task 5

Question 1

gamma motor neurone

Answer 1

A neuron whose axons form synapses with intrafusal muscle fibers.

Question 2

three principles of sensorimotor system

Answer 2

1. it is hierarchy ordered
   > information flows from the highest level (association cortex) to the lowest (muscles)
   > sensorimotor system differs from sensory system in terms of information direction
   - efferent neurones: send impulses from CNS to limbs / organs
   - afferent neurones: receive information from our sensory organs (eyes, skin) & transmit it to CNS
   > functional segregation: sensory system contains functionally distinct areas that specialise in different kinds of analysis
2. motor output is guided by sensory input
   > sensory feedback: feedback provided within sensory system where information from sensory receptors is returned along the afferent pathways -> brain can monitor consequences of action
   - ballistic movements: occur too fast to be modified by feedback
3. learning changes nature & locus of sensorimotor control
   > sensorimotor learning: at first each individual response (movement) is performed under conscious control -> after ‘learning’ (practice / repetitions) these responses become more organised & are performed without conscious regulation

Question 3

sensorimotor association cortex

Answer 3

association cortex is at the top of sensorimotor hierarchy and is divided into two areas:
> posterior parietal association cortex &
> dorsolateral parietal association cortex

Question 4

posterior parietal association cortex

location / functions

Answer 4

consists of the portion of parietal neocortex posterior to primary somatosensory cortex (= postcentral gyrus)
> among its functions: perception & memory of spatial relationships / reaching / grasping / control of eye movement / direction of attention

> sensory input comes in and motor output goes out
-> as requirement, nervous system must know:
a. original position of parts of body that are to be moved
b. positions of any external objects with which body is going to interact during movement
it provides spatial information to guid behaviour & direct attention:
> input: receives information from three sensory systems that play role in localisation of external objects in space
- visual system -> occipital lobe
- auditory system -> superior temporal gyrus
- somatosensory system -> postcentral gyrus
> output: after receiving information, it sends it out to areas of motor cortex
- dorsolateral prefrontal association cortex
- areas os secondary motor cortex
- frontal eye field -> small area of prefrontal cortex that controls eye movement

Question 5

consequences of damaged posterior parietal cortex

Answer 5

apraxia: disorder of voluntary movement
> when told to make specific movements, patients have difficulty
> are able to perform them unconsciously though

contralateral neglect: disturbance of ability to respond to stimuli on side of body opposite to side of brain lesion
> egocentric (self-to-object): represents location of objects in space relative to the body axes of self
> allocentric (object-to-object): encoded information about location of object or its parts with respect to other objects -> location of object is defined relative to location of another object

Question 6

dorsolateral prefrontal association cortex

Answer 6

consists of portion of frontal cortex anterior to precentral gyrus
> among its functions: evaluation of external stimuli / initiation of voluntary reactions to them / motor sequences under conscious control (=newly learned)

> interacts with posterior parietal cortex to initiate voluntary movements
> input: receives information from posterior parietal cortex
> output: sends information to areas of secondary motor cortex / primary motor cortex / frontal eye field

dorsolateral neurones: what sends information out
> activity of them is dependent on several factors:
- location of objects
- characteristics of objects
- combination of them two
> these neurones tend to fire first in response -> suggests that decisions to initiate voluntary movement may be in this area of cortex

Question 7

consequences of damaged dorsolateral prefrontal cortex

Answer 7

confabulation: inability to distinguish a true memory from a false memory or from a memory inappropriate for context
> due that dorsolateral prefrontal cortex is important for metamemory -> it decides whether retrieved memory is plausible for given context, does strategic searching of memory store & temporally delivers memories

Question 8

secondary motor cortex

location / functions

Answer 8

located in posterior of frontal gyri extending medially
> among its function: storage of programs motor activity resulted from past experience / control of sequences of movement / control of spatial & postural orientation movements / control of bimanual movements

> > input: receives information from areas of association cortex (both posterior & dorsolateral prefrontal cortex)
output: sends information to the primary motor cortex & most areas of this cortex are thought to be involved in programming of specific patterns of movement

Question 9

secondary motor cortex

functional areas

Answer 9

8 areas in each hemisphere:
1. supplementary motor area (SMA), Area 6: wraps over the top of frontal lobe and extends down its medial surface into longitudinal fissure; anterior to primary motor cortex
> function: control of internally generated movement / programming specific sequences of movement after taking instructions from dorsolateral prefrontal cortex
> three different areas: SMA / preSMA / supplementary eye field

2. premotor cortex (PMA), Area 6: runs in a strip from the supplementary motor area to the lateral fissure; anterior to PMC
   > function: control of externally generated movement / learning & executing complex movement guided by sensory information
   > two different areas: dorsal & ventral PMA
3. cingulate motor areas: three small areas in the cortex of cingulate gyrus

Question 10

mirror neurones

Answer 10

neurones that fire when an individual performs a particular goal-directed hand movement or when the same individual observes the same goal-directed movement being performed by another
> neurones match observed behaviour with internal motor representation of that behaviour
> its discovery provided insight possible mechanism for social cognition: knowledge of the perceptions / ideas / intensions of others
> its existence has not been yet confirmed in human brain

Question 11

primary motor cortex

Answer 11

located in precentral gyrus of frontal lobe; often called M1 or Area 4
> function: controls parts of body that are capable of intricate movements (e.g. hands / mouth)

> major point of convergence of cortical sensorimotor signals

Question 12

consequences of damaged PMC

Answer 12

large lesions may:
> disrupt a person’s ability to move one body part independently of others
> produce astereognosis: inability to identify an object by active touch of the hands without other sensory input (visual / sensory)
> reduce speed / accuracy / force of movements

lesions do not eliminate voluntary movement: there are parallel pathways that fo not pass through the PMC to reach the secondary motor areas

Question 13

cerebellum

Answer 13

constitutes 10% of brain mass and 50%+ of brain’s neurones
> among its functions: precise control over movements / performance of everyday voluntary tasks such as waking & writing / essential to being able to stay balanced & upright

>

Question 14

cerebellum

Answer 14

constitutes 10% of brain mass and 50%+ of brain’s neurones
> among its functions: precise control over movements / performance of everyday voluntary tasks such as waking & writing / essential to being able to stay balanced & upright

> plays major role in motor learning (of sequences) in which timing is critical
- cerebellar circuits include a system that measures time -> feeds calculations to primary motor cortex -> sends signal to muscles
ensures that when one set of muscle initiates a movement the opposing set of muscles acts as a break -> body part in question arrives accurately at its target
cerebellum is systematically organised in lobes / columns / layers

> > input: receives information from:

• primary motor cortex
• secondary motor cortex
• descending signals from brain stem motor nuclei
• sensory feedback from motor responses from the somatosensory & vestibular systems

> > output: compares these sources and corrects ongoing movement that deviates from their intended course

Question 15

consequences of damaged cerebellum

Answer 15

> asynergia: loss of ability to maintain proper muscle coordination
loss of ability to adapt patterns of motor output to changing conditions
difficulty maintaining a steady posture -> attempts to do so lead to tremors
disturbances in balance / gait / speech/ control of eye movement
difficulty learning new motor sequences

Question 16

basal ganglia

Answer 16

Action plans that are made in the parietal and frontal brain areas are fed down to the basal ganglia and then routed, via the thalamus, back up to the SMA and PMC before execution.

> basal ganglia are thought to act as filter -> blocking plans that are inappropriate
-> e.g. inhibiting automatic, environment-triggered responses such as grasping food
neural loop: they receive cortical input form various cortical areas, including those areas known to have cognitive functions and transmit it back to cortex via thalamus

> > input: receive input from:
- primary motor cortex
primary somatosensory cortex
substantia nigra -> dopamine

> > output: transmit information to:

• primary motor cortex
• supplementary motor area
• premotor cortex

Question 17

consequences of damaged basal ganglia

Answer 17

> Parkinson’s disease: problems controlling speech / movement / posture
Huntington’s disease: disorder in which nerve cells in certain parts of brain waste away, degenerate
Wilson’s disease: disorder causing too much copper in body’s tissues
Dystonia: muscle tone problems
progressive supranuclear palsy: movement disorder from damage to certain nerve cells in brain
=> mostly movement disorders

Question 18

descending motor pathways

Answer 18

neural signals are conducted from the primary motor cortex to the motor cortex to the motor neurones of the spinal cord over four different ways:
> 2 pathways descend in dorsolateral region of the spinal cord -> control the independent limb movements:
- dorsolateral corticospinal tract
- dorsolateral corticorubrospinal tract
> 2 pathways descend in the ventromedial region of spinal cord -> control body movements & posture:
- ventromedial corticospinal tract
- ventromedial cortico-brainstem-spinal tract

similarity of those 2 groups:
> two major tracts; one descended directly in spinal cord / one descended in brain stem on neurones that in turn descend in spinal cord
> both are about voluntary movements

differences of 2 groups:
>

Question 19

dorsolateral pathways

Answer 19

1. dorsolateral corticospinal tract:
   > group of axons that synapses on small interneurones of spinal grey matter, which then synapse on motor neurones of distal muscles of wrist / hands / fingers / toes
   - direct pathway
   - most notable neurones: Betz cells: large pyramidal neurones of the PMC
2. dorsolateral corticorubrospinal tract:
   > group of axons that synapses on interneurones, which then synapses on motor neurones that project to the muscles of arms / legs
   - indirect pathway

Question 20

ventromedial pathways

Answer 20

1. ventromedial corticospinal tract:
   > group of axons that synapse on muscles of upper leg / trunk
   - direct pathway
2. ventromedial cortico-brainstem-spinal tract:
   > group of axons that synapse on muscles of trunk / limbs via four brain stem structures:
   - tectum: receives auditory / visual information about spatial information
   - vestibular nucleus: contains motor programs that regulate complex movements such as walking / swimming / jumping
   - motor nuclei: control muscles of face
   > indirect pathway

Question 21

sensorimotor spinal circuits

Answer 21

lowest level of sensorimotor system hierarchy
> consists of:
- spinal circuits (capable of independent functioning)
- muscles (controlled by spinal circuits)

Question 22

muscles

motor units

Answer 22

each motor unit (= smallest unit of motor activity) comprises a single motor neurone & all of individual fibres it innervates

> when motor neurone fires -> all muscle fibres of its unit contract together
those with fewer fibres (fingers / face) allow higher degree of selective motor control
- lowest number of fibres connected to motor neurones = highest degree of selective muscle control
- muscles can only contract in one direction
two types of skeletal muscle fibres:
1. fast:
- contract and relax quickly (e.g. jumping)
- fatigue quickly because of poor vascularising (= few blood vessels, giving them a pale colour)
2. slow:
- slower and weaker (walking)
- able to sustain contraction longer -> rich vascularising (= much redder)
each muscle has both, fast & slow fibres

Question 23

muscles

motor end-plate / categories / contraction types

Answer 23

motor end-plate:
> acetylcholine (released by neurones are neuromuscular junctions) activates it on each muscle fibre -> causes muscle to contract
- contraction is only method muscles have for generating force
- motor pool: all of motor neurones that innervate the fibres of a single muscle

skeletal muscles belong to one of two categories:
1. flexors: act to bend or flex a joint (biceps)
2. extensors: act to straighten or extend a joint (triceps)
also:
> synergistic muscles: two muscles whose contraction produces the same movement (flexor + extensor)
> antagonist muscles: two muscles that act in opposition (biceps vs. triceps)

muscle contraction can be of two types:
1. isometric contradiction:
> activation of a muscle that increases tension that it exerts on two bones without shortening and pulling them together
2. dynamic contradiction:
> shortening muscle and pulling it together
> tension in muscle can be increased by:
- increasing number of neurones in its motor pool that are firing
- increasing the firing rates of those that are already firing
- combination of two changes above

Question 24

tendon

Answer 24

end of muscle which is attached to the bone

Question 25

receptor organs of tendon sand muscles

Answer 25

activity of skeletal muscles is monitored by two types of receptors:
1. Golgi tendon receptor:
> embedded in tendons
> connect each skeletal muscle to bone
- respond to increased muscle tension but not sensitive to changes in length
- provide the CNS with information about muscle tension
- protective function: when contraction is extreme & there is risk of damage -> Golgi tendon organs excite inhibitory interneurones to relax muscle & avoid damage

2. muscle spindles:
   > embedded in muscle tissue itself
   - respond to changes in muscle length but not changes in tension
   - each has its own intrafusal muscle that is innervated by its own intrafusal motor neurone
   -> without its intrafusal motor input muscle spindle fall slack each time its skeletal muscle (= extrafusal) contracts -> would disable it to respond to slight changes in extrafusal muscle length

Question 26

stretch reflex

Answer 26

involuntary contraction of a muscle induced by a brisk stretch of the muscle.
=> not controlled by higher functioning center (brain) and is monosynaptic response transmitted through spinal cord

> automatic / subconscious responses to changes within or outside the body
reflexes function to maintain homeostasis (= autonomic reflexes) [incl. breathing / blood pressure regulation / heartbeat]
- other reflexes: carry out automatic things we don’t need to think about to perform (swallowing / sneezing / coughing / vomiting)

example reflexes:
> patellar tendon reflex
> knee-jerk reflex

Question 27

spinal reflex

Answer 27

reflexes that maintain posture and truncal balance

Question 28

brainstem reflexes

Answer 28

eyes movement reflexes

Question 29

patellar tendon reflex

Answer 29

> sudden stretch of thigh muscle = stretch of its muscle stretch receptors
receptors initiates AP’s
AP’s getting carried from stretch receptors into spinal cord by spindle afferent neurones
AP’s excite motor neurones in ventral part of spinal cord
as response: AP’s sent back to muscle
compensatory muscle contraction and sudden leg extension

• used by doctors to test spinal-nerve function

Question 30

knee-jerk reflex

Answer 30

variant of stretch reflex in which stretching of tendon below knee leads to upward kick of leg

Question 31

withdrawal reflex

Answer 31

spinal reflex intended to protect body form damaging stimuli
=> polysynaptic reflex causing stimulation of sensory / association / motor neurones

> automatic withdrawal of an extremity (hand) from a painful stimulus
inhibitory signals arising from the brain can prevent the withdrawal reflex from e.g. causing the person to drop the casserole
- brain recognises consequences of dropping something
-> these neural circuits send information to spinal cord that prevents withdrawal reflex

Question 32

reciprocal innervation

Answer 32

antagonistic muscles are innervated in a way that permits a smooth, unimpeded motor response
= when one is contracted the other one relaxes

> ‘bad news’ of suddenly painful event triggers excitatory & inhibitory responses
- movements are quicker when these two responses work simultaneously
there are two effects:
1. excitatory interneurones excite motor neurone of flexor
2. inhibitory interneurones inhibit motor neurone of extensor

how it works:

1. during withdrawal reflex sensory neurones conduct AP’s from pain receptors to spinal cord
2. sensory neurones synapse with excitatory interneurones that are part of withdrawal reflex
3. collateral branches of sensory neurones als synapse with inhibitory interneurones that are part of reciprocal innervation
4. inhibitory interneurones synapse with alpha motor neurones supplying extensor muscles causing them to relax & not oppose flexor muscle of the withdrawal reflex which are contracting

Question 33

alpha motor neurones

Answer 33

Lower motor neurones whose cell bodies are found in the anterior horn of the spinal cord and whose axons travel down to the body to innervate skeletal muscle to cause muscle contraction

Question 34

recurrent collateral inhibition

Answer 34

> negative-feedback system
prevents rapid, repeated firing of the same motor neurone
- to accomplish: one branch of axons loops back toward cell body of neurone and communicates with inhibitory Renshaw cell
- Renshaw cell in return inhibits neurone

Question 35

Renshaw cell

Answer 35

Neurone that inhibits motor neurones near the spinal cord.

Question 36

spinal cord

Answer 36

long, tube.like structure that begins at the end of brainstem & continues almost till bottom of spine

> consists of nerves that Carr incoming & outgoing messages between brain & rest of body
centre for reflexes (knee-jerk reflex)
covered in three layers of tissue (= meninges)
- spina cord & meninges are contained in spinal canal (runs through centre of spine)
is composed of individual back bones (26) called vertebrae
- skull protects brain / vertebrae protects spinal cord
- vertebrae is made of cartilage (reducing forces generated by movements)
- vertebrae + disks of cartilage = vertebral column (=spinal column)

Question 37

spinal cord

grey & white matter

Answer 37

consists of grey & white matter

butterfly shaped center of cord -> grey matter:
> ‘front wings’ contain motor nerve cells (= neurones):
- transmit information from Brian or spinal cord to muscles
> ‘back wings’ contain sensory nerve cells:
- transmit sensory information from other parts of body through spinal cord to brain

surrounding white matter contains:
> ascending tracts: columns of nerve fibres that carry sensory information to brain from rest of body
> descending tracts: columns of nerve fibres that carry motor impulses from brain to muscles

Question 38

spinal nerves

Answer 38

emerging from spinal cord between vertebrae are 31 pairs of spinal nerves

> one at front of spinal cord: motor or anterior root
- motor roots carry commands form brain & spinal cord to other parts of body (particular to skeletal muscles)
one at back of spinal cord: sensory or posterior root
- sensory roots carry information to the brain from other parts of body
cauda equina: spinal cord ends about 3/4 of the way down of spine but a bundle of nerves extends beyond the cord
- carries nerve impulses to and from legs

Question 39

central sensorimotor programs

definition / characteristics

Answer 39

central sensorimotor program theory suggests that all but the highest levels of sensorimotor system have certain patterns of activity programmed into them and that complex movements are produced by activating appropriate combinations of these programs

> once activated each level of sensorimotor system is capable of operating on the basis of current sensory feedback without direct control of higher levels

1. central sensorimotor programs are capable of motor equivalence:
   > same basic movement can be carried out in different ways involving different muscles
2. sensory information that control central sensorimotor programs is not necessarily conscious:
   > e.g. optical illusions
3. central sensorimotor programs can develop with our practice :
   > CSP for many species typical behaviours are established without explicit practice of behaviour
4. practice can create central sensorimotor programs:
   > response chunking: practice combines CSP’s that control individual response into programs that control sequences (chunks)
   > shifting control to lower levels: frees up higher levels to deal with more esoteric aspects of performance & permits great speed ( cerebellum & basal ganglia are mechanisms to ensure that programs of action at different levels of the hierarchy are well coordinated & effective

Question 40

motor disorders

Answer 40

can be divided into two principal groups
1. hyperkinesia (overactivity):
> includes wide range of motor disorders
- from involuntary, slow shaking to uncontrollable ticks (rapid, disjointed movement / sounds)
2. hypokinesia (too little movement):
> concludes general slowness of movement (=bradykinesia) / ‘freezing’ / inability to begin a movement or involuntary arrest of a movement / postural instability (= loss of ability to maintain posture)

Question 41

consequences of damage to brain areas

Answer 41

primary motor cortex:
> paralysis
> weakness on opposite side of body from lesion

supplementary motor area:
> may prevent planning of movements
> ‘blocked’ pathways from here to motor cortes -> forms of paralysis

parietal area:
> misjudgements of distance / position / speed of objects

midbrian: 
> tics 
> block voluntary movements 
injury to substantia nigra: 
> reduces ability to initiate movement 

cerebellum:
> prevent fine timing of movements
> can cause tremors

spinal cord:
> paralysis
> loss of motor control