Nervous System PDF

Table of Contents Types of Reflexes................................................ 19 Lesson 5: Nervous System.............................................. 2 Central Nervous System.............................................. 22 In...

Table of Contents Types of Reflexes................................................ 19 Lesson 5: Nervous System.............................................. 2 Central Nervous System.............................................. 22 Introduction to the Nervous System............................ 2 Functional Anatomy of the Brain............................. 22 Organization of the Nervous System............................ 2 Cerebral Hemispheres............................................ 22 Structural Classification............................................ 3 Cerebral Cortex................................................... 24 Central Nervous System........................................... 3 Cerebral White Matter.......................................... 27 Peripheral Nervous System...................................... 3 Basal Nuclei........................................................ 27 Functional Classification........................................... 4 Diencephalon.......................................................... 28 Sensory Division....................................................... 4 Thalamus............................................................ 28 Motor Division.......................................................... 4 Hypothalamus..................................................... 28 Somatic Nervous System...................................... 4 Epithalamus........................................................ 28 Autonomic Nervous System.................................. 4 Brain Stem.............................................................. 29 Nervous Tissue: Structure and Function..................... 6 Midbrain.............................................................. 29 Supporting Cells in CNS............................................ 6 Pons................................................................... 29 Astrocytes................................................................ 6 Medulla Oblongata.............................................. 29 Microglia.................................................................. 6 Reticular Formation............................................. 29 Ependymal Cells...................................................... 6 Cerebellum............................................................. 30 Oligodendrocytes..................................................... 6 Homeostatic Imbalance....................................... 30 Supporting Cells in PNS............................................ 6 Insula...................................................................... 30 Schwann Cells......................................................... 6 Protection of the Central Nervous System.............. 33 Satellite Cells........................................................... 6 Meninges................................................................ 33 Neurons...................................................................... 8 Homeostatic Imbalance....................................... 33 Anatomy................................................................... 8 Cerebrospinal Fluid................................................. 33 Cell Body.............................................................. 8 Homeostatic Imbalance....................................... 33 Processes............................................................. 8 Blood-Brain Barrier................................................. 34 Myelin Sheaths................................................... 10 Brain Dysfunction.................................................... 34 Homeostatic Imbalance.......................................... 10 Traumatic Brain Injuries.......................................... 34 Terminologies......................................................... 10 Cerebrovascular Accident....................................... 34 Classification of Neurons........................................ 13 Alzheimer’s Disease............................................... 35 Functional Classification......................................... 13 Parkinson’s Disease............................................... 35 Sensory Neurons................................................ 13 Huntington’s Disease.............................................. 35 Motor Neurons.................................................... 13 Spinal Cord............................................................... 36 Interneurons....................................................... 13 Gray Matter of the Spinal Cord and Spinal Roots..... 37 Structural Classification.......................................... 14 Homeostatic Imbalance....................................... 37 Multipolar Neurons.............................................. 14 White Matter of the Spinal Cord............................... 39 Bipolar Neurons.................................................. 14 Homeostatic Imbalance....................................... 39 Unipolar Neurons................................................ 14 Peripheral Nervous System......................................... 40 Physiology............................................................... 16 Structure of Nerves.................................................. 40 Nerve Impulses...................................................... 16 Cranial Nerves.......................................................... 44 Electrical Conditions of a Resting Neuron’s Spinal Nerves and Nerve Plexuses.......................... 48 Membrane.......................................................... 16 Autonomic Nervous System.................................... 51 Action Potential Initiation and Generation............ 16 Somatic Vs. Autonomic Nervous System................. 51 Propagation of the Action Potential...................... 16 Anatomy of the Parasympathetic Division................ 53 Repolarization..................................................... 16 Anatomy of the Sympathetic Division...................... 53 Initial Ionic Conditions Restored.......................... 16 Autonomic Functioning............................................ 55 Transmission of the Signal at Synapses.............. 17 Sympathetic Division........................................... 55 Reflexes................................................................. 19 Parasympathetic Division..................................... 55 Somatic Reflexes................................................ 19 Development Aspects of the Nervous System........... 56 Autonomic Reflexes............................................ 19 Homeostatic Imbalance............................................ 56 5 Elements of a Reflex Arc.................................. 19 1 LESSON 5: NERVOUS SYSTEM Organization of the Nervous System Introduction to the Nervous System → master controlling & communicating system of the body → electrical impulses ▪ signaling device or means of communicating with body cells → has 3 overlapping functions: ▪ Sensory Input  uses millions of sensory receptors to monitor changes inside and outside the body  changes = stimuli  gathered information = sensory input ▪ Integration  it processes and interprets the sensory input  decides what should be done at each moment ▪ Motor Output  it then effects a response by activating muscles or glands (effectors) via motor output → works with the endocrine system to regulate and maintain homeostasis ▪ a second important regulating system ▪ the nervous system controls with rapid electrical nerve impulses ▪ the endocrine system controls through hormones produced by its organs and released into the blood ▪ brings effects in a more leisurely way 2 Structural Classification → includes all nervous system organs → has 2 subdivisions: ▪ Central Nervous System (CNS) ▪ Peripheral Nervous System (PNS) Central Nervous System → consists of the brain and spinal cord ▪ occupy the dorsal body cavity → act as the integrating and command centers of the nervous system → interpret incoming sensory information → issue instructions based on experience and current conditions Peripheral Nervous System → part of the NS outside the CNS → consists of mainly nerves ▪ extend from the brain and spinal cord ▪ Spinal nerves  carry impulses to and from the spinal cord ▪ Cranial nerves  carry impulses to and from the brain → these nerves serve as communication lines → link all parts of the body ▪ by carrying impulses from sensory receptors to the CNS and from the CNS to the appropriate glands or muscles → sensory receptors → impulse → CNS → impulse → glands/muscles 3 Functional Classification Motor Division → concerned only with PNS structures → aka efferent division → divides PNS into 2 principal subdivisions: → carries impulses from the CNS to: ▪ Sensory Division ▪ effector organs ▪ Motor Division ▪ muscles ▪ glands  these impulses activate muscles and Sensory Division glands → aka afferent division  they effect (bring about) a motor → consists of nerves response ▪ composed of nerve fibers → has 2 subdivisions: ▪ send impulses to the CNS from sensory ▪ Somatic Nervous System receptors ▪ Autonomic Nervous System → this division keeps the CNS informed of events happening Somatic Nervous System inside and outside the body → aka voluntary nervous system → somatic sensory fibers ▪ aka somatic afferents → allows us to consciously or voluntarily control our skeletal muscles ▪ sensory fibers that deliver impulses from: ▪ but NOT ALL skeletal muscle activity controlled  skin by this subdivision is voluntary  skeletal muscles  skeletal muscle reflexes like the stretch  joints reflex are an exception → visceral sensory fibers  these are initiated involuntarily by ▪ aka visceral afferents these same fibers ▪ transmits impulses from visceral organs Autonomic Nervous System → aka involuntary nervous system → regulates events that are automatic or involuntary ▪ such as the activity of smooth and cardiac muscles and glands → has 2 subdivisions: ▪ Sympathetic Nervous System  stimulates  fight or flight ▪ Parasympathetic Nervous System  inhibits  rest and digest 4 Astrocytes (a) form a living barrier between neurons and capillaries in the CNS. Microglia (b) are phagocytes, whereas ependymal cells (c) line the fluid-filled cavities of the CNS. The oligodendrocytes (d) form myelin sheaths around nerve fibers in the CNS. (e) The relationship of Schwann cells (myelinating cells) and satellite cells to a neuron in the peripheral nervous system 5  Nervous Tissue: Structure and Function Oligodendrocytes → nervous tissue is made up of 2 principal types of cells: → glia that wraps their flat extensions tightly around nerve ▪ Supporting Cells fibers ▪ Neurons → produces fatty insulating coverings called myelin sheaths Supporting Cells in CNS Important Note: → lumped together as neuroglia → glial cells resemble neurons structurally ▪ literally means “nerve glue” ▪ both cell types have cell extensions → includes many types of cells that generally: However, ▪ support → glial cells cannot transmit nerve impulses which ▪ insulate neurons can ▪ protect delicate neurons → glial cells never lose their ability to divide → each different types of neuroglia have special functions ▪ most neurons lose this ability ▪ can be called also as:  glia → most brain tumors are gliomas  glial cells ▪ tumors formed by glial cells (neuroglia) → CNS glia includes: ▪ Astrocytes Supporting Cells in PNS ▪ Microglia ▪ Ependymal Cells → comes in 2 major varieties: ▪ Oligodendrocytes ▪ Schwann Cells ▪ Satellite Cells Astrocytes Schwann Cells → star-shaped cells ▪ account for nearly half of the neural tissue → form myelin sheaths around nerve fibers found in the PNS → their numerous projections have swollen ends that cling Satellite Cells to neurons ▪ braces and anchors them to blood capillaries → act as protective and cushioning cells for neural cell  their nutrient supply bodies → form a living barrier between capillaries and neurons ▪ play a role in making exchanges between the 2 ▪ help protect neurons from harmful substances found in blood → help control the chemical environment in the brain by: ▪ mopping up leaked potassium ions ▪ recapturing released neurotransmitters Microglia → spiderlike phagocytes ▪ dispose of:  debris  dead brain cells  bacteria Ependymal Cells → line the central cavities of the brain and spinal cord → the beating of their cilia helps circulate cerebrospinal fluid ▪ help fills cavities ▪ forms a protective cushion around the CNS 6 7 Neurons Processes → processes or fibers vary in length Anatomy ▪ from microscopic to 3 - 4 feet → neurons ▪ aka nerve cells → the longest processes in humans reach from the lumbar ▪ highly specialized to transmit messages (nerve region of the spine to the great toe impulses) from one part of the body to another → dendrites → common features of neurons: ▪ convey incoming messages (electrical signals) ▪ cell body TOWARD the cell body  contains nucleus  metabolic center of the cell → axons ▪ generate nerve impulses ▪ process  conduct them AWAY from the cell body  one or more slender processes extending from the cell body → neurons may have hundreds of branching dendrites ▪ dendr = tree Cell Body ▪ but has only one axon which arises from the → the metabolic center of the neuron axon hillock  conelike region of the cell body → has a nucleus that contains a conspicuous nucleolus → occasional axon gives off a collateral branch along its → has cytoplasm surrounding the nucleus length ▪ contains usual organelles ▪ but all axons branch profusely at their terminal  except for centrioles ends  gives the amitotic nature of  forming hundreds to thousands of most neurons axon terminals → abundant organelles in the cell body: → axon terminals ▪ Rough Endoplasmic Reticulum ▪ contains hundreds of tiny vesicles or  aka Nissl substance membranous sacs that contain chemicals called neurotransmitters ▪ Neurofibrils  axons transmit nerve impulses away  intermediate filaments are important in from the cell body maintaining cell shape  when these impulses reach the axon terminals it stimulates the release of these chemicals into the extracellular space → synaptic cleft ▪ the tiny gap that separates an axon terminal from the next neuron ▪ the tiny gaps are close but never touch other neurons ▪ synapse  a functional junction  syn = to clasp or join 8 (a–c) As illustrated (top to bottom), a Schwann cell envelops part of an axon in a trough and then rotates around the axon. Most of the Schwann cell cytoplasm comes to lie just beneath the exposed part of its plasma membrane. The tight coil of plasma membrane material surrounding the axon is the myelin sheath. The Schwann cell cytoplasm and exposed membrane are referred to as the neurilemma. 9 Myelin Sheaths ▪ the affected person may:  have visual and speech disturbances → myelin  lose the ability to control muscles ▪ covers most long nerve fibers  become increasingly disabled ▪ whitish, fatty material with a waxy appearance → there is no cure but injections of interferon hold the ▪ protects and insulates fibers symptoms at bay and provide some relief ▪ a hormone substance released by some ▪ increases transmission rate of nerve impulses immune cells ▪ axons around the CNS are myelinated by Terminologies Schwann cells → nuclei → these cells wrap themselves around an axon in a jelly-roll ▪ cell bodies cluster in CNS fashion ▪ when the wrapping process is done, the myelin ▪ a well-protected location within the bony skull or sheath encloses the axon vertebral column  a tight coil of wrapped membranes ▪ essential to the well-being of the nervous system → neurilemma ▪ the outermost nucleated cytoplasmic layer of → neurons do not undergo cell division after birth Schwann cells that surrounds the axons ▪ if their cell bodies are damaged  the cell dies and is not replaced → nodes of Ranvier ▪ gaps or indentations formed due to many → ganglia individual Schwann cells ▪ ganglion if singular ▪ occurs at regular intervals ▪ small collections of cell bodies found outside the CNS (in the PNS) → myelinated fibers are also found in the CNS ▪ it is the oligodendrocytes that form the CNS → tracts myelin sheaths ▪ bundle of nerve fibers (neuron processes) running through the CNS ▪ Schwann cells  coil around a small segment of one → nerves nerve fiber ▪ bundle of nerve fibers (neuron processes) running through the PNS ▪ Oligodendrocytes  coil around as many as 60 different → white matter nerve fibers at the same time ▪ a dense collection of myelinated fibers (tracts) ▪ CNS sheaths LACK neurilemma → gray matter ▪ contains mostly unmyelinated fibers and cell → neurilemma plays an important role in fiber regeneration bodies ▪ PNS nerve fibers have this ability ▪ CNS nerve fibers lack this ability Group Of: Inside CNS Outside CNS (PNS) cell bodies nuclei ganglia nerve fibers tracts nerves Homeostatic Imbalance → multiple sclerosis ▪ the immune system attacks the protective sheath (myelin) that covers nerve fibers ▪ causes communication problems between your brain and the rest of your body ▪ eventually, the disease can cause permanent damage or deterioration of the nerves ▪ myelin sheets are converted to hardened sheaths called sclerosis ▪ electrical current is short-circuited 10 Sensory (afferent) neurons conduct impulses from sensory receptors (in the skin, viscera, and muscles) to the central nervous system; most cell bodies are in ganglia in the PNS. Motor (efferent) neurons transmit impulses from the CNS (brain or spinal cord) to effectors in the body periphery. Interneurons (association neurons) complete the communication pathway between sensory and motor neurons; their cell bodies reside in the CNS. 11 (a) Naked nerve endings (pain and temperature receptors). (b) Meissner’s corpuscle (touch receptor). (c) Pacinian corpuscle (deep pressure receptor). (d) Golgi tendon organ (proprioceptor). (e) Muscle spindle (proprioceptor). 12 Classification of Neurons Motor Neurons → may be classified according to their: function or structure → aka efferent neurons → neurons carrying impulses from the CNS to the viscera Functional Classification and muscles and glands → groups neurons according to the direction of the nerve impulse relative to the CNS → their cell bodies are always located in the CNS → has 3 classifications: Interneurons ▪ sensory neurons ▪ motor neurons → aka association neurons ▪ interneurons → they connect the motor and sensory neurons in neural pathways Sensory Neurons → aka afferent neurons → their cell bodies are always located in the CNS ▪ afferent = “to go toward” → neurons carrying impulses from sensory receptors to the CNS → their cell bodies are found in a ganglion outside the CNS → keep us informed about what is happening inside and outside the body → their dendrite endings are associated with specialized receptors ▪ activated by specific changes occurring nearby → simple types of sensory receptors are seen in: ▪ skin (cutaneous sense organs) ▪ muscles and tendons (proprioceptors) → pain receptors ▪ bare nerve endings ▪ least specialized of the cutaneous receptors ▪ most numerous receptor ▪ warns us of body damage that is occurring or about to occur ▪ strong stimulation of cutaneous receptors is also interpreted as pain such as:  searing heat  extreme cold  excessive pressure → proprioceptors ▪ detect the amount of stretch or tension in:  skeletal muscles  joints  tendons ▪ send information to the brain for proper adjustments in maintaining:  balance and normal posture ▪ Propia → Latin word = “one’s own” ▪ constantly advise the brain of movements 13 Structural Classification Multipolar Neurons → neurons with several processes → the most common structural type ▪ all motor and association neurons are of this kind Bipolar Neurons → neurons with two processes ▪ an axon and a dendrite → rare in adults ▪ found only in some special sense organs in the eyes and nose ▪ act in sensory processing as receptor cells Unipolar Neurons → neurons with a single process emerging from the cell body → very short and divides almost immediately into proximal (central) and distal (peripheral) processes → only the small branches at the end of the peripheral process are dendrites ▪ the remainder of it and the central process function as axons → based on the number of processes extending from the ▪ conducts impulses both toward and away from cell body the cell body → sensory neurons found in PNS ganglia are of this kind 14 15 Physiology Repolarization → Repolarization. Nerve Impulses → membrane permeability changes again—becoming → functional properties of neurons: impermeable to sodium ions and permeable to ▪ Irritability potassium ions  ability to respond to a stimulus and convert it to a nerve impulse → potassium ions rapidly diffuse out of the neuron, repolarizing the membrane ▪ Conductivity  ability to transmit the impulse to other → repolarization involves restoring the inside of the neurons, muscles, or glands membrane to a negative charge and the outer surface to a positive charge Electrical Conditions of a Resting Neuron’s Membrane Initial Ionic Conditions Restored → Resting membrane is polarized. → the plasma membrane at rest is inactive (polarized) → Initial ionic conditions restored. → initial conditions of sodium and potassium ions are → fewer positive ions are inside the neuron’s plasma restored using the sodium-potassium pump membrane than outside ▪ K+ is the major positive ion inside the cell → this pump, using ATP, restores the original configuration ▪ Na+ is the major positive ion outside the cell → 3 sodium ions are ejected from the cell while 2 → as long as the inside of the membrane is more potassium ions are returned to the cell negative (fewer positive ions) than the outside, the cell remains inactive → until repolarization is complete, a neuron cannot conduct another nerve impulse Action Potential Initiation and Generation → Stimulus initiates local depolarization. → a stimulus changes the permeability of the neuron’s membrane to sodium ions → sodium channels now open, and sodium (Na+) diffuses into the neuron → the inward rush of sodium ions changes the polarity at that site and is called depolarization → Depolarization and generation of an action potential. → a graded potential (localized depolarization) exists where the inside of the membrane is more positive and the outside is less positive → if the stimulus is strong enough and sodium influx great enough, local depolarization activates the neuron to conduct an action potential (nerve impulse) Propagation of the Action Potential → Propagation of the action potential. → if enough sodium enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon → all-or-none response means the nerve impulse either is propagated or is not → fibers with myelin sheaths conduct nerve impulses more quickly 16 Transmission of the Signal at Synapses → Step 1: ▪ when the action potential reaches the axon terminal, the electrical charge opens calcium channels → Step 2: ▪ calcium, in turn, causes the tiny vesicles containing the neurotransmitter chemical to fuse with the axonal membrane → Step 3: ▪ the entry of calcium into the axon terminal causes pore-like openings to form, releasing the neurotransmitter into the synaptic cleft → Step 4: ▪ the neurotransmitter molecules diffuse across the synaptic cleft and bind to receptors on the membrane of the next neuron → Step 5: ▪ if enough neurotransmitter is released, a graded potential will be generated  eventually, an action potential (nerve impulse) will occur in the neuron beyond the synapse → Step 6: ▪ the electrical changes prompted by neurotransmitter binding are brief ▪ the neurotransmitter is quickly removed from the synapse either by reuptake or by enzymatic activity ▪ transmission of an impulse is electrochemical  transmission down neuron is electrical  transmission to the next neuron is chemical 17 (a) The five basic elements of all reflex arcs. (b) A two-neuron reflex arc (example, patellar reflex). (c) A three-neuron reflex arc (example, the flexor reflex). 18 Reflexes Types of Reflexes → these are: → Two-neuron reflex arcs ▪ rapid ▪ the simplest type of reflex ▪ predictable ▪ involuntary responses ▪ Example: patellar (knee-jerk) reflex  to stimuli  tested in physical exams to determine the general health of the motor portion → once it begins, it always goes in the same direction of the NS → occur over neural pathways called reflex arcs ▪ most reflexes are more complex than this ▪ involve both CNS and PNS structures  they involve synapses between one or more interneurons in the CNS → 2 types of reflexes: ▪ somatic reflex → Three-neuron reflex arcs ▪ autonomic reflex ▪ consists of five elements:  sensory receptor  sensory neuron Somatic Reflexes  interneuron → include all reflexes that stimulate the skeletal muscles  motor neuron  effector organ → involuntary ▪ although skeletal muscle is normally under ▪ Example: flexor (withdrawal) reflex voluntary control  the limb is withdrawn from a painful stimulus → Example: pulling your hand away from a hot object → there is always a delay at synapses ▪ it takes time for the neurotransmitters to diffuse Autonomic Reflexes through the synaptic cleft → regulate the activity of: ▪ smooth muscles ▪ the more synapses there are in a reflex pathway, ▪ heart the longer the reflex takes to happen ▪ glands → many spinal reflexes involve only the spinal cord neurons → regulate body functions such as: ▪ they can occur without brain involvement ▪ digestion ▪ elimination ▪ as long as the spinal cord is functional spinal ▪ blood pressure reflexes will work ▪ sweating  such as flexor reflexes → Example: ▪ secretion of saliva (salivary reflex) ▪ change in pupil size (pupillary reflex) 5 Elements of a Reflex Arc → Sensory receptor ▪ reacts to a stimulus → Sensory neuron ▪ carries the message to the integration center → Integration center (CNS) ▪ processes information and directs motor output → Motor neuron ▪ carries the message to an effector → Effector organ ▪ the muscle or gland to be stimulated 19 The brain can be considered in terms of four main parts: cerebral hemispheres, diencephalon, brain stem, and cerebellum. (a) In the developing brain, the cerebral hemispheres, initially smooth, are forced to grow posteriorly and laterally over the other brain regions by the bones of the skull. (b) In the adult brain, the cerebral hemispheres, now highly convoluted, enclose the diencephalon and the superior part of the brain stem. The left cerebral hemisphere is drawn so that it looks transparent, to reveal the location of the deeply situated diencephalon and superior part of the brain stem. 20 (a) Diagrammatic view of major structural areas. (b) Photograph. (c) Functional areas of the cerebral hemisphere, diagrammatic view. More intense colors (red and blue) indicate primary cortical areas (motor and sensory areas). Pastel colors (pink and pale blue) represent association areas of the cerebral cortex. 21  Central Nervous System Cerebral Hemispheres → during embryonic development, → cerebral hemispheres ▪ the CNS first appears as a simple tube called a ▪ exist in pairs neural tube  extends down the dorsal median plane ▪ collectively called cerebrum of the developing embryo’s body ▪ the most superior part of the brain → by the 4th week, ▪ the anterior end of the neural tube begins to ▪ include more than half of the brain mass expand ▪ covers the diencephalon and superior part of the ▪ brain formation begins brain stem → the rest of the neural tube posterior to the forming brain → its entire surface exhibits elevated ridges called gyri becomes the spinal cord ▪ gyrus (singular) = “twisters” → the central canal of the neural tube, ▪ it is separated by: ▪ continuous between the brain and spinal cord  sulci ▪  shallow grooves ▪ becomes enlarged in 4 regions of the brain  sulcus (singular) = “furrows”  forming chambers called ventricles  fissures  less numerous than sulci Functional Anatomy of the Brain  deeper grooves → brain ▪ 2 good fistfuls of pinkish-gray tissue ▪ longitudinal fissure  single deep fissure ▪ wrinkled like walnut  separates the cerebral hemispheres ▪ has the texture of a cold oatmeal ▪ other fissures or sulci divide each hemisphere into lobes ▪ weighs a little over 3 pounds  named for the cranial bones that lie over them ▪ largest and most complex mass of nervous tissue in the body → 3 basic regions of the cerebral hemisphere: ▪ cortex ▪ has 4 major regions:  superficial gray matter  cerebral hemispheres  unmyelinated  diencephalon  brain stem ▪ white matter  cerebellum  internal  myelinated ▪ basal nuclei  islands of gray matter deep within the white matter 22 The relative amount of cortical tissue devoted to each function is indicated by the amount of the gyrus occupied by the body area diagrams (homunculi). The primary motor cortex is shown on the right, the somatic sensory cortex is on the left. 23 Cerebral Cortex → Broca’s area ▪ specialized cortical area → the function of its neurons: ▪ speech ▪ involved in our ability to speak ▪ memory ▪ logical and emotional response ▪ found at the base of the precentral gyrus anterior ▪ consciousness to the central sulcus ▪ interpretation of sensation ▪ voluntary movement ▪ usually located on the left hemisphere → primary somatic sensory area ▪ damage to this area causes the inability to say ▪ located in the parietal lobe posterior to the words properly central sulcus → anterior association area ▪ receives impulses from the body’s sensory ▪ located in the frontal lobe receptors (except for special senses) ▪ involved in: ▪ allows us to recognize:  higher intellectual reasoning  pain  socially acceptable behavior  coldness  light touch → speech area ▪ located at the junction of the temporal, parietal, ▪ has a spatial map called the sensory and occipital lobes homunculus  means “little man” ▪ allows one to sound out words ▪ lips and fingertips are body regions with the ▪ present usually in one cerebral hemisphere most sensory receptors → frontal lobe ▪ sensory pathways are crossed pathways ▪ houses areas involved in language  the left side of the primary somatic comprehension (word meanings) sensory area receives impulses from the right side (and vice versa) ▪ stores complex memories (in the temporal lobe also) → impulses from special senses are interpreted in cortical areas ▪ visual area (occipital lobe) ▪ auditory area (temporal lobe) ▪ olfactory area (temporal lobe) → primary motor area ▪ located in the frontal lobe anterior to the central sulcus ▪ allows us to consciously move skeletal muscles ▪ axons of these motor neurons form the pyramidal (corticospinal) tract  descends to the spinal cord  major voluntary motor tract ▪ has a spatial map called the motor homunculus ▪ motor pathways are crossed pathways as well ▪ control body areas having the finest motor control:  face  mouth  hands 24 Notice the tight band of projection fibers, called the internal capsule, that passes between the thalamus and the basal nuclei. 25 (a) A midsagittal section of the brain. (b) The reticular formation, which extends the length of the brain stem. Ascending arrows indicate sensory input to the cerebrum. Descending arrows indicate the efferent output of reticular neurons. 26 Cerebral White Matter → composed of fiber tracts deep into the gray matter ▪ carries impulses from, or within the gray matter (cortex) → corpus callosum ▪ very large fiber tract ▪ connects the cerebral hemispheres ▪ such fiber tracts are called commissures  aka commissural fibers ▪ arches above the structures of the brain stem ▪ allow both hemispheres to communicate with each other  important because some cortical functions are present in one hemisphere only → association fiber tracts ▪ connect areas within a hemisphere → projection fiber tracts ▪ connect the cerebrum with lower CNS centers Basal Nuclei → “islands” of gray matter buried deep within the white matter of the cerebrum → regulate voluntary motor activities ▪ by modifying instructions sent to skeletal muscles by the primary motor cortex ▪ particularly in starting or stopping movements → individuals with basal nuclei problems are often unable to walk normally or carry out other voluntary movements normally 27 Diencephalon Epithalamus → aka interbrain → forms the roof of the 3rd ventricle → sits on top of the brain stem → houses important parts such as the: ▪ pineal body (an endocrine gland) → enclosed by the cerebral hemispheres ▪ choroid plexus of the 3rd ventricle → major structures of the diencephalon:  forms the cerebrospinal fluid (CSF) ▪ thalamus ▪ hypothalamus ▪ epithalamus Thalamus → encloses the 3rd ventricle of the brain → a relay station for sensory impulses passing upward to the cerebral cortex → transfers impulses to the correct part of the cortex for localization and interpretation Hypothalamus → literally “under the thalamus” → makes up the floor of the diencephalon → an important autonomic nervous system center ▪ because it regulates:  body temperature  water balance  metabolism → houses the limbic system ▪ aka emotional-visceral brain ▪ center for many drives and emotions  thirst  appetite  sex  pain  pleasure → regulates the nearby pituitary gland ▪ an endocrine organ ▪ produces 2 hormones ▪ hangs from the anterior floor of the hypothalamus by a slender stalk → houses mammillary bodies ▪ reflex centers involved in olfaction (smell) ▪ it is the bulge from the floor of the hypothalamus posterior to the pituitary gland 28 Brain Stem Medulla Oblongata → attaches to the spinal cord → the most inferior part of the brain stem that merges into the spinal cord → about the size of a thumb in diameter and approx. 3 ▪ without obvious changes in the structure inches long → includes important fiber tracts → its structures are: ▪ midbrain → contains important centers that control: ▪ pons ▪ heart rate ▪ medulla oblongata ▪ blood pressure ▪ breathing → provides a pathway for ascending and descending tracts ▪ swallowing ▪ vomiting → has many small gray matter areas ▪ these nuclei produce the programmed → 4th ventricle lies posterior to the pons and medulla autonomic behaviors for survival Reticular Formation → some are associated with cranial nerves and control vital activities → diffuse mass of gray matter along the brain stem ▪ such as breathing and blood pressure → involved in motor control of visceral organs Midbrain → Reticular Activating System (RAS) → a relatively small part of the brain stem ▪ a special group of reticular formation neurons → extends from the mammillary bodies to the pons inferiorly ▪ plays a role in awake/sleep cycles and consciousness → cerebral aqueduct ▪ a tiny canal that thrives through the midbrain ▪ a filter for incoming sensory information ▪ connects the 3rd and 4th ventricles ▪ damage to this area causes permanent → cerebral peduncles (anterior) unconsciousness (coma) ▪ two bulging fiber tracts ▪ literally “little feet of the cerebrum” ▪ convey ascending and descending impulses → corpora quadrigemina (dorsal) ▪ four rounded protrusions ▪ visual and auditory reflex centers Pons → rounded structure protruding just below the midbrain → it means “bridge” → mostly composed of fiber tracts → includes nuclei involved in the control of breathing 29 Cerebellum Insula → cauliflower-like that projects dorsally under the occipital → a small region of the cerebral cortex located deep within lobe the lateral sulcus ▪ a large fissure that separates the frontal and → has two hemispheres with convoluted surfaces parietal lobes from the temporal lobe → has an outer cortex of gray matter and an inner region of → important for: white matter ▪ gustatory and sensorimotor processing ▪ risk-reward behavior → controls balance ▪ autonomics ▪ pain pathways → fibers reach the cerebellum from the equilibrium ▪ auditory and vestibular functioning apparatus of the: ▪ inner ear → because of this part, people can perceive pain and have ▪ eye an awareness of their body and self ▪ proprioceptors of the skeletal muscles and tendons → compares the brain’s intentions with the actual body's performance ▪ through monitoring body position and amount of tension in body parts → provides precise timing for skeletal muscle activity and coordination of body movements → sends messages to initiate appropriate corrective measures Homeostatic Imbalance → if the cerebellum is damaged, it results in ataxia ▪ movements become clumsy and disorganized ▪ victims can’t maintain balance and appear to be drunk ▪ they can’t touch their finger to their nose with their eyes closed 30 (a) Three-dimensional frontal section showing the meninges—the dura mater, arachnoid mater, and pia mater—that surround and protect the brain. The relationship of the dura mater to the falx cerebri and the superior sagittal (dural) sinus is also shown. (b) Posterior view of the brain in a place surrounded by the dura mater. 31 (a) and (b) Three-dimensional views of the ventricles of the brain. (c) Circulatory pathway of the cerebrospinal fluid (indicated by arrows) within the central nervous system and the subarachnoid space. (The relative position of the right lateral ventricle is indicated by the pale blue area deep to the corpus callosum.) 32 Protection of the Central Nervous System Homeostatic Imbalance → nervous tissue → meningitis ▪ very soft and delicate ▪ inflammation of the meninges ▪ injured by even the slightest pressure ▪ a threat to the brain due to bacterial or viral meningitis → protection of the brain and spinal cord  may spread to the nervous tissue of the ▪ bone (skull and vertebral column) CNS ▪ membranes (meninges) ▪ watery cushion (CSF) ▪ this condition of brain inflammation is called ▪ blood-brain barrier encephalitis  protection from harmful substances in the blood ▪ diagnosed by taking a sample of CSG from the subarachnoid space Meninges Cerebrospinal Fluid → includes 3 connective tissue membranes covering and protecting CNS structures → a watery broth similar to blood plasma in composition ▪ less protein; more vitamin C; ion composition is → Dura mater different ▪ means “tough or hard mother” ▪ outermost leathery layer → formed continually by the choroid plexuses ▪ double-layered external covering (membrane) ▪ capillaries in the ventricles of the brain  periosteal layer  forms the periosteum → CSF forms a watery cushion to protect the brain and  attached to the inner surface spinal cord of the skull → it circulates from the 2 lateral ventricles (in the cerebral  meningeal layer hemispheres) into the 3rd ventricle (in the diencephalon)  the outer covering of the brain ▪ and then through the cerebral aqueduct of the  continues as the dura mater midbrain into the fourth ventricle dorsal to the of the spinal cord pons and medulla oblongata ▪ dural layers are fused together except in 3 areas ▪ some of the fluid reaching the fourth ventricle where they enclose the dural venous sinuses simply continues down into the spinal cord, but  collects venous blood most of it circulates into the subarachnoid space through three openings in the walls of the fourth ▪ folds inward in several areas ventricle  falx cerebri ▪ the CSF returns to the blood in the dural venous  attaches the brain to the sinuses through the arachnoid villi cranial cavity → CSF forms and drains at a constant rate  tentorium cerebelli ▪ normal pressure and volume are maintained  separates the cerebellum  150ml – about half a cup from the cerebrum → lumbar (spinal) tap → Arachnoid mater ▪ procedure in obtaining CSF samples for testing ▪ middle meningeal layer ▪ Arachnida means “spider” Homeostatic Imbalance ▪ subarachnoid space is filled with cerebrospinal → CSF begins to accumulate and exert pressure on the fluid brain if something obstructs its drainage ▪ this condition is called hydrocephalus ▪ arachnoid granulations (arachnoid villi)  literally “water on the brain” protrude through the dura mater and absorb cerebrospinal fluid into the venous blood → shunting ▪ surgical treatment for hydrocephalus → Pia mater ▪ internal layer ▪ inserting a shunt (plastic tube) to drain excess fluid into a vein in the neck or into the abdomen ▪ clings to the surface of the brain and spinal cord 33 Blood-Brain Barrier Brain Dysfunction → the brain is dependent on a constant internal environment Traumatic Brain Injuries ▪ chemical changes might result in uncontrolled neural activity → Concussion ▪ slight brain injury → blood-brain barrier ▪ separates neurons from bloodborne substances ▪ the victim may become:  dizzy ▪ composed of the least permeable capillaries of  see stars the body  lose consciousness briefly ▪ allowed to pass through capillary walls: ▪ typically, little permanent brain damage occurs  water  glucose → Contusion  amino acids ▪ marked nervous tissue destruction occurs ▪ coma may occur ▪ not allowed to pass through capillary walls:  urea → death may occur after head blows due to:  toxins ▪ Intracranial hemorrhage  proteins  bleeding from ruptured vessels  most drugs ▪ Cerebral edema ▪ nonessential amino acids and potassium ions  swelling of the brain due to an are prevented and actively pumped from the inflammatory response to injury brain to the blood ▪ useless as a barrier against: Cerebrovascular Accident  fats → aka strokes  respiratory gases  fat-soluble molecules → results when blood circulation to a brain area is blocked  they diffuse easily through all and brain tissue dies plasma membranes → loss of some functions or death may result:  explains why these substances affect the brain: ▪ Hemiplegia  alcohol  one-sided paralysis  nicotine  anesthetics ▪ Aphasia  damage to the speech center in the left hemisphere  motor aphasia  involves damage to Broca’s area  loss of ability to speak  sensory aphasia  loss of ability to understand written/spoken languages → Transient ischemic attack (TIA) ▪ incomplete stroke ▪ temporary brain ischemia or restriction of blood flow ▪ last from 5 – 50 minutes with symptoms such as:  numbness  temporary paralysis  impaired speech 34 → Thrombotic strokes Parkinson’s Disease ▪ are strokes caused by a thrombus (blood clot) → a basal nuclei problem that develops in the arteries supplying blood to the brain → results from a degeneration of the dopamine-releasing neurons of the substantia nigra → Embolic strokes ▪ a critical brain region for the production of ▪ occurs when a blood clot that forms elsewhere dopamine in the body breaks loose and travels to the brain via the bloodstream ▪ it affects many systems of the central nervous system ranging from movement control, ▪ when the clot lodges in an artery and blocks the cognitive executive functions, and emotional flow of blood, this causes a stroke limbic activity Alzheimer’s Disease → they have trouble initiating movement or getting their muscles going → a progressive degenerative disease of the brain that ultimately results in dementia → the drug L-dopa helps to alleviate some of the symptoms ▪ mental deterioration ▪ not a cure → cause good-natured people to become: ▪ irritable ▪ becomes ineffective as more and more neurons ▪ moody die off ▪ confused ▪ violent → a newer treatment drug is deprenyl → hallucinations occur ▪ slows the neurological deterioration to some extent and delays the need to administer L-dopa → associated with a shortage of acetylcholine (ACh) and for up to 18 months with structural changes in the brain ▪ particularly in areas involved with thought and ▪ can prolong the effectiveness of L-dopa memory → deep-brain (thalamic) stimulation via implanted electrodes ▪ gyri shrinks and the brain atrophies ▪ proved helpful in alleviating tremors but does little else → treatment, for now, are drugs that inhibit ACh breakdown → intrabrain transplant of embryonic substantia nigra tissue ▪ engineered adult nigral cells or dopamine- producing cells from fetal pigs ▪ more promising for long-term results Huntington’s Disease → is a genetic disease that strikes during middle age ▪ leads to massive degeneration of the basal nuclei and later of the cerebral cortex → initial symptoms are chorea ▪ Greek for “dance” ▪ wild jerky continuous flapping movement ▪ appear to be voluntary but are not → progressive and usually fatal within 15 years of the onset of symptoms → signs and symptoms are opposite of Parkinson’s disease ▪ Parkinson’s disease  inhibition of the motor drive ▪ Huntington’s disease  overstimulation of the motor drive → usually treated with drugs that block, dopamine’s effects 35 Spinal Cord → Cauda equina ▪ a collection of spinal nerves at the inferior end of → continuation of the brain stem the vertebral canal → two-way conduction pathway o and from the brain ▪ means “horse tail” → major reflex center → 31 pairs of spinal nerves arise from the spinal cord → extends from the foramen magnum of the skull to the first or second lumbar vertebra → cushioned and protected by meninges 36 Gray Matter of the Spinal Cord and Spinal Roots Homeostatic Imbalance → looks like a butterfly or H in a cross-section → flaccid paralysis ▪ results when there is damage to the ventral root → dorsal horns ▪ aka posterior horns ▪ nerve impulses don’t reach the muscles affected ▪ posterior projections  no voluntary movement occurs ▪ includes 2 ▪ contains interneurons ▪ muscles begin to atrophy due to non-stimulation → ventral horns ▪ aka anterior horns ▪ anterior projections ▪ includes 2 ▪ contains cell bodies of motor neurons of the somatic nervous system  sends their axon out the ventral root of the cord → dorsal horns + ventral horns = spinal nerves → central canal ▪ surrounded by gray matter ▪ at the center of the spinal cord ▪ contains CSF → dorsal root ganglion ▪ cell bodies of sensory neurons  fibers that enter the cord by the dorsal root ▪ if damaged, the sensation from the body area served will be lost 37 38 White Matter of the Spinal Cord → composed of myelinated fibers ▪ some running to higher centers ▪ some traveling from the brain to the cord ▪ and some conducting impulses from one side of the spinal cord to the other → has 3 regions: ▪ dorsal column ▪ lateral column ▪ ventral column → each column contains fiber tracts made up of axons with the same destination and function → sensory tracts ▪ aka afferent tracts ▪ conducts sensory impulses to the brain from sensory receptors → motor tracts ▪ aka efferent tracts ▪ carry impulses from the brain to skeletal muscles → dorsal columns ▪ ascending tracts that carry sensory input to the brain → lateral and ventral columns ▪ contain both ascending and descending (motor) tracts Homeostatic Imbalance → spastic paralysis ▪ results from crushed or transected spinal cord ▪ affected muscles stay healthy due to stimulation of spinal reflex arcs  movements still occur ▪ however, movements are involuntary and uncontrollable ▪ there is a loss of feeling or sensory input in the body areas below the point of cord destruction ▪ quadriplegic  spinal cord injury occurs high in the cord  all 4 limbs are affected ▪ paraplegic  legs are only paralyzed 39  Peripheral Nervous System → nerves are classified according to the direction in which they transmit pulses → consists of: ▪ mixed nerves ▪ nerves  nerves carrying sensory and motor ▪ scattered groups of neuronal cell bodies fibers (ganglia)  all spinal nerves are of this class  found outside the CNS  both afferent and efferent Structure of Nerves ▪ sensory nerves  aka afferent nerves  carry impulses toward the CNS only ▪ motor nerves  aka efferent nerves  carry only motor fibers  carry impulses from the CNS → nerve ▪ a bundle of neuron fibers outside the CNS → endoneurium ▪ surrounds each fiber with a delicate connective tissue sheath → perineurium ▪ surrounds each group of fibers with a coarser connective tissue wrapping ▪ forms fiber bundles called fascicles → epineurium ▪ surrounds all fascicles with a tough fibrous sheath ▪ forms cordlike nerve 40 41 42 Distribution of cranial nerves. Sensory nerves are shown in blue, and motor nerves are in red. Although cranial nerves III, IV, and VI have sensory fibers, these are not shown because the sensory fibers account for only minor parts of these nerves 43 Cranial Nerves → has 12 pairs of nerves ▪ mostly serving the head and neck ▪ numbered in order ▪ names reveal structures they control → pair of vagus ▪ only the nerve that extends to the thoracic and abdominal cavities → most are mixed nerves, but 3 are sensory only: ▪ Optic nerve ▪ Olfactory nerve ▪ Vestibulocochlear nerve → acoustic nerve ▪ the old name of the vestibulocochlear nerve ▪ has a role in hearing but not in equilibrium → cranial nerves mnemonic: ▪ Oh – Olfactory ▪ Oh – Optic ▪ Oh – Oculomotor ▪ To – Trochlear ▪ Touch – Trigeminal ▪ And – Abducens ▪ Feel – Facial ▪ Very – Vestibulocochlear ▪ Green – Glossopharyngeal ▪ Vegetables – Vagus ▪ A – Accessory ▪ H – Hypoglossal 44 (a) Relationship of spinal nerves to the vertebrae. Areas of plexuses formed by the anterior rami are indicated. (b) Relative distribution of the ventral and dorsal rami of a spinal nerve (cross-section of the left trunk). 45 46 47 Spinal Nerves and Nerve Plexuses → there are 31 pairs of spinal nerves ▪ formed by the combination of ventral and dorsal roots of the spinal cord ▪ named for the region of the cord from which they arise → after being formed, ▪ each spinal nerve divides into dorsal and ventral rami ▪ spinal nerves are about ½ inch long → rami (singular: ramus) ▪ branch of a spinal nerve ▪ contain both motor and sensory fibers ▪ smaller dorsal rami  serve the skin and posterior body trunk muscles ▪ ventral rami of spinal nerves T 1 – T12  form the intercostal nerves  supply the muscles between ribs and skin and anterior and lateral trunk muscles ▪ ventral rami of all other spinal nerves (except T1 – T12)  form plexuses  complex networks of nerves  serve the motor and sensory needs of limbs → damage to the spinal nerve or the rami results in: ▪ loss of sensation ▪ flaccid paralysis of the area of the body served → plexus ▪ networks of nerves serving the motor and sensory needs of the limbs ▪ form from ventral rami of spinal nerves in the regions of:  cervical  lumbar  sacral ▪ 4 plexuses:  cervical  brachial  lumbar  sacral 48 49 Parasympathetic fibers are shown in purple and sympathetic fibers in green. Solid lines represent preganglionic fibers; dashed lines indicate postganglionic fibers. 50 Autonomic Nervous System Somatic Vs. Autonomic Nervous System → the motor subdivision of the PNS → somatic nervous system ▪ controls body activities automatically ▪ motor neuron cell bodies originate inside the CNS → consists only of motor nerves ▪ axons extend to skeletal muscles that they serve → regulates: ▪ cardiac muscle → autonomic nervous system  the heart ▪ has a chain of 2 motor neurons:  preganglionic ▪ smooth muscles  aka 1st motor neuron  in walls of visceral organs and blood vessels  originates in the brain or spinal cord ▪ glands  synapses with the 2nd motor → homeostasis depends largely on the working of this neuron system  postganglionic → controls the body automatically  aka 2nd motor neuron ▪ aka involuntary nervous system  receives synapse from the 1st motor neuron  extends synapse to organs it serves → 2 arms of the ANS: ▪ both serve the organ but cause opposing effects ▪ sympathetic division  mobilizes body in extreme situations  fear  exercise  rage ▪ parasympathetic division  allows us to unwind and conserve energy 51 (a) Synapse in a sympathetic chain ganglion at the same level. (b) Synapse in a sympathetic chain ganglion at a different level. (c) Synapse in a collateral ganglion anterior to the vertebral column 52 Anatomy of the Parasympathetic Division Anatomy of the Sympathetic Division → aka craniosacral division → aka thoracolumbar division ▪ its preganglionic neurons are in the gray matter → preganglionic neurons originate in: of the spinal cord from T1 through L2 ▪ cranial nerves III, VII, IX, and X  vagus nerve – most important → its preganglionic axons the cord in the ventral root ▪ it enters the spinal n