Communication and Homeostasis

Created by: Imogen
Created on: 15-02-13 14:47

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Communication and Homeostasis
- Maintaining the internal environment of cells
  - Tissue Fluid
  - Excretion
  - pH
  - Temperature
  - Cell Signalling
    - Hormonal System
      - Endocrine - A gland that secretes hormones directly into the blood capillaries
      - Exocrine - A gland that secretes hormones into a duct
      - Slow
      - Long term
    - Neuronal System
      - Short term
      - Rapid Response
- Homeostasis
  - Keeping internal conditions constant despite external conditions
    - Temperature
    - Glucose
    - pH
    - Carbon Dioxide
    - Water potential of the blood
    - Concentration of ions in the blood
    - Blood pressure
  - Negative Feedback
    - Optimum Conditions
      - Change from Optimum Conditions
        Effector works to restore optimum conditions
        Optimum Conditions
        Change from Optimum Conditions
        Effector works to restore optimum conditions
  - Positive Feedback
    - Optimum Conditions
      - Change from Optimum Conditions
        Effector reacts to increase the change
  - Endotherms
    - Relies on external sources of heat to regulate body temp.
      - Advantages
        Energy from food can be used for growth
        
        Needs to eat less regularly
      - Disadvantages
        Inactive in colder temperatures
        Vulnerable
        
        May be incapable of activity during winter
  - Endotherms
    - Uses internal sources of heat, heat generated from metabolism, to maintain body temp.
    - Advantages
      - Activity in all weather
      - Ability to inhabit cold habitats
      - Constant body temp.
    - Disadvantages
      - Significant amount of energy from food is used to generate heat energy
      - More food required
      - Less energy from food used for growth
- The Nervous System
  - Sensory Receptors
    - Sensory Neurones
      - Features of Neurones
        Motor Neurones
        
        Gated ion channels in csm
        
        Na+/K+ pumps in csm
        
        Potential difference across csm
        
        Surrounded by a myelin sheath
        
        Contain dendrites connected to other neurones
    - Motor Neurones
    - Relay Neurones
  - Resting Potentials
    - Inside of cell is negative compared to outside
      - 3 Na+ ions out for every 2 K+ ions in
      - Csm is permeable to K+ ions
      - Large organic anions in the neurone
      - -60 mV
      - Polarised
  - Action Potential
    - Depolarisation -50mV
      - Voltage gated Na+ channels open
        Na+ diffuse into cell down concentration gradient
        +40 mV
        Na+ channels close, K+ channels open
        K+ diffuse out of neurone down concentration gradient
        Repolarisation
        Hyperpolarisation
        Refractory Period
        Action Potential
        Depolarisation -50mV
        Voltage gated Na+ channels open
        Na+ diffuse into cell down concentration gradient
        +40 mV
        Na+ channels close, K+ channels open
        K+ diffuse out of neurone down concentration gradient
        Repolarisation
        Hyperpolarisation
        Refractory Period
        Allows cell to recover after AP
        
        Local Currents
        Na+ diffuse into cell
        High concentration of Na+ at this point
        Na+ diffuse away from point of entry
        Movement of charged particles = local current
        Increased concentration of Na+ cause voltage gated channels to open
        Local Currents
        Na+ diffuse into cell
        High concentration of Na+ at this point
        Na+ diffuse away from point of entry
        Movement of charged particles = local current
        Increased concentration of Na+ cause voltage gated channels to open
        
        Allows cell to recover after AP
  - Myelin Sheath
    - Impermeable to ions
      - Saltatory Conduction
        Nodes of Ranvier
        Myelin Sheath
        Impermeable to ions
        Saltatory Conduction
        Nodes of Ranvier
        
        Protects neurone from activity of surrounding neurone
        Increased rate of conduction
        
        Schwann Cells
        
        Increased rate of conduction
      - Protects neurone from activity of surrounding neurone
    - Schwann Cells
Synapses
- Action Potential
  - Ca2+ channels open
    - Ca 2+ diffuse into cell
      - Vesicles containing neurotransmitter move to csm
        N.T diffuses across cleft
        N.T binds to receptors on postsynaptic membrane
        Na+ channels open
        Action Potential
        Ca2+ channels open
        Ca 2+ diffuse into cell
        Vesicles containing neurotransmitter move to csm
        N.T diffuses across cleft
        N.T binds to receptors on postsynaptic membrane
        Na+ channels open
- Cholinergic Synapse
  - Acetlycholine
    - Acetylcholinesterase
- Summation
- Acclimatisation
- One Direction
- Reflex Arc

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Communication and Homeostasis

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