Topic 6: NS - Motor Output Flashcards
what are the 2 divisions of the efferent (motor) nervous system?
-autonomic nervous system
-somatic nervous system
what are the 2 further divisions of the autonomic nervous system?
-sympathetic nervous system
-parasympathetic nervous system
what is the role of the autonomic nervous system?
-transmits signals from the CNS to autonomic effectors (smooth muscle, cardiac muscle, and glands)
-regulate internal processes continuously and automatically (HR, SNS increases, PSNS decreases)
how does the autonomic nervous system bring signals from the CNS to the effector?
-2 neurons (preganglionic and postganglionic)
-these neurons can further be identified by the type of neurotransmitter they release onto the adjacent neuron/effector
what are the 2 categories of neurons in the autonomic nervous system?
-cholinergic neurons (release acetylcholine)
-adrenergic neurons (release norepinephrine)
what is the function of the sympathetic nervous system?
-prepares the body for activity
-generates a fight or flight response
-activated during exercise
-more emergency + quick acting responses (less control, hence why nt = NE)
which category does each neuron (preganglionic and postganglionic) in the sympathetic nervous system fall under?
-preganglionic = cholinergic
-postganglionic = adrenergic
what is the exception to the postganglionic neuron of the sympathetic nervous system when the effector is a sweat gland?
-the postganglionic neuron is cholinergic instead of adrenergic
what is the pathway in the sympathetic nervous system?
-preganglionic neuron has cell bodies in the spinal cord (CNS)
-axons of these neurons will exit via spinal nerves from T1-L2
-the preganglionic neuron releases acetylcholine onto the postganglionic neuron
-the postganglionic neuron has cell bodies in the PNS (ganglion)
-the postganglionic neuron releases norepinephrine onto the effector (cardiac or smooth muscle, or a gland)
-if a sweat gland, it releases acetylcholine
how is the chemical stimulation of the postsynaptic cell stopped?
-neurotransmitter is broken down or removed
-typically broken by enzymes
how is acetylcholine broken down? where does this occur?
-enzyme acetylcholinesterase
-on the postsynaptic membrane (cell body/dendrites of the postsynaptic cell)
how is norepinephrine broken down? where does this occur?
-enzyme monoamine oxidase
-norepinephrine is actively transported out of the synaptic cleft back into the synaptic end bulb where it came from (presynaptic neuron and it then broken down
what is the function of the parasympathetic nervous system?
-rest + digest processes
-essentially keeping the body happy and making sure everything is running smoothly
-need more controlled and long lasting responses (hence why nt = Ach)
which category does each neuron (preganglionic and postganglionic) in the parasympathetic nervous system fall under?
-both are cholinergic
what is the pathway in the parasympathetic nervous system?
-preganglionic neuron has cell bodies in the brain stem or sacral spinal cord
-the preganglionic neuron releases acetylcholine onto the postganglionic neuron
-the postganglionic neuron has cell bodies in the PNS (ganglion)
-the postganglionic neuron releases acetylcholine onto the effector (cardiac or smooth muscle, or gland)
do organs controlled by the autonomic nervous system receive input from both divisions or just one?
-most organs will receive input from both the PSNS and the SNS
-effects of each are usually opposite to one another
what is an example of how the two divisions of the autonomic nervous system act on the pupils of eyes (iris muscles)?
-SNS = dilate
-PSNS = constrict
what is an example of how the two divisions of the autonomic nervous system act on the heart?
-SNS = increase heart rate and force of contraction (squeeze more blood)
-PSNS = decrease heart rate
what is an example of how the two divisions of the autonomic nervous system act on the gastrointestinal tract?
-SNS = decrease motility
-PSNS = increase motility
-when we are in fight or flight, the digestive organs are put to rest so we decrease their actions
what is an example of how the two divisions of the autonomic nervous system act on the smooth muscle within blood vessels?
-SNS = vasoconstriction
-PSNS = no innervation of blood vessels except for those of the penis and clitoris
what is an example of how the two divisions of the autonomic nervous system act on the sweat glands?
-SNS = increase secretion (cold sweat if scared)
-PSNS = no innervation
what is an example of how the two divisions of the autonomic nervous system act on the digestive glands?
-SNS = decrease in secretions (except saliva)
-PSNS = increase in secretion for all
-when we are in fight or flight, the digestive organs are put to rest so we decrease their actions (do not need secretions)
what is an example of how the two divisions of the autonomic nervous system act on the genitals?
-SNS = ejaculation (less control)
-PSNS = erection, lubrication (more control, do not want to get erections randomly or lubricate unnecessarily)
what is the higher control pathway of the ANS (in the brain)?
-hypothalamus will send info to the medulla oblongata (brain stem) to trigger the ANS
-the cerebrum can have some input on the hypothalamus (not always since the cerebrum does not have conscious control of the effectors) but since it is another part of the limbic system, emotions can have autonomic effects (blushing, fainting, cold sweat, increased HR, etc)
what is the role of the somatic nervous system?
-transmits signals from the CNS to somatic effectors (skeletal muscle)
-can create different movements as a response
what is the pathway of the somatic nervous system?
the upper motor neuron in the brain will innervate the lower motor neuron in the spinal cord which then innervates the effector (skeletal muscle)
how does the somatic nervous system bring signals from the CNS to the effector?
-through lower motor and upper motor neurons
what are the 3 types of movement possible in the somatic nervous system?
-reflexes
-voluntary
-rhythmic
what are examples of reflexes?
-spinal reflexes
-postural reflexes
what are spinal reflexes?
-least complex
-require sensory information from sensory receptors like proprioceptors (muscle spindles), pressure/pain receptors
what are postural reflexes?
-for balance and posture
-require sensory input from proprioceptors (muscle spindles), eyes, and inner ear
what is voluntary movement?
-most complex
-no external stimuli is required (act of will)
what is rhythmic movement?
-walking, running, etc
-combination of reflex and voluntary movements
what structures are at each of the 4 levels of motor control?
-level 1 = premotor cortex, supplementary area, association areas (planning)
-level 2 = primary motor cortex
-level 3 brain stem nuclei
-level 4 = spinal cord
what occurs at the first level of motor control?
-do you want to move?
-if yes then what movement is needed and what muscles need to contract
-plans a sequence of muscle contractions with input from the cerebellum
-sending signals to the primary motor cortex
what occurs at the second level of motor control?
-signals are sent directly to the lower motor neurons via the corticospinal tract
-specifically for fine skilled movements
what occurs at the third level of motor control?
-brain stem nuclei will signal to descending motor tracts to the lower motor neurons (indirect)
-receive info from the cortex, basal nuclei, and cerebellum
-involved in the coordination of large muscle groups for maintenance of posture and locomotion
what occurs at the fourth level of motor control?
-where the cell bodies of the lower motor neurons are
-networks of neurons that are central pattern generators (set rhythmic and repeated movements like walking and running)
-require cortical signals (from the motor cortex) to begin or stop movement
how does the cerebellum work in motor control?
-has roles in planning and initiating movement by communicating with cortical areas (communication also allows for correcting of the plan)
-stores planned movement and compares it to the actual movement using sensory input (from proprioceptors, eyes, and ears)
-maintains balance, controls eye movements, and maintains muscle tone
-can coordinate skilled voluntary muscle movements and timing of contractions involving more than 1 joint
what is muscle tone? which parts of the brain maintain it?
-the continuous low level of contraction in muscles
-for balance and posture
-maintained by the cerebellum and basal nuclei
how do the basal nuclei work in motor control?
-aids in planning movement
-suppresses unwanted motions at rest
-maintains muscle tone
what are the parts of the corticospinal pathway? where does it signal to and from?
-contains upper and lower motor neurons
-signals to the skeletal muscle from the primary motor cortex
where are the cell bodies and axons of upper motor neurons?
-cell bodies in the primary motor cortex
-axons in the spinal cord
where are the cell bodies and axons of lower motor neurons?
-cell bodies in the ventral horn of the spinal cord
-axons exit via spinal nerves
what is the pathway of a neural signal for motor control?
-starts with sensory input which gets relayed to the cerebellum through proprioceptors, eyes, and ears
-sensory input also gets relayed to the sensory cortex which relays to the basal nuclei
-sensory input can also get directly relayed to the spinal cord for reflexes
-basal nuclei then relay to the first level (premotor cortex, supplementary areas, association areas)
-the basal nuclei also relay to the brain stem nuclei which also relays signals back for feedback
-the cerebellum will relay info to both the brain stem nuclei and the first level (premotor cortex, supplementary areas, association areas)
-the pathway now goes down each level
-at level 2 (primary motor cortex) signals can be relayed directly through corticospinal tracts or get relayed to the brain stem nuclei for indirect tracts
-in the end info all reaches the spinal cord to reach the lower motor neurons, and eventually affect skeletal muscles
what is the general role of the cerebellum, sensory input, sensory cortex, and basal nuclei in the motor control pathway?
-plan, modify, and control the movement as it is happening
what do the indirect and corticospinal direct tracts represent?
-the axons of upper motor neurons
-relay signals to the cell bodies of lower motor neurons in the spinal cord
what happens with the destruction of upper motor neurons?
-reflex arcs are still present because sensory neurons can still send signals directly to lower motor neurons
-results in spastic paralysis and exaggerated reflexes
what is spastic paralysis?
-presence of reflex arcs increases muscle tone
-no muscle atrophy
what are exaggerated reflexes?
-reflexes that are stronger than usual (patellar, achilles) because there are no inhibitory signals coming from the upper motor neurons
-ex: plantar reflex that is initiated by scratching the sole of the foot will show the babinski sign
what is the normal response to the plantar reflex? what is the babinski sign?
-normal = plantar flexion (toes curl under)
-babinski sign = extend the big toe (shows damage to upper motor neurons)
when is the babinski sign normal?
-in babies when their corticospinal tract is not yet fully myelinated
what happens with the destruction of lower motor neurons?
-loss of reflex arcs (sensory neurons can no longer signal to the lower motor neurons)
-flaccid paralysis
what is flaccid paralysis?
-decreased muscle tone and obvious muscle atrophy
what is an example of a virus that destroys lower motor neurons?
-polio (poliomyelitis)
-destroys cell bodies of lower motor neurons in the ventral horn of the spinal cord
what is muscle atrophy?
-loss of muscle tissue
what does language involve?
-complex interactions between the nervous system and muscular systems that allow speech production, comprehension, and expression
-mainly involves areas of the left cortex (equivalent areas on the right side provide emotional components of language such as tone and gestures)
what are the important brain areas for language?
-cerebral cortex (concepts + ideas)
-language implementation system (analyzes the incoming and produces the outgoing word sounds and grammer)
-visual + auditory cortex areas (processes incoming language that is seen like reading + facial expressions or that is heard like sounds)
what are the parts of the language implementation system?
-wernicke’s area (language comprehension)
-broca’s area (motor control of speech production and grammar)
-basal nuclei (regulate speech production by communicating with broca’s area
how do signals pass to produce speech?
-signals pass from language areas to the premotor cortex (plan muscle contraction)
-the premotor cortex then signals to the primary motor cortex to initiate planned contractions and therefore produce speech
what happens when there is damage to wernicke’s area?
-cannot understand spoken or written words (poor comprehension)
-can speak but words are meaningless + mixed up
what happens when there is damage to broca’s area?
-can understand words (have comprehension)
-difficult to speak or write sensibly
-loss of motor control of speech
