Anatomy of the Nervous System PDF

ANAPHY (NERVOUS SYSTEM) NERVOUS SYSTEM - The master body system FUNCTIONS: 1. SENSORY INPUT - gathering information To monitor changes occurring inside and outside the body Changes = stimuli 2. INTEGRATION - to process and interpret sensory input and...

ANAPHY (NERVOUS SYSTEM) NERVOUS SYSTEM - The master body system FUNCTIONS: 1. SENSORY INPUT - gathering information To monitor changes occurring inside and outside the body Changes = stimuli 2. INTEGRATION - to process and interpret sensory input and decide if action is needed 3. MOTOR OUTPUT - a response to integrated stimuli, the response activates muscles or glands - The muscles and the glands are the effectors or effector organs STRUCTURAL CLASSIFICATION OF THE NERVOUS SYSTEM 1. CENTRAL NERVOUS SYSTEM (CNS) Brain and spinal cord CNS develops from the embryonic neural tube The neural tube becomes the brain and spinal cord The opening of the neural tube becomes the ventricles: - 4 chambers within the brain - Filled with cerebrospinal fluid (CSF) 2. PERIPHERAL NERVOUS SYSTEM (PNS) Nerve outside the brain and spinal cord NERVES (bundle of neuron fibers) leave at the level of each vertebra GANGLIA (neuron cell bodies) NEURONS - cells capable of generating communication between different locations FUNCTIONAL CLASSIFICATION OF NEURONS 1. SENSORY (AFFERENT) DIVISION (PNS) Nerve fibers that carry information to the central nervous system Means “to” or “toward” Carry impulses from the sensory receptors Cutaneous sense organs Found in the dorsal root of the spinal cord Also called as dorsal root ganglion Proprioceptors - detect stretch or tension 2. MOTOR (EFFERENT) DIVISION (PNS) Nerve fibers that carry impulses away from the central nervous system Takes care of the nerve fibers that carry the motor output Located in the ventral or anterior horn of the gray matter Means “away” or “exiting” 2 SUBDIVISIONS: A. SOMATIC NERVOUS SYSTEM - voluntary, conscious perception B. AUTONOMIC NERVOUS SYSTEM (ANS) - involuntary, visceral nervous system, consists of only motor nerves - PARASYMPATHETIC AND SYMPATHETIC ANATOMY OF THE SYMPATHETIC DIVISION Originates from T1 through L2 Ganglia are at the sympathetic trunk(near the spinal cord) Short preganglionic neuron and long postganglionic neuron transmit impulse from CNS to the effector Norepinephrine and epinephrine are neurotransmitters to the effector organs Another name is thoracolumbar division ANATOMY OF THE PARASYMPATHETIC DIVISION  Originates from the brain stem and S1 through S4 Terminal ganglia are at the effector organs Always uses acetylcholine as a neurotransmitter Another name is craniosacral division AUTONOMIC FUNCTIONING SYMPATHETIC -fight-or-flight - Response to unusual stimulus - The “E division” = exercise, excitement, emergency, and embarrassment - Takes over to increase activities PARASYMPATHETIC - Housekeeping activities - Conserves energy - Maintains daily necessary body functions - Remember as the “ D division” = digestion, defecation, and diuresis - Diuresis is urine formation DIFFERENCES BETWEEN SOMATIC AND AUTONOMIC NERVOUS SYSTEMS: NERVES: SOMATIC - one motor neuron AUTONOMIC - preganglionic and postganglionic nerves EFFECTOR ORGANS: SOMATIC - skeletal muscle AUTONOMIC - smooth muscle, cardiac muscle, and glands NEUROTRANSMITTERS SOMATIC - always use acetylcholine (ACh) AUTONOMIC - use acetylcholine, epinephrine, or norepinephrine 3. INTERNEURONS (CNS) Found in neural pathways in the CNS Connect sensory and motor neurons Found in the lateral horn of the gray matter NERVOUS TISSUE: SUPPORT CELLS (NEUROGLIA or GLIAL CELLS) GLIAL CELLS - provides structure and support to the neurons and their activities CENTRAL NERVOUS SYSTEM 1. ASTROCYTES - Most abundant, star-shaped cells - Brace neurons - From barrier between capillaries and neurons - Control the chemical environment of the brain 2. MICROGLIA - Spider-like phagocytes - Dispose of debris - Act as resident immune cells 3. EPENDYMAL CELLS - Line cavities of the brain and spinal cord - Cavity of the brain = ventricle, Cavity in the spinal cord = central canal - Circulate cerebrospinal fluid (CSF) - Filters blood to make CSF 4. OLIGODENDROCYTES - Produce myelin sheath around nerve fibers in the CNS - Myelin sheath acts as an insulator that protects the nerve fibers or the axon from damage - Myelin sheath tends to facilitate the transmission of electrical impulses - Glial cell types that insulate axons in the CNS PERIPHERAL NERVOUS SYSTEM 1. SATELLITE CELLS - protect neuron cell bodies 2. SCHWANN CELLS - form myelin sheath in the PNS NERVOUS TISSUE: NEURONS Neurons = nerve cells Cells specialized to transmit messages Exclusive property: conductivity MAJOR REGIONS OF A NEURON: 1. CELL BODY OR SOMA - nucleus and metabolic center of the cell 2. PROCESSES - fibers that extend from the body: AXON - transmit impulses AWAY from the neuron cell body - Longer process DENDRITE - transmit impulses TOWARDS the neuron cell body - Shorter process NEURON ANATOMY: CELL BODY OR SOMA 1. NUCLEUS 2. NUCLEOLUS 3. NISSL SUBSTANCE or GRANULES - specialized rough endoplasmic reticulum 4. MITOCHONDRIA - supplies ATP 5. NEUROFIBRILS - intermediate cytoskeleton that maintains cell shape CELL PROCESSES ❖ AXONS - transmit impulses AWAY from the neuron cell body - Longer process - Common name: Nerve fiber - Some axons are myelinated, some axons are unmyelinated - When they are myelinated, they are provided with myelin sheath. Unmyelinated’s appearance is color gray - Arises at the axon hillock and at the distal end they become knob-like structures called axon terminal ❖ DENDRITES - transmit impulses TOWARDS the neuron cell body - Shorter process NEURON CELL BODY LOCATION Most are found in the central nervous system Gray matter - contains cell bodies and unmyelinated fibers NUCLEI - cluster of cell bodies within the white matter of the central nervous system GANGLIA - collection of cell bodies outside the central nervous system (must be in the PNS) NERVE FIBER COVERINGS SCHWANN CELLS - produce myelin sheaths in jelly-roll like fashion, generally white - Found mostly in the white matter NODES OF RANVIER - gaps in myelin sheath along the axon - Facilitates the transmission of electrical impulses AXONS AND NERVE IMPULSES Axonal terminals contain vesicles with neurotransmitters Axonal terminals are separated from the next neuron by a gap SYNAPTIC CLEFT - gap between adjacent neurons - Bait in the interstitial fluid SYNAPSE - junction between nerves NEURON CLASSIFICATION GRAY MATTER - butterfly-shaped REGIONS: VENTRAL/ANTERIOR HORN - contains the cell bodies of motor neurons that are sending out motor signals to the skeletal muscle DORSAL/POSTERIOR HORN - contains the axons of sensory neurons INTERMEDIOLATERAL HORN - contains neurons of the autonomic nervous system  CENTRAL CANAL - contains the cerebrospinal fluid WHITE MATTER - outside the gray matter ROOTS - the lateral projections of the spinal cord DORSAL ROOT VENTRAL ROOT STRUCTURAL CLASSIFICATION OF NEURONS - Focuses on the number of processes 1. MULTIPOLAR NEURONS - many extensions from the cell body - Most common type of neuron according to structure - Multiple dendrites, one axon 2. BIPOLAR NEURON - one axon, one dendrite - Types of neurons that are found in the eyes and the ears 3. UNIPOLAR NEURONS - have a short single process leaving the cell body FUNCTIONAL PROPERTIES OF NEURONS 1. IRRITABILITY - ability to respond to stimuli, also called responsiveness 2. CONDUCTIVITY - ability to transmit an impulse - The plasma at rest is polarized - Fewer positive ions are inside the cell than outside the cell STARTING A NERVE IMPULSE DEPOLARIZATION - a stimulus depolarizes the neuron’s membrane - A depolarized membrane allows sodium (Na+) to flow inside the membrane - Sodium ions are the most common extracellular cation - There’s also a positivity inside the membrane that is mostly brought about by the presence of the potassium ions, the potassium ion is the most common intracellular cation - The exchange of ions initiates an action potential in the neuron - If the action potential (nerve impulse) starts, it is propagated over the entire axon - Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane - The sodium-potassium pump restores the original configuration CONTINUATION OF THE NERVE IMPULSE BETWEEN NEURONS Impulses are able to cross the synapse to another nerve Neurotransmitter is released from a nerve’s axon terminal The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter An action potential is started in the dendrite HOW NEURONS COMMUNICATE AT SYNAPSES STAGES IN IMPULSE CONDUCTION: 1. RMP 2. Local Depolarization 3. Depolarization and generation of action potential 4. Propagation of action potential 5. Repolarization 6. Restoration of ionic concentrations THE REFLEX ARC REFLEX - rapid, predictable, and involuntary response to stimuli REFLEX ARC - direct route from a sensory neuron, to an interneuron, to an effector SIMPLE REFLEX ARC A. MONOSYNAPTIC REFLEX - Patellar reflex or knee jerk reflex - One synapse formed by the sensory neuron directly with the motor neuron B. POLYSYNAPTIC REFLEX TYPES OF REFLEX AND THEIR REGULATION 1. AUTONOMIC REFLEXES  Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation 2. SOMATIC REFLEXES Activation of skeletal muscles REGIONS OF THE BRAIN 1. CEREBRAL HEMISPHERES (CEREBRUM) Forms the bulk of the brain Include more than half of the brain mass The surfaces is made of ridges (gyri) and grooves (sulci) and fissures (larger grooves) divide the cerebrum into lobes LOBES OF THE CEREBRUM SURFACE LOBES OF THE CEREBRUM: Frontal Lobe - separated from the parietal lobe by the central sulcus Parietal Lobe - separated from the occipital lobe by the parieto-occipital sulcus Occipital Lobe has no obvious anatomical border between it and the surrounding lobes, most likely because it is intensely functionally connected to other portions of the brains Temporal Lobe - the boundaries of the temporal lobe is the lateral sulcus Insula - deeper 5th lobe SPECIALIZED AREA OF THE CEREBRUM: SOMATIC SENSORY AREA - receives impulses from the body’s sensory receptors PRIMARY MOTOR AREA - sends impulses to skeletal muscles BROCA’S AREA - involved in our ability to speak CEREBRAL AREAS INVOLVED IN SPECIAL SENSES: GUSTATORY AREA (TASTE) OR GUSTATORY CORTEX - Found in the parietal lobe VISUAL AREA - Occipital lobe AUDITORY AREA - Temporal lobe OLFACTORY AREA - Temporal lobe INTERPRETATION AREAS OF THE CEREBRUM: SPEECH/LANGUAGE REGION LANGUAGE COMPREHENSION REGION GENERAL INTERPRETATION AREA LAYERS OF THE CEREBRUM: GRAY MATTER - Outer layer - Composed mostly of neuron cell bodies WHITE MATTER - Fiber tracts inside the gray matter - Example: corpus callosum connects hemispheres - The corpus callosum is the major tract of communication between the two hemispheres of the cerebral cortex - Inner layer BASAL NUCLEI/BASAL GANGLIA - Internal islands of gray matter - The basal ganglia include: Corpus striatum Claustrum The amygdala Substantia nigra - nucleus deep within the midbrain that functions to inhibit motor neurons and contributes to the fluidity of motor movements Subthalamic sails FUNCTIONS OF THE BASAL GANGLIA: Regulates attention and individual cognitive processes Participates in motor planning and learning Assists the cerebral cortex in making subconscious, learned movements 2. DIENCEPHALON  Sits on top of the brain stem Enclosed by the cerebral hemispheres MADE UP OF THREE PARTS: THALAMUS - Surrounds the third ventricle - The relay station for sensory impulses - Transfers impulses to the correct part of the cortex for localization and interpretation HYPOTHALAMUS - Forming the floor of the diencephalon - Dangling at the inferior end is the pituitary gland - Under the thalamus - Important autonomic nervous system center - Helps regulate body temperature - Controls water balance - Regulates metabolism - An important part of the limbic system (emotions) EPITHALAMUS - Forming the roof of the third ventricle - Houses the pineal body (an endocrine gland) - Includes the choroid plexus - forms cerebrospinal fluid - Choroid plexus are capillary-membrane tangles lined by specialized cells 3. BRAIN STEM PARTS OF THE BRAIN STEM: MIDBRAIN - Mostly composed of tracts of nerve fibers - Has 2 bulging fiber tracts: the cerebral peduncles - Has 4 rounded protrusions: the 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 - Main connection between the cerebellum and brain stem MEDULLA OBLONGATA - connects to the spinal cord inferiorly just below the foramen magnum - The lowest part of brain stem - Merges into the spinal cord - Includes important fiber tracts - Most inferiorly structure located in the brain - Contains important control centers: Heart rate control Blood pressure regulation Breathing Swallowing vomiting RETICULAR FORMATION - Diffuse mass of gray matter along the brain stem - Involved in motor control of visceral organs - RETICULAR ACTIVATING SYSTEM (RAS) - plays a role in awake/sleep cycles and consciousness 4. CEREBELLUM 2 hemispheres with convoluted surfaces Provides involuntary coordination of body movements The “little brain” Covered in gyri and sulci like the cerebrum Looks like a miniature version of that part of the brain Accounts for approximately 10% of the brain PROTECTION OF THE CENTRAL NERVOUS SYSTEM SCALP AND SKIN SKULL AND VERTEBRAL COLUMN MENINGES 3 TYPES OF MENINGES DURA MATER - Thick, collagen-rich fibrous layer that acts as a strong protective sheath over the entire brain and spinal cord - Comes from the same root “durable” - Outer periosteal layer - Inner meningeal layer ARACHNOID MATER - A thinner fibrous membrane that forms a loose sac around the CNS PIA MATER - Thinnest membrane, which hugs all of the bumps, grooves, and indentations of the brain like a thin layer of paint - The name comes from Latin for “tender mother” describing this thin membrane as a gentle covering for the brain THE BRAIN… - Nervous tissue contained within the skull, appears as dull gray, solid mass in the skull, attached to the long solid spinal cord CEREBROSPINAL FLUID (CSF) Similar to blood plasma composition Formed by the choroid plexus found in the epithalamus Forms a watery cushion to protect the brain Circulated in subarachnoid space, ventricles, and central canal of the spinal cord BLOOD BRAIN BARRIER (BBB) Includes the least permeable capillaries of the body Excludes many potentially harmful substances Useless against some substances: - Fats and fat soluble molecules - Respiratory gases - Alcohol - Nicotine - Anesthesia TRAUMATIC BRAIN INJURIES (TBI) CONCUSSION - Caused by a bump, blow, or jolt to the head or by a hit to the body that causes the head and brain to move rapidly back and forth CONTUSION - Type of injury that leads to a bruise of the brain tissue; may involve damage to brain structure CEREBRAL EDEMA - Swelling from the inflammatory response - May compress and kill brain tissue CEREBROVASCULAR ACCIDENT (CVA) - Commonly called a “stroke” - The result of the ruptured blood vessel supplying a region of the brain - Brain tissue supplied with oxygen from that blood source dies - Result in loss of some functions or death - Common among hyperintensive individuals 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 - Associated with memory loss, irritability, confusion, and ultimately hallucinations SPINAL CORD Extends from the medulla oblongata to the region of T12 Below T12 is the cauda equina (a collection of spinal nerves, appears much like a horsetail) Enlargements occur in the cervical and lumbar regions  Extension of nervous tissue within the vertebral column SPINAL CORD ANATOMY INTERNAL GRAY MATTER - mostly cell bodies EXTERIOR WHITE MATTER - conduction tracts STRUCTURE OF A NERVE ENDONEURIUM - surrounds each fiber PERINEURIUM - connective tissue covering the fascicle EPINEURIUM - fascicles are bound together by this CRANIAL NERVES 12 pairs of nerves that mostly serve the head and neck (page 562) I. Olfactory - sensory II. Optic - sensory III. Oculomotor - motor IV. Trochlear - motor V. Trigeminal - mixed (both) VI. Abducens - motor VII. Facial - mixed (both) VIII. Vestibulocochlear - sensory IX. Glossopharyngeal - mixed (both) X. Vagus - mixed (both) XI. Accessory - motor XII. Hypoglossal - motor Numbered in order, front to back Most are mixed nerves, but three are sensory only SPINAL NERVES There is a pair of spinal nerves a 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 31 pairs of spinal nerves ANATOMY OF SPINAL NERVES - Spinal nerves divide soon after leaving the spinal cord into: DORSAL RAMI - serve the skin and muscles of the posterior trunk VENTRAL RAMI - form a complex networks (plexus) - Cervical plexus (C1-C5) - Brachial plexus (C5-C8; T1) - Lumbar plexus (L1-L4) - Sacral plexus (L4-L5;S1-S4) ❖ No plexus is formed in T1-T12 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 brain to develop No more neurons are formed after birth, but growth and maturation continues for several years The brain reaches maximum weight as a young adult