Module 14: The Nervous System PDF

References: MLS 1104 LECTURE Module 14 The Nervous System Reference: Seeley’s Essentials of Anatomy & Physiology 11th Edition by Vanputte, Regan Russo...

References: MLS 1104 LECTURE Module 14 The Nervous System Reference: Seeley’s Essentials of Anatomy & Physiology 11th Edition by Vanputte, Regan Russo Prepared by: Cherry Grace A. Dabucon, MD 1 Nervous System Nervous system is involved in some way in nearly every body function. a communication system, receiving signals from and sending commands to different areas of the body ➔helps to coordinate the body functions to maintain homeostasis Major functions of the nervous system 1. Receiving sensory input sensations from some stimuli, such as vision, hearing, taste, smell, touch, pain, body position, and temperature blood pH, blood gases, and blood pressure, are processed at a subconscious level 2. Integrating information. The brain and spinal cord are the major organs for processing sensory input and initiating responses 3. Controlling muscles and glands. Skeletal muscles normally contract only when stimulated by the nervous system. participates in controlling cardiac muscle, smooth muscle, and many glands 4. Maintaining homeostasis depends on the nervous system’s ability to detect, interpret, and respond to changes in internal and external conditions 5. Establishing and maintaining mental activity  DIVISIONS OF THE NERVOUS SYSTEM The nervous system can be divided into two major divisions: 1. Central Nervous System (CNS) consists of the brain and spinal cord 2. Peripheral Nervous System (PNS) consists of all the nervous tissue outside the CNS, including nerves and ganglia PNS is the communication link between the CNS and the various parts of the body PNS carries information about the different tissues of the body to the CNS and delivers commands from the CNS to other body tissues that alter body activities 2-directional flow of information, the PNS can be subdivided into two parts: (basis of their function) 1. The sensory division, or afferent (toward) division, of the PNS conducts action potentials from sensory receptors to the CNS neurons that transmit action potentials from the periphery to the CNS are called sensory neurons. 2. The motor division, or efferent (away) division- conducts action potentials from the CNS to effector organs, such as muscles and glands. neurons that transmit action potentials from the CNS toward the periphery are called motor neurons. afferent (toward) division efferent (away) division transmits action potentials from the CNS to skeletal muscles transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands Enteric Nervous System (ENS) is a unique part of the PNS has both sensory and motor neurons contained within the digestive tract. can function without input from the CNS or other parts of the PNS, although it is normally integrated with the CNS by sensory neurons and ANS motor neurons  CELLS OF THE NERVOUS SYSTEM A. Neurons or nerve cells receive stimuli, conduct action potentials and transmit signals to other neurons or effector organs. A neuron has three parts: (1) a cell body single nucleus (source of information for gene expression) Extensive rough ER, a Golgi apparatus, and mitochondria surround the nucleus Neurofilaments (intermediate filaments) and microtubules organize the cytoplasm into distinct areas. (2) two types of processes: dendrites are short, often highly branching cytoplasmic extensions that are tapered from their bases at the neuron cell body to their tips receive information from other neurons or from sensory receptors and transmit the information toward the neuron cell body (3) axons. single long cell process extending from the neuron cell body. area where the axon leaves the neuron cell body is called the axon hillock uniform diameter and may vary in length Axons of sensory neurons conduct action potentials towards the CNS axons of motor neurons conduct action potentials away from the CNS  CELLS OF THE NERVOUS SYSTEM axon may remain unbranched or may branch to form collateral axons surrounded by a highly specialized insulating layer of cells called the myelin sheath Structural Types of Neurons (based on the Arrangement of their Processes) neurons within the CNS retina of the eye most sensory neurons all motor neurons the nasal cavity vestibulocochlear  Nasal cavity: Olfactory Nerve cells (Bipolar) Retina of the Eye (Optic nerve head is a unique part of CN II) Skin sensory neurons: (Pseudo-unipolar)  CELLS OF THE NERVOUS SYSTEM B. Glial cells, or neuroglia (nerve glue), supportive cells of the CNS and PNS do not conduct action potentials carry out different activities that enhance neuron function and maintain normal conditions within nervous tissue. more numerous than neurons retain the ability to divide, whereas neurons do not 4 TYPES OF GLIAL CELLS in the CNS 1. Astrocytes major supporting cells in the CNS can stimulate or inhibit the signaling activity of nearby neurons participate with the blood vessel endothelium to form a permeability barrier, called the blood-brain barrier, between the blood and the CNS. help limit damage to neural tissue ➔the repair process can form a scar that blocks regeneration of damaged axon 2. Ependymal cells line the fluid-filled cavities (ventricles and canals) within the CNS. Some ependymal cells produce cerebrospinal fluid, Those with cilia, help move the cerebrospinal fluid through the CNS. 3. Microglia act as immune cells (macrophage) of the CNS. help protect the brain by removing bacteria and cell debris. 4. Oligodendrocytes provide an insulating material (myelin) that surrounds axons  The Glial Cells Of The PNS 1. Schwann cells provide insulating material (myelin which forms the myelin sheath) around axons. 2. Satellite cells found around the cell bodies of certain neurons of the PNS. provide support and nutrition to the neurons protect the neurons from heavy-metal poisons, such as lead and mercury "COPS" (Central - Oligodendrocytes, Peripheral - Schwann) Myelin Sheaths specialized layers that wrap around the axons of some neurons. are formed by the cell processes of oligodendrocytes in the CNS and Schwann cells in the PNS Axons with these myelin sheaths are called Myelinated axons Each oligodendrocyte process or Schwann cell repeatedly wraps around a segment of an axon to form a series of tightly wrapped cell membranes➔ excellent insulator that prevents almost all ion movement across the cell membrane nodes of Ranvier : gaps in the myelin sheath, Multiple sclerosis: Autoimmune condition; may every millimeter between the myelinated areas. be initiated by viral infection; Ion movement can occur at the nodes of Ranvier. inflammation in Myelination of an axon increases the speed & efficiency of action brain and spinal cord with potential generation along the axon. demyelination and sclerotic (hard) sheaths typical small nerve results in poor conduction of action potentials; symptoms include exaggerated reflexes, tremor, and speech defects Unmyelinated axons lack the myelin sheaths axons rest in indentations of the oligodendrocytes and the Schwann cells  Organization of Nervous Tissue 1. Gray matter (darker outer) consists of groups of neuron cell bodies and their dendrites, where there is very little myelin CNS, gray matter on the surface of the brain is called the cortex, and clusters of gray matter located deeper within the brain are called nuclei. the PNS contains gray matter, a cluster of neuron cell bodies is called a ganglion 2. White matter consists of bundles of parallel axons with their myelin sheaths, which are whitish in color. CNS forms nerve tracts, or conduction pathways, which propagate action potentials from one area of the CNS to another. PNS consists of bundles of axons and associated connective tissue that form nerves.  ELECTRICAL SIGNALS AND NEURAL PATHWAYS The flow of ions through these channels can also be influenced by their electrical charges, because of the attraction between opposite charges. TWO BASIC TYPES OF ION CHANNELS: (1) Leak channels– are always open: ions can “leak” across the membrane, down their concentration gradient K+ leak channels have the greatest contribution to the resting membrane potential (2) Gated channels are closed until opened by specific signals a. Chemically gated channels are opened by specific chemicals (neurotransmitters) b. Voltage-gated channels are opened by a change in the electrical property of the cell membrane (membrane potential) When opened, the gated channels can change the Sodium-potassium pump is required to maintain the membrane potential and are thus responsible for the greater concentration of Na+ outside the cell action potential membrane and K+ inside  Resting Membrane Potential 1. In a resting cell, there is a higher concentration of K+ inside the cell and a higher concentration of Na+ outside the cell. 2. Movement of ions through leak channels 3. Sodium-potassium pump maintains resting levels of ions across the cell membrane consumes 25% of all the ATP in a typical cell and 70% of the ATP in a neuron Neuron Communication Neurons are excitable cells, meaning that the resting membrane potential changes in response to stimuli. In muscle cells, this change in the resting membrane potential results in contraction; but in neurons, this change is a means by which the cell communicates with other cells. Neuron communication into 3 stages  3 stages of Neuron communication I. Generation of action potentials (electrical signals that are conducted along the cell membrane from one region of the cell to another) Depolarization and repolarization constitute an action potential Hyperpolarization: the charge of the cell membrane briefly becomes more negative than the resting membrane potential (elevated permeability to K+) Action potentials occur in an all-or-none fashion Action potentials in a cell are all of the same magnitude II. Action potential propagation along the cell membrane occur in one of two ways: (1) Continuous conduction (2) Saltatory conduction. III. Communication with target cell at the synapse. I. Generation of action potentials II. Action potential propagation along the cell membrane III. Communication with target cell at the synapse II. Action potential propagation along the cell membrane a. Continuous conduction (unmyelinated axons) an action potential in one part of a cell membrane stimulates local currents in adjacent parts of the cell membrane action potential is conducted along the entire axon cell membrane b. During saltatory conduction, (myelinated axons) action potentials occur at successive nodes of Ranvier, resulting in faster propagation compared to continuous conduction action potentials “jump” from one node of Ranvier to the next along the length of the axon  III. Communication with target cell at the synapse. Synapse is a junction where the axon of one neuron interacts with another neuron or with cells of an effector organ, such as a muscle or gland three major components of Synapse: a. the end of the axon forms a presynaptic terminal b. the space separating the presynaptic and postsynaptic membranes is the synaptic cleft c. the membrane of the dendrite or effector cell is the postsynaptic membrane Acetylcholine: An enzyme called acetylcholinesterase breaks down the acetylcholine Norepinephrine is either actively transported back into the presynaptic terminal or broken down by enzymes  CENTRAL AND PERIPHERAL NERVOUS SYSTEMS CNS: consists of the brain and spinal cord The brain is housed within the skull; the spinal cord is in the vertebral column. PNS: consists of all the nerves and ganglia outside the brain and spinal cord. The nerves of the PNS can be divided into two groups: 12 pairs of cranial nerves and 31 pairs of spinal nerves ✓ PNS collects information from numerous sources both inside and on the surface of the body and relays it by way of sensory neurons to the CNS One of three results is possible (information): 1. information is ignored 2. triggers a reflex 3. evaluated more extensively  SPINAL CORD extends from the foramen magnum at the base of the skull to the second lumbar vertebra Spinal nerves communicate between the spinal cord and the body The inferior end of the spinal cord and the spinal nerves exiting there resemble a horse’s tail and are collectively called the cauda equina The white matter in each half of the spinal cord is organized into three columns: Each column of the spinal cord (1) the dorsal (posterior) column contains ascending and (2) the ventral (anterior) column, descending tracts, or pathways. (3) the lateral column. Gray matter of the spinal cord shaped like the letter H, with dorsal(posterior) horns ventral (anterior) horns lateral horns exist in levels of the spinal cord associated with the autonomic nervous system. central canal is a fluid-filled space in the center of the spinal cord Relationship of sensory and motor neurons to the spinal cord Dorsal root has a region called the dorsal root ganglion a swelling or knot contains the cell bodies of pseudo-unipolar sensory neurons  Reflex A reflex is an involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS. Reflexes allow a person to react to stimuli more quickly than is possible if conscious thought is involved. Most reflexes occur in the spinal cord or brainstem rather than in the higher brain centers. A reflex arc is the neuronal pathway by which a reflex occurs and has five basic components. Reflex Arc Components 1. A sensory receptor 2. A sensory neuron 3. Interneurons, which are neurons located between and communicating with two other neurons 4. A motor neuron 5. An effector organ (muscles or glands). Note: The simplest reflex arcs do not involve interneurons Stretch reflex Patellar reflex The withdrawal reflex/flexor reflex moves a body part away from a painful stimulus  SPINAL NERVES arise along the spinal cord from the union of the dorsal roots and ventral roots Spinal nerves are categorized by the region of the vertebral column from which they emerge: The spinal nerves are also numbered (starting superiorly) according to their order within that region. The 31 pairs of spinal nerves : C1 through C8, T1 through T12, L1 through L5, S1through S5, Coccygeal DERMATOME is the area of skin supplied with sensory innervation by a pair of spinal nerves. Each of the spinal nerves except C1 has a specific cutaneous sensory distribution  SPINAL NERVES Most of the spinal nerves are organized into Three Major Plexuses 1. THE CERVICAL PLEXUS 3. THE LUMBOSACRAL PLEXUS originates from spinal nerves C1 to C4 Four major nerves supply the lower Phrenic nerve, which innervates the diaphragm limb: obturator nerve innervates 2. THE BRACHIAL PLEXUS themuscles of the medial thigh spinal nerves C5 to T1 tibial nerve innervates the Axillary nerve innervates 2 shoulder muscles and the skin of the shoulder posterior thigh muscles Radial nerve innervates all the muscles in the posterior arm & forearm &hand common fibular nerve Ulnar nerve innervates 2 anterior forearm muscles & most of the intrinsic hand innervates the muscles of the muscle lateral thigh and leg and some location is called the “funny bone.” intrinsic foot muscles Median nerve innervates anterior forearm muscles and & radial side of the hand. Sciatic nerve  THE MAJOR REGIONS OF THE BRAIN: BRAIN 1. the BRAINSTEM 2. the CEREBELLUM 3. the DIENCEPHALON 4. the CEREBRUM 1. the BRAINSTEM connects the spinal cord to the remainder of the brain control of heart rate, blood pressure, and breathing. damage to small areas of the brainstem can cause death, whereas damage to relatively large areas of the cerebrum or cerebellum often do not. Nuclei for all but the first two cranial nerves are also located in the brainstem It consists of three parts: a. the medulla oblongata b. the pons c. the midbrain a. the Medulla Oblongata most inferior portion of the brainstem continuous with the spinal cord Pyramids: two prominent enlargements at the anterior surface descending nerve tracts, which transmit action potentials from the brain to somatic motor neurons of the spinal cord and are involved in the conscious control of skeletal muscles b. the Pons “bridge” Immediately superior to the medulla oblongata relay information between the cerebrum and the cerebellum functions such as breathing, swallowing, and balance are controlled in the lower pons, as well as in the medulla oblongata also chewing and salivation c. the Midbrain just superior to the pons, is the smallest region of the brainstem dorsal part of the midbrain consists of four mounds of tissue called the colliculi two inferior colliculi are major relay centers for the auditory nerve pathways in the CNS two superior colliculi are involved in visual reflexes and receive touch and auditory input substantia nigra- black nuclear mass involved in regulating general body movements 2. the CEREBELLUM attached to the brainstem by several large connections called cerebellar peduncles cerebellar cortex is composed of gray matter and has gyri and sulci, but the gyri are much smaller than those of the cerebrum. Internally, the cerebellum consists of gray nuclei and white nerve tracts. involved in maintaining balance and muscle tone and in coordinating fine motor movement. If the cerebellum is damaged, muscle tone decreases, and fine motor movements become very clumsy major function of the cerebellum is that of a comparator (sensing device that compares the data from two sources—in this case, the motor cortex and peripheral structures) proprioceptive neurons, which innervate joints, tendons, and muscles and provide information about the position of body parts 3. the DIENCEPHALON the part of the brain between the brainstem and the cerebrum Its main components are: a. The thalamus largest part shaped somewhat like a yo-yo, with small interthalamic adhesion influences mood and registers an unlocalized, uncomfortable perception of pain. b. the epithalamus small area superior and posterior to the thalamus involved in the emotional and visceral response to odors pineal (pinecone-shaped) gland is an endocrine gland that may influence the onset of puberty and may play a role in controlling some long-term cycles that are influenced by the light-dark cycle c. the hypothalamus most inferior part for maintaining homeostasis major role in controlling the secretion of hormones from the pituitary gland Sensations such as sexual pleasure, rage, fear, and relaxation after a meal “nervous perspiration” or “emotional eating,” funnel-shaped stalk, the infundibulum extends from the floor of the hypothalamus to the pituitary gland 4. the CEREBRUM is the largest part of the brain It is divided into left and right hemispheres by a longitudinal fissure. most conspicuous features on the surface of each hemisphere are numerous folds called gyri and intervening grooves called sulci The gyri greatly increase the surface area of the cerebral cortex. Each cerebral hemisphere is divided into lobes, which are named for the skull bones overlying them. 1. Frontal lobe control of voluntary motor functions, motivation, aggression, mood, and olfactory (smell) reception. 2. Parietal lobe the principal center for receiving and consciously perceiving most sensory information, such as touch, pain, temperature, and balance. The frontal and parietal lobes are separated by the central sulcus. 3. Occipital lobe functions in receiving and perceiving visual input and is not distinctly separate from the other lobes. 4. Temporal lobe is involved in olfactory (smell) and auditory (hearing) sensations and plays an important role in memory. Its anterior and inferior portions, called the “psychic cortex,” are associated with functions such as abstract thought and judgment 5. Deep within the lateral fissure is the insula often referred to as the fifth lobe, which is involved in the perception of taste  Sensory Areas of the Cerebral Cortex premotor area motor functions are organized before they are actually initiated in the primary motor cortex prefrontal area: motivation and foresight to plan and initiate movements Motor Areas of the Cerebral Cortex occur  Communication Between the Right and Left Hemispheres Commissures: connections between the two hemispheres so that sensory information received by one hemisphere is shared with the other Corpus callosum largest of these commissures a broad band of nerve tracts at the base of the longitudinal fissure Language & artistic activities, are not shared equally between the two hemispheres. Researchers believe the left hemisphere is the more analytical hemisphere, emphasizing such skills as mathematics and speech, the right hemisphere is more involved in functions such as three-dimensional or spatial perception and musical ability. Speech Two major cortical areas are involved in speech: (1) The sensory speech area (Wernicke area), located in the parietal lobe, functions in understanding and formulating coherent speech. Damage to these part of the brain or to associated brain (2) The motor speech area (Broca area), located in the frontal regions may result in APHASIA (absent or defective lobe, controls the movement necessary for speech speech or language comprehension) Electroencephalogram: Electrodes placed on a person’s scalp and attached to a recording device can record the brain’s electrical activity EEG patterns can be detected as wavelike patterns known as brain waves 1. Alpha waves are observed in a normal person who is awake but in a quiet, resting state with the eyes closed. 2. Beta waves have a higher frequency than alpha waves and occur during intense mental activity. During the beginning of sleep, a rapid transition takes place from a beta rhythm to an alpha rhythm. As sleep deepens, progressively more delta waves occur. 3. Delta waves occur during deep sleep, in infants, and in patients with severe brain disorders. 4. Theta waves, are usually observed in children, but they can also occur in adults who are experiencing frustration or who have certain brain disorders  Memory Storage of memory can be divided into three stages: 1. Working memory (Prefrontal cortex) task-associated memory few seconds to minutes and occurs mostly in the frontal cortex. 2. Short-term memory (Prefrontal cortex) lasts longer than working memory and can be retained for a few minutes to a few days susceptible to brain trauma, such as physical injury or decreased oxygen, and to certain drugs that affect neural function, such as general anesthetics 3. Long-term memory (Cerebellum and other) become permanent, by consolidation, a gradual process involving the formation of new and stronger synaptic connections Subdivided based on the type of the memory: (a) those dealing with facts (declarative) explicit memory, involves the retention of facts, such as names, dates, and places, as well as related emotional undertones (b) those dealing with skills (procedural). reflexive memory, involves the development of motor skills, such as riding a bicycle. Only a small amount of procedural memory is lost over time Memory engrams, or memory traces: involved in the long-term retention of a given piece of information, a thought,or an idea  Limbic System and Emotions Made up of: 1. olfactory cortex 2. certain deep cortical regions 3. nuclei of the cerebrum 4. diencephalon Influences long-term declarative memory, emotions, visceral responses to emotions, motivation, and mood. major source of sensory input to the limbic system is the olfactory nerves. The limbic system responds to olfactory stimulation by initiating responses necessary for survival, such as hunger and thirst. connected to, and functionally associated with, the hypothalamus. Lesions in the limbic system can result in voracious appetite, increased (often perverse) sexual activity, and docility (including loss of normal fear and anger responses)  MENINGES, VENTRICLES, AND CEREBROSPINAL FLUID Meninges Three connective tissue membranes, the meninges surround and protect the brain and spinal cord. The meninges include (1) the dura mater most superficial and thickest of the meninges epidural space between the dura mater and the vertebrae (injection site for epidural anesthesia of the spinal nerves, which is often given to females during childbirth) (2) the arachnoid mater subdural space : between the dura mater and the arachnoid mater is the, which is normally only a potential space containing a very small amount of serous fluid. area as a spinal block or to take a sample of cerebrospinal fluid in a spinal tap (meningitis) (3). The pia mater tightly bound to the surface of the brain and spinal cord  Ventricles fluid-filled cavities Each cerebral hemisphere contains a relatively large cavity called the lateral ventricle (2). 3rd ventricle is a smaller, midline cavity located in the center of the diencephalon between the two halves of the thalamus and connected by foramina (holes) to the lateral ventricles. 4th ventricle is located at the base of the cerebellum and connected to the third ventricle by a narrow canal, called the cerebral aqueduct. The fourth ventricle is continuous with the central canal of the spinal cord. also opens into the subarachnoid space through foramina in its walls and roof.  Cerebrospinal Fluid Cerebrospinal fluid (CSF) bathes the brain and spinal cord, providing a protective cushion around the CNS. The choroid plexuses produce the CSF. specialized structures located in the ventricles and composed of ependymal cells. CSF fills the brain ventricles, the central canal of the spinal cord, and the subarachnoid space 1. CSF is produced by the choroid plexuses of the ventricles. 2. The CSF flows from the lateral ventricles into the third ventricle. 3. CSF then flows through the cerebral aqueduct into the fourth ventricle. Hydrocephalus: Blockage of the openings in the fourth ventricle or 4. The CSF exits the fourth ventricle the cerebral aqueduct can cause CSF to accumulate in the ventricles through small openings in its walls and accumulation of fluid creates increased pressure that dilates the roof and enters the subarachnoid ventricles and compresses the brain tissue, which usually results in space. irreversible brain damage CRANIAL NERVES: The cranial nerves transmit and relay information to and from the brain.  AUTONOMIC NERVOUS SYSTEM autonomic nervous system (ANS) comprises motor neurons that carry action potentials from the CNS to the periphery autonomic neurons innervate smooth muscle, cardiac muscle, and glands. Autonomic functions are largely controlled unconsciously Composed: sympathetic division parasympathetic division thoracolumbar craniosacral  Innervation of Organs by the ANS Anatomy of the Sympathetic Division first thoracic (T1) and the second lumbar (L2) segments Collateral ganglia are located nearer target organs. The collateral ganglia include the celiac, superior mesenteric, and inferior mesenteric ganglia fight-or-flight (increasing heart rate and blood pressure, dilating respiratory passageways to increase airflow, and stimulating the release of glucose from the liver for energy.) Anatomy of the Parasympathetic Division Brainstem nuclei of CN III, VII, IX, X to the regions of S2-S4 Craniosacral terminal ganglia either located near effector organs in the head or embedded in the walls of effector organs in the thorax, abdomen, and pelvis rest-and-digest (digestion, defecation, and urination.) Thank You for Listening Nervous System