Anaphy (Midterms) - DI MATETEGI I SWEAR PDF

pairs of spinal nerves emerge from the spinal cord, NERVOUS TISSUE each serving a specific region on the right or left side of the body. The excitable characteristic of nervous tissue allows -...

pairs of spinal nerves emerge from the spinal cord, NERVOUS TISSUE each serving a specific region on the right or left side of the body. The excitable characteristic of nervous tissue allows - Ganglia are small masses of nervous tissue, for the generation of nerve impulses (action potentials) consisting primarily of neuron cell bodies, that are that provide communication with and regulation of located outside the brain and spinal cord. most body tissues. - Ganglia are closely associated with cranial and spinal nerves. NEUROLOGY: - In the walls of organs of the gastrointestinal tract, - The branch of medical science that deals with the extensive networks of neurons, called enteric normal functioning and disorders of the nervous plexuses, help regulate the digestive system. system. - The term sensory receptor is used to refer to the dendrites of sensory neurons as well as separate, NEUROLOGIST: specialized cells that monitor changes in the internal - Physician who specializes in the diagnosis and or external environment, such as photoreceptors in the treatment of disorders of the nervous system. retina of the eye. Structures of the Nervous System: SENSORY FUNCTION: - Detect internal - With a mass of only 2 kg, about 3% of total body stimuli, such as an increase in blood acidity, weight, the nervous system is one of the smallest and and external stimuli, such as a raindrop landing yet the most complex of the 11 body systems. on your arm. - An intricate, highly organized network of billions of - This sensory information is then carried into neurons and even more neuroglia. the brain and spinal cord through cranial and spinal nerves. Structures of the Nervous System: - The structures that make up the nervous system INTEGRATIVE FUNCTION: - Integrates include the: (processes) sensory information by analyzing and storing some of it and by making decisions Brain for appropriate responses. Cranial nerves and their branches - An important integrative function is Spinal cord perception, the conscious awareness of Spinal nerves and their branches, ganglia, sensory stimuli. enteric plexuses, and sensory receptors - Perception occurs in the brain. Structures of the Nervous System: MOTOR FUNCTION: Once sensory - The skull encloses the brain, which contains about information is integrated, the nervous system 100 billion neurons. may elicit an appropriate motor response by - Twelve pairs (right and left) of cranial nerves, activating effectors (muscles and glands) numbered I through XII, emerge from the base of the through cranial and spinal nerves. brain. - Stimulation of the effectors causes muscles to - A nerve is a bundle of hundreds to thousands of contract and glands to secrete. axons plus associated connective tissue and blood vessels that lies outside the brain and spinal cord. Subdivisions of the Nervous System: Structures of the Nervous System: CNS - Brain and spinal cord - Each nerve follows a defined path and serves a specific region of the body. PNS - Cranial nerves and spinal nerves and all - For example, the cranial nerve I carry signals for the nervous tissue outside the CNS sense of smell from the nose to the brain. - The spinal cord connects to the brain through the Histology of Nervous Tissue: Consists of neurons foramen magnum of the skull and is encircled by the and neuroglia bones of the vertebral column. Neurons: Neurons provide most of the unique Structures of the Nervous System: functions of the nervous system, such as sensing, - It contains about 100 million neurons. Thirty-one thinking, remembering, controlling muscle activity, and A nerve fiber: general term for any neuronal process regulating glandular secretions. (extension) that emerges from cell body of a neuron. - Most neurons have two kinds of processes: multiple Neuroglia: Support, nourish, and protect the neurons dendrites and a single axon. and maintain homeostasis in the interstitial fluid that bathes them. DENDRITES - Are the receiving or input portions of a neuron. Neurons: Neurons (nerve cells) possess electrical - They are usually short, tapering, and highly excitability, the ability to respond to a stimulus and branched. convert it into an action potential. - In many neurons, the dendrites form a tree-shaped array of processes extending from the cell body. Stimulus: Is any change in the environment that is - Their cytoplasm contains Nissl bodies, mitochondria, strong enough to initiate an action potential. and other organelles. Action potential (nerve impulse): - Is an electrical AXONS: The single axon (axis) of a neuron signal that propagates (travels) along the surface of propagates nerve impulses toward another neuron, a the membrane of a neuron. muscle fiber, or a gland cell. - An axon is a long, thin, cylindrical projection that - It begins and travels due to the movement of ions often joins the cell body at a cone-shaped elevation (such as sodium and potassium) between interstitial called the axon hillock (small hill). fluid and the inside of a neuron through specific ion - The part of the axon closest to the axon hillock is the channels in its plasma membrane. initial segment. - Nerve impulses travel these great distances at - In most neurons, nerve impulses arise at the junction speeds ranging from 0.5 to 130 meters per second (1 of the axon hillock and the initial segment, an area to 280 mi/hr). called the trigger zone, from which they travel along Parts of a neuron - Most neurons have three parts: a the axon to their destination. cell body, dendrites, and an axon. - An axon contains mitochondria, microtubules, and neurofibrils. Because rough endoplasmic reticulum is THE CELL BODY - Also known as the perikaryon or not present, protein synthesis does not occur in the soma, contains a nucleus surrounded by cytoplasm axon. that includes typical cellular organelles such as lysosomes, mitochondria, and a Golgi complex. Axoplasm - The cytoplasm of an axon, called - Neuronal cell bodies also contain free ribosomes and axoplasm, is surrounded by a plasma membrane prominent clusters of rough endoplasmic reticulum, known as the axolemma (lemma sheath or husk). termed Nissl bodies. - Along the length of an axon, side branches called axon collaterals may branch off, typically at a right The ribosomes: - Are the sites of protein synthesis. angle to the axon. - Newly synthesized proteins produced by Nissl bodies - The axon and its collaterals end by dividing into are used to replace cellular components as material many fine processes called axon terminals for growth of neurons and to regenerate damaged (telodendria). axons in the PNS. Synapse - The site of communication between two The cytoskeleton: - Includes both neurofibrils, neurons or between a neuron and an effector cell. composed of bundles of intermediate filaments that - The tips of some axon terminals swell into provide the cell shape and support, and microtubules, bulb-shaped structures called synaptic end bulbs; which assist in moving materials between the cell others exhibit a string of swollen bumps called body and axon. varicosities. - Many neurons also contain lipofuscin, a pigment that - Both synaptic end bulbs and varicosities contain occurs as clumps of yellowish-brown granules in the many tiny membrane-enclosed sacs called synaptic cytoplasm. vesicles that store a chemical neurotransmitter. - Lipofuscin is a product of neuronal lysosomes that - Many neurons contain two or even three types of accumulates as the neuron ages but does not seem to neurotransmitters, each with different effects on the harm the neuron. postsynaptic cell. - When neurotransmitter molecules are released from synaptic vesicles, they excite or inhibit other neurons, ○ Once an appropriate stimulus activates muscle fibers, or gland cells. a sensory receptor, the sensory neuron forms an action potential in its axon, Classifications of neurons: and the action potential is conveyed into the CNS through cranial or spinal 1. Multipolar neurons: nerves. ○ Usually have several dendrites and one ○ Most sensory neurons are unipolar in axon. structure. ○ Most neurons in the brain and spinal 2. Motor or efferent neurons: cord are of this type. ○ Convey action potentials away from the 2. Bipolar neurons: CNS to effectors (muscles and glands) ○ Have one main dendrite and one axon. in the periphery (PNS) through cranial ○ They are found in the retina of the eye, or spinal nerves in the inner ear, and in the olfactory ○ Most motor neurons are multipolar in (olfact to smell) area of the brain. structure. 3. Unipolar neurons: 3. Interneurons: ○ Have dendrites and one axon that are ○ Are mainly located within the CNS fused together to form a continuous between sensory and motor neurons process that emerges from the cell ○ Interneurons integrate (process) body. incoming sensory information from ○ These neurons are more appropriately sensory neurons and then elicit a motor called pseudounipolar neurons response by activating the appropriate because they begin in the embryo as motor neurons. bipolar neurons. ○ Most interneurons are multipolar in ○ During development, the dendrites and structure. axon fuse together and become a single process. Neuroglia: ○ The dendrites of most unipolar neurons function as sensory receptors that Make up about half the volume of the CNS. detect a sensory stimulus such as Generally, neuroglia are smaller than neurons, touch, pressure, pain, or thermal and they are 5 to 50 times more numerous. stimuli. In contrast to neurons, glia do not generate or ○ The trigger zone for nerve impulses in a propagate action potentials, and they can unipolar neuron is at the junction of the multiply and divide in the mature nervous dendrites and axon. system. ○ The impulses then propagate toward In cases of injury or disease, neuroglia multiply the synaptic end bulbs. to fill in the spaces formerly occupied by ○ The cell bodies of most unipolar neurons. neurons are located in the ganglia of Brain tumors derived from glia, called gliomas, spinal and cranial nerves. tend to be highly malignant and grow rapidly. ○ Several examples of sensory receptors Of the six types of neuroglia, four—1. that are dendrites of unipolar neurons. astrocytes, 2. oligodendrocytes, 3. microglia, and 4. ependymal cells—are found only in the Functional Classifications: CNS. The remaining two types—Schwann cells and According to the direction in which nerve satellite cells—are present in the PNS. impulse, action potential is conveyed with respect to CNS. Neuroglia of the CNS: 1. Sensory or afferent neurons: ○ Either contain sensory receptors at Are classified on the basis of size, cytoplasmic distal ends (dendrites) or are located processes, and intracellular organization into just after sensory receptors that are four types. separate cells. 1. Astrocytes:  ○ These star-shaped cells have many ○ Responsible for forming and processes and are the largest and most maintaining the myelin sheath around numerous of the neuroglia. CNS axons. ○ There are two types of astrocytes: ○ The myelin sheath is a multilayered 1. Protoplasmic astrocytes: lipid and protein covering around some Have many short axons that insulates them and branching processes increases the speed of nerve impulse and are found in gray conduction. matter. ○ Such axons are said to be myelinated. 2. Fibrous astrocytes: 3. Microglia: Have many long ○ Function as phagocytes, removing unbranched processes cellular debris formed during normal and are located mainly in development of the nervous system white matter. and phagocytizing microbes and The processes of damaged nervous tissue. astrocytes make contact 4. Ependymal cells: with blood capillaries, ○ Are cuboidal to columnar cells arranged neurons, and the pia in a single layer that possess microvilli mater (a thin membrane and cilia. around the brain and ○ These cells line the ventricles of the spinal cord). brain and central canal of the spinal cord (spaces filled with cerebrospinal Functions: fluid, which protects and nourishes the brain and spinal cord). ○ Contain microfilaments that give them ○ Functionally, ependymal cells produce, considerable strength, enabling them to possibly monitor, and assist in the support neurons. circulation of cerebrospinal fluid. ○ Processes of astrocytes wrapped ○ They also form the blood-cerebrospinal around blood capillaries isolate neurons fluid barrier. of the CNS from harmful substances by secreting chemicals that maintain the Neuroglia of the PNS: selective permeability characteristics of the endothelial cells of the capillaries. 1. Schwann cells: ○ In the embryo, astrocytes secrete ○ Produce myelin in the PNS. chemicals that regulate the growth, ○ Each Schwann cell myelinates a single migration, and interconnection among axon in the PNS. neurons in the brain. ○ Schwann cells participate in axon ○ Astrocytes help maintain the regeneration, which is more easily appropriate chemical environment for accomplished in the PNS than in the generating nerve impulses, regulating CNS. the concentration of important ions 2. Satellite cells: such as K+, taking up excess ○ These flat cells surround the cell bodies neurotransmitters, and serving as a of neurons in PNS ganglia conduit for the passage of nutrients ○ Besides providing structural support, between blood capillaries and neurons. satellite cells regulate the exchanges of ○ Astrocytes may also play a role in materials between neuronal cell bodies learning and memory by influencing the and interstitial fluid. formation of neural synapses. Myelination: Myelinated axons are surrounded by a multilayered lipid and protein covering called the myelin sheath, which insulates the axon and increases 2. Oligodendrocytes: nerve impulse conduction speed. Schwann cells wrap ○ Are smaller and contain fewer about 1 mm of a single axon by spiraling multiple processes. layers around it, creating up to 100 layers of plasma ○ In the brain, a thin shell of gray matter membrane (the myelin sheath). covers the cerebrum and cerebellum. The neurolemma (outer nucleated CNS: cytoplasmic layer of the Schwann cell) encloses the myelin sheath and is present only Consists of the brain and spinal cord and is in the PNS. also the source of thoughts, emotions, and Neurolemma helps axon regeneration by memories. forming a regeneration tube that guides axon Most nerve impulses that stimulate muscles to regrowth. contract and glands to secrete originate in the Nodes of Ranvier (gaps in the myelin sheath) CNS. appear along the axon. CNS axons display little regrowth after injury PNS: due to the absence of a neurolemma and Includes all nervous tissue outside the CNS. inhibitory influences from oligodendrocytes. Components of the PNS include cranial nerves and their branches, spinal nerves and their branches, ganglia, and sensory receptors. The PNS may be subdivided further into a somatic nervous system (SNS), an autonomic Clusters of Neuronal Cell Bodies: nervous system (ANS), and an enteric nervous system (ENS) (enter- intestines). Ganglion: A cluster of neuronal cell bodies located in the PNS, associated with cranial and Somatic NS: spinal nerves. Nucleus: A cluster of neuronal cell bodies Consists of: located in the CNS. 1. Sensory neurons that convey information from somatic receptors in Bundles of Axons: the head, body wall, and limbs and from receptors for the special senses of Nerve: A bundle of axons in the PNS. Cranial vision, hearing, taste, and smell to the nerves connect the brain to the periphery, and CNS. spinal nerves connect the spinal cord to the 2. Motor neurons that conduct impulses periphery. from the CNS to skeletal muscles only. Tract: A bundle of axons in the CNS, Because these motor responses can be interconnecting neurons in the spinal cord and consciously controlled, the action of this part of brain. the PNS is voluntary. Gray and White Matter: White matter: Composed primarily of ANS (Autonomic nervous system) myelinated axons, giving it a whitish color from the myelin. Consists of: Gray matter: Contains neuronal cell bodies, ○ Sensory neurons that convey dendrites, unmyelinated axons, axon terminals, information from autonomic sensory and neuroglia. receptors, located primarily in visceral ○ Appears gray due to the presence of organs such as the stomach and lungs, Nissl bodies and the absence of myelin to the CNS. in these areas. ○ Motor neurons that conduct nerve ○ Blood vessels are present in both white impulses from the CNS to smooth and gray matter. muscle, cardiac muscle, and glands. ○ In the spinal cord, white matter Because its motor responses are not normally surrounds an inner core of gray matter under conscious control, the action of the ANS shaped like a butterfly or the letter "H." is involuntary.  The motor part of the ANS consists of two branches: the sympathetic division and the parasympathetic division. With a few exceptions, effectors receive nerves from both divisions, and usually the two Classification of Nerve Fibers: divisions have opposing actions. A fibers: ○ For example, sympathetic neurons ○ The largest-diameter axons (5–20 μm) increase heart rate, and and are myelinated. parasympathetic neurons slow it down. ○ Conduct nerve impulses (action ○ Sympathetic division: In general, the potentials) at speeds of 12 to 130 sympathetic division helps support m/sec (27–280 mi/hr). exercise or emergency actions, ○ The axons of sensory neurons that so-called "fight-or-flight" responses. propagate impulses associated with ○ Parasympathetic division: Takes care touch, pressure, position of joints, and of "rest-and-digest" activities. some thermal and pain sensations are ENS (Enteric nervous system): A fibers, as are the axons of motor neurons that conduct impulses to The operation of the ENS, the "brain of the skeletal muscles. gut," is involuntary. B fibers: Once considered part of the ANS, the ENS ○ B fibers are axons with diameters of consists of approximately 100 million neurons 2–3 micrometers. in enteric plexuses that extend most of the ○ B fibers are myelinated and exhibit length of the gastrointestinal (GI) tract. saltatory conduction at speeds up to 15 Many of the neurons of the enteric plexuses m/sec (32 mi/hr). function independently of the ANS and CNS to ○ Conduct sensory nerve impulses from some extent, although they also communicate the viscera to the brain and spinal cord. with the CNS via sympathetic and C fibers: parasympathetic neurons. ○ The smallest-diameter axons (0.5–1.5 Sensory neurons of the ENS monitor chemical μm) and all are unmyelinated. changes within the GI tract as well as the ○ Nerve impulse propagation ranges from stretching of its walls. 0.5 to 2 m/sec (1–4 mi/hr). Enteric motor neurons govern contraction of GI ○ These unmyelinated axons conduct tract smooth muscle to propel food through the some sensory impulses for pain, touch, GI tract, secretions of the GI tract organs such pressure, heat, and cold from the skin, as acid from the stomach, and activity of GI and pain impulses from the viscera. tract endocrine cells, which secrete hormones. NEUROTRANSMITTERS: 2 Types of Propagation: Acetylcholine: Saltatory conduction: Occurs along myelinated axons. The best-studied neurotransmitter is Continuous conduction: Occurs in acetylcholine (ACh), which is released by unmyelinated axons and in muscle fibers. many PNS neurons and by some CNS neurons. Factors That Affect the Speed of Propagation: ACh is an excitatory neurotransmitter at some synapses, such as the neuromuscular junction, The speed of propagation of an action potential where the binding of ACh to ionotropic is affected by three major factors: receptors opens cation channels 1. Amount of myelination. It is also an inhibitory neurotransmitter at other 2. Axon diameter. synapses, where it binds to metabotropic 3. Temperature: Axons propagate action receptors coupled to G proteins that open K potentials at lower speeds when channels. cooled.  For example, ACh slows heart rate at inhibitory The muscular stiffness that occurs in synapses made by parasympathetic neurons Parkinson’s disease is due to degeneration of of the vagus (X) nerve. neurons that release dopamine. The enzyme acetylcholinesterase (AChE) inactivates ACh by splitting it into acetate and Catecholamines: choline fragments. Norepinephrine, dopamine, and epinephrine Amino Acids: are classified chemically as catecholamines. Are neurotransmitters in the CNS. Serotonin: Glutamate (glutamic acid) and aspartate (aspartic acid) have powerful excitatory effects. Is concentrated in the neurons in a part of the Most excitatory neurons in the CNS and brain called the raphe nucleus. perhaps half of the synapses in the brain It is thought to be involved in sensory communicate via glutamate. perception, temperature regulation, control of Gamma aminobutyric acid (GABA) and glycine mood, appetite, and the induction of sleep. are important inhibitory neurotransmitters. Neuropeptides: GABA is found only in the CNS, where it is the most common inhibitory neurotransmitter. Neurotransmitters consisting of 3 to 40 amino As many as one-third of all brain synapses use acids linked by peptide bonds called GABA. neuropeptides are numerous and widespread Antianxiety drugs such as diazepam (Valium®) in both the CNS and the PNS. enhance the action of GABA. Besides their role as neurotransmitters, many neuropeptides serve as hormones that Biogenic Amines: regulate physiological responses elsewhere in Certain amino acids are modified and the body. decarboxylated (carboxyl group removed) to Enkephalins: produce biogenic amines. Those that are prevalent in the nervous system Their potent analgesic (pain-relieving) effect is include norepinephrine, epinephrine, 200 times stronger than morphine. dopamine, and serotonin. Other so-called opioid peptides include the Biogenic amines may cause either excitation or endorphins and dynorphins. inhibition, depending on the type of Opioid peptides are thought to be the body’s metabotropic receptor at the synapse. natural painkillers. Acupuncture may produce analgesia (loss of Norepinephrine (NE): pain sensation) by increasing the release of Plays roles in arousal (awakening from deep opioids. sleep), dreaming, and regulating mood. These neuropeptides have been linked to A smaller number of neurons in the brain use improved memory and learning, feelings of epinephrine as a neurotransmitter. pleasure or euphoria, control of body Both epinephrine and norepinephrine also temperature, regulation of hormones that affect serve as hormones. puberty, sexual drive, and reproduction, as well Cells of the adrenal medulla, the inner portion as mental illnesses like depression and of the adrenal gland, release them into the schizophrenia. blood. Substance P: Brain neurons containing the neurotransmitter dopamine (DA) are active during emotional Is released by neurons that transmit responses, addictive behaviors, and pain-related input from peripheral pain pleasurable experiences. receptors into the CNS, enhancing the Dopamine-releasing neurons help regulate perception of pain. skeletal muscle tone and some aspects of Enkephalin and endorphin suppress the movement due to contraction of skeletal release of substance P, decreasing the number muscles.  of nerve impulses relayed to the brain for pain Despite this, the neurolemma remains intact. sensations. Degeneration of the distal portion of the axon Substance P has also been shown to counter and myelin sheath is called Wallerian the effects of certain nerve-damaging degeneration. chemicals, suggesting it might be useful for After chromatolysis, signs of recovery in the treating nerve degeneration. cell body become evident as macrophages phagocytize debris. REGENERATION & REPAIR: Synthesis of RNA and protein accelerates, promoting the regeneration of the axon. Throughout life, the nervous system exhibits Schwann cells on either side of the injury plasticity, the ability to change based on multiply by mitosis, grow toward each other, experience. and may form a regeneration tube across the At the level of individual neurons, changes injured area. include the sprouting of new dendrites, synthesis of new proteins, and changes in synaptic contacts with other neurons. Both chemical and electrical signals drive these changes, but mammalian neurons have limited powers of regeneration (the ability to replicate or repair themselves). In the PNS, damage to dendrites and myelinated axons may be repaired if the cell body remains intact and if Schwann cells (which produce myelination) remain active. Regeneration in the CNS: In the CNS, little or no repair of damage to neurons occurs. Even when the cell body remains intact, a severed axon cannot be repaired or regrown. Damaged & Repair in the PNS: Axons and dendrites associated with a neurolemma may undergo repair if the cell body is intact, Schwann cells are functional, and scar tissue does not form too rapidly. Most nerves in the PNS consist of processes covered with a neurolemma. A person who injures axons of a nerve in an upper limb, for example, has a good chance of CNS regaining nerve function. After damage to an axon, changes occur in Ectodermal Neural Tube: The internally both the cell body and the portion of the axon positioned neural tube develops into the brain distal to the injury site. and spinal cord. The anterior part of the neural Changes may also occur in the axon proximal tube expands, along with the associated neural to the injury site. crest tissue. Constrictions in this expanded About 24 to 48 hours after injury, the Nissl tube soon appear, creating three regions called bodies break up into fine granular masses, a the Primary Brain Vesicles: process called chromatolysis. ○ Prosencephalon: Subdivides further, By the third to fifth day, the axon distal to the forming secondary brain vesicles. damaged region swells and breaks up into ○ Mesencephalon: Remains undivided fragments, and the myelin sheath deteriorates but forms key structures. (Figure 12.29b).  ○ Rhombencephalon: Also subdivides Meningeal Layer (internal) further, forming secondary brain vesicles. Three extensions of the dura mater separate parts of the brain: The various brain vesicles give rise to the following adult structures: Falx Cerebri: Separates the two hemispheres of the cerebrum. Telencephalon: Develops into the cerebrum Falx Cerebelli: Separates the two and lateral ventricles. hemispheres of the cerebellum. Diencephalon: Forms the thalamus, Tentorium Cerebelli: Separates the cerebrum hypothalamus, epithalamus, and third ventricle. from the cerebellum. Mesencephalon (midbrain): Gives rise to the midbrain and the aqueduct of the midbrain Cerebrospinal Fluid (CSF) (cerebral aqueduct). Metencephalon: Becomes the pons, CSF is a clear, colorless liquid composed cerebellum, and the upper part of the fourth primarily of water (H₂O) that protects the brain ventricle. and spinal cord from chemical and physical Myelencephalon: Forms the medulla injuries. oblongata. It carries small amounts of oxygen, glucose, and other needed chemicals from the blood to The walls of these brain regions develop into nervous neurons and neuroglia. tissue, while the hollow interior of the tube is CSF contains small amounts of glucose, transformed into its various ventricles (fluid-filled proteins, lactic acid, urea, cations (Na⁺, K⁺, spaces). Ca²⁺, Mg²⁺), and anions (Cl⁻ and HCO₃⁻), anw white blood cell. CSF continuously circulates through cavities in the brain and spinal cord and around them in the subarachnoid space (the space between the The adult brain consists of four major parts: arachnoid mater and pia mater). Brain Stem: Continuous with the spinal cord, it The total volume of cerebrospinal fluid is 80 consists of the medulla oblongata, pons, and mL to 150 mL (3 to 5 oz) in adults. midbrain. Cerebellum: Located posterior to the brain Ventricles of the Brain stem. Diencephalon: Located superior to the brain The four CSF-filled cavities within the brain, which stem, consisting of the thalamus, are called ventricles (little cavities). There is one hypothalamus, and epithalamus. lateral ventricle in each hemisphere of the cerebrum. Cerebrum: The largest part of the brain, (Think of them as ventricles 1 and 2.) Anteriorly, the supported on the diencephalon and brainstem. lateral ventricles are separated by a thin membrane, the septum pellucidum (pellucid = transparent). The Cranium and cranial meninges - surround and third ventricle is a narrow, slit-like cavity along the protect the brain. Cranial meninges are continuous midline, lying superior to the hypothalamus and with the spinal meninges, share the same basic between the right and left halves of the thalamus. structure, and have the same names: Dura Mater (outermost layer) Arachnoid Mater (middle layer) Pia Mater (innermost layer) FUNCTION The cranial dura mater has two layers, unlike the spinal dura mater, which has only one. The two layers 1. Mechanical Protection: of the cranial dura mater are: CSF serves as a shock-absorbing medium that protects the delicate tissues of the brain and Periosteal Layer (external)  spinal cord from jolts that would otherwise More CSF is added by the choroid plexus in cause them to hit the bony walls of the cranial the roof of the third ventricle. cavity and vertebral canal. The fluid also buoys The fluid then flows through the aqueduct of the brain so that it “floats” in the cranial cavity. the midbrain (cerebral aqueduct), which 2. Homeostatic Function: passes through the midbrain into the fourth The pH of the CSF affects pulmonary ventricle. ventilation and cerebral blood flow, which is The choroid plexus of the fourth ventricle important in maintaining homeostatic controls contributes more fluid. for brain tissue. CSF also serves as a transport system for polypeptide hormones secreted by CSF enters the subarachnoid space through the hypothalamic neurons that act at remote sites three openings in the roof of the fourth ventricle: a in the brain. single median aperture and paired lateral apertures, 3. Circulation: one on each side. CSF is a medium for minor exchange of nutrients and waste products between the CSF then circulates in the central canal of the blood and the adjacent nervous tissue. spinal cord and in the subarachnoid space around the surface of the CNS (brain and CSF Formation in the Ventricles spinal cord). CSF is gradually absorbed into the blood The majority of CSF production is from the choroid through arachnoid villi, fingerlike extensions plexus (membrane-like networks of blood capillaries of the arachnoid mater that project into the in the walls of the ventricles, figure 14.4a). dural venous sinuses, especially the superior sagittal sinus. A cluster of arachnoid villi is Ependymal cells joined by tight junctions called an arachnoid granulation. cover the capillaries of the choroid plexus. Selected substances (mostly water, H₂O) from Normally, CSF is reabsorbed as rapidly as it is formed the blood plasma, which are filtered from the by the choroid plexus, at a rate of about 20 mL/hr (480 capillaries, are secreted by ependymal cells to mL/day). Because the rates of formation and produce cerebrospinal fluid. reabsorption are the same, the pressure of CSF This is bidirectional and accounts for remains constant. For the same reason, the volume of continuous production of CSF and the CSF remains constant. transport of metabolites. Thalamus Because of the tight junctions between ependymal Measures about 3 cm (1.2 inches) in length cells, materials entering CSF from choroid capillaries Makes up 80% of the diencephalon cannot leak between cells; instead, they must pass Consists of paired oval masses of gray matter through ependymal cells. organized into nuclei with interspersed tracts of white matter This blood-cerebrospinal fluid barrier permits certain substances to enter the CSF Interthalamic adhesion (intermediate mass) but excludes others, protecting the CNS from A bridge of gray matter potentially harmful blood-borne substances. Joins the right and left halves of the thalamus in about 70% of human brains In contrast to the blood-brain barrier, which is formed mainly by tight junctions of brain capillary endothelial BRAIN BLOOD FLOW AND THE BLOOD-BRAIN cells, the blood-cerebrospinal fluid barrier is formed by BARRIER tight junctions of ependymal cells. Through a network of blood arteries, the brain obtains its blood supply. It is the internal carotid arteries, as CSF Circulation well as the vertebral arteries. The CSF formed in the choroid plexus of each lateral Internal Carotid Arteries: These arteries, one on ventricle flows into the third ventricle through two each side of the neck, supply the front and middle narrow, oval openings, the interventricular foramina parts of the brain. (singular: foramen; figure 14.4b). Vertebral Arteries: These arteries, originating from the subclavian arteries, supply the back part of the Nuclei in the medulla also control reflexes for: brain. Vomiting Swallowing Coughing Sneezing Hiccupping The blood-brain barrier (BBB) consists mainly of tight junctions that seal together the endothelial cells of The vomiting center of the medulla causes vomiting, brain blood capillaries, and a thick basement the forcible expulsion of the contents of the upper membrane that surrounds the capillaries. gastrointestinal (GI) tract through the mouth. The brain's microvascular endothelial cells (BMVEC) The deglutition center of the medulla promotes form a unique barrier known as the blood-brain barrier deglutition (swallowing) of a mass of food that has (BBB) that protects the brain from toxins in the blood, moved from the oral cavity of the mouth into the nourishes brain tissue, and filters harmful substances pharynx. out of the brain and back into the bloodstream. Sneezing: Involves spasmodic contraction of breathing muscles that forcefully expel air through the THE BRAINSTEM AND RETICULAR FORMATION nose and mouth. The brainstem is the part of the brain located Coughing: Involves a long-drawn and deep between the spinal cord and diencephalon. inhalation, then a strong exhalation that sends a blast It consists of three structures: of air through the upper respiratory passages. Hiccupping: Caused by spasmodic contractions of Medulla oblongata the diaphragm, producing a sharp sound on inhalation. Pons Midbrain INFERIOR OLIVARY NUCLEUS Receives input from the cerebral cortex, red nucleus Extending through the brain stem is the reticular of the midbrain, and spinal cord. formation, a net-like region of interspersed gray and Neurons of the inferior olivary nucleus extend their white matter. axons into the cerebellum, regulating the activity of cerebellar neurons. MEDULLA OBLONGATA Influences cerebellar neuron activity, providing The medulla oblongata, often referred to simply as the instructions that the cerebellum uses to adjust muscle medulla, is a crucial component of the brainstem and activity as new motor skills are learned. serves multiple vital functions. It is located at the base of the brain, starting from the foramen magnum and GRACILE AND CUNEATE NUCLEI extending to the lower border of the pons. These nuclei are the right and left gracile nucleus and cuneate nucleus. White Matter: The medulla contains white matter Nuclei associated with sensations of touch, pressure, that houses sensory (ascending) and motor vibration, and conscious proprioception are located in (descending) tracts connecting the spinal cord to other the posterior part of the medulla. brain regions. Ascending sensory axons of the gracile fasciculus Prominent structures called pyramids are formed by and the cuneate fasciculus, two tracts in the the corticospinal tracts, which control voluntary posterior columns of the spinal cord, form synapses in movements of limbs and trunk. these nuclei. Decussation of Pyramids: Near the junction of the Postsynaptic neurons then relay the sensory medulla with the spinal cord, a significant portion of information to the thalamus on the opposite side of the axons in the pyramids cross to the opposite side of the brain. brain. This crossing, known as the decussation of The tracts of the posterior columns and the axons of pyramids, explains the contralateral control of the medial lemniscus are collectively known as the voluntary movements. posterior column–medial lemniscus pathway. The medulla also contains several nuclei that control CRANIAL NERVES OF THE MEDULLA vital body functions. The medulla contains nuclei that are the origins of Cardiovascular (CV) Centre: Regulates the rate cranial nerves. and force of the heartbeat and the diameter of blood 1. Vestibulocochlear (VIII) Nerve: Nuclei in the vessels. medulla receive sensory input and provide Medullary Respiratory Centre: Adjusts the basic motor output to the cochlea of the inner ear via rhythm of breathing.  the vestibulocochlear nerves, which convey breathing alongside the medullary impulses related to hearing. respiratory center. 2. Glossopharyngeal (IX) Nerves: Nuclei in the medulla relay sensory and motor impulses Cranial Nerves Associated with the Pons related to taste, swallowing, and salivation via the glossopharyngeal nerves. 1. Trigeminal (V) Nerves 3. Vagus (X) Nerves: Nuclei in the medulla ○ Nuclei in the pons receive sensory receive sensory impulses from and provide impulses for somatic sensations from motor impulses to the pharynx and larynx and the head and face. many thoracic and abdominal viscera via the ○ Provide motor impulses that govern vagus nerves. chewing via the trigeminal nerves. 4. Accessory (XI) Nerves (Cranial Portion): 2. Abducens (VI) Nerves These fibers are part of the vagus nerves. ○ Nuclei in the pons provide motor Nuclei in the medulla are the origin for nerve impulses that control eyeball movement impulses that control swallowing via the vagus via the abducens nerves. nerves. 3. Facial (VII) Nerves 5. Hypoglossal (XII) Nerves: Nuclei in the ○ Nuclei in the pons receive sensory medulla are the origin for nerve impulses that impulses for taste. control tongue movements during speech and ○ Provide motor impulses to regulate swallowing via the hypoglossal nerves. secretion of saliva and tears, and contraction of muscles of facial THE BRAINSTEM AND RETICULAR expression via the facial nerves. 4. Vestibulocochlear (VIII) Nerves FORMATION ○ Nuclei in the pons receive sensory Pons impulses from and provide motor impulses to the vestibular apparatus via The pons (= bridge) lies directly superior to the the vestibulocochlear nerves, which medulla and anterior to the cerebellum and is convey impulses related to balance and about 2.5 cm (1 in.) long. equilibrium. The pons consist of both nuclei and tracts. It acts as a bridge that connects parts of the MIDBRAIN brain with one another. These connections are provided by bundles of The midbrain or mesencephalon extends from axons. the pons to the diencephalon and is about 2.5 Some axons of the pons connect the right and cm (1 in.) long. left sides of the cerebellum. The aqueduct of the midbrain (cerebral aqueduct) passes through the midbrain, TWO MAJOR STRUCTURES OF THE PONS connecting the third ventricle above with the fourth ventricle below. 1. Ventral Region The midbrain contains both nuclei and tracts. ○ Forms a large synaptic relay station consisting of scattered grey centers Cerebral Peduncles called the pontine nuclei (PON-tīn). ○ Plays an essential role in coordinating Consist of axons of the corticospinal, and maximizing the efficiency of corticobulbar, and corticopontine tracts. voluntary motor output throughout the Part of the reticular formation. body. Tectum 2. Dorsal Region ○ Contains ascending and descending The posterior part of the midbrain is called the tracts along with the nuclei of cranial tectum. nerves. Contains the superior colliculi and inferior ○ Also includes the pontine respiratory colliculi. group (PRG), which helps control 1. Superior Colliculi  ○ Reflex centers for certain visual Consists of sensory axons that project to the activities. cerebral cortex, both directly and through the ○ Involved in eye movements for tracking thalamus. moving images and scanning stationary The most important function of the RAS is images. consciousness. ○ Governs reflexes of the head, eyes, ○ Visual and auditory stimuli, and mental and trunk in response to visual stimuli. activities stimulate the RAS to maintain 2. Inferior Colliculi consciousness. ○ Part of the auditory pathway, relaying ○ Helps prevent sensory overload by impulses from the inner ear to the filtering out insignificant information. brain. Inactivation of the RAS induces sleep. ○ Involved in the startle reflex (sudden Damage to the RAS results in coma. movements of the head, eyes, and ○ In the lightest stages of coma, trunk due to loud noise). brainstem and spinal cord reflexes persist. MIDBRAIN STRUCTURES ○ In the deepest states, these reflexes are lost, and respiratory and Contains several nuclei, including the left and cardiovascular controls may be lost, right substantia nigra and the left and right red resulting in death. nuclei: ○ Drugs like melatonin affect the RAS to ○ Substantia Nigra: Large and darkly induce sleep. pigmented. ○ Anaesthetics turn off consciousness via ○ Red Nuclei: Look reddish due to rich the RAS. blood supply and an iron-containing The descending portion of the RAS helps pigment in their neuronal cell bodies. regulate muscle tone by connecting to the ○ Axons from the cerebellum and cerebellum and spinal cord. cerebral cortex form synapses in the No input from the sense of smell; even strong red nuclei, helping control muscular odors may fail to cause arousal. movements. THE CEREBELLUM Cranial Nerves Associated with the Midbrain Second only to the cerebrum in size, the 1. Oculomotor (III) Nerves cerebellum occupies the inferior and posterior ○ Nuclei in the midbrain provide motor aspects of the cranial cavity. impulses that control movements of the Like the cerebrum, it has a highly folded eyeball. surface that greatly increases the surface area ○ Accessory oculomotor nuclei regulate of its outer grey matter cortex, allowing for a constriction of the pupil and changes in greater number of neurons. lens shape via the oculomotor nerves. The cerebellum accounts for about a tenth of 2. Trochlear (IV) Nerves the brain's mass yet contains nearly half of the ○ Control movements of the eyeball via brain’s neurons. the trochlear nerves. It is posterior to the medulla and pons and inferior to the posterior portion of the cerebrum. RETICULAR FORMATION Cerebellum Structure Broad region where white matter and grey matter exhibit a netlike arrangement. A deep groove called the transverse fissure, Extends from the superior part of the spinal along with the tentorium cerebelli, separates cord, throughout the brain stem, and into the the cerebellum from the cerebrum. inferior part of the diencephalon. In superior or inferior views, the cerebellum Has both ascending (sensory) and descending resembles a butterfly, with a central constricted (motor) functions. area called the vermis and lateral "wings" or lobes referred to as the cerebellar RETICULAR ACTIVATING SYSTEM (RAS) hemispheres. Cerebellar Lobes processing between high and lower brain centers. 1. Anterior Lobe and Posterior Lobe It includes: ○ Govern subconscious aspects of ○ Thalamus skeletal muscle movements. ○ Hypothalamus 2. Flocculonodular Lobe ○ Epithalamus ○ Contributes to equilibrium and balance. Thalamus Cerebellar Cortex Measures about 3 cm (1.2 inches) in length The superficial layer, known as the cerebellar Makes up 80% of the diencephalon cortex, consists of grey matter in a series of Consists of paired oval masses of gray matter slender, parallel folds called folia (leaves). organized into nuclei with interspersed tracts of white matter Cerebellar Peduncles Three paired cerebellar peduncles attach the Interthalamic Adhesion (Intermediate Mass) cerebellum to the brain stem. A bridge of gray matter These bundles of white matter consist of axons Joins the right and left halves of the thalamus that conduct impulses between the cerebellum in about 70% of human brains and other parts of the brain. 1. Superior Cerebellar Peduncles Internal Medullary Lamina ○ Contain axons that extend from the cerebellum to the red nuclei of the Vertical Y-shaped sheet of white matter midbrain and to several nuclei of the Divides the gray matter of the right and left thalamus. side of the thalamus 2. Middle Cerebellar Peduncles Consists of myelinated axons entering and ○ Largest peduncles; axons carry leaving the various thalamic nuclei impulses for voluntary movements from the pontine nuclei (which receive input Internal Capsule from motor areas of the cerebral cortex) into the cerebellum. A thick band of white matter lateral to the 3. Inferior Cerebellar Peduncles thalamus ○ Consist of axons of the spinocerebellar Where axons that connect to the thalamus and tracts, which carry sensory information cerebral cortex pass through to the cerebellum from proprioceptors in the trunk and limbs. Seven Major Groups of Nuclei ○ Include axons from the vestibular apparatus of the inner ear, vestibular The thalamus is the major relay station for nuclei of the medulla and pons, and the most sensory impulses that reach the primary inferior olivary nucleus of the medulla. sensory areas of the cerebral cortex from the ○ Regulate cerebellar neuron activity spinal cord and brainstem during motor skill learning. Contributes to motor functions by transmitting ○ Axons extend from the cerebellum to information from the cerebellum and basal the vestibular nuclei and reticular nuclei to the primary motor area of the cerebral formation. cortex Diencephalon Anterior Nuclei Forms a central core of brain tissue just Receives input from the hypothalamus, sends superior to the midbrain output to the limbic system Almost completely surrounded by the cerebral Functions in emotion and memory hemispheres and contains numerous nuclei involved in a wide variety of sensory and motor Seven Major Groups of Nuclei - Medial Nuclei  Receives input from the limbic system and Forms a thin band adjacent to the 3rd ventricle basal nuclei, sends output to the cerebral Has a presumed function in memory and cortex olfaction Functions in emotions, learning, memory, and cognition (thinking and knowing) Reticular Nucleus Lateral Group Surrounds the lateral aspect of the thalamus, next to the internal capsule Receives input from the limbic system, Monitors, filters, and integrates activities of superior colliculi, and cerebral cortex, sends other thalamic nuclei output to the cerebral cortex Hypothalamus Nuclei in the Lateral Group: A structure deep in your brain, acts as your Lateral Dorsal Nucleus: Functions in the body's smart control coordinating center expression of emotions Its main function is to keep your body in a Lateral Posterior Nucleus and Pulvinar stable state called homeostasis Nucleus: Help integrate sensory information It does its job by directly influencing your autonomic nervous system Seven Nuclei Groups: Ventral Group The Hypothalamus Produces Hormones That Ventral Anterior Nucleus Group: Receives Control: input from the basal nuclei and sends output to the motor areas of the cerebral cortex Body temperature Ventral Lateral Muscle: Receives input from Heart rate the cerebellum and basal nuclei, sends output Hunger to motor areas of the cerebral cortex Mood Ventral Posterior Nucleus: Relays impulses Release of hormones from many glands, for somatic sensations like touch, pressure, especially the pituitary gland vibration, itch, tickle, temperature, nociception, Sex drive and proprioception from the face and body to Sleep the cerebral cortex Thirst Lateral Geniculate Nucleus Hypothalamic Dysfunction: Hypothalamic dysfunction can occur due to: Relays visual impulses for sight from the retina to the primary visual area of the cerebral cortex Genetic causes (often present at birth or during childhood) Medial Geniculate Nucleus Infection or inflammation Injury resulting from trauma, surgery, or Relays auditory impulses for hearing from the radiation ear to the primary auditory area - Because the hypothalamus controls so many different functions, hypothalamic disease can Intralaminar Nuclei have many different symptoms, depending on the cause. Lie within the internal medullary lamina and make connections with the reticular formation, Symptoms of Hypothalamic Dysfunction: cerebrum, basal nuclei, and wide areas of the cerebral cortex Increased appetite and rapid weight gain Function in arousal (activation of the cerebral Extreme thirst and frequent urination (diabetes cortex from the brainstem reticular formation) insipidus) Integration of sensory and motor information Low body temperature Slow heart rate Midline Nucleus Epithalamus:  The epithalamus is part of the dorsal forebrain Parts of the diencephalon that lie in the wall of and includes the pineal gland and a region in the third ventricle. the roof of the third ventricle. Monitor chemical changes in the blood since The function of the epithalamus is to connect they lack a blood-brain barrier. the limbic system to other parts of the brain. Include parts of: Some functions of its components include the ○ Hypothalamus secretion of melatonin by the pineal gland ○ Pineal gland (involved in circadian rhythms), and regulation ○ Pituitary gland of motor pathways and emotions. ○ A few other nearby structures The epithalamus (PL: epithalami) is a posterior These regions coordinate homeostatic (dorsal) segment of the diencephalon. activities of the endocrine and nervous The epithalamus includes the habenular systems such as: trigone (the habenular nuclei and their ○ Regulation of blood pressure habenular commissure), the stria medullaris, ○ Fluid balance and the pineal gland. ○ Hunger ○ Circadian rhythm: The “internal body ○ Thirst clock” that regulates the 24-hour cycle Also thought to be sites of entry into the brain of biological processes in animals and of HIV (the virus that causes AIDS). plants. In the brain, HIV may cause dementia ○ Pineal gland: A small, pinecone-shaped (irreversible deterioration of mental state) and endocrine gland found near the center other neurological disorders. of the brain that produces melatonin. The Cerebrum Melatonin The cerebrum is the "seat of intelligence" and A hormone related to serotonin that is secreted provides us the ability to read, write, speak, by the pineal gland and stimulates color make calculations, and compose music. change in the skin of reptiles. It helps us remember the past, plan for the It is involved in the sleep/wake and future, and imagine things that have never reproductive cycles in mammals. existed before. Consists of: ○ An outer cerebral cortex ○ An internal region of cerebral white matter ○ Gray matter nuclei deep within the Pineal Gland white matter The pineal gland (also called the pineal body, Cerebral Cortex epiphysis cerebri, epiphysis, conarium, or the “third eye”) is the only unpaired midline brain A region of gray matter that forms the outer rim structure. of the cerebrum It is about the size of a grain of rice (5–8 mm) 2–4 mm (0.08–0.16 in) thick and contains in humans. billions of neurons arranged in layers The pineal gland lies between the laterally positioned thalamic bodies and behind the Gyri or Convolutions habenular commissure. It is located behind the third ventricle and is During embryonic development, the gray bathed in cerebrospinal fluid supplied through matter of the cortex enlarges much faster than a small pineal recess of the third ventricle. the deeper white matter. As a result, the cortical region rolls and folds Circumventricular Organs (CVO) of the Third on itself. Ventricle These folds are called gyri or convolutions. Fissures – The deepest grooves between folds.  Sulci – Shallower grooves between folds. 3. Projection Tracts – Contain axons that Longitudinal Fissure – The most prominent conduct nerve impulses from the cerebrum to fissure that separates the cerebrum into right lower parts of the CNS (thalamus, brain stem, and left halves called the cerebral spinal cord) or from lower parts of the CNS to hemispheres. the cerebrum. Corpus Callosum – A broad band of white ○ Example: Internal capsule – thick band matter containing axons that internally of white matter containing both connects the cerebral hemispheres. ascending and descending axons. Cerebral Lobes Each cerebral hemisphere can be further subdivided into several lobes, named after the bones that cover them: frontal, parietal, Basal Nuclei temporal, and occipital lobes. Receive input from the cerebral cortex and Notable Features: provide output to motor parts of the cortex via the medial and ventral group nuclei of the Central Sulcus – Separates the frontal lobe thalamus. from the parietal lobe. Major function is to help regulate initiation and ○ Precentral Gyrus – Contains the termination of movements. primary motor area of the cerebral Also control subconscious contractions of cortex; located immediately anterior to skeletal muscles. the central sulcus. Deep within each cerebral hemisphere are 3 ○ Postcentral Gyrus – Contains the nuclei collectively termed the "basal nuclei." primary somatosensory area of the 1. Globus Pallidus – Closer to the thalamus; cerebral cortex; located immediately helps regulate the muscle tone required for posterior to the central sulcus. specific body movements. Lateral Cerebral Sulcus – Separates the 2. Putamen – Closer to the cerebral cortex. frontal lobe from the temporal lobe. ○ Together, they are called the "Lentiform Parieto-occipital Sulcus – Separates the Nucleus." parietal lobe from the occipital lobe. 3. Caudate Nucleus – Has a large head Insula – The fifth part of the cerebrum, which connected to a smaller "tail" by a long cannot be seen on the surface of the brain comma-shaped body. because it lies within the lateral cerebral The Lentiform Nucleus and Caudate sulcus, deep to the parietal and frontal lobes. Nucleus are known as the Corpus Striatum. Nearby structures that are functionally linked Cerebral White Matter to the basal nuclei: ○ Substantia Nigra of the midbrain – Consists primarily of myelinated axons in 3 types of their axons terminate in the caudate tracts: nucleus and putamen. ○ Subthalamic Nuclei of the 1. Association Tracts – Contain axons that diencephalon – interconnect with the conduct nerve impulses between gyri in the globus pallidus. same hemisphere. ○ Claustrum – Thin sheet of gray matter 2. Commissural Tracts – Contain axons that situated lateral to the putamen. conduct nerve impulses from gyri in one cerebral hemisphere to corresponding gyri in Limbic System the other cerebral hemisphere. ○ Three important groups of commissural Encircling the upper part of the brainstem and tracts: a. Corpus Callosum – Largest corpus callosum is a ring of structures on the fiber bundle in the brain that contains inner border of the cerebrum and floor of the about 300 million fibers. b. Anterior diencephalon. Commissure c. Posterior Commissure Main Components of the Limbic System: Stimulation of limbic system areas in animals produces tameness and signs of 1. Limbic Lobe – Rim of cerebral cortex on the affection. medial surface of each hemisphere. ○ Includes: Rage Cingulate Gyrus – "Cingul" = belt; lies above the corpus A behavioral pattern produced by stimulation of callosum. a cat’s amygdala or certain nuclei of the Parahippocampal Gyrus – In hypothalamus. the temporal lobe below. A person whose amygdala fails to recognize Hippocampus – "Seahorse"; fearful expressions in others or to express fear portion of parahippocampal in situations where this emotion would normally gyrus that extends to the floor of be appropriate. the lateral ventricle. Has cells reported to be Functional Organization of the Cerebral capable of mitosis. Cortex Portion of the brain responsible for some SENSORY AREAS aspects of memory. 2. Dentate Gyrus – "Dentate" = toothed; lies Sensory impulses arrive mainly in the between the hippocampus and posterior half of both cerebral parahippocampal gyrus. hemispheres, in regions behind the central 3. Amygdala – "Amygda" = almond-shaped; sulci. composed of several groups of neurons In the cerebral cortex, primary sensory areas located close to the tail of the caudate nucleus. receive sensory information that has been 4. Septal Nuclei – Located within the septal area relayed from peripheral sensory receptors formed by the regions under the corpus through lower regions of the brain. callosum and paraterminal gyrus. Sensory association areas often are adjacent 5. Mammillary Bodies of the hypothalamus – to the primary areas. Two round masses close to the midline near Sensory areas are involved in perception, the the cerebral peduncles. conscious awareness of a sensation, and 6. Two Nuclei of the Thalamus – The anterior integrate sensory experiences to generate nucleus and medial nucleus participate in meaningful patterns of recognition and limbic circuits. awareness. Olfactory Bulbs Primary Somatosensory Area Flattened bodies of the olfactory pathway that Areas 3, 1, and 2. rest on the cribriform plate. Located directly posterior to the central sulcus of each cerebral hemisphere in the Other Structures Linked by Bundles of Myelinated postcentral gyrus of each parietal lobe. Axons: Extends from the lateral cerebral sulcus, along the lateral surface of the parietal lobe to the Fornix, Stria Terminalis, Stria Medullaris, longitudinal fissure, and then along the medial Medial Forebrain Bundle, and surface of the parietal lobe within the Mammillothalamic Tract. longitudinal fissure. Receives nerve impulses for touch, pressure, Limbic System Functions: vibration, itch, tickle, temperature (coldness and warmth), nociception, and proprioception Sometimes called the "emotional brain" (joint and muscle position). because it plays a primary role in a range of Involved in the perception of these somatic emotions, including pain, pleasure, docility, sensations. affection, and anger. A ‘map’ of the entire body is present in the Also involved in olfaction and memory. primary somatosensory area; each point within  the area receives impulses from a specific part Located in the precentral gyrus of the frontal of the body. lobe. The size of the cortical area receiving impulses A ‘map’ of the entire body is present in the from a particular part of the body depends on primary motor area; each region within the the number of receptors present there rather area controls voluntary contractions of specific than on the size of the body part. muscles or groups of muscles. ○ For example, a larger region of the Electrical stimulation of any point in the primary somatosensory area receives impulses motor area causes contraction of specific from the lips and fingertips than from skeletal muscle fibers on the opposite side of the thorax or hip. the body. This distorted somatic sensory map of the Different muscles are represented unequally in body is known as the sensory homunculus. the primary motor area. The primary somatosensory area allows you to ○ More cortical area is devoted to those pinpoint where somatic sensations originate, muscles involved in skilled, complex, or so that you know exactly where on your body delicate movement. to swat that mosquito. ○ For instance, the cortical region devoted to muscles that move the Primary Visual Area (Area 17) fingers is much larger than the region for muscles that move the toes. Located at the posterior tip of the occipital This distorted muscle map of the body is called lobe mainly on the medial surface (next to the motor homunculus. the longitudinal fissure). Receives visual information and is involved in Broca’s Speech Area (Areas 44 & 45) visual perception. Located in the frontal lobe close to the Primary Auditory Area (Areas 41 & 42) lateral cerebral sulcus. Speaking and understanding language are Located in the superior part of the temporal complex activities that involve several sensory, lobe near the lateral cerebral sulcus. association, and motor areas of the cortex. Receives information for sound and is involved In about 97% of the population, these in auditory perception. language areas are localized in the left hemisphere. Primary Gustatory Area (Area 43) The planning and production of speech occur Located at the base of the postcentral gyrus in the left frontal lobe in most people. superior to the lateral cerebral sulcus in the ○ From Broca’s speech area, nerve parietal cortex. impulses pass to the premotor regions Receives impulses for taste and is involved in that control the muscles of the larynx, gustatory perception and taste discrimination. pharynx, and mouth. ○ The impulses from the premotor area Primary Olfactory Area (Area 28) result in specific, coordinated muscle contractions. Located in the temporal lobe on the medial ○ Simultaneously, impulses propagate aspect. from Broca’s speech area to the Receives impulses for smell and is involved in primary motor area. olfactory perception. ○ From here, impulses also control the breathing muscles to regulate the MOTOR AREAS proper flow of air past the vocal cords. The coordinated contractions of your speech Motor output from the cerebral cortex flows and breathing muscles enable you to speak mainly from the anterior part of each your thoughts. hemisphere. People who suffer a cerebrovascular accident (CVA) or stroke in this area can still have clear Primary Motor Area (Area 4) thoughts but are unable to form words, a  phenomenon referred to as non-fluent Auditory Association Area (Area 22) aphasia. Located inferior and posterior to the primary ASSOCIATION AREAS auditory area in the temporal cortex. Allows you to recognise a particular sound as Consist of large areas of the occipital, speech, music, or noise. parietal, and temporal lobes and of the frontal lobes anterior to the motor areas. Orbitofrontal Cortex (Area 11) Connected with one another by association tracts. Corresponding roughly to area 11 along the lateral part of the frontal lobe. Somatosensory Association Area (Areas 5 & 7) Receives sensory impulses from the primary olfactory area. Just posterior to and receives input from This area allows you to identify odors and to the primary somatosensory area, as well as discriminate among different odors. from the thalamus and other parts of the brain. During olfactory processing, the orbitofrontal This area permits you to determine the exact cortex of the right hemisphere exhibits greater shape and texture of an object by feeling it, to activity than the corresponding region in the determine the orientation of one object with left hemisphere. respect to another as they are felt, and to sense the relationship of one body part to Wernicke’s Area another. Another role of the somatosensory association Posterior Language Area area is the storage of memories of past Area 22, and possibly areas 39 & 40 somatic sensory experiences, enabling you to A broad region in the left temporal and parietal compare current sensations with previous lobes, interprets the meaning of speech by experiences. recognizing spoken words ○ For example, the somatosensory It is active as you translate words into thoughts association area allows you to The regions in the right hemisphere that correspond recognise objects such as a pencil and to Broca’s and Wernicke’s areas in the left hemisphere a paperclip simply by touching them. also contribute to verbal communication by adding emotional content, such as anger or joy, to spoken Visual Association Area (Areas 18 & 19) words Unlike those who have CVAs in Broca’s area, people Located in the occipital lobe, receives who suffer strokes in Wernicke’s area can still speak, sensory impulses from the primary visual but cannot arrange words in a coherent fashion (fluent area and the thalamus. aphasia, or ‘word salad’ It relates present and past visual experiences and is essential for recognising and evaluating what is seen. ○ For example, the visual association area allows you to recognise an object such as a spoon simply by looking at it. Common Integrative Area Facial Recognition Area Area 5, 7, 39, & 40 Bordered by somatosensory, visual, and auditory Corresponding roughly to areas 20, 21, and 37 association areas in the inferior temporal lobe, nerve impulses It receives nerve impulses from these areas and from from the visual association area. the primary gustatory area, the primary olfactory area, This area stores information about faces, and it the thalamus, and parts of the brain stem allows you to recognise people by their faces. This area integrates sensory interpretations from the The facial recognition area in the right association areas and impulses from other areas, hemisphere is usually more dominant than the allowing the formation of thoughts based on a variety corresponding region in the left hemisphere. of sensory inputs It then transmits signals to other parts of the brain for t