Unit 5 Nervous System part 4: Autonomic Nervous System (ANS) & Reflex Arc Pathways

Autonomic Nervous System Subdivison of the peripheral nervous system that regulates involuntary effectors (cardiac and smooth muscle, glands) Controls internal body processes such as: Production of bodily fluids Blood pressure Heart rate Digestion 2 Divisions: Sympathetic & Parasympathetic Act as antagonists

1) Sympathetic Division The major function of the sympathetic division is to serve as an “emergency system” called the “fight-or-flight” response When the body is under stress, or might be threatened, the sympathetic responses increase greatly to prepare our body to “fight” or “flee” Nerve fibers that play a role in the sympathetic response release epinephrine (more commonly known as adrenaline)

Epinephrine may cause the following responses: Increased heart rate Dilation of blood vessels in skeletal and cardiac muscles Constriction of blood vessels in non-essential organs Dilation of respiratory airways Increased sweating Increased blood glucose levels Pupil dilation

This is a normal reaction in times of stress, which enables us to retreat or resist a perceived threat However, chronic exposure to such stress can lead to dysfunction of the ANS

2) Parasympathetic division At rest, the parasympathetic division controls most effectors Sometimes called: “rest and repair” Parasympathetic division slows heart rate, promotes digestion, allows for urination, tears and salivation Maintains homeostasis Relax!

Reflex Arcs: simplest nerve pathway Reflex- automatic subconscious response to changes (stimuli) within or outside the body 2 types: autonomic reflex arc, affecting inner organs somatic reflex arc, affecting muscles Help to maintain homeostasis by controlling involuntary processes like breathing, heart rate, blood pressure, etc. Usually used to describe only involuntary responses (swallowing, sneezing, coughing, vomiting)

There are 5 main components of a reflex arc: 1) Sensor/Receptor- receives a stimulus 2) Sensory Neuron- Sends the sensory information to the CNS 3) Interneuron- conducts/relays nerve impulse from sensory neuron to motor neuron 4) Motor Neuron- carries the motor response to an effector 5) Effector- Muscle or gland that responds to motor neuron stimulation

Sensory neuron: passes “hot” message to CNS 2. 2. 2. 1. 3. 4. 4. 5. 4. Receptor: senses heat Sensory neuron: passes “hot” message to CNS Interneuron: routes message to motor neuron Motor neuron: passes “contract” message to arm muscle Effector: contracts to pull arm away from heat

Today we will test your somatic (voluntary body muscle) reflexes because the somatic reflexes have an important clinical significance Abnormalities may be present in certain diseases Somatic reflexes deal with muscles instead of internal organs

Patellar Reflex- animation (first one)

Biceps Jerk- animation

Achilles Reflex (Ankle Jerk)- animation

Plantar Flexion- animation

Testing the Pupillary Reflex- animation (stop at 55sec) CN: cranial nerve