animal phys exam 4: neurons and neuroglia

what are neurons

basic functional units of the nervous system that are specialized for transmitting electrical signals

what are the three key parts of neurons

dendrites, soma (cell body), axon

what are the neuron properties

excitability, conductivity, and secretion

what does excitability mean for a neuron

it’s response to environmental changes (stimuli)

what does conductivity mean for a neuron

respond to stimuli by producing electrical signals that are quickly conducted to tother cells at distant locations

what does secretion mean for a neuron

when electrical signals reach the end of a nerve fiber, a chemical neurotransmitter is secreted that influences the next cell

what are the three different neuron classes

sensory (afferent) neurons, interneurons, and motor (efferent) neurons

what doe sensory (afferent) neurons do

detect stimuli and transmit information about them towards the CNS

what do interneurons do

receive signals from many neurons and carry out integrative functions and it’s only within CNS connecting motor and sensory pathways

what do motor (efferent) neurons do

send signals out to muscles and gland cells

what is the soma (cell body)

the control center of the neuron that does not undergo mitosis, so no new neurons are generated

what are dendrites

branches that originate from the soma and is the primary site for receiving signals from other neurons, and the more dendrites the more information received

what is the axon

it’s a cylindrical nerve fiber originating from the soma and consists of axon collaterals, axoplasm, and axolemma

what are the axon collaterals

branches within the axon that are specialized for rapid signal conduction

what is the axoplasm

cytoplasm of the axon

what is the axolemma

plasma membrane of the axon

what is the function of neuroglia (supportive cells)

they protect neurons and aid in function, bind neurons together and form framework for nervous tissue, help guide migrating neurons to their destination in fetuses

what are oligodendrocytes

an arm-like processes that wrap around the axon and form myelin sheaths in CNS that speed signal transmission

what are ependymal cells

cuboidal epithelium with cilia on apical surface that line internal cavities of the brain and secrete and circulate cerebral spinal fluid

what are microglia

they develop from white blood cells and wander through the CNS looking for debris and damage

what are astrocytes

must abundant neuroglia that covers the brain surface and non-synaptic regions of neurons

what are the different functions of the astrocyte

• form supportive framework

• extensions (perivascular feet) contact blood capillaries and form a seal (blood-brain barrier)

• convert glucose to lactate and supply lactate to neurons

• secrete nerve growth factors

• communicate electrically with neurons

• absorb excess neurotransmitters and ions (regulate chemical composition of tissue fluid

• respond to damaged neurons (form hardened scar tissue and fill in space)

what are satellite cells

they surround the soma of neurons in the PNS and provide electrical insulation around the soma and regulate chemical environment of the neurons

what are schwann cells

they envelope nerve fibers in PNS and wind repeatedly around a nerve fiber that also produce a myelin sheath and assist in regeneration of damaged fibers

what is a myelin sheath

a protective insulating layer surrounding the axons that is composed of lipids and proteins and is essential for rapid and efficient transmission of electrical impulses along nerve fibers

what are the functions of the myelin sheath

speeds signal conduction, insulates to prevent electrical signals from dissipating ensuring effective transmission, and protects nerve fibers from damage

how is myelin formed

formed through the CNS by oligodendrocytes or PNS by schwann cells

when does myelination begin

week 14 of fetal development and proceeds rapidly during infancy and is completed in late adolescence, dietary fat is important for CNS development

what makes up myelin

the sheath is segmented and has nodes of Ranvier (gaps between segments) and internodes that are the myelin covered segments

what are myelinated axons composed of

they have initial segments and trigger zones

what are initial segments of myelinated axons

short section of nerve fiber between the axon hillock and first glial cell

what is the trigger zone of the myelinated axon

the axon hillock + initial segment and is an important role in initiating a nerve signal

what makes up the axon distal ends

terminal arborization, synaptic knobs (terminal button), synaptic vesicles full of neurotransmitters

what is terminal arborization

extensive complex of fine branches

what are synaptic knobs

swelling that forms a synapse with the next cell

what do neurotransmitters fo

neuron-to-neuron communication

what are the steps of signal transmission

1. reception: dendrites and soma

2. integration: axon hillock

3. conduction: axon

4. transmission: axon terminal

what do the dendrites and soma do in zone one of signal transmission

dendrites- sense incoming signals and convert the signal into electrical signals, soma- performs all routine cell functions

what happens during the integration step (zone 2)

incoming signals from the dendrites/soma are integrated in the axon hillock and assessed if the signal is strong or weak

what happens during the conduction step (zone 3)

axon forms the third functional zone specialized for conduction and sends signals from place-to-place, the axon size (long or short) is dependent on the function

what happens in the transmission step (zone 4)

axon terminal- transfers electrical signals to target cells and are enlarged at the end to form a synapse, motor neurons- control movement, electrical signals are converted into chemical signals at the synapse- neurotransmitters binds to receptors on target cells to trigger response

what is conduction speed

speed of signal transmission dependent on fiber diameter and presence or absence of myelin

what do you need for faster signals

larger fibers and myelin

where are slow signals to to

GI tract

where are fast signals sent

skeletal muscles where speed improves balance and coordinated body movement