MTHAPP100LEC CHAPTER 8 NERVOUS SYSTEM.pdf

MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 CHAPTER 8: NERVOUS SYSTEM...

MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 CHAPTER 8: NERVOUS SYSTEM 8.1 FUNCTIONS OF THE NERVOUS SYSTEM OUTLINE Functions of the Nervous System 8.1 Functions of the Nervous System 1. Receiving sensory input 8.2 Divisions of the Nervous System Sensory receptors monitor numerous external and 8.3 Cells of the Nervous System internal stimuli 8.3.1 Neurons 2. Integrating information 8.3.2 Glial Cells Brain and spinal cord – major organs for processing 8.3.3 Myelin Sheaths sensory input and initiating responses 8.3.4 Organization of Nervous Tissue 3. Controlling muscles and glands 8.4 Electrical Signals and Neural Pathways Skeletal muscles – contract only when stimulated by 8.4.1 Resting Membrane Potential the nervous system 8.4.2 Neuron Communication Controls major movements of the body 8.4.3 Neuronal Pathways Controlling cardiac muscle, smooth muscle, and 8.5 Central and Peripheral Nervous Systems 8.6 Spinal Cord many glands 8.6.1 Reflexes 4. Maintaining homeostasis 8.7 Spinal Nerves Homeostasis depends on the nervous system’s 8.8 Brain ability to detect, interpret, and respond to changes in 8.8.1 Brainstem internal and external conditions 8.8.2 Cerebellum 5. Establishing and maintaining mental activity 8.8.3 Diencephalon Brain – center of mental activity, including 8.8.4 Cerebrum consciousness, memory, and thinking 8.9 Sensory Functions 8.9.1 Ascending Tracts 8.9.2 Sensory Areas of the Cerebral Cortex 8.2 DIVISIONS OF THE NERVOUS SYSTEM 8.10 Somatic Motor Functions 8.10.1 Motor Areas of the Cerebral Cortex 8.10.2 Descending Tracts Two Major Divisions 8.10.3 Basal Nuclei 8.10.4 Cerebellum Central Nervous System 8.11 Other Brain Functions o Brain and spinal cord 8.11.1 Communication Between the Right and Left Peripheral Nervous System Hemispheres o Nervous tissue, nerves and ganglia 8.11.2 Speech 8.11.3 Brain Waves and Consciousness Peripheral Nervous System 8.11.4 Memory 8.11.5 Limbic System and Emotions Communication link between the CNS and the various parts of 8.12 Meninges, Ventricles, and Cerebrospinal Fluid the body 8.12.1 Meninges Carries information about the different tissues of the body to 8.12.2 Ventricles the CNS 8.12.3 Cerebrospinal Fluid Delivers commands from the CNS to the other body tissues 8.13 Cranial Nerves that alter body activities 8.14 Autonomic Nervous System Subdivided into two parts: 8.14.1 Anatomy of the Sympathetic Division o Sensory Division or Afferent Division 8.14.2 Anatomy of the Parasympathetic Division ▪ Conducts action potentials from sensory 8.14.3 Autonomic Neurotransmitters receptors to the CNS 8.14.4 Functions of the Autonomic Nervous System ▪ Sensory neurons – transmit action 8.14.5 Diseases and Disorders of the Nervous System 8.15 Enteric Nervous System potentials from the periphery to the CNS o Motor Division or Efferent Division 1  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 ▪ Conducts action potentials from the CNS 8.3 CELLS OF THE NERVOUS SYSTEM to effector organs, such as muscles and glands ▪ Motor neurons – transmit action potentials Two types: neurons and glial cells from the CNS toward the periphery Effectors controlled by the motor division: o Muscle tissue (skeletal, cardiac, smooth) 8.3.1 NEURONS o Glands Subdivisions of Motor Division: o Somatic Nervous System Neurons ▪ Voluntary actions Nerve cells ▪ Transmits action potentials from the CNS Receive stimuli, conduct action potentials, and transmit signals to skeletal muscles to other neurons or effector organs o Autonomic Nervous System Three parts: ▪ Involuntary actions; self-governing o Cell body ▪ Transmits action potentials from the CNS o Dendrites to cardiac muscle, smooth muscle, and o Axons glands Each neuron’s cell body contains a single nucleus ▪ Divided into sympathetic and parasympathetic divisions Dendrites Enteric Nervous System o Unique part of the peripheral nervous system Short, often highly branching cytoplasmic extensions that are o Has both sensory and motor neurons contained tapered from their bases at the neuron cell body to their tips wholly within the digestive tract Extensions of the neuron cell body o Can function without input from the CNS or other Dendrite-like structures also project from the peripheral ends parts of the PNS of some sensory axons Receive information from other neurons of from sensory receptors and transmit toward the neuron cell body Axon Single long cell process extending from the neuron cell body Axon hillock – area where the axon leaves the neuron cell body Each has a uniform diameter and may vary in length from a few millimeters to more than a meter Axons of sensory neurons – conduct action potentials towards the CNS Axons of motor neurons – conduct action potentials away the CNS Also conduct action potentials from one part of the brain or spinal cord to another part May remain unbranched or may branch to form collateral axons Myelin sheath – highly specialized insulating layer of cells; may surround axons Types of Neurons Classified according to the basis of their function and structure Functional Classification o Sensory neuron – carries info to the CNS from a specific receptor 2  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 o Motor neuron – sends info to an effector of the body from the CNS Structural Classification o Multipolar neuron ▪ Have many dendrites and a single axon ▪ Most of the neurons within the CNS and nearly all motor neurons are multipolar o Bipolar neurons ▪ 2 processes: one dendrite and one axon ▪ Located in some sensory organs: retina of the eye and in the nasal cavity o Pseudo-unipolar neurons ▪ Single process extending from the cell body Two extensions o Extends to the periphery o Extends to the CNS These two functions as a single axon with small dendrite-like sensory receptors at the periphery Axon receives sensory information at the periphery and transmits that information in the form of action potentials to the CNS 8.3.2 GLIAL CELLS ▪ With the exception of the bipolar neurons described earlier, most sensory neurons Glial Cells are pseudo-unipolar Neuroglia; nerve glue Supportive cells of the CNS and PNS o Do not conduct action potentials Carry out different activities that enhance neuron function and maintain normal conditions within nervous tissue More numerous than neurons Most retain the ability to divide whereas neurons do not Glial cells in the CNS o Astrocytes ▪ Major supporting cells in the CNS ▪ Can stimulate or inhibit the signaling activity of nearby neurons ▪ Blood-brain barrier – glial cells participate with the blood vessel endothelium to form a permeability barrier ▪ Help limit damage to neural tissue ▪ The repair process can form a scar that blocks regeneration of damaged axons o Ependymal cells ▪ Line the fluid-filled cavities (ventricles and canals) within the CNS 3  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 ▪ Some ependymal cells produce 8.3.3 MYELIN SHEATHS cerebrospinal fluid ▪ Others, with cilia, help move the cerebrospinal fluid through the CNS Myelin Sheaths o Microglia Specialized layers that wrap around the axons of some ▪ Act as immune cells of the CNS neurons ▪ Help protect the brain by removing bacteria Formed by the cell processes of oligodendrocytes in the CNS and cell debris and Schwann cells in the PNS o Oligodendrocytes Myelinated axons – axons with myelin sheaths ▪ Provide an insulating material that Each oligodendrocyte process or Schwann cell repeatedly surrounds axons wraps around a segment of an axon to form a series of tightly Glial cells in the PNS wrapped cell membranes o Schwann cells Excellent insulator that prevents almost all ion movement ▪ Provide an insulating material that across the cell membrane surrounds axons Nodes of Ranvier – gaps in the myelin sheath o Satellite cells o Occur about every millimeter between the ▪ Found around the cell bodies of certain myelinated areas neurons of the PNS o Ion movement can occur at the nodes of Ranvier ▪ Provide support and nutrition to the Myelination of an axon – increases the speed and efficiency of neurons and protect the neurons from action potential generation along the axon heavy-metal poisons, such as lead and Unmyelinated axons - lack the myelin sheaths; however, these mercury axons rest in indentations of the oligodendrocytes in the CNS and the Schwann cells in the PNS A typical small nerve, which consists of axons of multiple neurons, usually contains more unmyelinated axons than myelinated axons Cells of the Nervous System Cell Type Description Function Neuron Most motor Many dendrites Multipolar neurons and most and one axon CNS neurons Found in special One dendrite and sense organs, Bipolar one axon such as eye and nose Appears to have a Most sensory Pseudo-unipolar single axon neurons Glial Cells of the CNS Provide structural Astrocytes Highly branched support; regulate neuronal signaling; 4  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 contribute to o Nerve tracts – white matter of the CNS which blood-brain propagate action potentials from one area of the barrier; help with CNS to another (also called conduction pathways) neural tissue repair o Nerves – white matter of the PNS consists of Line ventricles of bundles of axons and associated connective tissue brain and central that form nerves canal of the spinal cord, circulate Ependymal Cells Epithelial-like cerebrospinal fluid 8.4 ELECTRICAL SIGNALS AND NEURAL PATHWAYS (CSF); some form choroid plexuses, which produce 8.4.1 RESTING MEMBRANE POTENTIAL CSF Protect CNS from infection; become Cells – have electrical properties Microglia Small, mobile cells phagocytic in o Cell membrane – prevents free movement of ions response to into and out of the cell inflammation o Bc of the cell membrane’s hydrophobic interior, ions Cell processes cross it through ion channels Cells with form myelin ▪ Flow of ions through these channels is due processes that can sheaths around Oligodendrocytes to their differences in concentration across surround several axons or enclose the membrane axons unmyelinated axons in the CNS ▪ The flow of ions through these channels Glial Cells of the PNS can also be influenced by their electrical Form myelin charges, because of the attraction sheaths around between opposite charges Single cells Two basic types of ion channels: (+2 apparently) Schwann Cells axons or enclose surrounding axons o Leak channels – always open unmyelinated axons in the PNS o Gated channels – are closed until opened by specific Support neurons, signal providing o Chemically gated channels – are opened by specific Single cells nutrients; protect chemicals Satellite surrounding cell neurons from o Voltage-gated channels – are opened by a change in bodies heavy-metal the electrical property of the cell membrane poisons Inside of cell membrane – negatively charged Outside of cell membrane – positively charged 8.3.4 ORGANIZATION OF NERVOUS TISSUE Polarized – membrane is polarized due to uneven charge distribution across the cell membrane Potential – small voltage difference which can be measured Nervous tissue – varies in color due to the location and across the cell membrane arrangement of the parts of neurons and glial cells Resting membrane potential – small voltage difference which o Exists as gray matter and white matter can be measured across the cell membrane in an unstimulated Gray matter – consists of groups of neuron cell bodies and or resting cell their dendrites, where there is very little myelin o Generated primarily by the uneven distribution of K+, o Cortex – gray matter on the surface of the brain in Na+, and negatively charged proteins across the cell the CNS membrane o Nuclei – clusters of gray matter located deeper within the brain o Ganglion – cluster of neuron cell bodies in the PNS White matter – consists of bundles of parallel axons with their myelin sheaths, which are whitish in color 5  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 Action Potentials Opening and closing of gated ion channels can change the permeability characteristics of the cell membrane and hence 8.4.2 NEURON COMMUNICATION change the membrane potential Electrical signals that are conducted along the cell membrane from one region of the cell to another Neurons and muscle cells – are excitable cells, meaning that Voltage-gated Na+ and K+ channels – responsible for the the resting membrane potential changes in response to stimuli action potential o Muscle cells – change in the resting membrane potential results in contraction o Neurons – this change is a means by which the cell communicates with other cells Three stages of neuron communication o Generation of action potentials o Action potential propagation along the cell membrane o Communication with target cell at the synapse 6  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 o Threshold depolarization – causes voltage- gated Na+ channels to open ▪ Most often reached at the axon hillock near the cell body ▪ Opening of these channels causes a massive, 600-fold increase in membrane permeability to Na+. Voltage- gated K+ channels also begin to open ▪ As more Na+ enters the neuron, depolarization continues at a much faster pace ▪ Eventually a brief reversal of charge takes place across the cell membrane—the inside of the cell membrane becomes positive relative to the outside of the cell membrane 3. Charge reversal – causes Na+ channels to close and Na+ then stops entering the cell. Also, during this time, more K+ channels are opening and K+ leaves the cell. Outward flow of K+ – repolarizes the cell membrane to its resting membrane potential Action potential – depolarization and repolarization Hyperpolarization – the charge of the cell membrane briefly becomes more negative than the resting membrane potential at the end of repolarization The resting membrane potential is set by the activity of the leak channels When stimulated – chemically gated channels are opened and Action Potential Sequence initiate local potentials 1. When the cell membrane is at rest, the voltage-gated o If sufficiently strong, the local potentials activate channels are closed. voltage-gated channels to initiate an action potential 2. Local current – when a stimulus is applied to a muscle cell or Action potentials occur in an all-or-none fashion neuron, following neurotransmitter activation of chemically o If threshold is reached, an action potential occurs; gated channels, Na+ channels open very briefly, and Na+ o If threshold is not reached, no action potential occurs diffuses quickly into the cell Action potentials in a cell are all of the same magnitude—in Causes the inside of the cell membrane to become other words, the amount of charge reversal is always the same positive which is called depolarization o Variation in stimulation is not due to stronger or weaker action potentials, because all action Depolarization – results in a local potential potentials have the same pattern of changes in the membrane potential. If depolarization is not strong enough, the Na+ o Instead, stronger stimuli produce a greater frequency channels close again, and the local potential of action potentials. Thus, neural signaling is based disappears without being conducted along the on the number of action potentials neuron cell membrane If depolarization is large enough, Na+ enters the cell Action Potential Conduction so that the local potential reaches a threshold value Once an action potential is generated, it is conducted along the cell membrane 7  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 Two ways (pattern of action potential conduction along a neuron cell membrane) o Continuous conduction ▪ Occurs in unmyelinated axons (slowly) ▪ Action potential in one part of a cell membrane stimulates local currents in adjacent parts of the cell membrane ▪ Action potential is conducted along the entire axon cell membrane o Saltatory conduction ▪ Occurs in myelinated axons (rapidly) ▪ An action potential at one node of Ranvier causes a local current to flow through the surrounding extracellular fluid and through the cytoplasm of the axon to the next node, stimulating an action potential at that node of Ranvier ▪ Action potentials “jump” from one node of The Synapse Ranvier to the next along the length of the axon Synapse – junction where the axon of one neuron interacts ▪ Saltatory conduction greatly increases the with another neuron or with cells of an effector organ, such as conduction velocity because the nodes of a muscle or gland Ranvier make it unnecessary for action Three major components of a synapse: potentials to travel along the entire cell o Presynaptic terminal – end of the axon membrane o Postsynaptic membrane – membrane of the dendrite Speed of action potential conduction varies widely even or effector cell among myelinated axons o Synaptic cleft – space separating the presynaptic o Medium-diameter, lightly myelinated axons, and postsynaptic membranes characteristic of autonomic neurons, conduct action At most of the synapses in the body, communication between potentials at the rate of about 3–15 meters per the neuron and its target cell occurs through chemical signals second (m/s) Neurotransmitters – chemical substances that act as these o Large-diameter, heavily myelinated axons conduct chemical signals and are stored in synaptic vesicles in the action potentials at the rate of 15–120 m/s presynaptic terminal o These rapidly conducted action potentials, carried Synaptic vesicles – store neurotransmitters by sensory and motor neurons, allow for rapid responses to changes in the external environment. o Several hundred times fewer ions cross the cell membrane during conduction in myelinated cells than in unmyelinated cells. Much less energy is therefore required for the sodium-potassium pump to maintain the ion distribution 8  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 Neurotransmitters Do not normally remain in the synaptic cleft indefinitely o Their effects on the target cell are typically very short-term Reduced in concentration when they are either rapidly broken down by enzymes within the synaptic cleft or are transported back into the presynaptic terminal 8.4.3 NEURONAL PATHWAYS Two Simplest Pathways Converging Pathways Both the specific channel type and whether or not the channel o Two or more neurons synapse with the same opens or closes depend on the type of neurotransmitter in the postsynaptic neuron presynaptic terminal and the type of receptors on the o Allows information transmitted in more than one postsynaptic membrane neuronal pathway to converge into a single pathway The response may be either stimulation or inhibition of an Diverging Pathways action potential in the postsynaptic cell o The axon from one neuron divides and synapses Hyperpolarized - If K+ or Cl− channels open, the inside of the with more than one other postsynaptic neuron postsynaptic cell tends to become more negative o Allows information transmitted in one neuronal pathway to diverge into two or more pathways Summation - summation of signals in neuronal pathways allows integration of multiple subthreshold local potentials o Summation of the local potentials can bring the membrane potential to threshold and trigger an action potential o Two types of summation: 9  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 ▪ Spatial summation – occurs when the local 8.6 SPINAL CORD potentials originate from different locations on the postsynaptic neuron ▪ Temporal summation – occurs when local Spinal Cord potentials overlap in time Extends from the foramen magnum at the base of the skull to the second lumbar vertebra Spinal nerves – communicate between the spinal cord and the body Cauda equina – inferior end of the spinal cord and the spinal nerves exiting there resemble a horse’s tail 8.5 CENTRAL AND PERIPHERAL NERVOUS SYSTEMS CNS Brain o Housed within the skull Spinal cord o In the vertebral column PNS All nerves and ganglia outside the brain and spinal cord Collects information from numerous sources both inside and on the surface of the body and relays it by way of sensory Consists of a superficial white matter portion and a deep gray neurons to the CNS, where one of three results is possible: matter portion o Information is ignored o White matter – consists of myelinated axons o Triggers a reflex o Gray matter – collection of neuron cell bodies o Evaluated more extensively White matter in each half of the spinal cord is organized into Motor neurons – relay info from the CNS to muscles and three columns: glands in various parts of the body o Dorsal column Nerves, 2 groups: o Ventral column o 12 pairs of cranial nerves o Lateral column o 31 pairs of spinal nerves Each column contains ascending and descending tracts or pathways o Ascending tracts – consist of axons that conduct action potentials toward the brain o Descending tracts – consist of axons that conduct action potentials away from the brain 10  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 8.6.1 REFLEXES Reflex Involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS Allow a person to react to stimuli more quickly than is possible if conscious thought is involved Reflex arc – neuronal pathway by which a reflex occurs o Basic functional unit of the nervous system because it is the smallest, simplest pathway capable of receiving a stimulus and yielding a response o 5 basic components: ▪ A sensory receptor; ▪ A sensory neuron; ▪ In some reflexes, interneurons, which are neurons located between and communicating with two other neurons; ▪ A motor neuron; and ▪ An effector organ (muscles or glands). The Gray matter of the spinal cord – shaped like the letter H simplest reflex arcs do not involve o Dorsal horns interneurons. Most reflexes occur in the o Ventral horns spinal cord or brainstem rather than in the Small lateral horns – exist in levels of the spinal cord higher brain centers associated with the autonomic nervous system Central canal – fluid-filled space in the center of the spinal cord Ventral root – ventral rootlets on the ventral side of the spinal cord Dorsal root – dorsal rootlets on the dorsal side of the spinal cord at each segment Dorsal root ganglion – contains the cell bodies of pseudo- unipolar sensory neurons o Axons of these neurons originate in the periphery of the body o Passes through spinal nerves and the dorsal roots to Knee-Jerk Reflex the dorsal horn of the spinal cord gray matter o In the dorsal horn, the axons either synapse with Simplest reflex – stretch reflex interneurons or pass into the white matter and o Occurs when muscles contract in response to a ascend or descend in the spinal cord stretching force applied to them Ventral and lateral horns of the spinal cord gray matter – Knee-jerk reflex / patellar reflex contain the cell bodies of motor neurons, which regulate the o Classic example of the stretch reflex involving the activities of muscles and glands spinal cord Somatic motor neurons – in ventral horn o Determine if the higher CNS centers that normally Autonomic neurons – in the lateral horn influence this reflex are functional Axons from the motor neurons form the ventral roots and pass into the spinal nerves. Thus, the dorsal root contains sensory axons, and the ventral root contains motor axons. Each spinal nerve therefore has both sensory and motor axons 11  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 8.7 SPINAL NERVES Spinal Nerves Arise along the spinal cord from the union of the dorsal roots and ventral roots Mixed nerves – contain axons of both sensory and somatic motor neurons Some spinal nerves also contain parasympathetic or sympathetic axons Most of the spinal nerves exit the vertebral column between adjacent vertebrae Categorized by the region: o Cervical (C) o Thoracic (T) o Lumbar (L) o Sacral (S) o Coccygeal (Co) The spinal nerves are also numbered (starting superiorly) according to their order within that region. The 31 pairs of spinal nerves: Withdrawal Reflex o C1 through C8 Flexor reflex o T1 through T12 Remove a limb or another body part from a painful stimulus o L1 through L5 Sensory receptors – pain receptors; stimulation of these o S1 through S5 receptors initiates the reflex o Co Nerves arising from each region of the spinal cord and vertebral column supply specific regions of the body Dermatome – area of skin supplied with sensory innervation by a pair of spinal nerves Each of the spinal nerves except C1 has a specific cutaneous sensory distribution 12  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 Plexuses – neurons of several spinal nerves come together Originates from spinal nerves C5 to T1 and intermingle Five major nerves emerge from the brachial plexus to supply o Reorganizes the neurons so that branches of nerves the upper limb and shoulder extending from each plexus contain neurons from o Axillary nerve – innervates two shoulder muscles and different spinal segments the skin over part of the shoulder Three major plexuses: o Radial nerve – innervates all the muscles in the o Cervical plexus posterior arm and forearm as well as the skin over o Brachial plexus the posterior surface of the arm, forearm, and hand o Lumbosacral plexus o Musculocutaneous nerve – innervates the anterior Major nerves of the neck and limbs are branches of these muscles of the arm and the skin over the radial plexuses surface of the forearm Coccygeal plexus – supplies motor innervation to the muscles o Ulnar nerve – innervates two anterior forearm of the pelvic floor and sensory cutaneous innervation to the muscles and most of the intrinsic hand muscles skin over the coccyx ▪ Also innervates the skin over the ulnar side of the hand ▪ The ulnar nerve can be easily damaged where it passes posterior to the medial side of the elbow ▪ The ulnar nerve at this location is called the “funny bone.” o Median nerve – innervates most of the anterior forearm muscles and some of the intrinsic hand muscles ▪ Also innervates the skin over the radial side of the hand Lumbosacral Plexus Originates from spinal nerves L1 to S4 Four major nerves exit the lumbosacral plexus to supply the lower limb o Obturator nerve – innervates the muscles of the medial thigh and the skin over the same region o Femoral nerve – innervates the anterior thigh muscles and the skin over the anterior thigh and medial side of the leg o Tibial nerve – innervates the posterior thigh muscles, the anterior and posterior leg muscles, and most of the intrinsic foot muscles ▪ Also innervates the skin over the sole Cervical Plexus of the foot o Common fibular nerve – innervates the muscles Originates from spinal nerves C1 to C4 of the lateral thigh and leg and some intrinsic Branches from this plexus innervate several of the muscles foot muscles attached to the hyoid bone, as well as the skin of the neck and ▪ Also innervates the skin over the posterior portion of the head anterior and lateral leg and the dorsal Phrenic nerve – one of the most important branches of the surface (top) of the foot cervical plexus; innervates the diaphragm Sciatic nerve – tibial and common fibular nerves are bound o Contraction of the diaphragm is largely responsible together within a connective tissue sheath for our ability to breathe Brachial Plexus 13  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 8.8 BRAIN o Breathing o Swallowing o Vomiting Major regions of the brain o Coughing o Brainstem o Sneezing o Cerebellum o Balance o Diencephalon o Coordination o Cerebrum Anterior surface of MO – two prominent enlargements called pyramids Pyramids – consist of descending nerve tracts, which transmit 8.8.1 BRAINSTEM action potentials from the brain to somatic motor neurons of the spinal cord and are involved in the conscious control of Brainstem skeletal muscles Connects the spinal cord to the remainder of the brain Pons Three parts: o Medulla oblongata Superior to the medulla oblongata o Pons Contains ascending and descending nerve tracts, as well as o Midbrain several nuclei Contains several nuclei involved in vital body functions: Some of the nuclei in the pons relay information between the o Control of heart rate cerebrum and the cerebellum o Blood pressure o Resembles an arched footbridge o Breathing Several nuclei of the medulla oblongata extend into the lower Damage to small areas of the brainstem can cause death part of the pons, Nuclei for all but the first two cranial nerves are also located in o Functions such as: the brainstem ▪ Breathing ▪ Swallowing ▪ Balance; are controlled in the lower pons, as well as in the medulla oblongata Other nuclei in the pons control functions such as chewing and salivation Midbrain Superior to the pons Smallest region of the brainstem Colliculi – four mounds of tissue in the dorsal part of the midbrain Two inferior colliculi – major relay centers for the auditory nerve pathways in the CNS Two superior colliculi – involved in visual reflexes and receive touch and auditory input Contains nuclei involved in coordinating eye movements and Medulla Oblongata controlling pupil diameter and lens shape Substantia nigra – black nuclear mass; part of the basal nuclei; Most inferior portion of the brainstem and is continuous with involved in regulating general body movements the spinal cord Rest of the midbrain consists largely of ascending tracts from Extends superiorly from the level of the foramen magnum to the spinal cord to the cerebrum and descending tracts from the pons the cerebrum to the spinal cord or cerebellum Contains ascending and descending nerve tracts, which convey signals to and from other regions of the brain Reticular Formation Contains discrete nuclei with specific functions: o Regulation of heart rate and blood vessel diameter Group of nuclei scattered through the brainstem 14  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 Plays important regulatory functions Small area superior and posterior to the thalamus o Regulating cyclical motor functions Consists of a few small nuclei ▪ Respiration o Involved in the emotional and visceral response to ▪ Walking odors, and the pineal gland ▪ Chewing Pineal gland – endocrine gland that may influence the onset of Reticular activating system – plays an important role in puberty and may play a role in controlling some long-term arousing and maintaining consciousness and in regulating the cycles that are influenced by the light-dark cycle sleep-wake cycle o Ringing alarm clock, sudden bright lights, smelling Hypothalamus salts, or cold water splashed on the face can arouse Most inferior part consciousness Contains several small nuclei that are very important in Conversely, removal of visual or auditory stimuli may lead to maintaining homeostasis drowsiness or sleep Plays a central role in the control of body temperature, hunger, o General anesthetics suppress the reticular activating and thirst system Sensations such as sexual pleasure, rage, fear, and relaxation Damage to cells of the reticular formation can cause coma after a meal are related to hypothalamic functions Emotional responses 8.8.2 CEREBELLUM o Nervous perspiration o Emotional eating Infundibulum – funnel-shaped stalk; extends from the floor of Cerebellum the hypothalamus to the pituitary gland Also plays a major role in controlling the secretion of hormones Attached to the brainstem by cerebellar peduncles from the pituitary gland Cerebellar peduncles – several large connections Mammillary bodies – form externally visible swellings on the o Provide routes of communication between the posterior portion of the hypothalamus; are involved in cerebellum and other parts of the CNS emotional responses to odors and in memory 8.8.3 DIENCEPHALON Diencephalon Part of the brain between the brainstem and the cerebrum Main components: o Thalamus o Epithalamus o Hypothalamus Thalamus Largest part of the diencephalon Consists of a cluster of nuclei and is shaped somewhat like a 8.8.4 CEREBRUM yo-yo, with two large, lateral parts connected in the center by a small interthalamic adhesion Cerebrum Most sensory input that ascends through the spinal cord and brainstem projects to the thalamus Largest part of the brain Ascending neurons synapse with thalamic neurons, which in Longitudinal fissure – divides into left and right and right turn send their axons to the cerebral cortex hemispheres Influences mood and registers an unlocalized, uncomfortable Gyri – numerous folds on the surface of each hemisphere perception of pain Sulci - intervening grooves Central sulcus – separates the frontal and parietal lobe Epithalamus 15  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 Lateral fissure – separates the temporal lobe from the rest of 8.9.1 ASCENDING TRACTS the cerebrum 5 Lobes of the Cerebrum Ascending Tracts 1. Frontal lobe – voluntary motor functions, motivation, Pathways that transmit information via action potentials from aggression, mood, and smell reception the periphery to various parts of the brain 2. Parietal lobe – principal center for receiving and consciously Found in spinal cord and brainstem perceiving most sensory information, such as touch, pain, Each tract is involved with a limited type of sensory input: temperature, and balance o Pain 3. Occipital lobe – receiving and perceiving visual input and is not o Temperature distinctly separate from the other lobes o Touch 4. Temporal lobe – olfactory (smell) and auditory (hearing) o Position sensations and plays an important role in memory o Pressure Psychic cortex – anterior and inferior portions ▪ Each tract contains axons from specific associated with abstract thought and judgment sensory receptors specialized to detect a 5. Insula – deep within the lateral fissure; perception of taste particular type of stimulus Spinothalamic Tract Transmits action potentials dealing with sensations such as pain and temperature to the thalamus and on to the cerebral cortex Dorsal Column Transmits action potentials dealing with sensations such as touch, pressure, and proprioception Proprioception – body position Spinocerebellar Tracts Transmit information about proprioception to the cerebellum 8.9 SENSORY FUNCTIONS Sensory input – results in perception which is the conscious awareness of stimuli 16  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 ▪ Thalamic neurons – relay the information to the primary somatosensory cortex o Sensory fibers from specific parts of the body project to specific regions of the primary somatosensory cortex so that a topographic map of the body, with the head most inferior, exists in this part of the cerebral cortex o Other primary sensory areas ▪ Visual cortex in the occipital lobe ▪ Primary auditory cortex in the temporal lobe ▪ Taste area in the insula Association areas o Cortical areas immediately adjacent to the primary sensory areas involved in the process of recognition 8.10 SOMATIC MOTOR FUNCTIONS Somatic Motor System Responsible for maintaining the body’s posture and balance, as well as moving the trunk, head, limbs, tongue, and eyes Allows us to communicate through facial expressions and speech Reflexes mediated through the spinal cord and brainstem are responsible for some body movements Involuntary movements – occur without conscious thought Voluntary movements – consciously activated to achieve a specific goal, such as walking or typing Voluntary Movements Result from the stimulation of neural circuits that consist of two motor neurons: o Upper motor neurons 8.9.2 SENSORY AREAS OF THE CEREBRAL CORTEX o Lower motor neurons ▪ Have cell bodies in the ventral horn of the spinal cord gray matter or in cranial nerve Primary sensory areas nuclei o Ascending tracts project to specific regions of the ▪ Axons of lower motor neurons leave the cerebral cortex where sensations are perceived central nervous system and extend Primary somatosensory cortex through spinal or cranial nerves to skeletal o General sensory area muscles o Is located in the parietal lobe posterior to the central sulcus o Sensory fibers carrying sensory input 8.10.1 MOTOR AREAS OF THE CEREBRAL CORTEX ▪ Pain ▪ Pressure ▪ Temperature Primary motor cortex – located in the posterior portion of the ▪ Synapse in the thalamus frontal lobe, directly anterior to the central sulcus 17  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 o Action potentials initiated in this region control voluntary movements of skeletal muscles Premotor area of the frontal lobe – where motor functions are organized before they are actually initiated in the primary motor cortex Prefrontal area – anterior portion of the frontal lobes in which motivation and foresight to plan and initiate movements occur o Involved in motivation and regulation of emotional behavior and mood 8.10.2 DESCENDING TRACTS Direct tracts – extend directly from upper motor neurons in the cerebral cortex to lower motor neurons in the spinal cord Indirect tracts – no direct connection exists between the cortical and spinal neurons 8.10.3 BASAL NUCLEI Basal Nuclei Group of functionally related nuclei Two primary nuclei: o Corpus striatum – located deep within the cerebrum o Substantia nigra – group of darkly pigmented cells in the midbrain Important in planning, organizing, and coordinating motor movements and posture Disorders of the basal nuclei result in difficulty rising from a sitting position and difficulty initiating walking 18  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 8.10.4 CEREBELLUM Commissures – connections between two hemispheres where sensory info is received by one hemisphere and shared to the other Cerebellum Corpus callosum – largest commissure; a broad band of nerve tracts at the base of the longitudinal fissure Attached by cerebellar peduncles to the brainstem Cerebellar cortex – composed of grey matter and has gyri and sulci 8.11.2 SPEECH Maintaining balance and muscle tone and in coordinating fine motor movement If damaged – muscle tone decreases, and fine motor Left cerebral cortex – speech area movements become very clumsy Two major cortical areas: Major function – comparator o Sensory speech area (Wernicke area) – located in Comparator – sensing device that compares the data from two the parietal lobe, functions in understanding and sources – motor cortex and peripheral structures formulating coherent speech o The result of the cerebellar comparator function is o Motor speech area (Broca area) – located in the smooth and coordinated movements frontal lobe controls the movement necessary for Another function of the cerebellum involves participating with speech the cerebrum in learning motor skills Aphasia – damage to these parts of the brain or to associated brain regions o Most common cause – stroke Speech related functions – sensory and motor pathways To repeat a word that you hear involves the following sequence of events: 1. Action potentials from the ear reach the primary auditory cortex, where the word is perceived. 2. The word is recognized in the auditory association area and comprehended in portions of the sensory speech area. 3. Action potentials representing the word are then conducted through nerve tracts that connect the sensory and motor speech areas. 4. In the motor speech area, the muscle activity needed to repeat the word is determined. 5. Action potentials then go to the premotor area, where the movements are programmed. 6. Finally, action potentials are conducted to the primary motor cortex, where specific movements are 8.11 OTHER BRAIN FUNCTIONS triggered. Speaking a written word involves a slightly different pathway: 8.11.1 COMMUNICATION BETWEEN THE RIGHT AND LEFT 1. The information enters the visual cortex, then passes HEMISPHERES to the visual association area, where it is recognized. 2. The information continues to the sensory speech area, where it is understood and formulated as it is to Right cerebral hemisphere – receives sensory input from and be spoken. From the sensory speech area, it follows controls muscular activity in the left half of the body the same route for repeating words that you hear: o More involved in 3-dimensional or spatial perception 3. Through nerve tracts to the motor speech area, and musical ability 4. To the premotor area, and then to Left cerebral hemisphere – receives input from and controls 5. The primary motor cortex. muscles in the right half of the body o More analytical, mathematical and speech 19  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 8.11.3 BRAIN WAVES AND CONSCIOUSNESS Limbic System Limbic – olfactory cortex and certain deep cortical regions and Different levels of consciousness can be revealed by different nuclei of the cerebrum and the diencephalon are grouped patterns of electrical activity in the brain together under this title Electroencephalogram (EEG) – brain’s electrical activity Influences long-term declarative memory, emotions, visceral Electrodes – detect the simultaneous action potentials in large responses to emotions, motivation, and mood number of neurons Major source of sensory input – olfactory nerves Most of the time, EEG patterns are irregular Brain waves – EEG patterns detected as wavelike patterns Alpha waves – observed in a normal person who is awake but in a quiet, resting state with eyes closed Beta waves – higher frequency than alpha waves; occur during intense mental activity Delta waves – occur during deep sleep, in infants, and in patients with severe brain disorders Theta waves – usually observed in children but can also occur in adults who are experiencing frustration or who have certain brain disorders 8.11.4 MEMORY 8.12 MENINGES, VENTRICLES, AND CEREBROSPINAL FLUID Three divisions of storage of memory: 8.12.1 MENINGES o Working o Short-term Meninges o Long-term Working memory – brain briefly stores information required for Surround and protect the brain and spinal cord the immediate performance of a task Include: Short-term memory – lasts longer than working memory and o Dura mater can be retained for a few minutes to a few days o Arachnoid mater o Stored by a mechanism involving increased synaptic o Pia mater transmission Dura mater – most superficial and thickest o Susceptible to brain trauma, such as physical injury o Consists of two layers or decreased oxygen, and to certain drugs that affect ▪ In contact over much of their surface neural function, such as general anesthetics ▪ In some areas, the two layers separate to Long-term memory – may be stored for only a few minutes or form dural folds and dural venous sinuses become permanent, by consolidation Subdural hematoma – damage to the veins crossing between o Consolidation – a gradual process involving the the cerebral cortex and the dural venous sinuses can cause formation of new and stronger synaptic connection bleeding into the subdural space which can put pressure on o Declarative memory – explicit memory; involves the the brain retention of facts, such as names, dates, and places, Epidural space – space between the dura mater and the as well as related emotional undertones vertebrae o Procedural memory – reflexive memory; involves the o Injection site for epidural anesthesia of the spinal development of motor skills, such as riding a bicycle nerves; often given to females during childbirth Memory engrams – memory traces; involved in the long-term Arachnoid mater – second meningeal membrane; very thin, retention of a given piece of information, a thought, or an idea and wispy Subdural space – space between dura mater and arachnoid mater 8.11.5 LIMBIC SYSTEM AND EMOTIONS o Potential space containing a small amount of serous fluid 20  MTHAPP111 – ANATOMY & PHYSIOLOGY W/ PATHOPHYSIOLOGY LECTURE | FIRST SEMESTER TRINITY UNIVERSITY OF ASIA VERDE, E.J. | 1MT03 Pia mater – third meningeal membrane; tightly bound to the surface of the brain and spinal cord Subarachnoid space – space between the arachnoid mater and the pia mater which is filled with cerebrospinal fluid and contains blood vessels 8.12.3 CEREBROSPINAL FLUID Cerebrospinal Fluid Bathes the brain and spinal cord, providing a protective cushion around the CNS Choroid plexus – produces CSF o Specialized structures located in the ventricles and composed of ependymal cells Fills the brain ventricles, the central canal of the spinal cord, and the subarachnoid space Hydrocephalus – blockage of the openings in the fourth ventricle or the cerebral aqueduct can cause CSF to