2 EvolutionThe ability of cells to respond to the environment has evolved over billions of yearsPlants use signal-transduction pathways to recognize environmental signals and create cellular responses; they have impulses called action potentials that resemble the nervous system messages in animals (Chapter 39)Embryonic development of the vertebrate brain reflects the evolution from three anterior bulges of the neural tube (forebrain, midbrain and hindbrain)
3 Nervous systems range in complexity from simple nerve nets to highly centralized nervous systems having complex brains and central nerve cords. The nerve cord lies near the ventral body surface in invertebrates and near the dorsal surface in vertebrates.
5 Why is the Nervous System Necessary? The Nervous System is responsible for picking up stimulus and signals, processing them and creating a reaction (either voluntary or involuntary)The Central Nervous System (CNS) processes informationThe Peripheral Nervous System (PNS) communicates sensory and motor signals between the CNS and the rest of the body
6 The Nervous System Consists of Two parts A. Central Nervous System (CNS) B. Peripheral Nervous System (PNS) I. Sensory II. Motor a. Somatic System b. Autonomic System i. Sympathetic ii. Parasympathetic
7 In terms of function, Somatic NS voluntary muscles and reflexes vs Autonomic NS visceral/smooth and cardiac muscle Sympathetic NS increases energy expenditure prepares for action Parasympathetic NS decreases energy expenditure gains stored energy these have the opposite effects on the same organs --OR-- In terms of location, Peripheral NS sensory and motor neurons vs Central NS (CNS) interneurons: brain and spine covered with three membranes, the meninges inflammation of these is called meningitis brain has gray matter on outside and white in center spine has white matter on outside and gray in center
10 A. The Neuron cell body with a nucleus and other organelles cytoplasmic extensionsdendrites- can have hundreds; sensory; receive incoming messages from other cells and carry the electrical signal to the cell bodyaxons- only one, but can be several feet long in large mammals; transmits an impulse from the cell body outward to another cell
11 A. The Neuron Myelin Sheath- speeds the passage of an impulse Glial cells are essential for the normal functioning of neurons; there are many more glial cells than neuronsSchwann cells- glial cells that form the myelin sheathNodes of Ranvier-between myelin sheathsTerminal Branch-works with synapse to as the final point the impulse is in one neuron before going to the next
12 B. Types of NeuronsSensory neurons- receive an initial stimulus from a sense organ or from another neuronMotor neuron- stimulates effectors (muscles or glands)Interneuron or association neuron- within spinal chord and brain; receives sensory stimuli and transfers the info directly to a motor neuron or to the brain for processingExample of a sense organ- eyes or earsMotor neurons can stimulate muscles to contract
14 Resting PotentialMembrane potential---difference in electrical charge between the cytoplasm (negative ions) and extracellular fluid (positive ions)Measured in microelectrodesPotential should be between -50 mV and -100mVPolarized state (resting potential)--- neuron in an unstimulated state has a membrane potential of-70mVNerves can only fire if the stimulus is large enough to overcome the resting potentialNegative sign means that the inside of the cell is negative relative to the outside of the cell
15 Gated ChannelsThe sodium-potassium pump maintains the polarization by actively pumping ions that leak across the membraneGated-ion channels- in neurons; open and close in response to stimuli; help transmit electrical impulsesSodium ion-gated channels---when opened, sodium flows into the cytoplasm; decreases polarization (to about -60mV, usually); depolarizedPotassium ion-gated channel----when opened, potassium levels are increased in the cell and the membrane becomes hyperpolarized and therefore harder for the neuron to fireInside the cell Na+ has a lower concentration than K+
16 Action Potential Impulse Generated in axons action potentials relay different intensities of information by changing the frequency of the action potentiali.e. a strong stimulus sets up more action potentials than a weak oneWave of depolarization-reverses polarity of the membrane (Na+ in, K+ out)With this change, the message moves along the axonRefractory period-quickly (a few milliseconds) reverts back to correct potentialWhen a stimulus is strong enough to overcome the membrane potential, the permeability of the membrane changes. Sodium channels open and sodium floods into the cell, down the concentration gradient.During the refractory period, another stimulus can not be responded to which makes sure the impulse moves in one direction only
17 Synapse Electrical Chemical In crustaceans Impulses travel from neuron to neuron with no delayMuch less commonChemicalUses Ca2+Synaptic vesicles contain thousands of neurotransmitters (substance is released as an intercellular messenger)Acetylcholine is a common example (see page 1037)The cytoplasm at the terminal branch of the presynaptic neuron contains many vesicles, each containing thousands of molecules of neurotransmiter. Ca molecules rush into terminal branch and stimulates vesicles to fuse with the presynaptic membrane and release the neurotransmitter by exocytosis into the synaptic cleft. The neurotransmitter either inhibits or excites the postsynaptic cell. The enzyme esterase destroys the neurotransmitter
20 The Nervous System Consists of Two parts A. Central Nervous System (CNS) B. Peripheral Nervous System (PNS) I. Sensory II. Motor a. Somatic System b. Autonomic System i. Sympathetic ii. ParasympatheticSensory- conveys info from sensory receptors or nerve endings
21 Autonomic System Sympathetic Parasympathetic Fight or flight response Increases heart and respiratory rateLiver converts glycogen to glucoseBronchi of lungs dilate and increase gas exchangeAdrenalin raises blood glucose levelsOpposes the sympathetic systemCalms the bodyDecreases heart and respiratory rateEnhances digestion
26 The BrainBrainstem-contains the Medulla and pons, and the midbrain; control areas include movement of the eyes and mouth, relaying sensory messages, hunger, respirations, consciousness, cardiac function, body temperature, involuntary muscle movements, sneezing, coughing, vomiting, and swallowingPons-A deep part of the brain, located in the brainstem; contains many of the control areas for eye and face movementsMedulla- The lowest part of the brainstem; contains important control centers for the heart and lungs; extremely vital
27 The Brain con’tThalamus- main input center for sensory information; incoming info sorted in thalamusCerebellum- back of the head; coordinates voluntary muscle movements and maintains posture, balance, and equilibrium.Hypothalamus-posterior pituitary hormone and releasing hormones; regulates temperature, hunger, thirst and other basic survival mechanisms; circadian rhythms
28 CerebrumFrontal Lobe-The largest section of the brain located in the front of the head; involved in personality characteristics and movement.Parietal lobe-The middle part of the brain; helps to identify objects and understand spatial relationships; also involved in interpreting pain and touch in the body.Occipital lobe-back part of the brain; involved with vision.Temporal lobe-The sides of the brain; involved in memory, speech, and sense of smell.
29 Cerebrum Different regions are specialized for different functions Main functions of Cerebrum includeLanguage and Speech, Emotions (Limbic System), Memory and Learning, Human Consciousness etc.
30 InterdependenceThe nervous system often works with the endocrine and immune systems to regulate body functions and behaviorIn all systems many functions are started because of signals to either voluntary or involuntary systemsRespiratory, Muscular, Digestive
31 Main PointsNervous systems gather, process and respond to information from stimuliNetworks of neurons work together to form the nervous systemEvery cell has a membrane potential that must be overcome to transport a signalThe signal is passed as an impulse along axonsThe same neurotransmitter can produce different effects on different types of cellsThe nervous system is composed of the CNS and the PNSThe separate parts of the peripheral nervous system interact in maintaining homeostasisThe cerebrum is the most highly evolved structure in mammal’s brains
32 Diseases and Disorders There are many common diseases and disorders because the nervous system is such a complex system- there is much that can go wrongThe list of Neurological diseases and disorders include Parkinson’s Disease, Cerebral Palsy, Multiple Sclerosis, Alzheimer’s Disease, Stroke, Epilepsy/Seizures,
33 Multiple SclerosisA chronic disease of the nervous system that can affect young and middle-aged adults.The myelin sheaths surrounding nerves in the brain and spinal cord are damaged, which affects the function of the nerves involved. The underlying cause of the nerve damage remains unknown.Multiple Scerosis affects different parts of the brain and spinal cord, resulting in typically scattered symptoms.These can include:Unsteady walk and shaky movement of the limbsRapid involuntary movements of the eyesDefects in speech pronunciationInflammed optic nerve
34 Cerebral Palsy Non-progressive disorder results from damage to the brain before , during or directly after birthThe most common disability is a spastic paralysis. Sensation is often affected, leading to a lack of balance and intelligenceposture and speech are frequently impaired.Other associated features include epilepsy, visual impairment, squint, reduced hearing, and behavioral problems.
35 SciaticaOften refers to any pain in lower back, which is relatively commonCaused by compression of, or damage to, a nerve or nerve rootStiff pain felt down the back and outer side of the thigh, leg and footNumbness and weakness in the leg
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