Nervous 5

• Spinal cord

  • found within spinal cavity
  • protected by bone, meninges, CSF and adipose tissue (back fat)
  • presents a ventral and dorsal nerve roots
  • oval shaped with 2 grooves: anterior median fissure and posterior median sulcus
• Nerve: bundle of hundreds to thousands of axons and associated connective tissue. It is found outside the CNS. Each nerve follows a defined path and serves a specific region of the body
• Ganglion: group of neuronal cell bodies found outside CNS
• Each nerve fiber that stems out of the spinal cord has a dorsal and ventral nerve root
• Dorsal nerve root carries informations from receptors into the CNS and the cell bodies are found in the ganglion
• Ventral nerve root carries motor information out of the spinal cord and the cell bodies are found in the grey matter of the spinal cord
• The spinal cord extends from the base of the skull down to the second lumbar vertebra in the vertebral column
• Spinal nerves are both sensory and motor neurons full of axons. There are 2 nerves for the left and right side
• Posterior root ganglions contain cell bodies of sensory neurons
• Posterior root contain sensory neuron axons
• Anterior root contain motor neuron axons
• Anterior horns of gray matter contain motor neuron cell bodies
• Posterior horns of gray matter contain cell bodies and axons of interneurons
• 2 main functions of the spinal cord

  • white matter: communication highway for sensory impulses traveling toward the brain and motor impulse travel from the brain to skeletal muscle
  • grey matter: receives and integrates incoming and outgoing information (site for integration of refexes)
• Reflex: fast, involuntary sequence of actions that occur in response to a particular stimulus
• Some reflexes are inborn like pulling your hand away from a hot surface and others are learned or acquired like driving skills
• The spinal reflex is when the integration takes place in the spinal cord grey matter VS cranial reflex is when the integration takes place in the brain stem
• Reflex arc: pathway followed by nerve impulses from neuron to neuron that produce a reflex
• 5 main components to every reflex arc

  • sensory receptor
  • sensory neuron
  • integrating center
  • motor neuron
  • effector
• Sensory receptor are dendrites of the sensory neuron that respond to a specific type of stimulus
• Sensory neuron: AP conducts from sensory receotir along axon of sensory neuron to posterior horn of gray matter (axon branches also relay message to the brain)
• Integrating center: one or more regions of gray matter where synapse occurs between sensory and motor neuron, possibly interneurons in complex reflexes
• Motor neuron: AP trigerred by integrating center leaves spinal cord from anterior horn of gray matter travels down anterior root to spinal nerve and sends signal to the responding part of the body
• Effector: part of the body that responds and results in action. Could be a muscle or gland
• Somatic reflex: skeletal muscle effector (eg: patellar reflex) VS autonomic reflex: smooth muscle, cardiac muscle or gland (swallowing, urinating)
• Patellar reflex: tendon and muscles are stretched, stimulating muscle spindles and initiating conduction over a two neuron reflex arc
• Other reflexes

  • ankle jerk
  • plantar reflex
  • babinski sign
• There are 31 pairs of spinal nerves. Their numbers are according to the level of the vertebral column at which they emerge
• Dermatomes

  • skin area supplied by a specific spinal nerve
  • helps explain specific skin sensation (chicken pox)
  • identify site of specific spinal cord affected areas
• Myotomes

  • skeletal muscle that receives motor axons from a specific spinal nerve
  • identify specific spinal cord affected areas
• There are 12 pairs of cranial nerves that connect mainly on the brainstem. They pass through small foramina in the cranial cavity of the skull and extend to or from their destination
• Cranial nerves are bundle of axons that can be sensory, motor or mixed
• Examples of cranial nerves

  • olfactory
  • optic
  • oculomotor
  • facial
  • vestibulocochlear
  • vagus (heart)
• Olfactory nerves carry information about sense of smell
• Optic nerve carry visual information from the eyes to the brain
• Oculomotor innervate muscles of the eye to regulate the amount of light
• Vestibulocochlear nerve has information from the semicircular canals and organ of Corti in the inner ear. Damage of the nerve results in deafness
• Facial nerves include motor fibers, arise from the pons, extend to the muscles of the face and scalp and fibers extending to the salivary glands and from the taste buds to the medulla oblongata
• PNS is made up of everything outside the CNS (cranial nerves, spinal nerves, sensory receptors)
• PNS acts as the communication lines between the body and the CNS. It is divided into the somatic nervous system, autonomic nervous system and enteric nervous system