- Advantages of multicellularity o Differentiation/specialization of cellso Disadvantages : cells cannot carry out all processes necessary for life by themselves and must rely on other parts of the body for support (nutrients, gases, signals)—various parts of body must be coordinated- Tissue : aggregate of cells with similar function and structure1. Cells are often organized into epithelial layerso Epithelium (plural epithelia)-layer of cells connected by lateral edges In many epithelia, cells are polarized o Cuboidal (secretion in kidneys/glands), simple columnar (absorption in intestines), stratified squamous (protection in skin), simple squamous (exchange in blood vessels and lung)o Simple = one layer, stratified = more than one layero Basal lamina : layer of EC proteins that separates layers of cellso Basal surface of epithelia is next to basal lamina, apical surface is the exposed sideo Intestinal epithelia : single layer of columnar epithelial cells (protection, regulation/exchange of chemicals, secretion/absorption)2. Connective tissues : distributed throughout the bodyo Cells make an ECMo Loose connective tissue : meshwork of protein fiberso Fibrous : tendons attach muscle to bone—consists of small fibroblast cells embedded in a lot of ECMo Bone : consists of small osteocyte cells embedded in a rigid matrix of EC protein and inorganic salts – strong but not brittleo Cartilage : pads of ECM (between bones = padding and lubrication)o Adipose : store fat for E for later use (efficient fuel, pads, insulates)o Blood : liquid ECM functionally connects all parts of the body cells (rbc, wbc, platelets) & aqueous solution (plasma)3. Muscle tissue: made from fiber cells that are specialized to exert forceo Skeletal : long parallel muscle fibers--multiple nuclei, striated, unbranched, sarcomeres form fibers—every nuclei stays active Exert force that moves body partso Smooth : mononucleate, unstriated--found in walls of hollow organs (urinary tract, digestive tract, blood vessels)o Cardiac : bundles of muscle fibers: mononucleate, striated, branched toconnect cells and synchronize contraction--found only in the heart Force generates pressure on blood to push it around bodyo All of these muscle fibers generate force by pulling from the ends of the fiber towards the middle of the fiber- Nervous tissue : Neurons and glia cells- Body temp can change based on your activity level, but is still considered homeostatic because it is not far off from average (approximate)o Negative feedback : keep variables in a loop at a constant valueo Positive feedback : drives variables to extreme values (usually = death)- Keeping internal body temperature relatively constant o Increased temperature hypothalamus activates cooling mechanisms Sweat glands secrete sweat evaporates and cools the body Vessels in skin dilate, capillaries fill, heat radiates from skino Decreased temp hypothalamus activates warming mechanisms Skeletal muscles contract = shivering produces heat Blood vessels constrict, reducing heat loss- Nervous system : collect and process information and then generate outputo NS and endocrine control and coordinate function in all of the bodyo Major organs : brain, spinal cord, ganglia, nerveso Neural plasticity : capacity for nervous system to be remodeledo Neuron : receives/transmits info vial chemical and electrical signalso Glia : support neuronal cells (nourish, insulate, regulate)- CNS : brain and spinal cordo Spinal cord = neurons + glial cellso Spine = neurons + glial cells + vertebrae boneso Most nerve cells have their cell bodies in the CNS- PNS : all of the nervous system outside the CNSo Neurons that extend from the cell bodies of the CNSo Collection of axons (no neuron cell bodies) = nerveo Ganglia = collection of cell bodies that are located outside the CNS- Sensor Sensory input via PNS (dendrites) integration in CNS (dendrites,soma MB, spike-initiating zone and terminals) motor output in PNS (axon) Effector- Sensory receptors inside the body (joint closed/open, or muscle is stretched)- Sensory modality : different types of sensory information- Axon : extends from soma and transmits signal without decrement - Axon hillock : where axon extends from the cell body- Dendrite : extends from soma and receives input- Reflex : change in a physiological function or behavior that is initiated by sensory input and produced by motor output- Monosynaptic reflex : one kind of sensory neuron directly synapses on one subset of motor neurons to produce the reflexo Muscle stretch reflex is called monosynaptic because although muscle stretch receptors make more than 1 synapse within the CNS, only synapses directly onto spinal motor neurons are necessary for reflex- Motor neuron : cell body is in CNS, axon terminal is by skeletal muscle- Sensory neuron has it’s fiber (process) split at a T-junctiono One side goes to the same skeletal muscle, and the other side goes to the CNS where the motor neuron’s cell body iso Sensory neuron in reflex pathway is a muscle stretch receptor Has stretch-activated Na+ channelso Sensory neuron’s axon meets motor neuron’s cell body = synapseSaline is found in the synaptic cleft- No neurons act alone—they act in chains or networkso Neuronal circuits — set of connected (or interconnected) neurons cause a particular output as a result of their activity Can be simple (muscle stretch reflex) or very complex Some circuits include tens or hundreds of neurons- Interneuron : entire neuron is within the CNSo Integrates sensory and motor outputo Can be inhibitory, excitatory, afferent, efferent or neithero Interneuron reduces the activity of another motor neuron which may relax another muscle (hamstring relaxes while quad contracts = antagonist because they have opposite effects on the same joint)- Joint flexing = it closes, Joint extension = it opens- Electrical signals in neurons are based on the movement of ions across MB (and within the cell) in response to electrical fieldso Ions are always both chemical and physical (physical charge carriers) - Specific proteins provide pathway for ions to cross the plasma MBo Channels do not produce ion flow, they permit it- Want to see if cell has E potential across the MB o Take tip that is <0.1um diameter and poke MB, 60mV is recordedo outside is positive
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