Nerve and Muscle Tissue – Key Vocabulary

Vocabulary flashcards covering essential terms from nerve and muscle tissue histology.

Neuron

Excitable cell of the nervous system with a soma, dendrites, and a single axon that conducts impulses.

Glial Cells

Supportive neural cells with short processes that protect, nourish, and insulate neurons.

Central Nervous System (CNS)

Brain and spinal cord; integrative command center of the nervous system.

Peripheral Nervous System (PNS)

Cranial, spinal, and peripheral nerves plus ganglia that connect CNS to body.

Sensory (Afferent) Division

Pathway carrying sensory information from receptors to the CNS.

Motor (Efferent) Division

Pathway transmitting commands from CNS to effectors (muscles / glands).

Soma (Perikaryon)

Neuron cell body containing nucleus, Nissl substance, and the metabolic machinery.

Dendrite

Neuron process that receives synaptic input and conveys it to the soma.

Axon

Long neuronal process that conducts action potentials to other cells.

Axon Hillock

Pyramidal region of soma where the axon originates; lacks Nissl bodies.

Nissl Substance

Basophilic aggregates of rough ER and polyribosomes in neuron soma and dendrites.

Axolemma

Plasma membrane of an axon.

Axoplasm

Cytoplasm within an axon.

Synapse

Specialized junction where a presynaptic neuron transmits a signal to a postsynaptic cell.

Astrocyte

Most numerous CNS glial cell; forms blood-brain barrier, regulates ions, supports neurons.

Oligodendrocyte

CNS glial cell that myelinates and insulates multiple axons.

Microglial Cell

Phagocytic immune cell of CNS derived from monocytes; removes debris and pathogens.

Ependymal Cell

Ciliated glial cell lining brain ventricles and spinal cord canal; helps produce / circulate CSF.

Schwann Cell (Neurolemmocyte)

PNS glial cell that myelinates a segment of a single axon; forms Nodes of Ranvier.

Satellite Cell (of ganglia)

PNS glial cell surrounding neuronal cell bodies in ganglia, providing support and exchange.

Blood-Brain Barrier

Selective barrier formed by tight-junctioned capillary endothelia and astrocytic feet that protects CNS milieu.

Myelin Sheath

Lipid-rich wrapping of oligodendrocytes (CNS) or Schwann cells (PNS) that insulates axons and speeds conduction.

Nodes of Ranvier

Gaps between myelin segments where action potentials are regenerated.

Muscle Tissue

Contractile tissue classified as skeletal, cardiac, or smooth based on structure and control.

Skeletal Muscle

Voluntary, striated muscle composed of long multinucleated fibers with peripheral nuclei.

Cardiac Muscle

Involuntary, striated muscle of the heart; branched cells with central nuclei and intercalated discs.

Smooth Muscle

Involuntary, non-striated fusiform cells found in viscera and vessels; slow, sustained contractions.

Sarcolemma

Plasma membrane plus external lamina of a muscle fiber.

Sarcoplasm

Cytoplasm of a muscle cell containing myofibrils and organelles.

Sarcoplasmic Reticulum (SR)

Smooth ER of muscle that stores and releases Ca²⁺ for contraction.

Sarcomere

Basic contractile unit between two Z discs in striated muscle.

Triad

Two terminal cisternae of SR plus a T-tubule at the A-I junction in skeletal muscle.

Epimysium

Dense irregular connective tissue sheath surrounding an entire muscle.

Perimysium

Connective tissue layer encasing each muscle fascicle; carries vessels and nerves.

Endomysium

Delicate reticular fiber layer surrounding individual muscle fibers within a fascicle.

Myofibril

Cylindrical bundle of myofilaments organized into repeating sarcomeres inside a muscle fiber.

A Band

Dark band of a myofibril containing overlapping thick and thin filaments.

I Band

Light band containing only thin filaments; bisected by the Z disc.

Z Disc

Structural line anchoring thin filaments and marking sarcomere boundaries.

Thick Filament

Myosin filament containing 200–500 myosin molecules.

Thin Filament

Filament of F-actin, tropomyosin, and troponin in striated muscle.

Intercalated Disc

Specialized junctional complex joining cardiac muscle cells; contains fascia adherens, desmosomes, and gap junctions.

Dyad

Cardiac muscle junction of one T-tubule with one terminal cisterna of SR.

Dense Body

α-Actinin-rich structure in smooth muscle anchoring actin filaments and transmitting contractile force.

Calmodulin

Ca²⁺-binding protein that activates MLCK to initiate smooth muscle contraction.

MLCK (Myosin Light-Chain Kinase)

Enzyme phosphorylating myosin in smooth muscle, enabling actin-myosin interaction.