Unit 1.2 Flashcards
What is the CNS protected by?
-skull and spinal cord
What is the CNS covered by?
- connective tissue meninges
What is the brain?
- site of thoughts and intelligence
- processes info received and sends messages to body
What is the PNS made of?
- nerves and ganglia
What are nerves
- bundled axons that carry signals to and from the CNS
-extend from brain and spinal cord
How are nerves organized?
- epineurium
-perineurium
-endonerium
What is the epineurium?
connective tissue surrounding outer nerve surface
What is the perineurium?
- connective tissue that surrounds and separates bundles of axons organized into fascicles
What are ganglia?
cluster of neuron cell bodies outside of the CNS along the length of a nerve in the PNS
- localizeed
What are the types of afferent systems?
- somatic sensory
-visceral sensory
Whats an example of a visceral sensory organ?
the heart
Whats and example of a somatic sensory organ?
- eyes, ears, skin
What is the afferent pathway?
- sensory nervous system detects stimuli and transmits info from receptors to the CNS
What is the somatic sensory system?
- sensory input that is consciously perceived from receptors
What is the visceral sensory system?
- sensory input that is not consciously perceived by receptors of blood vessels
and internal organs
What is the efferent sensory system?
- motor nervous system that initiates and transmits info from CNS to effectors
What are the parts of the efferent sensory system?
- somatic motor
- autonomic motor
-sympathetic division - parasympathetic division
What is the autonomic motor system?
- motor output that is not consciously or involuntarily controlled
What are the parts of the efferent system?
-sympathetic
-parasympathetic
What is the somatic motor system?
- motor output that is consciously or voluntarily controlled
What is an example of somatic motor system?
-effector is skeletal muscle
What is the sympathetic division?
-fight, flight, or freeze stress response
What is the parasympathetic division?
- resting and digesting branch
-maintains homeostasis
What is an example of the autonomic motor division?
- cardiac muscle
-smooth muscle - glands
What is a fascicle?
bundle of axons
What nervous system do cranial and vertebral nerves a part of?
-PNS
Are nerves an organ or a cell?
-organ
What are axons bundled by?
- connective tissue layers
Are neurons an organ or a cell?
cells
What are multipolar neurons made of?
- Multiple processes extend directly from the neuron cell body
- multiple dendrites and 1 axon
What type of neuron is the most common?
multipolar
What type of neuron are motor neurons and interneurons?
multipolar
What are bipolar neurons made of?
- 2 processes extending directly from cell body
-1 dendrite and one axon
Where are bipolar neurons found?
- eye retina
-olfactory epithelium of nose
What are unipolar neurons made of?
- 1 process attached to cell body/soma
- forms a t-intersection with the 2 processes (peripheral and central) of 1 long axon
dendrites directly attached to the peripheral process of axon
Where are unipolar neurons found?
- most sensory organs
Which type of neuron are part of ganglion in PNS?
- unipolar neuron
What are anaxonic neurons?
- neurons with no axons
What are anaxonic neurons made of?
- processes are only dendrites that extend from cell body
What are interneurons?
connections between neurons
Where are anaxonic neurons fire?
-only in the CNS
What are the functional classifications of neurons?
- sensory/afferent
- interneurons
-motor/association neuron
What do sensory/afferent neurons do?
- receive somatic and visceral sensory input
- conduct AP signals to the CNS
What structural type of neuron are sensory neurons?
- unipolar
- receptive region and cell body in PNS and azon end in CNS
Where are interneurons found?
-entirely in CNS
What structural type of neurons are interneurons?
- multipolar or anaxonic
What do interneurons do?
- receives signals from sensory neurons and sends signals to motor neurons
What pathway are motor/association neurons a part of?
- efferent pathway
What do motor neurons do?
- conducts motor output from CNS to effectors in the PNS
Where are motor neurons found?
- innervate somatic (skeletal) muscle and autonomic effectors (smooth muscle)
What are motor neurons made of?
multiple neurons
What kind of gaps do electrical synapses have?
- no gap
-has a physical connection
-has a gap junction
-Gap junctions use proteins to create pores for ions
What is an electrical synapse?
- junction between 2 neurons that allows for the two way transmission of electrical signals
What type of synapse is the most common?
- chemical
What kind of gaps do chemical synapses have?
-has synaptic cleft
- no physical connection
How do chemical synapses work?
-Electrical signals get turned into chemical signals (NT)
-presynaptic neurons axon terminal which produces signal in the form of NT
-postsynaptic neuron receives signal as NT and binds to receptor and cause a postsynaptic potential
What do postsynaptic potentials do?
- depolarization or hyperpolarization
What is a pro to chemical synapse?
-allows for variability
-smart
What is a pro to electrical synapses?
-fast (but dumb)
What do excitatory NT do?
-depolarization, makes membrane more positive
What do inhibitory NT do?
-hyperpolarization
-membrane more negative
Why is the resting membrane potential negative?
- at the inside is more negative than the outside
-compares membrane innerface to membrane outerface
What does anterograde transport do?
moves newly synthesized material toward synaptic knob
What do retrograde transporters do?
moves used materials from Axon for breakdown and recycling in the cell body
What causes slow transport?
flow of axoplasm?
Where does slow transport occur?
within the azon
Does slow transport require energy?
no
What does slow transport?
- anterograde transport of enzymes, cytoskeleton components, new axonplasm
-diffuses through the axon?
Does fast transport require ATP?
yes
What does fast transport do?
- components are made in one area of neuron and shipped to another
Which way does fast transport go?
- both ways
-anterograde (cell body to axon terminal) or retrograde (axon to cell body) - Antero moves vesicles, organelles, glycoproteins
- Retrograde can be used to move vesicles
-inside axon
What is a negative to retrograde transport?
- can be hacked by infections to effect the cell
What do glial cells do?
- support neurons
Do glial cells carry Ap?
- no (not firing)
What are glial cells
-nonexcitable mitotic support cells found in CNS and PNS
Are glial cells excitable?
no
Which glial cells are in the CNS?
-oligodendrocytes
-astrocytes
-microglial
- ependymal
Which glial cells are in the PNS?
-Satellite cell function
- neurolemocytes
Are there more neurons or glial cells?
- glial cells
- 1/2 the volume of the nervous system
What are all glial cells good for?
- critical function at neural synapses
What do astrocytes do?
- forms part of the blood-brain barrier
-regulates interstitial fluid composition within CNS - assists with neuronal development
- provides structural support and organization
How do astrocytes provide structural support and organization?
- can act as a filler for things like dead neurons
-replicates itself to do that
What do oligodendrocytes do ?
- myelinates and insulates axons in the CNS
- has multiple extensions to reach out to various neuron axons allowing one oligodendrocyte cell to multiple neuron axons
What does myelin do?
-allows for faster AP conduction
What do microglial do?
- phagocytic
-essentially WBCs of the neurons - monitors neuronal health
What do ependymal cells do?
lines ventricles of brain and central canal of spinal cord
-assists with production and circulation of CSF
What do satelite cells do?
- electrically insulates PNS
- regulates nutrient and waste exchange for cell
- monitors health
What are neurolenmoyctes?
- associated with axon and PNS of neurons
- partially surround unmyelinated axons and form myelin sheaths of myelinated axons
What do positive signals do?
- excitatory, depolarizing
What do negative signals do?
- inhibitory, hyperpolarization
What are dendrites?
-short unmyelinated processes branching off the cell body
What do dendrites do?
- receives input and transfers signal to cell body
- receives graded potentials when we have chemically gated channels
What does the cell body contain?
nucleus and organelles
What does the cell body do?
- receives signals and transfers them to axon hillock region
What is the axon hillock?
-contains the initial segment where summation of inputs occurs to determine if threshold is met
Can an AP be partially sent?
no
full send only
What does AP depend on
voltage gated channels
What happens if threshold is met?
- an AP is initiated in the axon Hillock region and conducted down axon
Is the axon the receiving end?
no
What does the axon do?
conducts AP from azon hilcock region to axon terminal
Are all axons myelinated?
no
What happens when an AP reaches the axon?
- NTs released from axon terminal (synaptic knob region) in response
What are post synaptic potentials?
- graded potentials that change the membrane potential
How do AP effectors come in?
-ligand/chemically gated receptors
Where do post-synaptic potentials rest?
depolarization or hyperpolarization of the membrane
Are all post synaptic potentials the same strength?
- no, they vary in strength and decrease with distance over time
How does increasing the distance traveled affect post synaptic potentials?
- they decrease their strength
Are ions distributed evenly across the membrane?
no
Why aren’t ions distributed evenly across the membrane?
- pumps
Where are the levels of Na+ higher
extracellular
Where are the levels of Cl- higher?
extracellular
Where are the levels of Ca2+ higer?
extracellular
Where are levels of K+ higher?
intracellular
What is the resting membrane potential?
- an electrical charge difference across the membrane (intracellular and extracellular face)
-inside is negative compared to outside
-70mv
How is the resting membrane potential maintained?
-leak channels
-NaK+ pumps
Do leak channels require ATP
no
What has the largest impact on RMP?
leak channels
Are there more K+ or Na+ leak channels
K+
Does the NaK+ pump require ATP?
yes
- in neurons, NaK+ pump can account for 75% energy expenses
What does the NaK+ pump do?
- produces ion movement against the gradient
-3Na+ out
-2K+ in
-(unequal movement of ions)
What are the types of receptive sements?
-chemically gated cation
-chemically gated K+
-chemically gated Cl-
What do chemically gated cation channels do?
- cause a net influx of Na+
- membrane potential becomes more positive
-causes depolarization
-excitatory
-moves 2 ions
What do chemically gated K+ channels do?
- net efflux of K+
-only moves K+ - causes hyperpolarization
- inhibitory
What do chemically gated Cl- channels do?
- net influx of Cl-
-movement of only Cl-
-hyperpolarization
-inhibitory
What are chemically gated channels caused by?
NT binding
Where do chemically gated channels occur?
postsynaptic membrane
Can chemically gated channels change the membrane potential?
-yes
-causes temporary small localized change in membrane potential
How do signals from gated channels vary?
- direction
-charge (hyper vs depolarization)
-strength of signals
-signals are multidirectional and weaken with distance
How do excitatory NT and EPSP get generated?
- presynaptic neuron releases excitatory NT which binds to chemically gated receptors
- chemically gated cation channels open, net Na= influx
3, the inside of the neuron becomes more positive - EPSP propagates toward axon hillock, and weakens with distance
How do inhibitory NT and IPSP get generated?
- inhibitory NT released from presynaptic neurons bind to chemically gated K+ and or Cl-channels
- K+ efflux and or CL- influx causing the inside of the neuron to become more negative
- IPSP propagates towards axon hillock, weakens with distance
What is temporal summation?
- the same presynaptic neuron initiates postsynaptic potentials rapidly within a narrow period of time
- like a tempo speeding up
How many synapses cause temporal summation?
- a single synapse
How does temporal summation change graded potentials?
they cause graded potentials to vary in strength
What is spatial summation?
- different presynaptic neurons initiate postsynaptic potentials within a narrow window of time
- looking at different spaces in time, the cumulative effect of released things at the moment
What happens if the IPSP and the EPSP are the same strength?
they cancel eachother out
How many synapses does spatial summation apply to?
2+
What is summation?
the cumulative impact of all simultaneously received graded potentials (IPSP and EPSP)
What is threshold?
- 15mv from RMP
- determines if an AP is initiated due to the opening of voltage-gated channels
Can an AP be partially generated?
no
all or nothing
Do AP lose intensity as they are propogated?
no
Can AP be triggered sub threshold?
no
Can you go from a negative number to a positive number when calculating AP propogation?
no it stops at 0
What is the charge of threshold?
-55mv
Describe voltage-gated Na+ channels.
- have activation and inactivation gate which allow for 3 different receptor states
- once activated receptor state cycles in sequence back to resting
-nothing binds to it, opened by changes in membrane potential (same for K+)
What are the three receptor states?
- resting state
-activation state
-inactivation state
What is the resting receptor state?
- channel closed
-inactivation gate opened - activation gate closed
What is the activation receptor state?
- channel open
-Na diffuses in
-inactivation and activation gate opened
What is the inactivation receptor state?
- channel closed
- activation gate opened
- inactivation gate closed
- lasts a short time, resets quickly
What is depolarization and what causes it?
- voltage gated Na+ channels open (activation state)
-Na+ influx makes the inside more positive resulting in a reversal of polarity - K+ channels closed
-peaks at about 30
Describe repolarization and what causes it?
- Na+ channels closed (inactivation state)
- K+ voltage gated channels open
-K+ efflux causes a return to RMP (-70)
Describe the return to RMP and what causes it?
- remains at -70 until a new signal is recieved
-maintained by Na+ and K+ leak channels and the NaK+ pump
-all voltage gated channels closed
Which receptor state allows movement through channels?
activation state
Can both gates be closed in the different receptor states?
no- one gate must always be open
What is the absolute refractory period?
-no ap can be generated
-Na+ v-gated channels are not in the resting state
-they are either open (activated) or closed (inactivated)
-ensures Ap only moves forward towards the terminal (synaptic knob)
What is the relative refractory period?
- can open but harder
-since its hyperpolarized its harder to get to the threshold - voltage-gated Na+ channel returned to resting state, but membrane is still hyperpolarized
What makes sure that AP is a unidirectional movement?
- refractory period
What initiates the release of the NT?
synaptic knob
What are the steps of myelination in the PNS?
- neurolemocyte starts to wrap around a portion of an axon
- neurolemocyte cytoplasm and plasma membrane begin to form consecutive layers around the axon as wrapping continues
- the overlapping inner layers of the neurolemmocyte plasma membrane form the myelin sheath
- eventually the neurolemocyte cytoplasm nucleus is pushed to the periphery of the cell as the myelin sheath is formed
Where does saltatory conduction occur?
unmyelinated regions of the axon (Nodes)
What characterizes nodes?
-no myelin
-high volume of Na+ and K+ voltage-gated channels present
What are the advantages of myelinated areas?
-Na+ diffuses through (part of saltatory conduction)
- well-insulated areas that have a limited number of voltage-gated Na+ K+ channels
What are the steps in saltatory conduction?
- Neurofibril (node) initiates Ap by having Na+ diffuse into the axon leading to AP conduction
- myelinated regions see diffusion through the axoplasm of the axon, the signal becomes weaker with distance
- next neurofibril nod sees the arrival of the weak Na+ current sufficient to cause opening of voltage-gated Na+ channels and a new AP is initiated
Where are NT released from?
-synaptic knob
How many NT can one neuron synthesize?
a NT can synthesize multiple NT but can only release one at a time
What determines what NT the neuron releases?
- dependent on the frequency of the AP that reaches the knob
Why are the NT effects on the postsynaptic membrane is short-lived?
- NT binding is temporary, and NT can diffuse away from the synapse
- NT may be moved back into the neuron through transport proteins and
- NT may be degraded by enzymes located at the synaptic cleft
What are the steps to NT transmission?
- AP reaches the synaptic knob
- v-gated Ca2+ channels open, Ca2+ enters knob and binds with proteins of synaptic vesicles
- synaptic vesicles merge with synaptic knob plasma membrane and NT released by exocytosis
- NT crosses synaptic cleft and attaches to receptors on a muscle or to receptors of a neuron or gland
