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What is an organ system?
a group of organs each with specific structures and functions that coordinate and integrate with one another
What are examples of an organ system?
Nervous, circulatory, respiratory, digestive, excretory, endocrine, and reproductive
Ganglia are not as ____ as _____, but they do have a specific _____ and ____.
obvious, organs, structure, function
What is the general function of the nervous system?
short term coordination and integration of body functions
What is the nervous system controlled by?
electrochemical communication (nerve impulses or action potentials)
Without impulses and action potentials, what would happen?
There would be no coordination of body functions
What is irritability or excitability?
the ability to react to stimuli followed by the generation of nerve impulses
What is conductivity?
the ability to transmit nerve impulses/APs from one area of the body to another
(if the NS could not do this, there would be no function for APs or nerve impulses)
What is the functional sequence of events for short term coordination?
1. reception of stimuli
2. conversion of stimuli
3. transmission of APs
4. Production of a response or an action
What is an example of production of a response or an action for short term coordination?
Muscle contraction --> gland secretion
What are the two divisions of the nervous system?
central nervous system and peripheral nervous system (CNS, PNS)
What does the PNS consist of?
1. Nerves and ganglia of somatic NS
2. Nerves and ganglia of autonomic NS
What are the 3 histological elements of the nervous system?
Neurons (nerve cells), neurological/glial cells, and white fibrous collagenous connective tissue
Where is white fibrous collagenous connective tissue found?
mainly in peripheral nerves, little is found directly in the brain
What are the three morphological classifications of neurons?
What is the function of pseudo-unipolar neuron axons?
they carry APs to the cell body then continue to carry the AP away from the cell body
Describe a pseudo-unipolar neuron fiber
the fiber is divided in two but in both cases, it is an axon, and the term dendrite is not used in classification
What is typical of sensory neurons?
they have a fiber that is divided in two but in both cases, they are axons
Where are bipolar neurons found?
1. the retina of the eye
2. the olfactory epithelium of the nose (detect odors)
3. the taste buds of the tongue
Cytoskeletal components contain what structures?
Where are cytoskeletal components found?
in all parts of the neuron, cell bodies, dendrites and axons
What is a neurotubule's function?
they assist in the transport of neurotransmitters vesicles down the axon
Neurotubules allow ___ ___ to move from the ___ ___ to ____ ___.
synaptic vesicles, cell body, synaptic knob
What do schwann cells do?
1. they line up on one axon
2. each one individually wraps around the axon
3. they produce a myelin sheath
What is a myelin sheath composed of?
layers of schwann cell plasma membranes rich in the lipid myelin
In the nodes of ranvier, the plasma membrane of the axon is not...
exposed to the extracellular fluid
In unmyelinated axons, axon _____ are exposed to ____ all along the length of ____.
membranes, ECF, axons
What is the perineurium?
a layer of white fibrous connective tissue that extends from the epineurium into a nerve and makes compartments called fascicles
What is a function of connective tissue components?
serve as a pathway for blood vessels to penetrate a nerve
What do oligodendrocytes produce?
myelinated axons and myelinated dendrites from late fetus through 2 years
What is the function of a microgliocyte?
to destroy microorganisms and dead cellular debris in tissues of the nervous system
What happens in a hemorrhagic stroke?
damage occurs to blood vessels with bleeding into nervous tissues
In a hemorrhagic stroke, large numbers of microgliocytes appear where?
at the site to eliminate dying tissues
What do astrocytes assist in?
the regulation of chemical concentration of substances in the ECF of the CNS
What is the BBB function?
it impedes movement of water-soluble substances in ECF of brain and spinal cord tissues
What do perivascular feet of astrocytes associated with blood capillaries do?
help control the concentration/level of K+ in the brain ECF
What helps the concentration/level of K+ in the brain ECF?
perivascular feet of astrocytes associated with blood capillaries
Covered capillaries of ventricles of brain and spinal cord are made of what?
a combination of ependymal cells and capillaries (choroid plexes)
Ependymal cells have ciliated surfaces for what function?
moving cerebrospinal fluid through ventricles and central canal
What is a resting potential?
electrical potential difference that exists across the cell membrane of a neuron that is NOT conducting an action potential
What is the basis of a resting potential?
it is produced by UNEQUAL electrical charges on either side of the axon membrane
What are factors that produce the unequal charge distribution?
1. sodium pump
2. differential permeability of Na+ and K+ in terms of diffusion
3. presence of non-diffusible anions
What does the sodium pump establish outside the axon in ECF?
-high Na+ concentration
-low K+ concentration
What does the sodium pump establish inside the axon in ICF?
-low Na+ concentration
-high K+ concentration
How do Na+ and K+ ions diffuse?
through always open or non-gated leak channels with their concentration gradient (high to low)
K+ diffuses ___ of the axon 100x ___ than Na+ diffuses ____ the axon through their respective ___ ___.
OUT, faster, INTO, leak channels
Why is ICF negative relative to the ECF?
because the axon is losing more positive charges (K+) than it is gaining positive charges (Na+)
Because the axon is losing more positive charges (K+) than it is gaining positive charges (Na+)...
the ICF is negative relative to ECF
K+ ions move ___ of an axon 100x ___ than Na+ ions move ___ an axon by ____.
OUT, faster, INTO, diffusion
Why is the ICF more negative compared to the ECF?
because there is a net loss of positive charges in the ICF
How many local depolarizations does it take to raise the resting potential to the threshold potential?
at least 2 or more
It takes at least two or more local depolarizations to do what?
raise the resting potential to the level of threshold potential
Sequence of events of AP being stimulated: step 3
increased Na+ permeability (Na+ can move from outside of axon to inside)
How does Na+ move from the ECF into the ICF?
through Na+ voltage-gated channels of the axon membrane
Sequence of events of AP being stimulated: step 4
Reversal of electrical charge due to Na+ entry-full depolarization results in action potential
What happens during repolarization?
1. Na+ voltage-gated channels close
2. K+ voltage-gated channels open
Ion concentrations after hyperpolarization:
are NOT normal in ICF so the sodium pump returns ion concentrations to normal levels associated with the resting potential
All or none law
AP has a full magnitude of 100mV or it does NOT occur at all; either you get the full AP or you get nothing
Importance of absolute refractory period
no other AP can be stimulated during absolute refractory period
What does the relative refractory period limit?
the number of APs that can pass over an axon (100-1000/sec)
Unmyelinated axon-sequence of events
1. axon hillock depolarizes and repolarizes
2. segment to segment stimulation
3. AP is self-propagating
Segment to segment stimulation: where does electron current flow from?
depolarized axon hillock to next adjacent segment of the axon causing depolarization at the new location and is followed by a repolarization
AP is self propagating (stimulates a series of APs down the length of an axon)
Myelinated axons: sequence of events
1. axon hillock depolarizes and repolarizes
2. depolarization of axon hillock causes electrical current to flow to the first node of ranvier, and it will go through a depolarization/repolarization cycle
Myelinated vs. unmyelinated axons: conduction
conduction is 10x faster in myelinated axons compared to unmyelinated axons of the same diameter
What does saltatory conduction eliminate?
a large surface area of axon membrane that must participate in conduction (thats why it is faster)
Example of myelinated axons involved in conduction:
hand on a burner; you want myelinated axons involved because they are faster
In AP trasmission from neuron to neuron, how are neurons sent?
the presynaptic neuron sends AP to a postsynaptic neuron
What happens during electrical synapse?
AP passes through gap junctions between neurons without use of chemicals
What does chemical synapse require?
release of a chemical neurotransmitter from a presynaptic neuron to stimulate an AP in a post-synaptic neuron
What does the structure of chemical synapse include?
1. synaptic knob
2. synaptic cleft
3. postsynaptic membrane
Synaptic knob job in chemical synapse
a synaptic knob from a presynaptic neuron terminates on a dendrite, cell body, or axon of a postsynaptic neuron
What is the postsynaptic membrane?
portion of the cell membrane of a postsynaptic neuron at the synapse
What does the postsynaptic membrane contain?
receptors (protein molecules) that specifically bind to a neurotransmitter as it crosses the synapse
Both _____ and ____ presynaptic neurons may ____ on the same _____ neuron.
excitatory, inhibitory, synapse, postsynaptic
What happens during "excitation at the synapse"?
presynaptic neuron stimulates an AP in a postsynaptic neuron
Sequence of excitation at the synapse: step 1
AP moves down presynaptic axon terminal to synaptic knob
Sequence of excitation at the synapse: step 2
AP arrives at synaptic knob; stimulates Ca+2 entry into synaptic knob
Sequence of excitation at the synapse: step 3
-Ca+2 causes vesicles to release their neurotransmitter by exocytosis into the synaptic cleft
-it diffuses across the synaptic cleft
-it combines with receptors on the postsynaptic membrane
Sequence of excitation of the synapse: step 4
if sufficient amounts of neurotransmitter combine with the receptors, this initiates local depolarization called excitatory postsynaptic potentials
ESPSs can ____, reach ____ potential and initiate APs in the ____ ____ of the _____ neuron.
summate, threshold, axon hillock, postsynaptic
Examples of excitatory neurotransmitters:
-dopamine and substance P
What are different ways to eliminate the neurotransmitter?
1. enzymatic degradation in synaptic cleft
2. re-uptake into presynaptic neuron
3. diffusion out of synaptic cleft to ECF
(these all destroy ACh)
Sequence of inhibition at the synapse: A
a. AP moves down presynaptic axon terminal to synaptic knob
Sequence of inhibition at the synapse: B
b. AP arrives at synaptic knob; stimulates Ca+2 entry into synaptic knob
Sequence of inhibition at the synapse: C
c. Ca+2 causes vesicles to release their neurotransmitter by exocytosis into the synaptic cleft and it diffuses across the synaptic cleft and combines with receptors on the postsynaptic membrane
Sequence of inhibition at the synapse: D
d. sufficient amount of neurotransmitter combines with its receptors on postsynaptic membrane
Sequence of inhibition at the synapse: E
e. increase permeability of K+ or Cl-1 in the postsynaptic membrane
During step E, what happens for inhibition?
potassium leaves and chloride enters the postsynaptic neuron
Increased K+ or Cl- permeability causes the resting potential to do what?
go from -70mV to -80mV (hyperpolarization)
Examples of inhibitory neurotransmitters?
gamma-amino butyric acid
Inhibitory neurotransmitters are very important in what?
nervous tissues, stimulation, and inhibition
Which two inhibitory neurotransmitters are important in repressing painful stimuli in the CNS?
enkephalins and endorphins
What is the neuro transmitter junction structure?
end plate, synaptic cleft, and motor plate (a structure)
Sequence of events: step 2
Ach diffuses across synaptic cleft and combines with its receptors on the motor end plate
What is the EPPs function?
they summate and initiate an AP that spreads from the neuromuscular junction over the entire surface of the sarcolemma, causing the cell to contract
What causes the cell to contract?
the EPPs summate and initiate an AP that spreads from the neuromuscular junction over the entire surface of the sarcolemma
Acetylcholine esterase does what?
destroys ACh in the synaptic cleft after it has stimulated the muscle cell to contract
What are 3 exogenous chemicals affecting transmission at the neuromuscular junction?
curare, atropine, and physostigmine
What is eserine's function?
it inhibits acetylcholine esterase in synaptic cleft; ACh is not destroyed so it keeps stimulating the motor end plate and muscle cell contractions
What kind of disease is myasthenia gravis?
autoimmune disease; antibodies are made against ACh receptors and ACh cannot properly stimulate the motor end plate
What does physostigmine allow ACh to do?
exist in the synaptic cleft for longer than normal, giving it time to stimulate the motor end plate
What are the two layers dura mater is composed of?
1. cranial/periosteal dura mater
2. meningeal dura mater
potential free space located between the meningeal DM of brain/spinal cord and the arachnoid membrane
fine partitions that create compartments within sub-arachnoid space below arachnoid membrane
inner meninge, highly vascularize and is in direct contact with the brain and spinal cord
connect DISTANT gyri within different lobes of the same cerebral hemisphere to each other
connect cerebral cortex to ALL OTHER parts of the CNS such as basal ganglia, thalamus, hypothalamus, and spinal cord
Parts of sensory cortex:
1. primary sensory/somesthetic cortex
2. olfactory cortex
3. auditory cortex
4. taste cortex
5. visual cortex
Primary sensory/somesthetic cortex function:
specifically interprets sensory stimuli that comes from skin surface, skeletal muscles, and joints
Taste cortex function:
interprets stimuli from dissolved chemical substances in the oral cavity (taste)
Prefrontal cortex function:
involves emotional responses, judgement and reasoning...the "picking" part of the brain, the logical part
What are basal ganglia?
cerebral or basal nuclei; contain regions of gray matter scattered in white matter of cerebrum
Basal ganglia main function:
modify motor output from cerebral cortex by inhibition of some nervous stimuli to skeletal muscles
(this allows for the production of fine and even muscular contractions)
Caudate, putamen, and globus pallidus are located where?
in regions of grey matter suspended in white matter of the cerebrum
Thalamus function- sensory relay station:
all sensory impulses pass through the thalamus and are directed to the correct portions of the sensory complex EXCEPT olfactory sensory impulses
What is a 3rd function of the thalamus?
modification of sensory input from other brain centers to cerebral nuclei at the cerebellum
Thalamus assists in what?
reticular formation in maintaing consciousness by sending stimuli to reticular formation
Hypothalamus posterior region connects...
DIRECTLY to the posterior pituitary gland (neurohypophsis)
Hypothalamus- regulation of body temperature:
-region of the hypothalamus that stimulates vasodilation and vasoconstriction in dermal arterioles
-stimulates sweating in skin (too high)
-stimulates shivering in skeletal muscles (too low)
Hypothalamus- regulation water balance:
produces antidiuretic hormone (ADH) that stimulates water reabsorption in the kidneys
Hypothalamus- feeding/satiety center:
-monitors levels of glucose, fatty acids, and amino acids in blood
-stimulates "hunger" feelings before a meal and "full" feelings after a meal
Hypothalamus- produces releasing hormones:
that in turn control secreting activity of the anterior pituitary gland
The hypothalamus affects cardiovascular reactions that are related to what?
gross emotional, fear, anger, and rage responses
Outer surface of cerebellum:
is gray matter; made of small ridges (folia/gyri) and shallow grooves (sulci)
Cerebellum nerve tracts make connections towhat?
the pons, medulla oblongata, midbrain, thalamus, and cerebellum
What does the cerebellum coordinate?
synergistic and antagonistic voluntary muscle contractions for manual dexterity
(putting thread through a needle is an example of precise motor function)
Cerebral peduncles function:
-send sensory fibers from spinal cord to pons to thalamus
-send motor fibers from cerebrum to pons
associated with sensory reflexes related to very bright light stimuli (visual reflexes)
associated with sensory reflexes related to very loud sound stimuli (auditory reflexes)
The inferior colliculi provides two levels of protection:
2. inhibition of eardrum movement momentarily
What does Parkinson's disease cause?
muscular tremor and muscular rigidity (facial expressions, flailing arms)
What do nerve tracts connect?
-the medulla to the thalamus, cerebellum, and cerebrum
-the motor fibers to the medulla
Medulla oblongata location:
posterior and inferior to the pons; terminates at foramen magnum where spinal cord begins
What does the medulla oblongata contain?
physiological centers that are diffused regions of gray matter
Physiological centers of medulla oblongata:
1. cardiac center
2. vasomotor center
3. respiratory center
4. coughing, swallowing, and vomitting centers
Reticular activating system/reticular formation is a:
diffuse system of neurons and their fibers located throughout the brainstem
Reticular formation function:
sends impulses up to the cerebrum to maintain arousal and consciousness
Ventricular system structure:
-ventricles are fluid filled spaces found in all lobes of the cerebral hemispheres EXCEPT the insula
-also located in the brainstem
Where are ventricles found?
in all lobes of the cerebral hemispheres EXCEPT the insula and the brainstem
Ventricular system is responsible for the formation and circulation of what?
cerebrospinal fluid (CSF)
Formation of CSF: what is the fluid called after it enters ventricles from blood?
cerebrospinal fluid (CSF)
CSF concentrations of ____ and ____ are not the same as found in ____ ____.
ions, glucose, blood plasma
Why are concentrations of ions and glucose in CSF not the same as found in blood plasma?
because of active transport mechanisms present in ependymal cells of the choroid plexes
What is the flow of CSF through ventricles?
foramina of monro-->
What happens once CSF gets to the 4th ventricle?
fluid must exit the system and get OUTSIDE of the brain/spinal cord
What are the 3 foramina the 4th ventricles exits from?
-foramen of magendie
-foramina of luschka (2)
What is the flow of CSF in the subarachnoid space of the spinal cord?
down the posterior side of the spinal cord, laterally and up the anterior side to the brain
What is the flow of CSF in the subarachnoid space of the brain?
1. upward from the base of the brain
2. over the cerebrum and cerebellum, toward the longitudinal fissure
3. arachnoid villi
4. venous sinuses
5. veins found in the meninges
6.internal jugular vein
Once the CSF flows into the internal jugular vein, the fluid has...
now been returned to the circulatory system
Properties of CSF:
1. normal volume 90-150 ml
2. clear watery fluid
3. contains less protein, glucose, and K+ than blood plasma
4. contains more Na+ and Cl- than blood plasma
What can one identify through a lumbar puncture obtaining CSF?
multiple sclerosis, infection, tumors
What is the location and length of the spinal cord?
location and length extends from foramen magnum to L1 vertebra within vertebral canal
Some nerves exit the ___ ___ whereas others exit the ___ ___ by ___ ___.
vertebral canal, sacral canal, sacral foramina
Filum terminale location:
extends from the conus to the coccyx to anchor the terminal end of the spinal cord
Spinal cord: cross sectional structure:
-almost divided in half by dorsal median sulcus and ventral median fissure
Cross sectional structure of spinal cord is almost divided in half by:
dorsal median sulcus and ventral median fissure
Functions of the spinal cord:
1. two way conduction pathway for passage of nerve impulses between the brain and all other body regions
2. acts as a reflex center in association with spinal nerves
The spinal cord is a two way conduction pathway for passage of what?
nerve impulses between the brain and all other body regions
Some nerve fibers of ___ ___ nerve go to the ___ ___ and then enter the ___ ___ on the same side of the brain.
one optic, optic chiasma, optic tract
Other nerve fibers from the same optic nerve go to the optic chiasma BUT?
cross over to the optic tract on the opposite side of the brain!
-sensory: head, neck, teeth and gums
-motor: muscles of mastication and muscles of swallowing
-sensory: taste buds, anterior 2/3 of tongue
-motor: muscles of facial expression, salivary glands, and lacrimal glands
-balance and equilibrium
-associated with semicircular ducts, utricle, and saccule
-sensory: taste buds, posterior 1/3 of tongue; sensations from throat and monitors blood pressure
-motor: muscles for swallowing, muscles of vocal cords, secretion of some salivary glands
-sensory: monitors blood pressure sensations form respiratory and digestive tracts to brain
-motor: slows heart rate, stimulates secretion of gastric glands (stomach acid) and pancreas (digestive enzymes); stimulates peristalsis in digestive tract
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