Ch.13 - The Spinal Cord and Spinal Nerves Flashcards
Spinal cord and Spinal nerves
The spinal cord and spinal nerves contribute to homeostasis by providing quick, reflexive responses to many stimuli. The spinal cord is the pathway for sensory input to the brain and motor output from the brain.
Spinal Cord Anatomy: Protective Structures
- Vertebral Column - provides a bony covering of the spinal cord by providing strong protective defenses against damaging blows or bumps
- Meninges - 3 protective connective tissue coverings that encircle the spinal cord and the brain
- Dura Mater - outermost layer; thick, strong layer composed of dense irregular CT; also continuous with the epineurium, which is the outer covering of spinals and cranial nerves
- Arachnoid mater - middle layer; thin avascular covering comprised of cells and thin, loosely arranged collagen and elastic fibers; called arachnoid mater because its spider’s-web arrangement of delicate callogen fibers and some elastic fibers that extend between the arachnoid mater and pia mater
- Subdural space - space between the dura and arachnoid mater which contains interstitial fluid
- Pia mater - innermost meninx that is a thin transparent CT layer that theres to the spinal cord and brain ; consists of thin squamous to cuboidal squamous within interlacing bundles of callogen fibers and some fine elastic fibers
- Denticulate ligaments - thickenings of the pia mater that suspend the spinal cord in the middle of its dural sheath
- Subarachnoid space - between arachnoid and pia mater; carries cerebrospinal fluid (CSF) - Spinal meninges - cover the spinal cord
- Cranial meninges cover the brain
- Epidural space - space between the dura mater and the wall of the vertebral canal
Think P.A.D
Spinal Cord and Spinal Nerves
- The spinal cord extends extends from the medulla oblongata of the brain to the superior border of the second lumbar vertebra. Elongation of the spinal cord stops around ages 4-5, but growth of the vertebral column continues.
- The spinal nerves are paths of communication between the spinal cord and specific regions of the body:
- Cervical: 8 pairs (C1 -C8)
- Thoracic: 12 pairs (T1 - T12)
- Lumbar: 5 pairs (L1 - L5)
- Sacral: 5 pairs (S1 - S5)
- Coccygeal: 1 pairs ( Co1 )
Spinal Cord Anatomy: External
Cervical Enlargement (Superior) - extends from C4 to T1; nerves rom the upper limb arise from here
Lumbosacral Enlargement (Inferior) - extends from T9 to T12; nerves to and from the lower limb arise from here
Conus (cone) Medullaris - inferior to the lumbosacral enlargement; the tapered portion of the spinal cord; ends between L1 and L2 in adults
Filum Terminale - arises from the conus medullaris; anchors to the spinal cord and coccyx; extension of the pia mater and fuses with the arachnoid and dura mater
Cauda Equina - Roots of nerves that arise from the lumbar, sacral, and coccygeal regions of the spinal cord; they do not exit the vertebral column at the same level they exit the cord, they angle inferiorly alongside the filum terminale
Roots - Two bundles of axons, called roots, connect each spinal nerve to to a segment of the cord by even smaller bundles of axons called Rootlets
Posterior Root - Contains only sensory axons; Each posterior root has a swelling, or Spinal Ganglion, which contain the cell bodies of sensory neurons
Anterior Root - Contain axons of motor neurons
Spinal Cord Anatomy: Internal
- Anterior median fissure - a narrow furrow on the anterior (ventral) side
- Posterior median sulcus - a narrow furrow on the posterior (dorsal) side
- Gray commissure - forms the cross bar of the H, or gray matter in the spinal cord
- Central canal - in the center of the gray commissure that extends the entire length of the spinal cord and is filled with CSF; superior end is continuous with the fourth ventricle in the medulla oblongata
- Anterior white commissure - connects the white matter of the right and left sides of the spinal cord
- Nuclei - in the gray matter of the spinal cord and brain, clusters of neuronal cell bodies form functional groups called nuclei
- Horns - the gray matter on each side of the spinal cord is subdivided into regions called horns
- Posterior gray horns - contain axons of incoming sensory neurons as well as cell bodies and axons of interneurons
- Anterior gray horns - contain somatic motor nuclei, which are clusters of cell bodies of somatic motor neurons that provide nerve impulses for contraction of skeletal muscles
- Lateral gray horns - contain autonomic motor nuclei, which are clusters of cell bodies of autonomic motor neurons that regulate the activity of cardiac muscles, smooth muscle, and glands; ONLY present in thoracic, upper lumbar, and mid-sacral segments of the spinal cord
- Funiculi - the anterior and posterior gray horns divide the white matter on each side into 3 broad areas called funiculi
(1) Anterior white funiculi (2) Posterior white funiculi (3) Lateral white funiculi - each funicular contains distinct bundles of axons having a funiculus origin or destination and carrying similar information. - Tracts - These bundles ^ are called Tracts or fascicle, which extend long distances up or down the spinal cord; bundles of axons.
- Sensory tracts - conducts nerve impulses towards the brain
- Motor tracts - carry nerve impulses from the brain; conduct impulses down the cord
- Sensory and motor tracts are continuous with sensory and motor tracts in the brain
- The spinal cord is classified as a Mixed Nerve because it contains both sensory axons (in the posterior root) and motor axons (in the anterior root)
Connective Tissue Coverings of Spinal Nerves
- Endoneurium - surrounds individual axons (innermost layer)
- Perineurium - surrounds bundles of axons, known as Nerve Fascicles (middle layer)
- Epineurium - surrounds the entire nerve (outermost layer)
4 . Blood Vessels are present within the coverings, which nourish the spinal meninges
Distribution of Spinal Nerves: Branches
A short distance after passing through its vertebral foramen a spinal nerve divides into several branches known as Rami:
- Posterior (dorsal) ramus - serves the deep muscles and skin of the posterior surface of the trunk
- Anterior (ventral) ramus - serves the muscles and structures of the upper and lower limbs and the skin of the lateral and anterior surfaces of the trunk
- Meningeal branch - this branch reenters the vertebral cavity through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges.
- Communicating rami (rami communicates) - components of the ANS
Distribution of Spinal Nerves: Plexuses
Axons from the anterior rami of spinal nerves (except thoracic nerves T2-T12) do not go directly to the body structures they supply, instead they form networks on both left and right sides of the body by joining with various numbers of axons from anterior rami of adjacent nerves called a Plexus
- Cervical Plexus
- Brachial Plexus
- Lumbar Plexus
- Sacral Plexus
- Coccygeal Plexus
Distribution of Spinal Nerves: Intercostal Nerves
The anterior rami of spinal nerves T1-T12 do not enter the formation of the plexuses are known as intercoastal nerves or thoracic nerves. These nerves directly connect to the structures they supply.
Dermatomes
The area of skin that provides sensory input to the CNS via one pair of spinal nerves or trigeminal (V) nerve
Cervical Plexus
Supplies the skin and muscles of the head, neck, and upper part of the shoulders and chest; connects with some cranial nerves and supplies the diaphragm.
- Roots: C1-C4 with contributions from C5
- Nerves:
Superficial (Sensory) Branches
- Lesser occipital
- Greater auricular
- Transverse cervical
- Supraclavicular
Deep (Largely Motor) Branches
- Ansa cervicales
- Superior root
- Inferior root
- Phrenic
- Segmental branches
Brachial Plexus
Provides almost the entire nerve supply of the shoulders and upper limbs
Roots: C5-C8 and T1
Nerves:
- Dorsal scapular
- Long thoracic
- Nerve to subclavius
- Suprascapular
- Musculocutaneous
- Lateral Pectoral
- Superior subscapular
- Thoracodorsal
- Inferior subscapular
- Axillary
- Median
- Radial
- Medial pectoral
- Medial cutaneous nerve of arm
- Medial cutaneous nerve of forearm
- Ulnar
MNEMONIC for subunits of the brachial plexus: Risk Takers Don’t Cautiously Behave. Roots, Trunks, Divisions, Cords, Branches
Lumbar Plexus
Supplies the anterolateral abdominal wall, external genitals, and part of the lower limbs
Roots: L1-L4
Nerves
- Illiohypogastric
- Illioinguinal
- Genitofemoral
- Lateral femoral cutaneous nerve
- Femoral
- Obturator
