Nervous Tissue I Flashcards by Emmaly Smith

What is nervous tissue specialized for?

Processing, integrating, transmitting, and receiving information

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What are general characteristics of nervous tissue?

cells > ECM

All cells directly in contact with other cells

CNS ground substance mostly GAGs and glycoproteins - no fibers

PNS ECM compositions varies, ground substance + some fibers

CT compartmentalizes nervous tissue in PNS peripheral nerves

Vascularized

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What are the 2 resident cells of nervous tissue?

Neurons

Neuroglia

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What are neurons and their function?

Nerve cells

Highly specialized cells

Generate, receive, process, integrate, and send information

Some specialized for sensing information about the internal or external environment

Do not divide in adults

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What are neuroglia and what are their functions?

Glia, Glial cells

Support, nurture, and protect neurons in CNS and PNS

In the CNS only, synthesize and secrete ECM components; wound healing and more

Neuroglia > neurons

Can divide

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What is the CNS made up of?

Brain and spinal cord

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What is grey matter and what structures are brain grey matter and spinal cord grey matter?

Regions with high numbers of neurons and neuroglia cell bodies

Brain grey matter includes the cerebral cortex, cerebellar cortex, and basal nuclei

Spinal cord grey matter includes columns (horns) and grey commissure

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What is white matter and what structures are brain white matter and spinal cord white matter?

Regions with high number of myelinated axons

Brain white matter includes tracts that run between grey matter regions

Spinal cord white matter includes tracts, fasciculi, and commissures

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What is the PNS and what is its function? What can it be subdivided into?

PNS is all nervous tissue outside the CNS

Connects body with CNS

Includes clusters of neuron cell bodies called ganglia

Includes collections of axons called nerves and nerve plexuses

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What is a neuron and how does it communicate?

Basic functional unit of nervous system

Function to communicate with other cells - communicate across synapses and sometimes gap junctions

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What is the soma of the neuron and its function?

Cell body

Metabolic center of cell

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What are characteristics of neurons?

Very acting protein synthesis via exocytosis - large euchromatic nucleus with prominent nucleolus

Lots of RER for neurotransmitter synthesis

Nucleus usually round or oval

Nissl bodies - clumps of RER (basophilic)

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What does the soma contain?

Contains other typical organelles

Neuronal cytoskeleton

Cytosolic inclusions like lipid droplet, lipofuscin, and melanin granules

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What does the neuronal cytoskeleton include?

Actin (thin) filaments

Neurotubules - microtubules

IFS - neurofilaments

Neurofibrils = bundles of neurofilaments and neurotubules

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What is the tau protein?

Microtubules associated protein that helps stabilize microtubules

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What are neurites and their function?

Cell processes - dendrites

Receive signals from other cells, convert signals into small electrical impulses, and transmit them toward soma

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What are the characteristics of neurites?

Never myelinated

Allow neurons to receive signals simultaneously from many other neurons

Cell membrane on dendrites has very high number of neurotransmitter receptors

Dendrite cytoplasm has Nissl bodies and other organelles

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How do neurons receive signals simultaneously from other neurons?

Dendrite terminals are arborized (bushy, branching)

Dendritic spines on dendrite surfaces further increase available surface area for synapse formation

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How many axons per neuron?

What is the axon and its function?

Very long cytoplasmic processes

Transmit impulses away from soma and towards the axon terminal to the synapse and to the other cells

What are characteristics of the axon?

Diameter and length of axons vary a lot

Axon diameter directly and positively correlates with conduction velocity

Often myelinated, not always

Originate from the axon hillock

May have collateral branches, especially close to axon hillock

What is an axon hillock?

Specialized pyramid shaped region of soma

No Nissl bodies, ribosomes, or Golgis in axon hillock

Contains other organelles

What are the parts of an axon and their function?

Collateral branches

Axolemma - cell membrane of axon; transmits action potentials

Axoplasm - cytoplasm; no Nissl bodies, ribosomes, or Golgis. Lots of vesicles, microtubules, and mitochondria

Inititial segment - most proximal; Action potentials initiate here and numerous ion channels

Terminal arborizations

Terminal boutons - includes presynaptic membrane

What is anterograde transport?

From soma to axon terminal

Kinesin motor proteins attach organelles, vesicles, or cytoskeletal proteins to microtubules and can travel fast

What is retrograde transport?

From axon to soma Dynein motor proteins attach cargo to microtubules Transport endocytosed substance and mol's that need to be degraded

What are multipolar neurons?

Multiple processes extend from soma. 1 axons and 2 or more dendrites. Dendrites and soma can receive signals Direction of impulses: Dendrite -> Soma -> Axon OR soma -> axon

What are bipolar neurons?

2 processes extend from soma. 1 axon and 1 dendrite. Dendrites and soma can receive signals. Impulses move from dendrite -> soma -> axon

What are pseudounipolar neurons (unipolar neurons)?

1 axon and 1 dendrite. Dendrites and soma can receive signals. Impulses go from dendrites to peripheral processes to central processes Impulses bypass the soma! Examples: Neurons in dorsal root ganglion which relay sensory info and most sensory ganglia of cranial nerves

What direction does information flow?

Afferent neurons send impulses towards CNS/brain and carry sensory info. Efferent neurons take impulses away from brain/CNS and toward effectors and carry motor information (visceral or somatic)

What is the function of sensory neurons?

Detect changes in the internal or external environment and send that sensory information towards the CNS Always afferent neurons

What is the function of motor neurons?

Send motor impulses from the CNS towards skeletal muscle fibers or to secretory cells in an endocrine or exocrine gland Always efferent neurons

What is the function of interneurons?

Transmit (relay) impulses between other neurons Between sensory and motor, between CNS and PNS, and between brain regions

What are sensory receptors?

Nerve endings or specialized cells that convert stimuli from external or internal environment into afferent impulses to CNS

What is the morphology of the receptor?

Free nerve ending Encapsulated nerve ending - surrounded by CT capsule, often fluid filled Specialized sensory cell Peripheral cell processes

What are the main neuroglia of CNS?

Astrocytes, oligodendrocytes, microglia, and ependymal cells

What are the main neuroglia of PNS?

Schwann cells and satellite cells

What are astrocytes and their functions?

Largest neuroglia in CNS and numerous processes extend in all directions Some cytoplasmic processes end in vascular feet Provide most physical and physiological support in CNS Synthesize and secrete ECM and maintain its chemistry - monitor and maintain ECM pH, ionic concentration Form glial scar tissue Contributes to blood brain barrier Create glymphatic vessels

What are 2 kinds of astrocytes?

Protoplasmic astrocytes Fibrous astrocytes

Where are protoplasmic astrocytes located and what do they do?

Primarily in grey matter Form glial scar tissue Form protective sealed barrier between pia mater and brain tissue Regulate tissue fluid flow through grey matter at night - activity influences how much debris remains in tissue fluid

Where are fibrous astrocytes located and what are their functions?

Primarily in white matter Form glial scar tissue During embryonic development, forms a cellular scaffold that helps guide developing neurons to their correct location in the brain

Where are microglia located and their functions?

Present in grey and white matter Macrophages of CNS, derived from monocytes Immune cells that phagocytose pathogens, dead cells, damaged CNS tissue, and foreign materials Release cytokines that attract T cells to injured tissues and present antigens to those T cells when they arrive

Where are oligodendrocytes located and what do they do?

White matter - myelinate CNS axons In grey matter too

What is myelin?

Lipid rich Insulates axons and icnreases conduction velocity of action potentials as they are propagated down the axon

What is the structure and function of ependymal cells?

Simple cuboidal or columnar epithelial cells with motile cilia Line ventricles in brain and line central canal of spinal cord Circulate cerebrospinal fluid and cover the surface of the choroid plexus

What are the functions of Schwann cells?

Myelinate the axons of PNS neurons - each Scwann cell myelinates 1 short segment of one neuronal axon Assist in axon repair following injury to PNS nerves

What do satellite cells do?

Regulate extracellular ionic environment