Spinal Cord, Reflexes and Muscle Tone Flashcards
What are the 4 main types of movement?
- Voluntary
- Reflexive
- Rhythmic
- Postural
Rhythmic movements are coordinated by networks of neurons called what? Describe their basic characteristics.
Central pattern generators:
- CPGs recruited by descending projections from the brain - “command neurons”.
- CPGs able to operate relatively autonomously.
- Command neurons can alter the patterns of movement generated, such as different gait patterns in horses: walk, trot, canter, gallop.
The stretch reflex is controlled by how many neurons?
- Monosynaptic
- 1 sensory, 1 motor neuron connected by a synapse
Postural adjustments are made in response to changes in position, which are detected by what?
- Vestibular apparatus of the inner ear
- Proprioceptors
Postural movements are mediated by what pathway?
Reticulospinal (descending)
Describe what is meant by indirect cortical pathways and give an example.
- The cerebral cortex is able to generate movements directly via the corticospinal tract, but also indirectly via projections to the basal ganglia, brain stem, cerebellum and spinal cord.
- These indirect motor pathways allow the cortex to influence movements, posture and muscle tone - e.g. cortical projections to the reticular formation influence the descending reticulospinal pathways which contribute to the normal regulation of muscle tone.
What is cerebellar ataxia?
Clumsiness and poor coordination caused by damage to the cerebellum
What information does the cerebellum receive, and how does this allow it to carry out its role?
- Pathways from the frontal lobe, via the pons, to the contralateral cerebellum provide information about intended movements.
- The cerebellum receives sensory information from proprioceptors, the inner ear and the visual system etc. which provides continuously updated information about the precise relative positions of the head, limbs and trunk.
- Planned movements can then be compared with actual movements and any discrepancies can be detected.
- This information is fed back to the frontal lobe via efferent (outgoing) projections from the cerebellum which represents an “error signal” that is used to correct on-going movements and make them more accurate.
- The cerebellum is only able to correct non-ballistic movements.
In the developing spinal cord the neural tube is divided into what regions?
- Anterior (ventral) and posterior (dorsal) region
- Separated by a groove called the sulcus limitans
- The anterior part is called the basal plate and contains motor neurons
- The posterior part is the alar plate and has sensory functions
- Motor neuron axons grow out of the anterior region to form the ventral spinal nerve roots
- Sensory axons grow out of the posterior region to form the dorsal spinal nerve roots, with the sensory cell bodies in the dorsal root ganglia
What are the spinal cord funiculi?
- 3 longitudinal columns: posterior, lateral and anterior
- These columns contain ascending and descending pathways
Cross sections at different spinal levels shows that which regions contain the most white and grey matter?
- White matter - cervical because all ascending and descending tracts are present at this level
- Grey matter - cervical and lumbosacral because grey matter varies in proportion to the amount of muscle tissue at each level
Which “Rexed” laminae make up the dorsal horn, anterior horn and mid-region of the spinal cord? Where do LMNs arise from?
- Dorsal horn - laminae I - VI
- Mid-region - laminae VII and X
- Anterior horn - laminae VIII and IX
- “Lamina IX” consists of discrete longitudinal columns containing the cell bodies of anterior horn LMNs
- Each column in “lamina IX” supplies a particular functional muscle group e.g. forearm flexors, and usually spans more than 1 spinal segement
- For example, the lamina IX column that supplies the biceps brachii spans C5-C6
Describe the orderly arrangement of LMNs in the spinal cord.
- Proximal muscles supplied by medial columns
- Distal muscle supplied by lateral columns
- Flexors supplied by dorsal columns
- Extensors supplied by ventral columns
- Anteromedial columns supply proximal extensors - e.g. erector spinae
- Posterolateral columns supply distal limb flexors - e.g. in the hand
Describe the functional roles of the phrenic nucleus, spinal accessory nucleus and Onuf’s nucleus.
- Phrenic nucleus - C3,4,5 - keeps the diaphragm alive!
- Spinal accessory nucleus - C5,6 - supplies trapezius and sternocleidomastoid
- Onuf’s nucleus - S2,3,4 - important for continence as it supplies the external urethral and anal sphincters
Muscle spindles are found throughout all skeletal muscles except those of which region?
The face
