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Grey columns
The grey columns are three regions of the somewhat ridge-shaped mass of grey matter in the spinal cord. These regions present as three columns: the anterior grey column, the posterior grey column, and the lateral grey column, all of which are visible in cross-section of the spinal cord.
The anterior grey column is made up of alpha motor neurons, gamma motor neurons, and small neurons thought to be interneurons. It affects the skeletal muscles.
The posterior grey column receives several types of sensory information regarding touch and sensation from receptors in the skin, bones, and joints, including fine touch, proprioception, and vibration.[citation needed] It contains the cell bodies of second-order sensory neurons and their synapses with the pseudounipolar first-order sensory neurons (whose cell bodies are located within the sensory ganglia (a.k.a. dorsal root ganglia)).
The lateral grey column is only present in the thoracic region and upper lumbar segments (T1-L2). It contains preganglionic cell bodies of the autonomic nervous system and sensory relay neurons.
The anterior grey column, (also known as the anterior horn of spinal cord and anterior cornu) is broad and of a rounded or quadrangular shape. Its posterior part is termed the base, and its anterior part the head, but these are not differentiated from each other by any well-defined constriction. It is separated from the surface of the spinal cord by a layer of white substance which is traversed by the bundles of the anterior nerve roots. In the thoracic region, the posterolateral part of the anterior column projects laterally as a triangular field, which is named the lateral grey column. It comprises three different types of neurons, two types of lower motor neuron – large alpha motor neurons, and medium gamma motor neurons, and small neurons thought to be interneurons. These neurons differ in both their morphology and in their patterns of connectivity. They are organized in the same manner as the muscles they innervate.
Alpha motor neurons are lower motor neurons that innervate extrafusal muscle fibers to generate force at neuromuscular junctions at the start of a muscle contraction. They have large cell bodies and receive proprioceptive input. They have been shown to reduce in population, but not in size with age. Damage to these cell bodies can lead to severe muscle weakness and loss of reflexes, and is also associated with ALS.
Gamma motor neurons innervate intrafusal muscle fibers that control the sensitivity of muscle spindles to stretch. They have smaller cell bodies than alpha motor neurons and do not receive proprioceptive input. They have been shown to reduce in numbers but not size with age.
The physiology of the small neurons in the anterior column is not well understood. Their effects can be both excitatory and inhibitory. They are suspected to be interneurons and have been shown to reduce in size but not numbers with age.
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Grey columns
The grey columns are three regions of the somewhat ridge-shaped mass of grey matter in the spinal cord. These regions present as three columns: the anterior grey column, the posterior grey column, and the lateral grey column, all of which are visible in cross-section of the spinal cord.
The anterior grey column is made up of alpha motor neurons, gamma motor neurons, and small neurons thought to be interneurons. It affects the skeletal muscles.
The posterior grey column receives several types of sensory information regarding touch and sensation from receptors in the skin, bones, and joints, including fine touch, proprioception, and vibration.[citation needed] It contains the cell bodies of second-order sensory neurons and their synapses with the pseudounipolar first-order sensory neurons (whose cell bodies are located within the sensory ganglia (a.k.a. dorsal root ganglia)).
The lateral grey column is only present in the thoracic region and upper lumbar segments (T1-L2). It contains preganglionic cell bodies of the autonomic nervous system and sensory relay neurons.
The anterior grey column, (also known as the anterior horn of spinal cord and anterior cornu) is broad and of a rounded or quadrangular shape. Its posterior part is termed the base, and its anterior part the head, but these are not differentiated from each other by any well-defined constriction. It is separated from the surface of the spinal cord by a layer of white substance which is traversed by the bundles of the anterior nerve roots. In the thoracic region, the posterolateral part of the anterior column projects laterally as a triangular field, which is named the lateral grey column. It comprises three different types of neurons, two types of lower motor neuron – large alpha motor neurons, and medium gamma motor neurons, and small neurons thought to be interneurons. These neurons differ in both their morphology and in their patterns of connectivity. They are organized in the same manner as the muscles they innervate.
Alpha motor neurons are lower motor neurons that innervate extrafusal muscle fibers to generate force at neuromuscular junctions at the start of a muscle contraction. They have large cell bodies and receive proprioceptive input. They have been shown to reduce in population, but not in size with age. Damage to these cell bodies can lead to severe muscle weakness and loss of reflexes, and is also associated with ALS.
Gamma motor neurons innervate intrafusal muscle fibers that control the sensitivity of muscle spindles to stretch. They have smaller cell bodies than alpha motor neurons and do not receive proprioceptive input. They have been shown to reduce in numbers but not size with age.
The physiology of the small neurons in the anterior column is not well understood. Their effects can be both excitatory and inhibitory. They are suspected to be interneurons and have been shown to reduce in size but not numbers with age.
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