Nervous System

The nervous system is the part of the body that coordinates voluntary and involuntary actions and transmits signals to and from different parts of its body. It detects and responds to changes inside and outside the body. Along with the endocrine system, the nervous system controls the vital functions of the body and maintains homeostasis. The response of the nervous system is much faster than that of the endocrine system.


The nervous system consists of:

  • Brain
  • Spinal cord
  • Peripheral nerves

The nervous system can be divided into:

  • The central nervous system (CNS): Consisting of brain and spinal cord
  • The peripheral nervous system (PNS): Consisting all the nerves outside brain and spinal cord

The central nervous system receives sensory information through afferent nerves. It then processes this information and responds appropriately by sending impulses through motor nerves to the effector organs. For example, responses to changes in the internal environment regulate important functions such as respiration and blood pressure. Similarly, responses to changes in the external environment result in voluntary actions such as change in posture or other activities.

The peripheral nervous system (PNS) consists of paired cranial and sacral nerves. Some of these nerves are sensory (afferent) i.e. transmit impulses to the CNS. Some are motor nerves (efferent) i.e. transmit impulses from the CNS. Some others are mixed.

The PNS can be divided into two functional parts:

  • Sensory division
  • Motor division

The motor division has two parts:

  • Somatic nervous system: Controls voluntary movements of skeletal muscles
  • Autonomic nervous system: Controls involuntary functions such as heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal

The autonomic nervous system has two divisions:

  • Sympathetic: Stimulates the body’s “fight-or-flight” response
  • Parasympathetic: Stimulates “rest-and-digest” or “feed and breed” activities that occur when the body is at rest

Topics in this Section

  • Neurons
    • Properties of neurons
    • Cell bodies
    • Axons and dendrites
    • The nerve impulse (action potential)
    • Types of nerves
    • The synapse and neurotransmitters
  • Central nervous system
    • Neuroglia
    • Membranes covering the brain and spinal cord (the meninges)
    • Ventricles of the brain and the cerebrospinal fluid
  • Brain
    • Blood supply to the brain
    • Cerebrum
    • Brain stem
    • Cerebellum
  • Spinal cord
    • Grey matter
    • White matter
  • Peripheral nervous system
    • Spinal nerves
    • Thoracic nerves
    • Cranial nerves
  • Autonomic nervous system
    • Sympathetic nervous system
    • Parasympathetic nervous system
    • Functions of the autonomic nervous system
      • Effects of autonomic stimulation
      • Afferent impulses from viscera
  • Response of nervous tissue to injury
    • Neuron damage
    • Neuron regeneration
    • Neuroglia damage
    • Effects of poisons on the central nervous system
  • Disorders of the brain
    • Increased intracranial pressure
      • Effects of increased ICP
      • Cerebral edema
      • Hydrocephalus
    • Head injuries
      • Blow to the head
      • Acceleration-deceleration injuries
      • Complications of head injury
    • Circulatory disturbances affecting the brain
      • Cerebral hypoxia
      • Stroke (cerebrovascular disease)
    • Dementia
    • Parkinson’s disease
  • Infections of the central nervous system
    • Pyogenic infection
    • Viral infections
    • Creutzfeldt-Jakob disease
    • Myalgic encephalitis (ME)
  • Demyelinating diseases
    • Multiple (disseminated) sclerosis (MS)
    • Acute disseminating encephalomyelitis
  • Phenylketonuria
  • Diseases of the spinal cord
    • Motor neurons
    • Sensory neurons
    • Mixed motor and sensory conditions
  • Diseases of peripheral nerves
    • Neuropathies
    • Neuritis
  • Developmental abnormalities of the nervous system
    • Spina bifida
    • Hydrocephalus
  • Tumors of the nervous system
Cells and Tissues of the Nervous System