Spinal Nerves and Autonomic Nervous System

Spinal Nerve Plexuses

• Nerve groupings where nerves intersect.
• Four plexuses exist: cervical, brachial, lumbar, and sacral.

Cervical Plexus

• Origin: Cervical spinal nerves C1-C4.
• Innervates: Muscles of the neck and the diaphragm.
• Diaphragm: Skeletal muscle separating the thoracic cavity from the abdominal pelvic cavity.
• Diaphragm's Role in Breathing: It contracts and dips into the abdominal cavity, increasing the volume within the thoracic cavity, thereby decreasing pressure. Air is drawn into the lungs because the pressure is less than the atmospheric pressure.

Brachial Plexus

• Origin: Cervical nerves C5-C8 and thoracic nerve T1.
• Innervates: Pectoral girdles and upper limbs (shoulder, arm, hand).

Lumbar Plexus

• Origin: L1-L4.
• Innervates: Pelvic girdle and lower limbs.

Sacral Plexus

• Origin: L4-L5, S1-S4.
• Innervates: Back of the thigh, most of the lower leg, the foot, and part of the pelvis.
• Often grouped with the lumbar plexus as the lumbosacral plexus.

Dermatomes

• Regions of the skin connected to specific spinal nerves.
• 31 spinal nerves but 30 dermatomes; no dermatome for C1.
• Cervical nerves: Correspond to the green regions.
• Thoracic nerves: Correspond to the thoracic dermatomes.
• Lumbar nerves: Correspond to the lateral and medial sides of the thighs and interior region of the legs and thighs.
• Sacral nerves: Correspond to the gluteal region, posterior region of the thigh and leg, and perineal region.

Autonomic Nervous System

Receptors and Divisions

• Receptors detect changes or stimuli.
• Somatic sensory receptors: Monitor position and external environment.
• Visceral sensory receptors: Monitor internal body and organ systems.
• Afferent Division: Sensory division bringing information into the central nervous system (CNS).
• Efferent Division: Motor division exiting the CNS to effectors (muscles and glands).
• Examples of sensory information: Pain, touch, chemoreceptors, nociceptors, photoreceptors, thermoreceptors.
• Motor commands via efferent division: Voluntary (skeletal muscles) and involuntary (smooth muscle, cardiac muscle, glands).

Somatic vs. Autonomic Nervous Systems

• Somatic Nervous System: Voluntary control of skeletal muscles.
• Autonomic Nervous System: Involuntary control of smooth muscle, cardiac muscle, and glands.

Sympathetic vs. Parasympathetic

• Parasympathetic: "Rest and digest."
• Sympathetic: "Fight or flight."

Peripheral Nervous System

• Nerves extend from the brain and spinal cord to the skin, muscles, and tissues.
• Relays vital information between the body and brain via electrical impulses.
• Three types of peripheral nerves: motor, sensory, and autonomic.

Afferent and Efferent Pathways

• Afferent Division: Brings sensory information into the CNS.
• Efferent Division: Brings motor information away from the CNS.
• Noisy receptors: Connect to a sensory neuron entering the back (dorsal or posterior region) of the spinal cord.
• Dorsal Root Ganglion: Contains cell bodies associated with sensory/afferent neurons.
• Sensory information connects with a motor/efferent neuron to cause movement.

Somatic vs. Autonomic Control Recap

• Somatic: Voluntary; deals with skeletal muscle.
• Autonomic: Involuntary; deals with smooth muscle, organs, and glands.

Divisions of the Autonomic Nervous System

Sympathetic Nervous System

• Fight or flight response.
• Increases heart rate and breathing rate.
• Causes dilation of pupils.
• Originates near the thoracic and lumbar regions.

Parasympathetic Nervous System

• Rest and digest or feed and breathe response.
• Originates in the cranial and sacral regions.

Comparative Functions

• Pupils: Sympathetic dilates, parasympathetic constricts.
• Heart Rate: Sympathetic increases, parasympathetic decreases.
• Bronchial Tubules: Sympathetic dilates, parasympathetic constricts.
• Liver: Sympathetic increases breakdown of glycogen into glucose; parasympathetic releases bile.
• Sweat Glands: Sympathetic activates sweat glands.
• Blood Vessels: Sympathetic causes constriction.
• Digestive System: Sympathetic decreases activity, parasympathetic stimulates activity.
• Adrenal Glands: Sympathetic stimulates adrenal medulla to release adrenaline (epinephrine) and noradrenaline (norepinephrine).
• Uterus: Sympathetic stimulates orgasm, parasympathetic relaxes the uterus.
• Urinary System: Sympathetic relaxes, parasympathetic increases urinary output.

Preganglionic and Postganglionic Fibers

• Preganglionic fibers: Typically cholinergic.
  • Release acetylcholine
• Postganglionic fibers

Mural Board Image Analogy

• Somatic nervous system (voluntary) vs. autonomic nervous system (involuntary).

Sympathetic Division

• Preganglionic fibers leave the thoracic and lumbar region.
• Ganglia are close to the spinal cord.
• Short preganglionic fibers, long postganglionic fibers.

Parasympathetic Division

• Originates from the cranial and sacral regions.
• Ganglia are located near or within the targeted organs.
• Long preganglionic fibers, short postganglionic fibers.

Neurotransmitters

• Both sympathetic and parasympathetic preganglionic fibers release acetylcholine (cholinergic).
• Parasympathetic postganglionic fibers are cholinergic.
• Sympathetic postganglionic fibers are adrenergic (releasing norepinephrine).

Additional Definitions

• Cholinergic: Referring to acetylcholine.
• Postsynaptic neurons: After the synapse.
• Ganglia: Accumulation of cell bodies within the peripheral nervous system.

Cholinergic Receptors

• Two types: Nicotinic and muscarinic.
• Sympathetic nervous system preganglionic: Nicotinic.
• Parasympathetic nervous system preganglionic: Nicotinic.
• Parasympathetic division postganglionic: Muscarinic.

Reflex Arc

• Somatic nervous system: one motor neuron.
• Autonomic nervous system: two motor neurons; preganglionic and postganglionic.