nerve tissue Flashcards
it solely constitutes our nervous system
nerve tissue
classification of nervous system
anatomically:
CNS - brain (cerebellum and cerebrum) and spinal cord
PNS - ganglia, nerve, nerve endings
functionally:
somatic NS - voluntary movement
autonomic NS - involuntary movement
functional and structural unit of the nervous system
neurons
what are the 2 principal types of cells in nerve tissue
neurons:
conducts and delivers the impulse or action potentials that is generated
neuroglial cells (supporting cells):
aka glial cells/ glia
non conducting cells located near to the neurons
supports neurons by
- aid in conduction of nerve impulse
- protect neurons
- maintain nutrients or metabolites that is needed by the neurons
briefly explain the 3 categories of neuron
- Sensory neurons (Afferent)
collects info
generates action potential from an external environment (touch, sound, temp) to the CNS - Motor neurons (Efferent)
receives info from CNS to the effector organs (mucles or glands)
*responsible for actions like moving muscles or secreting hormones
example: decide to pick up a book, motor neurons send signals from your brain to your arm muscles to make the movement happen.
- Interneurons (Integrative)
it makes up 99% of all neurons in the body as it is the “travel spot”/ neurons that r involved in the delivery of info from
sensory neurons > CNS > motor neurons
usually have many dendrites and axons to connect with multiple neurons
2 types:
there is a process that delivers the information, while there is a single process that accepts the information from another cell
bipolar
[1process receives information (dendrite) from another cell.
1process delivers information (axon) to another cell.]
what are the 2 types of sensory neurons and interneurons
afferent
- pseudounipolar
1 axon but branches out into 2 axons that are directed in diff directions
- bipolar
integrative:
- purkinje cells
contains numerous branching of dendrites
- pyramidal cells
usually found in nerophil
(triangular shaped cell body)
how are neurons classified based on structure
usually based on # of axons present in a singular neuron
etc:
○ Multipolar
○ Bipolar
○ Pseudounipolar
extends from the entire neuron
cell body/ perikaryon/ soma
delivers the info from the cell body to the other neurons
axons
- has a singular process that extends from the cell body
[carry electrical signals away from the neuron to other cells]
usually receive the information from other neurons or the external environment
dendrites
- also extends from the axons and branches out into diff branches
represent ribosomes and rough ER inside cell body
nissl bodies
enlargement of cell body where axon originates
axon hillock
- location where action potential was generated
connections between the axons of another cells to the dendrites of receiving cells
synapse
covers the axon
myelin sheath
generate or produce myelin that covers axon
schwann cells
gaps found between 2 schwann cells
node on ranvier
this results when dendrites branches into a fine number of branches
dendritic trees
- each branches contain dendritic spines
they are small protrusions of the dendritic plasma membrane
dendritic spines
- contain actin filaments and postsynaptic density
[helps neurons connect and communicate w each other]
*it is where axons form synapses at dendritic spines as it contains postsynaptic density (PSD)
[Think of dendritic spines as “docking stations” where axons deliver messages]
what does the dendritic spines contain
Neurotransmitter receptors – receive chemical signals from other neurons.
Gated channels – bind with a neurotransmitter that are usually found at the end of the axon
[open or close to allow messages to pass through]
Actin filaments – Help maintain their shape and flexibility.
briefly explain the parts of axon
Axon hillock
whr axon potentials are generated
Axon initial segment
portion of the axon, immediately to the axon hillock
whr action potentials are FIRST generated before travelling down the axon
[Think of the axon hillock as the “trigger zone” and the axon initial segment as the “launch pad” for nerve signals]
there are unique and critical to the functional polarity (direction) of neurons
microtubule organization
- composed of tubulin heterodimers (protein pairs) with 2 distinct end
PLUS ENDS
growing end whr new tubulin units are added
extend outward, away form the its starting point
MINUS ENDS
anchored end
attached to a microtubule-organizing center (the place whr microtubules start growing)
*stays fixed in place while the plus ends grows
[microtubules like a train track: the minus (-) end is the station, and the plus (+) end is where the track keeps expanding outward]
microtubules in axons vs dendrites
Axons → Microtubules are uniform
(+) end points outward, away from the cell body
Dendrites → Microtubules have mixed directions
(+) end outward, while others have their (-) end outward.
[axons as having organized, one-way traffic, while dendrites have a flexible, two-way road system]
Why Is Neuronal Transport Important?
Most materials (like proteins and nutrients) are made in the soma
- these materials need to move axons and dendrites to keep neuron working properly
what are the 2 types of neuronal transport
Anterograde Transport
Moves materials from the soma → toward the axon terminals.
protein: Kinesin
Retrograde Transport
Moves materials from the axon terminals → back to the soma.
protein: Dynein
[ASK.RAD]]
its a nerve impulse - an electrical signal that neurons use to send messages
action potentials
4 stages:
1. Resting Membrane Potential
neuron is at rest (not sending a signal).
Inside neuron = (-) charge
Outside neuron = (+) charge
*balance is maintained by ion channels.
- Depolarization
stimulus (like a signal from another neuron) causes gated channels to open.
Sodium (Na⁺) ions rush inside = more positive.
*triggers a chain reaction, spreading the signal along the neuron. - Generation of Action Potentials
the charge change (positive inside, negative outside) moves along the neuron like a wave.
this traveling charge is called the action potential. - Repolarization
the neuron resets itself to prepare for the next signal.
(K⁺) ions move out to restore the negative charge inside = return to resting stage
it is a specialized junctions between neurons that facilitate the transmission of impulses from one neuron to another neuron or effector cells
synapses
types of synapses based on morphological classification (structures)
■ Axodendritic
Axon synapses with dendrites
*most common type
■ Axosomatic
Axons synapse with a cell body, soma
■ Axoaxonic
An axon synapses with another axon
[synapses=connect]
types of synapses based on mechanism of conduction (based on how they work)
- chemical synapse
common in: mammals like humans
use neurotransmitters (chemical messenger) to pass signals between neurons - electrical synapse
common in: animals like invertebrates’ nervous system
directly passes electrical signals using gap junctions
* Faster but less flexible than chemical synapses.
enlargement of the axons that contain neurotransmitters in certain locations of the axons
Boutons en passant
- capable to synapse w dendrite found during the passing in the axon, length of axon
- results of efficient delivery of impulses and can deliver to numerous postsynaptic neurons
[can release signals while passing by dendrites, making communication more efficient.
allows one axon to signal multiple neurons at once.]
the major synapse found in mammals
chemical synapses
parts of chemical synapse
- presynaptic element
neurons transmits (sends) information
found in the end of the axon terminal (terminal bouton)
contains nerve transmitters packed inside the synaptic cleft - synaptic cleft
space btwn pre-synapse and post-synapse - postsynaptic cleft
accepts info from presynaptic neuron
contains postsynaptic density (has special receptors that catch the neurotransmitters released by the presynaptic element)
[chemical synapses like a mail delivery system: the sender (presynaptic neuron) sends a letter (neurotransmitter), which crosses a short distance (synaptic cleft) and is received by the recipient (postsynaptic neuron)]
What Happens When Neurotransmitters Are Released?
Excitatory Synapses
Opens (Na⁺) channels in the postsynaptic neuron.
Na enters = inside more positive (depolarization).
Triggers an action potential (signal continues).
usual neurotransmitters:
Acetylcholine
Glutamate
Serotonin
Inhibitory Synapses
Opens (Cl⁻) channels instead.
Cl (negatively charged) enters = inside more negative.
prevents action potentials
usual neurotransmitters:
GABA (Gamma-Aminobutyric Acid)
Glycine
What Happens During a Synapse?
action potential travels down the axon to the end of the neuron (terminal bouton).
the signal opens voltage-gated Cachannels, allowing (Ca²⁺) to enter the neuron
Ca triggers the movement of synaptic vesicles, which contain neurotransmitters.
These vesicles fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft (the gap between neurons).
Neurotransmitters travel across the synaptic cleft and bind to receptors on the next neuron (postsynaptic membrane).
These receptors open ion channels, allowing ions (Na⁺, Cl⁻, etc.) to flow in or out, triggering an effect.
what are the types of neurotransmitter receptors
Ionotropic Receptors (Fast Response)
Directly open ion channels when neurotransmitters bind.
ex: Ligand-gated ion channels (Na⁺, Cl⁻, etc.)
Metabotropic Receptors (Slow but Long-lasting)
Do NOT directly open channels. Instead, they trigger signaling pathways inside the cell using a special protein called G-protein.
his process activates enzymes, creating second messengers, which modulate neuron activity.
when a neurotransmitter binds to this receptor, it results in the influx of certain ions due to the opening of there gated channels
ionotropic receptors
- contain integral transmembrane ion channels aka transmitter-gated channels or ligand-gated channels
the binding of certain neurotransmitters to G-proteins does not result in an influx/ opening of certain channels
metabotropic receptors
however, results in a signaling mechanism, it conveys a signals from the outside to the inside of the cell by triggering the activities of enzymes involved in the synthesis of the secondary messengers
functions of neuroglial cells
aka supporting cells
- physical support for neurons (protection)
- insulation for nerve cell bodies and processes that facilitates raid transmission of nerve impulses
repair of neuronal injury - regulation of the internal fluid environment of the CNS (the CSF)
- clearance of neurotransmitters from synaptic clefts
- metabolic exchange between the vascular system and the neurons of the nervous system
what are the 2 types of neuroglial cells
peripheral neuroglia
central neuroglia
Usually just the Schwann Cells and Satellite Cells
peripheral neuroglia
what are the 3 main type of peripheral neuroglial
- myelinating schwann cells
produces myelin sheath that surrounds the peripheral nerve - non myelinating remark schwann cells
schwann cells that do not produce myelin sheath but still cover axons
found in the neuromuscular junction - repair schwann cells
facilities the repair of the schwann cells that were destroyed during nerve damage/ injury
surround the process of nerve cells and isolate them from adjacent cells an the type of extracellular matrix
schwann cells
these are small cuboidal cells that surrounds the neuronal cell bodies of the ganglia
satellite cells
[Small cells that surround neurons in ganglia (clusters of nerve cell bodies).]
Nerve fibers = individual nerves
Ganglia = clusters of nerve fibers + cell bodies outside the brain/spinal cord
briefly explain the 4 central neuroglia
astrocytes:
heterogenous cells
provide physically and metabolic support for neurons in the CNS
form network of cells within CNS and communicate w neurons to support and modulate many of their activities
function:
- communicate w other neurons
- modulate activities from BV to the neurons
- maintain blood-brain barrier
- regulate the K+ ion concentration
oligodendrocytes:
microglia;
ependymal cells:
briefly explain the 2 kinds of astrocytes
Protoplasmic astrocytes
Contains more branching processes compared to fibrous astrocytes
More common: gray matter of CNS
Fibrous astrocytes
Processes are smaller/fewer but longer
More common: white matter of CNS
it is the end processes/ end terminals of Astrocyte processes that bind to the blood vessels
perivascular/ perinular feet
- maintains tight junctions in the endothelium of the blood vessels or capillaries = more stringent movement of the molecules to the neurons/ nervous system
how does astrocytes regulate potassium?
They have numerous potassium-gated ion channels in their plasma membrane.
significant increase in potassium ion concentration in the surrounding environment = astrocytes redirect and buffer excess K⁺ ions through their processes, preventing neuronal over-excitation.
[Astrocytes are star-shaped cells in the brain and spinal cord that help maintain a balanced environment for nerve cells. When nerve cells (neurons) are active, they release potassium ions (K⁺) into the space around them. If too much potassium accumulates, it can cause neurons to become overly excited, leading to problems like seizures.
Astrocytes prevent this by absorbing the excess potassium through specialized channels in their membranes. They then redistribute these ions within themselves or pass them to neighboring astrocytes, effectively diluting and removing the surplus potassium. This process, known as potassium spatial buffering, ensures that potassium levels remain stable, preventing neuronal over-excitation.
]
small cells that are active in the formation and maintenance of myelin in the CNS, analogs
oligodendrocytes
- produce and maintain the myelin sheath in CNS
[small glial cells in the central nervous system (CNS) that are responsible for forming and maintaining the myelin sheath around neurons.]
inconspicuous cells w flat, small, dark, elongated nuclei that have phagocytic properties
microglial
columnar cells that line the ventricles of the brain and the central canal of the spinal cord
ependymal cells
- form the epithelial-like lining of the ventricles of the brain and spinal canal
[key role in cerebrospinal fluid (CSF) regulation]
what are the subtypes of ependymal cells
- tanycytes
Special ependymal cells without cilia (lack movement)
Do not produce CSF - choroid plexus (a structure in the brain’s ventricles)
Contains modified ependymal cells
Main function:
- Produce CSF
- Water and ions from blood vessels transfer into the choroid plexus
- These components form CSF, which protects and nourishes the brain and spinal cord
what do the peripheral nervous system consist of
nerve fibers and schwann cells that are held tgt by CT
briefly explain the 3 layers that a nerve fiber is coated with
1.endoneurium
-loose CT
- perineurium
- special CT that covers a bundle of nerve fibers
- metabolically active diffusion barrier (whr blood vessels and capillaries passes through)
- important in the diffusion of several molecules and is involved un the blood-brain barrier - epineurium
- dense regular CT that surrounds the nerve fascicles (collection of nerve fibers)
this includes cranial nerves which is usually located in the brain, considered as nerves
peripheral nerve
what are the nerve functions of the cranial nerve
transes
ganglia are clusters of neuronal cell bodies located outside the CNS
peripheral ganglia
briefly explain the 2 types of peripheral ganglia
- sensory ganglia
lie outside the CNS
contain the cell bodies of sensory nerves
carry impulses into the CNS - autonomic ganglia
- peripheral motor ganglia of the ANS
-contain cell bodies of postsynaptic neurons that conduct nerve impulses to smooth muscles, cardiac muscle and glands
specialized structures located at the distal tips of the peripheral processes of sensory neurons (basically the nerve endings)
afferent (sensory) receptors
types of afferent (sensory) receptors
- exteroceptors
- react to stimuli from the external enviro
- coodinates w hair follicles in the skin and the CT - enteroreceptors
- react to stimuli from within the body
- can react to stretching/ filling of the inside of the visceral organs - proprioceptors
- react to stimuli within the body, providing sensation of body position
- reacts/ senses the changes in the body position in the visceral and outside of the body
[Exteroceptors detect stimuli from the outside world, like touch, temperature, and pain, often working with hair follicles and connective tissue in the skin.
Enteroreceptors sense internal body changes, such as the stretching of organs like the stomach or bladder.
Proprioceptors help you sense your body’s position and movement, reacting to changes inside the body and in limb positioning.]
the portion of the PNS that conducts involuntary impulses to smooth muscle, cardiac muscle and glandular epithelium
autonomic nervous system
what are the 3 divisions of the autonomic nervous system
- Sympathetic division
- Thoracolumbar Division
- It is called the thoracolumbar division because its nerves and ganglia originate from the thoracic and lumbar regions (T1-L2) of the spinal cord.
- “fight-or-flight” response - Parasympathetic division
- Craniosacral division
- rest and digest division is involves in the rest and digestion mechanism of the body
● Increases the digestive capability of the intestines and stomach
● Slows down the heart/respiratory rate
● Slows down the metabolic activity of the liver, pancreas, etc. - Enteric division
The sympathetic division of the autonomic nervous system (ANS) is responsible for the “fight-or-flight” response, preparing the body for action.
Sympathetic Division (Thoracolumbar Division)
function of the sympathetic division
○ Skin:
○ Heart:
○ Lungs:
○ Liver:
○ Kidney:
○ Blood Vessels:
readies the body for physical activity such as exercise, walking or any type of movement to increase in certain activity
○ Skin: increase sweat production
○ Heart: increased heart rate
○ Lungs: increase respiratory rate
○ Liver: increases metabolism activity
○ Kidney: increase hormonal production
○ Blood Vessels: vasodilation to facilitate movement of blood towards the blood vessel
its nerves and ganglia are usually found at the brain stem and sacra portion of the spinal cord
Parasympathetic division
- readies the body for resting phase or regulates the resting function of the body (sleeping)
involved in maintaining the movement of the digestive system . covers the gut or intestines
enteric division
- has its own sympathetic and parasympathetic nerve fibers
- provides innervation for maintaining peristalsis of certain smooth muscles and the release of certain chemicals involved in the digestion of the molecules
also called Gut Brain because it can provide instructions to the nerves independently from the centra nervous system
enteric division
composition of white and gray matter
white:
axons, myelinated
(myelin sheath is 80% lipid)
gray: cellular bodies/ soma
(darker in staining cos of less lipid content)
it has a characteristics variety of cell bodies associated with a meshwork of axonal, dendritic and glial processes
gray matter
it is the organized matter of gray matter
neurophil
Found in the cerebral cortex
the 6 layers:
molecular layer
- outer layer
- consists of pia mater
external granula layer
external pyrimidal layer
internal granular layer
ganglionic layer (internal pyrimial cells)
multiform (polymorphic) cell layer
what does cerebral cortex contains
purkinje cells (organization of cellular bodies)
ex: during rabies, the virus goes inside the purkinje cells and during the biopsy f the cerebrum, it darkens (Negri bodies) which become the cellular division center of the rabies virus
a flattened cylindrical structure that is directly continuous with the brainstem
spinal cord
- divided into 31 segments
8 cervical
12 thoracic
5 lumar
5 sacral
1 coccygeal
the brain and spinal cord are covered by three protective layers
meninges
1.dura mater (tough outer layer)
- arachnoid mater (web-like middle
layer)
composed of subarachnoid layer - pia mater (thin inner layer)
beneath the arachnoid space
thin lining between the nerve tissue and subarachnoid spaces
in the fissures, when it comes f2f with another dura mater
dural reflections
- thicker since it has 2 layers
- found in the Falx cerebri and tentorium cerebelli
2 layers:
PERIOSTEAL LAYER
immediately after the periosteum or parietal bone
MENINGEAL LAYER
underlying layer of periosteal layer
maintains the optimal microenvironmentin the CNS for proper brain function
blood-brain barrier
[like a security checkpoint that controls what enters and exits the brain. It helps keep harmful substances out while allowing essential nutrients in, ensuring the brain has the perfect environment to function properly.]
what are the functions of the BBB
1, protect the brain from potential blood-borne toxins
Prevents toxins and large molecules from entering.
Only small molecules (less than 500 Daltons) can pass through.
Those that can enter bind to efflux transporters
- AWAY, from nerve tissue to blood vessels
- meet the metabolic demands of the brain tissue
influx transporters (ex:
Glucose Transporters (GLUT-1) – Bring glucose (brain’s main energy source) inside.
Amino Acid Transporters – Help essential nutrients reach brain cells.)
permit entry of impt mol. needed by nerve tissues
- TOAWRDS, blood vessels to nerve tissue - regulate the homeostatic microenvironment in CNS
- maintains water enviro inside erve tissue through the water channels present (Aquaporin Channels, AQPOR)
how does the nervous system responds to injury
1.axonal degeneration
injured part of the axon starts to degrade.
macrophages enter the area and digest the damaged myelin sheath
= allows Schwann cells to rebuild the axon properly
- neural regeneration
✔ Schwann Cells Help Repair
support the growth of new axons by providing guidance and nourishment.
once repaired, the Schwann cells form a new myelin sheath = restore normal function.
✔ Regeneration is Easier in the PNS
blood-nerve barrier breaks down easily, allowing macrophages to clear debris and help repair.
✔ Regeneration is Harder in the CNS
BBB blocks macrophages, so damaged myelin takes longer to clear.
instead of healing, astrocytes form scars (gliosis), preventing axon regrowth.
scar formation in the CNS after neuronal injury
reactive gliosis
- usually astrocytes bind to myelin and stay there
- once binding is done, it is more preserved =scarring or gliosis
what causes the COVID 19 Fog
causes neuroinflammation, meaning the brain’s immune system becomes overly active
Microglial cells (brain immune cells) respond by breaking down myelin, which disrupts brain function.
leads to symptoms similar to Cancer Therapy-Related Cognitive Impairment (CRCI):
- Memory problems (especially short-term memory loss)
- Anxiety and depression
- Speech difficulties (e.g., stuttering)
Terminal end of Schwann cells is aka
Teloglia
Consists of:
Axon terminal
Junction Al folds of muscle cell motor end plate
Synaptic cleft
Nicotine ACh receptor
