the nervous system

• Nervous system


  A body-wide system of nerve cells that collects information from the world, processes this information, and then takes action by directing bodily organs and muscles through the transmission of electrochemical messages
• Nervous system


  • Broken down into two parts: the central nervous system (CNS) and the peripheral nervous system (PNS)
• Central nervous system (CNS)


  Provides complex processing and contains the brain (where conscious and unconscious processing happens) and the spinal cord (receives and transmits information to/from the brain and body, can also perform basic motor reflexes)
• Peripheral nervous system (PNS)

  A body-wide network of messenger neurons that collect sense impressions and deliver instructions to the body from the CNS
• Components of the PNS

  • Sensory (afferent) neurons (deliver information to the CNS)
  • Motor (efferent) neurons (transmit information away from the CNS)
• Somatic nervous system (SNS)


  Controls skeletal muscles, a voluntary system under conscious control
• Autonomic nervous system (ANS)


  Controls internal organs and glands, an involuntary system not under conscious control
• Components of the ANS


  • Sympathetic branch (activates in stress response, increases bodily activities)
  • Parasympathetic branch (activates in rest, decreases bodily activities)
• Homeostasis


  The process by which the internal environment is maintained, involving a balance between the sympathetic and parasympathetic systems
• Reflex arc


  1. Sensory neuron

  2. Relay neuron

  3. Motor neuron
• Neuron


  • Cell body containing nucleus
  • Axon
  • Dendrites
• Axon terminals


  Almost but not quite touch the dendrite of the next neuron
• Synapse


  Structure where axon terminals and dendrites almost touch
• Myelin sheath


  Made of Schwann cells, protects the cell and increases speed of electrical transmission
• Effector


  Muscle activated by the motor neuron
• Reflex arc function


  1. Sensation detected in sensory receptors

  2. Electrical signal rushes along neuron

  3. Converted to chemical signal at synapse

  4. Detected by relay neuron

  5. Reflex response passed to motor neuron

  6. Effector (muscle) activated
• Reflex responses are passed immediately to the motor neuron, while information is also sent to the central nervous system for processing
• Nervous system


  Not the only information signal system in the body
• Endocrine system


  Uses chemical messengers called hormones released into the bloodstream by glands, with profound and long-lasting effects on the body and behavior
• Major endocrine glands


  • Pituitary
  • Hypothalamus
  • Pineal
  • Thyroid
  • Thymus
  • Pancreas
  • Adrenal
  • Testes/Ovaries
• Pituitary gland


  Often called the "master gland", its hormonal secretions influence the release of hormones by other glands
• ACTH


  Adrenocorticotropic hormone, released by pituitary as part of the fight-or-flight response, resulting in release of cortisol from adrenal glands
• Hypothalamus


  Works with pituitary gland, telling the nervous system to the rest of the endocrine system, maintains homeostasis
• CRH


  Corticotropin-releasing hormone, released by hypothalamus and detected by pituitary in fight-or-flight response
• Pineal gland


  Modulates sleep pattern by releasing melatonin
• Thyroid gland


  Influences metabolic rate by releasing thyroid hormones
• Thymus gland


  Active until puberty, stimulates development of T-cells for immune response
• Pancreas


  Regulates blood sugar levels by releasing insulin and glucagon
• Adrenal glands


  Release cortisol and adrenaline in stress response
• Testes/Ovaries


  Reproductive glands that produce sex hormones testosterone and estrogen
• Fight-or-flight response


  A system with deep evolutionary roots that is triggered when a person is shocked and frightened, causing time to seem to slow down, increased heart rate and breathing, body tensing up and poising for action, and difficulty calming down afterwards
• The fight-or-flight response evolved to help people fight or run away from predators
• When the modern world triggers stress responses

  The stress effects are not always negative, as the extra alertness and ability to think on one's feet can be positive in some situations like job interviews
• Chronic stress is different from short-term stress, as the system that evolved to cope with immediate threats is now triggered by worries that won't kill the person
• The process of the fight-or-flight response

  1. Recognize the threat

  2. Stress response activated

  3. Hypothalamus activates sympathetic nervous system and endocrine system

  4. Adrenal gland releases adrenaline and cortisol

  5. Wide range of physiological effects to prepare the body for action
• Effects of adrenaline and cortisol

  • Increased blood flow to brain and muscles, decreased blood flow to non-essential systems, dilated pupils, faster breathing, sweating, increased mental alertness
• Chronic stress can lead to physical and mental health problems like heart disease, obesity, IBS, low immunity, and depression
• Tend and befriend response


  An alternate stress response in women where they focus on social connections and working together to overcome difficulties, as fighting or running is often not an option for them