NERVOUS SYSTEM - DIVISION OF NS.pdf
- 1. FUNCTIONS OF THE NERVOUS SYSTEM 1. Sensory input— gathering information • Sensory receptors monitor changes, called stimuli, occurring inside and outside the body. 2. Integrating Information • Nervous system processes and interprets sensory input and decides whether action is needed 3. Motor output • A response, or effect, activates muscles or glands 4. Maintaining Homeostasis • The nervous system plays an important role in maintaining homeostasis. This function depends on the nervous system’s ability to detect, interpret, and respond to changes in internal and external conditions. 5.Establishing and maintaining mental activity • The brain is the center of mental activity, including consciousness, memory, and thinking. DIVISIONS OF NS Central Nervous System • Brain - Part of the CNS that is located in the skull and contains about 85 billion neurons • Spinal Cord - Connected to the brain through the Foramen Magnum of the occipital bone and is encircled by the bones of the vertebral column. Peripheral Nervous System • Nerve 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 → Somatic Sensory Fibers – carry info from stimuli coming from the skin, skeletal, muscles, joints → 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 → 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 ➢ Sympathetic – fight-or-flight system ➢ 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 action potentials, transmit signals Cell body (Soma) – contains a single nucleus; source of information for gene expression 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 ➢ Axon of sensory neurons – conduct action potentials towards the CNS ➢ Axon of motor neurons – conduct action potentials away from the CNS Axon hillock – where the axon leaves the neuron cell body The “control center” of the body NERVOUS SYSTEM "One of the smallest yet most complex body system"
- 2. 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 • Can divide to produce more cells 1. Astrocytes – major supporting cells in the CNS; stimulate/inhibit the signaling activity of nearby neurons; help limit damage to neural tissue • 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 4. Oligodendrocytes (CNS) and (5) 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 (3-15 meters/sec) by salutatory conduction • Nodes of Ranvier – gaps in the myelin sheath; where ion movement can occur
- 3. Continuous Conduction in an Unmyelinated Axon Organization of Nervous Tissue Gray Matter groups of neuron cell bodies + their dendrites; very little myelin In the CNS; ➢ Cortex – GM on the surface of the brain ➢ Nuclei – GM located deeper within the brain In the PNS; ➢ Ganglion – a cluster of neuron cell bodies White Matter bundles of parallel axons + myelin sheaths In the CNS ➢ Nerve tracts – conduction pathways; propagate action potentials from one area of the CNS to another In the PNS; ➢ Nerves – bundles of axons + connective tissue sheaths 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 → Higher concentration of K+ inside CM → Higher concentration of Na+ outside CM → Greater permeability of CM to K+ than to Na+ • Leak channels – always open; K+ channels • Gated channels – closed until opened by specific signals; Na+ channels • Chemically gated channels – opened by neurotransmitters • 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
- 4. • Excitable cells – RMP changes in response to stimuli that activate gated ion channels • Local current – Na+ diffuses quickly into cell • Depolarization – a change that causes the inside of the CM to become positive • Local potential – result of depolarization • 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 Ranvier to the next 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 • Neurotransmitters – chemical messengers’ • Synaptic vesicles – where neurotransmitters are stored • Hyperpolarized – the inside of the postsynaptic cell tends to become more negative
- 5. REFLEX • an involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS 2 types of reflex Somatic reflexes → Reflexes that stimulate the skeletal muscles → Involuntary, although skeletal muscle is normally under voluntary control → Example: pulling your hand away from a hot object Autonomic reflexes → Regulate the activity of smooth muscles, the heart, and glands → Example: regulation of smooth muscles, heart and blood pressure, glands, digestive system Reflex arc neuronal pathway by which a reflex occurs 5 elements of Reflex Arc 1. Sensory receptors – reacts to a stimulus 2. Sensory (afferent) neurons – carries message to the integration center 3. Interneurons (Association) neuron- processes information and directs motor output 4. Efferent (motor) neurons - send response to effector 5. Effector - muscle, gland, or organ Types of Reflex Arc Two – neuron arcs : simplest type Three – neuron arcs: Consists of five elements: receptor, sensory neuron, interneuron, motor neuron, and effector. 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 Converging and Diverging Pathways in the Nervous System
- 6. BRAIN • Soft, wrinkled mass of tissue that is highly • complex and adaptive; 3 pounds • 25 billion neurons • Requires a continuous supply of oxygen and glucose I. Brainstem • Connects the spinal cord to the remainder of the brain • Controls the heart rate, blood pressure, and breathing • Damage can cause death 1. 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 → Cardiac centers – control HR → Vasomotor centers – regulates BP but controlling blood vessel diameter → Respiratory centers – initiates and regulates breathing • Pyramids – two prominent enlargements 2. Pons (bridge) • Relay information bet. the cerebrum and the cerebellum • Resembles an arched footbridge • Regulates respiration, swallowing, sleep 3. Midbrain Location: above pons Function: coordinated eye movement, pupil diameter, tuning head toward noise. Smallest region of the brainstem • 4 mounds called the colliculi → 2 inferiors; major relay centers for the auditory nerve pathways in the CNS → 2 superiors; visual reflexes and receive touch and auditory input 4. 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 II. Diencephalon Part bet. the brainstem and the cerebrum 1. Thalamus • Largest part of the diencephalon • Major relay center for all sensory info (except smell) to the cerebrum; plays a gating role • Influences mood and registers an uncomfortable perception of pain • Interthalamic adhesion – connects the two large, lateral parts of the thalamus 2. Epithalamus • Smallest area superior + posterior to the thalamus • Consists of few small nuclei (emotional and visceral response to odors) + pineal gland Pineal gland – an endocrine gland that may influence the onset of puberty; role in controlling some long-term cycles
- 7. 3. 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. ❖ 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. Cerebellum • Second largest part of the brain; 2hemispheres • 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 1. Helps in smooth and coordinated body movements (comparator function). 2. Maintains muscle tone posture. 3. Maintain balance and equilibrium 4. Important in learning motor skills. IV. Cerebrum Largest and most prominent part of the brain 1. Sensory Function – receives info from sensory receptors and interprets it 2. Motor Function – responsible for all voluntary movement and some involuntary ones 3. Association Function – responsible for all of the intellectual activities of brain 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 – responsible 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) Sulci – shallow grooves 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 left hemispheres 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
- 8. • Corpus striatum – located deep within the cerebrum • Substantia nigra – darkly pigmented cells in the midbrain Right and Left Hemispheres • Right hemisphere – three dimensional or spatial perception, musical ability • 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 Amygdala – filter sensory info and evaluates it in terms of emotional needs MENINGES, VENTRICLES, AND CEREBROSPINAL FLUID Meninges Surround and protect the brain and spinal cord 1. Dura mater Most superficial and thickest meninges ❖ Epidural space – bet. the dura mater & the vertebrae ❖ Epidural anesthesia – clinically important as the injection site of spinal nerves; given to women during childbirth 2. Arachnoid mater Thin, wispy, 2nd meningeal membrane ❖ Subdural space – space bet. the dura mater and the arachnoid mater; contains small amt. of serous fluid ❖ Spinal block – to inject anesthetic into the area ❖ 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 ❖ Subarachnoid space – bet. the arachnoid and pia matter Ventricles • Fluid filled cavities Lateral ventricle – relatively large cavity in each cerebral hemisphere Third ventricle – a smaller, midline cavity Fourth ventricle – located at the base of the cerebellum
- 9. Cerebral aqueduct – a narrow canal that connects the 3rdand 4th ventricle Cerebrospinal fluid • Provides a protective cushion around the CNS • Fluid that bathes the brain and spinal cord Choroid plexus – produces CSF; specialized structures made of ependymal cells 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; where words are heard and comprehended Motor speech area – Broca area; inferior portion of the frontal lobe; where words are formulated Aphasia – absent/defective speech/language comprehension Brain Waves and Consciousness Electroencephalogram (EEG) - electrodes plated on scalp to record brain’s electrical activity Brain waves – wave like patterns Alpha waves – awake but in a quiet, resting state with eyes close Beta waves – occur during intense mental activity Delta waves – occur during deep sleep in infants and in patients Theta waves – observed in children; also, in adults who are frustrated or have brain disorders INNERVATION OF ORGANS BY THE ANS
- 10. 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. White Matter of the SC Outside of spinal cord Contains myelinated fibers 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 1. Posterior horns 2. Anterior horns 3. Small lateral horns → Central canal – fluid filled space in the center of the cord → Ventral root – formed by ventral rootlets; → Dorsal root – formed by dorsal rootlets → Dorsal root ganglion – ganglion in a dorsal root Reflex Action • Predictable, automatic response to a specific stimulus 1. Reception of the stimulus. 2. Transmission of info to the CNS. 3. Integration (interpretation and determination of an appropriate response). 4. Transmission of info from the CNS to a muscle. 5. 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 the periphery to various parts of the brain Spinothalamic tract – transmits pain, light touch, and deep pressure 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 – muscle tone and skilled movements (hand) Anterior corticospinal – muscle tone and movement of trunk muscles Rubrospinal – movement coordination
- 11. Reticulospinal – posture adjustment Vestibulospinal – posture & balance Tectospinal – movement in response to visual reflexes CROSS SECTION OF THE SPINAL CORD CRANIAL NERVES • Transmit info to the brain form the sensory receptors SPINAL NERVES Arise along the spinal cord; contains mixed nerves • 31 pairs • 8 Cervical • 12 Thoracic • 5 Lumbar • 5 Sacral • 1 Coccygeal Mixed nerves contains both sensory and somatic motor neurons Plexuses where nerves come together and then separate Cervical Plexus • Originates from spinal nerves C1 to C4 • Innervates muscles attached to hyoid bone and neck • Contains phrenic nerve which innervates diaphragm Phrenic nerve - most important branch of the CP; innervates the diaphragm (responsible for our ability to breathe) Brachial Plexus • Originates from the spinal nerves C5 to T1 • Supply nerves to upper limb, shoulder and hand 1. Axillary nerve – innervates 2 shoulder muscles the skin over part of it 2. Median nerve – innervates the anterior forearm and intrinsic muscles 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 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 • Supply nerves lower limbs 1. Obturator nerve – innervates the muscles of the medial thigh + skin over it
- 12. 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 Sciatic nerve – CT sheath that bounds the tibial and common fibular nerve AUTONOMIC NERVOUS SYSTEM • Preganglionic neuron • Postganglionic neuron • Maintain internal homeostasis Autonomic ganglia Where preganglionic neurons synapse with postganglionic neurons I. Sympathetic ANS • ’Fight-or-flight’ • Prepares the body for action • Most active during stressful situations • Norepinephrine (main neurotransmitter) II. 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 Autonomic Neurotransmitters • Acetylcholine – neurotransmitters of the parasympathetic division • Norepinephrine – postganglionic neurons of the sympathetic division Functions of the Autonomic Nervous System Sympathetic Division Prepares a person for action by increasing HR, BP, respiration, release of glucose 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. Sensory neurons – connect the digestive tract to the CNS 2. Sympathetic & parasympathetic neurons –connect the CNS to the digestive tract 3. Enteric neurons – located entirely within enteric plexus Capable of monitoring and controlling the digestive tract independently of the CNS