Unit 7 - Nervous System PDF

The Nervous System Functions of the Nervous System 1. The nervous system monitors changes occurring inside and outside the body (gathering information) These changes are called stimuli The information it gathers it called sensory input 2. The nervous nystem processes and...

The Nervous System Functions of the Nervous System 1. The nervous system monitors changes occurring inside and outside the body (gathering information) These changes are called stimuli The information it gathers it called sensory input 2. The nervous nystem processes and interprets this sensory input It decides if action is needed – immediately This is called integration 3. The nervous system then makes a mechanical (muscle) or chemical (gland) response to the sensory interpretation This response is called motor output General Senses  Sensitivity to temperature, pain, chemicals, touch, pressure, vibration, and proprioception  Picked up by sensory receptors General Sensory Receptors – Classification 1. Nociceptors - Pain receptors 2. Thermoreceptors - Temperature receptors located in dermis, skeletal muscles, liver, hypothalamus 3. Chemoreceptors – Chemical receptors that respond to substances dissolved in body fluids General Sensory Receptors – Classification 4. Mechanoreceptors - Sensitive to plasma membrane change (stretching, compression, twisting, or other mechanical distortion) Proprioceptors – monitor positions of joints and muscles Baroreceptors – detect pressure changes in walls of blood vessels and portions of system tracts Tactile receptors – provide touch, pressure, vibration sensation (large number in skin) General Sensory Receptors in Skin  Greatest diversity of general sensory receptors Baroreceptor Locations  Carotid sinus and aortic sinus – monitor blood pressure  Lungs – monitor degree of lung expansion  Colon – monitor fecal matter volume; trigger defecation  Chemoreceptors  Detect small changes in specific chemicals or compounds  Play major role in control of respiration and CV function Within medulla - monitor CSF pH and CO2 levels In carotid and aortic bodies - monitor blood pH, CO2 and O2 Functions of the Nervous System System  Central nervous system (CNS) Brain and spinal cord  Peripheral nervous system (not PNS) Spinal nerves Cranial nerves  Both have afferent (sensory) and efferent (motor) pathways  Serve as communication lines among sensory organs, the brain and spinal cord, and Functional Classification of the Peripheral Nervous System  Sensory (afferent) division - Nerve fibers that carry information to the CNS Somatic receptors - touch, position, pain, temperature Visceral receptors - monitor internal organs Special receptors - smell, taste, sight, balance, hearing  Motor (efferent) division - Nerve fibers that carry impulses away from the CNS Two subdivisions  Motor (efferent) Division Somatic nervous system = voluntary or conscious – allows us to control our actions through the musculoskeletal system Autonomic nervous system = involuntary control of actions  Regulates smooth and cardiac muscle, and glands  Divisions – sympathetic and parasympathetic nervous systems Organization of the Nervous System Nervous Tissue: Support Cells  Support cells in the CNS are grouped together as “neuroglia” or “glial cells”  Function: to support, insulate, and protect neurons  Resemble neurons  Unable to conduct nerve impulses  Never lose the ability to divide Nervous Tissue: Support Cells  Account for half the volume of the nervous system 1. Astrocytes (CNS) 2. Microglia (CNS) 3. Ependymal (CNS) 4. Oligodendrocytes (CNS) 5. Schwann Cells (in PNS) 6. Satellite Cells (in PNS) Nervous Tissue: Support Cells 1. Astrocytes Abundant, star-shaped cells that brace neurons to blood capillaries Form barrier between capillaries and neurons to maintain the blood-brain barrier and control the brain’s chemical environment (ions, nutrients, etc) Neuroglia of the CNS Astrocytes Oligodendrocytes Section of Capillary spinal cord Ependymal cells Unmyelinated axon Microglia Axon Neurons Myelinated axons Myelin (cut) Nodes Gray matter White matter Nervous Tissue: Support Cells 2. Microglia Mobile cells roaming through neural tissue, similar to macrophages Spiderlike phagocytes that monitor health of nearby neurons and dispose of debris Nervous Tissue: Support Cells 3. Ependymal cells Line cavities of the brain and spinal cord Produce, monitor, and circulate CSF (assisted by cilia) Nervous Tissue: Support Cells 4. Oligodendrocytes Wrap around nerve fibers in the central nervous system to produce myelin sheaths Myelination in CNS  Oligodendrocytes - form concentric layers of lipid-rich material called myelin sheath around axons Regions in CNS with myelinated axons are white matter Regions of CNS with cell bodies and unmyelinated axons are gray matter Neuroglia of the CNS Astrocytes Oligodendrocytes Section of Capillary spinal cord Ependymal cells Unmyelinated axon Microglia Axon Neurons Myelinated axons Myelin (cut) Nodes Gray matter White matter Nervous Tissue: Support Cells  Schwann cells Form myelin sheath in the peripheral nervous system  Satellite cells Protect neuron cell bodies Myelin Sheath  The purpose of the myelin sheath is to: protect and insulate the nerve fibers increase the transmission (speed) of the nerve impulse  Nerve impulses do not function properly if the myelin sheath is damaged or is missing entirely or in spots Once damaged it does not regenerate Nervous Tissue: Neurons  Neurons = nerve cells Cells specialized to transmit messages from one part of the body to another – these messages are called nerve impulses Neurons are amiotic Major regions of neurons  Cell body – nucleus, organelles and metabolic center of the cell  Processes - fibers that extend from the cell body (vary in length up to 4 feet!)  dendrites and axons Neuron Anatomy  Dendrites Receive stimuli from environment or other neurons  Axon Carries information away from cell body toward other cells Nervous Tissue: Neurons Nervous Tissue: Neurons  Axons continue into axon collaterals or branches, which end in axon terminals  Axonal terminals contain vesicles with neurotransmitters End of axon terminal adjacent to synapse (where neuron communicates with another cell) Three Functional Classes of Neurons 1. Sensory neurons About 10 million 2. Interneurons About 20 billion 3. Motor neurons About half a million SIMple! 1. Sensory Neurons  Deliver information from receptors to CNS along afferent fibers  Somatic sensory neurons External receptors detect changes in external environment Proprioceptors monitor body position and movement  Visceral sensory neurons Internal receptors monitor internal conditions  Special sensory neurons 1. Sensory Neurons Proprioceptors: - Golgi tendon organ - Muscle spindles 2. Interneurons  Receive sensory information from PNS and from other interneurons in CNS  Responsible for memory, planning, and learning 3. Motor Neurons  Carry information from CNS to effectors along efferent fibers  Somatic motor neurons Innervate skeletal muscle under voluntary control  Visceral motor neurons Innervate smooth muscle, glands, cardiac muscle, adipose tissue Function of a Neuron 1. Responds to stimuli and creates a nerve impulse – this is called irritability 2. Transmits impulses to other neurons – this is called conductivity Reflexes  Reflex - rapid, predictable, and involuntary response to a stimulus Occurs over pathways called reflex arcs  Reflex arc - direct route from a sensory neuron, (sometimes an interneuron), to motor neuron Types of Reflexes and Regulation  Somatic reflexes Activation of skeletal muscles  Autonomic reflexes Heart rate and blood pressure regulation Regulation of glands Digestive system regulation Pupillary reflex Saliva and goosebumps How do neurons actually work and communicate with each other? Action potentials again! At the Synapse  Synapse activity involves: Presynaptic cell releasing neurotransmitters Neurotransmitters bind to receptors on postsynaptic cell, changing membrane permeability  Some neurotransmitters stimulate neuron  Some neurotransmitters inhibit neuron Speed of Action Potential Propagation  Propagation speed fastest along: Large-diameter axons Myelinated axons  Urgent information carried myelinated axons Threats to survival or motor commands to prevent injury  Less urgent information carried on unmyelinated fibers Synapses  Action potentials (nerve impulses) propagate along axon  Transfer of action potential from one neuron to another neuron or effector occurs at synapse  Presynaptic cell axon forms axon terminal Contains neurotransmitters packaged in synaptic vesicles  Narrow space between presynaptic membrane and postsynaptic membrane is synaptic cleft Neurotransmitters  The electrical changes prompted by neurotransmitter binding are brief  The neurotransmitter is quickly removed from the synapse by either: Reuptake Enzymatic activity types in total! Central Nervous System Functional Anatomy of the CNS  CNS consists of: Spinal cord Brain  Contains 97 percent of body's neural tissue  Weighs about 1.4 kg (3 lb) with 1200 mL volume  No correlation between brain size and intelligence Regions of the Brain 1. Cerebrum – divided into two central hemispheres 2. Diencephalon 3. Brain stem 4. Cerebellum Regions of the Brain: Cerebrum  Cerebral hemispheres are paired (left and right) superior parts of the brain Includes more than half of the brain mass The surface is made of ridges (gyri) and grooves (sulci) Regions of the Brain: Cerebrum  Lobes of the cerebrum Fissures (deep grooves) divide the cerebrum into lobes Surface lobes of the cerebrum  Frontal lobe  Parietal lobe  Occipital lobe  Temporal lobe Lobe Functions  Frontal Lobe - concentration, judgment, abstract thinking, personality, motor function (primary motor area)  Parietal lobe - sensory processing (somatic) – pain, cold, light touch, position  Temporal – receptive area (hearing, smell)  Occipital – vision interpretation  Central sulcus Primary motor cortex Primary somatic Premotor area sensory cortex Anterior Gustatory area association area (taste) Working Speech/language memory and (outlined by dashes) judgment Posterior Problem association solving area Language comprehension Visual area Broca’s area (motor speech) Olfactory area Auditory area Regions of the Brain: Cerebrum  Specialized areas of the cerebrum Primary somatic sensory cortex  Receives impulses from the body’s sensory receptors Pain, temperature, light touch  Located in parietal lobe posterior to central sulcus  Sensory homunculus is a spatial map  Left side of the primary somatic sensory area receives impulses from right side (and vice versa) Regions of the Brain: Cerebrum  Specialized areas of the cerebrum Primary motor cortex  Sends impulses to skeletal muscles  Located in frontal lobe  Motor neurons form corticospinal (pyramidal) tract, which descends to spinal cord  Motor homunculus is a spatial map (see previous slide)  Posterior Motor Sensory Motor map in Anterior Sensory map in Shou precentral gyrus postcentral gyrus Ha earm Trunk Armad Neck Trunk Hip Knee Fo w He Leg Elb st Arm Wr Hip Ha lder s o nd r Fi er Elb ow i nd ng ng Knee e Fi Th rs um b um b Foot Ne e Th Bro ck Ey w ose Eye N e Toes Fac s Face Genitals Lip Lips Primary motor Primary somatic Teeth cortex sensory cortex Gums (precentral gyrus) (postcentral gyrus) Jaw Jaw Tongue Tongue Pharynx Intra- Swallowing abdominal Regions of the Brain: Cerebrum  Cerebral areas involved in special senses Visual area (occipital lobe) Auditory area (temporal lobe) Olfactory area (temporal lobe) Gustatory area (parietal lobe) Regions of the Brain: Cerebrum  Other specialized areas of the cerebrum Broca’s area (frontal lobe)  Involved in our ability to speak (vocalize words)  Usually only in left hemisphere Anterior association areas  Higher intellectual reasoning and social behavior Posterior association areas  Recognizing patterns and faces; blending all inputs into an understanding of the Regions of the Brain: Cerebrum  Layers of the cerebrum Gray matter—outer layer in the cerebral cortex; composed mostly of neuron cell bodies White matter—fiber tracts deep to the gray matter  Corpus callosum connects hemispheres  Basal nuclei (ganglia)—islands of gray matter buried within the white matter Regulates the information coming from the primary motor cortex going to the thalamus Longitudinal fissure Superior Association fibers Lateral Commissural fibers ventricle (corpus callosum) Basal nuclei Corona (basal radiata ganglia) Fornix Internal Thalamus capsule Third ventricle Projection Pons fibers Medulla oblongata Superficial Landmarks between Lobes  Lateral sulcus - Separates frontal lobe from temporal lobe  Central sulcus - Separates frontal lobe from parietal lobe  Contains primary motor cortex (anterior) and primary sensory cortex (posterior)  Parieto-occipital sulcus - Separates parietal lobe from occipital lobe Regions of the Brain: Diencephalon  Sits on top of the brain stem  Enclosed by the cerebral hemispheres  Made of three parts Thalamus Hypothalamus Epithalamus Regions of the Brain: Diencephalon  Thalamus Relay station for sensory impulses Transfers impulses to the correct part of the cortex for localization and interpretation Regions of the Brain: Diencephalon  Hypothalamus Under the thalamus Important for ANS control  Regulate body temperature  Controls water balance  Regulates metabolism Houses mammillary bodies for olfaction (smell) Houses the limbic center for emotions Regulates the nearby pituitary gland Regions of the Brain: Diencephalon  Epithalamus Houses the pineal body (an endocrine gland) Includes the choroid plexus – produces CSF Regions of the Brain: Brain Stem  Attaches to the spinal cord  Parts of the brain stem Midbrain Pons Medulla oblongata Regions of the Brain: Brain Stem  Midbrain Composed mostly of tracts of nerve fibers to convey ascending and descending impulses (between cerebrum and spinal cord) Also contains visual and auditory reflex centers  Pons Mostly composed of fiber tracts Includes nuclei involved in the control of breathing Regions of the Brain: Brain Stem  Medulla Oblongata The lowest part of the brain stem - merges into the spinal cord Contains critical control centers  Heart rate control  Blood pressure regulation  Breathing  Swallowing  Vomiting  At the level of the medulla, fibers decussate (cross over) and merges into the spinal cord – thus the right brain control the left side of the body and visa versa Regions of the Brain: Brain Stem  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  Filter for incoming sensory information Regions of the Brain: Cerebellum  Coordinates complex somatic (motor) patterns from cerebral cortex Adjusts postural muscles to maintain balance Provides precise timing for skeletal muscle activity and coordination of body movements Protection of the Central Nervous System  Scalp and skin  Skull and vertebral column  Meninges  Cerebrospinal fluid (CSF) and blood-brain barrier Meninges  Thick fibrous connective tissue that covers the brain and spinal cord Epidural space – space between the dura and the skull – contains arteries  Dura mater – outmost, thick, attaches to the skull (two layers) Subdural space – space between the dura and the brain – contains bridging veins between blood vessels from epidural space and capillaries in subarachnoid space (which reabsorb CSF)  Arachnoid – middle membrane, thin, spider web in appearance – tight to the brain Subarachnoid Space – below the arachnoid –  Cranial meninges Subdural space Cranium (skull) 1 Dura mater 2 Arachnoid mater Dura mater (outer layer) Arachnoid mater Dural sinus Subarachnoid space Dura mater (inner layer) 3 Pia mater Cerebral cortex Figure 7.8 1 1 Ventricles and Cerebrospinal Fluid (CSF)  Similar to blood plasma composition (produced by ependymal cells) Clear, colorless, contains sugar, no WBC's or RBC's  Forms a watery cushion to protect the brain and keep it buoyant so as to not compress blood vessels  Circulated in arachnoid space, ventricles, and central canal of the spinal cord Blood-Brain Barrier  Includes the least permeable capillaries of the body  in part due to presence of tight junctions, with slight help from astrocytes  Excludes many potentially harmful substances  Useless as a barrier against some substances Fats and fat-soluble molecules  Respiratory gases  Alcohol  Nicotine  Anesthesia Blood-Brain Barrier  Water-soluble items that can travel through barrier: Water Glucose Essential amino acids  Items prevented from passing through into CSF: Metabolic wastes Most drugs Nonessential amino acids Potassium ions Cerebral Arteries Spinal Cord  Extends from the foramen magnum of the skull to the first or second lumbar vertebra Eight pairs – cervical Twelve pairs – thoracic Five pairs – lumbar Five pairs – sacral Spinal Cord Anatomy  Meninges cover the spinal cord  Spinal nerves leave at the level of each vertebrae Dorsal root - afferent nerves (sensory) Ventral root - efferent nerves (motor) Pathways Between Brain and Spinal Cord Peripheral Nervous System Nervous System  Central Nervous System Processes sensory information and responds  Peripheral Nervous System (PNS) Network of peripheral nerves Structurally divided into:  Cranial nerves – 12 pairs; connect directly to brain  Spinal nerves – 31 pairs; connect directly to spinal cord Peripheral Nervous System  Nerve - bundle of neuron fibers found outside the CNS  Neuron fibers are bundled by connective tissue Classification of Nerves 1. Mixed nerves Both sensory and motor fibers 2. Sensory (afferent) nerves Carry impulses toward the CNS 3. Motor (efferent) nerves Carry impulses away from the CNS Cranial Nerves  12 pairs of CN to serve head and neck (except Vagus X)  Classified as sensory, motor, or mixed Three are only for special senses (optic, olfactory, vestibulocochlear)  Roman numeral corresponds to position on brain (numbered in order from front to back)  Odor Of Orangutan Terrified Tarzan After Forty Voracious Gorillas Viciously Attacked Him Cranial Nerves Mnemonic Device  Oh – Olfactory  Oh – Optic  Oh – Oculomotor  To – Trochlear  Touch – Trigeminal  And – Abducens  Feel – Facial  Very – Vestibulocochlear  Green – Glossopharyngeal  Vegetables – Vagus  A – Accessory  H – Hypoglossal © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Distribution of Cranial Nerves Rhyming Time!  (One) smells first, olfactory.  (Two) optic for stuff we see.  (Three) oculomotor tie  (Four) with trochlear round the eye.  (Five) trigeminal the great.  (Six) abducens eyes rotate.  (Seven) facial faces near.  (Eight) vestibulocochlear.  (Nine) glossopharyngeal.  (Ten) vagus, lungs, guts, heart and all.  (Eleven) accessory shoulders reach.  (Twelve) hypoglossal tongue and speech. Spinal Nerves  There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs  Contain both sensory and motor fibres (dorsal and ventral roots)  Named for the region from which they arise  Four plexuses 1. Cervical 2. Brachial 3. Lumbar 4. Sacral Spinal Nerves © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Autonomic Nervous System  Motor subdivision of the peripheral nervous system Consists only of motor nerves Also known as the involuntary nervous system  Regulates activities of cardiac and smooth muscles, glands and adipose tissue  Two subdivisions 1. Sympathetic division 2. Parasympathetic division Autonomic Nervous System  Allows the organs to respond to changing body needs  Carries out automatic and unconscious visceral responses  Regulates organ function (visceral reflexes) Examples:  Pupillary response to light  Blood pressure reflex  Regulation of heart rate  Secretions and motility of the digestive tract Division  Preganglionic neurons originate from the craniosacral regions: The cranial nerves III, VII, IX, and X S2 through S4 regions of the spinal cord  Thus also known as the craniosacral division  Neurotransmitter: acetylcholine SNS: Anatomy of the Sympathetic Division  Preganglionic neurons originate from T1 through L2 Also known as the thoracolumbar division  norepinephrine and epinephrine (effector organs) Autonomic Functioning  Body organs served by the autonomic nervous system are mostly controlled from both divisions Exceptions: blood vessels, structures of the skin, some glands, and the adrenal medulla  receive only sympathetic fibers SNS: Autonomic Functioning  Sympathetic—“fight or flight” division Response to unusual stimulus Takes over to increase activities Remember as the “E” division:  Exercise  Excitement  Emergency  Embarrassment PNS: Autonomic Functioning  Parasympathetic—“housekeeping” activites Conserves energy Maintains daily necessary body functions Remember as the “D” division  Digestion  Defecation  Diuresis 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 Premature babies have trouble regulating body temperature because the hypothalamus is one of the last brain areas to mature prenatally. System  Development of motor control indicates the progressive myelination and maturation of a child’s nervous system.  Brain growth ends in young adulthood. Neurons die throughout life and are not replaced; thus, brain mass declines with age.  Healthy aged people maintain nearly optimal intellectual function.  Elderly SNS not efficient – poor ability to constrict blood vessels – so easily get faint when standing up from a lying down position – Review Questions  Name the structural components of a typical neuron.  Classify neurons according to their structure.  Why is a CNS neuron not usually replaced after it is injured?  Identify the neuroglia of the central nervous system.  Which glial cell protects the CNS from chemicals and hormones circulating in the blood?  Which type of neuroglia would occur in increased numbers in the brain tissue of a person with a CNS infection?  Classify neurons into three categories according to their function.  Define membrane potential.  List three body functions that result from changes in the membrane potential of a cell.  Describe depolarization and repolarization.  What is the relationship between myelin and the propagation speed of action potentials?  Describe the structure of a synapse.  Describe the events that occur at a synapse when an action potential arrives at the axon terminal.  Why is the depolarization on the postsynaptic cell temporary?  Name the major regions of the brain and the distinct structures of each.  Describe the role of the medulla oblongata.  Which ventricles would lose communication by a blocked cerebral aqueduct?  From superficial to deep, name the three layers that make up the cranial meninges.  Identify the lobes of the cerebrum and indicate the basis for their names.  What effect would damage to the left primary sensory cortex  Where is the primary motor cortex located?  Which senses are affected by damage to the temporal lobes?  A stroke patient is unable to speak. Which part of the brain has been affected?  A typical spinal cord has how many pairs of spinal nerves, and where does the spinal cord end?  What are the three layers of the spinal meninges?  Where is the epidural space located and what does it contain?  Identify the cranial nerves by name and number.  Which cranial nerves have motor functions only?  Which cranial nerves are mixed nerves?  Define nerve plexus and list the major plexuses.  Injury to which nerve plexus would interfere with the ability to breathe?  List the major nerves of the brachial plexus.  What are the common characteristics of reflexes?  Define reflex and list the components of a reflex arc.  In the patellar reflex, identify the response observed and the effectors involved.  List general responses to increased sympathetic activity and to parasympathetic activity.