nervous sytem

• The central nervous system consists of the brain and spinal cord
• The peripheral nervous system consists of nerves outside the CNS
• The somatic nervous system controls voluntary movements
• The autonomic nervous system controls involuntary actions such as heart rate and digestion
• Main role of PNS:

  • carry sensory neurons to CNS
  • carry motor neurons away from CNS
  • composed of nerve fibres and ganglia
• Afferent division: (sensory)

  • somatic sensory neurons - from skin and muscles
  • visceral sensory neurons - from internal organs
• Efferent division:

  • somatic - controls voluntary movement
  • autonomic - regulates involuntary functions
• Ganglion:

  • group of neuron bodies outside the CNS
• Fight or flight response:

  • rate and force of heart contraction increase → increased blood pressure
  • blood vessels dilate in organs involved and constricts in others
  • lung airway dilates → increased breathing rate and depth
  • increased blood glucose levels and perspiration
  • relase of adrenaline and noradrenaline
• CNS is protected by:

  • bone
  • meninges (membranes)
  • cerebrospinal fluid
• Bone:

  • cranium - protects the brain
  • vertebral canal - protects the spinal cord
• Meninges: (contains three layers)

  • covers surface of the CNS
  • outside (dura mater) - tough and fibrous
  • middle (arachnoid mater) - loose mesh of fibres
  • inner (pia mater) - blood vessels that stick close the the CNS’s surface
• Cerebrospinal fluids: (CSF)

  • found between the middle and inner layers of the meninges
  • acts as a shock absorber
  • takes waste away and nutrients to cells of the CNS
  • the brain floats in CSF
• The control of movement involves:

  • cerebral cortex
  • cerebellum
  • muscles
• Primary motor area:

  • upper motor neurons - carry impulses away from the primary motor area
  • lower motor neurons - carry impulses from spinal cord to muscles
• Cerebellum:

  • cortex sends impulses to the cerebellum
  • receives information from - eye, inner ear, muscle, joint receptors
  • coordinates information to create smooth movement
  • maintains posture and balance
• Corpus callosum:

  • wide band of nerve fibres
  • underneath the cerebrum
  • allows communication between the two hemispheres
• Hypothalamus:

  • lies within the brain
  • maintains homeostasis
• Medulla oblongata:

  • continuation of the spinal cord
  • automatically adjusts body functions
  • cardiac centre - regulates heart rate and force
  • respiratory centre - controls breathing rate and depth
  • vasomotor centre - regulates blood vessel diameter
• Spinal cord:

  • 44cm long in adult
  • enclosed in the vertebral canal
  • grey matter is within the white matter
  • central canal - contains cerebrospinal fluid
  • ascending tracts - carry impulses away from the primary motor area
  • descending tracts - carry impulses from spinal cord to muscles
• Tracts of the brain’s white matter:

  • connects areas of the cortex in the same hemisphere
  • carry impulses between the hemispheres
  • connects the cortex to other brain areas or with the spinal cord
• Areas of the cerebrum:

  • sensory areas - receives and processes nerve impulses
  • motor areas - sends impulses to muscles
  • association areas - interprets stimuli and makes it useful
• Autonomic pathway:

  effectors - heart and involuntary muscles or glands

  general function - maintains homeostasis

  efferent - 2 nerve fibres with a synapse in a ganglion

  neurotransmitters - acetylcholine or noradrenaline
• Somatic pathway:

  effectors - skeletal muscles

  general function - respond to external environment

  efferent - one nerve fibre only

  neurotransmitters - acetylcholine
• Cranial nerves:

  • 12 pairs of nerves
  • arises from the brain
  • contains fibres carrying impulses to and from the brain
  • sensory fibres - impulse to brain (3)
  • motor fibres - impulse from brain (5)
• Spinal nerves:

  • 31 pairs of nerves
  • contains both sensory and motor fibres (mixed)
  • each nerve joined to the spinal cord by two roots
  • ventral root - contains axons of motor neurons with the cell bodies in grey matter
  • dorsal root - contains axons of sensory neurons with the cell bodies in the dorsal root ganglion
• • convolutions (gyrus) - round ridges on the cerebrum’s surface
  • sulci - shallow downfolds
  • fissures - deep downfolds almost separating the hemispheres