Homeostasis

• Cell membrane

  Dynamic boundary that encloses the cell's contents while allowing for the exchange of materials with the external environment
• Cell membrane


  • Primarily composed of a lipid bilayer, proteins, and carbohydrates
• Selective Permeability


  The cell membrane regulates the entry and exit of substances, allowing essential molecules to enter while keeping harmful ones out
• Cell Signaling


  Integral membrane proteins serve as receptors, detecting extracellular signals such as hormones, neurotransmitters, and growth factors. These receptors initiate intracellular responses by triggering second messenger systems or altering ion permeability.
• Transport


  Various membrane proteins facilitate the transport of ions and molecules across the membrane through passive diffusion, facilitated diffusion, or active transport
• Adhesion and Support


  The membrane contains proteins that help cells adhere to each other and to the extracellular matrix, contributing to tissue structure and stability
• The human body is a complex biological system composed of various organs, tissues, and cells working together to maintain life
• Homeostasis


  The body's ability to maintain a stable internal environment despite external changes
• Homeostatic regulation


  1. Negative feedback

  2. Positive feedback
• Negative Feedback


  The most common form of regulation, involving detecting and responding to deviations from a set point to return a variable to its normal range
• Positive Feedback


  Amplifies a response, moving a variable further from its set point
• Mechanisms of Homeostatic Regulation

  1. Sensors (receptors)

  2. Integrating center (often the brain)

  3. Effectors (muscles or glands)
• Systems of Regulation


  • Nervous system (rapid transmission)
  • Endocrine system (slower, long-term control)
• Homeostasis can occur at multiple levels, including the cellular, tissue, organ, and organismal levels
• Irritability


  The ability of cells to respond to stimuli, which can be physical, chemical, or electrical
• Excitable tissues


  • Nerve and muscle cells
  • Have voltage-gated ion channels that open in response to changes in membrane potential, allowing ions like sodium and potassium to flow in and out of the cell
• Resting membrane potential


  The electrical charge difference across a cell membrane when the cell is at rest, typically around -70 millivolts in nerve cells
• Action potential


  1. Resting Phase

  2. Depolarization

  3. Repolarization

  4. Hyperpolarization
• Accommodation


  A property of excitable cells where they gradually become more excitable and eventually generate an action potential with continued stimulation
• Horvég-Weiss curve


  Representation of the relationship between stimulus intensity and response in excitable tissues, illustrating the minimum stimulus intensity required to generate a response and the optimal duration for that stimulus to be effective
• Intensity utilization time ratio

  Describes how the strength and duration of a stimulus affect excitation, helping to understand the initiation and propagation of action potentials
• Inhibition


  A process where certain stimuli or neurotransmitters reduce the excitability of a cell, making it less likely to generate an action potential
• Electrically excitable membranes


  Can generate action potentials, primarily found in nerve cells and muscle cells
• Non-excitable membranes


  Lack the ability to generate action potentials, typically found in non-neural, structural cells
• Coding in excitable cells

  Representing information through patterns of action potentials
• Conduction of excitation


  The process by which action potentials are propagated along nerve fibers through the sequential opening and closing of voltage-gated ion channels
• Chemical synapses


  More common type of synapse, function by releasing neurotransmitters into the synaptic cleft
• Neurotransmitters


  Chemical messengers released by neurons at synapses, transmit signals from one neuron to another or to target cells (e.g., serotonin, dopamine, acetylcholine)
• Neuromodulators


  Substances that can influence the strength or duration of synaptic transmission, enhancing or inhibiting the effects of neurotransmitters (e.g., endorphins, neuropeptides)
• Postsynaptic potentials


  Changes in membrane potential in the postsynaptic neuron in response to neurotransmitter binding at a synapse, can be excitatory (EPSPs) or inhibitory (IPSPs)
• Summation of postsynaptic potentials

  The process where EPSPs and IPSPs are integrated at the postsynaptic neuron, if the net result is a depolarization exceeding the threshold, an action potential is generated
• Functions of the nervous system

  • Sensory input
  • Integration
  • Motor output
  • Regulation of homeostasis
• Neuron


  • Transmits electrical and chemical signals
  • Has three main parts: dendrites (receiving input), cell body (integrating signals), and axon (transmitting output)
• Glial tissue


  Non-neuronal cells that support and protect neurons, play crucial roles in maintaining the structural and functional integrity of the nervous system
• Convergence


  Multiple neurons synapsing onto a single neuron, which can amplify signals
• Divergence


  A single neuron synapsing onto multiple neurons, spreading the signal
• Oscillating circuits


  Neural networks that produce rhythmic patterns of activity, like those controlling breathing
• Inhibition within networks


  Helps regulate and modulate the flow of information, preventing excessive excitation
• Reflex


  A rapid, automatic, and involuntary response to a stimulus, typically involving sensory neurons, interneurons (in some cases), and motor neurons
• Types of reflexes according to their mechanism of formation

  • Innate Reflexes
  • Conditioned Reflexes