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Biology LibreTexts

35.4C: Spinal Cord

  • Page ID
    13880
  • LEARNING OBJECTIVES

    • Describe the structure and function of the spinal cord

    Connecting to the brainstem and extending down the body through the spinal column is the spinal cord: a thick bundle of nerve tissue that carries information about the body to the brain and from the brain to the body. The spinal cord is contained within the bones of the vertebral column, but is able to communicate signals to and from the body through its connections with spinal nerves (part of the peripheral nervous system). A cross-section of the spinal cord looks like a white oval containing a gray butterfly-shape. Myelinated axons (the part of neurons that send signals) compose the “white matter,” while neuron and glial cell bodies (neuronal “support” cells) compose the “grey matter.” Grey matter is also composed of interneurons, which connect two neurons, each located in different parts of the body. Axons and cell bodies in the dorsal (facing the back of the animal) spinal cord convey mostly sensory information from the body to the brain. Axons and cell bodies in the ventral (facing the front of the animal) spinal cord primarily transmit signals controlling movement from the brain to the body.

    image

    Spinal cord cross-section: A cross-section of the spinal cord shows grey matter (containing cell bodies and interneurons) and white matter (containing axons).

    The spinal cord also controls motor reflexes. These reflexes are quick, unconscious movements, such as automatically removing a hand from a hot object. Reflexes are so fast because they involve local synaptic connections. For example, the knee reflex that a doctor tests during a routine physical is controlled by a single synapse between a sensory neuron and a motor neuron. While a reflex may only require the involvement of one or two synapses, synapses with interneurons in the spinal column transmit information to the brain to convey what happened (the knee jerked, or the hand was hot).

    In the United States, there around 10,000 spinal cord injuries each year. Because the spinal cord is the information superhighway connecting the brain with the body, damage to the spinal cord can lead to paralysis. The extent of the paralysis depends on the location of the injury along the spinal cord and whether the spinal cord was completely severed. For example, if the spinal cord is damaged at the level of the neck, it can cause paralysis from the neck down, whereas damage to the spinal column further down may limit paralysis to the legs. Spinal cord injuries are notoriously difficult to treat because spinal nerves do not regenerate, although ongoing research suggests that stem cell transplants may be able to act as a bridge to reconnect severed nerves. Researchers are also looking at ways to prevent the inflammation that worsens nerve damage after injury. One such treatment is to pump the body with cold saline to induce hypothermia. This cooling can prevent swelling and other processes that are thought to worsen spinal cord injuries.

    Key Points

    • The spinal cord consists of a butterfly-shaped area of grey matter, containing neuronal and glial cell bodies, surrounded by white matter that contains the axons of the neurons.
    • Neurons at the back of the spinal cord ( dorsal ) generally transmit information from the body to the brain, while neurons at the front of the spinal cord ( ventral ) primarily transmit information from the brain to the body.
    • The spinal cord controls reflexes, which are incredibly fast reactions to stimuli; the speed at which they operate is due to the fact that they involve only a local connection between neurons and are not relayed through the brain.
    • Spinal cord injuries often result in paralysis; they do not heal, as spinal nerves lack the ability to regenerate.

    Key Terms

    • grey matter: a collection of cell bodies and (usually) dendritic connections, in contrast to white matter
    • synapse: the junction between the terminal of a neuron and either another neuron or a muscle or gland cell, over which nerve impulses pass
    • axon: long slender projection of a nerve cell that conducts nerve impulses away from the cell body to other neurons, muscles, and organs
    • white matter: a region of the central nervous system containing myelinated nerve fibers and no dendrites
    • interneuron: a multipolar neuron that connects afferent and efferent neurons

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