Lec 8- Nervous system org and reflexes Flashcards
Ascending Spinal Tract
Transmit to the brain signals derived from afferent input
Descending Spinal Tract
Relay messages from the brain to efferent neurons.
Pyramidal/corticospinal
Fibers originating from neuronal cell bodies known as pyramidal cells within the primary motor cortex descend directly without synaptic interruption to terminate on motor neurons in the spinal cord.
Reticulospinal/extrapyramidal
Include synapses that involve regions of the brain.
Ganglia
The nerve cells in the outermost layer of the retina whose axons form the optic nerve.
Dorsal root
Sensory fibers.
Afferent fibers carrying incoming signals from peripheral receptors enter the spinal cord through the dorsal root.
Ventral root
Motor fibers.
The cell bodies for the efferent neurons originate in the gray matter and send axons out through the ventral root.
Nerve
A bundle of peripheral neuronal axons, some afferent and some efferent, enclosed by a connective tissue covering and following the same pathway.
Spinal nerves
31 pairs (8 cervical, 12 thoracic, etc...) Bring info to the CNS.
Cranial Nerve X = Vagus
Most branches of the vagus nerve supply organs in the thoracic and abdominal cavities.
Major nerve of the PNS.
Peripheral nervous system (PNS)
Nerve fibers that carry information between the CNS and the body.
Afferent
Sensory; carries input to CNS.
Efferent
Motor; carries info to an effector organ.
Transduce
to convert (something, such as energy or a message) into another form essentially sense organs transduce physical energy into a nervous signal.
Modality
The energy form to which receptors respond such as light, heat, pressure, and chemical changes.
Sensory receptors
An efferent neuron’s peripheral ending, which is specialized to respond to a particular stimulus in its environment.
Chemoreceptor
A sensory receptor sensitive to specific chemicals.
Photoreceptor
A sensory receptor responsive to light.
Thermoreceptor
A sensory receptor responsive to heat and cold.
Mechanoreceptor
A sensory receptor responsive to mechanical enegry; such as stretching or bending.
Nociceptor
A pain receptor, sensitive to tissue damage.
Proprioceptor
A sensory receptor responsive to body position and movement.
Acuity
Discriminative ability, the ability to discern between two different points of stimulation
Receptive field
The circumscribed region surrounding a sensory neuron within which the neuron responds to stimulus information
Cutaneous receptors
The cutaneous receptors’ are the types of sensory receptor found in the dermis or epidermis. They are a part of the somatosensory system. Cutaneous receptors include cutaneous mechanoreceptors, nociceptors (pain) and thermoreceptors (temperature).
Adequate stimulus
the specific stimulus or modality that a receptor is specialized to respond to.
Tonic receptors
Do not adapt or adapt slowly.
Phasic receptors
Rapidly adapting receptors.
Generator potentials
stationary depolarization of a receptor that occurs in response to a stimulus and is graded according to its intensity and that results in an action potential when the appropriate threshold is reached
Rods
The eye’s photoreceptors used for night vision.
Cones
The eye’s photoreceptors used for color vision in the light.
Fovea centralis
Exact center of the retina; region with the greatest acuity.
Optic disk/Blind spot
Blind spot, lacks photoreceptors.
Route for passage of the optic nerve and blood vessels
Accommodation
The ability to adjust the strength of the lens in the eye so that both near and far sources can be focused on the retina.
Refelx arc
includes;
- sensory receptor
- afferent pathway
- integrating center
- efferent pathway
- effector
Golgi tendon organ
they can respond to changes in the muscle’s tension rather than to changes in its length.
Muscle spindle apparatus
Muscle spindles are stretch receptors within the body of a muscle that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers.
Intrafusal fibers
Lie within the spindle-shaped connective tissue capsules
Extrafusal fibers
Ordinary muscle fibers
Nuclear bag fiber
Sudden stretch.
A nuclear bag fiber is a type of intrafusal muscle fiber that lies in the center of a muscle spindle. Each has many nuclei concentrated in bags and they cause excitation of both the primary and secondary nerve fibers. There are two kinds of bag fibers based upon contraction speed and motor innervation.
Nuclear chain fibers
Sustained stretch.
Alpha motor neurons
Motor neurons that supply the extrafusal fibers
Gamma motor neurons
The efferent neuron that innervates a muscle spindle’s intrafusal fibers.
Coactivation
Simultaneous stimulation.
Takes the slack out of the spindle fibers as the whole muscle shortens.
Monosynaptic stretch reflex
local negative feedback mechanism to resist any passive changes in muscle length so that optimal resting length is maintained.
Reciprocal innervation
Stimulation of the nerve supply to one muscle and simultaneous inhibition of the nerves to antagonistic muscle.
Crossed-extensor reflex
a reflex in which the contralateral limb compensates for loss of support when the ipsilateral limb withdraws from painful stimulus in a withdrawal reflex.
