Nervous System Flashcards
Meninges
Brian and spinal cord and the roots of peripheral nerves are enveloped by a series of connective tissue sheaths:
Dura mater: outermost (attached to skull)
Arachnoid: membrane attached to dura mater
subarachnoid space: contains CSF
pia mater: highly vascular, adherent to brain and spinal cord
Leptomeninges: Arachnoid + Pia Mater
Brain Divisions (embryonic)
Forebrain (telencephalon, diencephalon)
Midbrain (Mesencephalon)
Hindbrain (metencephalon, myelencephalon)
Forbrain
Cerebrum, Basal nuclei, Hippocampus, Amygdala
Thalamus and hypothalamus
Midbrain
Midbrain
Hindbrain
Pons and cerebellum
Medulla oblongata
CNS cells
Astrocytes, Oligodendroglia, Microglial Cells, Ependymal Cells
PNS cells
Schwann Cells
Satellite Cells
White Matter
Formed by dense accumulations of myelinated axons. The myelin sheath is rich in lipids and has a white appearance
Contains myelinated axons and glial cells, blood vessels. Peripheral in spinal cord, central in brain
Grey Matter
Rich in neuronal cell bodies, glial cells, and neuropil. The neuropil represents the axons, dendrites and cytoplasmic projections of glial cells that form the background matrix to neuronal cell bodies within the grey matter
Contains neurons, glial cells, and axons, blood vessels. Peripheral in brain, central in spinal cord
CNS: ectodermal origin
Sensitive to hypoxia: neurons, astrocytes, oligodendrocytes
CNS: Mesodermal origin
Not as sensitive to hypoxia: Microglia, vascular endothelium
Neurons
The functional cells of the nervous system in which two protoplasmic properties are highly developed:
Irritability (generation of an impulse) and
Conductivity (ability to transmit such an impulse from one locality to another
Neurons are dispersed throughout the CNS and grouped in specific areas in PNS
Neurons Structure
Cell body/perikaryon/soma
The cell body of the neuron contains the nucleus and the organelles. The axon and the dendrites branch off the cell body
Neuron Soma Structure
Euchromatic nucleus with prominent nucleolus
Basophilic cytoplasm = Nissl substance: RER and ribosomes
They are long living cells -> aging pigment=lipofuscin
Synapses
Specialized junctions with other cells that are along the length or at the end of an axon
Act as transmission points for electrical impulses
Can trigger the generation of an action potential in the postsynaptic cell; they can be excitatory or inhibitory
Synapses at end of an axon or axon branches are swollen into a club shape (boutons terminaux)
Those along the length of axon result in varicosities (swellings) in the axon (boutons en passant)
Synaptic Knob Structure
Presynaptic part= termination of axon Intersynaptic cleft Postsynaptic part (dendritic thorn)
Synaptic Vesicles
Contain different types of neurotransmitters (Ach, Noradrenaline, and adrenaline, GABA, Dopamine, etc)
Neurons Synapse with:
Neuron
Muscle
Gland
Stimulatory Synsapse
Synaptic vesicles contain ACh
Inhibitory Synapse
Synaptic oval vesicles contain GABA
Oligodendrocytes
Provide support and the myelin sheath to axons within the CNS
Unlike schwann cells (PNS), these can form myelin sheaths for several axons at once (octopus)
Produce and can repair myelin sheath
Small dark nuclei (between myelin sheaths or around neurons)
Can be destroyed by viruses/toxins resulting in primary demyelination
Microglia
Private security system of CNS- CNS is very particular
Functions: Immunosurveillance, Immunoregulation, Reparative (phagocytic), Gitter cells (myelophages)
Derived from blood-borne monocyte
Resident macrophage of CNS
Gitter Cells
Microglial cells that are activated during necrosis or inflammation -> globular and swollen after having phagocytized debris from injured cells
Note the cytoplasmic vacuolation due to ingestion of cellular debris (foamy cytoplasm)
Astrocytes
Star shaped
CNS counterpart of the fibroblast
Involved in cell communication and the functioning of the BBB
2 types: protoplasmic (grey matter) and fibrillar (white matter)
Glial fibrillary acidic protein staining
Astrocytes Functions
Transport of nutrients
Part of BBB
Antigen presentation
Ependymal Cells
Form an epithelium that lines ventricular cavities within the brain and the central canal of the spinal cord
The cells are typically cuboidal or columnar with numerous motile cilia on their apical surfaces
Central canal ependymal cells have cilia to help the circulation of the CSF
Ependymal Cells Function
Important barrier function that protects neural tissue from potentially harmful substances by mechanisms that are still incompletely understood
Have only limited regenerative capacity and this typically do not undergo mitotic proliferation
Ventricular System
Ependymal cells line the inside of ventricles in the CNS, which also communicates with the subarachnoid space. Both circulate CSF
Cerebrospinal Fluid
Produced by choroid plexus by specific modified ependymal cell
Produced and must be drained away at a constant rate
The total volume of CSF is formed and renewed 3x a day
can be sampled for clinical examination
CSF: roles
Medium for filtration system -> facilitates the removal of metabolic waste from the brain and exchange of biomolecules into and out of the brain (not glucose or O2, but will do hormones, vitamins etc)
Helps maintain the delicate extracellular environment required by the brain to function optimally (homeostasis)
Cushions the CNS in case of impacts
Choroid Plexus
CSF is formed as plasma and filtered from the blood through the choroid plexus ependymal cells
Produced by a mechanism that involves active secretion of Na into the ventricles, then water follows the resulting osmotic gradient
The ependymal cells are joined by tight junctions so it is impermeable to large molecules
One choroid plexus in each ventricle
Choroid Plexus: Organization
Consists of a layer of cuboidal epithelial cells surrounding a core of capillaries and loose connective tissue
The epithelium is specific modified ependymal cells, that have microvilli and are linked to adjacent cells by tight junctions (unlike ependymal)
These tight junctions prevent the majority of substances from crossing the cell layer into the CSF- acts as a blood-CSF barrier
Folds into many villi around each capillary, creating frond-like processes that project into the ventricles
The villi, along with a brush border of microvilli, greatly increases the surface area of the choroid plexus
CSF circulation
Being secreted by choroid plexus in lateral and fourth ventricle
go from lateral ventricle to third to fourth and then to the central canal or to the subarachnoid space where it travels around the brain. some goes through arachnoid villus to be resorbed back into venous circulation
Blood-CSF barrier
A pair of membranes separate blood from CSF and CSF from brain tissue
blood-CSF boundary at the choroid plexus is a membrane composed of the ependymal cells and tight junctions that link them. (choroid plexus capillaries are fenestrated-no tight junctions)
Brain-CSF boundary is the arachnoid membrane, which envelops the surface of the brain
Blood-CSF Barrier functions
prevents the passage of most blood-borne substances into the brain
facilitates the transport of different substances into the brain due to the distinct structural characteristics between the two barrier systems (for a number of substances, the BCSFB is the primary site of entry into brain tissue)
facilitates the removal of brain metabolites and metabolic waste into blood
Modulates the entry of leukocytes from blood into the CNS
Choroid plexus cells secrete cytokines which recruit monocyte-derived macrophages, among other cells, to the brain-this cell trafficking has implications in normal brain homeostasis and neuroinflammatory processes
Cerebellum
Cortex cerebelli- grey matter
1. Molecular layer-basket cells
2. Ganglionic cell layer- Pukinje cells
3. Granular cell layer- granule cells in stratum granulosum
4. White matter core- myelinated nerve fibers
All layers communicate with each other in a complex fashion
Fine tuning motion and maintaining body position in space
not essential to survival but then all movements will need to be consious
Fetal Cerebellum
an additional exterior cortical lamina. These cells will populate the internal granular cell layer during early postnatal development External granular cell layer molecular layer ganglionic cell layer granular cell layer
Nucleus in CNS
A cluster of neurons in the CNS, located deep within the cerebral hemispheres and brainstem, performing a common function
Spinal Cord
In cross sections, white matter is peripheral and gray matter is centra, assuming H shape
Horizontal bar of H is central canal, which is a remnant of the lumen of the embryonic neural tube
Lined with ependymal cells. The grey matter of the legs of the H forms the anterior horns,. These contain motor neurons whose axons make up the ventral roots of the spinal nerves
Grey matter also forms the posterior horns (arms of H) which receive sensory fivers from neurons in the spinal ganglia (dorsal roots)
Spinal cord neurons are large and multipolar, esp in the anterior horns, where large motor neurons are found
Dorsal and ventral roots will come together to forma trunk
Functional PNS division
Somatic Nervous System
Autonomic Nervous System
Somatic Nervous System
a one neuron system that innervates (voluntary) skeletal muscle or somatosensory receptors of the skin, muscles and joints
Autonomic Nervous System
a two neuron visceral efferent system, that innervates cardiac and smooth muscle and glands. It is involuntary and has two major subdivisions:
Sympathetic (thoracolumbar)
Parasympathetic (craniosacral)
Nerves
collection of axons/dendrites outside CNS
consist of axons, dendrites, blood vessels, glial cells, and conective tissue investments
Endoneurium, perineurium, epineurium.
cells present in a nerve: endothelial cells, fibroblasts, schwann cells
Ganglia
Collections of Neuronal cell bodies and processes found outside the CNS
Cells of a ganglion: neurons, neuroglial cells, amphicytes
Schwann cells, endothelial cells. Axons are also present
Two types of ganglia: sensory (craniospinal), autonomic
Satellite glial cells
(amphicytes)
surround the neurosomas in ganglia of PNS
provide electrical insulation around the soma
regulate the chemical environment of the neurons
Schwann Cells
Envelope nerve fibers in PNS
Wind repeatedly around a nerve fiber
produces a myeline sheath similar to the ones produced by oligodendocytes in CNS
Assist in the regeneration of damaged fibers
Schwann cells: Myeline sheath
AN insulating layer around a nerve
formed by oligodendrocytes in CNS and schwann in PNS
consists of the plasma membran of glial cells
20% protein, 80% lipid
Schwann cells: myelination
Production of the myelin sheath
begins the 14th week of fetal development
proceeds rapidly during infancy
completed in late adolescence
dietary fat is important to nervous system development
Myenteric Plexus
Situated between the inner and outer longitudinal layers of the tunica muscularis
This structure helps to control peristaltic movement of the GI tract
Group or cluster of neurons in PNS called
Ganglion
Regarding Microglia
They have a reparative role through phagocytosis
What is contained in the area enclosed by the circle
Myelinated axons
Which is a cell of the PNS
Schwann cell
CSF produced by___
Choroid Plexus
Cytoplasmic projections of glial cells
are part of the neuropil
CT surrounding whole nerve is ___
epineurium
Regarding CSF
Filtered from plasma, acts as cushion, can be sampled for clinical evaluation
Large neuronal bodies within the ganglionic layer known as?
Purkinje Cells
Medulla Oblongata Nucleus
Nuclei are aggregates of neuronal cell bodies
Identify some of the small nuclei in medulla oblingata
Glial support cells: astrocytes, oligodendrocyts, microglia
Specialized glial cell that lines the central canal?
Ependymal cells
Create, absorb, and circulate CSF
Ventral horn
Innervates motor
Doral Horn
Innervates interneurons (recieves sensory afferents)
Lateral horn
Innervation of the autonomic nervous system
Granular substance in neurons?
Nissl substance. Represents the RER and ribosomes of the neuron
Satellite cells
Responsible for insulation and nutrition of the neurons
Endoneurium
Surrounds each individual myelinated neuron (nerve fiber)
Perineruium
Nerve fibers bundled to form fasicle surrounded by perineurium
Epineurium
Bundle of fasicles forms nerve and it is surrounded by epineurium
