WEEK 6: The spinal cord & motor control Flashcards
What can the spinal cord be described as, in simple terms?
a column of nervous tissue
What two things does the spinal cord connect?
the brain to the peripheral NS
What is the spinal cord enclosed within (protected by)?
The vertebral canal
What type of communication occurs in the spinal cord?
2 way communication?
What are the two tracts of communication?
ascending tract (afferent pathway)
descending tract (efferent pathway)
What are some inner components of the spinal cord?
White matter (myelinated axons)
grey matter (cell bodies, glia)
central canal (CSF flows through)
What are the two roots that carry nerves coming in and out of the spinal cord?
dorsal and ventral roots
What information does the dorsal root carry, and what type of tract is it?
sensory input, afferent tracts
What information does the ventral root carry, and what type of tract is it?
motor output, efferent tracts
somatic motor/sensory neurons carry signals to the?
skeletal muscles
visceral motor/sensory neurons are part of the?
autonomic nervous system
visceral motor/sensory neurons carry signals to the?
cardiac muscle, smooth muscle and glands
Briefly explain what would occur if an individual were to hold their finger close to the stimulus of a candle light
- thermoreceptors will detect the change in heat, and the information will be sent through afferent tracts in the spinal cord via the sensory nerves.
- the sensory information will travel through sturctures known as the dorsal root ganglion
- the dorsal root ganglion will then split off into dorsal roots
- sensory information will be carried through dorsal roots to the back of the spine, where information will be processed by interneurons
- interneurons will synapse with motor/efferent neurons which will carry this information out via the motor nerves, into the channels known as ventral roots.
- motor information is sent to muscles in finger to flinch away from the flame
what are interneurons
they process sensory information and transform it into motor information
what is a dorsal root ganglion?
a cluster/collection of nerve cell bodies
What is the spinal nerve
a structure that both dorsal and ventral roots meet at the middle of, that serve as a tunnel that holds a shared space for two way communication, and then structurally splits out to the ventral and dorsal roots
What are the 3 horns involved in spinal cord organisation?
- dorsal (houses somatic & visceral sensory nuclei)
-ventral (houses somatic motor nuclei)
-lateral (houses visceral motor nuclei)
grey matter can be divided into what 3 sections?
dorsal horn (sensory)
lateral horn (autonomic)
ventral horn (motor)
white matter can be divided into what 3 columns?
dorsal column (sensory only)
lateral column (sensory & motor)
ventral column (sensory & motor)
What regions of the brain can be involved in visceral motor activity?
brain,
basal ganglia, cerebellum (indirect modulation)
What are the two motor neurons?
Upper motor neurons (UMN)
Lower motor neurons (LMN)
What is the location of UMNS?
start in the motor cortex (motor/pre motor areas of the brain), and axons extend to either the brainstem or continue to various regions of the spinal cord
What is the function of UMNS?
send signals from the brain to LMNS
initiate/coordinate voluntary movement
regulate reflexes and muscle tone
Where are LMNs located?
they sit at the level of the brainstem/various parts of the spinal cord
What is the function of LMNS?
they carry information from UMNS to muscles, by sticking their axons out in descending tracts and innervating muscles, causing contractions
Where can the lower motor neurons be found in abundance?
- the cervical spinal cord (LMNs innervate upper limbs)
- the lumbar spinal cord (LMNs head out to innervate lower limbs)
What are the two types of lower motor neurons? (LMNs)
alpha motor neuron and gamma motor neuron
what do alpha motor neurons supply?
extrafusal muscle fibres or main muscle mass
What are the 3 different inputs an alpha motor neuron can receive
input from spinal interneurons, sensory input from muscle spindles ad input from UMNs
What do gamma motor neurons supply?
intrafusal muscle fibres (muscle spindles)
what is an intrafusal muscle fibre?
a specialised sensory receptor involved in helping body sense stretch in muscles, maintaining muscle tone and posture
What is a word for the types of sensory inputs we get to the motor unit?
proprioceptive
What are the two kinds of proprioceptive information?
Muscle spindles
Golgi Tendon organs
What do muscle spindles do?
- they encode muscle length and synapse on alpha motor neurons
what do golgi tendon organs do?
- they encode muscle tension (hence more haphazard fibres)
- they synapse on inhibitory interneurons
What can interneurons receive input from?
- sensory axons
- other interneurons
- descending UMNs and LMNs
T or F: interneurons can be both excitatory or inhibitory
T
What does an interneuron eliciting both an excitatory and inhibitory effect require?
reciprocal inhibition eg. agonist and antagonist muscles like the stretch reflex
What is the motor homunculus?
a visual representation of how the motor cortex controls different parts of the body
Where is the primary motor cortex (M1)- BA4 found?
in the pre-central gyrus
The pre-motor areas and supplementary motor areas are found in?
BA 6
Other contributions to the motor areas of the cerebral cortex include?
posterior parietal cortex (spatial awareness) & prefrontal cortex (making decisions)
What is the other name for the pyramidal motor system?
the corticospinal tract
What is the primary function of the corticospinal tract?
motor planning and initiation
Through what pathway do axons travel through in the corticospinal tract?
cell bodies -> corona radiata -> internal capsule -> brainstem (pyramidal decussation) -> spinal cord to synapse onto LMNs
what is pyramidal decussation?
when the axon travels from being on the left side of the brain and switches to the right (at the lower medulla of the brainstem)
What parts of the brain are involved in the fine tuning of movement?
basal ganglia and cerebellum
what does the basal ganglia do in relation to the fine-tuning of movement?
- it modulates movement
- it selects and initiates willed movements
what does the cerebellum do in relation to the fine-tuning of movement?
- generates appropriate movement sequences on demand (coordination)
What is the neural pathway that controls a reflex called?
a reflex arc
What are the 5 components of the reflex arc?
- Receptor
- Sensory neuron - transmit info to CNS via afferent pathways
- Integration centre - CNS where
- Motor neuron- transmit info to effector via efferent pathways
- Effector - muscle fibre/glandular cell that produces response
What are the different classifications of reflex arcs?
Spinal - integration happens in the spinal cord
Cranial - integration happens in the brainstem
Visceral - involves smooth muscle, cardiac muscle, glands
Somatic- involves skeletal muscle contraction (patellar reflex)
What does superficial stimulation refer to?
stimulation of sensory afferents in the skin
What does deep tendon stimulation refer to?
stimulation of sensory afferents within muscle, such as tendons
What are the two different classifications based on number of synapses?
monosynaptic - one synapse in the CNS between a single sensory neuron and a single motor neuron
polysynaptic - 2+ synapses in the CNS between sensory, motor and interneurons
What happens in the deep tendon patellar reflex?
it is a monosynaptic reflex arc that helps maintain posture and muscle tone
explain what happens during the patellar reflex
- a reflex hammer strikes the tendon below the kneecap
- there is a passive stretch of muscle spindle fibres in the thigh (quadriceps)
- intrafusal muscle spindle fibres detect this lengthened stretch
- a sensory signal is sent via afferent tracts to the spinal cord
- the sensory neuron directly synapses (monosynaptic) with an alpha motor neuron
- in response, a motor neuron sends a signal via efferent tracts back to the quadriceps muscle, causing it to contract
- knee jerking action
- simulatenously, inhibitory interneurons participate in reciprocal inhibition to prevent the antagonist muscle (hamstrings) from contracting
* important to note that while this reflex arc only occurs in the spinal cord, some input will ascend to the brain
what does the grading system range from?
0 Absent
+ Present (reduced)
++ Normal
+++ Increased , possibly normal
++++ Greatly increased (clonus)
