Practical Exam 2 - Nervous System and Neurology Flashcards
Stimulus-response reaction
All living things must detect changes in the environment and react appropriately; Involves receptors that detect change, sensory neurons, which send the information to the central nervous system where it is processed, and motor neurons that send the information to effectors that produce a response appropriate to the situation; If motor response is initiated, it usually involves a series of action potentials that produce a muscle contraction and a movement of one or more parts of the body; Example: Reflexes
Learned reflexes
Result from repetition; Example: Reflexes needed to drive a car where, with practice, the activity is mostly automatic and subconscious
Inborn reflex
A rapid, predictable, involuntary, and unlearned, motor response to a stimulus, and is part of all our neural pathways; Below consciousness and do things like keep us breathing, maintain posture, and avoid pain; An inborn reflex to a painful stimulus can be so rapid that a response is generated before you can even perceive the pain; Many inborn reflexes are regulated by the spinal cord; Example: Myotatic reflex
Myotatic reflex
Produced by a tap on the tendon under the kneecap; Knee-jerk reflex; Simple spinal reflex;
Employs only four neurons; Striking the patellar ligament just below the patella stretches the quadriceps muscle; This stimulates sensory muscle spindle receptors in the muscle that trigger an impulse in a sensory axon whose cell body lies in the dorsal root ganglion in the lumbar region of the spinal cord; The sensory axon synapses directly with a motor neuron that conducts the impulse to the quadriceps, triggering contraction in extrafusal fibers of the stretched muscle; Sensory axon also has reciprocal inhibition;
Patellar knee-jerk reflex is tested to determine if motor and sensory connections between the spinal cord and the thigh muscles are functioning
Brain not required
5 parts of reflex arcs
1) The receptor that senses the stimulus and initiates the signal
2) A sensory neuron that carries afferent nerve impulses to the central nervous system
3) An integration center where the signal is processed; Either a single synapse, a few synapses and interneurons, or the central nervous system
4) The motor neuron that carries efferent signals to the effector from the integration center
5) The effector such as a muscle or a gland which generates a response to a signal
Monosynaptic reflex
Signal is processed at a single synapse between a motor and sensory neuron
Polysynaptic reflex
Signal is processed by a few synapses and interneurons
Somatic reflex
Activates skeletal muscle
Autonomic reflex
Controls visceral effectors such as smooth muscle, cardiac muscle, or a gland
Spinal reflexes
Do not involve higher brain centers to function; Brain often receives communication from these reflexes and can facilitate or, at least partially, inhibit the reflex; Produced via single synapses between sensory axons and motor neurons; Essential central circuitry is confined to the spinal cord
What indicate damage to the nervous system
Distorted, exaggerated, or absent reflexes indicate damage to the nervous system
Proprioceptors
Receptors that supply information to the central nervous system about the body’s position in space and how much a muscle has moved, or not moved, in its insertion; Examples: Muscle spindles and Golgi tendon organs
Muscle spindles and Golgi tendon organs
Proprioceptors
Muscle spindles in a skeletal muscle convey information about muscle length or the amount of stretch
Golgi tendon organs convey information about tendon tension so that proper regulation of these reflexes takes place
Reciprocal inhibition
In spinal reflex, sensory axon synapses in the spinal cord with an inhibitory interneuron that, in turn, synapses with a motor neuron that conducts impulses to the antagonistic muscle to inhibit contraction; This allows for contraction of the stretched muscle without impedance from the basal muscle tone of the opposing muscle
Stretch and tendon reflexes
Stretch and tendon reflexes help coordinate smooth movements of skeletal muscle groups
Stretch reflexes
Stimulates muscle contraction when muscle length is increased or the muscle is stretched; All stretch reflexes are ipsilateral and monosynaptic in the contracting portion of the pathway; The inhibitory portion of the pathway in the reflex arc is polysynaptic making the total stretch reflex also technically polysynaptic
Ipsilateral
Involves motor activity on the same side of the body
Tendon reflex
Polysynaptic; Opposite of stretch reflex; Causes muscles to relax in circumstances of high tendon tension
Magnitude of response indicates
Magnitude of response indicates the level of inhibition being processed at the spinal cord; Many biological processes are largely regulated by controlling inhibition and the brain prevents extraneous movements of the body by sending out inhibitory signals to prevent awkward and uncoordinated movements
Exaggerated reflex
Could indicate damage to the brain or spinal cord
Absent reflex
Could indicate damage of peripheral nerves
Complex reflexes
Usually involve additional cells, interneurons, and more than one population of motor neurons; results in a longer delay between stimulus reception and the more complex response; Example: Pupillary reflex
Pupillary reflex
Direct light reflex; Example of a complex reflex; Involves four neurons that connect the retina to the mid-brain and then convey information back to the pupillary sphincter muscles; When light is focused upon the eye, the pupillary sphincter muscle in the iris constricts reducing the diameter of the pupil; At the same time, the pupillary sphincter of the other eye constricts too; Miosis; Consensual light reflex
Consensual light reflex
When light is focused upon one eye, the diameter of the pupil constricts; At the same time, the diameter of the other eye constricts as well, even if there is no light shining in the eye
Miosis
Pupillary constriction
Superficial reflexes
Stimulated by gentle stroking of the skin in specific locations; These are used to test spinal-cord reflex arcs and upper motor pathways; Example: Plantar reflex
Plantar reflex
Superficial reflex; Elicited by running blunt object down the lateral aspect of the sole of the foot; Normally, toes should flex; Indirectly indicates the functionality of the corticospinal tracts and directly indicates spinal cord integrity from L4 to S2; If corticospinal tract or primary motor cortex is impaired, an abnormal reflex is displayed called Babinski’s sign
Babinski’s sign
Abnormal reflex displayed in substitution of plantar reflex if corticospinal tract or primary motor cortex is impaired; Instead of toes flexing, the great toe dorsiflexes and the other toes laterally fan; Because the nervous system is not yet completely myelinated, infants will normally display Babinski’s reflex instead of the toe flexion plantar reflex until reach approximately the age of 1
Abdominal reflex
Elicited by stroking the lateral skin of the abdomen on any side of the umbilicus; Doing so normally produces an abdominal contraction which moves the umbilicus into the direction of the stimulus; Tests spinal integrity from T8 to T12; An absence of this reflex indicates a corticospinal tract lesion
Voluntary reactions
Considerably more complicated than reflexes; Require brain functions instead of relying on exclusively neuronal circuitry of the spinal cord; During voluntary reaction, a signal from your eyes sends a muscle to a part of your brain that controls your muscles; Brain must then send a signal to muscles, telling them to perform action
Major delay in reaction time occurs where
Although it takes some time for signal to travel along each nerve, the major delay in reaction time occurs at synapses between different neurons involved
Simple reaction times for college-aged individuals
About 190ms for light stimuli; About 150ms for sound stimuli; About 155ms for touch stimuli; About 8-10ms for auditory stimuli to reach the brain; About 20-40ms for visual stimulus to reach the brain
Reaction time factors
Age: For both males and females, reaction time shortens from infancy into late 20s, then increases slowly until the 50s and 60s, and then lengthens faster as the person gets into 70s and beyond
Arousal: reaction time is fastest with an intermediate level of arousal, and deteriorates when subject is too relaxed or too tense
Distraction: Distractions increase reaction time significantly, especially in younger individuals
Gender: Males have faster reaction times than females
Practice: Practice at a take decreases reaction time
Errors: When a volunteer makes an error the subsequent reaction time are slower likely due to the subject being more cautious
Fatigue: Reaction time deterioration due to fatigue is more marked when the task is more complicated; Mental fatigue, especially sleepiness, has the greatest effect
Drugs: Stimulants decrease reaction time, to a point; Depressants increase reaction times
Warnings: Generally, reaction times are faster when the subject has been warned that a stimulus will arrive soon
Nerves of peripheral nervous system
Divided into two groups depending on the part of the CNS they communicate with; Cranial and spinal nerves; Provide two-way communication (efferent and afferent) containing large numbers of bundled axons
Epineurium
Outer covering that wraps a nerve
Perineurium
Beneath epineurium; Separates axons into bundles
Axon fascicles
Bundles of axons; Fascicles are separated by the perineurium
Endoneurium
Surrounds each axon and isolates it from neighboring axons; Found inside of fascicles
Glial cells
One of the two types of cells in the nervous system; Supportive role in protecting and maintaining nerve tissue; Make up a network called neuroglia; Protect, support, and anchor neurons into place; 6 types of glial cells
Neurons
One of the two types of cells in the nervous system; Communication cells of the nervous system and are capable of propagating and transmitting electrical impulses
Glial cells in the CNS
Involved in the production and circulation of cerebrospinal fluid that circulates in the ventricles of the brain and in the central canal of the spinal cord; 4 types of glial cells in CNS: Astrocytes, microglia, ependymal cells, oliogendrocytes
Glial cells in both CNS and PNS
Glial cells isolate and support neurons with myelin to increase conduction velocity; 2 types of glial cells in PNS: Satellite cells and Schwann cells
Astrocytes
Glial cell in CNS; Most abundant and versatile glial cells; Has a role in making exchanges between capillaries and neurons, in helping to determine capillary permeability, guiding the migration of young neurons and in synapse formation; Provide scaffolding for dendrite and axon projections, ensure proper nutritional uptake by neurons, and assist in regulating neurotransmitter andion concentrations of extracellular fluid
Microglia
Glial cell in CNS; Small oval cells with relatively long “thorny” processes; These processes touch nearby neurons, monitoring their health, and when they sense that certain neurons are injured or in other trouble, microglia migrate toward them
Ependymal cells
Glial cell in CNS; Line the central cavities of the brain and spinal cord; Cell’s cilia help to circulate cerebrospinal fluid that cushions the brain and spinal cord
Oliogendrocytes
Glial cell in CNS; Line up along the thicker neuron fibers in CNS and wrap their processes tightly around the fibers, producing insulating covers called myelin sheaths
Satellite cells
Glial cell in PNS: Surround neuron cell bodies and are thought to have many of the same functions in the PNS as astrocytes do in CNS (Role in making exchanges between capillaries and neurons, in helping to determine capillary permeability, guiding the migration of young neurons and in synapse formation