5.5.8 Mammalian Nervous System

The structural organisation of the nervous system into the central and peripheral nervous systems

• The human nervous system consists of the:
  • Central nervous system (CNS) – the brain and the spinal cord
  • Peripheral nervous system (PNS) – all of the nerves in the body

• The human nervous system allows us to make sense of our surroundings and respond to them, as well as to coordinate and regulate body functions
• Information is sent through the nervous system as nerve impulses – electrical signals that pass along nerve cells known as neurones
• A bundle of neurones is known as a nerve
• Neurones coordinate the activities of sensory receptors (eg. those in the eye), decision-making centres in the central nervous system, and effectors such as muscles and glands

The human nervous system

The functional organisation of the nervous system into the somatic and autonomic nervous systems

• Functionally, the nervous system can be divided into two parts:
  • The somatic nervous system
  • The autonomic nervous system

• The somatic nervous system is required for the voluntary control of body movements
• The somatic nervous system consists of three types of nerves:
  • Sensory nerves - these consist of sensory neurones and carry impulses from sense organs to the CNS
  • Motor nerves - the consist of motor neurones and carry impulses from the CNS to muscles and glands
  • Spinal nerves - found in the spinal cord, these are mixed nerves that consist of both sensory and motor neurones

• The autonomic nervous system is a self-controlling system that is required for involuntary actions and functions, such as heart rate, regulation of blood vessel diameter, and peristalsis in the gut
• The autonomic nervous system can itself be divided into two parts:
  • The sympathetic nervous system, which controls 'flight-or-fight' responses
  • The parasympathetic nervous system, which controls the 'rest and digest' system

The 'flight-or-fight' response controlled by the sympathetic nervous system

• The sympathetic nervous system controls the release of adrenaline, a hormone produced by the adrenal glands
• This hormone is released during a fight-or-flight response
  • For example, when a zebra sees a lion starting to chase it

• It causes the heart rate to increase
• The increase in heart rate is beneficial as it allows for a rapid increase in blood supply to respiring muscles
  • This means the muscles will have more oxygen and glucose for respiration

• It enables high-intensity activities like running away from a predator to be an immediate response