Motor System Flashcards
What are movements of the skeletal muscles and functions of the smooth muscle, cardiac muscle, and glands controlled by
- skeletal muscle = somatic motor system
2. Smooth muscle, cardiac muscle, glands = autonomic system
What anatomy is in the somatic motor system?
What is important about all these structures?
- Motor cortex in telencephalon = highest centre. Involved with organising fine voluntary movements
- Basal nuclei (corpus striatum) = planning motor function
- Thalamus
- Red nucleus and substantia nigra in the mesencephalon, midbrain = generate motor output
- Cerebellum: compare what planned to do with what happened
- Nuclei in pons and medulla oblongata
- Spinal cord
- Cranial and spinal nerves
- efferent spinal nerves which supply skeletal muscle via NMJ
- ## Skeletal muscleAll these structures must be functioning for a muscle to do what you want it to do
What influences what in the somatic motor system?
- Higher centres influence lower
When do and how come skeletal muscle act in isolation?
Even though the higher centres influence the lower, spinal/ cranial nerves and the skeletal muscles they innervate also communicate directly with the sensory system and can act in isolation (reflexes)
Diff types of SOMATIC motor neurons
- Upper motor neurons (take info from brain to lower motor neurone)
- Lower MN (synapses with muscle via NMJ)
What is the highest centre involved in motor system
Motor cortex which is involved in organising really fine, complex movements
What is the role of the Basal nuclei (corpus striatum)
involved in planning and decide what movement going to do
Role of thalamus
relay point for lot of functions.
Involved in sending info to areas where motor output is generates from
Red nucleus and substantia nigra
- in midbrain (first part of brain stem)
2. generate motor output
Cerebellum
- involved in coordination and comparing what planned to do with what actually happened
Nuclei in pons and medulla oblongata
- Nuclei in very back of brain in brain stem
2. contain nuclei that are cell bodies that can generate motor output
Upper motor neurones
- contained entirely within the CNS, cell bodies in the motor cortex or motor nuclei of other areas of the brain
- synapse directly on lower motor neurons or via interneurons
- Initiate, regulate, modify and terminate LMN activity required for voluntary movement of skeletal muscle
- not required for muscle function*
Lower motor neurons
- cell body in the CNS (brain or spinal cord)
- axon in the peripheral nervous system. = form NMJ
- Run via spinal or cranial nerves to innervate skeletal muscle
- If AP in LMN = contraction
- Functionality regulated by UMN but can fire without UMN input = REFLEX = INVOLUNTARY
- Muscle can onyl contract with intact LMN
What are 2 diff pathways UMN can run?
- Run entirely in brain = area of brain to cell bodies for a particular cranial nerve
- from brain, down spinal cord to synapse
- whole job to tell LMN what to do
- Initiate, regulate, modify and terminate movement
- needed for any kind of movement
- Not required for muscle function
- Exitatory or inhibitory (more)
What is different about the UMN synapsing for particular vs general movement?
- Specific = UMN synpase directly onto LMN
2. supplying several diff muscles at once = via internerone
Where do the UMN that are supplying LMN for flexor and extensor muscles
- UMNs to spinal LMNs supplying flexor muscles travel in the lateral funiculi (outsides) of the spinal cord.
- UMNs to LMNs
supplying extensor muscles travel in the ventral funiculi of the spinal cord. - Helps to localise lesion e.g. if issue with extensor muscles
LMN for fore and hind limb location
- forelimb = cervical intumescence (C6-T2)
- ## Hindlimb = lumbar intumescence (L4-S3)so thick as loads of motor cell bodies
Why does muscle feel slightly hard even when not contracting?
- LMNs have constant sub threshold depolarisation so ACh is being released.
- If lost LMN funciton or under deep anaesthesia = flacid
What clinical sings would you except to see in hindlimbs of an animals which had damage to spinal cord in the region of the lumbosacral intumescence
- Lost muscle tone in muscles of hind limb
- no reflexes
- just to motor = can still feel just not do anything about
- won’t be able to walk as can’t make muscle move
- bulk of muscle would atrophy v quickly
What is a motor unit
LMN, NMJ and skeletal muscle fibres
How would damage to radial nerve affect the function of the muscle supplied by this nerve
- Radial nerve = LMN in terms of motor function
- atrophy, loss of reflexes, loss of tone
- doesn’t matter where along nerve damage occurs = same sing
What is happening is super rigid
- Inhibitory UMN help to reduce output of LMN = upright but not stiff.
- Damage to UMN inhibitory as muscles can still contract and not being told not to.
- UMN modulate amount of movement and contraction
What are reflexes and what do they require
- Sensory input leading to motor output
2. don’t require input of UMN
Injury to UMN
- Exaggerated or normal movmeent as Lot of UMN = inhibitory
- Tone inc as lose inhibitory
- Atrophy = less able to move so muscle dec
- remain strong as still LMN
Injury to LMN what happens
RAT
- Reflexes reduced/ absent
- Atrophy (loss of bulk)
- Tone loss
dog with prolapsed intervertebral disc at C7 what effect would you expect to see in fore and hind limbs and why?
Functional region = cervical intumescence = lot of nerves
- Fore = no input from UMN because LMN damages as cell bodies for LMN supplying fore limb. Can’t move voluntarily at all. No reflexes, atrophy, tone loss.
- hind = cell bodies for LMN in hind = lumber intumescence = UMN sings in hing. reflexes present, tone normal. But movement might be exaggerated s lost inhibitory bit. Movmeent also bit wild
Where are cell bodies for forelimb LMN lcoated
C6-T2
You can only have a reflex if you have booooth:
- sensory input
2. motor output
How can somatic reflexes be described anatomically?
- monosynaptic = 1 synapse = sensory input synapse directly onto monot
- polysynaptic = synapse via a interneurone or synapses on several mtoor outputs
- send info to higher centres
- Ipsilateral = occurs on same side of stimulus
- Contralateral = cause effect on other side of stimulus
- Intrasegmental = WITHIN = communication between sensory and motor happens within a spinal segment
- Intersegmental = BETWEEN sensory input occurs within one segment and results in motor output in other spinal segments
What is the stretch receptor in patella reflex?
- Stretch receptor which is called a muscle spindle
What are muscle spindles roles?
How are they arranged
- sensory stretch receptors
- Tells about positions of muscles
- Arranged throughout INTRAFUSAL muscle fibres arranged in parallel (rest of muscle fibres = extrafusal!)
How are muscle spindles innervated?
- by a sensory neuron - if muscle stretched, sends info up
2. also innervated by motor nerve as have to be able to contract along with the rest of the muscle
Golgi tendon organ
- another receptor in skeletal msucle
- in tendon
- arranged in series with muscle
- so when muscle contracts GTO gets stretched = detects contraction!
- sensory input
What effect does the fact that the GTO are arranged in series have to on the outcome
- When muscle contracts GTO stretched
- senseory input back up to spinal cord
- reduces strength of muscle contraction so can’t contract muscle so strong the tendon is hoiked off the bone
- protects muscle against over contraction
How is the sensitivity of the muscle spindle maintained when muscle fibres contract?
- muscle contracts = shortend
- Ends of intrafusal muscle fibres shorted too
- so even when msucle is shorter, muscle spindle stays sensitive = not lose and floppy!
What is happening in the patella reflex
- Bash patella tendon = stretch muscle
- stimulates muscle spindle (stretch)
- sensory input up sensory neruon 1 A afferent nerve fibre
- into dorsal spinal cord, synapses on motor neuron
- causes alpha motor neuron to cause contraction quad
- msucle shorteding stimulates golgi tendon organ
- sends info up 1B afferent nerve fibre = intrafusal muscle fibres to shorten slightly so spindle stays senstive
Voluntary movement
- UMN synapses on gamma LOWER motor neurone (supplies intrafusal muscle fibres
- IFMF contract = tells the muscle that muscle spindle fibres have been stretched (which it hasn’t)
- info back to spinal cord via 1 A afferent fibre then stimualtes alpha LOWER motor neurone to cause extrafusal msucle fibres to contract
- allows signal from UMN to be AMPLIFIED
Where are the UMN cell bodies/ nuclei located?
what is a nucleus in this area?
a) (nuclei = collection of cell bodies)
1. Corticospinal tract
2. Rubrospinal Tract
3. Tectospinal tract
4. Vestibulospinal - brain stem
5. Reticulospinal - brain stem
Corticospinal tract
- Location: motor cortex in the cerebral cortex
- cell bodies giving UMN to the body = from cortex to spinal cord
- tract Fine motor skills
- decussates
Rubrospinal tract
- Location = red nucleus in midbrain
- From Red nucleus to spinal
- some input from motor cortex = sued for skilled movements particularly in non-primartes
Tectospinal tract
- Lcoation = Tectum = roof of midbrain
- from tectum to spinal
- orientate head and eyes in resposds to sights and sounds
Reticulospinal tract
- Location = pons and medulla oblongata (brian stem)
- Nueclei in pons and medulla oblongata
- STABILISING body
Vestibulospinal
- Location = vestibular nuclei
- To do with ability to maintain posture with respect to gravity = balance
- vestibular system
- posn adn medulla ob
What tracts from cortex to cranial nerve nuclei?
Corticonuclear = never to spinal cord
What is the name for something going from the spine to something adn from something to spine?
- Spinal something = spinal cord to the brain
What is the corticospinal tract often called? why?
- Pyramidal tract
- Ventral medulla the corticospinal tract runs caudally
- Tracts form triangular shape when cut transversley
What is more important to our species: pyramidal or extrapyramidal?
- EXTRAPYRAMIDAL
2. Pyramidal = only corticospinal tract = not necessary for basic locomotion and even some more skilled movements
What are the differences in importance of the pyramidal and extrapyramidal tracts in diff species?
- humans - equally important
- horse - not much P at all as not much fine movement = deosn’t extend much past neck (lips)
- cat - pyramidal = pretty improtant for fine skilled bashing of mice
What are basal nuclei (Corpus striatum) involved in
- involved in motor PLANNING
- main area of motor control in birds
- relay loops between the cortex, thalamus and limbic system enable decision making based on all of these inputs
Cerebellum job
- coordinate and integrate sensory input (vestibular) and input frm cerebral cortex
- send output to UMN nuclei
- info from what happened, what actually happened, integrates this and then tells UMN what needs changing to make it all match up
- DOESN’T INITIATE movement but does coordinate
Structure of Cerebellum
- cortex of grey matter around outside
- deep nuclei
- corticonuceli (on outside) = only inhibitory output
- Their output to the deep cerebellar nuclei which only have excitation output to UMN
- dysfuction leads to loss of coordiantion
If damage cerebral cortex what effect?
- more excitatory output to UMN
- EXCESSIVE movement
- due to loss of inhibitory input
- Where are the cell bodies of the rubrospinal tract located?
- What do we call the tract that originates in motor cortex
- what tracts origionate in medulla + pons?
- what origionates in cervical intumescence
- RED nucleus
- Corticospinal
- vestibular spinal and reticulospinal
- Lower motor neurons for forelimb
Best description of the withdrawal reflex?
Polysegmetnal intersegemental bilateral
What motor deficits might you expect to see from a lesion in the left motor cortex of a dog?
- expect to see largely on RHS
2. Fine learnt voluntary movements will be affected
