Chapter 12 - Neural Tissue Level Of Organization Notes Flashcards
Nervous system is
Control center for the body
The nervous system controls and coordinates
All function in the body
The NS includes
All neural tissue in the body
Neuron
Basic functional unit
Glial cells
Otherwise called neuroglia
Separate and protect the neurons
Providing a framework of support for neural tissue
And act as phagocytes
Glial cells account for
50% of the cell volume of the NS
How many divisions in the NS?
Two: central nervous system (CNS) and peripheral nervous system (PNS)
CNS
Includes the brain and spinal cord
PNS
Includes all the nervous tissue outside the CNS
Division of PNS
Afferent division and efferent divison
Afferent division
Brings information from the body to the CNS
Efferent division
Carries information from the CNS to the periphery of the body
Divisions of the efferent division
Somatic division and autonomic division
Somatic division
Controls skeletal muscle tissue
Autonomic division
Controls smooth muscle, cardiac muscle, and glandular tissues
Cell body
perikaryon
The PERIKARYON contains
- large round nucleus
- neurofilaments
- neurotubules
- organelles
- neurotransmitters
Neurotransmitters are required for:
cell-to-cell communication in the NS
Nissl bodies are
regions of the neuron that contain rough endoplasmic reticulum and ribosomes
-this gives the neuron its dark appearance
Why can’t neurons divide
lack centrioles
Dendrites are:
slender processes that extend out away from the cell body
-contain dendrite spines which receive info from other neurons in the CNS
Axon
tends to be a long process from the soma which carries an impulse away from the soma
Axon hillock is where
the axon is attached to the cell body
Collaterals may be found
on the axons that branch off this allows one neuron to communicate with many surrounding neurons
Telodendria
end of the axon
which are fine extensions of the axon that end at the synaptic terminals
Where does communication between neurons occur?
synaptic terminals
Synapse
the site where neural communication occurs, and involves neurotransmitters.
Presynaptic neuron will release
neurotransmitter substance to direct the response of the post synaptic cell
Post synaptic cell
can be a neuron or any other type of cell, such as a muscle cell, or glandular cell
Synaptic knob
is found when the post synaptic cell is a neuron. Each knob contains organelles and vesicles that are filled with neurotransmitter substances.
Neurons are classified by
either structure or function
Anaxonic neurons:
are small and the axons and dendrites are indistinguishable.
They are found in the brain and special sense organs
Bipolar neurons:
have two distinct processes, one dendrite and one axon
These are rare and found in the special sense organs
Unipolar neurons:
have a continuous axon and dendrite.
These are found in the PNS as sensory neurons
Multipolar Neurons:
have two or more dendrites and one axon.
They are the most common neuron found in the CNS. All neurons that control skeletal muscle are multipolar.
List of Structural Classification of Neurons:
- Anaxonic neurons
- Bipolr Neurons
- Unipolor Neurons
- Multipolar Neurons
List of Functional Classification of Neurons:
- Sensory Neurons
- Motor Neurons
- Interneurons
Sensory Neurons (afferent neurons)
carry information to the CNS from the periphery.
Are Unipolar and collect info about the internal and external environment and relay it back tot he CNS.
How many sensory neurons in body?
about 10 million
Receptors are:
processes on sensory neurons that feed info to the sensory neuron.
3 Types of Sensory Receptors:
- Exteroreceptors
- Proprioceptors
- Interceptors
Exteroreceptors
provide info about the external environment
Proprioceptors
monitor position and movement of joints and muscle tissues
Interceptors
Monitor the visceral organs and systems
Motor neurons (efferent neurons)
carry info from the brain or CNS to the body or peripheral effectors.
Visceral motor neurons
innervate all the peripheral effectors except skeletal tissue.
carry info from the CNS to an automatic ganglia and then travel from the ganglia to the effectors
First order neuron
to the ganglia is a presynaptic autonomic fiber
Second order neuron
to the effectors is called the post synaptic autonomic fiber
Interneurons (associated neurons)
are the most numerous of all the neurons combined.
These are found in the brain and the spinal cord.
function in the distribution and coordination of sensory and motor activity of the nervous system.
Neuroglial Cells of the CNS
- Ependymal Cells
- Astrocytes
- Oligodendrocytes
- Microglia
ependymal cells
cubodial to columnar cells that line the ventricles of the brain, and the central canal of the spinal cord
They function in monitoring the regulation and production of cerebrospinal fluid
They are covered in cilia or hair like structures that snese changes in the CSF.
Astrocytes
are the largest and most numerous of the neuroglia.
Function in the maintenance of the blood brain barrier.
Responsible for creating a 3D framework for the CNS
Function in repair of damaged neural tissue, guiding neuron development, and controlling the interstitial environment.
Control the concentration of sodium ions, potassium ions, and carbon dioxide ions, as well as providing a rapid transit system for the transporiting of nutrients, ions, and gases to the capillaries
Oligodendrocytes
function in the formation of myalin around the axons in the CNS
Myalin acts as an insulator for conduction of current along the axon.
Mylelinated neurons in the CNS make up the white matter
Node of Ranvier
small areas of unmyelnated axon
Microglia
these are the least and smallest of the neuroglia in the CNS.
They clean up the neural tissue similar to macrophages in the blood stream
Cell bodies of neurons in the PNS are:
ganglia
Types of Ganglia (PNS)
Satellite cells
Schwann Cells
Satellite cells
Also called amphicytes
surround the neuron cell bodies in ganglia. They regulate the environment around the neurons
Schwann Cells
also called neurolemmal cells
Form a sheath around every peripheral axon, myelinated or note. Schwann cells myelinate segments of axons in the PNS
Membrane Potential (at rest)
-70mv charge
Membrane Potential
passive and active forces act across the cell membrane to determine this
Changes in voltage in membrane
changes either by chemical or electrical forces will either cause the membrane to become more negative or more positive.
These forces wil determine if an ACTION POTENTIAL will be generated.
Na+ and K+
The electrochemical gradeint for these are the primary factors that affect the membrane potential of most cells.
What regulated chemical gradient
sodium potassium pump in the cell
It will exchange 3 intercellular sodium ions for 2 extracellurlar potassium ions, which requires the use of ATP or energy
Membrane channels
Control the movement of ions across the membrane.
Leak channels
Passive channels
Gated channels
Active channels
Which channel maintains the normal resting membrane potential of the cell
Leak or passive channel
3 types of gated or regulated channels in the neuron
Chemically regulated
Voltage regulated
Mechanically regulated
Chemically regulated channel
Will open or close in response to certain chemicals present at the membrane.
These are found at the synaptic junction of most neurons
Voltage regulated channels
Are found on areas of excitable membranes, or membranes that are generating an action potential, they are common on the axons of unipolar and multipolar
Mechanically regulated channels
Will open or close in response to physical stimulation of the membrane. These are found in the sensory receptors for touch and pressure.
Graded potentials
Or local potentials
Are membrane changes that will not travel far from the site of stimulation.
Depolarization
Of the cell membrane occurs when increased sodium ions enter the cell making it more positive and closer to 0mv.
When this occurs an action potential will be generated.
Hyper polarization
occurs when the cell becomes more negative by K* ions flowing out.
This makes it harder for the action potential to be stimulated.
Action principle
All or nothing principle.
Stimulus will generate along whole membrane. The stimulus will either cause an action or not.
Action Potentials are generated in this order:
- Depolarized
- Activation
- Inactivation
- Return to normal resting membrane voltage
Stage 1 of Action Potential
The cell membrane is depolarized to threshold by local graded potentials
Stage 2 of Action Potential
Activation of sodium channels occur causing rapid depolarization of the membrane
Stage 3 of Action Potential
The inactivation of sodium channels and the activation of K+ channels occurs. The flow of NA+ back out of the cell and K+ back into the cell brings the membrane closer to a negative resting potential
Stage 4 of Action Potential
Return to normal resting membrane voltage. The refractory period is the time between the action potential and the return to membrane resting potential, an action potential cannot be reinitiated during this time.
Relatively Refreactory Period
when the impulse (starts action potential) is strong enough, in some cases, a continuation of the impulse can occur.
Action potential propagation
is the relaying of the action potential across the cell membrane in steps
Continuous propagation
is an action potential moving along an unmyelinated axon in steps this occurs at a rate of 1 meter per second
Saltatory propagation
occurs in a myelinated axon, has to jump over the nodes of Ranvier.
What affects the speed of action potential
diameter and myelination
3 groups based on speed (propagation)
- Type A fibers
- Type B fibers
- Type C fibers
Type A Fibers
largest axons w/diameter of 4 to 20 um.
They carry an action potential at a speed of 140 meters per second or 300 mph.
these fibers carry info INTO the CNS regarding balance, touch, pressure, and motor fibers to skeletal muscles.
Type B Fibers
smaller, myelinated axons w/diameter of 2-4 um. They transmit action potentials at a rate of 18 meters per second. B and C fibers carry info regarding general touch and pain. As well as info to smooth muscle, cardiac muscle, and glands
Type C Fibers
are unmyelinated and less than 2 um. They transmit action potentials at a speed of 1 meter per second.
What is a neural junction where an action potential or never impulse is carried to another neuron and then passed on to another neuron or an effector
Synapse
3 types of synapses
electrical
chemical
cholinergic
Electrical synapses
are rare types, they occur in the vestibular nuclei of the eye and the ciliary ganglia
chemical synapses
the cells are not directly connected or touching, there is a synaptic space between the two cells. The action potential reached the presynaptic side and releases neurotransmitter substance there must be enough neurotransmitter to fire the action potential on the post synpatic side for the action ptoential to be sent down to the next axon
cholinergic synapses
release the neurotransmitter ACH. THese are found at the neuromuscluar junciton. ACH is released by all neuromuscluar junctions, many synapses in the CNS, at all neuron to neuron synapses in the PNS, and all the neuromuscular and neuroglandular junctions of the parasympathetic division of the ANS.
synaptic delay
occurs from the time that the action potential reaches the synaptic knob and travels to the postsynaptic membrane
synaptic fatigue
occurs when the synaptic activity is so high that the synaptic knob is depleted of ACH and an action potential cannot be genreated until more ACH is generated
norepinephrine
found in the brain and part of the ANS
Dopamine
is a CNS neurotransmitter
Serotonin
is a neurotransmitter found in the CNS
Gamma aminobutyric acid (GABA)
has an inhibitory effect on the CNS
Nitric oxide
is generated by synaptic terminals that innervate smooth muscle in the wall of blood vessels in the PNS
carbon monoxide
is generated by synaptic knobs in the brain
neuromodulators
influence the release of neurotransmitter substance at the presynaptic neuron or influence the postsynaptic neurons response tot he neurotransmitter.
opiods
neuropeptides that are classified as endorphins, enkephalons, and dynorphins. They function in natural pain relief
3 groups of neuromodulators
- compounds - direct effect
- compounds - indirect effect
- lipid soluble gases
post synaptic potentials
are graded potentials that develop in the postsynaptic membrane in response to a neurotransmitter, these may be inhibitory or excitatory
summation
the combining of 2 or more EPSPs to generate an action potential
temporal summation
the rapid recurring stimulus of the synapse repeatedly to generate an action potential
spatial summation
cum effect of simultaneous stimuli at many different sites on the neuron, this will generate action potential
facilitation
bringing of a neuron closer to threshold, thus allowing a smaller stimulus to generate an action potential
presynaptic inhibition
GABA releases at the axon-to-axon synapse will inhibit the opening of the calcium channels. This activity at the 2 axons will increase the amount of neurotransmitter present at the knob thus making it easier to generate an action potential.
Neuranol pools
groups of interconnected neurons with specific collective functions.
Divergence
is the spread of information from one neuron to several neurons, or from one pool to several pools
convergence
is when several neurons synapse on the same postsynaptic neuron
Parallel Processing
when several neurons or pools process the same info at one time
PNS organization
cell bodies of neurons = ganglia
axons bundled together to form nerves connected tot he spinal cord and cranial nerves connected to the brain.
CNS organization
collectoin of neurons or cell bodies with a common function= centers
Nucleus is a center with an anatomical boundary
CNS white matter contains axons with common destinations = tracts
tracts in spinal cord = columns
Centers and tracts that link the brain with the rest of the body = pathways
