Nervous System part 1

Nervous System Overview

• The nervous system detects and responds to internal and external changes in the body.
• It works alongside the endocrine system to control body function and maintain homeostasis.
• The nervous system provides immediate responses, while endocrine activity is slower and prolonged.

Nervous System Divisions

• The nervous system is divided into the central and peripheral systems:
  • Central Nervous System (CNS): Brain and spinal cord
  • Peripheral Nervous System (PNS): All other nerves

Peripheral Nervous System Divisions

• The PNS is further divided into sensory and motor divisions:
  • Sensory Division: Carries sensory information from the body to the CNS
  • Motor Division: Carries motor commands from the CNS to the body
    • Somatic Nervous System: Voluntary control of skeletal muscles
    • Autonomic Nervous System: Involuntary control of internal organ functions
      • Sympathetic Nervous System: "Fight or flight" response
      • Parasympathetic Nervous System: "Rest and digest" response

Nervous Tissue: Cells

• Nervous tissue consists of three main cell types:
  • Neurones: Specialized cells that transmit nerve impulses
  • Schwann Cells: Supporting cells that form the myelin sheath around axons in the PNS
  • Neuroglial/Glial Cells: Supporting cells of the CNS

Neurone Structure

• Neurones have distinct structural features:
  • Cell Body: Contains the nucleus and other organelles
  • Axon: Long, slender projection that conducts nerve impulses away from the cell body
  • Schwann Cells: Wrap around axons to form the myelin sheath
  • Nodes of Ranvier: Gaps between Schwann cells, facilitating rapid impulse transmission
  • Dendrites: Short, branched projections that receive nerve impulses from other neurones
  • Synaptic End Bulb: Terminal of the axon, containing neurotransmitters

Neurone Properties

• Neurones exhibit two key properties:
  • Irritability: Ability to initiate nerve impulses in response to stimuli
  • Conductivity: Ability to transmit nerve impulses

Neuroglial (Glial) Cells

• Neuroglial cells are non-excitable cells that support neurones in the CNS.
• They continue to replicate throughout life.
• There are three main types:
  • Microglia: Phagocytic cells that remove debris and pathogens
  • Astrocytes: Star-shaped cells that provide structural support and regulate nutrient and waste exchange
  • Oligodendrocytes: Form and maintain myelin sheaths around axons in the CNS

Blood-Brain Barrier

• The blood-brain barrier is a selectively permeable membrane that protects the brain from toxic substances and blood fluctuations.
• It allows the passage of essential substances like oxygen, carbon dioxide, glucose, and lipid-soluble molecules.

Synaptic End Bulbs and Neurotransmission

• Synaptic end bulbs are specialized structures at the end of axons, responsible for transmitting nerve impulses to other neurones or effector cells.
• They contain synaptic vesicles that store neurotransmitters, such as acetylcholine and noradrenaline.
• Neurotransmission occurs through the release of neurotransmitters at the synapse.

Synapse

• The synapse is the junction between two neurones or a neurone and an effector cell.
• It consists of:
  • Pre-synaptic Neurone: Releases neurotransmitters
  • Pre-synaptic Knob: Terminal of the axon containing synaptic vesicles
  • Neurotransmitters: Chemical messengers released at the synapse
  • Post-synaptic Knob: Receptor sites on the receiving cell
  • Post-synaptic Neurone: Receives the neurotransmitter signal

Neuro-transmission

• Neurotransmission involves a series of steps:
  • Action Potential Arrival: Nerve impulse reaches the pre-synaptic knob
  • Calcium Influx: Calcium ions enter the pre-synaptic knob
  • Neurotransmitter Release: Synaptic vesicles fuse with the pre-synaptic membrane and release neurotransmitters
  • Neurotransmitter Binding: Neurotransmitters bind to receptors on the post-synaptic membrane
  • Post-synaptic Potential: Binding triggers a change in the post-synaptic cell's membrane potential
  • Neurotransmitter Removal: Neurotransmitters are removed from the synapse, either by re-uptake into the pre-synaptic neurone or by enzymatic breakdown.

Anatomy & Physiology of Nervous Tissue