Nervous system

• Nervous system


  Consists of two divisions: central nervous system (brain and spinal cord) and peripheral nervous system (network of nerves and neural tissues branching out throughout the body)

  
• Neurons


  Nerve cells, the structural and functional units of the nervous system. They conduct impulses that enable the body to interact with its internal and external environments.

  
• Types of neurons


  • Motor neurons
  • Sensory neurons
  • Interneurons

  
• Motor neurons


  • Usually have one axon and several dendrites
  • Axon is covered with an insulating fatty layer called a myelin sheath and transmits signals a long distance
  • Dendrites are short and unsheathed
  • Cause muscle contractions and control secretions from glands and organs, controlling body functions
• Sensory neurons


  • Do not have true dendrites
  • Attached to sensory receptors and transmit impulses to the central nervous system, which then stimulate the interneurons, and then motor neurons

  
• Interneurons


  • Located entirely within the central nervous system
  • Intercept the impulses from the sensory neurons and transmit the signals to the motor neurons
• Nerve fibers in the central nervous system

  No Schwann cells, so damage is not reversible
• Nerve


  A bundle of nerve fibers
• Afferent nerves


  Conduct impulses to the central nervous system
• Efferent nerves


  Conduct impulses to the muscles, organs, and glands
• Schwann cells


  Found only on peripheral nerves, which can regenerate
• Myelin sheath


  A fatty layer of insulation on some nerve fibers
• Axon


  Transmits the message
• Synapses


  Connectors that hook dendrites and axons from one neuron to another
• Central nervous system


  Receives impulses, processes the information, and responds with the appropriate action
• Gray matter


  • Unsheathed nerve fibers in the cortex or surface layer, cannot be regenerated if damaged
• White matter


  • Myelinated nerve fibers in the internal structure
• Meninges


  The three membranes (dura mater, arachnoid, pia mater) that enclose the brain and spinal cord

  
• Cerebrum


  • Governs all sensory and motor activity, including sensory perception, emotions, consciousness, memory, and voluntary movements
  • Divided into left and right hemispheres
  • Surface or cortex is arranged in bulging folds (gyri) and furrows (sulci)
  • Divided into 4 lobes (frontal, parietal, temporal, occipital) that specialize in different functions

  
• Cerebellum


  • Second largest part of the brain
  • Contains nerve fibers that connect it to every part of the central nervous system
  • Coordinates voluntary and involuntary patterns of movements, and adjusts muscles to automatically maintain posture

  
• Diencephalon


  • Consists of the thalamus (relay center for all sensory impulses except olfactory and motor areas of the cortex) and the hypothalamus (regulates behavior, emotional expression, body temperature, metabolic activities, and hormonal secretions)
• Brainstem


  • Consists of the midbrain (controls visual reflexes and sense of hearing), pons (plays a role in regulating visceral control), and medulla oblongata (regulates breathing, swallowing, coughing, sneezing, vomiting, heartbeat, and blood pressure)

  
• Spinal cord

  • 31 segments that correspond to the vertebrae, with left and right pairs of sensory and motor nerves branching out to the peripheral nervous system
  • Shorter than the spinal column, so segments do not perfectly correspond to the vertebrae
• Cerebrospinal fluid


  Colorless fluid produced in the ventricles of the brain, surrounds the brain and spinal cord, cushions them from shocks
• Cranial nerves

  • Olfactory nerve (smell)
  • Optic nerve (vision)
  • Oculomotor nerve (eye and eyelid muscles)
  • Trochlear nerve (eyeball)
  • Trigeminal nerve (face, nose, mouth, forehead, top of head, jaw)
  • Abducens nerve (eyeball)
  • Facial nerve (face and scalp muscles, part of tongue for taste)
  • Auditory/cochlear nerve (hearing and equilibrium)
  • Glossopharyngeal nerve (saliva, swallowing, taste)
  • Vagus nerve (heart, lungs, stomach, intestines)
  • Accessory nerve (head and shoulder movement)
  • Hypoglossal nerve (tongue muscles)
• Sympathetic nervous system


  Responsible for 'flight or fight' responses - increased alertness, metabolic rate, respiration, blood pressure, heart rate, sweating, and decreased digestive and urinary function
• Parasympathetic nervous system


  Counteracts the responses of the sympathetic system, restoring homeostasis