Lecture 1: Nervous System 1 Flashcards
What are simple pattern reflexes?
automated, unlearned, and predictable reflexes which involve spinal cord circuits only (do NOT require cortical input)
What are complex postural (reflex movements) adjustments?
are not predictable reflexes, instead they are flexible and goal-oriented reflexes -> mostly coordinate their action with voluntary movements, hence require cortical input (spinal cord and supraspinal centres)
What do voluntary movements involve?
involve spinal cord, brainstem and motor cortex (more CNS areas involved)
What is the hierarchy of motor neurons?
upper motor neurons -> lower motor neurons
motor cortex / brainstem -> spinal cord -> skeletal muscles
What are some examples of upper motor neurons?
cortical motoneurons of the motor cortex (pyramidal tract)
motor neurons of brainstem nuclei (red nucleus, tectum, reticular formation, and vestibular nuclei)
What are some examples of lower motor neurons?
alpha and gamma motor neurons of the spinal anterior horn
motor neurons of cranial nerves in the brainstem
Where do upper motor neurons always remain?
within the CNS, their axons do not depart to the PNS
Where are cell bodies and axons of lower motor neurons located?
cell bodies are located in the CNS but their axons project out into the PNS to target the skeletal muscles that they innervate
What is a motor unit?
a group of muscle fibers which is innervated by a motor neuron
What is the size of motor units in muscles used for precise contraction?
small
What is the size of motor units in power-generating muscles, which do not necessarily need precise contraction?
large
What is the neuromuscular junction?
a synapse or junction between an axon terminal of a motor neuron and muscle fibers
What are nerves?
collections of thousands of individual axons within a common external connective tissue sheath (epineurium) -> in the periphery
What are the fascicles into which nerve axons are sub-grouped?
the epineurium, perineurium and endoneurium -> all surrounded by a perineurial sheath
How many nerves are there for each part of the spine?
cervical: 8 pairs
thoracic: 12 pairs
lumbar: 5 pairs
sacral: 5 pairs
coccygeal: 1 pair
What are the two different types of peripheral nerve axons?
efferent nerve axons which carry motor signals from the CNS and afferent nerve axons which carry sensory signals to the CNS
Where are efferent and afferent axons segregated? How do sensory and motor axons join the CNS?
at the point just before they contact the CNS (spinal cord or brainstem)
sensory axons join the CNS via a dorsal root and motor axons join the CNS at a ventral root
What is a dermatome?
an area of skin that is mainly supplied by a single spinal nerve
What is a myotome?
the group of muscles that a single spinal nerve innervates
What can a peripheral nerve be often comprised of?
multiple spinal nerves, i.e. several spinal segments contribute axons to a single peripheral nerve (nerve plexus)
What are some examples of nerve plexuses?
cervical plexus (head, neck, diaphragm) brachial plexus (upper limbs) lumbosacral plexus which is made up of the lumbar and sacral plexus (lower limbs)
Which nerves are found in the brachial plexus?
musculocutaneous (lateral)
median (lateral/medial)
ulnar (medial)
radial and axillary (posterior)
What is the autonomic nervous system?
an effector system in the CNS and PNS mediating unconscious homeostatic control of organ and body physiology
What are the two main divisions of the autonomic nervous system? Specify the type of outflow of each of these divisions.
sympathetic (thoracolumbar outflow) and parasympathetic (craniosacral outflow)
