IB DP Biology: SL复习笔记6.5.1 Neurones: Function & Structure

Function & Structure of Neurones

The nervous system

  • The human nervous system consists of:
    • Central nervous system (CNS) – the brain and spinal cord
    • Peripheral nervous system (PNS) – all of the nerves in the body
  • It allows us to make sense of our surroundings and respond to them, and to coordinate and regulate body functions
  • Information is sent through the nervous system in the form of electrical impulses – these are electrical signals that pass along nerve cells known as neurones
    • A bundle of neurones is known as a nerve
  • The nerves spread out from the central nervous system to all other regions of the body and importantly, to all of the sense organs
    • The CNS acts as a central coordinating centre for the impulses that come in from, and are sent out to, any part of the body

The-human-nervous-system

The human nervous system is comprised of the CNS and the PNS

Neurones

  • The following features are found in neurones:
    • Neurones have a main, long, fibre known as an axon
    • They have a cell body that contains the nucleus and other cellular structures
    • Their cell bodies and axon terminals contain many extensions called dendrites
    • These dendrites allow them to connect to many other neurones and receive impulses from them, forming a network for easy communication

Nerve-Cell

Neurones have a characteristically elongated structure which allows them to transfer information between the central nervous system and the rest of the body

Research

NOS: Cooperation and collaboration between groups of scientists; biologists are contributing to research into memory and learning

  • Some of the so-called 'higher' functions of the brain e.g., memory and learning, are still not fully understood and are the focus of much current research
  • Biologists are becoming increasingly involved in this research, which uses techniques from the fields of neurobiology, molecular biology, and biochemistry to understand the mechanisms behind these brain functions
  • The Centre for Neural Circuits and Behaviour (CNCB) at the University of Oxford is a good example of an institution in which scientists with different areas of expertise collaborate, or work together, with a common research goal
    • The research team at the CNCB contains experts in various fields of biological science, including medicine, physiology, genetics, molecular biology, neurobiology, and neurogenetics
  • Research into functions of the brain such as memory and learning not only involves collaboration between scientists from different specialities, but also from different countries

Myelination

  • Neurones have a main, long, fibre known as an axon
  • The axons of neurones are surrounded by specialised cells called Schwann cells
  • Schwann cells wrap themselves around the axon, forming a structure known as a myelin sheath
    • Myelin contains the phospholipids of the Schwann cell membranes; it is built up in layers as the Schwann cells grow around the axon
    • The lipid content of the myelin sheath gives it a high electrical resistance
  • The myelin sheath acts as an electrical insulator; impulses cannot pass through the myelin sheath
  • The myelin sheath has small, uninsulated sections in the gaps between the individual Schwann cells
    • These gaps are called nodes of Ranvier
  • Electrical impulses effectively jump from one node of Ranvier to the next
    • This process is known as saltatory conduction
    • It greatly speeds up the rate of transmission of impulses along myelinated neurones
    • In non-myelinated neurones the axon is  not insulated by myelin, so the impulse travels more slowly

The-structure-of-a-myelinated-neurone

An impulse travels down a neurone via saltatory conduction

 

 

 

 

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