Ch. 13 - Lecture Notes

Spinal Cord Learning Outcomes * Describe the protective structures of the spinal cord * Describe the external and internal anatomical structures of the spinal cord * Describe the sensory and motor pathways Video: Spinal Cord Anatomy Video: Lecture 13.1 Subtopic: Spinal Cord Anatomy Central Nervous System (CNS): spinal cord & brain * Spinal cord is protected by 1) vertebrae and 2) meninges and 3) Cerebral Spinal Fluid. * Spinal cord begins as as a continuation of the medulla oblongata and terminates at the second lumbar. * The tapered portion of the spinal cord is the conus medullaris (filum terminale and cauda equina arise from) Meninges * Protective 3-layers covering (meninges): these layers run continuously around the spinal cord and brain. 1. pia mater: thin delicate inner layer; denticulate ligaments are thickenings of pia mater that suspend the spinal cord. 2. Arachnoid mater: middle spider web-like layer 3. Dura mater: tough protective outer layer called the dura mater; extends to cover and protect the pairs of spinal nerves that extend from the cord at the level of each vertebra. * Epidural space: outside of the dura mater is a space filled with fat and large blood vessels; adipose tissue contributes to the protection of the spinal cord. * Epidural analgesic injection: provides pain relief during childbirth. Cerebrospinal Fluid (CSF): * Subarachnoid space: space associated with the arachnoid mater filled with cerebrospinal fluid (helps protect too). * CSF is clear and colorless fluid; produced by the choroid plexus of the brain. * CSF acts as a cushion to help prevent injury. * CSF is found in the subarachnoid space (between the arachnoid and pia mater). * Spinal Tap: is done to withdraw CSF for diagnostic purposes. Vertebrae * Protective structures of the vertebrae include the vertebral arch, body of vertebrae and spinous process. More Spinal cord anatomy.... * Spinal cord gives rise to the axons of the dorsal roots and ventral roots, which come together to make up the paired spinal nerves. * The spinal nerves exit from each intervertebral foramen. * A thickening of the cord at the cervical enlargement and lumbar enlargement accounts for the extra tissue required for sensory and motor functions of the upper and lower extremities. * The cord ends at about L1/L2 (1st or 2nd lumbar vertebrae) in adults or L3/L4 in infants and small children. The difference between adults and infants is because the bones continue to grow long after the nervous tissue has stopped. * The spinal cord ends in a point called the conus medullaris and the pia mater extends as a fiber called the filum terminale which, along with the denticulate ligaments, contributes to the stability of the cord in the vertebral canal. * Along with the filum terminale, the spinal roots hang off the end of the cord on their way to the intervertebral foramen of the lower vertebrae and, because they appear similar to a horse’s tail, are called the cauda equina Subtopic: Cross Section Anatomy- Gray matter vs. White matter * The nervous tissue of the spinal cord itself is arranged into gray matter shaped like a butterfly with white matter surrounding it. * White matter: composed of myelinated axons; ascending sensory pathways delivering sensory information from receptors to the brain and the descending motor pathways carrying motor commands from the brain to the muscles. * Gray matter: composed of cell bodies and unmyelinated axons; (sensory neurons, interneurons involved in the integration of information, and the cell bodies of the lower motor neurons that give rise to the axons that control our muscles. * The wings of butterfly-shaped gray matter in the spinal cord cross-section have dorsal and ventral regions. * Towards the dorsal surface are called the posterior (dorsal) horns and contain cell bodies of sensory neurons. * The neurons that bring sensory information into the cord from the body enter here as dorsal roots. * These sensory neurons have cell bodies in the dorsal root ganglia which are outside of the CNS. * The parts of the wings towards the ventral surface are called the anterior (ventral) horns and are where we find the large cell bodies of the lower motor neurons. The axons of these lower motor neurons exit each spinal segment as ventral roots. Finally, in the thoracic spinal segments, we find lateral horns composed of the cell bodies of certain autonomic neurons that are part of the fight or flight response. Subtopic: Pathways * Motor: descending; efferent * Sensory: ascending; afferent * Ipsilateral: traveling same side of the stimulus or muscle * Contralateral: traveling on the opposite side. Subtopic: Motor Pathways * Motor information: travels from the brain down the spinal cord to the effectors (muscles and glands) * UMN and LMN form a two-neuron circuit. * UMNs originate in the cerebral cortex and travel down to the brainstem or spinal cord * LMNs begin in the spinal cord (ventral horn) and go to innervate muscles/ glands Corticospinal tracts: controls skeletal muscles 1. UMN cell body is in the primary motor cortex of the frontal lobe of the brain 2. synapses on LMN (ventral horn of the spinal cord) 3. projects to the skeletal muscle Direct Pathways: * Lateral corticospinal tract (also known as pyramidal tract) * travel from the cortex (cortico-) to the spinal cord (spinal) * decussates in the medulla (at pyramids) * Cervical, thoracic, lumbar, sacral muscles * Anterior corticospinal tract (also known as pyramidal tract) * Travel from the cortex to the spinal cord * Decussates at the spinal cord * Trunk muscles * Corticobulbar tract: allows the brain to control muscles of the head and neck by innervating lower motor neurons in the brainstem (which travel in the cranial nerves). Indirect Pathways (extra pyramidal pathways) * Tectospinal tract involves reflexive movements of the head, equilibrium, and coordination of visual reflexes. * Vestibulospinal tract controls muscle tone and posture that responds to vestibular input from the inner ear allowing us to maintain balance. * Rubrospinal tract controls limb movement on the basis of cerebellar processing and originates in the red nucleus of the brain. * Reticulospinal tract controls body posture as a response to the reticular system of the brain which controls (level of alertness). Subtopic: Sensory Pathways * Sensory pathways involve three neurons! * Information from receptors travels up the spinal cord to the brain along two main routes on each side of the cord: 1) spinothalamic tract and 2) posterior column tract. * Spinothalamic tracts: carry information about pain and temperature * Dorsal column-medial lemniscus tract: carries general somatosensory and proprioceptive information. 1. First-order sensory neuron: delivers the information from the receptor to the spinal cord. 2. Second-order sensory neurons: decussate and synapse on neurons in the thalamus. 3. Third-order sensory neurons: project to the location on the brain where stimulus is perceived (primary somatosensory cortex in the postcentral gyrus of the parietal lobe of the brain). Decussation * Decussate happens at different levels * Example from your textbook: 1. The first-order sensory neurons of the dorsal column-medial lemniscus pathway travel in the spinal cord ipsilaterally to the stimulus before synapsing in the medulla. That means that some general sensory neurons travel from your big toe all the way to your brain and are the longest cells in your body. These neurons travel in two bundles in the dorsal columns called the fasciculus gracilis (lower body) and the fasciculus cuneatus (upper body) that carry information. 2. Second-order sensory neurons decussate and travel to the thalamus in a tract called the medial lemniscus. 3. Third-order sensory neurons then project to the primary somatosensory cortex in the parietal lobe of the brain where the stimulus is perceived. Subtopic: Spina Bifida * Vertebrae fail to develop posteriorly (at the lamina); spinal cord vulnerable or exposed * Spina bifida is associated with a decrease of folic acid intake during fetal development. * Occulta: least severe form that involves a hidden defect. * Meningocele: projection of meninges * Meningomyelocele: projection of meninges and spinal cord through the skin * Causes of spina bifida are not known. * Spina bifida occurs in the first few weeks of pregnancy. Spinal Nerve & Plexus Learning Outcomes * Describe the structures and functions of the spinal nerves * Define the connective tissue coverings of spinal nerves * Describe the peripheral nerves of the cervical, thoracic, lumbar, and sacral plexuses Video: Spinal Nerves & Plexuses Video: Lecture Video 13.2 Subtopic: Spinal Nerve * Spinal nerves that exit from between the vertebrae (via the intervertebral foramen) consist of: * fused dorsal (incoming sensory or afferent) and ventral (outgoing motor or efferent) roots. * After they come together every subsequent division is considered mixed motor and sensory. * Spinal Nerves: (31 pairs) 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal * C1 spinal nerve exits above C1 vertebrae; C2 - C7 spinal nerves are named for the vertebra below it; C8 is found under cervical vertebral bone of C7. Subtopic: Nerve Structure * structure of a nerve is organized by the layers of connective tissue on the outside, around each fascicle, and surrounding the individual nerve fibers. * Layers: endoneurium, perineurium, and epineurium * Epineurium: cover the outside of the nerve. * Perineurium: layer covering the fascicles. * Endoneurium: layer covering the nerve fiber. Subtopic: Plexuses * Four main nerve plexuses in the human body. 1. Cervical plexus supplies nerves to the posterior head and neck, (and diaphragm). 2. Brachial plexus supplies nerves to the arm. 3. Lumbar plexus supplies nerves to the anterior leg. 4. Sacral plexus supplies nerves to the posterior leg. Cervical Plexus * Receives input from spinal nerves C1-C5 gives rise to, among others, the phrenic nerve. * Phrenic Nerve: important nerve because it controls the diaphragm (breathing). * Spinal segments that contribute to this nerve are C3-C5. * Any damage above C5 will likely involve the patient being on mechanical ventilation for the rest of their lives. Brachial Plexus * Brachial plexus, which receives input from C6-T1 gives rise to the peripheral nerves of the arm. * Axillary nerve * radial nerve: Damage to the radial nerve can cause wrist drop * median nerve: carpal tunnel syndrome results from compression of the median nerve. * ulnar nerve: “funny bone” due to the sensation resulting from impacting the nerve where it passes over the medial epicondyle of the humerus * Brachial plexus avulsion: * Shoulder Dystoica: During birth, sometimes the baby’s shoulders get stuck. This can cause a tremendous amount of force to be exerted on the arm of the baby which can cause damage to the brachial plexus leading to motor and sensory impairments of the arm. Lumbar & Sacral Plexus * Lumbar plexus (L1-L5) and the sacral plexus (S1-S5) give rise to several large nerves including the femoral nerve, the obturator nerve, and the sciatic nerve. * The sciatic nerve is the source of pain for those who suffer from sciatica, a peripheral neuropathy which can cause pain, paresthesia (abnormal sensation) and/or muscle weakness along the back of the leg to the feet. * This pain can be debilitating and can be caused by nerve compression from a ruptured or bulging intervertebral disc, plexus damage, or muscle compression of the nerve often involving the piriformis muscle. Learning Outcomes * Define sensation and perception * Describe sensory modalities * Describe general senses and types of sensory receptors * Describe the significance of dermatomes Video: Lecture 13.3 Subtopic: General Senses Sensation & perception * Sensation is the activation of sensory receptor cells at the level of the stimulus and perception is the central processing of sensory stimuli into a meaningful pattern where we become aware of the stimulus. * Receptors are the cells or structures that detect stimuli and convert the energy of the stimulus into an action potential in a process called sensory transduction. * General senses: light, sound, touch, temperature, etc. * Special Senses: taste, smell, vision, hearing and balance (vestibular) * General senses are distributed throughout the body and have receptor cells within the structures of other organs that are not dedicated to the function of sensation. * Mechanoreceptors are found in the skin, muscles, or the walls of blood vessels. * Somatosensation: touch, proprioception, and interoception (sensation of the internal state of the body). Includes pressure, vibration, light touch, tickle, itch, temperature, pain, and proprioception. Many somatosensory receptors are located in the skin, but receptors are also found in muscles, tendons, joint capsules, ligaments, and the walls of visceral organs. Subtopic: Tactile sensations Tactile Sensations * Tactile epithelial cells (Merkel cells); Tactile epithelial cells are located in the stratum basale of the epidermis * Lamellated (Pacinian) corpuscles: Deep pressure and vibration; encapsulated endings found deep in the hypodermis * Tactile (Meissner) corpuscles: light touch, encapsulated endings. * Hair root plexus: nerve endings detect the movement of hair at the surface of the skin (ex: insect on your skin) * Bulbous corpuscles (Ruffini corpuscles; type II cutaneous mechanoreceptors): stretch receptors of the skin. Thermal sensations * Two types of somatosensory signals: pain and temperature (free nerve endings) * Temperature uses thermoreceptors and Pain uses nociceptors. * Temperature receptors are stimulated when local temperatures differ from body temperature. We have cold and warm thermoreceptors. Pain sensations * Nocioception is the sensation of potentially damaging stimuli * Nociceptors (pain receptors) are in every tissue of the body (except the brain). * Mechanical, chemical, thermal or even photo (bright light) stimuli beyond a set threshold will elicit painful sensations. * There are two types of pain, fast and slow. * Fast or acute pain occurs rapidly, within 0.1 seconds after a stimulus is applied. myelinated Type A nerve fiber. * Slow pain is processed and propagated by the unmyelinated Type C nerve fibers. Slow pain tends to increase in intensity and can last a longer time. Subtopic: Dermatomes Dermatomes link * A dermatome: an area of the skin that provides sensory input via the spinal nerves and one cranial nerve to the central nervous system. * The trigeminal nerve (V) is the cranial nerve that serves most of the skin of the face and scalp. * Each nerve relays the sensory information from the specific region of the skin to the brain. (C1 has no dermatome) * Spinal nerves - sensory neurons arise from the dorsal root ganglion. * Pain from a certain area of the skin may indicate problems with a specific spinal nerve or its dorsal root or root ganglion. Subtopic: Referred Pain * The referred pain is served by the same segment of the spinal cord. * Example: Heart attacks s/s (signs & symptoms) include shortness of breath, chest discomfort, and pains in the arms, neck, or jaw. Pain in jaw or arm would be the referred pain. * Example: the sensory nerves which serve the heart and the skin area medial of the left arm enter the T1 to T5 segments of the spinal cord. * Example: “ice cream freeze” or “brain freeze” where you develop a headache after eating shaved ice or a cold drink too quickly. The nerve responds by causing rapid constriction and dilation of the blood vessels. Subtopic: Pain Relief * Aspirin: non-steroidal anti-inflammatory drug (NSAID) * It inhibits pain and inflammation by inhibiting the enzyme called cyclooxygenase (COX). * COX produces a local hormone, prostaglandins, which stimulate the nociceptors and leads to pain sensation and inflammation. * With the intake of aspirin, there is less prostaglandin present and less inflammation and pain sensation. * Aspirin is an acid -may damage the linings of the gastrointestinal tract causing gastric ulcers and bleeding. * Acupuncture * Component of traditional Chinese medicine where a metallic hair-thin needle is inserted into the skin. * Western practitioners view the acupuncture points as locations to stimulate nerves, muscles, and connective tissues and sometimes apply an electrical current to the needles. Subtopic: Proprioception and Balance * somatosensory receptors are found in the joints and muscles. * Stretch receptors monitor the stretching of tendons, muscles, and the components of joints. * Example: you stretch your muscles before or after exercise and noticed that you can only stretch so far before your muscles spasm back to a less stretched state? This spasm is a reflex that is initiated by stretch receptors to avoid muscle tearing. * Stretch receptors can also prevent the over-contraction of a muscle! * Muscle spindles: stretch receptor in skeletal muscle tissue. * Tendon organs (Golgi tendon organs): transduce the tension levels of tendons. * Bulbous corpuscles: present in joint capsules; where they measure pressure in the components of the skeletal system within the joint providing an awareness of limb and body position or proprioception. * Lamellated corpuscles: in joints, detect the vibrations that result from movement. Kinesthesia is the detection and awareness of movement. Learning Outcomes * Describe the different types of reflexes * Define the components of a reflex arc * Describe the stretch reflex, tendon reflex, flexor, and crossed extensor reflexes Subtopic: Reflexes Video: Golgi Tendon Reflex Video: Withdrawal reflex Video: Crossed Extensor reflex 1. Sensory receptors: respond to changes in the environment. 2. Sensory neurons: carry signals from the sensory receptors to gray matter in the spinal cord or brainstem. 3. Integration (reflex) center: the gray matter of the brain and spinal cord (CNS). 1. Monosynaptic reflex single synapse between the sensory neuron and the motor neuron (no interneurons). 2. Polysynaptic reflex: has at least one interneuron in between the sensory neuron and the motor neuron. (Interneurons carry signals to other interneurons and motor neurons.) 4. Motor neurons: carry signals from the CNS to the effector. 5. Effector: creates the action at the end of the reflex arc. Learning Outcomes * Describe spinal cord injury and types of neurological exams Video: Lecture 13.5 Subtopic: Spinal Cord Injury * The most common cause of spinal cord injury is motor vehicle accidents (MVAs) followed closely by falls. (average age: early 40's). * Paresis: partial paralysis or weakness of a limb * Paraplegia: paralysis of the lower extremities * Quadriplegia: paralysis of all four limbs * Hemiplegia which is paralysis of one side of the body Subtopic: Brown-Se'quard hemisection (spinal cord hemisection) Video: Brown Se'quard Syndrome * Brown- Se'quard syndrome: incomplete pattern of injury showing a hemisection of the spinal cord; results in weakness and paralysis on one side of the damage and loss of pain and temperature sensations on the opposite side. The left side or the right side of the spinal cord is transected (severed). * Spinal cord pathways: axons travel in different pathways * Pain & temperature: (second-order neurons) located in the dorsal horns and decussate contralaterally to the spinothalamic tract. * Touch & proprioception: (second-order neurons are in the brain) * the first-order neurons - dorsal column of the spinal cord travel ipsilateral to the stimulus. * Descending upper motor neurons (UMN) decussate in the medulla and therefore travel ipsilateral to the muscle in the corticospinal tracts of the spinal cord. * Hemisection injury: * paralysis on the same side as the injury * loss of sensation and proprioception on the same side as the injury * lose pain and temperature sensation on the opposite side of the injury. Subtopic: Neurological Exams Tactile and Tonicity Exams Sensory Testing * Two-point discrimination * Tests a patient’s ability to distinguish between two points of contact on the skin as being separate. * Dermatomes ( figure 13.16) you can find the location of the lesion within one or two spinal segments. * Other sensory tests: pain and temperature tests a patient’s ability to distinguish hot versus cold or to sense painful stimuli (needle prick). Motor Testing * Tested by instructing the patient to push against your hand and pull using different muscles. (example: pushing down on a patient’s shoulders and telling them to shrug or push against your hand) * Motor impairment is paralysis. Paralysis can be described as spastic or flaccid. * Spastic paralysis is due to upper motor neuron (UMN) damage * Flaccid paralysis is due to lower motor neuron (LMN) damage Reflex Examination Stretch Reflex: most common spinal reflex tested. * Test involves tapping the muscle tendon with the reflex hammer- deep tendon reflexes (DTRs). * Deep tendon reflexes: * Tap on the tendon * Reflex can be described as normal, hyporeflexic, or hyperreflexic. * Hyporeflexia: absent diminished reflex * Hyperreflexia: repeating reflexes; hyperactive. * Common DTRs * patellar reflex (the knee jerk reflex) * triceps brachii reflex * biceps brachii reflex * brachialis reflex * Achilles reflex (the ankle jerk reflex) * Cutaneous reflexes: stimulating the skin. * Plantar reflex: tested by dragging the sharp end of the reflex hammer across the bottom of the foot from heel to toe. (Normally this causes the toes to flex) * Babinski sign: toes dorsiflex and fan out. * In adults: positive babinski sign = upper motor neuron damage * In infants: positive Babinski sign is normal (due to incomplete myelination in newborns) Proprioception * Simple tests: touching the nose with a finger or touching a location on the skin after it has been touched by the clinician. * Gait observation: observing the patient’s gait (the way that they walk) or walking heel to toe. * Romberg test: overall measurement of balance. * Coordination and balance require input to the cerebellum from proprioceptive information in the spinocerebellar tract, vestibular information from the inner ear, and visual information. The loss of one or more of these sensory inputs will cause impairments in balance and loss of proprioception or vestibular input will cause swaying when a patient stands with feet together and their eyes closed. Severity of the damage reflects patient’s ability to maintain an upright posture. Subtopic: Shingles * Shingles is a virus known as varicella-zoster virus (VZV); causes chickenpox * Affects your nerves. * After recovering from chickenpox, the virus travels from the skin retrogradely inside of the axons of sensory neurons and stays dormant in the dorsal root ganglia. * For most individuals, the virus will remain dormant and they don’t even know that it’s there. * 1/3 adults may experience shingles when the virus becomes active again and is transported anterogradely inside of the axon back to the skin. * We do not yet understand the reasons why the virus switches from inactive to active state, but a weakened immune system or stress may trigger the switch. * A patient with shingles may experience tingling and numbness of the skin, develop blisters, pain, chills, and fever. Once the blisters dry up, the patient will see the scab clearing up. Most cases last from three to five weeks. Some people choose to get vaccinated for shingles, depending on their situation.

* CSF is clear and colorless fluid; produced by the choroid plexus of the brain. 
   * CSF acts as a cushion to help prevent injury.  
   * CSF is found in the subarachnoid space (between the arachnoid and pia mater). 
   * Spinal Tap: is done to withdraw CSF for diagnostic purposes. 
Vertebrae
   * Protective structures of the vertebrae include the vertebral arch, body of vertebrae and spinous process.
More Spinal cord anatomy....
   * Spinal cord gives rise to the axons of the dorsal roots and ventral roots, which come together to make up the paired spinal nerves.
   * The spinal nerves exit from each intervertebral foramen.
   * A thickening of the cord at the cervical enlargement and lumbar enlargement accounts for the extra tissue required for sensory and motor functions of the upper and lower extremities.
   * The cord ends at about L1/L2 (1st or 2nd lumbar vertebrae) in adults or L3/L4 in infants and small children. The difference between adults and infants is because the bones continue to grow long after the nervous tissue has stopped.
   * The spinal cord ends in a point called the conus medullaris and the pia mater extends as a fiber called the filum terminale which, along with the denticulate ligaments, contributes to the stability of the cord in the vertebral canal.
   * Along with the filum terminale, the spinal roots hang off the end of the cord on their way to the intervertebral foramen of the lower vertebrae and, because they appear similar to a horse’s tail, are called the cauda equina
Subtopic: Cross Section Anatomy- Gray matter vs. White matter
   * The nervous tissue of the spinal cord itself is arranged into gray matter shaped like a butterfly with white matter surrounding it. 
   *  White matter: composed of myelinated axons; ascending sensory pathways delivering sensory information from receptors to the brain and the descending motor pathways carrying motor commands from the brain to the muscles.
   * Gray matter: composed of cell bodies and unmyelinated axons; (sensory neurons, interneurons involved in the integration of information, and the cell bodies of the lower motor neurons that give rise to the axons that control our muscles.
   * The wings of butterfly-shaped gray matter in the spinal cord cross-section have dorsal and ventral regions.
   * Towards the dorsal surface are called the posterior (dorsal) horns and contain cell bodies of sensory neurons.
   * The neurons that bring sensory information into the cord from the body enter here as dorsal roots.
   * These sensory neurons have cell bodies in the dorsal root ganglia which are outside of the CNS.
   * The parts of the wings towards the ventral surface are called the anterior (ventral) horns and are where we find the large cell bodies of the lower motor neurons. The axons of these lower motor neurons exit each spinal segment as ventral roots. Finally, in the thoracic spinal segments, we find lateral horns composed of the cell bodies of certain autonomic neurons that are part of the fight or flight response.
Subtopic: Pathways
   * Motor: descending; efferent
   * Sensory: ascending; afferent
   * Ipsilateral: traveling same side of the stimulus or muscle
   * Contralateral:  traveling on the opposite side.
Subtopic: Motor Pathways
   * Motor information: travels from the brain down the spinal cord to the effectors (muscles and glands)
   * UMN and LMN form a two-neuron circuit.
   * UMNs originate in the cerebral cortex and travel down to the brainstem or spinal cord
   * LMNs begin in the spinal cord (ventral horn) and go to innervate muscles/ glands 
Corticospinal tracts: controls skeletal muscles
1. UMN cell body is in the primary motor cortex of the frontal lobe of the brain 
2. synapses on LMN (ventral horn of the spinal cord)
3. projects to the skeletal muscle
Direct Pathways:
   * Lateral corticospinal tract (also known as pyramidal tract)
   * travel from the cortex (cortico-) to the spinal cord (spinal)
   * decussates in the medulla (at pyramids)
   * Cervical, thoracic, lumbar, sacral muscles
   * Anterior corticospinal tract (also known as pyramidal tract)
   * Travel from the cortex to the spinal cord
   * Decussates at the spinal cord
   * Trunk muscles
   * Corticobulbar tract: allows the brain to control muscles of the head and neck by innervating lower motor neurons in the brainstem (which travel in the cranial nerves).
Indirect Pathways (extra pyramidal pathways) 
   * Tectospinal tract involves reflexive movements of the head, equilibrium, and coordination of visual reflexes.
   * Vestibulospinal tract controls muscle tone and posture that responds to vestibular input from the inner ear allowing us to maintain balance.
   * Rubrospinal tract controls limb movement on the basis of cerebellar processing and originates in the red nucleus of the brain.
   * Reticulospinal tract controls body posture as a response to the reticular system of the brain which controls (level of alertness). 
Subtopic: Sensory Pathways
   * Sensory pathways involve three neurons!
   * Information from receptors travels up the spinal cord to the brain along two main routes on each side of the cord: 1) spinothalamic tract and 2) posterior column tract. 
   * Spinothalamic tracts: carry information about pain and temperature
   * Dorsal column-medial lemniscus tract: carries general somatosensory and proprioceptive information. 
   1. First-order sensory neuron: delivers the information from the receptor to the spinal cord. 
   2. Second-order sensory neurons: decussate and synapse on neurons in the thalamus.
   3. Third-order sensory neurons: project to the location on the brain where stimulus is perceived (primary somatosensory cortex in the postcentral gyrus of the parietal lobe of the brain).
Decussation
   * Decussate happens at different levels
   * Example from your textbook: 
   1. The first-order sensory neurons of the dorsal column-medial lemniscus pathway travel in the spinal cord ipsilaterally to the stimulus before synapsing in the medulla. That means that some general sensory neurons travel from your big toe all the way to your brain and are the longest cells in your body. These neurons travel in two bundles in the dorsal columns called the fasciculus gracilis (lower body) and the fasciculus cuneatus (upper body) that carry information.
   2. Second-order sensory neurons decussate and travel to the thalamus in a tract called the medial lemniscus. 
   3. Third-order sensory neurons then project to the primary somatosensory cortex in the parietal lobe of the brain where the stimulus is perceived.
Subtopic: Spina Bifida
   * Vertebrae fail to develop posteriorly (at the lamina); spinal cord vulnerable or exposed
   * Spina bifida is associated with a decrease of folic acid intake during fetal development.
   * Occulta: least severe form that involves a hidden defect.
   * Meningocele: projection of meninges 
   * Meningomyelocele: projection of meninges and spinal cord through the skin
   * Causes of spina bifida are not known. 
   * Spina bifida occurs in the first few weeks of pregnancy.
Spinal Nerve & Plexus
Learning Outcomes 
   * Describe the structures and functions of the spinal nerves
   * Define the connective tissue coverings of spinal nerves
   * Describe the peripheral nerves of the cervical, thoracic, lumbar, and sacral plexuses
Video: Spinal Nerves & Plexuses
Video: Lecture Video 13.2
Subtopic:  Spinal Nerve
   * Spinal nerves that exit from between the vertebrae (via the intervertebral foramen) consist of:
   * fused dorsal (incoming sensory or afferent) and ventral (outgoing motor or efferent) roots.
   * After they come together every subsequent division is considered mixed motor and sensory.
   * Spinal Nerves: (31 pairs) 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal
   * C1 spinal nerve exits above C1 vertebrae; C2 - C7 spinal nerves are named for the vertebra below it; C8 is found under cervical vertebral bone of C7.
Subtopic:  Nerve Structure
   * structure of a nerve is organized by the layers of connective tissue on the outside, around each fascicle, and surrounding the individual nerve fibers.
   * Layers: endoneurium, perineurium, and epineurium
   * Epineurium: cover the outside of the nerve.
   * Perineurium: layer covering the fascicles.
   * Endoneurium: layer covering the nerve fiber.
Subtopic: Plexuses
   * Four main nerve plexuses in the human body.
   1. Cervical plexus supplies nerves to the posterior head and neck, (and diaphragm).
   2. Brachial plexus supplies nerves to the arm.
   3. Lumbar plexus supplies nerves to the anterior leg.
   4. Sacral plexus supplies nerves to the posterior leg.
Cervical Plexus
   * Receives input from spinal nerves C1-C5 gives rise to, among others, the phrenic nerve.
   * Phrenic Nerve:  important nerve because it controls the diaphragm (breathing).
   * Spinal segments that contribute to this nerve are C3-C5.
   *  Any damage above C5 will likely involve the patient being on mechanical ventilation for the rest of their lives.
Brachial Plexus
   * Brachial plexus, which receives input from C6-T1 gives rise to the peripheral nerves of the arm.
   * Axillary nerve
   * radial nerve: Damage to the radial nerve can cause wrist drop
   * median nerve: carpal tunnel syndrome results from compression of the median nerve.
   * ulnar nerve: “funny bone” due to the sensation resulting from impacting the nerve where it passes over the medial epicondyle of the humerus
   * Brachial plexus avulsion: 
   * Shoulder Dystoica: During birth, sometimes the baby’s shoulders get stuck.  This can cause a tremendous amount of force to be exerted on the arm of the baby which can cause damage to the brachial plexus leading to motor and sensory impairments of the arm.
Lumbar & Sacral Plexus
   * Lumbar plexus (L1-L5) and the sacral plexus (S1-S5) give rise to several large nerves including the femoral nerve, the obturator nerve, and the sciatic nerve.
   * The sciatic nerve is the source of pain for those who suffer from sciatica, a peripheral neuropathy which can cause pain, paresthesia (abnormal sensation) and/or muscle weakness along the back of the leg to the feet.
   * This pain can be debilitating and can be caused by nerve compression from a ruptured or bulging intervertebral disc, plexus damage, or muscle compression of the nerve often involving the piriformis muscle.
Learning Outcomes
   * Define sensation and perception
   * Describe sensory modalities
   * Describe general senses and types of sensory receptors
   * Describe the significance of dermatomes
Video: Lecture 13.3
Subtopic: General Senses
Sensation & perception
   * Sensation is the activation of sensory receptor cells at the level of the stimulus and perception is the central processing of sensory stimuli into a meaningful pattern where we become aware of the stimulus.
   * Receptors are the cells or structures that detect stimuli and convert the energy of the stimulus into an action potential in a process called sensory transduction.
   * General senses:  light, sound, touch, temperature, etc. 
   * Special Senses: taste, smell, vision, hearing and balance (vestibular)
   * General senses are distributed throughout the body and have receptor cells within the structures of other organs that are not dedicated to the function of sensation. 
   * Mechanoreceptors are found in the skin, muscles, or the walls of blood vessels.
   * Somatosensation: touch, proprioception, and interoception (sensation of the internal state of the body). Includes pressure, vibration, light touch, tickle, itch, temperature, pain, and proprioception.  Many somatosensory receptors are located in the skin, but receptors are also found in muscles, tendons, joint capsules, ligaments, and the walls of visceral organs.
Subtopic: Tactile sensations
Tactile Sensations
   * Tactile epithelial cells (Merkel cells); Tactile epithelial cells are located in the stratum basale of the epidermis
   * Lamellated (Pacinian) corpuscles: Deep pressure and vibration; encapsulated endings found deep in the hypodermis
   * Tactile (Meissner) corpuscles: light touch, encapsulated endings.
   * Hair root plexus:  nerve endings detect the movement of hair at the surface of the skin (ex: insect on your skin)
   * Bulbous corpuscles (Ruffini corpuscles; type II cutaneous mechanoreceptors): stretch receptors of the skin. 
Thermal sensations
   * Two types of somatosensory signals: pain and temperature (free nerve endings)
   * Temperature uses thermoreceptors and Pain uses nociceptors.
   * Temperature receptors are stimulated when local temperatures differ from body temperature. We have cold and warm thermoreceptors.
Pain sensations
   * Nocioception is the sensation of potentially damaging stimuli
   * Nociceptors (pain receptors) are in every tissue of the body (except the brain).
   * Mechanical, chemical, thermal or even photo (bright light) stimuli beyond a set threshold will elicit painful sensations. 
   * There are two types of pain, fast and slow.
   * Fast or acute pain occurs rapidly, within 0.1 seconds after a stimulus is applied. myelinated Type A nerve fiber.
   * Slow pain is processed and propagated by the unmyelinated Type C nerve fibers. Slow pain tends to increase in intensity and can last a longer time.
Subtopic: Dermatomes
Dermatomes link
   * A dermatome: an area of the skin that provides sensory input via the spinal nerves and one cranial nerve to the central nervous system.
   * The trigeminal nerve (V) is the cranial nerve that serves most of the skin of the face and scalp.
   * Each nerve relays the sensory information from the specific region of the skin to the brain. (C1 has no dermatome)
   * Spinal nerves - sensory neurons arise from the dorsal root ganglion.
   * Pain from a certain area of the skin may indicate problems with a specific spinal nerve or its dorsal root or root ganglion.
Subtopic: Referred Pain
   * The referred pain is served by the same segment of the spinal cord.
   * Example: Heart attacks s/s (signs & symptoms) include shortness of breath, chest discomfort, and pains in the arms, neck, or jaw. Pain in jaw or arm would be the referred pain.
   * Example: the sensory nerves which serve the heart and the skin area medial of the left arm enter the T1 to T5 segments of the spinal cord.
   * Example: “ice cream freeze” or “brain freeze” where you develop a headache after eating shaved ice or a cold drink too quickly. The nerve responds by causing rapid constriction and dilation of the blood vessels.
Subtopic: Pain Relief
   * Aspirin:  non-steroidal anti-inflammatory drug (NSAID) 
   * It inhibits pain and inflammation by inhibiting the enzyme called cyclooxygenase (COX).
   * COX produces a local hormone, prostaglandins, which stimulate the nociceptors and leads to pain sensation and inflammation.
   * With the intake of aspirin, there is less prostaglandin present and less inflammation and pain sensation.
   * Aspirin is an acid -may damage the linings of the gastrointestinal tract causing gastric ulcers and bleeding.  
   * Acupuncture
   * Component of traditional Chinese medicine where a metallic hair-thin needle is inserted into the skin.
   * Western practitioners view the acupuncture points as locations to stimulate nerves, muscles, and connective tissues and sometimes apply an electrical current to the needles. 
Subtopic: Proprioception and Balance
   * somatosensory receptors are found in the joints and muscles.
   * Stretch receptors monitor the stretching of tendons, muscles, and the components of joints.
   * Example:  you stretch your muscles before or after exercise and noticed that you can only stretch so far before your muscles spasm back to a less stretched state? This spasm is a reflex that is initiated by stretch receptors to avoid muscle tearing.
   * Stretch receptors can also prevent the over-contraction of a muscle!
   * Muscle spindles:  stretch receptor in skeletal muscle tissue. 
   * Tendon organs (Golgi tendon organs):  transduce the tension levels of tendons.
   * Bulbous corpuscles: present in joint capsules; where they measure pressure in the components of the skeletal system within the joint providing an awareness of limb and body position or proprioception.
   * Lamellated corpuscles:  in joints, detect the vibrations that result from movement. Kinesthesia is the detection and awareness of movement.
Learning Outcomes
   * Describe the different types of reflexes
   * Define the components of a reflex arc
   * Describe the stretch reflex, tendon reflex, flexor, and crossed extensor reflexes
Subtopic: Reflexes
Video: Golgi Tendon Reflex
Video: Withdrawal reflex
Video: Crossed Extensor reflex
   1. Sensory receptors: respond to changes in the environment. 
   2. Sensory neurons: carry signals from the sensory receptors to gray matter in the spinal cord or brainstem. 
   3. Integration (reflex) center: the gray matter of the brain and spinal cord (CNS). 
   1. Monosynaptic reflex single synapse between the sensory neuron and the motor neuron (no interneurons). 
   2. Polysynaptic reflex: has at least one interneuron in between the sensory neuron and the motor neuron. (Interneurons carry signals to other interneurons and motor neurons.)
   4. Motor neurons: carry signals from the CNS to the effector.
   5. Effector: creates the action at the end of the reflex arc.
 
Learning Outcomes 
   * Describe spinal cord injury and types of neurological exams
Video: Lecture 13.5
Subtopic: Spinal Cord Injury
   * The most common cause of spinal cord injury is motor vehicle accidents (MVAs) followed closely by falls. (average age: early 40's).
   * Paresis: partial paralysis or weakness of a limb
   * Paraplegia: paralysis of the lower extremities
   * Quadriplegia: paralysis of all four limbs
   * Hemiplegia which is paralysis of one side of the body
Subtopic: Brown-Se'quard hemisection (spinal cord hemisection)
Video: Brown Se'quard Syndrome
   *  Brown- Se'quard syndrome: incomplete pattern of injury showing a hemisection of the spinal cord; results in weakness and paralysis on one side of the damage and loss of pain and temperature sensations on the opposite side. The left side or the right side of the spinal cord is transected (severed).
   * Spinal cord pathways: axons travel in different pathways
   * Pain & temperature: (second-order neurons) located in the dorsal horns and decussate contralaterally to the spinothalamic tract.
   * Touch & proprioception: (second-order neurons are in the brain)
   * the first-order neurons - dorsal column of the spinal cord travel ipsilateral to the stimulus.
   * Descending upper motor neurons (UMN) decussate in the medulla and therefore travel ipsilateral to the muscle in the corticospinal tracts of the spinal cord. 
   * Hemisection injury:
   * paralysis on the same side as the injury
   * loss of sensation and proprioception on the same side as the injury
   * lose pain and temperature sensation on the opposite side of the injury.
Subtopic: Neurological Exams
Tactile and Tonicity Exams
Sensory Testing
   *  Two-point discrimination
   * Tests a patient’s ability to distinguish between two points of contact on the skin as being separate. 
   * Dermatomes ( figure 13.16) you can find the location of the lesion within one or two spinal segments.
   * Other sensory tests: pain and temperature tests a patient’s ability to distinguish hot versus cold or to sense painful stimuli (needle prick).
Motor Testing
   * Tested by instructing the patient to push against your hand and pull using different muscles. (example: pushing down on a patient’s shoulders and telling them to shrug or push against your hand)
   * Motor impairment is paralysis. Paralysis can be described as spastic or flaccid.
   * Spastic paralysis is due to upper motor neuron (UMN) damage
   * Flaccid paralysis is due to lower motor neuron (LMN) damage
Reflex Examination
Stretch Reflex: most common spinal reflex tested.
   *  Test involves tapping the muscle tendon with the reflex hammer- deep tendon reflexes (DTRs).
   * Deep tendon reflexes: 
   * Tap on the tendon
   * Reflex can be described as normal, hyporeflexic, or hyperreflexic.
   * Hyporeflexia: absent diminished reflex
   * Hyperreflexia: repeating reflexes; hyperactive.
   * Common DTRs 
   * patellar reflex (the knee jerk reflex)
   * triceps brachii reflex
   * biceps brachii reflex
   * brachialis reflex
   * Achilles reflex (the ankle jerk reflex)
   * Cutaneous reflexes: stimulating the skin.
   * Plantar reflex: tested by dragging the sharp end of the reflex hammer across the bottom of the foot from heel to toe. (Normally this causes the toes to flex)
   * Babinski sign: toes dorsiflex and fan out. 
   * In adults:  positive babinski sign = upper motor neuron damage
   * In infants: positive Babinski sign is normal (due to incomplete myelination in newborns)
Proprioception
   * Simple tests: touching the nose with a finger or touching a location on the skin after it has been touched by the clinician.
   * Gait observation: observing the patient’s gait (the way that they walk) or walking heel to toe. 
   * Romberg test: overall measurement of balance.
   * Coordination and balance require input to the cerebellum from proprioceptive information in the spinocerebellar tract, vestibular information from the inner ear, and visual information. The loss of one or more of these sensory inputs will cause impairments in balance and loss of proprioception or vestibular input will cause swaying when a patient stands with feet together and their eyes closed. Severity of the damage reflects patient’s ability to maintain an upright posture.
Subtopic: Shingles
   * Shingles is a virus known as varicella-zoster virus (VZV); causes chickenpox 
   * Affects your nerves.
   * After recovering from chickenpox, the virus travels from the skin retrogradely inside of the axons of sensory neurons and stays dormant in the dorsal root ganglia.
   * For most individuals, the virus will remain dormant and they don’t even know that it’s there.
   * 1/3 adults may experience shingles when the virus becomes active again and is transported anterogradely inside of the axon back to the skin.
   * We do not yet understand the reasons why the virus switches from inactive to active state, but a weakened immune system or stress may trigger the switch.
   * A patient with shingles may experience tingling and numbness of the skin, develop blisters, pain, chills, and fever. Once the blisters dry up, the patient will see the scab clearing up. Most cases last from three to five weeks. Some people choose to get vaccinated for shingles, depending on their situation.

Transcript for:Ch. 13 - Lecture Notes

Transcript for:
Ch. 13 - Lecture Notes