Anatomy Lec Nervous System PDF

ANAPHY LEC NERVOUS SYSTEM The Nervous System Nervous Tissue: Support Cells Functions of the Nervous System Functions of the (Neuroglia)—glia Nervous System Sensory input– gathering information...

ANAPHY LEC NERVOUS SYSTEM The Nervous System Nervous Tissue: Support Cells Functions of the Nervous System Functions of the (Neuroglia)—glia Nervous System Sensory input– gathering information a) Astrocytes To monitor changes occurring inside and outside ▪ Abundant, star-shaped cells the body ▪ Brace neurons Changes = stimuli ▪ Form barrier between capillaries and neurons Integration and make exchanges between the two To process and interpret sensory input and decide ▪ Control the chemical environment of the brain by Integration if action is needed capturing ions and neurotransmitters Motor output A response to integrated stimuli The response activates muscles or glands Structural Classification of the Nervous System Central nervous system (CNS) ▪ Brain and Spinal cord ▪ Acts as integrating and command center– b) Microglia interpret incoming sensory information and issue ▪ Spider-like phagocytes instructions incoming sensory information and ▪ Dispose of debris dead cells and bacteria 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 CNS and back c) Ependymal cells Functional Classification of the Peripheral Nervous ▪ Line cavities of the brain and spinal cord System ▪ Circulate cerebrospinal fluid with cilia Sensory (afferent) division Nerve fibers that carry information d) Oligodendrocytes to the ▪ Wrap their flat extensions tightly around the central nerve around the nerve fibers nervous ▪ Produce myelin sheath around nerve fibers system in the central nervous system Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system Two subdivisions a) Somatic nervous system = voluntary nervous nervous system ▪ Skeletal muscle reflexes such as stretch e) Satellite cells reflex are initiated involuntarily by same fibers ▪ Protect neuron cell bodies b) Autonomic nervous f) Schwann cells system = involuntary ▪ Form myelin sheath in the peripheral nervous nervous system system system ▪ Sympathetic and g) Neuroglia are not able to transmit nerve impulses but parasympathetic do not lose their ability to divide, unlike neurons divisions Organization of the Nervous Nervous Tissue: Neurons System Neurons = nerve cells ▪ Cells specialized to transmit messages Major regions of neurons ▪ Cell body– nucleus and metabolic center of the cell ▪ Processes– fibers that extend from the cell body ANAPHY LEC NERVOUS SYSTEM Neuron Anatomy Functional Classification of Neurons Functional a) Sensory (afferent) neurons ▪ Cell bodies in a ganglion outside the CNS ▪ Carry impulses from the sensory receptors to CNS o Cutaneous (skin) sense organs o Proprioceptors– detect stretch or tension in muscles, tendons, joints b) Motor (efferent) neurons ▪ Cell bodies found in the CNS ▪ Carry impulses from the central nervous system c) Interneurons (association neurons) ▪ Found in neural pathways in the central nervous system o Cell bodies in the CNS Cell body --------------------------------------- ▪ Connect sensory and motor neurons ▪ Nissl substance specialized rough endoplasmic reticulum ▪ Neurofibrils intermediate cytoskeleton that maintains cell shape ▪ Nucleus ▪ Large nucleolus Extensions outside the cell body------- ▪ Dendrites conduct impulses toward the cell body ▪ Axons conduct impulses away from the cell body Structural Classification of Neurons Structural Axons and Nerve Impulses Multipolar neurons– many extensions from the cell body ❖ Axons end in axonal terminals ❖ Axonal terminals contain vesicles with neurotransmitters ❖ Axonal terminals are separated from the next neuron by a gap ▪ Synaptic cleft– gap between adjacent neurons ▪ Synapse– junction between nerves Bipolar neurons– one axon and one dendrite ✓ Rare in adults– in eye and ear only Nerve Fiber Coverings ❖ Schwann cells o produce myelin sheaths in jelly-roll like fashion Unipolar neurons– have a short, single process leaving ❖ Nodes of Ranvier from the cell body o gaps in myelin sheath ✓ Axon conducts nerve impulses both to and from along the axon the cell body Neuron Cell Body Location Most are found in the central nervous system in clusters called nuclei Bundles of nerve fibers in CNS = tracts ✓ Gray matter– cell bodies and unmyelinated Functional Properties of Neurons fibers Two main functions impulse ✓ White matter– myelinated fibers Irritability– ability to respond to stimuli Bundles of nerve fibers in PNS = nerves Conductivity– ability to transmit an impulse Ganglia– collections of cell bodies outside the central The plasma membrane at rest is polarized nervous system Fewer positive ions (usually K+) are inside the cell than outside the cell (usually Na+)  ANAPHY LEC NERVOUS SYSTEM Starting a Nerve Impulse The Reflex Arc Reflex– rapid, predictable, and involuntary responses 1) Depolarization– a stimulus to stimuli depolarizes the neuron’s Reflex arc– direct route from a sensory neuron, to an membrane interneuron, to an effector 2) A deploarized membrane allows sodium (Na+) to allows sodium (Na) to flow inside the membrane 3) The exchange of ions initiates an action potential (nerve impulse) in the neuron The 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 repolarizes the membrane membrane The sodium-potassium pump restores the original configuration This action requires ATP Until repolarization occurs, a neuron cannot conduct Types of Reflexes and Regulation another impulse a) Autonomic reflexes Nerve Impulse Propagation ▪ Smooth muscle regulation ▪ Size of eye pupils The impulse continues to ▪ Heart and blood pressure regulation move toward the cell body ▪ Regulation of glands and sweating Impulses travel faster ▪ Digestive system and elimination regulation when fibers have a myelin b) Somatic reflexes sheath ▪ Activation of skeletal muscles Nerve impulse literally Reflex arcs have a minimum five elements jumps from node to ▪ A sensory receptor– reacts to stimuli node because it cannot ▪ An effector receptor– muscle or gland cross myelin insulation stimulated ▪ Afferent and efferent neurons connecting the two Continuation of the Nerve Impulse between Neurons ▪ The CNS integration center ▪ Impulses are unable to cross the synapse to another nerve Central Nervous System (CNS) ▪ Neurotransmitter is released from a nerve’s axon CNS develops from the embryonic neural tube– a terminal simple tube ▪ The dendrite of the next neuron has receptors that are ▪ The neural tube becomes the brain and spinal cord stimulated by the neurotransmitter ▪ The opening of the neural tube becomes the ▪ An action potential is started in the dendrites of the ventricles next neuron Four chambers within the brain ▪ Transmission of an impulse is an electrochemical Filled with cerebrospinal fluid event Regions of the Brain How Neurons Communicate at Synapses ▪ Cerebral hemispheres ▪ Diencephalon ▪ Brain stem ▪ Cerebellum ANAPHY LEC NERVOUS SYSTEM Cerebral Hemispheres (Cerebrum) Specialized Area of the Cerebrum ▪ Paired (left Cerebral areas involved in special senses and right) Gustatory area (taste) superior Visual area parts of the Auditory area brain Olfactory area ▪ Include Interpretation areas of the cerebrum more than Speech/language region half of the Language comprehension region brain mass General interpretation area ▪ The surface is made of elevated ridges (gyri) and shallow grooves (sulci) Lobes of the Cerebrum ▪ Fissures (deep grooves) divide the cerebrum into lobes ▪ Surface lobes of the cerebrum– named for cranial bone over them cranial bone over them Frontal lobe Parietal lobe Occipital lobe Layers of the Cerebrum Temporal lobe 1) Gray matter Outermost layer Composed mostly of neuron cell bodies Cerebral cortex 2) White matter Fiber tracts inside the gray matter Example: corpus callosum connects hemispheres 3) Basal nuclei → internal islands of gray matter Helps regulate voluntary motor activities by modifying instructions sent to the skeletal muscles Specialized Areas of the Cerebrum Diencephalon—interbrain ▪ Sits on top of the brain stem ❖ Somatic sensory area in parietal lobe- ▪ Enclosed by the cerebral hemispheres receives impulses from the body’s sensory ▪ Made of three parts receptors (except special senses) ✓ Thalamus Occipital lobe– vision and temporal lobe– auditory ✓ Hypothalamus ✓ Epithalamus ❖ 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 localization and interpretation ANAPHY LEC NERVOUS SYSTEM Hypothalamus Cerebellum Under the thalamus Two hemispheres with convoluted surfaces Important autonomic nervous system center Provides involuntary coordination of body ✓ Helps regulate body temperature movements– of skeletal muscles, balance ✓ Controls water balance movements– of skeletal muscles, balance and ✓ Regulates metabolism equilibrium An important part of the limbic system Automatic pilot– continually comparing brain’s (emotions)– emotional-visceral brain intentions with actual body performance 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 Brain Stem Attaches to the spinal cord Parts of the brain stem o Midbrain o Pons o Medulla oblongata Protection of the Central Nervous System Midbrain ▪ Scalp and skin Mostly composed of tracts of nerve fibers ▪ Skull and vertebral column The cerebral aqueduct– the canal that connects ▪ Meninges the 3rd ventricle of the diencephalon to the 4th ▪ Cerebrospinal fluid ventricle ▪ Blood brain barrier 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 Includes nuclei involved in the control of breathing Medulla Oblongata Meninges The lowest part of the brain stem a) Dura mater Merges into the spinal cord Double-layered external covering the brain Includes important fiber tracts ▪ Periosteum– attached to surface of the skull Contains important control centers ▪ Meningeal layer– outer covering of the brain ✓ Heart rate control and continues as the dura matter of the ✓ Blood pressure regulation spinal cord ✓ Breathing Folds inward in several areas that attaches the ✓ Swallowing brain to cranial cavity ✓ Vomiting b) Arachnoid layer Reticular Formation Middle layer that is web-like Diffuse mass of gray matter along the brain c) Pia mater stem organs Internal layer that clings to the surface of Involved in motor control of visceral organs the brain following every fold Reticular activating system plays a role in d) Subarachnoid space filled with cerebrospinal fluid awake/sleep cycles and consciousness Arachnoid villi– projections of arachnoid Damage here results in a permanent coma membrane protruding through the dura matter 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 Circulated in arachnoid space, ventricles, and central canal of the spinal cord ANAPHY LEC NERVOUS SYSTEM Alzheimer’s Disease ▪ Progressive degenerative brain disease ▪ Mostly seen in the elderly, but may begin in middle age ▪ Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons ▪ Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death Spinal Cord ▪ Extends from the medulla oblongata to the region of T12 ▪ Below T12 is the cauda equina (a collection of equina (a collection of spinal nerves) ▪ Enlargements occur in the cervical and lumbar regions Blood Brain Barrier Spinal Cord Anatomy ▪ Includes the least permeable capillaries of the body– only H2O, glucose, and essential amino Internal gray matter- mostly cell bodies that surround the acids get through central canal of the cord ▪ Excludes many potentially harmful substances Dorsal (posterior) horns ▪ Useless against some substances Anterior (ventral) horns o Fats and fat soluble molecules ▪ Contains motor neurons of the somatic o Respiratory gases nervous system, which send their axons out the o Alcohol ventral root o Nicotine Together they fuse to form the spinal nerves o Anesthesia Nerves leave at the level of each vertebrae Cell bodies of sensory neurons, whose fibers enter the Traumatic Brain Injuries cord by the dorsal root, are found in an enlarged area called the dorsal root ganglion a) Concussion Damage to this area causes sensation from the body Slight brain injury– dizzy or lose area served to be lost consciousness briefly Exterior white mater– conduction tracts No permanent brain damage Posterior, lateral, and anterior columns b) Contusion ▪ Each contains a number of fiber tracts make up of Nervous tissue destruction occurs- does not axons with the same destination and function regenerate Central canal filled with cerebrospinal fluid If cortex is damaged, coma for hours or life c) Cerebral edema Peripheral Nervous System Swelling from the inflammatory response Nerves and ganglia outside the central nervous system May compress and kill brain tissue Nerve = bundle of neuron fibers Cerebrovascular Accident (CVA) Neuron fibers are bundled by a connective tissue sheath Commonly called a stroke Structure of a Nerve The result of a clot or a ruptured blood vessel ▪ Endoneurium surrounds supplying a region of the brain each fiber Brain tissue supplied with oxygen from that ▪ Groups of fibers are blood source dies bound into fascicles Loss of some functions or death may result bound into fascicles by perineurium ▪ Fascicles are bound together by epineurium ANAPHY LEC NERVOUS SYSTEM Classification of Nerves Spinal Nerves Classified according to the direction in which they transmit There is a pair of spinal nerves at the level of each impulses vertebrae for a total of 31 pairs Mixed nerves– carry both sensory and motor fibers– Spinal nerves are formed by the combination of the spinal nerves motor fibers– spinal nerves ventral and dorsal roots of the spinal cord Afferent (sensory) nerves– carry impulses toward Spinal nerves are named for the region from which the CNS they arise Efferent (motor) nerves– carry impulses away from the CNS Cranial Nerves ▪ 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 ▪ I Olfactory nerve– sensory for smell ▪ II Optic nerve– sensory for vision Anatomy of Spinal Nerves ▪ III Oculomotor nerve– motor fibers to eye Spinal nerves divide soon after leaving the spinal cord muscles a) Dorsal rami– ▪ IV Trochlear– motor fiber to eye muscles serve the skin ▪ V Trigeminal nerve– sensory for the face; motor and muscles of fibers to chewing muscles the skin and ▪ VI Abducens nerve- motor fibers to eye muscles muscles of the motor fibers to eye muscles posterior trunk ▪ VII Facial nerve– sensory for taste; motor fibers posterior trunk to the face b) Ventral rami– ▪ VIII Vestibulocochlear nerve- sensory for forms a complex balance and hearing of networks ▪ IX Glossopharyngeal nerve– sensory for taste; (plexus) for the motor fibers to the pharynx anterior, which serve the motor and sensory needs of ▪ X Vagus nerves– sensory and motor fibers for the limbs pharynx, larynx, and viscera fibers for pharynx, larynx, and viscera ▪ XI Accessory nerve– motor fibers to neck and upper back ▪ XII Hypoglossal nerve– motor fibers to tongue Autonomic Nervous System ❖ The involuntary branch of the nervous system ❖ Consists of only motor nerves ❖ Divided into two divisions a) Sympathetic division– mobilizes the body b) 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 ANAPHY LEC NERVOUS SYSTEM Effector organs Autonomic Functioning Somatic– skeletal muscle Autonomic– smooth muscle, cardiac muscle, and glands Sympathetic– “fight-or-flight” Neurotransmitters ✓ Response to unusual stimulus Somatic– always use acetylcholine ✓ Takes over to increase activities Autominic– use acetylcholine, epinephrine, or ✓ Remember as the “E” division = exercise, norepinephrine excitement, emergency, and embarrassment Parasympathetic– housekeeping activites ✓ Conserves energy ✓ Maintains daily necessary body functions ✓ Remember as the “D” division- digestion, defecation, and diuresis Development Aspects of the Nervous System ❖ The nervous system is formed during the first month of embryonic development ❖ Any maternal infection can have extremely harmful effects ❖ The hypothalamus is one of the last areas of the brain to develop– contains centers for regulating body temperature ❖ No more neurons are formed after birth, but growth Anatomy of the Parasympathetic Division and maturation continues for several years largely Originates from the brain stem and S2– S4 due to myelination Neurons in the cranial region send axons out in cranial ❖ The brain reaches maximum weight as a young nerves to the head and neck organs adult They synapse with the second motor neuron They synapse with the second motor neuron in a terminal ganglion Terminal ganglia are at the effector organs Always uses acetylcholine as a neurotransmitter Anatomy of the Sympathetic Division–– thoracolumbar division thoracolumbar division Originates from T1 through L2 Preganglionic axons leave the cord in the ventral root, enter the spinal nerve, then pass through a ramus communications, to enter a sympathetic chain communications, to enter a sympathetic chain ganglion at the sympathetic chain (trunk) (near the spinal cord) Short pre-ganglionic neuron and long postganglionic neuron transmit impulse from CNS to the effector Norepinephrine and epinephrine are neurotransmitters to the effector organs ANAPHY LEC NERVOUS SYSTEM