Chapter 13: Spinal Cord, Spinal Reflexes Flashcards
Functions of the spinal cord
Conduction, Neural Integration, Locomotion and Reflexes
Two areas of the cord are thicker than elsewhere
Cervical enlargement—nerves to upper limb
- Lumbar enlargement—nerves to pelvic region and lower limbs
Ascending tracts
carry sensory signals up the spinal cord. First-order neurons: detect stimulus and transmit signal to spinal cord or brainstem
Second-order neurons: continues to the thalamus at the upper end of the brainstem
Third-order neurons: carries the signal the
Descending tracts
Descending tracts—carry motor signals down brainstem and spinal cord
Involve two motor neurons
Upper motor neuron (UMN): originates in cerebral cortex or brainstem and terminates on a lower motor neuron
Lower motor neuron (LMN): neurosoma is in brainstem or spinal cord
Poliomyelitis
infectious viral disease that effects the CNS and can cause temporary or permanent paralysis
Amyotrophic lateral sclerosis (ALS) or Lou Gehrig disease
Destruction of motor neurons and muscular atrophy Also sclerosis (scarring) of lateral regions of the spinal cord Astrocytes fail to reabsorb the neurotransmitter glutamate from the tissue fluid
Nerve
a cord-like organ composed of numerous nerve fibers (axons) bound together by connective tissue
Sensory (afferent) nerves
Carry signals from sensory receptors to the CNS
Motor (efferent) nerves
Carry signals from CNS to muscles and glands
Mixed nerves
Consists of both afferent and efferent fibers
31 pairs of spinal nerves (mixed nerves)
8 cervical (C1–C8) First cervical nerve exits between skull and atlas Others exit at intervertebral foramina 12 thoracic (T1–T12) 5 lumbar (L1–L5) 5 sacral (S1–S5) 1 coccygeal (Co1)
Somatosensory Function
carry ensory signals from bones, joints, muscles, and skin
Dermatome
a specific area of skin that conveys sensory input to a spinal nerve
Reflexes
quick, involuntary, stereotyped reactions of glands or muscle to stimulation
Somatic Reflexes
reflexes involving the somatic nervous system innervating skeletal muscle
Muscle Spindle
stretch receptors embedded in skeletal muscles
Proprioceptors
specialized sense organs to monitor position and movement of body parts
Flexor (withdrawl) reflex
the quick contraction of flexor muscles resulting in the withdrawal of a limb from an injurious stimulus
Polysynaptic reflex arc
pathway in which signals travel over many synapses on their way to the muscle
Crossed extension reflex
contraction of extensor muscles in limb opposite of the one that is withdrawn
Tendon Reflex
in response to excessive tension on the tendon
