chapter 13

List the functions of the spinal cord

Conduction Neural Integration Locomotion Reflexes

Define proprioceptors

Proprioceptors-A sensory receptor of the muscles, tendons, and joint capsules that detects muscle contractions and joint movements.

Explain the stretch (Myotatic) reflex

When a muscle is suddenly stretched, it "fights back"—it contracts, increases tone, and feels stiffer than an unstretched muscle. This response, called the stretch (myotatic) reflex, helps to maintain equilibrium and posture

Characterize poliomyelitis and ALS

-ALS -is also known as Lou Gehrig disease. It is marked not only by the degeneration of motor neurons and atrophy of the muscles, but also sclerosis (scarring) of the lateral regions of the spinal cord. Most cases occur when astrocytes fail to reabsorb the neurotransmitter glutamate from the tissue fluid, allowing it to accumulate to a neurotoxic level. -Poliomyelitis- is caused by the poliovirus, which destroys motor neurons in the brainstem and anterior horn of the spinal cord. Signs of polio include muscle pain, weakness, and loss of some reflexes, followed by paralysis, muscular atrophy, and sometimes respiratory arrest.

Describe decussation, contralateral and ipsilateral

-Decussation- tracts that cross over from the left side of the body to the right, or vice versa. As a result, the left side of the brain receives sensory information from the right side of the body and sends motor commands to that side, while the right side of the brain senses and controls the left side of the body. -Contralateral- When the origin and destination of a tract are on opposite sides of the body. -Ipsilateral- When the origin and destination of a tract is on the same side of the body.

List the 3 pairs of funiculi

-Posterior (dorsal) -Lateral -Anterior (ventral) column

List and describe the 3 meninges

Dura Mater- Most superficial layer, it forms a fitting sleeve called the dural sheath around the spinal cord. It's a tough collagenous membrane about as thick as a rubber kitchen glove. the space between the sheath and vertebral bones, called the epidural space. Arachnoid Mater- consists of a simple squamous epithelium. the arachnoid membrane connects to the inside of the dura. its a loose mesh of collagenous and elastic fibers spanning the gap between the arachnoid membrane and the pia. Pia Mater- Transparent membrane that closely follows the contours of the spinal cord. It has a fibrous strand called the terminal filum.

Define dermatome and list how much each overlaps

Each spinal nerve except C1 receives sensory input from a specific area of skin called a dermatome. -The dermatomes overlap at their edges by as much as 50%. Therefore, severance of one sensory nerve root does not entirely deaden sensation from a dermatome. It is necessary to sever or anesthetize three successive spinal nerves to produce a total loss of sensation from one dermatome.

Describe a nerve plexus

Except in the thoracic region, the anterior rami branch and anastomose (merge) repeatedly to form five webs called nerve plexuses.

Describe the filium terminale and the denticulate ligaments

Fillium Terminale- a fibrous strand in the pia mater. Denticulate ligaments- extensions of the pia mater it then extends through the arachnoid mater to the dura, which then anchors the cord and limits the side to side movement.

Explain the Flexor Withdrawal & Crossed-Extensor Reflexes

Flexor (withdrawal)-he quick contraction of flexor muscles resulting in the withdrawal of a limb from an injurious stimulus. Crossed-extensor- The contraction of extensor muscles in the limb opposite from the one that is withdrawn. It extends that limb and enables you to keep your balance. To produce this reflex, branches of the afferent nerve fibers cross from the stimulated side of the body to the contralateral side of the spinal cord. There, they synapse with interneurons, which, in turn, excite or inhibit alpha motor neurons to the muscles of the contralateral limb.

Describe a ganglion

Ganglion- a cluster of neurosomas outside the CNS. It is enveloped in an epineurium continuous with that of the nerve.

Explain the composition of gray matter and white matter

Gray Matter- a zone or layer of tissue within the nervous system where the neuron cell bodies, dendrites, and synapses are found; forms the cerebral cortex and basal nuclei; cerebellar cortex and deep nuclei; nuclei of the brainstem; and core of the spinal cord. White Matter-White myelinated nervous tissue deep to the cortex of the cerebrum and cerebellum and superficial to the gray matter of the spinal cord. *Nervous tissue is often histologically stained with silver compounds, which give the gray matter a brown or golden color and white matter a lighter tan to amber color.*

Describe spina bifida and how it can be prevented

Spina bifida is a congenital defect in which one or more vertebrae fail to form a complete vertebral arch for enclosure of the spinal cord. A woman can reduce the risk of having a child with spina bifida by taking ample folic acid. it typically forms within the first 4 weeks of development.

Explain how spinal trauma leads to paraplegia and quadriplegia

The most serious permanent effect of spinal cord trauma is paralysis. The flaccid paralysis of spinal shock later changes to spastic paralysis as spinal reflexes are regained but lack inhibitory control from the brain. Spastic paralysis typically starts with chronic flexion of the hips and knees (flexor spasms) and progresses to a state in which the limbs become straight and rigid (extensor spasms). Forms of muscle paralysis are paraplegia, a paralysis of both lower limbs resulting from spinal cord lesions at levels T1 to L1; quadriplegia, the paralysis of all four limbs resulting from lesions above level C5; Spinal cord lesions from C5 to C7 can produce a state of partial quadriplegia—total paralysis of the lower limbs and partial paralysis (paresis, or weakness) of the upper limbs.

Define a somatic reflex

The reflexes of skeletal muscle are called somatic reflexes, since they involve the somatic nervous system.

Describe the Cross-Sectional Anatomy of the Spinal Cord

The spinal cord, like the brain, consists of two kinds of nervous tissue called gray and white matter. It is composed of bundles of axons, called tracts, that carry signals from one level of the CNS to another. Both gray and white matter also have an abundance of glial cells.

Explain the Golgi Tendon Reflex

The tendon reflex is a response to excessive tension on the tendon. It inhibits alpha motor neurons to the muscle so the muscle does not contract as strongly. This serves to moderate muscle contraction before it tears a tendon or pulls it loose from the muscle or bone.

Describe the Anatomy of the Spinal Cord

a cylinder of nervous tissue that arise from the brainstem at the foramen magnum of the skull. It is divided into Cervical,theoratic, lumbar, and sacral regions. Two areas of the spinal cord is thicker then the rest. Cervical enlargement and Lumber enlargement. The cord tapers to a point called the Medullary cone. Arising from the lumbar enlargement and medullary cone is bundle of nerve roots that occupy the vertebral canal from L2 to S5. This bundle is called Cauda Equina.

List the 5 nerve plexuses and their locations

the small cervical plexus in the neck, the brachial plexus near the shoulder, the lumbar plexus of the lower back, the sacral plexus immediately inferior to this, and finally, the tiny coccygeal plexus adjacent to the lower sacrum and coccyx.