The Autonomic Nervous System and Visceral Sensory Neurons The - - PowerPoint PPT Presentation

The Autonomic Nervous System and Visceral Sensory Neurons

The Autonomic Nervous System and Visceral Sensory Neurons

• The ANS – a system of motor neurons

– The general visceral motor division of the PNS – Innervates smooth muscle, cardiac muscle, and glands – Regulates visceral functions

• Heart rate, blood pressure, digestion, urination . . .

The Autonomic Nervous System and Visceral Sensory Neurons

Comparison of Autonomic and Somatic Motor Systems

• Somatic motor system

– One motor neuron extends from the CNS to skeletal muscle – Axons are well myelinated, conduct impulses rapidly

• Visceral Motor (Autonomic nervous) system

– Chain of two motor neurons

• Preganglionic neuron
• Ganglionic neuron

– Conduction is slower due to thinly or unmyelinated axons

Comparison of Autonomic and Somatic Motor System Pathways

Divisions of the Autonomic Nervous System

• Sympathetic and parasympathetic divisions

– Chains of two motor neurons

• Exhibits dual innervation

– Nerves of both divisions innervate mostly the same structures

• Cause opposite effects
• Sympathetic – “fight, flight, or fright”

– Activated during exercise, excitement, and emergencies – Concerned with liberating energy resources

• Parasympathetic – “rest and digest”

– Concerned with conserving and storage of energy

Differences in ANS Divisions

• From different

regions of the CNS

– Sympathetic – also called the thoracolumbar division – Parasympathetic – also called the craniosacral division

Differences in ANS Divisions

• Length of postganglionic fibers

– Sympathetic – long postganglionic fibers – Parasympathetic – short postganglionic fibers

• Branching of axons

– Sympathetic axons – highly branched

• Influences many organs

– Parasympathetic axons – few branches

• Localized effect
• Neurotransmitter released by postganglionic axons

– Sympathetic – most release norepinephrine (adrenergic) – Parasympathetic – release acetylcholine

Sympathetic Pathway

Parasympathetic Pathway

The Parasympathetic Division

• Cranial outflow

– Comes from the brain – Innervates organs of the head, neck, thorax, and abdomen

• Sacral outflow

– Supplies remaining abdominal and pelvic organs

The Sympathetic Division

• Basic organization

– Issues from T1‐L2 – Preganglionic fibers form the lateral gray horn – Supplies visceral organs and structures of superficial body regions – Contains more ganglia than the parasympathetic division

• Sympathetic trunk ganglia
• Prevertebral ganglia

The Role of the Adrenal Medulla in the Sympathetic Division

• Major organ of the sympathetic nervous

system

• Constitutes largest

sympathetic ganglia

• Secretes great quantities of

norepinephrine and adrenaline

• Stimulated to secrete by

preganglionic sympathetic fibers

Visceral Sensory Neurons

• General visceral sensory neurons monitor:

– Stretch, temperature, chemical changes, and irritation

• Cell bodies are located in the dorsal root

ganglia

• Visceral pain – perceived to be somatic in
• rigin

– Referred pain

A Map of Referred Pain

Visceral Reflexes

• Visceral sensory and autonomic neurons

– Participate in visceral reflex arcs

• Defecation reflex
• Micturition reflex
• Some are simple spinal reflexes
• Others do not involve the CNS

– Strictly peripheral reflexes

Visceral Reflex Arc

Special Senses

• Senses that have specific concentration of

receptors

– Vision – Hearing/Equilibrium – Smell – Taste

Visual Pathway

• Optic nerve
• Optic chiasma
• Optic radiations

– Lateral geniculate body radiates to visual cortex – Pulvinar (lateral thalamic mass) radiates to visual association areas – Other radiations to various nuclei involved in visual reflexes

Vision

• The Eye

Vision

• Retinal Layers

– Outer

• Photoreceptors

– Inner

• bipolar, horizontal

and amacrine cells

– Ganglion layer

• Ganglion cells

– Optic fiber layer

• Forms the optic

nerve

The Ear – Hearing & Equilibrium

1 2 3 1. Sound waves enter 2. Sound waves modified 3. Sound waves parsed & transduced 4. Action potentials sent 4

The Ear – Cochlea Detail

• 1. scala vestibuli
• 2. scala media

(chochlear duct)

• 3. scala tympani
• 4. hair cells
• 5. tectorial

membrane

• 6. cochlear nerve

fibers

• 7. basilar membrane
• 8. spiral lamina

(osseous)

1 4 5 6 3 2 7 8

Basilar Membrane Resonance Frequencies

The Ear – Vestibule & Semicircular Canals

Relationship between bony and membranous labyrinth in the inner ear

Olfaction

Taste

Taste