A&P Unit 4/Final

somatic nervous system

includes sensory and motor neurons

under voluntary control and its effect is always excitation

autonomic nervous system

receives sensory input from interoceptors located in organs, blood vessels, muscles and the nervous system

regulates smooth muscle, cardiac muscle, and glands

acts without conscious control and can be excitatory or inhibitory

somatic motor pathway

axon of single, myelinated somatic motor neuron extends from the central nervous system to the skeletal muscles fiber it innervates

autonomic motor pathway

consists of two motor neurons in a series— preganglionic and postganglionic

preganglionic neuron

has its cell body in CNS and the axon extends to an autonomic ganglion

postganglionic neuron

unmyelinated axon extending from the ganglion to the effector

sympathetic pathway

spinal cord → sympathetic preganglionic neuron → autonomic ganglion → sympathetic postganglionic neuron → effectors

OR
spinal cord → parasympathetic preganglionic neuron → suprarenal gland/adrenal gland → blood vessel

parasympathetic pathway

spinal cord → parasympathetic preganglionic neuron → autonomic ganglion → parasympathetic postganglionic neuron → effectors

dual innervation

organs receive nerves from the sympathetic nervous system and the parasympathetic nervous system

sympathetic division

cell bodies of preganglionic neurons are in the lateral horns of the gray matter in the 12 thoracic and first 2-3 lumbar segments (thoracolumbar)

axons exit the spinal column and form the sympathetic trunk, a chain of nervous tissue that runs paralell to the spine bilaterally

parasympathetic division

cell bodies of preganglionic neurons are in the nuclei of four cranial nerves (III, VII, IX, and X) in the brain stem and in the lateral gray matter of the sacral segments 2-4 of the spinal cord (craniosacral)

sympathetic ganglia

sympathetic trunk ganglia: lie in vertical row on either side of vertebral column

prevertebral ganglia: lie anterior to the vertebral column and close to the large abdominal arteries 

since sympathetic ganglia are close to the spinal cord, the sympathetic division has short preganglionic axons and long post ganglionic axons

sympathetic preganglionic neurons → sympathetic trunk ganglia connecting to postganglionic neurons (4 ways)

1. axons may synapse with postganglionic neurons in the first ganglion it reaches

2. axon may ascend or descend to a higher or lower ganglion before synapsing with postganglionic neurons

3. axon may continue, without synapsing, through the sympathetic trunk ganglion to end at a prevertebral ganglion and synapse with postganglionic neurons

   1. axon may pass, without synapsing, through the sympathetic trunk ganglion and a prevertebral ganglion and then extend to the adrenal medullae

parasympathetic ganglia

where preganglionic axons of parasympathetic division synapse with postganglionic neurons

parasympathetic division has long preganglionic axons and short postganglionic axons

sympathetic trunk

anterior and lateral to vertebral column

2 cervical, 11 or 12 thoracic, 4 or 5 lumbar, 4 or 5 sacral sympathetic trunk ganglia dn 1 coccygeal ganglion

cell bodies parasympathetic preganglionic neurons

located in nuclei in brain stem and in the lateral gray matter of the 2nd-4th sacral segements of spinal cord

cranial parasympathetic outflow

extends from brain stem in 4 cranial nerves

sacral parasympathetic outflow

extends from 2nd-4th sacral spinal nerves

sympathetic preganglionic fiber

has many axon collaterals (branches) and may synapse with 20+ post-ganglionic neurons

sympathetic post ganglionic neurons

terminate in several visceral effectors

this is why many sympathetic responses affect almost entire body simultaneously

parasympathetic preganglionic axon

travel to ganglia near or within visceral effectors

only synapse with 4-5 postsynaptic neurons, all of which supply a single visceral effector

this allows parasympathetic responses to be localized to a single effector

vagus nerve

carries nearly 80% of total craniosacral (parasympathetic) outflow

sends exons to heart, lungs, liver, gallblader, stomach, pancreas, small intesting, and part of the large intestine

vagal tone

increased levels help body relax faster after stress

increase by cold exposure, deep and slow breathing, singing, humming, chanting, socializing, and laughing

cholinergic neurons

autonomic neurotransmitter

release the neurotransmitter ACh

include nicotinic and muscarinic receptors

effects are brief becuase ACh is quickly inactivated by AChE

adrenergic neurons

autonomic neurotransmitter

release norepinephrine

-can be released as neurotransmitter or hormone is bloodstream, epi is released as a hormone

include alpha and beta receptors

effects last longer because NE lingers in synaptic cleft longer than ACh

nicotinic receptors

found in postganglionic dendrites, adrenal medulla, and skeletal muscle (motor end plate)

effect is excitation

muscarinic receptors

found in effectors with parasympathetic innervation, also in sweat glands

effect can be excitation of inhibition

agonist

substance that bind to and activates a receptor, mimicking the effect of its natural neurotransmitter or hormone

antagonist

substance that binds and blocks a receptor, preventing its natural neurotransmitter or hormine from exerting its effect

hypothalamus

regulates sympathetic and parasympathetic responses

sympathetic responses

pupils dilate

heart rate, force of contraction, and blood pressure increase

airways dilate

blood vessels supplying kidneys and digestive tract constrict

blood vessels supplying skeletal muscles and cardiac muscles dilate

glycogenolysis and lipolysis increase

parasympathetic responses

salivation

lacrimation

urination

digestion

defecation

smell

chemical sense

nose contains 10-100 million receptors for smell in the olfactor epithelium

olfactory sensory neurons

olfactory cell

exposed dendrite with non-motile cilia, which are site of olfactory transduction

axon projects through cribriform plate to the olfactory bulb

supporting epithelial cells

olfactory cell

provides physical support, nourishment, and electrical insulation for the olfactory sensory neurons

basal epithelial cells

olfactory cell

stem cell which continually undergo cell division to produce new olfactory sensory neurons, whcih only live for about 2 months before being replaced

olfactory glands/Bowman’s glands

produce mucus that is used to dissolve odor molecules so that transduction may occur

sense of smell

receptors in the nasal mucosa send impulses along branches of olfactory (I) nerve

-through cribriform plate

-synapse with the olfactory bulb

-impulses travel along olfactory bulb

-interpretation in the primary olfactory area in the cerebral cortex (temporal lobe)

—olfactory sensations are the only sensations that reach the cerebral cortex without first synapsing in the thalamus

—some axons project to the limbic system, explaining emotional response to odors

taste

chemical sense, much simpler than olfaction

primary tastes

sour

sweet

bitter

salty

umami (meaty savory)

sense of taste

olfactory, tactile, and thermal sensations contribute to perception of flavor

odors from food can pass upward from the mouth into the nasal cavity

—olfaction is much more sensitive than taste

taste buds

receptors for sensation of taste

~10,000 taste buds found mostly on tongue

supporting epithelial cells

taste bud epithelial cell

surround about 50 gustatory epithelial cells in each taste bud

gustatory microvilli

taste bud epithelial cell

project from each gustatory epithelial cell to the external surface through the taste pore, an opening in the taste bud

basal epithelial cells

taste bud epithelial cell

stem cells found at the periphery of the taste bud near the connective tissue layer

produce supporting epithelial cells, which then develop into gustatory epitherlial cells

-gustatory epithelial cells have lifespan of ~10 days

-gustatory epithelial cells synapse with dendrites of first-order neurons

papillae

elevations on tongue where taste buds are located

vallate papillae

contains taste buds

about 12 that form an inverted V at the back of tongue and contain 100-300 taste buds

fungiform papillae

contains taste buds

scattered over the tongue with about 5 taste buds each

foliate papillae

contains taste buds

located in lateral trenches of the tongue (most of thei taste buds degenerate in early childhood)

filiform papillae

covers entire surface of tongue

contains tactile receptors but no taste buds

cranial nerves and sense of taste

facial nerve (VII): carries taste information from anterior 2/3 of the tongue

glossopharyngeal nerve (IX): carries taste and information from posterior 1/3 of the tonuge

vagus nerve (X): carries taste information from taste buds on the epiglottis and in the throat

vision

uses visible light (400-700nm on EM spectrum)

more than half of the sensory receptors in body are located in the eyes

wavelength

distance between two consecutive peakes of an electromagnetic wave

accessory structures of eye

eyelids, eyelashes, eyebrows, lacricmal apparatus, extrinsic eye muscles

palpebral muscles

control eyelid movement

extrinsic eye muscles

responsible for moving eyeball itself in all direction

superior, inferior, lateral, and medial rectus, superior and inferior oblique

conjunctiva

thin, protective mucous membrane that lines the eyelids and covers the sclera

tarsal plate

fold of connective tissue that gives form to the eyelids

contains row of sebacias glads (tarsal glands/Meibomian glands) that keeps the eyelids from sticking to each other

lacrimal appartus

produces and drains tears

pathway for tears

lacrimal glands (secrete lacrimal fluid)

lacrimal ducts (empty onto conj of upper lid)

anterior surface of eye

lacrimal puncta

lacrimal canaliculi

lacrimal sac

nasolacrimal ducts (carry tears into the nasal cavity)

tunics over retina

fibrous tunic- corena and sclera

vascular tunic- choroid, ciliary body, and iris

retina- inner layer

cornea

curved, transparent layer over iris

contains 5 layers

corneal epithelium

5-7 cell layers of non-keratinized stratified squamos epithelium

cell junctions help maintain relatively dehydrated state of cornea

cells secrete the epithelial basement membrane- critical in corneal healing

lifespan of 7-10 days

Bowman’s layer

acellular collagen layer

highly resistant to damage, but cannot regenerate if injured

stroma

organized network of collagen fibrils in a gel-like ground substance

thickest layer of cornea

descemet’s membrane

essentially functions as the basement mebrane to corneal endothelium

highly resistant to trauma, but can regenerate if damaged

endothelium

single cell layer that maintains the cornea’s deturgescence via ionic pumps

cannot undergo cell division

sclera 

“white” of eye

dense connective tissue that covers the entire eyeball except cornea

gives shape to eye, protects inner parts, serves as an attachment for extrinsic muscles

choroid

highly vascularized

lines internal surface of sclera

contains many melanocytes

-provides dark background to prevent glare

ciliary body

anterior to choroid

consists of ciliary processes and ciliary muscle

ciliary processes

capillaries that secrete aqueous humor

ciliary muscle 

circular band of smooth muscle which alters the tightness of zonular fibers to alter shape of the lens to adapt to near or far vision

zonular fibers

extend from ciliary processes and attach and suspend the lens

iris

color flattened doughnut between cornea and lens

contains melanocytes and circular and radial smooth muscle fibers

principle function is to regulate the amound of light entering through the pupil

retina

lines posterior three-quarters of the inner layer of the eyeball

optic disc (blind spot) is the site where the optic nerve (II) exits the eyeball

consists of pigmented layer and neural layer

contains photoreceptors- rods and cones

rods

allow vision in dim light

no color vision, only black, white, and shades of grey

cones

stimulated by brighter light

produce color vision

three types: blue, green, and red, which are sensitive to that color of light

most vision mediated by cones

mascula

spot in the exact center of the posterior portion of the retina, at the visual axis of the eye

fovea centralis

small depression in the center of the macula

only contains cones

neural cells that cover rest of retina are pushed to periphery of fovea centralis

area of highest visual acuity

lens

avascular transparent refractive structure held in position by zonular fibers

helps focus image on retina

divided into anterior and posterior segment

anterior segment of retina

between cornea and lens

filled with aqueous humor

further divided into anterior and posterior chamber by iris

posterior segment of retina

between lens and retina

filled with vitreous humor

light passes through

cornea

anterior chamber

pupil

posterior chamber

lens

vitreous humor

retina