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Nervous System (Chapters 9 & 10) Divisions of the Nervous System Brain Cranial nerves • Central Nervous System (CNS) • Brain • Spinal cord • Peripheral Nervous System (PNS) • Cranial nerves (12 pairs) • Spinal nerves (31 pairs) *Each nerve can be either afferent (sensory), efferent (motor), or both. Spinal cord Spinal nerves Divisions of PNS • Sensory Division: • Picks up sensory information & delivers it to CNS • Motor Division: • Carries information to muscles & glands • Divisions of the Motor Division: • Somatic – voluntary; carries information to skeletal muscle • Autonomic – involuntary; carries information to smooth muscle, cardiac muscle, glands • Sympathetic – speeds up reaction • Parasympathetic – slows Central Nervous System (brain and spinal cord) Brain Peripheral Nervous System (cranial and spinal nerves) Cranial nerves Sensory division Spinal cord Sensory receptors Spinal nerves Motor division Somatic Nervous System Skeletal muscle Autonomic Nervous System Smooth muscle Cardiac muscle Glands Functions of Nervous System • Sensory Function (receiving information) • Info gathered by sensory receptors • Info carried to the CNS • Integrative Function (deciding what to do about information) • Sensory info used to create: • Sensations, memory, thoughts, decisions • Motor Function (acting on information) • Decisions acted upon • Impulses carried to effectors Cell Types (Review) • Neurons • Neuroglial cells (aka neuroglia, glia, glial cells) Dendrites Cell body Nuclei of neuroglia Axon Structure of a Neuron Cell Descriptions Chromatophilic substance (Nissl bodies) Dendrites Cell body • Neurons vary in shape & size • All neurons have a cell body, an axon, and dendrites • Axon – convey info away from soma • Dendrites – convey info to soma • They differ in length and size of their axons & dendrites Neurofibrils Impulse Axon Synaptic knob of axon terminal Nodes of Ranvier Myelin (cut) Axon Portion of a collateral Myelination of Axons Dendrite Unmyelinated region of axon Myelinated region of axon Node of Ranvier Axon • White Matter • Contains myelinated axons • Considered fiber tracts • Gray Matter Neuron Neuron cell body nucleus • Contains unmyelinated structures • Cell bodies, dendrites Enveloping Schwann cell Schwann cell nucleus Longitudinal groove Unmyelinated axon Classification of Neurons • Neurons vary in function (can be sensory, motor, integrative neurons) • They vary in size, shape, number of axons & dendrites • Classified into three major groups: • Unipolar neurons • Bipolar neurons • Multipolar neurons Dendrites Structural Differences between Neurons: • Multipolar neurons • 99% of neurons • Many processes • Most neurons of CNS Peripheral process • Bipolar neurons • Two processes • Eyes, ears, nose Axon Direction of impulse Central process • Unipolar neurons • One process • Ganglia of PNS • Sensory Axon (a) Multipolar Axon (b) Bipolar (c) Unipolar Functional Differences between Neurons: • Sensory Neurons • Afferent (approach) • Carry impulse to CNS • Most are unipolar, some bipolar Central nervous system Cell body • Motor Neurons • Efferent (exit) • Carry impulses away from CNS to effectors • Multipolar Dendrites Sensory receptor Cell body Axon (central process) • Interneurons • Link neurons in CNS (aka association neurons) • Multipolar Peripheral nervous system Axon (peripheral process) Sensory (afferent) neuron Interneurons Motor (efferent) neuron Axon Effector (muscle or gland) Axon Axon terminal Types of Neuroglial Cells in PNS • Schwann cells • Produce myelin found on peripheral myelinated neurons • Speed up neurotransmission • Satellite cells • Support clusters of neuron cell bodies (ganglia) Types of Neuroglial Cells in CNS 1. Microglia • Phagocytic cells of the CNS 2. Astrocytes • • • • Scar tissue Get rid of excess ions Induce synapse formation Connect neurons to blood vessels 3. Oligodendrocytes • Myelinating cells of the CNS 4. Ependymal cells • • • • Ciliated Line central canal of spinal cord Line ventricles of brain Keep CSF moving Neuroglial Cells Fluid-filled cavity of the brain or spinal cord Neuron Ependymal cell Oligodendrocyte Astrocyte Microglial cell Axon Myelin sheath (cut) Capillary https://www.youtube.com/watch?v=qPix_X-9t7E Node of Ranvier Regeneration of a Nerve Axon Skeletal muscle fiber Motor neuron cell body Changes over time Site of injury Schwann cells Axon (a) Distal portion of axon degenerates (b) Proximal end of injured axon regenerates into tube of sheath cells (c) Schwann cells degenerate (d) Schwann cells proliferate (e) Former connection reestablished The Synapse • Nerve impulses pass from neuron to neuron at synapses • They move from a presynaptic neuron to a postsynaptic neuron Synaptic cleft Dendrites Axon of presynaptic neuron Axon of postsynaptic neuron Axon of presynaptic neuron Cell body of postsynaptic neuron Direction of nerve impulse Synaptic Transmission • Neurotransmitters are released when impulse reaches synaptic knob Axon Ca+2 Synaptic knob Synaptic vesicles Presynaptic neuron Ca+2 Cell body or dendrite of postsynaptic neuron Mitochondrion Ca+2 Synaptic vesicle Vesicle releasing neurotransmitter Axon membrane Neurotransmitter Synaptic cleft Polarized membrane https://www.youtube.com/watch?v=90cj4NX87Yk Depolarized membrane Cell Membrane Potential • Cell membrane is electrically charged or polarized • Inside of membrane is negative, with respect to positively-charged outside • Due to unequal distribution of ions inside/outside • Thanks to… Distribution of Ions • K+ ions = major intracellular cation • Na+ ions = major extracellular cation • Distribution created by Na+ /K+ pump • Actively transports Na+ out of cell, K+ into the cell Resting Potential • Resting Membrane Potential (RMP) • • • • 70 mV difference from inside to outside of cell Polarized membrane Inside of cell = negative relative to outside of cell RMP = -70 mV • Due to distribution of ions inside vs. outside from Na/K pump • Na/K pump resets/restores this membrane potential Local Potential Changes • Changes caused by various stimuli: • Temperature changes, light, pressure • Environmental changes affect membrane potential by opening a gated ion channel • Channels can be: • Chemically gated • Voltage gated • Mechanically gated Gatelike mechanism (a) Channel closed (b) Channel open Local Potential Changes • Hyperpolarization: membrane potential becomes more negative • Depolarization: membrane potential becomes less negative • Graded to intensity of stimulation reaching the threshold potential • Reaching threshold potential results in a nerve impulse, starting an action potential Na+ Na+ –62 mV Chemically-gated Neurotransmitter Na+ channel (a) Presynaptic neuron Voltage-gated Na+ channel Trigger zone Na+ Na+ Na+ Na+ –55 mV (b) Na+ Action Potentials Na+ • At rest, the membrane potential is polarized (RMP = -70 mV) • Threshold stimulus reached (-55) • Na+ channels open and membrane depolarizes (toward 0) • K+ leaves cytoplasm and membrane repolarizes (+30) • Brief period of hyperpolarization (-90) Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ Na+ Na+ Na+ Na+ –0 –70 Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ (a) K+ Na+ Na+ Na+ K+ K+ Threshold stimulus K+ K+ Na+ Na+ K+ Na+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ Na+ Na+ –0 Na+ channels open K+ channels closed –70 Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Region of depolarization (b) K+ K+ K+ Na+ Na+ K+ Na+ Na+ Na+ K+ K+ K+ K+ K+ K+ Na+ Na+ Na+ K+ K+ K+ K+ K+ K+ K+ K+ Na+ Na+ Region of repolarization (c) Na+ Na+ Na+ Na+ Na+ –0 –70 Na+ K+ channels open Na+ channels closed Action Potentials Membrane potential (millivolts) +40 Action potential +20 0 –20 –40 –60 Resting potential reestablished Resting potential –80 0 Hyperpolarization 1 2 3 4 5 Milliseconds 6 7 8 Region of action potential Action Potentials + + + + + + + + + + + – – – – – – – – – + + – – – – – – – – – + + + + + + + + + + + + + + + – – – – – – – – – – – – + + + (a) + – + + – – + + Direction of nerve impulse – – – + + + + + + + + + + + + + + + + + (b) https://www.youtube.com/watch?v=OZG8M_ldA1M – – – – – – – + + – – – – – – – – – + + – – + (c) + + + + + + + + All-or-None Response • If a neuron responds at all, it responds completely • A nerve impulse is conducted whenever a stimulus of threshold intensity or above is applied to an axon • All impulses carried on an axon are the same strength Refractory Period • Absolute Refractory Period • Time when threshold stimulus does not start another action potential • Relative Refractory Period • Time when stronger threshold stimulus can start another action potential Synaptic Transmission • Where released neurotransmitters cross the synaptic cleft and reacts with receptors in the postsynaptic neuron membrane • Effects of neurotransmitters vary • Some may open ion channels, others may close them, making it more or less likely for an action potential to occur https://www.youtube.com/watch?v=VitFvNvRIIY Synaptic Potential • EPSP • • • • Excitatory postsynaptic potential Graded Depolarizes membrane of postsynaptic neuron Action potential of postsynaptic neuron becomes more likely • IPSP • • • • Inhibitory postsynaptic potential Graded Hyperpolarizes membrane of postsynaptic neuron Action potential of postsynaptic neuron becomes less likely Summation of EPSPs and IPSPs • EPSPs and IPSPs are added together in a process called summation • More EPSPs lead to greater probability of an action potential • More IPSPs lead to lower probability of an action potential Neuron cell body Nucleus Presynaptic knob Presynaptic axon Impulse Processing • Different ways the nervous system processes nerve impulses and acts upon them: • Neuronal pools of interneurons • Convergence • Divergence • Neuronal pools • Groups of interneurons that make synaptic connections with each other • Interneurons work together to perform a common function (can be excitatory or inhibitory) • Each pool receives input from other neurons • Each pool generated output to other neurons Impulse Processing • Convergence • Neuron receives input from several neurons • Incoming impulses represent information from different types of sensory receptors • Allows nervous system to collect, process, and respond to information • Makes it possible for a neuron to sum impulses from different sources 1 3 2 Impulse Processing • Divergence • One neuron sends impulses to several neurons via its branched axon • Can amplify an impulse • Impulse from a single neuron in CNS may be amplified to activate enough motor units for muscle contraction or glandular secretion 4 6 5 Central Nervous System (CNS) • Consists of brain & spinal cord • Brainstem connects the brain to the spinal cord • Communication to the PNS is by way of the spinal cord Meninges • Membranes of the CNS; protection • Three layers: • Dura mater “tough mother” • Venous sinuses • Arachnoid mater “spider mother” • Space contains cerebrospinal fluid (CSF) • Pia mater “little mother” • Encapsulates blood vessels Skin Scalp Subcutaneous tissue Cranium Bone of skull Cerebrum Dural sinus (superior sagittal sinus) Tentorium cerebelli Arachnoid granulation Dura mater Cerebellum Vertebra Arachnoid mater Pia mater Spinal cord Subarachnoid space Falx cerebri Meninges (a) Meninges Gray matter White matter (b) Cerebrum Spinal cord Ventral root Dorsal root Spinal nerve Dorsal root ganglion Subarachnoid space Pia mater Arachnoid mater Epidural space Dura mater Dorsal root Dorsal branch (dorsal ramus) Spinal nerve Ventral branch (ventral ramus) Dorsal root ganglion Spinal cord Ventral root Epidural space Thoracic vertebra (a) (b) Body of vertebra Ventricles Lateral ventricle Interventricular foramen Third ventricle • They are interconnected cavities within cerebral hemispheres and brain stem • Continuous with the central canal of the spinal cord • Filled with CSF • Four ventricles: • 2 lateral ventricles (first and second) • Third, fourth ventricles Cerebral aqueduct (a) Fourth ventricle To central canal of spinal cord Interventricular foramen Lateral ventricle Third ventricle Cerebral aqueduct • Other nearby components: interventricular foramen & cerebral aqueduct Fourth ventricle (b) To central canal of spinal cord CSF Arachnoid granulations Blood-filled dural sinus Choroid plexuses of third ventricle • Secreted by choroid plexus Third ventricle Cerebral aqueduct (ependymal cells) Fourth ventricle • Circulates in ventricles, central canal of spinal cord, and subarachnoid space • Completely surrounds brain & spinal cord • Excess or wasted CSF is absorbed by arachnoid villi • It is a clear fluid similar to blood plasma • Provides nutrients, protection, and a stable concentration of ions in the CNS Pia mater Subarachnoid space Arachnoid mater Dura mater Choroid plexus of fourth ventricle Central canal of spinal cord Pia mater Subarachnoid space Filum terminale Arachnoid mater Dura mater Spinal Cord Brainstem Foramen magnum • Slender column of nervous tissue, continuous with brain and brainstem • Extends downward through vertebral canal • Begins at formamen magnum in skull, ends at L1/L2 interspace (lumbar vertebrae) • Conduit for nerve impulses to/from brain and brainstem • Center for spinal reflexes Cervical enlargement Cervical enlargement Spinal cord Vertebral canal Lumbar enlargement Conus medullaris Lumbar enlargement Conus medullaris Cauda equina Filum terminale (a) (b) Structure of Spinal Cord Posterior horn Posterior funiculus Posterior median sulcus White matter Gray matter Gray commissure Lateral funiculus Dorsal root of spinal nerve Central canal Anterior funiculus Dorsal root ganglion Ventral root of spinal nerve Anterior horn Anterior median fissure Portion of spinal nerve Tracts of the Spinal Cord • Ascending tracts (dorsal) conduct sensory impulses to the brain • Descending tracts (ventral) conduct motor impulses from the brain to motor neurons reaching muscles & glands Reflex Arcs • Automatic, subconscious responses to stimuli • Simple reflex arc (sensory – motor) • Most common reflex arc (sensory – association – motor) Sensory or afferent neuron Receptor Central Nervous System Motor or efferent neuron Effector (muscle or gland) Interneuron Spinal cord Dorsal 1 Receptor 3 2 Sensory neuron Cell body of sensory neuron White matter Gray matter 4 Ventral Motor neuron 5 Effector (muscle or gland) Central canal Reflex Behavior • Example: Knee-jerk reflex; a simple monosynaptic reflex • Helps maintain an upright posture Axon of sensory neuron Cell body of sensory neuron Direction of impulse Spinal cord Cell body of motor neuron Axon of motor neuron Effector (quadriceps femoris muscle group) Receptor associated with dendrites of sensory neuron Patella Patellar ligament Reflex Behavior • Example: Withdrawal reflex • Prevents or limits tissue damage Direction of impulse Dendrite of sensory neuron Pain receptor in skin Tack Cell body of sensory neuron Axon of sensory neuron Interneuron Axon of Effector (flexor motor neuron muscle contracts and withdraws part being stimulated) Spinal cord Cell body of motor neuron Reflex Arc • Example: crossed extensor reflex • Crossing of sensory impulses +– == Stimulation Inhibition within the reflex center to produce an opposite effect Sensory neuron Interneuron – + – Extensor relaxes + Extensor contracts Flexor relaxes Motor neurons Flexor contracts Motor neurons The Brain • Interprets sensations • Determines perception • Stores memory • Reasoning • Makes decisions • Coordinates muscular movements • Regulates visceral activities • Determines personality • Major parts: • Cerebrum • • • • • Frontal lobes Parietal lobes Occipital lobes Temporal lobes Insula • Diencephalon • Cerebellum • Brainstem • Midbrain • Pons • Medulla oblongata Gyrus Skull Meninges Cerebrum Diencephalon Midbrain Sulcus Corpus callosum Fornix Brainstem Pons Medulla oblongata Cerebellum Spinal cord (a) Fornix Cerebrum Corpus callosum Diencephalon Midbrain Pons Transverse fissure Cerebellum Medulla oblongata Spinal cord Structure of the Cerebrum Central sulcus Parietal lobe Gyrus • Corpus callosum • Connects cerebral hemispheres • Gyri • Bumps or convolutions Sulcus Frontal lobe Lateral sulcus Occipital lobe Temporal lobe Transverse fissure (a) Cerebellar hemisphere Central sulcus Parietal lobe • Sulci • Grooves in gray matter • Fissures Central sulcus Longitudinal fissure Parietal lobe Occipital lobe • Longitudinal: separates the cerebral (b) hemispheres • Transverse: separates cerebrum from cerebellum Occipital lobe Frontal lobe Insula Retracted temporal lobe (c) Split Brain Research • Video 1 – corpus callosum severed http://www.youtube.com/watch?v=lfGwsAdS9Dc&feature=related • Video 2 – corpus callosum missing http://www.youtube.com/watch?v=VHgClWAPbBY&feature=related Lobes of the Cerebrum • Five lobes bilaterally: • Frontal, parietal, temporal, occipital, and insula • Insular cortex functions in awareness & judging intensity of pain, among other things Central sulcus Parietal lobe Occipital lobe Frontal lobe Insula Retracted temporal lobe Cerebrum Functions • Interprets impulses • Initiates voluntary movements • Stores information as memory • Retrieves stored information • Reasoning • Seat of intelligence and personality Cerebral Cortex • Thin layer of gray Concentration, planning, matter that problem solving constitutes the Frontal eye field outermost portion of Auditory area Front lobe the cerebrum Motor speech area • Contains 75% of all (Broca’s area) Lateral sulcus neurons in the Interpretation of auditory patterns nervous system Motor areas involved with the control of voluntary muscles Temporal lobe Central sulcus Sensory areas involved with cutaneous and other senses Parietal lobe Sensory speech area ( Wernicke’s area) Occipital lobe Combining visual images, visual recognition of objects Visual area Cerebellum Brainstem Sensory Areas (post-central sulcus) • Cutaneous sensory area • Parietal lobe; interprets sensations on skin • Visual area • Occipital lobe; interprets vision • Auditory area • Temporal lobe; interprets hearing • Sensory area for taste • Near base of central sulcus • Sensory area for smell • Arises from centers deep within the cerebrum Motor & Sensory Areas Arm Forearm Trunk Pelvis Trunk Pelvis Neck Forearm Arm Thigh Thigh Thumb, fingers, and hand Leg Foot and toes Facial expression Hand, fingers, and thumb Upper face Leg Foot and toes Genitals Lips Salivation Vocalization Mastication Teeth and gums Swallowing Tongue and pharynx Longitudinal fissure (a) Motor area Longitudinal fissure (b) Sensory area Frontal lobe Motor area Sensory area Central sulcus Parietal lobe Association Areas • • • • • • • Regions that are not primary motor or primary sensory areas Widespread throughout cerebral cortex Analyze & interpret sensory experiences Provide memory, reasoning, verbalization, judgment, emotions Frontal – concentration/planning/complex problem solving Parietal – understanding speech/choosing words to express thought Temporal – interpret complex sensory experiences/store memories of visual scenes, music, and complex patterns • Occipital – analyze and combine visual images with other sensory experiences Hemisphere Dominance • Left dominant in most individuals • Dominant hemisphere controls: • Speech, writing, reading • Verbal skills, analytical skills, computational skills • Non-dominant hemisphere controls: • Nonverbal tasks, motor tasks • Understanding and interpreting musical and visual patterns • Provides emotional and intuitive thought processes Memory • Short term • Working memory; closed neuronal circuit • Circuit is stimulated over and over • When impulse flow ceases, memory does also unless it enters long-term memory via memory consolidation • Limited information storage • Long term • Changes structure or function of neurons • Enhances synaptic transmission Diencephalon • Between cerebral hemispheres and above the brainstem • Surrounds the third ventricle • Contains: Superior Corpora quadrigemina colliculus Optic nerve • • • • • • • • • Thalamus Epithalamus Hypothalamus Optic tracts Optic chiasm Infundibulum Posterior pituitary Mammillary bodies Pineal gland Optic chiasma Inferior colliculus Pituitary gland Mammillary body Thalamus Optic tract Third ventricle Pons Cerebral peduncles Pineal gland Fourth ventricle Pyramidal tract Olive Cerebellar peduncles Medulla oblongata Spinal cord (a) (b) Diencephalon • Thalamus • Gateway for sensory impulses heading to cerebral cortex • Receives all sensory impulses except smell • Channels impulses to appropriate part of cerebral cortex for interpretation • Epithalamus • Functions to connect the limbic system to other parts of the brain • Hypothalamus • Maintains homeostasis by regulating visceral activities • Links nervous and endocrine systems • Limbic System • Consists of parts of the frontal & temporal lobes, hypothalamus, thalamus, basal nuclei, other deep nuclei • Functions to control emotions, produce feelings, and interpret sensory impulses Hypothalamus Diencephalon Brainstem Thalamus Corpus callosum • Midbrain • Pons • Medulla oblongata Corpora quadrigemina Midbrain Pons Cerebral aqueduct Reticular formation Medulla oblongata Spinal cord Pons & Medulla Oblongata • Pons • Rounded bulge on underside of brainstem • Helps regulate breathing • Relays nerve impulses to/from medulla oblongata and cerebellum • Medulla oblongata • Continuation of spinal cord • Cardiac, vasomotor, respiratory control centers • Non-vital reflexes (coughing, sneezing, swallowing, vomiting) Longitudinal fissure Cerebellum Thalamus • Inferior to occipital lobes Superior peduncle • Posterior to pons & medulla Pons Middle peduncle Inferior peduncle • Two hemispheres Medulla oblongata (like cerebrum) • Integrates sensory information concerning position of body parts • Coordinates skeletal muscle activity • Maintains posture Corpus callosum Cerebellum Lifespan Changes • • • • • • • • • • Brain cells begin to die before birth Over average lifetime, brain shrinks 10% Most cell death occurs in temporal lobes By age 90, frontal cortex has lost half its neurons Number of dendritic branches decreases Decreased levels of neurotransmitters Fading memory Slowed responses and reflexes Increased risk of falling Changes in sleep patterns that result in fewer sleeping hours