Somatic Nervous System And Autonomic Nervous System

• Somatic Nervous system (SNS)

  • Controls the voluntary movement of the

  body’s skeletal muscles

  • Involves both sensory and motor neurons

  (pathways)

  • Responsible for bringing about certain

  involuntary reflexes for example limb
• Autonomic Nervous System(ANS)

  • The Autonomic nervous system regulates the

  internal environment by homeostatic control.

  • Controls the heart, blood vessels, bronchioles

  and alimentary canal.

  • Control is generally involuntary as it is

  automatic, usually without the persons

  conscious thought.
• Autonomic Nervous system

  • Autonomic nervous system nerves come from nerve cells in brain and emerge at various points down the spinal cord to reach the effectors (cardiac muscle, smooth muscle and glands) they stimulate with nerve

  impulses

  • Sympathetic (fight or flight) and parasympathetic (rest and digest) systems operate in opposition to each other i.e. antagonistic
• Autonomic Nervous system

  • It is concerned with maintaining a stable internal environment by playing a part in homeostasis

  • Normally both systems are constantly working in an equal but opposite manner (antagonisitic)

  • Activity in an organ is the result of the two opposing influences

  • So it is normally midway between the extremes of hypo and hyper activity
• Autonomic Nervous system

  Fight or Flight

  • On stimulation the sympathetic system arouses the body in preparation for action and expenditure of energy

  • i.e. “Fight or flight”
• The sympathetic system:

  • Heart rate and blood pressure increase

  • Blood supplies diverted to skeletal muscles to increase supply of oxygen

  • Blood diverted away from gut and skin

  • Slows down peristalsis and production of intestinal secretions.

  • Rate of sweat production increases

  • Producing symptoms:

  – Thudding heart

  – Face pale with fear

  – Clammy sensation in armpits and palms of hands
• The sympathetic system:

  • The hormone adrenalin helps to sustain the

  arousal effect until the emergency is dealt

  with

  • Taking a defensive stand or running away

  both require vast amounts of extra energy

  • This is supplied by the increased blood flow

  to the muscles
• The parasympathetic system:

  • When the excitement is over the parasympathetic system takes over for a

  brief spell calming the body down, returning it to normal

  • Heart rate and blood pressure drop

  • Peristalsis in intestine increases

  • Parasympathetic nerves help body to

  – Conserve resources

  – Store energy
• Complex Neural Pathways

  • Neurones connected in many different ways in CNS

  • Allows many complicated interactions between neurones

  • Allows nervous system to carry out many complex functions
• Diverging Neural Pathways

  • Allows a nerve impulse from a single neurone to be transmitted to several destinations simultaneously

  • Diverging neural pathways influence several neurons at the same time.

  – coordinated temperature control by hypothalamus

  – fine motor control

  – balance
• Converging Neural Pathways

  • Small impulses from several receptors are passed to one sensory neurone

  • Converging neural pathways increase the sensitivity to excitatory or inhibitory signals.

  • The additive effect stimulates this neurone enough to cause it to transmit a nerve impulse

  e.g rods and cones in the eyes
• Rods And Cones

  • In the eye there are 2 kinds of light receptors using different pigments

  – rods

  – cones

  • Cones detect colour but only react to strong light

  • Rods react to dim light and do not detect colour
• Converging Neural Pathways

  • Rods react to dim light but:

  – they only produce a small response

  • Efficiency of rods is increased by connecting several to the same neurone

  – A nerve impulse from one rod would not be enough to stimulate neurone
• Reverberating pathways

  • Reverberating pathway neurones later in the pathway link with earlier ones

  sending the impulse back through the pathway.