Phys 2 Exam 1

What is a chemical gradient?

concentration of ions differs across membrane

high inside cell (K+) vs low outside cell (K+)

low inside (Na+) vs high outside (Na+)

What is an electrical gradient?

difference of charges across membrane

relatively negative inside cell

leakage of K+ contributes to negative charge

What is equilibrium?

natural tendency to return to an even concentration

What is potential?

increased strength is created by larger concentration differences across membrane

measured in volts or mV

What is membrane potential held at?

-70mV

How does Sodium/Potassium pump work?

maintains -70mV despite leakage

Actively pumps 3 Na+ out of cell

Actively pumps 2 K+ into the cell

What is depolarization?

influx of positively charged ions (Na+) into cells

What is the threshold for action potentials?

-55mV

What may lead to changes permeability of cell membrane to various ions?

Neuron to neuron communication (chemical synapses)

How does stimulatory neurotransmitters change the permeability of cell membrane?

Increase in permeability to cations (Na+) leads to the cell becoming more positive (Depolarization)

How does inhibitory neurotransmitters change permeability of cell membrane?

Increase in permeability lead to (Cl- influx) or (K+ efflux) leads to the cell becoming more negative (Hyperpolarization)

What are examples of stimuli/modalities for sensory neurons?

1. touch

2. pressure

3. vibration

4. chemical

5. sound waves

6. photons of light

how will a depolarized sensory neuron transmit information?

Will transmit information to the next neuron in a sensory pathway via an action potential

What is the difference between a graded potential and an action potential?

Graded (sensory) potential: local incoming signal that degrades and doesn’t use voltage gated channels to send signals.

Also, must be strong to reach initial segment of axon

Action Potential: signal begins at the initial segment of axon and the signal do NOT degrade.

Axon+ initial segment will contain voltage gated Na+ channels, and they are useful for sending long distances

Where is stimulus received for a graded potential?

Initial stimulus received by sensory neuron or pre-synaptic neuron

What generates an action potential?

initial segment of axon and down axon

What is an ionotropic receptor?

receptor type that regulates “fast” synaptic transmission

the speed is due to the receptor being able to initiate immediate changes in membrane permeability

What is a metabotropic receptor?

receptor type that regulates “slow” synaptic transmission

speed due to the receptor needing to initiate a cascade of biochemical reactions to alter membrane permeability

Does excitatory neurotransmitters bring signal towards or away from depolarization?

towards- since neuron becomes more positive

Do inhibitory neurotransmitters bring signal towards or away from depolarization?

away (hyperpolarized): neuron becomes more negative

What helps a neuron reach threshold and generate action potentials?

summation- increased presynaptic input onto post-synaptic neuron

What is spatial summation?

threshold is reached due to increased number of presynaptic neurons

multiple inputs

What is temporal summation?

threshold is reached due to increased frequency of firing from presynaptic neuron

one input with increased frequency

How is a signal pathway reinforced in nervous system?

Potentiation

What is potentiation?

repeated activation of neuronal pathways that leads to cell being more receptive of postsynaptic neurons (strengthens signal)

What is long term potentiation?

repeated high intensity stimulation

influx of Ca++ triggers cascade in postsynaptic neurons that leads to increased number of AMPA receptors which increases responsiveness

What regulates long term potentiation?

Glutamate Receptors: NMDA and AMPA

What weakens a signal pathway?

1. inhibition

2. synaptic fatigue

3. acidosis and alkalosis

4. hypoxia

5. drugs

What type of inhibition do most sensory pathways use?

Lateral inhibition

What does lateral inhibition do?

increase localization of stimulus

it increases signal near the center and decreases signal strength in periphery

“Better able to tell exact location of stimulus”

What is synaptic fatigue?

temporary decrease in strength of synaptic transmission that occurs after prolonged or high frequency activity at a synapse

What is the result of synaptic fatigue?

progressively weaker synaptic activity and depletion of synaptic vesicles and neurotransmitters

What is long term depression for a synapse?

long lasting weakening of connection between neurons

low intensity stimulation and opens only AMPA receptors

What is the result of long-term depression on a synapse?

results in low intracellular Ca++ levels

initiates intracellular cascade that removes AMPA receptors

weakens neuron’s responsiveness

How does acidosis impact neurons?

decrease in neuronal excitability

What is an example of acidosis on neurons?

Diabetic Ketoacidosis

What impact does alkalosis have on neurons?

increases neuronal excitability

What is an example of alkalosis on neurons?

Hyperventilation causes loss of CO2 and increased pH which then leads to overactivity and seizures

nicotine

T/F Oxygen deprivation for only 3-7 seconds lead to unconsciousness

True

T/F Caffeine increases excitability by decreasing the threshold

True

T/F Anesthetics decrease excitability by increasing threshold

True

How is signal sped increased?

myelination

What is saltatory conduction?

Nerve impulses jump from one node of Ranvier to the next

What type of neurons are somatic sensory receptors (first order spinal nerves)?

pseudo-unipolar neurons

What is sensory transduction?

conversion of an environmental stimulus to electrical stimulus/impulse

Where does transduction occur?

Receptor of 1st order neurons only

What are examples of mechanoreceptors?

1. Touch

2. Vibration

3. Pressure

4. Stretch

5. Equilibrium

6. Audition

What are examples of nociceptors?

Pain-free nerve ending (extreme intensity)

What are examples of thermoreceptors?

1. Warm

2. Cold

What is an example of photoreceptors?

vision

What are examples of chemoreceptors?

1. Taste

2. Smell

3. Osmolality

4. O2, CO2

What are the rapidly adapting (phasic) mechanoreceptors?

1. Pacinian Corpuscle

2. Meissner Corpuscle

3. Hair Follicles

What are Pacinian corpuscle?

#1 fastest adapting mechanoreceptors

Where are Pacinian Corpuscle found?

Deep Dermis and Intramuscular

Does Pacinian corpuscle have a large or small receptive field?

Large- encodes vibration

What is Meissner (tactile) corpuscle?

rapidly adapting mechanoreceptor

Where are Meissner (Tactile) corpuscles located?

Superficial Dermis: especially fingertips and lips

Does Meissner (Tactile) corpuscle have a small or large receptive field?

small- encodes precise touch

What are the slowly adapting (tonic) mechanoreceptors?

1. Ruffini Corpuscle

2. Merkel Disc

3. Tactile Disc

What are Ruffini and Merkel Receptors?

Slowly adapting mechanoreceptors

Where are Ruffini corpuscle located?

Deep Dermis and Joint Capsules

Does Ruffini Corpuscle have a large or small receptive field?

Large-stretch

Where are merkel receptors located?

Superficial Dermis-Epidermis junctions

Do Merkel receptors have a small or large receptive field?

Small- light touch/pressure

How do adaptations work with receptors?

Decrease in receptor action potentials over time with a constant stimulus

how quickly the receptor gets used to the stimulus and stops firing

How does the nervous system determine strength of stimulus?

frequency determines intensity

Strong Stimulus- extreme increase in frequency of action potentials

Weak Stimulus- decrease in frequency of action potentials

What are examples of free nerve endings?

1. Nociceptors

2. Thermoreceptors

3. Tickle and Itch Receptors

What are common features of all types of free nerve endings?

1. Not specialized

2. Non-encapsulated

3. Present nearly everwhere in body

4. Most common in epithelia and connective tissue

   Connected to Type A Delta and C fibers

What are multimodal nociceptors?

capable of transducing mechanical, thermal, and chemical (Acute or Chronic)

What are mechanical nociceptors?

transduce extreme mechanical intensity (extreme pressure, stretch, pinching, cutting)

What are thermal nociceptors?

Extreme- temperatures (greater than 120 F or less than 42 F)

What are chemical nociceptors?

inflammatory chemicals, markers of ischemia, strong acid/bases

Where are nociceptors found in dense concentrations?

Skin, joints, periosteum, arterial walls, falx

Where are there low concentrations of nociceptors?

Deep tissues (visceral)- brain, GI tract

What are the slowest fibers in the body?

C fibers

What are examples of stimuli that causes fast pain?

1. Needle stick

2. skin cut

3. heavy impact of object

4. bone fracture

What are the characteristics of fast pain?

1. Sharp and well localized

2. travels in A-delta fibers

3. Nociceptors of A delta fibers have smaller receptive fields

What are examples of stimuli that cause slow pain?

1. Inflammation

2. Ischemia

3. Burned skin

4. Chronic injuries

5. Deep/visceral structures

What are characteristics of slow pain?

1. Diffuse and poorly localized

2. Travels in C fibers

3. Nociceptors of C fibers have a larger receptive field

4. Annoying and intolerable compared to fast pain

What is the range for thermoreceptors?

43-120 degrees F

What channels do warmth thermoreceptors use?

utilize vanilloid transient receptor potential channels (TRP)

TRPV transduces heat and capsaicin (in spicy foods)

What channels do cool thermoreceptors use?

utilize melastatin transient receptor potential channels (TRPM)

TRPM transduces cool and menthol found in pain relievers

Where are tickle and itch free nerve endings located?

Almost exclusive to superficial skin

What are some characteristics of tickle free nerve endings?

1. Very thin fibers

2. Very low threshold

3. Sensitive to very light touch

   Mosquito on neck, sway it away

What are some characteristics of tickle free nerve endings?

1. Very thin fibers

2. respond to chemical stimuli- Histamine

What are Erlanger’s fibers?

A alpha

A beta

A gamma

A delta

B

C

Are Erlanger’s fibers motor or sensory or both?

Both motor and sensory

What is the fastest Erlanger’s fiber?

A alpha

What do A alpha fibers deal with?

Muscle spindles- sensory, alpha motor neuron

What do A beta fibers deal with?

discriminative (fine) touch and vibration

What do A delta fibers deal with?

Fast pain, crude touch, deep pressure, cold temperature

What do C fibers deal with?

Slow pain, heat, tickle, and postganglionic autonomic olfaction

Are Lloyd’s fibers sensory, motor, or both?

Only sensory

What are Lloyd’s fibers?

used for proprioception

Ia

Ib

II

III

IV

What do Ia fibers do?

muscle spindle afferents

What do Ib fibers do?

Golgi tendon organ afferents

What do II fibers do?

discriminative touch, vibration, muscle spindle

What do III fibers do?

crude touch, pressure, fast pain, temperature

What do IV fibers do?

slow pain, olfaction