Lecture 13 : Movement Flashcards
What 2 pathways are contained in the spinal cord?
- Sensory pathways
- Motor pathways
What is the white and grey matter?
- White matter = axons
- Grey matter = cell bodies
What is the spinal cord involved in?
- Reflexes
* Stretch reflex
* Golgi tendon organ (tension) reflex
* Withdrawal reflex - Rhythmic motor patterns
* locomotion, chewing - Processing motor commands from brain
- Send sensory information to brain
What are spinal reflexes?
- Responses mediated by the spinal cord
- Bypass the brain for quick response
- The brain can over-ride the reflex
What is a stretch reflex?
- To maintain muscle length
- Initiated by stretch receptor (muscle spindle)
- Causes contraction to resist further stretching
What is a monosynaptic arc?
When sensory neurons directly excite motor neurons
What is a polysynaptic arc?
When a sensory neuron activates an inhibitory/excitatory interneuron in order to inhibit/excite a motor neuron
What does a monosynaptic arc cause in a stretch reflex?
Contraction of stretched muscle
What does a polysynaptic arc cause in a stretch reflex?
Relaxation of opposing muscle
Describe a monosynaptic arc of a stretch reflex:
- Sensory neuron in dorsal root ganglion
- Unipolar - one axon that splits into 2 branches
- 1 goes out to periphery - dendrites become part of a muscle spindle (stretch receptors in muscle)
- 1 goes into spinal cord to synapse onto the motor neuron to activate the quadricep
Describe a polysynaptic arc of a stretch reflex:
- The sensory neuron synapses onto an inhibitory interneuron
- This inhibits the motor neuron for the hamstrings
(reciprocal inhibition)
What is an interneuron?
Neuron in the spinal cord which form bridges between neurons
- Can be excitatory or inhibitory
- Innervate motor neurons and facilitate movement during a reflex: relax opposing muscle groups and coordinate muscles on the contralateral side (polysynaptic withdrawal reflex)
What is a tension reflex (golgi tendon reflex)?
- To regulate muscle force
- Initiated by golgi tendon organ
- Causes relaxation to prevent excessive force and potential injury - protects tendon from rupturing
Describe a tension reflex (golgi tendon reflex):
- Dendrites wrap around a tendon of a muscle - this is called a golgi tendon organ
- If muscle is generating too much force and potential damage is about to happen to tendon, it activates the golgi tendon organ
- Action potential propagates to spinal cord
1. Synapses onto inhibitory interneuron to inhibit the motor neuron for the quadricep - preventing contraction, extension
2. Synapses onto excitatory interneuron to activate the motor neuron for the hamstrings - causing contraction, flexion
What is the role of a polysynaptic arc in a tension reflex?
- Causes relaxation of muscle responsible for causing high tension on the tendon
- Causes contraction of opposing muscle
What type of synapse does a sensory neuron make?
Excitatory
What is a withdrawl reflex?
- To move away from painful stimulus
- Initiated by pain receptors
- Pain detected by sensory neuron
- Causes motor reflex to withdraw the affected limb from the pain stimulus
What is the role of the crossed extensor reflex?
- Stabilises the body when one limb withdraws
- Compensates for loss of support to maintain balance
How does the withdrawal reflex trigger the crossed extensor reflex?
- Painful stimuli in foot
- Ipsilateral:
- Flexors active
- Extensors relaxed
- Limb withdrawn
* Withdrawal from painful stimuli - Contralateral:
- Extensors active
- Flexors relaxed
- Limb extends, takes weight
* Postural adjustment to help maintain balance
What does the spinal cord & brainstem circuits generate patterns of rhythmic muscle activity for?
- Locomotion
- Breathing
- Chewing
- Swallowing
What is the role of the primary motor cortex?
Regulates spinal cord motor systems via Corticospinal tract
What is the role of the supplementary motor cortex?
Involved in planning movement with the basal ganglia
What is the role of the cerebellum?
Balance and coordination
What is somatotopy in the primary motor cortex?
- Organisation of motor representations in the primary motor cortex
- Spatial with distinct areas representing different body parts
- Body parts that require fine motor control have larger areas of the primary motor cortex
- Cortex is plastic and can be reorganised
What is the corticospinal pathway?
- Descending motor pathway from the primary motor cortex to the motor neuron in the spinal cord - most input is to interneurons
- For controlled movements
- Contralateral control
What is the brainstem pathway?
- Descending pathway from brainstem nuclei to motor neurons
- For posture and balance
- Mostly ipsilateral control
