Anatomy and Physiology 9 PDF

Structural Classification of Neurons There are 3 types of neurons, based on differences in size, shape, and structure: Multipolar neurons: have many dendrites and one axon arising from their cell bodies; most neurons with cell bodies in CNS (interneurons and motor neurons) are...

Structural Classification of Neurons There are 3 types of neurons, based on differences in size, shape, and structure: Multipolar neurons: have many dendrites and one axon arising from their cell bodies; most neurons with cell bodies in CNS (interneurons and motor neurons) are multipolar. Loading… Bipolar neurons have 2 processes extending from the cell body, a dendrite and an axon; found in some of the special senses, such as the eyes, nose, and ears. Unipolar neurons have only 1 process extending from the cell body; outside the cell body, it soon splits into 2 parts that function as 1 axon; the peripheral process has dendrites near a peripheral body part, and the central process runs into the CNS; the cell bodies are found in ganglia outside the CNS; these are sensory neurons. © McGraw Hill, LLC 11 Figure 9.4: Structural Classification of Neurons & Part A: Multipolar neurons consist of one axon with several dendrites protruding from the cell body. Part B : Bipolar neurons consist of one axon and one dendrite. The dendrite extends to form several minute branches. Part C: Unipolar neurons consist of only one axon on either side of a round cell body devoid of dendrites. One section of the axon is labeled the peripheral process (extending to the peripheral nervous system). The other section of the axon is labeled the central process (extending to the central nervous system). © McGraw Hill, LLC 12  important for exam Functional Classification of Neurons Sensory (afferent) neurons: conduct impulses from peripheral receptors to the CNS; usually unipolar, although some are bipolar. Interneurons (association or internuncial neurons): multipolar neurons lying within the CNS that form links between other neurons; the cell bodies of some interneurons aggregate in specialized masses called nuclei. Motor (efferent) neurons: multipolar neurons that conduct impulses from the CNS to peripheral effectors (muscles or glands). © McGraw Hill, LLC 13 Figure 9.5: Functional Classification of Neurons The nervous system is divided into two, the central nervous system (CNS) and the peripheral nervous system (PNS). Signals (information) are received by the sensory receptors in the PNS which leads to the sensory neuron. It is noted that the sensory (afferent) neurons transfer sensory information to neurons in the CNS. The information is transferred to the interneuron in the CNS which leads to the next interneuron. © McGraw Hill, LLC 14 Figure 9.5: Functional Classification of Neurons From the second interneuron, the information is released to the motor neuron. It is noted that the interneurons transfer information from one part of the CNS to another. From the motor neurons of the CNS, information is released to the effector muscle or gland of the PNS. It is noted that the motor (efferent) neurons transfer instructions from the CNS to the effectors. © McGraw Hill, LLC 15  9.4: Neuroglia Neuroglia (glial cells, “nerve glue”) are cells that support neurons. Functions: fill spaces, structurally support, protect, and insulate neurons Do not generate or conduct nerve impulses - only thereto support 4 types in CNS, 2 types in PNS Central nervous system neuroglia: Microglia: small cells that function as phagocytes for bacterial cells and cellular debris and produce scar tissue in sites of injury Oligodendrocytes: form the myelin sheath around axons in the brain and spinal cord Ependymal cells produce cerebrospinal fluid in CNS. © McGraw Hill, LLC 16  Types of Neuroglia Astrocytes: lie between blood vessels and neurons; functions: Structural support Regulation of nutrient and ion concentrations Formation of the blood-brain barrier, which protects brain tissue from chemical fluctuation and prevents entry of many substances Peripheral nervous system neuroglia: Schwann cells: produce the myelin sheath around PNS axons Satellite cells: provide protective coating around cell bodies of neurons in the PNS © McGraw Hill, LLC 17 Figure 9.6: Neuroglia of the Central Nervous System Four types of neuroglia are found in the CNS namely the microglial cell, oligodendrocyte, astrocyte, and ependymal cell. A microglial cell consists of a round structure with filaments and branches protruding from it. Oligodendrocyte is a round structure extending from the Schwann cells of two neurons. Astrocytes are structures that consist of a round head with branches extending to the capillaries and neighboring neurons. The fluid-filled cavity of the brain or spinal cord is enclosed by a line of ependymal cells. © McGraw Hill, LLC 18  Figure 9.7: Satellite Cells and Schwann Cells of the PNS Several rod-shaped Schwann cells are present on the axon. Schwann cells produce the myelin sheath that surrounds the axons of peripheral nerves. From one of the axons protrudes the round structure of the neuron cell body. The neuron cell body is enclosed by a lining of satellite cells. Satellite cells provide a protective coat around the cell bodies of peripheral neurons. © McGraw Hill, LLC 19  Membrane Potential and Distribution of Ions Membrane Potential: the charge inside a cell Resting Membrane Potential: the charge in a cell when it is at rest; this is about -70 mV in neurons Charge inside a neuron results from unequal distribution of ions inside and outside of cells There is a greater concentration of sodium ions on the outside the cells than inside, and a greater concentration of potassium ions inside the cells than outside. Many large negatively charged ions and proteins are found on the inside of cells. © McGraw Hill, LLC 22 Figure 9.8: Resting Membrane Potential The voltmeter is attached to the intracellular fluid of the cytosol and the extracellular fluid. A channel is located on the cell membrane of the cell. ATP molecules from the cell reach the extracellular fluid via the channel. ADP from the extracellular fluid enters the cell via the channel. Protein particles are present inside the cell. Inside and outside the cell are several chloride ions, potassium ions, and sodium ions. Potassium ions are high in number inside the cell while chloride and sodium ions are high in number outside the cell. The voltmeter reads 70 volts. © McGraw Hill, LLC 23  big exam question Stimulation and the Action Potential A neuron remains at rest until stimulated. A stimulus can change resting potential in either direction. An excitatory stimulus opens chemically-gated Nat channels; ions flow into cell due to concentration gradient, causing inside of neuron to become less negative. Threshold stimulus: a stimulus strong enough to cause so many ions to enter neuron, that potential changes from -70 to -55 mV (the threshold potential). Upon reaching threshold potential, voltage-gated Nat channels open, changing charge to about +30 mV; this begins an action potential. g Change from negative to positive charge inside neuron is called depolarization, since now, inside and outside are both positive. © McGraw Hill, LLC 24  big exam question Stimulation and the Action Potential Reaching an action potential is all-or-none response: Action potential either occurs or does not. & An action potential occurs when the charge reaches -55 mV. Action potentials of a neuron are all of the same strength. * When an action potential is reached, cell responds by returning to resting of Potassium potential (-70 mV) by process of repolarization. opening mannels - * Repolarization returns the polarized state and is accomplished by outward flow of potassium ions through potassium channels. At end of repolarization, a slight overshoot called hyperpolarization occurs, in which potential dips below -70 mV. + Finally, the Nat/k Pump moves Nat back out of cell, and Nat back into cell. © McGraw Hill, LLC 25  Figure 9.9: Ion Channels and the Action Potential moresodium inside Potassium outside 55mU mainly sodium Flowe sodiumis coming inside positive making Inside 70mV back to · resting Potential © McGraw Hill, LLC 26  Important test question Figure 9.10: A Recording of an Action Potential The horizontal x-axis shows milliseconds from 0 to 8 in increments of 1. The vertical y-axis shows membrane potential in millivolts from minus 80 to 40 in irregular increments. A line in the graph represents the membrane potential. The membrane potential begins as a resting potential and increases to reach a peak at (2.5, 30) during depolarization. The membrane potential then decreases during repolarization. It then reaches the point (3.2, minus 70) which is marked as hyperpolarization. The line then extends quite steadily where the resting potential is re-established. © McGraw Hill, LLC 27  9.6: Impulse Conduction An action potential at the trigger zone causes an electrical current to flow to adjacent regions of the axon’s membrane. This spreads by a local current flowing down the fiber that stimulates the next region and continues down the axon to the axon terminal. This process is called impulse conduction. Refractory period: period during and after an action potential, during which a threshold stimulus will not cause another action potential: Limits frequency of action potentials Ensures the impulse is only transmitted in one direction – down the axon © McGraw Hill, LLC 28  : - A series of action The Process of Impulse Conduction Potential occurs along the axon TABLE 9.1 Impulse Conduction 1. Neuron membrane Neuron membrane maintains potential restingresting potential. zomu - 1. 2 Threshold stimulus is received. 1. 3 Sodium channels in the trigger zone of the axon open. Inside + 30mv 1. & Sodium ions diffuse inward, depolarizing the axon membrane. 1. S Potassium channels in the axon membrane open. 6 1. Potassium ions diffuse outward, repolarizing the axon membrane. out 7 1. The resulting action potential causes a local electric current that stimulates the adjacent portions of the axon membrane. © McGraw Hill, LLC 30  Types of Impulse Conduction Continuous conduction: Occurs in unmyelinated axons no node of ranvier - Conduct impulses sequentially over the entire length of their membrane slower - Saltatory conduction: Fat > - Occurs in myelinated axons The myelin sheath insulates axons from ion movement across the cell membrane Impulses “jump” from one Node of Ranvier to the next, since sodium and potassium channels occur only at the nodes Speed of impulse conduction is proportional to axon diameter: Thick, myelinated motor axons conduct at 120 m/s Thin, unmyelinated sensory axons conduct at 0.5 m/s © McGraw Hill, LLC 31  Figure 9.12: Saltatory Conduction in a Myelinated Axon © McGraw Hill, LLC 32  9.7: The Synapse A synapse is a junction between 2 communicating neurons. The small gap between the neurons is called the synaptic cleft; the impulse must be conveyed across the cleft. The neuron sending the impulse is the presynaptic neuron. The neuron receiving the impulse is the postsynaptic neuron. Neural communication across the cleft is called synaptic transmission. Communication is accomplished by a chemical called a neurotransmitter, which is stored in synaptic vesicles and released from an expansion at the distal end of the presynaptic neuron, called the synaptic knob. Neurotransmitters are released in response to a nerve impulse reaching the synaptic knob; they diffuse across the cleft and bind to receptors on the membrane of the postsynaptic neuron. © McGraw Hill, LLC 33  Important for exam 9.8: Synaptic Transmission Excitatory and Inhibitory Actions: Excitatory Neurotransmitters: Increase entry of ions into postsynaptic neuron Bring membrane closer to threshold, making action potential more likely Inhibitory Neurotransmitters: Increase flow of (i ions into neuron or flow of kT ions out of the neuron Makes charge inside the neuron more negative, making action potential less likely The postsynaptic neuron may have many presynaptic neurons influencing it, so it sums the excitatory & inhibitory inputs from all of these neurons to derive its response. © McGraw Hill, LLC 37 Figure 9.16: Excitatory versus Inhibitory Stimulus In both graphs, the horizontal and vertical graphs are not labeled. The horizontal axes are devoid of units. The vertical axes read units of -80, -70, and -55 (from the origin). The graphs show the two types of stimulus excitatory and inhibitory generated due to the neurotransmitter. Part A: Excitatory cells spread the network activity in and out of the network. As a result, a line begins at -70, extends steadily, increases diagonally to reach a peak, and curves. Part B: Inhibitory cells provide recurrent feedback. It is regulated by the rate of synaptic activity. As a result, a line begins at -70, extends steadily, decreases diagonally with a slight curve, reaches a peak, and ends at a point. © McGraw Hill, LLC 38  Neurotransmitters More than 100 neurotransmitters are produced in synaptic knobs and stored in synaptic vesicles. Neurotransmitters include acetylcholine, monoamines, amino acids, neuropeptides. The action of the neurotransmitter depends on type of receptors in a specific synapse. Some neurons produce one type of neurotransmitter, while others produce two or three. © McGraw Hill, LLC 39  Important Some Neurotransmitters & Their Actions TABLE 9.2 Some Neurotransmitters and Representative Actions Neurotransmitter Locatio Major Actions n Acetylcholine CNS Controls skeletal muscle actions. PNS Stimulates skeletal muscle contraction at neuromuscular junctions; may excite or inhibit autonomic nervous system actions, depending on receptors. Monoamines Norepinephrine CNS Creates a sense of feeling good; low levels may lead to depression. PNS May excite or inhibit autonomic nervous system actions, depending on receptors. Dopamine CNS Creates a sense of feeling good; deficiency in some brain areas is associated with Parkinson disease. PNS Limited actions in autonomic nervous system; may excite or inhibit, depending on receptors. Serotonin CNS Primarily inhibitory; leads to sleepiness; action is blocked by LSD, enhanced by selective serotonin reuptake inhibitor drugs (SSRIs). © McGraw Hill, LLC 40  Histamine CNS Release in hypothalamus promotes alertness. Some Neurotransmitters & Their Actions TABLE 9.2 Some Neurotransmitters and Representative Actions Neurotransmitter Locatio Major Actions n Amino acids GABA CNS Generally inhibitory. Glutamic acid CNS Generally excitatory. Neuropeptides Substance P PNS Excitatory; pain perception. Endorphins, CNS Generally inhibitory; reduce pain by inhibiting substance P release. enkephalins Gases Nitric oxide PNS Vasodilation. CNS May play a role in memory. © McGraw Hill, LLC 41  Events Leading to Release of a Neurotransmitter TABLE 9.3 Events Leading to the Release of a Neurotransmitter 1. Action Potential Action potentialPasses passes along along an anaxon and over axon theover and surface of itssurface the of Its synaptic knob synaptic knob. 1. 2 Synaptic knob membrane becomes more permeable to calcium ions, and they diffuse inward. 1. 3 In the presence of calcium ions, synaptic vesicles fuse to synaptic knob membrane. 1. A Synaptic vesicles release their neurotransmitter into synaptic cleft. © McGraw Hill, LLC 42  Facilitation, Convergence, and Divergence Facilitation: An increase in the release of neurotransmitter in response to one impulse, which occurs in an excitatory presynaptic neuron upon repeated stimulation; this response increases the likelihood that the postsynaptic neuron will reach threshold Convergence: The transmission of nerve impulses to a single neuron within a pool from two or more fibers; this makes it possible for the neuron to summate impulses from different sources Divergence: The transmission of nerve impulses from a neuron in a pool to several output fibers; this serves to amplify an impulse © McGraw Hill, LLC 45 Figure 9.17: Impulse Processing: Convergence and Divergence Part A: Impulses from neurons 1 and 2 together lead to neuron 3. Part B: Impulses from neuron 4 reaches neurons 5 and 6 separately. © McGraw Hill, LLC 46  9.12: Meninges The brain and spinal cord are surrounded by 3 membranes called meninges that lie between the skull bones & vertebrae and the soft CNS tissues. The meninges consist of the dura mater, arachnoid mater, and pia mater. Dura mater: Outermost layer of meninges Made up of tough, dense connective tissue, and is very thick Contains many blood vessels Forms the internal periosteum of the skull bones In some areas, the dura mater forms partitions between lobes of the brain, and in others, it forms dural sinuses. The sheath around the spinal cord is separated from the vertebrae by an epidural space. © McGraw Hill, LLC 56  Meninges Arachnoid mater: The middle layer of meninges Thin, weblike layer that lacks blood vessels Between the arachnoid and pia mater is the subarachnoid space, which contains cerebrospinal fluid (CSF) Pia mater: The innermost layer of the meninges Thin layer, which contains many blood vessels and nerves Attached to the surface of the brain and spinal cord and follows their contours © McGraw Hill, LLC 57 Figure 9.22: The Meninges of the Brain Part A shows the posterior view of the head. The view shows the scalp and cranium, cerebrum & cerebellum, vertebra, spinal cord, & the layer of meninges forming the outer layer of the brain stem. Part B shows the layers present in the meninges. The illustration shows the outer skin followed by the subcutaneous tissue, bone of the skull, & dural sinus. The meninges is comprised of three layers namely the dura mater, arachnoid mater, and pia mater. The Dura mater is the outermost layer, the pia mater is the innermost layer & the arachnoid mater is the middle layer. The space between the arachnoid mater and the pia mater is the subarachnoid space. Outside the pia mater are the cerebrum which is composed of grey matter and white matter (neurons). © McGraw Hill, LLC 58 Figure 9.23: The Meninges of the Spinal Cord Part A shows the structure of the dura mater which encloses the spinal cord. The parts located in the illustration are the Spinal cord, Pia mater, Subarachnoid space filled with cerebrospinal fluid, Arachnoid mater, Dura mater, Anterior root, Posterior root, Spinal nerve, Posterior root ganglion, & Thoracic vertebra. Part B shows a segment of the vertebra with meninges covering it. The parts located in the illustration are the Pia mater, Subarachnoid space filled with cerebrospinal fluid, Arachnoid mater, Dura mater, Spinal nerve, Posterior root ganglion, Central canal, Subarachnoid space, Epidural space, Posterior root, Spinal cord, Anterior root, and Body of vertebra. © McGraw Hill, LLC 59  9.13: Spinal Cord Spinal cord: Begins at the base of the brain at the foramen magnum Extends as a thin cord to the level of the intervertebral disc between the 1st and 2nd lumbar vertebrae Cervical enlargement: A thickened area near top of spinal cord Provides nerves to upper limbs Lumbar enlargement: A thickened region near the bottom of the spinal cord Gives rise to nerves that serve the lower limbs. Cauda equina (horse’s tail): Structure formed where spinal cord tapers to a point inferiorly Consists of spinal nerves in the lumbar & sacral areas © McGraw Hill, LLC 60 Figure 9.24: Lateral View of Spinal Cord The illustration shows the midsagittal section of the brain which shows the various parts of the brain. The base of the brain consists of the foramen magnum. The brain stem extends to form the cervical enlargement, the spinal cord, the vertebral canal, lumbar enlargement, and cauda equina at the tail of the spinal cord © McGraw Hill, LLC 61  Structure of the Spinal Cord Spinal cord consists of 31 segments, each of which connects to a pair of spinal nerves. Two deep grooves (anterior median fissure and posterior median sulcus) divide the cord into right and left halves. White matter, made up of bundles of myelinated nerve fibers (nerve tracts), surrounds a butterfly-shaped core of gray matter housing interneurons and neuron cell bodies. Cell bodies of sensory neurons that enter the spinal cord are found in the posterior root ganglia outside the spinal cord. The upper and lower wings of gray matter form the posterior and anterior horns; between them is the lateral horn. The gray matter divides the white matter into three regions: anterior, lateral and posterior funiculi (columns), each consisting of longitudinal bundles of axons called tracts. A central canal in the middle of the gray matter contains cerebrospinal fluid. © McGraw Hill, LLC 62 Figure 9.25: A Cross Section of the Spinal Cord Part A: A cross-section of the spinal cord shows the white matter and gray matter. The illustration shows the following parts: Butterfly-shaped structure of the gray matter which is comprised of posterior horn, lateral horn, and anterior horn; gray commissure at the center of the mirror structures of gray matter, posterior median sulcus; a white matter which is composed of the posterior funiculus, lateral funiculus, and anterior funiculus; dorsal root of the spinal nerve; dorsal root of the ganglion; posterior of the spinal nerve; ventral root of the spinal nerve; anterior median fissure, and central canal. Part B shows the micrograph of the cross-section of the spinal cord. The gray matter, white matter, dorsal root of the spinal nerve, dorsal root of the ganglion, and posterior of the spinal nerve are visible. © McGraw Hill, LLC (b): Ed Reschke/Photolibrary/Getty Images 63  Functions of the Spinal Cord Major functions: transmit impulses to and from the brain, and to house spinal reflexes Ascending tracts carry sensory information to the brain; descending tracts carry motor information from brain to muscles or glands The names that identify nerve tracts identify the origin and termination of the fibers in the tract: Spinothalamic tracts: carry sensory information from the spinal cord to the thalamus Corticospinal tracts (pyramidal tracts): carry motor impulses from the cerebral cortex to the spinal cord; pass through pyramid-shaped areas in the medulla oblongata Extrapyramidal tracts: descending tracts involved with balance and posture Spinal reflexes: controlled by reflex arcs that pass through the spinal cord © McGraw Hill, LLC 64  Figure 9.26: Ascending Tracts The ascending tract begins from the skin. Impulses from the temperature receptors or pain receptors are originated in the skin. The impulses reach the sensory fibers of the spinal cord where the cross-over happens. The transverse section of the spinal cord is located. The impulse reaches the brainstem which follows the order of the medulla oblongata, pons, spinothalamic tract, and midbrain, and finally reaches the thalamus in the frontal section of the cerebrum. © McGraw Hill, LLC 65  Figure 9.27: Descending Tracts The descending tract begins from the motor cortex in the frontal section of the cerebrum. The impulses begin at the cerebrum and reach the corticospinal tract followed by the brainstem in the order of midbrain, pons, and medulla oblongata where the motor fibers cross-over takes place. The impulse then reaches the spinal cord and is directed to the skeletal muscle. © McGraw Hill, LLC 66  9.14: The Brain The brain is the largest, most complex portion of the nervous system, containing 100 billion multipolar neurons, and many neuroglia to support the neurons. Structure is reversed from that of spinal cord; gray matter outside and white matter inside. The 4 main parts of the brain: Cerebrum: largest portion; associated with higher mental functions, and sensory & motor functions Diencephalon: processes sensory input and controls many homeostatic processes Cerebellum: coordinates muscular activity Brainstem: coordinates and regulates visceral activities and connects different parts of the nervous system © McGraw Hill, LLC 67 Figure 9.28a: Midsagittal Section of the Brain (Diagram) The illustration of the midsagittal section of the brain shows the following parts: The outer hard layer of the skull; dura mater; gyrus and sulcus of the brain; cerebrum; diencephalon which is comprised of the thalamus, pineal gland, hypothalamus, and posterior pituitary gland; brainstem which is comprised of the midbrain, pons, and medulla oblongata, corpus callosum which bridges the hemispheres of the brain, cerebellum at the base of the brain, and spinal cord which extends from the brain stem. © McGraw Hill, LLC 68  Structure of the Cerebrum The Cerebrum is the largest portion of the mature brain. Consists of 2 cerebral hemispheres, which are mirror images Corpus callosum: flat bundle of nerve fibers that connects the hemispheres. The surface of the brain is marked by these features: Gyri (singular is gyrus): ridges Sulci (singular is sulcus): grooves Fissures (longitudinal and transverse): deep grooves © McGraw Hill, LLC 70  Structure of the Cerebrum Four lobes of the cerebrum are named according to the bones they underlie: frontal, parietal, temporal, and occipital lobes. The fifth lobe is the insula; it lies deep in the lateral sulcus. A thin layer of gray matter, the cerebral cortex, lies on the outside of the cerebrum, and contains 75% of the neuron cell bodies in the nervous system. -mylinated Beneath the cortex lies a mass of white matter made up of myelinated nerve fibers connecting the cell bodies of the cerebral cortex with the rest of the nervous system. © McGraw Hill, LLC 71  Figure 9.29a: Lateral View of the Human Brain (Diagram) The brain is comprised of four major lobes namely the frontal lobe, temporal lobe, parietal lobe, and occipital lobe. Between the frontal and temporal lobes is the insula. Sensory areas: which interpret impulses that arrive from all sensory receptors in body. Motor areas: contain pyramidal cells, impulses travel from pyramidal cells down corticospinal tracts in spinal cord before reaching skeletal muscle. Frontal eye field: controls voluntary movements of eyes & learned movement patterns such as writing. © McGraw Hill, LLC 72  Functions of the Cerebrum The cerebrum provides higher brain functions: Interpretation of sensory input Initiating voluntary muscular movements Stores information for memory Integrates information for reasoning Intelligence Personality © McGraw Hill, LLC 73  Functional Areas of the Cerebral Cortex The functional areas of the brain overlap, but the cortex can generally be divided into sensory, association, and motor areas. The sensory areas are located in several areas of the cerebrum; they interpret sensory input, producing feelings or sensations: Cutaneous senses: anterior parietal lobe Visual area: posterior occipital lobe Auditory area: posterior temporal lobe Taste area: base of central sulcus and insula Smell area: deep in temporal lobe Sensory fibers from the PNS cross over in the spinal cord or the brainstem; this results in sensory impulses from the right side of the body being interpreted by centers in the left cerebral hemisphere. © McGraw Hill, LLC 74  Functional Areas of the Cerebral Cortex Association areas of the brain analyze and interpret sensory impulses, and function in reasoning, judgment, emotions, verbalizing ideas, and storing memory: Association areas of the frontal lobe control a number of higher intellectual processes (planning, problem solving). Association areas of the parietal lobe function in understanding speech and choosing the proper words. Association areas in occipital lobe help analyze visual patterns and combine visual images with other sensory information. Association areas next to sensory areas are important for analyzing the sensory input. A general interpretive area is found at the junction of the parietal, temporal, and occipital lobes, and plays a primary role in complex thought processing and integration. Not all association areas are bilateral; Wernicke’s area of the temporal lobe is g usually on the left side only; it helps with understanding of written and spoken exam language. question © McGraw Hill, LLC 75  Functional Areas of the Cerebral Cortex The primary motor areas lie in the posterior frontal lobes, anterior to the central sulcus. This region includes the pyramidal cells that are also called upper motor neurons; they synapse with lower motor neurons that exit the spinal cord and reach the skeletal muscles. There is also crossover in the brainstem in motor systems, so that the right cerebral hemisphere controls muscles on the left side of the body. Broca’s motor speech area is in the frontal lobe, usually on the left side; controls muscle movements for speech. Frontal eye field in the frontal lobe controls voluntary eye movements. © McGraw Hill, LLC 76  The Basal Nuclei The basal nuclei are masses of gray matter (nuclei) located deep within the cerebral hemispheres. Basal nuclei are also called basal ganglia. Consist of the caudate nucleus, the putamen, and the globus pallidus Produce the inhibitory neurotransmitter, dopamine Relay motor impulses from the cerebrum and help control motor activities by interacting with the motor cortex, thalamus, and cerebellum Help facilitate voluntary movement Altered activity of these nuclei neurons produces the signs of Parkinson disease and Huntington disease. © McGraw Hill, LLC 78