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Biology Sylvia S. Mader Michael Windelspecht Chapter 37 Neurons and Nervous Systems Lecture Outline See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Evolution of the Nervous System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. eyespot auricle ventral nerve cord with ganglia cerebral ganglia nerve brain nerve net lateral nerve cords transverse nerves a. Hydra b. Planarian c. Earthworm 2 Evolution of the Nervous System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. cerebrum in forebrain hindbrain giant nerve fiber spinal cord brain eye brain thoracic ganglion d. Crab tentacle e. Squid f. Cat 3 Evolution of the Nervous System • Division of Nervous System: – The Central nervous system (CNS) • Includes the brain and spinal cord – The peripheral nervous system (PNS) • Consists of all nerves that lie outside the CNS – Somatic nervous system » Sensory and motor functions that control skeletal muscle – Autonomic nervous system » Controls smooth muscle, cardiac, muscle, and gland » Divided into sympathetic and parasympathetic divisions 4 Organization of the Human Nervous System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. brain cranial nerves cervical nerves thoracic nerves spinal cord radial nerve median nerve ulnar nerve lumbar nerves sacral nerves sciatic nerve tibial nerve common fibular nerve a. 5 37.2 Nervous Tissue • Neurons (nerve cells) – Cell body contains nucleus and organelles – Dendrites receive signals from sensory receptors or other neurons – Axon conducts nerve impulses to another neuron or to other cells • Covered by myelin sheath 6 Nervous Tissue • Types of Neurons • Motor (efferent) neurons – Accept nerve impulses from the CNS – Transmit them to muscles or glands(away) • Sensory (afferent) neurons – Accept impulses from sensory receptors – Transmit them to the CNS • Interneurons – Convey nerve impulses between various parts of the CNS 7 Neuron Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. cell body dendrite direction of conduction myelin sheath axon terminal node of Ranvier axon a. Motor neuron (multipolar) muscle 8 a: © M.B. Bunge/Biological Photo Service Neuron Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. axon cell body direction of conduction sensory receptor axon b. Sensory neuron (unipolar) myelin sheath skin 9 Neuron Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. axon cell body dendrite c. Interneuron (multipolar) c: © Manfred Kage/Peter Arnold, Inc. 10 Nervous Tissue • Transmission of Nerve Impulses – Resting Potential • The membrane potential (voltage) when the axon is not conducting an impulse – The inside of a neuron is more negative than the outside, around -70 mV – Due in part to the activity of the sodiumpotassium pump 11 Nervous Tissue • An action potential is a rapid change in polarity across a portion of an axonal membrane • An action potential is generated only after a stimulus larger than the threshold (-55mV) – Gated channel proteins • One channel protein suddenly allows sodium to enter the cell • Another channel protein allows potassium to leave the cell 12 Resting and Action Potential of the Axonal Membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. +60 +40 Na+ moves to inside axon K+ moves to outside axon action potential +20 Voltage (mV) 0 –20 –40 threshold –60 resting potential 0 1 2 3 4 5 6 Time (milliseconds) d. An action potential can be visualized if voltage changes are graphed over time. 13 Nervous Tissue • Propagation of Action Potentials – In nonmyelinated axons, the action potential travels down an axon one small section at a time – In myelinated fibers, an action potential at one node causes an action potential at the next node • Saltatory (jumping) Conduction – Conduction of a nerve impulse is an all-or-nothing event • Intensity of signal is determined by how many impulses are generated within a given time span 15 Nervous Tissue • Transmission Across a Synapse – A synapse is a region where neurons nearly touch – Small gap between neurons is the synaptic cleft – Transmission across a synapse is carried out by neurotransmitters • Sudden rise in calcium in the axon terminal of one neuron • Calcium stimulates synaptic vesicles to merge with the presynaptic membrane • Neurotransmitter molecules are released into the synaptic cleft 16 Nervous Tissue • Synaptic Integration – A single neuron is on the receiving end of • Many excitatory signals, and • Many inhibitory signals – Integration • The summing of excitatory and inhibitory signals 17 End of Nervous system Notes PT. 1 37.3 The Central Nervous System • The Central Nervous System – Consists of the brain and spinal cord – Three specific functions: • Receives sensory input • Performs integration • Generates motor output 19 The Central Nervous System • The Central Nervous System – Consists of the brain and spinal cord – Spinal cord and brain are wrapped in three protective membranes called meninges • Spaces between meninges are filled with cerebrospinal fluid • Fluid is continuous with that of central canal of spinal cord and the ventricles of the brain 20 The Central Nervous System • The Spinal Cord – Two main functions • Center for many reflex actions • Means of communication between the brain and spinal nerves – Composed of grey matter and white matter • Cell bodies and short unmyelinated fibers give the gray mater its color • Myelinated long fibers of interneurons running in tracts give white mater its color 21 The Central Nervous System • The Brain – The cerebrum is the largest portion of the brain in humans • Communicates with, and coordinates the activities of, the other parts of the brain • Longitudinal fissure divides the cerebrum into left and right cerebral hemispheres 22 The Human Brain Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cerebrum (telencephalon) opening to lateral ventricle third ventricle skull meninges corpus callosum pituitary gland Diencephalon thalamus (surrounds the third ventricle) hypothalamus pineal gland fourth ventricle Brain stem midbrain Cerebellum pons medulla oblongata a. Parts of brain spinal cord b. Cerebral hemispheres 23 The Lobes of a Cerebral Hemisphere Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. central sulcus Frontal lobe primary somatosensory area primary motor area premotor area motor speech (Broca’s) area prefrontal area Parietal lobe leg trunk arm hand somatosensory association area primary taste area general interpretation area face tongue Occipital lobe primary visual area lateral sulcus Temporal lobe visual association area auditory association area primary auditory area sensory speech (Wernicke’s) area 24 The Central Nervous System • Cerebral Cortex • A thin but highly convoluted outer layer of gray matter • Covers the cerebral hemispheres • Contains motor areas and sensory areas as well as association areas – Primary motor area is in the frontal lobe, just ventral to the central sulcus – Primary somatosensory area is in the parietal lobe, just dorsal to the central sulcus 25 The Central Nervous System • Basal nuclei – Integrate motor commands – Ensures that the proper muscle groups are either activated or inhibited 26 The Central Nervous System • Other Parts of the Brain • Diencephalon • A region encircling the third ventricle • Includes three structures – Hypothalamus • Forms the floor of the third ventricle • Integrating center that maintains homeostasis • Controls the pituitary gland 27 The Central Nervous System • Other Parts of the Brain • Diencephalon (continued) • Thalamus • Consists of two masses of gray matter located in the sides and roof of the third ventricle • Receives all sensory input except smell • Integrates sensory information and sends it to the cerebrum • Pineal gland • Secretes melatonin 28 The Central Nervous System • Other Parts of the Brain • Cerebellum • Separated from the brain stem by the fourth ventricle • Largest portion of the brainstem • Receives sensory input from the eyes, ears, joints, and muscles • Sends motor impulses out the brain stem to the skeletal muscles 29 The Central Nervous System • Other Parts of the Brain • Brain Stem • Contains the midbrain, pons, and the medulla oblongata • Midbrain • Acts as a relay station for tracts passing between the cerebrum and the spinal cord or cerebellum • Pons • Contains axons that form a bridge between the cerebellum and the rest of the central nervous system • Medulla Oblongata • Contains reflex centers for vomiting, coughing, sneezing, hiccupping, and swallowing 30 The Central Nervous System • The Reticular Activating System (RAS) – A complex network of: • Nuclei (masses of gray matter) • Nerve fibers that extend the length of the brain stem – The reticular formation is a major component of the RAS – The RAS arouses the cerebrum via the thalamus and causes a person to be alert 31 The Reticular Activating System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. radiations to cerebral cortex thalamus reticular formation ascending sensory tracts (touch, pain, temperature) 32 The Central Nervous System • Limbic System – Complex network of tracts and “nuclei” – Incorporates • Medial portions of the cerebral lobes, • The basal nuclei, and • The diencephalon – Integrates higher mental functions and primitive emotions – Important structures in the limbic system are • The hippocampus and the amygdala 33 The Limbic System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. corpus callosum thalamus hypothalamus hippocampus olfactory bulb amygdala olfactory tract 34 The Central Nervous System • Learning and Memory – Memory • The ability to hold a thought in mind or recall events from the past – Learning • Takes place when we retain and use past memories – Short term memory is associated with the prefrontal area of the frontal lobe – Long term memory is associated with the hippocampus 35 37.4 The Peripheral Nervous System • Somatic system – Includes cranial nerves and spinal nerves • Gather information from sensors and conduct decisions to effectors • Controls the skeletal muscles – Voluntary • Autonomic system – – – – Controls the smooth muscles, cardiac muscles, and glands Innervates all internal organs Usually involuntary Divided into two divisions • Sympathetic division • Parasympathetic division – Utilizes two neurons and one ganglion for each impulse 36 Cranial and Spinal Nerves Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. spinal cord gray matter vertebra white matter frontal lobe olfactory bulb dorsal root olfactory tract dorsal root ganglion optic nerve optic chiasma spinal nerve ventral root vertebra b. temporal lobe central canal cerebellum gray matter medulla white matter a. c. c: © Karl E. Deckart/Phototake 37 The Peripheral Nervous System • Reflex Arc • Sensory receptors generate a nerve impulse that moves along sensory axons through a dorsal root ganglion toward the spinal cord • Sensory neurons pass signals on to many interneurons in the gray matter of the spinal cord • Nerve pulses travel along motor axons to an effector, which brings about a response to the stimulus 38 A Reflex Arc Showing the Path of a Spinal Reflex Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pin dorsal root ganglion sensory receptor (in skin) axon of sensory neuron central canal white matter dendrites Dorsal gray matter dorsal horn cell body of sensory neuron interneuron dendrites axon of motor neuron cell body of motor neuron effector (muscle) ventral root ventral horn Ventral 39 The Peripheral Nervous System • Sympathetic division – Especially important during fight or flight responses – Accelerates heartbeat and dilates bronchi • Parasympathetic division – Promotes all internal responses associated with a relaxed state – Promotes digestion and retards heartbeat 40 Autonomic System Structure and Function Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. inhibits tears stimulates tears constricts pupils dilates pupils ganglion inhibits salivation Sympathetic Division Parasympathetic Division stimulates salivation cranial nerves slows heart speeds heart dilates air passages cervical nerves constricts bronchioles stimulates liver to release glucose stimulates gallbladder to release bile stimulates adrenal secretion thoracic nerves vagus nerve increases activity of stomach and pancreas inhibits activity of kidneys, stomach, and pancreas increases intestinal activity decreases intestinal activity lumbar nerves ganglion inhibits urination stimulates urination causes orgasmic contractions sympathetic ganglia causes erection of genitals sacral nerves Acetylcholine is neurotransmitter. Norepinephrine is neurotransmitter. 41 Comparison of Somatic Motor and Autonomic Motor Pathways 42 Drugs of Abuse • Drug abuse - person takes a drug at a dose level that increases the potential for a harmful effect. • Addiction - when more of the drug is needed to get the same effect • Withdrawal - when the user stops taking the drug • Alcohol, drugs, and tobacco can all adversely affect the developing embryo, fetus, or newborn. 43 Drug Use: Brain Activity Before and After the Use of Cocaine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. brain activity Before cocaine use, brain is less active. After cocaine use, brain is more active. © Science VU/Visuals Unlimited 44 End Nervous system Notes PT. 2 Evolution of the Nervous System • Vertebrate Nervous-System Organization – Central nervous system • Vertebrate brain is organized into three areas – Hindbrain – Midbrain – Forebrain 46 37.1 Evolution of the Nervous System • Invertebrate Nervous System Organization – Hydras • Nerve net composed of neurons in contact with one another • Also in contact with contractile cells in the body wall – Planarians • Ladderlike nervous system • Cephalization - a concentration of ganglia and sensory receptors in the head – Annelids, Arthropods and Molluscs • Complex animals • True nervous systems 47 Organization of the Human Nervous System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Central Nervous System brain and spinal cord Peripheral Nervous System somatic sensory fibers (skin, special senses) visceral sensory fibers (internal organs) somatic motor fibers (to skeletal muscles) autonomic motor fibers (to cardiac and smooth muscle, glands) sympathetic division parasympathetic division 48 b. Resting and Action Potential of the Axonal Membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. reference electrode outside axon recording electrode inside axon + + + + + + + + + + – – – – – – – – – – – – – – – – – – – + + + + + + + + + axonal membrane inside axon K+ Na+ gated K+ channel gated Na+ channel outside axon a. Resting potential: more Na+ outside the axon and more K+ inside the axon causes polarization. 49 Resting and Action Potential of the Axonal Membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. – – + + + + + + + + + + – – – – – – – – direction of impulse + + – – – – – – – – – – + + + + + + + + open Na+ channel b. Action potential begins: depolarization occurs when Na+ gates open and Na+ moves to inside the axon. 50 Resting and Action Potential of the Axonal Membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. + + – – – – – – – – – – + + + + + + + + direction of impulse – – + + + + + + + + + + – – – – – – – – open K+ channel c. Action potential ends: repolarization occurs when K+ gates open and K+ moves to outside the axon. 51 Synapse Structure and Function Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. path of action potential 1. After an action potential arrives at an axon terminal, Ca2+ enters, and synaptic vesicles fuse with the presynaptic membrane. Ca2+ axon terminal synaptic vesicles enclose neurotransmitter cell body of postsynaptic neuron synaptic cleft 2. Neurotransmitter molecules are released and bind to receptors on the postsynaptic membrane. presynaptic membrane neurotransmitter neurotransmitter receptor Na+ postsynaptic neuron postsynaptic membrane 3. When an excitatory neurotransmitter binds to a receptor, Na+ diffuses into the postsynaptic neuron, and an action potential begins. 52