Unit 5 Lecture Flashcards
What are the two types of cells?
- Nerve Cells (Neurons)
- Involved in the generation and interpretation of ‘Electrical Signals’
- Glial Cells (Neuroglia)
- Support neuronal cell activity
What do the dendrites, cell body, axon, and synapses do?
- Dendrites
- Collect information
- Cell Body
- Process Information
- Axon
- Propagate info
- Synapses
- Transmit info
What are the two components of bioelectricity
Resting Membrane Potential
Action Potential
What is the resting membrane potential and what are the 2 parameters that it depends on?
- Baseline electrical conditions (of ALL cells)
- Depends on 2 parameters
- Transmembrane ion gradients (particularly Na+ and K+)
- Membrane permeability to those ions
What do ion concentrations look like for a resting membrane potential in a muscle cell interior
How is the resting membrane potential maintained?
- Ion gradients!!!
- 3 sodium is pumped out of the cell and 2 potassium are pumped into the cell
- K+ leak channels present in all cells
- Na, K-ATPase develops and maintains steady-state ion gradients for ALL cells
- Notice the inside it negitive outside is positive
- 3 sodium is pumped out of the cell and 2 potassium are pumped into the cell
- Permeability
- K has leak channels (highly permeable)
- Not very permeable to sodium
What are three key points about the resting membrane potential and the intracellular (cytoplasm) vs extracellular areas
- Pumping creates ionic gradient for K+
- K+ “leaks” out, down its concentration gradient, so that the inside of the cells becomes more negative
- Now two kinds of forces push/pull on K+ (chemical and electrical)
What are the 2 opposing forces regarding resting membrane potential?
- Chemical and electrical
- Chemical forces (K+ gradient)
- Tends to push K+ out
- Developed Electrical Force (inside negative)
- Tends to pull K+ in
- Chemical forces (K+ gradient)
What is in a typical cell (includinh neuronal cells)
- Chemical and electrical forces for K+ are nearly in balance
- What does that mean to us?
- Outwardly-directed K+ gradient results in an inside-negative electrical potential
What is the typical electrical potential difference?
Typical value -0.05 volts to -0.1 volts
What is a characteristic of all cells at rest?
K+ dominated inside-negative membrane potential. K+ dominates because it has so many leak channels in the membranes
What does the distribution of ions during a resting membrane potential lookl ike?
What does the distribution of charges look like regarding resting membrane potential?
What can changes in ‘Membrane permeability’ do?
Can produce large changes in the ‘membrane potential’
Membrane permeability to an ion (K+ or Na+) = open channels for that ion
What are keys to manipulation of membrane potential
- Maintain (stable) Na+ and K+ gradients (Na/K ATPase)
- Vary the activity of specific ion channels
How are membrane permeabilities manipulated?
- Ion channels
- Integral membrane proteins
- Channels can be “open” or “closed”
- Some channels are routinely open
- e.g. K-leak channel is the basis of the inside-negative resting membrane potential
- Some channels have their open states regulated
Discuss how some channels have their open states regulated
- Chemically (ligand)-gated channels open when a signal molecule binds to the channel protein (ACh)
- Mechanically-gated channels open when membrane gets stretched
- Voltage-gated channels open when the membrane potential gets less negative ‘depolarized’
What does it mean that neurons are ‘excitable cells’
In Nerve and muscles, can change membrane potential to generate an electrical signal
What is the principal mechanism for a neuronal action potential
Voltage-gated Na+ Channel
What is the first step of the chain of events in the generation of the action potential?
- Local change in membrane potential
- Such local changes can be hyperpolarizing (more negative) or depolarizing (less negative)
- (‘graded’ potentials)
What does an action potential begin with
A local depolarization
Discuss what graded potentials are
- Occur in dendrites and cell body of neuron
- Size varies with strength of stimulus
- Usually generated by chemically and mechanically gated channels
What are the two types of graded potentials?
- Inhibitory Post-Synaptic Potential (IPSP)
- Excitatory Post-Synaptic Potential (EPSP)
What is the second step of the chain of events in the generation of the action potential?
Depolarization to a threshold value induces a population of voltage-gated Na-channels within the local region of membrane to open….
What is the third step of the chain of events in the generation of the action potential?
Critical point: shortly after Na-Channels open, -> They spontaneously close ‘inactivation’
What is the fourth step of the chain of events in the generation of the action potential?
Depolarization also opens (more slowly) a second population of channels: Voltage-gated K channels
-Inactivation of the voltage-gated Na-Channels, combined with activity of the voltage gated K-channels results in ‘repolarization’ of membrane potential back toward the resting value
Look at the graded channels and the chart comparison
What is a refractory period?
Periods during which it is difficult or impossible to generate a second AP
What is an absolute refractory period vs a relative refractory period
- Absolute Refractory Period: Immediately following inactivation of Na-channels, membrane cannot be restimulated to produce AP
- Involves resetting of Na-channels
- Relative Refractory Period: A period during which a new AP can be produced, but it takes a larger than normal stimulation
- Involves resetting of K-channels
What is the importance of refractrory periods?
- Establish maxiumum rate of action potentials
- Influence the characteristics of AP propagation - forward propagation from axon hillock to axon terminal
What is the first step in the propagation of the Action potential?
- Entry of Na+ produces a ‘local current’
- Spreads laterally to depolarize adjacent areas of membrane
- If the adjacent membrane area is depolarized to ‘threshold’ it starts a new cycle of action potential in this new region of membrane
What is the second step in the propagation of the action potential?
- Entry of Na+ in the new region of membrane produces a local current that spreas to adjacent areas…
- If the ‘new’ adjacent membrane area is depolarized to ‘threshold’ it starts a new cycle of action potential in this ‘new’ new region of membrane
What are two factors that affect velocity of propagation?
- Size (diameter of axon)
- ‘Myelination’
Discuss size as a factor that affects velocity of propagation
Size: Bigger is Faster
Resistance to current flow in ‘axoplasm’ decreases as diameter increases
Discuss myelination as a factor that affects velocity of propagation
Certain glial cells (oligodendrocytes CNS and Schwann cells PNS) form insulating layer (‘sheath’) around axons
Discuss saltatory conduction:
- Jumping conduction
- When sodium comes into one channel is opens channels at next node and the previous nodes become refractory
Look at continuous conduction versus saltatory conduction in an axon
Explain demyelination
How is an electrical signal (Action Potential) transmitted from one excitable cell to another?
Synaptic Transmission
-Same general events that occur during neuromuscular transmission
Look at the pre and post-synaptic cells
These ‘post-synaptic’ electrical events (graded potentials) are:
- Depolarizing (If Na+ enters)
- Excitatory post-synaptoc potential: EPSP
- Hyperpolarizaing (If K+ leaves; or Cl- enters)
- Inhibitory Post-Synaptic Potential: IPSP
Discuss spatial summation
Discuss temporal summation
What are general senses?
Receptors distributed throughout body (particularly on body surfaces)
-Not collected within specialized ‘sense organs’
What are 4 types of general sense?
- Pain (nociceptors)
- Temperature (thermoreceptors)
- Touch, pressure, body postion (mechanoreceptors)
- Chemical stimuli (chemoreceptors)
What are somatic senses?
Body surface
Surface temp, touch, pain, and muscle soreness
What are visceral senses?
Internal organs
-Stomach ache, ‘gut cramps’ etc.
What are special senses?
Receptors congregated in specialized ‘sense organs’
What are the five types of special sense?
- Smell (olfactory)-nose
- Taste (gustation)-tongue
- Sight (vision)-eye
- Balance/equilibrium-ear
- Sound (hearing)-ear
Regardless of stimulus ‘________’ all sensation is ‘_____’ in the CNS as electrical signals
modality, read
Why can we discriminate between different types of stimuli?
We can discriminate between different types of stimuli because different receptor types respond preferentiallt to different stimuli
- A mechanoreceptor is more sensitive to tough than to light;
- A photoreceptor is more sensitive to light than to tough
What is a receptive field?
Discrimination between two similar stimuli (e.g., two points on body surface; two sounds of similar pitch) is dependent ont he number of receptors within an area of ‘sensory surface’
What do smaller receptive fields permit?
Smaller receptive fields (increased density of receptors) permit high resolution discrimination
What are the four common steps for sensory transduction?
- Stimulus arrives at receptor and alters membrane potential of receptor
- ‘graded potential’ depolarizing or hyperpolarizing
- ‘Receptor potential’
- ‘graded potential’ depolarizing or hyperpolarizing
- Receptor potential influences (directly or indirectly) rate of AP production in a sensory neuron (the ‘afferent pathway’)
- APs travel to CNS along afferent pathway
- CNS interprets/processes these incoming signals
Discuss interpretation of afferent (sensory) input in sensory transduction
The brain ‘assumes’ that any signals coming in along a sensory afferent from a particular receptor (e.g., touch; photoreceptor) reflects stimulation by the appropriate stimulus (i.e., pressure; photon)
-all other characteristics of the stimykys (e.g. intensity, duration) are conveyed by the frquency and pattern of the incoming signals
What are two critical issues associated with the special sense of vision?
- How is an image formed and displayed on the snesory surface of the eye?
- How is the stimulus of a photon striking the sensory surface ‘transduced’ into an electrical event
Look at the parts of the eye
What is the neural tunic?
It contains the photoreceptors
Look at the optics of the eye slide
How does refraction of light rays work
Where does refraction take place?
How does iris regulate based on light entry?
How does refracted light work within an eyeball?
What are the three steps of changing of lens shape (“accomodation”)
What does the lens look like from cross sections when accomidation of the lens occurs?
What is presbyopia?
- As lens ages, it loses elasticity - even when tension on the suspensory ligaments is relieved, lens retains its elongated shape
- Failure to ‘round up’ means the image of close-up objects cannot be focused on the retina
- Loss of this ability to accommodate means the ‘ages’ eye cant focus on close-up objects
How does Emmetropia, Hyperopia, and Myopia differ?
- Emmetropia = normal
- Hyperopia = farsightedness
- Myopia = nearsightedness
Discuss the retina
- Several cell layers
- Photoreceptor layer has 2 cell types
- Rods-monochromatic, very sensitive, dim light
- Cones - color vision, not as sensitive, bright light
- Neuron layers process the photoreceptor signal
- Ganglion cells carry the signal to the brain
Rods vs cones
Look at a rod photoreceptor cell
Look at visual receptor rod
Look at the process that leads to cell hyperpolarization
look at the light and dark in receptor cells
What are the 5 steps of rod phototransduction
Look at the external (outer) ear
Look at the middle ear
Look at the internal (inner) ear
Look at the whole ear model
How does sound move through the ear?
Where do we hear higher frequency sounds?
Closer to the oval window
What weird about endolymph
Perilymph is like CSF endolymph is weird it contains lots of K+ and extracellular fluid where typically cells contain a lot of inner K+
Look at the anatomy of hair cells
What happens when K+ enters the endolymph?
Summarize auditory transduction
What happens to crista when head rotates?
Discuss gravity and acceleration in the ear
Involves patterns of hair cell activation in the utricle and saccule
What are major events in neuromuscular funcation?
Summarize the key features of Neuromuscular Function
What are the major classes of neuromuscular disease?
What does neuromuscular defect look like?
What is Lambert Eaton Syndrome?
What is Myasthenia Gravis?
Discuss FWS Venom
What does ACTX blocking the sodium channel look like?
What are ACTX Effects on the Action Potential?
What are ACTX explained symptoms?
Explain the output of both branches of ANS with ACTX
What is a take home message about venom?
