Nervous System 4 - Dermatomes, Reflexes and Arcs Flashcards
Knowing which spinal cord segments supply each dermatome makes it possible to detect damaged regions of the spinal cord. True or False?
True
What is a dermatome?
An area of skin that provides sensory input to the CNS via one pair of spinal nerves
What are the 2 principle functions for the spinal cord maintaining homeostasis?
Nerve impulse propagation | Integration of information
What are white matter tracts?
Highways for nerve impulse propagation
Sensory input – Toward brain
Motor output - From brain to skeletal
muscle or other effectors
What are grey matter tracts?
Receive & integrate incoming
& outgoing information
Nerve impulses from sensory neurons propagate up the spinal cord to brain via 2 main routes. What are they?
Spinothalamic tract
Sense pain, warmth, coolness itching & tickling
Posterior column (2 tracts)
Fasciculus Gracilis | Fasciculus Cuneatus
Touch, pressure, vibration & conscious proprioception
(e.g. awareness of limb position)
Motor output to skeletal muscles travel down the spinal cord in two types of descending pathways. What are they?
Direct pathways
Lateral & anterior corticospinal & corticobulbar tracts
Cause voluntary movements | Innervate skeletal muscle
Indirect pathways
Rubrospinal, tectospinal, vestibulospinal, lateral
reticulospinal & medial reticulospinal tracts
Cause automatic movements | Regulate muscle tone,
posture, balance etc.
What is a reflex?
A fast, automatic, unplanned sequence of
actions that occur in response to a particular stimulus
What is an example of an inborn reflex?
Pulling hand away from a flame
What is an example of a learned (acquired) reflex?
Slamming on a car brake pedal
What is a somatic reflex?
Reflexes which generate skeletal muscle contraction |e.g. Stretch reflex
What is an autonomic (visceral) reflex?
Reflexes which generate contraction of cardiac muscle, smooth muscle & glands | e.g.
Changing heart rate
What is a reflex arm (circuit)?
Nerve impulses propagating into, through & out of the central nervous system follow specific pathways
Sensory receptor
Sensory neuron responds to a specific
stimulus using a generator potential
Generator potential causes depolarisation of
sensory neuron – Nerve impulse generated
Sensory neuron
Axons of sensory neuron propagate
nerve impulses to axon terminal located
in spinal cord grey matter or brain stem
Integrating centre
One or more regions of grey matter act
as an integrating (processing centre)
Monosynaptic arc – Single synapse between sensory
neuron & motor neuron (simplest type of reflex)
Polysynaptic arc – More than two types of neurons &
more than one CNS synapse
Integrating centre consists of one or more interneurons,
which relay impulses to other interneurons & a motor
neuron
Motor Neuron
Impulses triggered by the integrating centre
propagate out of the CNS along a motor neuron
Effector
The part of the body that responds to the
motor nerve impulse (e.g. muscle or gland)
If effector is skeletal muscle – Somatic reflex
If effector is cardiac muscle, smooth muscles
or a gland – Autonomic reflex
What are the 4 important somatic spinal reflexes?
Stretch reflex - Causes reflex contraction of a muscle that has been stretched
Tendon reflex- Causes relaxation of the muscle attached to the stimulated tendon organ
Flexor reflex - Causes withdrawal of a part of the body in response to painful stimulus
Crossed extensor reflex - Causes contraction of muscle that extend joints in the limb opposite a painful stimulus
What is the stretch reflex?
Monosynaptic reflex arc that causes contraction of a stretched skeletal muscle | e.g. knee jerk
