Unit 5 - Intro & Autonomic NS

Body cavities - thoracic

• Thoracic cavity:

  • Plural cavities (2) → each surrounds a lung

  • Mediastinum → surrounds heart & other structures

    • Pericardial cavity → central portion of thoracic within the mediastinum that houses ONLY the heart

Body cavities - abdominopelvic

(Diaphragm splits thoracic and abdominopelvic cavities)

• Abdominopelvic cavity

  • Abdominal cavity → stomach, spleen, liver, gallbladder, small intestine, most of large intestine

  • Pelvic cavity → portions of large intestine, urinary bladder, internal reproductive organs

Ventral body cavity - chart

Membranes in Ventral Body Cavity

• Viscera (organs) & walls of ventral body cavity are lined in a serous membrane

  • Parietal layer - lines cavity walls

  • Visceral layer - adheres to surface of organ

• Serous fluid is b/w the 2 layers to reduce friction

Named Serous Membranes

• Parietal/visceral pleura - pleural cavity & lung surface

• Parietal/visceral pericardium - pericardial cavity & heart surface

• Parietal/visceral peritoneum - abdominopelvic cavity & viscera inside it

Membranes in Ventral Body Cavity - representation

Membranes in Ventral Body Cavity - heart visual

Organization of NS - chart

Autonomic

• Motor: smooth muscle, cardiac muscle, glands

• Sensory: from organs

• Divides into…

  • Sympathetic - fight or flight

  • Parasympathetic - rest & digest

Somatic NS

• Conscious control

• Effector: skeletal muscle

• Efferent pathway: one neuron system

• Neurotransmitter & response of target organ: acetylcholine (excitatory)

Autonomic NS

• Automatic control

• Effector: cardiac & smooth muscle & glands

• Efferent pathway: 2 neuron system (presynaptic & postsynaptic)

• Neurotransmitter & response of target organ:

  • Presynaptic neuron: acetylcholine (excitatory)

  • Postsynaptic neuron: varies b/w sympathetic (epi & norepi) & parasympathetic (acetylcholine)

    • Either excitatory or inhibitory

Somatic vs. Autonomic - neurons

2 divisions of Autonomic NS

• Sympathetic (fight of flight)

  • Thoracolumbar region (T1-L2)

• Parasympathetic (reset & digest)

  • Brain stem & sacral (S2-S4) → craniosacral

  • CN 3, 7, 9, 10 = parasympathetic function

Sympathetic NS - neurons

• Origin of presynaptic neuron cell body:

  • Thoracolumbar region of spinal cord

• Fiber length:

  • Presynaptic → short

  • Postsynaptic → long

• Location of ganglia:

  • Close to spinal cord

Parasympathetic NS - neurons

• Origin of presynaptic neuron cell body:

  • Brain & sacral spinal cord (craniosacral division)

• Fiber length:

  • Presynaptic → long

  • Postsynaptic → short

• Location of ganglia:

  • In/near visceral effector organs

Sympathetic & parasympathetic neurons - compared

Parasympathetic NS - info

• Only innervates internal organs

• Generally inhibits body function

  • Only major body function not inhibited is digestion

• Location of presynaptic neuron cell bodies: craniosacral

  • Nuclei for CN 3, 7, 9, 10

  • S2-S4 spinal cord levels

• Synapse b/w pre & post synaptic ganglia:

  • At terminal ganglia

Parasympathetic NS - cranial outflow

• Presynaptic fibers run via:

  • Oculomotor n. (CN 3) - smooth muscle in eye

  • Facial n. (CN 7) - lacrimal, submandibular, & sublingual glands

  • Glossopharyngeal n. (CN 9) - parotid gland

  • Vagus n. (CN 10) - organs in thorax & GI tract → 2/3 tranverse colon

Parasympathetic NS - sacral outflow

• Presynaptic neurons originate from S2-S4 level of spinal cord

  • Fibers of presynaptic neurons travel through ventral root → spinal n. → ventral rami

  • Exit ventral rami as pelvic splanchnic nerves

    • Pelvic splanchnic nerves synapse in intramural ganglia (at/near effector)

    • Postsynaptic fibers innervates remainder of GI tract from distal 1/3 of transverse colon & pelvic viscera

Parasympathetic NS - summary

Sympathetic NS - info

• More widespread than parasympathetic NS

• Generally stimulates body functions

  • Only major body function not stimulated is digestion

• Location of presynaptic neuron cells bodies:

  • Thoracolumbar region of spinal cord (T1-L2) → lateral horn

• Synapse b/w pre & post synaptic neurons:

  • Paravertebral ganglia: sympathetic chain

  • Prevertebral ganglia: on abdominal aorta

Sympathetic NS - outflow

3 options for pathways:

• 1. Synapse at same level

• 2. Synapse at different level

• 3. Leave & synapse at prevertebral (Spanchnic nerve)

Adrenal Medulla

• Postsynaptic sympathetic neurons

• Located in medulla of adrenal gland

• Does not develop axons, but still produces epinephrin & norepinephrine which will have sympathetic effects on target structures

Effects of Autonomic Divisions - chart