1.Nervous system

-quick, short lived communication

2. Endocrine system

-use hormones (chemical messengers)

-slower, but longer lasting

 Central Nervous System (CNS)

brain and spinal cord

2. Peripheral Nervous System

(PNS)

-nerves coming from the brain and spinal cord (cranial nerves and spinal nerves)

Somatic Nervous System

-made of neurons that affect skeletal muscle

. Autonomic Nervous System (ANS)

Parasympathetic division

-relaxed state          

-fibers leave the brain and lower part of the spinal cord

Sympathetic Division

-stressful state (fight or flight)

-fibers leave the middle portion of the spinal cord

-conduct impulses

-~ 100 billion (brain)

-~ 1 billion (spi cord)

Neuroglial cells

-functions to supprt and nourish neurons

1900 billion

Astrocytes

-in CNS only

-largest, most numerous

-found between neurons and capillaries, holding them together to form protective grid (blood brain barrier)

-this barrier makes capillaries impermeable to many compounds (doesn’t allow harmful substances to impact neurons)

-also, nourishes neurons by picking up 02 and glucose from capillaries

Microglial Cells

-in CNS

-Rarest, smallest

-derived from wbc’s originally

-phagocytic cells that perform protective function by disposing of pathogens and cellular debris

Ependymal Cells

-in CNS, ciliated

-lines spaces of CNS (ventricles of brain, central canal of spinal cord)

-formulates and moves cerebrospinal fluid through these spaces

. Oligodengroglial cells (oligodendrocytes)

-in CNS

-produces myelin (fatty insulating material)

-processes of these cells are made up of myelin, wrap around axons (forming sheaths) to increase speed of impulse conduction

Schwann Cells (neurolemmocyte)

-in PNS

-produce myelin

-wind layers of myelin around fibers to increase speed of conduction

-nuclei and cytoplasm of these cells remain outside layers of myelin, called neurilemma

-neurilemma essential to regeneration of injured nerve fibers in PNS

-forms a “guiding tunnel” to allow severed end of the fiber to regrow

-not found in the CNS

-support clusters of cell bodies called ganglia, found in PNS

Dendrites “little trees”

-thin threadlike extensions

-usually many per neuron

-receive information to be interpreted

Cell body, soma, perikaryon

-bulge in the neuron where nucleus and most organelles found

-unmyelinated

-clusters of cell bodies in PNS are called ganglia (ganglion) Ex. Dorsal root ganglion

-clusters in CNS are called nuclei Ex. Basal or cerbral nuclei

Axon

-singular extension from cell body

-originates from area of cell body called axon hillock

-conducts impulses away from cell body

-may have branches called collaterals

-distal of terminal end is called synaptic knob, which is very close but does not touch the next cell

Neurofibrils

-inside neuron

-network of “threads” to help maintain shape of neuron

Nissl Bodies

-inside neurons

-scattered within cytoplasm (of cell body and dendrites)

-modified rough endoplasmic reticulum

-makes proteins useful in impulse transmission

Unipolar neuron

-one extension (process) from cell body

-carry info to CNS so these are sensory or afferent neurons

Bipolar neuron

-2 extensions (processes) arising from cell body at either end

-one dendrite and one axon

-least numerous type

-only found in inner ear, retina, olfactory pathway (smell)

Multipolar neuron

-many extensions from cell body

-one axon, many dendrites

-most common neurons in CNS: neurons of brain and spinal cord

-also all motor neurons that control skeletal muscles

Sensory or Afferent Neurons

-pick up changes within body of in environment

-carry impulses from sense organ or internal organ to the CNS

-smallest number of neurons

Interneuron’s

-multipolar

-in CNS

-carry impulses (Signals) between sensory and motor neurons

-integration occurs here

-makes up ~99% of neurons in body

-the more complex the response is to a given stimulus, the greater the # of interneuron’s involved

Motor or Efferent neurons

-carry impulses away from CNS to effector organ (muscles or glands)

-multipolar

-cell bodies are typically located in CNS (with axons leaving the CNS à PNS)

*If effector is skeletal muscle than somatic motor (efferent) neuron of somatic NS

*if effector is cardiac or smooth muscle or glands than visceral motor (efferent) neurons of autonomic NS

Motor or Efferent neurons

-carry impulses away from CNS to effector organ (muscles or glands)

-multipolar

-cell bodies are typically located in CNS (with axons leaving the CNS à PNS)

*If effector is skeletal muscle than somatic motor (efferent) neuron of somatic NS

*if effector is cardiac or smooth muscle or glands than visceral motor (efferent) neurons of autonomic NS

-bundle of nerve fibers(axons) in the PNS

Tract

-bundle of nerve fibers(axons) in the CNS

myelinated

 unmyelinated ex. Cerebral cortex, central area of spinal cord

Neuron physiology

-plasma membrane of neuron is polarized at rest

-due to slight difference in #s of positive and negative ions on either side of membrane

-negative on inside compared to outside

-this charge separation creates electricity and is measured in voltage (millivolts)

-resting(not conducting an impulse) membrane potential (RMP) is -70mV

-negative sign refers to inside of neuron (as it is negatively charged to outside of neuron)

Resting Membrane Potential is maintained by:

1. Unequal distribution of ions outside neuron compared to inside

-extracellular: rich in Na+, compared to inside

-intracellular: rich in K+, compared to outside

2. Membrane is selectively permeable

-more leakage channels for K+ than Na+ (more permeable to K+ than Na+)

-allows more K+ ions to diffuse down concentration gradient out of cell than Na+ ions to diffuse down its concentration gradient into cell

(as more K+ leaves, inside tends to become more negative compared to outside)

3. Inability for most anions (negatively charged ions) to leave neuron

-membrane not as permeable to anions (phospates, sulfates, proteins) that are made inside cell

3. Na+/K+ pumps (use ATP)

-pump move substances against concentration gradient

-there are some Na+ leakage channels and if  left alone, slowly Na+ would move into ell, down its concentration gradient (destroying resting membrane potential)

-pumps expel 3Na+ out for every 2K+ it brings in (removing more positive ions than bringing in)

Depolarization

-reduction in membrane potential

-inside cells less negative than resting potential (may approach or even go above zero)

            -happens during action potential

Repolarization

-moving back to resting potential (-70mV)

Hyperpolarization

-membrane potential is increased becoming even more negative than resting potential (-70mV -> -90V)

-brief reversal of membrane potential from -70mV to ~ +30mV

-accomplished in milliseconds

-depolarizes membrane

Generating an action potential

1.Resting state

-RMP maintained at -70mV

Keep in mind:

-neurons are excitable and respond to stimuli from sense receptors or other neurons via neurotransmitters

2.Depolarization

-when adequate stimulus is applied to neuron (threshold stimulus), Na+ channels open locally

(Na+ much more permeable at this time)

-K+ channels close

-Na+ diffuses rapidly down conc. gradient depolarizing membrane to ~+30mV

-diffusion stops

3. Repolarization

-Na+ channels close

-K+ channels open and K+ moves out of cells until inside is back to its resting state (-70mV) Na/K pump helps here too!

*Rapid change of charge is called an action potential (AP)

4. AP is then passed to adjacent portion of plasma membrane, depolarizing it (chain reaction)

-referred as an impulse

From the time Na+ channels open until Repolarization is complete (return to resting potential), membrane cannot respond normally to further stimulation

Called refractory period

-limits rate at which AP can be generated

-ensures one way transmission of AP (can’t go backwards as that area still in refractory period) it is still repolarizing when in refractory period

The speed of the impulse depends on:

1. Diameter of the fiber

-larger is quicker

(greater surface area, more Na+ channels open during depolarization, and more rapid stimulation of adjacent membrane area)

2. Myelination

-myelinated fibers carry the impulses more quickly

-due to the nodes of Ranvier (constrictions in the myelin sheath)

-impulses are able to “leap” between nodes

-this is called salutatory conduction

Use neurotransmitters (chemicals) to move across cleft, and communicate to next neuron

-secreted by axon of presynaptic neuron

-will impact the dendrites or cell body of the postsynaptic neuron

Communication between neurons

1. When AP arrives at axon terminal (synaptic knob) Ca++ channels open in the plasma membrane

2. Extracellular Ca++ moves into synaptic knobs of presynaptic neuron.

3. Ca++ causes release of NT from vesicles by exocytosis (into the cleft)

4. NT diffuses across cleft to bind to receptor on plasma membrane of postsynaptic neuron.

5. Signal then begins in postsynaptic neuron (Na+ rushes in…) depolarization if excitatory

Neurotransmitters 

-some neurons release only one NT while others can release more

-classify NTs by chemical structure (amine, amino acid, neuropeptide, etc.) or by function (excitatory or inhibitory)

excitatory

-NT depolarizes the post synaptic neuron, causin an action potential

inhibitory

-NT causes Hyperpolarization (more neg!) (reduces the ability of the post synaptic neuron to generate an action potential)

NT:Norepinephrine

In CNS: creates sense of well being

PNS: excite or inhibit ANS, depending on receptors.

(important in sympathetic division of ANS)

CNS: control of skeletal muscle, sense of well being, (deficiency in some brain areas is associated with Parkinson disease)

PNS: limited action in ANS

NT:Serotonin

CNS: primarily inhibitory, leads to sleepiness

-action can be enhanced by SSRI’s (selective serotonin reuptake inhibitors)

(antidepressant drugs like Prozac, Zoloft, Celexa, Paxil, Lexapro)

Reflex

-predictable response to a stimulus 

Somatic Reflexes

-skeletal muscle contractions

Autonomic (visceral) reflexes

There are 5 components in all reflex arcs

1. Receptor

-site of stimulus where change is detected

temp? pressure? Light? Stretching?

2. Sensory (afferent) neuron

-transmits afferent impulse to CNS

3. Integration Center

-within CNS

-may have single or multiple synapses between neurons

4. Motor (efferent) neurons

-conducts efferent impulses from integration center to effector

5. Effector

-muscle fiber to gland cell that responds to efferent impulses

Central Nervous System (CNS)

brain, spinal cord protection

1. Bones

2. Meninges (connective tissue)

3. Fluid (cerebrospinal fluid)

Dura Mater

-outermost meninges

-strong

-dense fibrous connective tissue

-contains blood vessels, nerves

-in brain attaches to inside of cranial bones

The dura extends inward to form flat partitions to subdivide cranial cavity : (supports brain tissue)

Falx cerebri

attaches to crista galli

-extends downward into longitudinal fissure, separating right and left cerebral hemispheres

-space is formed sagitally: superior sagittal sinus

-this space collects venous blood from bain and it is area that cerebrospinal fluid empties into 

Falx cerebelli

-extension of dura mater between hemispheres of cerebellum

Tentorium cerebelli

-extension that seperates cerebrum from cerebellum

-the dura mater continues from brain to surround the spinal cord, terminating as a dead end sac at the level of S2 (below) the end of the spinal cord itself)

- the dura does not attach to the vertebrae but is separated by a space, epidural space

Arachnoid mater

-delicate, web-like membrane, lacks blood vessels

-many thin strands of this membrane extend from its undersurface to attach to the pia mater

Pia Mater

-innermost layer

-contains nerves and blood vessels

-attaches directly to surface of brain and spinal cord

Subdural space

-created between the dura and the arachnoid

-potential space (small!)

Subarachnoid space

-created by “webby” arachnoid

-between arachnoid and pia

-cerebrospinal fluid passes through this space

Epidural space

(above the dura)

-space that contains blood vessels, some adipose tissue

-found in spinal cord, not in brain

Cerebrospinal Fluid (CSF)

Functions of CSF?

1.Protection, shock absorber

-gives buoyancy to CNS structures

2. Delivers nutrients and carries away wastes (as does blood)

Ventricles of brain (4 of them)

-interconnected cavities

-filled with CSF

-continuous with central canal of sp.cord

Lateral ventricles (2, left and right)

-one in each cerebral hemisphere

-connected to 3^rd ventricle by midline interventricular foramen

-3^rd ventricle connected to the 4^th ventricle by cerebral aqueduct (aqueduct of sylvius)

-4^th ventricle is continuous with central canal of spinal cord

Formation of CSF

-masses of specialized capillaries and ependymal cells, called the choroid plexuses secrete CSF from blood

-plexuses separate blood plasma from formed elements and large proteins of blood

-choroid plexuses are found in ventricles (most of CSF formed in lateral ventricles)

- fluid then circulates with help of ciliated ependymal cells that line these spaces.

CSF

-140mL are in CNS at all times

-continuous flow

-if flow is blocked, can have a build up of CSF with increased pressure on brain

-pressure may kill neurons if pressure is not relieved

-called hydrocephalus

             causes – tumor? Developmental problem of a fetus?

-shunt inserted to drain fluid

Spinal Cord

-extends from foramen magnum to L-1 or L-2 (the tip at l-1 or l-2 is called conus medullaris

-spinal nerves branch off throughout its length

-extending downward from conus medullaris are lumbar and sacral nerves, plus thein cord of connective tissure (filum terminale) used to anchor cord to coccyx

-these nerves form the cauda equina (“horses tail”)

Anterior median fissure (ventral)

-deeper and wider

Posterior median sulcus (dorsal)

Gray Matter(spinal cord)

-butterfly shaped

-non-myelinated

-situated around central canal

(unmyelinated)

-can be divided into 3 regions or columns

posterior white columns

anterior white columns

lateral white columns

-each column contains tracts whose axons are carrying sensory or motor information

ascending tracts

descending tracts

Dorsal root ganglion (swelling)

-collection of cell bodies of sensory (afferent) neurons

Ventral root

-made up of axons of motor (efferent) neurons, carrying impulses(information) away from spinal cord

Functions of spinal cord

1. Spinal reflex (integration center)

2. Transmits sensory impulses to brain via ascending or sensory tracts

3. transmits motor impulses down the brain via descending or motor tracts

Tracts: 

bundles of nerve fibers in CNS (no nerves in CNS, just tracts)

How are tracts named? 

-        by where impulse originates to where it is going

-        often these tracts cross over (decussate) in spinal cord or medulla of brain

ex. Cortcospinal tract (descending)

-begins in cerebral cortex and carries motor impulses downward through cord providing conscious control of skeletal muscles

-sometimes called pyramidal tracts after pyramid shaped regions in the medulla through which they pass

ex. Spinothalmic tract (Ascending)

-begins in spinal cord and carries sensory impulses associated with pain to the thalamus

-fibers decussate in spinal cord

Brain

-contains over 90% of all neurons and glial cells of body

-adult brain weighs about 3 lbs

-neurons go through the cell cycle and mitosis during prenatal development (producing 100,000 new cells per minute during the first month of pregnancy)

-can continue for several months after birth

-afterwards the size and their connections of neurons but not the #s.

Cerebrum

-largest portion

-cortex is outer layer (gray matter)

-divided into right and left cerebral hemispheres which are connected at the corpus callosum (deep)

-medial line divides the cerebrum into 2 hemispheres: longitudinal fissure

-infoldings of cortex creates more surface area

            -ridges are called gyri, separated by shallow depressions (sulci) or by deeper grooves (fissures)

                        ex. Central sulcus : seperates the parietal and frontal loves of the cerebrum

Frontal lobe: 

Parietal lobe:

Temporal lobe:

Occipital lobe: 

Generalized function of cerebrum

-sensory info is evaluated

-responds to this info-conscious decisions made

Postcentral gyrus

-somatic sensory area, receives impulses about heat, cold, touch (in parietal lobe)

Precentral gyrus

-somatic motor area, stimulates skeletal muscles in response to sensory info (in frontal lobe)

-somatic motor area, stimulates skeletal muscles in response to sensory info (in frontal lobe)

Cerebellum

-“little cerebrum”

-outer surface, cortex

-ext.surface has gyri and sulci

-right and left hemispheres

1. Coordinates muscular activities by comparing motor commands from cerebrum with position sense from ears; performing adjustments needed to make movements smooth

2. Maintains balance and posture

Diencephalon

-located between cerebrum and midbrain

-composed of thalamus, hypothalamus, optic chiasma, pineal gland, pituitary gland

Thalamus

-dumbell shaped mass of gray matter forming the upper, lateral walls of 3^rd ventricle with connecter called intermediate mass

-is sensory relay station via ascending tracts to cerebral cortex

-acts as filter, passing on to primary sensory cortex only small portion of arriving info “edits info”

-plays a part in associations between sensory impulses and emotions (crude – pleasant or not?)

Hypothalamus

-forms floor and lower lateral walls of 3^rd ventricle

-midportion gives rise to infundibulum à stalk leading to pituitary

-posterior portion consists of mamillary bodies (involved in olfactory sensation)

HOMEOSTASIS

1. autonomic control center

-controls activity of autonomis centers of brain stem, influencing blood pressure, rate and force of heart contractions, motility of digestive tract, respiratory rate and depth

2. Center for emotional response and behavior

-numerous connections with cerebral complex association areas

-perception of emotions and initiation of physical expression of emotions

ex. Fear à pounding heart, ^ blood pressure, sweating palms

3. Body temperature regulation

-recieves messages from body and other parts of brain, initiating a response, shiver? Sweat?

4. Regulation of food intake

-response to a change in blood levels of nutrients (glucose, amino acids)

-regulates feelings of hunger and satiety

5. Regulation of H20 balance and thirst

-responds to h20 and salt concentrations of blood

-if too salty? Holds on to more h20 (kidneys) and thirst (dries out salivary glands)

6. Links N.S to endocrine system

-produces hormones that are stored and secreted by posterior pituitary

-produces releasing hormones that go to endocrine glands to stimulate those glands to secrete their hormones (ex. Gonadotropin releasing hormones which travels to anterior pituitary so it secrets FSH and LH)

Pituitary gland (hypophysis)

-stores hormones produced by hypothalamus (ADH, oxytocin)

-makes and releases own hormones (growth hormones, FSH, LH)

Pineal gland “pine cone shaped” small ~ 1cm

-involved in regulating biological clock (response to light, 24 hour cycle)

-produces melatonin (sleep inducing signal)

Midbrain

-above pons, below diencephalon

-cerebral aqueduct is marker for midbrain

-white matter includes ascending tracts carrying sensory info to thalamus and descending tracts carrying motor info from cerebrum to spinal cord

-corpora quadrigemina is part of midbrain

            2 parts:

                        -superior colliculi: visual centers

                        -inferior colliculi: auditory centers

-located below midbrain, above medulla

-tracts passing through pons, links cerebellum with brain stem, cerebrum and spinal cord

-also helps medulla with involuntary pace and depth of respiration

Medulla Oblongata

-below pons, above foramen magnum

-broadest near pons

-descending tracts controlling skeletal muscle movements (conscious control from cerebrum) come through medulla and cross over

so..

right side of brain controls left side skeletal movements

-ascending tracts come through too (some cross over here while others have already crossed over in spinal cord)

Vital ANS reflex centers are found in medulla (these are under control of hypothalamus)

1. Cardiac center

-adjusts force and rate of heart contractions

2. Vasomotor center

-controls smooth muscle in walls of blood vessels : vasoconstriction will increase blood pressure and vasodilation with lower blood pressure

3. Respiratory center

-along with pons controls rate and depth of breathing

Cranial nerves

-12 pairs that arise from underside of brain

-originate in brain stem (exception: first two pairs connected to the cerebrum)

-service head and neck with exception of Vagus(X) that services much of organs (viscera) of trunk

-designated by a Roman  Numeral and a name I à XII

-some are special sensory infuction, others are primarily motor in function, while still others have both sensory and motor fibers (mixed nerves)a

. Olfactory nerves (smell)

-sensory only

-all bipolar afferent neurons make up this nerve

-dendrites, cell bodies of neurons originate in upper nasal epithelium with axons exiting through holes of cribriform plate(of ethmoid)

-synapse in olfactory bulb(of cerebrum) and then through olfactory tracts to cerebral centers for interpretation

II. Optic nerves

-sensory only

-originate in retina of eye

-fibers intersect at optic chiasma where half of them cross over to other side of brain

-continue as optic tracts to thalamus and then to occipital lobe where vision is interpreted.

VIII. Vestibulocochlear nerves

-sensory only

-combination of vestibular nerve and cochlear nerve from inner ear

-nerve seperates again when gets to brain

            vestibular fibers -> cerebellum (equilibrium

            cochlear fibers -> temporal lobe (hearing)

X. Vagus nerves “wanderer”

-longest cranial nerve

-leaves medulla, travels down to thoracic and abdominal cavities

-mixed nerve (Carries sensory and motor neurons)

-info to and from pharynx, ext. ear, diaphragm, visceral organs of cavities

-most of parasympathetic neurons “piggyback” on vagus

Spinal nerves

-leave spinal cord

-31 pairs

-all are mixed nerves (both sensory and motor neurons present

-when dorsal and ventral roots come together, form spinal nerve (short, 1-2cm)

-named according to the region of the vertebral column from which they originate

C1-C8 (first one above atlas, giving 8!)

Then

T1->12

L->5

S1->5

One pair of coccygeal

Dorsal ramus- 

turns posteriorly and innervates muscles and skin of back

Ventral ramus

-continues forward to supply muscles and skin of front and sides of trunk and limbs

-bigger branch!

-in thoracic and lumbar regions, some fibers spilt away from ventral rami to white rami and then to ganglia of ANS

(except in thoracic region) branch and merge repeatedly to form complex networks – plexuses, instead of continuing directly to peripheral body part

Cervial plexuses

-beneath sternocleidomastoid

-formed by ventral rami of c1->4

-innervate muscles of skin and neck

-most important nerves from these plexuses are phrenic nerves (conduct motor impulses to diaphragm)

Brachial plexuses

-deep in shoulders between neck and axilla

-formed by ventral rami of c5->8, t1

-innervates shoulders, arms and hands

Sensory(afferent) pathways typically include three neurons

-initial sensory neuron comes into spinal cord through dorsal root

-synapses with 2^nd sensory neuron in gray matter of spinal cord

or

-continues up to medulla to synapse with 2^nd sensory neuron there

-where it synapses, crosses over to white matter on other side of spinal cord or medulla and goes up an ascending tract to thalamus

-synapses in thalamus with 3^rd neuron

-synapses in thalamus with 3^rd neuron which takes message to sensory cortex of cerebrum

-cortex is more stimulated (by more neurons) from tongue than from skin on back (as there are more sense receptors/unit area there sends up more info)

*may not happen is thalamus chooses not to send messages up to conscious brain

                        adaptation, ex. Clothes on your body

In response to sensory info, CNS issues motor commands that are distributed by

Somatic nervous system and the Autonomic nervous system

-initial motor neuron stimulated in cerebrum (dendrites, cell body there)

-axon extends from cortex à medulla where crosses over (decussates) and continues down descending tracts

-synapses in spinal cord (2^nd neuron)

-final neurons motor axon leaves spinal cord via ventral root to effector (sk. Muscle)

-this is multipolar neuron with dendrites and cell body in gray matter of spinal cord

NOTE: there is onlt one efferent neuron traveling in PNS with somatic nervous system

work antagonistically to bring about homeostasis

*most organs receive dual innervation – instructions from both autonomic divisions

Sympathetic Division (thoracolumbar div) 

-under stress, “fight or flight” response

-hypothalamus, with cerebral cortex of frontal love recognizes stressful situation

-sends message to medulla and from there to visceral effectors, via the spinal cord

^ in heart rate ^blood pressure ^ breathing rate ^secretion of sweat glands

-stimulates breakdown of glycogen to glucose

-secretion of epi and norepi by adrenal glands

-digestive system turned off, decrease in peristalsis and decrease in salivary glands

-“rest and digest”

-opposite effect of sympathetic division

decrease in HR, BP, breathing rate, inhibit adrenals…

*Stimulate digestion

Structure of ANS

-sensory (afferent) pathway is same as somatic

-motor pathway is anatomically different than somatic

-there are 2 efferent neurons from spinal cord à effector in ANS (somatic had only one)

-relay through these 2 to get a response by visceral organ or gland (effector)

Preganglionic neuron

Postganglionic neuron

-conducts impulse from ganglion to effector (visceral organ)

Sympathetic Division (thoracolumbar) efferent pathways

-preganglionis fibers leave spinal cord in ventral root to form spinal nerve

-after short distance, pregangliotic fibers leave spinal nerve through small branches called white rami and enter sympathetic chain (vertebral) ganglia

-22 pairs of ganglia running along either side of spinal cord

Axons of postganglionic neurons extend

from ganglia to visceral effector

-fibers leave chain through small branch (gray rami) to return to spinal nerve on way to effector and ventral branch rami

*important exception!

-when innervating adrenal medulla gland

-only preganglionic fibers

-they pass through chain to synapse directly at adrenal gland to stimulate secretion of epe and norepi-fibers leave chain through small branch (gray rami) to return to spinal nerve on way to effector and ventral branch rami

*important exception!

-when innervating adrenal medulla gland

-only preganglionic fibers

-they pass through chain to synapse directly at adrenal gland to stimulate secretion of epe and norepi-fibers leave chain through small branch (gray rami) to return to spinal nerve on way to effector and ventral branch rami

*important exception!

-when innervating adrenal medulla gland

-only preganglionic fibers

-they pass through chain to synapse directly at adrenal gland to stimulate secretion of epe and norepi

-preganglionic neurons have dendrites and cell bodies in brain stem or sacral region of spinal cord.

-fibers (axons) are found in cranial or sacral nerves.

-they synapse in ganglia with postganglionic neurons very vlose to or embedded in effector organ (don’t go through sympathetic chain)

-short postganglionic neurons continue from ganglia to specific muscles or glands within these organs

-75% of preganglionic axons are found in Vagus (X), which leads out of medulla

-vagus “wanders” through body cavities with branches leading to many internal organs(heart, lungs, liver, stomach…)

Autonomic Neurotransmitters

-neurons that secrete acetylcholine are called cholinergic.

-this includes both pre and postganglionic neurons of parasympathetic division and preganglionic neurons of sympathetic division.

Exception: parasympathetic neurons that secrete nitric acid

To blood vessels in certain body parts

To dilate those vessels

-neurons that secrete norephinephrine are called adrenogenic. 

Parasympathetic Division

Preganglionic neuron -> (Ach) postganglionic neuron->(ach)->effector

*inhibitory-lowers heart rate, lowers strength of contraction, constriction of bronchioles

*excitatory-increases digestive tract functions

*due to receptors of effectors

Sympathetic division

Preganglionic neuron->Ach->postganglionic neuron ->norepi->effector

*mainly excitatory in heart: increase heart rate, increase strength of contraction, (beta receptors stimulated by norepi)

dilates bronchioles

*inhibitory – digestive tract, (lowers peristalsis, lowers sal.gland secretions)

*again depends on receptors

 Mechanoreceptors

-movement:touch, pressure, motion, vibrations, stretching

ex. Proprioreceptors: sense changes in tension of muscles, tendons (sense nonvisually position of body in space)

baroreceptors: detect changes in pressure against blood vessel walls.

stretch receptors: lungs,detect degree of inflation

Chemoreceptors

-detect chemical changes

-smell: nasal cavity

-taste: taste buds

-detectors for H+ (pH) of blood

-detect temp.changes

-skin

-detect light

-only found in retina (rods, cones)

 Nociceptors

-detects tissue damage, pain

-widely distributed in skin, int.organs.

Sense of taste (gustation)

-chemoreceptors (gustatory cells) in taste buds

-hairs on these cells are sensitive to specific chemicals dissolved in saliva

-senses: sour, bitter, sweet, salty, umami (metallic, like putting a penny in your mouth

-sensitivity lowers with age.

-sensory info travels to brain through 2 cranial nerves.

            Facial nerve (VII) : ante.tongue

            Glossopharyngeal n.(IX): past tongue

*True taste comes from sense of taste and sense of smell.

Smell-olfaction

-chemoreceptors are cilia of olfactory neurons of cranial nerve 1.

-stimulated by chemicals in air (more sensitive than taste)

-message sent through olfactory bulb -> olfactory tract à temporal lobe

-only sense that works well at birth.

Vision

-retina contains photoreceptors

-occipital lobe does “seeing”

With the eye:

There are 3 layers (tunics)

Fibrous, outer layer (tunic)

Vascularized layer

Inner, retinal layer (neural)

Sclera (fibrous tunic)

-tough, protective, outer layer

-white

-anteriorly, specialized area which is transparent :cornea

-no blood vessels in cornea

-vascularized, so can nourish surrounding tissues

-contains melanocytes, prod.melanin. giving it a dark color (absorb as much light as possibly on to retina

-anterior portion has a group of specialized structures

            ciliary body: includes ciliary muscles and ciliary processes.

-attaches to processes are suspensory ligaments which hold lens in place and allow it to change shape when focusing

-accommodation (lens able to change shape)

-when muscles relaxed, lens is flattened and distant images are in focus

-when contracted, elastic lens becomes more rounded and closer images are in focus

-presbyopia-inability of lens to “round up” as you age

-pigmented (dark, more melanocytes prod.pigment)

-made up of blood vessels, connective tissue, smooth muscle tissue

-attaches to ciliary body, anterior to it.

-regulates light passing deeper into eye

-smooth muscle acts reflexively (2 sets: circular, radial)

-incomplete layer (no anterior portion)

-lines post. 2/3 of eye

-very delicate

-poorly attached to choroid

-composed of 3 layers

1.ganglion cells (neurons) – closest to posterior cavity

2. bipolar cells (neurons) – middle

3. photoreceptor cells (rods, cones) – closest to choroid

-more rods(125 mil) than cones/retina(6 mil)

-cones concentrated in macula lutea(where visual image should arrive after being focused there by cornea, lens)

-highest concentration of cones in center of macula: fovea centralis

-fovea is center of color vision and visual acuity (sharpness)

-should fall on this portion of retina

-rods are more sensitive to light, (useful in low light conditions) but don’t discriminate between colors

-rods distributed more in periphery of retina (further away from fovea, more rods)

Rods and cones synapse with bipolar neurons which in turn synapse with ganglion cells

-axons of ganglion cells (which make up optic nerve) deliver message to brain

Blind spot or Optic disc (medial to fovea)

-axons of ganglion neurons come together to leave back of eye, forming optic nerve

-blood vessels that supply retina are here too

-no rods, or cones

-if light strikes this area, doesn’t stimulate any photoreceptors – blind spot (usually not apparent as eye movements keep visual image moving and brain fills in missing info.)