Muscles undergo increased demand, leading to a rise in heart rate.
Example of autonomic response: heart rate increases to meet oxygen needs.
Increased oxygen is crucial under threat situations to support bodily functions.
Eye Muscles and Pupil Dilation
Different muscles in the eye are involved in pupil dilation.
Radial muscles: Allow pupil dilation to let in more light during dangerous situations.
Circular muscles: Lead to pupil constriction.
Knowledge of specific muscles may not be necessary: focus on the concept of dilation allowing more light entry.
Blood Flow and Digestive System During Stress
In threat situations, blood flow shifts from the digestive system to the muscles, enhancing physical readiness.
Example of blood flow diversion: blood vessels in lungs expand to increase airflow, while blood to intestines reduces.
Sympathetic vs Parasympathetic Responses
These systems are antagonistic:
Sympathetic: Activates during threats, increasing heart rate and blood flow to muscles.
Parasympathetic: Activates post-threat to restore body to calm state by decreasing heart rate and increasing digestion (vasodilation in intestines).
Autonomic Reflexes
Autonomic reflexes operate without conscious control; include heart rate regulation and digestion.
Example: Some individuals can control heart rate consciously.
Mind over Matter: Managing perceived threats can help control some autonomic functions.
Structure of Autonomic Reflexes
The sensory pathway for autonomic and somatic systems almost identical, featuring:
Receptor
Sensory neuron to the central nervous system
The message to the effector differs:
Autonomic: Involves two neurons with ganglia.
Somatic: Involves a single continuous neuron.
Definition of Ganglion
A ganglion functions as a junction box in electricity, connecting neurons in the autonomic nervous system for widespread signaling.
Sympathetic Nervous System
Definition: Subdivision of the autonomic nervous system controlling processes such as digestion, heart rate, and respiration; often related to energy expenditure and fight or flight responses.
Origin of Nerves: Arise from thoracic and lumbar spinal cord. Typically, they do not travel directly to targets but synapse at sympathetic ganglia.
Ganglia Types:
Sympathetic chain ganglia: Close to the spinal cord.
Prevertible ganglia: Closer to target organs.
Neurons:
Preganglionic neurons: Extend from spinal cord to ganglia; release acetylcholine.
Postganglionic neurons: Extend from ganglia to target organs; mainly release norepinephrine.
Parasympathetic Nervous System
Definition: Also a subdivision of the autonomic nervous system, it is focused on energy conservation and activities such as digestion; sometimes termed "rest and digest."
Origin of Nerves: Arise from brainstem and sacral spinal cord; synapse at ganglia near or within the target organs.
Neurons:
Like sympathetic system:
Preganglionic neurons: Release acetylcholine.
Postganglionic neurons: Also primarily release acetylcholine, providing innervation to the body.
Functional Differences between Somatic and Autonomic Systems
Somatic Reflexes:
Voluntary.
Fast, one long neuron to effector.
Autonomic Reflexes:
Involuntary.
Slower with two neurons and ganglia for more sustained responses.
Neurotransmitter Activity
Somatic:
Neurotransmitter: Acetylcholine released from the single neuron to the muscle.
Autonomic:
Sympathetic Nervous System: Pre-ganglionic releases acetylcholine; post-ganglionic typically releases norepinephrine.
Parasympathetic Nervous System: Both pre-ganglionic and post-ganglionic neurons release acetylcholine.
Receptor Types and Functions
Sympathetic Nervous System Receptors:
Postganglionic target receptors: Called adrenal receptors (alpha and beta forms for norepinephrine).
Parasympathetic Nervous System Receptors:
Target cell receptors are termed muscarinic for acetylcholine.
Receptor names origin: Derived from chemicals used in discovery.
Nicotinic receptors: Bind acetylcholine.
Muscarinic receptors: Bind acetylcholine for parasympathetic activity.
Duration of Neurotransmitter Effects
Acetylcholine in autonomic responses is quickly broken down by enzymes in the synaptic cleft, leading to rapid cessation of receptor activation.
Norepinephrine, associated with sympathetic responses, takes longer to clear from the synapse due to reuptake mechanisms and enzymatic breakdown, resulting in prolonged effects.
Hormonal Influence in Sympathetic Responses
During fight or flight, norepinephrine release is complemented by adrenaline from adrenal glands, enhancing sympathetic responses.
Differences in Receptor Functions
Vasodilation vs Constriction:
Receptors allow for diverse responses depending on the organ involved.
Example: In fight or flight, blood flow to skeletal muscles increases, while it decreases to the digestive organs.
Alpha receptors: Cause vasoconstriction in intestines to redirect blood.
Beta receptors: Cause dilation in heart tissues to increase oxygen supply.
Summary Tasks
Create visual representations (mind maps, diagrams, tables) to summarize somatic vs autonomic pathways and neurotransmitter differences.
Focus on understanding the primary neurotransmitters, their receptors, and their implications for bodily responses during various states (rest/digest vs. fight/flight).