5.1.5 - Plant and Animal responses

• The human nervous system consists of:

  • central nervous system - the brain and spinal cord
  • peripheral nervous system - all nerves in the body
• The human nervous system allows us to:

  • coordinate and regulate body functions
  • respond to changes in the surroundings
• Information is sent through the nervous system as nerve impulses
• Neurones coordinate the activities of:

  • sensory receptors
  • decision making centres in the central nervous system
  • effectors
• Functionally the nervous system can be divided into:

  • somatic
  • autonomic
• The somatic nervous system is required for voluntary control of body movements
• The somatic nervous system consists of three types of nerves:

  • sensory
  • motor
  • spinal
• Sensory nerves consist of sensory neurones and carry impulses from sense organs to the central nervous system
• Motor nerves consist of motor neurones and carry impulses from the central nervous system to effectors
• Spinal nerves consist of sensory and motor neurones, and are found in the spinal cord
• Autonomic nervous system is self-controlling and is required for involuntary actions
• The autonomic nervous system can be divided into:

  • sympathetic nervous system
  • parasympathetic nervous system
• Sympathetic nervous system controls flight or fight response
• Parasympathetic nervous system controls rest and digest system
• Nerves are made of bundles of nerve cells called neurones
• The sympathetic nervous system controls the release of adrenaline causing the heart rate to increase which allows for a rapid increase in blood supply to respiring muscles
• An increased blood supply to muscles means the muscles have more oxygen and glucose for respiration
• The brain is responsible for controlling complex behaviours
• Within the brain different regions carry out different functions:

  • cerebrum
  • hypothalamus
  • pituitary gland
  • cerebellum
  • medulla oblongata
• The cerebrum carries out functions involved with conscious activities including:

  • vision
  • hearing
  • speech
  • thinking
  • memory
• The cerebrum consists of five lobes, divided into two halves (called cerebral hemispheres), joined by the corpus callosum (a band of nerve fibres), with a thin outer layer called the cerebral cortex
• The right cerebral hemisphere controls the left side of the body, the left cerebral hemisphere controls the right side of the body
• The outer layer of the cerebral cortex is called grey matter
• The cerebral cortex consists of cell bodies of neurones:

  • highly folded = increases surface area to contain more neurones
  • more neurones = more connections between neurones
  • more connections = greater ability of the brain to carry out complex behaviour
• Underneath the cerebral cortex is the white matter which is made of myelinated axons of neurones
• The hypothalamus is found above the pituitary gland

  • it monitors blood flowing through it, releases hormones itself or stimulates the pituitary gland to release hormones
• Main functions of the hypothalamus:

  • thermoregulation
  • osmoregulation
  • regulating digestive activity - controls enzyme secretion in the gut, peristalsis and generates feeling of hunger
  • controlling endocrine functions - secretes chemicals that stimulate pituitary gland to secrete hormones
• The pituitary gland secretes a range of hormones that either directly regulate processes or stimulate secretion of further hormones from specific locations
• The pituitary gland is divided into the:

  • anterior
  • posterior - stores and releases hormones produced by hypothalamus e.g. ADH
• The cerebellum is below the cerebrum
• The cerebellum functions subconsciously (all actions controlled are involuntary)

  • controls motor coordination including balance
• The medulla oblongata contains three centres:

  • cardiac - controls heart rate
  • vasomotor - controls contraction of smooth muscle in arteriole walls to control blood pressure
  • respiratory - controls breathing rate
• Reflex actions are involuntary responses to certain stimuli, they are very fast, have a protective purpose or survival value
• Different reflex actions include:

  • withdrawal reflex - pulling body part away from source of pain
  • pupil reflex - constricting iris muscles in response to bright light
• The sequence of a reflex action follows:

  1. stimulus
  2. receptor
  3. coordinator
  4. effector
  5. response
• There are different types of receptors:

  • produce electrical activity in nerve cells in response to stimuli
  • secrete substances in response to stimuli
• In reflex action, nerve impulses sent by receptor cells travel to coordinator in the central nervous system
• In most reflexes the coordinator is the spinal cord
• In a reflex action, from the coordinator the impulse is conducted to the specific effector that will produce an appropriate response
• The knee jerk reflex is used to assess whether the nervous system of a patient is working properly or not