Nervous System Flashcards
The most complex system
NERVOUS SYSTEM
Components of the Nervous System
network of nerve cells (neurons)
supporting glial cells
nerve tissue
is distributed throughout the body as an integrated communications network
Nerve tissue
Structural Divisions of the NS
Central nervous system (CNS)
Peripheral nervous system (PNS)
overall “command center,” processing and integrating information
Central nervous system (CNS)
Central nervous system (CNS) components
brain
spinal cord
division of the nervous system in charge of relaying messages to and from the command center
Peripheral nervous system (PNS)
Peripheral nervous system (PNS) components
cranial, spinal, and peripheral nerves
ganglia
conduct impulses to and from the CNS (motor and sensory nerves respectively)
cranial, spinal, and peripheral nerves
which are small groups of nerve cells outside the CNS
ganglia
Functional Divisions of the NS
Sensory Nervous System
Motor Nervous System
Sensory Nervous System components
Some CNS and PNS components
Somatic sensory
Visceral sensory
FUNCTIONAL DIVISION - Includes all axons that transmit impulses from a peripheral structure to the CNS
Some CNS and PNS components
FUNCTIONAL DIVISION - Transmits input from skin, fascia, joints, and skeletal muscles
Somatic sensory
FUNCTIONAL DIVISION - Transmits input from stomach and intestines (viscera)
Visceral sensory
Motor Nervous System components
Motor Nervous System
Somatic motor (somatic nervous system)
Autonomic motor (autonomic nervous system)
FUNCTIONAL DIVISION - Includes all axons that transmit nerve impulses from the CNS to a muscle or gland
Some CNS and PNS components
FUNCTIONAL DIVISION - Voluntary control of skeletal muscle
Somatic motor (somatic nervous system)
FUNCTIONAL DIVISION - Involuntary control of smooth muscle, cardiac muscle, and glands
Autonomic motor (autonomic nervous system)
ionic gradient that exists between the inner and outer surfaces of their membranes
Altered by neurons in respo nse to stimuli
Electrical potential
cells that can rapidly change this potential in response to stimuli (eg, neurons, muscle cells, some gland cells)
Excitable or irritable cells
is capable of traveling long distances along neuronal processes, transmitting such signals to other neurons, muscles, and glands
action potential, the depolarization wave, or the nerve impulse
steps of Neurulation in the Embryo
- Neural folds and neural groove form from the neural plate
- Neural folds elevate and approach each other
3.Neural crest cells loosen and become mesenchymal
- Neural folds merge creates neural tube, neural crest lies atop newly made tube
functional unit of the nervous system
NEURONS
NEURONS consist of three parts :
Cell body (perikaryon)
Dendrites
Axon
synthetic or trophic center for the entire nerve cell and is receptive to stimuli
Cell body (perikaryon)
many elongated processes specialized to receive stimuli from the environment, sensory epithelial cells, or other neurons
Dendrites
a single process specialized in generating and conducting nerve impulses to other cells (nerve, muscle, and gland cells)
Axon
distal portion of the axon is usually _________ as the terminal arborization
branched
part of the axon that interact with other neurons or nonnerve cells at structures called synapses
end bulbs (boutons)
CLASSIFICATION OF NEURONS according to the number of processes extending from the cell body:
Multipolar neurons
Bipolar neurons
Unipolar or pseudounipolar neurons
CLASSIFICATION OF NEURONS according to the number of processes extending from the cell body:
one axon and; two or many dendrites
**Most neurons are ________
Multipolar neurons
CLASSIFICATION OF NEURONS according to the number of processes extending from the cell body:
one dendrite
one axon
Bipolar neurons
CLASSIFICATION OF NEURONS according to the number of processes extending from the cell body:
have a single process that bifurcates close to the perikaryon, with the longer branch extending to a peripheral ending and the other toward the CNS
Unipolar or pseudounipolar neurons
Bipolar neurons are found in
retina
olfactory mucosa
and the (inner ear) cochlear and vestibular ganglia
where they serve the senses of sight, smell and balance respectively.
Unipolar or pseudounipolar neurons are found in the
spinal ganglia (the sensory ganglia found with the spinal nerves)
and in most cranial ganglia.
CLASSIFICATION OF NERVES according to function
Motor (efferent) neurons
Sensory (afferent) neurons
CLASSIFICATION OF NERVES according to function
control effector organs such as muscle fibers and exocrine and endocrine glands
Motor (efferent) neurons
CLASSIFICATION OF NERVES according to function
involved in the reception of sensory stimuli from the environment and from within the body
Sensory (afferent) neurons
contains the nucleus and surrounding cytoplasm, exclusive of the cell processes
it is primarily a trophic center
CELL BODY (PERIKARYON)
nucleus of nerve cells are
spherical
unusually large
euchromatic (pale-staining)
prominent nucleolus
most are single nucleated but sometimes bi nucleated neurons are sometime found in
sympathetic and sensory ganglia
Chromatin of neurons are _________, reflecting the intense synthetic activity of these cells
finely dispersed
Cell bodies of neurons contain a
highly developed rough ER organized into aggregates of parallel cisternae.
chromatophilic substance made of basophilic clumps of RER and free ribosomes which can be seen under LM with appropriate stains
abundant in large nerve cells such as motor neurons
Nissl bodies
Golgi apparatus of the neuron is only found in the
cell body
Mitochondria- found throughout the cell and usually abundant in the
axon terminals
intermediate filaments are abundant both in
perikarya and processes
neurofilaments cross-linked with certain fixatives becoming visible with the light microscope when impreganated with silver salt
Neurofibrils
Neurons also contain microtubules and may also contain pigmented materials like_______ (consists of residual bodies left from lysosomal digestion)
lipofuscin
are usually short and divide like the branches of a tree
often covered with many synapses and are the principal signal reception and processing sites on neurons
Dendrites
sites of synapses with other neurons o found on dendrites surfaces o length and morphology are dependent on actin filaments and are highly plastic
Dendritic spines
are cylindrical process that varies in length and diameter according to the type of neuron.
Axon
All axons originate from a pyramid-shaped region, the ________, arising from the perikaryon
axon hillock
plasma membrane of the axon
Axolemma
cytoplasm of the axon
Axoplasm
Bidirectional Transport of Molecules along the Axon
Anterograde transport
Retrograde transport
movement of organelles and macromolecules synthesized in the cell body along the axon from the perikaryon to the synaptic terminals
Anterograde transport
macromolecules, such as material taken up by endocytosis (including viruses and toxins), are taken from the periphery to the cell body
Retrograde transport
Bidirectional Transport of Molecules along the Axon
both directions utilizes
motor proteins attached to microtubules
a microtubule-activated ATPase, attaches to vesicles and allows them to move along microtubules in axons away from the perikarya
kinesin
is a similar ATPase that allows retrograde transport in axons, toward the cell bodies
dynein
anterograde and retrograde transport both occur fairly rapidly, at rates of
50 to 400 mm/day.
MEMBRANE POTENTIALS
Resting membrane potential
Action potential or nerve impulse
a potential difference across the axolemma of about 65 mV with the inside negative to the outside brought by movement of sodium and potassium out and into the cell
Resting membrane potential
there is a sudden influx of extracellular Na+ that changes the resting potential from –65 mV to +30 mV and makes the cell interior positive in relation to the extracellular environment
Action potential or nerve impulse
In action potential or nerve impulse +30 mV potential rapidly ______ the sodium channels and _______ the K+ channels, allowing this ion to leave the axon by diffusion and returning the membrane potential to –65 mV
closes the sodium channels
opens the potassium channels
Medical Application of action potentials
Local anesthetics bind to sodium channels which stops sodium transport
no sodium transport = no action potential = no nerve impulse
SYNAPSE structures
Presynaptic axon terminal
Postsynaptic cell membrane
Synaptic cleft
(terminal bouton) from which neurotransmitter is released
Presynaptic axon terminal
with receptors for the transmitter and ion channels or other mechanisms to initiate a new impulse
Postsynaptic cell membrane
separating the presynaptic and postsynaptic membranes
Synaptic cleft
TYPES OF SYNAPSES SEEN BETWEEN NEURONS
Axosomatic Synapse
Axodendritic Synapse
Axoaxonic Synapse
axon forms a synapse with a cell body
Axosomatic Synapse
axon forms a synapse with a dendrite
Axodendritic Synapse
axon forms a synapse with an axon
Axoaxonic Synapse
responsible for the unidirectional transmission of nerve impulses from neuron to another cell
converts electrical signal (impulse) from the presynaptic cell into a chemical signal that acts on the postsynaptic cell
transmit information by releasing neurotransmitters during this signaling process.
Synapse
are chemicals that bind specific receptor proteins to either open or closed ion channels or initiate second-messenger cascades
Neurotransmitters
chemical messengers that modify neuron sensitivity to synaptic stimulation or inhibition, without acting directly on synapses
Neuromodulators
transmit ionic signals directly through gap junctions between the pre- and postsynaptic membranes
prominent in cardiac and smooth muscle
Electrical synapses
Glial Cell Types
Oligodendrocyte
Neurolemmocyte
Astrocyte
Ependymal Cells
Microglia
Origin and Location of Oligodendrocyte
Neural tube
CNS
Origin and Location of Neurolemmocyte
Neural crest
Peripheral nerves
Origin and Location of Astrocyte
Neural Tube
CNS
Origin and Location of Ependymal Cells
Neural Tube
CNS
Origin and Location of Microglia
Bone Marrow
CNS
Oligodendrocyte MAIN FUNCTION
Myelin production, electric insulation
Neurolemmocyte MAIN FUNCTION
Myelin production, electric insulation
Astrocyte MAIN FUNCTION
Structural support,
repair processes,
Blood-brain barrier,
metabolic exchanges
Ependymal Cells MAIN FUNCTION
Lining cavities of Central nervous System
Microglia MAIN FUNCTION
Immune-related activity
myelinate parts of several axons
Oligodendrocytes
have multiple processes and form perivascular feet that completely enclose all capillaries
Astrocytes
are epithelial-like cells that line the ventricles and central canal
Ependymal cells
have a protective, phagocytic, immunerelated function
Microglial cells
commonly called Schwann cells, form a series enclosing axons
Neurolemmocytes
are restricted to ganglia where they cover and support the large neuronal cell bodies
Satellite cells
a disease where myelin sheath is damaged by an autoimmune mechanism with various neurologic consequences
microglia phagocytose and degrade myelin debris by receptor-mediated phagocytosis and lysosomal activity
Multiple Sclerosis
microglia are infected by HIV-1 o interleukin-1 and tumor necrosis factor- , activate and enhance HIV replication in microglia
AIDS dementia complex
CENTRAL NERVOUS SYSTEM PRINCIPLE STRUCTURES
Cerebrum
Cerebellum
Spinal cord
All of the 3 structures of CNS has a region of these two types of matter
white and gray matter
composed of myelinated axons and oligodendrocytes
white matter
does not contain neuronal cell bodies, but microglia are present
gray matter
Has no connective tissue and is therefore a relatively soft, gel-like organ
CENTRAL NERVOUS SYSTEM
layer of the cerebral cortex formed by very small neurons (the smallest in the body), which are densely packed together
inner granule layer
Coordinates muscular activity throughout the body
CEREBRAL CORTEX
central layer of the cerebral cortex are made up of
very large neurons called Purkinje cells
CEREBRAL CORTEX Three Layers
outer molecular layer
central layer
inner granule layer
conspicuous even in H&E stained material and their dendrites extend throughout the molecular layer as a branching basket of nerve fibers
central layer of the cerebral cortex
SPINAL CORD
white matter is __________
gray matter is ___________
white matter is PERIPHERAL
gray matter is INTERNAL
SC gray matter is internal and has the general shape of an
H
Forms found in the spinal cord:
anterior horns
posterior horns
central canal
contain motor neurons whose axons make up the ventral roots of spinal nerves
anterior horns
receive sensory fibers from neurons in the spinal ganglia (dorsal roots).
posterior horns
develops from the lumen of the embryonic neural tube and is lined by ependymal cell
central canal
Spinal cord neurons are
large and multipolar
MENINGES IN THE SPINAL CORD
pia mater
arachnoid
dura mater
MENINGES AROUND THE BRAIN
The dura, arachnoid, and pia mater also cover the entire surface of the brain
Arachnoid villi
outpocketings of arachnoid away from the brain which penetrate the dura mater and enter bloodfilled venous sinuses found within the vasculature of the periosteum
Arachnoid villi
function in releasing excess CSF into the blood from the subarachnoid space into venous sinuses
Arachnoid villi
external layer consisting of dense, fibroelastic connective tissue continuous with the periosteum of the skull
Dura mater
separates the dura mater from periosteum of the vertebrae
Epidural space
separates the dura mater from the arachnoid by the thin__________
subdural space
ARACHNOID Two Components:
a sheet of connective tissue in contact with the dura mater
a system of loosely arranged trabeculae containing fibroblasts and collagen
is a large, sponge-like cavity
communicates with the ventricles of the brain.
Subarachnoid space
forms a hydraulic cushion that protects the CNS from trauma.
subarachnoid space, filled with CSF that surrounds the trabeculae
True or false: Arachnoid is vascular because larger blood vessels run through it
false, it is AVASCULAR because it lacks nutritive capillaries
is lined internally by flattened, mesenchymally derived cells closely applied to the entire surface of the CNS tissue
Pia mater
a thin limiting layer between the pia mater and the neural elements o adheres firmly to the pia mater
Astrocytic processes
Together the _________ form a physical barrier at the CNS periphery that separates the CNS tissue from the CSF in the subarachnoid space
pia mater and glial layer
functional barrier that allows much tighter control than that in most tissues over the passage of substances moving from blood into the CNS tissue, protecting the nature of the neuronal microenvironment
Blood Brain Barrier
main structural component of the BBB o cells are tightly sealed together with well-developed occluding junctions and show little or no transcytosis
capillary endothelium
consists of highly specialized regions of CNS tissue containing ependyma cells and vascularized pia mater that project from specific walls of the ventricles
Choroid plexus
remove water from blood and release it as cerebrospinal fluid (CSF)
Choroid plexus
is clear, has a low density, contains Na+, K+ , and Cl– ions but very little protein, and its only cells are normally very sparse lymphocytes
important for metabolism within the CNS and acts to absorb mechanical shocks
CEREBROSPINAL FLUID
PERIPHERAL NERVOUS SYSTEM Main components:
nerves
ganglia
nerve endings
provide the main pathway for absorption of CSF into the venous circulation since there are no lymphatic vessels in CNS tissue
arachnoid villi
consist of axons enclosed within a special sheath of cells derived from the embryonic neural crest
Nerve fibers
sheathe axons, also called neurolemmocytes
Schwann cells
- progressively thicker axons generally sheathed by increasingly numerous concentric wrappings of the enveloping cell
Myelinated nerve fibers
a layer formed by multiple layers of Schwann cell membrane
Myelin
a whitish lipoprotein complex whose abundant lipid component is partly removed by standard histologic procedures, as in all cell membranes
Myelin
With the TEM the myelin sheath can appear as a ______________ in which individual membrane layers are seen
thick electron-dense cover
PNS, even all unmyelinated axons are enveloped within
simple folds of Schwann cells
In the PNS nerve fibers are
grouped into bundles to form nerves
Connective Tissue Layers Enclosing Axons and Schwann Cells of Nerves
Epineurium
Perineurium
Endoneurium
an external dense, irregular fibrous coat
Epineurium
a sleeve of specialized connective tissue formed by layers of flattened epithelial-like cells - a barrier that protects the nerve fibers and helping maintain the internal microenvironment
Perineurium
enveloping connective tissue of Schwann cell–covered axons
Endoneurium
ovoid structures containing neuronal cell bodies and glial cells supported by connective tissue
serve as relay stations to transmit nerve impulses, one nerve enters and another exits
Ganglia
receive afferent impulses that go to the CNS
associated with both cranial nerves and the dorsal root of the spinal nerves
Sensory ganglia-
effect the activity of smooth muscle, the secretion of some glands, modulate cardiac rhythm and other involuntary activities by which the body maintains a constant internal environment
Autonomic nerves
Two parts of Autonomic Nervous System
Sympathetic division
Parasympathetic division
Neuronal cell bodies of Sympathetic division
location
thoracic and lumbar segments of the spinal cord
Neuronal cell Parasympathetic division location
medulla and midbrain and in the sacral portion of the spinal cord
Second neurons location of the Sympathetic division
located in small ganglia along the vertebral column
Second neurons location of the Parasympathetic division
very small ganglia always located near or within the effector organs
