Ch. 14 PNS Flashcards
Peripheral nervous system (PNS)
Composed of nerves found outside the brain and spinal cord. The pianist can be divided into two subdivisions the sensory (afferent) and motor (efferent) divisions.
There are three major components to the PNS
Sensory receptors
Nerves
Motor endings
Explain sensory receptors in the different types based on “ classification by stimulus detected”
Mechanoreceptors - respond to touch pressure vibration and stretch
Thermoreceptors - sensitive to changes in temperature
Photoreceptors - respond to light energy
Chemoreceptors - respond to chemicals (eg. smell taste, changes in blood chemistry)
***Chem detectors in the aorta and carotid artery sense in increased CO2 (low PH) and transmit this information to breathing centers of the brainstem
Nociceptors - sensitive to pain-causing stimuli or damage to tissues (eg. extreme heat or cold, excessive pressure, inflammatory chemicals)
Explain sensory receptors and the different types based on “classification by location”
Exteroceptors
-respond to stimuli arising outside body
-receptors in skin for touch, pressure, pain, and temperature
-Most special sense organs (vision, hearing, taste and smell)
Interoceptors (visceroceptors)
-respond to stimuli arising in internal viscera and blood vessels
-sensitive to chemical changes, tissue stretch, and temperature changes
-Sometimes causes discomfort, but usually unaware of their workings
Proprioceptors
-respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue covering of bones and muscles
-inform brain of one’s movement, help with spatial orientation
Explain sensory receptors and different types based on “classification by structural complexity”
Majority of sensory receptors in the PNS belong to the general senses (pressure stretch, vibration, temperature, pain, and muscle sense)
Most of the receptors are modified dendritic endings of sensory neurons
-these type of receptors are found throughout the body
-Receptors associated with general senses may be free or encapsulated
-the main difference between the two is that free nerve endings do not have complex sensory structures while the encapsulated nerve endings have either a brush border or fluid filled sacks at the end
Describe the three levels of neural integration in the sensory system
Survival depends upon sensation and perception
-Sensation is the awareness of changes in the internal and external environment
-Perception is the conscious interpretation of those stimuli
There are three basic levels of neural integration and sensory systems
Receptor level -sensory receptor
Circuit level -processing in ascending pathways
Perceptual level -cortical sensory areas (cerebral cortex)
Identify and describe the anatomical structure of a nerve ending
Define ganglia and where they are located
- The PNS doesn’t just contain nerve fibers(axons)-there are also cell bodies of neurons found in the PNS collections of these nerve cell bodies are called ganglia
- ganglia are associated with both sensory and motor neurons
- ganglia associated with century nerve fiber contains cell bodies of sensory neurons
(ex. Dorsal root ganglia-contains sensory neurons cell bodies; these are unipolar neurons- one process extends to receptors the other process extends to the spinal cord
-ganglia associated with motor nerves contain autonomic motor neuron cell bodies
(ex. Autonomic ganglia, which are associated with the visceral organs)
* there are no somatic motor ganglia*
Describe how nerves can be classified by the direction in which they carry impulses (what is the most common type?)
Sensory nerves-carry sensory input to the brain or spinal cold from the environment (afferent)
Motor nerves - Carrie motor impulses from the brain or spinal cord, muscle or glands (efferent)
Mixed nerves - have a combination of sensory and motor neurons in one nerve
***** most nerves are mixtures of motor and sensory fibers as well as somatic and autonomic (visceral) fibers
Differentiate between the major types of peripheral nerves
Cranial vs Spinal
There are 12 pairs of cranial nerves
-to arise from the cerebrum (optic and olfactory) the rest from the brainstem
- Other than vagus nerves which extended into the abdomen, the other 10 cranial nerves, serve only head and neck structures
- Most are mixed nerves (that is they have both sensory and fiber) 2 pairs are purely sensory
- each numbered ( I - XII ) and named from rostral - caudal
There are 31 pairs of spinal nerves
-Each are mixed nerves (Cary motor and sensory fibers or outgoing and incoming signals)
-Spinal nerves in all parts of the body except the head and part of the neck
-spinal nerves are named point of issue from the spinal cord
Identify and describe an anatomy of spinal nerves
Explain the type of fibers carried in the ventral and dorsal roots and rami
Each spinal nerve arises from the spinal cord via two roots, the ventral root, and the door sold route
* ventral roots- contains somatic motor fibers from ventral horn motor neurons and autonomic motor fibers from the lateral horn motor neurons
*** dorsal roots- contain sensory fibers from sensory neuron cell bodies located in the dorsal root ganglia. They are conducting impulses from peripheral receptors
- dorsal root (spinal) ganglia -cell bodies of sensory neurons….. these connect with neurons in the dorsal horn (or elsewhere in the spinal cord)
***rami- Carrie, both sensory and motor fibers
- dorsal and ventral rami and their main branches supply the entire somatic region of the body (skeletal muscle and skin) from the neck down
- the dorsal rami supply the posterior body trunk
- the ventral rami supply the rest of the trunk and limbs
- the ram communicants contain autonomic nerves that carry Vistro motor and sensor information to and from the visceral organs
Peripheral motor endings and neuromuscular junction on skeletal muscle
Motor endings are PNS elements that activate effectors (skeletal, smooth or cardiac muscle and glands) by releasing neurotransmitters
- innervation of skeletal muscle takes place at the neuromuscular junction
-neurotransmitter acetylcholine (ACh) released when nerve impulses reach axon terminal - ACh vines to receptors resulting in
* movement of Na+ and K+ across membrane
*** depolarization of muscle cell
*** an end plate, potential triggers, and action potential —-> muscle contraction
