Biology F214: Section 1

Communication and Homeostasis
1. Nervous System
  1. Types of Neuron
    1. Motor Neurone
      1. Short dendrites (CNS to Cell Body)
      2. One long axon (Cell Body to Effector cells)
    2. Sensory Neurons
      1. Short dendrites
      2. One long dendron to carry impulses from receptor cells to the cell body
      3. Short axon that carries impulses from the cell body to the CNS
  2. Sensory Receptors
    1. Act as transducers (they convert one form of energy into another)
    2. Resting Potential
      1. Resting state, the inside of the cell is -ve so there is a p.d. across the membrane. This is maintained by ion pumps and ion channels
    3. Generator Potential
      1. Change due to a stimulus
      2. Due to the cell membrane becoming excited and more permeable, makes the inside of the cell more +ve
      3. The bigger the stimulus the bigger the generator potential
    4. Action Potential
      1. If the g.p. is big enough it'll trigger an a.p. (threshold level)
  3. The Nervous Impulse
    1. r.p. => -70mV
    2. Sodium (3 x Na+) and Potassium (2 x K+)
      1. Use active transport to move Na+ out for K+ into cell
        Electrochemical Gradient
        Potassium channels also exist that allow K+ to move out by facilitated diffusion
    3. Action Potential
      1. STIMULUS - Sodium channels open, neurone becomes less negative
      2. DEPOLARISATION - p.d. reaches threshold (-55mV), voltage gated channels open so more sodium ions move in.
      3. REPOLARISATION - At +30mV, the sodium ion channels close and the potassium channels open. Neurone becomes more negative.
      4. HYPERPOLARISTION - Overshoot, P.d. becomes more -ve than resting potentialn (less than -70mV)
      5. R.P. - ion channels are reset
      6. Refractory period - too negative to become excited agian, makes a time delay, also it means the impulse can't travel backwards
    4. Waves of Depolaristion
      1. Mexican wave of sodium channels opening. The impulse propagates along the neuron, movement of action potential
    5. All-or-nothing
      1. The stimulus must reach the threshold to become an active action potential
      2. The bigger the stimulus the more frequent the impulses
    6. Speed of conduction
      1. Saltatory conduction, caused by the impulse jumping between nodes of Ranvier (between myelin sheaths made of Schwann cells)
      2. Faster if - big axon diameter or a higher temperature (until 40 degrees as enzymes will denature in the cells)
  4. Synapses
    1. Neurotransmitters are removed from the synaptic cleft so the response doesn't keep happening, they're taken back to the pre-synaptic cleft, or they are broken down
    2. Example: Cholinergenic Synapse
      1. Neurotransmitter: Acetylcholine
      2. 1. ARRIVAL OF ACTION POTENTIAL
        Arrives as impulse at the presynaptic knob, this stimulates voltage-gated calcium ion channels. They diffuse in and are actively transported out.
      3. 2. FUSION OF VESICLES
        Ca+ causes vesicles containing acetylcholine to fuse with the presynaptic membrane
      4. 3. DIFFUSION OF ACh
        ACh diffuses across the cleft and binds to the specific cholinergic receptors on the postsynaptic membrane. This causes sodium ion channels in the postsynaptic neurone to open, which causes depolarisation. An action potential is generated if the threshold is reached.
        ACh is removed by acetylcholinerase (AchE) and the products are reabsorbed by the presynaptic neurone to make more ACh
    3. Disruption of synaptic transmission
      1. Same shape as neurotransmitters
        Nicotine
        AGONISTS
      2. Block receptors
        Muscle can't be stimulated, paralysis.
      3. Inhibit breakdown enzyme
        More neurotransmitters in the synaptic cleft to bind to receptors and they're there for longer
        Loss of nerve control
      4. Inhibit the release of neurotransmitters
        Fewer receptors are activated
        Block the calcium channels in the presynaptic knob, meaning fewer vesicles fuse with the membrane
    4. Roles of synapses
      1. Divergence
        One neuron is connected to many neurones, therefore information can be dispersed to different areas of the body
      2. Convergence
        Amplification
      3. Spatial summation
        Multiple synapses that together surpass the threshold potention
      4. Temporal Summantion
        Two or more nerve impulses arrive in quick succession from the same presynaptic neuron
      5. Unidirectional
        The presense of a pre and postsynaptic neuron means the impulse can only travel in one direction
  5. Structure of the Nervous System
    1. CNS
      1. Peripheral NS
        Somatic NS (conscious activities)
        Autonomic NS (unconscious activities)
        Sympathetic NS (fight or flight)
        Parasympathetic NS (rest and digest)
  6. Example: Heart Rate
    1. High Blood Pressure
      1. Impulses sent to m. oblongata which sends impulses along PARASYMPATHETIC neurones. ACETYLCHOLINE binds to SAN
        Heart rate decreases
      2. Baroreceptors detect
    2. Low Blood Pressure
      1. Baroreceptors detect. Impulses sent to m. oblongata which sends impulses along SYMPATHETIC neurones.NORADRENALINE binds to SAN
        Heart rate increases
    3. High Blood O2, Low CO2 or high blood pH
      1. Chemoreceptors detect
    4. Low Blood O2, High CO2 or high blood pH
      1. Chemoreceptors detect
    5. Adrenaline
      1. When an organism is threatened, adrenaline is released, it binds to specific receptors on the heart to increase contraction frequency and strength
2. Endocrine System
  1. Hormonal Communication
    1. Information via chemical signals (hormones) that are secreted by glands. Many proteins are peptides e.g. insulin, however some are steriods, e.g. progesterone
    2. Glands can be stimulated by a change in concentration of a specific substance or by electical impulse
    3. Diffuse directly in the blood, binds to specific receptors on target cells. Tissues that contain a lot of target cells are kknown as target tissues
  2. Glands
    1. endocrine - secrete hormones directly into the blood
    2. exocrine - secrete chemicals through ducts
  3. Action of Hormones
    1. Hormones are first messengers, from the endocrine gland to the receptor
      1. Catalyses the action of a second messenger inside the cell
        Second messengers activate a cascade inside the cell
    2. Adrenaline
      1. Adrenal Gland
        Cortisol /Adrenalin
      2. Release when there is low concentration of glucose in the blood, when stressed and when exercising
        Activates glycogenolysis
        (As a first messenger) Adrenaline binds to receptors on many cells like liver cells
        It then activates an enzyme in the membrane that activates the second messenger called cAMP
        cAMP activates a cascade (that makes glucose more available to the cell)
  4. The Pancreas
    1. Endocrine Function
      1. Islets of Langerhan
        Alpha cells
        Glucagon
        Binds receptors onto the cell membranes of liver cells (to release glycogen) and actives glycogenolysis (breaks down glycogen) and gluconeogenesis)
        Beta cells
        Insulin
        Increases the permeability of cell membranes to glucose and activates glycogenesis
    2. Exocrine Function
      1. Makes up most of the pancreas
      2. Acinar cells
        Secrete digestive enzymes into the pancreatic duct
    3. Blood Concentration
      1. Low
      2. High
  5. Homeostasis
    1. The maintenance of a constant internal environment
      1. Keeping your internal environment roughly constant (within limits)
    2. Temperature
      1. As the rate of metabolic reactions increases (so does the kinetic energy) the temperature's increases in turn
        Too hot and enzymes will denature, to low and the enzyme activity will be reduced/
    3. Negative feedback
      1. Involves receptors, a communication system and effectors
      2. The receptors detect change and the effectors counteract the change
      3. Only works within certain limits, always in flux
    4. Postive feedback
      1. Amplifies the change
      2. E.g. cervical dilation or platelets to form a clot
  6. Temperature
    1. Ectotherms
      1. Relies on external temperature, also more active at higher temperature
    2. Endotherms
      1. Control body temperature using internal homeostasis
      2. Constantly have a high metabolic rate
        Can constantly be active at any temperature
    3. Mechanisms
      1. To reduce temperature
        Sweating, hairs lie flat, vasodilation
      2. To increase temperature
        Shivering, hormones, much less sweat, hairs stand up, vasoconstriction
      3. Uses the hypothalamus and thermoreceptors
  7. Diabetes Mellitus
    1. Insulin from GM bacteria
      1. (rather than from a pigs pancreas) Cheaper, more produced, human so less likely to trigger an allergic response or be rejected, ethical reasons such as religion or vegetarianism.
    2. Could possibly cure with differentiated stem cells
3. Communication
  1. Receptors and Effectors
    1. Responding to the Environment
      1. To aid survival
      2. make sure conditions are optimal for metabolism
      3. Any change to the internal or external environment (e.g. temperature, light intensity or pressure is called a stimulus
    2. Receptors are specific - e.g. pressure, light, glucose conc. therefore there are many different types of receptor, some are on the CSM and some are whole cells
    3. Effectors are cells that bring about a response to produce an effect. These include muscle or cells from in glands
  2. Cell signalling
    1. Both nervous and hormonal
    2. Ways in which cells communicate with each other

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