Nerves and Neural Tissue Notes

Introduction to Nerves and Neural Tissue

  • Definition of Nerves:

    • Nerves are cables carrying electrical impulses between the brain and the rest of the body.

    • Impulses enable sensations and muscle movements, and regulate autonomic functions (breathing, sweating, digestion).

    • Neurons are the nerve cells forming the foundational structure of the nervous system.

    • Peripheral Nervous System (PNS) refers to the nerves outside the brain and spinal cord.

Types of Nerves

  • Main Types of Nerves:

    • Sensory Nerves:

    • Carry signals to the brain related to touch, taste, smell, and vision.

    • Motor Nerves:

    • Carry signals to muscles or glands for movement and function.

  • Cranial Nerves:

    • 12 pairs originating in the brain, serving functions in the face, head, and neck.

    • They enable facial expressions, eye movement, and processing smells.

  • Spinal Nerves:

    • 31 pairs branching from the spinal cord, with sensory and motor functions.

    • They carry signals from joints and muscles to the spinal cord and control reflex actions (e.g., pulling hand from a hot stove).

Functions of the Nerves

  • Nerves are crucial for performing the following functions:

    • Voluntary Movement: consciously controlled actions.

    • Sensation: various touch and environmental feedback (e.g., temperature, pain).

    • Autonomic Functions: includes regulating blood pressure, breathing, and heart rate.

    • Stress Response: bodily reactions to stressors.

Nervous System Overview

  • Components:

    • Consists of the Central Nervous System (CNS) (brain and spinal cord) and the Peripheral Nervous System (network of nerves).

    • The CNS interprets and processes signals from the PNS.

  • Communication:

    • Peripheral nerves transmit signals to the spinal cord, which is part of the CNS, facilitating communication for movements, behaviors, and reflexes.

Neuronal Structure

  • Parts of Neurons:

    • Cell Body:

    • Contains the nucleus and organelles, involved in protein synthesis (via rough ER/Nissl substance).

    • Dendrites:

    • Receive inputs from the environment and other neurons.

    • Axon:

    • Transmits nerve impulses towards synaptic terminals.

    • Covered in myelin (insulating layer made by Schwann cells in PNS and oligodendrocytes in CNS).

    • Contains Nodes of Ranvier for saltatory conduction (jumping of impulses between nodes).

    • Axon Terminals:

    • Release neurotransmitters to communicate with other neurons or muscles.

Classification of Neurons

  • Structural Classification:

    • Unipolar: Single unbranched axon, no dendrites (e.g., sensory neurons in cochlear nucleus).

    • Pseudounipolar: Axon branches with a single cell body, typical in sensory neurons.

    • Bipolar: Two processes (axon and dendrite) from cell body (found in retina).

    • Multipolar: One axon with multiple dendrites (typical in motor neurons).

  • Functional Classification:

    • Sensory (Afferent): Small axons and are pseudounipolar.

    • Motor (Efferent): Larger axons, typically multipolar.

    • Intermediate Neurons: Found in CNS; have one cell body and many dendrites.

Neuroglia

  • Types of Neuroglia:

    • Astrocytes: Provide structural and metabolic support.

    • Microglial Cells: Act as immune cells in the CNS.

    • Ependymal Cells: Line fluid-filled brain cavities.

    • Oligodendrocytes: Produce myelin in CNS.

    • Schwann Cells: Produce myelin in PNS and aid in regeneration.

Clinical Relevance

  • Multiple Sclerosis (MS):

    • Characterized by loss of myelin in CNS, leading to impaired nerve signal transmission.

    • Symptoms may include visual, motor, and auditory problems.

  • Motor Neurone Disease (MND):

    • Includes conditions like Amyotrophic Lateral Sclerosis (ALS), affecting motor neurons.

    • Progressively damages neurons leading to muscle weakness and disability; median survival post-diagnosis is 3-5 years.