Cell Communication, Sensory and Motor Mechanisms

Flashcards about Cell Signaling, Neurons, Sensory Systems, and Muscle function and contraction.

Local Regulation

Cells communicate locally via paracrine signaling, synaptic signaling, or direct contact.

Paracrine signaling

Local regulators (e.g., growth factors) diffuse to nearby cells.

Synaptic signaling

Neurons release neurotransmitters to target cells across a synapse.

Direct contact

Communication via gap junctions (animals) or plasmodesmata (plants); or membrane-bound signal molecules

Hormones (Long-Distance Signaling)

Hormones travel via bloodstream in animals and through vessels, cells, or air in plants.

Reception

Signal molecule (ligand) binds receptor.

Transduction

Signal relayed via proteins (often in a cascade).

Response

Cell changes behavior (gene expression, enzyme activity, etc.).

Ligand

Signaling molecule that binds specifically to a receptor.

Plasma membrane receptors

For water-soluble ligands.

Intracellular receptors

In cytoplasm or nucleus; for small, nonpolar ligands (e.g., steroids).

G Protein-Coupled Receptors (GPCRs)

Work via G protein which activates enzyme or ion channel

Receptor Tyrosine Kinases (RTKs)

Dimerize & autophosphorylate which triggers multiple pathways.

Ligand-Gated Ion Channels

Open or close when ligand binds which changes ion flow.

Intracellular Receptors

Activated by hydrophobic molecules which regulate gene expression.

Kinases

Transfer phosphate groups (ATP → protein).

Protein Phosphatases

Remove phosphates which turns off signal.

Second Messengers

Small, nonprotein, water-soluble molecules that spread signal.

Second Messengers Examples

Examples include cAMP, Ca²⁺, IP₃.

cAMP (Cyclic AMP)

Formed from ATP by adenylyl cyclase and activates protein kinase A, which phosphorylates other proteins.

Ca²⁺ Signaling

Involved in muscle contraction, secretion, cell division, and is stored in ER or mitochondria and released via IP₃ or other signals.

Cytoplasmic Responses

Changes enzyme activity, cell shape, etc.

Nuclear Responses

Affects gene expression via transcription factors.

Signal Amplification

One ligand activates thousands of molecules via cascade.

Scaffolding Proteins

Organize key relay proteins in one place to speed up and coordinate signal transduction.

Presynaptic neuron

Sends signal

Synaptic terminal

Contains vesicles with neurotransmitter

Synaptic cleft

Tiny space between neurons

Postsynaptic neuron

Receives signal and has receptors

Step 1 of Chemical Synapse Signal Transmission

Action potential arrives which opens voltage-gated Ca²⁺ channels.

Step 2 of Chemical Synapse Signal Transmission

Ca²⁺ enters terminal which triggers vesicles to fuse with membrane.

Step 3 of Chemical Synapse Signal Transmission

Neurotransmitter is released into the cleft.

Step 4 of Chemical Synapse Signal Transmission

Neurotransmitter Binds to receptors on postsynaptic membrane.

Step 5 of Chemical Synapse Signal Transmission

Opens ion channels which leads to EPSP or IPSP.

EPSP (Excitatory Postsynaptic Potential)

Na⁺ in → depolarization which brings neuron closer to threshold. Acts like gas pedal.

IPSP (Inhibitory Postsynaptic Potential)

Cl⁻ in or K⁺ out → hyperpolarization which makes it harder to fire action potential. Acts like brake pedal.

Summation

Neurons add up EPSPs and IPSPs to decide whether to fire an action potential.

Temporal Summation

Multiple signals from one synapse in quick succession.

Spatial Summation

Signals from multiple synapses at the same time.

Acetylcholine (ACh)

Excitatory at neuromuscular junctions (causes muscle contraction), and can be inhibitory in heart muscle and is broken down by acetylcholinesterase.

Biogenic Amines

Made from amino acids, includes Dopamine, Serotonin, Norepinephrine, and Epinephrine.

Dopamine

Motivation, reward, movement

Serotonin

Mood, sleep, appetite

Norepinephrine

Alertness, attention

Epinephrine

Similar to norepinephrine; also a hormone

Glutamate

Major excitatory neurotransmitter in CNS.

GABA (gamma-aminobutyric acid)

Major inhibitory neurotransmitter in brain.

Glycine

Inhibitory neurotransmitter in spinal cord.

Aspartate

Another excitatory neurotransmitter

Neuropeptides

Small protein-like signaling molecules.

Substance P

Involved in pain perception

Endorphins

Natural painkillers that inhibit substance P.

Gas Neurotransmitters: Nitric Oxide & Carbon Monoxide

Act as local regulators, are not stored in vesicles—made on demand, and Diffuse into neighboring cells

Nitric Oxide (NO)

Causes vasodilation (e.g. in erectile tissue)

Carbon Monoxide (CO)

May modulate inflammation or sensory processing.

Sensation

The raw input received by sensory neurons (e.g., light, sound, pressure).

Perception

The interpretation of that input by the brain (e.g., recognizing sound as music).

Sensory Reception

Detect a specific type of stimulus (e.g., light, vibration, chemicals).

Transduction

Convert stimulus energy into a receptor potential (electrical signal).

Perception of Stimuli

The CNS processes the incoming signal and interprets it.

Sensory transduction

The process of converting a stimulus (e.g., pressure) into a receptor potential.

Receptor potential

The graded electrical change in the receptor cell membrane caused by the stimulus (can lead to action potentials).

Mechanoreceptors

Mechanical pressure/stretch; example: touch, hearing, balance

Chemoreceptors

Chemical changes (pH, molecules); example: taste, smell, blood pH

Electromagnetic receptors

Light, electricity, magnetism; example: vision (photoreceptors)

Thermoreceptors

Heat or cold; example: skin temp sensors

Nociceptors (pain receptors)

Extreme pressure, temperature, or chemicals; example: detect injury or inflammation

Role of Mechanoreceptors in Hearing and Balance

Detect physical movement (vibration, pressure, motion).

Mechanoreceptors Sense

Sound waves (air pressure changes), movement of fluid in the inner ear, and shifts in body position relative to gravity.

Invertebrate Statocysts

Balance-sensing structures in many invertebrates (e.g., jellyfish, crustaceans).

Statocysts Structure

A chamber lined with hair cells and contains a small, dense particle called a statolith

Statocysts Function

When the animal tilts, the statolith presses on different hair cells, sending information about orientation and balance.

Tympanic membranes

Thin, stretched membranes found in insects that vibrate when sound waves contact them, stimulating sensory neurons behind it.

Pinna

Funnel sound into the ear.

Auditory canal

Directs sound waves to eardrum.

Tympanic membrane (eardrum)

Vibrates with sound waves.

Ossicles (3 tiny bones)

Amplify vibrations and transmit to inner ear.

Cochlea

Spiral-shaped organ for hearing.

Semicircular canals

Detect rotational movement (balance).

Utricle & Saccule

Detect gravity and linear movement.

Auditory (Eustachian) tube

Equalizes pressure with the atmosphere.

Semicircular Canals Detail

Detect rotational movement; contain fluid and hair cells, and movement of fluid bends hair cells, sending signals to brain.

Utricle & Saccule Detail

Detect tilt and linear motion; contain otoliths (tiny crystals) that shift with gravity shift which bends hair cells to give info on head position.

Eye cup

Cup-shaped pit of light-sensitive cells and detects light direction, not images.

Compound eye

Many units (ommatidia), each with its own lens and produces a mosaic image, excellent motion detection.

Single-lens eye

One lens focuses light onto retina and forms detailed images; similar to a camera.

Cornea

Transparent outer layer that bends incoming light.

Iris

Colored part that controls light entry by adjusting pupil size.

Pupil

Opening that lets light in.

Lens

Focuses light onto retina (changes shape for near/far focus).

Retina

Inner layer with photoreceptors (rods & cones).

Optic nerve

Sends visual info to the brain.

Aqueous humor

Fluid in front of the lens

Vitreous humor

Gel-like fluid behind the lens

Sclera

White outer layer that is protective.

Choroid

Dark middle layer that provides nutrients and absorbs stray light.

Fovea

Center of visual focus with high density of cones.

Blind spot

Where optic nerve exits, with no photoreceptors.

Rods

Detect light intensity and are very sensitive (night vision) and spread throughout retina, but have no color vision

Cones

Detect color; less sensitive (need bright light) concentrated in fovea.