L16: Nervous System

What is an Excitatory Postsynaptic Potential (EPSP)? what is an Inhibitory postsynaptic potential (IPSP)?

- depolarization caused by neurotransmitter at postsynaptic membrane - chemically gated channels lead to depolarization of plasma membrane - if large enough, neuron is stimulated - hyperpolarization caused by neurotransmitter at postsynaptic membrane - ex: chemically gated chloride channels open and lead to hyperpolarization of plasma membrane as Cl- moves in - ex: chemically gated potassium channels open and K moves out making interior more negative - hyperpolarization - neuron is inhibited

what is Acute Flaccid Myelitis (AFM)?

- may be caused by an enterovirus - causes a respiratory illness - can be letha, usually recover - acute myelitis = acute inflammation of spinal cord

Types of synapses: 1. axosomatic 2. axodendritic 3. axoaxonic

1. attach to the soma. Soma has high concentration of voltage activated ion channels (Na/K or K or Cl or Na) 2. attach to the dendrites of a different cell. Dendrites have a high concentration of ligand activated channels - neurotransmitters. 3. attach to axon hillock. Axon hillock has high concentration of voltage activated sodium channels- imitation zone for action potentials.

What 4 bodily components protect the brain?

1. bone (skull) 2. membranes (meninges)- 3 3. fluid (Cerebrospinal fluid = CSF)- cushions and supports brain 4. Blood brain barrier = BBB

what are the 3 states of a sodium voltage-gated channel?

1. closed but can open, at -70mV. At resting potential. Activation gate is closed. 2. open (activated) at -50 to 30mV. From threshold to peak potential. Activation is rapidly opened. Na+ blasts into the cell. 3. closed but can't open (inactivated) at 30mV to -70mV. From peak to resting potential. Inactivation is slowly triggered to close. Stays closed until -70mV. resting -> activated -> inactivated -> resting

Explain the following characteristics of a graded potential: 1. origin 2. type of channel 3. conduction 4. amplitude 5. duration 6. polarity 7. refractory period

1. dendrites (receptive area) and cell body 2. chemically, ligand, or mechanically gated 3. not propagated (not all/nothing) 4. depends on strength of stimuli (1-20mV) 5. several milliseconds to several minutes 6. hyperpolzarizing (inhibitory) or depolarizing (excitatory)-- depends on what channel is affected! 7. not present, summation can occur - can leave gate open

What are the 3 causes of resting membrane potential?

1. different ionic composition 2. selective permeability 3. permeability varies by ion (how many channels there are, etc.)

Dendritic spines make up what percent of the neuron's surface area?

80-90%

Propagation in bare, unmyelinated, and myelinated axons?

bare plasma membrane (without voltage-gated channels) = as on a dendrite, voltage decays because current leaks across the membrane. unmyelinated: - voltage gated Na+ & K+ channels regenerate action potential at each point along the axon, so voltage does not decay. conduction is slow because movements of the ions and of the gates of channel proteins take time and must occur before voltage regeneration occurs. myelinated - myelin keeps current in axons so voltage doesn't decay much. Action potentials are only generated in the nodes of Ranvier and rapidly jump from node to node. this is saltatory propagation! (saltare= leaping)

T/F: Like action potentials, graded potentials have a refractory period.

False! graded potentials don't have a refractory period.

What cuases sodium to flood in and depolarize the cell? What causes potassium to flood out and hyper polarize the cell?

When sodium channels open due to the application of a chemical stimulus. When potassium channels open due to the application of another chemical stimulus.

What is repolarization of a membrane potential?

When transmembrane potential returns to its resting state.

compare continuous propagation vs. saltatory conduction?

continuous propagation = involves step-by-step depolarization and repolarization of each segment of the plasma membrane as ions flow through each voltage-gated channel along the membrane. occurs in unmyelinated axons. saltatory conduction = involves "leaping" or action potential propagation along a myelinated axon because of uneven distribution of voltage-gated channels found at nodes of Ranvier (where there si no myeline sheath). Occurs in myelinated axons. Action potential at first node opens voltage gated Na channels at the second node. Action potential "leaps" node to node as current flows from node to node.

what is the texture of the brain?

cottage cheese

what type of cells carry out membrane potential?

neurons, muscle cells, specialized cardiac cells (all have voltage gated channels!)

is a virus a complete cell?

no, it lacks organelle or cytoplasm

what is temporal summation?

occurs on a membrane that receives 2 depolarizing stimuli from the same source in rapid succession. the effects of the second stimulus are added to those of the first.

what is spatial summation?

occurs when sources of stimulation arrive simultaneously but at different locations. local currents spread the depolarizing effects and ares of overlap experience combined effects.

what does arachnoid mater mean?

spider-like mother. middle later of meninges. lace-like trabeculae

what is the absolute refractory period of an action potential?

time from when voltage-gated Na channel activation gates open to when inactivation ends (.4-1msec). Cell can't respond to another stimuli since Na channels are either open or inactivated.

what does dura mater mean?

tough mother

T/F: The brain has its own circulation, slight differences in chemistry, pH, osmolarity from BBB (blood brain barrier)

true!

define greek/latin root glioma

tumor of the glial cell

what is the relative refractory period of an action potential?

voltage gated K channels are still open after inactivated Na channels have returned to their resting state and continue transmembrane potential returns to normal. A stronger stimuli can be applied for another action potential to occur (additional depolarization)

The brain is symmetrical with 2 hemispheres. Can you live without one hemisphere?

yes

what is the threshold for an action potential?

~-60mV

What is an excitatory graded potential?

Depolarization = membrane potential becomes more positive.

define greek/latin word myel

spinal cord

What are the 4 basic characteristics of graded potentials?

1. Transmembrane potential is most changed at the site of stimulation, and the effect decreases with distance. 2. The effect spreads passively, due to local currents (nothing propagates the current) 3. The graded change in transmembrane potential may involve either depolarization or hyper polarization. The properties and distribution of the membrane channels involved determine the nature of the change. For example, in a resting membrane, the opening of sodium channels causes depolarization, whereas the opening of potassium channels causes hyper polarization. That is, the change in transmembrane potential reflects whether positive charges enter or leave the cell. 4. The stronger the stimulus, the greater is the change in transmembrane potential and the larger is the area affected.

What are the 4 events in the functioning of a cholinergic synapse?

1. an action potential arrives and depolarizes the synaptic terminal. 2. extracellular Ca2+ enters the cytoplasm of the synaptic terminal, triggering the exocytosis of ACh through synaptic vesicles. ACh release ceases when calcium ions ae removed from the cytoplasm of the synaptic terminal. 3. ACh diffuses across the synaptic cleft and binds to receptors. Chemically gated sodium channels open, this depolarizes the postsynaptic membrane, initiating the graded depolarization, which might be an action potential. 4. ACh is removed by AChE (acetylcholinesterase). Action potential is propagated if it was created. .

compare and contrast graded vs. action potential according to the following characteristics? 1. depolarizing or hyper polarizing? 2. threshold? 3. change in membrane potential? 4. how is it spread? 5. propagation? 6. refractory period? 7. where does it occur?

1. gradient = either action = always depolarizing 2. gradient doesn't have a threshold value. Action = depolarization to threshold must occur before action potential begins. 3. gradient = amount of depolarization or hyperpolariztion depends on intensity of stimulus action = all-or-none; all stimuli that exceed threshold produce identical action potentials 4. gradient = passive spread from site of stimulation action = action potential at one site depolarizes adjacent sites to threshold 5. gradient = effect on membrane potential decreases with distance from stimulation site. action = propagated along entire membrane surface without decrease in strength. 6. gradient = no refractory period action = refractory period occurs! 7. gradient = occur in most plasma membranes action = occur only in excitable membranes of specialized cells such as neurons and muscle cells

what are the 2 states of the potassium gated channel?

1. resting at -70mV 2. opened at 30mV (slow activation, channel opens) below -70mV, hyper polarization occurs

Describe the 3 brain meninges: 1. Dura Mater 2. Arachnoid Mater 3. Pia Mater

1. tough mother - superficial layer of connective tissue is attached to th periosteum of the skull. The layer externally covers the brain and continues as the spinal dura mater - separates brain structures with dural folds. The 2 hemispheres of the cerebrum are separated by dura mater via the Falx cerebra; the fall cerebella separates the lobes of the cerebellum. The tentorium cerebella separates the cerebrum from the cerebellum. Has several dural sinuses (full of blood; O2, and nutrients) 2. spider-like mother - middle layer, loose brain covering. does not dip into the sulk. contains lace-like network (trabeculae) between dura and pia mater 3. gentle mother - inner layer, sings tightly to the brain and follows at convolutions - fuses with the ependyma (membranous lining of ventricles to form the choroid plexus)

Explain the following characteristics of an action potential: 1. origin 2. type of channel 3. conduction 4. amplitude 5. duration 6. polarity 7. refractory period

1. trigger zones of a neuron, axon hillock and propagates along axon 2. Na+/K+ voltage gated (also Ca2+) 3. propagated 4. All or none (100mV) 5. 0.5-2 msec 6. always depolarizing phase then depolarizing phase and return to resting membrane potential 7. present, summation CANNOT occur

what percent of blood flow goes to the brain?

20% = the brain is very metabolically active so it needs a constant oxygen and energy supply

What is the decay of membrane potential with distance during graded potentials?

Because current is lost through the "leaky" plasma membrane, the voltage declines with distance from the stimulus (the voltage is decremental). Consequently, graded potentials are short-distance signals.

What is synaptic activity?

Graded potentials in the plasma membrane of postsynaptic plasma membrane. One example is neurotransmitter release interacting with a ligand-gated channel on the postsynaptic membrane.

What is an inhibitory graded potential?

Hyper polarization = membrane potential becomes more negative.

What is an action potential?

If a graded potential is large enough, and voltage gated channels are present it generates and action potential which is potentiated along the axon and does not diminish as it moves away from the source.

What is depolarization of a membrane potential?

Intracellular space near the membrane becomes less negative = it moves toward 0. This increases the likelihood of a nerve impulse, such as when a gated sodium channel opens.

What is hyper polarization of a membrane potential?

Intracellular space near the membrane becomes more negative. This decreases the likelihood of a nerve impulse, such as when a gated potassium channel opens.

What is a graded potential?

Temporary, localized change in the resting potential. Effect decreases with distance from the stimulus.

What happens during the time lag in closing all potassium ion channels leads to temporary hyper polarization step of an action potential?

The voltage-gated sodium channels remain inactivated until the membrane has depolarized to near threshold level. At this time, they regain their normal status: closed but capable of opening. The voltage-gated potassium channels begin closing as the membrane reaches the normal resting membrane potential (about -70mV). Until all of these potassium channels have closed, potassium ions continue to leave the cell. This produces a brief hyper polarization.

What happens during the inactivation of sodium ion channels and activation of potassium ion channels starts repolarization step of an action potential?

This is step 3. As the membrane potential approaches +30mV, the inactivation gates of the voltage-gated sodium channels closes. This step is known as sodium channel inactivation, and it coincides with ht opening of voltage-gated potassium channels. Positively charged potassium ions move out of the cytosol, shifting the membrane potential back toward the resting level. Repolarization now begins.

What happens during the depolarization to threshold step of an action potential?

This is the first step! When the stimulus that initiates and action potential is a graded depolarization large enough to open voltage-gated sodium channels. The opening of the channels occurs at a membrane potential known as threshold. purple is sodium. orange is potassium.

What happens during the activation of sodium ion channels and rapid depolarization step of an action potential?

This is the second step. Sodium channel activates gates open, then the plasma membrane becomes much more permeable to Na+. This drives sodium into the cytosol, and rapid depolarization occurs. The inner membrane surface now has more positive ions than negative ones, and the membrane potential has changed from -60mV to a positive value. purple is sodium. orange is potassium.

T/F: The amplitude of an action potential is always the same once generated: all or none principle.

True!!!!

entero vs. rhino virus?

entero = relating to the intestine - stabl in acidic pH rhino = nose - most common virus - not stable in acidic pH

what are the layers of meninges and spaces in the brain from superficial to deep?

epidural space (on top of dura mater) dura mater subdural space (under dura mater) arachnoid mater subarachnoid space (under arachnoid mater; filled with CSF) pia mater

T/F: The brain has pain fibers so touching it is excruciating.

false! the brain has no pain fibers.

what does pia mater mean?

gentle mother. clings tightly to brain

what is the synapse?

junction between two neurons

what are cholinergic synapse?

synapse that uses acetyl choline as its neurotransmitter