Muscles, motor neurons, spinal cord

_____: elastic fibers that can change in length and tension

______: parts of the body that can move

Movement comes from changes in the _______ that controls an _______.

muscles

effectors

muscle/muscle group, effector

Muscles: attach to the skeleton in ______ pairs

Enable effector to ______ or _______.

antagonistic

flex or extend

Interaction between muscles and the nervous system.

______ ______ ______ release Ach that bind to receptors on the muscle, causing it to contract.

alpha motor neurons

 [image]

Spinal reflex: highest/lowest level of input to alpha motor neurons

Does/doesn't require the brain for relex.

______  provide input to alpha motor neurons within the spinal segment.

cortical and subcortical structures via dorsal/ventral columns of the spinal cord.

outputs to alpha motor neurons and interneurons enable _____ _____

lowest

doesn't

interneurons

ventral

motor control

Inhibiting reflexes to allow voluntary movement:

When we flex our arm, the biceps _____ causing the triceps to ______.

A reflex would cause the triceps to _____, restoring the arm to its _____ position.

Voluntary movements involve both _____ the agonist muscle and ____ the antagonist muscle via spinal cord interneurons.

contract, extend

contract, normal

exciting, inhibiting

Role of Spinal Cord and PNS

Sherrington (1895): disconnected _____ and _____ from the brain.

______ were left intact (in fact, they were exaggerated due to decreased inhibition from the brain )

Animals could/couldn't walk.

alpha motor neurons and interneurons

reflexes

could

Role of Spinal Cord and PNS:

Brown (1911): disconnected _____ and _____ from the brain.

Sectioned the _____ to prevent sensory information from entering the spinal cord.

Animals could/couldnt walk.

Neurons in the spinal cord can/cannot generate an action sequence without input from the brain or sensory feedback.

alpha motor neurons and interneurons

dorsal roots

could

can

Role of Spinal Cord and PNS:

Taub and Berman (1968): movement does/doesn't require sensory feedback

Severed ___ ___ carrying sensory information to the brain from one arm or both arms.

If sever sensory input from one limb, _______.

If sever sensory input from both limbs, ______.

Spinal cord neurons can/cannot produce movement w/o input from the brain or other limbs.

doesn't

dorsal roots

animal will not use that limb.

animal will use both

can

Central Pattern Generators:

Neurons in the ____ ____ that can generate action sequences w/o input from the brain or sensory feedback.

Allow unlimited/limited set of special movements.

Hierarchy for motor control: high-level motor structures ____ ____

low-level structures translate the _____ into_____

spinal cord

limited

issue commands

command, movement

Brain areas involved in motor control:

Cortical Regions:

Prefrontal cortex (4), frontal eye fields (3+ inputs, 1), SMA and pre-motor cortex (2 inputs, 1, 1 output), primary motor cortex (2 inputs, 2, 1 output), posterior parietal cortex (2 codes, 3 areas of control, 1 output)

PFC: planning, working memory, attention, high-level control of behavior

FEF (BA8): inputs from PFC, superior colliculus, posterior parietal cortex (PPC) and many other areas... helps control eye movements

SMA and pre-motor: inputs from PFC and PPC, represents actions at abstract levels (context of a movement), project to primary motor cortex

 Primary motor cortex (BA4): produces movement, inputs from premotor and SMA, distorted representations of body parts, projects directly to alpha motor neurons in spinal cord

PPC: codes locations of objects in environment and how to interact with them, seperate areas that mediate eye movement - arm movement - hand movements, project to premotor cortex

Motor control hierarchy: Can we activate a process at the lowest level and execute it, example?

Can movement occur without feedback?

Do both cortical and subcortical regions contribute to motor control?

Fact that movements can occur without feedback argues for central representation of movement.

Central pattern generators:  Brain doesn’t have to control all aspects of walking.  It only has to activate the program of walking that is stored at a lower level.

Movements as guided by a "motor program".

Both cortical and subcortical contribute.

Motor programs not always linked to specific effectors because they are _____representations of action goals.

Can explain how some people can show excellect transfer of ____ ____ from one output system to another. 

Mental Practice can be _____, learning is/isn't in the muscles.

Abstract

Motor Skills

Useful, isn't really

Endpoint Control:

Evidence from monkey study and resistance

Action representations: neurons in motor cortex seem to code for _____ of movement rather than _____.

 Monkey moves lever from center to one of 8 locations, what did they find?

Population coding in motor cortex, directional tuning in M1 cells is _____.

Single cells do not code the ______ direction of movement, instead direction of movement is coded by _____ of _____.

direction, location

Found that neuron preferes downward movement and doesn't care about final destination.

broad, cells respond well to several directions of movement

exact, populations of neurons

Each cell's response in a particular movement can coded as a ______.

_____ _____: plotted in the cell's preferred movement direction

_____ _____: firing rate for target direction

 _____ _____: actual movement is coded by the summed activity of many cells 

vector

vector direction

vector length

population vector

Population Vectors:

Patient M.N.: quadradriplegic

record activity in motor cortex when M.N. ____ moving a cursor on the screen and explanation

4 other abilities of M.N.

Movement can reflect the outcome of a _____ between possible responses

imagines, found which cells fire for different directions of movement, able to tune machine to move cursor for imagined movement (up,down, left, right)

use email, draw pictures, play ping-pong, control robotics to reach and grasp objects

competition

Parietal Neurons Code for _____

Optic ataxia: ____ deficit

(Can or cannot) ___ recognize objects but ___ use visual information to guide actions.

 ____ Lesion

Location

Grasping

Can, Cannot

Parietal

Do different neurons code space in eye-centered/head-centered/arm-centered coordinates?

Premotor cortex: abstract representation of actions

ventral Premotor (F5) neurons code ____ actions (____,____,____) rather than ____ movements.

Mirror neurons in _____ cortex fire when ____ performs an action and when they _____ _____ performing that action.

Mirror neurons _____ to a specific action, regardless of whether the final hand-object interaction is visible.  Finding of object grabbing experiment with object visible, object behind screen, or no object.

Yes

Specific (grasping, holding, tearing), single

Premotor cortex, an individual, watch someone

respond, mirror neurons mediate action understanding.

Motor planning versus execution:

____ combinations of areas activate for ____ types of motor tasks:

simple finger movement: _

sequence of finger movements: _

imagery of movements:_

different, different

M1

M1 + SMA + PFC

SMA

The will to act, including speech action, required for an ______ _____ _____, comes from the prefrontal lobe which is engaged in deciding what action to perform and how to execute the action, which you need to decide before you can decide when to exectute the action.

______ ______ ______ ______ _____ do not appear to require prefrontal areas.  Lateral premotor cortex is engaged for externally triggered actions but not involved in internally generated actions.

Internally generated action

Externally triggered actions towards objects

Externally triggered movements (visually guided): external loop (3 components), monkey experiment

Self-guided/ internally guided movements (previously learned): internal loop (3 components), monkey experiment

Motor Learning: learning a new movement sequence vs. performing a learned movement sequence

Parietal Cortex, Cerebellum, PMC, 3 buttons light up in succession and monkey presses each button in turn

Prefrontal Cortex, SMA, Basal Ganglia, monkey presses buttons in a learned (memorized) sequence

learning new is mostly external and performing a learned is mostly internal

Movement disorders

Hemiplegia: loss of motor control on _____ side of the body following damage to PMC (primary motor cortex)

Reflexes often _____ due to reduced inhibition from the cerebral cortex.

contralateral

stronger

________:

Motoric problems that cannot be attributed to hemiplegia, motoric problems of weakness, sensory loss, or motivation

Tests show impaired ______ of goal-directed gestures.

(saluting, pretending to manipulate an object)

Show impaired perception of ____ ____ ____.

Often observed following damage to ___ ___ ___.

Apraxia

Pantomiming

Other people's gestures

Left parietal cortex

Two Types of Apraxia

_____: patient appears to have rough sense of the action, but has trouble executing it properly (knocking fist into head when asked to mime hair brushing)

______: patient's knowledge about the intent of an action may be disrupted (using comb instead of toothbrush)

Ideomotor

Ideational

______ ______: too much movement

Description: -loss of striatal neurons

- cause is genetic, no cure

-progressive and degenerative

3 Symptoms

Huntington's Disease

Involuntary choreoform movements

Cognitive problems- memory, problem-solving

Emotiona and personality changes

______ ______: too little movement

Description: -loss of dopaminergic neurons in substantia nigra

-unknown cause

-treated with dopamine  precursors that can cross the blood-brain barrier (L-dopa) and deep brain stimulation(DBS

6 Symptoms

Movement deficits are most pronounced when movement is guided by _____ cues.

Parkinson's Disease

Impaired initiation of movement

Tremors

Muscular rigidity

Very slow movements

Problems with posture, balance

Progressive and degenerative

Internal

When receiving no input, the basal ganglia _____ the cortex and _____ movement.

When receiving input it affects two output pathways: __1__ , __2__

1: inhibits the GPi and allows movement

2: excites the GPi and inhibits movement

Which takes longer to traverse and what is effect?

inhibit, prevent

1: direct pathway

2: indirect pathway

indirect, movement occurs and is quickly followed by the inhibition of that movement

Basal ganglia helps resolve response competition in 2 ways:

Strong ____ baseline allows cortical representations of possible movements to become activated without engaging the muscles.

As a specific signal ____ ____, the _____ signal is reduced for specific neurons.

inhibitory

gains strength, inhibitory

Function of the Basal Ganglia:

____ ____ ____

in the motor domain, problems initiating a movement can be seen as a set shifting deficit.

Parkinson's patients get stuck in one position or posture and cannot shift to another.

Hypothesis: the ___ ___ may playa general role in set shifting in both the ___ and the ___ domains.

set shifting hypothesis

basal ganglia, motor and the cognitive domains

Alpha Motor Neurons, Basal Ganglia, Cerbellum, Prefrontal Cortex, Parietal Cortex, Pre-SMA/SMA, Premotor Cortex, Primary Motor Cortex, Spinal Cord

____: action planning (internally guided movements)

____: codes for object locations in space and how to interact with objects.

_____: specify actions and action sequences to be carried out by motor cortex

____: controls externally guided movements and represents the movements of others

____: descending motor neurons

____: input from PFC via thalamus, modify action plans, send info back to PFC, control action timing

____: motor coordination, timing of actions

____: contains central pattern generators that initiate movement sequences by controlling multiple muscles

____: directly excite muscle fibers

Prefrontal cortex

Parietal cortex

Pre-SMA/SMA

Premotor cortex

Primary motor cortex

Basal ganglia

Cerebellum

Spinal cord

Alpha motor neurons