The brain and spinal cord, coordinates the activity of all parts of the bodies of multicellular organisms

star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical support of endothelial cells which form the blood-brain barrier, the provision of nutrients to the nervous tissue, and a principal role in the repair and scarring process of the brain and spinal cord following traumatic injuries

Functions:

-found within the CNS

1. provide structural support for neurons

2. regulate the extracellular concentrations of ions and neurotransmitters

3. respond to activity in neighboring neurons by facilitating information transfer at those neuron’s synapses

4. induces formation of tight junctions between capillary cells to help form the blood-brain barrier: restricts the passage of substances into the CNS

5. can also act as stem cells, generating neurons and other glia

a crucial brain region for homeostatic regulation: Factors such as blood pressure, body temperature, fluid and electrolyte balance, and body weight are held to a precise value called the set-point.

1. the source of posterior pituitary hormones and releasing hormones that act on the anterior pituitary

2. contains centers involved in thermoregulation, hunger, thirst, sexual and mating behavior, and pleasure

a reduction in the absolute value of a cell's membrane potential from changes in membrane voltage in which the membrane potential becomes less negative

*In neurons and some other cells, a depolarization large enough may result in an action potential. A stimulus strong enough to produce a depolarization that reaches the threshold triggers a different type of response, called an action potential.

*changes in membrane potential are called graded potentials because the magnitude of the change—either hyperpolarization or depolarization—varies with the strength of the stimulus: A larger stimulus-->larger change in membrane permeability-->larger change in membrane potential

*In most neurons, depolarizations are graded only up to a certain membrane voltage, called the threshold.

1. short lived depolarizations or hyperpolarizations of an area of membrane; EPSPs and IPSPs are summed to either depolarize or hyperpolarize a postsynaptic neuron

a. changes cause local flows of current (current reflects the movement of ions) that decrease with distance

b. magnitude is a direct reflection of the intensity or strength of the stimulus: more intense the stimulus

-->more ion channels that are opened-->greater voltage change (hyper or de- polarization)-->farther the current flows

-a neurotransmitter that is naturally produced in the body

-present in the regions of the brain that regulate movement, emotion, motivation and the feeling of pleasure (affect sleep, mood, attention, and learning)

-stabilizes brain activity, regulates flow of information to other parts of the brain and controls movement

-plays a major part in addiction

-similar to adrenaline

1. Axons from every sensory system (except olfaction) synapse here as the last relay site before the information reaches the cerebral cortex

2. relays all sensory information to the cerebrum and relays motor information from the cerebrum:

a. Incoming information from all the senses is sorted and sent to the appropriate cerebral centers for further processing

b. also receives input from the cerebrum and other parts of the brain that regulate emotion and arousal

1. a region of the brain that plays an important role in the integration of sensory perception, coordination and motor control

2. functions to error-check and coordinate motor activities, and perceptual and cognitive functions

a. involved in learning and remembering motor skills

b. also coordinates motor commands issued by the cerebrum

3. relays sensory information about joints, muscles, sight, and sound to the cerebrum

1. change in membrane potential that returns the membrane potential to a negative value after the depolarization phase of an action potential has just previously changed the membrane potential to a positive value

2. Repolarization results from the movement of positively charged K+ ions out of the cell.

a. Typically the repolarization phase of an action potential results in hyperpolarization, attainment of a membrane potential that is more negative than the resting potential

1. means by which action potentials are transmitted along myelinated nerve fibers, is faster than unmyelinated

2. In the myelinated neurons of vertebrates: voltage-gated Na+ and K+ channels are concentrated at gaps in the myelin sheath called nodes of Ranvier-->only unmyelinated regions of the axon depolarize-->the impulse moves faster than in unmyelinated neurons

 1. contain gap junctions that do allow electrical current to flow directly from cell to cell

a. action potentials travel directly from the presynaptic to the postsynaptic cell

2. synchronize the activity of neurons responsible for rapid, stereotypical behaviors

3. a mechanical and electrically conductive link between two abutting neuron cells that is formed at a narrow gap between the pre- and post-synaptic cells known as a gap junction

a. faster than chemical synapse, but no learning can occur

• subdivision of the motor nervous system of vertebrates that regulates the internal environment
• consists of the sympathetic, parasympathetic, and enteric divisions.

1) are graded – magnitude varies depending on how much neurotransmitter

2) do not regenerate

3) diminish with distance

4) can depolarize or hyperpolarize

5) can have temporal or spatial summation

6) use of both is what allows integration to happen

7) summed effects of ALL EPSP and IPSP is at the axon hillock

8) EPSP and IPSP can cancel each other out.

oligodendendrocyte: form myelin sheaths AROUND neurons IN the CNS

Schwann cells: form myelin sheaths  AROUND axons OUTSIDE the CNS

-70mV

-80mV 

more Na 

Diffusion of K 

More Na comes in than K going out BUT off set by 3Na/2K pump

EPSP adding together to increase stimulus to trigger an action potential

1. temporal summation 
2. spatial summation 

Somatic afferent neurons 

1. conduct impulses initiated in external receptors

ex) skin, skeletal muscles, tendons, & joints. 

Somatic efferent neurons 

1) motor neurons that conduct impulses from the spinal cord to skeletal muscles. 

Visceral afferent neurons (enteroceptors or visceroceptors) 

1) sensory neurons that conduct impulses initiated in receptors in smooth muscle & cardiac muscle. 

Visceral efferent neurons

1) motor neurons that conduct impulses to smooth muscle, cardiac muscle, & glands.

2) make up theAutonomic Nervous System.

3) Some visceral efferent neurons begin in the brain; others in the spinal cord. 

1. endothelial cells and associated astrocytes are stitched together by tight junctions to form BBB
2. separation of circulating blood and cerebrospinal fluid(CSF) maintained by the choroid plexus in the (CNS). 
3. restrict the diffusion of  bacteria and large or hydrophilicmolecules into the CSF
4. allow the diffusion of small hydrophobic molecules (O2, hormones, CO2).  
5. actively transport metabolic products such as glucose across the barrier with specific proteins.

·      voltage difference (or electrical potential difference) between the interior and exterior of a cell.

·      fluid on both sides contains mobile ions, (Na+), (K+), (Cl–), (Ca2+) potential arises from the interaction of ion channels and ion pumps embedded in the membrane

two basic functions

1.   function as a battery,

2.   in cells such as neurons, used for transmitting signals between different parts of a cell. Opening or closing of ion channels > produces a local change in the membrane potential> electric current to flow rapidly to other points in the membrane.

·      gaps formed between the myelin sheaths generated by different cells.

·      At nodes of Ranvier, the axonal membrane is uninsulated and therefore capable of generating electrical activity.

Action Potential - action potential has two methods to travel down the axon – continuous conduction for unmyelinated axons, and saltatory conduction for myelinated axons.

Saltatory Conduction- action potential moving in discrete jumps down a myelinated axon.

 charge passively spreading to the next node of Ranvier > depolarize it to threshold > trigger an action potential in this region > passively spread to the next node and so on.

1.   saves energy by decreasing the use of sodium-potassium pumps in the axonal membrane.

2.   the increased speed afforded by this mode of conduction assures faster interaction between neurones.

Continuous conduction / unmyelinated axon

speed is proportional to the diameter of axons directly proportional 

§  Sympathetic:  “flight or fight” /  arousal and energy

1. hormonal and neuronal influences 

hormonal:

adernaline/ephinephrine >constrict blood vessel > increase heart rate

Acetyl choline (pregang )via circulation

2. all leave from thoracic system 

3. neurotransmitter : norepinephrine (postgang )via synapse

§  parasympathetic nerves: rest and digest” / promotes calming and return to self-maintenance functions

1. 90% is the vagus nerve 

2. neurotransmitter: Ach for pre and postganglionic

junction between two neurons OR between a neuron and an effector

1.  specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands.
2.  allow neurons to form circuits within the CNS 
3. involves neurostransmitter and synaptic cleft 

1. subdivided to Mesencephalon
2. function: visual reflexes & relay center for auditory information
3. part of brain stem
4. cavity: fourth ventricle

Absolute refractory period:

During the millisecond when axon is depolarized, axon cannot transmit another rxn potential.

Why? Voltaged activated Na chancels are inactivated.

vs

Relative refractory period : period after being reset from absolute refractory period. Threshold is higher here

 ex) beta endorphins and enkephalin)

·      messengers that enhance/inhibit synaptic function: type of neuromodulators

·      like opiods produce feelings of “relieving pain”

·     type of neuropeptide

1. type of endorphins (neuropeptide)
2. internally made  and bind to the body's opioid receptors. 
3. gives filling of 'relieve of pain'

• any member of the group of drugs used to relieve pain 
•  opioid drugs such as morphine 

1. Glia Cells-essential for the structural integrity of the nervous system and for the normal functioning of neurons

a. types in brain and spinal cord:

i. Astrocytes (CNS):

-provide structural support for neurons (most prevalent-responsible for physical support of neurons and biochem. environment)

-regulate the extracellular concentrations of ions and neurotransmitters

-respond to activity in neighboring neurons by facilitating information transfer at those neuron’s synapses

-induce formation of tight junctions between capillary cells to help form the blood-brain barrier, which restricts the passage of substances into the CNS

-*Blood-brain barrier-CNS sep. from rest of body (in terms of flow of mols. to protect from toxins)-glial cell interaction with capillaries

-role in producing new neurons-behave as stem cells→plasticity, not hard-wired (change # of neurons and how they communicate)

ii. microglial cells-important in health in nerve cells-rel. growth factors-role in healing (damage)

-immune system of CNS (bodily immune system-no access to brain)

-phagocyte-cell that eats another cell

iii. ependymal cell-line all cavities of CNS (hollow system-spinal cord; brain-folds back, wrinkled)

-produce and secrete cerebrospinal fluid (CSF)-lumbar puncture/spinal tap-look at liquid for abnormalities-blood, bacteria

-source of new neurons

(Radial glia-form tracks along which newly formed neurons migrate from the neural tube; act as stem cells, generating neurons and other glia

iv. Oligodendrocytes (in the CNS) and Schwann cells (in the PNS) are glia that form myelin sheaths around the axons of vertebrate neurons

-sheaths provide electrical insulation of the axon

Characteristics:

1. generated by influx of Na+ and efflux of K+

a. when voltage reaches threshold level (-55mV)

2. positive feedback system-as Na+ flow into cell down concentration gradient, cytosol becomes + charged rel. to extracell. fluid→depolarizes neuron→more voltage-activated Na+ channels open→increases permeability of Na+

3. all or none response

a. no variation exists in strength of a single impulse

4. self-propogating

a. continuous conduction-travels slowly in unmyelinated neurons

b. salutatory conduction-myelinated neurons transmit impulses rapidly

i. when nodes of Ranvier far apart→less of axon must depolarize→axon conducts impulse faster

ii. reqs. less energy than cont. conduction

Role of membrane permeability changes and ion gates:

1. voltage reaches threshold→channel protein changes shape→Na+ activation gates open→Na+ flows through channel→inside fo neuron becomes + charged→a.p.

a. inactivation gates close during depolarization

b. depolarized neuron→voltage activated Na+ channels open→increasing membrane permeability to Na+→Na+ diffuse into cell→cytosol becomes charged→further depolarization causes more voltage-activated Na+ channels to open→increases membrane permeability to Na+→inactivation Na+ gates close→membrane impermeable to Na+→repolarization

Action potential propagated along a neuron:

self-propogating: during depolarization, affected area of membrane more + relative to adjacent regions where membrane is still at RP→diff. in potentials btw. active and resting membrane regions causes ions to flow btw. them (electric current)→flow of Na+ into adj. region causes voltage-activated Na+ channels in one area to open→next adj. ion channels open→Na+ enters→repeated until end of axon

Definition: membrane potential of a neuron that is not transmitting signals

Four factors:

1. maintain ionic gradients that exist across plasma membrane by Na/K pump

a. In mammals, the extracellular fluid has a Na+ concentration of 150 millimolar (mM) and a K+ of 5 mM.

b. In the cytosol, Na+ concentration is 15 mM, and K+ concentration is 150 mM.

c. the K+ and Na+ currents are equal and opposite (membrane is more permeable to K+ than to Na+)

d. maintain membrane’s permeability to particular ions

2. ungated, open ion channels for diffusion

1. Cell body-contains nucleus of neuron

2. Axon- a longer, singular extension of the cell body that transmits signals to neurons or effector cells (sends nerve impulses)

a. joins the cell body at the axon hillock, where signals that travel down the axon are generated

b. enclosed in a myelin sheath

c. near its end, axons divide into several branches, each of which ends in a synaptic terminal

d. where a.p. occurs

3. Dendrites- smaller (short), highly branched extensions of the cell body that receive signals from other neurons

Classified by function:

-three stages in the processing of information by nervous systems: sensory input, integration, and motor output.

1. Sensory neurons (afferent neurons) transmit sensory impulses from the skin and other sensory organs or from various places within the body toward the central nervous system (CNS, or brain and spinal cord).

Definition: a steady state in which opposing chemical and electrical fluxes are equal and there is no net movement of the ion; magnitude of the membrane voltage at equilibrium given by the Nernst Equation

Explanation:

*cells live at -70mV (resting potential)-->few channels allow Na+ to leak back in, but  membrane much more permeable to K+ than to Na+→-85mV (equilibrium potential for K+)

Definition: a local response that functions as a signal only over a very short distance; varies in magnitude

-->pot. charge varies dep. on strength of stimulus applied

graded potential-changes in membrane potential

1. magnitude of change varies with strength of stimulus

a. larger stimulus→larger change in permeability→greater change in membrane potential

2. a local response that functions as a signal only over a very short distance

3. all cells generate

action potential- signals conducted by axons; generated by influx of Na+ and efflux of K+; nerve impulse-electrical signal that travels rapidly down the axon into the synaptic terminals

1. all or none phenomenon

2. magnitude independent of strength of triggering stimulus

3. very brief in duration, high frequency

4. both voltage-gated Na+ channels and voltage-gated K+ channels are involved

5. only neurons, muscle cells generate

resting potential-membrane potential of a neuron not transmitting signals

1. activation gate on most K+ channels is closed; inactivation gate open on most Na+ channels

EPSP and IPSP are forms of direct synaptic transmission

Overall: Neurotransmistter on ligand gated ion channel > open channel > EPSP or IPSP

EPSP: excitatory, depolarize postsynaptic neuron

1. a change in membrane pot. to more positive (inside) that brings neuron closer to firing

a. binding of NT to postsynaptic receptors > opens gated channels that allow Na+ to diffuse into and K+ to diffuse out of the cell > temporal and/or spatial summation >depolarize

2. graded responses

IPSP: inhibitory, hyperpolarize postsynaptic neuron

1. membrane potential becomes more negative→takes neuron farther away from firing level (membrane is farther away from threshold and a stronger stimulus is req. to fire the neuron)

a. binding of NT to postsynaptic receptors > open gated channels that allow K+ to diffuse out of the cell and/or Cl- to diffuse into the cell > HYPER polarize 

2. graded responses

·      1) diffuse through the synaptic cleft

·      2) presynaptic neuron takes it back through active transport -> repackaged to synaptic vesciles

·      3) glia metabolizes as fuel

·      4) acetylcholine is degraded by enzyme

Describe synaptic transmission across an electrical synapse and a chemical synapse. Describe the role of cholinesterase and explain what would happen if acetylcholine were not destroyed.

Across an electrical synapse:

1. pre and postsynaptic neurons occur very close together and form gap junctions

a. interiors of two cells physically connected by protein channel

2. let ions pass from cell to cell, allowing impulse to be directly and rapidly transmitted from a pre to postsynaptic neuron

3. synchronize the activity of neurons responsible for rapid, stereotypical behaviors (escape responses)

Across chemical synapse:

1. majority of synapses

2. pre and postsynaptic neurons separated by a space-synaptic cleft

3. NT=chemical messengers that conduct neural signal across synapse and bind to chem. activated ion channels in membrane of postsynaptic neuron→triggers specific gated ion channels to open→changes in permeability of postsynaptic membrane

a. presynaptic neuron synthesizes NT→packages it in synaptic vesicles, which are stored in the neuron’s synaptic terminals

b. When an action potential reaches a terminal→depolarizes terminal membrane→opening voltage-gated calcium channels in the membrane

c. Ca2+ then diffuse into the terminal, and the rise in Ca2+ concentration in the terminal causes some of the synaptic vesicles to fuse with the terminal membrane, releasing the neurotransmitter by exocytosis

d. The NT diffuses across the narrow gap, called the synaptic cleft, which separates the presynaptic neuron from the postsynaptic cell

Role of cholinesterase: enzyme in synaptic cleft that degrades NT acetylcholine

*if acetylcholine-NT rel. from motor neurons that triggers muscle contraction- is not destroyed→muscle contraction, does not relax→cannot breathe and dies

Distinguish between sensory(afferent) nerves and motor (efferent) nerves.

Sensory neurons:

·      transmit information from external stimuli and internal environment (blood pressure, muscle tension)

·      information sent to CNS

Motor neurons:

·      motor output leaves the CNS through motor neurons

·      communicate with muscle or endocrine cells.

·      Carry out body’s response to a stimulus

Biogenic amines: affects mood

1. catecholamines:

a. norepinephrine (rel. by adrenergic neurons)-in CNS, PNS- excitatory or inhibitory

b. dopamine (CNS)- helps maintain bal. btw. excitation and inhibition of neurons; important in motor functions

2. serotonin (CNS)- excitatory effect on pathways that control muscle action; inhibitory effect on sensory pathways; helps regulate food intake

Amino acids:

1. glutamate (CNS)-major excitatory NT in brain; functions in learning and memory

2. glycine (CNS)- inhibitory

3. Gamma-aminobutyric acid (GABA) (CNS)- inhibitory

4. aspartate (CNS)- excitatory; functions in learning and memory

Neuropeptides:

1. endorphins and enkephalins (CNS, PNS)- neuromodulators-messenger mols. that stimulate long-term changes that enhance or inhibit synaptic function

a. endogenous opioids-powerful analgesics-drugs that relieve pain w/o causing loss of consciousness

b. bind to opioids receptors and block pain signals

c. modulate effect of other NT such as substance P- activates the pathways that transmit pain signals

Gaseous NTs:

1. nitric oxide (NO)-signaling mol.

a. acts as a retrograde messenger at synapses- transmits info. from post to presynaptic neuron (opp. dir. of transmissions from other NTs)

2. carbon monoxide (CO)-neuromodulator

Explain how a neuron integrates incoming information, including a description of summation.

> Receives 100s of EPSP and IPSP 

> temporal or spatial summation of EPSP or IPSP

> action potential transmitted along postsynaptic neuron 

temporal summation:

two EPSP made in rapid succession at the SAME synapse > have additive affect

spatial summation

two EPSP made simultaneously by DIFFERENT synapse on same neuron > hadve additive affect 

List two classes of neuropeptides and explain how they illustrate overlap between endocrine and nervous control.

neuropeptide:

·      short chains of amino acids

·      serve as neurotransmitter

classes: 

1) endorphins (beta endorphins and enkephalin)

·      messengers that enhance/inhibit synaptic function: neuromodulators

·      like opiods produce feelings of “relieving pain”

2) substance P:

·      neuromodulator and transmitter

·      transmit information about pain

Overlap btw endocrine and nervous control: 

endocrine works with nervous systems to regulate physical and physiological behaviors

endocrine: gives slow and long lasting regulation

nervous: gives rapid brief response

List three criteria for a compound to be considered a neurotransmitter.

1) stored in presynaptic cell

2) released and respond to action potential

3) influence the postsynaptic cell

4) have removal mechanism to HAVE it removed / turned off.

Describe two mechanisms by which a neurotransmitter affects the postsynaptic cell. 

Direct or indirect 

Indirect synaptic transmission:

Neurotransmistter (Norepinephrine or serotonin) binds to receptor > activates signal transduction pathway > activates G protein > activates adenylyl cyclase (enzmye) > coverts ATP to cAMP > activates protein kinase A > phosphorylates specific channel proteins > open or close channels

*Slower but longer duration

Direct synaptic transmission:

reaches presynaptic terminal… 

Define reflex and describe the pathway of a simple spinal reflex.

• aka “knee jerk” “patella” reflex
• response to a specific stimulus
• not adjustable
• very rapid
• type of “monosynaptic reflex” 

Spinal cord:

·      Transmit impulses to and from the brain

·      Controls many reflex activities

Reflex action:

·      Simple

·      Involuntary motor response to a stimulus

Simple Spinal Reflex:

hit knee > tendon has a golgi tendon organ (a proprioceptive receptor) that senses pressure > signal down sensory neuron via dorsal root side > axon cont' to gray matter of spinal cord (CNS) > CNS integrates info > synapse with motor neuron > out ventral side > synapse with muscle cell > muscle contracts  > kick out knee

Describe three major trends in the evolution of the vertebrate brain.

All vertebrates have the same basic brain structure.

Difference: different part of brain are specialized

Evolutionary trend: toward increasing complexity in cerebrum and cerebellum

Early embryonic division:

·      neural tube: Brain and spinal cord connected by single tube of tissue

·      Anterior (front) expands to become brain

o   bulges: hindbrain, midbrain, forebrain

·      Posterior (back) expands to become spinal cord.

Hindbrain:

1) metencephalon

·      cerebellum and pons

2) myelencephalon (fourth ventricle

·      medulla

Midbrain

1) mesencephalon (cerebral aqueduct)

·      superior and inferior colliculi in mammals

Forebrain:

1) telencephalon (first and second ventricle – lateral ventricles)

o   cerebrum

2) diencephalon (third ventricle)

o   A) thalamus

o   B) hypothalamus

o   C) epiphysis (pineal body

Distinguish between white matter and gray matter.

Gray matter:

·      unmyelinated axons, nuclei (in neuron cell bodies) and dendrites

·      Outside (brain) ; middle (spinal cord)

White matter:

·      bundles of mylinated axons

·      within white matter is basal nuclei (brain)

·      inside (brain); outside (spinal cord)

Distinguish between the functions of the autonomic nervous system and the somatic nervous system.

Both part of PNS

Both help maintain homeostasis.

o   somatic:

-carries signals to and from skeletal

-response to external stimuli

 -have afferent nerves and efferent nerves                    - receptors > afferent nerves > transmit info to CNS

     - CNS > efferent (motor nerves) transmit info > effectors (skeletal muscles and glands)

o   automatic:

- regulates internal environment

- have afferent nerves and efferent nerves

- receptors > afferent nerves > transmit info to CNS

- CNS > efferent (sympathetic/parasympathetic nerves) transmit info > effectors (smooth muscles, cardiac muscle and glands)

§  Sympathetic:  “flight or fight” /  arousal and energy

§  parasympathetic nerves: rest and digest” / promotes calming and return to self-maintenance functions

§  Enteric:

a) network of neurons that control the secretions of the digestive tract, pancreas, and gallbladder.

b)activity in the smooth muscles that produce peristalsis.

c)Regulated by sympathetic and parasympathetic division

List the major components of the central nervous system.

1) CNS

·      composed of: need small brain and longitudinal nerve cord

·      derived from: dorsal embryonic nerve cord (hollow)

·      humans: spinal cord + 4 ventricles of the brain

  filled with cerebrospinal fluid

·      input info and think of appropriate output through CNS

·      does NOT have the ability to repair itself

2) PNS

·      composed of: sensory receptors + nerves

·      humans: left-right pairs of cranial and spinal nerves + ganglia

·      nerves that connect and transmits information to and from the CNS with the rest of the body

·      regulate physical movement and internal environment

·      has the ability to repair itself

·      somatic and autonomic nervous system

a)  somatic:

b) automatic:

-sympathetic, parasympathetic or enteric

Why is the resting potential more closer to the Eq potential for K? 

• bc membrane is more permeable to K
• because Cl and negative charged large protein
• all these help it become more negative

Na activation gates closed (no Na)

Inactivation gate opened (no Na)

K Acitvation gate closed (no K)

Can all cells generate action potentials? 

 No. only neurons, muscle cells and others

how do antidepressents work?

Inhibit the update of neurotransmitter serotonin in brain so serotonin stays in the synaptic cleft which elevates mood. 

How do anesthetics work? 

Novocaine and such bind to voltage activated Na and block them. They do not open in response to depolarization > cannot send impulse to brain > no pain

1. Passive ion – allow, Na, K, Cl and Ca2+
2. Voltage gated activated
3. Chmically gated activated

Overall: 6 steps

Stimulus (external or internal) > reception (internal or external organs) > transmit information (afferent neurons) > integration CNS (brain and spinal cord) > transmit impulse/action potential (efferent neurons) > (muscle and glands, another neurons) > actions 

Specific:

Resting potential > Na activation and K Activation gated CLOSED/ Na Inactivation gate OPENED

Stimulus > threshold (greater than -55mV) > depolarize by leaving Na inactivation gates open and opening Na gates >incoming of Na >inside cell is now positively charged > increase permeability to Na >more Na come in > overshoot > inactivation Na gates close, activation Na gate opened > absolute refractory period> > repolarization > K gates open > diffuse out of cell > undershoot > return cell to negative state > K gate close when resting potential has been restored  > return to resting state > current between nodes / action potential “jumps” > propagate neighbor that is at resting potential > action potential reaches presynaptic terminal… 

1) electric synapse

>reach gap junction where two cells physically touch > ions pass to postsynaptic > motor neurons

OR

2) chemical synapse (majority)

> Ca2+ channel open > Ca2+ from outside come in > Ca2+ cause synaptic vesicles (that store neurotransmitter/ligand) to fuse with plasma membrane> release neurotransmitter into synaptic cleft ….

A) neurotransmitter binds with ligand gated channel of postsynaptic neuron>ion channel open (ie: Na) > EPSP (graded) > depolarization

B)neurotransmitter (GABA) binds with receptor > ISPS(graded) > ion channel K opens or open Cl> hyperpolarization > become more negative

OR

>neurotransmitter binds with receptor >activates signal transduction pathway> activate G protein > activates adenylyl cyclaseenzyme > coverts ATP to cAMP > activates protein kinase A > phosphorlyates protein > close K + channels

ex) serotonin or Norepinephrine

Neural INTEGRATION : summing / integrating incoming signals

Receives 100s of EPSP and IPSP > temporal or spatial summation of EPSP or IPSP> action potential transmitted along postsynaptic neuron > Transmit to motor neuron > muscle contracts

*only happens at nodes

*self propagate 

• an automatic, involuntary reaction to a stimulus mediated by the spinal cord or lower brain
  
• generally functions to restore homeostasis

Reflex Pathway

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1-    sensory receptors detect a change in homeostasis

2-     sensory neurons convey the info to the spinal cord

3-     in spinal cord info travels btwn sensory neurons and motor neurons

4-     motor neurons convey the signal to the appropriate effector cells

• the narrow gap between a synaptic terminal of an axon and a signal receiving portion (dendrite or body cell) of another neuron or effector cell
• 2 kinds of synapses: electrical and chemical

  a muscle cell or gland cell that performs the body’s response to stimuli  (nerve impulses)

membranous sacs containing thousands of neurotransmitters at the tip of the presynaptic axon

• rounded knobs at the presynaptic terminals of axons that contain numerous synaptic vesicles

• when a nerve impulse reaches a knob, some of the vesicles respond by releasing a neurotransmitter, which diffuses across the synaptic cleft
• responsible for the typical one-way transmission from axon to cell body (cell bodies lack synaptic knobs)

• a neurotransmitter of the biogenic amine group synthesized from tryptophan
  
• helps regulate food intake
  
• inhibitory effect on sensory pathways
  
• excitatory effect on muscle action pathways
  
• involved in sleep
  
• secreted in CNS

an efferent (output) nerve cell that transmits signals away from the CNS to skeletal muscle or glands

an afferent (input) nerve cell that receives information from the internal and external environments and transmits the signals to the CNS

• one of three bilaterally symmetrical regions of the embryonic brain
• subdivides into telencephalon and diencephalon at 5 wks old

part of embryonic forebrain that develops into the adult cerebrum

(cerebrum: the sophisticated center of homeostasis control and integration which includes the cerebral hemispheres (white matter, internal grey matter, cerebral cortex)

the plasma membrane is polarized - more negatively charged inside the cell than outside

part of embryonic forebrain that develops into the adult thalamus, and hypothalamus

• the membrane potential of a nonconducting, unstimulated neuron (ie: a neuron in which no action potential is occurring)
  
• typically -70mV
  
• equilibrium prevented and resting potential maintained by:

  1-    the Na⁺/K⁺ pump: uses ATP to pump Na⁺ out and K⁺ in against their [ ] gradients and gradients)

  2-    selective permeability of the plasma membrane: [A^-] trapped inside cell

  3-    selective permeability of the plasma membrane: [Cl^-] can diffuse into cell

  4-    ???

• the part of a neuron that connects the cell body to the axon
•  where the action potential begins (the point where the summation of inhibitory and excitatory postsynaptic potentials from numerous synaptic inputs on the dendrites or cell body occurs)

the fluid (blood derived) that bathes surrounds, protects, nourishes and cushions the  CNS (brain and spinal cord)

nervous tissue in the brain and spinal cord that contains cell bodies, dendrites and unmyelinated axons

nervous tissue in the brain and spinal cord that contains myelinated axons

any of the terminal or smaller branches of an axon that terminates with specialized endings that releases neurotransmitters

fluid filled cavities in the brain filled with cerebrospinal fluid

the three layers of connective tissue that protect the brain and spinal cord

1-    the dura matter - tough outer layer

2-    arachnoid - middle layer

3-    pia matter - thin vascular layer that adheres closely to the tissue of CNS

• relatively short chains of amino acids that act as messenger molecules that stimulate long term changes that enhance or inhibit synaptic function
  
• produced in neural tissue

the potential an neuron, or other excitable cell membrane must reach for an action potential to be initiated

• a neurotransmitter of the biogenic amine group derived from the amino acid tyrosine
  
• excitatory or inhibitory
• [ ] in brain affects mood
  
• a hormone secreted by the adrenal medulla (produced in response to stress)
• secreted in CNS & PNS (specifically, autonomic nervous system)

• (sensory /afferent neuron)
•  proprioceptive sensory receptor 
• allows you to regulate balance, stand on one leg and such. 

• both controlled by hypothalamus.
• both control by reflex – where the blood is going.
• Both receive info about internal and external.
• both are on at the same time. 

1. anatomical distinction

sympathetic: post ganglion travels longer distance than the preganglion

parasympathetic, preganglion goes the longer distance.

2. neurotransmitter distinction

sympathetic:

preganglionic - ACh

postganglionic - norephinprhine

parasympathetic,

preganglionic - ACh

postganglionic - ACh

3. one represent pedal and brake pedal.

if one raises heart rate, one lowers it.

except for a couple such as raise arousal vs raise orgasm. Usually happens together. 

• supplies motor parasympathetic fiber
• conveys sensory information to CNS
• 90% of the nerve fibers are afferent. (part of parasympathetic)
• Branches and goes to several places.
• when over stimulated, you pass out because heart slows down and makes you go horizontal so there can be more oxygen to your brain.

fibers from the central nervous system to the ganglia

Postganglionic cell

ganglia to the effector organ

ganglion

collection of nerve cell body outside CNS. 

Difference between norephinephrine and epinephrine? 

epinephrine =hormone
norephinephrine = neurotransmitter

• delivery is different
• hormone: circulation 
• neurotransmitter: synapse