Week 8 - Peripheral Nervous System (PNS) Flashcards
What is the Peripheral Nervous System?
- PNS consists of nerves and ganglia outside the CNS
What is the structure of a nerve?
- bundles of neurons found outside the CNS
- endoneurium is a connective tissue sheath that surrounds each fiber
- perineurium wraps groups of fibers bound into a fasicle
- epineurium binds groups of fascicles
What are mixed nerves?
- contain both sensory and motor fibers
What are sensory (afferent) nerves?
- carry impulses toward the CNS
What are motor (efferent) nerves?
- carry impulses away from the CNS
What are Cranial nerves?
- 12 PAIRS*** of nerves serve mostly the head and neck
- only the pair of vagus nerves extends to thoracic and abdominal cavities
- most are mixed nerves, but three are sensory only
1. optic
2. olfactory
3. vestibulocochlear
Function of Olfactory nerves (I)
- purely sensory
- carries impulses for the sense of smell
Function of Optic nerves (II)
- purely sensory
- carries impulses for vision
Function of Oculomotor nerves (III)
- supplies motor fibers to four of the six muscles (superior, inferior, and medial rectus, and inferior oblique)
- that direct the eyeball
- to the eyelid
- and to the internal eye muscles controlling lens shape and pupil size
Function of Trochlear nerves (IV)
- supplies motor fibers for one external eye muscle (superior oblique)
Function of Trigeminal nerves (V)
- conducts sensory impulses from the skin of the face and mucosa of the nose and mouth
- contains motor fibers that activate the chewing muscles
Function of Abducens nerves (VI)
- supplies motor fibers to the lateral rectus muscle, which rolls the eye laterally
Function of Facial nerves (VII)
- activates the muscles of facial expression and the lacrimal and salivary glands
- carries sensory impulses from the taste buds of anterior tongue
Function of Vestibulocochlear nerves (VIII)
- purely sensory
- vestibular branch transmits impulses for the sense of balance
- cochlear branch transmits impulses for the sense of hearing
Function of Glossopharyngeal nerves (IX)
- supplies motor fibers to the pharynx (throat) that promote swallowing and saliva production
- carries sensory impulses from taste buds of the posterior tongue and from pressure receptors of the carotid artery
Function of Vagus nerves (X)
- fibers carry sensory impulses from and motor impulses to the pharynx, larynx, and the abdominal and thoracic viscera
- most motor fibers are parasympathetic fibers that promote digestive activity and help regulate heart activity
Function of Accessory nerves (XI)
- mostly motor fibers that activate the sternocleidomastoid and trapezius muscles
Function of Hypoglossal (XII)
- motor fibers control tongue movements
- sensory fibers carry impulses from the tongue
What are spinal nerves?
- 31 pairs
- formed by the combination of the ventral and dorsal roots of the spinal cord
- named for the region of the spinal cord from which they arise
What are spinal nerves plexus?
- plexus = networks of nerves serving motor and sensory needs of the limbs
- form from ventral rami of spinal nerves in the cervical, lumbar, and sacral regions
How many plexuses are there and what are they?
- 4
- cervical
- brachial
- lumbar
- sacral
What is the origin of the cervical plexus?
C1 - C5
What is the origin of the Brachial plexus?
C5 - C8 and T1
What are the important nerves of the cervical plexus?
- phrenic
what are the important nerves of the brachial plexus?
- axillary
- radial
- median
- musculocutaneous
- ulnar
What body areas does the cervical plexus serve?
- diaphragm
- skin and muscles of shoulder and neck
What body areas does the brachial plexus serve?
- deltoid muscle and skin of shoulder
- muscles and skin of superior thorax
- triceps and extensor muscles of the forearm
- skin of posterior upper limb
- flexor muscles and skin of forearm and some muscles of hand
- flexor muscles of arm
- skin of lateral forearm
- some flexor muscles of forearm
- wrist and many hand muscles
- skin of hand
What is the origin of the lumbar plexus?
L1 - L4
What are the important nerves of the lumbar plexus?
- femoral (including lateral and anterior cutaneous branches)
- obturator
What body areas does the lumbar plexus serve?
- lower abdomen
- anterior and medial thigh muscles (hip flexors and knee extensors)
- skin of anteromedial leg and thigh
- adductor muscles
- skin of medial thigh and hip joint
What is the origin(s) of the sacral plexus?
L4 - L5 and S1 - S4
What are the important nerves of the sacral plexus?
- sciatic (largest nerve in the body; splits to common fibular and tibial nerves just above knee)
- – common fibular (superficial and deep branches)
- – tibial (including sural and plantar branches)
- superior and inferior gluteal
What body areas does the sacral plexus serve?
- lower trunk and posterior surface of thigh (hip extensors and knee flexors)
- lateral aspect of leg and foot
- posterior aspect of leg and foot
- gluteus muscles of hip
What is the Autonomic Nervous System?
- motor subdivision of the PNS
- consists only of motor nerves
controls the body automatically (aka “involuntary nervous system”) - regulates cardiac and smooth muscles and glands
Somatic Nervous System VS. Autonomic Nervous System
Somatic Nervous System
- motor neuron cell bodies originate inside the CNS
- axons extends to skeletal muscles that are serves
Autonomic Nervous System
- Chain of TWO (2) motor neurons
- —- preganglionic neuron is in the brain or spinal cord
- —- postganglionic neuron extends to the organ
- Has TWO arms
- —- sympathetic division
- —- parasympathetic division
What is the anatomy of the Parasympathetic division?
- aka “Craniosacral division”
- preganglionic neurons originate in:
- – cranial nerves III, IX and X
- – S2 through S4 regions of the spinal cord
- preganglionic neurons synapse with terminal ganglia
- – from there, postganglionic axons extend to organs that are served
What is the anatomy of the Sympathetic division?
- aka “thoracolumbar division”
- preganglionic neurons originate from T1 - L2
- —- axons pass through a ramus comminicans to enter a sympathetic trunk ganglion
- —- sympathetic trunk, or chain, lies near the spinal cord
- after synapsing at the ganglion, the axon may synapse with a second neuron at the same or different level
- or, the preganglionic neuron may pass through the ganglion without synapsing and form a part of the splanchnic nerves
- —- splanchnic nerves travel to the collateral ganglion
- —- collateral ganglia serve the abdominal and pelvic organs
What is Autonomic functioning?
- body organs served by the autonomic nervous system receive fibers from both divisions
- – exceptions: blood vessels, structures of the skin, some glands, and the adrenal medulla
- – these exceptions receive ONLY sympathetic fibers
- when body divisions serve the same organ, they cause antagonistic effects due to different neurotransmitters
- – parasympathetic (cholinergic) fibers release acetylcholine
- – sympathetic postganglioinic (adrenergic) fibers release norepinephrine
- – preganglionic axons of BOTH divisions release acetylcholine
What is the autonomic functioning of the Sympathetic division of SYMPATHETIC?
- sympathetic “fight or flight” division
- response to unusual stimulus when emotionally or physically stressed or threatened
- takes over to increase activities
- remember as the “E” division
- – exercise
- – excitement
- – emergency
- – emergency
- – embarrassment
What are the Spinal Nerves in the PNS?
- dorsal root => brings sensory impulses from periphery to spinal cord
- dorsal root ganglion => cell bodies of sensory neurons
- ventral root => sends motor impulses out to skeletal muscles via motor neuron axons
- **dorsal root and ventral root fuse to form the spinal nerve
What is the Autonomic Functioning of PARASYMPATHETIC?
“housekeeping” activities
- rest-and-digest system
- conserves energy
- maintains daily necessary body functions
- remember as the “D” division
- – digestion
- – defecation
- – diuresis
What are the Developmental aspects of the Nervous System?
- Brain growth ends in young adulthood. Neurons die throughout life and are not replaced; thus, brain mass declines with age
- Orthostatic hypotension is low blood pressure due to changes in body position
- healthy aged people maintain nearly optimal intellectual function
- disease — particularly cardiovascular disease — is the major cause of declining mental function with age
- —- arteriosclerosis is decreased elasticity of blood vessels
