Zoology 120 Animal Physiology Lecture (Central Nervous System) PDF

20373-X: ZOOLOGY 120 ANIMAL PHYSIOLOGY | LECTURE CENTRAL NERVOUS SYSTEM LECTURER: BRIAN ALLISON MARTOS DATE OF LECTURE: MARCH 14, 2024 2ND SEMESTER 2023-2024 Astrocytes OUTLINE Largest and most abundant glial cells. Central Nervous System I. Brain Protoplasmic astrocytes (mossy cells) vs. fibrous A....

20373-X: ZOOLOGY 120 ANIMAL PHYSIOLOGY | LECTURE CENTRAL NERVOUS SYSTEM LECTURER: BRIAN ALLISON MARTOS DATE OF LECTURE: MARCH 14, 2024 2ND SEMESTER 2023-2024 Astrocytes OUTLINE Largest and most abundant glial cells. Central Nervous System I. Brain Protoplasmic astrocytes (mossy cells) vs. fibrous A. Components Nourishment astrocytes B. Neuroglial Cells J. Brain Plasticity Have multiple processes and form perivascular feet that C. Protection of the K. Neurogenesis completely enclose all capillaries (only a few such feet CNS L. Spinal Cord are shown here to allow their morphology to be seen) II. Brain Anatomy III. Processes and Activities Astrocytes are the most abundant glial cells of the CNS A. Overview of Brain of the Brain and are characterized by numerous cytoplasmic Functions A. Reflex processes (P) radiating from the glial cell body or soma B. Brain Stem B. Learning and (S). C. Cerebellum Memory Astrocytic processes are not seen with routine light D. Basal Nuclei C. Sleep microscope staining but are easily seen after gold E. Diencephalon D. Electroencephalog staining. F. Limbic System ram Morphology of the processes allows astrocytes to be G. Cerebrum E. Consciousness classified as fibrous (relatively few and straight H. Cerebral Cortex processes) or protoplasmic (numerous branching processes), but functional differences between these I. Central Nervous System types are not clear. (x500. Gold chloride. Components Fibrous astrocytes— prevalent among myelinated nerve Brain fibers in the white matter of the central nervous system. ○ Brain Stem Protoplasmic astrocytes— occur in the gray matter of ○ Cerebellum the central nervous system ○ Cerebrum Spinal cord ○ Dorsal root ganglia —contain the cell bodies of afferent nerve fibers (those carrying impulses toward the central nervous system) ○ Ventral root ganglia — contain cell bodies of efferent neurons (carrying motor impulses away from the central nervous system) A N G EL IK A A N TO N IO I. Figure 2. Astrocyte. Microglial Cells JA N A H Figure 1. Cross section of spinal cord. Neuroglial Cells Also called glial cells or supporting cells Physically, metabolically, and functionally support interneurons Oligodendrocytes Present in white matter (predominant cells) and gray matter Myelinate parts of several axons Figure 1. Neuroglial cell. Smallest and rarest glial cells found in gray and white matter. Migrate through the neuropil for protective and immune functions. Microglia— monocyte-derived, antigen-presenting cells of the CNS, less numerous than astrocytes but nearly as common as neurons and evenly distributed in both gray and white matter. By immunohistochemistry, here using a monoclonal antibody against human leukocyte antigens (HLA) of immune-related cells, the short branching processes of microglia can be seen. Routine staining demonstrates only the small dark nuclei of the cells. Unlike other glia of the CNS, microglia are not interconnected; they are motile cells, constantly used in immune surveillance of CNS tissues. When activated by products of cell damage or by invading microorganisms, the cells retract their processes, begin phagocytosing the damage- or danger-related material, and behave as antigen-presenting cells. (x500. Antibody against HLA-DR and peroxidase.) Figure 3. Microglial cell. TRANSCRIBED BY: JANAH ANGELIKA R. ANTONIO | BIOLOGY 1 LECTURE 3A - CENTRAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY Ependymal Cells Columnar or cuboidal cells (may have cilia or microvilli). No basal lamina, basal projections extend to the neuropil. Ependymal cells— epithelial-like cells that form a single layer lining the fluid-filled ventricles and central canal of the CNS. (a) Lining the ventricles of the cerebrum, columnar ependymal cells extend cilia and microvilli from the apical surfaces into the ventricle (V). These modifications help circulate the CSF and monitor its contents. ○ Ependymal cells have junctional complexes at their apical ends like those of epithelial cells but lack a basal lamina. The cells’ basal ends are tapered, extending processes that branch and penetrate some distance into the adjacent neuropil (N). ○ Other areas of ependyma are responsible for production of CSF. X100. H&E. (b) Ependymal cells (E) lining the central canal (C) of the spinal cord help move CSF in that CNS region. (x200. H&E.) II. Overview of Brain Functions Figure 6. Brain anatomy. A N G EL IK A Brain Component Cerebral cortex Figure 4. Ependymal cell. Protection of the CNS JA N A H Enclosed by hard, bony structures: skull and vertebral column Wrapped by three protective and nourishing membranes – meninges ○ Dura mater — nearest to the skull ○ Arachnoid mater — middle portion ○ Pia mater — nearest to the brain Floats in cushioning fluid— CSF Blood-brain barrier (BBB)— limits access of blood-borne materials into nervous tissues. Figure 5. The ventricles of the human brain. Blood-Brain Barrier (BBB) Protects brain from chemical fluctuations in blood Main component is the endothelium Minimizes possibility that harmful blood-borne substances might reach central nervous tissue Prevents certain circulating hormones that could also act as neurotransmitters from reaching brain Limits use of drugs for treatment of brain and spinal cord Brain Anatomy A N TO N IO disorders ○ Many drugs cannot penetrate BBB ○ Keeps K+ low and Na+ High Cells joined by tight junctions Basal nuclei Thalamus Hypothalamus 1. 2. 3. 4. 5. 1. 2. 3. 1. 2. 3. 4. 1. 2. 3. Cerebellum 4. 1. 2. 3. Brainstem 1. 2. Major Functions Sensory perception Voluntary control of movement Language Personality traits Sophisticated mental events such as thinking, memory, decision-making, creativity, and self-consciousness Inhibition of muscle tone Coordination of slow, sustained movements Suppression of useless patterns of movement Relay station for all synaptic input Crude awareness of sensation Some degree of consciousness Role in motor control Regulation of many homeostatic functions such as temperature control, thirst, urine output, and food intake. Important link between nervous and endocrine systems Extensive involvement with emotion and basic behavioral patterns Role in sleep-wake cycle. Maintenance of balance Enhancement of muscle tone Coordination and planning of skilled voluntary muscle activity Origin of majority of peripheral cranial nerves Cardiovascular, CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 2 LECTURE 3A - CENTRAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY 3. 4. 5. respiratory and digestive control centers Regulation of muscle reflexes involved with equilibrium and posture Reception an integration of all synaptic input from spinal cord, arousal and activation of cerebral cortex Role in sleep-wake cycle. ○ Critical connecting link between rest of brain and spinal cord Consists of ○ Medulla ○ Pons ○ Midbrain Functions: ○ Most cranial nerves arise from the brain stem. ○ Neuronal clusters within the brain stem control heart and blood vessel function, respiration, and many digestive functions. ○ It plays a role in regulating muscle reflexes involved in equilibrium and posture. ○ Reticular formation within the brain stem receives and integrates all incoming sensory synaptic input. ○ Centers that govern sleep are in the brain stem (evidence suggests centers promoting slow-wave sleep lie in the hypothalamus). Cerebellum Limbic System “Little brain” Attached at top rear portion of brain stem Maintains proper position of the body in space Subconscious coordination of motor activities Plays key role in learning skilled motor tasks Functions: JA N A H THREE PARTS OF CEREBELLUM 1. Vestibulocerebellum ○ Important in maintaining balance and controls eye movements 2. Spinocerebellum: ○ Enhances muscle tone and coordinates skilled, voluntary movements 3. Cerebrocerebellum ○ Plays role in planning and initiating voluntary activity by providing input to cortical motor areas ○ Stores procedural memories Act by modifying ongoing activity in motor pathways Primary functions ○ Inhibiting muscle tone throughout the body ○ Selecting and maintaining purposeful motor activity while suppressing useless or unwanted patterns of movement ○ Helps in monitoring and coordinating slow, sustained contractions, especially those related to posture and support Houses two brain components ○ Hypothalamus Controls many homeostatic functions Controls body temperature Controls thirst and urine output Controls food intake Controls anterior pituitary hormone Located on the interior underside of the temporal lobe Functions ○ Site where link between unconditioned and conditioned stimulus is formed ○ Activates the flight-or-fight stress system ○ GABA to condition someone from a certain stimulus Neurotransmitters of the Limbic System Diencephalon Figure 7. Limbic system. Amygdala Basal Nuclei Includes portions of the hypothalamus and other forebrain structures that encircle brain stem Responsible for ○ Emotions ○ Basic, inborn behavioral patterns related to survival and perpetuation of the species ○ Plays important role in motivation, learning, and memory A N G EL IK A Thalamus Performs some primitive sensory processing Serves as “relay station” and synaptic integrating center for processing sensory input on its way to cerebral cortex Along with brain stem and cortical association areas, important in ability to direct attention to stimuli of interest Capable of crude awareness of various types of sensation but cannot distinguish their location or intensity A N TO N IO Brain Stem secretion Produces posterior pituitary hormones Controls uterine contractions and milk ejection Serves as a major ANS coordinating center Plays role in emotional and behavioral patterns Participates in sleep-wake cycle Norepinephrine and Dopamine ○ Elicit highest rates of self-stimulation equipped with self-administering devices Norepinephrine and Serotonin ○ Deficiency leads to depression ○ Prozac and Escitalopram — SSRIs Selective serotonin reuptake inhibitors ○ SNRI — Serotonin and norepinephrine reuptake inhibitors; Duloxetine Cerebrum Highly developed Inner core houses basal nuclei Outer surface is highly convoluted cerebral cortex ○ Highest, most complex integrating area of the brain ○ Plays key role in most sophisticated neural CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 3 LECTURE 3A - CENTRAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY functions Cerebral Cortex Left and right cerebral hemispheres Each half of cortex divided into four major lobes; ○ Occipital Lobe— carries out initial processing of visual input ○ Temporal Lobe— initial reception of sound sensation ○ Parietal Lobe— somatosensory processing ○ Frontal Lobe— responsible for voluntary motor activity, speaking ability, elaboration of thought Motor Cortex JA N A H A N G EL IK A A N TO N IO PRIMARY MOTOR CORTEX Located in frontal lobe Confers voluntary control over movement produced by skeletal muscles Primarily controls muscles on the opposite side of the body Motor homunculus — depicts location and relative amount of motor cortex devoted to output to muscles of each body part Activated by readiness potential. ○ Widespread pattern of neuronal discharge which occur about 750 msec before electrical activity is detectable in the primary motor cortex ○ Three higher motor areas of the cortex are involved in this voluntary decision-making period: Supplementary motor area— lies on the Figure 8. Limbic system. medial (inner) surface of each hemisphere in front of the primary motor cortex; plays Cerebral Hemispheres preparatory role in programming complex Left Cerebral Hemisphere sequences of movement ○ Excels in logical, analytic, sequential, and verbal Premotor cortex— located on the lateral tasks surface of each hemisphere in front of the ○ Math, language forms, philosophy primary motor cortex; informed of the body’s Right Cerebral Hemisphere momentary position in relation to the target; ○ Excels in non language skills important in orienting the body and arms ○ Spatial perception and artistic and musical talents toward a specific target Posterior parietal cortex— guides the premotor cortex by processing sensory input about the body’s momentary position in Cerebral Integration relation to the target SOMATOSENSORY MOTOR CORTEX Initial cortical processing and perception of somesthetic and proprioceptive input Sensory homunculus — shows the distribution of sensory input to the somatosensory cortex from different parts of the body Primary areas of cortical specialization for language ○ Broca’s area— governs speaking ability ○ Wernicke’s area— concerned with language comprehension; responsible for formulating coherent patterns of speech that are transferred to Broca’s area Language disorders Aphasias Speech impediments Dyslexia Figure 9. Diagram for pathway of cerebral integration. CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 4 LECTURE 3A - CENTRAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY Spinal Cord A N G EL IK A A N TO N IO Two vital functions ○ Neuronal link between brain and PNS ○ Integrating center for spinal reflexes In humans, there are 31 pairs of spinal nerves ○ 8 pairs cervical nerves ○ 12 pairs thoracic nerves ○ 5 pairs lumbar nerves ○ 5 pairs sacral nerves ○ 1 pair coccygeal nerves III. Figure 11. Spinal cord. Processes and Activities of the Brain Reflex Figure 10. Cortical pathway for speaking a word seen or heard. Brain Nourishment JA N A H Substances may or may not pass through the BBB. ○ O2 and glucose ○ Neuroglobin ○ Glycogen in astrocytes ○ Drugs O2 binds to neuroglobin in neurons to get O2 for aerobic respiration to oxidize to glucose (neuronal oxygen homeostasis). Astrocytes can store glycogen for nourishment of neuron if glucose is depleted (glycogen broken down to glucose) Withdrawal Reflex Brain Plasticity Brain changes or is functionally remodeled in response to demands placed on it. Due to formation of new neural pathways ○ Arborizations ○ Dendrites Neurogenesis in the CNS Any response that occurs automatically without conscious effort Two types of reflexes ○ Simple, or basic reflexes Built-in, unlearned responses ○ Acquired, or conditioned reflexes Result of practice and learning Reflex Arc— neural pathway involved in accomplishing reflex activity ○ Five basic components Receptor Afferent pathway Integrating center Efferent pathway Effector Hippocampus— derived from the infolding of ventricles; residual stem/progenitor cells Subventricular zone— lateral ventricles ○ Olfactory epithelium Hypothalamus— cell division in relation to season and other environmental signals for the generation of long-term cycles Spinal canal— cell division repairing neural damage due to injury When an animal touches a hot object (such as an ember following a forest fire), a reflex is initiated to pull the limb away from the object (to withdraw from the painful stimulus). The skin has different receptors for warmth, cold, light touch, pressure, and pain. Even though all information is sent to the CNS by way of action potentials, the CNS can distinguish between various stimuli because specific receptors and consequently different afferent pathways are activated by different stimuli. When a receptor is stimulated sufficiently to reach a threshold, an action potential is generated in the afferent neuron. The stronger the stimulus, the greater the frequency of action potentials generated and propagated to the CNS. Once the afferent neuron enters the spinal cord, it diverges to synapse with the following different interneurons CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 5 LECTURE 3A - CENTRAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY same skeletal muscle to cause it to contract and counteract the stretch. Monosynaptic— Synapse is between the afferent and efferent neuron Polysynaptic— A number of synapses are involved in the reflex arc because of interneurons Other Reflexes Blushing, cough, cremasteric, photic sneeze, rooting, shivering, sneeze or sternutation, startle, vagovagal, yawn Question: What happens in these reflexes? Learning and Memory Figure 12. The withdrawal reflex. The withdrawal reflex. When a painful stimulus activates a receptor in the paw, action potentials are generated in the corresponding afferent pathway, which propagates the electrical signals to the CNS. Once the afferent neuron enters the spinal cord, it diverges and terminates on three different types of interneurons (only one of each type is depicted): (1) excitatory interneurons, which in turn stimulate the efferent motor neurons to the biceps, causing the leg to flex and pull the foot away from the painful stimulus; (2) inhibitory interneurons, which inhibit the efferent motor neurons to the triceps, thus preventing counterproductive contraction of this antagonistic muscle; and (3) interneurons that carry the signal up the spinal cord via an ascending pathway to the brain for awareness of pain, memory storage, and so on. Crossed Extensor-Withdrawal Reflexes JA N A H Crossed extensor reflex— ensures that the opposite limb will be in a position to bear the weight of the body as the injured limb is withdrawn from the stimulus. Spinal reflex action is not necessarily limited to motor responses on the side of the body to which the stimulus is applied. ○ Assume an animal steps on a sharp rock fragment. The ensuing reflex response includes the same neurons as those used for the withdrawal reflex but also recruits neurons that control extension of the opposite limb. A reflex arc is initiated to withdraw the injured foot from the painful stimulus, while the opposite leg simultaneously prepares to suddenly bear the extra weight so that the animal does not lose balance. Unimpeded bending of the injured extremity’s knee is accomplished by concurrent reflex stimulation of the muscles that flex the knee and inhibition of the muscles that extend the knee. At the same time, unimpeded extension of the opposite limb’s knee is accomplished by activation of pathways that cross over to the opposite side of the spinal cord to reflexively stimulate this knee’s extensors and inhibit its flexors. Memory Short-term Memory Figure 13.The crossed extensor reflex coupled with the withdrawal reflex. (a) The withdrawal reflex, which causes flexion of the injured extremity to withdraw from a painful stimulus. (b) The crossed extensor reflex, which extends the opposite limb to support the full weight of the body. Stretch Reflex Involves transient changes in synaptic activity Habituation— decreased responsiveness to repetitive presentations of an indifferent stimulus ○ Habituation example [1:08:00] Sensitization— increased responsiveness to mild stimuli following a strong or noxious stimulus Long-term Memory Declarative or explicit memory— learning of events, places, etc.; semantic memories (facts); episodic memories (events) Procedural or implicit memory— learning of skilled motor movements Imprinting— newborns are programmed to learn that situations and objects encountered early in life are both normal and important to life Memory trace— neural change responsible for retention or storage of knowledge Short-term memory— lasts for seconds to hours Long-term memory— Retained for days to years Consolidation— process of transferring and fixing short-term memory traces into long-term memory stores Working memory— Temporarily holds and interrelates various pieces of information relevant to a current mental task Hippocampus— Plays a vital role in short-term declarative memory involving the integration of various related stimuli Cerebellum— Procedural memories involving motor skills gained through repetitive training A N G EL IK A Learning— acquisition of abilities or knowledge as a consequence of experience, instruction, or both Memory— storage of acquired knowledge or abilities for later recall Rewards and punishments are integral parts of many types of learning. When behavioral responses that give rise to pleasure are reinforced or those accompanied by punishment are avoided, learning has taken place. ○ Housebreaking a puppy is an example. Learning is a change in behavior that occurs as a result of experiences. It highly depends on the organism’s interaction with its environment. A N TO N IO Involves the formation of new, permanent synaptic connection Activation of genes that control protein synthesis for the formation of new synaptic connections Long-Term vs. Short-Term Memory content Sleep An afferent neuron supplying the same skeletal muscle terminates directly on the efferent neuron supplying the Features ○ Periods of minimal movement ○ Reduced responsiveness to external stimuli CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 6 LECTURE 3A - CENTRAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY Electroencephalogram (EEG) Record of postsynaptic activity in cortical neurons “Brain waves” THREE MAJOR CAUSES OF EEG 1. Clinical tool in diagnosis of cerebral dysfunction 2. Used in legal determination of brain death 3. Used to distinguish various stages of sleep Slow wave sleep/Deep sleep — stage 3 REM sleep — similar with the EEG when you are awake; stage in sleep where a person dreams Function of Sleep A N TO N IO ○ Rapid reversibility ○ Characteristic body posture Sleep-wake cycle ○ Normal cyclic variation in awareness of surroundings ○ Active process consisting of two types of sleep characterized by different EEG patterns and different behaviors Slow-wave sleep (eg. unihemispheric sleep) Paradoxical, or REM sleep The function of sleep is unclear. Hypotheses ○ Restoration and recovery Adenosine (neuromodulator) — what makes you sleepy Caffeine — inhibits the binding of adenosine Norepinephrine and serotonin ○ Memory processing ○ Energy conservation Consciousness Figure 14.Title. EEG patterns during different types of sleep ▢ ▢ References Sherwood, L. (2012). Fundamentals of Human Physiology (4th ed.) CA, USA: Brooks/Cole Cengage Learning Sherwood. L., Klandorf, H. & Yancey, P. H. (2013). Animal Physiology From Genes to Organisms (2nd ed.). CA, USA: Brooks/Cole, Cengage Learning JA N A H Stage 4 is an even deeper sleep where the brain waves are further slow and sleepers are very difficult to wake. It's believed that tissue repair occurs during the stage of sleep and that hormones are also released to help with growth. Rapid eye movement (REM) sleep is called paradoxical sleep because it involves seemingly contradictory states of an active mind and a sleeping body. In a normal awake person, alpha rhythm is 8–13 Hz activity in the posterior head regions and beta at a frequency >13 Hz is seen in anterior areas. Theta (4–7 Hz) and delta (