ANAT 3001 pathways and autonomics

sensory vs motor pathways

• how information gets from body to brain and commands from brain to body

• each pathway relayed by several neurons

ascending pathway

• carry sensory information to brain

• travel through ascending tracts in spinal cord

descending pathway

• carry motor information from brain to targets

• travel through descending tracts in spinal cord

white matter

funiculi - functionally distinct regions of white matter in spinal cord

• each contain multiple tracts

sensory pathways

• utilize 2-3 neurons in a series to transmit information to brain

• primary, secondary, & tertiary neurons

• pathways

  • posterior funiculus

posterior funiculus

• carries information on fine touch, pressure, conscious proprioception

• medial lemniscal pathway (3 neurons)

  • primary neuron

  • secondary neuron

  • tertiary neuron

primary neuron

• cell body in dorsal root ganglia

• axon ascend in posterior funiculus to medulla oblongata

secondary neuron

• cell body in medulla oblongata

• axon cross over (decussate) in medulla oblongata (medial lemniscus tract), travel to thalamus

tertiary neuron

• cell body in thalamus

• axon travels to postcentral gyrus (primary somatosensory cortex)

motor pathways

• originate in cerebral cortex (or cerebral nuclie), descend from brian

• at least 2 neuron in pathway

  • upper motor neuron (UMN)

  • lower motor neuron (LMN)

• UMN synapses with LMN directly or with interneurons

corticospinal tract

• control precise, skilled voluntary movement (skeletal muscle)

corticospinal tract - UMN

• cell body in pre central gyrus (primary motor cortex)

• decussate at

  • medulla oblongata - lateral funiculus

  • spinal cord - ventral funiculus

corticospinal tract LMN

• cell body in ventral horn of spinal cord

• axon travels to target in body

functional organization of the nervous system

somatic vs visceral: sensory neurons

• visceral sensory is very similar to somatic sensory neurons

• both have a single neuron pathway in PNS

• both have cell bodies in dorsal root ganglia & synapse in dorsal horn

somatic vs visceral: motor neurons

visceral motor innervation (autonomics)

• generally to structures in body cavities (not always)

  • cardiac muscle (myocardium of heart)

  • smooth muscle (digestive tract, bronchi, blood vessels, eye muscles)

  • glands (salivary, digestive, lacrimal, reproductive, sweat glands)

• unlike somatic motor, can excite or inhibit the target

• regulates below conscious level (deep to cortex): heart function, blood pressure, body temp, respiration, sweating, digestion

sympathetic vs, parasympathetic

motor neuron comparison

components of autonomic nervous system

parasympathetics - cranial nerves

• oculomotor nerve (CN III)

• facial nerve (CN VII)

• glossopharyngeal nerve (CN IX)

• vagus nerve (CN X)

oculomotor nerve (CN III) - targets

• pupil - constrict pupil

  • contract sphincter pupillae muscle

• lens - thicken lens

  • ciliary muscle

lens

facial nerve (CN VII) - targets

• lacrimal gland - produce tears (lacrimation)

• submandibular and sublingual salivary glands - produce saliva (salivation)

glossopharyngeal nerve CN IX - targets

parotid salivary gland - produce saliva (salivation)

vagus nerve CN X - targets

• lungs - constrict bronchioles

  • decrease air to lungs

• heart - decrease heart rate

• GI tract - increase activity of digestive system

parasympathetics: S2-S4

• pelvic organs & external genitalia

sympathetics - targets & effects

• pupil - dilate pupil

• lens - thin lens

• lacrimal gland - decrease tear production

• salivary glands - decrease saliva production

• lungs - dilate bronchioles (increase air to lungs)

• heart - increase heart rate

• GI tract - decrease activity of digestive system

• sweat glands - produce sweat

sympathetic chain (trunk)

• nerve “chain” with ganglia

• pre and postsynaptic sympathetic neurons synapse in ganglia

  • presynaptic cell bodies in lateral horn os spinal cord between T1-L2

  • ganglia in sympathetic trunk contain cell bodes of postsynaptic neurons

• allows for sympathetic neurons to travel up and down thoracolumbar region

sympathetic chain (trunk) connection

• sympathetic chain connects to spinal nerves via short, communicating branches

how do sympathetics get to the body wall (pathway 1)

pathway 1

• presynaptic neuron enters sympathetic trunk

• synapses with postsynaptic neuron in chain ganglion

• postsynaptic neuron rejoins spinal nerve to body wall target

targets (no not have parasympathetic innervation)

• sweat glands

• blood vessels

• arrector pilli muscles

how do sympathetics get to the body cavity (pathway 2)

pathway 2

• presynaptic neuron enters sympathetic trunk

• joins splanchnic nerve

• synapses with postsynaptic neuron at collateral ganglion

• postsynaptic neuron travels to target

targets

• visceral organs (heart, digestive tract, kidneys, uterus)

fight or flight response (pathway 3)

pathway 3

• presynaptic neuron enters sympathetic trunk and pass through without synapsing

• presynaptic neuron travels directly to adrenal gland to synapse with cells in the medulla

• cells in adrenal medulla release epinephrine (adrenalin) and norepinephrine directly into bloodstream for rapid, systemic effect

fight or flight

• sympathetic division responding to emergency situation