Basic organization and Histology of the Nervous system Flashcards
What types of sensory information get’s sent to the brain?
Special sensory: hearing, equilibrium, sight, smell, taste (Cranial Somatic Sensory: Cranial nerves)
Visceral Sensory: stretch, pain, temperature, chemical stimuli (Cranial & Spinal nerves)
What types of sensory information get sent to the spinal cord?
Somatic sensory: (non-cranial): touch, pain, pressure, vibration, temperature (Spinal nerves)
What signals does the brain send out?
Somatic motor-cranial: Cranial skeletal muscles (cranial nerves)
Visceral motor: parasympathetic nervous system (Cranial Nerves)
What signals come out of the spinal cord?
Somatic motor-non-cranial: non-cranial skeletal muscles (Spinal nerves)
Visceral motor: autonomic nervous system-all SNS and sacral PaNS (Spinal Nerves)
Collections of myelinated axons in the central nervous system
White matter
Myelin
A multilayer lipid coat that “insulates” axons formed by specialized glial cells in the peripheral nervous system (PNS) and central nervous system (CNS)
Both the PNS and CNS have _____________, but only the CNS has _____________
myelinated axons;white matter
What does myelin do?
Increases the velocity signal transmission along an axon
Areas of the central nervous system that have relatively few myelinated axons
Grey Matter
Tract
A collection of axons in the CNS
-Large tracts are usually white matter
Nerve
a collection of axons in the PNS
The _______ the axon is, and the more “crucial” the information it carries => the more likely that it will be _________
Longer; Myelinated
_________ connect with other neurons via synapses
Dendrites
Inputs from other neurons are ________ => “decision” made, based on inputs, regarding whether the neuron will send a signal
Integrated
______________ are the sites of integration
Cell body, axon hillock
If the stimuli that the neuron receives excite it enough -> send a signal down the ______
Axon
The ________ are examples of tracts.
dorsal columns
Much of the volume of the cerebral cortex is ____________
White matter
___________ forms a relatively thin layer on the cerebrum superficially
Gray Matter
How does the PNS differ from the CNS?
-Different cells populate the PNS
-Axons/nerves in the PNS can sometimes regenerate after damage
-The PNS is much less “isolated” than the CNS-cells of the immune system are allowed to enter and exit the PNS more freely
-Fewer neuronal cell bodies in the PNS versus the CNS
-
Collections of neuronal cell bodies in the peripheral nervous system
Ganglia
ex) dorsal root ganglia and sympathetic trunk ganglia adjacent to the vertebrae
collections of neuronal cell bodies in the central nervous system
Nuclei
ex) the basal nuclei, the supra-optic nucleus, and the paraventricular nucleus.
Basal nuclei are often known as __________-widely accepted misnomer
Basal ganglia
Both nuclei and ganglia will contain _______, but more of the volume of these structures is devoted to neuronal and glial cell bodies.
axons
Name some glial cell types:
-Astrocytes
-Oligodendrocytes
-Microglia
Fluid spaces within the CNS:
-Ventricles, ependymal cells, choroid plexus
-Interstitial fluid
Functions of an astrocyte:
1) forms part of the BBB
2) regulates interstitial fluid composition
3) Provides structural support and organization to the CNS
4) Assists in neuronal development
5) Replicates to occupy space of dying neurons
Functions of ependymal cells:
1) Lines ventricles of brain and central canal of spinal cord
2) Assists in production and circulation of cerebrospinal fluid (CSF)
Functions of microglial cells:
1) Phagocytic cells that move through the CNS
2) Protects the CNS by engulfing infectious agents and other potential harmful substances
Functions of Oligodendrocyte:
1) Myelinates and insulates CNS axons
2) Allows faster action potential propagation along axons in the CNS
Most numerous calls in the CNS, highest numbers in the grey matter:
-Roughly 8-10X more astrocytes in the CNS than neurons
-Name means “star-cells”-many cellular processes that makes them look like stars (stellate)
Critical role in CNS physiology:
-Facilitate the formation and strengthening of synapses (neuroplasticity)
-Regulate the concentration of ions in the interstitial fluid: K+, NA+, CL-, HCO3-, CA+2
-Structural support for the brain
Intermediate filament-GFAP (glial fibrillary
acidic protein)
-Barrier functions-Induce the formation of the BBB at the brain microvasculature, form a “limiting membrane” at the external CNS surface
-“Feed” Neurons- help extract nutrients from the blood, provide nutrients to neurons to support energy metabolism
Astrocytes
Astrocytes are connected to eachother via _______________
gap junctions:
small “tunnels” that connect the intracellular fluid of astrocytes to each other (span the cell membranes and connect cell to cell) in a network known as a syncytium.
“waves” of __________ increases and general _________________ that move through the brain, astrocyte-to-astrocyte have been observed.
Calcium; depolarization
(may help the effectiveness of neuronal signaling and neuroplasticity-being actively studied)
Have many processes:
-Each process wraps around the axon of a CNS neuron many times, “sheathing” the axon in myelin.
-Myelin sheath= compacted layers of cell membrane rich in sphingolipids that have very little cytosol
Function of myelin:
-Increases the speed with which an action potential moves down an axon
-Reduces the energy consumed by movement of an action potential down an axon-more efficient signaling
Roughly twice as many of these as neurons in the CNS
Oligodendrocytes
Small-bodied glial cells that:
-Remove (phagocytosis) cellular debris
-Monitor the environment and fight pathogens
-If the pathogen cannot be eliminated by resident microglia, they “call in” other white blood cells through secretion of soluble factors (cytokines) and can be present antigen to other immune cells
Derived from blood-borne immune cells (monocytes) that migrate into the CNS.
-Roughly as numerous as neurons in the CNS
Microglial Cells
The brain and spinal cord are surrounded by _______________________ -roughly 150mL total
-Around the periphery of the brain=> subarachnoid space
-Within particular compartments of the brain=> 4 ventricles (shown at right)
-Within the subarachnoid space and central canal of the spinal cord
It is a specialized fluid formed from the choroid plexus-a complex of capillaries and epithelial cells.
-Mostly located in the lateral ventricles
Cerebrospinal fluid
Ventricular system and cerebrospinal fluid
Basic CSF Physiology
Ependymal cells that line the ventricles are ciliated-movement of cilia drives the movement of CSF
CSF production is carefully regulated in the choroid plexus:
-Selectively transports water, electrolytes, and nutrients from the blood to CSF
-Tight junctions prevent unwanted substances from entering the CSF
The interstitial fluid (extracellular fluid) of the brain and spinal cord is formed by:
-Filtration of CSF from the ventricles through the ependymal cells
-Regulated filtration of fluid through capillaries deeper in the CNS tissue
The central nervous system is isolated/protected from a number of factors that can circulate through the bloodstream.
-Immune cells: White blood cells attack pathogens and remove cellular debris.
-The CNS structure is delicate, and it’s
function depends on its precise
architecture; usually white blood cells aren’t
allowed into the CNS.
-Exception: microglial cells
Noxious wastes and toxins
Pathogens
Blood Brain Barrier (BBB)
Astrocytes contact capillaries in the CSF via structures known as ___________
Endfeet; cause increased tight junction expression in capillary endothelial cells
-Also “tell” capillaries what to transport into the CNS tissue: cause endothelial cells to express transport proteins for desirable molecules and inhibit expression of pro-inflammatory signals
Structure of a nerve includes:
-Epineurium
-Perineurium
-Endoneurium
Strong, fibrous connective tissue covering that surrounds each nerve.
Epineurium
-Blood vessels run within this layer-known as
the vasa nervorum
Surround bundles of axons (some myelinated, some not) known as fascicles.
Perineurium:
-The perineurium is formed by fibroblasts-like cells arranged in sheets 2-6 cells thick
-Tight junctions are found between these cells- therefore the perineurial layer can regulate what moves into the fascicle
__________ surround, protect, and nourish cell bodies located in ganglia.
Satellite cells (glial cells on the PNS)
They do not establish a “blood-ganglion barrier” - the dorsal root ganglia and autonomic ganglia don’t seem to need one
Multiple satellite cells are closely _________ to neuronal cell bodies
Apposed
-nutritional and ionic homeostasis roles
Dendrites are the _______ area of the neuron
Input
-Usually multiple processes that connect to the soma of the neuron
Dendritic spines stud dendrites:
The spines are positioned very close to axon terminals to form synapses.
-Spines and axons are almost touching (about 20 nm apart)
The morphologic relationship of the dendritic spine to the _____________ can influence the effectiveness of the synapse.
axon terminal
-More “effective” dendritic spines are ones that carry more information to the rest of the neuron-they tend to be larger, broader, and “mushroom-shaped”
“filopodia” dendritic spine is _________ and _______________ with an axon terminal
Immature; looking for a connection
“mushroom” and “branched” spines were shown to elicit ___________ neuronal responses when they were stimulated
more effective
Myelin sheaths are separated by myelin-free segments known as __________________
Nodes of Ranvier
-Crucial to action potential generation
Pseudo-unipolar neurons:
-these neurons have a distal process that either interacts with a sensory receptor or is a sensory receptor (A)
-The proximal process synapses in the CNS (B)
-Typical of dorsal root ganglion cells-somatic sensation
-These neurons have a distal process (A) that acts as a dendrite- it either serves as a sensory receptor or interacts with a sensory receptor.
-The proximal process synapses in the CNS -it is an axon and conducts action potentials (B)
-Typical of neurons that detect the special senses (vision, hearing, smell)
Bipolar neurons
-The most common neurons
-Dendrites receive information from other neurons via synaptic terminals
-The cell body summates and integrates this information
-The axon carries action potentials to: other neurons, glands, muscle tissue
-Typical of all interneurons and somatic motor neurons
Multipolar neurons
Afferent=
nerves that carry sensory information to the CNS.
Cranial afferents:
-Special senses ( CN I, II, VII, VIII, IX, X)
-Somatic senses (mostly CN V)
-Visceral senses (CN IX, and X, Baroreceptors, Visceral sensation from most of the alimentary tract, lungs, heart.
Review cranial nerves and their location:
Dorsal column system and spinothalamic tract review:
Motor cranial nerves:
Somatic motor:
-CN VII, V, XI
-CN IX, X, XII
-CN III, IV, VI
Efferents for skeletal muscles below the neck are part of the corticospinal tract:
-Axons from the neurons in the precentral gyrus decussate and descend down the spinal cord=>
-Synapse on anterior horn motor neuron=>
-Axon of anterior horn motor neuron exits the central nervous system as a spinal nerve
Visceral motor efferents:
CN X: PaNS control for the heart, lungs, and majority of the GI system
CN III: PaNS control of pupillary muscles
CN VII, IX: PaNS control over salivary, & tear glands
Visceral motor efferents:
Spinal nerve ANS & PaNS:
-SNS control for the heart, lungs, proximal GI tract
-SNS control for pupillary muscles, salivary & tear glands
-SNS and PaNS control for distal GI tract, reproductive structures, bladder
Organization of the sympathetic nervous system:
Adjacent to the vertebral column=> paravertebral ganglia
Anterior to vertebral column=> prevertebral ganglia (celiac superior mesenteric ganglia)
Organization of the parasympathetic nervous system:
Note the two paths:
-Vagus nerve: all of the visceral efferents up to the proximal large bowel
-Sacral nerves: all of the visceral efferents to the rest of the large bowel, kidney, reproductive organs
-Ganglia are located closer to target organs
