Nervous System

What does the circadian clock do?

regulates activity and sleep

• includes Body Temperature Rhythm (BTR) which tells us that our body temperature typically tends to rise during the day and decrease right when we are going to sleep

What things within our internal environment need to be homeostatically regulated?

• nutrients

• O2 and CO2 concentrations

• waste products

• pH

• water, salt, and other electrolytes

• volume and pressure

• temperature (thermoregulation)

What are the two types of direct intracellular communication?

• Gap Junctions

• Transient Direct Linkup of Surface Markers

Gap Junctions

proteins that link individual cells together

Transient Direct Link Up of Surface Markers

markers on the surface of the cell links up

• this is how immune system cells attack each other

What are two types of Indirect Intracellular Communication via chemical messengers?

• paracrine secretion

• neurotransmitter secretion

Paracrine Secretion

cell secretes a chemical messenger and these chemical messengers attach to receptors on a local target cell (emphasis on local)

• this is how nervous system signaling works

How does endocrine signalling work?

• form of indirect intracellular communication via chemical messengers

  • hormones from endocrine cells OR neurohormones from neurons

• Hormones/Neurohormones get secreted into the blood and bind to distant target cells

• Process relies on duration rather than speed

Autonomic Nervous System (3)

• plays a critical role in maintaining homeostasis

• complex network of cells that controls the body’s internal state

• regulates and supports processes outside of a person’s conscious awareness

What two parts make up the nervous system?

• Central Nervous System (CNS)

• Peripheral Nervous System (PNS)

  • both parts communicate with each other

Central Nervous System (CNS)

• consist of our brain and spinal cord

• this system receives afferent signals from the peripheral nervous system and sends efferent signals back to it

Peripheral Nervous System (PNS)

• present where we have nerve fibers

• Consist of the Autonomic Nervous System as well as the Somatic Nervous System

Efferent Signals

our response to afferent pathways/signals

• can be somatic (voluntary) such as skeletal muscle or autonomic (involuntary) such as smooth/cardiac muscle

Somatic Nervous System

• subcategory of the PNS

• system where the fibers of motor neurons connect to voluntary muscles such as the skeletal muscles

Autonomic Nervous System

• subcategory of the PNS

• fibers that connect/innervate involuntary things such as smooth muscle, cardiac muscle, and glands

• Includes

  • sympathetic nervous system (fight or flight)

  • parasympathetic nervous system (rest and digest)

Sympathetic Nervous System

• subcategory of the autonomic nervous system in the peripheral nervous system (PNS)

• prepares the body for strenuous physical activity

• “fight OR flight”

Parasympathetic Nervous System

• subcategory of the autonomic nervous system in the peripheral nervous system (PNS)

• maintains resting functions of the internal organs

• “rest and digest”

Enteric Nervous System

• nerve network of the digestive tract

• sometimes included as a subcategory of the autonomic nervous system or as a whole separate nervous system next to the central nervous system and the peripheral nervous system

Describe the autonomic nerve pathway.

• consist of a two-neuron chain (one being a neuron from the CNS, the second being from the ganglion in the PNS)

  • preganglionic fibers (from the CNS)

    • releases preganglionic neurotransmitter

  • postganglionic fiber (from the autonomic in the PNS)

    • accepts the preganglionic neurotransmitter from the preganglionic fiber and as a result releases postganglionic neurotransmitter to the effector organ

Describe the pre and post neurotransmitters used for the sympathetic and the parasympathetic nervous system.

Sympathetic

• pre-ganglionic neurotransmitter = acetylcholine

• post-ganglionic neurotransmitter = norepinephrine

Parasympathetic

• pre-ganglionic neurotransmitter = acetylcholine

• post-ganglionic neurotransmitter = acetylcholine

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 types of stress?

• physical (trauma, surgery, intense heat/cold)

• chemical (low O2, acid-base imbalance)

• physiologic (heavy exercise, hemorrhagic, shock, pain)

• infectious (bacterial invasion)

• psychological/emotional (anxiety, fear, sorrow)

• social (personal conflicts, change in lifestyles)

What are stressors?

cause of stress response and works by:

• activates the hypothalamus in the CNS which the travels to the PNS, in which it goes to the sympathetic nervous system (heightening stress) while inhibiting the parasympathetic system

• could also activate the HPA axis (hypothalamus-pituitary-adrenal cortex) to release cortisol which helps relieve the stress/prevent it

What is diffusion?

the process of movement of molecules under a concentration gradient (typically down a gradient)

• net diffusion: the direction in which the dominant diffusion occurs

What are the five factors that alter/influence diffusion?

1) magnitude of the concentration gradient

2) permeability of the membrane

3) surface area of the membrane

4) molecular weight of the substance

5) distance/thickness over which diffusion takes place

What are the two different types of diffusions?

• concentration/chemical gradient

• electrochemical gradient

Concentration/Chemical Gradient

the diffusion of nonpolar molecules (O2, CO2, fatty acids)

Electrochemical Gradient

diffusion of specific small ions, and since these ions are charged, this gradient combines the concentration/chemical gradient with an electrical gradient

Neurons

nerve cells that are specialized for electrical signaling over long distances and has a membrane potential/is polarized electrically in its plasmas membrane

Membrane Potential

separation of opposite charges across the plasma membrane

• typically measured in millivolts (mV)

• occurs near the surface/layer outside of the plasma membrane, anything father out or inside is relatively neutral

How to determine the magnitude of membrane potential?

dependent on the number of separated charges across the membrane

• the more separated charges, the greater the magnitude of the potential

Equilibrium Membrane Potential

when the force exerted by the electrical gradient exactly balances the force exerted by the concentration/chemical gradient

What is the Equilibrium Membrane Potential for Potassium (K+)?

= -90mV

• tend to have a high concentration of K+ inside the cell so the concentration gradient moves it out to the extracellular fluid, however this creates an electrical gradient that forces K+ to move back into the cell, counterbalancing the initial concentration gradient

What is the Equilibrium Membrane Potential for Sodium (Na+)?

= +60mV

• tend to have high concentration of Na+ outside of the cell so this concentration gradient forces Na+ into the intracellular fluid, however since it’s charged this causes an electrical gradient pushing Na+ back out to balance it

Nernst Equation

equation that describes/measures the equilibrium membrane potential for a particular ion

Resting Membrane Potential

the simultaneous K+ and Na+ effects on membrane potential that is present in reality

• =-70mV since K+ is 20-30 times more permeable by the membrane compared to Na+, so some of the K+ is being neutralized by the small net diffusion of Na+ hence why the equilibrium membrane potential of K+, -90mV, is reduced to -70mV in the resting potential

How do K+ and Na+ penetrate the cell memrane?

• passive leak channels which help ion flow down the concentration gradient

  • potassium out while sodium in

What establishes the concentration gradient of Na+ and K+?

• Sodium Potassium Pump (Na+/K+ ATPase)

• helps passive leak channels remain passive

• Pump 3 Na+ outside for every 2 K+ pumped inside the cell

At the resting membrane potential what you can say about the rate of passive leak channels and the Sodium potassium pump?

they are working at a balanced rate

Depolarization

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

Hyperpolarization

change in membrane polarization to more negative value than rest

Repolarization

return to resting membrane potential after depolarization

Action Potentials

brief all or nothing irreversible membrane potential spike caused by voltage gated ion channels that bring the membrane potential to the threshold

• 1msec

• occurs due to rapid changes in membrane permeability to Na+ and K+ ions

Describe what occurs during the different phases of an action potential graph?

Rising Phase:

• caused by Na+ moving into the cell making it more positive (depolarization) as a result of it’s activation gates opening

• Na+ VG channels have the ability to open quickly (<0.5ms)

Falling Phase:

• once peak membrane potential is reached K+ VG opens allowing K+ to flow out into the ECF. As K+ is moving out of the cell, the Na+ VG begin to close their inactivation gate

Repolarization:

• once back to its resting state the inactivation gates open and the activation gates close on the sodium VG channel

Hyperpolarization:

• K+ VG channel is still open causing hyperpolarization but it eventually closes, it is just slow to do so

What are the different parts of the neuron?

• nucleus

• dendrite

  • input zone, this is where the neuron receives info/incoming signal

• stoma/cell body

• axon hillock

  • trigger zone, this is where action potentials are initiated, located below the nucleus above the axon

• axon

• axon terminals

  • output zone, this is where neurotransmitters are released

Contiguous Conduction

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

• think domino effect that is repeated down the length of the axon

• while something is depolarizing, the previous region is simultaneously repolarizing

What/when are the two refractory periods?

• refractory periods are periods where another action potential cannot be propagated and helps to prevent “backward” current flow

  • absolute refractory period: brief period during a spike where the inactivation gates of Na+ are closed

  • relative refractory period: brief period following a spike where the activation gates of Na+ are closed however, bc the K+ channels are still open causing hyperpolarization, a higher intensity stimulus is needed to reach the threshold

Saltatory Conduction

the propagation of action potentials in myelinated fibers, jumping from node to node

• propagates action potentials more rapidly than contiguous conduction by 50x

• conduction speed: about 120m/s

Myelin

multilayered sheath of plasma membrane derived from specialized glial cells that wrap around axonal fibers and act as an insulator to the flow of current

Nodes of Ranvier

gaps in myelin insulation containing high densities of VG Na+ and K+ channels

What is the myelin on a neuron located in the CNS called?

oligodendrocytes

What is the myelin on a neuron located in the PNS called?

schwann cells

Multiple Sclerosis

autoimmune disease in which where the body’s defense system attacks the myelin sheath which results in slow transmission of impulse in affected neurons

Graded Membrane Potential

local changes in the membrane potential

• occurs in varying degrees of strength and moves in both directions

• spread by passive current flow

• dies out over short distances as it moves in opposite directions

• size correlates with the size of the stimulus

List similarities and differences between graded potentials versus action potentials.

• graded potentials

  • depends on stimulus

  • decrease with distance

  • triggered with stimulus (sensory receptor or neurotransmitter)

  • ligand gated, mechanically gated channels

  • initiated in dendrites to cell body and then to sensory receptors

• action potentials

  • all or nothing response

  • propagates over the entire cell

  • triggered by threshold

  • initiated in axon hillock to axon

  • voltage gated channels

Synapses

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

What are the two major types of synpases?

• Electrical Synapses

• Chemical Synapses

Electrical Synapses

neurons connected directly via gap junctions

• has brief 0.1 msec delay

Chemical Synapses

anatomical junction between two neurons or between a neuron and a muscle or gland where a chemical neurotransmitter is released

Convergence

the synaptic input of many neurons onto onto one neuron

Divergence

the synaptic output of one neuron onto many neurons

Explain how synaptic transmission (neuronal communication) works.

Presynaptic axon on the preganglionic neuron initiates the signal via a neurotransmitter

• this is initiated with an actional potential down the axon to the terminal button/axon terminal

• propagation of the action potential causes a voltage change and activates the VG Ca2+ channels

• as Ca2+ enters the synaptic knob, this causes the release of neurotransmitters to the synaptic cleft via exocytosis

Neurotransmitter carries the signal across the synapse and binds to receptors of the postsynaptic neurons/muscle/gland resulting in a postsynaptic potential (PSP)

What are two ways a neurotransmitter can act?

• EPSP (Excitatory Postsynaptic Potential)

• IPSP (Inhibitory Postsynaptic Potential)

  • both are graded potentials

Excitatory Postsynaptic Potentials (EPSP)

depolarizing graded potential that bring membrane potential towards the threshold for generation of an action potential

What are common EPSP neurotransmitters?

• glutamate (Glu)

• acetylcholine (ACh)

Inhibitory Postsynaptic Potentials (IPSP)

hyperpolarizing graded potential that brings membrane potential away from the threshold that generates an action potential

What are common IPSP neurotransmitters?

• gamma-amino butyric acid (GABA)

• glycine (Gly)

What are three different ways that neurotransmitters can be removed?

1) Degradation

2) Transport

3) Diffusion

Explain how neurotransmitters are removed via degradation.

there are enzymatic breakdowns of neurotransmitters

Explain how neurotransmitters are removed via transport.

does active transport back into the presynaptic cells (called reuptake and occurs through a transporter)

Explain how neurotransmitters are removed via diffusion.

the transmitter simply diffuses away from the synaptic cleft/terminal

What are four ways that synaptic potentials can work together?

1) temporal summation

2) spatial summation

3) cancellation summation

4) presynaptic inhibition

Temporal Summation

the additive effects of a postsynaptic potential when they occur close together in time (not the same time but same place)

• could be EPSP or IPSP

Spatial Summation

the additive effects of postsynaptic potentials occurring at nearby parts (same time, but different space/area)

Cancellation Summation

Excitatory postsynaptic potential (EPSP) and inhibitory postsynaptic potential (IPSP) cancel each other out if they are of the same magnitude

Presynaptic Inhibition

inhibition from a neuron to another neurons synaptic terminal, ultimately decreasing neurotransmitter release

What advantages do chemical synapses have over electrical synapses?

• can modify the strength of neurotransmitters (inhibitory, spatial/temporal summation, cancellation)

• convergence and divergence

  • allows for widespread network of neuron not just one neuron to another neuron (electrical synapse which use gap junctions)

What are the three functional types of neurons?

1) Afferent

2) Interneuron (links the afferent and efferent neuron together, located in the CNS)

3) Efferrent

Traumatic Brain Injury

an injury to the brain caused by an external force

What are four major features of the brain/CNS that help to protect the brain from injury?

1) Cranium (back of the head) and Vertebral Column (spine which shields our spinal cord)

2) Meninges

3) Cerebrospinal Fluid

4) Blood Brain Barrier

Meninges

• membraneous layers that surround and protect the central nervous system (brain and spinal cord)

• three layers

  • Pia Mater (innermost layer)

  • Arachnoid Mater (middle layer)

  • Dura Mater (outter layer)

    • in-between the pia mater and arachnoid mater there is cerebrospinal fluid

Cerebrospinal Fluid

• present between the pita mater and arachnoid mater layers of the meninges

• fluid that surrounds and cushions the brain and spinal cord

  • what causes our brain to float in our heads

Hydrocephalus

the build up of cerebrospinal fluid in the brain, exerting pressure on the brain

Blood-Brain Barrier

highly selective barrier that regulates exchanges between the blood and brain

• shields our brain from harmful blood borne material (bacteria, fungi, viruses, and parasites)

What are two things the brain depends on and thus requires its constant delivery?

1) oxygen

2) glucose

What do the 85 billion neurons making up our central nervous system allow us to do?

• subconsciously regulate homeostatic responses (hypothalamus)

• experience emotions

• voluntarily control movements (cerebral cortex + basal nuclei/ganglia)

• be aware of our body and surroundings (parietal)

• engages in other cognitive processes (hippocampus)

What two components make up the forebrain (largest overall region of the brain)?

• cerebrum (which houses the cerebral cortex made up of gray matter)

• diencephalon (inner part of the brain that is made up of white matter)

Cerebral Cortex

• makes up the cerebrum and is the surface of the brain that is organized into layers and five functional columns:

  • frontal lobe

  • parietal lobe

  • occipital lobe

  • temporal lobe

  • central sulcus

Frontal Lobe

houses the primary motor cortex

Parietal Lobe

houses the somatosensory cortex

Occipital Lobe

primary visual cortex

Temporal Lobe

primary auditory complex

Central Sulcus

divides the frontal lobe and the parietal lobe

Primary Motor Cortex

• located in the frontal lobe, north of the central sulcus

• motor homunculus

  • tells us that the motor cortex is proportional to the precision and complexity of motor skills required of the respective part

• more fine control of a particular body part means that there is more space on the primary motor cortex dedicated for those respective neurons

Somatosensory Cortex

• located in the parietal lobe, south of the central sulcus

• sensor homunculus

  • shows us the proportional degrees of sensitivity and great acuity (ability to distinguish two points/discriminative ability)

• have higher acuity in: finger, toes, and face

• lower acuity in: arms, legs, or torso

What are the three names for the different cross sections of the brain?

1) frontal plane: cut down vertically showing the back and front of the brain

2) sagittal plane: cut down vertically showing the left and right half of the brain

3) transverse plane: cut down horizontally showing the top half and bottom half of the brain

Diencephalon

part of the forebrain (center)

• contains the hypothalamus (smaller), the thalamus (larger), and the basal nuclei (surrounds the thalamus)

Thalamus

sensory relay station

• as it accounts for any input given to us through our sensory neurons

important for motor control

Hypothalamus

physically located beneath the thalamus and regulates homeostatic functions (circadian rhythms, thermoregulation, etc)

• integrating center for many important homeostatic functions

Brain Stem

• link the spinal cord and the higher brain regions (cerebral cortex)

• three parts (midbrain, pons, and medulla)

• has the most cranial nerves

• have centers that control cardiovascular, respiratory, and digestive function

• regulates equilibrium + postural reflexes

• controls overall degree of alertness

• is one of the centers that govern sleep (other one is the hypothalamus)