Nervous Tissue I Flashcards
What is nervous tissue specialized for?
Processing, integrating, transmitting, and receiving information
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
What are the 2 resident cells of nervous tissue?
Neurons
Neuroglia
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
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
What is the CNS made up of?
Brain and spinal cord
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
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
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
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
What is the soma of the neuron and its function?
Cell body
Metabolic center of cell
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)
What does the soma contain?
Contains other typical organelles
Neuronal cytoskeleton
Cytosolic inclusions like lipid droplet, lipofuscin, and melanin granules
What does the neuronal cytoskeleton include?
Actin (thin) filaments
Neurotubules - microtubules
IFS - neurofilaments
Neurofibrils = bundles of neurofilaments and neurotubules
What is the tau protein?
Microtubules associated protein that helps stabilize microtubules
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
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
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
How many axons per neuron?
1
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
