Nervous System: Part 1

• The nervous system detects and responds to changes inside and outside the body.
• Together with the endocrine system, the nervous system controls body functions and maintains homeostasis.
• Nervous system stimulation provides an immediate response, while endocrine activity is slower and more prolonged.

Divisions of the Nervous System

• There are two divisions of the nervous system.
• The central nervous system (CNS) consists of the brain and spinal cord.
• The peripheral nervous system (PNS) consists of all other nerves.

Peripheral Nervous System

• Sensory division
• Motor division
  • Voluntary (somatic nervous system)
  • Involuntary (autonomic nervous system)
    • Sympathetic ("fight or flight")
    • Parasympathetic ("rest and digest")

Nervous Tissue Cells

• Neurones
• Schwann Cells
• Neuroglial/Glial Cells

Key Features of a Neuron

• Cell body
• Axon
• Schwann cells
• Nodes of Ranvier
• Dendrites
• Synaptic end bulb

Axons

• They serve as a communication route between the cell body and axon terminals.
• Axons conduct electrical impulses away from the neuron's cell body.
• They are often longer than dendrites, sometimes exceeding 1 meter.
• Large axons and those in the peripheral nervous system are surrounded by a myelin sheath, which consists of a series of Schwann cells.

Schwann Cells

• Schwann cells wrap around the axon, forming layers.
• They mainly provide myelin insulation to axons in the peripheral nervous system.
• The myelin sheath has a high phospholipid (fatty) content, offering electrical insulation.

Nodes of Ranvier

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

Dendrites

• Dendrites are extensions of the cell body.
• They provide a large surface area to receive and pass information to the cell body.
• Dendrites share a similar structure to axons but are shorter.
• The plasma membrane contains dense chemical ion channels for impulse transmission.
• Dendrites form synapses with other dendrites or terminate in specialized sensory receptors like those in the skin.

Properties of Neurons

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

Neuroglial Cells

• Non-excitable glial (glue-like) cells support the neurones of the central nervous system.
• Unlike nerve cells, they continue to replicate throughout life
• Microglia
• Astrocytes
• Oligodendrocytes

Functions of Neuroglial Cells

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

Blood-Brain Barrier

• It's a selective barrier that protects the brain from potentially toxic substances and chemical variations in the blood.
• Oxygen, carbon dioxide, glucose, and lipid-soluble substances like alcohol can quickly cross the barrier into the brain.
• Large molecules, drugs, inorganic ions, and amino acids pass slowly or not at all from the blood to the brain.

Synaptic End Bulbs

• Synaptic end bulbs are important for nerve impulse conduction from one neurone to another or from a neurone to an effector.
• They contain enclosed sacs called synaptic vesicles.
• Synaptic vesicles store neurotransmitters.

Synapse Components

• Pre-synaptic neurone
• Pre-synaptic knob
• Neurotransmitters (e.g., acetylcholine/noradrenaline)
• Calcium
• Mitochondria
• Neurotransmitter receptors
• Post-synaptic knob
• Post-synaptic neurone