Exam 4 Study Guide Flashcards
- What is the difference between the CNS and the PNS? What are the subdivisions of the PNS? What are the subdivisions of the ANS?
CNS: integration centers- brain and spinal cord
PNS: all neuron cell bodies outside of the CNS (ganglia) and bundles of axons (nerve fibers). Sensory neurons and motor neurons act as communication lines.
Sensory PNS: somatic and visceral (organs) sensory nerve fibers
Motor PNS: motor nerve fibers. skeletal muscle. Branches into somatic and autonomic:
Somatic: conscious control. cardiac, smooth muscle, glands.
Autonomic: controls automatic processes. Branches into sympathetic and parasympathetic
Sympathetic: mobilizes NRG, fight or flight
Parasympathetic: conserves NRG, rest
What is the difference between a neuron and a glial cells?
neurons: excitable (rapidly change membrane potential)- function for control- 50% of brain volume
neuroglia: support and help neurons to send and receive impulses- 99% of cells in CNS
- Describes the structure of a neuron
neurons are amitotic, cannot divide and cannot proliferate. extreme longevity, high metabolic rate (high need for O2 and glucose to produce a ton of ATP), variable shape.
- What are the functional and structural classifications of neurons.
unipolar: sensory or afferent neuron, exclusively have an axon, they lack dendrites
Bipolar: ex. olfactory cell, the ear, and also in retina. Have one dendrite and one axon, but the process can branch.
Multipolar: ex. major type, motor interneurons. Have an axon and many dendrites.
Functional classification is afferent (unipolar), efferent (multipolar), and interneuron (contained in CNS, relays info between afferent and efferent).
astrocytes
CNS: astrocytes: physical support, control ECF (pick up extra neurotransmitters and ions that have been released from neurons) around neuron, surround capillaries and keep them close to neurons. have arms (cytoplasmic projections) and grab onto neurons and capillaries.
microglia
CNS: microglia: thorny cytoplasmic protrusions that grab onto neurons, monitor health status of neurons, act like macrophages. If not healthy, can engulf dead cells or cellular debris. Also reach out into ECF and pick up foreign material. Phagocytosis
ependymal cells
CNS: ependymal cells: line the ventricles, help produce CSF that fills ventricles. Have cilia to move CSF through ventricles. range in shape from squamous to columnar
oligodendrocytes
CNS: oligodendrocytes: Have a cell body and have arms to wrap around an axon to form myelin sheath. cellular protrusions ARE the myelin sheaths around axons. Are not phagocytic and do not help regenerate.
Satellite cells
satellite cells: same role as astrocytes, PNS
Schwann cells
Schwann cells: similar to oligodendrocytes form the myelin sheath. entire cell wraps around axon. Phagocytic (engulf foreign material and dead cell) and help regenerate damaged neurons. PNS
Myelin sheath
Acts as electrical insulator, meaning it is trying to keep the action potential contained in the myelin so to very efficient, and there is rapid transmission of action potentials. Formed by any layers of plasma/phospholipid membrane, act as insulators.
PNS: Schwann cell- layers of phospholipids and outer collar of perinuclear cytoplasm consists of Schwann cell cytoplasm and nucleus. entire cell wraps around axon
CNS: oligodendrocytes- no outer collar and only the arms/processes wrap around
Non myelinated fibers are also found in both the CNS and PNS- transmit action potentials slower
What are the differences between a Schwann cell and an Oligodendrocyte? How is a myelin sheath produced differently in the CNS compared to the PNS? Why can a regeneration tube be formed in the PNS following an injury to an axon, but not in the CNS?
Schwann cells form the myelin sheath around axons in the PNS and are phagocytic and have the ability to help regenerate and repair neurons in the PNS.
Oligodendrocytes also form the myelin sheaths in the CNS, but are not phagocytic and cannot regenerate neurons.
nodes of ranvier
gaps in the myelin sheath, where action potentials jump from one segment to the next.
regeneration of axons
Schwann cells surround the axon, then they participate in phagocytosis to clean up the debris from severed axon, then they form a regeneration tube and secrete growth factors and cell adhesion molecules to promote regeneration of axon and hook it back together.
multiple sclerosis
unregulated immune response where the body degrades the myelin sheath on the neuron. white matter has myelinated neurons, gray has non myelinated axons and cell bodies, so you can track proportions of both on an MRI. white matter is decreasing while gray matter is increasing.
voltage
the measure of potential energy generated by separated electrical charges
potential (potential difference)
voltage measured between two points. ex. charge difference on either side of plasma membrane because of different ion charges
current
flow of electrical charge
resistance
hindrance to charge flow. anything that prevents ions from moving across the plasma membrane.
relationship between voltage and current
the greater the voltage, the greater the current. The greater the resistance, the smaller the current
how do neurons function in general?
neurons change their membrane (action potential or nerve impulse) potential to receive info.
where neurons are passing action potentials to one another, it is known as a chemical transmission or a synapse.
RMP (resting membrane potentials)
all cells have a membrane potential, or difference in ion concentration and a difference in charge. range from about -50 to -100 mv.
in non excitable cells, membrane potential cannot be changed.
excitable cells can, in order to send and receive nerve impulses. Neurons have an RMP (when not sending and receiving impulses). RMP is -70 mv. Inside of the neuron is slightly negative due to difference in ion concentrations, so the membrane is polarized. Difference in charge only exists at the plasma membrane, overall charge inside and outside of cell are neutral.
Causes: difference in ionic concentrations inside and outside the cell, and difference in membrane permeability. Permeability of membrane can be changed by channels or transporter
Ionic differences in neurons
K+ and protein anions mostly inside cell.
Na+ and Cl- mostly outside cell.
Therefore, there is a gradient for K+ to diffuse out. and a gradient for Na+ to diffuse in.
Membrane ion channels
Leakage channels: non gated, always allows ions to move down their concentration gradients.
Important for generating RMP, allow K+ to move down its concentration gradient, out of the cell- makes RMP to be very negative.
Also allow Na+ to move inside the cell down its concentration gradient. Leakage channels combined equal -70 mv.
Membrane is 25x more permeable to K than Na, so there 25x more K channels than Na channels.
Gated channels: chemically gated/ligand channels, voltage gated channels, mechanically gated
What plays the biggest role in maintaining the ion gradient of -70 mv?
K+ channels, because there are 25x more of these channels than Na+ channels
sodium potassium pump
helps to maintain resting membrane potential
pumps 2 Na+ out, 3 K+ in
- Na+ binds to
How is a change in RMP produced?
- Graded potential: a brief localized change in RMP, occurs on cell body or dendrites. +30 mv
lead to action potentials
Generated on a subsequent neuron after one neuron passes an action potential to it and it spreads the graded potential toward the axon hillock. Then the subsequent neuron generates an action potential at the axon hillock and that action potential spreads toward the terminal.
Graded or vary in strength. Stronger graded potentials produce a greater change in RMP
+30 mv might be considered strong. -50 might not be as strong
Graded potentials are decremental, they decrease in strength as distance increases or they spread toward the axon hillock, so change gets smaller and smaller.
- post synaptic potential- two neurons communicating at a synapse passing action potentials
- receptor potential or generator potential- a receptor would be generating the graded potential
- Action potential: a brief reversal of membrane potential followed by a return to RMP.
exclusively found in excitable cells. In neurons, action potentials can only occur in the axon.
Action potential phases
Depolarization: membrane gets + (+30 mv)
Na+ enters through voltage gated (VG) Na+ channels- positive ions flood the cell and causes positive spike
Repolarization: Diving back down to RMP- go from +30 down to -70 mv, but it overshoots.
K+ leaves through VG K+- loss of positive ions causes negative spike
Hyperpolarization: -70 mv is overshot, membrane gets to -90 mv.
K+ continues to leave through VG K+ channels while VG K+ gates slowly close
sodium potassium pump helps return to normal RMP
action potentials are all or none and cannot summate (can’t be added together)- they are the exact same strength
VG Na+ channels
have two gates, activation and inactivation gates. Allows channels to open and close very quickly.
Activation gate opens first, allowing Na+ to enter, then right after, the inactivation gate slams closed to prevent more Na+ from entering.
closed at rest
open when axon hillock reaches threshold (sufficient stimulus) at -55 mv. -55 because graded potentials are decremental.
Below -55 at axon hillock, an action potential will not be generated (subthreshold)
VG K+ channels
slow to open, slow to close. They are sluggish, which is why the cell is hyper polarized during the last phase of the action potential.
no activation gate
closed at rest
Threshold and action potential sequence for VG channels
-55 mv
VG Na+ and K+ channels are triggered to open and tons of Na+ enters the cell.
K+ open slightly later just as Na+ channels close.
K+ now leaves the cell- repolarization +30mv to -70mv
K+ are sluggish so cells hyperpolarizes -70mv to -90mv
main players in maintaining RMP
K+ leakage channels
Na+ leakage channels
sodium potassium pump- maintaining ionic gradient- 3 Na out, 2 K+ in
Refractory Periods
absolute refractory period: the period of time following stimulation during which no additional action potentials can be evoked. even if graded potentials were spreading toward the hillock, another action potential will not occur because all of the VG + Na channels are already open. reason why each action potential is a separate all or nothing even
relative refractory period: when another action potential could occur, but you would need a greater than normal stimulus for action potential occur. during this period, the VG Na+ channels have closed, so it could be initiated at threshold. You would need a greater stimulus because K+ channels are still open, so to is harder to stay positive and get to threshold because you are losing positive ions.
action potential propagation
in neurons, propagation is only going to occur on the axon from the axon hillock. occurs because positively charged ions are attracted to negatively charged ions in adjacent neurons. during depolarization, Na+ ions are going to be present during depolarization, so adjacent membrane will have negative ions, so they attract because Na+ ions start to move to the adjacent membrane, and brings the adjacent membrane to threshold. This opens VG Na+ channels there.
But even then, membrane potentials decay with distance because of leakage channels, so AP are regenerated at every point to prevent decay of signal and spreading of AP in opposite direction. Graded potentials do not.
Depolarizations follows depolarization and VG K+ are opening.
Spreading of an action potential on myelinated vs non-myelinated fiber
continuous conduction
when myelin is not present, AP signal will decay with distance, so it must be regenerated at every point segment to segment
continuous conduction is very slow
in a myelinated fiber, the sheath acts as insulation by preventing the leakage of Na and K, so signal will not decay with distance, so AP won’t have to be generated at every single segment, only at the nodes of ranvier- known as saltatory conduction- AP jump from one node to the next. only get regenerated at the nodes of ranvier, and you only have VG sodium and potassium channels at the nodes. If one node gets to threshold, Na enters and current is carried to next node because of myelin sheath. extremely fast
Propogation speed
myelin sheath increases speed
diameter increases speed, larger axon allows for action potentials to spread much quicker, because there is more space for cellular machinery, so there are less structures obstructing the flow of ions, and less resistance to ion flow.
Ex. motor neurons- myelinated and large in diameter >15-150m/sec or almost 300 mph
Ex. pain afferents- small diameter and non myelination >1m/sec
Neuronal synapses
point of chemical communication between two neurons. between axon and cell body, dendrites, and between an axon and hillock rarely. One neuron can receive action potentials from multiple different neurons, and can branch and synapse at different neurons.
when an action arrives at the axon terminal, and triggers the opening of voltage gated Ca+ channels. Ca+ then floods the axon terminal and triggers the release of neurotransmitter via exocytosis into the synaptic cleft. The neurotransmitters then bind to chemically gated ligand gated channels on the postsynaptic neuron.
ligand gated channels only open when the neurotransmitter binds. channels then open, and graded potential is formed.
Differences between NJ channels
certain channels are excitatory (trying to bring postsynaptic neuron closer to threshold. Na+ will flood) or inhibitory (bringing the postsynaptic neuron farther from threshold. K+ will leave).
Possibilities for NT
-diffuse away
-enzymatic degradation
-reuptake
synaptic delay
the slowest step 0.3-0.5 msec
the time it takes for a NT to diffuse across the cleft and bind to ion channels and produce a graded potential
fewer synapses mean fewer synaptic delays, so less neurons are faster
excitatory and inhibitory postsynaptic potentials
postsynaptic potential is a graded potential, one of the two types. both are graded potentials.
excitatory (EPSP): open gated ion channels that let Na+ ions in and more K+ to leave. postsynaptic neurons depolarizes.
inhibitory (IPSP): open gated ion channels that let K+ ions leave or a channel that lets Cl- enter. Cell then becomes more negative.
whether or not a neuron reaches threshold is dictated by number of EPSPs or IPSPs. Must have more EPSPs to bring a neuron to threshold and generate an action potential. can summate
graded potentials can also summate (action potentials cannot)
temporal summation: adding together graded potentials being produced close in time (same neuron).
spatial summation: adding together graded potentials that are from different neurons producing graded potentials at different points.
hope is that potentials added together will produce an action potential
distance from the axon hillock matters for synapses
the size of a graded potential is determined by the amount of neurotransmitters released because more channels open so there is a larger change in membrane potential. current decreases with distance because of ion leakage in continuous conduction.
Synaptic plasticity
when a synapse is continuously used, it will lead to greater grade potentials because it become more efficient, and more likely that the postsynaptic neuron will fire
Ex. long term potentiation in hippocampus functions in learning and memory
Acetylcholine
excitatory or inhibitory. excitatory in CNS and NMJ, either in ANS
reduced levels can lead to Alzheimers because it causes pathways to not fire, specifically memory
Biogenic amines
norepinephrine: released from motor neurons in ANS
“feel good” neurotransmitter in CNS
amphetimes increase release
cocaine blocks removal from cleft
dopamine
feel good NT in CNS
too little can lead to Parkinson’s and too much can lead to schizophrenia
peptides
endorphins and enkephalins
inhibitory NT
endogenous opitates (natural painkillers)
runners high and childbirth
Functional Classification of NT
Excitatory: wants to produce AP
Inhibitory:
Direct NT: NT binds to a channel linked receptors (binds to channel and opens it) chemically gated channel, opens it, and causes ions to move.
Act quickly and produce a graded potential very efficiently and rapidly
Indirect NT: act through secondary messengers, longer lasting effect because it takes more time for a graded potential to be produced.
binds to a GPCR (G-protein coupled receptor) it initiates a signaling cascade in the neuron and produces a small molecule inside of the cell called a secondary messenger. Secondary messenger binds to and opens ion channel and causes ions to move and producing a graded potential.
Detailed:
Indirect NT bind to GPCR (have a G-protein coupled )
G protein is then activated and activates an enzyme called adenylate cyclase, AC catalyzes conversion of ATP to cyclic AMP. CAMP is the messenger that binds to the ion channe and causes a graded potential. Biogenic amines, peptides, gases such as nitrous oxide
neuromodulators
act on an area in the brain rather than a single synpase when released in the brain. trying to alter the cellular properties at a synpase, such as changing the RMP of a group of neurons making them more likely or less likely to fire.
mimics:
SSRI’s: prevents removal of serotonin (feel good) from synaptic cleft to treat depression. Block transporters that remove serotonin.
cholinesterase inhibitors: act on synapses to prevent breakdown of acetylcholine for dimentia or alzheimers.
Lateralization
left side: language abilities, math, logic
right side: visual spacial skills, intuition, emotion, artistic skills.
association fibers:
lobe to lobe, gyrus to gyrus communication
projection fibers
bundles of neurons that descend/ascend to and from the spinal cord to the brain
comissure:
Hemisphere to hemisphere communication
corpus collasum is major commisure
gray matter/basal nuclei
basal nuclei: collections of neuron cell bodies that control movement by relaying info to motor areas; filter unnecessary movement.
receieve plan from motor cortedx, edit plan, and send it back to motor areas.
huntingtons and parkinsons: degeneration of basal nuclei resulting in rapid uncontrolled jerking movement
dienceohalon
central core of forebrain.
thalamus, hypothalamus, epithalamus
thalamus
2 egg shaped areas on either side of 3rd ventricle
makor relay station
collection of neurons recieving all sensory information for sensory neurons in PNS, sort it, edit it, and send info to cerebral cortex
hypothalamus
sits right above the pituitary gland
main visceral (organs) control center (ANS. control)
heart rate, BP, respiration rate
temperature
food intake
water balance
sleep-wake cycle
sex drive
regulates anterior pituitary gland
synthesizes and releases 2 hormones from posterior pituitary
limbic system component: emotions
epithalamus
associated with pineal gland and secretes meletonin
midbrain
mesencephalon
cebral aqueduct goes directly through the midbrain- connects 3rd and 4th ventricles
corpora quadrigemina: largest midbrain nuclei
4 dome-like potrosions:
superior colliculi- visual reflex center
inferior colliculi- auditory reflex center (scream = startle)
substania nigra: pigmented nuclei that produces melanin, precursor to NT dopamine
functions with basal nuclei in order to control movements
degeneration is associated with parkinsons
cerebral peducles: tracts from large pyramidal motor neurons to effectors
brainstem
arrises from mesencephalon, metencephalon, and myelencephalon
acts as passageway for info
connection point to peripheral NS for 10 cranial nerves
pons
site of tracts (bundles of axons) that relay info from motor areas to cerebellum and from higher brain centers to the spinal cord
regulates respiration, group of neurons that functions as a respiratory center, sends motor output to intercostals and maintain normal breathing rhythm
medulla oblongotta
has nuclei that function for autonomic NS reflexes
cardiovasucular control center
respiratory control center
functions for ANS reflexes: vomiting, swallowing, coughing
continuous w spinal cord, so tracts relay info to higher brain
cerebellum
arrises from metencephalon, but not part of brainstem
coordination of muscle activity, balance, and equilibrium, recieves input about concious perception of the body in space, monitor motor output being sent to effectors, sends output to cortex and make adjustments in motor program
similar to basal nuclei
limbic system
emotional brain, parts of cerebral hemispheres and diencephalon
reticular formation
cluster neuronetwork within brainstem (medulla, pons and midbrain)
reticular activating system: relays info up to the cortex
filters out sensory info- 99% of sensory info halts at reticular formation (feeling of wearing clothes)
dura mater
most external meninge/membrane
outer periostial layer is continuous with periosteum of skull
inner meningal layer that is a true CT covering, continuous with spinal dura mater
separations in membranes are called dural venus sinus- a collection point for venus blood- returns blood from brain and bring back to heart
arachnoid mater
has arschnoid villi/granulations that protrude from arachoid mater into dural venus sinus- allows for CSF to empty into venus blood
subarachnoid space
between arachnoid and pia mater
contains CSF circulating through
CSF
acts as watery cushion for protection and nourishment as its a filtrate of blood
pia mater
innermost meninge, attaches directly to brain structures, site of some blood vessels that allow for production of CSF
ventricles
first produces CSF by choroid plexus (hanging from the roof of ventricle- ependymnal cells and leaky capillaries from pia mater
blood leaks through into ventricle) which circulates the brain and enter the subarachnoid space and enters median and appature in 4th ventricle
CSF lleaves through the apperatures
circulation of CSF
- choroid plexus of each ventricle produces CSF
- CSF flows through the ventricles and then leaves and enters the subarachnoid space via median and lateral appertures of the 4th ventricle
- then circulates through subarachnoid space and acts as watery cushion and provides nourishment to brain structures
- leaves the subarachnboid space and enters dural venus sinus via arachnoid granulation/villi so it can be absorbed into venus blood and goes back to the heart
superior sagittal sinus
largest dural venus sinus
Hydrocephalus
~150 mL of CSF is circulating at a time that gets turned over about every 8 hours
~500 mL is produced per day
hydrocephalus occurs when CSF is produced at a faster rate than its drained and it leads to increased pressure that can damage brain structures, but infants skulls can still stretch because bones aren’t fused.
Treatment: insert shunt to relieve pressure into the peritoneal cavity.
blood brain barrier
complex between tight junctions in endothelial cells. Between endothelial cells and astrocytes.
very selective barrier that maintains stable environment by preventing chemical variations in the blood stream from reaching the brain.
spinal cord
extends from foramen magnum to conus madullaris
31 pairs of spinal nerves banch off
nerves existing past spinal cord are known as cauda equina
has tracts or bundles of axons
protected by 33 vertabrae and meninges, but dura only has the meningeal layer, not periosteal layer
lumbar punctures and epidurals are done after L1, so there is no risk of hitting the spinal cord. spinal fluid may be sampled to see if infections like meningitis are present
also protected by fat in the epidural space external to the dura mater that adds cushioning.
characteristics of tracts
decussation: most tracts must cross at some point through the spinal cord (left and right info must cross)
relay: a chain of neurons
symmetry: tracts are paired to serve right and left sides of body
somatotopy: spatial relationship of tracts refelcts body map
whiter matter in spinal cord: has descending tracts (carrying motor output to effector organs) and ascending tracts (bring sensory input towards the brain).
descidning and ascending tracts
descending tract: relaying motor output to effector organs
pyramidal path: bringing motor output to skeletal muscle for precise or skilled movements
lateral corticospinal- left side of brain, crosses at medulla oblongata and down to lumbar vertebrae to skeletal muscle
has 3 neurons, pyramidal, inter, somatic motor neuron
ventral corticospinal- right side of brain, travels down to the lumbar spinal cord, then (decosate) crosses to the left side and then synapses with a somatic motor neuron in gray matter
has 2 neurons
ascending tracts: in dorsal columns, tracts carry sensory info from upper and lower limbs
fasiculus cuneatus: upper limb
fasiculus gracilis: lower limbs
both have 3 neurons in relay that are bringing info about discriminative touch
main difference between two is where they originate: FC: brings info from lower limbs
FG: brings info from lower limbs and
first order afferent neuron: enters white matter of dorsal column all the way up the medulla of the brainstem and synapses with medullary neuron
second order neuron: extends from the medulla and crosses from left to right side of the brain and synapses with a thrid order at thalamus.
third order neuron: starts in nuclei of thalamus (relay station) and it relays that info to the cerebral cortex
Reflexes
rapid, predictable motor responses to a stimulus
unlearned, involuntary and unpremediated
do not requre integration by higher brain centers (cerebral cortex does not play a role)
integration centers are either spinal cord or brain stem
visceral reflexes: smooth muscle, cardiac muscle, glands
integration centers typically in brainstem, specifically medulla
somatic reflexes: motor output is sent to skeletal muscle
typically have spinal cord for integration center
reflexive arc:
1. change in variable is sensed by receptor and sends it to sensory neuron
2. afferent (sensory) neuron sends it to integration center
3. integration center processes it and makes a plan
4. info is sent to efferent motor neuron
5. efferent motor neuron sends it to effectors
somatic: effectors are skeletal muscle
visceral: effectors are organs
stretch reflex
somatic
stimulus is stretch when patellar ligament is tapped
receptor is muscle spindle
sensory neuron brings info to spinal cord
1. synapses on somatic motor neuron
2. synapses on motor neuron telling hamstrings (antagonist) to relax
3. synapses on interneuron
integration center recieves info about stretched quad and makes a plan
efferent neuron goes to stretched muscle and causes a kick
ANS
Differences between SNS and ANS
SNS: innervate skeletal muscle (smooth, cariac muscle, glands)
single somatic motor neuron from spinal cord to effectors
cell bodies are exclusively in the spinal cord
ACh
heavily myelinated- faster AP
ANS: innervates organs
2 neurons in sequence, preganglionic and postganglionic
preganglionic cell body is in spinal cord, postganglionic is outside the CNS
NT: norepi and ACh can be exitatory or inhibitory
preganglionic are lightly myelinated, postganglionic is not at all
Dual inneravtion in ANS: one is not always stimulatory or inhibitory: depends on tissue
Sympathetic
dilate pupils
increase heart rate
dilate bronchioles
stimulate liver to release glucose
decreases GI tract activity
preganglionic neurons in thoracic and lumbar spinal cord- short pregang, long postgang
adrenal medulla- one instance where there is no postganglionic neuron
parasympathetic
constrict pupils
decrease heart rate
constrict bronchioles
increase GI activity
preganglionic neurons originate in cranial and sacral regions of spinal cord-
