Chapter 14 - Lecture notes for Dr. Kirifides PowerPoint presentations PDF

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Lecture notes for Dr. Kirifides PowerPoint presentations ...

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Chapter 14 NOTES

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Somatic sensory signals come through the spinal nerves Nuclei: a cluster of cell bodies in CNS Ganglia: a cluster of cell bodies in the periphery Spinal cord: a roughly cylindrical nervous system structure that extends through the vertebral column to the inferior border of the L1 Functions of the spinal cord: ○ Connects PNS to the brain ○ Transmits sensory information to the brain ○ Involved in decision making ■ Gray matter: cell bodies and dendrites ○ Conductive structure (transmission of information travels through axons) Spinal cord + spinal nerves: ○ Provide a structural and functional link between the brain and the torso and limbs ○ Spinal reflexes ■ Initiate our quickest reactions to a stimulus ● Ex. touching a hot stove In spinal cord: ○ Unipolar: sensory - cell body located in the posterior root ganglia (outside CNS) ○ Multipolar: motor - cell body located in the anterior horn of gray matter The spinal cord extends inferiorly from the medulla through the vertebral canal The spinal cord is associated with 31 pairs of spinal nerves

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Each side of the spinal cord contains: ○ 8 pairs of cervical nerves ○ 12 pairs of thoracic nerves ○ 5 pairs of lumbar nerves ○ 5 pairs of sacral nerves ○ 1 pair of coccygeal nerve Why does the spinal cord only go down to L1? ○ ANS: because the central nervous system is developed by age 4; however, the bones keep growing. ○ What is extending is the subarachnoid space that is full of CSF ■ Elongations of the dura and arachnoid mater During development, the individual vertebrae continue to grow after spinal cord growth is complete Unlike the brain, the spinal cord has gray matter on the inside and white matter on the outside ○ Gray matter looks like a butterfly White matter makes up ○ Posterior funiculus ○ Lateral funiculus ○ Anterior funiculus Gray matter makes up ○ Posterior horn ○ Lateral horn ○ Anterior horn ○ Gray commissure

Posterior horn = Dorsal horn = sensory Anterior horn = ventral horn = motor The cervical section has the thickest white matter because it has the most axons ○ Combines information coming from both the legs and arm Thoracic section: not as much white matter compared to the cervical section but still more than the others ○ Gets information from the legs only ○ Where lateral horns are the largest

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When the spinal nerve diverges, it is referred to as a root ○ Both sensory and motor neurons compose a spinal nerve ■ Mixed nerve - unipolar: cell body is sticking up off of the axons ● Think lollipop Each spinal nerve anchors to the spinal cord by two roots: a posterior and an anterior root ○ Each root is composed of multiple rootlets Spinal roots are single modality: either sensory or motor Posterior root: ○ Houses sensory neurons ○ Located externally to the spinal cord ○ Form the posterior root ganglion Anterior root: ○ Houses motor neurons ○ Relay nerve signals from the spinal cord and control muscles and glands Motor neuron axons exit from the spinal cord within the anterior root and extend through the spinal nerve to their terminal ends, which innervate an effector If you have a slipped disc, it will press up against the sensory root. You will feel pain but the motor functions will not be affected/ compromised Vertebral column: bony structure formed by 26 stacked vertebrae Meninges: ○ Pia mater ○ Arachnoid mater ○ Dura mater The meninges in the spinal cord are continuous with the meninges in the brain Subdural Hematoma: a serious condition where blood collects between the skull and the surface of the brain ○ Damages blood vessels underneath the dura

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Epidural space: space between the vertebrae and the dura mater ○ An epidural only numbs the sensory neurons because the fat, CT and blood vessels localize the anesthetic to the dorsal/posterior part only Cauda equina (horsetail): in the lumbar cistern; bundle of spinal roots whose nerves innervate hips and lower limbs The filum terminale comes out from the conus medullaris that is deep to the cauda equina What stabilizes lateral movements: ○ Denticulate ligaments ○ Filum terminale ■ Both are extensions of the pia mater Cerebrospinal fluid is in: ○ Central canal ○ Subarachnoid space How to get CSF into the central canal and subarachnoid space? ○ ANS: through 3 small apertures ■ One aperture from the 3rd ventricle ■ One from each side of the 4th ventricle Primary motor neurons of the direct motor pathway originate in the primary motor cortex, whereas primary motor neurons of the indirect motor pathway originate in the brainstem Sensory information transmitted along the spinocerebellar pathway ○ Proprioceptive ○ Limb position ○ Body movements Posterior root ganglion: a bulb that houses the cell bodies of the sensory neurons Posterior median sulcus: an indentation Anterior median fissure: a depression deeper than the sulcus The nerves are about an inch away from the spinal cord The spinal nerve is a product of the convergence of the anterior and posterior roots

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Gray commissure: the bridge through which the left and the right parts cross over. The cell bodies of upper motor neurons are found in the cerebral cortex Each lateral funiculus contains both ascending and descending tracts

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During the embryonic period, the spinal cord extends the entire length of the vertebral canal Sensory pathways ○ Transmit nerve signals from sensory receptors ■ Sensory receptors ascend from the anterior, posterior and lateral funiculi of the spinal cord to the brain ○ Use 3 neurons to transmit information ■ Primary, secondary, tertiary ● All of them stop at the thalamus Primary (1st order) neuron: ○ extends from sensory receptor to the CNS ○ Connects to the secondary neuron ○ Cell body located in posterior root ganglion ○ Ipsilateral Secondary (2nd order) neuron: ○ Interneuron ○ Extends from primary neuron to either tertiary neuron or cerebellum ○ Crossover to the contralateral side ○ Cell body located in the posterior horn Tertiary (3rd order) neuron: ○ Interneuron ○ Extends from secondary neuron to cerebrum ○ Cell body located in the thalamus ○ Crossover to the contralateral side Motor pathways: ○ Transmit nerve signals from the brain and descend to the effects ○ Travel through the anterior and lateral funiculi ○ Use 2 neurons ■ Upper and lower motor neurons ● The cell body of upper motor neuron is located in the cerebral cortex ○ Sends axons to the medulla ○ Responsible for the upper part of the body ○ Damage to it will be caused by damage to the motor neuron ● The cell body of lower motor neuron is located in the anterior horn ○ Sends axon from the anterior root to the lower part of the body ○ Damage to it will be caused by damage to the motor nerve

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Pathways that transmit sensory information: ○ Posterior funiculus - Medial Lemniscal Pathway ○ Anterolateral Pathway Medial lemniscal pathway: ○ Aka. dorsal column ○ Transmits tactile information (touch, pressure, vibration) from the skin ○ Transmits proprioceptive information from joints, muscles, and tendons(limb position) ○ Decussation of axons occurs just prior to the medial-lemniscus in the medulla oblongata ○ The secondary neuron is longer than the other neurons ■ it starts at the medulla, goes through the pons, midbrain, and brainstem to get to the thalamus ○ Damage to this pathway will cause the patient to lose the sense of pain from the contralateral side

Anterolateral pathway: ○ Aka. spinothalamic pathway ○ More primitive ○ Smaller ○ Transmits tactile information of pain, temperature, pressure, and crude touch from the skin and mucous membranes ○ Decussation of axons occurs at the level where the primary neuron axon enters the spinal cord

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Pathways that transmit motor information: ○ From primary motor cortex(frontal lobe) or brainstem to the lower body ○ Direct pathways that transmit voluntary motor control of skeletal muscles: corticospinal tracts Corticospinal Tracts: ○ Each tract is formed by a chain of two motor neurons ■ Lateral Corticospinal Tract: ● Transmits motor information of skilled movements to the appendicular limbs ■ Anterior Corticospinal Tract: ● Transmits motor information of the axial skeletal muscle to regulate posture and balance ○ Voluntary motor control originates in the precentral gyrus forming upper motor neurons Upper motor neurons: ○ Synapse directly onto lower motor neurons in the brainstem or within the anterior horn of the spinal cord ○ Decussate in the pyramids(lateral corticospinal tract) or the spinal cord (anterior corticospinal tract) Axons of lower motor neurons leave the brainstem or spinal cord, form the anterior roots of the spinal nerves and cranial nerves innervating skeletal muscles

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In general, secondary neurons in somatosensory pathways that transmit conscious sensations project to the thalamus and those that transmit unconscious proprioception project to the cerebellum Sense of touch and sense of pain run in parallel/ overlap in skin and muscles ○ When you’re feeling pain, your sense of touch decreases ○ Analgesics: ■ E.g. Advil ■ You will not lose your sense of touch; it only numbs anterolateral pathway ○ Anesthetic: ■ E.g. epidural ■ Numbs posterior funiculus ■ Knocks out both pathways The anterior, posterior, and lateral funiculi contain sensory tracts but only the anterior and lateral funiculi contain motor tracts Fasciculi: axons within each funiculus that are organized into smaller structural units (bundles of myelinated axons) Tracts: ○ White matter on each side of the spinal cord ○ Myelinated axons that have a common origin ○ Can be: ■ Sensory tracts ● Ascending ● Conduct nerve signals from the spinal cord to the brain ■ Motor tracts ● Descending ● Conduct nerve signals from the brain to the spinal cord

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The thalamus is the structure that registers pain ○ Pain is registered in the thalamus before it gets to the cortex (You feel pain before you know where it is) Ipsilateral: same side 2 main branches of the spinal nerve: ○ Ventral branch ○ Dorsal branch The name of each tract reflects its origin and destination: ○ Origin: Sensory tract: spino○ Destination: thalamus: -thalamic ■ Spinothalamic tract ○ Origin: motor tract: cortico○ Destination: spinal cord: -spinal ■ Corticospinal tract Upper motor neuron lesions: ○ Stroke ○ Multiple sclerosis ○ Traumatic brain injury ○ Cerebral palsy Symptoms of UMN Lesions: ○ Note: Overstimulation: inability to move muscles but it is constantly contracted ○ Spastic paralysis/paresis ■ loss of motor function along with increased muscle tone ○ Hypertonia (Hypertrophy) ■ increase in muscle tone in extensor muscles of lower limbs & flexor muscles of upper limbs ■ muscles become larger because they are overactive ○ Hyperreflexia ■ exaggerated tendon reflex ○ Clasp-knife ■ A response where initial resistance is followed by relaxation ■ Becomes clenched tightly ○ Babinski reflex ■ In newborns: toes go back instead of the front if there is damage Lower motor neuron lesions: ○ damage may span from the anterior horn of the spinal cord to muscle Symptoms of LMN lesions: ○ Flaccid paralysis/paresis ■ weakness or paralysis and reduced muscle tone ○ Fasciculation ■ a brief, spontaneous contraction affecting a small number of muscle fibers, often causing a flicker of movement under the skin ○ Hypotonia(atrophy) ■ a state of low muscle tone (the amount of tension or resistance to stretch in a muscle), often involving reduced muscle strength and atrophy.

Areflexia ■ the absence of reflexes Lateral horns are found in the T1-L2 parts of the spinal cord only The parts of the spinal cord that control the upper and lower limbs are larger because more neuron cell bodies are located there The end destination of upper motor neurons in the rubrospinal tract in the lateral funiculus The epidural space contains areolar CT, adipose CT, and blood vessels Motor axons in a spinal nerve originate in the spinal cord The anterior and posterior roots of the lumbar and sacral spinal nerves are longer than the roots of other spinal nerves Lou Gehrig's disease (ALS) ○ Degeneration of the primary motor cortex, UMN and cell bodies of LMN. ○ Symptoms include stiff muscles and muscle twitching. ○ Causes progressive muscle weakness and atrophy resulting in difficulty speaking, swallowing and eventually breathing. ○ 85% is idiopathic (unknown origin) and approx.15% is genetic. ○ Two (2) types, fast and slow progression. Typical survival 2-4 years after diagnosis of fast type. ○ The person cannot move any of their muscles as it progresses ○ .No known cure. Integration of motor systems: ○ Somatic motor pathways are divided into 4 distinct circuits via which they provide input into the lower motor neurons ■ Local circuit neurons: ● Located close to LMNs in the brainstem and spinal cord ● Involved with reflexes and rhythmic activity(walking, jogging, etc.) ● The brain is the command center and the spinal cord does the action over and over ○ Think “run like a chicken with its head cut off” ■ Upper motor neurons: ● Input to both lower circuit neurons and directly into LMNs ● Essential for the execution of voluntary muscles ■ Basal nuclei neurons: ● Assist movement by providing indirect input to UMNs via the thalamus ● Initiate and terminate movement (sculpts movement) ● Suppress unwanted movements ● Involved with cognitive functions such as attention, memory, and planning ■ Cerebellar neurons: ● Assist movement via control of activity of UMNs ○

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Disorders of the basal nuclei: ○ Parkinson’s Disease (Reduction of dopamine input from the substantia nigra of the midbrain) ■ Difficulty starting and stopping movement. ■ Disturbs transitional muscle movement. ■ Resting tremor ● uncontrollably rolling of the wrist when still ■ Bradykinesia ● decreases movement ○ Huntington’s disease (Reduction of acetylcholine due to caudate & putamen degeneration) ■ Rapid jerky uncontrollable movements ■ Symptoms occur between the ages of 30 to 40. ○ Tourette Syndrome ■ Involuntary body movements (motor tics) ■ Inappropriate sounds Functions of the cerebellum: ○ Monitoring intentions for movement (pre movements) ■ Cortex ■ Basal nuclei ○ Monitoring actual movement (real-time) ■ Proprioceptors (muscles, tendons, and joints) ■ Vestibular apparatus (inner ear) ■ Eyes (retina) ○ Comparing command signals with sensory information ■ Compares intentions with actual movements ○ Sending out corrective feedback ■ Determines if there is a discrepancy between intended movement and actual movement. ■ Sends corrective information to the premotor cortex via the thalamus. ■ Premotor cortex processes the information and regulates the upper motor neurons in the primary motor cortex.

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Disorders of the cerebellum: ○ Trauma ○ Tumor ○ Stroke ○ Multiple sclerosis ○ Toxicity Symptoms of cerebellar disorders: ○ Ataxia ■ of the ability to coordinate muscle movements ○ Intention tremor ■ The amplitude of a cerebellar tremor increases as the extremity approaches the endpoint of deliberate and visually guided movement. ○ Dysmetria ■ the lack of coordination of movement (overshoot & undershoot of intended target)

The 31 pairs of spinal nerves (C1-C5, T1-T5, L1-L5, S1-S5, and Co1) have axons of sensory and motor neurons ○ Sensory neurons: extend from sensory receptors through the posterior root to the spinal cord ■ Their cell bodies form the posterior root ganglia ○ Motor neurons: extend from the spinal cord to effectors (muscles and glands)

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Each spinal nerve (except C1 nad Co1) extends through an intervertebral foramen to exit the vertebral column The spinal nerve branches into two primary rami Spinal nerve branches: ○ Anterior ramus ○ Posterior ramus ○ Rami communicantes Anterior ramus: ○ Larger ○ Splits into multiple other branches that innervate the skin and skeletal muscles of the anterior and lateral portions of the trunk, upper limbs, and lower limbs (appendicular skeleton) ○ Go on to form nerve plexuses Posterior ramus: ○ Smaller ○ Innervates the deep muscles of the back (axial skeleton) Rami communicantes ○ Associated with spinal nerves ○ Associated with the autonomic nervous system

Dermatome: a specific segment of skin innervated by a single spinal nerve ○ All spinal nerves innervate a segment of skin except for C1 ○ The receptors of adjacent dermatomes overlap ○ Important because they indicate potential damage to one or more spinal nerves ○ Involved in referred visceral pain Referred visceral pain: pain or discomfort from one organ is mistakenly referred to a dermatome ○ Pain in a dermatome arises from an organ nowhere near the dermatome

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Dermatome Map: ○ A map that shows where each area of the skin is innervated by a specific spinal nerve Nerve plexus: a network of interweaving anterior rami of spinal nerves ○ Needed for intricate movements ■ Cervical ■ Brachial ■ Lumbar ■ Sacral Intercostal nerves: ○ Anterior rami of spinal nerves T1-T11 ■ Located within the intercostal space sandwiched between two adjacent ribs ○ T12: subcostal nerve ■ Arises inferior to the ribs (underneath the ribs) ○ They innervate much of the torso wall and portions of the upper limb Most of the thoracic spinal nerves, as well as nerves S5-Co1 do not form the plexuses Cervical plexus ○ C1-C4 (C5 is not considered part of the nerve plexus even though it contributes some axons to the plexus branches) ○ Located deep on each side of the neck ○ Phrenic nerve: ■ Most important nerve of the cervical plexus ■ Formed from C4 nerve and some contributing axons from C3 and C5 ■ Extends through the thoracic cavity to innervate the diaphragm

Brachial plexus ○ C5-C8, T1 ○ Composed of anterior rami, trunks, divisions and cords ○ Subdivided into anterior and posterior divisions ○ Responsible for providing innervation to the hand ○ 5 important nerves that emerge:

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Axillary nerve: innervates the axilla (armpit), deltoid, and teres minor muscles ● Receives sensory nerve signals from the superolateral part of the arm Median nerve: extends along the midline of the arm and forearm ● Extends deep to the carpal tunnel in the wrist ● innervates thumb, index and middle fingers on the anterior side ○ If you prick your finger it will go to the median nerve ● Receives sensory nerve signals from the palmar side of the lateral 3 and a half fingers and from dorsal tips of these fingers Musculocutaneous nerve: innervates anterior arm muscles (biceps brachii and brachialis) which flex the humerus and forearm ● Receives sensory nerve signals from the lateral surface of the forearm Radial nerve: innervates the forearm extensors (triceps) and wrist and digit extensors ● Receives sensory nerve signals from the posterior arm and forearm surface Ulnar nerve: descends along the medial side of the arm ● Receives sensory nerve signals from the skin of the pinky and medial half of the ring finger

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Carpal Tunnel Syndrome:

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Upper limb nerve supply: ○ Anterior compartment: innervated by the musculocutaneous nerve ■ Biceps brachii, brachialis, and coracobrachialis ○ Posterior compartment: innervated by the radialis nerve ■ Triceps brachii Lumbar plexus: ○ L1-L4 ○ Innervates inferior anterior wall, anterior thigh, medial thigh and skin of the leg (right above the hips ...