Peripheral Nervous System Flashcards
How many cranial nerves & where do they come from?
12 pairs of cranial nerves arise from the brain stem
What sort of nerves are cranial nerves?
Mixed, sensory & motor
How many spinal nerves?
31 pairs - 8 cervial, 12 thoracic, 5 lumbar, 5 sacral, 1 coccoygeal
What types of nerves are spinal nerves?
Only mixed - posterior contain sensory - anterior contain motor
What are the function of sympathetic fibers?
Fight or flight - increase alertness, metabolism and prepare for emergency
Sympathetic examples?
Exercise, emergency, embarrassment, stall unnecessary functions - urination & defecation effects longer lasting
What are the functions of parasympathetic fibers?
Rest & digest, energy conservation, control smooth muscle & replenish nutrients
Parasympathetic examples?
Salivation, lacrimation, urination, defacation, digestion
What is the autonomic tone?
The balance between sympathetic & parasympathetic fibers and controlled by hypothalamus
Somatic nervous system?
Contain sensory and motor neurons, consciously perceived sensation and stimulate only skeletal muscle
What are reflexes?
Fast, involuntary, planned sequence of events that occur in response to a stimulus that can be inborn, learnt or aquired
Use of reflexes?
Diagnosing abnormalities in skeletal functioning
What are somatic reflexes?
Involve skeletal muscle
Autonomic reflex?
involuntary reflex
Cranial reflex?
Involve brain stem
Ipsilateral reflex?
Sensory nerves enter spinal cord same way motor neurons exit - change occurs on same side of stimulus
Contralateral reflex?
nerves enter and exit the spinal cord through opposite sides - left responds to right
What happens during a stretch reflex (patella reflex)?
Causes contractions of skeletal muscle in response to muscle stretch - monosynaptic reflex arc
What is reciprocal innervation?
The contraction of a muscle results in the relaxation of its antagonistic muscle pair and prevents conflict between opposing muscles - polysynaptic
What is the function of the tendon reflex?
Controls muscle tension by relaxing muscle before rupture and can override stretch reflex - ipsilateral reflex
What is the Flexor & Crossed Extensor Reflex?
Reflexes that work together in response to dangerous stimuli and coordinate balance
What happens during the flexor reflex?
Stepping on tack stimulates nocicereceptors which generate sensory impulses to the spine where they activate interneurons across levels of spinal segments which in turn synapse with motor neurons which result in the release of Acetylcholine which causes flexor muscles to contract and step back - intersegmental reflex
What is an intersegmental reflex?
Stimulates more than one effector
What else do flexor reflexes do?
Initiate crossed extensor reflex
What happens during the crossed-extensor reflex?
When the right foot step on tack, sensory neurons activate multiple interneurons that synapse with motor neurons on the left side of spinal cord where incoming signals cross to the opposite side through interneurons which stimulate motor neurons across spinal segements, and cause extensor muscles in the left thigh to contract - contralateral reflex
What happens during the receptory or sensory level?
Stimulation of sensory receptors result in the transmission of the impulse through sensory afferent nerves to spinal cord
What happens during circuit level?
Stimulus converts energy into graded potentials which result in nerve impulses along sensory neurons that travel up the ascending tracts to spinal cord to the thalamus.
What happens during the Perception level?
Thalamus directs impulses to specific region of somatosensory cerebral cortex responsible for interpreting the specific region of the sensation
