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What is the basic structural and functional unit of nervous system?

Neuron (nerve cell)
Is excitable/irritable

What is trophic metabolic center of nerve cell?

Cell body

What is another name for cell body?


Where does most protein synthesis occur in nerve cell?

Cell body

Where is receptive area of multipolar neurons?

Cell body

What structures are found in cell body of nerve cell?

Neurofilaments, microfilaments, microtubules
Lipid droplets
Melanin granules (in certain neurons--substantia nigra)
Axon hillock

What shapes can cell body of nerve cell take?

Spherical, ovoid or angular

What are basophilic clumb found in cytoplasm of nerve cells?

Nissl bodies--stacks of rER
(Free ribosomes also found in cytoplasm)

Can neurons form tumors in adults?

Do not undergo mitosis

Describe nucleus of cell body of nerve cell

Large, clear, euchromatic
Encloses spherical dense nucleolus

How can neurons in adult regnerate?

Neurons do not divide
Adult brain may have neural stem cells that retain capacity to regenerate--migrate to site of injury where they differentiate into nerve cells

What is a yellowish-brown pigment found in cell body of nerve cells?

Lysosomal enzymatic residue

Describe axon hillock of nerve cell

Origin of axon, funnel-shaped
no rER--stains pale

What is chromatolysis?

Dissolution of Nissl substance following injury to nerve cell body

What processes radiate from cell body of nerve cell?

Branch and taper

What increases receptive area of neuron?


Describe structures found in dendrites

No Golgi apparatus
Mitochondria and rER may be present
Never myelinated

What is function of dendrite?

Receive stimuli from epithelial receptor cells or other neurons and transmit info to cell body of neuron

What structures are found in axon of neuron?

No rER

Describe axon of neuron

Variable length (1mm-1m)

What is function of axon?

Relay action potentials away from cell body to axon terminales and then transmit them to other neurons, smooth/skeletal/smooth muscle, gland cells

What is axolemma?

Axon cell membrane

What is axoplasm?

Axon cytoplasm

What is initial segment of axon?

Segment distal to axon hillock and proximal to where myelination begins

Where are collateral branches of axon located?

Near axon hillock

Where is action potential initiated in axon?

Dense undercoating of cell membrane

Describe regeneration of axon that occurs following injury?

Proximal axon regenerates
Distal axon degenerates

What are terminal arborizations of axon?

Terminal axonal branches

What are terminal buttons/axon terminals?

Dilated ends of arborizations

What is function of terminal buttons?

Form synapses
Some local protein synthesis

In which direction does anterograde transport occur?

Away from cell body

In which direction does retrograde transport occur?

Toward cell body

What microtubule-associated motor protein plays a role in anterograde transport?


What microtubule-associated motor protein plays a role in retrograde transport?


How do viruses and toxins that enter nerve endings enter CNS?

via retrograde transport

What substances are transported via slow anterograde transport system?

Tubulin molecules
Neurofilament proteins

Describe fast axoplasmic transport system

Requires ATP

What substances are transported via fast axoplasmic transport system?

Membranous organelles (sER, synaptic vesicles, mitochondria)
Sugars, amino acids, nucleotides

What is most common type of neuron?


Where are bipolar neurons found?

Inner ear

Describe bipolar neuron

2 processes--peripheral (dendrite) and central (axon)

Describe multipolar neuron

Numerous dendrites and single axon

Describe unipolar/pseudounipolar neuron

Single process arising from cell body which secondarily bifurates into 2 processes with axon characteristics
T shaped

How are impulses transmitted in pseudounipolar neurons?

Impulse transmitted down axon, bypassing cell body

What kind of neurons are motor (efferent) neurons?


What is function of sensory (afferent) neurons?

Receive sensory stimuli from environment or from within body

Where do skeletal motor neurons go?

To skeletal muscle fibers

Where do visceeral motor neurons go?

To smooth muscle, cardiac muscle or glands

Where are interneurons located?

Confined to CNS
99.9% of neurons

What kind of neurons are interneurons?


What is function of neuroglia?

Provide physical and physiological support, protecting nerve cells

How many neuroglia are present for every neuron?


Can neuroglia form tumors?

Yes, they can divide

Where is connective tissue found in CNS?

CNS (nerve tissue of brain and spinal cord) does NOT contain connective tissue
Only connective tissue found in brain and spinal cord is associated with blood vessels

What are largest neuroglial cells?

Astrocytes (astroglia)

What kind of neuroglia exhibit processes with mat-like vascular feet (pedicels) that ensheathe all blood vessels covered by a basal lamina?


What is function of astrocytes?

Assist in formation of blood-brain barrier
Form scar tissue following nerve tissue injury
Monitor ionic and chemical composition in extracellular space around nerve cells

What kind of neuroglia have processes that surround periphery of brain and spinal cord, forming a layer deep to pia mater?


What kind of astrocytes are found primarily in grey matter?

Protoplasmic astrocytes (granular cytoplasm)

Where are processes of protoplasmic astrocytes located?

Processes cover synapses, neurons and blood vessels

What kind of astrocytes are found primarily in white matter?

Fibrous astrocytes
(long thin processes, light staining)

With what structures are fibrous astrocytes associated?

Associated with blood vessels and pia mater
Cover nodes of Ranvier and synapses

What type of cancer makes up 80% of primary brain tumors in adult?

Fibrous astrocytomas

What kind of neuroglia form rows in white matter?

Oligodendrocytes (oligodendroglia)
smaller than astrocytes

What organelles are found in oligodendrocyte?

Many mitochondria
Golgi apparatus

What kind of neuroglia have small cell bodies and elongated nuclei? (other gila have round nuclei)

Condensed chromatin

Where are microglia found?

In both grey and white matter

What kind of neuroglia are phagocytic (CNS housekeepers)?

(derived from monocytes)

What are cuboidal-columnar cells lining brain and spinal cord cavities, containing CSF?

Ependymal cells

What structures are found in ependymal cells?

Motile cilia which move CSF
Abundant mitochondria
apical Golgi apparatuses
sparse rER
Gap junctions and zonula adherens

Describe unmyelinated axons in CNS

not covered by glia

Describe unmyelinated axons in PNS

Occupy a groove of Schwann cell; forms longitudinal uninterrupted sheath along length of axon

One Schwann cell envelops many axons

T/F There are no nodes of Ranvier along unmyelinated axons


What is function of myelin?

Increase impulse conduction and insulate neurons

What is mesaxon?

Fused cell membranes

From what structure are Schwann cells derived?

Neural crest cells

What is myelin?

Lipoprotein formed by concentric layers of cell membrane which have a high lipid content (~80%)

T/F Myelin is a substance that is secreted on the axon by a cell


Describe myelination of nerve cell axons in PNS

Schwann cell wraps its membrane repeatedly around one internode of a single axon, forming myelin sheath
Each myelinated axon is covered by a series of Schwann cells

What is name of uninsulated segment of axon?

Nodes of Ranvier

What is name of insulated segment of axon?

Internodal segment (internode)

What is delicate layer of loose connective tissue with collagen fibrils that covers individual axons?


What cells synthesize endoneurium?

Schwann cells

Describe layers of myelinated axon in PNS

Myelin sheath, basal lamina, endoneurium

What is specialized connective tissue, lined by layers of perineural cells, that surrounds a nerve bundle?


What inhibits passage of macromolecules between nerve cells?

Zonulae occludentes

What is enclosed by perineurium?

Schwann cell-ensheathed axons and endoneurium

What is dense irregular connective tissue with elastic fibers that covers several nerve bundles to form gross nerve?


What are satellite cells?

Support cells that surround cell bodies of neurons housed in ganglia
Function analogous to Schwann cell but do NOT form myelin

What is optic neuritis?

Inflammation of optic nerve

What is most common cause of optic neuritis?

Multiple sclerosis
(or other demyelinating disease)

What is affected by MS?

White matter (myelinated axons) of CNS
Any myelinated tract (bundle of axons) may be affected

What causes MS?

Autoimmune attack of myelin sheath formed by oligodendrocytes--demyelination of CNS nerve cell axons

What cranial nerves are susceptible to demyelination during MS?

Only optic nerve (CN II)--is tract of CNS

The other 11 CNs are components of PNS

What are typical symptoms of optic neuritis?

Visual loss affecting one eye (sometimes both)
Pain when moving eye
Papilledema (depending on segment of optic nerve affected)
Pupil of affected eye will not respond to light normally (if visual acuity severely impaired)

What is papilledema?

Swelling of optic disk

What is treatment of optic neuritis?

IV coritcosteroids over 3-5 days
Most cases completely within weeks or months

What is ependymoma?

Tumor that grows into (4th) ventricle, compresses surrounding structures as it expands
5% of primary brain tumors

What are clefts of Schmidt-Lanterman?

Schwann cell cytoplasm trapped in concentric layers of cell membrane myelinating an axon

What is a bundle of nerve cell axons in PNS?


How many cranial nerves are present?

12 pairs

How many spinal nerves are present?

31 pairs

What are collections of nerve cell bodies in PNS?


What is example of sensory ganglia in PNS?

Cranial nerve sensory ganglia
Dorsal root ganglia

What is example of autonomic ganglia in PNS?

Sympathetic trunk, visceral ganglia
Parasympathetic--ganglia associated with CNs and intramural ganglia within visceral walls

What is voluntary nervous system?

Somatic motor system
Influences skeletal muscle to produce movement

What is involuntary nervous system?

Autonomic nervous system/visceral motor system
Influences smooth muscle, cardiac muscle and glands

What nervous system is involved in "fight, firght, or flight" response?


What nervous system is referred to as "thoracolumbar outflow"?

(Connects with thoracic and lumbar regions of spinal cord-- T1-L2(3))

What nervous system maintains homeostasis?


What nervous system is referred to as "cranosacral outflow"?


What is cranial outflow portion of PANS?

PANS connects with brain through CNs (oculomotor, facial, glossopharyngeal, vagus)

What is sacral outflow portion of PANS?

PANS connects with spinal cord through sacral spinal nerves S2-S4

What is a junction between a neuron and another cell where action potential (nerve impulse) is transmitted from cell to cell?


What kind of cell can postsynaptic cell be?

Another neuron
Muscle cell (smooth, cardiac, skeletal)
Gland cell

Where are electrical synapses found in human?

NOT common in mammals
Present in brainstem, retina, and cerebral cortex

Describe electrical synapse

Gap junctions allow ions (electrical current) to pass from cell to cell

Which type of synapse results in faster impulse transmission: electrical or chemical?


What is most common type of synapse?


What structures are contained within terminal bouton (presynaptic component)?

Presynaptic membrane
Synaptic vesicles

What are contained within synaptic vesicles?


What is presynaptic density?

Cone-shaped structures that represent active site of synapse

What is a narrow extracellular space between presynaptic and postsynaptic membranes?

Synaptic cleft

What structures are contained with postsynaptic component?

Postsynaptic membrane (which displays postsynaptic density)
Receptors for neurotransmitter
Ligand-gated Na+ channels

What happens as action potential reaches presynaptic membrane?

Voltage-gated Ca++ channels on presynaptic membrane open
Ca++ ions enter presynaptic terminal

What occurs after Ca++ ions enter presynaptic terminal?

Synaptic vesicles approach and attach to inner surface of presynaptic membrane
The 2 membranes rupture at point of contact, releasing NT into synaptic cleft via exocytosis

What happens after NT is released from presynaptic terminal?

NT diffuses across synaptic cleft and binds to receptor sites on postsynaptic membrane

What happens after NT binds receptor sites on postsynaptic membrane?

Ligand-gated Na+ channels on postsynaptic membrane open
Na+ enters postsynaptic membrane, causing depolarization of membrane

What results from depolarization of postsynaptic membrane?

Voltage-gated Na+ channels open, generating nerve impulse

Where is choroid plexus located?

in ventricles (hollow cavities) of brain

Describe structure of choroid plexus

Folds of pia mater covered by simple cuboidal epithelium (ependymal cells held together by tight junctions/zonulae occludentes)

What kind of capillaries are found in choroid plexus?

Fenestrated (leaky) capillaries

What is function of choroid plexus?

Produce cerebrospinal fluid which is released into ventricular system

Where is CSF found?

Central canal of spinal cord
Subarachnoid space around brain and spinal cord

Describe composition of CSF

Low protein
High Na+, K+, Cl-
Clear, low density
90% water and ions, a few lymphocytes

How often is CSF replaced?

4 times/day

How does brain get rid of its metabolic waste?

Brain's metabolic waste products diffuse into CSF of subarachnoid space

Brain does NOT contain lymphatics

Where is CSF reabsorbed?

Reabsorbed by arachnoid villi in superior sagittal sinus
Passes into bloodstream

What is function of CSF?

Shock absorber around brain and spinal cord

What are 3 layers of cerebellar cortex?

Molecular layer (superficial)
Purkinje layer (middle)
Granular layer (deepest)

What cells are unique to cerebellum?

Purkinje cells

What are largest cells of nervous system?

Purkinje cells

What are smallest cells of nervous system?

Granule cells

What kind of changes occur distal to site of injury in nerve cell?

Anterograde changes (includes degeneration and elimination of debris)

What is Wallerian degeneration?

Segment of axon distal to nerve cell injury degenerates
(orthograde degeneration)

What kind of cells clean up debris following nerve cell injury?

Phagocytic cells derived from Schwann cells
Blood-derived monocytes (form macrophages)

What occurs in anterograde changes (after debris is eliminated) following nerve cell injury?

Schwann cells proliferate and along with their external lamina, form tubes/tunnels

What kind of changes occur proximal to site of injury in nerve cell?

Retrograde reaction and regeneration

What happens during chromatolysis of nerve cell following injury?

Cell body swells
Loss of Nissl bodies
Nucleus moves away from center of cell body

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