in all parts of the neuron, cell bodies, dendrites and axons
What is an axon?
a single long fiber that extends AWAY from the cell body
Can axons be branched?
What is the branch of an axon called?
an axon collateral
Where do axons carry APs?
from the cell body AWAY to other cells
Axons arise from where?
the cell body at a region called the axon hillock
Where do APs originate?
the axon hillock
What is the axon hillock?
a funnel shaped structure that leads into cell fibers
Axons or its _____ end in ____ ____.
collaterals, axon terminals
Are axon terminals highly branched?
Where do axon terminals end?
in structures called synaptic knobs
What is another term for synaptic knob?
boutons or end feet
What is another term for bouton?
Synaptic knob, end feet
What is another name for end feet?
synaptic knob, bouton
What does the synaptic knob innervate?
other neurons, muscle cells, or gland cells
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
Where do axons send APs?
away from the cell body
What are branches of axons called?
Where can one axon send one signal?
To several different cells
What are the two types of axons and dendrites in the PNS?
myelinated and unmyelinated
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
What is myelin?
Schwann cell plasma membranes are rich in what?
What type of cell is a schwann cell?
a glial cell in the PNS
What is the neurilemma?
a layer of schwann cell cytoplsam outside of the myelin sheath
Schwann cells exert a very important ____ on ____ that have them.
Where do schwann cells NOT cover?
the axon hillock or axon terminals
What are the ends of axons referred to?
What is the nodes of ranvier?
spaces between schwann cells where an axon is NOT covered
In the nodes of ranvier, the plasma membrane of the axon is not...
exposed to the extracellular fluid
Where is extracellular fluid located?
outside of the axon
Unmyelinated axons have several what?
fibers (axons or dendrites)
What fiber is most commonly found in unmyelinated axons?
Where are axons in unmyelinated embedded?
in the cytoplasm of a series of schwann cells
Multiple fibers in unmyelinated axons prevent what?
schwann cells from coiling around the axons
Can the multiple fibers of an unmyelinated axon form a myelin sheath?
In unmyelinated axons, axon _____ are exposed to ____ all along the length of ____.
membranes, ECF, axons
Peripheral components include what?
1. epineurium 2. perineurium and fascicles 3. endoneurium
What is the epineurium?
outer covering of peripheral nerve
What is the epineurium made of?
white fibrous connective tissue
The epineurium layer covers what?
the outer surface of the peripheral nerve
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 the perineurium made of?
white fibrous connective tissue
Where does the perineurium extend from?
the epineurium into a nerve
The perineurium makes compartments called?
What are fascicles?
sub-compartments of a nerve
The perineurium serves as the...
outer sheath of a fascicle
The fascicle is a group of...
axons and/or dendrites
The fibers of the axons and/or dendrites of a fascicle...
may be myelinated or unmyelinated
What is the endoneurium?
an areolar tissue that covers the surface of each fiber in a fascicle
What is a function of connective tissue components?
serve as a pathway for blood vessels to penetrate a nerve
What is the pathway for blood vessels to penetrate a nerve?
What is the function of the epineurium?
it holds fascicles together as a nerve
The function of the perineurium?
holds fibers together as a fascicle
The function of the endoneurium?
it interconnects fibers
Where are neurologlial cells found?
only in the CNS and PNS
Where are schwann cells found?
What do schwann cells produce?
myelinated axons and myelinated dendrites (mostly axons)
Where are oligodendrocytes found?
What do oligodendrocytes produce?
myelinated axons and myelinated dendrites from late fetus through 2 years
What is a glioma?
a brain tumor
What are brain tumors derived from?
glial cells, NOT neurons
What is multiple sclerosis?
a demyelinating disease (probably auto-immune)
The break down of myelin sheaths happens in what disease?
In multiple sclerosis, what happens to myelin sheaths?
they are broken down
What is an auto-immune disease where myelin sheaths are destroyed?
Microgliocytes are a type of what?
What are microgliocytes?
macrophage-like cells found only in the CNS
Where are microgliocytes found?
Microgliocytes possess what?
ameboid movement (they can move about)
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 are microgliocytes attracted to?
damage area of blood vessels
What are astrocytes nicknamed?
star shaped cells
Where are astrocytes found?
What kind of cells are astrocytes?
Astrocytes connect ___ to ___.
neurons, blood vessels
What do astrocytes assist in?
the regulation of chemical concentration of substances in the ECF of the CNS
What is the BBB?
the blood-brain barrier
What is the BBB established by?
morphology of brain capillaries
What is a brain capillary?
tight junctions of endothelial cells
What is the BBB function?
it impedes movement of water-soluble substances in ECF of brain and spinal cord tissues
What 3 elements move by special transport mechanisms?
Na+, K+, and glucose
Na+, K+ and glucose move by?
special transport mechanisms
Can penicillin cross the BBB?
Can erythromycin cross the BBB?
What are examples of lipid-soluble substances?
alcohol, anesthetics, and heroin
What can pass through the BBB easily?
How do lipid-soluble substances reach the brain tissue?
With ease because of lipid solubility
How do astrocytes contribute to BBB?
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
Where are ependymal cells located?
they line ventricles of brain and central canal of spinal cord
What is a ventricle?
a hollow fluid-filled interior space or cavity
How many ventricles in brain and spinal cord?
Covered capillaries of ventricles of brain and spinal cord are made of what?
a combination of ependymal cells and capillaries (choroid plexes)
What is a choroid plexes?
a combination of blood capillaries and the covering of ependymal cells
What do ependymal cells have for moving CSF through ventricles and central canal?
Ependymal cells have ciliated surfaces for what function?
moving cerebrospinal fluid through ventricles and central canal
How is CSF produced?
by filtration of blood through choroid plexes
What do ependymal cells help control?
substance levels in CSF
How do ependymal cells control substance levels in CSF?
by special transport mechanisms
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 a voltage?
electrical potential difference
Resting potentials are mostly studied in...
What is the value of the resting potential of an axon?
What is the basis of a resting potential?
it is produced by UNEQUAL electrical charges on either side of the axon membrane
What is the basis 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
The sodium pump is an active ____ ____, therefore it requires ____.
transport mechanism, ATP
What is the sodium pump function?
it moves 3 Na+ OUT of the axon and 2 K+ INTO the axon
Why is ATP used in sodium pump?
because ions are moving against their concentration gradients
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
What does the sodium pump establish but not maintain?
the resting potential
How do Na+ and K+ ions diffuse?
through always open or non-gated leak channels with their concentration gradient (high to low)
Potassium diffuses ____ than sodium.
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
What are non-diffusible anions?
negatively charged proteins in the ICF
Non-diffusible anions can't what?
move out of the axon
Non-diffusible anions contribute what?
a small degree of negative charges to the ICF
What ion is responsible for the resting potential?
K+ ions move ___ of an axon 100x ___ than Na+ ions move ___ an axon by ____.
OUT, faster, INTO, diffusion
The ICF is relatively more negative compared to what?
the charge in the ECF
Why is the ICF more negative compared to the ECF?
because there is a net loss of positive charges in the ICF
What is a threshold?
point where a local depolarization(s) stimulate an action potential
Another term for local depolarizations?
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
What is the level of threshold potential?
When is an action potential stimulated?
once it's at the threshold potential
When a threshold potential is reach, what happens?
an AP is stimulated
Sequence of events of AP being stimulated: step one
Axon is at resting potential
What is resting potential for an axon?
Sequence of events of AP being stimulated: step two
adequate stimulus is applied to an axon
What is an example of an adequate stimulus?
heat, cold, electrical, mechanical
What does an adequate stimulus result in?
increased Na+ permeability
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 makes the ICF become relatively positive?
enough Na+ enters the axon
What makes the ECF become relatively negative?
enough Na+ enters the axon
When enough Na+ enters the axon, membrane potential goes from?
-70mV to +30mV
What is the value of an AP?
Sequence of events of AP being stimulated: step 5
What happens during repolarization?
1. Na+ voltage-gated channels close 2. K+ voltage-gated channels open
What enters the axon during repolarization?
little to no Na+
What exits the axon during repolarization?
large quantities of K+
What does the loss of K+ in the axon do?
it returns the membrane potential back to -70mV or lower
What is hyperpolarization?
if an axon loses more K+ than Na+ gained
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
What are the refractory periods?
absolute and relative
Absolute refractory period
threshold potential to end of repolarization
-55 to +30 to -70
Relative refractory period
Importance of absolute refractory period
no other AP can be stimulated during absolute refractory period
In absolute refractory period...
it is impossible to stimulate a second AP
What can a higher than normal stimulus produce?
an AP during relative 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
stimulates a series of APs down the length of an axon
AP is self propagating (stimulates a series of APs down the length of an axon)
Continuous conduction occurs in what kind of 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
What does the first nodes of ranvier stimulate?
the same reaction in the next node
What is saltatory conduction?
APs jumping from node to node
Where does saltatory conduction occur?
myelinated axons ONLY
How do myelinated fibers conduct?
faster than unmyelinated
What is conduction velocity?
the speed of propagation down the length of an axon
Large vs. small diameter axons:
conduction is faster in LARGE diamater axons
Myelinated vs. unmyelinated axons: conduction
conduction is 10x faster in myelinated axons compared to unmyelinated axons of the same diameter
Why are myelinated faster?
because of saltatory conduction
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
Does the axon membrane under schwann cells depolarize?
What part of the axon membrane depolarizes?
the nodes of ranvier in myelinated axons
In AP trasmission from neuron to neuron, how are neurons sent?
the presynaptic neuron sends AP to a postsynaptic neuron
What is a synapse?
site where two neurons associate with one another
Types of synapse?
electrical and chemical
What happens during electrical synapse?
AP passes through gap junctions between neurons without use of chemicals
Where does electrical synapse occur?
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?
found in parietal lobe posterior to the fissure of rolando
Primary sensory/somesthetic cortex function:
specifically interprets sensory stimuli that comes from skin surface, skeletal muscles, and joints
found in the frontal lobe
Olfactory cortex function:
interprets odor stimuli (smell)
found in temporal lobe
Auditory cortex function:
interprets sound stimuli (hearing)
found in parietal lobe
Taste cortex function:
interprets stimuli from dissolved chemical substances in the oral cavity (taste)
found in occipital lobe
Visual cortex function:
interprets light stimuli (sight)
areas that relate past experiences to current incoming stimuli
Premotor cortex/motor ascending cortex:
found in frontal lobe anterior to primary motor cortex
Premotor cortex function:
coordinates contractions of skeletal muscle groups
found in frontal lobe anterior to premotor cortex
Prefrontal cortex function:
involves emotional responses, judgement and reasoning...the "picking" part of the brain, the logical part
Visual association cortex:
found in occipital lobe
Auditory association cortex:
found in the temporal lobe (singer)
found in parietal and temporal lobes
Wernicke's area function:
involves understanding of written and spoken word
What are basal ganglia?
cerebral or basal nuclei; contain regions of gray matter scattered in white matter of cerebrum
How many basal ganglia?
Where are most basal ganglia found?
in the 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
Substantial nigra and subthalamic nucleus are located where?
in the midbrain
Substantial nigra is associated with?
Subthalamic nucleus is associated with?
a unit by itself, gray matter
inferior to corpus callosum and superior to brainstem (between the two)
made of 20 functional groups of nerve cell bodies
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
Thalamus function- gross pain receptor:
perceives general pain and thermal stimuli readily
What is a 3rd function of the thalamus?
modification of sensory input from other brain centers to cerebral nuclei at the cerebellum
Sensory inputs in the thalamus are sent where?
to the motor cortex
Thalamus assists in what?
reticular formation in maintaing consciousness by sending stimuli to reticular formation
inferior to the thalamus
Hypothalamus posterior region connects...
DIRECTLY to the posterior pituitary gland (neurohypophsis)
Hypothalamus- regulation of body temperature:
-"human thermostat" -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
Hypothalamus- sexual response center:
related to sensations associated with sexual orgasms
posterior and inferior to the cerebrum
What is the 2nd largest portion of the brain?
How are the cerebellum and cerebrum separated?
by the transverse fissure
What is located in the transverse fissure?
a double layer of meningeal DM called the falx cerebelli
Cerebellum external structure:
two cerebellar hemispheres that are connected by a central structure
What is the central structure between the two cerebellar hemispheres?
Outer surface of cerebellum:
is gray matter; made of small ridges (folia/gyri) and shallow grooves (sulci)
Cerebellum internal structure:
made of white matter or nerve tracts (arbor vitae)
Cerebellum nerve tracts make connections towhat?
the pons, medulla oblongata, midbrain, thalamus, and cerebellum
What does the cerebellum compare?
sensory input from skeletal muscles to motor output from cerebrum
What does the cerebellum modify?
motor output to muscles for maintenance of balance and posture
Types of sensory inputs include:
light, sound, and equilibrium
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)
Brainstem is composed of?
midbrain, pons, and medulla oblongata
located posterior and inferior to the thalamus
-cerebral peduncles -corpora quadrigemina -substantia nigra
Cerebral peduncles function:
-send sensory fibers from spinal cord to pons to thalamus -send motor fibers from cerebrum to pons
Corpora quadrigemina contain:
superior and inferior colliculi
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:
1. startling 2. inhibition of eardrum movement momentarily
a basal ganglia but NOT located in the cerebrum!!
Describe a substantia nigra:
has a dark pigmented region (melanin)
What does the substantia nigra produce?
a neurotransmitter called dopamine
What does a gradual degeneration of the substantia nigra cause?
What does Parkinson's disease cause?
muscular tremor and muscular rigidity (facial expressions, flailing arms)
Initial treatment for Parkinson's disease?
posterior and inferior to midbrain
What passes through the pons?
nerve tracts (white matter) from the medulla oblongata
What do nerve tracts connect?
-the medulla to the thalamus, cerebellum, and cerebrum -the motor fibers to the medulla
Ancillary breathing centers:
1. pontine respiratory group (pneumotaxic center) 2. apneustic center
Medulla oblongata location:
posterior and inferior to the pons; terminates at foramen magnum where spinal cord begins
The medulla oblongata is largely composed of what?
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
Cardiac center controls:
Vasomotor center controls:
Respiratory center controls:
The medulla oblongata receives nerve tracts from?
The medulla oblongata transmits nerve tracts to?
the spinal cord
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
When impulses are active:
person is awake and conscious
When impulses are inactive:
person is asleep, unconscious, or in a coma
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
What is the fluid in ventricles?
cerebrospinal fluid (CSF)
What is another term for 1st and 2nd ventricles?
Where are the 1st and 2nd ventricles located?
one lacted in each cerebral hempisphere
Where is a portion of a ventricle found?
in ALL lobes of a cerebral hemisphere EXCEPT the insula
What is each lateral ventricle connected to?
the 3rd ventricle by a separate foramen of monro
What connects the lateral ventricle to the 3rd ventricle?
a separate foramen of monro
What is another term for the foramen of monro?
the interventricular foramen
What does the foramen of monro connect?
a lateral ventricle to the 3rd ventricle
located below corpus callosum and just above the midbrain
Cerebral aqueduct of slyvius passes through where?
Cerebral aqueduct of slycius connects what?
the 3rd ventricle to the 4th ventricle
4th ventricle location:
posterior to medulla oblongata
4th ventricle function:
exit of fluid from ventricular system to other regions
pons and medulla
The 4th ventricle opens into the ____ ____ of the ____ ____.
central canal, spinal cord
Ventricular system is responsible for the formation and circulation of what?
cerebrospinal fluid (CSF)
group of capillaries covered by ependymal cells found in ALL ventricles
Formation of CSF: blood filters through what?
Formation of CSF: fluid enters ventricles from where?
Formation of CSF: what is the fluid called after it enters ventricles from blood?
cerebrospinal fluid (CSF)
CSF contains very little what?
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