Please enable JavaScript.

Coggle requires JavaScript to display documents.

Nerve cells - Coggle Diagram

- - - - insulator that project the ac from node to node
  - - - increase surface area of a nerve cell to communicate with other neurons
        
        the number of dendrites present depends where the neuron is found in the nervous system
- - - - depolarization
      - membrane returns to -70 mV
        
        repolarization
        
        membrane overshoots and becomes -90 mV
        
        hyperpolarization
        
        membrane returns to return potential at -70 mV
    - - a strong depolarization at the axon hillock opens Na+ voltage-gated channels
        
        Na+ rushes into the neuron, with its electrochemical gradient
        
        membrane depolarizes to around +35 mV
        
        Na+ channels are inactivated
        
        K+ channels begin opening
        
        K+ rush out of cell down its electrochemical gradient
        
        1 more item...
        
        Na+ moving in and K+ starting to move out causes the rounded top/overshoot of the action
        
        axon hillock has most Na+ channels
    - - To fire an ac, enough Na+ channels must be open to let Na+ inside
        
        with a small depolarization, the cell tries to maintain its resting membrane potential at -70 mV
        
        buildup of positive charge (Na+) affect ions inside and outside the cell
        
        K+ leave the inside
        
        repolarizes the membrane back to normal
        
        Cl- will attracted into the cell
        
        the depolarization force of Na+ entering must be greater than the repolarizing forces of K+ and Cl-
        
        if large enough, the repolarization forces cannot counteract the positive charge
        
        requires most of the Na+ channels to open
        
        This occurs at the threshold aka -55mV
        
        when this value is reached, an ac will always occur
    - - no real change in the concentration gradient occurs after 1 ac due to very few ions moving through the membrane
      - thousands of ac can be generated before the concentration gradients for Na+ and K+ break down and prevent further ac generation
      - all or nothing principle
        
        if the threshold is not reached
        
        no ac produced
        
        if threshold is reached
        
        full ac produced
      - two ac cannot be fired on top of each other due to absolute refractory period of the Na+ voltage gated channels
        
        ac will almost always have a fixed amplitude
  - - - shows specificity for Na+
      - opens only when membrane depolarizes
      - events
        
        membrane depolarizes
        
        activation gate opens
        
        Na+ flows into the cell following the concentration gradient
        
        inactivation gate closes
        
        Na+ stops entering cell and the channel can no longer open
        
        1 more item...
        
        channel is in absolute refractory period
        
        1 more item...
    - - only has 1 gate
        
        only opens when membrane depolarizes
        
        specifically only opens when Na+ voltage gated channels begin to enter their deactivation period
      - events
        
        membrane depolarizes
        
        K+ voltage gated channels after a brief delay
        
        K+ leave cell down their electrical and chemical gradients
        
        gate closes
        
        returns to resting configuration
        
        1 more item...
        
        K+ leaves the cell because K+ gates are slow to close, causing the relative refractory period
      - note that unlike Na+ voltage-gated channels, they do not have an inactivation period
    - - required to transmit ac
        
        opens when the inside of the cell becomes more positive
- - - - the positive charge is pulled towards an adjacent area on the membrane which has a negative charge, creating a local current (+ --> -)
        
        this charge buildup causes the adjacent area of the membrane to depolarize
        
        depolarization opens Na+ channels
        
        Na+ rushes into the cell and depolarizes the area to threshold, creating a new ac
        
        steps are repeated to propagate the ac down the membrane
    - - the positive charge in an axon moves only in 1 direction
        
        cannot travel backwards due to inactivated Na+ voltage-gated channels in its absolute refractory period
        
        when the Na+ channels open again, the ac has gone too far for it to go backwards
  - - - myelin is made by Schwan cells in the peripheral nervous system and oligodendrocytes in the CNS
      - myelin prevents the leakage of most ions through the membrane
        
        the Na+ and K+ channels exist only at the node of Ranvier
    - - the positive charge from the existing ac is attracted by the the negative charge at the next node of Ranvier
        
        the node of Ranvier depolarizes
        
        the Na+ channels at that node are opened
        
        Na+ rushes into the cell and depolarizes the region to threshold and a new ac is created
        
        process repeats and the ac is propagated down the membrane
        
        process is called saltatory conduction
    - - moves faster than conduction in unmyelinated fibers
      - the ac cannot go backwards due to the absolute refractory period of the Na+ voltage gated channels (the inactivation channels)
    - - disease when the imm. system attacks and damages the myelin around axons
        
        disrupts natural flow of ac where no transmission can occur
        
        if nerve is connected to muscle, prevents contraction and can cause paralysis
- - - - neuromuscular junction
        
        where a nerve cell triggers an ac in the muscle cell leading to muscle contraction
        
        structure
        
        neuron that meets the muscle cell
        
        motor nerve fiber
        
        Ca++ voltage-gated channels at the presynaptic axon terminal
        
        opens when the cell membrane depolarizes
        
        axon terminal
        
        the axon terminal has synaptic vesicles
        
        vesicles contain Ach
        
        at its basement membrane, the enzyme acetylcholinesterase can be found
        
        the sarcolemma is thrown into folds under the axon terminal
        
        this region is called the end plate
        
        have acetylcholine receptors
        
        1 more item...
        
        synaptic cleft
        
        gap between the motor nerve fiber and muscle cell
        
        series of events
        
        ac on the presynaptic motor nerve fibers cause Ca++ channels to open
        
        Ca++ enter cell down the concentration gradient
        
        triggers fusion of vesicles to membrane
        
        Ach is released onto the synaptic cleft by exocytosis
        
        1 more item...
        
        important facts
        
        an ac on the motor nerve cell always creates an ac on the muscle
        
        an ac on the muscle cell causes a muscle contraction
      - a type of chemical synapse