compendium 8

• Neuron (nerve cell)


  Basic structural and functional unit of the nervous system

  
  

  Receive information, integrate it

  and send appropriate response to

  target

  
  

  highly modified cell, electrically excitable
• Neuroglia


  10-50 times more than neurones

  
  

  Supporting cells

  
  

  6 different types, 4 in CNS and 2 in

  PNS
• Axon


  Nerve fibre
• Nerve


  Bundle of axons (or nerve fibres) and their sheaths (outer covering)
• Sensory receptors


  Separate specialised cells which detect temperature, pain, touch, pressure, light, sound, outer and other stimuli
• Action potential


  Electrical signal
• Effector organ or effector cell

  The organ, tissue or cell in which an effect ot action takes place
• Synapse


  Junction of a neurone with another cell e.g end of a neuron with a muscle cell or another neuron
• Functions of the nervous system

  (1) Receive sensory input

  Internal

  External

  
  

  (2) Integrate information

  
  

  (3) Motor output

  
  

  (4) Maintaining homeostasis

  
  

  (5) Establish and maintain mental activity
• Nervous system- structural divisions

  CNS;

  brain

  spinal cord

  
  

  Peripehral nervous system (PNS)

  • Sensory receptors

  • Cranial nerves - 12 pairs

  • Spinal nerves - 31 pairs

  • Ganglia - collection of neuron cell bodies

  outside CNS

  • Plexuses - extensive network of usually

  axons outside CNS
• PNS functional divisions


  Somatic nervous system

  
  

  autonomic nervous system

  
  

  enteric nervous system
• What are the somatic, autonomic and enteric nervous system functional divisions


  Sensory (afferent)

  
  

  motor (efferent)
• What are the functional divisions of the autonomic nervous system Motor (efferent)


  Sympathetic (fight or flight)

  
  

  parasympathetic (rest and digest)See an expert-written answer!We have an expert-written solution to this problem!
• Compare and contrast the somatic vs autonomic nervous system


  Somatic NS;

  Voluntary and under conscious control

  Action potentials in the motor neurons

  travel from the CNS to skeletal

  muscles

  Single neuron system, one synapse

  Cell bodies are located in the CNS

  Skeletal muscle contracts

  Myelinated axons

  
  

  Autonomic NS

  Involuntary and under subconscious control

  Action potentials in the motor neurons

  travel from the CNS to smooth or cardiac

  muscle, or glands

  Two-neuron system, two synapses

  Cell bodies of first neuron are located in

  the CNS and second in an autonomic

  ganglion

  Target tissues stimulated or inhibited

  Preganglionic are myelinated and

  postganglionic are unmyelinated
• Enteric nervous system


  Nerve plexuses within the wall of the digestive tract
• What does the sensory neurones connect

  Digestive tract and CNS
• What does the ANS motor neurones connect

  CNS to digestive tract
• What are enertic neurones confined by

  Enteric pleuxses
• What are the functions of the enertic nervous system

  Stimulate/inhibit smooth muscle contraction

  
  

  stimulate/inhibit gland secretions

  
  

  detect changes in content of lumen
• Sensory vs motor division


  Sensory division

  Also called afferent division

  Detects external and internal

  environmental stimuli

  Collects input from specialised

  (sensory) receptors

  Transmit the input as electrical

  signals to CNS (nerves)

  Cell body of sensory neuron

  outside CNS (dorsal root

  ganglion)

  
  

  motor division

  Also called efferent division

  Transmits electric signals from CNS

  to effector (e.g., muscle, gland)

  Cell body of motor neuron located

  inside CNS
• Autonomic NS (motor division)


  Sympathetic and parasympathetic
• Sympathetic


  Fight or flight response

  
  

  Thoraco-lumbar region

  
  

  Primes the body to act in threatening

  situations

  
  

  Shorter neuron pathway, quicker response

  
  

  Complementary to action of

  Parasympathetic N.S.

  
  

  E.g., increased heart rate and respiratory

  rate, sweating, pupil dilation
• Parasympathetic


  Rest and digest/feed and breed response

  
  

  Cranio-sacral region

  
  

  Relaxes the body inhibiting high energy

  functions

  
  

  Longer neuron pathway, slower response

  
  

  Complementary to action of sympathetic

  N.S.

  
  

  E.g., stimulates digestion, defaecation, diuresis,

  pupil constriction
• What are the 3 main parts of a neurone

  Neuron cell body (soma)

  
  

  dendrties

  
  

  axon
• Neurone cell body (soma) COMPONENETS

  • Nucleus, nucleolus

  • Nissl bodies (RER)

  • Golgi apparatus

  • Mitochondria

  • Other cell organelles
• Dendrites COMPONENETS


  • Highly branched extensions of cell body

  
  

  • Generate electric current when stimulated

  
  

  • Flow of current from tip of dendrites to cell body
• Axon components


  • Can vary in length - a few mm to a metre

  
  

  • Sometimes branched - collateral axons

  
  

  • Often one arising from axon hillock

  
  

  • Trigger zone - axon hillock + initial segment

  
  

  • Presynaptic terminal/axon terminals/terminal boutons, synaptic

  knobs- axon endings

  
  

  • Myelin sheath

  
  

  • Node of Ranvier
• Describe the flow of an impulse in a neurone

  Unidirectional

  
  

  collects stimuli through dendrites, passes through axons to axon terminals
• Neurone structural classification

  Multipolar

  
  

  bipolar

  
  

  unipolar
• Multipolar


  One cell body

  
  

  Many dendritic

  processes and an axon

  
  

  Motor neurons and

  interneurons

  
• Bipolar


  One cell body and two processes, a dendrite and an axon

  
  

  Specialised sensory neurons

  
  

  Retina of eye, nasal cavity

  
• Unipolar


  One cell body and only one process, axon

  
  

  Dendrites connected to sensory receptors, axon terminals to CNS

  
  

  Sensory neurons

  
• Neurons- functional classification


  Sensory

  
  

  Motor

  
  

  Inter-neuron
• Sensory neuron


  Conduct action

  potential (AP)

  from sensory

  receptors to CNS

  
  

  Afferent neuron
• Motor neuron


  Conduct AP away

  from CNS towards

  muscles or glands

  
  

  Efferent neuron
• Inter-neuron


  Conduct AP within

  CNS from one

  neuron to another
• Neuroglia- CNS


  Astrocytes

  
  

  ependymal cells

  
  

  microglial cells

  
  

  oligodenrocytes
• Astrocytes


  Star shaped

  
  

  Highly branched cytoplasmic processes

  with end feet

  
  

  Scaffold CNS cells and capillaries, control

  blood-brain barrier permeability, form

  glial scar during injury, synaptic support,

  homeostasis in CNS (ions),
• Ependymal cells


  Line the ventricles of brain and central

  canal of spinal cord

  
  

  Ciliated/non-ciliated, simple cuboidal and

  columnar, Cilia to circulate CSF

  
  

  Production and regulation of CSF

  
  

  Protection, hormone transport
• Microglial cells


  Smallest of all glial cells

  
  

  Oval body with many projections

  Become active, mobile & phagocytic in

  response to inflammation

  
  

  Phagocytose foreign substances, necrotic

  tissue, pathogens