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Neurosensory > 10. Systems in the NS. the MOTOR system > Flashcards

10. Systems in the NS. the MOTOR system Flashcards

1
Q

MUSCLE CONTRACTION is caused be BINDING of ACTIN and MYOSIN triggered by…

A

CA2+ RELEASE from SR
(calcium induced calcium release)

due to depolarisation

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2
Q

why do MUSCLE CELLS (SARCOMERES) not need synapses between them

A

muscle cells MERGE within the membrane to form one big joined up cell : muscle fibril called SYNCYTIUM

which is undergoing rapid depolarisation

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3
Q

ACH released into NEUROMUSCULAR CLEFT from a neurone binds to which RECEPTORS on the adjacent muscle

A

LIGAND-GATED SODIUM CHANNELS
(Nicotinic ACH Receptors)

causing DEPOLARISATION by NA+ INFLUX

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4
Q

what triggers the release of ACH in a SYNAPSE

A

VOLTAGE GATED CA2+ CHANNELS OPEN

CA2+ INFLUX

causes vesicles to move and merge with membrane

(action potential by Na+ influx causes the ca2+ channels to open)

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5
Q

what happens after synapse is done

A

ACH REUPTAKE by axon terminal
or BREAKDOWN by ACETYLCHOLINESTERASE enzyme

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6
Q

MOTOR UNIT is the most basic element of output / the action unit
what does it include?

A

SINGLE MOTOR NEURON, ITS BRANCHES, and the MYOFIBRILS that it INNERVATES

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7
Q

MOTOR NEURON CELL BODY is located where

A

in the CENTRAL GREY of the VENTRAL (Anterior) HORN of the SPINAL CORD

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8
Q

MOTOR UNIT, FINAL COMMON PATHWAY includes..

A
  • motor neuron CELL BODY in central grey of ventral horn
  • MOTOR AXONS transverse the surrounding WHITE matter as a FASCICLE
  • the axons EXIT the cns as the VENTRAL RAMUS OF THE ROOT
  • the root transverses the FLUID of the SPINAL CANAL, and EXITS axial skeleton through INTERVERTEBRAL FORAMEN
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9
Q

MOTOR UNIT, FINAL COMMON PATHWAY includes..

A
  • motor neuron CELL BODY in central grey of ventral horn
  • MOTOR AXONS transverse the surrounding WHITE matter as a FASCICLE
  • the axons EXIT the cns as the VENTRAL RAMUS OF THE ROOT
  • the root transverses the FLUID of the SPINAL CANAL, and EXITS axial skeleton through INTERVERTEBRAL FORAMEN
  • roots corresponding to the spinal levels of the arm and leg INTERTWINE to form a PLEXUS from which the names PERIPHERAL NERVE ARISES (usually mixed sensory and motor nerve)
  • over the trunk the anatomy is more clearly segmented (rather than plexus)
  • the motor axons of a particular spinal root supply a certain group of muscles: MYOTOME
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10
Q

MOTOR NEURONs are recruited according to their SIZE
(SIZE PRINCIPLE)
which motor neurons are the FASTEST

A

LARGEST ones

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11
Q

which motor neurones are the LARGEST & FASTEST

A

ALPHA motor neurons

  • 13-20 μm diameter
  • 80-120 msec

aka lower motor neurones, ventral horn cell

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12
Q

which size motor neurons reach their FIRING THRESHOLD more READILY

A

SMALL

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13
Q

which A motor neurones are the SMALLEST and SLOWEST

A

GAMMA

  • 5-8 μm
  • 4-24 msec
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14
Q

GAMMA motor neurones go to where in the muscle

A

SPINDLE

  • INTRAFUSAL
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15
Q

ALPHA neurones are for SOMATIC MOTOR and …

A

PROPRIOCEPTION

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16
Q

which A NEURONS are for TOUCH & PRESSURE

A

BETA

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17
Q

which A NEURONS are for PAIN (fast), COLD, TOUCH

A

DELTA

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18
Q

the STRETCH (myotatic) REFLEX (aka Liddel-Sherrington reflex) uses which CIRCUIT

A

MONOSYNAPTIC CIRCUIT

  • 1 SYNAPSE (between a sensory and a motor neuron)
  • the SIMPLEST NEURAL CIRCUIT
19
Q

STRETCH REFLEX.
when a muscle is stretched unexpectedly, what AFFERENT in the SPINDLE Fires
(increased tonic firing)

A

Ia (SENSORY) AFFERENT

  • VERY FAST
20
Q

where is the SYNAPSE of the STRETCH REFLEX between the Ia Sensory AFFERENT and ALPHA MOTOR neuron

A

in the CENTRAL GREY of the Spinal cord

21
Q

STRETCH REFLEX.
Ia AFFERENT comes from the SPINDLE. where in the muscle does the ALPHA MOTOR return to

A

BODY, Outside the spindle - EXTRAFUSAL

22
Q

what is the purpose of the STRETCH REFLEX

A

muscle CONTRACTS to MAINTAIN ORIGINAL LENGTH

  • MAINTAINS POSITION AGAINST UNEXPECTED FORCES
23
Q

why is the STRETCH REFLEX the FASTEST of all neural responses

A
  • MONOSYNAPTIC
  • uses FASTEST NEURONAL FIBRES (Ia afferent, alpha efferent)
24
Q

STRETCH REFLEX
Related reflex is mediated by..

A

GOLGI TENDON ORGAN

25
Q

STRETCH REFLEX also sends an … RESPONSE to ANTAGONIST MUSCLE
and feedback to higher centres

A

INHIBITORY response

26
Q

ALPHA-GAMMA CO-ACTIVATION (step 2)

when higher centres trigger stimulation of ALPHA MOTOR neuron and EXTRAFUSAL Muscle fibres CONTRACT what happens to the MUSCLE SPINDLE?

A

CHANGE IN CONFORMATION

  • BECOME LAX (slack) instead of taut

and thus LOSS of SENSITIVITY of the reflex
(not taut to pick up changes)

27
Q

ALPHA-GAMMA CO-ACTIVATION (step 2)

although SPINDLE fibres become lax,
how is the STRETCH REFLEX SENSITIVITY still MAINTAINED

A

CO-ACTIVATION of GAMMA MOTOR NEURONS

  • STIMULATE the INTRAFUSAL (SPINDLE) FIBRES and so TENSION maintained
28
Q

when an ALPHA motor neuron fires to trigger target muscle (agonist), it also stimulates INHIBITORY CELLS (to the ANTAGONIST muscle)

the best known SPINAL INHIBITORY INTERNEURON is which cell:

A

RENSHAW CELL

  • INHIBIT MOTOR NEURONS that target ANTAGONIST muscle
29
Q

MOTOR DESCENDING PATHWAY examples that allow brain to send effect to spinal cord:

A

LATERAL CORTICOSPINAL TRACT (important)

also VENTRAL CORTICOSPINAL TRACT

and more

30
Q

reflex that is generated more SLOWLY than MONOSYNATPIC STRETCH reflex

A

LATERAL LATENCY REF;ECES

31
Q

DESCENDING PATHWYAS ie lateral corticospinal tract ORIGINATE where in the brain

A

PRIMARY MOTOR CORTEX

32
Q

where in the brain is the PRIMARY MOTOR CORTEX found
and in which broadmann area

A

PRE-CENTRAL GYRUS

in Broadmann area 4

33
Q

name of CELLS that form CORTICOSPINAL TRACT
/ neurons in the brain that have large/long axons that project to other parts of the CNS :

  • UPPER MOTOR NEURON cells
A

PYRAMIDAL CELLS

LARGE pyramidal cells are called BETZ CELLS

(have pyramidal shape)

34
Q

there are 6 cellular layers in the Cortex.

PYRAMIDAL CELLS in which layer form CORTICOSPINAL TRACT

A

LAYER 5

35
Q

UPPER MOTOR NEURONS are found in the cerebral cortex and brainstem. The primary tract which carries signals for voluntary movement is known as the … tract

A

PYRAMIDAL TRACT

-> corticospinal and corticobulbar

36
Q

what are INTERNEURONS

A

SMALL, GRANULAR (grain-like) NEURONS

found in the spinal cord, relays signals between sensory and motor neurons

37
Q

why does it get the name PYRAMIDAL tract

A

because it PASSES the PYRAMID of the MEDULLA

  • where it DECUSSATES
38
Q

Path of the CORTICOSPINAL (PYRAMIDAL) TRACT

A

from PRIMARY MOTOR CORTEX - PRECENTRAL GYRUS, BA 4

  • traverses GREY matter DEEP in the hemisphere (forms capsule around nuclei) in the INTERNAL CAPSULE
  • forms ANTERIOR part of MIDBRAIN (CEREBRAL PEDUNCLE)
  • passes through PONS
  • referred to as the PYRAMID in the ANTERIOR MIDBRAIN where it DECUSSATES

before passing to the SPINAL CORD

39
Q

what is meant by HOMONCULUS

A

the MAPPING of the brain along the CEREBRAL CORTEX
- where each part of the body is processed

40
Q

does Upper or Lower MOTOR NEURON SYNDROME (damage) have Negative (WEAKNESS) and Positive effects - INCREASED TONE (SPASTICITY) and EXAGGERATED REFLEXES

A

UPPER MOTOR NEURON SYNDROME

41
Q

why do you get INCREASED TONE (SPASTICITY) and EXAGGERATED REFLEXES in UPPER MOTOR NEURON SYNDROM

A

LOSS OF INHIBITION on lower motor neurons (via RENSHAW cells etc)

42
Q

symptoms of LOWER MOTOR NEURON SYNDROME

A
  • WEAKNESS
  • MARKED WASTING - loss of muscle bulk
    (due to loss of trophic stimulation)
  • ABSENT REFLEXES
  • FASCICULATION (muscle twitches)
    (lower motor neuron drops out so visible firing of large motor units which innervate a larger than normal number of muscle fibres to compensate. resting tone of muscles become more erratic)
  • FIBRILLATION
    on electrograph assessment. based on chemical hypersensitivity
43
Q

GAMMA MOTOR NEURONS have what effect on the STRETCH REFLEX

A

they are INTRAFUSAL (act on fibres in SPINDLE)

  • cause TENSION of these fibres / causes them to TIGHTEN when muscle contracts
    and thus MAINTAINS THEIR SENSITIVITY

(when alpha motor neurons contract so do gamma)

44
Q

what are RENSHAW CELLS

A

INHIBITORY INTERNEURONS
- INHBIT MOTOR NEURONS that act on ANTAGONIST MUSCLE

Neurosensory (17 decks)

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