A&P 1: exam 7

Peripheral Nervous System, Reflex Activity, and the PNS

peripheral nervous system

lies outside the CNS with 2 divisions: an incoming afferent (sensory) division and outgoing efferent (motor) division; made up of nerves

somatic nervous system

controls the voluntary movements of skeletal muscles

autonomic nervous system

controls involuntary responses of the cardiac muscle, smooth muscle, and glands

sensory (afferent) nerves

contain the axons of sensory neurons bringing information to the CNS

motor (efferent) nerves

carry the axons of motor neurons towards muscle

mixed nerves

contain both afferent and efferent fibers

ganglia

groups of masses of cell bodies

epineurium

outer surface of a nerve is fibrous connective tissue

fasicles

groups of axons bundled together

perineurium

layer of fibrous connective tissue that wraps around fasicles

endoneurium

loose connective tissue that surrounds individual axons

spinal nerves

31 pairs; originate from spinal cord and branch out to innervate the body; carry both sensory and motor fibers; cervical nerves (8 pairs), thoracic nerves (12), lumbar nerves (5 pairs), sacral nerves (5 pairs), coccygeal nerves (1 pair); numbered according to the level of the spinal cord where they emerge

dermatomes

region of skin that carries sensory information through a specific pair of spinal nerves to the spinal cord and up to the brain; most overlap so there is redundancy in the system; safeguards the body so that in case there is damage to a single spinal nerve there can still be sensation in the skin area it innervated

gray matter

contains the cell bodies of neurons and is where neurons synapse with the interneurons of the CNS

white matter

contains axons of neurons

ventral root (anterior)

contains the axons of efferent motor neurons, which conduct impulses away from the cord towards muscle or glands

dorsal (posterior) ramus

contains nerves that serve the dorsal portions of the trunk, carrying somatic motor information to the back muscles and sensory information to and from the skin and muscles of the back

ventral (anterior) ramus

larger than dorsal; contains nerves that serve the remaining ventral parts of the trunk and the upper and lower limbs carrying visceral motor, somatic motor, and sensory information to and from the body surface, structures in the body wall, and the limbs

rami communicantes

branches off of the ventral ramus that communicate with the sympathetic trunk

plexus

network of interconnecting nerves; contain axons from various spinal nerves

sensation

biochemical or electrochemical changes at the cellular level in a receptor cell that detect an imbalance in homeostasis or a change in the environment

perception

the identification, interpretation, and organization of the sensory signal that allows for construction of an appropriate response

ascending tracts

carry sensory information from the PNS to the CNS; carry the signals upwards towards the brain

descending tracts

carry the output downwards from the brain to the spinal cord and out to the periphery

sensory receptors

located in the skin, organs, muscles, and tendons, detect a specific stimulus and convert the stimulus into electrochemical signals that are sent to the CNS; 4 types: nociceptors, thermoreceptors, mechanoreceptors, chemoreceptors

nociceptors

detect pain due to the presence of chemicals from tissue damage, intense mechanical stimuli, or extreme temperature changes

thermoreceptors

a physical stimulus that has its own type of receptor is temperature, which is sensed through a thermoreceptor that is either sensitive to temperatures above (heat) or below (cold) homeostatic body temperature

mechanoreceptors

physical stimuli, such as light touch, pressure, and vibration, as well as the sensation of sound and body position (balance), are interpreted through mechanoreceptors; detect information by a change in the cell membranes through a physical distortion of the membrane, which opens mechanically regulated ion channels; types: meissner’s corpuscles, lamellar corpuscles, root hair plexuses, baroreceptors, proprioceptor

Meissner’s corpuscles (tactile discs)

touch receptors in the skin that detect fine touch and vibration

lamellar corpuscles (pacinian corpuscles)

neurons with encapsulated nerve endings that respond to deep pressure and touch found in the dermis of the skin

root hair plexuses

wrap around a hair follicle, perceiving information when a hair follicle moves

barorecptors

free nerve endings with branches in the walls of an organ or vessel that sense the pressure changes; found in blood vessels and the digestive, urinary, and respiratory tracts to monitor pressure changes

proprioreceptor

located near a moving part of the body that interprets the positions of the tissues as they move; work together to monitor the tension and stretch in muscles to prevent tearing or overstretching of muscles

chemoreceptors

chemical stimuli can be detected by chemoreceptors that are sensitive to specific chemical stimuli, such as the chemoreceptors used in detecting the chemical composition of taste and smell; sense the chemical composition of body fluids to monitor water and lipid-soluble substances

exteroceptor

receptor detecting stimuli coming from the external environment

telereceptors

specialized to detect stimuli from a far distance

introreceptors

detect stimuli from internal organs and tissues

osmoreceptors

primarily present in the hypothalamus and are a type of interoceptor that detect changes in the solute concentrations of blood

cranial nerves

12 pairs attached to the brain; either sensory nerves, motor nerves, or mixed nerves

sensory nerves

having long dendrites of sensory neurons only

motor nerves

having long axons of motor neurons only

mixed nerves

having both long dendrites and long axons

special sensory nerves

carry information responsible for sight, smell, hearing, or balance

plexuses

networks of intertwining nerves that stem from all of the ventral rami; innervate the muscles in the limbs and skin

cervical plexus

composed of ventral rami from spinal nerves C1 through C5 and branches in the posterior neck and head

phrenic nerve

one of the cervical plexuses major nerves that connects to the diaphragm

axillary nerve

supplies 3 muscles: the deltoid, teres minor, and long head of the triceps brachii; carries sensory information from the shoulder joint

radial nerve

supplies the tricep brachii muscle as well as 12 muscles in the forearm controlling wrist and finger extension; carries sensory information from the associated joints and overlying skin; follows the posterior surface of the humerus and then wraps around to the anterior surface close to the elbow joint

median nerve

supplies flexor muscles of the forearm and the skin of the first 3 and a half fingers; travels medially on the anterior surface of the elbow

ulnar nerve

supplies part of the flexor muscles of the forearm, wrist, and hand, as well as the skin of half the ring finger and pinky finger; travels posteriorly behind the medial side of the elbow, then travels along the ulnar side of the forearm

musculocutaneous nerve

responsible for the flexor muscles of the arm, including the biceps brachii and brachialis; travels along the radial side of the forearm

lumbar plexus

nerves arise from the ventral rami; has an anterior divison and posterior divison, which branch into the nerves to supply the pelvis and lower extremities

femoral nerve

major nerve from the lumbar plexus; supplies the hip flexors and knee extensors, as well as sensory detection from the skin of the anterior thigh

lateral femoral cutaneous nerve

receives sensory information from the skin of the anterior, lateral, and posterior surfaces of the thigh

obturator nerve

supplies the adductor muscles of the medial thigh

sciatic nerve

arises from the sacral plexus, and it is the largest nerve in the human body; supplies the inferior trunk and posterior surface of the thigh to innervate the hip extensors and knee flexors; 2 main branches in the lower leg: common fibular nerve and the tibial nerve

common fibular (peroneal) nerve

travels laterally to innervate the lateral aspect of the lower leg and foot

tibial nerve

travels along the posterior surface of the tibia to innervate the posterior lower leg and posterior foot

superior and inferior gluteal nerves

innervate the gluteal muscles of the hip

entrapment

when a nerve is compressed between 2 structures

carpal tunnel syndrome

compression of the medial nerve in the carpal tunnel; or decreased sensation in the first 3 digits and half of the fourth digit

sciatica

condition resulting in pain following the path of the sciatic nerve in the lower pelvis and posterior thigh

somatic nervous system

contains nerves that control skeletal muscles, skin, and joints and is responsible for conscious perception and voluntary motion; includes all nerves that serve the musculoskeletal system and exterior sense organs, including the skin receptors; motor commands begin with upper motor neurons then descend to lower motor neurons

autonomic nervous system (ANS)

responsible for the involuntary control of the body, usually for maintaining homeostasis and regulation of the internal environment; contains nerves that control the smooth muscles of the internal organs and glands; 2 divisions: sympathetic and parasympathetic nervous systems

autonomic tone

balancing of the sympathetic and parasympathetic innervation

sympathetic system (thoracolumbar division)

this division contains preganglionic fibers from the thoracic and upper lumbar segments of the spinal cord in the lateral grey horns; associated with “flight or flight” response; belong to a network of sympathetic chain ganglia that run alongside the vertebral column

parasympathetic system (or craniosacral division)

preganglionic fibers originate in the brainstem and sacral division of the spinal cord; promotes all the internal responses associated with a relaxed state

white rami communicantes

carry preganglionic sympathetic fibers from the spinal nerve to the sympathetic chain ganglia; are myelinated, giving them a white appearance and only exist between the first thoracic and the second or third lumbar spinal nerves

gray rami communicantes

postganglionic fibers; unmyelinated and thus appear gray; return to the spinal nerve via the gray rami communicantes; present at all levels of the spinal cord, innervating various target organs, facilitating the sympathetic response

collateral ganglia

found anterior to the vertebral bodies and are associated with controlling organs in the abdominal cavity

neuroendocrine cells

specialized neurons that release neurotransmitters into the bloodstream rather than targeting another neuron

cranial ganglia

associated with the oculomotor, facial, glossopharngeal and vagus nerves

sacral ganglia

situated near the sacral region of the spinal cord with targets to the reproductive organs, kidneys, and bladder