Neuroanatomy Physiology Part 2

Introduction to Neurophysiology

  • Importance of SI sessions and open lab sessions for exam preparation.

Synapses

  • Definition: A synapse is the junction between two neurons, allowing communication between them. The term synapse means "to clasp" or "to join".

  • Types of synapses: Electrical and Chemical.

    • Electrical synapses are fast and general, primarily used in cardiac and smooth muscle, enabling whole organ contractions.

    • Chemical synapses provide slower, controlled, and specific communication, mainly in skeletal muscle.

Mechanisms of Signal Transmission

  • Neurotransmitters: Chemical messengers that transmit signals between neurons, similar to hormones.

    • Essential for synaptic communication, released from the presynaptic neuron to receptors on the postsynaptic neuron.

  • Gap junctions: Facilitate rapid passage of information in electrical synapses by creating physical pathways.

Types of Synapses

  • Axodendritic synapse: Connection between the axon of one neuron and the dendrite of another.

  • Axosomatic synapse: Connection between an axon and the cell body of another neuron.

  • Axo-axonic synapse: Connections between multiple axons and a single postsynaptic neuron, allowing for complex communication.

Electrical vs. Chemical Synapses

  • Electrical synapses:

    • Used in quick-burst actions like heart contractions.

    • Less specific, facilitating whole organ responses.

  • Chemical synapses:

    • Utilize neurotransmitters released from synaptic vesicles, which need to diffuse across the synaptic cleft.

    • More specific in action, allowing for differing strengths of muscle contractions.

    • Longer transmission times due to the need to interact with receptor sites.

Information Processing in the Nervous System

  • Information flow:

    • Incoming signals through dendrites

    • Integration at the cell body

    • Transmission via the axon to the next neuron or effector organ.

  • In a reflex arc:

    • Sensory neuron → interneuron → motor neuron -> effector organ.

  • Complexity of neural pathways, often involving multiple neurons for reflex actions.

Neurotransmitters

  • Key neurotransmitters discussed:

    • Acetylcholine (ACh): Critical for muscle contraction, especially in skeletal muscles.

    • Norepinephrine (NE): Plays a significant role in the autonomic nervous system and responds to stress.

  • Variability in neurotransmitter actions facilitates different physiological responses.

Autonomic Nervous System (ANS)

  • Sympathetic Division: "Fight or flight" response.

    • Prepares the body for rapid actions in stressful situations. Example actions:

      • Dilate pupils and bronchioles for increased perception and air intake.

      • Increase heart rate and blood glucose concentration for energy availability.

      • Decrease digestive activity and non-essential functions (e.g., salivation).

  • Parasympathetic Division: "Rest and digest" response.

    • Sustains long-term bodily functions, facilitates recovery.

    • Key actions:

      • Constrict pupils and bronchioles.

      • Decrease heart rate and blood glucose levels.

      • Increase digestive activity and glandular secretions.

Comparison of Sympathetic and Parasympathetic Responses

  • Sympathetic:

    • Rapid energy mobilization and readiness for immediate action.

    • Survival-oriented physiological changes.

  • Parasympathetic:

    • Restoration and energy storage post-stress.

    • Maintenance of normal bodily functions in a relaxed state.

Closing Thoughts

  • Recap on the importance of understanding synapses and neurotransmitters in the context of neurophysiology.

  • Critical distinctions between synapse types, their uses, and their physiological effects during different states of the autonomic nervous system.