Neuroglia and Neurons

Largest most numerous neuroglia

astrocytes

Astrocytes

Repair damaged nervous tissue and produce scar tissue

Provide mechanical strength and framework by function of their microfilaments

Control interstitial environment with help of pedicels= increase surface area= control chemical content of interstitial space

Maintain blood brain barrier=cover capillary surface=secrete chemicals to maintain

Guide neuron development

Oligodendrocytes

tie clusters of axons together with myelin

Form myelin sheath

Internodes

large areas wrapped in myelin, single unit

myelin sheath gaps

small gaps between myelin sheaths of adjacent oligodendrocytes

Nodes (nodes of ranvier)

gaps between internodes of shwann cells

Microglia

phagocytic cells of CNS

appear early in development

Ependymal cells

line ventricles of brain and central canal of spinal cord

May act as receptors monitoring composition of CSF

Cillia and microvilli on apical surface linings of spinal cord, lateral ventricles, and 4th ventricle=help circulate CSF and absorb CSF

Satellite cells

Surround neuron cell bodies in ganglia

regulate nutrient and waste exchange between cell body and extracellular fluid

isolate neuron from stimuli not intended to pass from neuron to neuron

Shwann cells

Covers every peripheral axon (myelinated or not)

Covering = neurolemma

In a unmyelinated axon, shields multiple axons within superficial grooves

In myelinated, shields by wrapping cell and nucleus and cytoplasm of shwann cell is on the peripheral

Plasma membrane of an axon

axolemma

Cytoplasm of a neuron

perikaryon

Neurofibrils

Bundles of neurofilaments that extend into axon and dendrites to provide support

Nissl bodies (chromatophillic substance)

clusters of free ribosomes and RER

Collaterals

side branches of an axon

Anaxonic

small, difficult to distinguish axons from dendrites

only in CNS and special sense organs

Bipolar neurons

Cell body lies between an axon and a single dendrite with multiple dendrites at its end

Pseudounipolar neuron

Cell body lies to the side; continuous dendrites and axons

Multipolar axon

Several dendrites on cell body and a single axon

Most common in CNS

Neuronal pool

group of interconnected neurons with specific functions

Neural circuit

basic “wiring pattern” in a neuronal pool

Divergence

Spread of info from one neuron to several neurons, or from one pool to multiple pools

Broad distribution of a specific input like when sensory neurons bring info into CNS

Example of divergence

Visual information arriving from eyes reaches consciousness at same time it is distributed to areas of brain that subconsciously control posture and balance

Convergence

Several neurons on the same postsynaptic neuron; permits variable control of motor neurons by providing a mechanism for voluntary and involuntary control; two different motor pools involved both synapsing on same motor neurons

Convergence example

Movements of diaphragm and ribs are controlled outside of awareness but can also be controlled voluntary (when you take a deep breath)

Serial processing

relays info in a step wise sequence from one neuron to another, or from one neuronal pool to the next; sensory info relayed form one processing center in brain to another

Serial processing example

Pain sensations on way to your consciousness make stops at two neuronal pools along the pain pathway

Parallel processing

Several neurons or neuronal pools are processing the same info at one time; different responses occur simultaneously

Parallel processing example

Step on sharp object= withdrawl foot, shift weight, move arms, feel pain, shout OW at same time

Reverberation

Positive feedback; Collateral axons extend back toward source of an impulse and further stimulate presynaptic neurons

Reverberation example

In neuronal pools in brain, maintain consciousness, muscular coordination, and normal breathing

ganglia

Cell bodies of sensory and visceral motor neurons of PNS are found here; gray matter

Center

collection of neuron cell bodies with a common function in CNS; gray nuclei

Nucleus

a center with a distinct anatomical boundary; gray matter; CNS

Tracts

In CNS, bundles of axons sharing a common destination and origin (connect brain with other organs in body) ; white matter

Columns

Several tracts forming an anatomically distinct mass; white matter;CNS

Neural cortex

Gray matter; covers brain surface

Nerves

bundles of axons in PNS; white matter