The Spinal Cord

spinal cord
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The Central Nervous System is made up of 2 parts: the Brain and the Spinal Cord, both of which are connected to each other.

Retrieved from https://pocketdentistry.com/15-the-structure-of-the-central-nervous-system/ on 11th November 2021
Retrieved from https://www.bmj.com/content/372/bmj.n32 on 11th November 2021

Spinal Cord Terminology

  • WHITE MATTER – aggregations of myelinated axons from many neurones supported by neuroglia
  • GREY MATTER – contains nerve cell bodies and dendrites OR bundles of unmyelinated axons and neuroglia
  • NERVE – a bundle of fibres located outside the CNS
  • TRACT – a bundle of fibres located in the CNS which may run long distances up and down the spinal cord; tracts are also found in the brain, connecting parts of the brain with each other as well as with the spinal cord; tracts are used in instances where various retractions from various sources are required to work altogether, eg. withdrawal following a burn (hands, feet, body, all working together to move away from the burn source)
  • NUCLEUS – a mass of nerve cell bodies and dendrites with similar functions located within the CNS
Retrieved from https://slidetodoc.com/chapter-13-the-spinal-nerves-the-spinal-cord/ on 11th November 2021

Functions of the Spinal Cord

The spinal cord supports integration of the reflexes. It conveys sensory impulses from the periphery to the brain, and conducts motor impulses from the brain to the periphery.

Reflexes, which are associated with skeletal muscle contraction and body functions such as heart rate, respiration, digestion, urination and defaecation, are fast responses to changes in both the internal and the external environments with the aim of maintaining homeostasis.

  • Spinal reflexes are reflexes carried out by the spinal cord only
  • Somatic reflexes are reflexes resulting in skeletal muscle contractions
  • Visceral reflexes a.k.a. Autonomic reflexes are reflexes resulting in the contraction of smooth or cardiac muscle, as well as gland secretion

The Reflex Arc

  • The reflex arc contains two or more neurones over which impulses are conducted from a receptor to the brain or spinal cord, and then to an effector.
  • The receptor initiates a nerve impulse in a sensory neurone in response to a change in the internal or external environment.
  • A sensory neurone acts as a passageway for an impulse from the receptor to the CNS
  • The centre is an area in the CNS where an incoming sensory impulse generates an outgoing motor impulse. This impulse may be inhibited, transmitted or rerouted. An association neurone may also be found in the centre, connecting a sensory neurone to a motor neurone which leads to a muscle or a gland
  • A motor neurone transmits impulses generated by the sensory or association neurone to the responding body organ
  • An effector is the organ (muscle or gland) that responds to the motor impulse through a reflex

The Stretch Reflex

The stretch reflex is important for the maintenance of the muscle tone. It helps prevent injuries from muscle overstretching, and is vital for muscle functioning during exercise. It is also useful for testing purposes during neurological examinations.

The Tendon Reflex

The tendon is the point of attachment between the neuron and the bone. The tendon reflex is a polysynaptic reflex arc in which more than two neurones are involved, therefore more than one synapse is produced. Tendon organs can detect and respond to changes in muscle tension produced by passive stretching or muscle contraction.

The Flexor Reflex

The flexor reflex a.k.a. withdrawal reflex is based on a polysynaptic reflex as in the tendon reflex. It causes withdrawal following a painful stimulus.

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Claire
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Author: Claire

Claire Galea is a mum of three currently in her final year following a Degree in Nursing at the Faculty of Health Sciences, University of Malta, as a mature student. Claire is keen about public education on health-related subjects as well as holistic patient-centered care. She is also passionate about spreading awareness on the negative effects that domestic abuse leaves on its victims’ mental, emotional, social and physical wellbeing. Claire aspires to continue studying following completion of her Nursing Degree, because she truly believes in lifelong education.