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  • Information processed in the nervous system occurs in 3 stages:external image imagegethandler.axd?id=39585076&size=2
    1. sensory input
    2. integration
    3. motor output
  • Neurons:nerve cells that transfer (receive, transmit, regulate) information within the body.
    • Sensory neurons transmit information from the senses (light, sound, touch, heat smell, taste) or from internal conditions (blood pressure, carbon dioxide level) to the brain. In the brain interneurons integrate the signals and then motor neurons transmit the signals.
  • Central Nervous System (CNS): where integration takes place. Includes the neurons, brain, and longitudinal nerve cord
  • Peripheral Nervous System (PNS): neurons that carry information to and from the CNS.

external image imagegethandler.axd?id=39585062&size=2



  • A neurons organelles are located in the cell body.
  • Dendrites are branched extensions that receive signals from other neurons.
  • An axon is a long extension that transmits the signals.
  • Axons transmit information to other cells at a synapse. Here neurotransmittersare used to pass information.
    • Neuron sending signal is the presynaptic cell.
    • Neuron receiving signal is the postsynaptic cell.




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  • Membrane potential: the difference in voltage across the plasma membrane.
  • When a neuron is not sending a signal, its resting potentialis about -70 mV.
    • Potassium and sodium pumps are used for transport.
    • When the electrical and chemical gradients are are balanced it is at equilibrium.
  • Membrane potential changes in responses to stimuli. It is gated ion channels that open or close in response to stimuli.
  • An increase in magnitude of membrane potential is called hyperpolarizaion.
    • Ex: Gated K+ channels open, allowing K+ to diffuse out makes the cell's inside more negative.
  • A decrease in the magnitude of membrane potential is called depolarization.
    • Ex: Na+ channels are opened and Na+ diffuses into the cell.
=Generation of Action Potentials=

voltage-gated_ion_channels.jpg


  • Grade potential: a shift in membrane potential where the magnitude of the change varies with the stimulus strength.
  • Action potential:the result of a massive change in membrane potential.
    • Arise due to voltage gated ion channelswhich respond to changes in membrane potential.
      • Ex: Depolarization in the membrane causes Na+ channels to open, as Na+ diffuses into the cell it increases the depolarization which causes more Na+ channels to open.
    • Occurs when a stimulus causes the membrane voltage to cross the threshold. (about -55mV in mammals)
  • This image shows the role of voltage-gated ion channels in the generation of an action potential.
  • During the falling phase Na+ channels remain inactive, during this refractory period another action potential cannot occur.















Conduction of Action Potentials

external image 48_14ActionPotPropagation.jpg
  • Action potentials travel long distances by regenerating on the axon.

Steps of conduction:
  1. As Na+ flows inward across the membrane action potential is generated.
  2. Depolarization of the action potential spreads to neighboring regions, re-initiating action potential there. The region the was previously depolarized is then re-polarized as K+ flows out.
  3. The depolarization-repolarization process if repeated in the membranes next region. Carrying the action potential along the length of the axon.
  • external image imagegethandler.axd?id=39585079&size=2A larger axon diameter will result in a quicker action potential.
  • Myelin sheathsinsulate the axons of vertebrates. They cause action potential's speed to increase.
    • Myelin sheaths are made up of gila:
      • Oligodendrocytes in the CNS
      • Schwann cells in the PNS
  • Action potentials only occur at nodes of Ranvier (gaps in the myelin sheath where there are voltage-gated Na+ channels).
  • Action potentials use salatory conduction to move between nodes of Ranvier.




Neurons Communicate with other Cells at Synapses

  • Electrical synapse: electric current flows from neuron to neuron.
  • Chemical synapse:a chemical neurotransmitter carries information across the gap junction.
    • The majority of synapses are chemical.external image imagegethandler.axd?id=39585179&size=2
    • Sequence of events to chemically transmit an impulse:
      1. An action potential arrives, depolaraizing the presynaptic membrane. The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles.
      2. An influx of Ca2+ is triggered by the triggering to open voltage-gate channels.
      3. The neurotransmitter is released into the synaptic cleft and received by the postsynaptic cell.
    • The same neurotransmitter can produce different results in different cells.
    • There are five major classes of neurotransmitter:
      • acetylcholine
      • amino acids
      • biogenic amines
      • neuropeptides
      • gases
  • Postsynaptic potentials:
    • Excitatory postsynaptic potential (EPSP):depolarization that brings the membrane potential towards threshold.
      • Temporal summation: when two EPSP's occur at a single synapse in rapid succession that the postsynaptic neuron's membrane potential has not returned to resting potential, so the two EPSP's add together.
      • Spatial summation: when two EPSP's occuring at different synapses reach the postsynaptic neuron together, causing the two EPSP's to be added together.
    • Inhibitory postsynaptic potential (IPSP): hyperpolarization that brings the membrane potential further from the threshold.

Nervous Systems

  • As a general rule simpler organisexternal image systems.jpgms have simpler nervous systems and more complex organisms have more complex nervous systems.
  • Singled-celled organisms can respond to stimuli
  • Animals respond to stimuli using neuron systems
    • The simplest nervous systems are in cnidarians who's nerves are arranged in a nerve net, or a series of interconnected nerve cells.
    • More complex animals have nerves which are bundles that consist of multiple nerve cells axons.

  • Bilaterally symmetrical animals show cephalization, or the clustering of sensory organs at the front end of the body.
  • Simple cephalized animals have a CNS
    • Ex: flatworms
  • Annelids and arthropods have ganglia, which are segmentally arranged clusters of neurons.
  • In vertebrates the CNS is the brain and spinal cord and the PNS is nerves and ganglia.

Vertebrates Nervous System

external image 49_04VertNervousSystem-L.jpg
  • Vertebrates have a dorsal spinal cord.
  • Information is conveyed to and from the brain through the spinal cord.
  • The spinal cord can also independently to produce reflexes,or the body's automatic response to a stimulus.
    • Ex: Knee-jerk reflex
  • During development the CNS develops from the hollow dorsal nerve cord.
  • The nerve cord gives rise to the narrow central canal of the spinal cord and the ventricles of the brain.
  • external image 48_20VentriclesGrayWhite_L.jpgCerebrospinal fluidfills the canal and ventricles.
    • The fluid is filtered from blood and provides nutrients, removes waste, and cushions the brain and spinal cord.
  • The brain and spinal cord contain:
    • Gray matter: neuron cells bodies, dendrites, unmyelinated axons
    • White matter:bundles of myelinated axons
      • Predominantly on the inside, reflects the role of signaling between neurons and the brain.
  • Gliaare present throughout the brain and spinal cord.
    • Nourish, support, and regulate neurons
    • Radial glia help in development by forming tacks along which new neurons migrate.
    • Astrocytes then induce cells lining capillaries in the CNS to form tight junctions.
      • Results in a blood-brain barrier and restricts substances entry to the brain

The Peripheral Nervous System

  • Transmits information to and from the CNS.
  • Has two efferent components:
    1. The motor system: carries signals to skeletal muscles and is voluntary.
    2. The autonomic nervous system:regulates smooth and cardiac muscles and is usually involuntary. This system has three divisions:
      • The sympathetic division regulates arousal and energy generation ("fight or flight")
      • The parasympathetic division promotes calming and a return to self-maintenance functions.
      • The enteric division controls gallbaldder, pancreas, and digestive tract activity.

The Vertebrate Brain is Regionally Specilized

  • Specific brain structures arise during embryonic development.
    The limbic system
    The limbic system
  • The brainstem and cerebrum control arousal (state of awareness) and sleep (state in which external stimuli are received but not consciously perceived).
    • A network of neurons called the reticular formation is found at the core of the brianstem. Its purpose is to regulate the type and amount of information that reaches the cerebral cortex.
    • Melatonin is released by the pineal gland and plays a role in sleep cycles.
    • Sleep is essential to learning and memory.
  • Daily sleep and wakefulness cycles rely on a biological clock, a molecular mechanism that directs periodic gene expression.
    • Typically synchronized to light and dark cycles but can maintain the cycle in the absence of environmental cues.
  • The suprachiasmatic nucleus (SCN) is a group of neurons in the hypothalamus that coordinates circadian rhythms.
  • The limbic system is made up of the amygdala, hippocampus, and parts of the thalamus. Its function is in motivation, behavior, emotion, and memory.

  • Emotion generation and experience requires the limbic system and sensory areas of the cerebrum.
  • external image 48_27HumanCerebralCortex.jpgEmotional experiences are stored as memories in the amygdala, a mass of nuclei near the cerebrum's base.
  • The cerebrum (largest structure in the human brain) is essential for awareness, language, cognition, memory, and consciousness.
  • There are four lobes that serve as landmarks for function:
    • Frontal lobe
      • Broca's area is active when speech is generated
    • Temporal lobe
      • Wernicke's area is active when speech is heard
    • Occipital lobe
    • Parietal lobe
  • There are two hemispheres which function differently. This difference is called lateralization.
    • The left hemisphere is adept in language, math, logic, processing sequences.
    • The right hemisphere is adept at pattern recognition, nonverbal thinking, and emotional processing.
    • The two hemispheres communicate through corpus callosum fibers.
  • Information processing
    • Cerebral cortex receives input from sensory organs and somatosensory receptors.
    • Somatosensory receptors provide information on touch, pain, pressure, temperature, and limb/muscle position.
    • The thalamus directs different inputs to distinct locations.
    • Integrated sensory information passes to the prefrontal cortex, which helps plan actions and movements.
    • Neurons are arranged according to the part of the body that generates input or receives commands in the somatosensory cortex and motor cortex.
  • Frontal lobes have an effect on executive functions.
    • Frontal lobe damage can impair decision making and emotional responses but intellect and memory will remain intact.

Neural connections in memory and learning

  • The nervous system is established during embryonic development but can change after birth. The capacity for the nervous system to be modified after birth is called neural plasticity.
  • These changes can strengthen or weaken signaling at a synapse.
    • Autism is a result of a disruption of activity-dependent remodeling at synapses.
  • Memory formation is an example of neural plasticity.
    • Short-term memory: information held and released once it become irrelevant, is accessed via the hippocampus.
    • Long-term memory: retains knowledge longer, it is used with recollection, is stored in the cerebral cortex.
    • Memory consolidation may occur during sleep.
  • Long-term potential (LTP)is a form of learning that involves an increase in the strength of synaptic transmission.
    • For LTP to occur there must be a high-frequency of action potential in the presynaptic neuron. The action potential must arrive at the same time as the postsynaptic cell receives a depolarizing stimulus at another synapse.
    • Involves glutamate receptors.
    • Pg. 1078 shows LTP in the brain, I couldn't find this online to put in here.
  • Stem cells are in the adult human brain, they play an essential role in learning and memory.

Nervous System Disorders

  • Genetic and environmental factors contribute to diseases of the nervous systemexternal image nj7kTtDeKm3CLweQ1bmiqioKMDIiirpQXrJA_b5btAgzaLed-LSB9-BnMcGrDmoorD9tpmQ4BkQHpkMPeZkgVlyAn3f_Z24nFK88MsME0M_RKy0vy9I
  • Schizophrenia
    • Affects about 1% of the world's population
    • Patients have a distorted perception of reality
      • hallucinations, delusions, etc
    • Treatments focus on brain pathways that use dopamine as a neurotransmitter
  • Depression
    • Two broad forms of depression:
      • Major depressive disorder is periods of lack or interest or pleasure in most activities.
      • Bipolar disorder is characterized by mood swings from high (maniac) to low (depressive).
    • Treatments increase the activity of biogenic amines in the brain.
      • Ex: Prozac
  • Drug Addiction
    • Addiction is defined as compulsive consumption and an inability to control intake.
    • Drugs become addictive because they increase activity of the brain's reward system.
    • Cocaine, heroin, alcohol, tobacco, and amphetamine are all addictive.
    • Addictive drugs enhance the activity of the dopamine pathway.
    • Addiction leads to lasting changes in the reward circuitry that lead to craving for the drug.
  • Alzheimer's Disease
    • A mental deterioration characterized by confusion and memory loss.
    • Caused by neurofibrillary tanges and amyloid plaques in the brain.
    • There is no cure.
  • Parkinson's Disease
    • A motor disorder caused by the death of dopamine-secreting neurons in the midbrain.
    • Symptoms include: muscle tremors, flexed posture, shuffling gait
    • There is no cure, but deep brain stimulation and certain drugs can help manage symptoms.

Sensory Receptors

  • Sensory receptors begin with stimuli (represented in forms of energy) and convert it to a change in membrane potential, thereby regulating the output of action potentials to the CNS.
  • Stimulus may cause a simple or elaborate motor response to be generated.
  • Sensory pathways have four basic common functions:
    • Sensory reception:detection of stimuli by sensory receptors.
      • Beginning of the sensation.
      • Sensory receptors direly interact with stimuli inside and outside the body.
    • Sensory tranduction:the conversion of stimulus energy to a change in membrane potential of a sensory receptor.
      • Receptor potential is the change in membrane potential. Their magnitude varies with stimulus strength.
    • Transmission:after energy has been transducted, some sensory cells generate transmission of action potentials to the CNS.
      • Some sensory receptors are specialized neurons, others are specialized cells that regulate neurons.
        • Sensory neurons produce action potentials, their axons extend into the CNS.
    • Integration: begins as soon as information is received.
  • Response of a sensory receptor varies with stimuli intensity.external image sensory+receptors.jpg
    • Neuron receptor: larger receptor potential results in more frequent action potentials.
    • Non neuron receptor: larger receptor potential causes more neurotransmitters to be released.
  • Perceptions are the brain's construction of stimuli.
  • Amplification is the strengthening of stimulus energy be cells in sensory pathways.
  • Sensory adaptation is a decrease in responsiveness to continued stimulation.

Types of Sensory Receptors:

  • Mechanoreceptors sense physical deformation caused by stimuli such as pressure, stretch, motion, and sound.
  • Chemoreceptors
    • General chemoreceptors transmit information about the total solute concentration of a solutoin.
    • Specific chemoreceptors respond to individual kinds of molecules.
  • Electromagnetic receptors: detect electromagnetic energy such as light, electricity, and magnetism.
  • Thermoreceptors:detect heat and cold.
    • Help regulate body temperature.
  • Pain receptors or nociceptors: a class of naked dendrites in the epidermis that detect stimuli that can reflect harmful conditions.

Hearing and Equilibrium

  • Invertebrates maintain equilibrium using mechanoreceptors located in organs called statocysts.external image human-ear-internal-structure.jpeg
    • Statocysts contain mechanoreceptors that detect the movement of granules called statliths.
  • Vertebrates sensory organs for hearing and equilibrium are associated in the ear.
    • Hearing
      • Vibrating objects create waves in the air that cause the tympanic membrane to vibrate. The 3 bones of the middle ear transmit vibrations to the oval window, in the cochlea the vibrations create pressure waves that travel through the vestibular canal causing the basilar membrane to vibrate and bend its hair cells. This bending depolarizes the membranes of mechanoreceptors and send action potentials to the brain via the auditory nerve. The waves dissipate when they strike the round window t the end of the tympanic canal.
      • Volume is the amplitude of the sound wave.
      • Pitch is the frequency of the sound wave. Distinguished by the cochlea.external image 49_02TwoMechanoreceptorsB.jpg

    • Equilibrium
      • The utricle and saccule perceive position with respect to gravity or linear movement. The chambers contain a sheet of hair cells projected into a gelatinous material. In this gel are small calcium carbonate particleas called otoliths. Movement causes the otoliths to press into the hairs, this change is transformed to an output of sensory neurons that signal the brain telling it your heads at an angle
  • Other Vertebrates
    • Fish: have one pair of inner ears near the brain.
    • Have lateral line systems along both sides of their body that contain mechanoreceptors with hair cells that detect and respond to water movement.

Visual Receptors

external image Human%20Eye.jpg
  • Light detectors range from simple cell clusters to complex organs, but all contain photoreceptors, cells that contain light-absorbing pigment molecules.
  • Invertebrates have a light-detecting organ. One of the simplest is ocelli (eyespots) located near the head region. These allow movement away from light and helping to find shaded locations.
  • Insects and crustaceans have compound eyes, which consist of up to several thousand light detectors called ommatidia. Compound eyes are effective at detecting movement.
  • Jellies, polychaetes, spiders, and many molluscs have single-lens eyes. They have a small pupil through which light engers and an iris to change the diameter of the pupil, thus controlling light entry.
  • Vertebrate eyes detect color and light but we perceive the information as an image. Transduction begins when light induces the conversion of cis-retinal to trans-retinal, which activates a G protein, leading to hydrolysis of cyclic GMP. GMP breakdown causes Na+ channels to close, hyperpolarizing the cell. Information processing begins in the retina. In the dark rods and cones release glutamate into synapses with bipolar cells. These neurons are hyperpolarized or depolarized in response to glutamate. In the ligh, rods and cones hyperpolarize, shutting of the release of glutamate. Axons of ganglion cells form optic nerves that transmit signals to the brain. In the brain ganglion cell axons lead to the lateral geniculate nuclei which have axons reaching to the primary visual cortexin the cerebrum.
    • Ganglion cells transmit signals from bipolar cells to the brain.
    • Horizontal and amacrine cells integrate visual information before it is sent to the brain.
    • Interaction among different cells results in lateral inhibition, or an enhanced image contrast.
    • Color Vision: most vertebrates have good color vision. Humans see color based on red, green, or blue cones.

Taste and Smell

  • In terrestrial animals gustation (taste) is dependent on the detection tastants (chemicals) and olfaction (smell) is dependent on the detection of odorant molecues.
  • There is no distinction between taste and smell in aquatic animals.
  • Insects have sensory hairs for tast receptors.
  • Mammals have receptor cells called taste buds that can perceive sweet, sour, salty, bitter, and umami. Olfactory receptors are neurons that line the nasal cavity, when odorant molecules bind to receptors a signal transduction pathway is triggered, sending action potentials to the brain.

external image 49_15HumanSmell_L.jpg

Muscle Structure

external image skeletal_muscle_structure.jpg
  • Skeletal muscle moves bones and the body.
  • Skeletal muscle consists of a bundle of long fibers, each a single cell, running parallel to the length of the muscle.
  • Each muscle fiber is a bundle of smaller myofibrils.
    • Thin filaments consist of two strands of actin and two strands of regulatory protein.
    • Thick filaments are staggered arrays of myosin molecules.











Muscle Function

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Nervous systems (ch. 48-50)
  • Neuron organization (overview of cnidarians, echinoderms, flatworms, annelids, arthropods, mollusks, and vertebrates)
  • Neuron structure and function
  • Resting and action potentials, conduction of action potentials
  • Synapse structure and function, neurotransmitters
  • Organization of vertebrate nervous system
  • Brain structure and function
  • Neural connections, memory, and learning
  • Nervous system disorders: schizophrenia, depression, addiction, Alzheimer’s, Parkinson’s
  • Sensory receptors (general structure and function)
  • Types of sensory receptors
  • Hearing in humans vs. other vertebrates
  • Vision/light reception in vertebrates vs. other organisms
  • Taste and smell