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
Schwann cells
Surround and form myelin sheaths around larger nerve fibers in PNS; Vital to regeneration of damaged peripheral nerve fibers and increase speed of transmission of nerve impulses
Neuroglia
A network of glial cells within the nervous system
Fibrous astrocytes
Found in gray matter of the cerebral cortex and are surrounded by neuropil (fibrous) substance
Perivascular feet
Found on astrocytes; In contact with blood vessels and neuronal surfaces
Neurons consist of three parts
Dendrites, cell body (soma), and axon
Dendrite
Main receptors or input regions and provide enormous surface area for receiving signals from other neurons; Convey messages toward the cell body; These signals are not action potentials, but rather short distance signals called graded potentials
Cell body (soma)
Surrounds nucleus and contains mitochondria, ribosomes, Nissl bodies, etc.; Most neuron somas are in CNS
Nissl bodies
Rough endoplasmic reticulum granules in the soma that stain darkly in histological sections
Nuclei
Clusters of somas in CNS
Glanglia
Clusters of somas in PNS
Axon
Each neuron has a single axon that transmits signals from cell body to other neurons; First part of axon of a neuron is initial segment and extends from axon hillock; Axon further divides into several collateral branches, then again divides into smaller branches called telodendria; Distal tip of each telodendrion is a synaptic terminal and has synaptic vesicles that contain neurotransmitter molecules
Myelin sheath
Many nerve fibers are covered in myelin sheath; Myelin protects and electrically insulates fibers and increases the speed of transmission of nerve impulses; Associated only with axons, and dendrites are always unmyelinated
Myelinated fibers vs unmyelinated fibers
Myelinated fibers: Axons bearing a myelin sheath; Conducts nerve impulses rapidly
Unmyelinated sheaths: Axons with no myelin sheath and dendrites; Conduct impulses slowly in comparison
Chemically (ligand)-gated ion channels
Open when appropriate neurotransmitter binds to receptor, allowing simultaneous movement of Na+ and K+; Example: Acetylcholine receptors
Voltage-gated ion channels
Open and close in response to changes in membrane voltage; Example: Action potentials
Membrane ion channels
Large proteins that selectively allow certain ions to pass through the membrane; Example: Voltage-gated potassium channels
Gated channel proteins
Have a “gate” that opens and closes in order to allow an ion to pass; Example: Voltage-gated calcium channels in neuromuscular junction only open when action potential hits it
Voltage-gated channels
Open in response to changes in membrane potential; Example: Voltage-gated sodium channels opening when membrane potential depolarizes
Mechanically gated channels
Open in response to physical deformation of receptor
Gradients
Ions move passively along a chemical concentration gradient from an area of high concentration to an area of low concentration; Ions move along an electrical gradient when they move toward an area of opposite electrical charge; Signals move along an electrochemical gradient in neurons
Bare plasma membrane
Voltage decays because current leaks across membrane; Occurs in collateral branches
Unmyelinated axon vs myelinated axon
Unmyelinated axon: Voltage-gated Na+ and K+ channels regenerate the action potential at each point along the axon, so the voltage does not decay; Conduction is relatively slow because movements of ions and of the gates of channel proteins take time and must occur before voltage regeneration occurs
Myelinated axon: Myelin keeps current in axons and voltage does not decay much; Action potentials are generated only in the nodes of Ranvier and appear to “jump” rapidly from node to node
Cerebrum
Largest region of the brain and is divided into right and left cerebral hemispheres by the longitudinal fissure
Longitudinal fissure
A deep groove that divides cerebrum into left and right hemispheres
Hemispheres
Although largely symmetrical in structure, the two hemispheres are no equal in function; There is lateralization (specialization) of some cortical functions; Covered with a folded cerebral cortex of grey matter where neurons are no myelinated; Connected by corpus callosum
Gyrus
Fold in cerebral cortex
Sulcus
Shallow groove in cerebral cortex
Corpus callosum
White matter that connects cerebral hemispheres within the longitudinal fissure
Grey matter of cerebral cortex
Forms outer convoluted surface of cerebral hemispheres and the foliated surface of cerebellum
White matter
Lies deep to the cerebral and cerebellar cortices
Cortical grey matter
Made of multipolar neuron cell bodies and attendant dendrites
Bordering white matter
Borders grey matter; Composed of tracts of myelinated axons that project from overlapping grey matter; Tracts can connect one cortical region to another, to brain nuclei, and to motor neurons of the spinal cord
Pyramidal cells
Cells with pyramid or triangular shape; Many of the multipolar neurons of the cortex are pyramidal cells
5 layers of cerebral cortex
Superficial
1) Molecular layer: Contains mainly dendrites synapsing with cortical neuron axons
2) Outer granular layer: Mostly made up of stellate cells, axons, and dendrites
3) Outer pyramidal cell layer: Mostly made up of pyramidal cells that increase in size as you move deeper into the layer
4) Inner granular layer: Mostly made of densely packed stellate cells
5) Inner pyramidal and polymorphic layer: Mostly composed of large pyramidal cells in the more superficial portion of the layer and a wide variety of cell morphologies in the deepest parts of the layer
Deep
Diencephalon
Consists of the thalamus, hypothalamus, and epithalamus; Grey matter areas enclose the third ventricle
Thalamus
Part of diencephalon; Relay station for incoming information, such as sensory information or integration information, destined for higher brain areas such as the cerebral cortex
Cerebral cortex
Covers the cerebellum; Composed of grey matter; Responsible for integrating sensory impulses, directing motor activity, and controlling higher-level cognitive functions
Hypothalamus
Part of diencephalon; Autonomic control center, center for emotional response, body temperature regulation, regulation of food intake, regulation of water balance and thirst, regulation of sleep-wake cycles, and control of endocrine system functioning
Mamillary bodies
Part of hypothalamus; Relay stations in the olfactory pathways
Infundibulum
A stalk of hypothalamic tissue that connects to pituitary gland
Epithalamus
Part of diencephalon; Superior-most part of diencephalon; Contains the pineal gland that secretes the hormone melatonin that helps regulate the sleep-wake cycle
Pineal gland
Located in epithalamus; Under control of a complex feedback loop with the suprachiasmatic nucleus (SCN) of the hypothalamus; Secretes melatonin that regulates circadian rhythm
SCN
Anterior part of hypothalamus; Suprachiasmatic nucleus; Found in hypothalamus; Controls the pineal gland with a complex feedback loop
Cerebellum
Located dorsal to pons and medulla oblongata; Primarily involved in the coordination of somatic motor function, primarily skeletal muscle contractions; Learned muscle patterns, such as those used to play the piano; are stored and processed in the cerebellum; Functions in coordination of complex movements (walking, playing the piano, shooting a basketball); It is partitioned into cortical layers (gray and white matter)
Grey matter layers of the cerebellum
Superficial
1) Molecular layer: Composed largely of unmyelinated fibers and scattered basket cells and stellate cells
2) Intermediate layer: Composed of purkinje cells
Granular layer: Composed of granule cells
Brain stem
Consists of medulla oblongata, pons, and midbrain
Midbrain
Part of brain stem; Located between the diencephalon and the pons; Associated with inhibiting inappropriate muscle movements; Dopamine signals here to ease that inhibition to allow for smooth movements
Pons
Part of brain stem; Located between midbrain and medulla oblongata; Composed of conduction tracts between higher brain centers and the spinal cord or between the motor cortex and cerebellum
Medulla oblongata
Part of brain stem; Most inferior part of brain stem; Has control over some cardiovascular and respiratory systems
Spinal cord
Part of central nervous system; Has its own organization of grey and white matter; Has anterior median fissure
Anterior median fissure
Marks the dividing line between mirrored right and left halves of the spinal coed
Grey matter of spinal cord
Occupies a butterfly-shaped region that is bilaterally symmetrical about the median fissure
White matter of spinal cord
White matter surrounds the grey matter of the spinal cord; Composed of axonal tracts that propagate both afferent and efferent impulses, and from neurons on one side of the spinal cord to neurons on the other side and same side, as well as axons that project into the ventral nerve roots
Contralateral
Involves motor activity from one side to the other side
Cranial nerve I
Olfactory nerve I; Sensory; Tiny sensory nerves of smell, which run from the nasal mucosa to the olfactory bulbs
Cranial nerve II
Optic nerve II; Sensory; Sensory nerve of vision; Develops as an outgrowth of brain, so its technically a brain tract
Cranial nerve III
Oculomotor nerve III; Motor; Eye mover; Supplies four of the extrinsic muscles that move the eyeball into orbit
4 extrinsic muscles of Cranial nerve III
Inferior oblique, medial rectus, inferior rectus, superior rectus
Cranial nerve IV
Trochlear nerve IV; Motor; Pulley; Innervates the superior oblique, an extrinsic eye muscle that loops around a pully-shaped ligament in the orbit, termed the trochlea
Cranial nerve V
Trigeminal nerve V; Motor and sensory; Three branches spring from this, the largest of the cranial nerves; It supplies the sensory fibers to the face and motor fibers to the chewing muscles
Cranial nerve VI
Abducens nerve VI; Motor; Controls the lateral rectus (extrinsic eye muscle)
Cranial nerve VII
Facial nerve VII; Motor and sensory; Innervates muscles of facial expression
Cranial nerve VIII
Vestibulocochlear nerve VIII; Sensory; Hearing and balance
Cranial nerve IX
Glossopharyngeal nerve IX; Motor and sensory; Throat
Cranial nerve X
Vagus nerve X; Motor and sensory; Only nerve to extend beyond the head and neck to supply motor and sensory fibers to the visceral body organs of the thorax and abdomen
Cranial nerve XI
Spinal accessory nerve XI; Motor; Supplies the trapezius and sternocleidomastoid muscles
Cranial muscle XII
Hypoglossal nerve XII; Motor; Runs inferior to the tongue and innervates muscles of the tongue
Meissner’s corpuscles
Function as light pressure receptors of the dermis; Located within the dermal papillae just below the epidermal/dermal border
Nodes of Ranvier
Unmyelinated gaps between Schwann cells; Allows action potential to jump from node to node in the myelin sheath
Saltatory conduction
Jumping from node to node in axons with a myelin sheath; Increases action potential velocity
Meninges
Covers the brain and spinal cord; Three types:
Skin
1) Dura matter: Outer meninge
2) Arachnoid mater: Middle of three meninges
3) Subarachnoid space (not a meninge)
4) Pia mater: Clings to the brain and spinal cord
Subarachnoid space
The area between the arachnoid and pia maters; Filled with cerebrospinal fluid and houses blood vessels that supply the brain
