AnP Chapter 11 PNS (LO8) Flashcards
Spinal Nerves
relay info from the spinal cord to the rest of the body
A nerve
consists of many nerve fibers (axons) encased by connective tissue
The number of nerve fibers contained in a single nerve varies from a few to a million
Mixed nerves
contain both sensory and motor fibers
Transmit signals in two directions
Sensory nerves
contain only sensory (afferent) fibers
Carry sensations toward the spinal cord
Motor nerves
contain only motor (efferent) fibers
Carry messages to muscles and glands
spinal nerves and the numbers in each section
8 cervical nerves (C1-C8) 12 thoracic nerves (TI-T2) 5 lumbar nerves (LI-L5) 5 sacral nerves (S1-S5) 1 coccygeal nerve (Co)
Invertebral foramina
holes in the vertebra that nerves pass through
Plexuses
nerve networks formed by subdivided branches
4 major plexuses
cervical plexus
the brachial plexus
the lumbar plexus
the sacral plexus
Cervical plexus
contains nerves that supply the muscles and skin of the neck, tops of the shoulders, and part of the head
Phrenic nerve
stimulates the diaphragm for breathing
Brachial plexus
innervates the lower part of the shoulder and arm
Key nerves traveling into arm from Brachial plexus
Axillary nerve
Radial nerve
Ulnar nerve
Median nerve
Lumbar plexus
derive from the fibers of the first four lumbar vertebrae
Supplies thigh and leg
Femoral nerve: a key nerve that runs in this region
Sacral plexus
form for fibers from nerves L4, L5 and S1-S4
Sacral plexus and lumbar plexus often referred to as…
lumbosacral plexus
Sciatic nerve
the largest nerve in the body runs down the thigh
Dermatomes
each spinal nerve innervates a specific area of the skin
used to assess and diagnose the level of spinal cord injury
Paraplegia
a loss of sensory and motor function in all parts of the trunk, legs, and pelvic organs
Results from an injury between T1 and L1
Quadriplegic
produces a lot of sensory and motor functions in the arms, legs, trunk and pelvic organs
injury above C5
C4 injury:
C6 injury:
T5 injury:
L5 injury:
C4 injury: complete paralysis below the neck
C6 injury: paralysis of hands, arms, trunk and legs
T5 injury: paralysis of trunk and legs
L5 injury: loss of function in legs and hips
Reflexes
quick, involuntary, predictable response to a stimulus
Reflex arch
bypass regions of the brain or conscious decisions are made
Autonomic (visceral) reflexes
involve secretion from glands or the contraction of smooth muscle
Somatic reflexes
involves a contraction of skeletal muscle after being stimulated by somatic motor neuron
How to protect the body against harm
How somatic reflexes work
- somatic receptors located in the skin, and muscle, or a tendon detect a sensation
- afferent (sensory) nerve fibers send a signal directly to the spinal cord
- The impulse immediately passes to motor neuron
- The motor neuron initiates an impulse back to the muscle causing it to contract producing a reflex
Cranial nerves
relay messages to the rest of the body
The brain has 12 pairs of cranial nerves
Cranial nerves are part of the peripheral nervous system
Each cranial nerve is identified by name suggesting its function and a according to their order
Some cranial nerves contain only sensory fibers some contain primary motor fibers others contain both
Olfactory nerve
(I, sensory)
Governs sense of smell
Terminates in olfactory bulbs in the cribriform plate just above the nasal cavity
Impairment resulting in impaired sense of smell
facial nerve
(VII, Mixed)
Sensory portion concerned with taste
motor portion controls facial expression and secretion of tears and saliva
Damage causes sagging facial muscles in a distorted sense of taste
Vestibulocochlear nerve
(VIII, Sensory)
Concerned with hearing and balance
Damage results in deafness, dizziness, nausea, and loss of balance
Vagus Nerve
(X, mixed)
Longest and most widely distributed cranial nerve
Supplies organs in the head and neck as well as those in the thoracic and abdominal cavities
Please key role in many Heart, lungs, digestive and urinary functions
Damage causes hoarseness or loss of voice and impaired swallowing
Optic Nerve
(II, Sensory)
Concerned with vision
Links the retina to the brains visual cortex
Damage causes blindness in part or all of the visual field
oculomotor, Trochlear and Abducens nerves
(III, IV, VI, mainly motor)
Regulate voluntary movements of the eyelid and eyeball; oculomotor also controls pupil construction
Damage can cause drooping eyelid, dilated pupil, inability to move eye in some directions; double vision
Trigeminal nerve
(V, two sensory and one mixed branch)
sensory branches (ophthalmic and maxillary) sense touch, temperature and pain on the eye, Face and teeth
mixed branch (mandibular) controls chewing and detect sensations in lower jaw
ophthalmic branch triggers the corneal reflex: blinking in response to a light touch on the eyeball
Damage to sensory branches causes loss of sensation in upper face
Damage to mixed branches results and impaired chewing and loss of sensation in Jaw
Glossopharyngeal nerve
(IX, mixed)
Motor fibers govern tongue movements, swallowing and gagging
Sensory fibers handle taste, touch and temperature from the tongue also concerned with regulation of blood pressure
Damage causes impaired swallowing, choking and bitter or sour taste
hypoglossal nerve
(XII, mainly motor)
controls tongue movements
Damage causes impaired speech and swallowing as well as deviation of tongue toward injured side
Spinal accessory nerve
(XI, mainly motor)
Controls movement in head, neck and shoulders
Damage in pairs movement of head, neck and shoulders
mnemonic for cranial nerves
On Olfactory (I) Old Optic (II) Olympus’ Oculomotor (III) Towering Trochlear (IV) Top Trigeminal (V) A Abducens (VI) Friendly Facial (VII) Viking Vestibulochlear (VII) Grew Glossopharyngeal (IX) Vines Vagus (X) And Accessory (XI) Hops Hypoglossal (XII)
Autonomic Nervous System
responsible for regulating the activities that maintain homeostasis
The secretion of digestive enzymes, the construction and dilation of blood vessels for the maintenance of blood pressure, and the secretion of hormones
Sends motor impulses to cardiac muscles, glands, and smooth muscle
Visceral motor system
what the ANS is sometimes called because it Targets organs
Visceral reflexes
these reflexes affect an organ
Somatic pathways are structured as follows:
The neurons cell body lies within the CNS
A single myelinated axon enters from the brain stem or spinal cord to a skeletal muscle
At the target muscle the neurotransmitter acetylcholine (Ach) is released to cause muscle contraction
autonomic pathways are structured as follows:
A myelinated Preganglionic neuron extends from the brain stem or spinal cord to a ganglion
In the ganglion it synapses with a postganglionic neuron and the neurotransmitter ACH is released
The axon of the unmyelinated postganglionic neuron extends to the target organ
—-The neurotransmitter released varies: parasympathetic fibers release ACH whereas sympathetic fibers release norepinephrine
Somatic nervous system
Innervates skeletal muscle
Consists of one nerve fibre leading from CNS to target (no ganglia)
Secretes neurotransmitter acetylcholine
Has an excitatory effect on target cells
Operates under voluntary control
Autonomic nervous system
Innervates glands, smooth muscle, and cardiac muscle
Consists of two nerve fibers that synapse At the ganglion before reaching target
Secretes both acetylcholine and norepinephrine as neurotransmitters
May excite or inhibit target cells
Operates involuntarily
Divisions of the Autonomic Nervous System
sympathetic division in the parasympathetic division
The sympathetic division vs parasympathetic
prepares the body for physical activity and is responsible for the fight or flight reaction
has a calming effect on body functions
Sympathetic Division functions
Increases alertness
Increases heart rate
Dilates bronchial tubes to increase air flow to the lungs
Dilates blood vessels of skeletal muscle to increase blood flow
Inhibits intestinal motility
Stimulates secretion of thick salivary mucous
Stimulates sweat glands
Stimulates adrenal medulla to secrete epinephrine
Has no effect on the urinary bladder or internal sphincter
Causes “flight or fight” response
Parasympathetic Division functions
Has a claming effect
Decreases heart rate
Constricts bronchial tubes to decrease air flow in lungs
Has no effect on blood vessels of skeletal muscles
Stimulates intestinal motility and secretion to promote digestion
Stimulates secretion of thin salivary mucous
Has no effect on sweat glands
Has no effect on adrenal medulla
Stimulates the bladder wall to contract and the internal sphincter to relax to cause urination
Causes “resting and digesting” state
The Sympathetic Divison other name and where it arises from
Also called the Thoracolumbar division
Arises from the thoracic and lumbar regions of the spinal cord
The Adrenal Glands
triangular shaped glands perched on top of each kidney
Play a role in function of the sympathetic nervous system
Sympathetic preganglionic fibers pass through the outer cortex and terminate in the center
Adrenal medulla
the center of the adrenal gland
When stimulated it secretes epinephrine
epinephrine as well as norepinephrine can bind to the receptors of sympathetic effectors which helps prolong the sympathetic response
The Parasympathetic Division other name
Also called craniosacral division because The neurons of the parasympathetic division arise from the brain and the sacral region of the spinal cord
Parasympathetic fibers leave the brain stem by joining one of the following cranial nerves:
Oculomotor nerve (III): parasympathetic fibers carried in this nerve innervates ciliary muscle, which is against the lens of the eye, and the pupillary constrictor, which constricts the pupil
Facial nerve (VII): these parasympathetic fibers regulate the tear glands, salivary glands and nasal glands
Glossopharyngeal nerve (IX): the parasympathetic fibers carried in this nerve trigger salivation
Vagus nerve (X): this nerve carries about 90% of all parasympathetic preganglionic fibers
Sympathetic structure
Originates in the thoracolumbar region
Ganglia lie in chain along side spinal cord
Has short preganglionic and long postganglionic fiber
Employs most norepinephrine as a neurotransmitter
Produces widespread generalized effects
Parasympathetic structure
Originates in craniosacral region
Ganglia lie in or near target organs
Has long freaking lunatic and short postganglionic fiber
Employs acetylcholine As a neurotransmitter
Produces local effects
Effects of the ANS on Target Organs
The two divisions of the ANS tend to exert opposite effects
The ANS employs two different neurotransmitters
acetylcholine (Ach) and norepinephrine (NE)
define cholinergic fibers
Fibers that secrete acetylcholine
define adrenergic fibers
fibers that secrete norepinephrine
Cholinergic Fibers
Include the preganglionic fibers of both the sympathetic and parasympathetic divisions
Include the postganglionic fibers of parasympathetic division
Secrete acetylcholine
Adrenergic Fibers
Include most but not all of the postganglionic fibers of the sympathetic division
Secrete norepinephrine
The effects of ——— division tend to be short-lived whereas the effects of ———– division last longer
The effects of parasympathetic division tend to be short-lived whereas the effects of sympathetic division last longer
Remember in all pathways preganglionic fibers are —— and secrete ——-
Remember in all pathways preganglionic fibers are cholinergic and secrete acetylcholine
Receptors
After being released the neurotransmitter binds to receptors on the effector cells of the target organ
ACH binds to cholinergic receptors and norepinephrine behind to adrenergic receptors
Several subtypes of receptors that determine the effect produced by neurotransmitter
Cholinergic Receptors
Acetylcholine may bind to one of two different types of receptors: nicotinic receptors and muscarinic receptors
Nicotinic Receptors
These receptors occur within ganglia of the ANS in the adrenal medulla and in the neuromuscular junction
All cells with nicotinic receptors are excited by ACH
Muscarinic Receptors
These receptors occur on the glands, smooth muscle and cardiac muscle cells of the organs innervated by cholinergic fibers
Cells with muscarinic receptors exhibit a variable response to Ach: some are excited some are inhibited
This variable response allows ACH to stimulate intestinal smooth muscle while inhibiting cardiac muscle
Adrenergic Receptors
There are also two basic types of adrenergic receptors:
Alpha-a- adrenergic receptors and beta-b- adrenergic receptors
Alpha-a- adrenergic receptors and beta-b- adrenergic receptors
Cells with a- adrenergic receptors are excited by norepinephrine
Cells with b- adrenergic receptors are inhibited by norepinephrine
Neurotransmitters and Receptors
Sympathetic Division
Cholinergic fibers of preganglionic neurons secrete Ach
Ach binds to nicotinic receptors on postganglionic neurons
Most postganglionic neurons are adrenergic and secrete NE
- —-Occasionally cholinergic and secrete Ach
- —-Ach binds to muscarinic receptors
NE binds to alpha and beta adrenergic receptors
Neurotransmitters and Receptors
Parasympathetic Division
Cholinergic fibers of preganglionic neurons secrete Ach
Ach binds to nicotinic receptors on postganglionic neurons
Cholinergic postganglionic neurons secrete Ach
