Nervous System 1

• Nervous system


  A structure that enables us to react/respond to a situation/stimulus
• The nervous system typically has the following order: single-celled organisms like amoebas or individual mammalian cell
• Response to stimuli in single cells and single-celled organisms


  Achieved by membrane receptors
• Single celled organisms such as protists and bacteria can detect changes in their environment and respond to stimuli using receptor proteins embedded in their cells membranes
• Individual cells respond via receptors and signalling cascades but the responses of individual cells may accumulate - these are then converted to effector organs whose actions are coordinated by the nervous system to mediate a response
• Hippocampal Trisynaptic Circuit


  The DG (Dentate Gyrus), CA3 (Cornu Ammonis 3) and CA1 comprise the regions with neurons in layers and make a circular loop receiving information from layer 2 of the Entorhinal Cortex and returning it to the EC in layer 5
• Along this path from EC to DG (via PP), to CA3 (vie MF), to CA1 (via SC), back to EV the signal is changed and is 'tasted' by 1000s of neurons
• The hippocampus and cortex play a big role in learning, forming and retrieving memories
• Neural plasticity


  The ability for the brain or neuron's to adjust in response to a new situation or environment. Changes can strengthen or weaken signalling at a synapse
• Short-term Memory


  Accessed via the hippocampus
• The hippocampus also plays a role in forming long-term memory which is stored in the cerebral cortex not the hippocampus. Some consolidation of memory (short-term to long-term) is thought to occur during sleep
• Nerve Nets


  • A series of interconnected nerve cells
  • There is little or no integration or processing of signals
• Cephalisation


  • The cluster of sensory organs at the front end of the body
• Central Nervous System (CNS)

  • Consists of brain and longitudinal nerve cords
• Ganglia


  • Segmentally arranged clusters of neurons
• Ladder system


  • The development of paired longitudinal nerve cords and cephalisation
• Ventral nerve cord


  • Developed from the fusion the two longitudinal cord in ladder systems
• Centralised Brain


  • With many sense organs
• Insects have receptors for taste and smell on antennae and legs - antennae can detect odors or touch objects
• Insects also include simple eyes and compound eyes
• The nervous system organisation of a being correlates with lifestyle. Sessile molluscs (like calms and chitons) have simple systems, whereas more complex molluscs ( like octopuses and squids) have more sophisticated systems
• In squid, more complex behaviours are served by collections of neurons in specialised ganglia that process and integrate information
• Vertebrate Nervous System Organisation

  • The CNS is composed of the brain and spinal cord
  • The peripheral nervous system (PNS) is composed of nerves and ganglia
• The spinal cord conveys information form and to the brain but also produces reflexes independently of the brain
• Invertebrates usually have a ventral never cord while veretebrates usually have a ventral nerve cord while vertebrates have a dorsal spinal cord
• The spinal cord and brain develop from the embryonic nerve cord - this nerve cord gives rise to the central canal and ventricles of the brain
• Central Nervous System (CNS)


  • Most of the cells of the Nervous System are found in the brain and spinal cord
• Peripheral Nervous System (PNS)


  • Extends from the CNS and radiates through the rest of the body
  • All signals taken by the PNS is transported to the spinal cord first before being transported to the brain
• Afferent neurons


  • Transmit information to the CNS
• Efferent neurons


  • Transmit information away from the CNS
• Motor system


  • Carries signals to skeletal muscles and is voluntary (we control it)
• Autonomic nervous system


  • Regulates smooth and cardiac muscles and is generally involuntary
• Sympathetic division


  • Regulates arousal and energy generation (fight or flight)
• Parasympathetic division


  • Has antagonistic effects on tart organs and promotes calming and return to 'rest and digest' functions
• Enteric division


  • Controls activity of the digestive tract, pancreas, and gallbladder
• Parasympathetic System


  • The cell body of the preganglionic neurons is located within the CNS. They extend a long axon to the postganlionic neuron located close to the target organ. Acetylcholine is the neurotransmitter
• Sympathetic System


  • The preganglionic neuron is shorter originating within the spinal cord and synapse with the postganglionic neuron extending a long axon to the target organ. Catecholamines (epinephrine & norepinephrine) are the neurotransmitters
• The central canal of the spinal cord and ventricles of the brain are hallow and filled with cerebrospinal fluid
• Gray Matter


  Consists of neuron cell bodies, dendrites and unmyelinated axons
• White Matter


  Consists of bundles of myelinated axons