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

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