Phys II

Describe how a cell receives signals

A cell receives signals when an extracellular chemical messenger binds to a specific target protein on or inside the cell, triggering a conformational change that alters cellular activity.

What is a receptor?

A specific protein on the plasma membrane or in the cell that binds a chemical messenger and starts a cellular response.

What is a ligand?

Signaling molecule that binds specifically to a receptor site.

What is cell signal transduction?

Process by which a foreign chemical signal is received by a receptor and converted into a specific intracellular sequence of events leading to a cellular response.

What are the two types of receptors found in cells? Where are each found in the

cell?

Plasma Membrane Receptor-Lipid Bilayer

Intracellular Receptors-Cytoplasm

Define Specificity

The ability of a receptor to bind only one specific chemical messenger

Define Saturation

The degree to which receptors are occupied by ligands

Define Affinity

The structural strength of binding between a ligand and its receptor site.

Define Competition

The phenomenon where multiple structurally similar ligands vie for the same receptor binding pocket.

Define Antagonist

A molecule that binds to a receptor but does not activate it. It acts as a blocker to prevent the natural ligand from binding

Define Agonist

A molecule that binds to a receptor and triggers a biological response, mimicking the natural ligand.

Define Down-regulation

A decrease in the total number of target cell receptors, typically occurring in response to chronically high concentrations of a ligand.

Define Up-regulation

An increase in the total number of target cell receptors, typically occurring in response to a chronic deficiency of a ligand.

Define Increase sensitivity

An enhanced cellular responsiveness to a ligand, often resulting from up-regulation or enhanced downstream pathway efficiency.

Describe how receptor specificity maybe affects a cell.

Dictates which cells can respond to a chemical signal. If a cell lacks the specific receptor for a circulating hormone, it remains completely unaffected by it.

A beta-blocker; how does it affect receptors? Name of the receptor? What would it do to the cell?

Act as antagonists. They bind to beta-adrenergic receptors, preventing epinephrine and norepinephrine from binding

Is an antihistamine (drug) an agonist or antagonist-make sure you know why?

Antagonists. They block histamine receptors from initiating the inflammatory and allergic responses.

Describe how signal transduction pathways work.

Convert an outside chemical message into a specific action inside a cell through a series of step-by-step relay events reception, transduction, and response

-What is receptor activation? What are the 5 “forms of changes”?

The initial conformational change in the receptor protein structure caused by ligand binding.

1. Changes in plasma membrane permeability or transport properties.

2. Changes in cell metabolism (enzymatic rates).

3. Changes in secretory activity.

4. Changes in gene expression (protein synthesis via transcription/translation).

5. Changes in contractile or cytoskeletal activity (cell movement/shape)

What is an example of a lipid-soluble messenger? How does one get through the

plasma membrane?

Steroid hormones- testosterone, estrogen, cortisol. They are nonpolar, they pass through the lipid bilayer via diffusion.

What is an example of a water-soluble messenger? How do these have to get

through the plasma membrane?

Peptide hormones- insulin. They must interact with extracellular binding domains

Describe osmosis and osmolarity.

-diffusion of water molecules across a selectively permeable membrane from an area of low solute concentration to an area of high solute concentration.

-total solute concentration of a solution

 -What is the first messenger? How does this activate a signal transduction

mechanism with receptor complexes with ion channels? What about the other

forms (enzyme and G-protein)?

-Original extracellular ligand that binds to the receptor.

-The first messenger binds to a ligand-gated ion channel, changing its shape to open or close the pore, directly altering the flow of ions

-First-messenger binding activates the internal enzymatic domain to phosphorylate target proteins.

-The activated receptor alters the conformation of an attached membrane G-protein complex, causing the alpha subunit to swap GDP for GTP

How is cyclic AMP second messenger separate than most G-proteins?

Cyclic AMP (cAMP) is a small, water-soluble molecule that acts as a second messenger, whereas G-proteins are membrane-bound, multi-subunit proteins that act as molecular switches

What are the events that lead to a cell’s response

Reception

G-Protein Activation

Effector Activation

Transduction Cascade

Response

How does cAMP’s signal amplify?

Through an enzyme-driven chain reaction

Describe how Ca2+ can serve as a second messenger.

Serve as powerful second messengers because cells maintain an extremely steep concentration gradient between the cytoplasm and the outside environment

When signaled, from what source does Ca2+ enter the cell

From the Extracellular fluid, Voltage-Gated Calcium Channels, Ligand-Gated Calcium Channels or Internal storage Organelles: The Endoplasmic Reticulum\The Sarcoplasmic Reticulum

How does the first messenger signal for the release of Ca2+

initiates a biochemical cascade that bridges the outer cell membrane with the cell's internal calcium warehouses

Why is Ca2+ a common second messenger

Its concentration in the cytoplasm is kept near zero under resting conditions, allowing the cell to trigger an instant, high-contrast signal by opening a few channels.

How is Ca+ used by muscles

Act as the primary trigger and switch for muscle contraction

What are the five common second messengers? What do each do?

1.Cyclic AMP-Activates Protein Kinase A

2.Cyclic GMP-Activates protein Kinase G (blood vasodilation)

3.Inositol Triphosphate- Opens Ca2+ channels on ER

4.Diacylglycerol-In membrane activates Protein Kinase C

5.Calcium- Alter enzyme activity

How do aspirin and NSAIDs affect signal transduction in the body?

By cutting off the production of key lipid-based primary messengers called prostaglandins

What is cessation? How does cessation occur?

The formal ending, stopping, or pausing of a biological process, physiological function.

Self-Deactivation, Re-sequestering, Enzymatic Destructions

Define Soma

The central core and command center of the neuron

Define Dendrites

The thin, tree-like branches extending out from the soma. They act as the cell's antennae

Define Axon

A single, long, cable-like tail extending away from the soma. It acts as the transmission wire

Define Axon terminal

Branches at the very end of an axon. This is the output station converts electrical signals into chemical messages

Define Synapse

The junction or junction point where two communicating cells meet.

Define Presynaptic

Refers to the cell or structure before the synapse

Define Post-Synaptic

Refers to the cell or structure after the synapse

Define Target cell

The final destination cells intended to receive the nervous system's message.

Describe how a signal starts

When an external stimulus forces gated ion channels in the cell membrane to open.

Describe how the cell maintains the membrane potential

Through a precise balance of active transport and selective passive leaking, primarily via the Na+/K+Na raised to the positive power / K raised to the positive power Na+/K+ ATPase pump

What is an electrical potential? What is resting membrane potential for most cells?

It is a difference in voltage across the plasma membrane caused by an unequal distribution of positive and negative ions

All inactive cells in the body maintain a voltage difference across their membrane called membrane potential -70mV

How does the concentration difference of K+ and Na+ contribute to the membrane potential of a cell?

Act like a charged biological battery. They create two distinct forces—chemical concentration gradients and electrical gradients—that dictate the movement of ions and directly build the membrane potential.

What does the Nernst Equation measure? What are the components (variables) of the Nernst’s Equation?

It calculates the specific electrical charge (voltage) needed across a cell membrane to balance the concentration gradient of a specific ion Na/K

𝐸ion-(Equilibrium Potential)=

𝑅(61)- (Universal Gas Constant)/

𝑧-(Valence/Charge of the Ion)log

{C(out)-Extracellular concentration of the ion/

C(in)-intracellular concentration of the ion}

What are the chemical and electrical gradients of K+ and Na+ when a cell is at rest?

When a cell is at rest, the chemical and electrical gradients for potassium (K+) work in opposite directions, while both gradients for sodium (Na+) pull the ion inward.

Describe how influx and efflux of K+ and Na+ contribute to the membrane potential.

Change the electrical charge inside the cell, driving the membrane potential up or down

How do the ion pumps contribute to the resting membrane potential?

By building and preserving the steep concentration gradients of Na+ and K+ across the cell membrane.

What is 1.hyperpolarization, 2.depolarization, 3.repolarization, and 4.overshoot?

1-Become more negative

2.Become more positive

3.Reutring to Baseline

4.Going above 0mv

What causes the resting membrane potential to Depolarize? Repolarize?

Hyperpolarize?

Depolarize-(less negative)Channels open and allow positive ions

Repolarize-(resting potential)Na+ channels shut while K+ channels open allowing efflux

Hyperpolarize-(more negative) At the end of an action potential because potassium channels are slow to close, allowing too much K+ efflux

Describe the steps of an action potential

[Resting State] ➔ [Threshold Stimulus] ➔ [Depolarization/Overshoot] ➔ [Repolarization] ➔ [Hyperpolarization] ➔ [Reset]

A brief, rapid electrical impulse that travels down a neuron's axon to communicate signals

What are voltage-gated channels? How do they contribute to the action potential?

Specialized membrane proteins that open or close in direct response to changes in the electrical voltage across the cell membrane.

They drive the electrical impulses (action potentials) that allow nerve and muscle cells to communicate

What is action potential threshold? Which voltage gated channels are activated when threshold is reached?

-the critical membrane voltage a cell must reach to trigger an all-or-none electrical impulse

-Voltage-gated Na+ channels are the primary channels that are activated and opened.

In typical human neurons, the resting membrane potential sits around −70 mV. When incoming signals depolarize the cell (making the inside less negative) and hit a threshold—usually between −55 mV and −40 mV—an action potential fires

Describe and understand steps 1 through 7 in the action potential

1.Resting state-The neuron sits in a quiet, polarized state. The interior of the cell is negative relative to the outside.

2.Trigger and Depolarization to Threshold-An external stimulus arrives at the dendrites

3.Rapid Depolarization-The threshold wire is tripped, initiating an explosive "all-or-nothing" electrical cascade

4.Overshoot-The inward rush of sodium carries so much momentum that the cell's voltage doesn't just stop at zero.

5.Repolarization-At the peak of the voltage, the cell must immediately act to halt the positive charge and restore its baseline.

6.Hyperpolarization/undershoot-As the voltage crashes back down past the resting baseline, the slow-acting channels cause a brief over-correction

7.Refractory Reset-The voltage-gated channels are now all safely shut,

Do cells adjust the strength of an action potential?

No, cells cannot adjust the strength of an action potential. It is strictly an all-or-nothing event

What is the refractory period of an action potential? Absolute vs Relative refractory period?

Refractory period is the temporary "timeout" or recovery window immediately after a neuron fires an action potential during which the cell cannot fire another normal signal.

-Absolute no fire again

-Relative yes but a strong stimuli is needed

Describe how synapses can control neuronal integration.

Acting as tiny mathematical calculators that add and subtract incoming electrical signals before deciding whether to fire an action potential

What is an inhibitory synapse? What is an excitatory synapse

-excitatory synapse is a junction that drives a neuron closer to firing a signal

-inhibitory synapse is a junction that dampens activity and keeps a neuron from firing

What are convergent synapses? Divergent?

Convergent synapses-multiple separate neurons send signals to a single receiving neuron

Divergent synapses-a single neuron branches out to send signals to multiple receiving neurons

How does the axon terminal transfer the signal to the post-synaptic cell with gap junctions?

It skips the chemical step entirely. This connection is called an electrical synapse.

Instead of converting the electrical spark into floating chemical messengers (like neurotransmitters), the signal flows directly through open physical tunnels.(Connexons)

Explain the six steps of a chemical synapse

1. Action Potential Arrives] ➔ [2. Ca2+ Channels Open] ➔ [3. Neurotransmitter Released] ➔ [4. Transmitter Binds Receptor]➔ [5. Post-Synaptic Gates Open] new signal ➔ [6. Signal Cleaned Up] signal termination

How is a neurotransmitter released into the synapse. How is it removed

-Released into the synaptic cleft through calcium-dependent exocytosis

-Removed

1.REUPTAKE PUMPS (Sucked back into sending cell) 

2. ENZYMATIC DEGRADATION (Chopped up and destroyed)

3. PASSIVE DIFFUSION (Drifts away out of the cleft)

How can post-synaptic mechanism be affected by drugs and diseases?

Receptors and ion channels catch neurotransmitters and generate a new signal, any drug or disease that blocks, mimics, or destroys these structures will completely change how the message gets through

Review the synapses of the somatic nervous system, synaptic and parasympathetic nervous system.

-Somatic nervous system is a direct, one-neuron pathway controlling skeletal muscles.

-The autonomic branches are two-neuron pathways that must relay their signal through an intermediate charging station called an autonomic ganglion before reaching their target organs.

Describe how we perceive senses

sensory transduction. This is the biological mechanism by which our nervous system takes physical energy from the environment and translates it into an electrical language that the brain can read

What are the classes of receptors? Describe what mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, nociceptors are.

1. Mechanoreceptors (Physical Movement)

2. Thermoreceptors (Temperature Shifts)

3.Photoreceptors (Light Waves)

4.Chemoreceptors (Chemical Signatures)

5.Nociceptors (Pain and Damage)

What are slowly adapting receptors? Rapidly adapting receptors?

Slowly- Tonic receptors, keep firing nerve signals for as long as a constant stimulus stays present. They adapt very little or not at all

Rapidly-Phasic receptors, fire a brief burst of signals when a stimulus first starts or stops, but then quickly stop firing even if the stimulus continues prevent your brain from experiencing information overload.

What are the different types of stimulus modalities?

General Somatosensory Modalities (Distributed Senses)

General Somatosensory Modalities (Distributed Senses)

Describe how stimuli can vary

Modality What is it

Intensity How strong it is

Location Where is it

Duration How long does it last

What is stimulus intensity? How can signal frequency perceive different stimulus intensities?

-Intensity How strong it is

-A weak stimulus causes a sensory neuron to fire a slow, rhythmic stream of signals. A powerful stimulus forces that same neuron to fire an explosive, rapid-fire stream of action potentials.

How can receptor field overlap help determine location of a single stimulus?

Receptive field overlap allows the brain to pinpoint the location of a single stimulus with pinpoint accuracy through a mathematical process called population coding or vector averaging

Describe how afferent sensory neural pathways are designed in the body.

Designed as a hierarchical, three-neuron relay chain that connects peripheral sensory receptors directly to the cerebral cortex.

How are the sensory pathways generally formed?

a highly coordinated two-phase process: a genetically programmed wiring phase during embryonic development, followed by an activity-dependent refinement phase driven by real-world sensory experiences.

What are specific ascending pathways?

Dedicated, anatomically distinct neural tracks that carry a single, precise type of sensory information directly from peripheral receptors to specific regions of the cerebral cortex.

What region of the brain processes somatosensory (vision, sound, taste, smell) information?

Parietal Lobe processes somatosensory

Occipital Vision

Temporal Sound

Insular Taste

Temporal Smell

Describe how somatic sensation is categorized

Tactile/Thermal sensation

Proprioception (body position)

Pain (Nociception)

What “regions” of the body are part of the somatic sensation?

Somatic sensation encompasses virtually the entire body

What are the specific roles of the Meissner’s corpuscle, Merkel’s, Free neuron ending, Pacinian, and Ruffini corpuscles?

Meissner’s corpuscle-Detects light touch, flutter, and low-frequency vibration

Merkel’s-Detects sustained light touch, edges, and steady pressure

Free neuron ending-Acts as the primary responder for pain

Pacinian-Detects deep transient pressure and high-frequency vibration (phone/tools)

Ruffini corpuscles-Detects skin stretch and sustained joint deformation; allows you to sense the shape of an object held in your hand and tracks finger positioning.

What are the roles of muscle-spindle stretch receptors? Transient receptor potential proteins? Which sensation do these modulate?

-The absolute length of a muscle and the speed at which it is stretching. Proprioception (Position/Stretch)

-TRP proteins function as tiny environmental biosensors. Thermoception (Temp) & Nociception (Pain)

What type of receptors detect pain in the skin? What is referred pain?

Nociceptors are the specialized sensory receptors

where you feel pain in one area of your body but the actual source of the pain is located somewhere else entirely

What is analgesia?

The inability to feel pain while remaining fully conscious

Describe neural pathways of the somatosensory system

Uses three main neural pathways to carry sensory information.

Spinothalamic Pathway-Carrying pain , temperature, and crude (non-discriminative) touch

Dorsal Column-Medial Lemniscal (DCML) Pathway-Carries fine (discriminative) touch, vibration, and conscious proprioception (position sense)

Trigeminothalamic Pathway-carries all somatosensory information from the face and head

What signals (sensations) travel through the somatosensory system?

tactile (touch), thermal (temperature), position sense (proprioception), and noxious (pain

Describe the pathway of the anterolateral and dorsal column system

anterolateral-This pathway primarily transmits pain, temperature, and crude touch.

dorsal column-transmits fine touch, vibration, and conscious proprioception (position sense). It is built for speed and high-resolution spatial awareness.

Describe the location of the somatosensory system in the cerebral cortex.

The parietal lobe of the brain

Describe neural pathways of vision

the sequence of structures that transmits visual information from the retina of the eye to the brain to create conscious sight.

[ Retina ] │ ▼

[ Optic Nerve ] │ ▼

[ Optic Chiasm ] ─► (Partial Crossing/Decussation) │ ▼

[ Optic Tract ] │ ▼

[ Lateral Geniculate Nucleus (LGN) of Thalamus ] │ ▼

[ Optic Radiations ] │ ▼

[ Primary Visual Cortex (V1) ]

What is vision? The sensation of what stimuli? What is the visible spectrum of humans?

-Physiological process by which the brain interprets signals from the eyes to construct a conscious visual image

-sensation triggered by electromagnetic radiation

-between 380 nanometers (nm) and 750 nanometers

How does light pass through the three layers of the eye? What structure has the photoreceptors?

[ Light Source ] ──► [ 1. Fibrous Tunic (Cornea) ] ──► [ 2. Vascular Tunic (Pupil/Lens) ] ──► [ 3. Neural Tunic (Retina) [photoreceptors]

What is light refraction and how does it occur at the eye?

the bending of light rays as they pass from one transparent medium into another of a different density.

(1. Cornea) ──► [ Aqueous Humor ] ──► (2. Anterior Lens) ──► (3. Posterior Lens) ──► [ Vitreous Humor ] ──► [ Retina

What is the focal point? How does the eye bring objects into focus? What structures are involved when bringing things into focus?

-the precise spot where light rays converging through a lens intersect
-Accommodation is the dynamic process the eye uses to shift focus between near and distant objects

-ciliary muscles (relax for distant objects) (contract for near objects)

How does the light of path move through the regions and cells of the retina?

Light travels through the inner layers of the retina first before hitting the light-sensitive photoreceptor cells at the back

How does light information travel to the visual cortex?

Travels to the primary visual cortex at the back of the brain through a highly organized pathway known as the retinofugal pathway

[ Retina ] ──► 1. OPTIC NERVE ──► 2. OPTIC CHIASM ──► 3. OPTIC TRACT ──► [ Thalamus / LGN ]

Describe neural pathways of sound

[ Cochlea (Hair Cells) ] │ ▼

[ Spiral Ganglion / CN VIII ] │ ▼

[ Cochlear Nuclei ] (Lower Medulla) │ ▼

[ Superior Olivary Complex ] (Pons - First Bilateral Integration) │ ▼

[ Lateral Lemniscus ] (Pons/Midbrain Tract) │ ▼

[ Inferior Colliculus ] (Midbrain) │ ▼

[ Medial Geniculate Nucleus (MGN) ] (Thalamus) │ ▼

[ Auditory Cortex (A1) ] (Temporal Lobe)

What is sound? How is it detected by the middle ear?

-Physical phenomenon consisting of mechanical pressure waves that travel through a medium, such as air, water, or solids

Airborne Sound Waves ] │ ▼

1. TYMPANIC MEMBRANE (Eardrum) ──► Vibrates in response to air pressure changes │ ▼

2. AUDITORY OSSICLES ──► Amplifies and transfers the physical vibration (Malleus → Incus → Stapes) │ ▼

3. OVAL WINDOW ──► Pushes the mechanical force into fluid-filled inner ear

How does sound travels from the round window through and “out” of the cochlea?

Stapes Bone ] │ ▼

1. OVAL WINDOW ──► The "Entrance Door." The ear bone pushes here, starting a fluid wave. │ ▼

2. SCALA VESTIBULI ──► The "Inbound Hallway." The wave ripples forward through this top tunnel. │ ▼

3. HELICOTREMA ──► The "U-Turn." At the very tip of the cochlea, the wave loops around. │ ▼

4. SCALA TYMPANI ──► The "Outbound Hallway." The wave travels backward along this bottom tunnel. │ ▼

5. ROUND WINDOW ──► The "Exit Door." A flexible membrane bulges out here to let the energy escape.

Describe how hair cell deflection sends detected sounds to the cochlear nerve

Hair cell deflection converts mechanical sound waves into electrical signals that travel through the cochlear nerve to the brain

1.THE BEND ──► │ the hair-like tops are forced to bend (deflect) back and forth ▼

2. THE PULL ──► A tiny spring-like string pulls open a microscopic trapdoor on the hair. │ ▼

3. THE RUSH ──► Minerals (Potassium) flood inside through the open trapdoor. │ ▼

4. THE SPARKS ──► This influx creates an electrical charge that wakes up the cell. │ ▼

5. THE MESSAGE ──► The cell fires a chemical messenger (Glutamate) out of its base. │ ▼

6. THE NERVE FIRES ──► The cochlear nerve catches the chemical and sends a signal to your brain.

How is sound intensity detected by the hair cells?

Is detected by hair cells based on the size of the fluid wave moving through the cochlea

Describe neural pathways of the vestibular system

The neural circuit responsible for your sense of balance, motion, and spatial orientation.

1. THE EYES ──► Locks your vision while you move (VOR) │

2. THE SPINE ──► Automatically adjusts your posture so you don't fall │

3. THE CEREBELLUM ──► Fine-tunes your balance and coordination │

4. THE BRAIN CORTEX ─► Tells your conscious mind which way is "up"