Chapter 13: Spinal Cord And Spinal Nerves Flashcards
Vertebral Column
Vertebrae provide a sturdy shelter for the enclosed spinal cord.
The vertebral ligaments, meninges, cerebrospinal fluid provide additional protection.
Meninges
Singular: meninx
3 protective, connective tissue coverings that encircle the spinal cord and the brain.
Superficial to deep:
Dura mater
Arachnoid mater
Pia mater
Spinal Meninges
Surround the spinal cord. Are continuous with the cranial meninges.
Cranial Meninges
Encircle the brain.
Epidural Space
A space between the dura mater and the wall of the vertebral canal. Contains a cushion of fat and CT that protect the spinal cord.
Dura Mater
Most superficial layer of the 3 meninges.
Thick strong layer composed of dense irregular CT.
Arachnoid Mater
The middle layer of the meningeal membranes.
A thin, a vascular covering comprised of cells and thin, loosely arranged collagen and elastic fibers.
Subdural Space
Space between the dura mater and arachnoid mater, contains interstitial fluid.
Pia Mater
The innermost meninx is a thin transparent CT layer that adheres to the surface of the spinal cord and brain.
Contains thin squamous to cuboidal cells within interlacing bundles of collagen fiber and some fine elastic fibers.
Contains many blood vessels that supply O2 and nutrients to the spinal cord.
Denticulate Ligaments
Extensions in pia mater.
Thickenings , project laterally and fuse with the arachnoid mater and inner surface of the dura mater between the anterior and posterior nerve roots of spinal nerves on either side.
Subarachnoid Space
Space between the arachnoid mater and pia mater. Contains shock absorbing cerebrospinal fluid.
Spinal Cord
Is a roughly oval shape, being flattened slightly anteriorly and posteriorly.
Anatomy of Spinal Cord/Nerves
Spinal cord extends from the medulla oblong at the base of the brain to the superior boarder of the second lumbar vertebra.
Cervical Plexus C1-C5
Brachial Plexus C5-T1
Lumbar Plexus L1-L4
Sacral Plexus L4-S4
Cervical Plexus C1-C5
Formed by the roots of C1-C4 with contributions from C5.
There is one on each side of neck along the first 4 cervical vertebrae.
Supplies: skin and muscles of the head, neck and superior part of shoulder, chestnut and diaphragm.
Nerves:
Lesser Occipital Nerve
Greater Auricular
Ansa Cervicalis
Transverse Cervical nerve
Supraclaviculat nerve
Phrenic nerve
Brachial Plexus C5-T1
Roots of spinal nerves C5-C8 - T1. Extends inferiorly and laterally on either side of the last 4 cervical and 1st thoracic vertebra. Passes above the 1st rib to the clavicle and enters axilla. Provides entire nerve supply to shoulders and upper limbs.
Nerves:
Musculocutaneous Nerve
Axillary nerve
Median nerve
Radial nerve
Ulnar nerve
Intercostal nerves
Subcostal nerve
Second lumbar vertebra
Lumbar Plexus L1-L4
Roots of spinal nerves L1-L4. There is minimal intermingling of fibers in the lumbar plexus.
Supplies: anterolateral abd wall, external genitals and parts of lower limbs.
Nerves:
Lliphypogastric Nerve
Llioingunial nerve
Genitofemeral nerve
Lateral femoral cutaneous nerve
Femoral nerve
Obturator nerve
Sacral Plexus L4-S4
Roots of spinal nerves L4-L5 and S1-S4.
Situated largely anterior to the sacrum.
Supplies: buttocks, perineum and lower limbs.
Nerves:
Superior gluteal nerve
Inferior gluteal nerve
Sciatic nerve: largest nerve in body
Posterior cutaneous nerve of height
Pudendeal nerve
Cervical Enlargement
Superior enlargement, extends from the fourth cervical vertebra C4 to the first thoracic vertebra T1. Nerves to and from the upper limbs arise in this enlargement.
Lumbar Enlgargement
Inferior enlargement, extends from the 9th -12th thoracic vertebra. Nerves to and from the lower limbs arise from the lumbar enlargement.
Conus Medullaris
Where the spinal cord terminates as a tapering, conical structure.
Inferior to the lumbar enlargement
Filum Terminale
Arises from the conus medullaris. An extension of the pia mater that extends interiorly, fused with arachnoid mater and dura mater.
Anchors the spinal cord to the coccyx.
Spinal Nerves
Path of communication between the spinal cord and specific regions of the body.
31 pairs
Roots
Two bundles of axons that connect each spinal nerve to a segment of the cord by smaller bundles of axons.
Rootlets
Smaller bundle of axons.
Contains sensory axons.
Posterior Root
Only contain sensory axons. Conduct nerve impulses from sensory receptors in the skin, muslces and internal organs.
Posterior Root Ganglion
Contained in posterior root. Swelling which contains the cell bodies of sensory neurons.
Anterior Root
Contains axons of motor neurons which conduct nerve impulses from the CNS to effectors.
White Matter of Spinal Cord
Consists of bundles of myelinated axons of neurons.
Divided grooves into right and left sides.
Anterior Median Fissure
Is a wide groove on there anterior (ventral) side.
Posterior Median Sulcus
Narrow furrow on the posterior (dorsal) side.
Gray Commissure
Forms the crossbar of the H found in gray mater.
Central Canal
Small space in the center of the gray commissure.
Anterior White Commissure
Connects the white matter of the right and left sides of the spinal cord.
Nuclei
Found in gray matter of the spinal cord and brain. Clusters of neuronal cell bodies that form functional groups.
2 types:
1. Sensory Nuclei: recieve input from receptors via sensory neurons.
2. Motor Nuclei: provide output to effector tissues via motor neurons.
Horns
Subdivided regions of gray matter on each side of the spinal cord.
Posterior Gray Horns
contain axons of incoming sensory neurons and cell bodies.
Anterior Gray Horns
Contain somatic motor nuclei.
Clusters of cell bodies of somatic motor neurons.
Provide nerve impulses for contraction of skeletal muscles.
Lateral Gray Horns
Located between posterior and anterior gray horns.
Present only in thoracic and upper lumbar segments of the spinal cord.
Contain autonomic motor nuclei.
Regulate the activity of cardiac muscles, smooth muscle and glands.
White Matter Columns
Organized into regions: Divided into three broad areas:
1. Anterior white columns
2. Posterior white columns
3. Lateral white columns
Each columns contains distinct bundles of axons that have a common origin or destination and carry similar information.
Tracts
Bundles that extend long distances up and down the spinal cord.
Sensory Tracts
Bundle of nerves axon in the PNS.
Motor Tracts
Tracts consisting of axons that carry nerve impulses for the brain.
Spinal Nerve
Connect the CNS to sensory receptors, muscles and glands in all parts of the body.
Endoneurium
Innermost layer of CT of spinal nerves that wraps individual axons within a nerve.
Consists of a mesh of collagen fibers, fibroblast and macrophages.
Facicles
Bundles of axons covered with endoneurium. Wrapped in perineurium.
Perineurium
Middle layer of CT of Spinal nerves. Trickier layer of CT. Consists of up to 15 layers of fibroblasts within a network of collagen fibers.
Epineurium
Outermost covering of CT of spinal nerves. Consists of fibroblasts and thick collagen fibers.
Branches
When spinal nerves divide after passing through its intervertebral foramen.
Rami
Branches of spinal nerves
Posterior Ramus
Serve the deep muscles and skin of the posterior surface of the trunk.
Anterior Ramus
Serves the muscles and structures of the upper and lower limb and skin of the lateral and anterior surfaces of the trunk.
Meningeal Branch
Branch that recenters the vertebral cavity through the intervertebral foramen and supplies the vertebrae, its ligaments, blood vessels of spinal cord and meninges.
Plexuses
Network formed on both the left and right sides of the body that join with various numbers of axons.
Principal plexuses: cervical, brachial, lumbar, sacral and coccygeal.
Intercostal Nerves
Or thoracic nerves
Anterior rami of spinal nerves T2-T12. These do not enter into the formation of plexuses. These nerves directly connect to the structures they supply in the intercostal spaces.
Dermatome
Area of skin that provides sensory input to the CNS via one pair of spinal nerves or Trigeminal (V) nerve.
2 Principle Functions of spinal Cord
- Nerve impulse propagation
- Integration of information
White matter are highways for nerves impulse propagation
Gray matter receives and integrates in coming and outgoing information.
2 Main Routes of Nerve Impulses from Sensory Reception
- Spinothalamic tract: conveys nerve impulses for sensing pain, temperature, itch and tickle.
- Posterior column: consists of 2 tracts (1) gracile fasciculus (2) cuneate fasciculus. Convey nerve impounded for touch, pressure, vibration and conscious proprioception.
Sensory information is integrated by interneurons in the spinal cord and brain.
Motor Output Pathway
From skeletal muscles, travels down the spinal cord in 2 types of descending pathways;
1. Direct: (pyramidal pathways)convey nerve impulses that originate in the cerebral cortex and are destined to cause voluntary movements of skeletal muscles.
2. Indirect: (extrapyramid pathway) convey nerve impulses from the breaking stem to cause automatic movements and help coordinate body movements.
Reflex
Fast, involuntary, unplanned sequence of actions that occur in response to a particular stimulus.
Spinal Relflex
Integration that takes place in the spinal cord gray matter.
Ie: knee jerk
Cranial Reflex
Integration that occurs in the brain stem rather than spinal cord.
Ie: tacking movements of the eyes as you read a sentence.
Stretch Reflex
Causes contractions of a skeletal muscle in response to stretching of the muscle.
Occurs via: nonsynaptic reflex arc
Can be elicited by tapping on tendons attached to muscles at the elbow, wrist, knee, and ankle joints.
Muscle Tone
Small degree of contraction set by brain while muscle is at rest.
Reciprocal Innervation
Prevents conflict between opposing muscles and is vital in coordinating body movements.
Tendon Reflex
Operates as a feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might be torn.
Sensory receptor: tendon organs, lie within a tendon near its junction with a muscle.
Flexor Reflex
Or withdraw reflex
Involves a polysynaptic reflex arc in response to painful stimulus
Ie: you immediately withdraw a limb
Crossed Extensor Reflex
Helps maintain your balance.
Somatic Reflex
Effector that is a skeletal muscle
Autonomic (Visceral) Relfex
An effector that is smooth or cardiac muscle or a gland.
Ipsilateral Reflex
Where a sensory neuron enters the spinal cord in the same time from which the motor nerve impulses leave the spinal cord.
All monosynaptic reflexes are Ipsilateral.
Monosynaptic Reflex Arc
The stretch reflex occurs vis this arc. Occurs by activation of a single sensory neuron that forms one synapse in the CNS with a single motor neuron.
Muscle Spindles
Monitors changes in the length of the muscle. Responses when stimulated by sensory receptors when a slight stretch of a muscle occurs.
Polysnaptic Reflex
Reflex pathway that involves more than two types of neurons and more than one CNS synapse.
Corticospinal Tract
Direct motor pathway conducts nerve impulses that control voluntary sketeal muscle movements.
Like writing.
