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Please read Chapter 13 and answer the following questions. Turn this worksheet in for valuable points. 1. List and describe each of the three functions of the spinal cord. It sends motor commands from the brain to the body, send sensory information from the body to the brain, and coordinate reflexes . 2. Describe the physical features of the spinal cord (e.g. length/diameter/where in the vertebral column it terminates). Only 18 inches long and runs from foramen magnum to L1/L2. 0.5 – 0.75 inches in diameter, or the diameter of your little finger 3. List three things that protect the spinal cord from mechanical damage. The spinal cord is protected by bones, discs, ligaments, and muscles . 4. How many pairs of spinal nerves are there? There are 31 pairs of spinal nerves and roots. 5. List how many pairs of spinal nerves there are for each of the following portions of the spinal cord: a. Cervical – 8 pair b. Thoracic – 12 pair c. Lumbar – 5 pair d. Sacral – 5 pair e. Coccygeal (technically) – 1 6. Describe how spinal nerves are named. Give an example of one of the names of a spinal nerve pair. Describe the anomaly with regards to the naming scheme that occurs with the cervical spinal nerves. Naming is according to corresponding vertebrae such as cervical spinal cord and lumbar spinal cord. There are 7 cervical vertebrae but 8 spinal nerves. 7. Where along the spinal cord are the spinal cord enlargements found? What purpose do they serve? Cervical and Lumbar region is enlarged because there are a lot of structures to be innervated. 1

8. Define what the conus medullaris is. Define what the cauda equina is. The most distal bulbous part of the spinal cord is called the conus medullaris. Distal to this end of the spinal cord is a collection of nerve roots, which are horsetail-like in appearance and hence called the cauda equine. 9. For each of the following spinal meninges, describe the location of the layer relative to the spinal cord, what the layer is composed of, the function of the layer, and anything else of note: a. Dura mater – The dura mater is the outermost layer of the meninges and is located directly underneath the bones of the skull and vertebral column. It is thick, tough, and inextensible. b. Arachnoid mater – The arachnoid mater is the middle layer of the meninges, lying directly underneath the dura mater. It consists of layers of connective tissue, is avascular , and does not receive any innervation. c. Pia mater – The pia mater is located underneath the sub-arachnoid space. It is very thin, and tightly adhered to the surface of the brain and spinal cord. It is the only covering to follow the contours of the brain. 10. Describe the filum terminale and denticulate ligaments of the pia mater, and their functions. The denticulate ligaments and the filum terminale both function to anchor/stabilize the spinal cord in place. The denticulate ligaments are found midway between the roots from the spinal cord on each side (e.g. left and right). The denticulate ligaments attach to the dura and are made of pia mater. 11. Describe the epidural space of the spinal cavity. Make sure to indicate where this space is in relation to the meninges, and anything else of note, pertaining to the space. The epidural space is the area between the dura mater (a membrane) and the vertebral wall, containing fat and small blood vessels . The space is located just outside the dural sac which surrounds the nerve roots and is filled with cerebrospinal fluid. 12. Describe the epidural space of the spinal cavity. Make sure to indicate where this space is in relation to the meninges, and anything else of note, pertaining to the space. The epidural space is the area between the dura mater (a membrane) and the vertebral wall, containing fat and small blood vessels . The space is located just outside the dural sac which surrounds the nerve roots and is filled with cerebrospinal fluid. 13. Describe the purpose of conducting a lumbar puncture. Also describe the process, and in particular the specific location for the procedure. 2

A lumbar puncture (LP) or spinal tap may be done to diagnose or treat a condition . For this procedure, your healthcare provider inserts a hollow needle into the space surrounding the spinal column (subarachnoid space) in the lower back to withdraw some cerebrospinal fluid (CSF) or inject medicine. 14. Describe the gray matter of the spinal cord. Where is it located in the spinal cord? What is contained in the gray matter? Why does it appear gray? The grey matter in the center of the cord contains interneurons and the cell bodies of motor neurons, axons, and dendrites. Projections of the grey matter (the “wings”) are called horns. Together, the grey horns and the grey commissure form the H-shaped grey matter. 15. Label the following structures on the figure below: anterior gray horns, lateral gray horns, posterior gray horns, gray commissure, and central canal. 16. Describe what a nucleus of the spinal cord gray matter is. The nuclei are Collections of neuron cell bodies with similar function. 17. For each of the following nuclei of the spinal cord gray matter, describe where the nucleus is located, and its function: a. Somatic sensory nuclei – The main or principal sensory nucleus of the trigeminal nerve : This nucleus lies in the upper part of the pons, in the lateral part of the reticular formation. It lies lateral to the motor nucleus of the trigeminal b. Visceral sensory nuclei – The visceral sensory part of the brainstem has a single nucleus found in the medulla oblongata, the nucleus solitarius, which is located lateral to the motor nucleus of the vagus nerve . 3

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c. Visceral motor nuclei – The general visceral efferent fibers originate from the superior salivatory nucleus and the lacrimal nucleus in the dorsal pons and are carried distally within the nervus intermedius. d. Somatic motor nuclei – Somatic motor system is the motor system of the body and the neurons involved are the motor neurons. The cell bodies of these neurons are present in the motor nuclei of the cranial nerves of the brain stem and in the anterior horn of the spinal cord . 18. What comprises white matter of the central nervous system? What is the function of white matter? White matter: composed of bundles of axons. These axons are coated with myelin, a mixture of proteins and lipids, that helps conduct nerve signals and protect the axons. White matter conducts, processes, and sends nerve signals up and down the spinal cord . 19. In general, what is the function of the dorsal spinal cord, along with any dorsal nerve roots and rootlets? In general, what is the function of the ventral spinal cord, along with any ventral nerve roots and rootlets? Ventral roots (anterior roots) allow motor neurons to exit the spinal cord. Dorsal roots (posterior roots) allow sensory neurons to enter the spinal cord . 20. Using the figure below, label the following structures: anterior white columns, lateral white columns, posterior white columns, anterior median fissure, posterior median sulcus, and anterior white commissure. 4

21. What is the difference between the white columns and the tracts of the spinal cord white matter? What are the other terms often used for the white columns and the tracts? The white matter of the spinal cord is separated into columns. Ascending tracts of nervous system fibers in these columns carry sensory information up to the brain, whereas descending tracts carry motor commands from the brain . These, funiculus, fasciculus, tract, and pathway are commonly used terms. 22. Where are the ascending tracts of the spinal cord typically located? In general, what is the function of these tracts? They are found running along the dorsal, lateral, and ventral columns of the white matter. The main role of the ascending tracts of the spinal cord is to transmit somatosensory information. 23. Where are the descending tracts of the spinal cord typically located? In general, what is the function of these tracts? Descending tracts are the pathways by which motor signals are sent from the brain to the spinal cord. 24. Describe the function of each of the following sensory tracts: a. Gracile fasciculus – the medial portion of either of the dorsal columns of the spinal cord, composed of ascending fibers that terminate in the nucleus gracilis of the medulla oblongata b. Cuneate fasciculus – The cuneate fasciculus represents the first order neurons of the dorsal column medial leminiscal sensory pathway, that transmit the sensory information of vibration, conscious proprioception, and 2-point discrimination from the upper extremities c. Spinothalamic tracts – The spinothalamic tract (STT) is a sensory tract that carries nociceptive, temperature, crude touch, and pressure from our skin to the somatosensory area of the thalamus. d. Spinoreticular tracts – is part of the anterolateral system and carries pain sensations to the reticular formation in the brainstem. The spinoreticular tract is thought to be important in directing attention toward painful stimuli. e. Spinocerebellar (anterior and posterior) tracts – carry unconscious proprioceptive information gleaned from muscle spindles, Golgi tendon organs, and joint capsules to the cerebellum 25. Describe the function of each of the following motor tracts: 5

a. Corticospinal (anterior and lateral) tracts – is the major neuronal pathway providing voluntary motor function. b. Reticulospinal (lateral and medial) tracts – is responsible primarily for locomotion and postural control. c. Vestibulospinal (lateral and medial) tracts – p erforms the synchronization of the movement of the eyes with the movement of the head so that eyes do not lag behind when the head moves to one side. 26. What type of information (sensory, motor, or mixed) is carried by the dorsal roots? What type of information is carried by the ventral roots? What about the spinal nerves? The dorsal root transmits sensory information where as the ventral (anterior) root bundle is responsible for transmitting somatic motor output. Spinal nerves are mixed nerves that interact directly with the spinal cord to modulate motor and sensory information from the body's periphery. 27. What is the significance of the dorsal root ganglion? The significance of the dorsal root ganglia is to transmit sensory information from the peripheral nervous system to the central nervous system . 28. What is the name of the connective tissue that covers the axon of a neuron? Describe what a nerve fascicle is, and name the connective tissue that covers a fascicle. Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium. The axons are bundled together into groups called fascicles. Each fascicle is wrapped in a layer of connective tissue called the perineurium. 29. Multiple fascicles, along with blood and lymphatic vessels, bound by a connective tissue covering is known as what? What is the name of the connective tissue covering the surface of this structure? Blood vessels, the lymphatic and the nerves are all found in the perimysium . Each muscle fiber is surrounded by loose connective tissue, and these contain capillaries and nerve fibers. This connective tissue covering is known as the endomysium . 30. Name the two structures formed from the branching of a spinal nerve. For each structure, describe whether the structure is motor, sensory, or mixed? The divisions are the anterior or ventral ramus, and posterior or dorsal ramus . The Dorsal (posterior) carries sensory fibers. Ventral (anterior) carries motor fibers. 6

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31. _cervical, brachial, lumbar and sacral join together in four regions of the body to form structures known as nerve plexuses. 32. Do dorsal rami form nerve plexuses? What are the functions of the dorsal rami? The dorsal ramus carries information that supplies muscles and skin sensation to the human back. Areas of distribution of the cutaneous branches of the posterior divisions of the spinal nerves. 33. In a general sense, describe the structures of the body innervated by each of the following four plexuses, and be sure to indicate any nerves of note, that are important to that plexus: a. Cervical plexus – The cervical plexus is formed by the ventral rami of the upper four cervical nerves and the upper part of fifth cervical ventral ramus. The network of rami is located deep within the neck. b. Brachial plexus – The brachial plexus is formed by the ventral rami of C5–C8 and the T1 spinal nerves, and lower and upper halves of the C4 and T2 spinal nerves. The plexus extends toward the armpit (axilla). c. Lumbar plexus – The lumbar plexus is formed by the ventral rami of L1–L5 spinal nerves with a contribution of T12 form the lumbar plexus. This plexus lies within the psoas major muscle. d. Sacral plexus – The sacral plexus is formed by the ventral rami of L4-S3, with parts of the L4 and S4 spinal nerves. It is located on the posterior wall of the pelvic cavity. 34. Describe what a dermatome is. Dermatomes are areas of skin on your body that rely on specific nerve connections on your spine. 35. Define what a reflex is. A reflex is an involuntary, or automatic, action that your body does in response to something without you even having to think about it . 36. Give a brief description of each of the ways that reflexes can be categorized: e. Innate vs. acquired – Natural reflexes are the one in which no previous experience or learning is required . Conditional reflexes are one which develops during lifetime due to experience or learning. 7

f. Somatic vs. visceral (autonomic) – Somatic reflex occurs in the skeletal muscles while visceral reflex occurs in the smooth muscles of the inner organs. g. Monosynaptic vs. polysynaptic – Monosynaptic reflex: ↑ A reflex that only contains one space for an action potential to travel between a sensory and motor neuron. Receptor: ↑ A part of skin or muscle that senses a stimulus. Polysynaptic reflex: ↑ A complex reflex that contains many connections between neurons. h. Spinal vs. cranial – During a spinal reflex, information may be transmitted to the brain, but it is the spinal cord, not the brain, that is responsible for the integration of sensory information and a response transmitted to motor neurons. Cranial reflexes with pathways through cranial nerves and the brainstem. 37. List and describe in order the five components of a reflex arc. 1. Receptor: a specific receptor receives a stimulus and set up a sensory impulse. 2. An afferent fiber: afferent nerve fiber conveys the impulses from the specific receptor to the spinal cord. 3. An integration centre: association neuron connects the afferent and efferent neurons. 4. Efferent or motor neuron: transmits impulses to the effector organ. 5. Effector organ: the organ that responds to the impulses receive. 38. Are most reflex arcs a form of negative feedback, or positive feedback? The reflex arc is usually negative feedback . 39. List the four specific somatic reflexes discussed in the notes. Stretch, withdrawal (flexor), crossed extension, and tendon reflexes Stretch reflex is when a muscle “fights back” when stretched which is due to proprioceptors called muscle spindles Monosynaptic reflexes; happen quickly because only one synapse Ipsilateral: Specific to one side of the body 40. Describe how the stretch reflex works. Be sure to indicate the purpose of the reflex, the specific type of receptor involved, what the effector is, the number of synapses involved, the name of any commonly tested stretch reflexes in medicine, etc. The stretch reflex is activated (or caused) by a stretch in the muscle spindle. When the stretch impulse is received a rapid sequence of events follows. The motor neuron is activated and the 8

stretched muscles, and its supporting muscles, are contracted while its antagonist muscles are inhibited (relaxed). 41. Describe the structure and function of muscle spindles that are important to stretch reflexes. Be sure to mention the difference in structure (if applicable) and function between the intrafusal cells, extrafusal cells, gamma motor neurons, and alpha motor neurons. Functionally, muscle spindles are stretch detectors, and sense how much and how fast a muscle is lengthened or shortened. Accordingly, when a muscle is stretched, this change in length is transmitted to the spindles and their intrafusal fibers which are subsequently similarly stretched. 42. Describe reciprocal inhibition and the importance of this in certain reflexes such as the patellar reflex (a stretch reflex) and the withdrawal reflex. Because the interneuron is inhibitory, it prevents the opposing alpha motor neuron from firing, thereby reducing the contraction of the opposing muscle. Without this reciprocal inhibition, both groups of muscles might contract simultaneously and work against each other. 43. Describe how the withdrawal reflex works. Be sure to indicate the purpose of the reflex, what the effector is, the number of synapses involved, etc. The withdrawal reflex is polysynaptic, meaning that, in addition to the sensory and motor neurons, this response utilizes interneurons which pass signals between the sensory and motor neurons, ultimately creating multiple synaptic connections. 44. Describe how the crossed extension reflex works. Be sure to indicate the purpose of the reflex, what the effector is, the number of synapses involved, etc. The reflex occurs when the flexors in the withdrawing limb contract and the extensors relax, while in the other limb, the opposite occurs. An example of this is when a person steps on a nail, the leg that is stepping on the nail pulls away, while the other leg takes the weight of the whole body. 45. Describe how the tendon reflex works. Be sure to indicate the purpose of the reflex, what the effector is, the number of synapses involved, etc. The mechanism of eliciting a deep tendon reflex involves tendons, muscles, and the reflex arc. Tapping the appropriate tendon causes passive stretch of the associated muscle. The stretch of the muscle fiber is detected by the muscle spindle located within the muscle fibers 46. Check the appropriate boxes on the following table to accurately describe the various reflexes discussed in your notes: 9

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Category Stretch Reflex Withdrawal Crossed Extension Tendon Reflex Innate yes yes yes yes Acquired Somatic yes yes yes yes Visceral Monosynaptic yes yes Polysynaptic yes yes Spinal yes yes yes yes Cranial 10

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