Topic 1 - The Nervous System Flashcards
What are lower motor neurons (LMNs)?
LMNs are 2nd order motor neurons that directly innervate skeletal muscles. They include alpha and gamma motor neurons in the spinal anterior horn and motor neurons of cranial nerves.
Where are the cell bodies of lower motor neurons located?
In the central nervous system (CNS), specifically in the spinal cord and brainstem, but their axons project into the peripheral nervous system (PNS).
What is the role of upper motor neurons (UMNs)?
UMNs are 1st order motor neurons that remain within the CNS and modulate LMNs to coordinate movement.
What structures are involved in voluntary movement control?
The spinal cord, brainstem, and motor cortex work together to generate voluntary movements.
What is a motor unit?
A motor unit consists of a single motor neuron and all the muscle fibers it innervates.
How do motor units vary between muscles?
Muscles requiring fine control have small motor units (e.g., eye muscles), while power-generating muscles have large motor units (e.g., quadriceps).
What is the neuromuscular junction (NMJ)?
The NMJ is the synapse between a motor neuron and a muscle fiber, enabling neural control of muscle contraction.
What are peripheral nerves?
Bundles of thousands of axons grouped into fascicles within a connective tissue sheath (epineurium).
What are the two types of peripheral nerve axons?
Efferent (motor) axons carry signals from the CNS, while afferent (sensory) axons carry signals to the CNS.
How many pairs of spinal nerves exist?
31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.
What is a dermatome?
An area of skin mainly supplied by a single spinal nerve.
What is a myotome?
A group of muscles primarily innervated by a single spinal nerve.
What are the major nerve plexuses?
Cervical (head/neck/diaphragm), Brachial (upper limbs), Lumbar (lower limbs), and Sacral (lower limbs).
What are the two major sensory pathways in the spinal cord?
The dorsal column-medial lemniscus pathway (touch, vibration, proprioception) and the anterolateral system (pain, temperature, crude touch).
What are Brodmann areas relevant to motor and sensory functions?
BA4 (primary motor cortex), BA6 (pre-motor cortex), BA3,1,2 (primary sensory cortex), and BA5,7 (sensory association areas).
Simple pattern reflex vs Complex postural adjustment vs Voluntary movement
Simple pattern reflex: only spinal cord circuits
Complex postural (reflex) adjustment: spinal cord and supraspinal system
Voluntary movement: Spinal cord, brainstem and motor cortex
- covering of individual nerve fibre:
- covering of nerve fascicle:
- covering of nerve:
- endometrium
- perineurium
- epineurium
What are the major divisions of the spinal columns and their functions?
The spinal cord is divided into dorsal, lateral, and ventral columns, each containing tracts for sensory and motor functions
What is the difference between the pyramidal and extrapyramidal motor systems?
The pyramidal system controls voluntary movements via direct pathways, while the extrapyramidal system regulates movement coordination and posture via indirect pathways
What is the role of the corticospinal tract?
It is part of the pyramidal system and controls voluntary movements by transmitting signals from the motor cortex to the spinal cord
Where do corticospinal tract fibers decussate?
Most fibers decussate at the pyramidal decussation in the medulla, forming the lateral corticospinal tract
What are the four major extrapyramidal tracts?
Rubrospinal (upper limb control), Reticulospinal (automatic movements/posture), Vestibulospinal (balance/posture), and Tectospinal (head reflex movements).
What is the role of the motor homunculus?
It represents the motor control distribution in the precentral gyrus, with larger areas for finer motor control.
What are upper motor neuron (UMN) and lower motor neuron (LMN) lesions?
UMN lesions cause spastic paralysis (hypertonia), while LMN lesions cause flaccid paralysis (hypotonia/atonia).
