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NERVOUS SYSTEM (Neurons (Constitution (Axon (Conveys information to…

- - - - Central Nervous System (CNS)
        
        Brain & Spinal cord
        
        :bulb: Receives sensory formation from the PNS
        :bulb: Performs integration
        :bulb: Initiates motor command
      - Peripheral Nervous System (PNS)
        
        All the nerves that branched out from the CNS
        
        :bulb: Carries sensory information to the CNS
        :bulb: Sends motor command to the muscles and glands.
        
        Control system
        
        Information conveyed
        
        :star:Sensory information :arrow_right:sensory (afferent) neurons
        
        :star:Motor command :arrow_right: motor (efferent) neurons
        
        Motor neurons function
        
        Somatic nervous system
        
        Regulates voluntary actions
        -Controls skeletal (striped or striated) muscles
        -Eg. Picking up paper
        
        Autonomic nervous system
        
        Regulate involuntary actions
        -Controls smooth muscles, the heart & glands
        -Eg Breathing, hormone secretion &peristalsis
        
        Parasympathetic Division
        
        2 more items...
        
        Sympathetic Division
        
        3 more items...
- - - - Receive signals from sensory receptors or other neurons and transmit them to cell body
    - - Contains a nucleus and a variety of organelles
    - - Conveys information to another neuron or to other cells
      - Covered by myelin sheath
      - Axon & Myelin sheath bundled together to form nerve fibers
  - - - Occurs entirely within CNS
    - - Carry nerve impulses from CNS to muscles or glands
    - - Take nerve impulses from sensory receptors to the CNS
- - - - Membrane potential of sensory receptor
    - - Stimulus energy that is too weak to be carried into nervous system
    - - The actual detection of stimulus involves conversion of stimulus energy into membrane potential of sensory receptor cell
  - - - Two types
        
        Cold detect stimulus ~ < 30 °C
        
        Hot detect stimulus ~ > 22 °C
      - Peripheral thermoreceptor: detect skin and visceral body temperature
        Interothermoreceptor in anterior hypothalamus: detect deep brain temperature
      - Temperature information from skin, visceral organ and deep brain are sent to body’s thermoregulatory center in posterior hypothalamus
      - Thermoregulation
    - - Specific receptor
        
        Transmit information about specific molecules
        
        Chemoreceptor in antennae of male silkworm moth detect two chemical components of female moth sex pheromone
      - Receptor with intermediate specificity
        
        Gustatory (taste)
        
        Direct chemoreceptor – detect chemical in aqueous state
        
        Sweet, sour, salty, umami or bitter
        
        Olfactory (smell)
        
        Distance chemoreceptor – detect chemical in gaseous state
        
        Musky, putrid, pungent, floral
      - General receptor
        
        Transmit information about the total solute concentration in solution
        
        Osmoreceptor in mammalian brain detect blood osmolarity
      - Water receptor of house fly
      - Transduce chemical signal into receptor potential
    - - Detect pain from external or internal source
      - Different group of pain receptors responding to specific stimulus
        -Eg excess heat, pressure and chemicals released from damaged or inflamed tissue (eg: histamine)
        .
      - Two types of pain signal
        
        Fast pain
        
        lasting ~0.1 second
        
        transmitted via myelinated A delta fibers
        
        an acute or sharp pain
        
        Slow pain
        
        last a few seconds to minutes
        
        transmitted by unmyelinated C fibers
        
        chronic or burning pain
      - Naked dendrites of nociceptor in skin’s epidermis stimulated by chemical (eg: prostaglandin) released from damages tissue and Mast cell
    - - Detect various forms of electromagnetic energy
      - Photoreceptor - detect visible light
        
        Rod cell - sensitive to black & white vision at night
        
        Cone cell - account for colour vision in daylight
        
        Human and primate has trichromatic vision while most other vertebrates has dichromatic vision
        
        The eyes of nocturnal animal constitutes of mainly rod cells photoreceptor
        
        Allows them to have better vision in low light but sacrificing the sensitivity to differentiate colour
        
        Since the cone cell also contribute to better vision acuity, having more rod photoreceptor also means that animal have a lower image resolution
        
        Frog kept in captivity need to be given live food because they identify food based on movement due to low vision acuity
        
        The helmeted gecko is one of exceptional nocturnal vertebrate that have colour vision during the dusk hour
        
        Their pupils will become slit-shaped with four notches to filter excess light during the day time
        
        The four notches are presumably helps gecko to estimate distance without having stereoscopic vision by creating four separate images on each eyes
        
        Due to the lack of rod cells in their retina
      - Electroreceptor - detect changes in electric current
        
        Observed most exclusively in aquatic and amphibious animal – water is much better conductor than air
        
        Nearby object perturb the electric field
        
        Conductive objects concentrate the field
        
        Resistive objects spread the field
      - Specialized electromagnetic receptor
        
        Pit viper uses infrared receptor to detect body heat
        
        Magnitoreception in migrating animal uses earth magnetic field for orientation
        
        Magnitoreception in bird
        
        Iron-containing mineral magnetite in some of bird skulls
    - - Stimulated by physical deformation
        
        pressure, touch, stretch, motion & sound
        
        Eg: Bending or stretching of receptor membrane increases its permeability to both sodium and potassium ions → depolarization
      - Detect light touch: Near to the skin's surface
        Detect pressure &vibration: Deep skin layer
      - Other touch receptor detect hair movement
      - • Merkel’s receptor – sensitive to vibration and texture
        • Meissner’s corpuscle – sensitive to light touch
        • Pacinian corpuscle – sensitive to stronger pressure and vibration
        • Ruffini’s corpuscle – sensitive to skin stretch
- - - - A gated ion channel allows sodium (Na+) to pass into the axon
      - Another gated ion channel allows potassium (K+) to pass out of the axon
  - - - When an action potential begins, the gates of the sodium channels open, and Na+ flows into the axon
        
        Membrane potential changes from −65 mV to +40 mV
      - Called depolarization because inside axon changes from negative to positive
    - - Gates of potassium channels open, and K+ flows out of axon
        
        Action potential changes from +40 mV back to −65 mV
      - Called repolarization because inside of axon becomes negative again as K+ exits the axon
    - - Depolarization to +40 mV as Na+ gates open and Na+ moves to inside the axon
    - - Repolarization to −65 mV as K+ gates open and K+ moves to outside the axon
  - - - Negative sign indicates that the inside of the cell is more negative than the outside
    - - Due to the activity of the sodium-potassium pump, which moves three sodium ions (Na+) out of the neuron for every two potassium ions (K+), it moves into the neuron
  - - - As soon as an action potential has moved on, the previous section undergoes a refractory period, during which the Na+ gates are unable to open
      - The action potential cannot move backward and instead always moves down an axon toward its terminals
  - - - In the case of a neuron, the two points are the inside and the outside of the axon
    - - Resting potential > Threshold level > Action potential > Refractory period
- - - - In the PNS, ACh excites skeletal muscle but inhibits cardiac muscle
      - ACh has either an excitatory or inhibitory effect on smooth muscle or glands
    - - Serotonin, another neurotransmitter, is involved in thermoregulation, sleeping, emotions, and perception
    - - Once a neurotransmitter has been released into a synaptic cleft and has initiated a response, it is removed from the cleft
      - Short existence of neurotransmitters at a synapse prevents continuous stimulation (or inhibition) of postsynaptic membranes
  - - - If a neuron receives many excitatory signals the axon will transmit a nerve impulse
      - If a neuron receives both inhibitory and excitatory signals, the summing up of these signals may prohibit the axon from reaching threshold and firing
  - - - An excitatory neurotransmitter produces a signal that drives the neuron closer to threshold
      - An inhibitory neurotransmitter produces a signal that drives the neuron further from threshold
  - - - At synapse, membrane of first neuron is presynaptic
      - The membrane of the next neuron is the postsynaptic
      - Small gap between the neurons is the synaptic cleft
    - - Transmission across a synapse is carried out by molecules called neurotransmitters, which are stored in synaptic vesicles
    - - Each terminal lies very close to the dendrite (or the cell body) of another neuron