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Questions and Answers

What is the primary role of glial cells in the nervous system?

  • Initiate electrical potentials
  • Provide support and supply nutrients to neurons (correct)
  • Facilitate motor responses
  • Transmit signals between neurons

    • Which type of matter is primarily composed of myelinated axons?

  • Nuclei
  • Grey matter
  • White matter (correct)
  • Glial cells

    • What characterizes an action potential in neurons?

  • It occurs only at the dendrites.
  • It is a graded response.
  • It can vary in strength.
  • It is an all-or-nothing response. (correct)

    • Which part of the brain is primarily responsible for regulating homeostasis?

    <p>Hypothalamus</p> Signup and view all the answers

    Which sensory receptors are responsible for converting light energy?

    <p>Photoreceptors</p> Signup and view all the answers

    What is the function of proprioceptors in the sensory system?

    <p>Detect body position and movement</p> Signup and view all the answers

    Which visual processing pathway is primarily responsible for object perception?

    <p>Ventral stream</p> Signup and view all the answers

    What does the term 'convergence' refer to in sensory pathways?

    <p>Separate inputs leading to one location</p> Signup and view all the answers

    Which area of the brain is associated with higher-order thinking and behavior?

    <p>Frontal lobe</p> Signup and view all the answers

    What kind of information does the dorsal spinocerebellar tract primarily convey?

    <p>Proprioceptive information from lower limbs</p> Signup and view all the answers

    Which of the following describes 'reaction time' in the context of stimulus responses?

    <p>Time from stimulus onset to motor response initiation</p> Signup and view all the answers

    What is the primary role of the autonomic nervous system?

    <p>Regulate involuntary organs and glands</p> Signup and view all the answers

    Which type of receptor is primarily associated with the sense of pain?

    <p>Nociceptors</p> Signup and view all the answers

    What happens when a lesion occurs in the optic chiasm?

    <p>Loss of peripheral vision</p> Signup and view all the answers

    What principle emphasizes keeping processes as simple as possible in reaction time tasks?

    <p>KISS Principle</p> Signup and view all the answers

    Which type of reaction time is characterized by one stimulus leading to multiple responses?

    <p>Choice Reaction Time</p> Signup and view all the answers

    What is the primary function of gamma motor neurons?

    <p>Maintain tautness in muscle spindles</p> Signup and view all the answers

    Which reflex pathway involves the excitation of a sensory neuron that inhibits a motor neuron projecting to a different muscle?

    <p>Heteronymous Reflex Pathway</p> Signup and view all the answers

    What effect does stimulus intensity have on reaction time?

    <p>Higher intensity stimuli result in quicker response times</p> Signup and view all the answers

    Which nerve is responsible for innervating the lateral rectus muscle for eye movement?

    <p>Abducens Nerve</p> Signup and view all the answers

    What type of eye movement is characterized by rapid ballistic motion changing the point of fixation?

    <p>Saccades</p> Signup and view all the answers

    What is the purpose of the vestibulo-ocular reflex (VOR)?

    <p>Stabilize gaze during head rotation</p> Signup and view all the answers

    Temporal summation in synaptic transmission refers to?

    <p>Accumulation of neurotransmitters at synapses over time</p> Signup and view all the answers

    How do cation channels contribute to the action potential process?

    <p>By allowing positive ions to flow into the neuron</p> Signup and view all the answers

    What characterizes disconjugate movements of the eyes?

    <p>Eyes move in opposite directions</p> Signup and view all the answers

    Which neurotransmitter is primarily inhibitory in the spinal cord?

    <p>GABA</p> Signup and view all the answers

    What is the role of alpha motor neurons?

    <p>Control extrafusal muscle fibers for contraction</p> Signup and view all the answers

    Which statement is true regarding the influence of pre-synaptic modulation on reflexes?

    <p>Increases excitability of motor neurons without changing sensory input</p> Signup and view all the answers

    Study Notes

    Nervous System Overview

    • The nervous system is responsible for integrating stimuli and transmitting motor responses.
    • It is made up of neurons and glial cells.
    • Glial cells support neurons, supply nutrients and oxygen, insulate neurons, and clean debris.
    • Oligodendrocytes are found in the CNS and Schwann cells are in the PNS.

    Neuron Communication

    • Synaptic potential is a graded electrochemical response that converges at the axon hillock for integration.
    • Action potential (AP) is an all-or-nothing electrochemical response due to changes in membrane potential caused by ion permeability.

    Grey and White Matter

    • Grey matter consists of cell bodies, dendrites, and terminal endings.
    • It is the site of integration and transformation.
    • White matter is comprised of bundles of myelinated axons.
    • It functions as pathways connecting areas of grey matter.
    • In the brain, grey matter is on the outside and white matter is inside.
    • The opposite is true for the spinal cord.

    Brain Components

    • The central nervous system (CNS) includes the spinal cord and brainstem, located within the skeleton.
    • The brain is divided into the hindbrain, midbrain, and forebrain.
    • The peripheral nervous system (PNS) is located outside the skeleton.
    • It is divided into the somatic (skeletal muscles), autonomic (organs, smooth muscles, and glands), and enteric (GI tract and blood flow) nervous systems.
    • The autonomic nervous system is further divided into the sympathetic (fight or flight) and parasympathetic (rest and digest) nervous systems.

    Brainstem

    • The brainstem refers to the pons, medulla, and hindbrain.
    • It contains 12 cranial nerves that innervate the eyes, head, neck, and upper trunk.
    • The brainstem is vital for autonomic function, alertness, eye, and head movements.

    Cerebellum

    • The cerebellum is 10% of the brain's size but contains 50% of its neurons.
    • It has dense afferent and efferent connections with the brainstem and cortex.
    • It contributes to the control of movement, learning, cognition, and emotions.

    Thalamus and Hypothalamus

    • The thalamus is a relay area between the cortex and CNS.
    • It plays a role in alertness and is essential for sensorimotor processing (except smell).
    • The hypothalamus controls internal body functions and homeostasis.
    • It links the nervous and endocrine systems.

    Cerebral Cortex

    • The cortex is responsible for higher-order thinking, behavior, decision-making, executive function, and self-awareness.
    • It controls action, body movement, eye movement, and speech.
    • The occipital lobe receives visual input and processes visual information.
    • The parietal lobe receives and processes sensory information related to touch, taste, and temperature.
    • It integrates information from the occipital and temporal cortices for object perception and motor control.
    • The temporal lobe receives raw auditory input from the thalamus and processes sound.
    • It stores and retrieves memories, combines visual information for object perception, and participates in emotional processing.
    • The amygdala and hippocampus contribute to memory storage.
    • Brodmann's area is a region of the cortex categorized by cytoarchitecture, mirroring function and linking structure with function.
    • The cortex is divided into primary, secondary, and association areas.
    • Primary cortex is where sensory input first arrives or motor output ends.
    • Secondary cortex receives processed information.
    • Association areas integrate information from multiple sensory sources.

    Sensory Receptors

    • Sensory receptors are specialized cells or cell endings that convert stimuli into electrical potentials.
    • They allow the nervous system to interpret external and internal environments.
    • Mechanoreceptors convert mechanical energy, photoreceptors convert light energy, chemoreceptors convert chemical energy, and thermoreceptors convert thermal energy.

    Receptor Properties

    • Receptors can represent the type of stimulus, onset, offset, and duration of stimulus activity based on stimulus presence.
    • Intensity of the stimulus is represented by the frequency of action potentials generated per unit time.
    • The location of the stimulus is encoded by which receptors are activated.

    Stimulus Modality

    • Somatosensation: Sense of external and internal body states, including movement, proprioception, orientation, and pain.
    • Proprioception: Sense of body position.
    • Equilibrioception: Sense of movement and position relative to gravity.
    • Audioception: Sense of the environment through sound waves.
    • Opthalmoception: Sense of objects through visible light.
    • Olfaction: Sense of chemical odorants in the nasal cavity.
    • Gustation: Sense of substances that chemically react in the mouth.
    • Nociception: Pain due to injury or damage.

    Sensory Receptor Locations

    • Somatosensory Receptors: Found in the skin, fatty tissue beneath the skin, muscle, and musculoskeletal tissue (ligaments, tendons, and joint capsules).
    • Vestibular Receptors: Located within the labyrinths of the inner ear.
    • Visual Receptors (Photoreceptors): Found in the retina.
    • Auditory Receptors (Mechanoreceptors): Located in the cochlea.

    Receptor Adaptation

    • Rapidly Adapting: Produce a vigorous but transient response to changes in stimulus energy, ideal for detecting rates of change in energy intensity.
    • Slowly Adapting: Produce a measured but sustained response while the stimulus remains constant, reflecting actual stimulus energy intensity.

    Photoreception

    • Photoreceptors absorb photons from light wavelengths, triggering chemical reactions that generate receptor potentials.
    • Pigments absorb light, initiating second-messenger pathways that close sodium channels, decreasing the amplitude of the receptor potential.
    • This results in less neurotransmitter release as the receptor potential reaches the end of the receptor.
    • Photoreceptors do not directly influence sensory nerves, instead they act through intermediary bipolar cells.

    Central and Peripheral Afferent Pathways

    • Myelination: The amount of insulation around the axon of an afferent neuron, preventing ion leakage.
    • Axon Diameter: Larger diameter axons allow for faster signal transmission due to greater space for ion flow.
    • Proprioceptive afferent neurons: Fastest transmitters of afferent information.
    • Sensory information from different parts of the body converges in association areas to generate action potentials.

    Neuron Communication Patterns

    • Divergence: Same input separates and disperses to multiple locations.
    • Convergence: Multiple inputs project to a common location.
    • Topographic Projection: Ordered projection of a sensory surface (retina or skin) within nuclei in the CNS.
    • Topographic projection is found throughout all levels of the CNS.
    • Ipsilateral: Belonging to or occurring on the same side of the body.
    • Contralateral: Belonging to or occurring on the opposite side of the body.

    Visual Pathways

    • The visual system has two parallel pathways: the geniculostriate visual system (90% of fibers) and the tectopulvinar visual system (10% of fibers).
    • Geniculostriate Visual System (Primary Visual Pathway):
      • Retina - Lateral geniculate nucleus (LGN) - Primary visual cortex (V1)
    • Tectopulvinar Visual System (Secondary Visual Pathway):
      • Retina - Superior colliculus - Pulvinar nucleus of the thalamus
    • Optic Chiasm: Information from the contralateral visual field crosses the midline at the optic chiasm.
    • V1: A mirror image of the visual environment.

    Visual Pathway Lesions

    • Lesion of the right optic nerve: Inability to see anything on the right side.
    • Lesion of the optic chiasm: Loss of peripheral vision (tunnel vision), only central vision remains.

    Dorsal and Ventral Visual Streams

    • Dorsal Stream ("Where or How"): Relates the visual environment to movement and action.
    • Ventral Stream ("What"): Emphasizes object recognition and perception.

    Prosopagnosia

    • The inability to recognize faces is associated with damage to the ventral visual pathway.

    Somatosensory Pathway

    • Mechanoreceptors: Specialized cells that project to, or are part of, an afferent neuron.
    • Dorsal Horn: Somatosensory nerves (except those from the head) enter the spinal cord via the dorsal horn.
    • Trigeminal Nerve (CN V): Nerves from the head form the trigeminal nerve.
    • Ascending Pathways: Somatosensory nerves layer to form ascending pathways, while maintaining divergent projections in the spinal cord for reflexes and muscle group coordination.
    • Dorsal Root Ganglion: Cell bodies of sensory neurons reside outside the spinal cord in the dorsal root ganglion.

    Posterior Column Pathway

    • Nerve bundles in the posterior column pathway convey fine touch, vibration, and proprioceptive afferent information.
    • Third-Order Neuron: Axon projects from thalamic nuclei to the primary somatosensory cortex.
    • Second-Order Neuron: Axon crosses the body midline in the medulla and projects to thalamic nuclei.
    • First-Order Neuron: Axon projects from the receptor to the medulla.

    Spinothalamic Tracts

    • Anterior Spinothalamic Tract: Conveys crude, poorly localized touch information.
    • Lateral Spinothalamic Tract: Carries information about noxious stimuli and temperature.

    Spinocerebellar Tracts

    • Dorsal Spinocerebellar Tract (DSCT): Projects to the inferior peduncle of the cerebellum.
      • Carries proprioceptive information from the lower limbs (spindle fibers) via afferent neurons.
    • Rostral Spinocerebellar Tract (RSCT): Projects to the inferior peduncle of the cerebellum.
      • Carries proprioceptive information from the upper limbs.
    • Ventral Spinocerebellar Tract (VSCT): Projects to the superior peduncle of the cerebellum.
      • Carries proprioceptive information from the lower limbs (Golgi tendon organs) via Ib afferent neurons.

    Stimulus Evoked Responses and Simple Reflexes

    • Stimulus-evoked behavior: Involuntary, automatic, and immediate consequences of stimulation.
    • Reflexes: Direct, automatic, and relatively immediate responses to stimulation.
    • Timing: Measures the time between different points in the stimulus-response process.
      • This information reveals how long each part of the pathway takes.
    • Conduction Time: Time to conduct a signal along an axon pathway.
    • Synapse Time: Time for information exchange between neurons.
    • Processing Time: Time for neurons to process information.
    • Reaction Time: Time between stimulus onset and the motor system's response (latency or premotor time).
    • Movement Time: Time between the onset of the motor system's response and movement outcome.
    • Response Time: The combination of reaction time and movement time (time between stimulus and movement outcome).

    Measuring Stimulus-Response Transformations

    • Behavioral Measures: Assess timing, accuracy, response characteristics, and modifiability of the stimulus-response process.
    • Electrophysiology: Evaluates stimulus-response pathways (e.g., H-reflex, evoked potentials, brain hemodynamics, non-invasive brain stimulation).

    Stimulus Response Relationship

    • Longer reaction time with more choices.
    • Keep it Simple Stupid = KISS principle
    • Simple reaction time: One stimulus one response.
    • Choice reaction time: One stimulus, multiple responses.
    • Stimulus Response Compatibility: Reaction time is quicker the closer the stimulus’s relationship is to the response.
    • Stimulus Modality: Different stimulus types take longer to be identified and associated with a reaction.
    • Stimulus Intensity/Predictability: More intense stimuli result in quicker reaction times. Knowing when a response is required leads to a quicker response (preloaded response).

    Muscle Contraction

    • Extrafusal fibers: Directly connected with a motor neuron for contraction.
    • Intrafusal fibers: Specialized muscle spindle fibers detecting stretch.
    • More Extrafusal fibers in sensory nerves: Diverge to act on motor neurons innervating multiple extrafusal fibers.
    • Homonymous Reflex Pathway (HORP): A sensory neuron excites a motor neuron projecting back to the same muscle.
    • Heteronymous Reflex Pathway (HERP): A sensory neuron excites a motor neuron projecting to a different muscle.
    • Alpha Motor Neurons: Innervate extrafusal fibers to shorten or lengthen AP
    • Gamma Motor Neurons: Special segments at the end of intrafusal fibers, keep them taut as the muscle contracts.
    • Fusimotor Drive: Pulls ion channels open to generate a receptor potential.
    • Muscle spindle Fibers + Gamma Motor Neurons = Fusimotor System
    • Alpha-Gamma Coactivation: Coordinated action during muscle contraction.
    • Tonic Fusimotor Bias: Increase in spindle fiber tension due to Alpha motor coactivation during contraction
    • Modulation of Stimulus-Response Relationship: Changes in gamma motor neuron activity change spindle receptors' sensitivity altering the muscle's tautness, affecting the response to the same stretch.
    • Inhibition of the Reflex: Decreases the strength of sensory afferent effects on motor neurons.
    • Facilitation of the Reflex: Increases the gain at the sensory to motor synapse.

    Myotatic Reflex Pathway Assessment

    • Stimulation of the nerve removes muscle spindle influence to assess the stimulus-response relationship in a controlled manner.
    • Amplitude of the stimulus is sensitive to intensity.
    • H-reflex motor response: Stimulation of the afferent sensory nerve.
    • M-wave motor response: Stimulation of the efferent motor nerve.

    Inverse Myotatic Reflex

    • Golgi Tendon Organ (GTO): A sensory receptor located in the tendon which detects muscle tension.
    • Strong Excitation of Ib afferents: Overrides the alpha motor neuron excitation, inhibiting the muscle.
    • Initial Inverse Myotatic Reflex: Done with the muscle at rest. Alpha motor neuron inhibition, but excitatory afferent nerve facilitates alpha motor neuron excitation.

    Muscle Coordination

    • Ipsilateral: Same side of the body.
    • Contralateral: Opposite side of the body.
    • Stimulus initiates pain receptors, sensory neuron activates multiple interneurons.
    • Ipsilateral Motor Neurons: Flexor excited, ipsilateral flexor contracts.
    • Contralateral Motor Neurons: Extensor excited, extension of the leg.

    Eye Movements

    • Fovea: Portion of the retina with the highest density of cone photoreceptors providing high visual acuity.
    • Visual Axis: Straight path from the point of fixation to the fovea.
    • Optical Axis: Straight line passing through the center of the lens.
    • Direction of Gaze: Direction of the visual axis relative to the environment.
    • Gaze Angle: Angular measurement of the direction of gaze in a horizontal or vertical plane.
    • Effectors: Extraocular muscles that control horizontal, vertical, and rotational movements of the eye.
    • Nerves:
      • Abducens (VI): Lateral rectus muscle.
      • Oculomotor (III): Medial, superior, inferior rectus and inferior oblique muscles.
      • Trochlear (IV): Superior oblique muscle.
    • Classification of Movements:
      • Conjugate/Version: Coordinated eye movement in the same direction through the same angle.
      • Disconjugate/Vergence: Coordinated eye movement in the opposite direction through mirrored angles.

    Types of Movements

    • Vestibulo-Ocular Reflex (VOR): Stabilizes gaze in response to head rotation.
    • Input: Head rotation (vestibular nerve) -> Output: Extraocular muscle activity (Abducens, Oculomotor, Trochlear).
    • Optokinetic Reflex: Combination of slow and fast eye movements to keep a moving scene stationary.
    • Saccades: Rapid ballistic eye movement changing the point of fixation.
      • Exogenous: Driven by something outside the body
      • Endogenous: Driven by something inside the body
      • Express Saccades: Bypass the cortex (faster).
      • Prosaccades: Reflex saccades traveling through the visual cortex (slower).
      • Predictive Saccades: Stimulus expected but not yet occurring.
      • Memory-Guided Saccades: The stimulus was previously located but not anymore.
      • Anti-Saccades: Opposite direction of reflex saccades.
      • Saccade Sequence: Fixate on a series of points in space.
    • Smooth Pursuit: Eye movements that keep the eyes fixated on a moving object.
    • Vergence: Coordinated disconjugated movement of both eyes to obtain or maintain binocular vision

    Modulation of Stimulus-Evoked Behavior

    • Temporal Summation: Aggregation of multiple postsynaptic potentials occurring close in time.
    • Excitatory NT: Glutamate.
    • Inhibitory NT: GABA, Glycine.
    • Acetylcholine: Muscle contraction.
    • Dopamine, Serotonin, Norepinephrine: Other NTs.
    • Ionotropic Receptor: NT binds to a receptor, directly opening the ion channel.
    • Metabotropic Receptors: NT binds to the receptor, which then activates a second messenger signaling system.
    • Positive Charge: Opens voltage-gated ion channels, allowing calcium to flow into the postsynaptic neuron.
    • Calcium Influx: Signals vesicles holding glutamate (excitatory) to release their content at the synapse.
    • Glutamate Binding: Opens ion channels on the postsynaptic neuron, allowing sodium (Na+) to flow in.
    • Sodium Influx: Generates an excitatory postsynaptic potential (EPSP) that diffuses down the dendrite. If large enough, it will initiate an action potential.
    • Decrease in Presynaptic Calcium: Less calcium opens ion channels, fewer vesicles release glutamate. This leads to fewer postsynaptic ion channels opened, smaller EPSP, and less likelihood of triggering an action potential.
    • Increase in Presynaptic Calcium: More calcium opens ion channels, more glutamate released. This leads to more postsynaptic ion channels opened, larger EPSP, and higher likelihood of triggering an action potential.
    • Inhibitory NT Effects: Opposite charges cancel out, resulting in a smaller EPSP and less likelihood of triggering an action potential.
    • Facilitatory NT Effects: Positive charges summate with the sodium already flowing from glutamate release, causing a larger EPSP and higher likelihood of triggering an action potential.

    Sensory and Central Inputs

    • Sensory Inputs (Centripetal): Arise from primary afferent neurons, interneurons, or mediated by afferent input.
    • Central (Descending) (Centrifugal): Inputs arise from higher centers (cortex, cerebellum, brain stem).

    Examples of Pre-Synaptic Modulation

    • Soleus Reflex:
      • Control: Soleus reflex measured alone.
      • Conditioned:
        • Plantar flexor (anterior tibialis) exerts inhibitory influence over soleus.
        • Quadriceps exerts facilitatory influence.

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