Lecture#3 - sensorimotor System Flashcards
Involuntary Bodily Functions are controlled by what division of the PNS?
Autonomic Division
To be classified as a Neurotransmitter, a molecule must: (2)
- Released by the presynaptic action potential
- have a postsynaptic receptor
Peptides, Gases, lipids, purines, amino acids, biogenic amines and acetylcholine are all ______
Neurotransmitters
What are the most common neurotransmitters of the CNS? (2)
- Glutamate (excitatory)
- GABA (Inhibitory)
The action of a neurotransmitter depends on its _______
receptor
What are 2 types of potentials produced by stimulation?
- Graded Potential: stimulus produces opening of ion channels and cause depolarization
- Action Potential: depolarization beyond the threshold of excitation produces the opening of voltage-gated ion channels
The frequency of action potential discharge corresponds to the:
Intensity of the stimulus
The phenomenon where the initial response of a receptor decreases after a period of time is known as:
adaptation
The size of the adaptation is largest for ____ receptors
phasic receptors
The size of adaptation is the smallest for:
tonic receptors
Sensory Information for the spinocerebellar Pathways comes from:
Muscles and Tendon Stretch
The sensory information for teh Dorsal Column Median Leminsacal comes from:
Fine touch, vibration and proprioceptors
Sensory information from the spinpthalamic pathway come from:
Pain, Temperature, pressure and coarse touch
Which ascending pathway does not require conscious sensation?
Spinocerebellar Pathway
The First synapse of the Spinocerebeller pathway occurs in the:
Spinal Cord
Dorsal Horn
The second synapse of the spinocerebeller Pathway occurs in the:
Cerebellum
Where does the third synapse of the spinocerebeller Pathway occur?
It does not have a 3rd synapses
Where does the first synapse of the Dorsal Column Median Leminscal Pathway occur?
Medulla Oblongata
Where does the Second synapse of the Dorsal Column Median Leminscal Pathway occur
Thalamus
Where does the third synapse of the Dorsal Column Median Leminscal Pathway occur
Somatosensory cortex
Where does the first synapse of the spinothalamic pathways occur?
Spinal cord
Dorsal Horn
Where does the second synapse of the spinothalamic pathway occur?
Thalamus
Where does the third synapse of the spinothalamic pathway occur?
Somatosensory Cortex
Upper motor neurons of cranial nerves originate from the _____ _____
precentral gyrus
The first synapse of the corticospinal and corticobulbar tracts occurs with three nuclei:
- Cranial Nerve III - Oculomotor nucleus
- Cranial Nerve IV - Trochlear nucleus
- Cranial Nerve VI - Abducent nucleus
The corticobulbar tract continues down through the cerebral peduncles in the midbrain to the ____
Pons
corticobulbar tract Neurons branch off at the pons to synapse with 2 nucleus:
- Cranial never V - Motor trigeminal nucleus
- Cranial Nerve VII - Facial Nucleus
The corticobulbar tract continues down through the pons to the ______ ______
Medulla oblongata
At the medulla oblongata the neurons of the corticobulbar tract will synapse with 4 nuclei:
- Cranial Nerve IX: Glossopharyngeal nucleus
- CN X: The vagus nuclei
- CN XI: The accessory nuclei
- CN XII: The hypoglossal nuclei
All of the nuclei of the corticospinal and corticobulbar tracts contain neurons that innervate structures in the: (4)
Head
Face
Tongue
Neck (pharynx and larynx)
Neurons to the lower half of the face have _______ control
contralateral
Neurons to the upper half of the face have ______ control
bilateral
Descending pathways deliver _____ impulses: the brain ___ the spinal cord
Efferent Impulses
from the brain to the spinal cord
Pyramidal Pathways are also known as
Direct Pathways
In pyramidal pathways (direct) impulses are in precentral gyro and pass through _____ and _____ corticospinal tracts
lateral and ventral
Impulses on pyramidal (direct) pathways will descend directly without ______ until the axon reaches the end of the tract.
synapsing
In the spinal cord axons synapse with interneurons (lateral) or ventral horn motor neurons (ventral tract)
True or False
True
Pyramidal (Direct) pathways regulate
fast and fine (skilled) movements
Indirect pathways are ____ other pathways
all
Multinuronal Pathways is also known as
Indirect pathways
Indirect pathways are complex and ____
multisynaptic
Brain Stem motor nuclei and all motor pathways regulate
axial muscles - maintain balance and posture
Head and neck, and eye movements that follow objects in the field
Upper motor neurons are:
Pyramidal cells in the primary cortex
Lower motor neurons are:
Ventral horn and innervate skeletal muscles
The neuromuscular junction is the regions where:
the motor neuron contacts the skeletal muscle.
The neuromuscular junction consists of:
multiple axon terminals and the underlying junctional folds of the sarcolemma
What is the 1 step in the sequence of events leading to muscle contraction?
- events at the neuromuscular junction
- the motor neuron fires an action potential down its axon
- The motor neurons axon terminal releases ACh into the synaptic cleft
- ACh binds receptors on the junctional folds of the sarcolemma
- ACh binding causes a local depolarization called an End Plate Potential
What is the 2nd step in the sequence of events leading to muscle contraction?
Muscle fibre excitation
- The local depolarization (EPP) triggers an AP in the adjacent sarcolemma
What is the 3rd step in the sequence of events leading to muscle contraction?
Excitation-Contraction Coupling
- AP in sarcolemma travels down t-tubules
- Sracoplasmic Reticulum releases Ca+
- Ca+ binds to troponin, which shifts tropomyosin to uncover the myosin-binding sites on action. Myosin head binds actin
What is the 4th step in the sequence of events leading to muscle contraction?
Cross-Bridge Cycle
contraction occurs via cross bring the cycle
What is the cross-bridge cycle?
A series of events during which myosin heads pull think filaments toward the center of the sarcolemma
What is the 1st step of the cross bridge cycle?
Cross-Bridge Formation
Energized myosin head attaches to an actin myofilament, forming a cross bridge
What is the 2nd step of the cross-bridge cycle?
The power (working) stroke
The myosin head pivots and bends, pulling the actin filament toward the M line. This leaves the myosin head in its low energy state. ADP and P are also released
What is the 3rdst step of the cross bridge cycle?
Cross-bridge detachment
ATP binds to myosin and causes the myosin head to detach from actin (the cross bridge breaks)
What is the 4th st step of the cross bridge cycle?
Cocking of the myosin head
myosin hydrolyzes ATP to ADP and P. This causes the myosin head to return to its pre stroke high-energy or cocked position
The Cross-Bridge cycle will continue as long as there is ____ available and ___ is bound to troponin
ATP
Ca+
If ATP and Ca+ are not available where will the cross-bridge cycle be broken?
Steps 3 and 3
An end plate potential is generated at:
The Neuromuscular Junction
What is excitation-contraction (E-C) coupling?
A sequence of events by which transmission of an action potential along the sarcolemma leading to the sliding of filaments.
How do events at the neuromuscular junction set the stage for Excitation-concentration coupling
Providing excitation-release ACh binds to receptor proteins on the sarcolemma and triggers an action potential
What is Inborn (intrinsic) reflex
rapid, involuntary, predictable motor response to a stimulus. Maintains posture and controls visceral activities
Can the Inborn (intrinsic) reflex be modified?
yes by learning and conscious effort
Learned (acquired) reflexes result from:
practice or repition
Learning how to drive is an example of _____ reflex
learned (acquired) reflexes
What is the function classification of reflex arcs
- somatic reflexes
- Autonomic (visceral) Reflexes
Somatic reflexes activate:
skeletal muscles
Autonomic (visceral) Reflexes activate
visceral effectors (smooth or cardiac muscle)
Spinal Reflexes occur without direct involvement of _______
higher brain centers
Why is testing of somatic reflexes important?
Assess the condition of the nervous system. If the response is exaggerated, distorted or absent, there may indicate degeneration or pathology
What are the most commonly assessed reflexes
Stretch
Flexor
Superficial reflexes
To smoothly coordinate skeletal muscles the nervous system must receive proprioceptor input regarding:
- Length of muscle - sent from muscle spindles
- amount of strain - sent from tendon organs
Anulospiral Endings: (primary sensory ending) are:
Endings wrap around the spindle and are stimulated by rate and degree of stretch.
Flower Spray Endings(Secondary ending) are:
Small axons at spindle ends and are stimulated by degree of stretch only
Contractile end regions of spindles are innervated by:
gamma efferent fibres
ENd regions contain actin and _____filaments and can contract
myosin
Muscle spindles are composed of 3-10 modified skeletal muscle fibers called _____
intrafusal muscle fibres
The brain sets the muscles length via the
stretch reflex
What is the knee-jerk reflex?
stretch reflex that keeps knees from buckling when you stand upright
effector fibres of muscles are referred to as extrafusal muscle fibres. The extrafusal muscle fibres are innervated by _____ efferent fibers and large ___ motor fibres
alpha efferent
large alpha motor fibres
Muscle fibres are stretched and excited in 2 ways:
- External stretch
- Internal stretch
External force ________ the entire muscle
lengths
Gamma motor neurons stimulate spindle ends to contract and stretch. Stretch results in:
increased rate of impulses to spinal cords
Stretch Reflex: Sensory neurons synapse directly with:
Motor neurons in spinal cord
What is Reciprocal inhibition?
Afferent-fiber neurons synapse with interneurons that inhibit ___ motor neurons of antagonistic muscles
All Stretch are monosynaptic and ipsilateral(motor activity on the same side of body)
True or False
True
Tendon reflexes involve _____ _____
polysynaptic reflexes
Tendon reflexes help to ________ damage from excessive stretch
damage
What activates the tendon reflex?
Active or passive stretch
During muscle relaxation the muscle will:
lengthen
During a tendon reflex afferent impulses are transmitted ___ the spinal cord
to
When the contracting muscle relaxes, the antagonist will contract. This is called:
reciprocal activation
During a tendon reflex the information is transmitted to the _______ and used to adjust muscle tension
cerebellum
The flexor (withdrawal) reflex is initiated by ______ stimuli
painful
The flexor reflex causes:
automatic withdrawal of the threatened body part
The flexor reflex is ipsilateral and polysynaptic.
True or False
True
The flexor Reflex is protective important for _______
survival
Can the brain override the reflexor reflex?
yes.
Crossed-Extensor reflex occurs in weight bearing limbs to maintain ______
balance
The crossed-extensor Reflex consists of ipsilateral _____ reflex and ________ extensor reflex
withdrawal reflex and contralateral extensor reflex
The purpose the crossed-extensor reflex is maintain balance. Give an example of when it would be at work?
When you step barefoot on glass causes the damaged leg to withdrawal and the opposite leg to support the weight shift
Superficial Reflexes are excited by gentle cutaneous stimulation of the area. Clinically important because
reflexes signal problems in upper motor pathways or cord-level arcs:
Plantar Reflex: tests the integrity of cord from L4 to S2 Stimulus: Stroke lateral aspect of sole of foot
Response: downward flexion of toes
Damage to the motor cortex or corticospinal tracts cause an abnormal resposne known as Babinski’s sign
- hallux dorsiflexes; smaller toes fan laterally
Normal in infancy to age 1 year because myelination is still incomplete
Abdominal Reflexes: Tests integright of cord from T8-T12 Stimulus: stroking skin of lateral abdomen above. Below and to the side of the umbilicus Response: contraction of abdominal muscles of umbilicus toward stimulus is absent which may occur when
corticospinal tract lesions are present
