npb101 exam 2

homeostasis

maintaining a relatively stable internal environment

cell communication: direct

gap junction, transient direct linkup of cell’s surface markers

cell communication: indirect

paracrine, neurotransmitter secretion, hormone selection and neurohormone secretion

endocrine signaling

acts via hormones and neurohormones secreted into the blood to control processes that rely on duration rather than speed

nervous system vs endocrine system

nervous (neurotransmitters across synpatic cleft)

• fast response

• short duration

• short distance

• “wired”

endocrine (hormones secreted into blood)

• longer response time

• longer duration

• long distance

• “non wired”

what are the roles of the autonomic nervous system

1. plays a critical role in maintaining homeostasis

2. is a complex network of cells that controls the body’s internal state

3. regulates and supports many different internal processes, often outside of a person’s conscious awareness

   • involuntary control

how is the nervous system organized

• central nervous system: brain and spinal cord

• peripheral nervous system: nerve fibers

  • afferent and efferent divisions

• enteric nervous system: nerve network of the digestive tract

Efferent Division of PNS (peripheral nervous system)

** remember that the efferent = exiting the brain

autonomic nervous system: fibers that innervate smooth muscle, cardiac muscle, and glands

• sympathetic: division of the autonomic nervous system that prepares the body for strenuous physical activity

  • fight or flight

  • accelerates heart rate, goose bumps, sweating, raising blood pressure

  • ach → norepinephrin → apinephrine (ACNE)

  • parasympathetic: division of the autonomic nervous system that maintains resting functions of the internal organs

    • maintaining homeostasis

    • rest nad digest

    • ach → ach

autonomic nerve pathway

• consists of a two-neuron chain

  • preganglionic fiber and postganglionic fiber

what is stress

generalized, nonspecific response of the body to any factor that overwhelms, or threatens to overwhelm, the body’s compensatory abilities to maintain homeostasis

what are the different kinds of stress

1. physical (trauma, surgery, intense heat/cold)

2. chemical (reduced O₂ supply, acid-base imbalance)

3. physiologic (heavy exercise, hemmorrhagic shock, pain)

4. infectious (bacterial)

5. psychological or emotional (anxiety, fear)

6. social (personal conflicts, change in lifestyle)

what occurs when there is the presence of a stressor?

1. stressor is sensed

2. hypothalamus sends a signal to the pituitary gland (which controls most of the endocrine glands)

3. adrenaline is released

*stress activates sympathetic neurons of the Hypothalamus. HPA axis releases cortisol which resists stress

diffusion

the process of movement of molecules under a concentration gradient

net movement

due to random collisons between molecules

diffusion occurs…

down a concentration gradient

what affects rate of diffusion (and how so)

1. magnitude of the concentration gradient

   • larger magnitude increases rate of diffusion

2. permeability of the membrane

   • higher permeability = higher rate

3. surface area of the membrane

   • higher surface area = higher rate

4. molecular weight

   • higher molecular weight - lower rate

5. distance (thickness) over which diffusion takes place

   • higher distance = lower rate

** mp smd

what are the two different kinds of diffusion

1. concentration (chemical)

2. electrical

nonpolar molecules

O₂, CO₂, fatty acids

concentration/chemical gradient

specific small ions

(Na+, K+, Ca2+, Cl-)

electrical gradient + concentration gradient = electrochemical gradient

concentration/chemical gradient

high to low concentration

electrical gradient

electrostatic force caused by the separation of electrical charge

electrochemical gradient

the combined force of concentration and electrical gradients

what are nerve cells specialized for

electrical signaling over long distances

membrane potential

separation of opposite charges across the plasma membrane

** the greater the separation of charges across the membrane, the larger the potential

higher membrane potential = ?

higher separation of charges across the membrane

equilibrum potential for K+

-90 mV

1. K+ moves outside the cell (concentration gradient)

2. the outside becomes more positive

3. electrical gradient tends to move K+ into cell

4. electrical and concentration gradient balance each other out

5. no further net movement of K+ occurs (-90mV)

eq potential for Na+

+60mV

1. Na+ tends to move inside the cell

2. inside the cell becomes more positve

3. electrical gradient tends to move Na+ out the cell

4. electrical gradient counterbalances concentration gradient

5. no further movement of Na+ occurs

resting membrane potential (what happens)

-70 mV

1. K+ high in ICF and Na+ high in ecf

2. K+ drives equilibrium potential for K+ (-90 mV)

3. Na+ drives equilbrium potential for Na+ (+60mV)

• membrane is 20-30 times more permeable to K than to Na+

• the large net diffusion of K+ and the small net diffusion of Na+ neutralizes some of the potential created by K+

• the cell’s membrane potential (-90mV) is reduced

• = -70mV

what do leak channels do?

permit ions to diffuse down concentration gradients

Na/K ATPase

maintains Na+ higher concentration outside of the cell and K+ higher INSIDE tthe cell

pumps 3 Na+ out of the cell for every 2 K+ pumped into the cell

when is mV 0?

equal positives and negatives on both sides

is there membrane potential here? why?

no, it would be 0mV.

• no separation of charges

• equal - and + on both sides of the membrane

is there membrane potential here? why?

yes, there is membrane potential because the left side is more positive and will move to the right side

charge separation across a membrane

most of the fluid is electrically neutral, but separated charges will form a layer along the plasma membrane (all positives form a layer on one side, all negatives form layer on one side.)

which has the most membrane potential?

C: there is a greater separation of charges across the membrane and thus a larger potential

how does the cell create charge separation?

1. establishes and maintains concentration gradients for key ions (Na+, K+)

2. ions will diffuse through the membrane down their concentration gradients

3. diffusion through the membrane results in charge separation, which creates a membrane potential (electrical gradient)

4. net diffusion continues until all the force exerted by the electrical gradient exactly balances the forces exerted by the concentration gradient

5. the potential that would exist at this equilibrium is the equilibrium potential

how do K+ and Na+ penetrate the cell membrane?

leak channels

Na+ is higher ___ of the cell and K+ is higher ___ of the cell. Why?

Na+: higher outside

K+: higher inside

na/k atp ase: establishes and maintains concentration gradients by pumping 3 na+ outside of the cell for every 2 k+ inside the cell

NOKI

what are K+ and Na+ eq potentials at resting potential

they are NOT at their equilibrium potentials

• concentration gradients and permeabilities for Na+ and K+ remain constant in resting state

  • resting membrane potential established by these forces remain constant

why is the resting potential for a cell less than the K+ equilibrium potential?

at resting membrane potential, membrane permeability K+ > Na+

what would happen to a cell’s membrane potential if the cell was deprived of ATP

Na/K+ atpase is not functional, there is no membrane potential

depolarization

change in membrane potential to more positive values than resting membrane potential

hyperpolarization

change in membrane polarization to more negative values than resting membrane potential

graded potential

• all the potential BEFORE it hits the threshold

• can be low or high depending on the stimulus

repolarization

returning to resting membrane potential after depolarization

action potential

brief all or nothing in membrane potential, lasting on the order of 1 millisecond

borught about by rapid changes in membrane permeability to Na+ and K+ ions

Na+ IN (rise)

K+ OUT (fall)

voltage-gated Na+ channel

opens quickly in response to depolarization (becoming more positive), allowing K+ ions to flow out of the cell down their electrochemical gradient into the cell

rising phase

voltage-gated K+ channel

opens more slowly in response to depolarization allowing K+ ions to flow out of the cell down their electrochemical gradient

falling phase and after hyperpolarization

What are the channel states Na+ has?

1. open

2. close

3. inactivated

events underlying the rising phase of the action potential

@ threshold, Na+ activation gate opens, meaning the permeability of Na+ rises

after threshold, Na+ enters the cell and this causes the rising phase

what are K+ channel states

1. open

2. close

falling phase

K+ channels open, but Na+ INACTIVATE GATE CLOSES (INACTIVE — STOPS FLOW OF NA+)

K+ leaves cell

@ resting potential:

• Na+ activation gate closes and inactivation gate opens

• K+ leaves the cell due to the still open K+ channel

• K+ activation gate closes, and membrane returns to resting potential

components of neurons

• soma (cell body)

• nucleus

• dendrite

• axon hillock

• axon

• axon terminals

dendrite

input zone, receives incoming signal

axon hillock

trigger zone, initiating action potential

axon terminals

output zone: releases neurotransmitter

action potential propagation

locally generated depolarization current spreads to adjacent regions of the membrane, causing it to depolarize

action potentials:

• once initiated, action potentials are conducted throughout a nerve fiber

contiguous conduction

propagation of action potentials in unmyelinated fibers by spread of locally generated depolarizing current to adjacent regions of membranes, causing it to depolarize

non-myelinated action potential propagation

keeps going forward until it reaches the end of the axon, but it happens slowly

active area → action potential happens at that point = depolariztes

• channels behind it are inactivated so action potential cannot occur behind it (no backflow)

absolute refractory peroid

• a brief period during a spike:

  • repolarization: voltage gated Na+ channel inactivation gate closes: a second spike cannot be generated

refractory: repolarization (going down)

relative refractory period

• a brief period following a spike

  • below resting membrane potential, the voltage gated na+ channel inactivation gate opens

  • capable of opening in response to depolarization

  • hyperpolarization: a higher intensity stimulus is needed

what is the function of the refractory period

• prevents “backward” current flow

  • action potential cannot be initiated

  • limits frequency

saltatory conduction

propagation of action potentials in myelinated axons by jumping from node to node

(much faster)

myelin

multilayered sheath of plasma membrane made from specialized glial cells that wraps around axonal fibers and acts as an insulator to the flow of current

insulator

nodes of ranvier

gaps in myelin insulation containing high densities of voltage gated na+ k+ channels

schwann cells

myelin forming glial cells in the PERIPHERAL SYSTEM

swan → periperaoligo

oligodendrocytes

myelin-forming glial cells in the central nervous system

multiple sclerosis

the body’s defense system attacks the myelin sheath

slow transmission of impulse in the affected neurons

graded potential

local changes in membrane potential

• occur in varying grades or degrees of magnitude or strength (depending on stimulys)

• spread by PASSIVE current flow

• die out over short distances

Graded potential vs action potential

Graded:

• depends on stimulus

• decreases with distance

• triggered by stimulus (neurotransmitter-post-synaptic cells/sensory receptor in sensory neurons)

• dendrites, cell body, sensory receptors

• uses ion channels (ligand-gated, mechanically gated channels)

• can travel on both sides

action

• all or none

• propagates over entire cell

• triggered by threshold

• axon

• voltage-gated channels

synapse

junction between two neurons (or between neuron and a muscle or gland) that enables one cell to electrically and/or biochemically influence another cell

electrical synapses

• neurons connected directly by gap junctions

• the gap junctions are made up of multiple proteins called connexins

• small diameter of the tunnel in a gap junction allows water-soluble ions to pass between cells but blocks larger molecules

chemical synapses

• chemical neurotransmitter transmits the information one way across a space separating the two neurons

most synapses in the human nervous system are __ synapses

chemical synapses

convergence

the synaptic input of many neurons onto one neuron

divergence

the synaptic input of one neuron onto many neurons

synaptic transmission (what is it)

the primary means of rapid inter-neuronal communication in the brain

synaptic transmission steps

1. action potential propagation in the presynaptic neuron

2. Ca++ entry into the terminal button

3. release of neurotransmitter from presynaptic neuron

4. binding of neurotransmitter to receptor on postsynaptic neuron

5. channel opens on postsynaptic neuron and causes EPSP/IPSP

6. summation occurs

7. action potential

IPSP

• inhibitory postsynaptic potential

  • GABA, Gly

  • Hyperpolarization potential that brings Vm away from the threshold for the generation of an action potential

EPSP

• excitatory postsynaptic potential

  • ACh, Glutamate

  • Depolarization that brings Vmtowards the threshold for a Generation of an action potential

Summations

• Temporal: additive effect of PSP’s occurring at the same place and time

• spatial summation: additive effect of PSP’s occurring on the same cell but nearby parts

• cancellation summation: ESPSs and IPSPs cancelling each other out

• Presynaptic inhibition: synaptic inhibition of a synaptic terminal causing a decrease in transmitter release

neurotransmitter removal

1. degradation: enzymatic breakdown (AChE)

2. Transport: active transport back into the presynaptic cell “reuptake”

3. Diffusion: the transmitter simply diffuses away

Central VS Peripheral Nervous System (what they consist of, and function)

• CNS (brain and spinal cord)

  • integration and processing signals

• PNS (all nerves extending from CNS)

  • communicating and relaying signals from the CNS to the rest of the the body

PNS Organization

• Afferent Division

  • relay visceral and sensory stimuli to the brain

• Efferent Division

  • Autonomic:

    • involuntary functions

    • two neuron pathway

    • sympathetic and parasympathetic

  • somatic

    • voluntary movement of skeletal muscles (single neuron)

Protection of the Brain

1. Cranium and Vertebral Column

2. Meninges

3. Cerebrospinal fluid

4. Blood brain barrier

meninges

• 3 different Meningal membranes wrap, protect, and nourish the CNS

  • Dura matter

  • Arachnoid Matter

  • Pia Matter

    • gentle

cerebospinal fluid

surrounds and cushions the brain and spinal cord

blood brain barrier

• highly selective

• regulates exchanges between the blood and the brain

  • shields from harmful changes (viruses)