11 Nervous Tissue

Nervous Tissues Overview

Introduction to Nervous Tissues

  • The nervous system is responsible for controlling and communicating throughout the body.

Basic Functions of the Nervous System

  • Master Control: The nervous system acts as the primary control and communication center.

  • Rapid Communication: Sends quick signals using electrical impulses.

Information Flow Through the Nervous System:

  1. Sensory Input: Collects information from the body's surroundings using sensory receptors.

  2. Integration: Processes and interprets the information gathered to decide how to respond.

  3. Motor Output: Activates muscles or glands to carry out the response.

Structural Divisions of the Nervous System

  • Central Nervous System (CNS): Includes the brain and spinal cord; it integrates and controls.

  • Peripheral Nervous System (PNS): Consists of all nerves outside the CNS; responsible for relaying messages to and from the body.

Subdivisions of the PNS

  • Sensory (Afferent) Division: Conveys signals to the CNS.

    • Somatic Sensory Fibers: Send signals from skin, muscles, and joints.

    • Visceral Sensory Fibers: Carry signals from organs.

  • Motor (Efferent) Division: Sends signals from the CNS to effectors (muscles and glands).

    • Somatic Nervous System: Controls voluntary movements (skeletal muscles).

    • Autonomic Nervous System: Manages involuntary functions.

      • Sympathetic Nervous System: Activates body during stress (fight or flight).

      • Parasympathetic Nervous System: Conserves energy (rest and digest).

Types of Support Cells (Neuroglia)

  • Glial Cells: Support and protect neurons.

    • Astrocytes: Nourish and maintain neuron environment.

    • Microglia: Act like immune cells, cleaning up debris.

    • Ependymal Cells: Line brain cavities and help circulate cerebrospinal fluid.

    • Oligodendrocytes: Create insulation (myelin sheaths) in the CNS.

    • Satellite Cells: Provide support in PNS.

    • Schwann Cells: Form myelin sheaths around PNS axons.

Neurons: Structure and Function

  • Neurons: The main signaling cells, consisting of:

    • Cell Body: Contains the nucleus and organelles.

    • Dendrites: Branches that receive signals.

    • Axon: Long extension that sends signals away.

  • Neurons are unique: They don’t reproduce, live a long time, and use a lot of energy (high metabolic rate).

Membrane Potentials

  • Resting Membrane Potential: Usually around -70mV, meaning the inside of the cell is negatively charged compared to the outside.

  • Ion Channels: Proteins that regulate the entry/exit of ions, including:

    • Gated Channels: Open/close in response to stimuli.

    • Leak Channels: Always open, letting ions flow freely.

Graded Potentials

  • Small changes in membrane potential, usually occurring in dendrites.

  • Can be positive (depolarizing) or negative (hyperpolarizing) and depend on the stimulus strength.

Action Potentials

  • Rapid rise and fall in membrane potential, going from -70mV to +30mV.

  • Involves:

    1. Depolarization: Cell becomes less negative.

    2. Repolarization: Cell returns to a negative state.

    3. Hyperpolarization: Cell becomes more negative than resting potential temporarily.

Synapses: Communication Between Neurons

  • Synapses: Connections between neurons or between a neuron and another cell.

    • Electrical Synapses: Allow for fast direct connections.

    • Chemical Synapses: Use neurotransmitters to send signals across gaps.

Neurotransmitters

  • Chemicals that transmit signals in the nervous system.

    • Acetylcholine: Involved in muscle activation.

    • Biogenic Amines: Include dopamine (pleasure) and norepinephrine (stress response).

    • Amino Acids: Such as GABA (inhibitory) and glutamate (excitatory).

    • Peptides: Like endorphins (block pain).

Summary

  • Understanding nervous tissues is crucial for grasping their roles in body functions, including differences between graded and action potentials, and the importance of neurons and glial cells in the overall functioning of the nervous system.