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Physiology: Neurophysiology

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173 Questions

What is the primary function of the autonomic nervous system (ANS)?

to regulate smooth muscle, cardiac muscle, and glands

Where are parasympathetic ganglia typically located?

in or near the effector organs

What is the origin of preganglionic neurons in the sympathetic nervous system?

thoracolumbar region of the spinal cord

What is the function of chromaffin cells in the adrenal medulla?

to secrete epinephrine and norepinephrine into the circulation

What is the approximate proportion of epinephrine secreted by chromaffin cells?

80%

What is the name of the division of the ANS that includes the enteric nervous system?

not mentioned in the text

Where do postganglionic neurons of both divisions synapse?

on effector organs

What is the location of sympathetic ganglia?

in the paravertebral chain

What is the origin of preganglionic neurons in the parasympathetic nervous system?

cranial nerves and spinal cord segments S2-S4

What is the primary neurotransmitter released by cholinergic neurons in both the sympathetic and parasympathetic nervous systems?

Acetylcholine

Which of the following is NOT a characteristic of the sympathetic nervous system?

Innervates skeletal muscles

What is the primary receptor type in the ganglion of the sympathetic nervous system?

Nicotinic

Which neurotransmitter is released by nonadrenergic, noncholinergic neurons in the gastrointestinal tract?

Substance P

What is the primary receptor type in the effector organs of the parasympathetic nervous system?

Muscarinic

Which of the following tumors is associated with increased excretion of 3-methoxy-4-hydroxymandelic acid (VMA)?

Pheochromocytoma

What is the primary neurotransmitter released by adrenergic neurons in the sympathetic nervous system?

Norepinephrine

Which of the following is a characteristic of the parasympathetic nervous system?

Has long preganglionic nerve axons

What is the primary neurotransmitter released by postganglionic neurons in the parasympathetic nervous system?

Acetylcholine

What type of sensations are processed by the dorsal column system?

Fine touch, pressure, vibration, and proprioception

What is the primary function of the astrocytes in the nervous system?

To supply metabolic fuels to neurons and synthesize neurotransmitters

What type of fibers primarily make up the dorsal column system?

Group II and III fibers

What is the function of the dendrites in a neuron?

To receive information from adjacent neurons

What is the correct sequence of divisions of the CNS from bottom to top?

Spinal cord, brain stem, diencephalon, cerebellum, cerebral hemispheres

Where do the second-order neurons of the dorsal column system cross the midline?

Medulla

What is the term for the process by which sensory receptors transduce environmental signals into neural signals?

Signal transduction

What is the function of the anterolateral system?

Processing of pain, temperature, and light touch

What is the function of microglial cells in the nervous system?

To proliferate following neuronal injury and serve as scavengers for cellular debris

What type of adaptation is characteristic of Meissner corpuscles?

Rapidly adapting

What occurs in a photoreceptor when light is present?

Hyperpolarization

What is the result of a receptor potential that is depolarizing?

The membrane potential becomes closer to threshold

Where do the primary afferent neurons of the dorsal column system have their cell bodies?

Dorsal root ganglion

What is the term for the nerves that bring information into the nervous system?

Afferent nerves

What type of fibers primarily make up the anterolateral system?

Group III and IV fibers

What type of receptors respond repetitively to a prolonged stimulus?

Slowly adapting receptors

What is the region of the neuron where action potentials originate?

Axon hillock

What is the result of a large receptor potential in a sensory neuron?

The membrane potential exceeds threshold, and an action potential is generated

What is the function of oligodendrocytes in the CNS?

To synthesize myelin in the CNS

What type of receptors primarily detect the onset and offset of a stimulus?

Rapidly adapting receptors

What determines the size of a receptor potential?

The intensity of the stimulus

What occurs when ion channels are opened in the sensory receptor?

Current flows into the receptor

What is the change in membrane potential produced by a stimulus called?

Receptor potential

What is the primary function of sensory receptors in sensory pathways?

To transduce the stimulus into electrical energy

Where are the cell bodies of primary afferent neurons located?

In dorsal root or spinal cord ganglia

What is the function of second-order neurons in sensory pathways?

To receive information from primary afferent neurons and transmit it to the thalamus

What is the result of the information received by fourth-order neurons in the cerebral cortex?

Conscious perception of the stimulus

What is the characteristic of sensory information originating on one side of the body in the spinal cord?

It ascends to the contralateral thalamus

What is the type of sensory information that is included in the somatosensory system?

Touch, movement, temperature, and pain

Where are third-order neurons located in sensory pathways?

In the relay nuclei of the thalamus

What is the function of primary afferent neurons in sensory pathways?

To receive information from sensory receptors and send it to the CNS

What is the organization of information from different parts of the body in the thalamus?

Somatotopically

What is the consequence of destruction of the thalamic nuclei?

Loss of sensation on the contralateral side of the body

What is the primary purpose of the sensory homunculus in the somatosensory cortex?

To localize and process touch and pressure sensations

What is the neurotransmitter involved in the transmission of pain sensations?

Substance P

What is the characteristic of fast pain?

Rapid onset and offset, localized sensation

What is the characteristic of slow pain?

Aching, burning, or throbbing sensation

What is the rule followed by referred pain of visceral origin?

Dermatome rule

What is an example of referred pain?

Ischemic heart pain referred to the chest and shoulder

What is the arrangement of cones to bipolar cells in the fovea?

1:1

What is the purpose of horizontal and amacrine cells in the retina?

To form local circuits with bipolar cells

What happens when light strikes any one of the rods?

It activates a single bipolar cell

What is the route that fibers from the left nasal hemiretina take?

They cross at the optic chiasm and form the right optic tract

What is the result of cutting the optic nerve?

Blindness in the ipsilateral eye

What is the function of ganglion cells in the retina?

To transmit signals to the optic nerve

How many bipolar cells do many rods synapse on?

Multiple

What is the characteristic of fibers from the temporal hemiretina?

They remain ipsilateral

What is the location of the lateral geniculate body?

In the thalamus

What is the result of decreased release of glutamate from photoreceptors acting on ionotropic receptors?

Hyperpolarization (inhibition)

What is the effect of increasing light intensity on photoreceptor cells?

Hyperpolarization of the photoreceptor cell membrane

What is the function of phosphodiesterase in photoreceptor cells?

Converting cyclic guanosine monophosphate (cGMP) to 5'-GMP

What is the effect of decreased cGMP levels on Na+ channels?

Closing of Na+ channels

What is the result of decreased release of glutamate from photoreceptors acting on metabotropic receptors?

Depolarization (excitation)

What is the function of bipolar cells in the visual pathway?

Receiving input from many receptor cells

What is the receptive field of a ganglion cell composed of?

The center and surround of the receptive field

What is the function of horizontal cells in the visual pathway?

Forming the surround of the receptive field

What is the result of increased inward Na+ current in photoreceptor cells?

Depolarization of the photoreceptor cell membrane

What pattern of a ganglion cell receptive field is characterized by light striking the center of the receptive field depolarizing the ganglion cell, whereas light striking the surround of the receptive field hyperpolarizes the ganglion cell?

On-center, off-surround

What type of cells in the visual cortex respond best to moving bars or edges of light with the correct orientation?

Complex cells

What is the unit of measurement for the intensity of sound waves?

Decibels (dB)

What is the function of the outer ear in the auditory pathway?

To direct sound waves into the auditory canal

What type of cells in the visual cortex respond best to lines with particular length and to curves and angles?

Hypercomplex cells

What is the formula for calculating the decibel level of a sound wave?

dB = 20log(P/P0)

What is the difference between the on-center, off-surround and off-center, on-surround patterns of ganglion cell receptive fields?

The center and surround regions have opposite effects on the ganglion cell

What is the function of the middle ear in the auditory pathway?

To transmit sound waves from the outer ear to the inner ear

What type of hemianopia occurs when the optic chiasm is cut?

Heteronymous bitemporal hemianopia

What is the characteristic of simple cells in the visual cortex?

They have center-surround, on-off patterns, but are elongated rods rather than concentric circles

What is the role of metarhodopsin II in photoreception?

Activates a G protein called transducin

What is the result of vitamin A deficiency on photoreception?

Night blindness

What is the effect of light on the retina in rods?

Converts 11-cis retinal to all-trans retinal

What is the component of rhodopsin that belongs to the superfamily of G-protein-coupled receptors?

Opsin

What type of hemianopia occurs when the geniculocalcarine tract is cut?

Homonymous hemianopia with macular sparing

What is the result of the activation of phosphodiesterase in photoreception?

Closure of Na+ channels

What is the role of transducin in photoreception?

Activates phosphodiesterase

What is the effect of the closure of Na+ channels on photoreception?

Decreased release of glutamate

What type of sensations are detected by the fungiform papillae on the anterior two-thirds of the tongue?

Salty, sweet, and umami

Which cranial nerve is responsible for the sensation of taste in the posterior one-third of the tongue?

CN IX

What is the final destination of the taste information in the central nervous system?

Taste cortex

What is the unit of contraction in the motor system?

Motor unit

What determines the force of muscle contraction?

Recruitment of additional motor units

What is the term for the group of motoneurons that innervate fibers within the same muscle?

Motoneuron pool

What is the result of binding of taste chemicals to taste receptors?

Depolarization of the receptor cell

Where do the second-order neurons of the taste pathway project?

Ventral posteromedial nucleus of the thalamus

What is the primary function of muscle spindle reflexes?

To oppose increases in muscle length

What type of fibers detect the rate of change in muscle length?

Nuclear bag fibers

Which type of afferent fibers are stimulated when a muscle is stretched?

Group Ia and group II afferent fibers

What is the function of y-motoneurons?

To innervate intrafusal muscle fibers

What is the result of stimulation of group Ia afferents?

Contraction and shortening of the muscle

What is the function of the muscle spindle?

To detect changes in muscle length

What type of fibers are more numerous in muscle spindles?

Nuclear chain fibers

Which type of fibers have nuclei arranged in rows?

Nuclear chain fibers

Which nerve detects noxious or painful stimuli, such as ammonia?

CN V

What happens to the sense of smell after fracture of the cribriform plate?

The sense of smell is reduced or eliminated

What type of neurons are mitral cells in the olfactory bulb?

Second-order neurons

What is the result of the binding of odorant molecules to specific olfactory receptor proteins?

The activation of G proteins

What is the function of microvilli on taste receptor cells?

To increase the surface area for binding taste chemicals

What is the initial response of the olfactory receptor neuron to the binding of odorant molecules?

Depolarization

What is the role of adenylate cyclase in olfactory transduction?

To increase intracellular cAMP

What is the result of the depolarization of the olfactory receptor neuron?

The generation of action potentials

What type of reflex is the knee-jerk reflex?

Monosynaptic

What is the result of increased y-motoneuron activity on the muscle spindle?

Increased sensitivity of the muscle spindle

What type of reflex is the Golgi tendon reflex?

Disynaptic

What is the effect of contraction of the quadriceps muscle on the lower leg?

Extension of the lower leg

What is the result of the Golgi tendon reflex on the muscle that was originally contracted?

Relaxation of the muscle

What is the characteristic of the clasp-knife reflex?

It is an exaggerated form of the Golgi tendon reflex

What is the result of activation of the Golgi tendon reflex in a hypertonic arm?

Flexion of the arm like a jackknife

What is the result of the flexor withdrawal reflex?

Flexion on the ipsilateral side and extension on the contralateral side

What is the purpose of coactivating a-motoneurons and y-motoneurons during muscle contraction?

To maintain the sensitivity of muscle spindles to changes in muscle length

What type of reflex is the stretch reflex, in terms of the number of synapses involved?

Monosynaptic

Which type of afferent fibers are stimulated when a muscle is stretched, leading to the stretch reflex?

Group Ia afferent fibers

What is the response of the homonymous muscle when the a-motoneurons are stimulated during the stretch reflex?

Contraction

What is the purpose of the Golgi tendon reflex?

To prevent muscle injury by relaxing the muscle when it becomes too tense

What is the characteristic of the flexor withdrawal reflex?

It is a polysynaptic reflex

What is the effect of the stretch reflex on the muscle spindle?

It returns the muscle spindle to its original length

What is the result of the activation of synergistic muscles during the stretch reflex?

They contract to help the homonymous muscle

What is the primary function of the basal ganglia in movement?

To modulate thalamic outflow to the motor cortex to plan and execute smooth movements

What is the effect of dopamine on the indirect pathway in the basal ganglia?

Inhibitory

What is the result of lesions of the subthalamic nucleus in the basal ganglia?

Wild, flinging movements (e.g., hemiballismus)

What is the primary neurotransmitter used in the connections between the striatum and the substantia nigra in the basal ganglia?

Dopamine

What is the overall effect of dopamine on the basal ganglia?

Excitatory

What is the result of lesions of the globus pallidus in the basal ganglia?

Inability to maintain postural support

What is the function of the indirect pathway in the basal ganglia?

To inhibit movement

What is the result of lesions of the striatum in the basal ganglia?

Release of inhibition

What is the result of the destruction of dopaminergic neurons in patients with Parkinson disease?

Overall inhibition of motor movements

Which part of the brain is responsible for generating a plan for movement?

Premotor cortex and supplementary motor cortex

What is the dominant hemisphere with respect to language in most individuals?

Left hemisphere

During which stage of sleep do most dreams occur?

REM sleep

What is the organization of the primary motor cortex?

Somatotopically organized

What is the primary function of the corpus callosum?

To transfer information between the two hemispheres

What is the characteristic of the primary motor cortex during epileptic events?

It causes jacksonian seizures

What is the result of damage to the Wernicke area?

Sensory aphasia

What is the composition of EEG waves?

Alternating excitatory and inhibitory synaptic potentials

What is the role of the supplementary motor cortex in movement?

It programs complex motor sequences

What type of waves predominate in awake adults with eyes open?

Beta waves

What is the circadian rhythm driven by?

The suprachiasmatic nucleus of the hypothalamus

What is the effect of dopamine on the indirect pathway?

It inhibits the indirect pathway

What is the characteristic of REM sleep?

Rapid eye movements and loss of muscle tone

What is the result of the destruction of dopaminergic neurons in patients with Huntington disease?

Quick, continuous, and uncontrollable movements

What is the effect of benzodiazepines on REM sleep?

Decrease the duration of REM sleep

Which area of the brain is responsible for motor aphasia, where speech and writing are affected but understanding is intact?

Broca area

What is the primary difference between short-term and long-term memory?

Short-term memory involves synaptic changes, while long-term memory involves structural changes

What is the function of the choroid plexus epithelium in the formation of CSF?

To secrete or absorb substances from blood into CSF using carriers

Which of the following substances is NOT excluded from the CSF due to its large molecular size?

Glucose

What is the primary function of the blood-brain barrier?

To separate the cerebral capillary blood from the CSF

What is the composition of CSF similar to?

The composition of interstitial fluid of the brain

What is the result of bilateral lesions of the hippocampus?

The inability to form new long-term memories

Which of the following substances can freely cross the blood-brain barrier?

O2

What is the primary mechanism by which aspirin reduces fever?

By inhibiting cyclooxygenase, thereby reducing prostaglandin production

What is the effect of increased body temperature on the body's response to heat?

It increases the rate of heat loss through sweating and vasodilation

What is the primary cause of heat stroke?

Impaired sweating response

What is the effect of steroids on the production of prostaglandins?

They decrease the production of prostaglandins by blocking the release of arachidonic acid

What is the primary mechanism by which pyrogens increase body temperature?

By increasing the production of prostaglandins

What is the effect of hypothermia on the body's heat-generating mechanisms?

It decreases the body's heat-generating mechanisms

What is the primary cause of heat exhaustion?

Excessive sweating

What is the primary mechanism by which malignant hyperthermia is caused?

By the inhalation of anesthetics in susceptible individuals

Study Notes

Autonomic Nervous System (ANS)

  • The ANS is a set of pathways to and from the central nervous system (CNS) that innervates and regulates smooth muscle, cardiac muscle, and glands.
  • It is distinct from the somatic nervous system, which innervates skeletal muscle.
  • The ANS has three divisions: sympathetic, parasympathetic, and enteric.

Organization of the ANS

  • Synapses between neurons are made in the autonomic ganglia.
  • Parasympathetic ganglia are located in or near the effector organs.
  • Sympathetic ganglia are located in the paravertebral chain.
  • Preganglionic neurons of the sympathetic nervous system originate in spinal cord segments T1-L3 or the thoracolumbar region.
  • Preganglionic neurons of the parasympathetic nervous system originate in the nuclei of cranial nerves and in spinal cord segments S2-S4 or the craniosacral region.
  • Postganglionic neurons of both divisions have their cell bodies in the autonomic ganglia and synapse on effector organs.

Neurotransmitters of the ANS

  • Adrenergic neurons release norepinephrine as the neurotransmitter.
  • Cholinergic neurons, whether in the sympathetic or parasympathetic nervous system, release acetylcholine (ACh) as the neurotransmitter.
  • Nonadrenergic, noncholinergic neurons include some postganglionic parasympathetic neurons of the gastrointestinal (GI) tract, which release substance P, vasoactive intestinal peptide (VIP), or nitric oxide (NO).

Sensory Systems

  • Somatosensory system includes the sensations of touch, movement, temperature, and pain.
  • Pain is associated with the detection and perception of noxious stimuli (nociception).
  • The receptors for pain are free nerve endings in the skin, muscle, and viscera.
  • Neurotransmitters for nociceptors include substance P.

Organization of the Nervous System

  • The nervous system is composed of the central nervous system (CNS) and the peripheral nervous system (PNS).
  • The CNS includes the brain and spinal cord.
  • The major divisions of the CNS are the spinal cord, brain stem (medulla, pons, and midbrain), cerebellum, diencephalon (thalamus and hypothalamus), and cerebral hemispheres (cerebral cortex, basal ganglia, hippocampus, and amygdala).
  • Sensory or afferent nerves bring information into the nervous system.
  • Motor or efferent nerves carry information out of the nervous system.

Cells of the Nervous System

  • Structure of the neuron:
    • Cell body surrounds the nucleus and is responsible for protein synthesis.
    • Dendrites arise from the cell body and receive information from adjacent neurons.
    • Axon projects from the axon hillock, where action potentials originate and send information to other neurons or muscle.
  • Glial cells function as support cells for neurons:
    • Astrocytes supply metabolic fuels to neurons, secrete trophic factors, and synthesize neurotransmitters.
    • Oligodendrocytes synthesize myelin in the CNS (whereas Schwann cells synthesize myelin in the PNS).
    • Microglial cells proliferate following neuronal injury and serve as scavengers for cellular debris.

Sensory Transduction

  • Sensory receptors are specialized epithelial cells or neurons that transduce environmental signals into neural signals.
  • Steps in sensory transduction:
    1. Stimulus arrives at the sensory receptor.
    2. Ion channels are opened in the sensory receptor, allowing current to flow.
    3. The change in membrane potential produced by the stimulus is the receptor potential, or generator potential.
    4. If the receptor potential is depolarizing, it brings the membrane potential closer to threshold.
    5. If the receptor potential is large enough, the membrane potential will exceed threshold, and an action potential will fire in the sensory neuron.

Visual System

  • Photoreception in rods:

    • Light on the retina converts 11-cis retinal to all-trans retinal, a process called photoisomerization.
    • Rhodopsin is composed of opsin (a protein) belonging to the superfamily of G-protein-coupled receptors and retinal (an aldehyde of vitamin A).
    • Vitamin A is necessary for the regeneration of 11-cis retinal.
  • Steps in photoreception in rods:

    1. Metarhodopsin II activates a G protein called transducin (Gt), which in turn activates a phosphodiesterase.
    2. Phosphodiesterase catalyzes the conversion of cyclic guanosine monophosphate (cGMP) to 5'-GMP, and cGMP levels decrease.
    3. Decreased levels of cGMP cause closure of Na+ channels, decreased inward Na+ current, and, as a result, hyperpolarization of the photoreceptor cell membrane.
    4. When the photoreceptor is hyperpolarized, there is decreased release of glutamate, an excitatory neurotransmitter.### Muscle Spindles and Reflexes
  • Muscle spindles are responsible for detecting changes in muscle length and are composed of two types of intrafusal fibers: nuclear bag fibers and nuclear chain fibers.

  • Nuclear bag fibers detect the rate of change in muscle length and are innervated by group Ia afferents.

  • Nuclear chain fibers detect static changes in muscle length and are innervated by group II afferents.

  • Muscle spindle reflexes oppose increases in muscle length and are activated by group Ia and group II afferent fibers.

  • When a muscle is stretched, the muscle spindle is also stretched, stimulating group Ia and group II afferent fibers.

  • Stimulation of group Ia afferents activates α-motoneurons in the spinal cord, causing contraction and shortening of the muscle.

Golgi Tendon Reflex

  • The Golgi tendon reflex is a disynaptic reflex that is the opposite of the stretch reflex.
  • It is activated by active muscle contraction, which stimulates Golgi tendon organs and group Ib afferent fibers.
  • The group Ib afferents stimulate inhibitory interneurons in the spinal cord, which inhibit α-motoneurons and cause relaxation of the muscle.

Flexor Withdrawal Reflex

  • The flexor withdrawal reflex is a polysynaptic reflex that results in flexion on the ipsilateral side and extension on the contralateral side.
  • It is elicited by somatosensory and pain afferent fibers and is involved in withdrawing a stimulated body part from a noxious stimulus.

Muscle Reflexes

  • The stretch reflex is a monosynaptic reflex that is activated by muscle stretch.
  • The Golgi tendon reflex is a disynaptic reflex that is activated by muscle contraction.
  • The flexor withdrawal reflex is a polysynaptic reflex that is activated by somatosensory and pain afferent fibers.

Clinical Disorders

  • Lesions of the cerebellum can result in ataxia, characterized by a lack of coordination, including delay in initiation of movement, poor execution of a sequence of movements, and inability to perform rapid alternating movements.
  • Lesions of the basal ganglia can result in movement disorders, such as Parkinson's disease, Huntington's disease, and hemiballismus.

Basal Ganglia

  • The basal ganglia consist of the striatum, globus pallidus, subthalamic nuclei, and substantia nigra.
  • The basal ganglia modulate thalamic outflow to the motor cortex to plan and execute smooth movements.
  • Many synaptic connections in the basal ganglia are inhibitory and use GABA as their neurotransmitter.

Motor Cortex

  • The primary motor cortex is responsible for the execution of movement.
  • The premotor cortex and supplementary motor cortex are responsible for generating a plan for movement.
  • The motor cortex is somatotopically organized, meaning that different areas of the cortex are responsible for controlling different parts of the body.

Higher Functions of the Cerebral Cortex

  • The cerebral cortex is responsible for generating a plan for movement and executing it.
  • The EEG is a measure of the electrical activity of the brain and can be used to diagnose neurological disorders.
  • Sleep is a complex process that involves different stages, including REM sleep, non-REM sleep, and dreaming.

Blood-Brain Barrier and Cerebrospinal Fluid

  • The blood-brain barrier is a barrier between cerebral capillary blood and the CSF.
  • The CSF is formed by the choroid plexus epithelium and fills the ventricles and the subarachnoid space.
  • The composition of CSF is approximately the same as that of the interstitial fluid of the brain but differs significantly from blood.

Learn about the Autonomic Nervous System (ANS), its divisions, and organization. Understand how it regulates smooth muscle, cardiac muscle, and glands.

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