Neuromuscular Function Slides

Front 1

neuromuscular junction

Back 1

point where nerve and muscle communicate

product of communication will be muscle twitch rather than an AP

Front 2

motor unit

Back 2

consists of motor neuron, its axon and muscle fibers it innervates

terminal endplate- end of axon of motor neuron

acetylcholine- only neurotransmitter dumped into active zone of neuromuscular function

Front 3

miniature endplate potential (MEPP)

Back 3

if sufficient MEPPs, AP will be generated (contract & twitch)

takes many activated regions to excite muscle fiber

Front 4

striated (skeletal) muscle

Back 4

long ropelike structure made of muscle fiber strands called myofibrils

each myofibril is composed of either thin or thick myofilaments

Front 5

muscle fiber contraction

Back 5

occurs as a result of complex chemical reactions

many myofilaments make up one muscle fiber

many muscle fibers make up a muscle bundle

Front 6

neuromotor innervation

Back 6

each muscle fiber is innervated by one motor unit but each motor unit may innervate a large number of muscle fibers

Front 7

multiple motor unit summation

Back 7

use of many motor neurons to activate muscle

more motor neurons that are activated; greater number of fibers that will contract

Front 8

slow twitch fibers (know all 3)

Back 8

take longer time to move

remain contracted five times longer than fast twitch fibers

typically found in muscles that must contract for long periods of time ex. sitting position

tongue dorsum

Front 9

fast twitch fibers (know all 3)

Back 9

capable of much more rapid movement

remain contracted for much shorter period of time

found in muscles used to meet rapid contraction requirements

tongue tip

Front 10

slow twitch vs. fast twitch

Back 10

one motor neuron may innervate thousands of slow twitch fibers but one motor neuron may innervate only 10-20 fast twitch fibers

ex. extremely fine control: if you need to tense vocal folds quickly for a pitch change or maintaining an erect posture requires less precision and more stamina

Front 11

neuronal circuitry for spinal reflex

Back 11

reflex motor response- stereotyped movement to sensory stimulation

circuitry includes the following structures: muscle spindles, afferent fibers, alpha motor neurons (efferent), neuromuscular junction and muscle tissue

Front 12

reflex functions for spinal cord

Back 12

independent of voluntary control

reflexes are, however, indirectly influenced by descending impulses from motor cortex and brainstem motor centers

ex. in UMN lesion, spinal cord reflexes are released from higher levels of control and become hyperactive (exaggerated) vs. LMN- reduced

Front 13

muscle spindles

Back 13

complex, small sensorimotor organs that detect degree and rate of change in muscle length

consists of 3-5 specialized intrafusal fibers

help maintain muscle tone

Front 14

golgi tendon organs

Back 14

maintain degree of muscle tension during muscle contraction

reflexively inhibit muscle contraction; permit muscle to stretch to prevent injury caused by excessive contraction

Front 15

extrafusal fibers- alpha

Back 15

make up large mass of skeletal (striated) muscle

attached to bone by fibrous tissue extensions (tendons) and controlled by alpha motor neurons

composed of myosin filaments

responsibility for contractibility of a muscle

entirely surround intrafusals

Front 16

intrafusal fibers- gamma

Back 16

contain muscle spindles

attached to extrafusal fibers which are attached to bone

controlled by gamma-motor neurons

both ends contract but the central region does not contract

if entire skeletal muscle mass is stretched, it also stretches the spindles

Front 17

annulospiral (primary) sensory endings

Back 17

central region of intrafusal fiber is wrapped by these sensory endings

fast-conducting

two types of intrafusal fibers 1. nuclear bag fibers 2. nuclear chain fibers

Front 18

intrafusal fibers

Back 18

whenever central portion of this fiber stretches, annulospiral primary sensory endings become depolarized and discharge impulses

impulses travel on sensory (afferent) nerve fibers to the spinal cord

Front 19

sensory fibers

Back 19

Ia- fast fibers
II- slow fibers

AFFERENT!

Front 20

stretch of spindles

Back 20

surge of sensory input is directed to alpha motor neurons and reflexively contract muscle mass to decrease muscle length progressively

contract of extrafusal muscle halts stretch of spindles

stretching central intrafusal fibers can induce stretch reflex aka knee jerk reflex

Front 21

GTO

Back 21

type of specialized sensory muscle receptor

inntervate tough tissues that attach muscles to bone to regular muscle tension and prevent damage from excessive muscle contraction (too sudden or excessive force)

when contraction is excessive, stimulates GTO sensory fibers to activate intervening inhibitory interneurons of spinal cord

interneurons inhibit alpha motor nuclei which accounts of autogenic inhibition

Front 22

stretch or myotatic reflex

Back 22

most simple reflex
ex. knee jerk reflex

monosynaptic or two-neuron reflex

Front 23

knee jerk reflex

Back 23

tap patellar tendon of quadriceps muscle

leads to brief stretch of muscle, which stimulates sensory endings of spindles

sends volley of impulses to alpha motor neurons

activation of alpha motor neyrons causes a quick contraction (muscle jerk) of same muscle

Front 24

stretch reflex

Back 24

common element in all stretch reflexes: stretched muscle contracts after very brief delay