Peripheral nerves and dermatomes Flashcards
What are the 2 groups that peripheral neves can be grouped into according to their function? Briefly describe them
Sensory neurons - free nerve endings detect sensory information in skin and axon relays this to the CNS
Motor neurons - axons send information out of CNS to the muscles
How many cranial nerves are there?
12
how many pairs of spinal nerves are there and how are they organised?
31 Cervical: 8 Thoracic: 12 Lumbar: 5 Sacral: 5 Coccygeal: 1
What does one spinal segment give rise to?
a pair of spinal nerves
What are the roles of the dorsal and ventral horns and where do they lie in relation to each other?
Dorsal: receives sensory information (POSterior)
Ventral: sends out motor output (anterior)
What are grey and white matter made up of?
grey: nerve cell bodies
white: nerve cell axons
What do pairs of spinal nerves fuse together to form?
A Plexus
Describe the organisation of a perisperhal nerve
Axons are surrounded by a myelin sheath - which consists of several concentric layers of membrane.
A layer of connective tissue called the endoneurium surrounds axons and they bundle together to form a fascicle. Each fascicle is surrounded by a perineurium.
Bundles of fascicles are surrounded by a tough connective tissue called epineurium.
What is the difference in roles of myelinated and unmyelinated axons?
Myelinated: involved in perception of touch, vibrations, cause muscle contractions
Unmyelinated: involved in perception of temperature and pain
What type of peripheral neurones are sensory afferents?
Pseudo-unipolar cells
What are the receptors called that are involved in detection of pain?
Nocicepters
Describe the process of sensory fibre input
Skin stimulated
Action potential generated
AP is conducted centrally via dorsal root and terminates in the dorsal horn
Describe the process of motor fibre output
Cell bodies are in the ventral part of the spinal cord
Axons project out and exit the spinal cord via ventral roots.
Axons ultimately terminate in the target muscles
Where do the sensory cell bodies collect?
Dorsal root ganglia
Define a myotome
Muscle groups supplied by distinct spinal cord segments and they corresponding spinal nerves
Define a dermatome
Area of skin innervated by a distinct spinal cord segment and its corresponding spinal nerve
What is the ASIA scale used to do?
To evaluate the extent and level of spinal cord injury
BY what methods does the ASIA scale assess the severity and level of spinal cord injury
Assessing reflex and voluntary movement
Define proprioception
Awareness of where body is in 3D space
In what two senses can there be proprioception?
Movement sense: awareness of joint movement
Position sense: awareness of static joint position
Describe the pathway for voluntary movement
Upper motor neurons sit in the motor cortex of Brain
Axons of UMNs project through the white matter of spinal cord to target lower motor neurons.
LMNs sit in the ventral (anterior) horn of grey matter. Their axons exit the spinal cord through dorsal roots and target muscle groups.
How does the pathway for voluntary and reflex movement differ? Describe the pathway for reflex movement.
Reflex does not have an upper motor neuron component.
Reflex has 2 parts:
Lower motor neuron
Sensory inputs which originate from the same muscle group
The lower motor neuron innervates the muscle and causes it to contract. The sensory fibre which originates in the same muscle has an axon that projects along the same peripheral nerve. THE SENSORY FIBRE INNERVATES THE SAME MOTOR Neuron the caused it to contract.
List some potential contributors to proprioceptive sensations
Ruffini endings in skin and joints Muscle spindles (sensory ending in muscles) Tendon organs
