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CHAPTER 28 Nervous System 28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands • The nervous system has three interconnected functions – Sensory input: receptors-structures specialized to detect certain stimuli – Integration: through the spinal cord & brain – Motor output: effectors-respond to a stimulus such as muscles or glands 28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands II Nervous System cerebrum cerebellum spinal cord • Central nervous system – brain & spinal chord • Peripheral nervous system – nerves from senses – nerves to muscles cervical nerves thoracic nerves lumbar nerves femoral nerve sciatic nerve tibial nerve 2003-2004 Three types of neurons correspond to the nervous system’s three main functions – Sensory neurons convey signals from sensory receptors into the CNS – Interneurons integrate data and relay signals – Motor neurons convey signals to effectors Types of neurons sensory neuron (from senses) interneuron (brain & spinal chord) 2003-2004 motor neuron (to muscle) 28.2 Neurons are the functional units of nervous systems • Neurons are cells specialized to transmit nervous impulses • They consist of – a cell body ~contains the nucleus – dendrites (highly branched fibers) stimulus toward cell body – an axon (long fiber) carries impulses away from cell body Myelin coating signal direction Axon coated with insulation made of myelin cells speeds signal signal hops from node to node (Nodes of Ranvier) 330 mph vs. 11 mph myelin coating Multiple Sclerosis 2003-2004 immune system (T cells) attacks myelin coating loss of signal Supporting cells protect, insulate, and reinforce neurons • The myelin sheath is the insulating material in vertebrates – It is composed of a chain of Schwann cells linked by nodes of Ranvier – It speeds up signal transmission – Multiple sclerosis (MS) involves the destruction of myelin sheaths by the immune system NERVE SIGNALS AND THEIR TRANSMISSION 28.3 A neuron maintains a membrane potential across its membrane • The resting potential of a neuron’s plasma membrane is caused by the cell membrane’s ability to maintain – Polarity – outside axon membrane + – Inside axon membrane - • Resting potential is generated and maintained with help from sodiumpotassium pumps – These pump K+ into the cell and Na+ out of the cell 28.4 A nerve signal begins as a change in the membrane potential • A stimulus alters the permeability of a portion of the plasma membrane – Ions pass through the plasma membrane, changing the membrane’s voltage – It causes a nerve signal to be generated • An action potential is a nerve signal – It is an electrical change in the plasma membrane voltage from the resting potential to a maximum level and back to the resting potential 28.5 The action potential propagates itself along the neuron • An action potential is an all-or-none event 28.6 Neurons communicate at synapses – It is a junction or relay point between two neurons or between a neuron and an effector cell • Synapses are either electrical or chemical – Action potentials pass between cells at electrical synapses – At chemical synapses, neurotransmitters cross the synaptic cleft to bind to receptors on the surface of the receiving cell 28.9 Connection: Many drugs act at chemical synapses • Drugs act at synapses and may increase or decrease the normal effect of neurotransmitters – – – – Caffeine Nicotine Alcohol Prescription and illegal drugs 28.12 The peripheral nervous system of vertebrates is a functional hierarchy Peripheral nervous system Motor division Sensory division Sensing external environment Sensing internal environment Autonomic nervous system (involuntary Sympathetic division Somatic nervous system (voluntary Parasympathetic division 28.13 Opposing actions of sympathetic and parasympathetic neurons regulate the internal environment – The parasympathetic division primes the body for activities that gain and conserve energy – The sympathetic division prepares the body for intense, energy-consuming activities 28.15 The structure of a living supercomputer: The human brain 28.15 The structure of a living supercomputer: The human brain II Primitive brain • The “lower brain” – medulla oblongata – pons – cerebellum • Functions – basic body functions • breathing, heart, digestion, swallowing, vomiting (medulla) – homeostasis – coordination of movement (cerebellum) 2003-2004 Higher brain • Cerebrum – 2 hemispheres – left = right side of body – right = left side of body • Corpus callosum – connection between 2 hemispheres 2003-2004 Division of Brain Function • Left hemisphere – “logic side” – language, math, logic operations, vision & hearing details – fine motor control • Right hemisphere – “creative side” – pattern recognition, spatial relationships, non-verbal ideas, emotions, multi-tasking 2003-2004 Cerebrum specialization • Regions specialized for different functions • Lobes parietal frontal – frontal • speech, control of emotions – temporal • smell, hearing – occipital • vision – parietal • speech, taste reading temporal2003-2004 occipital Limbic system Controls basic emotions (fear, anger), involved in emotional bonding, establishes emotional memory 2003-2004 Simplest Nerve Circuit Reflex, or automatic response rapid response automated signal only goes to spinal cord no higher level processing advantage essential actions don’t need to think or make decisions about blinking balance 2003-2004 pupil dilation startle cerebrum cerebellum spinal cord cervical nerves thoracic nerves lumbar nerves femoral nerve Any Questions?? sciatic nerve tibial nerve 2003-2004