Nerves

Definition

Nerves are bundles of nerve fibers that transmit and receive signals between the central nervous system and the peripheral nervous system. They are composed of axons of neurons, which are surrounded by a layer of myelin that aids in faster transmission of signals.

Types of Nerves

• Motor nerves: transmit signals from the central nervous system to muscles and glands.
• Sensory nerves: transmit signals from sensory receptors to the central nervous system.
• Mixed nerves: contain both motor and sensory fibers.

Structure

• Nerve trunks: the main nerve fibers.
• Nerve fascicles: smaller groups of nerve fibers.
• Nerve terminals: the end of the nerve fiber where signals are transmitted.

Function

• Control and coordination of the body's movements.
• Transmission of sensory information from the environment.
• Regulation of various bodily functions such as heart rate, digestion, etc.

Developmental Process

• Nerve cells (neurons) develop from ectoderm during embryonic development.
• Nerve fibers grow and branch out to form a network of nerves.
• Nerve growth is guided by the development of the central nervous system.

Nerve Supply

• Nerve supply is provided by the autonomic nervous system, which regulates involuntary functions.
• Nerve supply is also provided by the somatic nervous system, which regulates voluntary functions.

Blood Supply

• Nerves receive blood supply from various arteries, including the vertebral and carotid arteries.
• Nerves also receive blood supply from the radial and ulnar arteries.

Lymph Drainage

• Nerves have lymphatic drainage, which helps in the removal of waste products.
• Lymphatic drainage of nerves is through the lymph nodes and lymphatic vessels.

Muscle Action Sequence

• Muscle contraction is initiated by the transmission of signals from motor nerves.
• Muscle contraction involves the sliding filament theory.
• Muscle relaxation is initiated by the transmission of signals from inhibitory neurons.

Sequence of Nerve Stimulation

• A → Sensory receptor → Sensory nerve → Central nervous system → Motor nerve → Muscle
• A → Sensory receptor → Sensory nerve → Central nervous system → Motor nerve → Muscle → Bone
• A → Sensory receptor → Sensory nerve → Central nervous system → Motor nerve → Muscle → Joint

Flowchart of Nerve Stimulation

Meiosis ↓ Formation of gametes ↓ Fertilisation ↓ Formation of zygote ↓ Nerve cell development ↓ Nerve fiber growth and branching ↓ Nerve supply and blood supply ↓ Muscle contraction and relaxation

Classify Nervous System

• The nervous system is classified into two main types:
  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
• Further classified into
  • Somatic Nervous System
  • Autonomic Nervous System
    • Sympathetic Nervous System
    • Parasympathetic Nervous System

Describe Neuron & Neuroglia

• Neuron
  • Building block of the nervous system
  • Highly specialized cells that transmit and process information
  • Consists of dendrites, cell body, and axon
• Dendrites: Receive signals from other neurons
• Cell Body: Contains nucleus and cytoplasm
• Axon: Transmits signals away from the cell body
• Neuroglia
  • Supportive cells of the nervous system
  • Provide protection, maintenance, and nutrition to neurons
  • Types: Astrocytes, Oligodendrocytes, Ependymal cells, Microglia

Describe the Formation of Typical Spinal Nerve

• Formation of Spinal Nerve
  • Root Value: Each spinal nerve arises from a specific nerve root
  • Root Value Formation 1 → Dorsal Root Ganglion: Receives sensory fibers from the body ↓ 2 → Dorsal Root Fibers: Carry sensory information to the spinal cord 3 → Dorsal Root Entry Points: Fibers enter the spinal cord at the level of the dorsal root entry points 4 → Spinal Nerve: Fibers mix with motor and other fibers to form the spinal nerve

Differentiate Sympathetic and Parasympathetic Nervous Systems

• Sympathetic Nervous System:
  • Also known as the "fight or flight" response
  • Increases heart rate, blood pressure, and energy levels
  • Divided into three trunks:
    • Thoracic trunk
    • Lumbar trunk
    • Sacral trunk
• Parasympathetic Nervous System:
  • Also known as the "rest and digest" response
  • Decreases heart rate, blood pressure, and energy levels
  • Divided into three trunks:
    • Cranial trunk
    • Sacral trunk
    • Cervical trunk