There are two parts of nervous system:

• Central nervous system
• Peripheral nervous system
  

Central nervous system (CNS)

Including:

• Brain
• Spinal Cord
  

CNS is protected by the meninges and floats in the CSF .
Meninges and cerebrospinal fluid protect the CNS against physical damage.

Meninges

3 protective membranes

• Dura mater: thickest & most outer
• Arachnoid mater: middle layer
• Pia mater: inner & most delicate
  • Firmly adheres to the brain surface

Cerebrospinal Fluid

Cerebrospinal Fluid allows:

• The brain to float to help offset the pressure that would be present if the brain were merely sitting on the base of the skull
• reduces shock to the brain and spinal cord during rapid accelerations or decelerations, such as when we fall or are struck on the head

Blood-brain barrier

• It is made up of a collection of cells with unique properties.
• Barrier between the brain’s blood vessels (capillaries) and the cells and other components that make up brain tissue.
• Protect the CNS against disease-causing pathogens and toxins that may be present in our blood.

Peripheral nervous system (PNS)

Includes：

• Nerves: bundles of Axons and glia

• Ganglia: clumps of nerve cell bodies outside of the CNS

• delivers sensory information to the CNS

• carries the motor commands from the CNS to the muscles

• supplies the CNS with a continuous stream of information about both the external environment and the internal environment of the body

• has somatic and autonomic divisions

Somatic nervous system

• sensory neurons that receive information from the skin, muscles, and joints.
• Receptors associated with these cells provide information about muscle and limb position and about touch and pressure at the body surface.
• Receptors transduce different types of physical energy (such as deep pressure or heat) into the electrical signals used by the nervous system.

Autonomic nervous system

• mediates visceral sensation as well as motor control of the viscera, vascular system, and exocrine glands.

Includes：

• #Sympathetic system : participates in the body’s response to stress
• #Parasympathetic system : acts to conserve body resources and restore homeostasis
• Enteric (nervous) system: controls the function of smooth muscle of the gut

The sympathetic system and parasympathetic system operate antagonistically.

Sympathetic system

• sympathetic system uses norepinephrine

Example:

• prepares the body for action (fight or flight) by stimulating the adrenal glands to release adrenaline
• increases heart rate
• diverts blood from the digestive tract to the somatic musculature

Parasympathetic system

• parasympathetic system uses acetylcholine

Example:

• helps the body with functions germane to maintaining the body
• Slows heart rate
• stimulates digestion