Chapter 14: Spinal Cord and Spinal Nerves Flashcards
Major functions of the spinal cord and nerves
- structural and functional link between the brain and the rest of the body
- exhibits some functional independence from the brain
2 types of conduction (spinal) pathways
1- sensory pathways
2- motor pathways
Sensory pathways
ascend towards the brain through the spinal cord
Motor pathways
descend from the brain through the spinal cord
3 Characteristics of pathways
- most pathways intersect while traveling through the white matter of the spinal cord
- consists of paired tracts
- are composed of two or three neurons working together
What is a dermatome?
a segment of skin supplied by a single spinal nerve and can help localize damage to one or more spinal nerves and is involved in visceral pain; all spinal nerves except C1
Referred pain
pain from one organ referred to a dermatome
What does it mean to be contralateral?
stimulus on one side and response on the other
What does it mean to be ipsilateral?
stimulus and response on the same side
2 types of sensory pathway receptors
1- somatosensory receptors
2-visceral sensory receptors
2 kinds of somatosensory receptors
1- tactile receptors
2- proprioceptors
Tactile receptors
detect characteristics of an object
Proprioceptors
detect stretch in joints, muscles, tendons
Visceral sensory receptors
detect changes in an organ
Characteristics of sensory pathways
- somatosensory pathways: carry signals from skin, muscles, joints
- visceral sensory receptors: carry signals from viscera
Characteristics of sensory pathways
- at least 2, maybe 3 sensory neurons in the path
- use a series of neurons to relay signals to brain
Primary (1st order) neuron
detects stimuli with dendrite receptors within the posterior root ganglion
Secondary neuron
is an interneuron located within the dorsal gray horns of the spinal cord or brainstem nucleus; integrates sensory info and directs to appropriate brain regions
Tertiary neuron
an interneuron located in the thalamus; consolidates sensory info deemed “important” by the thalamus and transfers to the appropriate sensory cortex
Characteristics of motor pathways
- control effectors such as skeletal muscles
- start in brain and include at least two neurons
2 types of motor pathways neurons
1- upper motor neuron
2- lower motor neuron
Upper motor neuron
cell body within the cerebral cortex or nuclei of the brainstem; excites or inhibits the activity of the lower motor neuron
Lower motor neuron
cell bodies housed within the anterior/ventral horn of the spinal cord or nuclei of the brainstem; always excitatory; axons exit CNS; excites a muscle and cause contraction
Main properties of a reflex
- a stimulus is required to initiate a reflex
- the response is rapid; it involves a chain of only a few neurons
- the response is preprogrammed; always the same
- the response is involuntary; no intent or awareness of the reflex before it happens
Shingles
- reactivation of chickenpox
- rash and blisters along the dermatome
Reflexes
rapid, preprogrammed, involuntary responses of muscles or glands to a stimulus
What is a reflex arc?
the neural “wiring” of a single reflex
The 5 steps involved in the activation of a reflex?
1- a stimulus activates a receptor
2- generates a nerve signal that travels by sensory neurons to the CNS
3- information processed by interneurons of CNS (only if it is a polysynaptic reflex)
4- motor neuron sends the nerve signal to an effector
5- the effectors (muscle or gland) resond
Reflex classifications
- spinal or cranial
- somatic or visceral
- monosynaptic or polysynaptic
- ipsilateral or contralateral
- innate or acquired
Spinal or cranial
is the spinal cord or brain the reflex integration center?
Somatic or visceral
is the effector a skeletal muscle or is it cardiac muscle, smooth muscle, a gland?
Monosynaptic or polysynaptic
do sensory neurons synapse directly with motor neurons or are they interneurons in the reflex arc?
Ipsilateral or contralateral
are receptor and effector on the same side of the body or on opposite sides?
Innate or acquired
are you born with the reflex or do you develop it after birth?
What is a monosynaptic reflex?
simplest reflex with no interneuron
What is a polysynaptic reflex?
more complex and always involves at least 1 interneuron
4 common spinal reflexes
1- stretch reflex
2- golgi tendon reflex
3- withdrawal reflex
4- crossed-extensor reflex
Stretch reflex
reflexive contraction of a muscle after it is stretched; stretch is detected by a muscle spindle proprioceptor
Tendon reflex
prevents muscles from contracting excessively
Withdrawal reflex
pulls a body part away from a painful stimulus
Crossed-extensor reflex
occurs in conjunction with withdrawal reflex; allows the opposite side limb to support body weight while hurt limb withdrawals
Stretch reflex classified as
- spinal
- somatic
- monosynaptic
- ipsilateral
- innate
Golgi tendon reflex classified as
- spinal
- somatic
- polysynaptic
- ipsilateral
- innate
Withdrawal reflex classified as
- spinal
- somatic
- polysynaptic
- ipsilateral
- innate
Crossed-extensor reflex classified as
- spinal
- somatic
- polysynaptic
- contralateral
- innate
Hypoactive reflex
diminished or absent; may indicate damage to the spinal cord, muscle disease, or damage to the neuromuscular junction
Hyperactive reflex
abnormally strong response; may indicate damage to the brain and spinal cord, especially if accompanied by clonus (rhythmic oscillating movements with reflex testing)
Reciprocal inhibition
inhibiting antagonistic muscle contraction
Reciprocal activation
stimulation of alpha motor neurons of antagonistic muscles
Muscle spindle
stretch receptors that signal the length and changes in length of muscles
