PSIO Final Exam (BLOCK 5 ONLY)

What is membrane potential?

The difference in charge across a membrane

Limb generation/regeneration is caused by…

Bioelectric memory

• 0-7 year olds slightly capable

• Lost over time

What does membrane potential have control of?

• anatomical plan

• Excitable tissues

• Cell cycle

• Proliferation

• Cell volume

• Wound healing

• Hormone release

What are the two parameters that membrane potential relies on?

1. Transmembrane ion gradients

2. Membrane permeability to those ions

What happens during depolarization?

Positively charged ions (K+, Na+) come inside the cell, making the charge less negative/more positive

For every ___ Na+ ions exiting the cell, ___ K+ ions enter the cell

3;2

What happens during polarization?

Positively charged ions leave the cell, making the cell’s interior more negative

What are the chemical forces as it comes to movement across a membrane?

Concentration differences → chemical gradient

i.e. Na+ is higher in concentration on the extracellular side of the membrane, therefore it ‘wants’ to move inside

What are the electrical forces as it comes to movement across a membrane?

Electric attractions across a membrane; electrical gradient

i.e. Na+ is electrically attracted to the cell’s interior because it is negatively charged at rest

What is equilibrium potential?

When electrical and chemical forces are equal

• around -90mV for K+

• around +55mV for Na+

What are the equilibrium potentials for…

• Na+

• K+

• Cl-

• Positive

• Negative

• Negative

Glutamate is an example of a(n) ____ neurotransmitter

Excitatory

GABA is an example of a(n) ____ neurotransmitter

Inhibitory

GABA Channels are an example of what kind of transport protein?

Ligand-gated ion channel

____ leads to electrical signals

Change in membrane permeability

The membrane potential will move toward the equilibrium potential the membrane is ___ permeable to

Most!

What is graded potential?

Small, localized changes in membrane potential

• size varies with stimulus

• Can trigger action potentials if graded potential helps reach threshold for excitability

Inhibitory signals…

Makes the membrane potential more negative (polarizing/hyperpolarizing)

Excitatory signals…

Makes the membrane potential less negative/positive (depolarizing)

Absolute Refractory Period

During the most depolarized moment in the action potential; another action potential cannot be fired

Relative Refractory Period

During the most hyperpolarized moment in the action potential; another action potential could be fired, but it would require more energy

Dendrites have which two protein channels?

Ligand-gated ion channels

Mechanically-gated ion channels

What are two types of graded potentials?

1. Inhibitory Post-Synaptic Potential (IPSP)

   1. Hyperpolarizing

2. Excitatory Post-Synatic Potential

   1. Depolarizing

What does spatial summation look like in graded potentials?

Post-synaptic neurons recieving inputs from multiple different pre-synaptic neurons

Where is the action potential “decision” (whether to or not to fire) made?

Axon hillock

What are the steps of generating an action potential?

1. Local changes in the membrane potential (graded potentials)

   1. IPSPs and EPSPs

2. Depolarization to threshold

   1. Opens v-gated Na+ channels

   2. v-gated ion channels spontaneously close (inactivate)

3. Repolarization

   1. K+ channels open (“brakes”)

What happens to the neuron when Na+ ion channels close?

The neuron enters the refractory period (think repolarization)

What does the refractory period establish for a neuron?

The rate at which it can fire an action potential

What do refractory periods prevent?

Backward movement of action potentials

What is propagation with respect to the nervous system?

How an action potential travels down an axon

What two factors determine the velocity of propagation?

1. Size of diameter (axial resistance)

   1. larger diameter = lower resistance

2. Myelination

   1. Insulation → prevent ion leakage

How do unmyelinated neurons propagate their action potentials?

Continuous Conduction: depolarization and repolarization down the length of an axon

• Slower

How do myelinated neurons propagate their action potentials

SALTATORY Conduction: v-gated ion channels at the Nodes of Ranvier ONLY

• Goes both TOWARD next node and BACK to original node

• Quicker

Describe the process of action potentials firing beginning with Ca+ v-gated ion channels

1. Activate Ca+ V-gated ion channel @ presynaptic cleft

2. Release neurotransmitters

3. Graded potentials

4. Action potentials!

Name the two different type of receptors we are looking at in this unit

1. Ionotropic receptors

2. Metabotropic receptors

Ionotropic receptors

The receptor is an ion channel

• Fast, short effects

• Changes in Vm

Metabotropic receptors

• Receptor = G-protein coupled receptor (GPCR)

  • Slower, long-lasting effects

What are modalities?

Types of sensory information

(i.e. light, smell, somatic (pressure, stretch), temperature, etc.)

What is sensory transduction? Where does it occur?

Sensing a stimuli and turning it into a electrical signal via the change in Vm

• Occurs on sensory receptors

Sensory discrimination

Different receptors detecting specific stimuli

Receptive field

An area around dendrites of a neuron that allows discrimination between stimuli

What is sensory resolution?

How well you detect stimuli

Why is the name mechanoreceptor misleading?

Because the ‘receptor’ itself is not a receptor, they are cells (neurons) with receptors on them

What is a receptor?

A special type of cell that can detect different changes via sensory transduction

Describe the steps of sensory transduction

1. Stimulus → receptor → changes in membrane potential

2. Receptor influences rate of action potential production (graded potentials)

3. Action potentials travel to CNS along afferent pathway

4. CNS interprets/processes incoming signals

Neural coding

The principle that different stimuli are conveyed by defining frequencies and patterns

What are special senses?

Receptors collected in specialized ‘sense organs’

• i.e. smell (olfaction) - nose

• taste (gustation) - tongue

• sound/equilibrium - ear

Where are olfactory receptors located?

Inside olfactory epithelial cells

• Which secrete mucus

What type of neurons are found here? (nose)

Bipolar sensory neurons

T/F: The substance being smelled has to dissolve in the nose mucus

True

Where are action potentials sent to in the nose?

Glomeruli in the cribiform plate

What is the function of each glomerulus?

Collect specific parts of a scent; all glomeruli together = scent

On what do glomeruli synapse?

Mitral cells

What is the function of mitral cells?

Their axons make up the olfactory tract

Odorant molecule

• Activated by olfactory receptor

• Activates g-proteins

What do the g-proteins do once activated by the odorant molecule?

Activate adenylate cyclase, which turns ATP to cAMP

• cAMP opens Na+ ion channels

What is the evolutionary/physiological purpose of our sense of smell?

Allows us to detect changes in the environment

Describe how light passes through the eye

Cornea → aqueous humor → pupil → lens → vitreous humor → retina

Where are photoreceptors at the highest density?

Fovea (on retina)

Describe the path of visual information as it comes in the brain

Optic nerves → Optic chiasm → thalamus → primary visual cortex

What two types of smooth muscles make up the iris?

1. Circular (sphincter pupillae)

2. Radial (dilator pupillae)

Circular (sphincter pupillae)

• *PARASYMPATHETIC control

• Constricts the pupil

Radial (dilator pupillae)

• *SYMPATHETIC control

• Dilates the pupil

What happens to water as it passes through mediums with different densities?

It refracts

What is accommodation as it comes to the eye?

Change of lens shape (for focusing)

• Rounder = focused

When the eye is unfocused, the suspensory ligaments are ____ and the ciliary muscles are _____

1. Tight

2. Relaxed

(focus on ciliary muscles, which control shape of lens directly)

When the eye is focused, the suspensory ligaments are ____ and the ciliary muscles are _____

1. Relaxed

2. Tight

What are the two types of photoreceptor layers?

Rods: monochromatic, dim lights

Cones: color vision, bright lights

What other types of layers are there in the retina?

Neuron processing layers (contrast, etc.)

Melanopsin

Detecting the intensity of light

• Sends to hypothalamus for circadian rhythm

Retinal Pigment Epithelium

Tissue that comprises the blood-retinal barrier

• Contains melanin to absorb light

• Absorbed light = better vision

• Prevents oxidative damage

Müller Glial Cells

Like astrocytes, but in the retina

• Guide photons to photoreceptors

• Reuptake NTs

Describe the path of light info as it comes in the retina to the optic nerve

Rods & Cones → Bipolar cells → Ganglion cells → optic nerve II

Where are the receptors for oderant molecules located?

Embedded in cilia in on the olfactory receptor neurons

T/F: We have a lot more CONES than RODS

False; we have more rods than cones

Rods

• Important for monochromatic, dull light vision

• On the periphery of the retina

• Permit the detection of movement

What are the membranous discs of rods?

Receptors that detect light

What is rhodopsin? What is it comprised of?

Light receptors embedded in the membranous discs

• Comprised of opsin + retinal

• G-coupled protein receptor

What does rhodopsin couple with a G-protein to activate? What does that become?

Beta-carotene (vitamin A) → 11-cis retinal

What happens when 11-cis retinal is struck by a photon?

It becomes trans-retinal

• This is detection of light

Cones

• Color vision, bright light vision

• Located in the center of the retina (fovea)

What are the vision steps of transduction in the DARK?

• High production of cGMP

  • cGMP opens Na+ channels

  • Depolarizes cell (“dark current”

  • Cells release NT (glutamate)

  • NT changes action potential frequency of bipolar cells

T/F: There are more action potentials in the dark with regards to vision

TRUE

What are the vision steps of transduction in the LIGHT?

Rhodopsin’s retinal absorbs the photons, activating opsin

• Enzymes break down cGMP

• Decrease in cGMP closes Na+ channels

• Hyperpolarization, decrease in glutamate

What type of hearing loss is associated with the middle ear? And the inner ear?

Middle: Conductive

Inner: Sensorineural

The movement of the stapes increases pressue in the cochlea for hearing. What structure regulates that pressure?

Round window

Basilar membrane

• Found along the organ of Corti

  • Vibrates in response to sound waves;

  • Different frequencies determine which part of the basilar membrane will move

What structures in the basilar membrane are directly responsible for triggering action potentials? How? What are they connected by?

Stereocilia

• Stereocilia move with the cochlear fluid’s direction

  • Whenever stereocilia bend, they open mechanically-gated ion channels

  • Ca++ channels (not Na+!!!)

• Connected via tip links

In the case of hearing, what causes depolarization?

K+ ions

• Endolymph is very high in K+

How is frequency and loudness determined on the basilar membrane?

Frequency: precise location on the basilar membrane

Loudness: How high/low is the movement of the basilar membrane

What might cause sensorineural hearing loss?

Inner ear damage; hair cell damage (cannot detect changes in frequency)

What is equilibrium? Balance?

Equilibrium: No change in speed

Balance: Process of stabilizing the body in response to changes in speed/gravity

What structures make up the vestibule?

• Semicircular canals

• Utricle

• Saccule

What type of movements do the semicircular canals detect?

Movement on X,Y, and Z axes

Rotational movements of the head or side to side

What is the ampulla?

Base of each semicircular canal

• Has stereocilia that project into crista

• Bends in response to movement

What is the vestibulocular reflex?

Keeping the eye focused on a fixed point even if your head moves

In the utricle and saccule, what membrane do the hair cells project into?

The otolithic membrane

How do hair cells move in the saccule and utricle?

Saccule: Up/down in response to gravity

Utricle: Left/right in response to acclerations