Chapter 8: Nervous System

• Functions of the nervous system

  receiving sensory input

  integrating information

  Controlling muscles and glands

  Maintaining homeostasis

  Establishing and maintaining mental activity
• Central nervous system (CNS)


  brain and spinal cord
• Peripheral nervous system (PNS)


  All the nervous tissue outside the CNS
• Sensory division


  Conducts action potentials from sensory receptors to the CNS
• Motor division


  Conducts action potentials to effector organs, such as muscles and glands
• Somatic nervous system


  Transmits action potentials from the CNS to skeletal muscles
• Autonomic nervous system


  Transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands
• Enteric nervous system


  A special nervous system found only in the digestive tract
• Neurons


  receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs.
• Glial cells


  supportive cells of the CNS and PNS, meaning these cells do not conduct action potentials. Instead, glial cells carry out different functions that enhance neuron function and maintain normal conditions within nervous tissue
• Cell body


  contains a single nucleus
• Dendrite


  is a cytoplasmic extension from the cell body, that usually receives information from other neurons and transmits the information to the cell body
• Axon


  is a single long cell process that leaves the cell body at the axon hillock and conducts sensory signals to the CNS and motor signals away from the CNS
• Multipolar neurons


  have many dendrites and a single axon.
• Bipolar neurons


  have two processes: one dendrite and one axon; are located in some sensory organs, such as in the retina of the eye and in the nasal cavity.
• Pseudo-unipolar neurons


  have a single process extending from the cell body, which divides into two processes as short distance from the cell body.
• Astrocytes


  serve as the major supporting cells in the CNS
• Ependymal cells


  line the cavities in the brain that contains cerebrospinal fluid.
• Microglial cells


  act in an immune function in the CNS by removing bacteria and cell debris
• Oligodendrocytes


  provide myelin to axons of neurons in the CNS.
• Schwanncells


  provide myelin to axons of neurons in the PNS
• Myelin Sheath


  are specialized layers that wrap around the axons of some neurons: an excellent insulator that prevents almost all ion movement across the cell membrane
• Nodes of Ranvier


  gaps in the myelin sheath; occur about every millimeter
• Multiple sclerosis


  is a disease of the myelin sheath that causes loss of muscle function.
• Unmyelinated axons


  lack the myelin sheaths.
• Spinal cord


  Extends from the foramen magnum to the 2nd lumbar vertebra; Protected by vertebral column; Spinal nerves allow movement; If damaged paralysis can occur
• Gray Matter


  center of spinal cord; looks like letter H or a butterfly
• White Matter


  outer layer of spinal cord; contains myelinated fibers
• Reflex


  an involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS; allow a person to react to stimuli more quickly than is possible if conscious thought is involved
• Reflex arc


  is the neuronal pathway by which a reflex occurs and has five basic components.
• Simplest reflex


  stretch reflex
• Stretch Reflex


  occurs when muscles contract in response to a stretching force applied to them.
• Knee-jerk reflex/Patellar reflex


  a classic example of a stretch reflex.
• Withdrawal reflex/Flexor reflex


  is to remove a limb or another body part from a painful stimulus
• Sensory receptors


  are pain receptors, and stimulation of these receptors initiates the reflex.
• Four major regions of the brain


  brainstem

  cerebellum

  diencephalon

  cerebrum
• Medulla Oblongata (Brainstem)


  continuous with spinal cord; regulates heart rate, blood vessel diameter, breathing, swallowing, vomiting, hiccupping, coughing, sneezing, balance
• Midbrain (Brainstem)


  above pons; coordinated eye movement, pupil diameter, turning head toward noise
• Reticular Formation(Brainstem)


  scattered throughout brainstem; regulates cyclical motor function, respiration, walking, chewing, arousing and maintaining consciousness, regulates sleep-wake cycle
• Cerebellum (Brainstem)


  attached to the brainstem by the cerebellar peduncles; means “little brain”; controls balance