The nervous System

• The human nervous system is split into two nervous systems:

  1. Central nervous system (Brain and spinal cord, relay neurones)
  2. Peripheral nervous system (Everything else, sensory and effector neurones)
• The peripheral nervous system is split into two nervous systems

  1. Somatic nervous system (voluntary responses, conscious decisions)
  2. Autonomic nervous system (involuntary responses in smooth muscles and glands)
• Sympathetic nervous system

  • fight or flight responses, with the neurotransmitter noradrenaline
• Parasympathetic system

  • rest and digest responses with neurotransmitter acetylcholine
  • decreases heart rate
  • constricts pupil
• Label ABCD

  A.Cerebrum

  B.Cerebellum

  C.Medulla

  D.Hypothalamus

  
• What is the role of the hypothalamus?

  • controls temperature and water homeostasis
  • controls the release of hormones from the pituitary gland such as LH, FSH, ADH and HGH
• What is the role of the Medulla?

  To control autonomic functions required for survival such as:

  • heart rate
  • Breathing
  • Peristalsis
  • Reflexes (coughing, swallowing, sneezing, vomiting)
• What is the role of the cerebellum?

  • coordinates muscle movement and controls balance
• What os the role of the Cerebrum?

  • responsible for all voluntary functions
  • split into two cerebral hemispheres, separated by the corpus callosum.
• Sensory neurones

  • carry action potentials from receptors to CNS
  • Short axon
  • Long dendron
  • Cell body located in the middle and to the side
• Relay neurones

  • connect sensory neurones to motor neurones
  • found in CNS
  • many short dendrites
  • short axon
• Motor neurone

  • carry action potentials from the CNS to effechord
  • long axon
  • short dendrites
• Label the cross section of a Spinal Cord

  A.Dorsal root ganglion

  B. Dorsal root

  C. White matter

  D. Grey matter

  E. Motor neurone

  G. Ventral root

  
• What is the resting potential of a nerve cell?

  • it is a dynamic equilibrium caused by an imbalance in the concentration of sodium and potassium ions.
  • Resting potential is -70mv
• how is a nerve cell polarised

  • due to sodium potassium pumps
  • for every three sodium ions pumped out, two potassium ions are pumped in.
  • this ensures that there are more positive ions outside than inside, creating a charge difference
• What is an action potential?

  • when a neurone is stimulated, the charge difference between the inside and outside of the membrane is lost, and the membrane is depolarised.
  • If depolarisation exceeds -55mv, an action potential will occur
• What is happening in stage one

  • depolarisation
  • The sodium voltage gated channels channels open
  • Causing sodium ions to quickly diffuse into the cell.
  • Making the inside more positive

  
• What is happening at stage 2?

  • repolarisation
  • Potassium voltage gated channels open
  • Causing potassium ions to diffuse out of the cell
  • Making the inside more negative again

  
• What is happening at stage 3?

  • hyperpolarisation
  • When too many potassium ions have moved out of the neurone

  
• What is happening at stage 4?

  • the refractory period
  • During this period, the voltage gated sodium channels are inactivated, and the inward movement of Na+ ions is prevented, therefore an action potential cannot be generated.
  • We can define this as ‘the time taken to reset the sodium voltage gated channels to their original configuration’

  
• how is the resting membrane potential maintained?

  • active transport of 3 sodium’s out, and 2 potassiums in
  • the membrane is not as permeable to sodium
• how do temperature, myelin sheath and axon diameter affect the speed of nerve impulses?

  • Higher temperature increases the kinetic energy store, meaning sodium and potassium ions diffuse across the membrane more quickly, speeding up depolarisation and repolarisation.
  • A larger axon diameter reduces the resistance to the flow of ions inside the axon, making it easier for electrical impulses to move along.
  • Myelin sheath increases impulse speed by allowing action potentials to jump large distances from node to node in a process called saltatory conduction
• What is happening at 1?

  • the arrival of the action potential causes the depolarisation of the pre synaptic membrane, which increases its permeability to calcium ions

  
• What is happening at 2?

  • voltage gated calcium channels open, causing calcium ions to enter via facilitated diffusion down an electrochemical gradient.
• What is happening at 3 and 4?

  • calcium ions cause vesicles containing neurotransmitters to fuse with the presynaptic membrane and be released into the synaptic cleft by exocytosis.
  • Neurotransmitters diffuse across the synaptic cleft

  
• What is happening at 5 and 6?

  5. Neurotransmitters bind to specific protein receptor sites on the post synaptic neurone.

  6. This causes a conformational change in the receptor protein, causing sodium voltage gated channels to open. Sodium diffuses into the post synaptic neurone down an electrochemical gradient.

  
• What is happening at 8 and 9?

  The neurotransmitter (acetylcholine) is broken down.

  • the enzyme acetylcholinesterase hydrolyses acetylcholine into acetate and choline.
  • these diffuse back into the presynaptic neurone by endocytosis

  
• What is happening at 10?

  • calcium is actively transported out of the presynaptic neurone

  
• What is happening at 11?

  • ATP is used to resynthesise and package the neurotransmitter