Chapter 11

Describe what happens at each of the three steps of general function of the nervous system:

1- Sensory Input

2- Integration

3- Motor Output

First - the stimulus/sensory input is sent to the brain along the afferent pathway

Second - Integration

The brain - it gives meaning to the sensory input and decides what you need to do with that information

The spine - involved in reflex arcs

Third - the brain (usually) responds and sends out some sort of electrical signal to a muscle (usually) along the efferent pathway 

List the Divisions of the Nervous System from biggest to smallest 

Central Nervous System ←→ Peripheral Nervous System 

Peripheral Nervous System is broken down into: 

The Sensory (afferent) Division and the Motor (efferent) Division

The Motor (efferent) Division is split into: 

Somatic Nervous System and the Autonomic Nervous System 

The Autonomic Nervous System is broken down into: 

The Sympathetic and Parasympathetic Division 

  Central (CNS) – consists of the______ and ___________. It is the __________________

brain; spinal cord; integration center

Peripheral (PNS) – consists of all the ________ coming off the _____ and __________, and they run through our entire body. It contains both the ________ and ________ pathway.

nerves; brain; spine; afferent; efferent 

Sensory is the ________ Division of the PNS

afferent

Motor is the ________ Division of the PNS

efferent

Somatic Nervous System – the ________part of your nervous system. It is what sends signals to your muscles to intentionally move

voluntary 

Autonomic Nervous System (ANS) – __________ part of the nervous system. It’s the stuff that keeps you alive – using the restroom, moving food through the digestive tract, changing BP, etc.

involuntary 

what is the voluntary part of the Motor Division of the PNS

somatic

What is the involuntary part of the motor division of the PNS

autonomic

 

Sympathetic (SNS) – ________________ , it takes over when there’s some sort of __________ ———— it is part of the ______ Nervous System 

fight or flight; stress; autonomic 

Parasympathetic (PNS) – __________________, ____________ – conserves energy and promotes “house-keeping functions). It does things like ________________________

rest and digest; relax and reproduce; digest food, slow your breathing

Parasympathetic nervous system is part of the ____________ nervous system

autonomic

For sympathetic and parasympathetic, one is ________ ________ and they switch when the ________________

always active; conditions change

Neuroglia definition; also called? 

non-conductive cells of the nervous system that support, protect, and insulate the neurons. Also called glial cells, or glia.

Neuroglia of the CNS – ___________ neurons, have ___________ __________ (extensions), and a central cell body. Distinguishable by their ______________, and ___________

outnumber; branching processes; much smaller size and dark staining nuclei 

Neuroglia of the CNS:

What do astrocytes do?

assist in exchanges between blood capillaries and neurons

Neuroglia of the CNS:

What are the most abundant glial cells?

astrocytes

Neuroglia of the CNS:

What are the additional functions of astrocytes?

participate in information processing in the brain

Support and brace neurons and anchor them to their nutrient supply lines

Control chemical environment around neurons; most importantly “mopping up” leaked potassium ions and recycling the released neurotransmitters

Neuroglia of the CNS:

Microglial cells (microglia) functions 

                                               i.     Monitor neuron health and migrate to any that are injured/in trouble

                                             ii.     If invading microorganisms or dead neurons are present, microglial cells transform into macrophages that phagocytize the neuron debris/microorganisms

Neuroglia of the CNS:

Ependymal cells line the central cavities of the brain and the spinal cord

What are their functions? 

Form a permeable barrier between the cerebrospinal fluid that fill the cavities and tissue fluid of the cells of the CNS

    Cilia helps circulate the fluid that cushions the brain and spinal cord

Neuroglia of the CNS:

Oligodendrocytes - what is their function? 

Oligodendrocytes wrap their processes tightly around thicker nerve fibers of the CNS, producing an insulating covering called a myelin sheath

What are the types of Neurologlia of the CNS? (4)

astrocytes, microglial cells, ependymal cells, and oligodendrocytes

What are the types of neuroglia of the PNS? (2)

Satellite cells and schwann cells

Neuroglia of the PNS

What is the function of satellite cells? 

Surround neuron cell bodies in the PNS; have many of the same functions of astrocytes of the CNS (supporting the neural cell body)

Neuroglia of the PNS

What do Schwann cells do?

Surround all nerve fibers in the PNS and form myelin sheaths around the thicker nerve fibers (functionally similar to oligodendrocytes)

Neurons (the structural units of the nervous system –

___________ _________ cells that communicate throughout the body)

electrically conductive 

What are the special characteristics of neurons? (3) 

• extreme longevity 

• amitotic (do not go through mitosis) 

• highly metabolic (they use a lot of ATP) 

Neuronal Structure

a. Cell body (also called the _______) - this is where the _______ are found

1. ____________ = the area around the nucleus; the cell body

2. Chromatophilic substance aka nissl bodies - the ________ __________ of neurons

soma; perikaryon; endoplasmic reticulum

Nuclei meaning in neurons = ? 

a cluster of neuronal cell bodies in the CNS

Ganglia meaning in neurons = ?

a cluster of neuronal cell bodies in the PNS

Nuclei vs ganglia?

the first is a cluster of neuronal cell bodies in the CNS; the second is the same thing in the PNS 

Processes extend from the cell body 

i. Groups named based on location

1. Tracts – a cluster of _______ in the ______

2. Nerves – a cluster of _______ in the______

axons; CNS; axons; PNS

Processes extend from the cell body 

Dendrites - what are they and what do they do

the receptive part of a neuron; they carry electrical signals towards the cell body

Processes extend from the cell body 

What are axons and what do they do? 

Axon – the sending part of a neuron; signal leaves along the axon ; they will either (depending on location) have nuclei or ganglion at the end

Processes extend from the cell body 

What is the axon hillock and what does it decide? 

Axon hillock – the end of the axon that connects to the soma (funnel shaped); the part of the neuron that determines if an electrical signal will be sent into the axon

Processes (extend from the cell body)

What are the axon terminals and what do they do?

terminal branches located at the end of the axon, if a signal is sent, it travels to the axon terminals

Disorders

hydrophobia (rabies) - what happens 

1.     viruses make their way into the motor neurons and move away from the bite toward the CNS and make their way to the brain, causing it to swell, salivary glands to become over active, and at that point it hurts to drink water so you become dehydrated. There is no cure.

Disorders

Chicken pox - what is it caused by and what is recurrence in relation to it 

a.     Caused by virus (similar to herpes)

 

b.    Recurrence – if you get chicken pox, the longer that you have the virus, the more likely it is to be reactivated (as Shingles)

What is myelin  and what does it do for a neuron?

insulation (not all neurons are myelinated) that helps the electrical signal to travel faster and more effectively

Myelin sheath - what is it

– a living (Schwann) cell that wraps itself around the axon

what are the Nodes of Ranvier

the exposed areas of the axon between cells that make up the myelin sheath, if the full thing were covered the axon would not be able to send electrical signals

Structural Classifications of Neurons (3) and what they are

Multipolar (99%) - Neurons with three or more processes – They have one axon and multiple dendrites, allowing them to integrate a lot of information from other neurons; most common neuron type in the CNS.

 

Bipolar (rare) - Neuron with axon and dendrite that extend from opposite sides of the cell body. Found in some of the special sense organs such as in the retina of the eye and in the olfactory mucosa (sense of smell)

 

Unipolar (PNS—sensory neurons) - They have a single short process that emerges from the cell body and divides T-like into proximal and distal branches. The more distal peripheral process is associated with a sensory receptor. The central process enters the CNS.

Functional Classifications of Neurons (3)

Sensory/afferent - transmit impulses from sensory receptors in the skin or internal organs toward or into the central nervous system.

Motor/efferent - carry impulses away from the CNS to the effectors (muscles and glands) of the body.

 

Interneurons/association neurons - lie between motor and sensory neurons in neural pathways and shuttle signals through CNS pathways where integration occurs.

Voltage definition

a separation of charge particles

In neurons – the ________ has a voltage – the inside is more ______ compared to the outside

membrane; negative

2. Leaky (leakage) channels – channels in the cell membrane that are __________ __________and theyre permeable to __________particles

always open; specific

Voltage gated channels – open and close in response to ______ ________ ________ and theyre specific to_______ particles

certain voltage levels; certain 

Chemically gated (ligand gated) channels – what are they and how do they work? 

“lock and key” closed until a certain chemical/ligand binds to it. Once it binds, it “unlocks” and the channel opens (also specific to certain particles)

Mechanically gated channels – open and close in response to ________ ________ (how touch receptors work)

physical deformation

define: 
a.     Concentration (chemical) gradient –  

b.    Electrical gradient –

c.     Electro-chemical gradient –

a.     Concentration (chemical) gradient – more of a substance in one area compared to another area

 

b.    Electrical gradient – more positive/negative in one area compared to another

 

c.     Electro-chemical gradient – both of the above at once

Are the concentrations of these ions higher inside or outside of the cell? 

a.     Sodium – Na+

b.    Potassium – K+

c.     Proteins – (sometimes written A- )

d.    Calcium – Ca++  

e.     Chloride – Cl-  

a.     Sodium – Na+ - higher concentration outside the cell

 

b.    Potassium – K+ - higher concentration inside the cell

 

c.     Proteins – (sometimes written A- ) – higher concentration inside the cell

 

d.    Calcium – Ca++ - higher concentration outside the cell

 

e.     Chloride – Cl-   -higher concentration outside the cell

What is the resting membrane potential of neurons and muscle cells?

a.     Neuron - -70mV while at rest

b.    Muscle Cell - -90mV while at rest

polarization of cells is due to __________

permeability

1.     Role of sodium-potassium pump –

compensates for leaking ions and maintains the concentration gradients (which results in/maintains the membrane potential)

1.     Graded potentials – by changing the permeability of a cell you can make it more or less polarized

 

a.     Depolarization - 

b.    Repolarization –  

c.     Hyperpolarization -

a.     Depolarization -  the act of becoming less negative (the membrane becomes more permeable to sodium (which has a positive charge)

 

b.    Repolarization – the process where a cell's electrical potential returns to its resting state after being stimulated

 

c.     Hyperpolarization - the act of becoming more negative (the membrane becomes more permeable to potassium, which when it leaks out it takes its positive charge with it, and makes the inside of the cell more negative)

1.     Action potentials – ? 

a.     Every action potential in a neuron goes from _____ to ______ and back to _______

b.    Action potentials have the ability to be __________ along the length of a cell and on to the next cell in line

 

c.     Threshold - ? 

1.     Action potentials – a brief reversal of membrane potential (takes just a little more than a millisecond)

a.     Every action potential in a neuron goes from -70 to -30 and back to -70

b.    They have the ability to be propagated/passed along the length of a cell and on to the next cell in line

 

c.     Threshold - the minimum level of depolarization needed to trigger a response in a neuron or muscle cell

All-or-none phenomenon -  ? 

that if a stimulus does not reach the threshold, then an action potential does not happen

a.     More intense stimuli produce ????

  More intense stimuli produce more frequent action potentials_

a.     All action potentials have the same ?????

a.     All action potentials have the same amplitude (-70 → 30 → -70)

a.     Absolute refractory period – ???? 

 

b.    Relative refractory period – ???

a.     Absolute refractory period – the period where another action potential cannot be sent because the ions are out of place and because the voltage gated channel inactivation gate is closed

 

b.    Relative refractory period – once the voltage gated channel inactivation gate is opened, and the ions are returning, it is difficult but not impossible to send another action potential (has to be a very strong stimulus)

1.     Conduction velocity – ????

how quickly the action potential travels the length of the axon

Conduction velocity in myelinated axons

in myelinated axons, conduction is very fast without decaying much. Aps are generated in the myelin sheath gaps and appear to jump rapidly from gap to gap 

Saltatory conduction – ?

occurs in myelinated axons, it is the jumping conduction that happens very quickly, from one node of ranvier to the next

Multiple sclerosis is an autoimmune disease where the disease attacks the myelin sheath. What does this mean? 

When this happens, because the area where there was a myelin sheath is exposed, and it has no proteins on it, more often than not, the signal dies before it gets to where its supposed to go. MS results in jerky movements or paralysis

local anesthetics impair _______ - how does that result in numbing of that area?

Impair voltage gated sodium channels - because they are what start the action potential, impaired voltage gated sodium channels stop all signal sending of that area

Passing APs from one neuron to another

1.     Presynaptic neuron – ?

 

2.     Postsynaptic neuron – ?

 

3.     Synaptic cleft – ?

1.     Presynaptic neuron – the sender of the AP

 

2.     Postsynaptic neuron – the receiver of the AP

 

3.     Synaptic cleft – the open space between the two neurons

Where are APs passed from one neuron to another 

at the synapse (the open space between to neurons or a neuron and another cell type

What two neurotransmitters do we need to know in this class? How do they work? 

a.     Acetylcholine (Ach) – exoxytocizes out of the presynaptic neuron, is the activating chemical that the ligand-gated channel on the postsynaptic neuron responds/opens up to, and Na+ rushes into that post synaptic cell. As long as the acetylcholine is attached, Na+ is rushing in. Sodium has a positive charge, and as it enters that post synaptic cell, it causes depolarization OF THIS AREA.

 

b.    Serotonin – in the case of serotonin, it would let in something that cause hyperpolarization, which means the neuron is less likely to send the action potential

Graded potentials occur at the _________;    either on the dendrites or on the soma because _______________

synapse; because they do not have voltage gated channels

Graded potentials can have varying ____________ ; meaning the greater the stimulus the greater the __________

magnitudes; magnitude 

action potentials can be propegated/passed down but graded potentials can affect anything from a very small to very big area because ?

they are dependent on the degree of the stimulus

Classes of synapses:

a.     Axodendritic –

b.    Axosomatic –

c.     Axoaxonal –

a.     Axodendritic – the axon is connecting to the dendrite of the receiving neuron 

b.    Axosomatic – the axon is connecting to the soma

c.     Axoaxonal – the axon connects with either the axon or the axon hillock the receiving neuron

  Termination of signals at synapses – how do you stop that AP from the first neuron to the second?

a.     Reuptake –

c.     Degradation –

d.    Diffusion away from synapse –

a.     Reuptake – the sending neuron pumps the neurotransmitter back into itself, retracting the neurotransmitter from the synaptic cleft 

c.     Degradation – breaking down of neurotransmitters, done by enzymes

d.    Diffusion away from synapse – the sending neuron stops exocytosing the neurotransmitter and eventually the concentration gradient causes diffusion away from the ligand gated channels

Postsynaptic potentials

1.      Excitatory (EPSP) -

 

2.     Inhibitory (IPSP) –

 

3.     Summation –

 

a.     Temporal summation –

 

b.    Spatial summation –

1.      Excitatory (EPSP) - the presynaptic neuron caused the post synaptic neuron to depolarize and therefore more likely to send an AP (this is called excitation), and results in an Excitatory Post Synaptic Potential 

2.     Inhibitory (IPSP) – Inhibitory Post Synaptic Potential – makes the neuron less likely to send an action potential

3.     Summation – what happens when more than one signal is sent to a receiving neuron

a.     Temporal summation – one neuron is sending signals to the receiving neuron very quickly, which will start to stack (if it is in a dendrite or a soma, it will affect a bigger area with a greater effect on the membrane potential (bigger waves on the chart))  

b.    Spatial summation – when more than one neuron is sending signals to the receiving neuron, and get stacked because multiple signals are sent at once

Reflex arcs - neural pathway for a rapid, involuntary response. (they have 5 components)

1.     Receptor  -

2.     Sensory neuron (afferent) –

3.     Integration center -

4.     Motor neuron (efferent) -

5.     Effector -

1.     Receptor  - Detects stimulus (e.g., stretch, pain).

a.     Starts action potential in sensory neuron.

2.     Sensory neuron (afferent) – transmits afferent signal to CNS

3.     Integration center - In simple reflex arcs, the integration center may be a single synapse between a sensory neuron and a motor neuron (monosynaptic reflex). More complex reflex arcs involve multiple synapses with chains of interneurons (polysynaptic reflex).

4.     Motor neuron (efferent) - Carries efferent signal from integration center to an effector

5.     Effector - Muscle (skeletal/smooth) or gland.

a.     Produces response (e.g., contraction, secretion).

Types of Circuits

1.     Diverging circuit

2.     Converging circuit

3.     Reverberating circuit –  

4.     Parallel after-discharge circuit

1.     Diverging circuit - a Single neuron AP _ can activate APs in many neurons 

2.     Converging circuit - Sensory input from different sources can activate a common memory (single output)

3.     Reverberating circuit – one neuron sends a signal that ends up feeding back the signal to a neuron along the pathway

a.     Rhythmic activities

                                                i.     Walking, sleep/wake, breathing 

4.     Parallel after-discharge circuit – one neuron sends a signal to multiple neurons but those all send the signal to a single neuron at the end

a.     Mental activities such as mathematical calculations