CH13: Spinal Cord Flashcards
What are the three meninges
- Dura mater: Thick and dense layer of connective tissue
- Arachnoid mater: The thin, middle layer of the meningeal membranes. It consists of loosely arranged collagen and elastic fibers, and called arachnoid mater because of its spider web arrangement of delicate collagen and elastic fiber that extend between it and the pia mater (thin, avascular, loosely packed
cells, collagen, elastic fibers, intermediate) - Pia mater: This innermost meninx is a thin transparent connective tissue layer that adheres to the surface of the spinal cord and brain. It consists of squamous to cuboidal cells with collagen and fine elastic fibers, and contains many blood vessels that supply oxygen and nutrients to the spinal cord
List the two enlargements and their vertebra regions
The superior enlargement is called the cervical enlargement, extending from the fourth cervical vertebra to the first thoracic vertebra (C4-T1), and the inferior enlargement is called the lumbosacral enlargement, extending from the ninth to the twelfth thoracic vertebra, (T9-T12)
List the spinal segments, their range within the vertebral column and how many spinal nerve pairs arise from there
8 pairs of cervical nerves (C1-C8)
12 pairs of thoracic nerves (T1-T12)
5 pairs of lumbar nerves (L1-L5)
5 pairs of sacral nerves (S1-S5)
1 Coccygeal nerves (Co1)
Name the function of the 3 horns
The posterior gray horns contain axons of incoming sensory neurons as well as cell bodies and axons of interneurons. Recall that cell bodies of sensory neurons are located in the spinal ganglion of a spinal nerve
The anterior gray horns contain somatic motor nuclei, which are clusters of cell bodies of somatic motor nuclei that provide nerve impulses for contraction of skeletal muscles.
Between the posterior and anterior gray horns are the lateral gray horns, present only in thoracic and upper lumbar and mid sacral segments of the spinal cord. The lateral gray horns contain autonomic motor nuclei, which are clusters of cell bodies of autonomic motor neurons that regulate the activity of cardiac muscle, smooth muscle and glands
What is the relation between fasciculi and funiculi
The spinal cord is divided into 3 white regions by the gray matter: these columns are called funiculi, which contain bundles of axons that have distinct funiculi origins and similar functions that travel along the spinal cord called tracts/fasciculi. Sensory tracts/fasciculi carry nerve impulses toward the brain, while motor tracts/fasc carry impulses from the brain
List the steps of sensory processing
- Sensory receptor detects stimulus
- Sensory neurons convey this sensory input in the form of nerve impulses along their axons, which extend from sensory receptors into the spinal nerve and then into the posterior root. From the posterior root, axons of sensory neurons may proceed along three possible paths (see steps 3,4,5)
- Axons of sensory neurons may enter the posterior gray horn and then extend into the white matter of the spinal cord and ascend to the brain as part of a sensory tract
OR - Axons of sensory neurons may enter the posterior gray horn and synapse with interneurons whose axons then extend into the white matter of the spinal cord and ascend to the brain as part of a sensory tract
OR - Axons of sensory neurons may enter the posterior gray horn and synapse with interneurons that inturn synapse with somatic motor neurons that are involved in spinal reflex pathways. Spinal cord reflexes are described in more detail later this chapter
- Motor output from the spinal cord to skeletal muscles involved somatic motor neurons of the anterior gray horn. Many somatic motor neurons are regulated by the brain. Axons from higher brain centers form motor tracts that descend from the brain into the white matter of the spinal cord. There they synapse with somatic motor neurons either directly or indirectly by first synapsing with interneurons that in turn synapse with somatic motor neurons
- When activated, somatic motor neurons convey motor output in form of nerve impulses along their axons, which sequentially pass through the anterior gray horn and anterior root to enter the spinal nerve. From the spinal nerve axons of somatic motor neurons extend to skeletal muscles of the body
- Motor output from the spinal cord to cardiac muscle, smooth muscle, and glands involves autonomic motor neurons of the lateral gray horn. When activated, autonomic motor neurons convey motor output in the form of nerve impulses along their axons, which sequentially pass through the lateral gray horn, anterior gray horn, and anterior root to enter the spinal nerve
- From the spinal nerve, axons of autonomic motor neurons from the spinal cord synapse with another group of autonomic motor neurons located in the peripheral nervous system (PNS). The axons of this second group of autonomic motor neurons in turn synapse with cardiac muscle, smooth muscle, and glands
What are the three layers of a spinal nerve
Individual axons within a nerve, whether myelinated or unmyelinated, are wrapped in endoneurium. This is the inner layer, consisting of a mesh of collagen fibers, fibroblast and macrophages
Groups of axons with their endoneurium are are held together in bundles called nerve fascicles, each wrapped in connective tissue called perineurium, the thick middle layer of connective tissue with 15 layers of fibroblasts and a network of collagen fibers
The outermost covering over the entire nerve is the epineurium. It consists of fibroblasts and thick collagen fibers. Extensions of the epineurium also fill the spaces between nerve fascicles
Name the branches of spinal nerves
The posterior ramus serves the deep muscles and skin of the posterior surfaces of the trunk
The anterior ramus serves the muscles and structures of the upper and lower lumbs and the skin of the lateral and anterior surfaces of the trunk
In addition to the posterior and anterior rami, spinal nerves also give off a Meningeal branch, which supply vertebrae, vertebral ligaments, spinal cord blood vessels and meninges
Communicating rami: Stay tuned for Chapter 15! (components of the autonomic nervous system)
How does information travel in the spinal cord?
The white matter tracts in the spinal cord are highways for nerve impulse propagation. Sensory input travels along these tracts toward the brain, and motor output travels from the brain along these tracts toward skeletal muscles and other effector tissues
Gray matter receives incoming and outgoing information and integrates it
What do the cervical, brachial, lumbar, sacral and coccygeal plexuses innervate?
The cervical nerve (C1-C4) innervates the muscles and skin of the head and neck, and the superior portion of the shoulder and chest
The brachial plexus (C5-C8) provides almost all innervation to the upper limbs and shoulders
The lumbar plexus (L1-L4) provides innervation to the external genitals, parts of lower limbs and anterolateral abdominal wall
The sacral plexus (L5-L4 & S1-S4) innervate the perineum, buttocks and lower limbs
The coccygeal plexus (S4-S5) innervates a small area of skin on the coccygeal region
What do the stretch, tendon, flexor and cross extensor reflex do
The stretch reflex causes contraction of a muscle that is stretched
The tendon reflex causes relaxation in order to prevent damage to a tendon during forceful contraction
The flexor reflex withdraws a body part from a painful stimulus
The crossed extensor reflex maintains balance during a withdrawal reflex
