Exam 2 Slides Flashcards
Action Potential
Triggered by stimulus exceeding threshold potential/ gated ion channels open and close
Absolute Refractory Period:
No stimulus of any strength can produce an action potential
- Due to inactivated Na+ channels
Relative Refractory period:
Strong stimulus can produce another AP, but with smaller amplitude
- Due to still open K+ channels
What happens to membrane potential during continuous stimulation?
Excitability of membrane decreases with time (threshold increases)
- Is Due to changes in sensitivity of membrane channels to depolarization
- This physiological change is called accommodation
Length constant:
distance over which a graded potential shows a 63% drop in amplitude.
Spreading of electrical signal is due to?
cable properties of nerve membrane.
The larger the length constant?
the further away a new AP will be generated, and the faster the propagation of APs.
Synapse:
connection between two neurons or a neuron and an effector cell
Electrical Synapse
Rapid transmission of signals. Faster than in chemical synapses!
- Used to synchronize electrical activity in groups of cells: e.g. vertebrate heart, oscillations and brain rhythms.
Chemical synapse: fast transmission
- NT release close to receptors.
- Receptors directly open ion channels (ionotropic).
- Small vesicles
Chemical synapse: slow transmission
- NT release distant from receptors.
- Receptors indirectly open ion channels (metabotropic).
- Large vesicles
Active zone:
area of NT release
Acetylcholine
Primary neurotransmitter at vertebrate neuromuscular junction
If depolarization exceeds threshold
Yes AP
If depolarization does not exceed threshold
No AP
Change in membrane potential is a
graded potential
If ion current depolarizes the membrane?
excitatory
- stimulates an AP in the postsynaptic cell
If ion current hyperpolarizes the membrane?
inhibitory
- prevents an AP in the postsynaptic cell
Opening Na+ or Ca2+ channels results in a graded depolarization called an?
excitatory postsynaptic potential
Opening K+ or Cl− channels results in a graded hyperpolarization called an
inhibitory postsynaptic potential
EPSPs move membrane potential
closer to threshold
- EPSPs from several neurons may be needed to actually produce action potential
IPSPs move membrane potential
farther from threshold
- Can counter EPSPs from other neurons
Summation of EPSPs and IPSPs at initial segment of axon dose what?
determines whether action potential occurs.
Presynaptic Inhibition
Inhibitory synapse on top of an excitatory synapse
Strychnine dose what?
binds to and blocks glycine receptors in the spinal cord.
Function of Sensory System
- Signal detection
2.Discrimination of some aspects of the sensory input
Receptor cell sends
- intensity of stimulus
frequency of APs - location of stimulus
receptive field
Receptive Field
Area of skin that, when stimulated, changes the firing rate of a neuron
The more receptors, the
smaller the field, the larger the brain area for processing.
Sensory Acuity
Ability to detect details
Degree of convergence of primary neurons on secondary neurons determines?
size of receptive field.
Range fractionation:
different cells with different but overlapping sensitivities, extending dynamic range
Phasic response:
Firing activity only when stimulus strength changes (on/off)
Tonic response:
Firing activity continues for the duration of the stimulus
Lateral Inhibition can occur with?
a group of adjacent receptor cells, such as found in the eye.
Olfactory
pathways from the nose project directly to the cortex
More brain area means
more information processing and relatively more important
Stimulus energy is “converted” to
action potential energy.
Signals are interpreted as sight, sound, taste, depending on
which sensory cells send the signal and which tissue in CNS receives it!
GUSTATION is what sense
Taste
Salty
Na+ entry: depolarization: NT release
Sour
H+ entry: depolarization: NT release.
Sweet and umami
Sugar or glutamate binds to receptor: closing K+ channels: depolarization: NT release.
Bitter
Quinine binds to receptor: Ca2+ entry : NT release
Labeled-Line Coding:
each receptor responds to limited range of stimuli and sends direct line to brain.
Across-Fiber Pattern or Ensemble Coding:
each receptor responds to wider range of stimuli and contributes to perception of each of them.
Cone cells:
less sensitive, distinguish colors.
Neural pathways for vision
Object on right goes to brain on left: Information crosses over!
Hair cells modulate release of NT:
Change in AP frequency above spontaneous frequency.
Actin
thin filament
Myosin
thick filament
Sarcomere:
functional unit of contraction
Z disk to Z disk
Sliding Filament Theory
Thin actin filaments slide past the thick myosin filaments
- More overlap, shorter sarcomere
Myosin structure
- Myosin heads stick out from the thick filament.
- Myosin connect with actin and sliding of the filaments occurs.
Cross bridge function
- Myosin cross bridge binds to actin
- Power stroke slides actin past myosin
- Cross bridge releases actin
T tubules
Narrow tunnels formed from the plasma membrane (sarcolemma)
Extend into center of cell
Muscle relaxation
Nerve action potentials stop
Muscle action potentials stop
Calcium-release channels close
Ca2+ pumps move Ca2+ back into SR (active transport)
No more Ca2+ is available to bind to troponin complex
Tropomyosin moves over myosin-binding sites on actin, no cross-bridges possible.
