Nervous System and Neurotransmission

Nervous System and Neurotransmission

Nervous System and Neurotransmission

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Why do we have a nervous system?

  • Sensory input
    • Monitors changes (stimuli) inside and outside the body
  • Integration
    • Processes and interprets sensory input to decide what should be done
  • Motor output
    • Supplies response by activating muscles or glands
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Central and Peripheral Nervous System

  • Central nervous sytem:
    • Brain: receives and processes sensory information, initiates responses, stores memories, generates thoughts and emotions
    • Spinal cord: conducts signals to and from the brain, controls reflux activities
  • Peripheral nervous system:
    • Sensory neurons (sensory organs to spinal cord)
    • Motor neurons (spinal cord to muscles and glands) with three subsets
      • Somatic neurons
      • Autonomic neurons (sympathetic and parasympathetic neurons)
      • Enteric neurons (control gut activities)
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Divisions of the Nervous System


  • Pyrimidal neurons: largely found in the cerebral cortex, hippocampus, amygdala and corticospinal tract
  • Grey matter = cell bodies, White matter = myelinated axons

Building Blocks of the Nervous System - Glia

  • Oligodendrocytes (CNS)/Schwann cells (PNS)
    • Produce myelin, facilitate transmission
  • Astrocytes
    • Enable homeostasis, physical barrier/connector
  • Microglia
    • Immune cells of the brain
    • Phagocytose dead cells and debris
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The Brain

  • Physiologically, the function of the brain is to exert centralised control over the other organs of the body
  • Approximately 86 billion neurons in 1.4-1.6 kg
  • Each neuron may receive up to 200,000 synapses - integration
  • 2% of body mass
  • Consumes 25% of energy (~500 calories a day)
  • In all other vertebrates it consumes 10%
  • ~95% is used for grey matter
  • Grey matter = cell bodies
  • White matter = myelinated axons
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Blood Supply to the Brain

  • Blood flows to the brain via the internal carotid and vertebral arteries which join (anastomose) to form the Circle of WIllis

The Blood Brain Barrier

  • Endothelial cells line the capillary walls with tight junctions between them
  • Processes from astrocytes form a barrier around blood vesicles
  • Prevents certain molecules entering from the blood stream
  • Specific transporters allow certain molecules to access the brain
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Protecting the Brain

  • The meninges are the membranes covering the brain and spinal cord
  • Composed of dura mater, arachnoid membrane, pia mater
  • Subarachnoid space (between arachnoid membrane and pia mater) is filled with cerebrospinal fluid (CSF)
  • Meningitis = inflammation of meninges

Cerebrospinal Fluid (CSF)

  • Secreted by the choroid plexus
  • Buoyancy - holding up 1.4kg with CSF feels like 25g
  • Protection from injury when jolted or hit
  • Chemical stability and homeostasis: rinses the metabolic waste of the central nervous system through the blood-brain barrier
  • Prevents ischemia (restricted blood supply = lack of oxygen)
  • Exits into the venous sinuses via the arachnoid villi
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Cerebrospinal Fluid (CSF)

Anatomy of the Brain

Brain and Spinal Cord

  • The spinal cord is where information comes into the central nervous system and directions are sent out
  • Messages are then sent to and from the brain
  • The spinal cord is divided into 31 segments, each gives rise to a pair of spinal nerves that supply a particular region of the body

Cranial Nerves


  • Specific blood supply
  • Blood brain barrier
  • Different myelin producing cells
  • Different immune defence - due to blood brain barrier
  • High level of connectivity
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