Spinal Cord – Anatomy, Functions and Clinical Aspects
The human body is included with Central Nervous System for functioning. The central nervous system consists of the Spinal Cord and Brain. The spinal cord is the most important structure that transfers data between the body and brain and from the brain to the body. The spinal cord is the elongated, almost cylindrical part of the Central Nervous System. It lies in the vertebral canal surrounded by the Meninges and Cerebro spinal fluid. The study of the Spinal cord is called Neuroscience.
Spinal Cord lies in the vertebral canal that is surrounded by meninges and Cerebrospinal fluid. It is continuous above the medulla oblongata and extends from the upper border of the Atlas to the lower border of the first lumbar vertebra as Conus Medullaris in adults and the third lumbar vertebra in the child. It is nearly 45 cm in an adult male, and 42cm in an adult female. It is surrounded by three meninges namely Dura mater(outer most), Arachnoid mater(middle) Pia mater(inner most). The space between dura and arachnoid matter is called as sub Dural space. The space between arachnoid and pia matter is called subarachnoid space, which contains the cerebral spinal fluid. The spinal cord is superiorly continuous with Medulla oblongata and inferiorly terminates as Conus Medullaris. The Spinal Cord has inner grey matter and outer white matter(no fibers). In the center of grey matter, it is the central canal containing cerebral spinal fluid. The central canal is lined by a single layer of ependymal cells.
Grey matter present in the spinal cord is in the form of letter H or butterfly structure, having 2 posteriors (sensory in function), 2 anterior(motor in function), and 2 lateral columns (visceral efferent, afferent). A transverse Grey commissure joins the grey matter of the right and left sides of the spinal cord. Grey matter comprises 1 posterior horn and 1 anterior horn on each side in the entire extent of the spinal cord. only in T1 – L2 and S2 – S4 segments there is an additional lateral horn for the supply of Viscera. This horn is a part of the autonomous nervous system. Dorsal Horn is the base of the anterior horn which is found at all spinal cord levels and is comprised of sensory neurons which receive impulses from the periphery of the body. Ventral Horn is the head of the anterior horn that comprises motor neurons that transmit impulses to the skeletal muscle. Nerve cells in the grey matter are multi polar, many of them are Golgi type 1 and type 2 nerve cells.
The white matter of the spinal cord is arranged in three columns or tracts. anterior, posterior, and lateral. These tracts are formed by sensory nerve fibers ascending to the brain, Motor nerve fibers descending from the brain, and fibers of connector neurons.
Sensory Nerve Tracts
These are afferent or ascending tracts in the spinal cord. There are two main sources of sensation transmitted to the brain via the spinal cord, they are
- the skin(cutaneous receptors): stimulated by pain, heat, cold, touch, and pressure
- the tendons, muscles, and joints (proprioceptors): are stimulated by stretching.
The ascending tracts consist of the following parts. Lateral Spino thalamic tract, Anterior Spino thalamic, Fasciculus Gracilis tract, fasciculus cuneatus tract, Dorsal Spinocerebellar tract, Ventral Spinocerebellar Tract, Spino-Olivary tract, Spino-Tectal tract.
Motor Nerve Tracts
Motor nerve tracts are efferent descending tracts in the spinal cord. Neurons that transmit nerve impulses away from the brain are called Motor Neurons. Motor neurons stimulation results in
- contraction of skeletal ( striated, voluntary )muscle,
- contraction of smooth ( involuntary) muscle, Cardiac muscle.
The descending tracts are of two types.
- Pyramidal or cortical spinal tracts: These tracts originate mainly from the pyramidal neurons of the motor and pre-motor cortex. It consists of two parts. 1. Lateral Corticospinal tract 2. Anterior corticospinal tract
- Extra pyramidal: The extra pyramidal system represents older motor path ways that are multi-synaptic with inhibitory influence over pyramidal tracts. It consists of 8 parts: Rubro spinal, lateral vestibulo spinal, medial vestibulo spinal, lateral reticulo spinal, medial reticulo spinal, tecto spinal, olivo spinal, interstitio spinal tracts.
Blood Supply to the Spinal Cord
The arterial supply of the spinal cord is by the following arteries. 1. Anterior spinal arteries 2. two posterior spinal arteries 3. the radicular arteries.
Spinal nerves arise in pairs. There are 31 pairs of spinal nerves 8 cervical, 12 thoracics, 5 Lumbar, 5 Sacral, and 1 Coccygeal. Each spinal nerve arises by a series of Six to Eight dorsal and ventral nerve rootlets. these rootlets unite in or near the intervertebral foramen to form the spinal nerve.
Dorsal Root Ganglion
As the dorsal rootlets converge, there is swelling. The Dorsal or Posterior Root Ganglion houses the cell bodies of all the Sensory Neurons in that particular nerve.
Branches of a typical Nerve
- Dorsal Ramus, supplies the dorsal one-third of the body wall.
- Ventral Ramus, supplies the vertebral two-thirds of the body wall.
It is a segment or part of the spinal cord to which a pair of dorsal nerve tools and a pair of ventral nerve roots are attached. Since the length of the spinal cord (45cm) is smaller than the length of the vertebral column (65cm). The spinal segments do not correspond to the vertebral levels. Spinal cord versus vertebral column:
The difference between the spinal cord and vertebral column is the spinal cord is one of the two components of the central nervous system extending from the brain stem to the lumbar region whereas vetrivel column is the individual component enclosing the spinal cord. The spinal cord is made up of narrow tissue where as the vertebral column is made up of bones and some cartilage bones. The spinal cord is located inside the vertebral column where as the vertebral column is surrounded by the spinal cord. The vertebral column is generally incorporated with 33 vertebrae which include 24 presacral vertebrae and 5 fused sacral vertebrae and 4 frequently fused Coccygeal vertebrae.
Function of the Spinal Cord
Spinal Cord had the following functions
- Conduction: This is known as an information highway. passes information between PNS and the brain. Carries information Up and down the Cord.
- Integration: In this Spinal Neurons receives info from many sources. It means it reports senses to the Brain such as sensations of touch, pain, and pressure.
- Reflexes: these are fast, involuntary, stereotype responses to stimuli that involve the brain, spinal cord, and peripheral nerves such as spinal reflexes for posture, muscle tone, and protection.
It is nothing but the problems or disorders that occur to the spinal cord in the person or a patient. when damage or injury occurs to the spinal cord, it stays lifelong and it is permanent in the human body. It affects the regular functioning of the spinal cord and there is no replacement for it.
some of the conditions that affect the spinal cord:
- Multiple Sclerosis (MS): This is a demyelinating condition that may affect the brain and spine. This disorder in the spine causes weakness, loss of the senses, tingling, and pain.
- Spinal cord compression: When the spinal cord is exposed to adverse conditions such as physical pressure, weakness, and loss of sense this will occur.
- Meningitis: When infection or inflammation is seen in the meninges is called meningitis. This is often called spinal meningitis. this disease can cause symptoms like headache, stiff neck, fever, and vomiting.
- Polio: Polio is the most contagious viral infection which affects the spinal cord. It can be usually prevented by using a vaccine. This causes muscle paralysis of the areas that are controlled by affected spinal cord regions.
- Cancer: Although spinal cord cancer is not a common disease the tumors can develop in any part of the cord. meningeal carcinomatosis is the spread of cancer cells throughout the meninges and CSF.
Question 1: Where is the spinal cord located in the human body?
The Spinal Cord is located in between the bottom part of the brain called medulla oblongata and the lower back forming a cone shape called conus medullaris.
Question 2: What is the length of the spinal cord?
The length of the spinal cord varies from person to person. In most the adults it is for about 45 centimeters ( 18 inches)
Question 3: How many nerves are present in the Spinal Cord?
There are 31 pairs of nerves and nerve roots present in the Spinal Cord. 8 cervical, 12 thoracic, 5 lumbar, 5 lumbar, 5 sacral, and 1 coccygeal.
Question 4: What is the composition of the Spinal Cord?
It is surrounded by three meninges namely Dura mater( outer most), Arachnoid mater( middle) Pia mater( inner most).
Question 5: What is the impact of the spinal cord injury?
Spinal cord injury not only has an impact on the spinal nerves and vertebral column but also affects the other muscles and vital organs as well.
Question 6: How do we keep the spinal cord healthy?
The spinal cord can be kept healthy by maintaining a healthy weight, staying away from nicotine and its products, maintaining a healthy diet by eliminating inflammation-causing products, and maintaining good cardio exercises keeps the spinal cord healthy.