The Nervous System: Organisation and cells

• The nervous system detects and responds to changes inside and outside the body
• The nervous system along with the endocrine system controls important aspects of body function and maintains homeostasis
• Stimulation through the nervous system provides an immediate response, while endocrine activity is typically slower and prolonged

Divisions of the Nervous System

• The central nervous system (CNS) includes the brain and spinal cord
• The peripheral nervous system (PNS) comprises all nerves outside the brain and spinal cord
• The PNS has sensory and motor divisions
• The motor division is split into:
  • The somatic nervous system (voluntary)
  • The autonomic nervous system (involuntary)
• The autonomic nervous system is divided into the sympathetic ("fight or flight") and parasympathetic ("rest and digest") branches

Nervous Tissue Cells

• Neurones
• Schwann cells
• Neuroglial/Glial cells

Neurone Features

• Cell body: contains the nucleus and other organelles
• Axon: a long fiber that conducts electrical impulses away from the cell body
• Schwann cells: surround large axons and those of the peripheral nervous system to form the myelin sheath
• Nodes of Ranvier: gaps between Schwann cells along the axon
• Dendrites: extensions of the cell body that receive information
• Synaptic end bulb: specialized endings where neurones communicate with other cells

Schwann Cells

• Schwann cells wrap around the axon
• They provide myelin insulation to axons in the peripheral nervous system
• The myelin sheath comprises a high phospholipid (fatty) content which offers electrical insulation

Nodes of Ranvier

• Nodes of Ranvier are exposed areas between Schwann cells
• They assist rapid transmission of action potentials in myelinated neurones

Dendrites

• Dendrites are extensions of the cell body
• They provide a large surface area to receive information and pass to the cell body
• Dendrites have a similar structure to axons, but are shorter
• The plasma has dense chemical ion channels for impulse transmission
• Dendrites form synapses with other dendrites or end in specialised sensory receptors

Properties of Neurones

• Irritability: the ability to initiate nerve impulses in response to stimuli from inside or outside the body
• Conductivity: the ability to transmit an impulse

Neuroglial Cells

• Neuroglial cells support the neurones of the central nervous system
• Unlike nerve cells, neuroglial cells continue to replicate throughout life
• The three types of cells are:
  • Microglia
  • Astrocytes
  • Oligodendrocytes

Neuroglial Cell Types

• Microglia are located mainly in the area of blood vessels, they enlarge and become phagocytic in areas of inflammation and cell destruction
• Astrocytes are the main supporting tissues of the central nervous system: star shaped with fine branching processes lie in a muccopolysaccharide ground substance: there are large numbers adjacent to blood vessels
• Oligodendrocytes are smaller than astrocytes, found in clusters around the neurone cell wall, adjacent to, and along the length of many myelinated nerve fibres in the CNS: they form and maintain myelin and have the same function as Schwann cells in the peripheral nerves

Blood-Brain Barrier

• A selective barrier which protects the brain from potentially toxic substances and chemical variations in the blood eg: after a meal
• Oxygen, carbon dioxide, glucose and other lipid soluble substances such as alcohol quickly cross into the brain
• some large molecules, many drugs, inorganic ions and amino acids pass only slowly or not at all

Synaptic End Bulbs

• Important for nerve impulse conduction from one neurone to another or neurone to an effector
• Contain enclosed sacs called synaptic vesicles
• Stores neurotransmitters

Synapse Components

• Pre-synaptic neurone
• Pre-synaptic knob
• Neurotransmitters like acetylcholine/noradrenaline
• Calcium
• Mitochondria
• Neurotransmitter receptors
• Post-synaptic knob
• Post-synaptic neurone

Explore the nervous system's role in detecting and responding to changes inside and outside the body. Learn about the central and peripheral nervous systems, their divisions, and the different types of nervous tissue cells, including neurons, Schwann cells and neuroglial cells.