(2) divisions of ANS
Structure of the Sympathetic Division
thorocolumbar (sympathetic) division- Preganglionic neurons originate from thoracic & lumbar levels of spinal cord (T1-L2).
Sympathetic ganglia - site of synapse between sympathetic pre & postganglionic
(2) types - sympathetic trunk & prevertebral (collateral) ganglia
Preganglionic & postganglionic neurons
preganglionic - cell body in CNS, exits as cranial/spinal nerve
axon = type B fiber (small, myelinated)
postganglionic - in PNS (outside CNS), cell body & dendrites in autonomic ganglia
axon = small, unmyelinated type C fiber
sympathetic ganglia (2)
Sympathetic trunk (vertebral chain) ganglia. - innervate organs above diaphragm
Prevertebral (collateral) ganglia: celiac, superior mesenteric, inferior mesenteric,
aorticorenal and renal.
innervate organs below diaphragm
Once axons of sympathetic preganglionic neurons pass to sympathetic trunk ganglia, they may connect with postganglionic neurons in the following ways (4)
1) synapse with neurons in nearest gangliaon
2) axons ascend/descend to higher/lower ganglion, sympathetic chains
3) through sympathetic trunk ganglion to synapse with neurons in prevertebral ganglion
4) through sympathetic trunk & prevertebral to chromaffin cells of adrenal medulla
A single sympathetic preganglionic fiber has many axon _______________ and may synapse with 20 or more postganglionic neurons.
sympathetic postganglionic axons typically terminate in several
therefore effects are more widespread than parasympathetic stimulation
Structure of the Parasympathetic Division
craniosacral divison - Preganglionic neurons originate from cranial
nerves III, VII, IX, X & sacral spinal nerves S2-S4
parasympathetic ganglia - preganglionic synapse with postganglionic in terminal (intramural) ganglia .
Parasympathetic Presynaptic neuron usually synapses with 4-5 postsynaptic neurons all of which supply ?
a single visceral effector
Autonomic Plexuses in Thorax, Abdomen & Pelvis
network of sympathetic & parasympathetic neurons
thorax plexus - heart
pulmonary plexus - bronchial tree
celiac (solar) plexus - largest. stomach, spleen, pancreas, liver, gallbladder & adrenal medulla
fight or flight
↑ ATP, heart rate, BP, blood supply to skeletel/cardiac muscles, liver & fat, blood glucose
dilation of pupils, constriction of blood vessels
breakdown of glycogen & lipids
rest & digest
conserve & restore energy
↑ digestive & urinary function
↓ body functions supporting physical activity
conscious & subconscious awareness of changes in environment
components of sensation
Stimulation of sensory receptor → transduction of stimulus → nerve impulses → integration of sensory input.
Classification of Sensory Receptors
- General senses
- Special senses
1) somatic & visceral
a. somatic - tactile, thermal, pain &proprioceptive sensations
b. Visceral- provide info about conditions within internal organs.
2) smell, taste, vision, hearing, equilibrium/balance
Types of Sensory Receptors
free nerve endings
encapsulted nerve endings
free nerve endings
pain & thermoreceptors
encapsulated nerve endings
dendrites enclosed in CT capsule
hair cells, photoreceptors & gustatory receptor cells
Generator Potential and Receptor Potential
Generator potential: produced by free nerve, encapsulated nerve endings, and olfactory receptors. When it reaches threshold, triggers 1+ nerve impulses in axon of first-order sensory neuron.
Receptor potential triggers release of neurotransmitters→ postsynaptic potential → action potential.
Classification of Sensory Receptors Based on the Location
o Exteroceptors: external surface
o Interoceptors: internal environment (vessels, organs & muscles & NS)
o Proprioceptors: muscles, tendons, joints & nner ear
Classification of Sensory Receptors based on the type of Stimulus
mechanoreceptors - mechanical stimuli (touch, proprioception)
nociceptors - pain
photoreceptors - light
chemoreceptors - chemicals in mouth, nose & body fluids
Adaptation of Sensory Receptors
rapidly adapting receptors: detect pressure, touch and smell.
slowly adapting receptors: detect pain, body position & blood chemical composition
sensory receptors in skin, muscles, tendons, joints & inner ear
Tactile Sensations include?
Tactile receptors in skin
hair root plexuses
free nerve endings.
Meissner Corpuscles or Corpuscles of Touch
egg-shaped mass of dendrites enclosed by capsule of CT
- dermal papillae of hairless skin
TOUCH & PRESSURE
Hair root plexuses
rapidly adapting- touch
in hairy skin
free nerve endings wrapped around hair follicles
detect movement on skin that disturbs hair
Merkel Discs or Tactile Discs
type I cutaneous mechanoreceptors
slowly adapting touch
fingertips, hands, lips, external genitals