Chapter 13 Spinal Cord
Nerve Plexus
Ventrral rami of adjacent spinal nerves that blend their fibers and produce a series of compound nerve trunks; 4 main plexuses: cervical, brachial, lumbar, and sacral
Rami communicantes
White and Grey rami together in the motor pathway
Dermatome
(body map) every region of the skin surface is monitored by a single pair of spinal nerves.
Cervical Plexuses
-C1-C5 -innervates muscles of the neck and diaphragm -Phrenic Nerve- provides nerve supply to the entire diaphragm
Brachial Plexus
-C5-T1 -innervates the pectoral girdle and upper limbs -originate from trunks (large bundles of axons contributed to by several nerves) and cords (smaller branches that originate at trunks) -Radial Nerve, ulnar nerve, and median nerve supply nerve function to the 14 muscles of the forearm for extension, flexion, supination, and pronation
Sacral Plexus
-L4-S4 -innervates the lower limbs -sciatic nerve branches into the fibular nerve and tibial nerve -the sural nerve is often used in nerve grafts -Saphenous
Lumbar Plexus
-T12-L4 -Innervates the lower limbs and pelvic girdle
Peripheral Distribution of Spinal Nerves
1. The sympathetic nerve, dorsal ramus, and ventral ramus carry sensory information through the dorsal root to the somatic and visceral nuclei of the spinal cord 2.Spinal cord interprets the info 3. response information is sent to to visceral and somatic motor nuclei in the ventral horn 4.information then travels through the ventral root and separates into the dorsal, ventral, or sympathetic rami
Polysynaptic reflexes
1.Tendon reflexes 2.withdrawal reflexes -Flexor reflex 3.crossed extensor reflexes pain response more than 2 neurons involved
Human body has
10 million sensory neurons 1/2 million motor neuron 20 billion interneurons
Columns
3 regions of white matter in the spinal cord
# of spinal nerve pairs?
31
lengthening of the spinal cord ends at age
4
there are ______ cervical vertebrae but ____ cervical nerves
7, 8
CSF (cerebrospinal fluid)
absorbs shock, acts as a diffusion medium for gases and nutrients.
in the thoracic section, a spinal nerve's name reflects the vertebrae type is just _____ it?
Above (T1 nerve is just inferior to T1 vertebrae)
Dorsal Root Ganglia
Cell bodies of sensory neurons just outside the spinal cord (afferent)
Ventral roots
Contain the axons of motor neurons (Efferent)
Neuronal pools
Functional groups of interconnected neurons; scattered or localized with a limited number of input sources and output destinations
Spinal cord ends between
L1 and L2
Ventral Horn
Motor nuclei
Dorsal Horn
Sensory nuclei
The spinal cord is divided into 31 sections that correlates with the origins of
Spinal Nerves
Nerves
a group of axons from many neurons with vascularization throughout 3 connective tissue layers
Stretch Reflex
a muscle that is stretched will automatically contract. They are mono-synaptic which means they only have 2 neurons. 1. muscle spindles (receptors in stretch reflexes) are stretched 2.sensory neurons become excited 3. motor neurons are stimulated 4. rapid muscle shortening or contraction to return muscle spindles to their resting state
Circuit Patterns: -Reverberation
a positive feedback mechanism, continually stimulates the pre-synaptic neuron. this cycle will continue until synaptic fatigue or an inhibitory function.
Spinal cord reflexes -Reflex
an involuntary response to a stimulus. very little variability in this response.
Spinal Nerves
are MIXED nerves; they contain both sensory and motor fibers with a sheath
in the Cervical section, a spinal nerve's name reflects the vertebrae type is just _____ it?
below, (C3 nerve is just superior to C3 vertebrae)
Tract
bundle of axons in CNS with similar structure and function; short tracts send sensory or motor infomation within the spinal cord, Longer tracts connect the spinal cord with the brain
CSF made where
choroid plexus and ependymal cell
CNS
contains one or more synapses
Grey Matter
deep to white matter making up the 'horns' of the spinal cord; consist of cell bodies, neuroglia, and unmyelinated axons
Receptor
detect a stimulus and generate impulses
Dura Mater
dura-=tough) outer most layer made of fibrous connective tissue. it lines the skull and the vertebral canal.
white rami
first branch from the spinal nerve carrying visceral motor fibers to a sympathetic ganglion (internal organs). myelination gives it a light color and therefore its name. only in motor
Innate reflexes
from during development ex: kids follow w/ eyes
Endoneurium
innermost layer surround individual axons
Acquired reflexes
learned motor patterns enhanced by repetition
Circuit Patterns: -Parallel processing
many neurons or pools process the same info at the same time allows for many responses at the same time. divergence has to happen first
Circuit Patterns: -Convergence
many neurons that synapse on one post-synaptic neuron ex: subconscious and concious
Nuclei
masses of grey matter within the CNS(gatherings of neurons that serve a specific function)
perineurium
middle layer, compartmentalize bundles of axons called fascicles
Arachnoid Mater
middle spinal membrane that has 2 layers simple squamous epithelium connected to the dura mater and the inner layer is called the arachnoid trabeculae, which is a network of collagen and elastin fibers.
Tendon reflexes
monitors tension on a tendon with collagen fibers stretching being the receptor. causes an inhibitory reflex on motor neurons to shut down the affected muscle.
withdrawal reflexes -Flexor reflex
move the affected body part away from the stimulus. (polysynaptic) Flexor reflex= where pain will cause the affected part to recoil. (polysynaptic)
Pia Mater
nner most layer, very thin membrane on the surface of the brain and spinal cord.
Epineurium
outermost layer of a nerve
Spinal Meninges
provides physical stability and shock absorption while provided oxygen and nutrients to the spinal cord tissue
Effector
performs its characteristic action
Grey rami
post-ganglionic fibers that innervate glands and smooth muscle in the body wall and limbs, unmyelinated giving it a grey color and therefore its name. only in motor
Spinal Cord Reflex
reflexes that don't depend on the brai
Anterior white commissure
regions where axons cross from one side of the spinal cord to the other
Circuit Patterns: -Serial processing
sequential process with info moving from one neuron to another.
Subarachnoid space
space between the arachnoid membrane and the pia mater. contains and circulates CSF of the CNS.
A spinal nerve is formed when...
the dorsal and ventral roots merge and are bound together
White Matter
superficial tissue of the spinal cord that contains myelinated and unmyelinated axons
crossed extensor reflexes
the motor response occurs on the side opposite the stimulus. ex. if you step on a tac the unaffected leg straightens to support you while the affected leg recoils.
Reflex Arc
the reflex arc is the pathway nerve impulses travel when a reflex is elicited; exhibits negative feedback; there are five parts: 1. receptor 2. sensory neurons 3. CNS 4. Motor Neurons 5. Effector
Circuit Patterns: -Divergence
the spread of info from one neuron to several neurons.
Motor neurons
transmit impulses from the CNS to the effector through the ventral root
Sensory neurons
transmits a graded potential that leads to an action potential that travels along the dorsal root