Anatomy & Physiology of Nervous System PDF

1.1 Introduction Thursday, August 10, 2023 9:25 AM Anatomy - structure of the body Physiology- how the body parts function together Nervous system- receives information, processes information, and sense our signals to muscles and glands to elicit a response. Nervous tissue- responsible for commun...

1.1 Introduction Thursday, August 10, 2023 9:25 AM Anatomy - structure of the body Physiology- how the body parts function together Nervous system- receives information, processes information, and sense our signals to muscles and glands to elicit a response. Nervous tissue- responsible for communication between cells of the body by forming a system of electrical impulses that communicate rapidly. Yellow indicates nervous tissue The nervous system is made up of two main systems: 1. CNS- Central Nervous System 2. PNS- Peripheral Nervous System Central Nervous System Made up of brain and spinal cord ○ Brain- protected by the skull ○ Spinal cord- protected by vertebral column Lies at the midline of the body Sends and receives impulses from the peripheral nervous system Nuclei- collection of cell bodies inside the central nervous system Tracts- collection of nerve axons inside the central nervous system Peripheral Nervous System Made up of all nerves that are not in the brain or spinal cord ○ Cranial nerves- project from the brain stem ○ Spinal nerves- project of the spinal cord The PNS can be divided into two divisions: ○ Sensory (afferent)  Receives info from sensory organs throughout the body PNS to CNS ○ Motor (efferent)  Relays signals from CNS to muscles and glands  CNS to PNS Ganglia- collection of cell bodies inside the peripheral nervous system Nerves- the collection of nerve axons in the peripheral nervous system Motor (efferent) can be further divided into the somatic nervous system (SNS) and the autonomic nervous system (ANS) ○ Somatic- nerves that are generally under conscious (voluntary control)  Controls movements of skeletal muscles, skin, and joints ○ Autonomic- nerves that control the glands and smooth muscles of the organs  Not under conscious control  Can be divided into two systems: □ Sympathetic  Activates and prepares body for activity, stress, and emergency situations ◊ Increase blood glucose levels ◊ Sends blood to muscles so that we can respond to emergency situations (like running away) □ Parasympathetic Operates during normal situations Permits digestions, conserves energy 1.2 Neurons Thursday, August 10, 2023 9:26 AM Neurons- nerve cells that conduct electrical impulses and relay information throughout the body. Neurons are made up three basic parts ○ Dendrite  Receiving end  Receives information from other neurons  Conducts impulses to the cell body ○ Cell body  Synthesizes all nerve cell products  Receives information from dendrites  Sends information towards the axon  Very large nucleus  Cytoplasm  Contains all normal organelles except centrioles  Main function is to manufacture neurotransmitters ○ Axon  Conducts nerve impulses away from cell body  Terminates in axon terminals  Vary in length  Contains regular cell components, but lacks rough endoplasmic reticulum □ Relies on cell body to send protein down, so it doesn't need rough ER ○ Axon terminals  Store neurotransmitters inside secretory vesicles at end of axon terminals  When neurotransmitters are released from axon terminals vesicles, they carry the nerve impulse from one neuron to the nexxt They DO NOT undergo mitosis (cell division). ○ If neurons die, they cannot be replaced. ○ Only survive minutes without oxygen. Neurotransmitters- chemical messengers to communicate between neurons across a synapse Synapse- space between two neurons Presynaptic neuron- neuron found before the synapse Postsynaptic neuron- neuron found after the synapse Neuron communication happens in only one direction Neurons can have different shapes depending on where the neuron is located ○ Multipolar  Three or more extensions from cell body.  One axon  Many dendrites  Motor neuons ○ Bipolar  Two extensions  Central cell body  Special receptor cells □ Visual and olfactors systems ○ Unipolar (pseudo unipolar)  One extension from cell body  Two branches □ Peripheral process from Sensory receptor □ Central process sends to CNS  Sensory neurons in the PNS   Sensory neurons in the PNS Neurons have different functions ○ Sensory (afferent) neurons  Carry information from PNS to CNS  Many are found in the skin or internal organs to the CNS ○ Interneurons  Found only in the CNS  Typically multipolar neurons  Transmits information within different parts of the CNS  Aka association neurons ○ Motor (efferent) neurons  Multipolar  Sends messages from CNS to PNS 1.3 Neuroglial Cells Thursday, August 10, 2023 4:12 PM Nerve- in the PNS system, a group of axons wrapped together in connective tissue Ganglia- in the PNS, cell bodies of neurons grouped together in masses SO, neuroglial cells are support cells for neurons Schwann cells (pictured to the right) ○ Composed of fatty myelin sheath ○ Protects nerve axon ○ Increase speed of nerve impulses ○ Wrapped around the axon Nodes of Ranvier ○ The gaps between the Schwann cells ○ Enables saltatory conduction  The electrical signal jumps between the nodes Satellite cells ○ surround the cell bodies of peripheral neurons, ○ help regulate the cell body environment Nodes of Ranvier Axons can regrow when the Schwann cells grow ahead of the axon, creating a new path to follow as it grows, known as axonal regeneration. Ependymal cells ○ Circulate cerebrospinal fluid (CSF)  Specialized liquid in brain and spinal cord ○ Allows fluid exchange between brain, spinal cord, and CSF ○ CSF is made in the ventricle of the brain Oligodendrocytes ○ Insulation for CNS axons ○ One cell can have multiple connections Astrocytes ○ Control chemical environment of neurons ○ Wrap around blood capillaries ○ Blood brain barrier  Physical barrier  Allows passage of only certain substances into CNS Microglial cells ○ Protect the CNS ○ Phagocytosis (eat up)  Dead cells  Pathogens  1.4 Action Potentials Thursday, August 10, 2023 7:35 PM Resting Potential Neurons: specializes to conduct electrical impulses Polarized: at rest, the plasma membrane has a different charge on the inside than on the outside Resting potential: at rest, this charge is about -70mv Maintained by sodium-potassium pump ○ Active transport via integral protein  Uses cell energy to maintain this ○ Carries ions across the plasma membrane ○ Three sodium (Na +) ions pumped out ○ Two potassium (K+) ions pumped in ○ Must be kept in constant operation ○ A pump is the same integral protein exchanging sodium At rest with no impulse, the inside and potassium within the same pump. of the cell has a net negative charge compared to the outside of the cell OUTSIDE CELL Integral protein that spans across the cell bilayer Because three positive ions are going out and only two positive ions are coming in, this creates the overall negative charge within the cell. INSIDE CELL Action potential occurs when the charge in the cell changes. This is done via: Sodium and potassium gates ○ Enable action potentials ○ Special protein-lined channels with gates in the membrane ○ Allow sodium or potassium to pass through ○ Gates are voltage activated and respond to changes in shape ○ Gates open and close to allow sodium or potassium to flow freely Action potential: rapid change in polarity across the membrane Depolarization: the membrane potential becomes more positive. The inside becomes more positive than the outside Re-polarization: the potential returns to normal Electrical propagation:  Cell body Axon Because it has all of these voltage gated channels that respond to the voltage change, that will carry the action potential all the way down the entire length of the axon Membrane depolarizes when the positive ions rush in through the channel; making the inside more positive Membrane repolarizes when it pushes the positive ions back to their original position, normalizing the charge inside the cell taking it back to resting potential This process happens down the entire axon of the neuron Actional Potentials Phase 1: Resting state/potential Sodium and potassium gates are closed Resting state is -70mv Sodium is waiting to rush in; potassium is waiting to rush out Phase 2: Depolarization Inside of cell is becoming more positive Stimulus occurs that triggers depolarization Sodium gates open; sodium freely rushes into the cell Voltage travels up to +40mv Phase 3: Repolarization Everything is returning to normal where inside Of cell is more negative Sodium gates close Potassium gates open; potassium freely rushes out Returns negative voltage to the inside of cell Phase 4: Afterpolarization (aka hyper polarization) A small drop where inside of cell becomes more negative than resting state before returning to the resting potential Potassium gates slow to close Undershoot of potential Drops below -70 but then returns as resting state is re-established. Once the cell body decides to send signal down the axon, it travels down the entire length of the axon. Known as self-propagation ○ The voltage channels automatically All-or-nothing response ○ If the signal does not meet the signal threshold, it's not going to send the signal  Known as a failed initiation ○ If the signal is strong enough and can pass the threshold, then it will automatically trigger depolarization which send the signal down the entire length of the axon. Determining intensity of sensation Number of neurons stimulated Frequency with which neurons are stimulated Chemical Transmission of an Action Potential Synapse- minute fluid-filled space between the axon terminal of the presynaptic neuron and dendrite of postsynaptic neuron. Electrochemical- transmission of nerve impulses is both electrical and chemical. Chemicals called neurotransmitters transmit the signal across the synapse. Electrical transmission Electrical impulse reaches the end of the axon Calcium ions rush inside the cell This causes the vesicles filled with neurotransmitters to fuse with plasma membrane Neurotransmitters are released and then bind to the dendrites of the receiving neuron Depolarization occurs in the next neuron The electrical impulse is carried forward ○ To another neuron, target organ, or gland. Chemical transmission Causes the vesicles filled with neurotransmitters to fuse with plasma membrane Neurotransmitters are released and then bind to the dendrites of the receiving neuron Short existence of neurotransmitters in the synapse ○ Sometimes the neurotransmitters are re-absorbed back into the presynaptic neuron ○ Enzymes will "eat up" the neurotransmitters in the synapse  Acetylcholinesterase or cholinesterase Synaptic inhibition- prevention of continuous simulation of postsynaptic neuron ○ The neurotransmitters have to be completely removed in order for another action potential to pass through the neuron Types of neurotransmitters Norepinephrine and epinephrine ○ Function as hormones and neurotransmitters ○ Produced in adrenal glands ○ Into general circulation Dopamine ○ Specialized brain neurotransmitter ○ Regulates emotional responses ○ Regulates muscle tone Acetylcholine ○ Found in neuromuscular junction (NMJ)  Motor neuron synapses on a muscles  Coordinates action between nervous and muscular system Neuromuscular Junction For a muscle to contract, the nervous system must work together with the muscular system Nerve impulse via motor neuron Neuromuscular junction Acetylcholine ○ Neurotransmitter released in the NMJ ○ Acetylcholine then binds to the muscle cell ○ Causes sodium enters sarcoplasm  Acetylcholine ○ Neurotransmitter released in the NMJ ○ Acetylcholine then binds to the muscle cell ○ Causes sodium enters sarcoplasm  cytoplasm of the muscle cell ○ Increase in sodium ions triggers action potential in the sarcolemma  Special name for cell membrane of muscle fiber ○ This triggers the sarcoplasmic reticulum to release calcium ions  Endoplasmic reticulum for muscle cell ○ This causes myosin to bind to actin and pull it, contracting the muscle fiber  Calcium + ATP allows the muscles to contract ○ For the muscle to retract, the calcium has to be returned and the motor neuron has to stop sending the signal 1.5 Reflexes Friday, August 18, 2023 12:43 PM Reflexes- instantaneous, automatic, and involuntary motor response within the nervous system. Reflexes start from stimuli occurring inside or outside the body. Always involves the CNS Examples of reflexes ○ Subconscious reflexes occur without conscious awareness  Regulation of blood sugar ○ Other reflexes occur and then afterwards there is an awareness that the reflex occurred.  Shivering to a temp drop  Eye blinking ○ Brainstem reflexes involve the midbrain, pons, and/or medulla  Reflex: eye blinking  We aren't going to talk about these, but you should know these do exist ○ Spinal reflexes involves spinal nerves and spinal cord  Withdrawing hand from hot object Reflex arc- the neural pathway that a nerve impulse travels. Certain reflexes can be tested to examine the function of the nervous system. Spinal Cord Anatomy Dorsal roots carry sensory information to the spinal cord (PNS to CNS) Ventral roots carry motor information away from the spinal cord (CNS to PNS) Both signals are travelling beside one another through the spinal nerve Dorsal root ganglion (DRG) ○ Cell bodies of sensory neurons ○ Basically a little bump on the dorsal root  Dorsal root contains axons of sensory neurons Gray matter ○ Cell bodies of neurons and where neurons synapse with other neurons ○ Butterfly shape in the middle ○ Posterior horn is where sensory neurons synapse on cells within the spinal cord ○ Anterior horn contains the motor neuron cell bodies  Sending information out via the ventral roots White matter  ○ Axons of neurons ○ Surrounds the gray matter Spinal nerve contains both sensory and motor neurons from the ventral and dorsal roots Spinal reflexes provide immediate response to dangerous stimuli Faster than a conscious response ○ Fewer neurons ○ Shorter distance  Comes into spinal nerve via dorsal root, into the spinal cord, and back out the spinal nerve via ventral roots  It does NOT have to travel up to the brain to respond, like in a conscious response Reflex Pathway Receptor at the end of a sensory neuron reacts to stimulus Sensory neuron conducts nerve impulses along the afferent pathway through the dorsal root to the CNS Integration center- consists of one or more synapses in the CNS Motor (efferent) neurons conducts a nerve impulse along the ventral root to the effector Effector muscle or gland responds to the efferent impulse to make change 1. Muscle spindle in quad detects stretch Stretch reflexes are special muscle reflexes that protects the muscle against 2. Sensory signal is sent along afferent neuron increases in length that may tear or damage the muscle fibers. a. Passes through spinal nerve Muscle spindles specialized stretch receptors in muscles that constantly 3. Signal travels through the DRG monitor the amount of stretch in a muscle 4. Synapses in gray matter of spinal cord directly onto efferent neuron 5. Efferent neuron travels out the ventral root 6. Synapses back on to the same muscle spindle a. Sending acetylcholine to that muscle fiber Effect: contraction of the muscle to prevent overstretching Patellar reflex ○ Also known as knee-jerk reflex ○ Commonly used in physician's offices ○ Tests the stretch reflex of the quadriceps femoris ○ Primary purpose is to prevent overstretch on quads  Tap patellar tendon while leg suspended off table  Stretches quadriceps muscle (knee extensor) Flexor withdrawal reflex ○ Allows for removal of hand from hot or dangerous object ○ Protection of skin and underlying tissue Sensory receptors in the skin (on the hand in the image) are detecting a threat (very hot/painful/dangerous) 1. Pain receptors in the skin generate nerve impulse 2. Moves along the dendrite of a sensory neuron to the cell body and CNS 3. Sensory neuron synapses within the gray matter on many interneurons (only found in the CNS) a. Excitatory interneurons: send excitatory signals, carrying the action potential forward i. Synapses on a motor neuron to the biceps, causing it to contract b. Inhibitory interneurons: send inhibitory signals, preventing the action potential from moving forward i. Simultaneously, inhibitory interneuron synapses on a motor neuron to the triceps, preventing triceps from contracting Effect: removal of hand from dangerous stimuli ○ Elbow flexion ○ Prevention of co-contraction of biceps and triceps  If both muscles contract at the same time, your hand will not be removed off the hot surface, causing more damage.  AModule 1: Problem Set Friday, August 18, 2023 3:36 PM Anatomy and Physiology of the Nervous System: Introduction 1. Anatomy is the structure of the body. Physiology is how the body parts function together. 1. What is the difference between anatomy and physiology? 2. The nervous system receives information from all over the body, processes the information received, and sends signals to muscles and glands to elicit a response. 2. The function of the nervous system is to integrate and control the other body systems. 3. The two parts of the nervous system is the central nervous system (CNS), which is composed of Explain how the nervous system does this. the spinal cord and brain, and the peripheral nervous system (PNS) which is made up of all the nerves that are NOT in the brain and spinal cord. 3. List the 2 parts of the nervous system. 4. The parts of the central nervous system are protected by the skull and spinal vertebrae. 5. Collections of cell bodies inside the central nervous system are called nuclei. The collection of 4. How are the parts of the central nervous system protected? nerve axons in the CNS are called tracts. 6. The peripheral nervous system include cranial and spinal nerves that project FROM the CNS. 5. Collections of cell bodies inside the central nervous system are called _____, and the collection of nerve axons in the central nervous system are called _____. 7. Collections of cell bodies inside the peripheral nervous system are called ganglia. The collection of nerve axons in the peripheral nervous system are called nerves. 6. What is included in the peripheral nervous system? 8. The two divisions of the PNS are the motor (efferent) and the sensory (afferent). 9. The peripheral nervous system receives impulses from the sensory organs via the afferent 7. Collections of cell bodies inside the peripheral nervous system are called _____, and the division and then relays signals or impulses from the central nervous system to muscles and collection of nerve axons in the peripheral nervous system are called _____. glands via the motor or efferent division. 10. Somatic and autonomic are the two divisions of the efferent division of the PNS. 8. What are the 2 divisions of the peripheral nervous system? 11. Somatic nerves are under voluntary control and are found in skeletal muscles, skin, and joints. Autonomic nerves are found in glands and smooth muscles of organs and are not under conscious control. 9. Describe the movement of nerve impulses in the peripheral nervous system. 12. The autonomic system is divided into sympathetic and parasympathetic systems. 10. What are the 2 divisions of the efferent division of the peripheral nervous system? 13. The sympathetic system activates and prepares the body for activity, stress, and emergency situations. 11. What is controlled by the somatic and autonomic nervous systems? 14. The parasympathetic system operates during normal situations, permitting digestion and conserving energy. 12. What are the 2 divisions of the autonomic nervous system? 15. A neuron is composed of the axon, cell body, dendrites, and axon terminals. 16. Three unusual characteristics of neurons: 13. What is the function of the sympathetic nervous system? a. Neurons do not undergo mitosis. b. Require enormous amounts of energy. c. Can only survive minutes without oxygen. 14. What is the function of the parasympathetic nervous system? d. Communication only happens in one direction. e. You have all the neurons you will have for your whole life. Neurons 15. Label the components of a neuron. 17. All neurons have dendrites, a cell body, and an axon. 18. The cell body is made up a very large nucleus, cytoplasm, and all normal organelles (excluding 16. List 3 unusual characteristics of neurons. centrioles). The main function of the cell body is to receive the signal from the dendrite, process that signal and manufacture into neurotransmitter, and then send that down the axon to head to the next neuron. 17. List the 3 parts that all neurons contain. 19. The dendrites are hair-like extensions attached to the cell body that receives information from other neurons and sends that signal to the cell body. 18. Describe the structure and function of the neuron cell body. 20. The axon is a single, rope-like section of the neuron attached to the cell body that is coated in a myelin sheath with nodes of Ranvier and includes an axon terminal at the end. The axon carries 19. Describe the structure and function of the dendrite. the signal from the cell body down to the axon terminals to be transmitted to the next neuron. The axon includes all the normal organelles, except the rough endoplasmic reticulum. 20. Describe the axon, including the number in each neuron, function, structure and 21. The synthesis of neurotransmitters occurs in the cell body, which is its main function. The axon organelles. terminals store the signals inside secretory vesicles at the end of the terminals, which are released during an electrochemical transmission in the synapse. 21. Describe the function and site of synthesis and storage of neurotransmitters. 22. The synapse is the liquid-filled space between the axon terminal of the presynaptic neuron and the dendrites of the postsynaptic neuron. 22. What is a synapse? 23. A postsynaptic neuron is a neuron that is found after the synapse. 24. Multipolar neurons have three or more extensions from the cell body and have one axon and 23. A post-synaptic neuron is a neuron that is found ____ the synapse. many dendrites. 25. Bipolar neurons have a central cell body with two extensions.  25. Bipolar neurons have a central cell body with two extensions. 24. ______neurons have three or more extensions from the cell body and have one axon and many dendrites. 26. Unipolar neurons have one extension off the cell body which branches into two: one central process running to the CNS and another peripheral process running to the sensory receptor. 25. _________ neurons have a central cell body with two extensions. 27. Sensory neurons are unipolar and function to carry information from the peripheral to the central nervous system. 28. Interneurons are also known as association neurons. 26. _____ neurons have one extension off the cell body which branches into two: one central process running to the CNS and another peripheral process running to the sensory receptor. 29. Motor neurons send messages from the central nervous system to the peripheral. 30. Neuroglial cells are support cells for neurons. 27. ______ neurons are unipolar and function to carry information from the peripheral to the central nervous system. 31. Schwann cells and satellite cells are PNS neuroglial cell types. 32. False; Axons can regrow when the Schwann cells grow ahead of the axon, creating a new path 28. These types of neurons are also called association neurons. to follow as it grows, known as axonal regeneration. 33. False; the myelin sheath has gaps called nodes of Ranvier. 29. _____ neurons send messages from the central nervous system to the peripheral. 34. Four types of support neuroglial cells and their functions: Neuroglial Cells a. Ependymal cells: circulate cerebrospinal fluid and allows fluid exchange between brain, spinal cord, and CSF 30. What is the function of neuroglial cells? b. Oligodendrocytes: insulate CNS axons c. Astrocytes: control chemical environment of neurons d. Microglial: protect the CNS by phagocytosis 31. What are the peripheral nervous system neuroglial cell types? 35. The technical term of a nerve impulse is action potential, which is caused by the movement of unequally distributed ions on either side of a plasma membrane. 32. True or False: Axons cannot regenerate in the peripheral nervous system. 36. The resting potential is -70mv because the inside of the cell membrane is more negatively charged than outside of the membrane. This is maintained by pumping three sodium ions out and two potassium ions inside the membrane, creating an overall negative charge. 33. True or False: Myelin sheath is continuous and has no gaps. 37. Four steps of action potential: a. Resting state 34. List the four types of support neuroglial cells in the central system and a function of b. Depolarization each. c. Repolarization d. Afterpolarization Action Potentials 38. During depolarization, the sodium gates open, allowing sodium to rush freely into the cell. This 35. What is the technical term used to describe a nerve impulse and what causes the causes the inside of the cell to become more positive, up to +40mv. impulse? 39. During repolarization, sodium gates close while potassium gates open, allowing potassium to flow out of the cell and attempting to return to resting potential by making the inside of the cell 36. An axon's membrane is polarized with a resting potential of -70 mV. Explain what this more negative. means and what maintains this resting potential. 40. Afterpolarization, or hyper-polarization, is when the potassium gates slowly close, causing the of the cell to dip slightly more negative before returning to the resting potential. 37. What are the four steps of an action potential in order? 41. The number of neurons and/or the frequency in which neurons are stimulated determine the intensity of a sensation. 38. Describe what happens to the charges on the axon cell membrane during depolarization and what causes this to happen. 42. False; an impulse can only travel in on direction down the axon. 38. Describe what happens to the charges on the axon cell membrane during repolarization and what causes this to happen. 43. Neuron signals are electrochemical in nature because the impulse uses both chemical and electrical measures to transmit the signal across the synapse. 39. Describe what happens during afterpolarization. 44. Chemical: Occurs within the synapse; when calcium ions rush in, the vesicles that contain the neurotransmitters fuse with the plasma membrane and release neurotransmitters into the synapse. These bind with the receptors on the next neuron, which open the sodium ion 40. What causes the difference in intensity of a sensation? channels in the receiving dendrites. 45. Impulses between nerve cells are passed through an area, called the synapse. It is a fluid-filled 41. True or False: An impulse from a neuron moves in both directions. space between the pre-synaptic(sending) neuron’s axon terminal and the post-synaptic (receiving) neuron’s dendrites. When the electrical signal reaches the axon terminal, neurotransmitters are released into the synapse and bind with receptors on the dendrite. This causes sodium ion channels to open, initiating depolarization in the receiving neuron, passing 42. What is meant by neuron signals being electrochemical in nature? the impulse to the receiving neuron. 46. Synaptic inhibition prevents the continuous stimulation of a postsynaptic neuron. Some 43. What is the chemical portion of neuron signal transmission? synapses contain enzymes, like Acetylcholinesterase or cholinesterase, that will eat up the remaining neurotransmitters. Other neurotransmitters are re-absorbed back into the presynaptic neuron. 44. How is an impulse passed from one nerve cell to another? 47. Dopamine helps regulate emotional responses and muscle tone. 45. What prevents continuous stimulation of a nerve synapse and how is this accomplished? 48. Acetylcholine is found in the neuromuscular junction. 46. What neurotransmitter helps regulate emotional responses and muscle tone? 49. Once the ACh is released in the NMJ, it binds to the muscle cells, which causes sodium to enter the sarcoplasm. The sodium ion increase triggers an action potential in the sarcolemma. Then, 47. What neurotransmitter is found at the neuromuscular junctions? the Sarcoplasmic reticulum releases calcium ions. This causes myosin to bind to actin and pull it, 47. What neurotransmitter is found at the neuromuscular junctions? the Sarcoplasmic reticulum releases calcium ions. This causes myosin to bind to actin and pull it, contracting the muscle. 48. Once ACh is released in the NMJ, what happens to cause muscle contraction to occur? 50. A reflex is an instantaneous, automatic, and involuntary motor response within the nervous system. An internal reflex would be something like blood sugar regulation. An external example would include touching a hot surface and jerking your hand away. 49. Once ACh is released in the NMJ, what happens to cause muscle contraction to occur? 51. Sensory information travels into the spinal cord via the dorsal roots of a nerve. 50. Define the term reflex. Give an internal and an external example. 52. Gray matter is the cell bodies of neurons and where neurons synapse with other neurons. White matter is composed of the axons of neurons and surrounds the gray matter. 51. Sensory information travels into the spinal cord via the _______ of a nerve 53. The dorsal root ganglion (DRG) contains the cell bodies of sensory neurons. 52. What is the gray and white matter of the spinal cord? 54. Sensory neurons synapse on cells in the posterior horn of the spinal cord. 53. What does the DRG contain? 55. Motor neuron cell bodies are in the anterior horn of the spinal cord. 54. Sensory neurons synapse on cells in the _______ of the spinal cord. 56. Motor neurons (axons) leave the spinal cord via the ventral roots. 55. Motor neuron cell bodies are in the _______ of the spinal cord. 57. I DON’T UNDERSTAND THIS QUESTION. 56. Motor neurons (axons) leave the spinal cord via the ____. 58. Parts of a spinal cord are in the attached image 57. When does a ventral root transition to a spinal nerve? 59. Spinal reflexes are faster because it requires fewer neurons and the signal does not have to 58. Label the components of the cross section of a spinal cord. travel all the way to the brain and back; the signal is sent to the signal cord and back, which is a shorter distance to travel. 59. Why is a spinal reflex faster than a conscious decision to move by the brain? 60. Five components of reflex arc: 60. List the 5 components of a reflex arc. a. The receptor at the end of a sensory neuron reacts to a stimulus. 61. The stretch reflex utilizes what type of specialized receptor to detect over-stretch? b. The sensory neuron conducts nerve impulses along an afferent pathway towards the central nervous system (CNS). 62. What is the purpose of the stretch reflex? c. The integration center consists of one or more synapses in the CNS. d. A motor (efferent) neuron conducts a nerve impulse along an efferent pathway from the integration center to an effector. e. An effector responds to the efferent impulses by contracting (a muscle) or secreting a product (a gland). 61. Muscle spindles monitor and detect over-stretch in muscles. 62. The purpose of the stretch reflex is to protect the muscle against increases in length that may tear or damage muscle fibers.