Nervous System Functions (CRIME) 1. Controlling muscles and glands. 2. Receiving sensory input. 3. Integrating information. 4. Maintaining homeostasis. 5. Establishing and maintaining mental activity. Divisions of the Nervous System I. Central Nervous System § Brain and spinal cord II. § Peripheral Nervous System Nerves and ganglia a. Sensory Division – afferent (toward) division; conducts action potentials from sensory receptors to the CNS • Sensory neurons – neurons that transmit action potentials from the periphery to the CNS i. Somatic Sensory Fibers – carry info from stimuli coming from the skin, skeletal, muscles, joints ii. Visceral Sensory Fibers – transmits impulses coming from the visceral organs b. Motor Division – efferent (away) division; conducts action potentials from the CNS to effector organs • Motor neurons – neurons that transmit action potentials from the CNS toward the periphery i. ii. iii. Somatic Motor Nervous System / Voluntary – transmits action potentials form the CNS to the skeletal muscles Autonomic Motor Nervous System / Involuntary – transmits action potentials from the CNS to cardiac, smooth muscles and glands 1. Sympathetic – figth-orflight system 2. Parasympathetic – resting and digesting system Enteric Nervous System – unique subdivision; both sensory and motor neurons contained within the digestive tract Cells of the Nervous System Neurons § Also called nerve cells § Receive stimuli, conduct transmit signals action potentials, Cell body – contains a single nucleus; source of information for gene expression n Dendrites – extensions of the cell body; receive information from other neurons; transmit the info toward the neuron cell body Axon – single long cell process; conduct action potentials from one part of the brain or spinal cord to another part Ø Axon of sensory neurons – conduct action potentials towards the CNS Ø Axon of motor neurons – conduct action potentials away from the CNS Axon hillock – where the axon leaves the neuron cell body Nissl bodies – rough ER found in the cell body of a neuron Schwann cells – form a myelin sheath (increases speed of impulse transmission) Collateral axons – branches of axons Types of Neurons 1. Multipolar neurons – many dendrites + a single axon 2. Bipolar neurons – two processes: 1 dendrite + 1 axon 3. Pseudo-unipolar neurons – single process that divides into 2 processes: extends to the periphery + extends to the CNS Neuroglia § Non-neuronal cells of the CNS + PNS § More numerous than neurons § Retain the ability to divide 1. Astrocytes – major supporting cells in the CNS; stimulate/inhibit the signaling activity of nearby neurons; help limit damage to neural tissue v Blood brain barrier – protects neurons from toxic substances in the blood; allows exchange of waster products + nutrients 2. Ependymal cells – produce cerebrospinal fluid; help move the cerebrospinal fluid through the CNS 3. Microglia – act as immune cells of the CNS’ protect the brain by removing bacteria and cell debris M o r a n o , M . A . 4 – 5. Oligodendrocytes (CNS) and Schwann cells (PNS) – provide an insulating material that surrounds axons Neural Signaling § Communication among neurons 1. Reception – stimuli received by visual receptors in the eye 2. Transmission – sensory neurons transmit info to CNS 3. Integration – info given is interpreted and an appropriate response is determined 4. Transmission – the CNS transmits info to motor neurons 5. Actual response – muscle/glands receive info and instruction from motor neurons Myelin Sheaths § Highly specialized insulating layer of cells Unmyelinated axons – action potentials are conducted slowly bcos in travels along the entire axon Myelinating axons – action potentials are conducted rapidly by salutatory conduction Electrical Signals and Neural Pathways Resting Membrane Potential Polarized cell membrane – uneven distribution of charge Resting membrane potential – uneven charge distribution in an unstimulated/resting cell; polarized Ø Higher concentration of K+ inside CM Ø Higher concentration of Na+ outside CM Ø Greater permeability of CM to K+ than to Na+ Leak channels – always open Gated channels – closed until opened by specific signals Chemically gated neurotransmitters channels – opened by Voltage gated channels – opened by a change in membrane potential Sodium potassium pump – required to maintain the greater concentration of Na+ outside the CM and K+ inside Action Potentials Excitable cells – RMP changes in response to stimuli that activate gated ion channels Local current – Na+ diffuses quickly into cell Nodes of Ranvier – gaps in the myelin sheath; where ion movement can occur Depolarization – a change that causes the inside of the CM to become positive Organization of Nervous Tissue Gray Matter – groups of neuron cell bodies + their dendrites; very little myelin Ø In the CNS; v Cortex – GM on the surface of the brain v Nuclei – GM located deeper within the brain Ø In the PNS; v Ganglion – a cluster of neuron cell bodies Local potential – result of depolarization White Matter – bundles of parallel axons + myelin sheaths Ø In the CNS v Nerve tracts – conduction pathways; propagate action potentials from one area of the CNS to another Ø In the PNS; v Nerves – bundles of axons + connective tissue sheaths Threshold value – attainable local potential (critical pt.) Action potential – constitution of depolarization and repolarization Hyperpolarization – the charge on the CM briefly becomes more negative than the RMP All-or-none fashion – threshold is reached = action potential occurs; if the threshold is not reached = action potential doesn’t occur Continuous conduction – the action potential is conducted along the entire axon CM Saltatory conduction – action potentials jump from one node of Ranbier to the next The Synapse Synapse – a junction where the axon of one neuron interacts with another Presynaptic terminal – end of the axon Postsynaptic membrane – membrane of the dendrite or effector cell Synaptic cleft – space separating the presynaptic & postsynaptic membrane M o r a n o , M . A . Neurotransmitters – chemical messengers Synaptic vesicles – where neurotransmitters are stored Hyperpolarized – the inside of the postsynaptic cell tends to become more negative Substance Acetylcholine Norepinephrine Serotonin Dopamine Gammaaminobutyric acid Glycine Endorphins Effect Excitatory or inhibitory Excitatory Generally inhibitory Excitatory or inhibitory Inhibitory Inhibitory Inhibitory Clinical Example Alzheimer disease Cocaine and amphetamines Mood, anxiety, and sleep induction Parkinson disease Treatment of epilepsy Poison strychnine Opiates morphine and heroin Reflexes Reflex – an involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS Reflex arc – neuronal pathway by which a reflex occurs Ø Sensory receptor Ø Sensory neuron Ø Interneurons Ø Motor neuron Ø Effector organ (muscle or glands) Neuronal Pathways Converging pathway – two or more neurons synapse with the same neuron Diverging pathway – the axon from one neuron divides and synapses with more than one other neuron Summation – allows integration of multiple sub threshold local potentials; brings the membrane potential to threshold and trigger an action potential Spatial summation – local potentials originate from diff. locations on the postsynaptic neuron Temporal summation – local potentials overlap in time M o r a n o , M . A . Spinothalamic tract – transmits pain, light touch, and deep pressure Spinal cord § § Extends from the foramen magnum to the 2nd lumbar vertebra Provides a two-way conduction pathway to and from the brain Cauda equina – inferior end of the SC; spinal nerves exiting there resemble a horse’s tail 2 Main Functions 1. Transmits info to and from the brain. 2. Controls many reflex activities of the body. Dorsal column – transmission of proprioception, touch, deep pressure, vibration Spinocerebellar tracts – proprioception to cerebellum Descending Tracts § Pathways that carry impulses from the brain to the periphery Lateral corticospinal movements (hand) White Matter of the SC 1. Dorsal (posterior) 2. Ventral (anterior) 3. Lateral Columns a. Ascending tracts – conduct action potentials toward the brain b. Descending tracts – conduct action potentials away from the brain Gray Matter of the SC (shaped like the letter H) 1. Posterior horns 2. Anterior horns 3. Small lateral horns Dorsal root – formed by dorsal rootlets Dorsal root ganglion – ganglion in a dorsal root Relfex Action § Predictable, automatic response to a specific stimulus Reception of the stimulus. Transmission of info to the CNS. Integration (interpretation and determination of an appropriate response). Transmission of info from the CNS to a muscle. Actual response. Spinal Cord Reflexes Knee-Jerk Reflex Stretch flex – simplest reflex; muscles contract in response to a stretching force applied to them Knee-jerk reflex – patellar reflex; used to determine if the higher CNS centers that normally influence this reflex are functional Withdrawal Reflex Withdrawal Reflex – flexor reflex; to remove a limb from a painful stimulus Ascending Tracts § Pathways that carry impulses form periphery to various parts of the brain tone and skilled Anterior corticospinal – muscle tone and movement of trunk muscles Rubrospinal – movement coordination Reticulospinal – posture adjustment Vestibulospinal – posture & balance Cranial Nerves § Transmit info to the brain form the sensory receptors § 12 pairs Ventral root – formed by ventral rootlets; 4. 5. muscle Tectospinal – movement in response to visual reflexes Central canal – fluid filled space in the center of the cord 1. 2. 3. – the I. II. Name Olfactory Optic S S III. Oculomotor M IV. Trochlear M V. Trigeminal B VI. Abducens M VII. Facial B VIII. Acoustic / Vestibulocochlear S IX. Glossopharyng -eal B X. Vagus B XI. Accessory M XII. Hypoglossal M Specific Function S: smell S: vision M: 4-6 extrinsic eye muscles; P: constricts pupils M: 1 extrinsic eye muscle S: face + teeth; M: muscles of mastification M: 1 extrinsic eye muscle S: taste; M: facial muscles; P: salivary + tear glands S: hearing + balance S: taste + touch to back of tongue; M: pharyngeal muscles; P: salivary glands S: pharynx, larynx, viscera; M: palate, pharynx, larynx; P: viscera of thorax + abdomen M: 2 neck + upper back muscles M: tongue muscles Spinal Nerves § Arise along the spinal cord; contains mixed nerves § 31 pairs v 8 Cervical v 12 Thoracic v 5 Lumbar M o r a n o , M . A . v 5 Sacral v 1 Coccygeal Mixed nerves – contains both sensory and somatic motor neurons Plexuses – where nerves come together and then separate Ø Cervical plexus Ø Brachial plexus Ø Lumbosacral plexus Autonomic Nervous System § Preganglionic neuron § Postganglionic neuron § Maintain internal homeostasis Autonomic ganglia – where preganglionic neurons synapse with postganglionic neurons I. § § § § Cervical Plexus § Originates from spinal nerves C1 to C4 Phrenic nerve – most important branc of the CP; innervates the diaphragm (responsible for our ability to breathe) Brachial Plexus § Originates from the spinal nerves C5 to T1 II. § § § § Sympathetic ANS ‘Fight-or-flight’ Prepares the body for action Most active during stressful situations Norepinephrine (main neurotransmitter) Parasympathetic ANS Activities result in conserving and restoring energy Helps return the body to resting conditions Active during periods of calm and rest PS fibers are in the vagus nerve 1. Axillary nerve – innervates 2 shoulder muscles + the skin over part of it Autonomic Neurotransmitters Acetylcholine – neurotransmitters parasympathetic division 2. Median nerve – innervates the anterior forearm and intrinsic muscles Norepinephrine – postganglionic sympathetic division 3. Radial nerve – innervates all the muscles in the posterior arm and forearm + skin over the posterior surface of the arm, forearm, hand 4. Musculocutaneous nerve – innervates the anterior muscles of the arm + skin over the radial surface of the forearm Functions of the Autonomic Nervous System Sympathetic Division § Prepares a person for action by increasing HR, BP, respiration, release of glucose 5. Ulnar nerve – innervates most of the anterior forearm muscles and some of the intrinsic hand muscles + skin over the radial side of the hand Lumbosacral Plexus § Originates from spinal nerves L1 to S4 1. Obturator nerve – innervates the muscles of the medial thigh + skin over it 2. Femoral nerve – innervates the anterior thigh muscles + skin over it & medial side of the leg 3. Tibial nerve – innervates the posterior thigh muscles, the anterior & posterior leg muscles, most of the intrinsic foot muscles + skin over the sole of the foot 4. Common fibular nerve – innervates the muscles of the lateral thigh & leg, some intrinsic foot muscles + skin over the anterior & lateral leg, dorsal surface of the foot of neurons the of the Parasympathetic Division § Involuntary activities at rest: digestion of food, defecation, urination Enteric Nervous System § Consists of plexus within the wall of the digestive tract 1. 2. 3. Sensory neurons – connect the digestive tract to the CNS Sympathetic & parasympathetic neurons – connect the CNS to the digestive tract Enteric neurons – located entirely within enteric plexus v Capable of monitoring and controlling the digestive tract independently of the CNS Sciatic nerve – CT sheath that bounds the tibial and common fibular nerve M o r a n o , M . A . 2. § Brain § § § I. § § § 1. § § § § 2. § § § 3. § § 4. § § § § II. § 1. § § § § Soft, wrinkled mass of tissue that is highly complex and adaptive; 3 pounds 25 billion neurons Requires a continuous supply of oxygen and glucose Brainstem Connects the spinal cord to the remainder of the brain Controls the heart rate, blood pressure, and breathing Damage can cause death Medulla Oblongata Most inferior portion of the brainstem Important reflex actions like vomiting, sneezing, coughing, swallowing Gray matter consists of various nuclei that serve as vital centers v Cardiac centers – control HR v Vasomotor centers – regulates BP bu controlling blood vessel diameter v Respiratory centers – initiates and regulates breathing Pyramids – two prominent enalargements Pons (bridge) Relay information bet. the cerebrum and the cerebellum Resembles an arched footbridge Regulates respiration, swallowing, sleep Midbrain Smallest region of the brainstem 4 mounds called the colliculi v 2 inferior; major relay centers for the auditory nerve pathways in the CNS v 2 superior; visual reflexes and receive touch and auditory input § Pineal gland – an endocrine gland that may influence the onset of puberty; role in controlling some long term cycles 3. § § § § Thalamus Largest part of the diencephalon Major relay center for all sensory info (except smell) to the cerebrum; plays a gating rol Influences mood and registers an uncomfortable perception of pain Interthalamic adhesion – connects the two large, lateral parts of the thalamus Hypothalamus Most inferior part Consists of several small nuclei; maintaining homeostasis Control of body temp., hunger, and thirst Sensations such as sexual pleasure, rage, fear, and relaxation Important Homeostatic Mechanisms 1. Control center of the ANS. 2. The link bet. the nervous and endocrine systems. 3. Helps maintain fluid balance. v Anti-diuretic hormone (ADH) – regulates water excretion by the kidneys 4. Regulates body temperature. 5. Regulates food intake (appetite and satiety centers). 6. Regulates sleep-wake cycles. 7. Influences sexual behavior and emotional aspects of sensory input. Infundibulum – controlling the secretion of hormones from the pituitary gland Mammillary bodies – involved in emotional responses to odors and in memory III. § § § Reticular Formation A group of nuclei scattered throughout the brainstem Regulating cyclical motor functions; respiration, walking, chewing Damage can result in coma Reticular activating system – plays an important role in arousing and maintaining consciousness Diencephalon Part bet. the brainstem and the cerebrum Epithalamus Smallest area superior + posterior to the thalamus Consists of few small nuclei (emotional and visceral response to odors) + pineal gland § 1. Cerebellum Second largest part of the brain; 2 hemispheres Responsible for coordination of movements Comparator – a sensing device that compares data from two sources Proprioceptive neurons – innervate joints, tendons, muscles; provide info about the position of body parts 2. 3. 4. Helps in smooth and coordinated movements (comparator function). Maintains muscle tone posture. Maintain balance and equilibrium Important in learning motor skills. § Cerebrum Largest and most prominent part of the brain IV. 1. 2. 3. body Sensory Function – receives info from sensory receptors and interprets it Motor Function – responsible for all voluntary movement and some involuntary ones Association Function – responsible for all of the intellectual activities of brain M o r a n o , M . A . 4 Lobes 1. Frontal Lobe § Control of voluntary motor functions, motivation, aggression, mood, olfactory reception § Primary motor area: consciously move our skeletal muscles § Broca’s area – speech center § Prefrontal area – reposible for executive functions 2. § § Parietal Lobe General Sensory Area – receives info from the sensory receptors in the skin and joints Wernicke’s area – sensory speech area 3. § § § Occipital Lobe Receiving and perceiving visual input Primary visual area – receives visual info Visual association area – portion where visual info is integrated 4. § Temporal Lobe Primary auditory area – center for reception of auditory messages Auditory association area – where auditory messages are integrated Psychic cortex – abstract thoughts and judgments § § Gyri – folds and convolutions; increase the surface area of the cortex and intervening grooves (sulci) Left Hemisphere – analytical hemisphere; mathematics and speech Memory Working memory – stores info required for the immediate performance of a task; 7 digit phone no. Short-term memory – last longer; can be retained for a few mins. to a few days Long-term memory – stored for only a few minutes or become permanent by consolidation Consolidation – a gradual process involving the formation of new and stronger synaptic connections Declarative memory – explicit memory; retains facts and related emotional undertones Procedural memory – reflexive memory; development of motor skills Memory engrams – memory traces; long-term retention of a thought/idea Limbic System § A group of interconnected nuclei involved in memory and regulation of emotion Hippocampus – formation and retrieval of memories Sulci – shallow grooves Amygdala – filter sensory info and evaluates it in terms of emotional needs Fissures – deep groves Longitudinal fissure – divides the cerebrum into left and right hemispheres Cerebral cortex – outermost layer of the cerebrum; consists of gray matter Corpus callosum – connects the right and hemispheres Right and Left Hemispheres Right hemisphere – three dimensional or spatial perception, musical ability Meninges, Ventricles, and Cerebrospinal Fluid Meninges § Surround and protect the brain and spinal cord 1. Dura mater – most superficial and thickest meninges v Epidural space – bet. the dura mater & the vertebrae v Epidural anesthesia – clinically important as the injection site of spinal nerves; given to women during childbirth 2. Arachnoid mater – thin, wispy, 2nd meningeal membrane v Subdural space – space bet. the dura mater and the arachnoid mater; contains small amt. of serous fluid v Spinal block – to inject anesthetic into the area v Spinal tap – to take a sample of CSF 3. Pia mater – 3rd meningeal membrane; very tightly bound to the surface of the brain and spinal cord; filled with CSF and contains blood vessels left Central sulcus – separates the frontal and parietal lobes Lateral fissure – separates the temporal love from the rest Insula – fifth lobe; deep within the fissure Basal Nuclei § Group of functionally related nuclei Corpus striatum – located deep within the cerebrum Substantia nigra – darkly pigmented cells in the midbrain M o r a n o , M . A . v Subarachnoid space – arachnoid and pia matter bet. the Aphasia – comprehension absent/defective Ventricles § Fluid filled cavities Brain Waves and Consciousness Electroencephalogram (EEG) - Lateral ventricle – relatively large cavity in each cerebral hemisphere Brain waves – wave like patterns speech/language Third ventricle – a smaller, midline cavity Alpha waves – awake but in a quiet, resting state with eyes close Fourth ventricle – located at the base of the cerebellum Beta waves – occur during intense mental activity Cerebral aqueduct – a narrow canal that connects the 3rd and 4th ventricle Delta waves – occur during deep sleep in infants and in patients Cerebrospinal fluid § Provides a protective cushion around the CNS Theta waves – observed in children; also in adults who are frustrated or have brain disorders Choroid plexus – produces CSF; specialized structures made of ependymal cells Effects of Aging on the Nervous System § Motor functions decline § Mental functions (memory) decline Arachnoid villi – structures that project from the arachnoid layer; where blood is reabsorbed Hydrocephalus – accumulation of CSF in the ventricles Motor Functions Involuntary movements – occur without a conscious thought Voluntary movements – consciously activated to achieve a specific goal; walking, typing Upper motor neurons – have cell bodies in the cerebral cortex Lower motor neurons – have cell bodies in the anterior horn Motor Areas of the Cerebral Cortex Primary motor cortex – control voluntary movements of skeletal muscles Premotor area – where motor functions are organized before they are actually initiated in the primary motor cortex Pre-frontal area – where planning and initiating movements occur Other Brain Functions Communication bet. the Right & Left Hemispheres Commissures – connection bet. the two hemispheres Corpus callosum – largest commissure Speech Sensory speech area – Wernicke area; a portion of the parietal lobe Motor speech area – Broca area; inferior portion of the frontal lobe M o r a n o , M . 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