peripheral nervous system (pns) part 3: integration & control
TRANSCRIPT
Peripheral Nervous System (PNS)
Part 3: Integration & Control
Peripheral Nervous System (PNS)
Peripheral Nervous System: All nervous tissue located outside the brain & spinal cord.
Components: Cranial NervesSpinal NervesAutonomic Nervous System
Subdivisions of the PNS
Afferent: The subdivision in charge of sensory information. Somatic Sensory Division: Carries signals
from the skin, muscle, bone, and joint receptors.
Visceral Sensory Division: Carries signals from the organs and tissue in the thoracic & abdominal cavities.
Subdivisions of the PNS
Efferent: The subdivision in charge of motor information.Somatic Motor Division: Carries signals
from the CNS to the skeletal muscles. Visceral Motor Division aka the Autonomic
Nervous System: Controls the part of the body we do not have conscious control over.
Sympathetic Division: “Fight or flight” Parasympathetic Division: Back to homeostasis!
Types of Nerves in the PNS
Sensory Neurons aka Afferent Neurons: Contain sensory fibers responsible for communicating information about stimuli.
Motor Neurons aka Efferent Neurons: Contain motor fibers responsible for relaying information to the muscular system.
Mixed Neurons: Contain both sensory and motor fibers.
The Nerve Cell
3 Basic Parts: Dendrites:
Receive information
Soma: Cell body.
Axon: Send information.
May be myelinated or unmyelinated.
Nerve Cells
Ganglion: A cluster of soma’s contained within the same epineurium tissue sheath.
Dorsal Root Ganglia: Contain the somas of the sensory neurons that send impulses to the CNS. Nerves lying lateral and dorsal to the spinal
cord.
Specific Nerve Locations
Dermatomes: Zones in the skin that are served by specific spinal nerves. In the face & scalp, these are zones served by Cranial
Nerve V (Trigeminal). Muscle Spindles: Contain receptors to allow for
stretching of the muscle and knowledge of how the muscle is moving in space. Intrafusal Muscle Fibers: Nerve endings wrapped
around specialized muscle fibers that allows the stretching reflex.
Gamma Motor Neurons: Allow the body to know how far the muscle has stretched.
Proprioceptors: Receptors in muscles and joints that provide knowledge of where the limbs are in space.
Cranial Nerves
Cranial Nerves: Located on the undersurface of the brain. 24 total held within 12 pairs.
YOU NEED TO KNOW the name, number, type, and function of each nerve!
Cranial Nerves
Cranial Nerve 1: The Olfactory NerveClassified as a sensory neuronSensory functions include the sense of smell.
Cranial Nerves
Cranial Nerve 2: The Optic NerveClassified as a sensory neuronSensory functions include the sense of vision.
Cranial Nerves
Cranial Nerve 3: The Oculomotor NerveClassified as a motor neuron, but has some
sensory functions. Sensory functions include proprioception
(where the body is in space).Motor functions include moving the eyelids &
eye muscles.Autonomic nervous system functions include
the moving the lens and the constriction of the pupil.
Cranial Nerves
Cranial Nerve 4: The Trochlear NerveClassified as a motor neuron, but serves
some sensory functions. Sensory functions include propriception
(where the body is in space).Motor functions include moving the eye
muscles.
Cranial Nerves
Cranial Nerve 5: The Trigeminal Nerve Classified as a mixed nerve, serving both autonomic
nervous system and sensory functions. Sensory functions include touch, pain, temperature
sensation in face and mouth. Autonomic nervous system functions include
operating the chewing muscles. 3 Branches of Cranial Nerve 5:
Ophthalmic Nerve: Enters the orbit through the superior orbital fissures; the smallest branch.
Maxillary Nerve: Enters the foramen rotundum; intermediate size.
Mandibular Nerve: Exits through the foramen ovale; the largest branch.
Cranial Nerves
Cranial Nerve 6: The Abducens NerveClassified as a motor neuron but serves some
sensory functions. Sensory functions include proprioception
(where the body is in space). Motor functions include moving the eye
muscles.
Cranial Nerves
Cranial Nerve 7: The Facial NerveClassified as a mixed neuron and serves
sensory, motor, and autonomic nervous functions.
Sensory functions include proprioception (where the body is in space) and taste.
Motor functions include the creation of facial expressions.
Autonomic nervous system functions include triggering the secretion of saliva and tears.
Cranial Nerves
Cranial Nerve 8: Vestibulocochlear Nerve aka Auditory Nerve Classified as a sensory nerve but serves sensory,
motor, and autonomic nervous system functions. Sensory functions include hearing and balance. Motor functions include modifying inner ear hair cells
in response to sound waves. Autonomic nervous system functions include two
branches: Vestibular Nerve: Carries impulses for equilibrium. Cochlear Nerve: Carries impulses for hearing.
Cranial Nerves
Cranial Nerve 9: Glossopharyngeal NerveClassified as a mixed neuron and serves
sensory, motor, and autonomic nervous system functions.
Sensory functions include taste sensations from the tongue and pharynx.
Motor functions include swallowing and speech production.
Autonomic nervous system functions include saliva secretion.
Cranial Nerves
Cranial Nerve 10: The Vagus Nerve Classified as a mixed neuron, serving sensory, motor,
and autonomic nervous system functions. Sensory functions include taste, blood pressure,
breathing & heart rate, and visceral sensations. Motor functions include swallowing, coughing, and
speech production. Autonomic nervous functions include being the main
nerve in control of the autonomic nervous system, particularly the parasympathetic division.
This is the only cranial nerve to leave the head & neck area; innervates the viscera
Cranial Nerves
Cranial Nerve 11: Accessory Nerve Classified as a motor neuron but also serves sensory
and autonomic nervous system functions. Sensory functions include proprioception (where the
body is in space) and voice production. Motor functions include swallowing and the movement
of the head and shoulders. Autonomic nervous system functions include control
of the muscles in the pharynx and larynx.
Cranial Nerves
Cranial Nerve 12: The Hypoglossal NerveClassified as a motor neuron but also serves
some sensory functions. Sensory functions include proprioception
(where the body is in space). Motor functions include movement of the
tongue.
Autonomic Nervous System (ANS)
Autonomic Nervous System: Controls vital functions that are not under conscious control. Serves the viscera, including the glands,
smooth muscle and cardiac muscle. Main function is to regulate & maintain
homeostasis. Contracts & relaxes smooth muscle Increases & decreases rate of contraction in
cardiac muscle Increases & decreases gland secretions.
Types of Neurons in the ANS
ANS Neurons: Instead of a single motor neuron, ANS uses two neurons. Signals start at a source point in the brain,
such as the hypothalamus.
Neurons in the ANS
Autonomic Ganglion: The point at which the neurons diverge. Preganglionic Neuron: The first neuron in the pair.
Also release acetylcholine (ACh) to stimulate the postganglionic neuron.
Postganglionic Neuron: The second neuron in the pair that leads to the effector neuron.
Secretes noradrenaline (norepinepherine).
Principle of Mass Activation: One preganglionic neuron can excite a large number of postganglionic fibers.
Subdivisions of the ANS
Two Subdivisions of the ANS: Sympathetic Division aka Sympathetic Nervous
System: Initiates the “fight or flight” response mechanism during stress or danger.
Parasympathetic Division aka Parasympathetic Nervous System: Reverses the effects of the sympathetic nervous system to return the body to homeostasis.
Dual Innervation: Concept that most visceral organs are supplied by nerves from both subdivisions. Allows for cooperative & antagonistic effects.
Sympathetic Division
Sympathetic Division aka Sympathetic Nervous System aka Thoracolumbar Division
Spinal nerves included: Thoracic (T1-12) and Lumbar (L1-2)
Paravertebral Gangli: Sympathetic ganglia located close to the vertebral column. Preganglionic nerves are much shorter than the
postgangionic nerves that must stretch all the way to their target.
Connects to the spinal nerve via both… White Communicating Rami: Myelinated axons. Gray Communicating Rami: Unmyelinated axons.
Sympathetic Division
Fight or Flight Mechanism: The body’s method of preparing for physical or emotional stress. Triggered by noradrenaline release.. Causes:
Simulates rate & force of cardiac muscle contractions Raises blood pressure Dilates pupils to allow more light & better vision Dilates trachea & bronchi to aid breathing Stimulates liver conversion of glycogen to glucose for energy Constricts blood vessels in the viscera & skin Dilates blood vessels in the skeletal muscles, heart, & brain Slows digestion & urine production
Sympathetic Division
Adrenal Glands: Produce epinephrine (adrenaline) & norepinephrine (noradrenaline) to enhance sympathetic postganglia activity. Pyramid-shaped glands Located on top of
each kidney. Includes an inner medulla containing modified
sympathetic neurons.
Parasympathetic Division
Parasympathetic Division aka Parasympathetic Nervous System aka Craniosacral Division
Contains Cranial Nerves 3, 7, 9, & 10 Contains Sacral Spinal Nerves (S2-4). Effector: The target muscle or gland for each
postganglionic neuron. Synapse between preganglionic & postganglionic
neurons occur near the effector, leaving postganglionic neurons shorter than the preganglionic
Oppoisite of sympathetic division!
Parasympathetic Division
Parasympathetic stimulation causes: Slowing of the heart rate to normal rates Lowers blood pressure to normal rates Constricts the pupils to normal dilation Triggers bronchoconstriction (constricting of the
airways) to a normal dilation Increases to normal levels…
Salivation Lacrimation Urination Digestion Defecation
Good to know about ANS
While ANS is under involuntary control, the parasympathetic division can be manipulated using relaxation techniques.
Examples: Yoga, Buddhist meditation, etc. Lowers heart rate & oxygen intake far past
normal changes of sleep or relaxation!
Cholinergic Receptors
Cholinergic Receptors: Neurons that release acetylcholine (ACh).
Two kinds of receptors on the postsynaptic membrane that bind to ACh: Nicotinic Receptors: Occur in sympathetic &
parasympathetic postganglionic neurons and motor end plates at neuromuscular junctions.
Muscarinic Receptors: Found in all effectors stimulated by the parasympathetic system.
Includes smooth muscle, cardiac muscle, & glands.
Adrenergic Receptors
Adrenergic Receptors: Release norepinephrine (NE). Make up the majority of sympathetic
postganglionic neurons. Norepinephrine tends to linger longer in the
synapses longer than acetylcholine. Causes effects of adrenergic neurons to last
longer.
CNS Control of the ANS
CNS can have a hand in controlling the ANS! Hypothalamus: Integrates & regulates ANS
function. Includes cardiac & pulmonary function, sweating, vasodilation & constriction.
Reticular Formation: Contains centers for cardiac, respiratory, vasomotor, & gastrointestinal functions.
Spinal Cord: Contains centers that regulate the excretory system, without brain involvement.
Side by Side: Sympathetic & Parasympathetic Functions
Sympathetic ParasympatheticInhibits digestion Promotes digestionIncreases glycogenolysis Increases glycogen (converts glycogen to synthesis
glucose)Increases heart rate Decreases heart rate & force
& forceDilates pupils Constricts pupilsDilates airways Constricts airwaysStops peristalsis (GI Reengages peristalsis
movement)Contracts sphincters Relaxes sphincters
Side by Side: Sympathetic & Parasympathetic Functions
Sympathetic ParasympatheticContracts arrector pili Relaxes arrector pili muscles musclesTriggers vasodilation in… Triggers skeletal muscles vasoconstriction or cardiac muscles vasodilation back to liver normal rangesTriggers vasoconstriction in…
kidneysGI tract
Increases sweatingCauses uterine contraction if pregnantDischarges all stored blood into circulation
