Anatomy Chapter 13

Reciprocal innervation is the arrangement in which one muscle contracts while its antagonistic muscle relaxes. This is important for preventing conflict between opposing muscles and is vital for coordinating body movements.

The stretch reflex helps maintain posture by causing muscles to contract when they are stretched. For example, if a person leans forward, the calf muscles are stretched, triggering the reflex to contract and restore upright posture.

The stretch reflex pathway is monosynaptic, involving just two neurons and one synapse. In contrast, the polysynaptic reflex arc involves three neurons and two synapses, including an inhibitory interneuron that relaxes antagonistic muscles.

The brain receives input about the state of stretch or contraction of skeletal muscles through ascending pathways, allowing it to coordinate muscular movements and maintain conscious awareness of the reflex.

The tendon reflex operates as a feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes excessive, preventing potential tendon damage.

The tendon reflex is less sensitive than the stretch reflex but can override it when tension is great, such as when dropping a heavy weight. Both reflexes are ipsilateral, but they respond to different stimuli: the stretch reflex responds to muscle length changes, while the tendon reflex responds to muscle tension changes.

1. Increased tension stimulates the tendon organ (sensory receptor).
2. Nerve impulses travel to the spinal cord along a sensory neuron.
3. The sensory neuron activates an inhibitory interneuron in the spinal cord.
4. The inhibitory neurotransmitter hyperpolarizes the motor neuron, reducing nerve impulses.
5. The muscle relaxes, relieving excess tension.

Golgi tendon organs are sensory receptors located within tendons that detect changes in muscle tension caused by passive stretch or muscular contraction, initiating the tendon reflex when tension increases.

Reciprocal innervation involves the simultaneous contraction of antagonistic muscles while the muscle attached to the stimulated tendon organ relaxes, allowing for coordinated movement and balance during the reflex action.

The tendon reflex protects the tendon and muscle from damage due to excessive tension by increasing the frequency of inhibitory impulses, which inhibits motor neurons to the muscle developing excess tension, causing relaxation of that muscle.

The tendon reflex involves reciprocal innervation as the sensory neuron from the tendon organ synapses with an excitatory interneuron in the spinal cord, which then synapses with motor neurons controlling antagonistic muscles, leading to contraction of antagonists while the muscle attached to the tendon organ relaxes.

1. Stepping on a tack stimulates the dendrites of a pain-sensitive neuron.
2. The sensory neuron is excited.
3. The integrating center in the spinal cord processes the information.
4. Motor neurons are excited.
5. The effectors (flexor muscles) contract and withdraw the leg.

The flexor reflex is classified as an intersegmental reflex arc because it involves multiple segments of the spinal cord, allowing for coordinated responses across different levels of the spinal cord, which is necessary for effective withdrawal from a painful stimulus.

1. A sensory neuron generates nerve impulses after detecting a painful stimulus.

2. The sensory neuron activates interneurons in the spinal cord that extend to several segments.

3. Interneurons activate motor neurons in multiple spinal cord segments.

4. Motor neurons generate nerve impulses that propagate to the axon terminals.

5. Acetylcholine is released, causing flexor muscles in the thigh to contract, resulting in withdrawal of the leg.

The spinal cord contributes to homeostasis by providing quick, reflexive responses to stimuli, serving as the pathway for sensory input to the brain and motor output from the brain.

A spinal cord reflex is a quick, automatic response to certain stimuli that involves neurons only in the spinal nerves and spinal cord, allowing for rapid reactions without conscious awareness.

The gray matter of the spinal cord is involved in the integration of excitatory and inhibitory postsynaptic potentials, processing reflexes, and facilitating communication between neurons.

The white matter of the spinal cord contains major sensory and motor tracts that act as 'highways' for sensory input traveling to the brain and motor output traveling from the brain to effectors.

Spinal cord injuries can have widespread effects because the spinal cord is integral to the central nervous system, affecting both sensory and motor pathways that control various bodily functions.

The protective structures of the spinal cord include:

1. Vertebral Column: Surrounds the spinal cord, providing a sturdy shelter.
2. Meninges: Three membranes (dura mater, arachnoid mater, pia mater) that encircle the spinal cord.
3. Cerebrospinal Fluid: Located in the subarachnoid space, it provides a shock-absorbing cushion.
4. Epidural Space: Contains fat and connective tissue that further protect the spinal cord.

The three layers of the meninges surrounding the spinal cord are:

Denticulate ligaments are triangular-shaped membranous extensions of the pia mater that:

• Suspend the spinal cord in the middle of its dural sheath.
• Protect the spinal cord against sudden displacement that could result in shock.

A spinal tap, or lumbar puncture, is a medical procedure that involves:

• Inserting a long hollow needle into the subarachnoid space to withdraw cerebrospinal fluid (CSF).
• It is used for diagnostic purposes, to introduce medications, measure CSF pressure, or evaluate treatment effects for diseases such as meningitis.

A spinal tap is performed between the L3 and L4 or L4 and L5 lumbar vertebrae because:

• This region provides safe access to the subarachnoid space without the risk of damaging the spinal cord, which ends around the second lumbar vertebra (L2).

The subarachnoid space contains cerebrospinal fluid (CSF), which cushions the spinal cord and provides nutrients. It also contains blood vessels that supply the spinal cord.

The anterior (ventral) root contains motor fibers that transmit signals from the spinal cord to muscles, while the posterior (dorsal) root contains sensory fibers that carry information from the body to the spinal cord.

The central canal is a small, fluid-filled channel that runs longitudinally through the center of the spinal cord, containing cerebrospinal fluid (CSF) that helps to nourish and protect the spinal cord.

The brachial plexus (C5-T1) connects with nerves of the upper limbs.

The two main enlargements of the spinal cord are:

1. Cervical Enlargement: Extends from the fourth cervical vertebra (C4) to the first thoracic vertebra (T1). It gives rise to nerves that innervate the upper limbs.

2. Lumbar Enlargement: Extends from the ninth to the twelfth thoracic vertebra (T9-T12). It gives rise to nerves that innervate the lower limbs.

The conus medullaris is the tapering, conical structure at the end of the spinal cord, terminating at the level of the intervertebral disc between the first and second lumbar vertebrae (L1-L2) in adults. It marks the end of the spinal cord and gives rise to the filum terminale, which anchors the spinal cord to the coccyx.

Spinal nerves connect to the spinal cord via two bundles of axons called roots:

• Posterior (Dorsal) Root: Contains sensory axons that conduct nerve impulses from sensory receptors to the central nervous system. It has a swelling known as the posterior root ganglion, which contains the cell bodies of sensory neurons.

• Anterior (Ventral) Root: Contains axons of motor neurons that conduct nerve impulses from the central nervous system to effectors (muscles and glands).

The posterior gray horn contains axons of sensory neurons and cell bodies of interneurons. It plays a crucial role in processing sensory information received from the body before relaying it to the brain or spinal cord for further processing.

The spinal cord is shorter than the vertebral column, which results in the lumbar and sacral nerves having to travel longer distances to exit the vertebral canal through the intervertebral foramina. This anatomical arrangement leads to the formation of the cauda equina, a bundle of spinal nerves that extends beyond the conus medullaris.

In the spinal cord, horns refer to the regions of gray matter that contain neuronal cell bodies, while columns refer to the regions of white matter that contain bundles of myelinated axons. Horns are involved in processing sensory and motor information, whereas columns are pathways for transmitting signals to and from the brain.

The three types of white columns in the spinal cord are:

1. Anterior (ventral) white columns
2. Posterior (dorsal) white columns
3. Lateral white columns

Each column contains distinct bundles of axons that carry similar information and have a common origin or destination.

The anterior (ventral) gray horns contain somatic motor nuclei, which are clusters of cell bodies of somatic motor neurons. These neurons provide nerve impulses for the contraction of skeletal muscles, facilitating voluntary movement.

The lateral gray horns are present only in the thoracic and upper lumbar segments of the spinal cord. They 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, thus controlling involuntary functions.

The central canal is a small space located in the center of the gray commissure of the spinal cord. It extends the entire length of the spinal cord and is filled with cerebrospinal fluid, which provides cushioning and nutrients to the spinal cord.

Sensory input is conveyed from sensory receptors to the posterior gray horns of the spinal cord, while motor output is conveyed from the anterior and lateral gray horns to effectors such as muscles and glands.

Sensory neurons may either:

1. Ascend into the white matter of the spinal cord as part of a sensory tract.
2. Enter the posterior gray horn and synapse with interneurons, whose axons then ascend to the brain as part of a sensory tract.

Somatic motor neurons in the anterior gray horn convey motor output to skeletal muscles. They are regulated by the brain, with axons from higher brain centers forming motor tracts that synapse with these neurons either directly or through interneurons.

Interneurons in the spinal cord can:

1. Synapse with sensory neurons that enter the posterior gray horn.
2. Connect with somatic motor neurons involved in spinal reflex pathways, facilitating reflex actions.

Lateral gray horns are typically found in the thoracic and upper lumbar segments of the spinal cord, associated with autonomic functions.

Somatic motor neurons pass through the anterior gray horn and anterior root to enter the spinal nerve. From the spinal nerve, their axons extend to skeletal muscles of the body.

Autonomic motor neurons convey motor output in the form of nerve impulses along their axons, passing through the lateral gray horn, anterior gray horn, and anterior root to enter the spinal nerve, where they synapse with another group of autonomic motor neurons in the PNS.

As the spinal cord ascends from sacral to cervical segments, more ascending axons are added to the white matter, forming more sensory tracts, resulting in an increase in white matter.

Dermatomes are important for understanding the sensory innervation of the skin and can help in diagnosing nerve root injuries or diseases affecting specific spinal nerves.

Spinal nerves are parallel bundles of axons and neuroglial cells wrapped in connective tissue, connecting the CNS to sensory receptors, muscles, and glands throughout the body.

The cauda equina is formed by the roots of lumbar, sacral, and coccygeal nerves that descend at an angle to reach their foramina before emerging from the vertebral column, significant for understanding spinal nerve arrangements.

A typical spinal nerve has two connections: the posterior root, which contains sensory axons, and the anterior root, which contains motor axons.

The three layers of connective tissue coverings of spinal nerves are:

1. Endoneurium: Surrounds individual axons.
2. Perineurium: Surrounds bundles of axons called fascicles.
3. Epineurium: Surrounds the entire nerve.

The posterior (dorsal) ramus serves the deep muscles and skin of the posterior surface of the trunk.

The 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.

The meningeal branch reenters the vertebral cavity through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, and blood vessels of the spinal cord.

The main branches of a spinal nerve are:

1. Posterior ramus
2. Anterior ramus
3. Meningeal branch
4. Rami communicantes

A plexus is a network of axons formed by the anterior rami of spinal nerves (except for thoracic nerves T2-T12) that join with axons from adjacent nerves. The principal plexuses include:

Intercostal nerves (anterior rami of spinal nerves T2-T12) differ from other spinal nerves in that they do not form plexuses. Instead, they directly connect to the structures they supply in the intercostal spaces, innervating:

• Intercostal muscles
• Skin of the anterior and lateral chest wall
• Abdominal muscles (T7-T12)
• Deep back muscles and skin of the posterior thorax (via posterior rami)

A dermatome is an area of skin that provides sensory input to the CNS via the posterior roots of one pair of spinal nerves or the trigeminal (V) nerve. Each spinal nerve serves a specific segment of the body, and adjacent dermatomes overlap, allowing for the identification of damaged spinal cord regions based on sensory loss.

Spinal nerves connect to the spinal cord through anterior and posterior roots. The anterior roots contain motor neurons that carry impulses away from the spinal cord, while the posterior roots contain sensory neurons that carry impulses into the spinal cord.

The cervical plexus supplies the skin and muscles of the head, neck, and the superior part of the shoulders and chest. It also gives rise to the phrenic nerves, which innervate the diaphragm.

The phrenic nerve, which arises from the cervical plexus, causes contraction of the diaphragm.

The C1 spinal nerve is the only spinal nerve that does not have a corresponding dermatome.

Injuries to the phrenic nerves, which originate from C3, C4, and C5, can lead to respiratory arrest. This occurs because the phrenic nerves are responsible for sending nerve impulses to the diaphragm. If the spinal cord is completely severed above the origin of the phrenic nerves (C3, C4, and C5), breathing stops. Additionally, phrenic nerve damage can occur due to pressure from malignant tumors in the mediastinum affecting the trachea or esophagus.

The brachial plexus is formed by the roots (anterior rami) of spinal nerves C5-C8 and T1.

The main components of the brachial plexus include:

1. Roots - Anterior rami of spinal nerves.
2. Trunks - Formed from the roots (superior, middle, inferior).
3. Divisions - Anterior and posterior divisions from the trunks.
4. Cords - Lateral, medial, and posterior cords formed from the divisions.
5. Branches - Principal nerves of the brachial plexus.

The five large terminal branches of the brachial plexus and their functions are:

1. Axillary nerve - Supplies the deltoid and teres minor muscles.
2. Musculocutaneous nerve - Supplies the anterior muscles of the arm.
3. Radial nerve - Supplies the muscles on the posterior aspect of the arm and forearm.
4. Median nerve - Supplies most of the muscles of the anterior forearm and some of the muscles of the hand.
5. Ulnar nerve - Supplies the anteromedial muscles of the forearm and most of the muscles of the hand.

Erb-Duchenne palsy, also known as the waiter's tip position, is caused by injury to the superior roots of the brachial plexus (C5-C6). This injury may occur from forceful pulling away of the head from the shoulder, such as in a heavy fall on the shoulder or excessive stretching of an infant's neck during childbirth. The presentation includes an upper limb with the shoulder adducted, arm medially rotated, elbow extended, forearm pronated, and wrist flexed.

Injury to the radial nerve can result in wrist drop, which is the inability to extend the wrist and fingers. This injury may occur due to improperly administered intramuscular injections into the deltoid muscle or a cast applied too tightly around the mid-humerus. Sensory loss is minimal due to the overlap of sensory innervation by adjacent nerves.

Median nerve palsy is characterized by symptoms such as:

• Numbness, tingling, and pain in the palm and fingers.
• Inability to pronate the forearm.
• Difficulty flexing the proximal interphalangeal joints of the fingers.

The axillary nerve supplies the deltoid and teres minor muscles, as well as the skin over the deltoid and the superior posterior aspect of the arm.

The ulnar nerve originates from spinal cord segments C8-T1 and distributes to:

• Flexor carpi ulnaris, ulnar half of flexor digitorum profundus, and most muscles of the hand.
• Skin of the medial side of the hand, little finger, and medial half of the ring finger.

Symptoms of ulnar nerve palsy include:

• Inability to abduct or adduct the fingers
• Atrophy of the interosseous muscles of the hand
• Hyperextension of the metacarpophalangeal joints
• Flexion of the interphalangeal joints (clawhand)
• Loss of sensation over the little finger

Injury to the long thoracic nerve results in paralysis of the serratus anterior muscle, leading to a condition known as winged scapula. This is characterized by the medial border of the scapula protruding and the inability to abduct the arm beyond the horizontal position.

Thoracic outlet syndrome is caused by compression of the brachial plexus and may also involve the subclavian artery and vein. Causes include:

• Spasm of the scalene or pectoralis minor muscles
• Presence of a cervical rib (embryological anomaly)
• Misaligned ribs

Symptoms include pain, numbness, weakness, or tingling in the upper limb, which are exacerbated during physical or emotional stress.

The mnemonic for the subunits of the brachial plexus is: Risk Takers Don't Cautiously Behave. This stands for:

1. Roots
2. Trunks
3. Divisions
4. Cords
5. Branches

The five important nerves that arise from the brachial plexus are:

1. Musculocutaneous nerve
2. Axillary nerve
3. Radial nerve
4. Median nerve
5. Ulnar nerve

The lumbar plexus is formed by the roots (anterior rami) of spinal nerves L1-L4.

The lumbar plexus passes obliquely outward between the superficial and deep heads of the psoas major muscle and anterior to the quadratus lumborum muscle.

The femoral nerve is the largest nerve arising from the lumbar plexus and is distributed to:

• Flexor muscles of the hip joint
• Extensor muscles of the knee joint
• Skin over the anterior and medial aspect of the thigh
• Medial side of the leg and foot

The largest nerve arising from the lumbar plexus is the femoral nerve.

Signs of femoral nerve injury include:

1. Inability to extend the leg.
2. Loss of sensation in the skin over the anteromedial aspect of the thigh.

Injuries to the obturator nerve result in:

• Paralysis of the adductor muscles of the thigh.
• Loss of sensation over the medial aspect of the thigh.

The sacral plexus is formed by the roots (anterior rami) of spinal nerves L4-L5 and S1-S4. Its primary function is to supply the buttocks, perineum, and lower limbs.

Injury to the common fibular portion of the sciatic nerve can lead to foot drop (plantar flexed and inverted foot) and loss of function along the anterolateral aspects of the leg and dorsum of the foot and toes.

Sciatica is characterized by pain extending from the buttock down the leg, often caused by compression or irritation of the sciatic nerve. Common causes include a herniated disc, dislocated hip, osteoarthritis, and pressure from the uterus during pregnancy.

The superior gluteal nerve innervates the gluteus minimus, gluteus medius, and tensor fasciae latae muscles.

The sciatic nerve originates from spinal nerves L4-S3 and is actually composed of two nerves, the tibial and common fibular, which are bound together by a common sheath. It supplies the hamstring muscles and adductor magnus in the thigh and splits into its two divisions at the knee.

The pudendal nerve supplies the muscles of the perineum and the skin of the penis and scrotum in males, as well as the clitoris, labia majora, labia minora, and vagina in females.

The sacral plexus originates from the ventral rami of spinal nerves L4, L5, S1, S2, S3, S4, and S5.

The two principal functions of the spinal cord in maintaining homeostasis are:

1. Nerve impulse propagation - Conducting sensory input toward the brain and motor output from the brain.
2. Integration of information - Receiving and integrating incoming and outgoing information in the gray matter.

The naming convention for spinal cord tracts indicates:

• Location in the white matter.
• Origin and destination of the tract.

For example, the anterior corticospinal tract begins in the cerebral cortex and ends in the spinal cord, indicating it is a motor (descending) tract.

The gray matter of the spinal cord serves as a site for:

• Integration of information, summing excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs).

The white matter of the spinal cord functions as the 'highways' for:

1. Conduction of sensory nerve impulses toward the brain.
2. Conduction of motor nerve impulses from the brain toward effector tissues.

The spinothalamic tract originates in the spinal cord and terminates in the thalamus of the brain. It is a sensory tract that conveys sensory information to the brain.

The cerebral cortex plays a major role in controlling precise voluntary muscular movements, while other brain regions help regulate automatic movements.

The two types of descending pathways are direct motor pathways (pyramidal pathways) and indirect motor pathways (extrapyramidal pathways).

A reflex is a fast, involuntary, unplanned sequence of actions in response to a stimulus. The spinal cord serves as an integrating center for some reflexes, processing sensory information and triggering motor responses.

The five components of a reflex arc are: 1. Sensory receptor - detects stimulus; 2. Sensory neuron - transmits signal to the spinal cord; 3. Integrating center - processes the signal; 4. Motor neuron - carries the response signal; 5. Effector - muscle or gland that responds.

A monosynaptic reflex arc involves a single synapse between a sensory neuron and a motor neuron, while a polysynaptic reflex arc involves one or more interneurons and multiple synapses in the CNS.

Reflexes provide useful information about the health of the nervous system; abnormalities or absence of reflexes can indicate damage or disease along the reflex arc.

The stretch reflex causes contraction of a skeletal muscle in response to its stretching, helping to maintain muscle tone and posture.

A nerve impulse in a sensory neuron is initiated by the detection of a stimulus by sensory receptors, such as muscle spindles, which respond to changes in the environment by producing a generator or receptor potential.

A monosynaptic reflex arc involves a single sensory neuron forming one synapse with a single motor neuron in the CNS. It functions as follows:

1. Slight stretching of a muscle stimulates sensory receptors (muscle spindles).
2. The muscle spindle generates nerve impulses that travel along a somatic sensory neuron to the spinal cord.
3. In the spinal cord, the sensory neuron activates a motor neuron in the anterior gray horn.
4. If excitation is sufficient, the motor neuron generates nerve impulses that travel to the muscle.
5. Acetylcholine released at neuromuscular junctions triggers muscle contraction, relieving the stretch.

An ipsilateral reflex is a reflex action where sensory nerve impulses enter the spinal cord on the same side from which motor nerve impulses exit. All monosynaptic reflexes are classified as ipsilateral, meaning they occur on the same side of the body.

The brain regulates muscle spindle sensitivity through pathways to smaller-diameter motor neurons that innervate the muscle spindles. This regulation adjusts the responsiveness of muscle spindles to stretching, ensuring proper signaling over a range of muscle lengths during voluntary and reflex contractions, thereby setting an overall level of muscle tone.

The stretch reflex helps avert injury by preventing overstretching of muscles. When a muscle is stretched, the reflex causes it to contract, thereby protecting it from excessive lengthening.

The flexor reflex is a polysynaptic reflex involving multiple muscle groups and several motor neurons, while the monosynaptic stretch reflex involves only one spinal cord segment and a single muscle group.

1. Stepping on a tack stimulates a pain-sensitive sensory neuron in the affected foot.

2. The sensory neuron generates nerve impulses that propagate into the spinal cord.

3. Interneurons in the spinal cord activate motor neurons on the opposite side, innervating extensor muscles.

4. Motor neurons generate impulses that cause contraction of extensor muscles in the opposite leg, allowing weight to shift and maintain balance.

Reflexes can indicate damage along specific conduction pathways. Abnormal or absent reflexes may suggest issues with sensory or motor nerves, or lesions in the spinal cord. Common reflex tests include the patellar reflex, Achilles reflex, Babinski sign, and abdominal reflex.

In children under 1½ years, the Babinski reflex results in extension of the great toe and possible fanning of other toes due to incomplete myelination. A positive Babinski sign after age 1½ is abnormal and indicates a potential lesion in the corticospinal tract.

The pupillary light reflex involves the pupils of both eyes constricting when either eye is exposed to light. Its absence may indicate brain damage or injury, as the reflex arc includes synapses in lower brain regions.

The crossed extensor reflex causes contraction of muscles that extend joints in the limb opposite a painful stimulus, allowing for coordinated movement and balance during withdrawal from a painful stimulus.

The crossed extensor reflex is classified as a contralateral reflex arc because sensory impulses enter one side of the spinal cord and motor impulses exit on the opposite side, synchronizing the extension of the contralateral limb with the withdrawal of the stimulated limb.

Reciprocal innervation refers to the process where one set of muscles contracts while the opposing set relaxes, preventing both sets from contracting simultaneously, which could immobilize the limb.

Ascending tracts carry sensory information from the body to the brain, while descending tracts transmit motor commands from the brain to the body.

Monosynaptic reflex arcs involve a single synapse between a sensory neuron and a motor neuron, while polysynaptic reflex arcs involve one or more interneurons between the sensory and motor neurons, allowing for more complex responses.

Common causes of spinal cord injuries include:

1. Automobile accidents
2. Falls
3. Contact sports
4. Diving accidents
5. Acts of violence

Complete transection of the spinal cord results in:

• Loss of all sensations and voluntary movement below the level of the transection.
• Permanent loss of sensations in dermatomes below the injury due to interrupted ascending nerve impulses.
• Loss of voluntary muscle contractions below the transection due to interrupted descending nerve impulses.

The symptoms of Brown-Séquard syndrome include:

1. Loss of proprioception and fine touch sensations on the ipsilateral (same) side as the injury due to damage of the posterior column.
2. Ipsilateral paralysis due to damage of the lateral corticospinal tract.
3. Loss of pain and temperature sensations on the contralateral (opposite) side due to damage of the spinothalamic tracts.

Spinal shock is an immediate response to spinal cord injury characterized by temporary areflexia (loss of reflex function). Signs of acute spinal shock include:

• Slow heart rate
• Low blood pressure
• Flaccid paralysis of skeletal muscles
• Loss of somatic sensations
• Urinary bladder dysfunction

Spinal shock may begin within 1 hour after injury and can last from several minutes to several months.

Methylprednisolone is an anti-inflammatory corticosteroid drug that may improve outcomes in spinal cord injury if administered within 8 hours post-injury. It helps reduce neurologic deficits caused by edema as the immune system responds to the injury.

Spinal cord compression can result from:

1. Fractured vertebrae
2. Herniated intervertebral discs
3. Tumors
4. Osteoporosis
5. Infections If identified early, spinal cord function may return to normal after addressing the source of compression.

Symptoms of spinal cord compression may include:

• Pain
• Weakness or paralysis
• Decreased or complete loss of sensation below the level of the injury

Post-polio syndrome is a neurological disorder that can develop decades after a severe polio attack. It is characterized by:

• Progressive muscle weakness
• Extreme fatigue
• Loss of function
• Pain in muscles and joints

Shingles is caused by the reactivation of the herpes zoster virus, which remains dormant in the posterior root ganglion after chickenpox. Symptoms include:

• Pain
• Discoloration of the skin
• A characteristic line of skin blisters that follows the distribution of the affected sensory nerve (dermatome)

The main symptoms of poliomyelitis include:

1. Fever
2. Severe headache
3. Stiff neck and back
4. Deep muscle pain and weakness
5. Loss of certain somatic reflexes In severe cases, it can lead to paralysis and potentially death from respiratory or heart failure.

Meningitis is the inflammation of the meninges, usually due to infection. Symptoms include fever, headache, stiff neck, vomiting, confusion, lethargy, and drowsiness.

• Bacterial meningitis: More serious, treated with antibiotics, can be fatal if untreated.
• Viral meningitis: Usually resolves on its own in 1-2 weeks, no specific treatment available.

Myelitis refers to the inflammation of the spinal cord, which can result from various causes including infections and autoimmune responses.

Neuralgia is characterized by attacks of pain along the entire course or a branch of a sensory nerve, often resulting from irritation or damage to the nerve.

An epidural block involves injecting an anesthetic drug into the epidural space to cause a temporary loss of sensation, commonly used to control pain during childbirth.

The spinal cord is protected by the vertebral column, meninges, cerebrospinal fluid, and denticulate ligaments.

The three meninges are the dura mater, arachnoid mater, and pia mater.

The spinal cord begins as a continuation of the medulla oblongata and ends at about the second lumbar vertebra in an adult.

The cervical and lumbar enlargements are regions of the spinal cord that serve as points of origin for nerves to the limbs.

The conus medullaris is the tapered inferior portion of the spinal cord, from which arise the filum terminale and cauda equina.

Spinal nerves connect to each segment of the spinal cord by two roots: the posterior (dorsal) root containing sensory axons and the anterior (ventral) root containing motor neuron axons.

The gray matter in the spinal cord is divided into horns, while the white matter is divided into columns. The gray matter processes information, and the white matter conveys sensory and motor information through ascending and descending tracts.

Dermatomes are specific, constant segments of the skin served by sensory neurons within spinal nerves. Knowledge of dermatomes helps physicians determine which segment of the spinal cord or which spinal nerve is damaged.

The components of a reflex arc are:

1. Sensory receptor
2. Sensory neuron
3. Integrating center
4. Motor neuron
5. Effector

A monosynaptic reflex arc consists of one sensory neuron and one motor neuron, such as the stretch reflex. A polysynaptic reflex arc contains sensory neurons, interneurons, and motor neurons, such as the tendon reflex and flexor (withdrawal) reflex.

Sensory input travels along the posterior column and the spinothalamic tract, while motor output travels along direct pathways and indirect pathways in the white matter of the spinal cord.

The tendon reflex is ipsilateral and prevents damage to muscles and tendons by inhibiting muscle contraction when muscle force becomes too extreme.

The flexor reflex is ipsilateral and serves to move a limb away from the source of a painful stimulus, thereby protecting the body from harm.

The crossed extensor reflex extends the limb contralateral to a painfully stimulated limb, allowing the weight of the body to shift when a supporting limb is withdrawn, thus maintaining balance.

Important somatic reflexes include:

1. Patellar reflex
2. Achilles reflex
3. Babinski sign
4. Abdominal reflex

The needle will pierce the following structures from most superficial to deepest:

1. Skin
2. Subcutaneous tissue
3. Supraspinous ligament
4. Interspinous ligament
5. Ligamentum flavum
6. Epidural space
7. Dura mater
8. Arachnoid mater
9. Subarachnoid space

Destruction of cells in the anterior gray horns in the lower cervical region may lead to:

• Weakness or paralysis of the muscles innervated by affected spinal nerves
• Loss of reflexes in the upper limbs
• Atrophy of the muscles due to denervation

The part of the spinal cord affected is likely the dorsal columns or posterior columns, which are responsible for proprioception and fine touch sensation.

The cervical enlargement connects with sensory and motor nerves of the upper limbs, facilitating movement and sensation in that region.

The spinothalamic tract is a sensory tract that contains ascending axons originating in the spinal cord and ending in the thalamus, responsible for transmitting pain and temperature sensations.

Reciprocal innervation is a neural circuit arrangement that involves the simultaneous contraction of one muscle and the relaxation of its antagonist, allowing coordinated movement.