Chapter 16-17: Nerve tracts and the Autonomic Nervous System Flashcards
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
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
- NO CEREBRAL CONNECTION
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
- preganglionic
- -soma in CNS
- -axon leaves CNS and forms synapse in autonomic ganglia
- postganglionic
- 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
- T1-L2
- 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
- ganglia:
- 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
- synapse with the ganglia at the point where they enter
- travel through the chain to synapse with another ganglion in the chain
- 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
- celiac
- 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
- preganglionic fiber is short; postganglionic is long
- synapsing occurs in sympathetic chain or collateral ganglia
- preganglionic fiber releases Ach
- postganglionic fiber releases NE
- prepares body for emergencies
- 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
functions
- 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
