Physiology 3140A Lecture Notes - Lecture 11: Lipid Bilayer, Biosynthesis, 45 Nanometer
2 May 2018
School
Department
Course
Professor
Physiology 3140 Lecture 11
October 4 2017
Electric currents for communications
- Electrical current/voltage in physical substance
- Electrical current/voltage in biological cells
- Following basic Physics!
Common electrical units used
Term
Unit
Typical range (electrophysiology)
Potential – V
Volt – V
mV (10-3V)
Current I
Ampere – A
nA (10-9 A), pA (10-12 A)
Resistance – R
Ohm - Ω
MΩ 6 Ω, GΩ 9 Ω
Conductance - G
Siemens - S
nS (10-9S), pS (10-12S)
Electrical voltage and current
- Current is produced by the movement of charges
o Charged particles moving in space produces current
- Direction of current is defined by the movement of positive charges from high to low electrical
potential (voltage)
o Direction of current is NOT defined by the actual movement of the particles; it depends on
what positive charge would move
- Higher the ball height = more electrical potential
- Steep slope = fast = higher current
Electric currents in excitable cells
- In biological tissues, electrical activities are carried by ions (not electrons as in metals)
- Ions = cations (+ ions) & anions (- ions)
- Cations: Na+, K+, Ca2+, Mg2+
- Anions: Cl-, HCO3-
find more resources at oneclass.com
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Ohm’s Law
- Amplitude of the current passing through the wire is proportional to the voltage applied to the
conductor, but inversely proportional to the resistance of the conductor
- Conductance is the INVERSE of resistance = 1/R
- Current is proportional to: conductance + voltage
ION CHANNELS
Brains, Neurons, and channels
- CNS has different communication between cells
- To study we reduce the brain into individual functional units
- Brain is organized by neurons
o Neurons take on different shapes: Unipolar, bipolar, multipolar
o Have same functional units
▪ Soma: carry DNA, messages needed for neuron to biosynthesize proteins required,
communication to neighbour cells
▪ Dendrites+ axons – excitable, can be electrically active
- Electrical activity in neurons is due to channels on the cell membrane
- Activity is due to the ion channels on the neuronal membrane
o Need it in order to fire action potential or have synaptic transmission
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Mmerane and ion channels
- Cell is covered by a thin membrane
- Phospholipid membrane
o Phospholipid bilayer; 4-5 nm
o Protein ion channels sitting on the membrane
▪ Ions can not pass through the lipid bilayer without it
▪ CHANNEL IS PROTEIN COMPLEX
- Important ions
o Na+, K+, Ca2+, Cl-
o Not evenly distributed
o More inside: K+
o More outside: Cl-, Na+, Ca2+
Ion channel
- Not passively sitting on the membrane
- Selectively filter that is a narrow part of the pore – what makes the channel selective to certain ions
o Classify which ion goes through the channel
- Gates: opens and closes the channel
o The sensor controls the gate -> senses changes to determine whether or not to open the
channel
- Ion channels are proteins that span the cell membrane to form pores, allowing charged ions to
traverse the generally impermeable lipid bilayer
o Can conduct ions
o Selective in MOST cases
o Open and close
o Sensor
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Typical range (electrophysiology) mv (10-3v) na (10-9 a), pa (10-12 a) M (cid:523)(cid:883)(cid:882)6 (cid:524), g (cid:523)(cid:883)(cid:882)9 (cid:524) ns (10-9s), ps (10-12s) Current is produced by the movement of charges: charged particles moving in space produces current. Higher the ball height = more electrical potential. In biological tissues, electrical activities are carried by ions (not electrons as in metals) Ions = cations (+ ions) & anions (- ions) Amplitude of the current passing through the wire is proportional to the voltage applied to the conductor, but inversely proportional to the resistance of the conductor. Conductance is the inverse of resistance = 1/r. To study we reduce the brain into individual functional units. Brain is organized by neurons: neurons take on different shapes: unipolar, bipolar, multipolar, have same functional units. Soma: carry dna, messages needed for neuron to biosynthesize proteins required, communication to neighbour cells: dendrites+ axons excitable, can be electrically active.
