS

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Ependymal Cell - Structure

Back 46

Cuboidal or low columnar shape

Front 47

Ependymal Cell - Function/Location

Back 47

Lines Cavities
CNS

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Microglia - Structure

Back 48

Small, ovoid with fine, highly branched processes

Front 49

Microglia - Function/Location

Back 49

Macrophagic Activity
CNS

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Myelin Sheath - Structure

Back 50

Segmented, multilamellar, lipid rich, wrapping of axons
Formed by plasma membranes of: Oligodendrocytes and Schwann Cells
Oligodendrocytes are capable of myelinating several internodes and several axons
Schwann Cells are capaply of myelinating only one internode and one axon

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Internode

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Single segment of myelin sheath on an axon

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Node of Ranvier

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Interval at which an axon is not covered by myelin sheath, located between intrnodes

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Myelin Sheath - Function

Back 53

Provides electrical insulation.
Increase speed of impulse conduction by saltation, method whereby an AP jumps, or saltates, from node to node

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Gray Matter

Back 54

Contains neuronal cell bodies, dendrites, unbyelinated axons, and glial cells.

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Gray Matter in Brain

Back 55

Occupies superficial outer layer and deeper regions.
Constitutes - cortex and nuclei

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Gray Matter in Spinal Cord

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Occupies central H-shaped region
Constitutes - nuclei of dorsal and ventral horns
(ventral horn is location of cell bodies of (mulipolar) motor neurons)

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White Matter

Back 57

Contains myelinated nerve axons and oligodendrocytes

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White Matter in Brain

Back 58

Occupies deeper regions
Constitutes tracts

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White Matter in Spinal Cord

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Occupies peripheral region
Constitutes tracts

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Dura Mater

Back 60

Outermost layer
Dense irregular CT
Continuous w/periosteum in skull
Separated from vertebrae in spine by epidural space
Separated from arachnoid mater by subdural space

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Arachnoid Mater

Back 61

Middle layer
Cell layer in contact with dura mater and a system of trabeculae connected to pia mater
Cavities between trabeculae form subarachnoid space and are filed w/CSF

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Pia Mater

Back 62

Innermost layer
Loose CT lying directly on surface of nervous tissue

Front 63

Blood Brain Barrier - Structure

Back 63

Capillary Endothelial (Epithelial) Cells - Tight junctions between adjacent cells
Astrocytes - End foot processes closely associated with endothelial cells

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Blood Brain Barrier - Function

Back 64

Highly Selective Barrier

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Aging of Neurons

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Atrophy of brain tissue due to loss and shrinkage
Decreased nerve conduction velocity in sensory and motor systems
Alterations in neuron structure and function
Diminished blood supply

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Ganglia

Back 66

Ovoid structures containing neuronal cell bodies and glial cells supported by connective tissue

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Sensory (Somatic and Visceral) Ganglia

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Associated with dorsal roots of spinal nerves and cranial nerves V, VII, VIII, IX, X
Contain cell bodies of (pseudounipolar) sensory neurons

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Motor (Visceral) Ganglia

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Sympathetic and Parasympathetic

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Nerves

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Consist of axon with its investing schwann cells
Peripheral nerve composed of one or more fascicles (bundles) of nerve fibers surrounded by connective tissue sheaths

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Afferent Nerve Endings

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Receptors - located at distal tips of peripheral processes of sensory neurons
Initiate nerve impulse in response to stimulus

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Afferent - Classified based on structure

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Nonencapsulated (Simple)- Free nerve endings. Detect relatively unsophisticated modalities (touch, pain, temp, etc.)
Encapulated (Compound)- Common. Detect sophisticated modalities (proproception, smell, taste, sight, hearing)

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Afferent - Classified by Function

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Exteroceptors - Respond to stimuli outside body (touch, cutaneous pain, temp, smell, sight, hearing)
Enteroceptors - Respond to stimuli from viscera. (Chemical composition of blood, blood pressure, visceral distention and pain, hunger, thirst, etc.)
Proprioceptors - Respond to stimuli regarding posture and movement of body parts. (vestibular apparatus of ear, muscles, tendons)

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Surface Coverings of Nerves

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Epineurium - Dense irregular CT surrounding entire nerve
Perineurium - Dense irregular CT surrounds bundles of nerve fibers (fascicles)
Endoneurium - Delicate layer of loose CT surrounding individular nerve fibers

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Aging of PNS

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Decreased number of myelinated fibers due to decrease in protein production needed to express myelin and vascular occlusion
Atrophy of axons
Decreased nerve conduction velocity
Altered density and morphology of sensory receptors