Nerve, Muscle, Synapse Physiology Flashcards
3 types of neurons
Afferent neurons - take info from periphery to CNS, contact efferent of interneurons, excitatory, PNS
Efferent neurons - take info from CNS to periphery, contact onto muscle, excitatory, PNS
Interneurons - carry info between neurons, contatct efferent or interneurons, excitatory or inhibitory, CNS
Glia
- glue of nervous system
- numerous and small
- Oligodendrocytes - myelin in CNS
- Schwann cells - myelin in PNS
Gray matter
in spinal cord
horn/butterfly shape
unmyelinated axons and interneurons
White matter
in spinal cord
surrounds horn/butterfly shape
myelinated axons
Afferent neurons use the _____ route
dorsal - back
Efferent neurons use the _____ route
ventral - front
Myelin
lipid protein mix
wrapped around axon (ensheathing)
acts as an insulator and does not allow ions to move across axon where myelin is present
quickens the speed of electronic conduction
Dendrites
receive information from periphery or other cells
Cell body
contains nucleus, also called soma
Axon hillock
Initial segment of axon, processes info coming from dendrites and generates nerve impulse if reaches threshold
Axon
propagates nerve impulse from axon hillock to axon terminal
Axon terminal/synaptic terminal
contains neurotransmitter in synaptic vesicles
Synapse
junction between 2 neurons
Presynaptic neuron
the neuron before the synapse
Postsynaptic neuron
the neuron after the synapse
Membrane of neuron
Phospholipid bilayer
Contains protein pumps - active transport
Contains ion channels - passive transport: passive channels, ligand-gated channels, voltage-gated channels
Resting membrane potential
- charge separation between inside and outside of cell at steady state
- around -70 mV
- important ions are Na+ and K+
Na+/K+ pump
3 Na+ pumped out of cell
2 K+ pumped into cell
Net +1 out of cell for each cycle
Net negative change inside cell
Uses ATP
Creates Na+ and K+ gradients
Leak K+ channels
Chemical force pushes K+ out of cell
Electrical force pushes K+ into cell
Equilibrium potential: -90 mV
K+ will move out of cell
More leak channels for K+ - greater membrane permeability
Leak Na+ channels
Chemical force pushed Na+ into cell
Electrical force pushed Na+ into cell
Equilibrium potential: +55 mV
Na+ will move into cell
Less leak channels for Na+
- Stimuli
disrupts steady state by causing ion selective channels in membrane to open
increased opening of Na+ receptors and entry of Na+ into afferent neuron
DEPOLARIZATION to reach threshold
- Threshold
around -50 mV
if neuron reaches this level then action potential is generated
voltage-gated Na+ channels open, activation gate is removed
- Action potential
electrical signals generated by activity of Na+ rushing in by voltage gated Na+ channels
-70 mV to +30 mV
- Repolarization
inactivation gate closes Na+ voltage channel
activation gate opens K+ channel and K+ leaves cell and takes positive charge with it
- Refractory period
Absolute refractory period - another action potential cannot be generated in response to stimulus due to inactivation of voltage-gated Na+ channels
Relative refractory period - another action potential will only be generated if stimulus is greater strength then usual threshold
Conductance
rate of ion travel through a channel
Action potentials: transmission
local depolarization of membrane causes adjacent voltage-gated Na+ channels to activate
new action potential is generated in adjacent membrane
transmitted from segment to segment along the axon
travels one direction due to refractory period
Electronic conduction
spread of current inside axon due to depolarization of segment to segments
proceeds in one direction
at node of Ranvier
Nodes of Ranvier
on a myelinated axon, it is an unmyelinated region
contain voltage gates Na+ channels
electronic conduction
Nodes of Ranvier PNS
single Schwan cell myelinates one segment of axon
Nodes of Ranvier CNS
single oligodendrocyte myelinates several axons and several regions of given axon
Saltatory conudction
propagation of action potential along myelinated axon such that action potentials jump from one node of Ranvier to another node
action potential can pass undiminished in size from each node
2 factors which determine speed or propagation
Size of the axon: the thicker the faster
Myelination: faster than unmyelinated
Synaptic transmission
one neuron communicates with other neuron or effecter at a synapse
action potential at presynaptic terminal depolarizes and opens voltage gated calcium channels to open
calcium causes vesicles containing neutrotransmitters to move to and fuse with membrane
Electrical synapse
physical connection between 2 very close cells
passage of ions and small molecules
connexin: protein channel
flows both ways
open or closed
fast communication
always excitatory
Chemical synapse
presynaptic and postsynaptic cell with no physical connection - definitive gap called synaptic cleft
one direction only
directly gated: receptor and ion channel are same protein, fast short lasting
indirectly gated: receptor and ion channel are different protein, slow long lasting
Neurotransmitter
stores in presynaptic terminal in synaptic vesicle
released from vesicle into synaptic gap and binds to receptors of postsynaptic cell and ligand gated ion channels
causes opening of ion channels on postsynaptic cell to either depolarize or hyperpolarize
either inhibitory or excitatory not both
Excitatory neutrotransmitter
glutamate released by excitatory neurons
will open a Na+ channel when bound, Na+ into cell
depolarization
excitatory post synaptic potential is generated (EPSP)
Inhibitory neutrotransmitter
glycine or GABA released by inhibitory neurons
will open a Cl- or K+ channel, Cl- into cell, K+ out of cell
hyperpolarization
inhibitory post synaptic potential is generated (IPSP)
Chemical synapses - indirectly gated
Neurotransmitter binds to receptor and activates 2nd messenger system
G protein - GTP activates adenylyl cyclase which converts ATP into cAMP - second messenger
cAMP activates protein kinases which phosphorylates a channel and causes it to open or close
Synaptic potential and integration
synaptic potentials decay as they travel away from the synapse
can only travel short distances INTEGRATION
axon hillock constantly calculates total amount of excitation and inhibition
Post synaptic potentials
generate enough depolarizations to bring to threshold and produce action potential by summation as they are only 0.2 mV by themselves
2 types of summation
Temporal: multiple PSPs from single presynaptic neuron arrive at cell body at same time
Spatial: multiple PSPs from different presynaptic neurons arrive at cell body at same time
Can receive EPSP and IPSP at same time and net voltage will occur
Complexity of behaviour
the exact same stimulus in two different situations can generate two completely different responses
because of an increase or decrease of inhibition or excitation of different neurons within a pathway
AP vs PSP: amplitude
AP: same size, depolarizing, all or nothing
PSP: small, depolarizing or hyperpolarizing
AP vs PSP: duration
AP: short duration (2-3 ms)
PSP: long duration (10-20 ms)
AP vs PSP: location
AP: initiated at axon hillock and transmitted down the axon to synaptic terminal
PSP: initiated at dendrites or soma as this is where synapse is location
AP vs PSP: conduction
AP: active, long distance, regenerate at each point
PSP: passive, short distance, decrease in amplitude
AP vs PSP: function
AP: generated if threshold is reached ad will travel to synaptic terminal to initiate neurotransmitter release
PSP: change electrical potential of post synaptic neuron, either depolarizing or hyperpolarizing based on neurotransmitter
PSP will trigger AP when axon hillock is depolarized to threshold
Skeletal muscle
muscle attached to skeleton, striated muscle, contraction is under voluntary control
Endomysium
membrane that sits over each muscle cell and electrically isolates the muscles cells from each other
Motor unit
the motor neuron (efferent neuron), its axon and all muscle fibers it activates
smallest increment of force that generates in a muscle
each muscle fiber has only one synapse
Neuromuscular Junction (NMJ)
synapse/synaptic cleft between efferent/motor neuron and muscle fiber
muscle fiber is the post synaptic cell
directly gated chemical synaptic transmission - opening of calcium channels
motor end plate - region of muscle fiber plasma that lies directly under terminal axon
Neuromuscular junction neutrotransmitter
Acetylcholine (ACH) - excitatory
binds to nicotinic receptors on postsynaptic membrane
nicotinic receptors open and allow Na+ to enter muscle cell (local depolarization)
no summation
no inhibitory transmitters
Motor neuron (muscle efferent neuron)
muscle cell = postsynaptic cell
one axon terminal synapses with one muscle cell
Transverse tubule (T-tubule)
extracellular space of muscle fiber that is positively charged with respect to negatively charged intracellular space
Action potential with T-tubule
- conformational change in DHP receptor
- through foot process opens ryanodine receptor channel located in sarcoplasmic reticulum
- calcium rushed out of sarcoplasmic reticulum into cytosol of muscle cell
- calcium interacts with contractile elements to produce a contraction
DHP receptor is physically coupled with _____
ryanodine receptor through foot process
Sarcomere
structural unit of a myofibril striated muscle
bound on either side by Z-lines (network of proteins)
contractile elements are the myofilaments
thick filaments - myosin
think filaments - actin
Myosin
forms thick filament
long tail with 2 globular heads (cross-bridges) attached to tails
Globular head myosin binding sites
top of head - actin
based of head - ATP
Myosin energy states
low energy state - head is bent and bound to ATP
high energy state - head if flat and bound to ADP
Actin
primary protein in thin filament
binding site for myosin
Tropomyosin
regulatory protein bound to actin
double helical shaped strand which wraps around actin and covers myosin binding sites
Troponin
calcium is released by sarcoplasmic reticulum after action potential and binds to troponin
troponin moves tropomyosin away from blocked myosin sites
Cross-bridge cycling
- calcium binds to troponin on thin filament causing tropomyosin to be dragged away and expose binding site
- high energy state ADP myosin binds to actin
- power stroke: myosin head pivots forward causing H zone to shorten, release of ADP
- low energy ATP myosin is bent forward and is released from actin
- re-energizing and repositioning of cross bridges and ATP converts to ADP
- removal of calcium ions back to sarcoplasmic reticulum, troponin/tropomyosin complex covers actin binding sites
calcium pump
active transport with ATP
after muscle contraction is complete, calcium moves back into sarcoplasmic reticulum
3 roles of ATP in muscle contraction
- energizing power stroke of myosin cross-bridge
- disconnecting myosin cross-bridge from binding site of actin
- pumping Ca2+ back into sarcoplasmic reticulum
2 types of muscle fibers
White: fast twitch, short lasting, large, high glycogen content, glycolysis, sprint
Red: slow twitch, long lasting, small, myoglobin, high blood supply, Krebs cycle and oxidative phosphorylation, endurance
Myoglobin
primary oxygen carrying protein of muscle tissues
Capillaries
bring oxygen to muscle cells
Glyocgen
storage form of glucose, broken down to release glucose
Glycolysis
use glucose to make ATP in absence of oxygen
