neurobiology final (motor system and memory)

Neural control of motor systems is a _______ process

integrative

___________ and ___________ require that we respond appropriately to opportunities and threats

survival, reproduction

sensory systems ________, _________, ________, and ___________ information (both internal and external)

receives, transduces, transmits, and processes

the brain processes sensory input to do what?

construct detailed representations of the environment (external and internal)

sensory systems do what?

contribute to our perception of the world

what does the motor system do?

acts on sensory information to produce an appropriate response, provide the ability to respond to sensory information

5 types of motor control

simple reflex, complex interactions requiring cognitive processing, unconscious, involuntary actions, speech and conversation, simple movements

What is volition?

some components of the motor system are under voluntary control

components of motor control

volition, coordination of signals that ctrl multiple mm groups, proprioception, postural adjustments, sensory feedback, compensation of physical characteristics, unconscious processing, adaptability

coordination of signals that control multiple muscle groups

motor system determines the forces and coordination at joints to produce smooth movement

proprioception

starting position of limb is critical for different patterns of muscle activation. Provide info on muscle length and forces applied to determine joint position and other variables needed for smooth motion

postural adjustments

compensate for changes in body center of mass as movement happens

sensory feedback

allows for corrections in movements during motion and modification to motor program to improve other motions

compensation for physical characteristics

characteristic of the object, muscles, bones, and joints, must be known in order to exert force on an object

unconscious processing

some movements can be done automatically without higher control, like walking

adaptability

the motor system can learn new skills and adapt to changing development and goals

motor control requires sensory input for…

involuntary reflexes and planned movement

motor system is organized in two ways

by task/functionally and hierarchically

how are hierarchical motor controls group?

level of conscious control and complexity

higher-order areas

when to act, sequence of actions, coordinating limbs

low-order areas

determine force and velocity of muscles, coordinates movements for posture changes

sympathetic division of autonomic nervous system

fight or flight

parasympathetic division of autonomic nervous system

rest and digest

how is the primary motor cortex organized?

somatotopically

what regulates descending motor tracts and side loops

parallel pathway from the motor cortex

basal ganglia

relay commands from motor cortex to lower levels

spinal cord

low level functions, site of motor neurons, interneurons, and neural circuits that process motor control

circuits in the spinal cord

execute low-level commands that make the forces on muscles to adapt movements, complex circuitry for rhythmic behaviors, enables motor cortex to plan movement, adapt sequences, and coordinate body motion

where does information enter the motor pathway

sensory/afferent neurons

receptors provide

sensory info about the current state of muscles and limbs

proprioceptors provide

info on position in space of muscles and tendons

muscle spindle fibers

changes in length of muscle

golgi tendon organs

detect changes in force and generate signals about force

alpha motor neurons

cause muscle contractions that generate movement by releasing ACh to initiate action potentials

location of motor neurons that control limb and body motion

anterior horn of spinal cord

location of motor neurons that control head and facial movements

motor nucleic of brainstem

how does the motor system communicate with muscles?

motor neurons

complex circuits that perform complex information processing

motor neurons are more than pathways

Motor neurons can integrate inputs from large numbers of neurons and calculate proper outputs due to what morphology?

highly branched dendritic trees

motor neuron pools

neurons clustered in columnar, spinal nucleic

neurons in a singular motor pool innervate…

they innervate a singular muscle (one-to-one relationship)

one neuron can innervate many muscle fibers, but

each muscle fiber can only be innervated by ONE neuron

motor unit

the motor neuron and all muscle fibers it innervates

innervation ratio

number of muscle fibers innervated by a motor unit

innervation ratio for delicate movements

small, each motor neuron innervates a small number of fibers

innervation ratio for coarse movements

high innervation ratio, more muscle fibers per neuron

what controls the amount of force exerted by muscle fibers

motor neurons

what regulates motor neuron activity and muscle force

rate code and size principle

Rate code

increase AP firing by motor neurons cause increase in force from a motor unit

tetanus

when a muscle cannot increase strength of contraction even if APs keep firing

what muscle result does one action potential from motor neuron cause

twitch and then relaxation

how do we get stronger muscle contractions?

the motor neuron must fire more action potentials before they relax to baseline, so they sum

size principle

smaller motor neurons are recruited to fire before larger ones

why are smaller motor neurons recruited first?

Ohm’s law, less surface area = more resistance

surface area and membrane resistance are _________ correlated

negatively correlated because of number of ion channels

small neurons reach firing threshold before large neurons when…

there are low levels of synaptic currents. membrane potential of large neurons will be reached as current increases.

different types of muscle fibers are innervated by…

small, intermediate, and large motor neurons

small neurons innervate…

slow twitch fibers (low force, maintained, like posture)

Intermediate sized neurons innervate…

fast twitch, fatigue resistant fibers

large neuron innervate…

fast twitch, fatigable muscle fibers

motor end plate

synapse between motor neurons and muscle fibers

end plate potential

excitatory post-synaptic potential

how does homeostasis work in relation to motor system?

adjusts control of motor system based on sensory input

movement is a dynamic process that requires constant communication between…

sensory input and motor output

which part of the brain deals with posture and balance

cerebellum

muscle spindle morphology and function

6-8 specialized intrafusal fibers within muscle, signal length and velocity

what are extrafusal muscle fibers

the fibers that enable the muscle to contract and do work

muscles for fine movement have…

more spindles than muscles for coarse movement

3 types of muscle spindle fibers

nuclear chain, static nuclear bag, dynamic nuclear bag

nuclear chain fibers

nucleic aligned in a single row, signal length

static nuclear bag fibers

nuclei in a bundle, signal length

dynamic nuclear bag fibers

nucleic form bundle, signal rate of change and length

which type of spindle is the most abundant in muscles?

nuclear chain fibers

What type of channels are the receptors on muscle spindles?

mechanically (stretch) gated receptors

group 1a afferent neurons

wrap around all 3 intrafusal fibers, have annulospiral endings that provide info on length and velocity

group II afferent neurons

innervate only the ends of nuclear chain and static bag fibers and have flower spray endings. provide info on muscle length

which afferent spindle neuron fires at a high rate during stretch

group 1a bc they encode velocity

What is group II afferent neurons doing during muscle stretch?

only encoding static length of the muscle fiber

Gamma motor neuron

causes weak contractions in the muscle spindle to keep it taut in order for afferent neurons to accurately send signals about muscle length

do muscle spindle contractions contribute to muscle extrafusal force?

no

gamma motor neurons innervate

the contractile components at the end of intrafusal fibers

why must muscle spindles remain taut?

to properly detect stretch over a range of muscle lengths and so afferent neurons can fire during stretch after a period of contraction

When do afferent 1a and II neurons fire and when do they not fire?

they fire when the muscle and muscle spindle is stretched and stop firing when the muscle contracts, however the spindle is never loose

When CNS sends signals to alpha motor neurons to contract the muscle, it also sends signals to…

gamma motor neurons to initiate weak contractions to muscle spindles

Alpha-gamma coactivation

coordinated activity of alpha and gamma motor neurons

golgi tendon organs

encode information about force applied to muscle

where is the golgi tendon organ located and what is it made of?

in between muscle and tendon, made of a capsule of collagen fibers

What innervates the golgi tendon organs?

group 1b primary afferent neurons, special endings woven between collagen fibers

How does the golgi tendon organ encode force changes?

force applied to muscle squeezes collagen fibers together and distorts the membrane of the 1b afferent neuron, depolarizing it and firing an AP (force gated)

reciprocal inhibition

muscle pairs work together to move/work, when one is signaled to contract, the other of the pair must be inhibited from contracting

stretch/myotatic reflex

alpha motor neuron signals bicept to contract, 1a inhibitory interneuron inhibits another alpha motor neuron from controlling the triceps

flexor reflex

initiated by pain receptors, coordinates activity at multiple joints

what kind of neurons are group III afferent?

nociceptors

renshaw cells

inhibitory interneurons that create a negative feedback loop to regulate firing rates of motor neurons

spinal reflexes can be modulated by…

descending brain stem and cortical pathways

hypersensitive flexor reflex

facilitates reflex when anticipating unpleasant sensory experience (touching hot iron)

suppressed flexor reflex

inhibits reflex when sensory stimulus initiates reflex (not dropping the hot pan)

corticospinal system controls:

motor neurons and interneurons in the spinal cord

corticobulbar system controls:

brainstem nuclei that innervate cranial muscles

flexor-extensor rule

motor neurons that innervate flexor muscles are posterior to motor neurons that innervate extensor muscles