PNS II Flashcards
PNS
All nervous pathways outside the brain and spinal cord - includes fibers present in: cranial nerves, spinal nerves, individual branches of cranial and spinal
Divsions
- Functional: sensory and motor 2. Motor: somatic motor and autonomic
Principles of somatice motor pathways
- involves the peripheral pathways to the skeletal muscles (somatic effectors) - all somatic motor pathways involve a single motor neuron whole axon stretches from the cell body in the CNS to the effector innervates by that neuron (motor unit) - involves all motor pathways outside of CNS
Reflex arc
Signal conduction route to and from CNS - most common are 3 neurons, simplest have 2
Reflex
The action that results from a nerve impulse passing over a reflex arc - predictable response to a stimulus - usually involuntary but can be conscious - consists of either muscle contraction or glandular secretion
Cranial reflex
Center of reflex arc is located in the brain (eye tracking while reading)
Spinal reflexes
Center of reflex arc is located in eh spinal cord (knee jerk)
Somatic reflexes
Contractions of skeletal mm - motor neurons are somatic motor neurons 1. Stretch 2. Tendon 3. Flexor (withdrawal) 4. Crossed extensor
Autonomic reflexes
Contractions of smooth or cardiac mm or secretion by glands
Why are reflexes important?
- clinical interest in reflexes stems from the fact that they deviate from normal in certain diseases/disorders - the testing of reflexes is a valuable diagnostic aid - stretch reflex tests neuromuscular integrity - protective reflex tests cranial nerve integrity
Knee jerk
Patellar reflex - stretch reflex - extension of the lower leg in response to tapping the patellar tendon - the tap results in stretch of the tendon and its mm; stimulates the mm spindles - conduction over a 2-neuron reflex arc - femoral nerve and spinal levels L2-4
Ankle jerk
Achilles reflex - plantarflexion of the foot in response to tapping the Achilles’ tendon - stretch reflex mediated by 2-neuron spinal arcs - spinal levels s1-s2
Plantar réflex
Curling under of all toes (plantarflexion) plus a slight turning in and flexion of the anterior part of the foot - in response to stimulation of the outer edge of the sole
Babinski reflex
- extension of the great tow, with or without fanning of the other toes - in response to stimulation of the outer margin of the sole of the foot - normal infants show the babinski sign - 18 mo, corticospinal fibers have become fullly myelinated and the babinski sign becomes suppressed
Corneal reflex
- blinking in response to the cornea being touched - 5th and 7th cranial nerves, pons
Abdominal reflex
Umbilicus moves in response to stroking the side of the abdomen - superficial reflex - decrease or absence of this reflex occurs in lesions involving pyramidal tract upper motor neurons - may be absent during pregnancy
ANS divisions
- regulates involuntary effectors to maintain homeostasis or respond to threats (internal and external) - heartbeat, smooth mm contraction, glandular secretions, metabolism - contains afferent and efferent components 1. Sypmathetic 2. Parasympathetic - consist of neural pathways that are separate from each other - many autonomic effectors are dally innervates (fibers from both sym and para) which allows the effector to be controlled with remarkable precision
Enteric nervous system
- intestinal aspect of ANS - controls visceral effectors in gut wall: endocrine cells, exocrine cells, smooth muscle - can funciton independice y, but is modulated by sympathetic and parasympathetic divisions
Structure of ANS
- each efferent autonomic pathway is made up of autonomic nerves, ganglia, and plexuses - all autonomic neurons function in reflex arcs - efferent autonomic regulation ultimately depends on feedback from sensory receptors - some effector organs regulated by ANS include: blood vessels, smooth mm, cardiac mm, sweat glands
Preganglionic neuron
Conducts impulses from CNS to an autonomic ganglion
Postganglionic neuron
Wishing the ganglion the pre-ganglionic neuron synapses with a second efferent neuron that conducts impulses away from the ganglion and to the effector
Pic
Autonomic transmitters
- axon terminal of autonomic neurons release one of two neurotransmitters - norepinephrine - acetylcholine
Functions of ANS
Regulate visceral effectors to maintain or quickly restore homeostasis - both sym and para are tonically active (continually conduct impulses to autonomic effectors) - exert antagonistic influences on visceral effectors - sym impulses tend to stimulate an effector - para impulses tend to inhibit it
Loops
The more chains involved in the loop the more complex the response and the longer the response takes to cause effect - the shorter the loop the quicker and shorter lasting the response
ANS functions in loops
- Spinal loops: afferent neuron to spinal cord to efferent neuron 2. Brain stem loop: afferent to spinal cord to brain stem to efferent 3. Hypothalamus loop 4. Hypothalamus + limbic system loop
Sym vs para
Dally innervates effectors continually receive both sympathetic and parasympathetic impulses - summation of the two opposing influences determines the dominating or controlling effect
Functions of the SNS
- serves as an emergency system “fight-flight-freeze” - only sym fibers innervates the smooth muscle in blood vessel walls - maintenance of normal vessels tone - crucial role in blood pressure under resting and active conditions
Functions of PSNS
Primary controller of most autonomic effectors most of the time - dominant during the rest and repair times
Big picture
- PNS is made of all afferent nervous pathways coming into the CNS and all the efferent pathways going out of the CNS - peripheral pathways are pathways that lead from he integrator (CNS) to the effectors - allows the CNS to communicate regulatory information to all of the nervous effectors - every major organ is influenced (directly or indirectly) by peripheral nervous system output
