Lect4 BIOSCI

BioSci 107 Lecture Overview

• Topic: Muscle and Nerve Tissue

• Date: 2025

• Instructor: Anthony Phillips

Objectives

• Muscle Tissue

  • Describe general features, including location, structure, and function.

• Nervous Tissue

  • Understand the function of its component cells.

Muscle Tissue

• Definition: Composed of elongated cells (muscle fibers or myocytes) using ATP hydrolysis to generate force.

  • Functions: Body movements, posture maintenance, and heat generation.

• Types: Three types comprise approximately 50% of body tissue mass:

  1. Skeletal Muscle

  2. Cardiac Muscle

  3. Smooth Muscle

Skeletal Muscle

• Approximately 650 named skeletal muscles.

• Location and Attachment: Attached to bones via tendons.

• Microscopic Appearance: Striated under the microscope.

• Control Type: Voluntary contraction (with some exceptions such as posture).

• Structure:

  • Cylindrical fibers (cells).

  • Longest muscle: Sartorius (up to 60 cm).

  • Smallest muscle: Stapedius (1.25 mm).

• Functions: Motion, posture, heat generation, and protection.

Structural Features of Skeletal Muscle

• Striations: Result from highly organized myofibrils filling the sarcoplasm.

• Myofibrils: Composed of two types of myofilaments:

  • Thin Filaments: Composed of actin, 8 nm diameter.

  • Thick Filaments: Composed of myosin, 16 nm diameter.

• Sarcomeres: Basic functional unit housing myofilaments separated by Z discs.

  • Parts include:

    • A Band: Dark part with thick filaments.

    • I Band: Thin filaments only.

    • H Zone: Thick filaments only.

    • M Line: Middle part of sarcomere.

Connective Tissue in Skeletal Muscle

• Epimysium: Surrounds the entire anatomical muscle.

• Perimysium: Surrounds fascicles.

• Endomysium: Surrounds individual muscle fibers (cells).

• Sarcoplasm: Cytoplasm of muscle cells.

• Sarcolemma: Cell membrane of muscle fibers.

Cardiac Muscle

• Location: Heart.

• Shape and Structure: Striated, branched fibers, single central nucleus, intercalated discs for cell junctions.

• Control Type: Involuntary.

• Functionality: Conduct electrical activity with specialized Purkinje fibers having fewer myofibrils and more gap junctions.

Smooth Muscle

• Location: Walls of hollow internal structures (e.g. intestines, blood vessels).

• Structure: Non-striated, spindle-shaped fibers with a single central nucleus.

• Control: Involuntary.

• Function: Regulates internal movements such as peristalsis and blood vessel constriction.

• Myofilament Arrangement: Thin filaments attaching to dense bodies; contraction results in twisting motion due to tension on intermediate filaments.

Nervous Tissue Overview

• Functions: Maintains homeostasis, initiates voluntary movements, responsible for perception, behavior, and memory.

• Components: Two main divisions:

  • Central Nervous System (CNS): Brain and spinal cord.

  • Peripheral Nervous System (PNS): All nervous tissue outside the CNS.

    • Divisions:

      • Sensory/Afferent: Carries information to CNS.

      • Motor/Efferent: Carries information from CNS to effectors (muscles and glands).

    • Major Functions:

      1. Sensory: Detection and transfer of stimuli.

      2. Integrative: Information analysis and storage.

      3. Motor: Activation of effectors through the PNS.

Neuron and Neuroglia Cells

• Two types of cells in nervous tissue:

  • Neurons: Longest cells, usually do not divide, high metabolic rate.

  • Neuroglia: Supportive cells, more numerous than neurons, can divide, do not propagate action potentials.

Neuron Structure

• Components:

  • Cell Body (Soma): Site for metabolic activity.

  • Dendrites: Conveys impulses to the neuron.

  • Axon: Conducts impulses away from the neuron.

Types of Neurons

• Multipolar Neurons: Most common in CNS, have multiple dendrites and one axon.

• Bipolar Neurons: Two distinct processes, rare; involved in special senses (sight, smell).

• Unipolar Neurons: Continuous dendrite and axon; common in sensory nerves.

• Anaxonic Neurons: Rare with unclear function, found in brain and special sense organs.

Neuroglia Types in CNS

• Astrocytes: Star-shaped, regulate environment, support neurons, maintain blood-brain barrier.

• Oligodendrocytes: Form myelin sheath around CNS axons.

• Microglia: Function as resident macrophages, providing protection.

• Ependymal Cells: Line ventricles, produce cerebrospinal fluid (CSF).

Neuroglia Types in PNS

• Schwann Cells: Myelinates PNS axons, supports unmyelinated axons.

• Satellite Cells: Surround neuron cell bodies in ganglia; function similarly to astrocytes in the CNS.

Textbook References

• Various editions of Tortora and Martini textbooks were used for information and images.