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UA / OTHER / PSIO 305 / What are the types of synapses?

What are the types of synapses?

What are the types of synapses?

Description

School: University of Arizona
Department: OTHER
Course: Integrative Systems Physiology
Professor: Douglas keen
Term: Spring 2019
Tags: nervous system, motor, control, neurons, synaptic transmission, neural science, brain motor skills, sensorimotor, receptor activation, Motor System, muscle, and Brain and Behavior
Cost: 25
Name: PSIO 305 Week 2 Notes
Description: - Motor control 101 - Key players of the Nervous System & their roles - Synaptic Transmission Steps - Proprioception - Association areas of the brain & their roles - Direct vs. Indirect pathways explained! - Historical/current methods of studying the NS - Summation - Intro to motor units
Uploaded: 01/18/2019
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PSIO 305 - Week 2 (Lectures 2-4)


What are the types of synapses?



Lecture 2 Notes: “Use it or Lose it!” 

● Motor Control 101 (generating a “Movement Plan”)

○ Know your starting position (where your body is in space)

○ Understand muscle groups required (to control speed, strength and direction of movement)

○ Know your stopping point (how/when to stop the motion)

● Key players of the Nervous system

○ Dendrites and cell body receive messages

○ Axon transmits signal to other neurons or effector cells

○ Synapse: area where the electrical signal becomes a chemical signal by the release of neurotransmitters

● Synaptic Transmission


What are the two different types of summation?



○ Steps

■ (1) Depolarization of axon terminal in the presynaptic cell

■ (2) Neurotransmitter (NT) is released from the synaptic vesicle

■ (3) NT binds to receptor on postsynaptic membrane (ligand-gated ion channel)

■ (4) Ligand binding opens the channel on the postsynaptic cell membrane ■ (5) This ion flux is what makes the communication “chemical,” but then soon after when the ligand diffuses off, the signal is considered “chemical” again Don't forget about the age old question of What are the three states of water?

○ Long-term potentiation: an adaptation at the synapse in which the signal lasts longer than normal (several seconds, compared to milliseconds)

■ Just know that the synapses are constantly being modified (Remember: the nervous system is incredibly ELASTIC!)


What are the steps in synaptic transmission?



■ Increasing the # of a particular receptor (ex: AMPAR receptors) will lead to a greater depolarization event

○ Types of Synapses (based on speed/role)

■ FAST ionotropic receptors

● Activate ion channels

● Affect current flow and voltage change

● In the basal nuclei, dopamine acts on ionotropic receptors,

ultimately affecting movement planning

■ SLOW metabotropic receptors

● Bind to GPCRs and change metabolism of the cell We also discuss several other topics like Why is dante's book open?

● Experience longer-lasting, downstream effects

● In the hypothalamus, dopamine acts metabotropically, regulating

hunger/thirst & body temperature

● Supportive network of the Nervous System: Neuroglia (Glia cells) If you want to learn more check out How does our brain work?
Don't forget about the age old question of What is indian removal act 1830 about?

○ Job summary:

■ Infrastructure and nourishment - astroglia (CNS)

■ Insulation by oligodendrocytes (CNS) and Schwann cells (PNS)

■ Environmental maintenance of ion concentrations and neurotransmitters ■ Trophic support and organization

● Proprioception (the knowledge of the body in space) happens through a complex spinal cord and Primary Sensory Cortex interaction

○ Organized somatotopically

○ Homunculus (“little man”) indicates the level of sensation regarding a specific body part & where in the brain that sensation occurs

○ Determining the intensity of a stimulus

■ Rate coding: as the intensity of a stimulus increases, the frequency (or rate) of action potentials also increases

■ Pattern coding: speed of onset and duration depends on a particular pattern which may contain a sensory code for stimulus intensity

● The “Movement Plan” takes into account many issues and involves multiple complex parts of the brain

○ Association cortex & premotor cortex (frontal lobe) - area initiates the idea to move We also discuss several other topics like What are the two major theologies?

○ Primary motor cortex (precentral gyrus)- relays final movement to the spinal cord to activate particular motor units and muscles

○ Primary sensory cortex (in the parietal lobe/postcentral gyrus) - receives proprioceptive and somatotopic information to be utilized during

movement

○ Association cortex (parietal lobe) - integrates information from various body parts and generates a sense of ‘whole body’ concerns (ex: making

sense of where your chapstick is on your nightstand in the dark)

○ Cerebellum - involved in balance, motor learning, coordination and

stopping movements (50% neural processing occurs here)

○ Basal nuclei - involved in the initiation of movement, learning, and

memory (dysfunctions of this seen in individuals with Parkinson’s disease)

● Pyramidal tract neurons (PTN) are motor neurons that originate in the cerebral cortex and terminate in the spinal cord

○ Just remember that producing a greater force requires a larger neuron to fire (as seen in the monkey flexion experiment)

Lecture 3 Notes: “Overview of the Motor System” 

● Experiments outlining the responsibilities of the Association Cortices (supplemental areas)

○ Finger movement experiment

■ Primary motor cortex and primary somatosensory cortex activated for simple finger flexion

■ More neuronal activity takes place in the association motor area upon undergoing a more complex finger movement If you want to learn more check out What are the two types of endoplasmic reticulum?

■ Rehearsing the movement (visualization) activates the association cortex, which is now known to perform the “planning” of movements

○ Chimp experiment

■ A normal monkey pushes food through a hole and simultaneously catches the food in the other hand below the tube

■ A lesioned animal (lesion in the association area) lacks the ability to plan the movement and thus uses both hands to push the food, picking it up

once it falls to the ground

○ Pyramidal cells

■ Located within the fifth layer of the cortex, these cells have incredibly long axons that project down the spinal cord through the ventral horn to

coordinate movement

● Continuation of the “Movement Planning Committee”

○ Cerebellum

■ Continuously monitors/coordinates movements and makes necessary corrections if the movement is not ideal

■ Associated parts

● Spinocerebellum gets info from the spinal cord and descends

laterally and medially to the rest of the body

● Cerebrocerebellum sends info to motor and premotor cortexes for planning movements

● Vestibulocerebellum sends info to vestibular nuclei to coordinate

balance and eye movement

■ Experiment: Cerebellar damage

● Abnormal movement patterns involve inaccuracy in range and

direction

○ Basal nuclei

■ Receives information from the entire cerebral cortex (not just restricted to sensorimotor regions like the cerebellum)

● Involved with more than just movement; it’s role also includes

decision-making, limbic system function, and eye movement

● No downward projections within the brain stem; basal nuclei only

projects to other nuclei in the thalamus which forwards to the

cortex

■ Lesion in this region known to be the root source of Parkinson’s disease ■ Direct and indirect routes of the basal nuclei

● There are two umbrellas of nuclei involved in this pathway

○ Input nuclei (striatum) - activated by glutamate

○ Output nuclei (GABAnergic) - includes the globus pallidus

internal segment and substantia nigra pars reticulata

● Direct pathway (excitatory) - stimulates movement coordinated

by the thalamus by inhibiting it’s inhibitors

1. Glutamate activates the striatum

2. Striatum utilizes GABA to inhibit main output nuclei (globus

pallidus interna & substantia nigra reticulata)

3. When main output nuclei are inhibited, they cannot inhibit

the thalamus from coordinating movement (during the

indirect pathway, these nuclei release GABA to suppress

movement)

● Indirect pathway (inhibitory) - inhibits/suppresses movement

coordinated by the thalamus by activating it’s inhibitors

1. Glutamate activates the striatum

2. Striatum utilizes GABA to inhibit globus pallidus externa

(globus pallidus externa typically inhibits subthalamic

nucleus from stimulating output nuclei via glutamate)

3. Subthalamic nucleus can thus effectively stimulate the

output nuclei to inhibit the thalamus by releasing GABA

● Dopamine can be either inhibitory or excitatory depending on the

specific receptors on the neurons stimulated

● Methods to study the CNS

○ Historical methods include phrenology (shape/size), injury/lesions, histology and electrical stimulation

○ More recent methods

■ fMRI/PET/CAT - provides high resolution images of sites in the brain that utilize more oxygen when performing specific tasks

■ EEG - indicates electrical activity in the brain

■ Knock-out/in experiments - removing/adding genes result in change in cell function or behavior

■ Immunohistochemistry/PCR - Identifying certain proteins and other cellular components based on chemical composition

■ Optogenetics - insertion of channels activated by a laser

● Specific neurons altered/activated by light shone on that region of

the brain

● Neurons stimulated are called “AGRP neurons” (agouti-related

protein)

● Experimental result: mouse eats continuously upon

photo-stimulation of a particular AGRP neuron but has no desire

to eat before or after the laser is inserted

● The Multiplicity and Complexity of Intercommunication

○ Vast numbers of pathways stimulate a wide variety of neurotransmitters (ex: ACh, NE, Epi, glutamate, GABA) and neuropeptides (ex: VIP, substance P, Enk) ■ Primary NTs vary in different motor areas (each binds to its own specific receptor)

■ Each NT-receptor complex generates a specific effect on a particular ion channel or GPCR

● Example: ACh is the motor cortex opens Na+ channels

(depolarization) whereas ACh in cardiac muscle inhibits the

opening of Na+

○ Benefits include flexibility, redundancy, variability, & adaptability

● Two different types of Summation

○ Spatial summation

■ One way cells become active is through a simultaneous arrival of multiple different axons at different portions of the soma

■ These signals are added together to reach threshold (sometimes the sum will not reach this value, but in many other cases they do)

○ Temporal summation

■ The frequency that the action potentials are being received by target neurons within a short period of time

■ Increases the likeliness (or prevention) that the postsynaptic cell will reach threshold

● Relaying the Motor Command

○ The motor cortex sends signals down descending tracts known as the “corticospinal tract” and the “vestibulospinal tract” which is responsible for balance and posture

○ Delivery conducted by motor units

■ Motor unit: the smallest functional unit of force in the body

■ A motor unit consists of the motor neuron and the muscle fibers it

innervates

Lecture 4 Notes: “Motor Control - Continued” 

● Motor Units

○ Motor units are heterogenous/extremely variable

○ Size of the motor unit (# fibers it innervates) varies per muscle

○ Force vs. Precision

■ The larger the number of fibers, the greater the force

■ The fewer the number of fibers, the greater the precision

● Ex: quads vs. the human eye (quads possess a greater number of

fibers to conduct a larger force, but the human eye is more precise

with fewer motor units)

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