Download Peripheral Nervous System PNS

Peripheral Nervous System PNS
Include the following
–Sensory receptors and sensation
–Transmission lines the Nerves
cranial and spinal
–Motor endings and motor activity
–Reflex activity
Sensory receptors and sensation
• Specialize to respond to environmental changes or
stimuli
• Simple receptors for pain, touch, pressure,
temperature in skin, as well as those found in skeletal
muscles and tendons and visceral organs
• Complex receptors are the sense organs, vision,
hearing, equilibrium, smell, and taste
• Classified by stimulus detected: mechanoreceptors,
thermoreceptors, photoreceptors, chemoreceptors,
and nociceptors
• Classified by location: exteroceptors, interoceptors,
proprioceptors
Sensation to Perception
• Sensation is awareness of internal and external stimuli
• Perception is conscious interpretation of those stimuli
• 3 levels of sensory integration: receptor, circuit (ascending
pathway), perceptual levels (cerebral cortex)
Function to transform generator potential to action potential
– Levels of perception: spinal cord reflexes, nonspecific
neurons, and then others to the thalamus
Levels of Motor Control
• Lowspinal cord and
reflex arc
• Middlemotor cortex
• High precommand
uses
cerebellum
and basal
nuclei
Components of Reflex arc
1. Receptor: site of stimulus action
2. Sensory neuron: transmits impulse to CNS
3. Integration Center: synapse between a signal neuron and
motor neuron, or a more complex network of multiple
synapses with a chain of interneurons
4. Motor neuron: conducts impulse from integration center
to an effector organ
5. Effector: muscle fiber or gland cell that responds by
contracting or secreting
- somatic reflex actives skeletal muscle
- autonomic reflex activates either smooth, cardiac muscle
or a gland
Autonomic Nervous System
Function of ANS
• The system of motor neurons that innervates
smooth and cardiac muscle and glands
• Signals from visceral organs send impulses to the
CNS and the autonomic nerves make adjustments
as necessary to ensure optimal support for body
activities
–
–
–
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Sending blood to needy areas
Speed or slow heart rate
Adjust blood pressure and body temperature
Increase or decrease stomach secretions
Neurotransmitters in ANS
Neurotransmitters
• Two major neurotransmitters: acetylcholine (Ach) and
norepinephrine (NE)
• ACh binds to Cholinergic receptors the effects often are
excitation or activation
• NE binds to Adrenergic receptors the effects vary
depending on the target cells
Effects are felt from the heart to kidney, lungs to digestive
tract, constricts blood vessels of the skin and visceral
organs except heart, think “adrenaline rush”
** inhibits insulin secretion by pancreas in order to elevate
blood sugar levels, stimulates fat cells to break down fat,
and liver to release stored sugars
Parasympathetic vs Sympathetic
Adrenal Medulla
• Embryologically, sympathetic ganglia and the
adrenal medulla arise from the same tissue
• Sometimes referred to as a “misplaced”
sympathetic ganglion, being located atop the
kidney not in the CNS
• The adrenal ganglia releases norepinephrine
and epinephrine, stimulating the secretion of
adrenaline into the blood from the adrenal
gland
• Produces the excitatory effect
Visceral reflexes
• Visceral sensory neurons
share pathways with
somatic reflex arcs
• This becomes an issue
when you have a heart
attack and the visceral pain
travels along the same
pathway as somatic pain so
the pain is perceived as
somatic in origin, radiating
to the superior thoracic wall
and along the medial aspect
of the left arm
Referred pain
Hypertension
• Results from homeostatic imbalance of the
ANS
• Overactive sympathetic vasoconstictor
response promoted by high levels of stress
• Increases the work load of the heart, causing
an enlarged heart which restricts the pumping
ability and can lead to heart failure
• Increases wear and tear on artery walls, this
increases risk of a tear causing a stroke, or
worse a fatal aorta rupture