University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2021
Views:

106

Pages:

24
Author:

Donavan Williams

The Patellar Ligament Reflex Arc Muscle Spindle • Muscle spindle senses the length of skeletal muscles. • The spindles are modified skeletal muscle cells that are wrapped with special sensory fibers that synapse with interneurons in the spinal cord that quickly activate motor neurons to compensate for the stretch and inhibit antagonistic muscles. Muscle Spindle Muscle Spindle Ascending Pathway Example: The Dorsal Column • Sensations of deep touch, visceral pain, vibration are relayed from First Order to Second Order to Third Order Neurons. • Third Order Neurons in thalamus carry signal to cerebral cortex where it is perceived. Descending Pathway Example: The Corticospinal Tract • Precise, coordinated limb movements are initiated in the motor cortex of the brain and relayed to the spinal cord. • Two neuron pathway starts with an upper motor neuron in cerebral cortex that makes a synapse with a lower motor neuron in the spinal cord that carries the signal to a muscle The Patellar Tendon Reflex Arc 5 Golgi Tendon Reflex • Golgi Tendon Organs are Proprioceptors in tendons. • Excessive tension on the tendon inhibits the motor neuron to that muscle and muscle contraction is decreased. The Spinal Cord • Conducts information between brain and body. • Extends through vertebral canal from foramen magnum to L1. • Each pair of spinal nerves receives sensory information and sends out motor signals to muscles and glands. • Spinal cord is part of the Central Nervous System while the spinal nerves are part of the Peripheral Nervous System Functions of the Spinal Cord • Conduction – bundles of nerve fibers pass information up and down spinal cord. • Locomotion – coordinates actions of several muscle groups – central pattern generators are pools of neurons that provide control of flexors and extensors as in walking. • Reflexes – involuntary, stereotyped responses to stimuli (remove hand from hot stove) involves brain, spinal cord and peripheral nerves. Spinothalamic Pathway • Pain, pressure, temperature, light touch, tickle & itch • Decussation of the second order neuron occurs in spinal cord Spinocerebellar Pathway • Proprioceptive signals in limbs and trunk travel up to the cerebellum • Second order nerves ascend in lateral column Descending Motor Tracts • Tectospinal tract – reflex movements of head • Reticulospinal tract – controls limb movements important to maintain posture • Vestibulospinal tract – postural muscle activity in response to inner ear signals Spinal Cord Trauma • • • • • 10-12,000 people/ year are paralyzed 55% occur in traffic accidents This damage poses risk of respiratory failure Early symptoms are called spinal shock Tissue damage at time of injury is followed by post-traumatic infarction Nerve Plexuses • Ventral rami branch & anastomose repeatedly to form 5 nerve plexuses – cervical in the neck, C1 to C5 • supplies neck and phrenic nerve to the diaphragm – brachial in the armpit, C5 to T1 • supplies upper limb and some of shoulder & neck – lumbar in the low back, L1 to L4 • supplies abdominal wall, anterior thigh & genitalia – sacral in the pelvis, L4, L5 & S1 to S4 • supplies remainder of butt & lower limb – coccygeal, S4, S5 and C0 Structure of a Nerve Plexus • Notice the branching and merging of nerves in this example of a plexus The Cervical Plexus The Brachial Plexus Dissection of the Brachial Plexus The Lumbar Plexus The Sacral and Coccygeal Plexuses Poliomyelitis and ALS • Diseases causing destruction of motor neurons and skeletal muscle atrophy • Poliomyelitis caused by poliovirus spread by fecally contaminated water – weakness progresses to paralysis and respiratory arrest • Amyotrophic lateral sclerosis – sclerosis of spinal cord due to astrocyte failure to reabsorb glutamate neurotransmitter – paralysis and muscle atrophy • White matter is divided into columns which are bundles of myelinated axons that carry signals up and down the spinal cord. • Each column is filled with tracts named for fibers with a similar origin, destination and function. Anatomy of Ganglia in the PNS • Ganglia in the PNS are clusters of neuron somas (cell bodies) in a nerve. • Example: Dorsal Root Ganglion is the location of the sensory neuron somas.