EXSS380: Neurons and Synapses

QUIZ 1

Define Motor Control

The study of how the neuromuscular system initiates and coordinates muscle activity to produce movement

What are 5 origins of disability?

1. societal limitations

2. disability

3. functional limitations

4. impairments

5. pathophysiology

Motor control and motor learning are sub-disciplines of two areas:

Neurophysiology and psychology

Motor skill

an activity that requires voluntary movement to achieve a goal

what are the three types of motor skill development?

1. skill acquisition: learning something for the first time

2. skill refinement: enhancement of prior skill, improvement

3. skill reacquisition: regaining skill following injury and disease, rehabilitation

motor development

changes in motor behavior over the lifespan, the processes that underlie these changes, and the factors that affect them

What are the main roles of nerve cells?

• perception of the world

• fix attention

• control actions

How many individual nerve cells do we have?

100 billion

What is the purpose of neuroscience?

explaining the ability of individual neurons to influence behavior

gaining insight on the complexity of the nervous system

What are the 3 functions of the nervous system?

1. Sensory: sensing changes in the internal and external environment

2. Integrative: analyze data, store data, decide which stimuli are important

3. Motor: respond to stimuli through muscular contractions or glandular secretion

What are the two divisions of the Principle Nervous System?

1. CNS: central nervous system

2. PNA: peripheral nervous system (spinal, cranial)

What are the divisions of the CNS?

1. brain

2. spinal cord

What are the divisions of the Peripheral Nervous System?

• Autonomic Nervous System: involuntary, connected to smooth/cardiac muscle or glands

• Somatic Nervous System: voluntary and reflective muscle activity to skeletal muscle only

What are the two subdivisions of motor stimuli in the Autonomic Nervous System?

either excitatory (sympathetic) or inhibitory (parasympathetic)

all motor stimuli are _________ in nature

excititory

What is the role of glial cells?

Glia = support cells (“glue”)

they provide structure as well as seperate and insulate synaptic connections

remove debris after neuronal death

direct growth and release growth factors that nourish neurons

regulate the properties of presynaptic terminals

prevent toxic substances in the blood from entering the brain

Which are more numerous: glial cells or neurons?

glial cells are 10-50x more numerous than neurons

Microglia

phagocytes that are mobilized after injury, infection, or disease

Macroglia

Oligodendroctyes, Schwann cells, Astrocytes

Oligodendrocytes envelop how many axonal internodes? How about Schwann Cells?

O (CNS): about 15

S (PNS): a single internode 1mm long

What are the most numerous of all glial cells?

astrocytes

What are 3 roles/qualities of astrocytes?

1. permeable to potassium

2. maintain potassium ion concentration in the extra cellular space

3. clear excess neurotransmitters

What is the functional unit of the nervous system?

Neuron

What is the metabolic center of the cell?

Soma

What are the functions of dendrites?

• input to the neurom

• conduct nerve impulses toward the cell body

• relay information from external environment

What is the function of the axon?

The long, thin, cylindrical process joins the cell body at the axon-hillock:

• transmit nerve impulses away from the cell body to other neurons, muscle fibers, glands, etc.

The nodes of ranvier function like:

an express train, allowing signals to pass by channels without having to stop at each one

True or false: presynaptic cell touches the post-synaptic cell

FALSE: they do NOT touch

How often do the following pre-synaptic terminals communication on the post-synaptic terminals

• dedrites

• soma

• axon

1. most often

2. occassionaly

3. rarely

Synapse

the point where two neurons communicate, composed of the presynaptic cell, postsynaptic cell, and synaptic cleft

Principle of dynamic polarization

electrical signals within a nerve cell flow in only one direction

Principle of connection specificity

neurons do not connect indiscriminately, rather making specific connections at particular points (no networks at random)

Orthodromic vs. Antidromic

Orthodromic: propogation along the acon in the normal physiological direction (ex: in an effect nerve, this is away from the soma

antidromic: propogation of an action potential in the opposite direction of orthodromic conduction (ex: this could happen with a strong enough mechanical stimulus to disrupt flow, like hitting your funny bone)

What are 3 types of neurons?

1. sensory

2. motor

3. interneurons

Nerve Fiber

neuronal process, like dedrite or axon

nerve definition

a bundle of nerve fibers in PNS

tract definition

a bundle of nerve fibers in CNS

Nucleus definition

cluster of nerve cell bodies in CNS

Ganglion

cluster of nerve cell bodies in PNS

what are 4 steps to a neuron affecting another neuron or an effector organ?

1. neurotransmitters alter the status of the post-synaptic membrane (excitatory or inhibitory)

2. Soma generates an “on” signal (action potential)

3. AP travels away from the soma via axon

4. AP causes the release of neurotransmitters

how does the tranmission of neural information make it in and out of cells?

information transfers based on the rapid changers in the electrical potential across cell membranes; the movement of charged particles (ions) governed by excitable membranes surrounding the cells.

How do ion channels function?

They recognize and select specific ions, opening and closing in response to specific electrical, mechanical, or chemical stimuli

Resting membrane potential

when inactive, a membrane will have an electrical potential of -60/-70 mV in nervous tissue and -80 in skeletal tissue

What charge do the inside/outside of the cell have?

inside: -

Outside: +

Excitation and inhibition are caused by:

changes in resting potential

Where are Na+ and Cl- concentrated?

outside the cell

Where are K+ and organic anions (-) concentrated?

inside the cell

What are 3 ways that the resting membrane potential is maintained?

1. concentration gradient: there are more K channels than Na channels, so there will be more K going out than Na coming in

2. nongated channels: the nongated K channels leak potassium ions out from the neuron, and the nongated Na channels leak sodium ions into the neuron

3. sodium potassium pump: this moves Na out and K into the cell

Inside/outside of the cell have more _____ and a ________ charge

inside; more K+, negative

outside: more Na+, positive

Action Potential

an action potential is generated when depolarization of a cell reaches threshold because of an Na+ influx

All or Nothing Phenomenon

once a membrane reaches threshold, it will always have the same strength action potential regardless of the strength of the signal when it got there

Action potential phases

1. depolarization

2. overshoot

3. repolarization

4. hyperpolarization

describe action potential conduction

• occurs via propogation

• flows to neighboring areas, creating new APs in adjacent segments (either on or off, all-or-none, meaning that adjacment segments will have identical APs)

hyperpolarization

extreme polarization following peak of AP, prevents action potential from occuring

essential period for the membrane to recover and be able to generate subsequent action potentials

allows for AP propogation by preventing backfire

What receives information from neurotransmitters?

dendrites

EPSP causes soma to generate:

Action potential:

1. selective membrane permeability altered

2. rapid influx of Na

3. depolarization

AP causes the release of:

neurotransmitters, influencing the next postsynaptic membrane

what transmits neural information to the skeletal muscle?

motor neuron

Motor Unit

a single motor neuron and all the muscle fibers it innervates

what is the smallest controllable neural component?

motor unit

what determines the level of control of a motor unit?

the number of fibers innervated

a muscle contraction occurs when a motor unit releases ____ and creates ______

• acetylcholine (ACh)

• end plate potential (EPSP)

Excitation coupling produces:

contraction: TWITCH

it can vary in contraction time and peak force

2 neural mechanisms for increased contraction force

1. rate coding: firing frequency

2. motor unit recruitment: # of active motor unites

twitch

mechanical response to single stimulus

tetanus

sustained maximal tension due to high frequency stimulation

Henneman Size principle

Motor units will always be recruited from smallest to largest, determined by a motor units size

the reduction of tension (relaxation) will be accomplished in reverse order

this allows for smooth changes in contractile forces

Fiber Type Comparison: I, IIa, IIb

fiber type affects muscle force, rate of force production, and recruitment order

Describe the role of sensory neurons

• Sense changes in the internal and external environment]

• Highly specialized nerve type: response to a VERY specific stimulus 

  • Ex; optic, senses light, we interpret that to some type of figure. The sensory nerve only takes part in the sensing process and only light 

  • Ex; Olfactory: smell something, interpret what the scent is, the sensory neuron only does the smelling, not the association, and only the scent 

Describe the role of integrative neurons

• Analyzes data 

• Stores data 

• Decide which stimuli are important 

describe the role of Motor neurons

Responses to information from the CNS, respond to stimuli through muscular contractions or glandular secretion

Schwann cells change how ____ the action potential can travel

fast; speed up!

tissue structure that makes up Schwann cells

myelin

Schwann cells increase:

conduction velocity

where are neurotransmitters made?

soma

where does an action potential start?

axon hillock: the neck looking part of the axon 

what charge does the axon hillock have to reach to begin an action potential?

 -55 mV

does the size of the soma affect an action potential?

the smaller the neuron, the more likely it is to overflow. Same amount of Na/excitation will be much easier to come to depolarization if it is smaller, think about like filling a small cup vs. large glass

what is the only nerve type located outside the CNS?

sensory: more vulnerable to injury, protected by the vertebrae 

the sensory neurons come in the ____ side, the motor neuron in the ______ side, and the soma ________

posterior, anterior, within the CNS

what moves information away from the soma?

axon

what brings input into the neuron/toward the soma?

dendrite

true or false: every neuron is excitatory

false

can neural signals decay?

Neural signals do not decay, they just propagate

Nodes of Ranvier

space between the nodes/myelin sheaths

why are the ends of neurons swollen?

swollen at the end of the neuron: more gates, larger surface area means more neurotransmitters sending out to more places, more efficient because it mechanically functions better, vesicles have room to travel down, dump, and head back up. Also allows for more exit sites to influence the post synaptic cleft 

are sensory and motor neurons afferent or efferent?

Afferent: sensory

efferent: motor

what are the orthodromic directions for sensory and motor neurons?

• Sensory: away from the receptor, toward the CNS

• motor neuron: away from the CNS, toward the muscle 

what are the antidromic directions for sensory and motor neurons?

• sensory: away from the CNS, toward the receptor

  • you would not be able to feel pain because it is using the pathway, so it cannot send a normal orthodromic response

• motor: toward the CNS, away from the muscle 

  • would cause inability to utilize motor neuron to contract the muscle, collides with the other response

how do you know something is capable of excitation?

it is charged

are their more potassium or sodium channels?

Double the amount of potassium channels: it will leak out more than sodium is going to come in. That means that it will trend positively, lower threshold 

can you have an AP begin in a non-resting state?

yes, you can during refractory period, you just need a stronger stimuli to get it to threshold

what is the easiest way to depolarize a cell?

let sodium in, most positively charged ion