Final Exam for Anatomy and Physiology 1 Mathew Lovelace

Spinal nerves

(31 pairs) are the paths of communication between the spinal cord and specific regions of the body. A spinal nerve may innervate multiple organs in a specific region Don't forget, there are many different types of organs in the body muscle, glands, skin, etc. Nerves are arranged in fascicles surrounded by a perineurium, with the entire nerve sheathed by a CT epineurium.

By passive spread, the current proceeds by

(a) continuous conduction in unmyelinated axons, or by the much faster process of (b) saltatory conduction in myelinated axons

Thalamus

80% of the diencephalon Functions as a relay station for all sensory impulses to the cerebral cortex, except smell.

Depression

A disorder in which people feel sad and helpless, have lack of interest, and may experience suicidal thoughts Major depression, dysthymia, bipolar disorder (manic-depressive illness), and seasonal affective disorder (SAD) are just a few of the many examples Depression is most likely due to a combination of factors. Some of these factors include stress, genetics, illness, personality traits, and hormonal changes Exact causes are still up for debate Current research shows that imbalances of particular neurotransmitters related to mood may be involved Serotonin, norepinephrine, and dopamine Selective serotonin reuptake inhibitors (SSRIs) Inhibits the reuptake of serotonin in the synapse by the presynaptic cell thus prolonging its duration and effects Prozac, Paxil, and Zoloft are a few of the more popular one

Pia mater

A very thin transparent layer that is pressed-up against the cord It is filled with blood vessels that supply nutrients to the spinal chord.

Graded potentials that result in depolarization of the neuron from RMP to threshold (about -55 mV in many neurons) will cause

AP

spinal cord

About 100 million neurons, even more neuroglia, comprise the spinal cord, the part of the central nervous system that extends from the brain.

absolute refractory period

After initiating an action potential, there is a period of time called the absolute refractory period during which a cell cannot generate another AP, no matter how strong the stimulus. This period coincides with the period of Na+ channel activation and inactivation (inactivated Na+ channels must first return to the resting state before they can be opened again.) During this period, there are not enough deactivated voltage gated Na channels to allow for another AP This places an upper limit of 10-1000 nerve impulses per second, depending on the neuron.

Somatic nervous system

All somatic motor neurons release acetylcholine (ACh) Effect is always stimulatory

Chemical protection

Also carries oxygen, glucose, and other needed chemicals from the blood to neurons and neuroglia Provides the optimal chemical environment for chemical signaling

Neurotransmitters are found in many different chemical forms

Amino acids Biogenic amines Peptides (neuropeptides) Purines Gases and lipids Endocannabinoids

Neurotoxins

An extensive class of exogenous chemicals which can adversely affect function in both developing and mature nervous tissue Sometimes, overproduction or release of endogenous neurotransmitters can be can be neurologically toxic Over-release of glutamate in the CNS from ischemia (low oxygen) can cause neuronal over-excitation leading to the death of the neuron (excito-neurotoxicity) This is what happens in a stroke

Late Depolarization Phase

As the AP approaches peak, gNa continues to increase. However, INa begins to decrease. As the membrane voltage gets closer to the Na Nernst value (ENa), the driving force for Na lessens. This means that sodium current will decrease despite a continued increase in conductance. gK is beginning to increase due to the slower opening voltage-gated K channels beginning to reach the open state. IK is also increasing due to the increase in gK. As the membrane voltage gets more positive (further away from the negative K Nernst value (EK)), the driving force for K increases. This means that K current will increase if the conductance allows.

Peak of AP

At the peak of AP, sodium current in and potassium current out are the same. Na influx = K efflux Thus there is no change in membrane voltage At the peak of AP, conductance (g) of Na is much greater than that of K, but the two currents are equal... Why? The membrane potential is close to the Nernst for Na which means that the diving force for Na is low. Thus Na flux is low. The membrane potential is far away (positive voltage) from the Nernst for K which means that driving force is very high for K. Thus K flux is as high as it can be based on K conductance at this point.

Diffusion

Away from synaptic cleft

ANS versus Somatic Nervous System (SNS)

Both have motor fibers but ANS and SNS differ in: Effectors Efferent pathways and ganglia Target organ responses to neurotransmitters

Major Parts of the Adult Brain

Brain stem Continuous with the spinal chord Consists of the medulla oblongata, pons and midbrain Cerebellum Diencephalon Consists of the thalamus, hypothalamus, and epithalamus Cerebrum Largest part of the brain

Reuptake

By astrocytes (in CNS) or axon terminal of releasing neuron

Degradation

By enzymes

arachnoid villi

CSF is gradually reabsorbed into the blood through arachnoid villi (fingerlike projections of the arachnoid mater that project into dural sinuses) CSF is formed at the same rate it is reabsorbed Pressure is kept constant Tumors, inflammation, or developmental malformations can cause interference with drainage and build up of pressure. The increased pressure can compress delicate neural tissue causing damage

Excitatory postsynaptic potential (EPSP)

Causes a depolarization of the postsynaptic cell Brings Vm closer to threshold. Although a single EPSP normally does not initiate a nerve impulse, the postsynaptic cell does become more excitable.

Mechanical protection

Clear, colorless liquid that protects the brain and spinal chord from shock

Cerebral white matter

Consists primarily of myelinated axons

Metabotropic Receptor

Contains an NT binding site but lacks an ion channel as part of its structure Metabotropic receptors are coupled to a separate ion channel by G-proteins G-proteins can go on to activate/deactivate separate ion channels (direct) G-proteins can activate other proteins that go on to activate/deactivate ion channels as well (indirect)

Medulla oblongata

Continuous with the superior part of the spinal chord Contains both sensory and motor tracts Contains Pyramids which are large corticospinal tracts that pass from the cerebrum to the spinal chord Contains many regions and structures involved in multiple functions. A few are listed here: Cardiovascular center Regulates heart rate and blood vessel diameter Medullary rhythmicity area Helps control breathing rate and rhythm

Circulation

Continuously circulates through cavities in the brain and spinal chord which allows the exchange nutrients and the removal of wastes

The Brain

Control center for: Registering sensations Correlating them with one another and with stored info Making decisions Taking actions Intellect Emotions Behavior Memory Different regions of the brain are specialized for different functions These parts also work together to perform shared functions Portion of CNS contained within the cranium About 100 billion neurons, and even more neuroglia Average adult brain weighs about 3lbs Each neuron forms roughly 1000 - 7000 synapses with other neurons Makes the total number of synapses between roughly one and seven thousand trillion Up to 7,000,000,000,000,000 Extraordinarily complex in signaling and feedback

Current (flux)

Current is the actual movement (flow) of ions through membrane channels High current means a high flow of ions across the membrane

Repolarizing phase

Decrease in membrane potential back toward RMP Voltage-Na channels begin to undergo inactivation

Specific for each ion

Dependent upon intra and extracellular concentrations If you change the concentrations, you change the equilibrium potential!!! Two very important Nernst values when discussing AP are those of Na and K

An AP has three main phases:

Depolarizing phase Repolarizing phase After-hyperpolarizing (hyperpolarization) phase

Electrochemical gradients

Diffusion Electrical force ionic movement

Local Anesthetics

Drugs that block pain or other somatic sensations around the site of injection. Mainly work by blocking neuronal voltage-gated Na channels Thus APs are blocked Lidocaine and Procaine (Novocaine) are examples Cooling can slow, or partially, block AP conductions as well Application of ice to an injury not only reduces swelling from inflammation but also decreases pain by affecting ion channel kinetics

General Anesthetics

Drugs that cause a reversible loss of consciousness Do not dull pain, just knock you out so you don't know it hurts Mechanisms for general anesthetics still not well understood

These three membranes, also found encasing the brain, are labeled from superficial to deep as follows:

Dura mater Arachnoid mater. Pia mater

posterior (dorsal) root ganglion

Each posterior root has a swelling, the posterior (dorsal) root ganglion, which contains the cell bodies of sensory neurons.

Structure of NT receptors

Each type of neurotransmitter receptor has one or more neurotransmitter binding sites where its specific neurotransmitter binds.

limbic system

Encircling the upper part of the brain stem and the corpus callosum (connects portions of left and right hemispheres) is a ring of structures on the inner border of the cerebrum and floor of the diencephalon it is more a functional system composed of parts of the cerebral cortex, diencephalon, and midbrain The limbic system is sometimes called the "emotional brain" because it plays a primary role in promoting a range of emotions, including pleasure, pain, docility, affection, fear, and anger. Together with parts of the cerebrum, the limbic system also functions in memory.

Midbrain

Extends from the pons to the diencephalon. Involved in multiple functions

According to the all-or-none principle, if a stimulus reaches threshold, the action potential is always the same.

FALSE A stronger stimulus will not cause a larger impulse.

Voltage-gated Na channels

Fast to open and fast to close Have three states Deactivated (closed) - can open if stimulated Activated (open) Inactivated (closed) - channels inactivate and cannot re-open until reset to deactivated state has taken place. Reset requires time and proper membrane voltages

The Cerebrum

Frontal Parietal Temporal Occipital Insula

Electrical Signals in Neurons

Graded potentials Action potentials

Hemispheric Lateralization

Hemispheres appear almost identical Each hemisphere specializes in performing certain unique functions, a feature known as hemispheric lateralization. Despite some dramatic differences between left and right function due to lateralization, there is considerable variation from one person to another. Also, lateralization appears to be less pronounced in females. Cerebral dominance - a particular hemisphere preforming most of the function of a specific mental process (ex: left hemisphere dominant for language in ~ 90% people)

Overlap of Somatic and Autonomic Function

Higher brain centers regulate and coordinate both systems Most spinal and many cranial nerves contain both somatic and autonomic fibers Adaptations usually involve both skeletal muscles and visceral organs Example: Active skeletal muscles require more oxygen and glucose. ANS output can speed up blood flow, direct blood flow, as well as open airways in order to support them

Cauda equina

Horse's tail Collection of nerve roots at inferior end of vertebral canal

Inhibitory postsynaptic potential (IPSP)

Hyperpolarizes the postsynaptic cell Takes the Vm further from threshold.

Cranial Nerves

I Olfactory Sensory- Some II Optic Sensory- Say III Occulomotor Motor- Marry IV Trochlear Motor- Money V Trigeminal Both- But VI Abducens Motor- My VII Facial Both- Brother VIII Vestibulocochlear Sensory- Says IX Glossopharyngeal Both- Big X Vagus Both- Insert B word XI Accessory Motor- Matter XII Hypoglossal Motor- More

Nernst for Potassium (EK)

If you plugged in the physiological K concentrations into the equation, the equilibrium voltage is a negative value For some excitable tissue, the value is roughly -78mV This means that if the intracellular membrane voltage reaches -78mV compared to the outside voltage (0mV), the inside is so negative that it will attract the positive potassium ions that are inside and keep them from leaving the cell despite K wanting to flow out of the cell down it's concentration gradient

Nernst for Sodium (ENa)

If you plugged in the physiological Na concentrations into the equation, the equilibrium voltage is a positive value For some excitable tissues, the value is roughly +55mV This means that if the intracellular membrane voltage reaches +55mV compared to the outside voltage (0mV), the inside is so positive that it will repel the positive sodium on the outside and keep it from entering the cell despite Na wanting to flow into the cell down it's concentration gradient

A cell that exhibits an RMP is said to be polarized

In this state, the cell is "primed" - it is ready to produce an action potential. In order to do so, graded potentials must first be produced in order to depolarize the cell to threshold.

Depolarizing phase

Increase in membrane potential (toward zero and above) Many fast voltage-gated Na+ channels are opening during the steep depolarization phase (gNa is increasing) allowing Na+ to rush into the cell (INa increases quickly and then decreases) making the inside of the membrane progressively more positive. Na influx > K efflux The amount of Na+ entering the cell is actually very little in terms of concentration differences of Na+ intra- vs. extracellular. Doesn't affect concentration gradient However, the Sodium entering causes a big change in membrane voltage

Automatic nervous system (ANS)

Innervate smooth muscle, cardiac muscle, and glands ANS output is used to make adjustments necessary to ensure optimal support for various body activities Shunt blood to areas that need it, adjust heart rate and blood pressure, affect digestive processes, affect ease of breathing, etc. Operate via subconscious control Also called involuntary nervous system or general visceral motor system

nerve cell bodies (gray matter)

Internal to this peripheral region, and surrounding the central canal, is the butterfly-shaped central region

Charges

Ions are charged atoms, or molecules, that have lost or gained electrons Opposite charges attract Positive likes negative... Na+ likes Cl- Cations are attracted to anions Negative likes positive Like charges repel Positive repels positive Negative repels negative

Electrical force and ionic movement

Ions of like charge repel each other and want to get as far away as possible An overall positive charge in a region will repel positive ions They are also attracted to opposite charges Na+ wants to get away from the positive extracellular region and into the negative intracellular region When Na channels are open, Na flows down it's electrical gradient in an attempt to reach equilibrium Na wants to flow down it's concentration gradient and towards the negative region (down it's electrical gradient) inside the cell membrane Thus when Na channels are open, Sodium flows down it's electrochemical gradient

Role of the Parasympathetic Division

Keeps body energy use as low as possible, even while carrying out maintenance activities Directs digestion, diuresis, and defecation among other processes Referred to as "rest-and-digest" system

A fibers

Largest diameter and fast (up to 12-130 m/sec or 27-280 mph) myelinated neurons that carry touch and pressure sensations; many motor neurons are also of this type.

Subarachnoid space

Lies between the arachnoid and pia mater Contains cerebral spinal fluid (CSF) that acts as a shock absorber, chemical environment, and suspension system for the brain and spinal chord.

Subdural space

Lies between the dura and the arachnoid. Contains interstitial fluid

Epidural space

Lies between the dura mater and the wall of the vertebral canal. Contains a cushion of fat to protect the spinal chord

Pons (bridge)

Lies directly superior to the medulla and inferior to the cerebellum Involved in many functions Together with the medulla, areas in the pons help control breathing (inhalation and exhalation).

The electrical signals produced in by excitable cells mainly rely on four types of ion channels

Ligand-gated channels Voltage-gated channels Mechanically-gated channels Leakage channels channels

Diencephalon

Located near the midline of the brain, above the midbrain Contains the thalamic structures.

Neurotransmitters

Major neurotransmitters of ANS are acetylcholine (ACh) and norepinephrine (NE)

Converging circuit

Many inputs, one output • A concentrating circuit • Example: Different sensory stimuli can all elicit the same memory

Cerebrospinal Fluid (CSF)

Mechanical protection Chemical protection Circulation

Role of the Sympathetic Division

Mobilizes body systems needed for support in increase of overall metabolic activity Referred to as "fight-or-flight" system

Botulinum toxin (Botox)

Most acutely lethal toxin known - average lethal dose 1.3-2.1 ng/kg Blocks the docking of neurotransmitter (NT) vesicle with plasma membrane Blocks NT release Blocking release of ACh from motor neuron terminal means no stimulation of skeletal muscle fiber contraction - paralysis of skeletal muscle innervated by that neuron

substantia nigra

Neurons that release dopamine, extending from the substantia nigra, help control subconscious muscle activities; loss of these neurons is associated with Parkinson disease. The midbrain contains several other nuclei, including the darkly pigmented

Temporal summation

Occurs when postsynaptic potentials arrive close to the same time.

Spatial summation

Occurs when postsynaptic potentials arrive near the same location at the same time.

Early Depolarization Phase

Once threshold value is met, many voltage gated Na channels begin to transition to the open state Na conductance sharply increases Na current increases Na driving force increases the more negative the membrane potential is compared to the Nernst value of sodium (+55mV in these graphs). This means that Na driving force is fairly high at the onset of AP.

Diverging circuit

One input, many outputs • An amplifying circuit • Example: A single neuron in the brain can activate 100 or more motor neurons in the spinal cord and thousands of skeletal muscle fibers

craniosacral division

Parasympathetic Division fibers originate from brain stem and sacral region of cord Long preganglionic fibers extend from CNS almost to target organs Synapse with postganglionic neurons in terminal ganglia that are close to, or within, target organs Short postganglionic fibers synapse with effectors

Sites or origin

Parasympathetic fibers are craniosacral; originate in brain and sacral spinal cord Sympathetic fibers are thoracolumbar; originate in thoracic and lumbar regions of spinal cord

Location of ganglia

Parasympathetic ganglia are located in or near the their visceral effector organ Most sympathetic ganglia lie close to spinal cord

Relative lengths of fibers

Parasympathetic has long preganglionic and short postganglionic fibers Sympathetic has short preganglionic and long postganglionic

intercostal nerves

Portions of spinal nerves may travel alone (such as the intercostal nerves which run underneath each of the 12 ribs),

ANS

Preganglionic fibers release ACh Postganglionic fibers release norepinephrine or ACh at effectors Effect is either stimulatory or inhibitory, depending on type of receptor

ANS: pathway uses a two-neuron chain

Preganglionic neuron: Postganglionic (ganglionic) neuron (outside  CNS)

Ion channels

Present in the plasma membrane of all cells in the body Are an especially prominent component of the nervous system. Much of the energy expended by neurons, and really all cells of the body, is used to create a net negative charge in the inside of the cell as compared to the outside of the cell.

Tetrodotoxin (TTX)

Present in the viscera of a type of Japanese puffer fish and many other animals Fast voltage-gated Na channel inhibitor Binds to and inhibits the opening of voltage-gated Na channels in the PNS Can cause paralysis in muscle and loss of sensation Can lead to paralysis of the diaphragm bad news for that breathing thing you like to do

Electrical Signals in Neurons

Producing electrical signals in neurons depends on the existence of a resting membrane potential (RMP or Vrm) A cell's RMP is created using ion gradients and a variety of ion channels that open or close in response to specific stimuli. Because the lipid bilayer of the plasma membrane is a good insulator, ions must flow through these channels.

The BBB

Protects the brain cells from harmful substances and pathogens by limiting the passage of substances from the blood into brain tissue Consists mainly of tight junctions these seal together the endothelial cells of the brain capillaries Thick basement membrane around capillaries also contributes BBB permeability is controlled by astrocytes Lipid soluble substances easily cross Oxygen, carbon dioxide, alcohol, most anesthetics Some water-soluble substances actively transported across Most proteins and antibiotics do not cross

Leakage channels

Randomly alternate between open and closed states Allow ions to "leak" across the membrane

Ionotropic Receptors

Receptor that has a neurotransmitter binding site and is an ion channel as well When NT bonds to receptor, it opens or closes the ion channel portion of the receptor

cerebral peduncles.

Relays information and assists in refining motor movements, learning of new motor skills, and converting proprioceptive information into balance and posture maintenance anterior part of the midbrain are found the "little feet"

Ligand-gated channels

Respond to specific chemical stimulus and are mainly concentrated at the synapse. A wide variety of chemical ligands- neurotransmitters, hormones, and even particular ions- can open or close their specific ligand-gated channels

the neurotransmitter effect is terminated in one of three ways

Reuptake Degradation Diffusion

Effectors

SNS innervates skeletal muscles ANS innervates cardiac muscle, smooth muscle, and glands

Efferent Pathways and Ganglia

SNS: cell body is in CNS, and a single, thick myelinated group A axon extends in spinal, or cranial nerves, directly to skeletal muscle

Cerebellum (little brain)

Second largest part of the brain lies inferior to the cerebrum and posterior to the brain stem. Very important in skeletal muscle motor control The cerebellum compares intended movements with what is happening with skeletal muscles, and regulates posture, equilibrium, and balance.

Electrical Potential

Separated electrical charges of opposite sign (+/-) have the potential to do work if they are allowed to come together

Parallel after-discharge circuit

Signal stimulates neurons arranged in parallel arrays that eventually converge on a single output cell • Impulses reach output cell at different times, causing a burst of impulses called an after-discharge • Example: May be involved in exacting mental processes such as mathematical calculations

Reverberating circuit

Signal travels through a chain of neurons, each feeding back to previous neurons • An oscillating circuit • Controls rhythmic activity • Example: Involved in breathing, sleep-wake cycle, and repetitive motor activities such as walking

Three main differences between sympathetic and parasympathetic divisions:

Sites or origin Relative lengths of fibers Location of ganglia

Voltage-gated K channels

Slow to open and slow to close

thoracolumbar division

Sympathetic Division Some structures are innervated only by sympathetic: sweat glands, arrector pili muscle of hair follicle, smooth muscle of all blood vessels Preganglionic neurons are in spinal cord segments T1-L2 Form lateral horns of spinal cord gray matter

Neurotransmitter effects can be modified in many ways:

Synthesis can be stimulated or inhibited. Release can be blocked or enhanced. Removal from synaptic cleft can be stimulated or blocked. The receptor site can be blocked or activated.

thalamic structures

Thalamus Epithalamus Hypothalamus

The Cerebral Cortex

The "seat of our intelligence" It's because of neurons in the cortex that we are able to read, write, speak, remember, and plan our life... or try to plan, anyway.

Blood Brain Barrier (BBB)

The adult brain is only roughly 2% of total body weight, but consumes about 20% of the oxygen and glucose, even at rest. Supplied by blood anteriorly by the internal carotid arteries and posteriorly by the vertebral arteries. Venous return is from the internal jugular Neurons almost exclusively use glucose for ATP production Virtually no glucose is stored in the brain Thus it needs a constant supply of blood When brain activity in specific regions increases, blood flow to those regions increase as well If blood flow to the brain has low glucose, confusion and even loss of consciousness may occur Even brief decreases in blood flow can cause unconsciousness, also

In addition to the nodes of Ranvier that allow saltatory conduction, the speed of an AP is also affected by:

The axon diameter Larger diameter = less resistance to current= faster The degree of myelination More myelination = faster The temperature Higher temp = faster...to a point Too high or low affects AP voltage peak and/or duration due to temperature effects on ion channel kinetics

Protective Coverings of the Brain

The cranium - Skull The cranial meninges Continuous with the spinal meninges Dura, arachnoid, and pia maters Cranial dura mater has mostly 2 fused layers, spinal has 1 There is no epidural space around the brain

Potential difference

The difference in potential (charge) between the outside of the cell and the inside If you increase the potential difference of a cell at resting membrane voltage, you make it more negative If you decrease the potential difference of a cell at resting membrane voltage, you make it more positive

integration

The gray matter of the cord is a site for integration of postsynaptic potentials (IPSPs and EPSPs).

Hypothalamus

The master gland! Controls many homeostatic functions: Controls the Autonomic Nervous System (ANS). Coordinates between NS and endocrine systems. We will cover the hypothalamus extensively in the endocrine system Controls body temperature (measured by blood flowing through it). Regulates hunger/thirst and feelings of satiety. Assists with the internal circadian clock by regulating biological activity. Involved in certain emotional responses

After-hyperpolarizing (hyperpolarization) phase

The membrane potential drops below the RMP value At this point, most of the voltage-gated Na channels have been closed and are deactivated, or in the reset phase During this phase, the voltage-gated K+ channels remain open and the membrane potential becomes even more negative than RMP. As the voltage-gated K+ channels close, the membrane potential returns to the RMP due to equilibrium in the rate of the Na/K ATPase and the K leakage.

Arachnoid mater

The middle meninx (singular for meninges) A delicate covering that has the appearance of cobwebs It is attached to the inside of the dura and forms the roof of the subarachnoid space (SAS)

Threshold Value

The minimum voltage required to elicit an action potential

Diffusion

The movement of an atom or molecule from a region of high concentration to a region of low concentration Na is at high concentration outside the cell and at low concentration inside the cell When Na channels are open, Na flows down it's chemical gradient in an attempt to reach equilibrium

Cerebral Grey Matter

The outer surfaces of the gyri are not the only areas of gray matter in the cerebrum. There are other regions of grey matter found deep within the brain, also

Dura mater

The outermost layer that forms a sac that encloses the entire cord.

Conductance

The permeability of the membrane to an ion Don't forget, the plasma membrane is relatively impermeable to charged atoms and molecules (they cannot pass... much!) To be physiologically relevant, ions must travel through transmembrane protein channels Therefore, the more ion channels that are open, the greater the conductance for that ion

A neuron's RMP is measured at rest, when it is not conducting a nerve impulse.

The resting membrane potential exists because of a difference in concentrations of charged ions in the fluids on both sides of the membrane. This difference is created, and maintained, by transport proteins in the cell's plasma membrane. The buildup of charge occurs only very close to the membrane - the cytosol elsewhere else in the cell is electrically neutral.

Choroid Plexuses

The site of CSF production within the walls of ventricles CSF produced by ependymal cells

conus medullaris

The spinal cord begins as a continuation of the medulla oblongata (the most inferior portion of the brain stem) extending from the foramen magnum of the occipital bone to its termination as the conus medullaris between L1 - L2.

Membrane Potential

The voltage of the intracellular region of the membrane compared to the extracellular (outside) If you increase the membrane potential, you excite the cell; make it more positive If you decrease the membrane potential, you inhibit the cell; make it more negative

sensory and motor tracts

The white matter of the cord contains major sensory and motor tracts to and from the brain.

Equilibrium Potential (Nernst Equation)

This is the voltage at which the electrical gradient cancels the chemical gradient The electrical repulsion force cancels out the diffusion force they oppose each other with equal force At this point, there is no net movement (current) of ions across the membrane

4 General Considerations of Cerebral Cortex

Three types of functional areas Motor areas—control voluntary movement Sensory areas—conscious awareness of sensation Association areas—integrate diverse information Each hemisphere concerned with contralateral side of body Tracts of axons can cross to either side when traveling to and from opposite hemispheres Thick bands of axons connect left and right side of brain Lateralization of cortical function in hemispheres Maintenance of body and consciousness involves entire cortex in some way You actually use most, if not all, of your brain... not just 10%

roots

Two bundles of axons, called roots, connect each spinal nerve to a segment of the cord.

Adrenergic Receptors

Two major classes that respond to NE or epinephrine Alpha () receptors Divided into subclasses: 1, 2 Beta () receptors Divided into subclasses: 1, 2, 3 ---Effects depend on which subclass of receptor predominates on target organ Example: NE binding to cardiac muscle 1 receptors causes increase in heart rate, whereas epinephrine causes bronchial smooth muscle relaxation when bound to 2 receptors

AP is a tug-of-war between Na and K

Which ever has the highest current (I) at a particular time determines which direction the membrane voltage goes Current is dependent upon driving force and conductance (g)

Understanding short-hand representations of concentrations

[K]o or [K]e = concentration of outside (o), or extracellular (e), potassium [K]i = concentration of intracellular potassium

Potassium

a cation, is at a much higher concentration inside the cell compared to outside

Calcium

a cation, is at a much higher concentration outside the cell compared to inside

Sodium

a cation, is at a much higher concentration outside the cell compared to inside More sodium ions outside

Phosphate

a polyatomic anion, is at a much higher concentration inside the cell vs outside However, the majority of phosphate is bound to proteins and ATP

norepinephrine (NE) is released by

adrenergic fibers at: Almost all sympathetic postganglionic axons, except those at sweat glands (release ACh)

The receptor site can be blocked or activated.

agonist antagonist

Action potentials

allow communication over long distances within the body.

Cloride

an anion, is at a higher concentration outside the cell compared to inside

Both excitatory and inhibitory neurotransmitters

are present in the CNS and PNS.

Graded potentials

are used for short-distance communication only.

Cholinergic Receptors

bind to Ach Nicotinic receptors ----Effect of ACh at PNS nicotinic receptors is always stimulatory ----Opens ion channels depolarizing postsynaptic cell Muscarinic receptors -----Can be either inhibitory or excitatory -----Depends on receptor type of target organ Example: Binding of ACh to cardiac muscle cells slows heart rate, whereas binding to intestinal smooth muscle cells increases motility

Driving force

can most easily be described as how much, or badly, something wants to go across the membrane Driving force for ions is dependent upon concentration and electrical gradients The greater the concentration difference across the membrane, the greater the driving force of that ion The greater the electrical gradient across the membrane, the greater the driving force for that ion These will play a huge roll in the movement of ions during AP!!!

Preganglionic neuron

cell body in CNS with  thin, lightly myelinated preganglionic axon  extending to ganglion (relay station)

Postganglionic (ganglionic) neuron (outside  CNS)

cell body synapses with preganglionic  axon in autonomic ganglion with  nonmyelinated postganglionic axon that extends to effector organ

Neurons process information when

changes occur at the trigger zone through spatial and temporal summation of IPSPs & EPSPs.

acetylcholine (Ach) (same as ACh used by somatic motor neuron) is released by

cholinergic fibers at: All ANS preganglionic axons and All parasympathetic postganglionic axons

Effects of neurotransmitter depends on whether it binds to

cholinergic receptor or adrenergic receptor

white matter of the cord

consists of millions of nerve fibers These fibers transmit electrical information between the limbs, trunk and organs of the body, and the brain.

anterior (ventral) root and rootlets

contain axons of motor neurons, which conduct nerve impulses from the CNS to effectors (muscles and glands).

posterior (dorsal) root and rootlets

contain only sensory axons, which conduct nerve impulses from sensory receptors in the skin, muscles, and internal organs into the central nervous system.

reflex circuits

control some of your most rapid reactions to environmental changes.

presynaptic neuron

converts an electrical signal (nerve impulse) into a chemical signal (released neurotransmitter).

cervical enlargement

correlates with the sensory input and motor output to the upper extremities.

Graded Potentials

depolarizing graded potential (excitatory) hyperpolarizing graded potential (inhibitory).

Types of circuits include

diverging, converging, reverberating, and parallel after-discharge.

Propagation of the AP

down the length of the axon begins at the trigger zone near the axon hillock.

The same neurotransmitter may be

excitatory in some locations and inhibitory in others.

A neurotransmitter causes either an

excitatory or an inhibitory graded potential:

Filum terminale

extends to coccyx Fibrous extension of conus covered with pia mater Anchors spinal cord to the coccyx

Names of tracts

formed by using compound words that denote the origin of the tract, and the place where it ends.

threshold stimulus

full strength nerve impulse (AP) is produced and spreads down the axon of the neuron to the axon terminals.

Voltage-Na channels begin to undergo inactivation

gNa actually reaches its peak during the onset of repolarization and then begins to progressively decrease as Na channels are closing Interestingly, sodium current is greater during a good portion of repolarization than during depolarization (more sodium is flowing in) However, K efflux > Na influx. Thus the membrane voltage moves in the negative direction. The inactivated Na channels must go through the reset phase in order to enter the deactivated state. Many will enter the deactivated state toward late repolarization/early after-hyperpolarization More and more slow voltage-gated K channels continue to open gK is increases IK increases in the first half of repolarazation and then begins to decrease in the second half despite a continued increase in gK Much like the Na story as we begin to approach the EK, the driving force for potassium decreases leading to a decrease in current

lumbar enlargement

handles motor output and sensory input to and from the legs.

red nucleus

helps control voluntary movements of the limbs.

Excitable cells

in their resting state have a negative charge on the inside of the membrane (-70mV is the average for neurons) compared to the outside (0mV)

Vm

internal membrane voltage

A graded potential occurs whenever

ion flow in mechanically gated or ligand-gated channels produce a current that is localized - it spreads to adjacent regions for a short distance and then dies out within a few millimeters of its point of origin.

A cell's RMP is created using

ion gradients and a variety of ion channels that open or close in response to specific stimuli. Because the lipid bilayer of the plasma membrane is a good insulator, ions must flow through these channels.

tract

is a bundle of neuronal axons that are all located in a specific area of the cord and all traveling to the same place (higher or lower in the brain or cord).

antagonist

is a chemical that blocks or diminishes the effects of a molecule at a given receptor. Atracurium besylate is a neuromuscular-blocking drug (skeletal muscle relaxant) used as a paralytic agent for intubation, surgery, or ventilators Binds to the nAChR on the NMJ effectively blocking the activity of ACh

Signal transmission at the synapse

is a one-way transfer from a presynaptic neuron to postsynaptic neuron.

action potential (AP) or impulse

is a signal which travels the length of the axon. During an AP, the membrane potential reverses and then eventually is restored to its resting state.

dermatome

is an area of skin that is innervated by a single spinal nerve indicated by the letter and number of a particular segmental potion of a spinal nerve. C = cervical T = thoracic L = lumber S = sacral C2 means this area is innervated by the 2nd cervical spinal nerve

agonist

is any chemical that enhances or stimulates the effects of a molecule at a given receptor. Nicotine can bind to most nAChRs and cause the same effect as ACh

Integration

is the process accomplished by the post-synaptic neuron when it combines all excitatory and inhibitory inputs and responds accordingly. This process occurs over and over as interneurons are activated in higher parts of the brain (such as the thalamus and cerebral cortex).

If a neurotransmitter could linger in the synaptic cleft

it would influence the postsynaptic neuron, muscle fiber, or gland cell indefinitely - removal of the neurotransmitter is essential for normal function and control.

If the leak permeability (leak conductance) for Na and K were equal, the RMP would

lie exactly in-between the two Nernst values The RMP is closer to the Nernst for K because there are much more K leak channels than Na. This means more is able to K+ leak out, than Na+ can leak in. More +'s leave the cell than +'s enter There are also large negatively charged proteins that always remain in the cytosol. If left unchecked, inward leakage of Na+ would push the resting membrane potential toward a positive direction. The small inward Na+ leak and greater outward K+ leak are offset by the Na+/K+ ATPases (sodium-potassium pumps) which pumps out Na+ as fast as it leaks in. Therefore RMP is due to Nernst values for Na and K as well as an equilibrium in the Na/K pump and the K leak rates

A negative current

means that ions are flowing into the cell

A positive current

means that ions are flowing out of a cell

B fibers

medium size diameter and speed (up to 15 m/sec or 32mph) comprise myelinated visceral sensory & autonomic preganglionic neurons.

Sympathetic division

mobilize body functions necessary to support demands of increased overall metabolic activity

Left hemisphere

more important for reasoning, numerical and scientific skills, spoken and written language, and the ability to use and understand sign language.

Right hemisphere

more specialized for musical and artistic awareness; spatial and pattern perception; recognition of faces and emotional content of language; discrimination of different smells; and generating mental images of sight, sound, touch, and taste

Dual innervation

most visceral organs are served by both divisions, but these divisions usually cause opposite effects Dynamic antagonism between two divisions used to maintain homeostasis based on need

subthreshold

no nerve impulse will result and the membrane will go back to resting value

spinal cord shape

oval in shape and slightly flattened anteriorly and posteriorly spinal cord becomes progressively smaller.

relative refractory period

period of time during which a second action potential can be initiated, but only by a larger-than-normal (suprathreshold) stimulus. It coincides with the period when the voltage-gated K+ channels are still open after enough inactivated Na+ channels have returned to their deactivated resting state to allow for another AP. In contrast to action potentials, graded potentials do not exhibit a refractory period.

Parasympathetic division

promotes maintenance functions, conserve energy

vertebral column

provides the backbone.

postsynaptic neuron

receives the chemical signal and in turn generates an electrical signal (postsynaptic potential).

Voltage-gated channels

respond to changes in the transmembrane electrical potential and are mainly located along the neuronal axon. Participate in the generation and conduction of AP

Mechanically-gated channels

respond to mechanical deformation (ex. applying pressure to, or stretching, a receptor).

depolarizing graded potential (excitatory)

stimulus that causes the intracellular membrane voltage to be less negatively charged with respect to the extracellular membrane voltage

hyperpolarizing graded potential (inhibitory).

stimulus that causes the intracellular membrane voltage to be more negatively charged

ventricles

subarachnoid space and cavities within the brain 2 Lateral ventricles Third ventricle Fourth ventricle

Epithalamus

superior and posterior to the thalamus. It consists of the pineal gland (secretes melatonin) and habenular nuclei (emotional responses to odors).

spinal meninges

surround the cord as a continuation of the cranial meninges that encircle the brain.

The more neurotransmitter released

the greater the number and intensity of graded potentials in the postsynaptic cell.

During embryonic development

the grey matter of the brain develops faster than the white matter This causes the cortical region to roll and fold in on itself. Convolutions and grooves are created in the cortex during this growth process Surface markings Ridges (gyri), shallow grooves (sulci), and deep grooves (fissures)

The frequency of AP plays a crucial role in determining

the perception of a stimulus, or the extent of our response. a second important factor is the number of neurons recruited (activated) to the cause.

C fibers

the smallest diameter and slowest (up to 2 m/sec or 4mph) comprise unmyelinated sensory and unmyelinated autonomic neurons.

a plexus of nerves

they can join together to form large "braided ropes There are a number of major nerve plexuses, all formed from portions of spinal nerves, and all located anterior to the spine: The cervical plexus, brachial plexus, celiac (solar) plexus, lumbar plexus, sacral plexus, and coccygeal plexus

corticospinal

tract goes from the cortex of the brain to the spinal cord - it is an efferent tract.

spinothalamic

tract goes from the spinal cord to the brain - it is an afferent tract.

vestibulospinal

tract originates from an area in the brain which you probably don't recognize; however, you can recognize the destination in the spine, and therefore deduce that it is a motor tract.

Two types of connective tissue coverings protect the cord and provide physical stability:

vertebral column spinal meninges

When an AP reaches the end bulb of axon terminals

voltage-gated Ca2+ channels open and Ca2+ flows inward, triggering release of the neurotransmitter. The neurotransmitter crosses the synaptic cleft and binds to ligand-gated receptors on the postsynaptic membrane.