patho phys exam 2 Flashcards
CHARACTERISTICS OF ACTION POTENTIALS
The frequency of action potentials depends on the strength of the stimulus - so the stronger the stimulus, the more frequent the action potential
Action Potentials occur in all or none fashion
- either it happens or it does not
- if the stimulus reaches the threshold then an AP will be generated
- A strong stimulus does not matter, what matters is if it reaches the threshold or not
The speed of action potentials depends on the diameter of nerve fiber & myelination
- if you go through a tunnel that is 3ft it is harder to walk through than a tunnel that is 7ft
- speed is proportional to the diameter of the nerve fiber and myelin sheath
larger stimulus = high frequency of AP = more NTs being released - hot object
smaller stimulus = low frequency of AP = few NTs being released - warm object
difference between a hot and warm object:
- hot object will generate a high frequency of AP because the stimulus is strong
- warm object will generate a low frequency of AP because the stimulus is not as strong
so we cannot change the duration or magnitude of an AP but we can change the frequency and that is how we know the difference between a hot or warm object - they both have different frequencies! :)
simplified:
- strong stimulus = more frequent action potential
- speed of action potentials depends on myelination & diameter of nerve fiber
MYELINATION
Schwann cells - make the myelin sheath in the peripheral nervous system while the oligodendrocytes make the myelin sheath in the central nervous system
- roll around the axon over and over again
myelin sheath
- mostly made of lipids
axon
nodes of Ranvier
- where the VGSC & VGPC are
- regions where there is no myelin sheath
- where the APs are generated
Saltatory conduction - the axon has myelin sheath
- increase conduction speed
- Conserves energy
- jumping
- uses nodes of Ranvier
- advantages of myelination
- works less, not generating as much APs
MULTIPLE SCLEROSIS
- Auto-immune disorder: damages the myelin sheath
- Slow or block the propagation of action potentials
- since there’s damage to the myelin sheath: the speed of the AP will be slow and over time the axon will lget affected
TYPES OF NERVE FIBERS
THREE TYPES
* Type A: myelinated, transmits cutaneous pressure, touch, cold sensation, mechanical pain & heat pain. Three types: Aa, AB & Agamma
- used for info that needs immediate attention - right because the action potential signal will travel the fastest here so the signal can be transmitted quickly
- biggest diameter and the fastest
- Type B: myelinated, cutaneous, and subcutaneous mechanoreceptors
Type C: unmyelinated, warm-hot sensation, and mechanical, chemical, & heat-cold induced pain
- used for info that does not need immediate attention - because there is no myelin sheath the signal will not be transmitted as quickly
- no diameter
graded potentials
triggering event
- stimulus, a combination of neurotransmitters with receptors or inherent shifts in channel permeability
ion movement producing a change in potential
- net movement of Na+, K+, Cl- or Ca2+ across the plasma membrane by various means
coding of the magnitude of the triggering event
- graded potential change; magnitude varies with the magnitude of the triggering event
duration
- varies with the duration of the triggering event
magnitude of the potential change with distance from the initial site
- decremental conduction; magnitude diminishes with distance from the initial site
refractory period - period where an AP can be regenerated
- none
summation
- temporal, spatial
the direction of potential change
- depolarization or hyperpolarization
location
- specialized regions of the membrane designed to respond to the triggering event
SYNAPSES
The junction between two neurons consisting of
* Presynaptic neuron (axon terminals) - before synaptic cleft
* Postsynaptic neuron (dendrites/cell body) - after synaptic cleft
* Synaptic cleft: space in between the two
the AP is coming down the neuron whether it is myelinated or not
components:
synaptic knob
synaptic vesicle
synaptic cleft
subsynaptic membrane
VGCCs
NTs
WORKING OF SYNAPSES
- AP reaches presynaptic terminal
- VGCCs open, Ca++ enters the synaptic knob
- NT is released by exocytosis from synaptic vesicle
- NT binds to ion channels
- LGICs open
- Summation of GPs → APs
- added together and brings membrane potential to threshold - NT is removed quickly
- tightly regulated
TYPES OF SYNAPSES
Excitatory synapse
- when AP reaches this synapse it generates a small EPSP
- generate a small depolarization
Inhibitory synapse
- when AP reaches this synapse it generates a small IPSP
- generate a small hyperpolarization
NEUROTRANSMITTERS VS. NEUROPEPTIDES
NEUROTRANSMITTERS
* Small molecules (amino acids)
* Act quickly, destroyed quickly
* Synthesized locally
* Stored in synaptic vesicles
* Most act to open LGICs, others use 2nd messenger systems in the post-synaptic neuron only
* Produce EPSPs or IPSPs
NEUROPEPTIDES
* Large molecules (2-40 AAs)
* Act slowly, prolonged response * Synthesized in cell body
* Stored in dense core vesicles
* Mostly use 2nd messenger systems, can act either pre- or post-synaptically
* Do not produce EPSPs or IPSPs so cannot transmit message from neuron to neuron
SYNAPTIC MODULATIONS
what do these modulations do? - Alter synthesis, transport, storage, or release of NT
- Modify NT interaction with postsynaptic receptors
- Modify NT reuptake or destruction - is this an SSRI?
- Replace deficient NT with a substitute
summary
presynaptic inputs
postsynaptic neuron
EPSP & IPSP are examples of
graded potentials
action potentials
graded potentials
Theoretically speaking, which will generate an action potential faster?
A
Specialized afferent endings
B
Separate receptor cell
A
Specialized afferent endings - where the receptor and the nerve fiber are connected
Are neurons the only type of cells present in the CNS?
A
Yes
B
No
no
- there are glial cells which are actually 90% of the cells in the CNS
Brain tumors are due to unchecked division of:
A
Neurons
B
Glial cells
C
Both A & B
B
Glial cells - BECAUSE neurons do not divide and so if they do not divide then cancer cannot happen in them because canncer has to do with the cells dividing too much
but
glial cells do divide
ORGANIZATION OF THE NERVOUS SYSTEM
central nervous system: input to CNS from the afferent periphery, output from CNS to the efferent periphery
- brain and spinal cord
peripheral nervous system
- afferent division
- efferent division
afferent division
- receive sensory stimuli
- visceral stimuli like thirst, hunger
efferent division
- somatic nervous system - skeletal muscles like arms so we can control it
- autonomic nervous system - smooth muscle like heart and lungs so we can not control it
somatic nervous system
- motor neurons
motor neurons
- skeletal muscles
autonomic nervous system
- sympathetic nervous system
- parasympathetic nervous system
- stimuli in the digestive tract enteric nervous system to digestive enzymes only
sympathetic nervous system to the parasympathetic nervous system
- smooth muscle
- cardiac
- exocrine glands
- some endocrine glands
effector organs
- smooth muscle
- cardiac
- exocrine glands
- some endocrine glands
- skeletal muscles
TYPES OF NEURONS
Afferent neuron:
- Sends signals to the CNS
- Generates AP from sensory receptors
- Long axon in the PNS
Interneurons:
- Found entirely within CNS
- Lies between afferent & efferent neurons
Efferent neuron:
- Sends signals away from the CNS to effector organs (muscle/gland)
- Long axon in the PNS
pathway of neuronal info.:
peripheral nervous system - afferent neuron
- receive a signal in the sensory receptor - seems to be specialized nerve ending which is faster!
- signal travels through the peripheral axon (afferent fiber)
- cell body (kinda left alone I guess)
- central axon
- axon terminal sends a message to the dendrites of the interneuron
central nervous system - interneuron
- receives message
- sends decisions through axon terminals to the dendrites of the efferent neuron
peripheral nervous system - efferent neuron
- efferent neuron gets message and the message is sent through the axon (efferent fiber) to the axon terminals
- axons terminals release message to the effector organs (muscle or gland)
AFFERENT NEURON: SENSORY RECEPTORS
SENSORY RECEPTORS
- Photoreceptors - light
- Mechanoreceptors: detect stimuli such as touch, pressure, vibration, and sound from the external and internal environments
- Thermoreceptors: temperature
- Nociceptors: pain
- Osmoreceptors: osmotic pressure
- Chemoreceptor: chemicals like taste
sensory receptors are
- Sensitive to different energy forms
- Responds to a stimulus
- Generates graded potentials and if enough, will generate an action potential
afferent sensory receptors
sensory receptor is attached to the afferent neuron
1 - in sensory receptors that are specialed afferent neuron endings, stimulus opens stimulus-sensitive channels, permitting net Na+ entry that produces receptor potential
2 - local current flow between depolarized receptor ending and adjacent region opens voltage gated Na+ channels
3 - Na+ entry initiates action potential afferent fiber that self-propagates to CNS
sensory receptor is not attached to the afferent neuron
1 - in sensory receptors that are separate cells, sitmulus opens stimulus-sensitive channels, permitting net Na+ entry that produces receptor potential
2 - this local depolarization opens voltage-gated Ca+ channels
3 - Ca+ entry triggers exocytosis of neurotransmitter
4 - neurotransmitter binding opens chemically gated receptor channels at afferent ending permitting net Na+ entry
5 - resultant depolarization opens voltage-gated Na+ channels in adjacent region
6 - Na+ entry initiates action potential inn afferent fiber that self propagtes to CNS
SENSORY RECEPTORS: ADAPTATION
Stimuli of same intensity do not produce same magnitude of receptor potentials from the same receptor
TONIC: TONE
- Do not adapt, or adapt slowly - Maintained information about stimulus is valuable
- so the stimulus is received and it is mainatined for a while until stimulus fades
- probably useful for pain
PHASIC: PHASE - Adapts rapidly, but generate an off response on removing the stimulus
- Change in stimulus intensity is important
- so stimulus is received and it is not maintained for a long time
- probably useful for touch that the body does not need to keep track of like putting glassess on your head
TRANSMISSION OF STIMULUS
Information travels in labeled lines
Sensory units
- Transmit sensory information from the periphery to the CNS
Ascending pathways
- Communicate with reflex networks in spinal cord & travel to thalamus
Processing center
- Relay information from thalamus to cerebral cortex
TYPES OF NERVE FIBERS
THREE TYPES
* Type A: myelinated, transmit cutaneous pressure, touch, cold sensation, mechanical pain & heat pain. Three types: A, A & A
- Type B: myelinated, cutaneous and subcutaneous mechanoreceptors
- Type C: unmyelinated, warm-hot sensation, and mechanical, chemical, & heat-cold induced pain
COMPONENTS OF THE CNS
Axon terminals of afferent neuron
Interneurons
Dendrites & cell body of efferent neuron
glial cells
do not send signals: provide physical, metabolic and functional support
90% of cells in CNS
GLIAL CELLS
ASTROCYTES: star shaped cells
- Supports & guides neurons
- in a 3-D space
- Establishes blood brain barrier (tight junctions)
- Repairs brain injuries
- Takes up neurotransmitters (GABA/glutamate)
- Takes up K+ ions during high frequency APs
- Forms & strengthens synapses: thrombospondin
MICROGLIA
- Immune defenders
- Scavengers
- Secrete NGF - neuronal growth factor
EPENDYMAL CELLS
- Formation & flow of CSF
- Serve as neural stem cells
OLIGODENDROCYTES
- Forms myelin sheath around axons
