Chapter 16-17: Nerve tracts and the Autonomic Nervous System Flashcards Preview

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Flashcards in Chapter 16-17: Nerve tracts and the Autonomic Nervous System Deck (48)
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2 types of sensory motor pathways

ascending: conduct sensory impulses TO brain
descending: conduct motor impulses FROM brain


sensory and motor pathways vary in complexity: sensory

-first order neuron: sensory info to CNS
-second order: receives impulse from first; spinal cord or brain stem
-third order: carries signal from thalamus to cerebral cortex


sensory and motor pathways vary inn complexity: motor

-somatic motor pathways (skeletal)
--upper motor neuron: in CNS
--lower motor neurons: from CNS to effector
--total of 2 neurons
- autonomic motor pathways-3 total neurons
1. upper motor neuron: in CNS
2. preganglionic neuron: from CNS to peripheral ganglion
3. postganglionic neuron: from ganglion to effector


ascending pathways: posterior column pathway

posterior column pathway
-sides cross in medulla
-sensory impulses from skin, muscles, tendons and joints
-perceived as fine touch, pressure, and body position


ascending pathways: spinothalamic pathway (lateral)

-sides cross in spinal cord
-lateral tract
--sensation of pain and temperature
-spine--> thalamus


ascending pathways: spinothalamic pathway (anterior)

-sides cross in spinal cord
-anterior tract:
--sensation of crude touch and pressure


ascending pathways: spinocerebellar pathways

-anterior tract:
--sides cross in spinal cord
-posterior tract
--do not cross over
-proprioception for fine coordination
-no synapse in thalamus
--never makes it to cortex
--subconscious processing


ascending pathways

posterior column pathway
spinothalamic pathway: lateral and anterior tract
spinocerebellar pathway: anterior and posterior tract


descending pathways:

coricospinal pathway: corticobubular tract, lateral corticospinal tract, anterior corticospinal tract
medial pathway: vestibulospinal tracts, tectospinal tracts, reticulospinal tracts
lateral pathway: rubrospinal tracts


corticospinal pathway (cortex->spine)

-controls voluntary movements
-generally direct
--upper motor neurons synapse onto lower motor neurons


corticospinal pathway tracts

-corticobubular tract:
--motor cranial nerves
-lateral corticospinal tract:
--motor spinal nerves
--crosses over in medulla
-anterior corticospinal tracts
--motor spinal nerves
--does not cross over


medial pathway

-stimulate and inhibit same lower motor neurons as corticospinal


medial pathway tracts

-vestibulospinal tracts: position movement of head
-tectospinal tracts: reflexive head movements
-reticulospinal tracts: gross movements and muscle tone of trunk and proximal limb


lateral pathway

-muscle tone and precise movements of distal upper limb
-stimulate and inhibit same lower motor neurons as corticospinal


lateral pathway tracts

-rubrospinal tracts
-start in red nucleus-> cross-over
-extend to cervical region of spinal cord
-skeletal muscles of distal upper limb


autonomic nervous system

-functions continuously and independently
-no conscious effort needed
-controls visceral activities
--HR, BP, breathing rate, body temperature, response to stress


Difference between autonomic and somatic

autonomic NS
-the pathway usually consists of two neurons
--results in an additional synapse
--may result in additional ganglia
somatic NS
-usually has only one peripheral motor axon
--no peripheral synapsing or ganglia


autonomic nerve fibers

2 neurons
--soma in CNS
--axon leaves CNS and forms synapse in autonomic ganglia
-- cell body in autonomic ganglia; axon goes to visceral effector


2 divisions of autonomic nervous system

-sympathetic: for stressful situations
-parasympathetic: restores body to restful state
-may work together
--each controlling one stage in a sequence of events
-often work antagonistically
--cause different behaviors for different situations
--certain organs are only innervated by one division


sympathetic division location

-preganglionic fibers originate from thoracic and upper lumbar region
-soma in CNS


sympathetic division: preganglionic fibers

-exit CNS
-join ventral root
-travel with motor neurons in spinal nerve
-leave spinal nerve
-enter sympathetic ganglia


sympathetic ganglia

-made of the soma of postganglionic neurons
-two types:
-chain ganglia
--sequence of ganglia running parallel to spinal column on either side
-collateral ganglia
--in other areas of the body


sympathetic chain

-one on each side
-3 cervical
-12 thoracic
-2-5 lumbar
-4-5 sacral
-1 coccygeal
-fusion causes individual variability


chain preganglionic fibers

-the chain ganglion is innervated by presynaptic fibers from nerves T1-L2 ONLY
-NO cervical nerve input
-NO input from nerve L3 or inferior


innervation of ganglia by corresponding spinal nerves

-cervical, sacral, and many lumbar ganglia are NOT innervated by their corresponding spinal nerves
-thoracic nerves innervate cervical ganglia
-thoracic nerves innervate thoracic ganglia
-ONLY T12, L1 and L2 innervate the lumbar and sacral ganglia


functional sequences of chain preganglionic fibers if damaged

-thoracic spinal nerves are damaged:
--no thoracic sympathetic function
-cervical spinal nerves damaged:
--cervical skeletal muscle paralysis
-retain sympathetic function


chain preganglionic fibers: route

-preganglionic fibers leave the spinal nerve and enter the chain via the white ramus
-once there, one of three paths are taken


3 paths of preganglionic chain fibers

1. synapse with the ganglia at the point where they enter
2. travel through the chain to synapse with another ganglion in the chain
3. pass through and go directly to collateral ganglia or a gland


chain postganglionic fibers

-post ganglionic fibers
-exit via gray ramus to spinal nerve to the effector
-exit via sympathetic nerve to the effector


collateral ganglia

-presynaptic fibers go straight through chain ganglion without synapsing
-synapse with postganglionic fibers win collateral ganglia
-postganglionic fibers usually go to abdominal viscera


collateral ganglia: major collateral ganglia

-superior mesenteric
-inferior mesenteric
-deal for the most part with the digestive processes


adrenal (suprarenal) medullae

-presynaptic fibers go through both the chain and collateral ganglia
-straight to the medulla of the adrenal gland
-stimulate the production of the hormones epinephrine and norepinephrine (adrenaline)
-no postganglionic fibers
-pumps E and NE into blood stream. Unlocalized


effects of sympathetic division

-increase alertness
-energy and euphoria
-excites cardiovascular and respiratory centers
-increased muscle tone
-mobilization of energy


sympathetic activation

-CNS stimulates preganglionic neurons
-preganglionic neurons:
--always release Ach (acetylcholine)
--known as a cholinergic synapse
--stimulates postganglionic neurons
-postganglionic neurons
--usually release NE to an effector
--known as an adrenergic synapse


adrenergic receptors: alpha

-respond to both E and NE
-target smooth muscle
-constrict sphincters and BV's


adrenergic receptors: Beta

-respond to E only
-target skeletal and smooth muscle of respiratory tract
-increase metabolic rate
-usually excitatory


symmary of sympathetic

1. preganglionic fiber is short; postganglionic is long
2. synapsing occurs in sympathetic chain or collateral ganglia
3. preganglionic fiber releases Ach
4. postganglionic fiber releases NE
5. prepares body for emergencies
6. effects widespread and persistent


parasympathetic system

-originates from neurons in midbrain, pons, medulla and sacral region of spinal cord
-exit CNS via
--cranial nerves, 3, 7, 9 and 10
--sacral nerves 2-4


preganglionic fibers

-cranial nerves III, VII, and IX go to ganglia near target organs
--eyes and facial glands
-cranial nerve X and S2-4
--converge in a large autonomic plexus
--exit plexus and then to target organs
--heart, lungs, GI tract, urinary tract, sexual organs


Dual innervation

parasympathetic organs innervate same ones as sympathetic


postganglionic fibers

-usually very short
-close to, or even within, target organs
-effects or parasympathetic system is more focused and localized



-constrict pupils
-stimulate secretion of digestive glands
-secretion of hormones promoting nutrient absorption
-increase motility of digestive tract
-stimulate defecation
-contraction of urinary bladder
-constriction of respiratory passages
-reduce HR and force of contraction
-sexual arousal


parasympathetic activation

-all neurons (pre- and postganglionic) release Ach
-quickly cleaned up after release by Acetylcholinesterase
-short lived effects that are localized
-much more local, can be shut down quickly


summary of parasympathetic

-presynaptic neurons are long and secrete Ach
-postsynaptic neurons are short, produce Ach; either excitatory or inhibitory
-innervate organs in head and abdominal pelvic region
-all ganglia in or near targets


dual innervation

-most organs receive innervation from both divisions
-cranial area
--sympathetic reaches via chain ganglia
--parasympathetic reaches via cranial region
-thoracic and abdominal area
--sympathetic and parasympathetic mingle at plexuses
--examples: cardiac plexus; esophageal plexus


visceral reflexes

-simple functional units of the ANS
-provide an autonomic motor response
-common for digestive system


2 types of visceral reflexes

-long reflexes: go to the CNS for processing
-short reflexes: are processed in the autonomic ganglion
--only behavioral loop that does not involve CNS
--goes sensory-ganglia-effector


control of autonomic activity

-many control centers in medulla
-hypothalamus regulate body temperature
-limbic system and cerebral cortex control ANS when person is stressed out