Week 10 Flashcards
pns- afferent division
conveys information from the sensors in the periphery to the cns
spinal cord
long cylinder of nerve tissue which extends down from the brainstem to the second lumbar vertebrae
pns- efferent division
somatic nervous system- nerve fibres innervate skeletal muscle
autonomic nervous system- nerve fibers innervate smooth and cardiac muscle and glands
- sympathetic and parasympathetic
neuroglia
non excitable
physical and biochemical support for neurons
occupy about half of the volume of the brain
four major types of glial cels serve as the connective tissue of the cns and as such help support the neurons both physically and metabolically
neuron
- excitable
- carry electrical signals
neuron is specialized to transmit electrical signals
cell body
axon
dendrites
mylin sheath
discontinuos sheath around the axon
composed of lipid and protein
nodes of ranvier: spaces between the segments of myelin sheath
- salutary conduction
salutary conduction
signal leaps from node to node
mylenaited nerve fibres have much faster conduction velocities than unmyleniated fibres
multiple sclerosis
autoimmune disease- body attacks myelin sheath within cns
break down in communication
exposed nerves can be destroyed irreversibly
fatigue, vision changes, numbness, loss of coordination, muscle weakness, cognitive dysfunction
synapse
the region where a neuron meets its target cell
chemical synapse: electrical signal converted to chemical signal for transmission to post synaptic cell
neuron structure
afferent neurons: carry impulses from the sensory receptors into spinal cord or brain
efferent neurons: transit impulses from the cns out of the effector organs- muscles and glands
interneurons: lie entirely within the cns. they account for 99% of all nerve cells
resting membrane potential
due to selective permeability characteristics of the nerve cell membrane a potential difference exists between the inside and outside
action potential
high concentration of positive sodium ions on the outside of the membrane causes it be electrically positive, while the inside is electrically negative, this causes sodium ions to rush to the inside of the nerve and reverses polarity
tetrodotoxtin
acts on the cns and pns
blocks sodium channels
prevents action potential
symptoms of poisoning: paresthesia in mouth then extremities
weakness, lack of coordination, paralysis, cyanosis
death within 4-6 hours
nerve to nerve synapses
nervous information is relayed across the synaptic cleft by means of a chemical transmitter substance
neural muscular junction
consists of axon terminals, motor end plates on the muscle membrane and schwas cell sheaths
spinal cord
The spinal cord is enlarged in two regions for innervation of the limbs:
a) The cervical enlargement which extends from the C4 through T1 segments of the spinal cord
b) The lumbosacral enlargement which extends from the T11 through L1 segments
of the spinal cord
plexus
a network on converging and diverging nerve fibres or blood vessels
dorsal roots
contain afferent fibres that carry information from the periphery to the spinal cord and brain
ventral roots
contain efferent fibers to the skeletal fibres
ganglion
collection of nerve cell bodies located outside the cns
spinal cord injury
transection (complete cut) of the spinal cord results in loss of all sensation and voluntary movement inferior to the point of damage
risk hanson
goal is to create an inclusive world where people with disabilities can reach their full potential
proprioceptors
Conduct sensory information to the CNS from muscles, tendons, ligaments, and joints kinesthetic sense
* Kinesthetic sense: gives information about the location of parts of our body in relation to their environment.
muscle spindles
change in length
golgi tendon organ
change in tension
joint receptors
change in angle
muscle spindles
Structure - several modified muscle fibers,
– four to 10 millimetres in length,
– containedinacapsule,
– with sensory nerve spiralling around its center.
muscle spindles function
send info to the cns regarding the degree of muscle stretch
- activation of the exact number of motor units to overcome a given resistance
tonic stretch
concerned with the final length of the muscle fibres
phasic stretch
spindle responds to the velocity of the change of length
gamma system
gamma efferent fibers innerverate the contractile ends of the intrafusal fibres
When the alpha motor neurons are activated, the gamma motor neurons are also activated (coactivation).
– Gamma system provides the mechanism for maintaining the spindle at peak operation at all muscle lengths.
– They help maintain muscle spindle sensitivity
stretch reflex
Muscle spindles are distributed throughout the muscle. Their density varies with the degree of control required by a given muscle.
five functional components of stretch reflex
Receptor (muscle spindle)
* Afferent (sensory) neuron
* Integrating Centre (spinal cord)
* Efferent (motor) neuron (both alpha and gamma) * Effector (muscle contraction)
golgi tendon organs location
encapsulated in tendon fibres near the junction of the muscle and tendon fibres
they are in a series with muscle fibres rather than in parallel as are muscle spindles
when a muscle contracts the GTO is stretched
gto functions
the firing rate is sensitive to changes in tension of the muscle
sensory input about the tension produced by muscles is a useful for a variety of motor acts such as maintaining a steady grip on an object
when stimulated by excessive tension send sensory information to the cns which causes contracted muscle to relax
joint receptors
supply information to the cns concerning joint angle, acceleration of joint, pressure, pain
control of motor functions
cerebral cortex and cerebellum are the main centres employed in learning new motor skills , voluntary control of movement patterns
primary motor cortex
ocated at the rear of the frontal lobe of the cerebral cortex.
* Stimulation of different areas of the primary motor cortex brings
about movement in different, specific areas of the body.
* Contains the motor homunculus. However, no coordinated movement can be elicited.
cerebral cortex
Corticospinal tract
* long axons which carry impulses from the primary motor cortex
where their cell bodies are located directly to lower motorneurons in spinal cord spinal nerves
* The corticospinal system primarily mediates performance of fine, discrete, voluntary movements of the hands and fingers.
premotor cortex
One of the three higher areas that command the primary motor cortex.
* Located on the lateral surface of each cerebral hemisphere in front of the primary motor cortex.
somatosensory cortex
The site for initial processing of pressure, touch, heat pain and proprioceptive input
* Located in the anterior section of the parietal lobe, immediately behind the central sulcus.
* Each region within the somatosensory cortex receives sensory input from a specific area of the body.
cerebellum
It functions by means of intricate feedback circuits to monitor and coordinate other areas of the brain involved in motor control.
* It receives signals concerning motor output from the cortex and sensory information from:
* receptors in muscles, tendons, joints and skin,
* visual, auditory and vestibular end organs
cerebellum function
Function - the major comparing, evaluating, and integrating center for
* postural adjustments, – locomotion,
– maintenance of equilibrium,
– perceptions of speed of body movement,
– and general motor coordination.
* Damage to the cerebellum results in impaired motor control.
symptoms of cerebellum damage
They cannot perform movements smoothly
* They walk awkwardly with their feet well apart. They have such difficulty maintaining their balance that their gait appears drunken.
* They cannot start or stop movements quickly or easily
* They cannot easily combine the movements of several joints into a single, smooth, coordinated motion. To move the arm, they must first move the shoulder, then the elbow, and finally the wrist.
