BIOL 16 note cards

In skeletal muscle, which regulatory protein binds Ca²⁺?

Troponin.

What is the main functional advantage of multi-unit smooth muscle?

Fine, precise control of contraction.

How does nerve input differ in multi-unit smooth muscle?

It has more localized autonomic innervation, with contractions regulated primarily by neural signals.

What is the main role of the posterior horn?

Receiving and processing sensory information.

What does reciprocal inhibition mean in the withdrawal reflex?

Activation of one muscle group is accompanied by inhibition of its opposing group.

Does Golgi tendon organ feedback always inhibit muscle activity?

No. Its effects can vary; the lecture describes the classical inhibitory pathway.

Why is a spinal nerve called a mixed nerve?

It contains both sensory and motor fibers.

In the patellar reflex, which muscle is stretched by the tendon tap?

Quadriceps.

What is the function of a sensory (afferent) neuron?

It carries information from sensory receptors toward the CNS.

What are the four fundamental properties of muscle tissue?

Excitability, contractility, extensibility, and elasticity.

What is a fixator?

A muscle that stabilizes a joint or muscle attachment during a movement.

What additional membrane may help separate compartments?

An interosseous membrane.

Does the crossed-extensor reflex act on the same side as the stimulus or the opposite side?

The opposite (contralateral) side, coordinated with ipsilateral withdrawal.

How does vascular smooth muscle influence blood pressure and blood flow?

By constricting or relaxing blood vessels to change their diameter.

Name three examples of multi-unit smooth muscle from the lecture.

Iris, ciliary muscle, and arrector pili muscles.

A muscle prevents the shoulder from moving while the elbow bends. Which role is it performing?

Fixator.

Why is single-unit smooth muscle suited for peristalsis?

Connected cells coordinate contractions that move contents through the GI tract.

What does the term stereotyped mean when describing reflexes?

The response follows a predictable pattern, although it can be modified.

What type of sensory afferent carries GTO signals to the spinal cord?

A group Ib afferent.

Where are the cell bodies of spinal sensory neurons located?

In the dorsal root ganglia.

What happens to muscle force in the classical autogenic inhibition pathway?

Muscle force decreases.

What can happen when bleeding or swelling occurs inside a fascial compartment?

Pressure can increase within the relatively enclosed space.

A reflex changes pupil diameter. Is its effector somatic or visceral?

Visceral (autonomic); it acts through smooth muscle.

What is a nerve fascicle?

A bundle of nerve fibers (axons) within a peripheral nerve.

Name three locations with single-unit smooth muscle in the lecture.

GI tract, uterus, and bladder.

Arrange the nerve coverings from an individual fiber outward.

Endoneurium → perineurium → epineurium.

What type of contraction often allows a fixator to stabilize a region?

An isometric contraction.

What does functional syncytium mean in single-unit smooth muscle?

Many connected cells act together as one functional group.

What general shape do smooth muscle cells have?

Fusiform (spindle-shaped), tapering at both ends.

What two changes promote smooth muscle relaxation?

Intracellular Ca²⁺ decreases and myosin is dephosphorylated.

Name two somatic reflexes from the lecture.

The stretch reflex and the withdrawal reflex.

What do gamma motor neurons regulate?

Muscle spindle sensitivity during movement.

Why is the flexor withdrawal reflex classified as polysynaptic?

Its sensory input activates spinal interneurons before the motor response.

What is a fascial compartment?

A closed space surrounded by deep fascia that contains a group of muscles and associated structures.

A neuron carries stretch information from muscle to the spinal cord. How is it classified by function?

Sensory (afferent) neuron.

What coordinates the motor responses on both sides in a crossed-extensor reflex?

Spinal interneurons.

What three major functional types of fibers can spinal nerves contain?

Sensory, somatic motor, and autonomic fibers.

Put the smooth muscle activation steps in order, beginning with Ca²⁺.

Ca²⁺ increases → binds calmodulin → activates MLCK → myosin is phosphorylated → cross-bridge cycling.

A person steps on something sharp with the left foot. Which leg extends to support the body?

The right leg, through the crossed-extensor reflex.

What information travels through the posterior (dorsal) root?

Sensory (afferent) information traveling toward the spinal cord.

Does smooth muscle have T-tubules like skeletal muscle?

No. Smooth muscle lacks T-tubules.

What is a familiar example of the stretch reflex?

The patellar (knee-jerk) reflex.

How do gap junctions support contraction in single-unit smooth muscle?

Electrical signals can spread between cells, coordinating their activity.

Where are interneurons located?

Within the CNS.

Why are reflexes described as rapid?

Their responses generally occur after relatively short delays.

Which connective tissue surrounds a fascicle?

Perineurium.

What does the anterior horn contain?

Somatic motor neurons.

Name the intermediate filament proteins mentioned for smooth muscle.

Desmin and/or vimentin.

What defines a polysynaptic reflex pathway?

It includes one or more interneurons between sensory input and motor output.

What happens during smooth muscle cross-bridge cycling?

Myosin pulls on actin filaments to generate tension.

Which horn contains autonomic preganglionic neurons in certain spinal cord regions?

The lateral horn.

Which property allows a muscle to generate active force?

Contractility.

What are dense bodies in smooth muscle cells?

Structures that anchor actin and intermediate filaments, functionally similar to skeletal muscle Z-discs.

How is gray matter organized in the spinal cord?

Into horns containing neuronal cell bodies and synapses.

Which spinal cord region would you associate with incoming sensory information?

The posterior horn.

How are smooth muscle cells often arranged in hollow-organ walls?

In layers or sheets.

What type of tissue is the effector in a somatic reflex?

Skeletal muscle.

What is the role of the pyloric sphincter?

It regulates stomach emptying.

Name two visceral reflex functions from the lecture.

Pupil constriction and blood pressure regulation.

What is the name of the condition associated with dangerously increased compartment pressure?

Compartment syndrome.

What are varicosities on autonomic nerve fibers?

Swellings along autonomic axons that release neurotransmitters near smooth muscle cells.

Which root would carry a command from a somatic motor neuron to skeletal muscle?

The anterior (ventral) root.

Where are somatic motor neuron cell bodies found in the spinal cord?

The anterior horn.

What does MLCK do to myosin?

It phosphorylates myosin light chains, enabling cross-bridge cycling.

During elbow flexion, what role does triceps brachii play?

Antagonist; it opposes or controls elbow flexion.

What protein binds Ca²⁺ to initiate the smooth muscle activation pathway?

Calmodulin.

How do muscle spindles and Golgi tendon organs differ in what they sense?

Muscle spindles sense muscle length/length changes; Golgi tendon organs sense tension.

Which muscles provide voluntary external sphincter control for urination and defecation?

The external urethral and external anal sphincters (skeletal muscle).

Name the three major white-matter funiculi.

Anterior, lateral, and posterior funiculi.

What is an antagonist?

A muscle that opposes or helps control a movement.

What is a reflex?

An automatic, predictable response to a sensory stimulus.

What is the efferent pathway in a reflex arc?

The motor neuron carrying commands from the spinal cord toward an effector.

How does airway smooth muscle affect airflow?

It adjusts airway diameter.

Why is grouping muscles into fascial compartments functionally useful?

Muscles with related actions are grouped for coordinated movement.

What defines a monosynaptic reflex pathway?

A direct synapse between a sensory neuron and a motor neuron.

What does phosphorylation mean in the smooth muscle activation pathway?

Adding a phosphate group to a myosin regulatory light chain.

Why does smooth muscle lack visible striations?

Its actin and myosin filaments are not organized into sarcomeres.

Which root would carry a signal from a skin receptor into the spinal cord?

The posterior (dorsal) root.

What supplies do muscles in the same fascial compartment usually share?

Nerve and blood supplies.

How does the sarcoplasmic reticulum (SR) of smooth muscle compare with skeletal muscle?

Smooth muscle generally has a less-developed SR.

What are the two sources of Ca²⁺ that raise intracellular Ca²⁺ during smooth muscle activation?

Ca²⁺ enters from extracellular fluid and is released from the SR.

What structural connections coordinate single-unit smooth muscle cells?

Gap junctions.

Which pathway component carries information into the spinal cord: afferent or efferent?

Afferent.

What stimulus activates the stretch (myotatic) reflex?

Stretching a muscle.

What are intermuscular septa?

Inward extensions of deep fascia that separate fascial compartments.

Which muscle tissue contracts to expel urine from the bladder?

Smooth muscle.

What activates myosin light-chain kinase (MLCK)?

The Ca²⁺–calmodulin complex.

Which pathway component carries commands out of the spinal cord: afferent or efferent?

Efferent.

What is found in the posterior (dorsal) root ganglion?

Cell bodies of spinal sensory neurons, which are pseudounipolar neurons.

What does a Golgi tendon organ detect?

Tension in the muscle–tendon unit.

Why is the crossed-extensor reflex polysynaptic?

nterneurons connect sensory signals to coordinated motor responses across the spinal cord.

What structures can act as effectors for motor output?

Muscles or glands.

How does sensory input activate quadriceps contraction in the stretch reflex?

Sensory neurons directly excite alpha motor neurons in the spinal cord.

Where is the Golgi tendon organ located?

Near the muscle–tendon junction.

What are the five components of a spinal reflex arc in order?

Receptor → afferent pathway → integration center → efferent pathway → effector.

What is the receptor's role in a reflex arc?

It detects a stimulus and converts it into an electrical signal.

During the crossed-extensor reflex, what happens in the contralateral limb?

Extensors contract and flexors are inhibited, allowing the limb to support weight.

What type of receptor detects the potentially damaging stimulus that triggers withdrawal?

A nociceptor.

What kinds of pathways travel through white-matter funiculi?

Ascending and descending axon tracts.