Nervous System PDF Notes

Transes by: Joshua Matthew Cayaban (@__mateorite) & Naomi Ashley Jose (@nm.shly) TOPIC #8 NERVOUS SYSTEM FUNCTIONS OF THE NERVOUS SYSTEM 1. Receiving Sensory Input - gathering information - To monitor...

Transes by: Joshua Matthew Cayaban (@__mateorite) & Naomi Ashley Jose (@nm.shly) TOPIC #8 NERVOUS SYSTEM FUNCTIONS OF THE NERVOUS SYSTEM 1. Receiving Sensory Input - gathering information - To monitor changes occurring inside and outside the body - Changes = stimuli - We are aware of sensations from some stimuli, such as vision, hearing, taste, smell, touch, pain, body position, and temperature. Other stimuli, such as blood pH, blood gases, and blood pressure, are processed at a subconscious level. 2. Integration - To process and interpret sensory input and decide if action is needed. - The brain and spinal cord are the major organs for processing sensory input and initiating responses. 3. Motor Output Organization of the Nervous System - A response to integrated stimuli - The response activates muscles or glands 4. Maintaining Homeostasis - The nervous system can stimulate or inhibit the activities of other systems to help maintain a constant internal environment. 5. Establishing and Maintaining Mental Activity - The brain is the center of mental activity, including consciousness, memory, and thinking. DIVISIONS OF THE NERVOUS SYSTEM Central Nervous System (CNS) ○ Brain and Spinal Cord ○ Acts as integrating and command center – interpret incoming sensory information and issue instructions based on past experiences and current conditions Peripheral Nervous System (PNS) ○ Nerves outside the brain and spinal cord ○ Link all parts of the body by carrying impulses to the CELLS OF THE NERVOUS SYSTEM CNS and back NEURONS (Nerve Cell) FUNCTIONAL CLASSIFICATION OF THE PNS Receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs. Cell Body Sensory (Afferent) Division ○ nucleus and metabolic center of the cell ○ Nerve fibers that carry information to the central ○ Nissl substance – specialized rough endoplasmic nervous system reticulum ○ The neurons that transmit action potentials from the ○ Neurofibrils – intermediate cytoskeleton that periphery to the CNS are called sensory neurons. maintains cell shape Motor (Efferent) Division ○ Nerve fibers that carry impulses away from the central nervous system ○ The neurons that transmit action potentials from the CNS toward the periphery are called motor neurons. ○ Somatic Nervous System - voluntary Skeletal muscle reflexes such as stretch reflex are initiated involuntarily by same fibers ○ Autonomic Nervous System - involuntary Transmits action potentials from the CNS to Processes cardiac muscle, smooth muscle, and glands. ○ fibers that extend from the cell body Sympathetic and Parasympathetic divisions ○ Dendrites conduct impulses toward the cell body usually receive information from other neurons or from sensory receptors and  transmit the information toward the neuron cell body. ○ Axon conduct impulses away from the cell body axons can be surrounded by a highly specialized insulating layer of cells called the myelin sheath. Axons end in axonal terminals Axonal terminals contain vesicles with neurotransmitters Oligodendrocytes Axonal terminals are separated from the ○ Wrap their flat extensions tightly around the nerve next neuron by a gap fibers Synaptic cleft – gap between ○ Produce myelin sheath around nerve fibers in the adjacent neurons central nervous system Synapse – junction between nerves NERVOUS TISSUE: SUPPORT CELLS (NEUROGLIA) - GLIA Glial cells are the supportive cells of the CNS and PNS, meaning these cells do not conduct action potentials. Instead, glial cells carry out different functions that enhance neuron function and maintain normal conditions within nervous tissue. Astrocytes ○ Abundant, star-shaped cells ○ Brace neurons Satellite Cells ○ Form barrier between capillaries and neurons and ○ Protect neuron cell bodies make exchanges between the two Schwann Cells ○ Control the chemical environment of the brain by ○ Form myelin sheath in the peripheral nervous capturing ions and neurotransmitters system ○ participate with the blood vessel endothelium to form a ○ provide insulating material around axons permeability barrier, called the blood-brain barrier Neuroglia are not able to transmit nerve impulses but do not lose their ability to divide, unlike neurons Myelin Sheaths– fatty, protective wrapping around axons Microglia of some neurons that are formed by oligodendrocytes ○ Spider-like phagocytes (CNS) and Schwann cells (PNS); serve as an excellent ○ Dispose of debris – dead cells and bacteria insulator that prevents almost all ion movements across cell membrane Nodes of Ranvier: gaps in the myelin sheath where the ion movement occurs & action potential develops NEURON CELL BODY LOCATION Most are found in the central nervous system in clusters called nuclei Ependymal Cells Bundles of nerve fibers in CNS = tracts ○ Line cavities of the brain and spinal cord ○ Gray matter ○ Circulate cerebrospinal fluid with cilia cell bodies and unmyelinated fibers In the 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. In the PNS, a cluster of neuron cell bodies is called a ganglion. ○ White matter  myelinated fibers White matter of the CNS forms nerve tracts. White matter of the PNS consists of bundles of axons and associated connective tissue that form nerves. Bundles of nerve fibers in PNS = nerves ○ Ganglia – collections of cell bodies outside the central nervous system Unipolar Neurons ○ have a short, single process leaving the cell body ○ Axon conducts nerve impulses both to and from FUNCTIONAL CLASSIFICATION OF NEURONS the cell body Sensory (Afferent) Neurons ○ Cell bodies in a ganglion outside the CNS ○ Carry impulses from the sensory receptors to CNS Cutaneous (skin) sense organs Proprioceptors – detect stretch or tension in muscles, tendons, joints Motor (Efferent) Neurons ○ Cell bodies found in the CNS ○ Carry impulses from the central nervous system Interneurons (Association Neurons) ○ Found in neural pathways in the central nervous system ○ Cell bodies in the CNS ○ Connect sensory and motor neurons NEURON CLASSIFICATION FUNCTIONAL PROPERTIES OF NEURONS Irritability – ability to respond to stimuli Conductivity – ability to transmit an impulse The plasma membrane at rest is polarized ○ Fewer positive ions (usually K+) are inside the cell than outside the cell (usually Na+) RESTING MEMBRANE POTENTIAL the point of equilibrium at which the tendency for K+ to move down its concentration gradient out of the cells is balanced by the negative charge within the cell, which Multipolar Neurons tends to attract the K+ back into the cell. Generated by three main factors: ○ many extensions from the cell body ○ a high concentration of K+ immediately inside the ○ have many dendrites and a single axon cell membrane ○ Most of the neurons within the CNS and nearly all ○ a higher concentration of Na+ immediately motor neurons are multipolar outside the cell membrane ○ greater permeability of the cell membrane to K+ than to Na+ SODIUM POTASSIUM PUMP required to maintain the greater concentration of Na+ outside the cell membrane and K+ inside; occurs in order to compensate for the constant leakage of ions across the membrane. Two Basic Ion Channels: Bipolar Neurons ○ Leak Channels - always open; K+ channels are ○ one axon and one dendrite much greater than Na+ channels ○ located in some sensory organs, such as in the ○ Gated Channels - closed until opened by retina of the eye and in the nasal cavity. specific signals  Chemically Gated: opened by neurotransmitters or other chemicals Voltage-Gated: opened by a change in membrane potential STARTING A NERVE IMPULSE Depolarization – a stimulus depolarizes the neuron’s membrane A depolarized membrane allows sodium (Na+ ) to flow inside the membrane The exchange of ions initiates an action potential (nerve impulse) in the neuron ACTION POTENTIAL If the action potential (nerve impulse) starts, it is propagated over the entire axon – all-or-none response Potassium ions rush out of the neuron after sodium ions rush in, which depolarizes the membrane The sodium-potassium pump restores the original configuration This action requires ATP Until repolarization occurs, a neuron cannot conduct another impulse TYPES OF ACTION POTENTIAL CONDUCTION Continuous Conduction NERVE IMPULSE PROPAGATION ○ occurs in unmyelinated axons; an action potential in one part of a cell membrane stimulates local The impulse continues to move toward the cell body currents in adjacent parts Impulses travel faster when fibers have a myelin Saltatory Conduction sheath ○ occurs in myelinated axons; an action potential Nerve impulse literally jumps from node to node because it jumps from one node of Ranvier to the next along cannot cross myelin insulation the length of the axon SYNAPSE A junction where the axon of one neuron interacts with another neuron or with cells of an effector organ; involved the release of neurotransmitter (ex: neuromuscular junction) Presynaptic Terminal ○ end of axon; has synaptic vesicles that store neurotransmitters Postsynaptic Membrane ○ membrane of the dendrite or effector cell Impulses are unable to cross the synapse to another Synaptic Cleft nerve ○ space separating the presynaptic terminal & ○ Neurotransmitter is released from a nerve’s axon postsynaptic membrane terminal ○ The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter  ○ An action potential is started in the dendrites of the next neuron REGIONS OF THE BRAIN Transmission of an impulse is an electrochemical event REFLEX ARC Reflex ○ rapid, predictable, and involuntary responses to stimuli ○ allow a person to react to stimuli more quickly than is possible if conscious thought is involved. Reflex arc ○ direct route from a sensory neuron, to an CEREBRAL HEMISPHERE (CEREBRUM) interneuron, to an effector ○ basic functional unit of the nervous system Paired (left and right) superior parts of the brain because it is the smallest, simplest pathway capable of receiving a stimulus and yielding a Include more than half of the brain mass response The surface is made of elevated ridges (gyri) and (sulci) Five Basic Components of Reflex Arc: ○ Sensory Receptor - pick up the stimulus LOBES OF THE CEREBRUM ○ Sensory Neuron - afferent; send stimulus to Fissures (deep grooves) divide the cerebrum into lobes interneurons in spinal cord Surface lobes of the cerebrum – named for cranial bone ○ Interneurons - located in CNS and connect to motor neurons; process stimulus to some over them reflexes ○ Frontal lobe ○ Motor Neuron - efferent; send response to ○ Parietal lobe effector 5. Effector Organ 3 muscles or glands ○ Occipital lobe ○ Temporal lobe Frontal Lobe ○ vital in control of voluntary motor functions, TYPES OF REFLEX AND REGULATION motivation, aggression, mood, & olfactory reception Autonomic reflexes Parietal Lobe ○ Smooth muscle regulation ○ principal center for receiving & consciously ○ Size of eye pupils perceiving most sensory information such as ○ Heart and blood pressure regulation touch, pain, temperature, and balance ○ Regulation of glands and sweating Occipital Lobe ○ Digestive system and elimination regulation ○ functions in receiving and perceiving visual input Somatic reflexes Temporal Lobe ○ Activation of skeletal muscles ○ Involved in olfactory & auditory sensations; plays Reflex arcs have a minimum five elements an important role in memory ○ A sensory receptor – reacts to stimuli Psychic Cortex: anterior & inferior ○ An effector receptor – muscle or gland stimulated portion of temporal lobe associated with ○ Afferent and efferent neurons connecting the two abstract thought & judgment ○ The CNS integration center Insula / Fifth Lobe ○ deep within the lateral fissure; it processes CENTRAL NERVOUS SYSTEM (CNS) interoception ○ the sensory information on physiologic condition CNS develops from the embryonic neural tube – a simple of body (heartbeat & blood pressure regulation & tube gastric motility) The neural tube becomes the brain and spinal cord The opening of the neural tube becomes the ventricles SPECIALIZED AREAS OF THE CEREBRUM ○ Four chambers within the brain Somatic sensory area in parietal lobe – receives impulses ○ Filled with cerebrospinal fluid from the body’s sensory receptors (except special senses)  Occipital lobe – vision and temporal lobe – auditory Primary motor area – sends impulses to skeletal muscles – frontal lobe Broca’s area – involved in our ability to speak – base of the precentral gyrus THALAMUS Surrounds the third ventricle of the brain The relay station for sensory impulses passing upward to the sensory cortex Transfers impulses to the correct part of the cortex for Cerebral areas involved in special senses localization and interpretation ○ Gustatory area (taste) ○ Visual area HYPOTHALAMUS ○ Auditory area Under the thalamus ○ Olfactory area Important autonomic nervous system center Interpretation areas of the cerebrum ○ Helps regulate body temperature ○ Speech/language region ○ Controls water balance ○ Language comprehension region ○ Regulates metabolism ○ General interpretation area An important part of the limbic system (emotions) – emotional-visceral brain The pituitary gland is attached to and regulated by the hypothalamus EPITHALAMUS Forms the roof of the third ventricle Houses the pineal body (an endocrine gland) Includes the choroid plexus – forms cerebrospinal fluid LAYERS OF THE CEREBRUM Gray matter ○ Outermost layer ○ Composed mostly of neuron cell bodies ○ Cerebral cortex White matter ○ Fiber tracts inside the gray matter ○ Example: corpus callosum connects hemispheres BRAIN STEM Basal nuclei – internal islands of gray matter Helps regulate voluntary motor activities by modifying Attaches to the spinal cord instructions sent to the skeletal muscles Parts of the brain stem: ○ Midbrain DIENCEPHALON - INTERBRAIN ○ Pons ○ Medulla oblongata Sits on top of the brain stem Enclosed by the cerebral hemispheres MIDBRAIN Made of three parts Mostly composed of tracts of nerve fibers ○ Thalamus The cerebral aqueduct – canal that connects the 3rd ○ Hypothalamus ventricle of the diencephalon to the 4th ventricle ○ Epithalamus Has two bulging fiber tracts – cerebral peduncles – convey ascending and descending impulses Has four rounded protrusions – corpora quadrigemina – Reflex centers for vision and hearing PONS  The bulging center part of the brain stem Mostly composed of fiber tracts PROTECTION OF THE CNS Includes nuclei involved in the control of breathing MENINGES MEDULLA OBLONGATA Dura mater The lowest part of the brain stem ○ Double-layered external covering the brain Merges into the spinal cord Periosteum – attached to surface of the Includes important fiber tracts skull Contains important control centers Meningeal layer – outer covering of the ○ Heart rate control brain and continues as the dura mater of ○ Blood pressure regulation the spinal cord ○ Breathing ○ Folds inward in several areas that attaches the ○ Swallowing brain to cranial cavity ○ Vomiting Arachnoid layer ○ Middle layer that is web-like Pia mater ○ Internal layer that clings to the surface of the brain following every fold Subarachnoid space filled with cerebrospinal fluid ○ Arachnoid villi – projections of arachnoid membrane protruding through the dura mater CEREBROSPINAL FLUID Similar to blood plasma composition ○ Less protein, more vitamin C, different ions Formed by the choroid plexus Forms a watery cushion to protect the brain RETICULAR FORMATION Circulated in arachnoid space, ventricles, and central Diffuse mass of gray matter along the brain stem canal of the spinal cord Involved in motor control of visceral organs Reticular activating system plays a role in awake/sleep cycles and consciousness Damage here results in a permanent coma CEREBELLUM Two hemispheres with convoluted surfaces Provides involuntary coordination of body movements – of skeletal muscles, balance and equilibrium Automatic pilot – continually comparing brain’s intentions with actual body performance BLOOD BRAIN BARRIER Includes the least permeable capillaries of the body – only H2O, glucose, and essential amino acids get through Excludes many potentially harmful substances Useless against some substances ○ Fats and fat soluble molecules Respiratory gasses ○ Alcohol  ○ Nicotine Cell bodies of sensory neurons, whose fibers enter the ○ Anesthesia cord by the dorsal root, are found in an enlarged area called the dorsal root ganglion TRAUMATIC BRAIN INJURIES Damage to this area causes sensation from the body area served to be lost Concussion ○ Slight brain injury – dizzy or lose consciousness briefly ○ No permanent brain damage Contusion ○ Nervous tissue destruction occurs - does not regenerate ○ If cortex is damaged, coma for hours or life Cerebral edema ○ Swelling from the inflammatory response ○ May compress and kill brain tissue Cerebrovascular Accident (CVA) ○ Commonly called a stroke ○ The result of a clot or a ruptured blood vessel supplying a region of the brain Exterior white matter ○ Brain tissue supplied with oxygen from that blood ○ Conduction tracts Posterior, lateral, and anterior source dies columns ○ Loss of some functions or death may result ○ Each contains a number of fiber tracts make up Alzheimer’s Disease of axons with the same destination and function ○ Progressive degenerative brain disease ○ Mostly seen in the elderly, but may begin in PERIPHERAL NERVOUS SYSTEM middle age ○ Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons Nerves and ganglia outside the central nervous system ○ Victims experience memory loss, irritability, Nerve = bundle of neuron fibers Neuron fibers are confusion and ultimately, hallucinations and death bundled by a connective tissue sheath STRUCTURE OF A NERVE SPINAL CORD Endoneurium surrounds each fiber Extends from the medulla oblongata to the region of T12 Groups of fibers are bound into fascicles by perineurium Below T12 is the cauda equina (a collection of spinal Fascicles are bound together by epineurium nerves) Enlargements occur in the cervical and lumbar regions CLASSIFICATION OF NERVES Classified according to the direction in which they transmit impulses SPINAL CORD ANATOMY ○ Mixed nerves – carry both sensory and motor Internal gray matter fibers – spinal nerves ○ Mostly cell bodies that surround the central canal ○ Afferent (sensory) nerves – carry impulses of the cord toward the CNS Dorsal (posterior) horns ○ Efferent (motor) nerves – carry impulses away Anterior (ventral) horns from the CNS ○ Contains motor neurons of the somatic nervous system, which send their axons out the ventral CRANIAL NERVES root ○ Together they fuse to form the spinal nerves ○ Nerves leave at the level of each vertebral 12 pairs of nerves that mostly serve the head and neck Numbered in order, front to back – names reveal structures they control  Most are mixed nerves, but three are sensory only Optic, olfactory, and vestibulocochlear Spinal nerves divide soon after leaving the spinal cord Dorsal rami – serve the skin and muscles of the posterior trunk Ventral rami – forms a complex of networks (plexus) for the anterior, which serve the motor and sensory needs of I Olfactory nerve – sensory for smell the limbs II Optic nerve – sensory for vision III Oculomotor nerve – motor fibers to eye muscles IV Trochlear – motor fiber to eye muscles V Trigeminal nerve – sensory for the face; motor fibers to chewing muscles VI Abducens nerve – motor fibers to eye muscles VII Facial nerve – sensory for taste; motor fibers to the face VIII Vestibulocochlear nerve – sensory for balance and hearing IX Glossopharyngeal nerve – sensory for taste; motor fibers to the pharynx X Vagus nerves – sensory and motor fibers for pharynx, larynx, and viscera XI Accessory nerve – motor fibers to neck and upper back XII Hypoglossal nerve – motor fibers to tongue Oh, Oh, Oh, To, Touch, And, Feel, Vivianne, Good, Vagina, And, Hip SPINAL NERVES There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs Spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal cord Spinal nerves are named for the region from which they arise AUTONOMIC NERVOUS SYSTEM The involuntary branch of the nervous system Consists of only motor nerves Divided into two divisions ○ Sympathetic division – mobilizes the body ○ Parasympathetic division – allows body to unwind DIFFERENCES BETWEEN SOMATIC AND AUTONOMIC NERVOUS SYSTEMS Nerves  ○ Somatic – one motor neuron – axons extend all the way to the skeletal muscle they serve ○ Autonomic – preganglionic and postganglionic nerves Effector organs ○ Somatic – skeletal muscle ○ Autonomic – smooth muscle, cardiac muscle, and glands Neurotransmitters ○ Somatic – always use acetylcholine ○ Autominic – use acetylcholine, epinephrine, or norepinephrine AUTONOMIC FUNCTIONING Sympathetic – “fight-or-flight” ○ Response to unusual stimulus ANATOMY OF PARASYMPATHETIC DIVISION ○ Takes over to increase activities ○ Remember as the “E” division = exercise, Originates from the brain stem and S2 – S4 excitement, emergency, and embarrassment Neurons in the cranial region send axons out in cranial Parasympathetic – housekeeping activities nerves to the head and neck organs ○ Conserves energy They synapse with the second motor neuron in a terminal ○ Maintains daily necessary body functions ganglion ○ Remember as the “D” division - digestion, Terminal ganglia are at the effector organs defecation, and diuresis Always uses acetylcholine as a neurotransmitter DEVELOPMENT ASPECTS OF THE NERVOUS SYSTEM The nervous system is formed during the first month of ANATOMY OF SYMPATHETIC DIVISION embryonic development Any maternal infection can have extremely harmful effects Originates from T1 through L2 The hypothalamus is one of the last areas of the brain to Preganglionic axons leave the cord in the ventral root, develop – contains centers for regulating body enter the spinal nerve, then pass through a ramus temperature communications, to enter a sympathetic chain ganglion at No more neurons are formed after birth, but growth and the sympathetic chain (trunk) (near the spinal cord) maturation continues for several years largely due to Short preganglionic neuron and long postganglionic myelination neuron transmit impulse from CNS to the effector The brain reaches maximum weight as a young adult Norepinephrine and epinephrine are neurotransmitters to the effector organs