Peripheral Nervous System

• The peripheral nervous system (PNS) and its components serve as messengers of impulses and governs our reflexes.
• Peripheral Nervous System - It consists mainly of nerves and scattered ganglia found outside the central nervous system.
• Nerves are bundles of axons encased in connective tissues which serve as the basic units of the nervous system.
• • Ganglia are scattered clusters of neuronal cell bodies found outside the spinal cord.
• • Nerves of the PNS may be classified into two based on their location.
  • cranial nerves (12 pairs)

  spinal nerves  (31 pairs)
• Cranial nerves are rooted from the areas of the skull that connect the brain to different parts of the head.
• • Spinal nerves originate from the spinal cord and extend to the peripheral areas of the body like the limbs. 
• Cranial and spinal nerves are classified based on the kind of impulses they carry and the direction to which they travel.

  • sensory neurons (afferent)
  • motor neurons (efferent)
•  sensory - oculomotor, trochlear, abducens, accessory, hypoglossal (cranial)
• motor - olfactory, vagus, vestibulocochlear, optic, trigeminal, facial, glossopharyngeal (cranial)
• Spinal nerves can be both sensory and motor by function. - TRUE
• • The PNS is functionally divided based on the kind of impulses.
  • Sensory division
  • Motor division
• Motor division

  somatic nervous system

  autonomic nervous system
• • Sensory pathways carry signals to the CNS from sensory receptors in the skin, bones, muscles, and other organs.
• Motor pathways convey information from the CNS to muscles and glands.
• Somatic nervous system (SNS) allows us to consciously, or voluntarily, control our muscles.
• • somatic nervous system - It is also referred to as the voluntary nervous system.
• • Somatic nervous system - It carries signals from the brain to the skeletal muscles.
• • Somatic nervous system (SNS)  - It also controls our reflex actions.
• • A reflex is a rapid, immediate, and involuntary action of the body as a response to a stimulus.
• • Autonomic nervous system (ANS) regulates events in our body that are automatic, or involuntary.
• • Autonomic nervous system - It is also referred to as the involuntary nervous system.
• • Autonomic nervous system - It carries impulses from the brain to involuntary muscles.
• Digestion of food is controlled by the Autonomic Nervous System
• Autonomic nervous system is further grouped into two subdivisions:

  1. sympathetic division
  2. parasympathetic division
• Sympathetic division is referred to as the “fight-or-flight” system.
• • Sympathetic division - It dominates when we are excited or under stress, including emergencies or threatening situations.
• Signs that the sympathetic division is dominating:

  pounding heart

  rapid and deep breathing

  cold and sweaty skin

  prickly scalp

  dilated eye pupils
• • Sympathetic division - Being chased by a dog: to “fight” or “flight”
• • Parasympathetic division is known as the “rest-and-digest” system. 
• Parasympathetic division - It dominates when the body is relaxed or not threatened.
• • Parasympathetic division - It also returns the body to normal conditions after being stressed.
• Signs that the parasympathetic division is dominating:  

  normal heart and respiratory rate

  normal blood pressure

  warm skin

  well-functioning digestive tract 

  constricted eye pupils
• • Parasympathetic division - Resting after a meal: to “rest” and “digest”
• • Sensory pathways of the PNS provide input to the CNS.
• The PNS and CNS create a dynamic balance to maintain homeostasis in our body
• The peripheral nervous system (PNS) is mainly composed of nerves and ganglia found outside the central nervous system.
• Nerves are bundles of axons encased in connective tissues.
• Ganglia are scattered clusters of neuronal cell bodies found outside the spinal cord. 
• Neurons may be classified as sensory neurons and motor neurons.