9. The Nervous System: Part One: The Information Super Highway. Multimedia Asset Directory. Slide 36Multiple Sclerosis Animation Slide 46Neurosynapses Video Slide 51Muscle Contraction Animation Slide 64Epidural Placement Video Slide 80Spinal Cord Anatomy Animation - PowerPoint PPT Presentation
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Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Introduction
• The control systems of your body are the nervous and endocrine systems which receive help from your special senses.
• Like any control system, they have a large, complex job that is sometimes difficult to understand. Thus, the systems themselves are perhaps the most complex and vital systems.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Pronunciation GuideClick on the megaphone icon before each item to hear the pronunciation.
dorsal root ganglion (GANG lee on)dura mater (DOO rah MAY ter)ependymal cells (eh PEN deh mall)epidural space (EPP ih DOO rall)ganglia (GANG lee ah)glial cells (GLEE all)gyri (JIE rie)meninges (men IN jeez)microglia (my KROG lee ah)
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Pronunciation GuideClick on the megaphone icon before each item to hear the pronunciation.
myelin (MY eh lin)neuroglia (glial cells) (noo ROG lee ah)nodes of Ranvier (ron vee AYE)oligodendrocytes (AH li go DEN droe sites)pia mater (PEE ah MAY ter)plexus (PLECK sus)Schwann cells (SHWAN)somatic nervous system (so MAT ick)spinocerebellar tract (SPY no ser eh BELL ar)
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Parts and Basic Operations
• The somatic nervous system controls skeletal muscle and mostly voluntary movements.
• The autonomic nervous system controls smooth muscle and cardiac muscle, along with several glands.
• The autonomic system is divided into the parasympathetic system that deals with normal body functioning while the sympathetic nervous system controls the “fight or flight” response system.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Real Life Example
• You park your car and get out to visit a friend. As you step on the walk a large dog bounds down the steps barking and snarling at you.
• Your sensory system gathers information including; a large unfriendly dog, you are far from the protection of your car, and no one is around to help.
• The information goes into your spinal cord and brain and you process the information to make decisions. You are in danger; something must be done!
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Real Life Example
• Your CNS sends directions to your organs to gear up for action via the autonomic nervous system.
• Your heart rate, blood pressure, and respiration rate increase. You begin to sweat. More blood is delivered to your skeletal muscles and heart in order to get you fully ready to respond. This is all involuntary, meaning you cannot consciously control it.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Real Life Example
• Your somatic nervous system readies your skeletal muscles to get you out of there. This is often called the “fight or flight” response and will be discussed later in further depth. If you can control your fear, you back slowly away from the situation. If you are scared witless, you run from the yard as fast as possible. Either way, you can hopefully escape the danger, with your skin and pride intact.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Classification of Neurons
• Neurons can be classified by how they look (structure)– Unipolar – 1 process with a peripheral and central
projection– Bipolar – 2 processes, 1 axon and 1 dendrite– Multipolar – many processes
• Or what they do (function)– Input neurons are known as sensory neurons.– Output neurons are known as motor neurons.– Neurons which carry information between neurons
are called interneurons (inter – between) or association neurons.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Action Potential
• When the cell is stimulated:– If the cell becomes more negative than resting
it is called hyperpolarized. – Action potential (AP) is the cell moving
through depolarization, repolarization, and hyperpolarization.
– The cell cannot accept another stimulus until it returns to its resting state, and this time period when it cannot accept another stimulus is called the refractory period.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Local Potentials
• Neurons can use their ability to generate electricity to send, receive, and interpret signals.
• If you hit your thumb with a hammer, dendrites in your thumb are stimulated by the blow and sodium gates open, sodium flows into the dendrites and they become depolarized. The number of cells affected depends on how hard you hit your thumb.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Local Potentials
• In local potential the size of the stimulus determines the excitement of the cell. Many sensory cells work via local potentials, which is how your CNS determines the size of the environmental change.
• The dendrites carry the depolarization to the sensory neuron cell body, which takes the information and generates an action potential if the stimulus is big enough.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Local Potentials
• One difference between action potentials and local potentials is that action potentials are “all-or-none,” meaning the depolarization always finishes and is always the same size, while local potentials vary in size depending on the stimulus.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Impulse Conduction
• Myelin is essential for speedy flow of AP’s down the axons. In an unmyelinated axon, the AP can only flow down the axon by depolarizing each and every centimeter of the axon (a relatively slow process). In myelinated axons there are nodes located periodically, and only the nodes must depolarize, allowing the impulse to travel quickly as it skips from node to node.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Clinical Application: Multiple Sclerosis
• Multiple sclerosis (MS) is a disorder of the myelin in the CNS. Many areas of myelin are destroyed. In these areas, impulse conduction is slow or impossible. Symptoms of MS differ depending on where the myelin damage occurs. Disturbances in balance, vision, speech, or movement is possible. MS occurs more in women, and patients are usually under 50.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Impulse Conduction and Diameter
• Small unmyelinated axons have speeds as low as 0.5 meters/second while large-diameter myelinated axons may be as fast as 100 meters/second. That’s 200 times faster!!
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
How Synapses Work
• When the AP arrives at the axon terminal, the terminal depolarizes and calcium gates open. Calcium flows into the cell. When calcium flows in, it triggers a change in the terminal.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
How Synapses Work
• There are tiny sacs in the terminal called vesicles which release their contents from the cell when calcium flows in. These vesicles are filled with molecules, called neurotransmitters, used to send the signal from the neuron across the synapse to the next cell in line.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Neurotransmitters
• The neurotransmitters bind to the cell receiving the signal, opening or closing gates. Some excite the receiving cell and some calm it down.
• The last step in the transfer of information is to clean up, removing the neurotransmitter from the synapse to prevent it from binding to the receiving cell.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Figure 9-6 The Chemical Synapse. Step 1: The impulse travels down the axon. Step 2: Vesicles are stimulated to release neurotransmitter (exocytosis). Step 3: The neurotransmitter travels across the synapse and binds with the receptor site of post synaptic cell. Step 4: The
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Chemical Synapses andMedications
• Selective serotonin reuptake inhibitors (SSRIs) are good examples. These medications prevent the clean up of the neurotransmitter serotonin from synapses, thus increasing the effects of serotonin on the receiving cell.
• Many antidepressants and anti-anxiety drugs are SSRIs.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
The Neuromuscular Junction
• The neuromuscular junction is a chemical synapse creating a specialized synapse between somatic (voluntary) motor neurons and the skeletal muscles they innervate.
• The surface of the muscles is studded with sodium channels that are ligand gated. These open or close when a molecule binds to a receptor that is part of the channel, like a key fitting into a lock.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
The Neuromuscular Junction
• In the case of skeletal muscles, the ligand is the neurotransmitter acetylcholine, which is released from the terminal of a motor neuron and binds to the surface of skeletal muscle, opening sodium channels and causing the skeletal muscle to depolarize. The muscle then contracts.
• Acetylcholinesterase is the enzyme responsible for cleaning up the synapse.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Spinal Cord and Spinal Nerves
• The spinal cord ends at L2 in a pointed structure called the conus medullaris. Hanging from the conus medullaris is the cauda equina (horses tail), spinal nerves which dangle loosely and float in a bath of cerebral spinal fluid (CSF).
• The spinal cord has two widened areas, the cervical and lumbar enlargements, which contain the neurons for the upper and lower limbs respectively.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Meninges
• They help to set up layers that act as cushioning and shock absorbers. – arachnoid mater
middle layer is a wispy, delicate layer, resembling a spider web, composed of collagen and elastic fibers acting as a shock absorber and transporting dissolved gases and nutrients as well as chemical messengers and waste products
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Meningeal Spaces
• These three membranes and their fluid-filled spaces, together with the bones of the skull and vertebral column, form a strong protective system against CNS injury.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Clinical Application:Epidural Anesthesia
• Often during labor, or in preparation for a cesarean section, a woman will receive “an epidural.” An epidural is an injection of local anesthesia into the epidural space. The anesthetic is usually delivered via a catheter (small tube). Ideally, epidural anesthesia allows a woman to continue to participate actively in the birth without severe labor pains.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Internal Anatomy of the Spinal Cord
• There are three types of horns: the dorsal horn is involved in sensory functions, the ventral horn involved in motor function, and the lateral horn dealing with autonomic functions. The horns are the regions where the neuron’s cell bodies reside.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Internal Anatomy of the Spinal Cord
• There are also dorsal, lateral, and ventral columns, the white matter of the spinal cord. These columns act as nerve tracts, pathways, or axons, running up and down the spinal cord to and from the brain.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Internal Anatomy of the Spinal Cord
• Ascending pathways carry information from your sense of touch to the spinal cord and then to your brain from all parts of the skin, joints, and tendons.– The dorsal column tract carries fine-touch and
vibration information to the cerebral cortex.– The spinothalamic tract carries temperature,
pain, and crude touch information to the cerebral cortex.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Internal Anatomy of the Spinal Cord
• Ascending pathways carry information from your sense of touch to the spinal cord and then to your brain from all parts of the skin, joints, and tendons.– The spinocerebellar tract carries information
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Internal Anatomy of the Spinal Cord
• Descending pathways carry motor information (orders for voluntary movements) from the brain to the spinal cord. The axons from all pathways synapse on motor neurons in the ventral horn.– The corticospinal tract carries orders from the
brain to the motor neurons in the ventral horn of the spinal cord.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Internal Anatomy of the Spinal Cord
• The axons from all pathways synapse on motor neurons in the ventral horn.– The corticobulbar tract carries orders from the
brain to motor neurons in the brain stem (more details later).
– The reticulospinal and rubrospinal tracts (along with several other tracts) carry information from the brain to the brain stem and ventral horn, which helps to coordinate movements.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Internal Anatomy of the Spinal Cord
• The commissures, gray and white, connect left and right halves of the cord so the two sides of the CNS can communicate. The central canal is a cavity in the center of the spinal cord filled with CSF.
• The spinal roots project from both sides of the spinal cord in pairs, and fuse to form spinal nerves.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Internal Anatomy of the Spinal Cord
• The dorsal root, with the embedded dorsal root ganglion, a collection of sensory neurons, carries sensory information while the ventral root is motor.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Spinal Nerves
• Spinal nerves from the thoracic spinal cord project directly to the thoracic body wall without branching, while all other spinal nerves branch extensively, recombining with nerves from other spinal cord segments before projecting to peripheral structures. These complex branching patterns are called plexuses.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Clinical Application: A Matter of Centimeters
• Did you know that the difference between being able to breathe on your own after a spinal cord injury and being dependent on a ventilator is literally a matter of centimeters? One of the nerves that projects from the cervical plexus is a nerve called the phrenic nerve, a motor nerve for your diaphragm, your main breathing muscle.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Clinical Application: A Matter of Centimeters
• If the spinal cord is damaged below the cervical plexus the phrenic nerve still functions, while an injury between the brain and the cervical plexus blocks the path to the phrenic nerve paralyzing your diaphragm.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
From the Streets:Reflexes
• Decreased reflex (hypoflexia) or absent reflex (areflexia) may result from temporary or permanent damage to:– Skeletal muscles– Dorsal or ventral nerve roots– Spinal nerves– The spinal cord– The brain
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Figure 9-13 Abdominal reflex. Gently stroking the skin of the abdomen should cause contraction of the underlying muscles and move the umbilicus toward the location of the
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Figure 9-13 Plantar reflex. Stroking the lateral aspect of the plantar surface of the foot should cause plantar flexion of the toes. Dorsiflexion of the great toe and fanning of the other toes following stimulation is considered a positive Babinski reflex, which suggests problems with
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Botulism
• The toxin keeps neurotransmitters from being released at the neuromuscular junction, causing paralysis.
• Initial symptoms include visual disturbances, slurred speech, dry mouth, and muscle weakness. Paralysis will spread to limbs and respiratory muscles.
• Botulism is treated with anti-toxin and supportive care.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Snapshots from the Journey
• The nervous system is the body’s computer. It has a sensory, integration, and motor system. The input and output nerves are in the PNS, and the brain and spinal cord are the SNS.
• The tissue of the nervous system is made up of two types of cells: neurons, which send, receive, and process information, and neuroglia, which support the neurons.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Snapshots from the Journey
• Neurons are excitable cells. They do their jobs by carrying tiny electrical currents caused by changes in cell permeability to certain ions. These tiny electrical currents can be all-or-none responses (action potentials), can change depending on the size of the stimulus (local potentials), can travel down axons (impulse conduction), or can be used to transmit information from one cell to another (synapses).
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Snapshots from the Journey
• Your CNS is surrounded by a three-layered membrane system: dura mater, arachnoid mater, and pia mater, collectively known as the meninges. Cerebrospinal fluid is also contained in the space between the arachnoid and pia maters.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Snapshots from the Journey
• The spinal nerves are made of a pair of spinal roots. The ventral root is integral to motor function, and the dorsal root is integral to sensory function. Spinal nerves are mixed; they carry both sensory and motor information.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Snapshots from the Journey
• A series of tracts run up and down the spinal cord to and from the brain. The tracts going toward the brain carry sensory information to the brain. The tracts coming from the brain toward the spinal cord carry motor information from the brain.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Case Study
During the biggest game of his high school football career, Bill, the best wide receiver in the league, leaps high into the air in the end zone to score the game-winning touchdown. A player for the other team hits him hard, knocking him into the goal post. Bill crumples to the ground, unmoving. When the EMT’s get to him, Bill is paralyzed on both sides of his body and in respiratory arrest.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
From the Streets
A 60-year-old female drives to your EMS department because she is experiencing “numbness and tingling” in her hands & fingers. Your patient interview reveals that the complaint has been going on for almost three months and has become worse over the last two weeks. She has a history of diabetes.
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
End of ChapterReview Questions
7. Sodium channel blockers, which prevent sodium channels from working, would block what part of the action potential?a. Hyperpolarizationb. Depolarizationc. Repolarizationd. Afterpotential
Essentials of A&P for Emergency CareBruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
End of ChapterReview Questions
5. A ______ is an involuntary, protective movement that is generated without the brain.
6. The virus polio causes loss of motor function but not of sensory function, because it infects neurons. These neurons are located in the ___________ horn of the spinal cord.