Nervous System

• Cells of the Nervous System:

  • Neurons: receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs
  • Glial cells (Neuroglia): supportive cells of the CNS and PNS; do not conduct action potential; enhancing neuron function and maintaining normal conditions within nervous tissue
• Neurons have:

  • Cell body: containing a single nucleus
  • Dendrites: for receiving information from other neurons and transmits the info to the cell body
  • Axon: leaves the cell body at the axon hillock; conducts sensory signals to the CNS and motor signals away from the CNS
• Myelin Sheath:

  • Specialized layers wrapping around axons of some neurons, those neurons termed, myelinated
  • Formed by oligodendrocytes in the CNS and Schwann cells in the PNS
  • Acts as an insulator that prevents almost all ion movement across the membrane
• Unmyelinated Neurons:

  • Lack myelin sheaths
  • Rest in indentations of oligodendrocytes in the CNS and Schwann cells in the PNS
  • Typical small nerves contain more unmyelinated axons than myelinated axons
• Structure and Function of the Cranial Meninges:

  • Protect the brain and spinal cord from mechanical injury
  • Provide blood supply to the skull and hemispheres and a space for cerebrospinal fluid flow
  • Composed of Dura mater, Arachnoid layer, and Pia mater
• Alpha receptors:

  • Alpha-1 receptors elicit an excitatory response
  • Alpha-2 receptors block cAMP production, leading to an inhibitory response
  • Adrenergic receptors are sensitive to Norepinephrine
• In multicellular organisms, the distance for substances to enter cells is larger due to a higher surface area to volume ratio
• Multicellular organisms require specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen
• Senses, also known as sensory reception or sense perception, are the means by which our brain detects and responds to stimuli in the internal and external environment
• Sensation, also known as perception, is the conscious awareness of stimuli received by sensory receptors
• General senses have simple receptors distributed throughout the body to detect internal and external environmental conditions
• Two types of General Senses:

  • Somatic senses provide sensory information about the body and environment, including touch, pressure, temperature, proprioception, and pain
  • Visceral senses provide information about various internal organs, primarily pain and pressure
• Special senses are more specialized in structure and located in specific parts of the body, including vision (eyes), hearing (ears), balance (ears), taste (tongue), and smell (nasal passages)
• Sensory Receptors are specialized nerve cells that respond to a stimulus by generating a nerve impulse, which travels along the sensory nerve to the central nervous system for processing and forming a response
• Types of Sensory Receptors:

  • Mechanoreceptors respond to mechanical forces like pressure, roughness, vibration, and stretching, mainly located in the skin for touch and inner ear for hearing & balance
  • Thermoreceptors respond to changes in temperature, mostly found in the skin
  • Photoreceptors detect and respond to light, mainly located in the eyes for vision
  • Chemoreceptors respond to certain chemicals, mainly found in taste buds for taste and nasal passages for smell
  • Nociceptors or pain receptors respond to chemical, thermal, or mechanical stimuli, found in internal organs and on the body's surface
• Pain is an unpleasant sensation that can range from mild discomfort to agony
• Types of pain include:

  • Phantom pain, feels like it's coming from a body part that's no longer there
  • Acute pain, short-term pain with a specific cause that usually goes away once treated
  • Chronic pain, lasts for more than six months, even after the original injury has healed
• Referred pain is felt in a region of the body that is not the source of the pain stimulus
• Visceral pain results from injuries or damage to internal organs, often hard to pinpoint the exact location
• Somatic pain results from stimulation of pain receptors in body tissues, easier to pinpoint the location, includes skin, muscles, joints, connective tissues, and bones
• Eyes are the body's most highly developed sensory organs, with a large part of the brain dedicated to vision
• Visual acuity refers to a person's ability to discern shapes and details of things
• The human ear functions for hearing and maintaining balance or equilibrium
• Two types of equilibrium:

  • Static equilibrium allows a person to feel the effects of gravity, provided by the utricle and saccule
  • Kinetic or dynamic balance allows a person to sense speed and direction of the body's motion
• The Rinne test is used to evaluate hearing loss in one ear by comparing sounds transmitted by air and bone conduction
• A Rinne test should be accompanied by a Weber Test to detect sensorineural hearing loss
• The Romberg Test is used to assess neurological function for balance and as a test for driving under the influence
• The Romberg Test is based on the premise that a person requires at least two of the three following senses to maintain balance while standing: proprioception, vestibular function, and vision
• Nodes of Ranvier

  • gaps in the myelin sheath
  • occurs about every millimeter
  • ion movement can occur here
• Myelination of an axon increases the speed and efficiency of action potential generation along the axon
• Multiple sclerosis

  • disease of the myelin sheath that causes loss of muscle function
• Slow unmyelinated fibers

  • quite sufficient for processes in which quick responsible particularly important, such as secreting stomach acid or dilating pupil
• Fast myelinated fibers

  • employed where speed is more important
  • motor commands to the skeletal muscles and sensory signals for vision and balance
• Neuron

  • excitable
  • receive, process, transmit information
• Microglia

  • innate immunity
• Astrocytes

  • maintain BBB integrity
  • participate in synapses
• Ependymal

  • build barriers between compartments
• Oligodendrocytes

  • produce myelin sheaths
• Satellite

  • support other cells bodies
• Schwann

  • produce myelin sheaths around axon