Homeostasis

• Homeostasis- the ability or tendency to maintain internal stability in an organism to compensate for environmental changes
• Homeostasis- the nervous system plays a key role in homeostasis by acting as a relay centre between the external enviroment and the internal environment
• The body has a complex communication system composed of the nervous system and the endocrine system which both work together to both Maintain homeostasis in your body and send messages around your body to adjust to internal and external conditions
• Nervous System- made up of neurons, neuroglia cells and nerves that transmit electrical impulses from one part of the body to another.
• Neuron- nerve cell with dendrites (receiving) and axons (transmitting)
• The messages that are sent by the endocrine system are: endocrine hormones. the messages that are sent by the nervous system are: nerve impulses
• The nervous system is faster than the endocrine system because nerve impulses are faster than hormone signals. nerve impulses are sent through electrochemical signals while hormones are sent through blood stream; cells Have to release hormones, travel through bloodstream to reach the target cell that receives the message
• Nervous system- there are billions of nerve cells in the brain and each nerve cell can have thousands of connections to other nerves
• Types of cells in the nervous system

  • Neurons
  • Glial cells
• Neurons

  Functional units of the nervous system
• Glial cells

  Support for neurons, nourishes them, removes waste and defend against infection
• Ratio of glial cells to neurons is 10:1
• It hurts if you hit your elbow on something hard because the ulnar nerve which runs over the elbow doesn't lie deep in the body for protection and banging your elbow causes the nerve to fire, resulting in a tingling sensation
• Neurons

  Individual cells in your nervous system
• Nerves

  Neurons Bundled together to make nerves which are tissue
• Types of neurons

  • Sensory neuron
  • Interneuron
  • Motor neuron
• Sensory neuron

  Carry impulses from the environment to the CNS
• Interneuron

  In the CNS and act as the links between the other two types of neurons
• Motor neuron


  Connects the CNS to muscles, glands and other organs
• CNS(central nervous system) is the brain(control centre) and spinal cord(communication centre, relays info to rest of body)
• PNS(peripheral nervous system) is the network of nerves that connects the CNS to the rest of the body. It contains the autonomic nervous system(involuntary) and the somatic nervous system(voluntary)
• the sympathetic nervous system is the fight or flight response and is the part of the nervous system that prepares the body for action and is part of the autonomic system
• The parasympathetic nervous system is responsible for rest and digest, returning you to homeostasis. also part of the autonomic system
• The sensory neurons are the neurons that carry information from the senses to the CNS. part of the somatic system
• The motor neuron is the neuron that carries the impulse from the CNS to the effector(away from the brain). Part of the somatic system
• Reflex arc happens when you pull away from something before you even realize the pain. the reflex arc is much faster than sending information to your brain because it uses fewer neurons to transmit a signal
• Reflex arc

  1. Receptor picks up stimulus, turns it into electrical energy

  2. Sensory neuron-electrical energy that transmits down the sensory (afferent) neuron

  3. Control centre-afferent signal is sent into control centre (interneuron, spinal cord)

  4. Motor neuron-signal is sent to motor (efferent) neuron

  5. Effector-efferent signal is sent to the effector (muscle) which contracts or pulls away to avoid tissue damage
• We need reflex arcs because they are protective; it’s faster to send a signal through only the spinal chord and saves you from damage
• neurons have lots of different shapes: bipolar (interneuron), unipolar (sensory neuron), multipolar (motor neuron) and pyramidal cell. structures are similar in all
• all neurons have a dendrite, axon, cell body and axon terminals

  
• dendrite- short branching ends that receive a nerve impulse

  
• cell body- part of the neuron that contains a nucleus

  
• axon- the long extension of a neuron that carries electrical impulses away from the cell body

  
• axon terminals- last part of the axon where synapses are

  
• some neurons have a myelin sheath, nodes of Ranvier and neurilemma

  
• myelin sheath- is the fatty insulation that protects the neuron and speeds the rate of transmissions of nerve impulses. theyre made of Schwann (glial) cells

  
• nodes of Ranvier are the gaps between Schwann cells

  
• neurilemma is the membrane that surrounds the axon and schwann cells which allows neurons to regenerate
• Kinds of neural tissue

  • White matter
  • Grey matter
• White matter


  Nerve cells that have a myelin sheath (PNS)