Bio Midterm 4

Schwann cells function and structure

Providing electrical insulation for faster nerve impulse transmission

Saltatory conduction

Occurs in a myelinated axon, Which nerve impulses move down a myelinated axon with excitation occurring only at nodes of Ranvier

How do K+ and Na+ channels contribute to membrane depolarization, action potentials and hyperpolarization

• Depolarization:

  • Na⁺ channels open → Na⁺ rushes in → Membrane becomes more positive.

• Action Potential Peak:

  • Na⁺ channels close, K⁺ channels open → Inside is most positive.

• Repolarization:

  • K⁺ rushes out → Membrane becomes more negative, returning toward resting.

• Hyperpolarization:

  • K⁺ channels slow to close → Too much K⁺ leaves → Membrane is extra negative.

Spatial summation

• If two different inputs arrive at the same time, their effects on the membrane potential of the spike initiating zone are cumulative.

  
  • If enough different inputs arrive at the same time, the spike initiating zone’s membrane potential can be brought to threshold.

Temporal summation

• One presynaptic neuron fires multiple times in rapid succession.

• Each signal adds onto the last before the previous one fades.

• Combined signals reach threshold → Action potential fires.

Why can action potentials only travel in one direction once initiated

(going down, motor unit —> muscle fiber)

Because the sodium
channels are in a inactive state in the region through which the action potential has just passed.

What types of ion channels are stimulated by the excitatory presynaptic axons and the inhibitory presynaptic axons.

Excitatory presynaptic axons:

• Stimulate ligand-gated Na⁺ channels.

• Na⁺ flows into the postsynaptic neuron → depolarization → action potential more likely.

Inhibitory presynaptic axons:

• Stimulate ligand-gated Cl⁻ channels or ligand-gated K⁺ channels.

• Cl⁻ flows in or K⁺ flows out → hyperpolarization → action potential less likely.

How do these two types of axons cause different changes in the membrane potential and how the signals are integrated at the axon hillock

Excitatory axons:

• Cause depolarization (membrane becomes less negative).

• Bring membrane potential closer to threshold → action potential more likely.

Inhibitory axons:

• Cause hyperpolarization (membrane becomes more negative).

• Move membrane potential farther from threshold → action potential less likely.

Integration at the axon hillock:

• All excitatory and inhibitory inputs are summed.

• If overall depolarization reaches threshold, an action potential fires.

• If not, no action potential happens.

What mechanisms by which an action potential promotes neurotransmitter release at the neuromuscular junction and stimulate action potential in the muscle cell (acetylcholine receptor)

• Action potential reaches the axon terminal of the motor neuron.

• Voltage-gated Ca²⁺ channels open → Ca²⁺ flows into the neuron.

• Ca²⁺ triggers vesicles to release acetylcholine (ACh) into the synaptic cleft.

• ACh binds to acetylcholine receptors (ligand-gated Na⁺ channels) on the muscle cell.

• Na⁺ enters the muscle cell → depolarizes the membrane.

• If threshold is reached, an action potential fires in the muscle cell, leading to contraction.

Sarcomeres

• The basic contractile units of muscle fibers.

• Made of actin (thin filaments) and myosin (thick filaments).

• Z lines mark the boundaries of each sarcomere.

• Contraction happens when myosin pulls actin, shortening the sarcomere.

• Sarcomeres line up end to end to form myofibrils inside muscle cells.

Muscle fibers

• Muscle cells that are long, cylindrical, and multinucleated.

• Contain bundles of myofibrils made of repeating sarcomeres.

• Surrounded by a plasma membrane called the sarcolemma.

• Specialized for contraction → shorten to produce movement.

• Rely on calcium, ATP, and actin-myosin interactions to contract.

Myofibrils

• Rod-like structures inside muscle fibers.

• Made of repeating sarcomeres (actin and myosin filaments).

• Responsible for the striated appearance of skeletal and cardiac muscle.

• Contract when sarcomeres shorten, causing the whole muscle fiber to contract.

Sarcolemma

• The cell membrane of a muscle fiber.

• Surrounds the entire muscle cell and helps conduct action potentials.

• Connects to T-tubules, allowing signals to reach deep inside the cell.

• Important for triggering contraction by helping spread electrical impulses.

Sarcoplasm

• The cytoplasm of a muscle fiber.

• Contains organelles, myofibrils, glycogen (for energy), and myoglobin (stores oxygen).

• Supports muscle contraction by providing energy and raw materials.

T tubules

• Extensions of the sarcolemma that dive deep into the muscle fiber.

• Help carry action potentials quickly into the interior of the muscle cell.

• Ensure that all myofibrils contract at the same time.

Sarcoplasmic reticulum

• A specialized smooth ER in muscle fibers.

• Stores and releases Ca²⁺ ions needed for muscle contraction.

• Surrounds each myofibril, closely associated with T-tubules.

• Calcium release from the SR triggers sarcomere contraction.

How does a stimulated motor neuron transfers an action potential via the T tubule, to the sarcoplasmic reticulum, which causes Ca+ levels of the sarcoplasm

• Motor neuron fires an action potential → releases acetylcholine at neuromuscular junction.

• ACh binds to receptors → muscle fiber depolarizes → action potential spreads across sarcolemma.

• T-tubules carry the action potential deep into the muscle fiber.

• Signal reaches sarcoplasmic reticulum (SR) → SR releases Ca²⁺ into the sarcoplasm.

• Ca²⁺ floods the sarcoplasm, triggering muscle contraction by allowing myosin to bind actin.

Function of the following proteins in excitation-contraction coupling: DIH receptor, Ry receptor, and SERCA

Excitation-Contraction Coupling Proteins:

• Dihydropyridine (DHPR) receptor:

  • Found in T-tubule membrane.

  • Senses action potential and activates RyR. (Acts like a voltage sensor.)

• Ryanodine (RyR) receptor:

  • Found in the sarcoplasmic reticulum (SR).

  • Releases Ca²⁺ from SR into the sarcoplasm when activated by DHPR.

• SERCA (Sarcoplasmic Endoplasmic Reticulum Calcium ATPase):

  • Pumps Ca²⁺ back into the SR after contraction.

  • Helps muscle relax by lowering Ca²⁺ levels in the sarcoplasm.

How does the sensation of pain in the finger lead to stimulation if inhibitory and excitatory neurons that causes to pull your arm back

• Pain activates nociceptors in the skin.

• A sensory neuron carries the pain signal to the spinal cord.

• In the spinal cord:

  • The sensory neuron activates excitatory interneurons → stimulate motor neurons → cause muscles to contractand pull the arm back.

  • It also activates inhibitory interneurons → inhibit opposing muscles from resisting the movement (this is called reciprocal inhibition).

Anatomy of the human eye

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• Cornea:

  • Clear, outer layer that bends (refracts) light into the eye.

• Aqueous Humor:

  • Clear fluid between cornea and lens; maintains eye pressure.

• Pupil:

  • Opening that controls how much light enters the eye.

• Iris:

  • Colored part; muscle that adjusts pupil size.

• Lens:

  • Focuses light onto the retina; changes shape to focus near or far.

• Vitreous Humor:

  • Gel-like substance filling the main chamber of the eye; maintains shape.

• Retina:

  • Inner layer containing photoreceptors (rods and cones) to detect light.

• Fovea:

  • Spot on the retina with highest concentration of cones; sharpest vision.

• Optic Nerve:

  • Carries visual signals from the retina to the brain.

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How do the ganglion, bipolar, rod and cone cells of the retina work together to deliver action potentials to the optic nerve

• Rods and cones detect light (photoreceptors).

• Rods = dim light, Cones = color and sharp vision.

• Rods and cones send graded signals (NOT action potentials) to bipolar cells.

• Bipolar cells integrate signals and pass them to ganglion cells.

• Ganglion cells generate action potentials.

• Action potentials travel through the optic nerve to the brain.

Contriburions of Santiago Ramon y Cajal to the understanding of visual perception

• Discovered that the nervous system is made of individual cells (neurons), not one continuous network ("Neuron Doctrine").

• Created detailed drawings of retinal cells (rods, cones, bipolar, ganglion, etc.).

• Showed how signals flow from photoreceptors → bipolar cells → ganglion cells.

• Helped explain the organization of the retina and how visual information moves toward the brain.

Anatomy of rod cell

• Outer segment:

  • Contains stacks of disks with rhodopsin (light-sensitive pigment).

  • Where light detection happens.

• Inner segment:

  • Contains nucleus, mitochondria, and other organelles.

  • Provides energy and cell maintenance.

• Cell body:

  • Houses the nucleus.

• Synaptic terminal:

  • Releases neurotransmitters to bipolar cells when light is detected.

Process by which photoreceptor cells transform light into action potentials

1. Light hits photoreceptor (rod or cone).

2. Rhodopsin (in rods) or similar pigment changes shape → activates a G-protein (transducin).

3. Transducin activates an enzyme that breaks down cGMP.

4. Low cGMP → cGMP-gated Na⁺ channels close → cell hyperpolarizes (becomes more negative).

5. Less neurotransmitter (glutamate) is released onto bipolar cells.

6. Depending on the bipolar cell type (ON or OFF), it depolarizes or hyperpolarizes.

7. Ganglion cells receive the signal and fire an action potential → sent to optic nerve.

Contributions of rhodopsin

• A light-sensitive pigment found in the outer segments of rod cells.

• Absorbs photons (light) and triggers the phototransduction cascade.

• Undergoes a shape change when hit by light (cis to trans form).

• Activates G-protein (transducin) → leads to closing Na⁺ channels → hyperpolarization of the rod cell.

• Essential for vision in low-light (scotopic) conditions.

Contributions of 11-cis-retinal

• A light-sensitive molecule bound to rhodopsin inside rod cells.

• Absorbs light and changes shape (isomerizes) to all-trans-retinal.

• This shape change activates rhodopsin, starting the phototransduction cascade.

• Without 11-cis-retinal, rhodopsin couldn't detect light, and vision wouldn't be triggered.

Contributions of all-trans-retinal and transducin to light sensitivity

All-trans-retinal:

• Formed when 11-cis-retinal absorbs light and changes shape.

• Triggers activation of rhodopsin, starting the phototransduction cascade.

• Essential for converting light energy into a biological signal.

Transducin:

• A G-protein activated by activated rhodopsin.

• Activates phosphodiesterase (PDE), which breaks down cGMP.

• Leads to closure of Na⁺ channels, hyperpolarization of the cell, and light signal transmission.

Know the signaling mechanisms that are associated with the dark response and light response in rod cells

Dark Response (no light):

• cGMP levels are high → cGMP-gated Na⁺ channels stay open.

• Na⁺ flows in → rod cell is depolarized.

• Rod cell releases lots of glutamate onto bipolar cells.

• No visual signal sent.

Light Response (light present):

• Light activates rhodopsin → activates transducin → activates PDE.

• PDE breaks down cGMP → Na⁺ channels close.

• Rod cell hyperpolarizes → less glutamate released.

• Changes in glutamate release trigger bipolar cells, leading to ganglion cell action potentials → visual signal sent.

How do rod cells transmit signals to bipolar cells and then on to ganglion cells

Rod Cell → Bipolar Cell → Ganglion Cell Signal Pathway:

• In darkness, rod cells are depolarized → they release glutamate onto bipolar cells.

• In light, rod cells hyperpolarize → less glutamate is released.

• Bipolar cells respond to changes in glutamate:

  • ON bipolar cells are activated by less glutamate (light).

  • OFF bipolar cells are activated by more glutamate (dark).

• Bipolar cells then adjust their membrane potential and signal ganglion cells.

• Ganglion cells fire action potentials and send the signal down the optic nerve to the brain.

What is the neurotransmitter released by rod cells

Glutamate

Difference in functionality between ON-bipolar and OFF-bipolar cells

ON-Bipolar Cells:

• Activated by light (when rod/cone releases less glutamate).

• Depolarize when glutamate levels drop.

• Promote action potential signaling to ganglion cells in light conditions.

OFF-Bipolar Cells:

• Activated by darkness (when rod/cone releases more glutamate).

• Depolarize when glutamate levels rise.

• Promote action potential signaling to ganglion cells in dark conditions.

Receptive Field

• The area of the retina (group of photoreceptors) that influences the activity of a single ganglion cell.

• Light hitting this area can increase or decrease the ganglion cell’s firing rate.

• Organized into center-surround regions:

• Helps with contrast detection and sharpens visual images.

Difference in cellular organization between the On-center receptive field and an Off-center recptive field

ON-Center Receptive Field:

• Center: Light → activates (depolarizes) the ganglion cell.

• Surround: Light → inhibits the ganglion cell.

• Connected mainly to ON-bipolar cells.

OFF-Center Receptive Field:

• Center: Light → inhibits the ganglion cell.

• Surround: Light → activates the ganglion cell.

• Connected mainly to OFF-bipolar cells.

Predict the action potential responses when light is directed at the central vs. peripheral region of an On-center receptive field; of an Off-center receptive field

ON-Center Receptive Field:

• Light on center:
  → Increases action potentials (ganglion cell fires more).

• Light on surround:
  → Decreases action potentials (ganglion cell fires less).

OFF-Center Receptive Field:

• Light on center:
  → Decreases action potentials (ganglion cell fires less).

• Light on surround:
  → Increases action potentials (ganglion cell fires more).

Developmental changes associated with the formation of the spinal cord

• Begins with the neural plate forming from the ectoderm (outer embryonic layer).

• The neural plate folds to form the neural tube.

• Neural tube closure happens around week 3–4 of embryonic development.

• The anterior (rostral) end of the neural tube becomes the brain, and the posterior (caudal) end forms the spinal cord.

• Cells along the neural tube differentiate into:

  • Neurons (nerve cells)

  • Glial cells (support cells)

• The tube’s inner cavity becomes the central canal of the spinal cord (filled with cerebrospinal fluid).

Developmental changes associated with the formation of the hindbrain

• The hindbrain further divides into two parts:

  • Metencephalon → becomes the pons and cerebellum.

  • Myelencephalon → becomes the medulla oblongata.

• These structures control basic life functions like breathing, heartbeat, and balance.

Developmental changes associated with the formation of the midbrain

• The midbrain (mesencephalon) stays undivided (unlike forebrain and hindbrain which split).

• The midbrain develops into structures that control:

  • Visual and auditory reflexes (tectum — superior and inferior colliculi).

  • Motor control (tegmentum, including substantia nigra).

• The cerebral aqueduct (canal for cerebrospinal fluid) also forms within the midbrain.

Developmental changes associated with the formation of the initial neural tube

• Starts with the neural plate forming from the ectoderm (outer embryonic layer).

• The neural plate folds upward to create neural folds with a neural groove between them.

• The folds move toward each other and fuse, forming the neural tube.

• Closure begins in the middle and moves upward (anterior) and downward (posterior).

• The anterior (rostral) end will form the brain; the posterior (caudal) end will form the spinal cord.

• Neural tube closure happens around weeks 3–4 of embryonic development.

Function of the cerebrum

• Controls higher brain functions like:

  • Thinking

  • Memory

  • Emotion

  • Voluntary movement

  • Sensory perception (touch, vision, hearing, etc.)

• Divided into right and left hemispheres, each controlling opposite sides of the body.

• Contains regions like the cerebral cortex (outer layer responsible for conscious thought) and basal nuclei (help regulate movement).

Function of the cerebellum

• Coordinates voluntary movements (like walking, writing, and reaching).

• Maintains balance and posture.

• Fine-tunes motor activity to make movements smooth and precise.

• Helps with motor learning (like riding a bike or playing an instrument).

Function of the Pons

• Acts as a bridge between different parts of the brain (cerebrum ↔ cerebellum ↔ medulla).

• Helps relay signals for sleep, respiration, swallowing, bladder control, hearing, taste, and facial expressions.

• Contains nuclei that assist in breathing regulation.

Function of the Medulla

• Controls vital automatic functions like:

  • Breathing

  • Heart rate

  • Blood pressure

  • Swallowing, coughing, and vomiting reflexes

• Connects the brain to the spinal cord.

• Essential for survival — damage can be life-threatening.

Function of the diencephalon

• Acts as a relay center and control hub for the brain.

• Includes key structures:

  • Thalamus: Relays sensory information to the cerebral cortex.

  • Hypothalamus: Regulates hormones, body temperature, hunger, thirst, and autonomic functions.

  • Epithalamus: Involved in sleep-wake cycles (via the pineal gland and melatonin production).

Anatomy of a spinal nerve

• Spinal nerves connect the spinal cord to the rest of the body.

• Each spinal nerve forms from two roots:

  • Dorsal root: Carries sensory (afferent) information into the spinal cord.

  • Ventral root: Carries motor (efferent) information out to muscles and glands.

• Dorsal root ganglion: Cluster of sensory neuron cell bodies on the dorsal root.

• Once roots merge, the spinal nerve is mixed (contains both sensory and motor fibers).

Gray matter

Gray Matter:

• Contains neuron cell bodies, dendrites, and unmyelinated axons.

• Responsible for processing and integrating information.

• In the spinal cord:

  • Forms an "H" or butterfly shape in the center.

  • Divided into dorsal horns (sensory) and ventral horns (motor).

• In the brain:

  • Found on the outer surface (cerebral cortex) and in deep nuclei.

White matter

• Made of myelinated axons (myelin gives it the white color).

• Responsible for transmitting signals quickly between different parts of the nervous system.

• In the spinal cord:

  • Surrounds the gray matter.

  • Organized into ascending (sensory) and descending (motor) tracts.

• In the brain:

  • Found deep inside, under the gray matter (except in some regions).

Dorsal horn

• Part of the gray matter in the spinal cord.

• Receives sensory (afferent) information from the dorsal root.

• Processes signals related to touch, pain, temperature, and pressure.

• Sends sensory information up to the brain for interpretation.

Ventral horn

• Part of the gray matter in the spinal cord.

• Contains motor (efferent) neuron cell bodies.

• Sends motor signals out through the ventral root to skeletal muscles.

• Controls voluntary muscle movement.

Dorsal root

• Carries sensory (afferent) signals into the spinal cord.

• Connects the sensory neurons to the dorsal horn of gray matter.

• Contains the dorsal root ganglion, which holds the cell bodies of sensory neurons.

Ventral root

• Carries motor (efferent) signals out of the spinal cord.

• Connects motor neurons from the ventral horn to muscles and glands.

• No ganglion here — it's purely outgoing motor fibers.

Sequence of events that comprise a knee-jerk reflex

Stretch receptors send axon potentials through dorsal horn to ventral horn, via sensory axons

• At synapses with motor neurons in ventral horn, action potentials are sent to leg muscles, causing contraction

Anatomy and functions of the reticular system

high area of brainstem; controls consciousness, sleep and wakefulness.

Low to mid-brainstem activity is involved with balance, coordination.

Important Areas of the Brainstem

Components of the limbic system and roles in regulating basic physiological drives

Structures in primitive regions of the telencephalon (cerebrum) form limbic system—responsible for basic physiological drives.

•Amygdala—involved in fear and fear memory

•Hippocampus—transfers short-term memory to long-term memory

How are the parasympathetic and sympathetic nervous systems related?

• Both are branches of the autonomic nervous system (ANS).

• They work together to maintain homeostasis by controlling involuntary body functions.

• Sympathetic system = "fight or flight" → prepares body for action (increases heart rate, dilates pupils, slows digestion).

• Parasympathetic system = "rest and digest" → conserves energy (slows heart rate, stimulates digestion, contracts pupils).

• They often have opposing effects on the same organs.

How do the parasympathetic and sympathetic nervous systems differ?

• Origin:

  • Sympathetic: Spinal cord (thoracic and lumbar regions).

  • Parasympathetic: Brainstem and sacral spinal cord.

• Function:

  • Sympathetic: Prepares body for stress ("fight or flight").

  • Parasympathetic: Promotes rest and recovery ("rest and digest").

• Effects on Body:

  • Sympathetic: Increases heart rate, dilates pupils, inhibits digestion.

  • Parasympathetic: Decreases heart rate, constricts pupils, stimulates digestion.

• Neurotransmitters:

  • Sympathetic: Mainly norepinephrine.

  • Parasympathetic: Mainly acetylcholine.

What activities does the parasympathetic nervous system regulate?

• Slowing heart rate

• Stimulating digestion (saliva, stomach, intestines)

• Increasing gland activity (like tear and saliva production)

• Constricting pupils

• Promoting urination and defecation

• Sexual arousal

• Overall: Rest, recovery, and energy conservation.

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What activities does the sympathetic nervous system regulate throughout the body?

• Increasing heart rate and blood pressure

• Dilating airways for more oxygen intake

• Dilating pupils to improve vision

• Inhibiting digestion (slow stomach and intestinal activity)

• Releasing glucose from the liver for quick energy

• Stimulating sweat glands to cool the body

• Activating adrenal glands to release epinephrine (adrenaline)

• Redirecting blood flow to muscles for "fight or flight" response

Different neurotransmitters between the parasympathetic and sympathetic nervous systems

Neurotransmitters:

• Parasympathetic Nervous System:

  • Uses acetylcholine (ACh) at both synapses:

    • Pre-ganglionic → ACh

    • Post-ganglionic → ACh

• Sympathetic Nervous System:

  • Uses acetylcholine (ACh) at the pre-ganglionic synapse.

  • Uses norepinephrine (NE) (or adrenaline) at the post-ganglionic synapse.

  • (Some sympathetic fibers, like those to sweat glands, still use ACh at the post-ganglionic synapse.)

What area of the brain contributes to language

Brain Areas Involved in Language:

• Broca’s Area (frontal lobe, usually left hemisphere):

  • Controls speech production (talking, forming words).

  • Damage → Broca’s aphasia (can understand language but struggle to speak).

• Wernicke’s Area (temporal lobe, usually left hemisphere):

  • Controls language comprehension (understanding spoken/written language).

  • Damage → Wernicke’s aphasia (can speak fluently but words may not make sense).

• Angular Gyrus (parietal lobe):

  • Involved in reading and writing language.

• Arcuate Fasciculus (fiber tract):

  • Connects Broca’s and Wernicke’s areas to coordinate understanding and speaking.

Wernicke’s area

In temporal lobe. Allow ability to understand spoken or

written language. Damage results in inability to speak sensibly; written or

spoken language not understood. Still can produce speech

Broca’s area

in frontal lobe; controls motor aspects of speech. damage

results in slow or lost speech; still can read and understand language

Primary motor cortex

• Located in the frontal lobe, specifically the precentral gyrus.

• Controls voluntary movements by sending signals to skeletal muscles.

• Organized somatotopically (motor homunculus) — different areas control different parts of the body.

• Damage can lead to muscle weakness or paralysis on the opposite side of the body.

Sequence of activity of the areas that lead to the repearing areas that lead to repeating of a word that is heard

• Auditory Cortex

  • Receives and processes the sound of the word.

• Wernicke’s Area

  • Interprets the meaning of the word (language comprehension).

• Arcuate Fasciculus

  • Transmits the information from Wernicke’s area to Broca’s area.

• Broca’s Area

  • Plans the motor movements needed to say the word.

• Primary Motor Cortex

  • Sends motor commands to the muscles of the mouth and throat to speak the word.

Contrast the activation of language areas that lead to speaking a word that is written

• Visual Cortex

  • Receives and processes the visual input (the written word).

• Angular Gyrus

  • Translates visual information into a language form that Wernicke’s area can understand.

• Wernicke’s Area

  • Interprets the word’s meaning (language comprehension).

• Arcuate Fasciculus

  • Relays information from Wernicke’s to Broca’s area.

• Broca’s Area

  • Plans motor movements to pronounce the word.

• Primary Motor Cortex

  • Executes the movement to actually speak the word.