Nervous co-ordination in humans

• Cerebrum is to control and coordinate the body's activities, and is divided into two hemispheres
• Cerebellum coordinates muscle movements and balance, and is responsible for learning and memory
• medulla acts as a pacemaker and controls heart rate and blood pressure
• Nerve impulse transmission across synapse

  1. presynaptic neurone and postsynaptic neurone are not in direct contact , they are separated by synaptic cleft
  2. Upon the arrival of the nerve impulses to the swollen end of axon, the vesicles are stimulated to release the neurotransmitters into the synapse
  3. The neurotransmitters diffuse across the synaptic cleft of the synapse
  4. They bind to the receptor sites on the membrane of the next neurone to generate a nerve impulse to continue the transmission
• Explain why people with mitochondrial complex deficiency may have muscle weakness and difficulty with nervous coordination of movement

  • people with mitochondrial complex deficiency disease can produce no ATP molecules which are the major source of energy for muscular contraction
  • nervous transmission across synapse is energy-requiring
  • It is because energy is required to synthesize the neurotransmitters
• • When a nerve impulse arrives at the end of the presynaptic neurone, neurotransmitter are released from the synaptic vesicles
  • The neurotransmitters diffuse across the synaptic cleft
  • then they combine with the receptor sites on the postsynaptic neurone
  • this triggers a nerve impulse in the postsynaptic neurone and thus newly generated nerve impulse is passed to the axon of the postsynaptic neurone electrically
• • Since one side of drug B is structurally similar as that of neurotransmitter A
  • by binding to the receptor sites of neurotransmitter A on the presynaptic neurone, drug B inhibits the reuptake of neurotransmitter A by the presynaptic neurone from the synaptic cleft
  • more neurotransmitter A would stay in the synaptic cleft and have a higher chance to bind to the receptor sites on the postsynaptic neurone
• Reflex arc:

  Receptor>sensory neuron>interneuron>motor neuron>effector
• The nerve impulses can still be transmitted to the sensory area of the cerebrum through the interneuron to produce sensation
• • The nerve impulse cannot be transmitted to the body part below the injured region through the spinal cord
  • therefore the effector below the injured area cannot receive the nerve impulses from the CNS, and produce responses/ the body parts below the injured area will become paralysed
• Dendron: transmits nerve impulses to the body cell


  Axon: transmits nerve impulses away from the body cell
• Most nerve fibres are surrounded by a fat material called the myelin sheath


  To protect the nerve fibres

  To insulate the nerve fibres and prevent loss of nerve impulses to the surroundings

  To speed up the transmission of nerve impulses
• Adjacent neurones communicate through junctions called synapses


  To ensure that nerve impulses only transmit in one direction
• Sensory neurone: from receptors to the CNS

  long dendron, short axon

  cell body lying outside the CNS

  Motor neurone: from the CNS to effectors

  very short dendrons, long axon

  cell body lying inside the CNS

  Interneurone: within the CNS, from sensory neurones to motor neurones or between interneurones

  short dendron, short axon

  cell body lying inside the CNS

  
• Two functions of mitochondria in the transmission of nerve impulses


  To provide energy for the synthesis of neurotransmitter/ formation of vesicles/ release of neurotransmitter from the vesicles
• • At a synapse, signals are transmitted from the axon of one neurone to the dendron or cell body of the next neurone
  • synaptic vesicles containing neurotransmitter are present only in the ending of axons
• Cerebrum: highly folded surface

  outer grey matter, inner white matter


  Site of memory and thinking

  controls voluntary actions
• Medulla oblongata: outer white matter, inner grey matter


  Controls involuntary actions, e.g. heart beat and breathing

  acts as the reflex centre for many reflex actions in the head
• • The outer layer of the cerebrum is called the cerebral cortex. It is made up of grey matter, which consists mainly of the cell bodies of the neurones.
  • beneath the cerebral cortex is the white matter, which consists of myelinated nerve fibres.
• Functions of Spinal cord:

  • It relays nerve impulses between the brain and other parts of the body
  • It acts as a reflex centre for reflex actions involving the trunk and limbs

  
• Reflex actions that involve the medulla oblongata include sneezing, coughing, saliva secretion, swallowing


  Reflex actions that involve the spinal cord includes the withdrawal reflex and the knee jerk reflex
• Withdrawal reflex- reflex arc with an interneurone:

  1. when the hand touches a sharp object, pain receptors in the skin are stimulated and they generate nerve impulses
  2. nerve impulses are transmitted along the sensory neurone to the spinal cord
  3. nerve impulses are transmitted along the interneurone and the motor neurone to the arm muscle
  4. the arm muscle contracts to withdraw the hand

  
• If the motor neurone is damaged, the person can still feel the pain as the nerve impulses can still be transmitted to the sensory area of the cerebrum through the interneurone to produce sensation
• Nervous pathway when withdrawing one’s hand upon touching a sharp object:

  Pain receptors in the skin>sensory neurone>interneurone in the spinal cord>motor neurone>muscle of the forearm
• Nervous pathway when running out of the building upon hearing the fire alarm:

  Sensory cells in the cochlea>sensory neurone in the auditory nerve>sensory area of cerebrum>association area of cerebrum> motor area of cerebrum> spinal cord> motor neurone> muscle of the leg
• A voluntary action can be initiated by the cerebrum directly and may not involve any stimuli
• We are conscious of some reflex actions, e.g. the withdrawal reflex. The reflex does not involve the brain, but nerve impulses are transmitted to the brain via another nervous pathway so that we are aware of it.
• How to synapses ensure that nerve impulses are transmitted in one direction only?

  Only synaptic knobs can secrete neurotransmitters and only dendrons possess the receptor sites for binding with neurotransmitters
• Explain why the pancreas is considered both an endocrine gland and an exocrine gland?

  As an endocrine gland, the pancreas secretes two hormones, insulin and glucagon, for regulating blood glucose. It is also an exocrine gland of the digestive system. It secretes enzymes through the pancreatic duct into the small intestine.
• The transmission of nerve impulses across synapses involves neurotransmitters which are chemical messengers.
• If the sensory neurone is cut, the person would not feel the pain and no withdrawal reflex would be evoked.