Anatomy & Physiology: Nervous System PDF

 ‫العضلة العاصرة‬ ‫يفرغ‬ ‫انتفاخ‬ Ministry of Health Oman Collage of Health Sciences- Sohar Anatomy & Physiology Nervous System Present by: Ms.Muna  Content Organization of the nervous system. Nervo...

 ‫العضلة العاصرة‬ ‫يفرغ‬ ‫انتفاخ‬ Ministry of Health Oman Collage of Health Sciences- Sohar Anatomy & Physiology Nervous System Present by: Ms.Muna  Content Organization of the nervous system. Nervous tissue: structure and function. Central nervous system. Peripheral nervous system. Autonomic nervous system.  Objective 1: List the general functions of the nervous system. The Nervous System The body responds to stimuli or irritant from outside (light, cold, sound…etc) & inside the body (decrease oxygen) The sensory preceptors detect the changes in temperature, pressure, and send messages (electrical impulses) to the brain & spinal cord, then CNS assess the information & then respond  The Nervous System The nervous system is the master control and communication system of the body Every action, thought and emotion reflects its activity It communicates with the body cells using rapid and specific electrical impulses that cause immediate responses Functions of the Nervous System  Objective 2: Explain the structural & functional classifications of the nervous system Objective 3: Define the central and peripheral nervous system & list the major parts of each.  Organization of the Nervous System To simplify the discussion the NS is divided into: Structural classification: the organs of the nervous system. 2. Functional classification: the functions or the activities of the nervous system. Structural Classification of All Nervous System Organs  Functional Classification: the PNS Structures 1. Sensory (afferent) division Nerve fibers that carry impulses from sensory receptors in various body parts to the CNS They keep the CNS consistently informed of events inside & outside the body Somatic sensory (afferent) fibers: deliver impulses from skin, skeletal muscles & joints Visceral sensory (afferent ) fibers: transmit impulses from the visceral organs  Functional Classification of the PNS 2. Motor (efferent) division Nerve fibers that carry impulses a way from the central nervous system to effector organs, the muscles & glands They effect: bring about or cause a motor response  Functional Classification of the PNS Motor (efferent) division has two subdivisions Somatic Nervous System Autonomic Nervous System Allow us to consciously or Regulates events that are automatic voluntarily control our skeletal or involuntary such as smooth & muscles cardiac muscles & glands. Known as voluntary nervous Known as involuntary nervous system system But not all skeletal muscles It is subdivided into two parts controlled by this division is Sympathetic nervous system voluntarily Parasympathetic nervous system Skeletal muscle reflexes e.g. stretch These brings opposite effects reflex are initiated involuntarily by If one stimulate the other inhibit the same fibers Organization of the Nervous System Figure 7.2  Objective 4: Describe the general structure of a neuron and name its important anatomical regions Objective 5: Describe the composition of gray matter and white matter  Nervous Tissue Nervous tissue is made up of two principle types of cells: Supporting tissue Neurons  Nervous Tissue: Neurons Neurons: nerve cells that are specialized to transmit messages (nerve impulses) Major regions of neurons: Cell body – nucleus and metabolic center of the cell. Processes – fibers that extend from the cell body.  Neuron Anatomy: Cell Body It is the metabolic center of the neuron Its transparent nucleus containing a large nucleolus The rough endoplasmic(ER) reticulum called the Nissl bodies & neurofibrils (intermediate filaments that maintains cell shape) are abundant in the cell body  Neuron Anatomy: Processes The arm-like processes or fibers vary in length from microscopic to about 7 feet in tallest person Extensions outside the cell body: Dendrites: conduct impulses toward the cell body. Axons: generate nerve impulses & conduct them away from the cell body. Some neurons have hundreds of branching dendrites Each neuron has one axon that rises from a cone-like region of the cell body called the axon hillock  Axons & Nerve Impulses Axons have a collateral branch along its length They end in axonal terminal (forming 100 to 1000 of axonal terminals) Axonal terminals contain vesicles that contains chemicals called neurotransmitters Impulses reaching the axon terminal stimulate release of neurotransmitters into the extracellular space between the neurons  Axons & Nerve Impulses Axonal terminals are separated from the next neuron by a gap called the synaptic cleft Synapse: a functional junction where an impulse is transmitted from one neuron to another Neuron never touch other neuron  Nerve Fiber Coverings Most long nerve fibers are covered with a whitish, fatty materials that have a waxy appearance called myelin sheath Functions of myelin sheath: Protects the nerve fibers Insulates the fibers Increases the transmission rate of nerve impulses  Nerve Fiber Coverings Axons outside the CNS are myelinated by Schwann cells Schwann cells: wrap themselves around the axon in a jelly-roll fashion The part of Schwann cell, external to the myelin sheath is called the neurilemma Nodes of Ranvier: gaps in myelin sheath along the axon  Neuron Cell Body Location Clusters of neuron cell bodies & collections of nerves fibers have different names in the CNS & PNS that include: 1. Nuclei: clusters of cell bodies found in the CNS that are well protected in the bony skull & vertebral column Neurons do not go cell division after birth The cell body carries out most of the metabolic functions of a neuron If it damaged , the cell dies & is not replaced  Neuron Cell Body Location 2. Ganglia: small collections of cell bodies in a few cites outside the CNS. 3. Tracts: Bundles of nerve fibers running through the CNS 4. Nerves: Bundles of nerve fibers running through the PNS 5. White & gray matters refer to myelinated versus unmyelinated regions of the CNS: The white matter: consists of dense collections of myelinated fibers (tracts) Gray matter: contains mostly unmyelinated fibers and cell bodies  Objective 6: Describe the functional & structural classification of neurons  Functional Classification of Neurons Functionally neurons are grouped based on their direction of the nerve impulse travels relative to the CNS into: Sensory (afferent) neurons Motor (efferent) neurons Association neurons (interneuron) Functional Classification of Neurons Sensory (afferent) Carry impulses from the sensory receptors in the internal organs or the skin (cutaneous sense organs) muscles & tendons (proprioceptors) to the CNS Their cell bodies found in a ganglion outside the CNS They keep us informed of inside & outside changes The dendrite endings of the sensory neuron have specialized receptors activated by specific changes The pain receptors are the least specialized of the cutaneous receptors, the most numerous  Functional Classification of Neurons Sensory (afferent) Sensory (afferent) neurons Proprioceptors: detect the amount of stretch or tension in the skeletal muscles, tendons & joints They send the information to the brain so proper adjustments can be made to maintain balance & normal posture Proprioceptors constantly advise our brain of our own movement Functional Classification of Motor Neurons (efferent) Carry impulses from the CNS to the viscera and/or muscles and glands Their cell bodies are located in the CNS Functional Classification of Neurons: Interneurons (Association Neuron) Connect sensory and motor neurons in neural pathways Their cell bodies are typically located in the CNS Cell body – nucleus and metabolic center of the cell. Processes – bers that extend from the cell body.  Structural Classification of Neurons It is based on the number of processes including dendrites and axon extending from the cell body Multipolar neurons: several extensions from the cell body They are the most common because all motor & associate neuron are multipolar Figure 7.8a  Structural Classification of Neurons Bipolar neurons: neuron with two processes: one axon and one dendrite They are rare in adult They are only found in special sense organs (eye and nose ) acting in sensory processing as receptor cells. Figure 7.8b  Structural Classification of Neurons Unipolar neurons: a short single process from cell body that divides immediately into proximal (central) & distal (peripheral) processes. Small branches at the end of the peripheral processes are dendrites & the reminder are axon The axon conducts impulses toward & away from the cell body Sensory neuron in the PNS ganglia are unipolar Figure 7.8c  Objective7: Describe the events that lead to the generation of nerve impulse and its conduction from one neuron to another.  Physiology: Nerve Impulses Irritability: ability to respond to stimuli & convert it into a nerve impulse Conductivity: ability to transmit an impulse to other neurons, muscles, or glands  Electrical Conditions of a Resting Neuron’s Membrane The plasma membrane of a resting, or inactive neuron is polarized Polarized means that there are fewer positive ions inside neuron’s plasma membrane than the outer surface The major positive ions inside the cell are potassium (K+) The major positive ions outside the cell are sodium (Na+) The neuron remain inactive when the inside is more negative than the outside  Action Potential Initiation & Generation Different stimuli excite neurons to become active & generate impulses. For example: Light excites the eye receptors Pressure excites some cutaneous receptors Most neurons are excited by neurotransmitter Regardless the stimulus, the result is always the same The permeability of the cell’s plasma membrane change for a short period  Action Potential Initiation & Generation Normally Na+ cannot diffuse through plasma membrane to a great extent. But when the neuron is adequately stimulated, the gate of Na+ channels in the membrane open So the Na+ diffuse quickly to the neuron from outside (high concentration than the inside) The inward rush of Na+ ions changes the polarity of the neuron’s membrane at that site (depolarization) The inside is now more positive & the outside is less positive. This local electrical situation is called graded potential Figure 7.9a– c  Action Potential Initiation & Generation If the stimulus is strong and the Na+ influx is great the local depolarization (graded potential) activates the neuron to initiate and transmit a long-distance signal called an action potential (nerve impulse in neuron) The nerve impulse is an all-or-none response, either propagated over the entire neuron or it does not happen  Action Potential Initiation & Generation After rush of Na+ ion into the neuron, the membrane becomes impermeable to Na+ ion & permeable to K+ ion So K+ ions are allowed to diffuse out of the neuron into the interstitial fluid very rapidly. This outflow of positive ions from the cells restores the electrical conditions at the membrane to the polarized or resting state (repolarization).  Restoring the Initial Ionic Condition The sodium-potassium pump restores the original concentrations of the Na+ & K+ ions inside & outside the neuron This action requires ATP to pump excess Na+ ions out of the cell & to bring K+ back into it Until repolarization occurs, a neuron cannot conduct another impulse  Nerve Impulse Propagation The impulse continues to move toward the cell body Impulses travel faster when fibers have a myelin sheath because the impulses jump or leaps from node to node This faster type of electrical impulse propagation is called salutatory conduction  Transmission of the Signal at Synapses Neurotransmitter crosses the synapse to transmit the signal from one neuron to another Action potential reaches an axon terminal The electrical change opens calcium channels The tiny vesicles containing neurotransmitter into the synaptic cleft The neurotransmitter diffuse across the synaptic cleft & to receptors on the membrane of the next neuron The neurotransmitter prompted a brief change (shorter than eye blinking) as it is quickly removed from the synaptic cleft  Transmission of the Signal at Synapses Transmission of an impulse is an electrochemical event Transmission down the length of the neuron’s membrane is electrical but the next neuron is stimulated by a chemical neurotransmitter Neuron received signals from & to other neuron & carry different conversation with different neurons at the same time. How Neurons Communicate at Synapses Figure 7.10  Objective 8: Define reflex arc & its elements and give typical example.  Reflexes Reflexes are rapid, predictable and involuntary responses to stimuli Once reflex begin, it always goes into same direction Reflexes occur over neural pathways called reflex arcs & involve CNS & PNS structures  Types of Reflexes Somatic Autonomic All reflexes that stimulate Regulate the activity of skeletal muscles smooth muscles, heart, and glands They are involuntary They are involuntary although skeletal muscles They regulate digestion, normally under voluntary elimination, BP, sweating control Example: pulling hand Secretion of saliva quickly away from a hot Changes in the size of pupils object The Five Elements of the Reflex Arcs Reflex arcs Function A receptor React to a stimulus An effector The stimulated glands or muscles Sensory neurons Connect the receptor & the Motor neurons effector Integration Processing the gathered information  Example of Reflex Arc (Two Neuron Reflex Arc) The simple patellar or knee-jerk, reflex is an example of two neuron reflex arc (the simplest type) It is usually tested during physical exam to determine general health of the motor portion of the nervous system Simple Reflex Arc  Three-Neuron Reflex Arc The flexor, or withdrawal, reflex: is a three-neuron reflex arc by which the limb is withdrawn from painful stimulus This reflex arch consists of receptors, sensory neuron, interneuron, motor neuron & effector The more the synapses the longer the reflex takes to happen as neurotransmitters takes time to diffuse via the synaptic cleft. Three-Neuron Reflex Arc  Central Nervous System Objective 9: Identify and describe the functions of the major regions of the cerebral hemisphere, diencephalons, brain stem, and cerebellum.  Central Nervous System The adult’s brain weighs a little over 3 pounds The brain is the largest and the most complex mass of nervous tissue Four major regions are: 1. Cerebral hemisphere 2. Diencephalon 3. Brain stem 4. Cerebellum  Cerebral Hemispheres Altogether are called cerebrum. Are the most superior part of the brain. Larger than the other three brain regions. As the hemispheres develop and grow they enclose and obscure most of the brain stem  Cerebral Hemispheres The elevated ridges of tissue of the cerebrum is called gyri Gyri are separated by shallow grooves (sulci) The deeper grooves that separate large region of the brain are called fissures  Cerebral Hemispheres A single deep longitudinal fissures separate the cerebral hemisphere. Other fissures divide each hemispheres into lobes. Each hemisphere has three basic regions: A superficial cortex of gray matter that looks gray in fresh brain tissue An internal area of white matter The basal nuclei: islands of gray matter deep within the white matter  Lobes of the Cerebrum Surface lobes of the cerebrum: Frontal lobe. Parietal lobe. Occipital lobe. Temporal lobe  Cerebral Cortex Functions of cerebral cortex: Speech Memory Logical and emotional responses Consciousness The interpretation of sensation Voluntary movement  Cerebral Cortex Functional areas of the cerebral cortex: Functional areas Location Function The primary somatic Parietal lobe posterior Localizing & interpreting impulses sensory area to the central sulcus received from body’s sensory receptors It allows us to recognize pain, differences in temperature or a light touch Impulses of special sense are interpreted in other cortical areas e.g. Visual area: posterior part of the occipital lobe Auditory area: temporal lobe bordering the lateral sulcus Olfactory area: deep inside the temporal lobe  Cerebral Cortex Functional areas of the cerebral cortex: Functional areas Location Function The primary motor area Anterior to the Allow us to consciously move our central sulcus in the skeletal muscles frontal lobe Control body areas having the finest motor control; the face, mouth & hands Primary motor area: sends impulses to skeletal muscles Broca’s area: involved in our ability to speak  Cerebral Cortex Functional areas of the cerebral cortex: Functional areas Location Function Broca’s area Base of the precentral Motor speech area gyrus If damaged the person will not be Located in only one able to say words properly hemisphere Primary motor area: sends impulses to skeletal muscles Broca’s area: involved in our ability to speak  Cerebral Cortex Functional areas of the cerebral cortex: Functional areas Location Function Anterior association area Anterior part of the Involved in higher intellectual frontal lobe reasoning & socially acceptable behavior Frontal lobe is also responsible for language comprehension & Primary motor area: sends impulses to skeletal complex memories muscles Broca’s area: involved in our ability to speak  Cerebral Cortex Functional areas of the cerebral cortex: Functional areas Location Function Posterior association area Encompasses part of Recognizing pattern & faces, the posterior cortex blending several different inputs into understanding of the whole situation Speech area Junction of the Allows us to sound out words temporal, parietal, & occipital lobes Located only in one cerebral hemisphere  Cerebral White Matter The deeper cerebral white matter composed of fiber tracts carrying impulses to, from, or within the cortex Corpus callosum (Commissures Fibers) connects the cerebral hemispheres and allows the cerebral hemisphere to communicate with one another Association fiber connects areas of hemisphere Projection fiber tracts connect cerebrum with lower CNS centers e.g. brain stem (fig. 7.15)  Cerebral Cortex Basal Nuclei: Most of the gray matter are in the cerebral cortex Basal nuclei are islands of gray matter buried deep within the white matter of the cerebral hemispheres Function: Basal nuclei help regulate voluntary motor activities by modifying instructions sent to the skeletal muscles by the primary motor cortex.  Diencephalon or interbrain Sits on top of the brain stem Enclosed by the cerebral hemispheres Made of three parts: Thalamus Hypothalamus Epithalamus  Diencephalon or interbrain Parts Location Function Thalamus Surrounds the shallow third The relay station for sensory ventricle of the brain impulses passing to the sensory cortex Localization & interpretation of pleasant & unpleasant sensation via the sensory cortex  Diencephalon or interbrain Parts Location Function Hypothalamus Under the thalamus Important autonomic nervous system center Makes up the floor of the diencephalon Helps regulate body temp, water balance, metabolism It is a center for many drives & emotions: limbic system (thirst, appetite, pain, pleasure) Regulates the pituitary gland & produce 2 hormones Reflex center for olfaction  Diencephalon or interbrain Parts Location Function Epithalamus Forms the roof of the Houses the pineal body (an endocrine third ventricle gland) and the choroid plexus of the 3rd ventricle Forms cerebrospinal fluid  Brain Stem It is about a size of a thumb & about 3inch long Attaches to the spinal cord Parts of the brain stem Midbrain Pons Medulla oblongata It provides a pathway for ascending and descending tracts It has many small gray matter areas It produce programmed autonomic behaviors for survival It is associated with control of vital activities  Brain Stem Parts Location Function Mostly composed of tracts of nerve fibers Midbrain Small part of the brain stem Has two bulging fiber tracts – cerebral peduncles Extends from mammillary Has four rounded protrusions – corpora quadrigemina bodies to the pons inferiorly Reflex centers for vision and hearing  Pons The rounded structure that protrude below the midbrain Pons means bridge This area is mostly fiber tracts within CNS Includes nuclei involved in the control of breathing  Medulla Oblongata The lowest part of the brain stem Merges into the spinal cord Includes important fiber tracts in the CNS Contains many nuclei that regulate vital visceral activities It contains centers that control: Heart rate Blood pressure Breathing Swallowing Vomiting  Reticular Formation It is a diffuse mass of gray matter that extends the entire length of the brain stem Involved in motor control of visceral organs e.g. control of smooth muscles of digestive tract Reticular activating system (RAS) plays a role in awake/sleep cycles and consciousness RAS also play a role in filtering sensory inputs streaming via the spinal cord & brain stem daily Damage to this area may lead to prolonged coma Reticular Formation  Cerebellum It is large cauliflower-like structure that projects dorsally from under the occipital lobe of the cerebrum Has two hemispheres with convoluted surfaces It has an outer cortex made up of gray matter & inner region of white matter Provides precise timing and coordination of skeletal muscle & controls balance & initiate correct measures  Objective 10: Name the three meningeal layers and state their functions Objective 11: Discuss the formation and function of cerebrospinal fluid and the blood-brain barrier  Protection of the CNS Nervous tissues are delicate & soft Slight pressure can injure the irreplaceable neuron The brain & spinal cord are enclosed within bone There are three additional barriers of CNS: The meninges Cerebrospinal fluid Blood-brain barrier  Meninges Three connective tissue membranes covering and protecting the CNS structures 1. Dura matter Double-layered external covering surrounding the brain Periosteal layer attached to surface of the skull Meningeal layer – outer covering of the brain They enclose dural venous sinuses that collect venous blood such as the superior sagittal sinus Extends inward to form a fold that attaches the brain to the cranial cavity Its folds : the falx cerebri & the tentorium cerebelli separate the cerebellum from the cerebrum  Meninges 2. Arachnoid mater: The web-like middle meningeal layer Arachnoid means spider & looks like cobweb It spans subarachnoid space to attach it to the innermost membrane (pia mater) Subarachnoid is filled with CSF that is produced by choroid plexuses CSF is absorbed into the venous blood in the dural sinus 3. Pia matter (gentle mother): Clings tightly to the surface of the brain & spinal cord  Cerebrospinal fluid Is a watery broth with components similar to blood plasma It contains less protein & more vitamin C Formed by the choroid plexus Circulated in arachnoid space, ventricles, and central canal of the spinal cord Functions:. Forms a watery cushion to protect the brain & nervous tissue from blows, trauma.. Help brain float to avoid damage due to pressure of its weight  The blood-Brain Barrier The blood-brain barrier keep neuron separated from blood-born substances Includes the least permeable capillaries of the body Excludes many potentially harmful substance Substances diffuse through all plasma Substances prevented membrane Fats and fat soluble molecules Metabolic waste such as Respiratory gases Urea Alcohol Toxins Nicotine Proteins Anesthesia Most drugs Nonessential amino acids & K+ are not only prevented but pumped from the brain into blood