carry sensory information into nervous system

specialized sensory neurons that convert stimuli --> AP

neurons organized into clusters

ganglia of diff func distributed around body

bilaterally symmetrical animals usu have pairs of gangllia

increased complexity --> ganglia fused / enlarged anterior end forming centralized integrative center or brain

peripheral nervous system

affectors / effectors;

neurons and supporting cells outside CNS

4 regions: cell body, dendrites, axon(s), axon terminals

cell body: nucleus, most of organelles

shrub-like denrites: bring info from other neurons or sensory cells to cell body, degree of branching among diff types of neurons

axon: much longer than other projections, AP --> target cell, tip = swelling called axon terminal close to membrange of target cell = synapse

more than neurons, physically support and orient neurons during embryonic dev, supply neurons with nutrients, etc

types: oligodendrocytes, schwann, myelin, astroctes, microglia

wrap around axons of neurons, concentric layers of insulating plasma membrane

CNS

covering produced by oligodendrocytes and schwann cells, white appearance

not all myelinated but myelin allows faster conduction of AP

multiple sclerosis, etc diseases affect myelin impair conduction of AP

look like stars, contribute to blood-brain barrier protecting brain from toxis chemicals in blood

surrounds smallest, most permeable blood vessels of brain to form blood-brain barrier

usu prevents antibodies from entering CNS

provides CNS with immune defenses, act as macrophages and mediate inflammatory resp

come from stem cells of bone marrow

actively expels Na+ ions in exchange for K+ ions

anti porter, requires ATP

keeps K+ concentration inside cell higher, Na+ lower inside cell

K+ leak channels allow K+ out = negative resting mem potential

chemical gradient = K+ diffuse out b/c pump increase concentration inside cell

electrical gradient = draws K+ back in

inside of neuron becomes less negative (more positive) in comparison to resting condition

Na+ channels opened, diffuse into neuron down electrochemical gradient

mem potential becomes more negative

K+ channels open = K+ out over normal leak

change from resting potential due to chemical or mechanical influences on ion channels

means of integrating inputs to a cell

transmit signals over short distances and impt in neuro muscular junctions

1. leak K+ channels create resting potential, gated channels closed

2. activation gates of some Na+ channels open, depolarization

3. additional voltage-gated Na+ channels open = rapid spike depolarization of AP

4. Na+ channel inactivation gates close, gated K+ channels open, repolarization and even hyperpolarization

5. all gated channels close, cell returns to resting potential

region of cell body at base of axon

concentration of voltage-gated Na+ channels

begins positive feedback of opening Na+ channels --> AP

mem depolarized to 5 - 10mV = threshold

large number of Na channels open and --> AP

Na+ channels have dely after open and close during which cannot open again

explained by activation and inactivation gates, resting = activationcl closed and inactivation open, depolar = both change but activation resp faster = channel open during brief open of activation and close of inactivation

inactivation closed for 1-2ms before spontaneously open again = refractory period

determines duration of after hyperpolarization of undershoot

all or none: once threshold reached AP will take place due to positive feedback mechanism

self-regenerating: spreads by local current flow to adf regions = depolar brings neighbors to threshold, AP generation stimulates to the end

travel faster in large-diameter axons because resitance to current flow decreases, faster in myelinated b/c jump

glia wrap around axons with regularly spaced gaps

axon fires AP only along nodes, increases speed of conduction b/c electric current flows through cytoplasm faster than ion channels can open / close

--> called saltatory conduction (rapid impulse propagation)

synapses between neurons and skeletal muscle cells

vertebrate neuromuscular transmitter = acetylcholine (ACh), synthesizsed in axon terminal

postsynaptic mem of neuromuscular junction, depression in muscle cell mem with embeded terminal of neuron

synaptic cleft = space between synapse

spatial summation: adds up simultaneous influences of synapses at diff sites on postsynaptic cell

temporal summation: adds up postsynaptic potentials generated at same site in rapid sequence

ion channels, neurotransmitter bonds to ionotropic receptor causing direct change in ion movement

fast, short-lived resp

electrical fast but do not integrate info well

gap junctions, connexons link neurons

fast either direction (versus transmission, slow / unidirectional)

does now allow low temporal summation, requires large area of contact, cannot be inhibitory ==> less common in vertebrates

ionotropic sensory receptors

metabotropic sensory receptors

mechanoreceptors, thermoreceptor, electroreceptor

chemoreceptor, photoreceptor

graded mem potentials spread over short distances, must --> action potentials

may generate AP within receptor cell itself

may trigger release of neurotransmitter indusing postsynaptic neuron to gen AP

dep on which sensory cell stimulated = translation of stimuli to senses

frequency = intensity of stimuli

diminishing resp to maintained or repeated stimulation

ignore background or unchanging conditions, sensitive to new info

chemical stimuli

taste and smell

monitoring internal environment ie CO2 blood levels

response: physiological and behavioral resp during actvities like feeding mating fighting recog

communication among mem of a species

attraction

sense of smell

dep on chemoreceptors

neurons embedded i layer of epithelial tissue at top of nasal cavity --> olfactory bulb of brain (integration)

mol that activates olfactory receptor protein

--> activates G protein --> enzyme --> second messenger -->cation channels --> AP

--> neurons in glomerulus receive input fr receptor cells expressing same receptor gene = able to differentiate smells

sense of taste

dep on chemoreceptors called taste buds

5 tastes: sweet, salty, sour, bitter, umami (savory)

muscle spindles stretch receptors 

sensory neurons transmit AP to CNS when stretched, initiate muscle contraction

golrgi tendon organs sense load and measure force of muscle contraction

if too forceful sensory neurons send AP to CNS to inhibit contraction and muscle relaxes

uses mechanoreceptors to convert pressure waves into receptor

pinnae of ear collect sound waves and direct toward auditory canal --> middle ear and inner ear

tympanic membrane covers end of auditory canal, vibrates in resp to pressure waves, middle ear on other side

osicles = three bones malleus (hammer), incus (anvil), stapes (stirrup), transmit vibrations fr tympanic mem to oval window, magnify vibrations

oval window: smaller, presure from bones >20x greater, behind window is fluid-filled inner ear

vestibular system (organ of balance)

cochlea (organ of hearing), snail shell shaped

reissner's mem and basilar mem sep parallel canals

on basilar = organ of corti = pressure waves --> AP, hair cells with stereocilia embedded in gelatinous tectorial membrane

fluid pressure creates flexions / waves in basilar mem

mem is thicker and stiffer at base and wider and thinner at apical end

diff freq = diff patterns of waves, higher pitch more at the end, diff pitches flex mem at diff locations and activate diff sets of hair cells (send neurotransmitters)

--> auditory cortex along auditory nerve

conduction deafness = loss of function of tympanic mem / ossicles of middle hear

nerve deafness = damage to inner ear or auditory pathways

hair cells: mechanoreceptors of hearing and equilibrium, release neurotransmitters --> AP

three bony semicircular canals and two bony chambers (saccule and utricle) of vestibular determine position and movement of head = balance

fluid filled (endolymph)

cupula encloses cluster of hair cell streocilia

family of pigments, basis of photosensitivity of all animal species

light stimulations --> neural signals

respond to light

outer secment = concentration of rhodopsins to capture photons

inner sement = cell nucleus, mito, etc

synaptic terminal = rod cell communicates with other neurons

flatworms organizationo f photoreceptor cells

paired bilateral

use info to move away from light

image forming eyes, wide angle

sclera = tough connective tissure around eye turns clear = cornea (where light passes into eye)

Iris = pigmented, controls amount of light let in by changing the size of pupil

lens: crystalline protein, focuses images on retina

cone cell: color receptors, low sensitivity to light, three types of cone cells

rod: highly sensitive black and white

fovea = highest density of cones, light from center of visual field

ganglion cells: front of retina, fire AP --> optic nerve of brain, photoreceptors and ganglion connected by bipolar cells

tube of neural tissue forms

anterior end = hindbrain, midbrain, forebrain

PNS sprout from midbrain and hind brain and spinal chord

medulla, pons, and cerebellum

medulla continuous with spinal cord, pons in front of medulla ctrl phsiological function like breathing / circulation / basic motor (swallowing and vommiting)

info from spinal to higher brain passes thru pons, medulla, and midbrain = brainstem

cerebellum coordinates muscle activity and balance

central region diencephalon surrounded by telencephalon

diencephalon core consists of thalamus (final relay for sensory info goin to telencepahlon) and hypothalamus (regulates physiological functions and biological drives ie hunger / thirst)

telencephalon = cerebrum consists of two cerebral hemispheres left and right, outer layer = cerebral cortex  thin layer rich in cell bodies

telencephalization = increase in size complexity importance major roles in sensory perception learning memory conscious behavior

conversion of afferent to efferent info in spinal cord w/out brain = spinal reflex

monosynaptic reflex = two neurons and one synapse ie knee-jerk reflex

network of brainstem neurons forming synapses with sensory axons, anatomically distinct gropu of neurons in CNS called nucleus

sensory axon info ascends through reticular formation and connect with nuclei involved in ctrl other body func ie muscles

also ctrl sleep and wakefulness, walking

reticular core called reticular activating system

component of limbic system

involved in fear and fear memory --> resp

upper region of temporal lobe receives and processes auditory information

association = recog, id, and naming objects, damage = agnosias, deficit in understanding spoken language, speaking reading and writing may be in tact

separated from parietal by central sulcus

primary motor cortex = ctrl specific muscles, fine motor control

feeling and planning, significant contribution to personality

primary somatosensory cortex

touch and pressure information relayed from body through thalamus, entire body surface mapped onto parietal lobe

ANS

output pathways of CNS ctrl involuntary functions ie heart rate, sweating, gut

two divisions = sympathetic and parasympathetic work in opposition: one increases activity other decreases

sympathetic = flight or fight resp