Lesson 3: Cells of the Nervous System and Organization of Tissues Flashcards
Two(2) Principal Kinds of Cells are:
Neuroglia
Neurons
are the “nerve glue” or the cells that support the neurons of the CNS.Their name originates from the idea of early histologists that they were the “glue” that held nervous tissue together
Neuroglia Cells / Supporting Cells
Neuroglia Cells / Supporting Cells provides:
SPIN
Support
Protection
Insulation
Nutrition
They are smaller but they greatly outnumber neurons, perhaps by as much as 5 to 25 times and they do not generate action potentials. They continue to divide throughout an individual’s lifetime.
Neuroglia Cells / Supporting Cells
Six types of Neuroglia:
Found in CNS:
Astrocytes
Oligodendrocytes
Microglia
Ependymal Cells
Found in PNS:
Schwann Cells
Satellite Cells
Type of Neuroglia:
- are star-shaped cells with many processes. The processes make contact with blood capillaries, neurons and the pia matter
Astrocytes (astro- = star; -cyte = cell)
2 types of Astrocytes:
Protoplasmic Astrocytes
Fibrous Astrocytes
Type of Astrocytes:
with many short branching processes (location:gray
matter)
Protoplasmic Astrocytes
Type of Astrocytes:
with long unbranched processes (location: mainly
white matter)
Fibrous Astrocytes
consists of cellular structure that selectively inhibit certain substances in the blood from entering the interstitial spaces of the brain or CSF, thus making the nervous system impermeable to large & potentially harmful molecules.
Blood Brain Barrier - BBB
A component of BBB:
- encircle the capillaries-secrete chemicals that maintain the permeability characteristics of the tight junctions
Astrocytes & astrocytic feet/processes
A component of BBB:
- Pericytes cover the basal lamina of the endothelium and contribute to the structural integrity of the BBB.
The capillary basement membrane/basal lamina with embedded pericytes.
A component of BBB:
- consists mainly of tight junctions that seal together the
endothelial cells of brain blood capillaries and a thick basement membrane that surrounds the capillaries.
The tight JUNCTION between the OVERLAPPING endothelial cells of the brain capillaries
Type of Neuroglia:
- These resemble astrocytes but are smaller and contain fewer processes.
- Give support by forming semi-rigid connective tissue rows between neurons in the CNS
- Produce phospho-lipid for the myelin sheath around axons of neurons in the CNS - responsible for forming and maintaining the myelin sheath around CNS axons.
Oligodendrocytes - (oligo- = few; -dendro- = tree)
Type of Neuroglia:
- These neuroglia are small cells with slender processes that give off numerous spinelike projections.
- Act as macrophages – they engulf & destroy microbes and cellular debris/act as macrophages formed during normal development of the nervous system and phagocytize microbes and damaged nervous tissue.
Microglia or Brain Macrophages or Microglial Cells
Type of Neuroglia:
- are cuboidal to columnar cells arranged in a single layer that possess microvilli and cilia. These cells line the ventricles of the brain and central canal of the spinal cord (spaces filled with cerebrospinal fluid, which protects and
nourishes the brain and spinal cord).
- Form a continuous epithelial lining for the ventricles of the brain & the central canal of the spinal cord
- Assist in the formation & circulation of CSF in the ventricles of the brain & the central canal of the spinal cord
Ependymal Cells or Ependymocytes - (epen-= above; -dym- = garment)
Type of Neuroglia:
- Form myelin sheath around axons of neurons of the peripheral nervous system
o myelinates a single axon
o A single Schwann cell can also enclose as many as 20 or
more unmyelinated axons (axons that lack a myelin
sheath)
- participate in axon regeneration, which is more easily
accomplished in the PNS than in the CNS.
Schwann Cells
Type of Neuroglia:
- these flat cells surround the cell bodies of neurons of PNS ganglia
- Provides structural support,
- Regulate the exchanges of materials between neuronal cell bodies and interstitial fluid.
Satellite Cells
- are the basic functional unit of the nervous system
- they are the primary cells of the nervous system.
- its primary function is the conduction of impulses from one part of the body to another.
- it has the ability to respond to a stimulus and convert it into action potential (electrical excitability).
Neurons or Nerve Cells
The fuel source for neurons is predominantly…
Glucose
responsible for most special functions of the nervous system like perception, rationalization, memory, muscle control and glandular secretion regulation.
Neurons
- they are irreplaceable
- they are highly specialized cells, most have lost the ability to undergo mitotic divisions
Neurons
Parts of Neuron:
Cell Body
Dendrite
Axon
The main portion of a neuron and contains a nucleus surrounded by
cytoplasm where organelles such as lysosomes, mitochondria & Golgi
complex are found.
Cell Body
- are clusters of rough Endoplasmic reticulum and free ribosomes.
- are the site of protein synthesis in neurons and are used to substitute cellular components, as material for growth of neurons, and to restore damaged axons in the PNS.
Nissl bodies
cytoskeleton; for cell shape and support
Neurofibril
cytoskeleton; assist movement of material to and from the cell body and axon
Microtubules
can be found in aging neurons that is the result of accumulated
neuronal lysosomes associated with aging. Studies have identified that these yellow brown granules in the cytoplasm cause no harm to the neuron.
Lipofuscin
- are short with often highly branching cytoplasmic extension,
hence, the origin of the name. - their cytoplasm comprises Nissl bodies, mitochondria, and other organelles.
- receives information/input from other neurons or sensory receptors & carry the information toward the neuron’s cell body; the receiving
or input portions of a neuron
Dendrite - (DEN-drı¯ts little trees)
- a long thin, cylindrical projection that joins the cell body at a
cone-shaped elevation called axon hillock. The initial segment is nearest to the axon hillock. - contains mitochondria, microtubules, and
neurofibrils. - proliferates nerve impulses towards another neuron or
muscular or glandular tissue
Axon - (single= axis)
Part of Axon:
- cone-shaped elevation where cell body joins an axon; The
part of the axon closest to the axon hillock is the initial segment.
Axon Hillock
Part of Axon:
- cytoplasm
Axoplasm
Part of Axon:
- plasma membrane surrounding the axoplasm
Axolemma
Part of Axon:
- side branches along the length of an axon, typically at a
right angle to the axon
Axon Collateral
Part of Axon:
- a multi-layered lipid and protein covering of an axon
which insulates the axon and increases the speed of nerve impulse
conduction.
- It is necessary for SALTATORY CONDUCTION.
Myelin Sheath
impulse propagation/transmission that skips from node to node, providing rapid transmission of impulses.
Saltatory Conduction
Part of Axon:
- unmyelinated gaps between segments of the myelin sheath
Node of Ranvier
Part of Axon:
- fine processes where the axon/axon collaterals end
Axon Terminal or Axon Telodendria
Part of Axon:
- bulb-shaped structures at the tips of axon terminals
Synaptic End Bulbs
Part of Axon:
- membrane-enclosed sacs of the synaptic end bulbs which store neurotransmitters
Synaptic Vesicles
Enumerate the Classifications of Neurons According to Structure:
Multipolar Neuron
Bipolar Neuron
Unipolar Neuron
Classifications of Neurons According to Structure:
- the most common. They have multiple dendrites and
one axon
Multipolar Neuron
Classifications of Neurons According to Structure:
- have 2 distinct processes: one main dendrite and one axon
arising from the cell body. These are very rare types of neurons
Bipolar Neuron
Classifications of Neurons According to Structure:
- are made up of only one projection from the cell body. These are very short neurons that divide into DISTAL (peripheral) and PROXIMAL (central) processes and only the most distal process acts as dendrites.
Unipolar Neuron
Enumerate the Classifications of Neurons According to Function:
Sensory/Afferent Neurons
Motor/Efferent Neurons
Association/ Connecting Neurons/ Interneuron
Classifications of Neurons According to Function:
- either contain sensory receptors at their distal ends (dendrites) or are located after sensory receptors that are separate cells. They receive stimuli/info from either the internal or external environment thru the
AFFERENT/SENSORY nerve pathways.
Sensory / Afferent Neurons
Most sensory neurons are ________ in structure.
Unipolar
Classifications of Neurons According to Function:
- are structurally multipolar, carry impulses from the CNS
to other parts of the body to effectors (muscles and glands) in the periphery through cranial or spinal nerves.
Motor / Efferent Neurons
Classifications of Neurons According to Function:
- that are also structurally multipolar, interprets/process the information received in order to determine appropriate response to take. Their axons extend only for a short distance and contact nearby neurons in the brain, spinal cord or in a ganglion.
Interneurons
universal term for any neuronal process (extension)
whether dendrite or axon, that emerges from the cell body of a neuron.
Nerve Fiber
a bundle of many nerve fibers.
Nerve
are cluster of cell bodies in the CNS.
Nuclei
are small groups of nervous tissue containing primarily of cell
bodies which are found in the PNS.
Ganglia
a bundle of nerve fibers in the CNS.
Tract
Enumerate Classifications of Layers of Nerve Fibers:
Endoneurium
Perineurium
Epineurium
Classifications of Layers of Nerve Fibers:
- surrounds an entire nerve
Epineurium
Classifications of Layers of Nerve Fibers:
- are thin connective tissue sheath that surrounds each nerve
fiber/axon
Endoneurium
Classifications of Layers of Nerve Fibers:
- surrounds bundles of axons known as fascicles
Perineurium
Group of Nerve Fibers:
- conduct nerve impulses from the skin, skeletal muscles and joints to the CNS
General somatic afferent fibers
Group of Nerve Fibers:
- conduct nerve impulses from the CNS to the skeletal muscles
General Somatic efferent fibers
Group of Nerve Fibers:
- convey nerve impulses from the viscera and blood vessels to the CNS
General Visceral Afferent Fibers
Group of Nerve Fibers:
- convey nerve impulses from the CNS to help contractions
of smooth and cardiac muscles and rate of secretions of glands
General Visceral Efferent
nerves carrying both sensory & motor impulses
Mixed Nerves
nerves that carry impulses toward the CNS only
Afferent/Sensory Nerves
nerves that convey impulses from the CNS only
Efferent/ Motor Nerves
