HPHY 322 Midterm 2
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- selectively permeable bi-layer
- lipid soluble substances diffuse easily
- otherwise require protein channel
ion movement across membrane
ion movement that requires interaction with a protein to move across membrane
- ion movement across membrane that requires interaction with protein and energy
- against the gradient
Na+/K+ ATPase Pump
pumps Na+ out and K+ in
How do neurons utilize protein channels in the membrane to create a system of neuronal communication?
Through maintenance of electrochemical gradients and gated channel reactions, action potentials can occur and permit "communication" between cells/neurons.
Na+/K+ ATPase Pump
- maintains gradients
- helps produce negative membrane potential
- requires energy
- Electrical difference (voltage) when comparing the outside and inside of the cell membrane (mV)
- refer to the voltage inside the membrane relative to the outside
- calculates electrical potential required to balance a single ion's concentration gradient
The membrane potential of the cell combining information about multiple ions' permeability and concentrations
Resting membrane potential of most neurons is thought to be approximately...
between -70 and -90mV
Mechanisms of the Action Potential
- 1. Resting membrane potential
- 2. Depolarizing stimulus
- 3. membrane depolarizes to threshold. Voltage-gated Na+ channels open and Na+ enters cell. Voltage-gated K+ channels begin to open slowly.
- 4. Rapid Na+ entry depolarizes cell.
- 5. Na+ channels close and slower K+ channels open.
- 6. K+ moves from cell to extracellular fluid
- 7. K+ channels remain open and additional K+ leaves cell, hyperpolarizing it.
- 8. Voltage gated K+ channels close, some K+ enters cell through leak channels.
- 9. Cell returns to resting ion permeability and resting membrane potential.
Relative Refractory Period
Next action potential can being during relative refractory period, but only if there is a more positive graded potential than usually necessary to meet threshold
starts above threshold at its initiation point but decreases in strength as it travels through the cell body
Cell-to-Cell Communication Via Synapses
- 1. action potential depolarizes the axon terminal
- 2. depolarization opens voltage gated Ca2+ channels and Ca2+ enters the cell
- 3. Calcium triggers exocytosis of synaptic vesicle contents
- 4. neurotransmitter diffuses across the synaptic cleft and binds with receptors on the postsynaptic cell
How is neurotransmitter/receptor coupling "deactivated"?
- 1. NT degraded by enzymes on receptor protein
- 2. NT re-sequestered into presynaptic axon terminal or diffuses away from synapse
found on ion channels
- activate a G-protein complex which results in:
- 1. ion channel opening
- 2. 2nd messenger activation
What is the difference between an excitatory and inhibitory synapse or stimulus?
Whether the stimulus causes the membrane potential to become more positive (excitatory) or more negative (inhibitory).
What systems of the body utilize the actions of G-proteins?
- cardiac muscle
- smooth muscle
- odor receptors
G-Proteins bind to? How many subunits does the G-Protein have?
- guanosine nucleotides
- three- alpha, beta, gamma
What is bound to the G-Protein in the inactive state?
GDP (guanosine diphosphate)
When the G-Protein couple receptor is bound to its ligand, what happens to the GDP?
conformational change on G-Protein causes GDP to be swapped for GTP and the G-Protein complex is associated with receptor
What can activated G-alpha subunit do?
- 1. open an ion channel
- 2. affect intracellular enzymes
- b)phospholipase C
What does adenylate cyclase do?
- converts ATP into cAMP
- cAMPa activates Protein Kinase A (PKA)
What can Protein Kinase A (PKA) do?
can phosphorylate (activate) a protein
Stimulatory vs Inhibitory G alpha
- stimulatory- causes adenylate cyclase to increase production of cAMP
- inhibitory- causes adenylate cyclase to decrease production of cAMP
When G-alpha-q is activated...
- stimulates phospholipase c (PLC)
- PLC cleaves phosphondylinositol (PIP2) into: diacylglycerol (DAG) + Inositol triphosphate (IP3).
cAMP, IP3 & DAG
Effects of G-Protein Alpha q
receptors found on the sarcolemma at the NMJ
What happens at the NMJ?
acetlycholine activates nicotinic receptors (opening chemically gated channels on the sarcolemma) leading to sodium influx
What is triggered on the NMJ once the membrane potential is less negative?
voltage gated Na+ channels open and action potentials move along sarcolemma
at rest where is the highest concentration of calcium in the muscle?
When AP reaches voltage-triggered DHP receptors it leads to...
mechanical change in ryanodine channels on the SR
Excitation-Contraction Coupling from NMJ to SR
- 1. ACh released from alpha motorneuron at the NMJ
- 2. AP in sarcolemma and T-tubules
- 3. DHP receptors in T-tubules react to depolarization
- 4. open ryanodine Ca2+ channels on SR
What blocks the myosin head from binding with G-actin at rest?
- 3 polypeptides
- TnI- binds to actin
- TnT- binds to tropomyosin
- TnC- binds to Ca2+
What is necessary for sequential myosin head power strokes (muscle contraction) to occur?
- 1. action potential from motor neuron
- 2. calcium released from SR
- 3. available ATP
Bands/Zones during contraction
- 1. Z-lines move closer together
- 2. sarcomeres shorten
- 3. I bands shorten
- 4. A bands stay the same length
- 5. H bands shorten
myosin head moves to "cocked" (90 degree) position when...
ATP is broken down into ADP+Pi at the myosin head
Molecular Basis of Contraction
- 1. rigor state- tight binding between G-actin and myosin
- 2. ATP binds to myosin head - dissociation
- 3. myosin head ATPase breaks down ATP into ADP+Pi
- 4. released energy changes angle between myosin head and myosin filament ("cocked" position)
- 5. power stroke: ADP + Pi are released
- 6. back to rigor state
two-way highway, plus reflex control
all but cerebral cortex; unconscious control
cerebral cortex; thinking & memory integration
muscle spindles send action potentials along afferent neurons to synapse at the spinal cord with alpha motor neurons to the agonist muscle
- afferent information to CNS regarding
- 1. length
- 2. rate of change in length
Golgi Tendon Organs
- afferent information to CNS regarding:
- 1. tension
- 2. rate of change in tension
What are the various aspects of a sensory-motor response that affect time?
- 1. complexity of receptor
- 2. fiber type/size & distance travelled
- 3. number of synapses
A (I-II) neurons
- large to medium in size
What allows for better 2-point discrimination on some areas of the skin compared to others?
- size of receptor field per afferent neuron
- receptor density
- "lateral inhibition"
- convergence of first order neurons onto second order neurons
achetylcholine, norepinepherine, epinepherine
- mostly release norepinephrine
- some epinephrine
- few acetylcholine
what is special about the adrenal gland?
- cells of the adrenal gland originated embryologically as nervous tissue and are rudimentary postganglionic neurons that secrete neurotransmitters into blood
- epinephrine 80%
- norepinephrine 20%
sympathetic vs. parasympatheic
muscarinic cholinergic & adrenergic receptors are both...
g-protein couple receptors that open ion channels directly or produce second messengers
Why is parasympathetic fastest but sympathetic longer in duration of response?
- parasympathetic- long presynaptic neurons are myelinated and fast
- sympathetic- medulla of adrenal glands release epi into bloodstream which takes time to clear
neurologic dysfunction from biomechanical force
diffuse axonal injury
a type of brain injury caused by shearing forces that occur between different parts of the brain as a result of rotational acceleration
what happens when don't get enough glucose to the brain?
- - inability to clean up excess K+
- - inability to transmit signals
under normal conditions cerebral blood flow is tightly coupled to
- neuronal activity
- metabolic waste byproducts
symptoms of reduced CBF
- persisting symptoms
- exertion-based symptoms (headache)
vision steps (3)
- 1.light enters eye: focused by lens onto the retina
- 2. photoreceptors transduce light energy: change it into electrical signals
- 3. Electrical signals transmitted to brain: eventually allows visual perception.
through retinal cells, is absorbed in posterior layer of eyeball, then stimulates the photoreceptors.
dim light, night vision, black & white, dominate periphery of retina
color vision, mostly cones are found in fovea
What absorbs the light and prevents reflection within the eye?
Melanin in pigmented epithelium
First step in the process of transducing light?
- photochemical rhodopsin changes from 11-cis to all-trans
- changes to its activated form
generic g-protein vs. light g-protein
- ligand - photon
- coupled g-protein receptor - rhodopsin
- g-protein - transducin
- breaks down cAMP or cGMP
what happens to rhodopsin when it absorbs light?
changes shape and activates g-protein transducin
whats going on in the rod?
- 1. cGMP gated channels = Na & Ca influx
- 2. K leak channels, allowing efflux
- 3. Na/K ATPase pump
- -40mV membrane potential
when light activates a rod cell does it hyperpolarize or depolarize it?
- rhodopsin is inactive
- cGMP is high
- and ion channels are open
- releases neurotransmitters
- light bleaches rhodopsin
- opsin decreases cGMP
- ion channels are open
- does not release NT
how does hyperpolarization affect glutamate release?
decreases NT release
vertical circuit synapses
rods and cone synapse with bipolar neurons which synapse with ganglion cells
optic nerve is made of
ganglion cell axons
optic neve fibers terminate
in the lateral geniculate nucleus of the thalamus
- perception of frequencies
- higher frequency = higher pitch
- normal from 20-20,000Hz
- perception of intensity
- normal 0-120 dB
middle ear gain
- ossicular coupling
- transfers energy from tympanic membrane to the foot plate of stapes
acoustic coupling vs ossicular coupling
works at low frequencies , works at high frequencies
cells of spiral organ
- supporting cells
- one row of inner hairs
- three rows of outer hairs
shearing forces caused by
different pivotal points
deflection of stereocilia
- opens mechanically gated ion channels
- inward K and Ca current causes graded potential and release of NT glutamate
- cochlear fibers transmit impulses to the brain
deflection away from kinocllium
- close K channels
deflection towards kinocillium
- opens channels
- increase NT
at rest stereoclia
- some channels open
- no stimulus
defelction towards longest cillium
- all channels open
deflection away from longest cillium
- all channels close
double the ability to perform exocytosis
what is required for exocytosis
- Ca & Ca channel
- action potential
outer hair cells
inervated by efferent neurons
inner hair cells
send afferent signals
Low frequency sound causes which portion of the basilar membrane to vibrate?
the portion closes to the apex
high frequency cause which portion of the basilar membrane to vibrate?
the portion close to stapes
For both taste and smell what happens prior to the chemicals stimulating the receptors?
disolved in aqueous solution mucus or saliva
How does a taste cell convert chemical signals into action potentials?
- the taste receptor cell depolarizes when stimulated due to opening of ion channels or 2nd messenger actions
- the taste receptor cell releases a NT onto the sensory nerve fibers, which transmits the signal via action potential
Which cranial nerves carry info about taste to the brain?
vagus, glossopharyngeal, facial
afferent info regarding taste continues to which areas in the brain?
- brain stem
- sensory cortex
- gustatory cortex (insula)
- taste stimuli produce this reflex
- synapse in the thalamus with efferent neurons to salivary glands
How is the stimulus from a chemical odorant converted into neuronal signals?
- G-protein coupled receptor in cilia
- activates adenylate cyclase
- increases cAMP
- opens cAMP gated sodium channels
- depolarization of cell beyond -55mV
in gustatory and olfactory cells, where are the receptors located?
in the membrane of the cilia or hairs
- reflexes related to salvation- hypothalamus & limbic system
- memory of food likes and dislikes- hippocampus and/or cortex
- analysis of smells- thalamus & frontal cortex
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