ch 5a motor systems and actions Flashcards
major divisions of the CNS
-cerebrum (includes cerebral cortex)
-diencephalon
-brainstem
-cerebellum
-spinal cord
what does the cerebrum consist of?
- Cerebral cortex
-wrinkled grey matter that covers the cerebrum; higher function of the CNS
–> gyrus= ridge of a wrinkle
–> sulcus= groove between two gyri - Subcortical structures
- hippocampus
-amygdala (memories, emotions; fear, anxiety..)
-parts of the basal ganglia
Diencephalon
- Thalamus
-a collection of nuclei that relay info between cerebrtal cortex and spinal cord, brainstem, and peripheral senses - Subthalamus
-includes the subthalamic nuclei; part of the basal ganglia - Hypothalamus
Brainstem consists of..
- Hindbrain
-pons: main connection to the cerebellum
-medulla - Midbrain
–>tectum:
-superior colliculi (control of eye movements)
-inferior colliculi (auditory system)
–> tegmentum:
-red nucleus
-substantia nigra (part of the basal ganglia) - Reticular formation
Cerebellum
consists of 3 functional zones
spinal cord; how many nerves?
connects to body via 31 pairs of nerves
spinal cord organization (of nerves)
-31 spinal nerves total
-coccygeal (coc 1), sacral (S1-5), lumbar (L1-5), thoracic (T1-12) and cervical (C1-8) nerves
what is the spinal cord protected by?
vertebral column
role of spinal nerves?
-control upper limb muscles
-thoracic nerves control muscles of the trunk and chest
-lumbar nerves control lower limb and lower back muscles
-sacral nerves control bowel and bladder muscles
(S1 and S2 also involved in controlling leg muscles)
Two components of spinal cord
- grey matter
-made up of cell bodies and neurons - white matter
-made of myelinated axons forming the ascending and descending tracts
4 types of neurons in the spinal cord that allow for coordinated movement
- local interneurons: axons are confined to same/adjacent spinal segment
- propriospinal neurons: axons reach distant spinal centres
- projection neurons: axons ascend to higher brain centres
- motor neurons: axons exit nervous system to innervate muscles
motor nuclei innervating proximal muscles (closer to body) lie more —– in the spinal cord
medially (closer to centre of spinal cord)
motor nuclei that lie more laterally (further from centre) in the spinal cord would innervate muscles that are…
more distal muscles (further away towards extremeties)
example of proximal muslces
closer to the body; muscles around the shoulder
example of distal muscles
further away from the body (ex. hand or forearm muscles
What type of info do ascending tracts carry?
mostly sensory info
What type of info do descending tracts carry?
motor info
ventral roots=?
motor output
dorsal roots=?
somatosensory info from peripheral receptors
motor unit
the motor neuron + the muscle it innervates
Which twitch fibres are recruited first?
slow twitch
first fibres to activate are more resistant to
fatigue
SIZE of motor unit is related to the need for
the need for refined movement
(more refined movement=fewer fibres per motor unit)
NUMBER of motor units recruited is related to the
power needed to generate movement
How can the CNS increase muscle force?
- recruiting different size motor units
-activating more motor units (means activating more motor units)
-increasing frequency of action potentials in muscle fibre (increase alpha motor neuron stimulation)
larger motor units contain more
muscle fibers
larger motor units generate more
force/tension when activated
muscles involved in fine movements have
small motor units
tension can be increased by
recruitment of multiple motor units within a muscle
characteristics of small motor units
- lower threshold for activation
- activated at a lower frequency of stimulation from CNS
what happens as frequency of stimulation from brain increases?
-action potential frequency and tension in the increases in motor unit Y increases
-larger motor units reach threshold and contribute to total muscle tension
the importance of muscle
-largest consumer of energy
-generates heat–> temp regulation
-mechanical function
monosynaptic stretch reflex
muscle is stretched, spindles sense the change in length, muscle contracts in response to stretch. Monosynaptic pathway causes this stretch (one synapse); 1a afferent directly inhibitory neuron in spinal cord which connects to alpha motor neuron
Withdrawal (flexion) reflex
limb flexion in response to a painful stimulus
ex. when your hand touches a hot stove
-polysynaptic
crossed-extension reflex
increases body support
(occurs during withdrawal reflex)
when would the crossed-extension reflex not be needed?
if you are able to hold onto something (for example a chair etc.)
descending commands can suppress a spinal reflex which would…
allow you to continue your movement
ex. when you are carrying something that is getting hotter the longer you hold it, but you can’t put it down
descending commands that enhance a reflex would…
make your response larger
tonic excitation or inhibition
tonic= continues
stimulus combined with tonic excitation may
evoke a response/muscle contraction because it is a stronger stimulus than without tonic excitation
describe postural reflex
balance is perturbed (ex. on a bus that accelerates), muscle is stretched, muscle spindles detect the stretch: 1a and group 2 afferents carry this info to the spinal cord which will send the info elsewhere
name three general routes that somatosensory info about the perturbation is transmitted
- Short Latency Response (SLR)
- Medium Latency Response (MLR)
- Long Latency Response
Short latency response (describe)
1a afferent synapses in the spinal cord with the alpha motor neuron, which activates the muscle that was stretched to recover balance
The short latency response is essentially the…
-monosynaptic stretch reflex
-it occurs very fast
-plays a minimal role if perturbation is of sufficient magnitude
Medium latency response (describe)
1a afferents synapse with neurons that go up to the brainstem. Info gets integrated in the brainstem. Motor commands to activate muscles are sent down descending tracts (dorsal column medial lemniscus) to the spinal circuits
Long latency response (describe) “loop responses”
1a afferents synapse with neurons that go to the cortex (via the dorsal-column medial lemniscus tract). Info gets integrated in the cortex. Cortex activates descending tracts to send motor commands to the spinal circuits and active muscles.
-less of a “reflex”
spinally mediated postural response?
SLR
cortically (cortex) mediated postural response?
LLR
brainstem mediated postural response?
MLR
most complex spinal response?
LLR. it relies on the cortex which has more info about environment than brainstem and spinal cord
which is more complex and functional? MLR or SLR?
MLR
Name other inputs of the spinal neural circuits
-cutaneous receptors and GTOs send input that can be incorporated into MLR and LLR
-vestibular info can be used to activate exterior muscles in the leg to recover balance
-visual info about surroundings can be integrated in the cortex and used as part of LLR leading you to grab an object for balance etc.
Central set concept
tuning of sensorimotor system for upcoming events
–> a state of the nervous system that is determined by the context of the task
the spinal cord implicitly “knows”…
where the limbs are positioned
Central Pattern Generators (CPGs)
a neuronal network capable of generating a rhythmic pattern of motor activity without sensory input
Examples of movement using CPGs
walking, swimming, respiration, swallowing
the flexor circuit and extensor circuit mutually… each other
–> what does it lead to?
-inhibit
-leads to alternating flexor and extensor motorneurons (which result in stance and swing phase of walking respectively)
