Physiology · MU Sofia

80. Reflex activity of the nervous system. Organization of neurons in neural networks. Inhibition in the central nervous system

Explains reflexes as predictable involuntary responses and walks through the reflex arc, then sorts reflexes into innate monosynaptic and polysynaptic types, reciprocal inhibition, and acquired conditioned reflexes with examples such as the biceps tendon test and Pavlov's dogs. Goes on to cover convergence, divergence, parallel and feedback circuits, spatial, temporal and population coding, and closes with postsynaptic, presynaptic, lateral, feedforward and feedback inhibition, followed by recap questions.

Inside: 5 sections · 16 labelled pictures · 20 flashcards · 7 min

Topic 79 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 5 sections, about 934 words (7 min of reading), with 20 flashcards.

In this note

  1. Reflex activity of the nervous system. Organization of neurons in neural networks. Inhibition in the central nervous system.
  2. Organization of Neurons in Neural Networks
  3. Encoding Information in Neural Networks
  4. Inhibition in the Central Nervous System
  5. Recap Questions

Reflex activity of the nervous system. Organization of neurons in neural networks. Inhibition in the central nervous system.

A reflex is a predictable, involuntary response to a specific stimulus. Reflexes occur without conscious thought and are essential for maintaining posture, protecting from harm, and regulating bodily functions. They involve a pathway called a reflex arc, which typically includes:

  1. 1. Sensory Receptor: Detects the stimulus.
  2. 2. Sensory (Afferent) Neuron: Transmits information from the receptor to the CNS. The cell body of this neuron is located in the dorsal root or cranial nerve ganglia.
  3. 3. Interneurons (optional): Located within the CNS, interneurons process and modify the sensory information.
  4. 4. Motor (Efferent) Neuron: Carries signals from the CNS to the effector organ.
  5. 5. Effector Organ: Muscle or gland that produces the response.

Types of Reflexes

  1. (1) Based on the mechanism of formation:-
  • Innate (Unconditioned) Reflexes: Genetically determined, present at birth.
  • Monosynaptic Reflexes: Only one synapse between sensory and motor neurons (e.g., the stretch reflex). For e.g. biceps reflex test is when a tendon hammer is used on the biceps brachii tendon in the cubital fossa. It activates stretch receptors sending a signal to the dorsal horn, which in monosynaptic reflex, is directly connected to the anterior horn alfa motoneuron and the biceps contracts jerking the forearm.
  • Polysynaptic Reflexes: Involve multiple synapses and interneurons (e.g., the flexor-withdrawal reflex).
  • For e.g. when you touch a hot object and the pain receptors are activated, they send a signal to the dorsal horn and there the signal is passed to an interneuron, then the interneuron synapses with the anterior horn alfa motor neuron and an efferent signal is sent to the flexor muscles to flex and remove the hand.
  • Reciprocal inhibition: is the coordinated inhibition of a muscle(s) that is antagonist to the muscle(s) that is stimulated to contract. For .e.g. if biceps brachii is stimulated to contract then triceps brachii is inhibited so it doesn’t interrupt the flexion. The reflexes are via spinal reflex pathways
  • Acquired (Conditioned) Reflexes: Learned through experience (e.g., Pavlov's dog).

Its when we are conditioned to respond or anticipate something based on certain stimulus. Pavlovs dogs are a very famous e.g. of this. The associative learning mechanism causes a reflex formation which will react when stimulated, but it is learned and not like the innate spinal reflexes.

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