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BIO201 - Chapter 13 (Spinal Cord, Spinal Nerves, and Somatic Reflexes)

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Foramen Magnum
The spinal cord extends from the
L1
The spinal cord extends to
Central Nervous System
The spinal cord is a component of which system
Peripheral Nervous System
The spinal nerves are a component of which system
Conduction, Locomotion, Reflexes
3 Functions of the Spinal Cord
Conduction
Bundles of fibers passing information up and down the spinal cord, connecting different levels of the trunk with each other and with the brain
Central Pattern Connectors
Pools of neurons providing control of flexors and extensors that cause alternating movements of the lower limbs
Reflexes
Involuntary, stereotyped responses to stimuli
31
Total pairs of spinal nerves
Cervical, Thoracic, Lumbar, Sacral
4 Regions of Spinal Cord
Cervical Enlargement
Nerves to the upper limb
Lumbar Enlargement
Nerves to the pelvic region and lower limbs
Medullary Cone
Tapered tip of the spinal cord
Cauda Equinae
Bundle of nerve roots that occupy the vertebral canal from L2 to S5 (horse's tail)
Meninges
Three fibrous connective tissue membranes that enclose the brain and spinal cord
Dura Mater
Tough collagenous membrane surrounded by epidural space filled with fat and blood vessels
Arachnoid Mater
Layer of simple squamous epithelium lining the dura mater and loose mesh of fibers filled with CSF (creates subarachnoid space)
Pia Mater
Delicate membrane adherent to the spinal cord (should never penetrate this layer)
Subarachnoid Space
Comprised of a majority of CSF
Epidural Space, Dura Mater, Arachnoid Mater, Subarachnoid Space, Pia Mater
5 Layers of Meninges in the Spinal Cord
Gray Matter
Neuron cell bodies with little myelin; site of information processing (synaptic integration)
White Matter
Abundantly myelinated axons; carry signals from one part of the CNS to another
Dorsal
Root of spinal nerve that is totally sensory fibers
Ventral
Root of spinal nerves that is totally motor fibers
Gray Commissure
Connects the dorsal and ventral roots of gray matter
Central Canal
Punctures the gray commissure; lined with ependymal cells and filled with CSF
White Column
Consists of bundles of myelinated axons that carry signals up and down, to and from the brainstem
Ascending Tracts
Tracts that carry sensory information up the spinal cord
Descending Tracts
Tracts that carry motor information down the spinal cord
Decussation
As the fibers pass up or down the brainstem and spinal cord they cross over from the left to the right side and vice versa
Contralateral
When the origin and destination of a tract are on opposite sides of the body
Ipsilateral
When the origin and destination of a tract are on the same side of the body
3
Number of neurons sensory signals travel across in ascending tracts
First Order Neurons
Detect stimulus and transmit signals to spinal cord or brainstem (in ascending tracts)
Second Order Neurons
Continues to the thalamus at the upper end of the brainstem (in ascending tracts)
Third Order Neurons
Carries the signal the rest of the way to the sensory region of the cerebral cortex (in ascending tracts)
Dorsal Column Pathway
Pathway that functions in deep touch, visceral pain, vibration, and proprioception
Proprioception
Nonvisual sense of the position and movements of the body
Spinothalmic Pathway
Pathway that functions in pain, pressure, temperature, light touch, tickle, and itch
Spinocerebellar Pathway
Proprioceptive signals from limbs and trunk travel up to provide the cerebellum with feedback needed to coordinate muscle actions
2
Number of neurons involved in descending tracts
Upper Motor Neuron
Originates in the cerebral cortex or brainstem and terminates on a lower motor neuron (descending tract)
Lower Motor Neuron
Axon leads the rest of the way to the muscle or other target organ (descending tract)
Corticospinal Tract
Descending tract from the cerebral cortex for precise, finely coordinated limb movements
Tectospinal Tract
Descending tract that functions as a reflex turning of the head in response to sights and sounds
Reticulospinal Tract
Descending tract that functions in controlling limb movements important to maintain posture and balance
Vestibulospinal Tract
Descending tract that functions in postural muscle activity in response to inner ear signals
Nerve
A bundle of nerve fibers (axons)
Epineurium
Covers a nerve
Perineurium
Surrounds a fascicle
Endoneurium
Separates individual nerve fibers
Perineurium
Blood vessels penetrate only the...
Neurilemma
Outer membrane formed by Schwann cells of a PNS nerve axon
Sensory (Afferent) Nerves
Carry signals from sensory receptors to the CNS
Motor (Efferent) Nerves
Carry signals from the CNS to muscles and glands
Mixed Nerves
Consist of both afferent and efferent fibers; conduct signals in two directions
Ganglion
Cluster of neurosomas outside of the CNS
Proximal Branches
Branches of nerves that includes the dorsal and ventral roots
Distal Branches
Branches of nerves that includes the dorsal and ventral ramus
Shingles
Skin eruptions along path of nerve; remains for life in dorsal root ganglia
Cervical Plexus
Plexus that supplies the neck and phrenic nerve to the diaphragm
Brachial Plexus
Plexus that supplies the upper limb and some of the shoulders and neck
Lumbar Plexus
Plexus that supplies the abdominal wall, anterior thigh and genitalia
Sacral Plexus
Plexus that supplies the remainder of the lower trunk and lower limb
Coccygeal Plexus
Plexus found on S4, S5 and C0
Somatosensory Function
Plexuses carry signals from bones, joints, muscles, and skin
Dermatome
A specific area of the skin (cutaneous) that receives sensory input from a pair of spinal nerves
Require Stimulation, Quick, Involuntary, Stereotyped
4 Properties of a Reflex
Conditioned Reflexes
Learned responses
Muscle Spindle
Stretch receptors embedded in skeletal muscles
Proprioceptors
Specialized sense organs to monitor the position and movement of the body parts
Length, Movement
Muscle spindles inform the brain of muscle... (2)
Intrafusal Fibers
Muscle fibers within a spindle
Stretch (Myotatic) Reflex
When a muscle is stretched, it contracts and maintains increased tonus; Knee-jerk reflex
Flexor (Withdrawal Reflex)
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 back to the muscle
Crossed Extensor Reflex
The contraction of extensor muscles in the limb opposite of the one that is withdrawn; maintains balance by extending the other leg
Ipsilateral Reflex Arc
Reflex arc in which the sensory input and the motor output are on the same sides of the spinal cord
Contralateral Reflex Arc
Reflex arc in which the input and output are on opposite sides of the spinal cord
Intersegmental Reflex
Reflex in which the input and output occur at different levels of the spinal cord
Tendon Organs
Proprioceptors in a tendon near its junction with a muscle
Golgi Tendon Organ
1mm long, nerve fibers entwined in collagen fibers of the tendon
Tendon Reflex
Response to excessive tension on the tendon; inhibits muscle from contracting strongly; moderates muscle contraction before it tears a tendon or pulls it loose from the muscle or bone