Neural Tissue (ch12) Flashcards
Central Nervous System
brain and spinal cord
Peripheral Nervous tisse
neural tissue outside the CNS
Neural tissue cells
Neurons and Neuroglia
Neurons
unable to divide, send a receive signals
Neuroglia
support, nourish and protect neurons, maintains interstitial fluid the surrounds neurons, maintaiin regeneration capabilities
we have lots of neurons at _______
birth
neuron cytoskeleton includes
intermediate filament and microtubules
slow transport
1-5mm/day, moves material in one direction only
fast transport
200-400mm/day, moves material by way of motor proteins, flow can go in both directions
forward movement
anterograde
backward movement
retrograde
which cells makes up about half of the volume of cells of CNS
neuroglia cells
which cell can multiply in times of injury or illness to fill space formerly occupied by neurons
Neuroglia
Astrocytes
- produce scar tissue
- largest and most numerous neuroglia
- connects with capillaries
- helps surround blood vessels
function of astrocytes
- create blood-brain barrier
- transfer nutrients between capillaries and neurons
- in embryo = help regulate growth and migration
- maintain interstitial fluid
ependymal cells
- cuboid or columnar cells
- produce cerebrospinal fluid
- long extensions
microglial cells
- small cells with slender projections
- immune cell
- function as phagocyte
oligodendrocytes
- responsible for forming & maintaining myelin sheath around axons
- around 15-20 flat processes (extend to axons)
- absent neurolemma, limits regrowth after injury
schwann cells
- form and maintain myelin sheath around axon
- neurolemma permits regeneration of axons following injury
satellite cell
- surrounds bodies of neurons & peripheral nerves
- regulate exchange of material between cells
which nervous tissue has a possibility of repair?
PNS if cell body is intact
_______ cannot grow if gaps are _______ or ______
Axons, too large, filled with collagen fibers
which nervous tissue has little to no repair
CNS - because of rapid formation of scar tissue
overall the body is ___________
electrically neutral
membrane potential is established by
chemical disequilibrium between ICF and ECF
resting membrane potential for cells in the body is
-5mV- -100mV
what creates membrane potential
- unequal distribution of ions across plasma membrane
- most intracellular anions
- electrogenic nature of Na+ and K+
Nernst equation
looks at 1 ion and describes membrane potential
Goldman-Hodgkins-Krats equation
predicts membrane potential of all ions that can cross membrane potential
how is resting membrane potential altered
changing membrane ion permeability
channels that open is response to depolarization will only close when cell ______
repolarizes
channels may spontaneously ______
inactivate with continual stimulus
what are the gated channels
- ligand-gated channel
- mechanically-gated channel
- voltage-gated channel
what happens to the cell when the membrane potential becomes less negative than the resting potential
the cell depolarizes
what happens to the cell if the membrane potential becomes more negative
the cell hyperpolarizes
Recovery from hyperpolarization is known as what
repolarization
graded potentials
- take place in dendrite and cell of body neurons
action potentials
circulate along the axon through voltage-gated channels
why are graded potentials decremental
- they take place in the dendrites and cell body of neuron
- signal strength depends of the number of open channels
- signal loses strength due to: current leak and cytoplasmic resistance
trigger zone at axon hillock contains high concentration of what
voltage-gated channels
how many gates does voltage-gated channels have?
2
- activation gate
- inactivation gate
activation gate
- fast
- first to respond
- influx of Na depolarizes membrane
inactivation gate
- .5msec delay
- depolarization stops
repolarization phase (AP)
- Na+ channels reset
- membrane becomes permeable to K+
- delay in closing hyperpolarizes membrane
hyperpolarization phase
- some but not all channels have a reset
- K+ channels are slowly closing
- natural permeability to Na+ and K+ allow membrane to return to resting potential
absolute refractory period
-typically 1-2 msec
- time required for Na+ channels to resent to resting position
relative refractory period
- may last as long as 15 msec
- stronger than normal graded potential required to reopen Na+ channels
two methods of propagation
continuous propagation & saltatory propagation
saltatory propagation
- myelin sheath prevents Na+. and K+ from leaving cell
- allow action potential to leap from node to node
- myelinated axons
continuous propagation
unmyelinated axons
Demyelinating diseases
- multiple sclerosis
- reduces or block conduction
factors that affect the speed of propagation
- amount of myelination
- axon diameter
- temperature
hypokalemia
low K+ concentration
hyperkalemia
high K+ concentration
hyperpolarized cell
- harder to reach threshold
- trouble activating muscle
depolarized cell
- easier to reach threshold
- muscle spasm
hyponatremia
low Na+
hypernatremia
high Na+
synapses communication occurs between
- two neurons (interneural synapse)
- neuron and an effector cell (neuromuscular or neuroglandular)
electrical synapse
- pass electrical signals through gap junctions
- signal can be bi-directional
- allows for fast communication
- found in the CNS as well as in cardiac and smooth muscle
chemical synapse
- use neurocrine molecules to transmit signal
- chemicals cross synaptic cleft and bind onto receptor
neurotransmitters
- direct affect on signal post-synaptic membrane
neuromodulators
- diffuse away from synaptic cleft to influence many other neurons
neurohormone
- diffuse into blood and behave as a hormone
inonotropic receptors
- binding sit and ion channel
- mediate rapid responses
- how most neurotransmitters function
- specific to ion
matabotropic receptors
- G-protein mediated receptors
- mediate slower responses
- how most neuromodulators function
types of chloinergic receptors
- nicotinic receptors
- muscarinic receptors
nicotinic receptors
- produces EPSP
muscarinic receptors
- G-protein coupled receptors
- Mostly produces IPSP
Convergent circuit
- several presynaptic neurons influence one postsynaptic neurons
diverging circuit
- one presynaptic neurons influence several postsynaptic neurons
reverberating circuit
- impulses are ultimately sent back to the original neuron
- ex) brainstem
parallel after discharge circuit
one presynaptic neuron stimulates a group of neurons which synapse on a common neuron