Muscle Histology Part 2 - Video Notes Review

A set of 50 vocabulary-flashcards focusing on muscle histology concepts from the notes, including skeletal muscle proprioceptors, cardiac and smooth muscle structure, neuromuscular junctions, and contraction mechanisms.

Skeletal muscle proprioceptors

Sensory receptors in skeletal muscle that detect muscle length and position (proprioception).

Muscle spindle

A proprioceptor within a muscle consisting of intrafusal fibers that detects changes in muscle length.

Intrafusal fibers

Specialized skeletal muscle fibers inside the muscle spindle that transduce stretch information.

Extrafusal fibers

The ordinary skeletal muscle fibers that generate force outside the spindle.

Afferent fibers

Sensory nerve fibers carrying information toward the central nervous system.

Efferent fibers

Motor nerve fibers carrying commands away from the central nervous system to muscles.

Golgi tendon organ

Proprioceptor at the myotendinous junction that monitors muscle tension.

Myotendinous junction

Junction where muscle fibers meet tendon; site of the Golgi tendon organ.

Type 1b sensory nerves

Sensory fibers associated with Golgi tendon organs.

Proprioception

Sensation of body position and movement mediated by proprioceptors.

Cardiac muscle

Striated, branched heart muscle with intercalated discs; has dyads and spontaneous rhythmicity.

Intercalated discs

Junctions between cardiac muscle cells containing desmosomes and gap junctions for coordinated contraction.

Branched cardiac muscle fibers

Cardiac muscle cells that are branched and interconnected to coordinate pumping.

Dyad

Structure in cardiac muscle: a T-tubule paired with a single sarcoplasmic reticulum; located at the Z-band.

Z-disc (Z-band)

Sarcomere boundary where actin attaches; dyads are located near the Z-band in cardiac muscle.

T-tubule

Transverse invagination of the sarcolemma; forms a dyad with SR near the Z-band in cardiac muscle.

Sarcoplasmic reticulum (SR)

Calcium storage organelle; in cardiac muscle it is present but less extensive than in skeletal muscle.

Atrial natriuretic factor (ANF)

Hormone secreted by the atria that promotes sodium excretion and regulates water balance.

Autonomic nervous system (ANS)

Nervous system that modulates heart rhythm and smooth muscle contraction via sympathetic and parasympathetic input.

Smooth muscle

Fusiform, non-striated muscle lacking organized sarcomeres; contracts slowly and is regulated by the ANS and hormones.

Fusiform cells

Spindle-shaped smooth muscle cells.

Gap junctions

Intercellular channels enabling electrical coupling between smooth muscle cells.

Syncytium

A network of smooth muscle cells that contracts as a unit due to gap junctions.

Central nucleus

Nucleus located near the center of the cell; common in certain cardiac cells (often 1–2 per cell in cardiac).

No organized sarcomeres

Smooth muscle lacks the orderly sarcomere structure seen in skeletal muscle.

No T-tubules

Smooth muscle does not have transverse tubules; calcium entry occurs via other structures like caveolae.

Caveolae

Small invaginations of the smooth muscle cell membrane that aid calcium entry.

No motor end plate

Smooth muscle receives neural input via diffuse junctions rather than a specialized motor end plate.

Slow, prolonged contraction

Characteristic of smooth muscle: contraction is slow and can be sustained for a long time.

Dense bodies

Anchoring points in smooth muscle where actin and intermediate filaments attach, similar to Z-discs.

Actin (thin filaments)

Thin contractile filaments; in smooth muscle actin associates with calmodulin.

Myosin (thick filaments)

Thick contractile filaments; in smooth muscle, cross-bridge cycling is regulated by MLCK.

Calmodulin

Calcium-binding protein that activates MLCK in smooth muscle.

Myosin light-chain kinase (MLCK)

Enzyme that phosphorylates myosin light chains to enable contraction in smooth muscle.

Calcium-calmodulin (Ca2+-CaM)

Calcium-bound calmodulin that activates MLCK to initiate smooth muscle contraction.

Phosphorylation of myosin light chains

MLCK-mediated addition of phosphate groups to myosin light chains enabling contraction.

Cross-bridge cycling

Interaction of phosphorylated myosin with actin to generate force.

Latticelike network

Network of actin filaments arranged with dense bodies providing a lattice in smooth muscle.

Visceral (unitary) smooth muscle

Smooth muscle where cells are electrically coupled and contract as a unit (often in hollow organs).

Multi-unit smooth muscle

Smooth muscle where individual fibers are sparsely innervated and can contract independently.

Inner circular layer

The circular smooth muscle layer surrounding the lumen in hollow organs.

Outer longitudinal layer

The longitudinal smooth muscle layer arranged along the length of the organ.

Diffuse junctions

Diffuse synapses in smooth muscle where neurotransmitters are released onto the muscle matrix.

Varicosities

Swellings along autonomic nerve fibers that release neurotransmitters near smooth muscle.

Postganglionic neuron

Autonomic neuron that sends signals to smooth muscle after synapsing in a ganglion.

Acetylcholine (ACh)

Neurotransmitter released by autonomic nerves; effects on smooth muscle depend on receptor type.

Norepinephrine (NE)

Autonomic neurotransmitter involved in smooth muscle regulation.

Desmosomes

Junctions in intercalated discs providing mechanical linkage between cardiac cells.

Spontaneous contractile rhythm

Inherent rhythmic beating of cardiac muscle modulated by autonomic input and hormones.

Renal effect of ANF

ANF promotes natriuresis and diuresis by reducing sodium reabsorption in the kidneys.

Junctional complexes in cardiac cells

Intercalated discs comprising desmosomes and gap junctions that coordinate contraction.

Branching appearance

Cardiac muscle cells are branched and interconnected, contributing to the heart’s architecture.

Z-band proximity of dyads

In cardiac muscle, dyads are located near the Z-band, a feature linked to calcium release sites.

Atrial natriuretic factor secretion in atria

ANF is secreted by the atria (R and L atria) to regulate fluid balance.

Contraction regulation by ANS and hormones

Smooth and cardiac muscle contractions are modulated by the autonomic nervous system and circulating hormones.

Uptake of calcium in smooth muscle via caveolae

Calcium entry into smooth muscle occurs partly through caveolae rather than T-tubules.

T-tubule absence in smooth muscle

Smooth muscle lacks T-tubules, differing from skeletal and cardiac muscle anatomy.

One SR (poorly defined) in cardiac muscle

Cardiac muscle has a sarcoplasmic reticulum that is less extensive and less defined than in skeletal muscle.

Central versus peripheral nuclei

Cardiac muscle cells typically have central nuclei, unlike peripheral nuclei in skeletal muscle.

Actin-myosin cross-bridges in smooth muscle

Cause contraction when myosin heads slide along actin filaments during MLCK-mediated activation.

Dense bodies as Z-disc analogs

In smooth muscle, dense bodies anchor actin and intermediate filaments similarly to Z-discs.

Carlial intercalated disc junctions

Cardiac intercalated discs contain desmosomes and gap junctions to couple cells.

Hormone that affects kidney function

ANF acts on kidney cells to promote sodium excretion and water balance.

Anatomy: inner circular and outer longitudinal layers in the intestine

Two-layer organization of smooth muscle in the small intestine: inner circular and outer longitudinal layers.

Skeletal muscle organization vs smooth/cardiac

Skeletal muscle is striated and typically voluntary, while cardiac is striated but involuntary, and smooth muscle is non-striated and involuntary.