sensors- monitor external and internal environment processing- receives information, integrates it,...

Sensors- monitor external and internal environment

Processing- receives information, integrates it, and decided what to do

Effectors- carries messages to effectors informing them what to do

Neurons- relay and process messages

Neuroglial- provide support to the neurons

Microglial cells› Scattered throughout CNS› Phagocytize bacteria or cellular debris

Oligodendrocytes› Along nerve fibers› Provide myelin sheath (made of a fatty

substance called myelin) around axon in CNS

Schwann cells› Same as oligodendrocytes but in PNS

Astrocytes› Provide connection between a neuron and

a blood vessel› Provide support, help regulate ion

concentrations in tissue, make-up scar tissue after injury

Ependymal cells› Forms epithelial-like linings on the ousides

of specialized parts or lining cavities within the CNS

Body Structure› Cell Body› Dendrites- carry messages to cell body› Axons – carry messages away from cell

body Structures

› Large nucleus with easily seen nucleolus› Chromatophilic substance- rough ER› Neurofibrils- help support cell shape

Can be myelinated or unmyelinated PNS

› Schwann cells form myelin sheath› Nodes of Ranvier- small breaks in myelin

sheath CNS

› Oligodendrocytes form myelin › Myelinated neurons form white matter › Unmyelinated neurons form gray matter

Multipolar› Many small branched dendrites› One axon › Found in CNS

Bipolar› Two processes off of cell membrane (one axon

and one dendrite)› Neurons in special sense organs

Unipolar› One process off of cell body (one axon)› Found throughout PNS

Sensory (afferent) neurons› Have sensitive dendrites that are stimulated

by changes in environment› Message is taken into CNS› Usually unipolar or sometimes bipolar

Interneurons› Transfer, direct, and process messages within

CNS› Usually multipolar

Motor (efferent) neurons› Carries message out of CNS to effoctors› Usually multipolar

Inside the neuron › High in K+

› High in negatively charged ions Outside the neuron

› High in Na+

Result› K+ tends to diffuse out of cell› Na+ tends to diffuse into cell› Negative ions cannot cross

Na/K pump- helps to restore concentration gradient across the cell membrane

Resting potential- difference is electrical charge across the membrane› Established by concentration gradients of

various ions› Inside of the membrane has a negative

charge of 70 mv› Membrane is said to be polarized

Stimuli cause changes to the resting potential by making the inside of the membrane less negative

Once a stimulus happens› The stimulus may not be strong enough to reach

threshold potential; cell membrane will return to resting potential

› The stimulus may be strong enough to reach threshold potential and start an action potential

Summation- if they occur close enough together, stimuli that would be to small to reach threshold potential add there effects together to reach the threshold

Starts at trigger zone of axon Threshold stimulus open sodium channels Sodium moves into axon

› Because of the concentration gradient› Because of the negative charge that attracts

the positive ions This depolarizes the membrane as

negative charge diminishes Potassium channels open and potassium

moves out of the axon, repolarizing the membrane

Action potential at the trigger zone stimulates the next part of the axon to do a action potential

Potentials spread along the axon like a wave

Unmyelinated axons- wave continues uninterrupted; relatively slow

Myelinated axons- wave goes through saltatory conduction (jump from one node to the next); very fast

All-or-none- neuron does not react until a threshold stimulus is applied, but once it is applied it reacts fully

Stimuli greater than threshold levels don’t change the size of the response but its frequency

After a action potential, there is a brief period of time called the refractory period where the nerve cannot be stimulated again.

The connection between two neurons Don’t touch, separated by synaptic cleft One-way communication between axon

of presynaptic neuron and dendrite of postsynaptic neuron

Neurotransmitters are made in the synaptic knob of the axon, stored in synaptic vesicles, and cross the cleft when needed

A neurotransmitter that puts a neuron closer to an action potential (facillitation)or causes an action potential is exitatory

A neurotransmitter that moves a neuron further away from an action potential is inhibitory

A neuron responds according to the sum of all the neurotransmitters received at one time

Acetylcholine Monoamines – modified amino acids Amino acids Neuropeptides- short chains of amino

acids Imbalances of neurotransmitters can

create disorders like depression Many drugs imitate neurotransmitters

When an action potential reaches the end of an axon, Ca channels in the neuron open

Ca rushes in and cause the synaptic vesicles to fuse with the cell membrane and release the neurotransmitters into the synaptic cleft

After binding, neurotransmitters will either be destroyed in the synaptic cleft or taken back in to surrounding neurons (reuptake)

Groups of highly interconnected neurons that work together in the CNS

Convergence- axons from different parts of the nervous system connect to the same neuron combining their affects

Divergence- a message from one neuron is sent to many neurons at once; amplifies message

Nerves are made of bundled axons, called nerve fibers

Nerve fibers› Sensory (afferent)- carry messages to CNS› Motor (efferent)- carry messages from CNS

to effectors Nerves- same definitions hold true, but

most nerves contain both types of fibers and are called mixed nerves

A nerve fiber (axon) is surrounded with endoneurium

Nerve fibers are bundled togther and surrounded with perineurium to form a fascicle

Fascicles are bundles together and surrounded with epineurium to form a nerve

Path that the message takes through the body

Includes› Sensor› Sensory neuron› Interneuron› Motor neuron› Effector

Simplest nerve pathway is a reflex Reflexes without pain

› Involve only sensory and motor neurons› Ex: knee-jerk reflex

Reflexes with pain› Involve interneurons in CNS› Ex: withdrawal reflex

Central nervous system

Consists of brain and spinal cord

Made of both gray and white matter

Covered in meningies

Cranial Bone Dura mater- first layer; tough, fibrous

connective tissue; forms inner periosteum of crania bone; folds into the cranium in some places to form division walls in the brain

Arachnoid mater- web-like membrane over CNS; does not dip into crevices

Subarachnoid space- below arachnoid layer; contains cerebrospinal fluid

Pia mater- lower layer of meninges; forms a tight covering over brain; does dip into crevaces

Same exept:› Vertebrae› Epidural space- filled with loose connective

and adipose tissue› Dura mater› All other are the same

Flows through ventricles (spaces in brain), in the subarachnoid space, and through the central canal of the spinal cord

Fluid is made by the choroid plexus

Stretches from brain to intervertebral disk between first and second lumbar vertebrae

31 pairs of spinal nerves come of the cord

Gray matter core surrounded by white matter

Responsible for communication between brain and body and spinal reflexes

Ascending tracts- nerves that send info to brain

Descending tracts- nerves that send into to effectors

Made up off about 100 billion neurons Four main sections

› Cerebrum- nerves for processing sensory and motor function; higher functions like reasoning

› Diencephalon- processes sensory information› Brainstem- regulates certain body functions

like breathing› Cerebellum- coordinates skeletal muscle

movements

Divided into two hemispheres (right and left)

Corpus callosum- connects the two sides

Other structures› Convolutions- ridges› Sulcus- shallow groove› Fissure- deep groove

Frontal lobe Parietal lobe Temporal lobe Occipital lobe Insula Each lobe has unique functions

Cerebral cortex- thin layer of gray matter surrounding cerebral hemisphere; contain most of the cell bodies in the cerebrum

Inner part of the cerebrum is mainly made of white matter

Motor areas› Primarily in frontal lobe› Send information out to effectors

Sensory areas› Interpret information from sensors› Area in parietal, temporal, and occipital lobes

Association areas› Analyze information from sensors› Located in areas in all lobes mentioned

above

Located between the cerebral hemispheres above the brainstem

Contains› Thalamus› Hypothalamus› Pituitary gland› Pineal gland

Thalamus- routes sensory impulses to the correct region of the cerebrum

Hypothalamus- monitors many internal conditions, link between nervous and endocrine system

Limbic system (thalamus, hypothalamus, and basal nuclei)- controls experience and expression (feelings)

Connection between spinal cord and the rest of the brain

Contains› Midbrain› Pons› Medulla oblongata

Located between diencephalon and pons

Contains some visual and auditory reflexs

Serves as the main connection for motor neurons between spinal cord and upper part of brain

Rounded bulge between midbrain and medulla oblongata

Relays impulses between medulla and cerebrum or between cerebrum and cerebellum

Lowest part of brain, connect to spinal cord

All ascending and descending tracts run through the oblongata

Serves as a control center for many vital function like heart rate, blood pressure, and respiratory center

Located in the lower back part of the brain

Structured liked cerebrum with inner white matter core and gray matter covering

Controls posture and complex skeletal movements

Peripheral Nervous system Includes

› 12 pairs of cranial nerves › 31 pairs of spinal nerves

Divided into› Somatic nervous system- controls conscious

activities; connects to skin and skeletal muscles› Autonomic nervous system- controls

unconscious activities; connects to internal organs or structures

Two branches› Parasympathetic- control under more

normal conditions› Sympathetic- control under stress or

emergency conditions (fight or flight)› Usually these two have antagonistic effects

or any one organ or structure; either might be utilized to maintain homeostasis

Chemoreceptors- respond to changes in chemical concentrations

Pain receptors- respond to tissue damage

Thermoreceptors- respond to temperature changes

Mechanoreceptors- respond to changes in pressure or movement

Photoreceptors- respond to light

The brain is where sensations come from; impulses are interpreted based on what area of the brain they end up in

The brain projects the sensation back to the sensor so the person feels the sensation at the sensor

Ability of the PNS or CNS to block sensory impulses that it deems unimportant or has become used to

Sensors are widely spread throughout body and are fairly simple

Include› Touch› Pressure› Temperature› Pain

Three kinds of receptors› Free nerve endings- sensations of touch

and pressure› Meissner’s corpuscles- provide sensations

of light touch, usually located in regoins of skin without hair

› Pacinian corpuscles- respond to heavy pressure, located in deeper tissues

Warm and cold receptors (free nerve endings)

Extreme temperatures stimulate pain receptors

Receptors adapt very fast

Sensations arise from free nerve ending throughout body except brain

Pain receptors adapt poorly Visceral pain- referrers pain to areas on

the skin

Sensations arise from specially adapted sensors

Includes› Smell › Taste› Hearing› Equilibrium› Sight

Olfactory receptors are located in small patches along the roof of the nasal cavity

They are chemoreceptors so incoming gases must dissolve in the mucous covering the nasal cavity

Dissolved particle interact with the cilia and may stimulate an action potential

Taste buds- located primarily on tongue, although some found on roof of mouth and sides of the throat

Each taste bud has many gustatory receptors and tiny cilia projections

These are chemoreceptors so incoming foods must be dissolved in saliva to be tasted

Four main taste areas› Sweet- concentrated on the tip of the

tongue› Sour- concentrated along the margins of

the tongue› Bitter- concentrated along the back of the

tongue› Salty- spread throughout

Sound waves are directed into the ear by the external auricle

They travel down the external acoustic meatus

Bounce against tympanic membrane (eardrum) and make the eardrum move

Occurs in the tympanic cavity Has three small auditory ossicles Vibrations at the tympanic membrane

cause the three bones to vibrate The final bone vibrates against the oval

window of the inner ear The bones amplify the sound Eustachian tube- connects middle ear to

throat, equalizes pressure for eardrum

Includes two labyrinths› Osseous labyrinth- bony canals› Membranous labyrinth- membrane-bound

tube inside the bony canals› Perilymph separates the two› Endolymph is found inside the membranous

labyrinth Two parts to the labyrinth

› Semicircular canals- used in equillibrium › Cochlea – organ for hearing

Vibrations at the oval window cause vibrations in the perilymph of the scala vestibuli

Vibrations pass through vestibular membrane into endolymph

Vibrations than pass through basilar membrane to perilymph of scala tympani

Organ of Corti- found in basilar membrane, contains hearing sensors with hairs; vibrations cause hairs to move

Two divisions› Static Equilibrium- senses posture while at rest

Occurs in vestibule Position of head is determined by hairs on the

macula, hairs respond to shifting of otoliths

› Dynamic Equilibrium – maintaining balance during movement Occurs in the semicircular canals, in particular

the ampulla Movements cause the perilymph to stimulate

hairs in the ampulla

Visual receptors located in eye Accessory organs aiding eye

› Eyelids› Lacrimal apparatus- gland that produces

tears to cleanse and protect eye and ducts to carry the tears to the nasal cavity

› Muscle- move the eye

Posterior portion› Sclera- tough fibrous covering › Choroid coat- contains melanocytes to help

darker the inside of the eye› Retina- thin complex inner layer that is

continuous with the optic nerve and contains the receptors

› Vitreous humor- jelly-like fluid filling internal eye

Anterior portion› Cornea- transparent covering › Aqueous humor- fluid that is made between

the iris and lens but can move to between the cornea and the iris through the pupil

› Iris- pigmented layer containing smooth muscle to control size of pupil

› Aqueous humor› Lens- layer that focuses the image on the

retina; can change shape to change focus

Contains receptors› Rods- black-and-white vision; more indistinct

image; pigment is rhodopsin› Cones- color vision; refined image; pigments

are sensitive to red, green, and blue hues Fovea centralis- part of retina containing

high concentration of cones; area with sharpest focus

Optic disc- area of retina with connection to optic nerve; lacks receptors (blindspot)