Chapter 3:Overview of the PNS

What are the parts of the PNS?

parts of the nervous system apart from the brain and spinal cord

A group of nerve cells in the PNS is called a ...

ganglion

What are the two divisions of the PNS?

efferent and afferent

What is afferent?

sensory

What is efferent?

motor

What is the role of afferent fibers?

carry sensory signals from receptors to the CNS

-visceral and somatic

What is the difference between visceral and somatic afferent fibers?

visceral carries from organs to CNS and somatic from the body to the CNS

What is the function of the efferent fibers?

carry motor signals from the CNS to the effectors (mainly glands and muscles)

What is the difference between the visceral and somatic efferent fibers?

visceral carries signals from CNS to glands, cardiac and smooth muscle; divides into sympathetic and parasympathetic divisions

somatic carries signals from CNS to skeletal muscles

What is the function of myelin, and is it present on all peripheral nerves?

myelin works to insulate and propagate (speeds conduction along the nerve fiber)

there are both myelinated and unmyelinated nerve fibers

Which signals travel faster - on a myelinated or unmyelinated fiber?

myelinated travel faster and are white in color

unmyelinated have slower conduction and are gray in color

What is the presentation of group A classification of nerves?

myelinated, thick, fast

What are the types of A fibers?

a-alpha, a-beta, a-delta, a-gamma

What are a-alpha fibers?

primary receptors of proprioceptors (muscle spindle and golgi tendon organs)

What are a-beta fibers?

cutaneous mechanoreceptors

what are a-delta fibers?

free nerve endings for pain, temp, and pressure

What are a-gamma fibers?

motor neurons that control intrinsic activation of muscle spindle

What are characteristics of the B-group classified fibers?

myelinated, thin, slower than A-group

What is the function of B-group fibers?

transmit autonomic information

What are the characteristics of C-group fibers?

unmyelinated, slowest

What is the function of C-group fibers?

polymodal - respond to combinations of thermal, mechanical, and chemical stimuli

Describe exteroceptors

receptors which provide information coming from the outside

pain, temperature, touch, pressure

Where are exteroceptors located?

skin

What is the function of proprioceptors?

movement and joint position information

Where are proprioceptors located?

muscles, tendons, and joints

What is the function of enteroceptors?

movement through the gut (gut motility), pH of blood

Where are the enteroceptors?

in the viscera

What are other types of receptors?

chemoreceptors, photoreceptors, thermoreceptors, mechanoreceptors, nociceptors

What are the types of skin receptors?

hair follicle receptors; merkel endings; meissner corpuscles; pacinian corpuscles; ruffini endings; nociceptors

What is the function of hair follicle receptors?

mechanoreceptors sensitive to touch

What is the function of merkel endings?

slowly adapting mechanoreceptors for pressure and low-frequency vibration

What is the function of Meissner corpuscles?

rapidly adapting, register light touch and fine discrimination in fingertips

What is the function of Pacinian corpuscles?

rapidly adapting, register vibration

What is the function of Ruffini endings?

slowly adapting, detect skin stretching and pressure

What is the function of nociceptors?

detect mechanical and thermal, molecules released in tissue damage and interpret information as pain

Golgi tendon Organs function for

slow adapting mechanoreceptors stimulated by tension in the tendon

What are the areas of a large muscle?

extrafusal fibers, intrafusal fibers, muscle spindle

What is the function of a muscle spindle?

sensory and regulation of muscle stretch reflex

What are examples of enteroceptors?

carotid sinus and aortic sinus; stretch receptors in the lungs, colon, GI tract, and bladder wall

What is a motor unit?

a somatic motor neuron and all of the muscle fibers it innervates

What type of synapse is a neuromuscular junction and what neurotransmitter is utilized?

chemical synapse, utilizes ACh

An inflow of what cation results in an influx of ACh and the ultimate contraction of muscle?

Ca++

What is a disorder related to the neuromuscular junction? (NMJ)

Myasthenia Gravis

-autoimmune

-antibodies for ACh receptors block the acceptance of ACh from the presynaptic neuron