Bio Notes Unit 7

7/28/2019 Bio Notes Unit 7

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Unit Seven The Nervous System- contains 2 types of cellsi) NEUROLOGICAL CELLS: support and serve cells (help neurons)ii)NEURONS: cells that actually conduct and transmit actual nerve impulses

NEURONS PERFORM 5 FUNCTIONSi) RECEIVE INFO (STIMULI): form both our internal and external environmental, or fromother neurons

ii) INTEGRATED DIFFERENT SIGNALS: often several signals must be integrated toproduce an appropriate response

iii) CONDUCT A SIGNAL: will move a signal (sometimes several feet) without diminishiv) TRANSMIT A SIGNAL: at the end of the neuron it must pass a signal to something

(ex. muscles, gland or other neuron)v) MAINTAIN HOMEOSTASIS: do all the functions of a living cell

ALL NEURONS HAVE 3 DISTINCT REGIONS

i) DENDRITES: receive stimuli from the environment- process branch outwards from the cell body and cover larger regions

NOTE: always sends signals towards the cell body, therefore impulses can only moveone way along the neuron.

ii) CELL BODY: integration center and it receives all signals coming from dendrites- many dendrites feed into cell body therefore many signals often at once- cell body integrates and determines whether to produce an impulse (action potential)- cell body also contains the organelles for keeping the cell a live (homeostasis)


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iii) AXON: carries an impulse (action potentials) from cell body towards a destination(gland, muscle, other neurons)

- can be very long (up to 3 feet)- impulses will travel a long the axon without diminish

- many neuron axons bundle together form nerve tissue

- the axon ends at a axon BULB or SYNAPSE- axon bulbs contain proteins called NEUROTRANSMITTERS

3 BASIC TYPES OF NEURONSi) SENSORY NEURON: brings impulses inwards- detect environmental stimuli and bring message towards the brainii) MOTOR-NEURONS: take the message outwards- from brain to tissues for responseiii) INTERNEURONS: link impulses between neurons

- Mechanism for an action potential (AP) (nerve impulses)

- an AP is how a neuron conducts a signal- a nerve before an AP has a RESTING POTENTIAL- when measured with an oscilloscope the inner neuron has a -65 mV potential

A) REASON FOR THE RESTING POTENTIAL

- its due to a difference ion distributionCHANNELSpurple = potassium gatesgreen = sodium gates(both closed at rest)PUMPS ( always working)


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- a greater concentration of Na+ ions pumped to the outside of cell membrane- a high concentration of K+ pumped to the inside

- because [Na+] is slightly greater it becomes slightly positive on the outsidecompared to inside

- Na+ and K+ are constantly diffusing to the opposite side (equilibrium), but the pumpsnever stop and therefore even at rest maintain the potential

B) ACTION POTENTIAL (AP)- a rapid change in charge or polarity across the axomembrane is an action potential

- therefore all nerve activity in our body is nothing more then a change inelectrical potential along neurons

- a stimulus causes Na+ ions to diffuse into the membrane a little quicker, therefore-65mV becomes -60, ....., -55, ...., etc.

- at -45mV (threshold) sodium gates open and Na+ ions rush into the axon- this will cause a rapid change in charge across the membrane- +40mV on the inside

1) stimulus causes axon to reach threshold

to reach -45mV2) Na+ gates open and Na+ rushes into the

axon (depolarization)3) at +40mV sodium gates close and K+

gates open therefore K+ rushes out ofaxon (-65mV) (re-polarization)

* after re-polarization ion distributions onwrong side of membrane


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- to redistribute ions (Na+ out) (K+ in) pumps never stop- once a sodium gate opens and closes it cannot open again until after the next sodium

gate opens and closes = REFRACTING PERIOD- this ensures impulse only travels one way- the stronger the stimulus the shorter the refracting period therefore the size of a

stimulus is indicated by frequency of action potentials not size (size is always thesame)

MYELIN: is a white insulating material (white material) composed of a neurologlia calledSCHWANN CELLS that wraps around the axon

-where ever there is myelin the AP willtravel faster impulses because the AP

jumps from Na+ and K+ gates to thenext open (non-myelinated) Na+ and K+-AP jumps to the NODES OF RANVIER(exposed gates)

-node to node conduction of an actionpotential is called SALTATORYCONDUCTION

Action potential along a neuron


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TRANSMISSION OF IMPULSE ACROSS SYNAPSE- the AP travels to the end of the axon (axon bulb) without diminish- at the end of it must transmit the signal to the next nerve, gland, or muscle- axon bulb does not actually make contact with next nerve, gland or muscle, but rathercomes in close proximity = SYNAPSE

KEY POINT:1) 1000s of axonsend at nerve cells(glands, muscle)*not just one asshown2) a synapse is whatwe call the entic

junction betweenaxon bulb and

dendrites3) the regionseparating pre-synaptic membraneand post synapticmembrane isSYNAPTIC CLEFT

4) pre and post synaptic membrane have different structuresPRE = vesicles with neurotransmitters

POST = specific receptors for neurotransmitters

STEPS OF TRANSMISSION ACROSS THE SYNAPSE1) during depolarization of axon bulb as sodium ions rush inwards calcium ions rush

inwards with themREASON: Ca+2 is found in high [] inside the synaptic cleft2) Ca+2 combine with MICROFILAMENTS, which cause them to interact with the

vesicles that carry the NEUROTRANSMITTERS- causes vesicles to be drawn towards the pre-synaptic membrane3) exocytosis of neurotransmitters into the synaptic cleftNOTE: this is an active process therefore lots of ATP and MITOCHONDRIA in axon bulb

4) neurotransmitters then passingly diffuse across the cleft5) neurotransmitters bind to specific protein receptor sites on the post synaptic

membrane6) what happens at post synaptic membrane is dependent on type of cell (nerve, gland,

muscle) and type of neurotransmittera) NERVE CELL: excitatory neurotransmitter cause the next neuron to fire (AP)

- NOREPINEPHRINE- inhibitory neurotransmitter which inhibit an AP at next neuron


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- ACETYLCHOLINEb) MUSCLE: NOREPINEPHRINE = contractionACETYLCHOLINE = relaxc) GLAND: NOREPINEPHRINE = gland to secrete hormonesACETYLCHOLINE = inhibits gland from secreting hormones

7) receptors on post synaptic membrane release neurotransmitters back into the cleft- here most are broken down by enzymes (important to prevent perpetual firing orinhibition)

ENZYMES: NOREPINEPHRINE is destroyed by an enzyme = MONOAMINE OXIDASE- ACETYLCHOLINE is destroyed by ACETYLCHOLINESTERASE8) Ca+2 ions are actually returned to cleft (active transport)*DRUGS: often somehow effect the transmission of neurotransmittersex. STIMULANTS- increase neurotransmittersDOWNERS- inhibiting neurotransmitters

SUMMATION AT RECEIVING END

- dendrites are on the receiving end of many synapse- there may be both EXCITATORY and INHIBITORY effects from neurotransmitters on a

single synapse- therefore the cell body must have a summative effect on all incoming signals

NORMAL NERVE AP PATHWAY- impulses travel inwards via SENSORY NERVES, which enter spinal cord on the

DORSAL SIDE- impulse travels to brain on outside of spinal cord (white matter) where its interpreted

for a response- response impulse sent back down spinal cord to MOTOR NERVES, which exit from

the VENTRAL SIDE


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REFLEX RESPONSE- an involuntary automatic response to a stimulus

- no choice- response can be innate, a twitch or pull away from the stimulus

- a reflex can be conditioned (trained for a specific response)

- during a reflex many internment are stimulated at once- therefore there may be multiple responses- jump back- look towards- scream- lift arms in defense

REFLEX PATHWAY

HUMAN NERVOUS SYSTEM- divide into 2 parts

i) Central nervous system (CPS)ii) Peripheral nervous system (PNS)

1) CENTRAL NERVOUS SYSTEM- consists of brain and spinal cord- *protected in 3 waysi) BONY ARMOR: brian is enclosed in a skull- spinal cord is surrounded by vertebrae


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ii) MENINGES: 3 layers of protective membrane- under or lining all bone and all CNSiii) CEREBRAL SPINAL FLUID: liquid that fills all empty spaces in and around our

central nervous system (CNS)- ventricles in brain

- central spinal canal- between meninges and spinal cord

SPINAL CORD: has 2 functionsi) acts as the interpretation center for the reflex actionii)provides a communication link between the brain and the peripheral nervous system

(PNS)- any damage or cuts to spinal cord will end communication between incoming and

outgoing messages (paraplegia and quadriplegia)NOTE: remember all sensory nerves enter a spinal cord on dorsal side and motornerves exit on ventral side

BRAIN: controls the conscious and subconscious thoughts and body systems

CONSCIOUS THOUGHT (CONTROL): largest portion of the brain and is called theCEREBRUMRESPONSIBLE: for higher thought processes" - memory

- learning- language- speech

- the outer part of cerebrum is composed of un-myelinated tissue (grey matter)

- is called CEREBRAL CORTEX- inner layer is myelinated ofter referred to as CEREBRAL MEDULLA- cerebral is divided into 2 halves:i) RIGHT CEREBRAL HEMISPHERE (controls creative side)ii) LEFT CEREBRAL HEMISPHERE (verbal/logical side)- each hemisphere is divided into surface lobes1) FRONTAL LOBE: touch, temperature, pressure, pain (skin)2) TEMPORAL LOBE: hearing, smells, visual, auditory memory3) OCCIPITAL LOBE: vision* 2 hemispheres are connected by a large chunk

of myelinated tissue called CORPUS

COLLASUM


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SUBCONSCIOUS BRAIN PARTS AND CONTROL: 4major regions1)MEDULLA OBLONGATA: brain stem (the mostupper part of spinal cord)-controls most of internal organs and regulates heartrate, breathing, lungs, blood pressure, digestion-reflex center: vomiting, coughing, sneezing,

swallowing2)HYPOTHALAMUS: links to internal balance(homeostasis)-hunger, thirst, sleep, body temp (regulations), waterbalance-also controls PITUITARY GLAND serves as the linkbetween the nervous system and the ENDOCRINESYSTEM = chemical trigger3)THALAMUS: gate keeper of the brain (acts as arelay station to direct incoming signals) -----> directs toCEREBRUM voluntary

4)CEREBELLUM: muscle co-ordinates, tone, and bodyposture (physical co-ordination) balance-integrates signals with frontal lobe (cerebrum,

voluntary)(specific skill)

PERIPHERAL NERVOUS SYSTEM- all nerves that connect to the spinal cord make-up PNS (all motor and sensory nerves)


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PERIPHERAL NERVES: includei) SENSORY NERVES: carry messages towards the CNS ----> process long dendrites

(for picking up stimuli)ii) MOTOR NERVES: carry messages away from CNS- tend to have longer axons

- *PNS also contains GANGLIA (ganglion) ------> collection of cell bodiesPNS: is divided into somatic NS (SNS) and automatic NS (ANS)SOMATIC: motor nerves that control our voluntary actions EX. running; thereforesomatic motor nerves synapse with our skeletal muscles and skinNOTE: same node that triggers reflex actionAUTOMATIC: (ANS) the nerves that synapse with our involuntary organs (glands, liver,heart, digestive system, kidneys, etc.)- part of brain sending signals to tissue nerves = hypothalamus and or medulla

oblongata- ANS can further be divided into:

i) sympathetic

ii) parasympathetic- 2 different types of MOTOR NERVES that attach to the same region

SIMILARITIES BETWEEN SYMPATHETIC AND PARASYMPATHETICi) function automatically and use subconscious parts of brain to trigger themii) both synapse with all our internal organsiii) both utilize 2 motor neurons (have ganglia) in each impulse

SYMPATHETIC NS (fight or flight response)- important during stress or emergency type situations


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- cause an increase in heart rate, breathing, dilation pupils, and increase inkidney activity *decrease in digestion

-neurotransmitter released = Norepinephrine-the ganglia are close to the spinal cord

- therefore a shorter pre-ganglionic fiber and a longer post ganglionic fiber

- sympathetic motor neurons tend to originate from our thoracic/lumbar regions of spinalcordPARASYMPATHETIC NS: housekeeper or relaxed nerves- promotes decrease hear and rate,breathing, gland activity, pupilconcentration- * increase digestion- neurotransmitter acetylcholine(Ach)- pre-ganglionic fiber tends to be

longer and post ganglionic fibershorter, therefore the ganglia arefound close to the organs theysynapse with-nerves tend to originate from theCRANIAL and SACRAL regions ofspinal cordNEUROENDOCRINE: there is adefinite link between the NS andendocrine system*ENDOCRINE GLAND: ductless

glands that dump hormones directlyinto bloodEX. fight or flight response-during emergencyNOREPINEPHRINE: (AKAnoradrenalin) are released by thesympathetic NS-our sympathetic NS stimulates theADRENAL MEDULLA (inneradrenal gland = on top of kidneys

- the adrenal medulla in return releases the hormone epinephrine (AKA adrenalin),

which continues fight or flight response increase heart rate, increase breathing, etc.

HYPOTHALAMUS(neurological) AND PITUITARY(endocrine) GLANDRELATIONSHIP- hypothalamus (brain) controls the activity of the pituitary gland (endocrine)

- some of the control is by AP- some of the control is by hormones

- pituitary gland lies below the hypothalamus and is approx. 1cm in diameter


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Its divided into:1) POSTERIOR PITUITARY2) ANTERIOR PITUITARY

POSTERIOR PITUITARY HORMONES:- hypothalamus produces hormones ADH(antidiuretic hormone) and OXYTOCIN, whichit then sends to the posterior pituitary for storage and release

- when the hypothalamus receives the stimuli it produces an AP that triggers the releaseof these hormones

ADH: used by the kidneys and causes water absorptionOXYTOCIN: causes uterine contractions

ANTERIOR PITUITARY HORMONES:- hypothalamus controls the anterior pituitary by hormone release

- hypothalamus releasing hormones- hypothalamus inhibiting hormones

- these releasing and inhibiting hormones are released into the blood by thehypothalamus (portal system) and make their way to the anterior pituitary

- 6 different hormones to be released or inhibitedi) *TSH ( thyroid releasing hormone) ---> thyroid gland = increase MBRii) ACTH (adrenocorticotropic hormone) ----> adrenal cortex ---> glucose uptakeiii) *FSH and LH (follicle stimulating hormone and leutinizing hormone) ---> testes and

ovariesiv)PRL ( prolactin) mammary glands = milk productionv)MSH (melanocyte stimulating hormone) ---> skin tone

vi)GH (growth hormone) ----> triggers long bone and skeletal muscle growth


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IMPORTANT DIAGRAMS


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Bio Notes Unit 7

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