Bio 141 - Exam 5 (Chapter 14)

Define dermatome

A dermatome is a specific segment of skin innervated by a single spinal nerve.

Explain why spinal nerves are mixed nerves

Because they house motor axons in the anterior root and sensory axons in the posterior root.

Explain why the left side of the brain controls the right side of the body, and vice versa

Decussation.

Define a motor pathway

Motor pathways are descending tracts that control effectors.

Describe the location and composition of the cauda equina.

The cauda equina is made up of the rootlets of the more inferior spinal nerves, includint L2-L5, S1-S5, and Co1, which extend inferiorly from the conus medullaris.

Name the three sensory pathways

- Posterior Funiculus-Medial Lemniscal Pathway: transmits sensory input concerned with proprioceptive (limb position / balance / posture) info , as well as discriminative touch, precise pressure, and vibrations sensations from teh skin. - Anterolateral Pathway (also called the spinothalamic pathway): relays sensory input related to crude touch and pressure as well as pain and temp. (Typically, sensations that require us to act in response to stimulus are relayed through the anterolateral pathway) - Spinocerebellar Pathway: conducts nerve signals from proprioceptors related to postural input to the cerebellum; information is integrated and acted on at a subconscious level. (Sensory pathways consists of somatosensory, which process stimuli from receptors w/in skin, muscles, and joints. Or Viscerosensory, which process stimuli from teh viscera)

Define nerve plexus

- Nerve Plexus: a network of interweaving anterior rami of spinal nerves, which then split into multiple named nerves that innervate various body structures.

List the five basic components in a reflex arc in order

A reflex arc includes a sensory receptor, an effector, and the neural wiring b/t the two. 1. Stimulus activates a sensory receptor 2. Sensory neuron transmits a nerve signal to the CNS 3. Information from the nerve signal is processed in teh integration center by interneurons 4. The motor neuron transmits a nerve signal from the CNS to an effector 5. The effector responds to the nerve signal from the motor neuron.

Define reflex

A reflex is a rapid, preprogrammed, involuntary response of muscles or glands to stimulus.

Identify the nervous system structures found in the anterior horn, posterior horn, and lateral horn

Anterior horns contain cell bodies of somatic motor neurons. Lateral horns contain cell bodies of autonomic motor neurns Posterior horns contain axons of sensory neurons and cell bodies of interneurons.

Name three spaces associated w/ the spinal meninges and identify their locations

- Pia Mater: directly adheres to the spinal cord; delicate, innermost layer composed of elaastic and collagen fibers that support some of the blood vessels supplying the spinal cord. - Arachnoid mater: external to pia mater; composd of a delicate web of collagen and elastic fibers termed the arachnoid trabeculae. - Dura mater: dense irregular connective tissue. Spinal dura mater only has 1 layer (vs the cranial dura mater). Provides stability to the spinal cord.

Explain how the referred pain associated w/ appendicitis follows the distribution of the dermatome

Dermatomes are involved in referred visceral pain, a phenomenon in whcih pain or discomfort from one organ is mistakenly referred to a dermatome. Ex: The appendix is innervated by axons from the T10 regions of the spinal cord, so appendicities typically causes referred visceral pain in the umbilicus region, rather than the abdominopelvic region of the appendix itself.

Identify the nervous system structures found in the anterior funiculus, posterior funiculus, and lateral funiculus

The axons w/in each white matter funiculus are organized into smaller structural units called tracts or fasciculi. Individual tracts conduct either sensory nerve signals or motor nerve signals. The lateral and anterior funiculi contain ascending and descending tracts, composed of both motor and sensory axons. Posterior funiculi contain sensory axons only, which extend as ascending tracts.

Identify and briefly describe the following structures given a cross section of the spinal cord: - anterior, posterior, and lateral horns - anterior, posterior, and lateral funiculus - gray commisure - central canal

- Anterior horns: left and right anterior masses of gray matter; house the cell bodies of somatic motor neurons, which innervate skeletal muscle. - Lateral horns: found in T1-L2 parts of the spinal cord only. Contain cell bodies of autonomic motor neurons, which innervate cardiac muscle, smooth muscle, and glands. - Posterior horns: left and right posterior masses of gray matter. houses axons of sensory neurons and the cell bodies of interneurons. - Gray commissure: horizontal bar of gray matter that surrounds a narrow central canal; contains unmyelinated axons; serves as communication route b/t right and left sides of gray matter - Central canal: - Posterior funiculus: lies b/t the posterior gray horns on the posterior side of the cord and mosterior median sulcus. - Lateral funiculus: white matter on each lateral side of the spinal cord. - Anterior funiculus: composed of white matter that occupies the space on each anterior side of the cord b/t the anterior gray horns and anterior median fissure.

List 5 anatomic subdivisions of the spinal cord and List the number of spinal nerves in relation to each anatomical subdivision

- Cervical part: 8 pairs of cervical spinal nerves - Thoracic part: 12 pairs of thoracic spinal nerves - Lumbar part: 5 pairs of lumbar spinal nerves - Sacral part: 5 pairs of sacral spinal nerves - Coccygeal Part: 1 pair of coccygeal nerves. (Spinal cord as a whole is associated with 31 pairs of spinal nerves.)

Name five major nerve plexuses

- Cervical plexus: located deep on each side of the neck, immediately lateral to C1-C4. Innervate anterior neck muscles as well as skin of the neck and portionsof the head and shoulders. - Brachial plexus: Formed by anterior rami of spinal nerves; extend laterally from the neck, pass superior to first rib, and continue into axilla. Each brachial plexus innervates the pectoral girdle and entire upper limb on one side. - lumbar plexus: formed from the anteior rami of spinal nerves L1-=L4, located lateral to the L1-L4 vertebrae and along the psoas major muscule in teh posterior abdominal wall; Innervates inferior abdominal wall, anterior thigh, medial thigh, and skin of medial leg. - sacral plexus: formed from anterior rami of spinal nerves L4-S4 and located immediately inferior to the lumbar plexuses. Innervate gluteal region, plevis, perineum, posterior thigh, and almost all of the leg and foot. -

Define filum terminale, conus medullaris, cervical enlargement, and lumbosacral enlargement.

- Filum terminale: a thin strand of pia mater that helps anchor the conus medullaris to the coccyx. - conus medullaris: the tapering end of the spinal cord, which marks the official "end" of the spinal cord. - Cervical enlargement: an enlarged portion of the inferior cervical part of the spinal cord, which houses the neurons that innervate the upper limbs. - lumbosacral enlargement: an enlarged region of the mid-lumbar part of the spinal cord; contains neurons that innervate the lower limbs.

Differentiate among first order, second order (central) , and third order neurons

- First order neuron (primary neuron): first neuron in the chain; cell body of a primary neuron resides in the posterior root ganglion of a spinal nerve and the axon extends to a secondary neuron. - Second order ( neuron is an interneuron that extends from teh primary neuron to the either the tertiatey neuron or the the cerebellum - Tertiary neuron (third order) is an interneuron that extends from the secondary neuron to the cerebrum (specifically the primary somatosensory cortex of the parietal lobe. (*Note: Pathways that lead to the cerebellum do not have a tertiary neuron)

Define the following terms: - Ipsilateral vs contralateral reflex - monosynaptic vs polysnyaptic reflex - somatic vs visceral (autonomic) reflex - spinal vs cranial reflex

- Ipsilateral vs contralateral reflex: Classified based on if it involves only one side of the body. Ipsilateral reflex is one where both the receptor and effector organs are on the same side of the spinal cord. A contralateral reflex involves an effector on the opposite side of the body of the receptor that detected the stimuli. - monosynaptic vs polysnyaptic reflex: Classification by the number of neurons participating in the reflex. A monosynaptic reflex has only one sensory and motor neuron (only one synapse). A polysynaptic reflex has one or more interneurons positioned b/t the sensory and motor neuron. - somatic vs visceral (autonomic) reflex: Classification determined by type of effector that is stimulated by the motor neurons. Somatic reflexes involve skeletal muscle as the effector. Visceral reflexes involve cardiac, smooth muscle or glands as the effector. - spinal vs cranial reflex: a reflex may be identified by the specific area of the CNS that serves as processing site. Spinal reflexes involve the spinal cord, whereas cranial reflexes involve the brain.

List the four different indirect motor pathways

- Lateral pathway: regulates and controls precise, discrete movements and tone in flexor muscles of the limbs (such as gently laying a baby in a crib) (Consists of the rubrospinal tract) - Medial pathway: regulate reflexive tone and gross movement of head, neck, proximal parts of limbs, and trunk. 3 groups: > Reticulospinal tract: controls mvt related to posture and balance. > Tectospinal tract: controls motor output from superior and inferior colliculi to regulate reflexive positional changes of upper limbs, eyes, head, and neck as consequence of visual and auditory stimuli > Vestibulospinal tract: originates w/in vestibular nuclei of the brainstem; regulates reflexive muscular activity that helps maintain balance during sitting, standing, and walking.

Briefly explain the purpose of the withdrawal and cross extensor reflexes

- Withdrawal reflex involves muscles contracting to withdraw the body part away from a painful stimulus. - Cross-extensor reflex usually occurs in conjunction w/ withdrawal reflex, and is the "balanced" response to the withdrawal reflex.

Determine the body part / muscle which is innervated by each of the following major nerves: - phrenic nerve - median nerve - radial nerve - femoral nerve - sciatic nerve

- phrenic nerve: formed primarily from C4 nerve, with some contributing axons from C3 and C5; travels through the thoracic cavity to innervate the thoracic diaphragm. - median nerve: travels alon the midline of the arm and forearm and deep to th ecarpal tunnel; innervates most of the anterior forearm muscles , the thenar muscles, and the lateral two lumbricals; receives sensory nerve signals from the palmar side of the lateral 3 1/2 fingers (thumb, index finger, middle finger, and later one half of the ring finger) and from the dorsal tips of these fingers. - radial nerve: travels along the posterior side of the arm and along the radial side of the forearm; innervates the posterior arm muscles (forearm extensors) and posterior forearm muscles (extensors of writs and digits); receives sensory nerve signals from teh posterior arm and forearm surface and the dorsolateral side of the hand. - femoral nerve: innervates the anterior thigh muscles (including quadriceps femoris, sartorius, psoas, and iliacus); receives sensory input from the anterior and inferomedial thigh as well as medial aspect of leg. - sciatic nerve: longest and largest nerve in the body; formed from portions of the anterior and posterior divisions of the sacral plexus.

Name two different direct motor pathways

1. Corticobulbar tracts: originate from teh fascial region of the motor homunculus w/in the primary motor cortext; these upper motor neurons extend to the brainstem, where they synapse with lower neurons housed w/in the brainstem cranial nerve nuclei. Axons of these lower motor neurons help form cranial nerves. 2. Corticospinal tracts: descend from the primary motor cortex of the cerebrum throught eh medulla and into the spinal cord where they synapse on lower neurons of the anterior horn of the spinal cord. > Lateral corticospinal tracts include 85% of axons of the upper motor neurons that decussate w/in the pyramids of the medulla. Innervate lower motor neurons that control movements in limbs, such as playing a guitar, typing on computer. >Anterior corticospinal tracts: represent remaining 15%; do not decussate atthe level of the medulla; instead decussate at the level of a spinal cord segment through anterior gray commissure. Innervate the axial skeletal muscles.

Explain the purpose of a lumbar puncture and indicate into which space it is administered and why it is done below the level of L1-L2 vertebrae

A lumbar puncture is a spinal tap, a clinical procedure for obtaining CSF. It is done below L1-L2, becuase that is where the adult spinal cord ends, and you don't want to hit the spinal cord when doing the lumbar puncture. It is administered into L3-L4 or L4-L5 space.

Distinguish b/t direct and indirect motor pathways

Direct motor pathways are responsible for conscious control of skeletal muscle activity. (Also called pyramidal pathway, from the pyramid-shaped of the upper neuron cell bodies in this area.) Consists of corticobulbar tracts (which extend from the cerebral cortex and synapse in the brainstem) and corticospinal tracts (which extend from the cerebral cortex and synapse in the spinal cord). Indirect motor pathways are responsible for subconscious (reflexive) control of skeletal muscle. They take an indirect pathway through the brain, which modifies or helps control the pattern of somatic motor activity by exciting or inhibiting the lower motor neurons that innervate the muscles. Consists of the lateral pathway (reponsible for precise, discrete movements and tone in flexor muscles) the medial pathway (resonsible for reflexive muscle tone and gross movement of muscles of the head, neck, proximal partss of limbs and trunk.)

Define gray and white matter

Gray matter - centrally located; shape resembles an H or butterfly.

Identify the start and end locations of the spinal cord

It extends inferiorly from the medulla oblongata through the vertebral canal and ends at the inferior border of the L1 vertebrae.

Briefly describe the process of reciprocal inhibition in relation to the stretch reflex.

Reciprocal inhibition is when the sensory nerve signals inhibit antagonistic muscle contraction to avoid opposition.

Explain why reflexes are important

Reflexes are a survival mechanism, allowing us to quickly respond to a stimulus that may be detrimental to our well-being without having to wait on the brain to process the information.

List sensations carried by each sensory pathway

Sensory pathways are ascending pathways that carry nerve signals from sensory receptors through the spinal cord to the brain; carry sensations of limb proprioception, touch, temp, pressure, and pain.

Explain why there are 8 pairs of cervical spinal nerves and only seven cervical vertebrae

The first cervical pair emerges inferior to the occipital bone and superior to the atlas (the first cervical vert), and the 8th cervical nerve arises inferior to the 7th cervical vertebra.

Differentiate b/t upper and lower neurons

Upper motor neurons are housed either w/in the cerebral cortex, cerebral nuclei, or nucleus w/in the brainstem.Synapses either directly on a lower motor neuron or on an interneuron. Upper motor neurons either excite or inhibit activity of lower motor neurons. Lower motor neurons are housed w/in the anterior horn of the spinal cord or w/in a brainstem cranial nerve nucleus. Axon of the lower neurons exits the CNS and projects to the skeletal muscle to be innervated. Lower neurons are ALWAYS excitatory b/t its axon connects directly to skeletal muscle fibers.

Identify and briefly describe the following structures given a cross section of the spinal cord: a. dorsal root ganglion b. dorsal (posterior) root c. ventral (anterior) root d. dorsal ramus e. ventral ramus f. rami communicans g. visceral sensory nuclei h. somatic sensory nuclei i. autonomic motor nuclei j. somatic motor nuclei

a. dorsal root ganglion: cell bodies of sensory neurons in the posterior root. b. dorsal (posterior) root: contains sensory axons and is formed from merging of multiple posterior rootlets. Relay nerve signals FROM receptors to the CNS c. ventral (anterior) root: contains motor axons only and is forme dform the mergine of multiple anterior rootlets. (conduct nerve signals from the CNS TO effectors) d. dorsal (posterior) ramus: smaller of the branch of the spinal nerves; innervates deep muscles of the back and skin of the back e. ventral (anterior) ramus: large of the two branches; splits into other vranches, which innervate the anterior and lateral portions of the trunk, upper limbs, and lower limbs. f. rami communicans: additional rami, which contain axons associated w/ the Autonomic nervous system. Extend b/t spinal nerve and a ball like structure called the sympathetic trunk ganglion. g. visceral sensory nuclei h. somatic sensory nuclei i. autonomic motor nuclei j. somatic motor nuclei