Nervous System PDF

Cells of the Nervous System Nervous System Neurons Functions (CRIME) § Also called nerve cells 1. Controlling muscles and glands. § Receive stimuli, conduct actio...

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