NS

Lecture 4: Muscle and Nerve Tissue

Lecture Objectives

  • Describe general features of muscle tissue, understand location, structure and function

  • describe general features of nervous tissue, understand the function of its component cells

Muscle Tissue

  • Definition: Comprised of elongated cells (muscle cells or myocytes) that utilize ATP hydrolysis to create force.

  • Functions:

    • Produces body movements

    • Maintains posture

    • Generates heat

Types of Muscle Tissue

  • Types: Three main types comprising about 50% of body tissue mass:

    1. Skeletal Muscle

    2. Cardiac Muscle

    3. Smooth Muscle

Skeletal Muscle

  • Characteristics:

    • Approximately 650 named skeletal muscles in the body

    • Attached to bones by tendons

    • Striated appearance under microscope due to arrangement of lots of myofibrils

    • Voluntary control (except in posture maintenance)

    • Made up of fibers are cylindrical and can vary in length (longest is up to 60 cm, e.g. sartorius)

    • Smallest muscle is stapedius (1.25 mm), alters loudness of sound

  • Structure:

    • Long cells

    • Multinucleate (nuclei pushed to the side)

Functions of Skeletal Muscle

  • Functions include:

    • Motion

    • Posture

    • Heat production

    • Protection

Myofibrils and Striations

  • Myofibrils:

    • Myofibrils Fill the muscle fiber's cytoplasm and are responsible for striations

    • Composed of Myofilaments

      • Thin filaments: Actin (8 nm diameter)

      • Thick filaments: Myosin (16 nm diameter)

    • Myofilaments are Arranged in sarcomeres, which are basic functional units for myofirbils

  • Sarcomere Structure:

    • Z discs: Separate sarcomeres

    • A band: Dark area (All thick filaments present)

    • I band: Light area (thin filaments only)

    • H zone: Thick filaments only

    • M line: Middle line, anchors thick filaments

Connective Tissue Components

  • Epimysium: Surrounds entire muscle

  • Perimysium: Surrounds fascicles

  • Endomysium: Surrounds individual muscle fibers (layer for nerves/capillaries)

  • Sarcoplasm: Cytoplasm of muscle cells

  • Sarcolemma: Plasma membrane of muscle cells

Cardiac Muscle

  • Characteristics:

    • Striated and branched

    • Single central nucleus

    • Intercalated discs join fibers end-to-end - Intercelated discs include desmosomes, and gap junctions

      - Intercelated discs contain desmosomes and gap junctions

  • Control: Involuntary

  • Function:

    • Conducts electrical impulses through specialized cells (Purkinje fibers)

Smooth Muscle

  • Characteristics:

    • Non-striated, spindle-shaped

    • Single central nucleus

    • Located in the walls of hollow internal structures (e.g., intestines, blood vessels, skin)

    • Thin filaments (actin) attach to dense bodies, dense bodies include protein Actinin - Very good at contracting a tubular structure

  • Control: Involuntary

Nervous Tissue

  • The nervous system helps to maintain homeostasis, initiates voluntary movements, responsible for perception, behaviour and memory

  • Activities are grouped under 3 functions:

    1. Sensory - Detection of internal and external stimuli then alert CNS

    2. Integrative - Analysis and storing of info

    3. Motor - Effector in response to stimuli through PNS

      • Nervous tissue contains 2 types of cells = neurons, neuroglia

Neurons

  • Axon - Carrays the nerve impulse away from neuron, and outputs the impulse

  • Dendrites - The receiving/input part of the neuron

  • Multipolar Neurons:

    - Has 2 or more dendrites and 1 axon

    - Most common neuron of CNS

    - All motor neurons are multipolar neurons

  • Bipolar Neurons:

    - Has a dendoooritic process and then an axon process (1 axon)

    - Has cell body between axon and dendrite

    - Special sense organs relay info from receptor to neurons

  • Unipolar Neurons:

    - Dendrites and axon are continuous

    - Cell body hanging off to one side

    - Most sensory nerves are unipolar

  • Anaxonic Neurons:

    - cannot distinguish dendrites and axon

    - Found in brain and special sense organs

Neouroglia

  • Found in both CNS and PNS

  • Maintains physical structure of nervous tissue, undertakes phagocytosis, nutrient supply to neurons, regulates interstitial fluid in neural tissue

  • Neuroglia are classified into CNS neuroglia and PNS neuroglia

  1. CNS Neuroglia:

    Astrocytes -

    • Star shaped

    • Maintains blood-brain barrier, and helps repair and support

    • Communicates via gliotransmitters

    • Maintains environment around neurons by e.g regulating ions

Oligodendrocytes -

  • Forms insulating myelin sheet around CNS axons - can myelinate omore that one neurons axon

Microglia -

  • Phagocytic - Helps protection

Ependymal Cells -

  • Produces CSF

  • They line the CSf filled ventricles in the brain and the central canal of spinal cord

    They have cilia (flow) and microvili (sampling)

  • Moves nutrients and waste

  1. PNS Neuroglia -

Schwann Cells -

  • Form insulating myelin sheet around axons (one schwann cell per axon for myelination)

Satellite Cells -

  • Surrond neuron cell bodies. Support and help fluid exchange