chamberlain college of nursing bios 242 final exam guide
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BIOS 242 Final Exam Study Guide
Chapter 12 Nervous Tissue (11)
CNS (central nervous system) – The brain and spinal cord
PNS (peripheral nervous system) – all nervous tissue outside of the CNS (composed of nerves,
ganglia, enteric plexus and sensory receptors)
Somatic: voluntary, connected to skeletal muscles
Autonomic: (smooth muscle, cardiac muscle and glands)
a) parasympathetic (rest & digest)
b) sympathetic (fight or flight)
Enteric: nervous system of the intestines; involuntary
Functions of the NS:
Sensory – detect stimuli; carry info to CNS via spinal and cranial nerves (most unipolar) PNS
CNS
Integrative – process sensory info, analyze, and make decision for response (most multipolar)
Motor – nervous system may elicit a response by activating receptors via motor neurons
(multipolar)
Neuron is larger than neuroglia
Neurons are electrically excitable (AP) neuroglia do not generate AP
Neurons cannot multiply or divide, neuroglia can
Types of Neuroglia in the CNS
Astrocytes (star shaped):
o Largest and most common
o Support neurons with their supportive microfilaments
o Wrap around capillaries forming blood brain barrier
o Secrete growth regulating chemicals in embryo
o Maintain chemical environment
Oligodendrocytes
o Form and maintain myelin sheath
Microglia
o Small and slender processes
o Phagocytic remove cellular debris
Ependymal cells:
o Cuboidal and columnar cells arranged in a single layer
o Line ventricles of the brain and central canal of the spinal cord
o Produce and assist in circulation of cerebrospinal fluid
Types of Neuroglia in the PNS
Schwann cells:
o Form myelin sheath
Satellite cells:
o Surround cell bodies and give structural support and help regulate nutrient exchange
Parasympathetic Verses Sympathetic Division Roles In Control
Parasympathetic: rest and digest
Sympathetic: fight or flight
Cells Of PNS, Types, Role
Nerves: bundle of axons plus associated CT and blood vessels (outside of brain/spinal cord)
Cranial Nerves: 12 pairs emerge from the brain
Spinal Nerves: 31 pairs emerge from the spinal cord
Ganglia: small masses of nervous tissue (consisting primarily of neural bodies outside of brain
and sc ganglia associate with cranial nerves)
Enteric Plexuses: extensive networks of neurons located in GI tract (regulate digestive system)
Sensory receptors: monitor changes in external or internal environment
Histology of Neurons
Electrical excitability (respond to stimulus and generate AP)
Cell Body (soma): contains nucleus, cytoplasm and other organelles
Nissl Bodies: free ribosomes and prominent clusters of RER; sites of protein synthesis
Cytoskeleton: includes neurofibrils (shape and support) and microtubules (movement of
material)
Dendrite: receptive portion
Axon: propagates the nerve impulse
o Joins to the cell body at the axon hillock
o Junction between hillock and initial segment is the trigger zone – where most
action potentials arise
, 3
o Contains mitochondria, microtubules and neurofibrils (no rough ER)
o Axoplasm – cytoplasm of axon
o Axolemma – plasma membrane
o Axon Collaterals – branches off side of the axon
o Axon terminals
AP, RMP
Action Potential:
- Sequence of rapidly occurring events that decrease and reverse the membrane potential and
then eventually restore it to resting state
Two types of electrical signals: graded potentials (short distance) and action potentials (long
distance)
Production depends on resting membrane potential (electrical difference across membrane)
and the presence of ion channels
a. Sensory receptor detects stimulus and develops a graded potential
b. Graded potential triggers sensory neuron to form an AP which travels to the CNS where
neurotransmitters are released
c. NTs stimulate interneurons to form GP in dendrites and soma
d. In response to GP, axons form AP in multiple interneurons, activating neurons in higher
parts of the brain; when reaches the cortex, perception occurs
e. Stimulus in brain causes GP in dendrites and soma of upper motor neurons AP
synapse with the lower motor neurons
f. GP in lower motor neuron trigger AP release NT at neuromuscular junction
g. Stimulation of effector
Resting Membrane Potential (RMP)
~ -70mV
Separation of charges results in potential energy
The cell is polarized (ECF rich in Na+ and CL-l cytosol rich in K+ but d/t many K+ leak
channels, K+ leaks out via concentration gradient inside of the cell become relatively
negative as there are less positively charged ions)
3 main factors creating RMP
1. Unequal distribution of ions in ECF and cytosol
2. Inability of most anions (-) to leave the cell
3. Electrogenic nature of Na+/K+ ATPase (sodium-potassium pump which expels 3Na+
for every 2K+ imported)
All Or None Law Of AP, Depolarization, Repolarization Threshold
The all-or-none law is a principle that states that the strength of a response of a nerve cell or
muscle fiber is not dependent upon the strength of the stimulus. If a stimulus is above a certain
threshold, a nerve or muscle fiber will fire. Essentially, there will either be a full response or
there will be no response at all.
Resting membrane: voltage-gated Na+ channels are in the resting state and voltage-gated K+
channels are closed.
Depolarization:
Depolarization occurs from (-70mV) to threshold (-55mV)
Voltage gated Na+ channel activation gates open rapid influx of Na+ into the neuron (-
55mV to +30mV)
Repolarization:
- Voltage gated K+ channels open and Na+ channels begin to inactivate
, 4
- Na+ inflow slows and K+ outflow increase return to resting state (-70mV)
Refractory:
- Neuron cannot generate another action potential in response to normal threshold
stimulus
- Absolute refractory: even strong stimulus cannot generate AP
- Relative refractory: 2n AP can be initiated by larger than normal stimulus
Propagation:
- AP travel from trigger zone to axon terminals (does not die out, dependent on positive
feedback)
- Influx of Na+ causes adjacent channels to open AP travels down axon
- Continuous conduction: step by step depolarization + repolarization (unmyelinated)
- Saltatory conduction: myelinated axons at the nodes of Ranvier (gaps in myelin) there
are many voltage gated channels AP leaps from nodes as each node depolarized to
threshold; much more efficient as only small regions depolarize/repolarize therefore less
ATP used in Na/K pumps
Signal Transmission at Synapsed
Neural Circuits /Definitions & Examples
Neural Circuits: functional groups of neurons that process specific types of information
- Simple series: presynaptic neuron stimulates single post synaptic neuron
- Diverging: single pre-synaptice with several post-synaptic (ie. small region of brain that
controls particular body movement stimulates a much larger number of spinal neurons;
sensory signals also arranged in diverging circuits allowing sensory impulse to be
relaying to many regions of the brain)
- Convergence: several presynaptic with single post synaptic (effective stimulation or
inhibition of posterior synaptic neuron)
- Reverberating: incoming impulse stimulates first neuron, which stimulates second, which
stimulates the third and so on. Branches from later neurons synapse with earlier ones
sending impulses back through the circuit again and again. (breathing, coordination,
waking up)
- Parallel After-discharge: single pre-synaptic neuron stimulates group of neurons that
synapses with a common post synaptic neuron
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