Reflex Lab

• Neurons can be classified by structure or function
• Structural divisions of neurons include:

  • multipolar - have many processes attached to its cell body, all but one (the axon) are dendrites.
  • bipolar - have two processes attached to the cell body, one dendrite and one axon
  • unipolar/pseudo polar - have one very short process which divides into the peripheral and central processes, extending from the cell body; only an axon
• Functional classifications of neurons include:

  • sensory/afferent - receive the signal
  • interneurons - transfer signals between afferent and efferent pathways
  • motor/efferent - carry the impulse to the viscera and/or muscles and glands
• Afferent nerves are typically unipolar; their cell bodies are always found in a ganglion outside the CNS
• Interneurons are multipolar; their cell bodies are always in the CNS
• Efferent neurons are often multipolar; their cell bodies are almost always in the CNS
• Reflexes are involuntary motor responses to stimuli
• Reflexes travel across neural pathways called reflex arcs
• Autonomic/visceral reflexes are mediated through the ANS, and we are usually unaware of them
• Somatic reflexes involve stimulation of skeletal muscles by the somatic division of the nervous system
• Many of our reflexes are learned/acquired, while others are intrinsic
• The receptor is the site of stimulus action; in the skin.
• The sensory neuron transmits afferent impulses to the CNS; dorsal root and spinal ganglion.
• Integration centre - between the sensory and motor areas; integration of monosynaptic centres are made of a simple synapse between an afferent and efferent neuron; polysynaptic reflexes have an integration centre made of at least one interneuron synapsing to form the integration centre; spinal chord.
• Motor neuron - conducts efferent impulses from the integration centre to effector organs; ventral root
• Effector - a muscle fibre or a gland cell that responds to efferent impulses by contracting or secreting
• The two categories of reflexes are somatic and autonomic
• Stretch reflexes - a somatic reflex important for maintaining and adjusting muscle tone for position, balance and movement; initiated by taping a tendon or ligament, which stretches the muscle the tendon is attached to; once stimulated, muscle fibres cause reflex contraction of the stretched muscle or muscles; branches of afferent fibres from the muscle spindles also synapse with interneurons and the agonist muscles (reciprocal inhibition) causing muscles to relax, and preventing them from resisting or reversing the contraction of the stretched muscle
• The five basic components of the reflex arc are:

  1. The receptor
  2. The sensory neuron
  3. The integration centre
  4. The motor neuron
  5. The effector
• Crossed extensor reflex - a somatic reflex; more complex than stretch reflexes; consist of a flexor/withdrawl reflex, followed by extension of the opposite limb
• The reflex pathway of both stretch and crossed-extensor reflexes are mediated only at the spinal cord
• Superficial reflex - a somatic reflex: initiated by stimulation of receptors in the skin and mucosa; depend upon both functional upper-motor pathways and on spinal cord-level reflex arcs
• Somatic cranial reflexes are a type of somatic reflex that can be further divided into:

  • corneal reflex - mediated through the trigeminal nerve; absence of the reflex indicated possible damage to the brain stem
  • gag reflex - tests somatic motor responses of cranial nerves IX and X (glossopharyngeal and vagus nerves)
• All somatic reflexes involve stimulation of skeletal muscles by the somatic nervous system
• Pupillary reflexes - a type of autonomic reflex, there are several subdivision:

  • pupillary light reflexes
  • cilliospinal reflex
  • salivary reflex (use glands as effectors)
• Autonomic/visceral reflexes involve the stimulation of smooth muscles, cardiac muscles, and the glands of the body; they are mediates through the autonomic nervous system
• Autonomic reflex functions include: regulating body functions like digestion, elimination, blood pressure, salivation, and sweating
• Muscle cells are stimulated by motor neurons via nerve impulses; the contact region between an axion of a motor neuron (axon terminal) and a muscle fibre (motor plate) is called a neuromuscular junction
• Sensory receptors respond to stimuli
• Sensory receptors of the general senses are activated by touch, pressure, pain, heat, cold, stretch, vibration, and changes in body position
• Special sense include: vision, hearing, equilibrium, smell, and taste
• Sensory receptors can be classified by the location of the stimulus:

  • exoreceptors
  • introceptors/visceroceptors
  • proprocetors
• Exoreceptors are sensitive to stimuli in the external environment and are found close to the body surface
• Introceptors/visceroceptors respond to stimuli arising within the body; they're found in the internal visceral organs and include stretch receptors, chemoreceptors, and others
• Proprocetors respond to internal stimuli, but are restricted to skeletal muscles, tendons, joints, ligaments, and CT coverings of bones and muscles; they provide information about body movements and position by monitoring the amount of stretch of the structures
• Reflex arc:

  A) integration centre (interneuron)

  B) motor neuron (ventral root)

  C) sensory neuron (dorsal root/spinal ganglion)