Neurophysiology Flashcards
collections of myelinated axons in the central nervous system
white matter
an multi-layer lipid coat that “insulates” axons - formed by specialized glial cells in the peripheral (PNS) and
central nervous system (CNS)
Myelin
Although both the PNS and CNS have myelinated axons, only the ____ has white matter
CNS
Myelin increases the velocity of signal transmission along an
_____
axon
areas of the central nervous system that have relatively few myelinated axons. Mostly comprised of neuronal and glial cell bodies.
Grey matter
A collection of axons in the CNS. _________ are usually white matter
Tract, Large tracts
a collection of axons in the PNS
PNS
The longer an axon is, the more
“crucial” the information it carries -> the more likely that it will be __________
myelinated
__________ connect with other neurons via synapses
dendrites connect with other neurons via synapses
Cell body, axon hillock are the sites of _________
integration
If the stimuli that the neuron receives
excite it enough -> send a _______ down the axon
signal
Much of the volume of the cerebral cortex is ______ matter
white
______ matter forms a relatively thin layer superficially
Gray
How does the peripheral nervous system (PNS) differ from the central nervous system (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
a collection of neuronal cell bodies in the peripheral nervous system
Ganglia
a collection of neuronal cell bodies in the central nervous system
Nuclei
Glial cell types in CNS
- Astrocytes
- Oligodendrocytes
- Microglia
Fluid spaces within the CNS
- Ventricles, ependymal cells, choroid plexus
- Interstitial fluid
Most numerous cells in the CNS, the highest numbers in the
gray matter
- Roughly 8 - 10X more astrocytes in the CNS than neurons
Astrocytes
The critical role of Astrocytes in CNS physiology
- Facilitate the formation and strengthening of synapses
(neuroplasticity) - Regulate the concentration of ions in the interstitial fluid
- Structural support for the brain
- Barrier functions: induce the formation of the BBB at the brain microvasculature, form a “limiting membrane” at the external CNS
surface - “Feed” neurons
how does the astrocyte provide structural support for the brain
Intermediate filament – GFAP (glial fibrillary acidic protein)
how does the astrocyte “feed” the neurons
help extract nutrients from the blood, provide nutrients to neurons to support energy metabolism
how does the astrocyte provide barrier functions
induce the formation of the BBB at the brain
microvasculature, form a “limiting membrane” at the external CNS
surface
Astrocytes are connected to each other 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
what is a syncytium?
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
“waves” of _______ increases and general depolarization that move through the brain, astrocyte-to-astrocyte have been observed
calcium
- may help the effectiveness of neuronal signaling and neuroplasticity – being actively studied
processes of the Oligodendrocytes
Each process wraps around the axon of a CNS neuron many times, “sheathing” the axon in myelin
compacted layers of cell membrane rich in sphingolipids that have very little cytosol
Myelin sheath
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 _____ as many oligodendrocytes as neurons in the CNS
twice
Microglial cells are 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 present
antigen to other immune cells
_________ cells are derived from blood-borne immune cells
(monocytes) that migrate into the CNS
Microglial cells
what glial cell is roughly as numerous as neurons in the CNS
microglial cells
the CF fluid is Around the periphery of the brain
in the ____________ space and central canal of the spinal
cord
subarachnoid and central canal of the spinal
cord
The brain and spinal cord are surrounded by cerebrospinal fluid – roughly ______ total
150 mL
CSF is a specialized fluid formed from the _______ plexus – a complex of capillaries and epithelial cells
choroid
Mostly located in the lateral ventricles
CSF production & circulation: Produced in the floor of the
__________ by the choroid plexus
lateral ventricle
CSF moves from the lateral ventricles -> __ ventricle -> ___ ventricle
3rd to 4th
CSF Circulates into the subarachnoid space and down the spinal cord. Eventually absorbed by specialized structures known as _________ granulations
arachnoid
- Transport CSF fluid into venous structures
what drives the movement of CSF
Ependymal cells that line the ventricles are
ciliated – movement of cilia drives the
movement of CSF
CSF production is carefully regulated in the ___________. Selectively transports water, electrolytes, nutrients from blood to CSF.
choroid plexus
________ _______ prevent unwanted substances from entering the CSF
Tight junctions
The interstitial fluid (extracellular fluid) of the
brain and spinal cord is formed by: Filtration of CSF from the ventricles through the _________ _______
ependymal cells
- there is 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 including (3)
immune cells (white blood cells)
noxious wastes and toxins
pathogens
The CNS structure is delicate, and its function depends on its precise architecture – usually white blood cells _______ allowed into the CNS
aren’t
Most capillaries in the body are quite
leaky. Immune cells cross capillaries with little
________ when endothelial cells express signals to call them in
difficulty
what is the name of the structures that cause increased tight junction expression in capillary endothelial cells?
Endfeet
what cell contacts capillaries in the CSf via structures known as endfeet
Astrocytes
Endfeet also ____ capillaries what to transport into the CNS tissue. How?
“tell”
Cause endothelial cells to express transport proteins for desirable molecules and inhibit the expression of pro-inflammatory signals
strong, fibrous connective tissue covering that surrounds each nerve. Blood vessels run within this layer – known as the vasa nervorum
Epineurium
surrounds bundles of axons (some myelinated, some not) known as fascicles
Perineurium
The perineurium is formed by __________-like cells arranged in sheets 2-6 cells thick
fibroblast
Tight junctions are found between these cells – therefore the perineural layer can regulate what moves into the fascicle
delicate connective tissue layer that surrounds individual axons
Endoneurium
The Blood-Nerve Barrier (BNB) is made up of
Barrier 1 and Barrier 2
Both barriers actively regulate the movement of ions
and immune cells into the fascicles
Barrier 1 of the BNB - the cells of the _________ and the tight junctions between them
perineurium
Barrier 2 of the BNB - the ________ cells that line the capillaries within the fascicles also express many tight junctions
endothelial
The BNB is much ______ (more/less) permissive to the entrance of white blood cells (leukocytes) than the BBB. Why might this be?
more
- May relate to the ability of peripheral nerves to regenerate after being severed
- White blood cells are crucial for repair in most tissues
provide the myelin sheath for axons within fascicles
Schwann cells (PNS)
how do schwann cells differe from oligodendrocytes
in that one cell only myelinates one axon
- Each oligodendrocyte myelinates multiple nearby axons
- Schwann cells can extend as far as 1 mm along an axon
what type of cells surround, protect, and nourish neuronal cell bodies located in ganglia
- Satellite cells
- Interestingly, they do not establish a “blood-ganglion barrier” – the dorsal root ganglia and autonomic ganglia don’t seem to need one
Multiple ____________ are closely apposed to neuronal cell bodies. They have Nutritional and ionic homeostasis roles
satellite cells
______ are the “input” area of the neuron
dendrites
- Usually multiple processes that connect to the soma
(body) of the neuron
- Dendritic spines stud dendrites – the spines are
positioned very close to axon terminals to form synapses
The morphologic relationship of the dendritic spine to
the axon terminal can influence the _________ of the synapse
effectiveness
- spines and axon terminals are almost touching
(about 20 nm apart)
More “effective” dendritic spines are ones that carry
more information to the rest of the neuron – they tend to
be…. (what do they look like?)
larger, broader, and “mushroom-shaped”
Spine maturation makes the synapse more effective.
The “filopodia” dendritic spine below is _______ and
“looking for a connection” with an axon terminal.
immature
The “mushroom” and “branched” spines were shown to elicit more _________ neuronal responses when they are stimulated
effective
Site of protein synthesis for the rest of the neuron
the soma or neuronal cell body
basophilic area near the nucleus composed of lots of free ribosomes and rER
Nissl substance
- The larger the neuron and the more extensive the
processes, the more protein synthesis is necessary
______________: intermediate filaments that are more concentrated in axons – provide structural stability for neuronal processes
Neurofilaments
______________: have opposite orientation in dendrites
vs. axons – this is arranged in the cell body. Ensures that dendritic and axonal components are directed to the right places
microtubules
_______, _________, and _________ are the sites of a unique electrical phenomenon of the cell membrane known as an action potential
The axon, axon hillock, and synaptic terminals
Axons can be myelinated by ______________ (in PNS) or _____________ (in CNS)
Axons can be myelinated by Schwann cells (PNS) or oligodendrocytes (CNS)
Myelin sheaths are separated by myelin-free segments are known as _______________. They are crucial to action potential generation
nodes of Ranvier
These neurons have a distal process that either interacts with a sensory receptor or serves as a sensory receptor. The proximal process synapses in the CNS. The process that connects A to B behaves as an axon
Pseudo-unipolar neurons
what type of neuron is Typical of dorsal root ganglion cells – somatic sensation
Pseudo-unipolar neurons
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
Bipolar neurons
what type of neuron is typical of neurons that detect the special senses – vision, hearing, smell
Bipolar neurons
this is the most common type of neuron. Dendrites receive information from other neurons via synaptic terminals. The cell body summates and integrates this information.
Multipolar neurons
The axon of a multipolar neuron carries action potentials to (3):
- Other neurons
- Glands
- Muscle tissue
what type of neuron is typical of all interneurons and
somatic motor neurons
Multipolar neurons
nerves that carry (sensory) information to the central nervous system
Afferent
Cranial nerve afferents special senses:
CN I, II, VII, VIII, IX, X
Cranial nerve afferents somatic senses:
Mostly CN V
Cranial nerve afferents visceral Sensory
CN IX and X
- Baroreceptors
- Visceral sensation from most of the alimentary tract, lungs, heart
Sensation is composed of a number of distinct steps:
- detection of physical/chemical stimulus by some type of receptor
- transduction
- other neurons at various levels of the CNS can detect the electrical impulse and modify its intensity and route the signal to CNS locations
- perception
transforming the physical stimulus into an
electrical impulse that can be carried along an axon
transduction
conscious awareness of the sensation – this
occurs at the level of the cortex
perception
- Some sensory afferent information is not perceived à
osmolarity, blood pressure, etc.
Somatic sensation below the neck: skin receptors
pain, temperature, fine
and coarse touch, vibration
Somatic sensation below the neck: Joint and intra-muscular receptors
golgi tendon organs, muscle spindles,
joint receptors -> proprioception
Visceral Sensation below the neck
- Distal portions of the colon
- Bladder
- Reproductive organs
a motor neuron synapses with some sort of
effector so that it can activate it when the neuron is excited
motor system
multiple electrical signals travelling down
the axon – known as action potentials
excitation
Examples of effectors:
- Skeletal muscle (voluntary movements)
- Smooth muscle (blood vessels, GI tract, genitourinary tract, respiratory tract)
- Glands (endocrine or exocrine
neurons that carry information from the CNS to the peripheral nervous system
Efferents
Somatic Motor efferents – control of skeletal muscles
Usually voluntary
Some we don’t have conscious control over (i.e. middle ear muscles)
Major cranial nerves – somatic motor: muscles of pharynx
IX, X, XII
Major cranial nerves – somatic motor: controls the position of the eyeballs
III, IV, VI
Major cranial nerves – somatic motor: the face, head and neck
CN V, VII, XI - trigeminal, facial and accessory (innverates SCM and trap)
Visceral motor efferents – cranial nerve PaNS: (3)
CN X – PaNS control for the heart, lungs, and majority of the GI system
CN III – PaNS control over pupillary muscles
CN VII, IX – PaNS control over salivary, tear glands
The Sympathetic Nervous System: Flight or Flight Effect
- Increases heart rate and cardiac output
- Improves ventilation
- Decreases digestive function
- Increases glucose availability (gluconeogenesis,
glycogenolysis) - Increases blood flow to skeletal muscles, heart
- Decreases blood flow to GI tract, skin, kidneys
- Major hormones/neurotransmitters: epinephrine and
norepinephrine
The Parasympathetic Nervous System: “Rest and digest” Effect
- Decreases heart rate and cardiac output
- Bronchoconstriction and increased mucous secretion
- Increases digestive function and GI motility
- Increases blood flow to the digestive tract
- Major neurotransmitter: acetylcholine
