Lecture 16
You stop noticing the feeling of your clothes after wearing them for a while. Which RAS function explains this?
Habituation — filtering out repetitive, unimportant stimuli.
A patient has trouble moving their eyes downward and inward after a head injury. Which cranial nerve is most likely affected?
Cranial nerve IV (trochlear)
If dopamine levels in the nigrostriatal pathway are too low, what type of movement disorder would likely occur?
If dopamine levels in the nigrostriatal pathway are too low, the patient would likely develop Parkinson’s disease–like movement disorders.
Nigrostriatal pathway: Substantia nigra → striatum (caudate and putamen)
Normal function: Dopamine here facilitates smooth, coordinated voluntary movement by modulating the activity of the basal ganglia motor circuits.
Low dopamine effects:
Reduced activation of the direct pathway (which normally promotes movement)
Increased activity of the indirect pathway (which normally inhibits movement)
Net effect: impaired initiation and execution of movement
A patient can speak fluently but their sentences are nonsensical. Which language area is likely damaged, and why?
Wernicke’s area is responsible for language comprehension and for formulating meaningful speech. Damage disrupts the ability to understand language and select correct words, but motor speech production via Broca’s area remains intact, so speech is fluent but meaningless.
The ANS is described as “self-governed.” What does this mean for our daily bodily functions, and can you give two examples of ANS activity that occur without conscious thought?
The autonomic nervous system (ANS) is called self-governed because it regulates involuntary bodily functions automatically, without conscious effort.
It continuously monitors and adjusts internal organ activity to maintain homeostasis.
This allows the body to respond rapidly to changes in the environment or internal state without needing conscious control.
Implication for daily life:
We don’t have to think about breathing, heart rate, digestion, or blood pressure for them to function properly.
The ANS ensures that essential physiological processes continue efficiently even while asleep or distracted.
Explain why damage to the medulla is often fatal.
It controls breathing, heart rate, and blood pressure — loss of these = death.
Describe the main purpose of white matter tracts in the cerebrum. Why is their myelination essential?
White matter tracts are bundles of myelinated axons that connect different parts of the nervous system. Their main purpose is to enable rapid communication between various regions of the brain and between the brain and spinal cord. White matter tracts serve as the communication highways of the brain, linking regions together for integrated function. Myelination ensures these connections are fast, efficient, and reliable, supporting everything from reflexes to higher-order thinking.
Describe how mesolimbic and mesocortical pathway dysfunction can contribute to both positive and negative symptoms of schizophrenia.
Schizophrenia involves a dual dopaminergic imbalance: too much dopamine in mesolimbic circuits → positive symptoms, and too little dopamine in mesocortical circuits → negative/cognitive symptoms.
Mesolimbic Pathway
Origin: Ventral tegmental area (VTA) → nucleus accumbens, amygdala, hippocampus.
Normal function: Involved in reward, motivation, and emotional salience.
Dysfunction in schizophrenia: Hyperactivity (too much dopamine release).
Clinical consequence:
Excess dopamine in this pathway produces positive symptoms:
Hallucinations
Delusions
Disorganized thinking
Mechanism: Overstimulation of D2 receptors in limbic regions → abnormal assignment of salience to irrelevant stimuli (“everything seems important or threatening”).
Mesocortical Pathway
Origin: VTA → prefrontal cortex.
Normal function: Executive function, working memory, attention, decision-making.
Dysfunction in schizophrenia: Hypoactivity (too little dopamine release).
Clinical consequence:
Deficient dopamine in this pathway produces negative and cognitive symptoms:
Apathy, lack of motivation (avolition)
Social withdrawal
Flattened affect
Impaired working memory and attention
Mechanism: Reduced D1 receptor stimulation in prefrontal cortex → impaired cortical processing and executive function.
Trace the path of an upper motor neuron from the primary motor cortex to the alpha motor neuron, naming at least four structures it passes.
Precentral gyrus → corona radiata → internal capsule → crus cerebri (midbrain) → pyramids in medulla → synapse on alpha motor neurons in spinal cord.
Explain how the SCN uses input from the eyes to regulate multiple body rhythms, such as sleep, hormone secretion, and body temperature.
The SCN receives direct input from retinal cells, allowing it to synchronize internal clocks with external light-dark cycles. It then regulates downstream structures like the pineal gland and hypothalamic nuclei to coordinate sleep, hormone secretion, and other daily rhythms.
Compare the superior vs inferior colliculi in location, function, sensory input, and main role.
Superior Colliculi - Upper pair of corpora quadrigemina; Visual reflex center; Receives input mainly from the retina, visual cortex, and other visual areas; Coordinates visual attention, eye movements, and head orientation toward visual stimuli
Inferior Colliculi - Lower pair of the corpora quadrigemina; Auditory reflex center; Receives input from the cochlear nuclei and auditory cortex; Processes and integrates auditory information and mediates reflexive responses to sound
Compare the hypothalamus and thalamus in terms of their primary roles in maintaining body function.
Thalamus - Acts as the relay and processing center for sensory and motor information going to and from the cerebral cortex
Hypothalamus - Acts as the main control center for homeostasis and link between the nervous and endocrine systems
The thalamus is like the “gateway” to the cerebral cortex — it processes and routes sensory and motor information.
The hypothalamus is the “command center” for homeostasis, integrating neural and hormonal signals to keep the body’s internal environment stable.
A neuron receives simultaneous excitatory and inhibitory inputs. Explain how EPSPs and IPSPs interact to determine whether an action potential occurs.
EPSPs (excitatory postsynaptic potentials): depolarize the membrane (make it more positive) and move the membrane potential closer to threshold.
IPSPs (inhibitory postsynaptic potentials): hyperpolarize the membrane (make it more negative) and move the membrane potential further from threshold.
An action potential occurs only if the net depolarization at the axon hillock reaches threshold (usually around −55 mV).
If IPSPs outweigh EPSPs, the neuron does not fire, even if EPSPs are present.
This integration allows the neuron to process complex information and respond selectively to relevant inputs.
Spatial summation - Multiple EPSPs and IPSPs from different synapses arrive at the neuron at the same time. The neuron sums these inputs. Example: if EPSPs collectively depolarize the membrane by +10 mV and IPSPs hyperpolarize it by −6 mV, the net change is +4 mV.
Temporal summation - EPSPs or IPSPs arriving rapidly from the same synapse can add together over time. Rapid EPSPs can push the neuron to threshold, while rapid IPSPs can prevent firing.
Explain how basal nuclei, cerebellum, and corticospinal tracts coordinate to produce smooth voluntary movement.
Basal nuclei - Selects and initiates appropriate movements, inhibits competing movements
Cerebellum - Coordinates timing, force, and trajectory; corrects errors; maintains posture
Corticospinal tracts - Transmits precise motor commands to muscles for execution
Voluntary movement is a coordinated effort: basal nuclei select and initiate, cerebellum refines and corrects, and corticospinal tracts execute. Disruption in any of these systems can cause abnormal, uncoordinated, or involuntary movements.
Compare and contrast the sympathetic and parasympathetic divisions in terms of their functional roles. How might these divisions work together during a stressful situation that ends in relaxation afterward?
Stressful Situation (Fight or Flight)
Sympathetic division dominates:
↑ Heart rate, ↑ blood pressure, ↑ respiration
↓ digestion, ↑ glucose release for energy
Pupils dilate for better vision
Purpose: maximize physical and mental performance to handle the threat.
After Stress Ends (Recovery/Relaxation)
Parasympathetic division dominates:
↓ Heart rate, ↓ blood pressure, normalizes respiration
↑ Digestive activity, energy storage resumes
Pupils constrict, body returns to baseline
Purpose: conserve energy, restore homeostasis, and repair tissues.
These divisions work antagonistically to maintain balance but coordinate temporally: sympathetic activity peaks during stress, parasympathetic activity restores homeostasis afterward.
Dural venous sinuses collect both venous blood and CSF.
Why is this arrangement beneficial to the brain?
The dural venous sinuses collect both venous blood (from the brain’s circulation) and cerebrospinal fluid (CSF) (from the subarachnoid space via the arachnoid villi).
This dual drainage system is highly beneficial for maintaining the brain’s internal environment.
By draining both venous blood (which carries metabolic waste) and CSF (which removes extracellular waste and toxins), the dural sinuses provide a combined clearance pathway, keeping the brain’s environment clean and stable.
Using a shared drainage route (the dural sinuses) streamlines fluid movement within the closed cranial cavity.
This avoids the need for a separate “plumbing system” for CSF, making regulation more efficient and integrated with cerebral blood flow.
The connection between the CSF and venous systems helps maintain osmotic and ionic balance in the brain’s extracellular fluid.
Name two basal nuclei and describe one motor function they regulate.
Basal Nucleus - C-shaped structure adjacent to the lateral ventricles; connects strongly with the prefrontal cortex; Regulates planning and initiation of voluntary, goal-directed movement; helps decide whether to start or stop a motion
Putamen - Lateral portion of the striatum; connected with motor and sensory cortices; Controls execution and coordination of automatic, learned, or repetitive movements (e.g., walking, typing)
Globus Pallidus - Medial to the putamen; has internal (GPi) and external (GPe) segments; Provides inhibitory output to the thalamus to suppress unwanted movements and maintain smooth motor control
Subthalamic Nucleus- Located below the thalamus; Modulates inhibitory and excitatory signals within the basal nuclei; helps prevent involuntary or excessive movement
Substantia Nigra - Releases dopamine to modulate activity in the caudate and putamen, facilitating movement initiation; contributes to movement output control
Nucleus Accumbens - Junction between the caudate and putamen (ventral striatum); Integrates motivation and reward with motor planning, influencing goal-directed and pleasure-driven movement
Contrast long-term potentiation (LTP) and long-term depression (LTD) in terms of structural synaptic changes and functional significance for learning.
LTP - A long-lasting increase in synaptic strength following high-frequency stimulation of a synapse.
- Often triggered by high-frequency stimulation → large postsynaptic Ca²⁺ influx via NMDA receptors.
- Increased number of AMPA receptors in the postsynaptic membrane.
- Enlargement of dendritic spines.
- Enhanced postsynaptic responsiveness.
- Strengthens synaptic connections, facilitating memory formation.
- Supports the encoding of specific experiences.
LTD - A long-lasting decrease in synaptic strength following low-frequency stimulation of a synapse.
- Often triggered by low-frequency stimulation → modest, prolonged Ca²⁺ influx via NMDA receptors.
- Removal of AMPA receptors from the postsynaptic membrane.
- Shrinkage or retraction of dendritic spines.
- Reduced postsynaptic responsiveness.
- Weakens synaptic connections, allowing for synaptic pruning.
- Helps filter irrelevant information, refining neural circuits for learning
Explain the three phases of voluntary movement and identify which cortical or subcortical structures are involved in each phase.
1. Planning Phase (Preparation/Intention)
Description: The brain decides what movement to perform and prepares a motor plan.
Key functions: Selecting target, sequencing movements, estimating force and direction.
Cortical/Subcortical structures involved:
Premotor cortex – plans movement based on external cues
Supplementary motor area (SMA) – plans internally generated movements and sequences
Prefrontal cortex – decision-making and goal-directed planning
Basal ganglia – selects and initiates appropriate motor programs
2. Initiation Phase (Movement Initiation)
Description: The motor plan is converted into a signal that triggers actual movement.
Key functions: Activating motor neurons to execute movement.
Cortical/Subcortical structures involved:
Primary motor cortex (M1) – sends signals via corticospinal tract to skeletal muscles
Basal ganglia – facilitates desired movement and inhibits competing movements (direct and indirect pathways)
Thalamus – relays processed signals from basal ganglia to cortex
Brainstem motor centers – for posture and coordination
3. Execution Phase (Movement Performance & Feedback)
Description: The movement is carried out and adjusted in real time using sensory feedback.
Key functions: Ensuring smooth, coordinated movement; correcting errors.
Cortical/Subcortical structures involved:
Primary motor cortex (M1) – continues sending commands to muscles
Cerebellum – fine-tunes movement, maintains balance and coordination
Basal ganglia – monitors and adjusts movement patterns
Sensory cortex & proprioceptive pathways – provide feedback on position and movement
Name the main neurotransmitters released by the sympathetic and parasympathetic neurons at their effectors. How would drugs that block these neurotransmitters affect organ function?
Sympathetic
Preganglionic neuron - ACh
Postganglionic neuron - NE for most organs, ACh for sweat glands
Target/Effector - Heart, blood vessels, lungs, digestive organs, sweat glands
Parasympathetic
Preganglionic - ACh
Postganglionic - ACh
Target/Effector - Heart, blood vessels, lungs, digestive organs, smooth muscle
Sympathetic postganglionic fibers are mostly adrenergic (NE) except sweat glands, which are cholinergic (ACh).
Parasympathetic fibers are cholinergic (ACh) at both pre- and postganglionic synapses.
Blocking these neurotransmitters disrupts normal autonomic regulation, either reducing organ activity (parasympathetic block) or preventing appropriate stress responses (sympathetic block).
NE (sympathetic) - Beta-blockers, alpha-blockers
↓ Heart rate & contractility, ↓ blood pressure, ↓ bronchodilation, impaired “fight or flight” response
ACh (parasympathetic) - Muscarinic antagonists (e.g., atropine)
↑ Heart rate (blocks vagal slowing), ↓ digestive secretions & motility, ↓ bronchoconstriction, pupil dilation
ACh (sympathetic) - Anticholinergic drugs
↓ Sweating → risk of overheating
Describe the 5 structural features that form the blood-brain barrier.
1. Endothelial Cells of Brain Capillaries - Line the capillaries in the brain and are the primary physical barrier; They are tightly connected by tight junctions, which seal the spaces between adjacent cells and prevent paracellular transport (movement between cells
2. Tight Junctions - Make the barrier highly selective and limit diffusion of hydrophilic or charged molecules
3. Basement Membrane - Thin extracellular matrix layer surrounding the endothelial cells; Composed mainly of collagen, laminin, fibronectin, and proteoglycans; Provides structural support and acts as an additional barrier to large or charged molecules
4. Astrocytes - End-feet induce and maintain BBB properties in endothelial cells by releasing signaling molecules
5. Pericytes - Embedded within the basement membrane and wrapped around endothelial cells; Contribute to capillary stability, regulate blood flow, and influence endothelial cell tight junction formation.
If a patient cannot coordinate emotional responses to sensory input (e.g., doesn’t react emotionally to pain), what diencephalic and cortical connections might be impaired?
This suggests a disconnection between sensory input and the emotional/affective response system.
The thalamus is the main relay center for sensory information. Specific nuclei, like the medial dorsal nucleus, project sensory information to limbic areas rather than just the primary sensory cortex. If these thalamic pathways are damaged, sensory signals may reach the cortex, but the emotional significance of the sensation is lost.
The limbic system (cingulate gyrus, orbitofrontal cortex, and amygdala) interpret sensory stimuli in an emotional context, producing affective responses (e.g., fear, discomfort, withdrawal). Damage to the thalamus–limbic cortex pathway or to the limbic cortex itself prevents appropriate emotional reactions to sensory events.
Painful stimulus → Spinothalamic tract → Thalamus (medial dorsal nucleus)
Thalamus → Limbic cortex (cingulate gyrus, amygdala) → Emotional response (facial expression, autonomic reaction, vocalization)
Impairment of the thalamus or its connections to the limbic cortex can cause loss of emotional responses to sensory stimuli.
Explain why a patient with damage to the tuberoinfundibular pathway may experience hormonal changes, specifically elevated prolactin levels.
The tuberoinfundibular pathway is one of the four major dopaminergic pathways in the brain. It originates in the arcuate nucleus of the hypothalamus, and dopamine released along this pathway travels to the anterior pituitary via the hypophyseal portal system. Dopamine acts as prolactin-inhibiting factor (PIF) in the anterior pituitary. This means dopamine normally suppresses prolactin secretion from lactotroph cells.
So, if the tuberoinfundibular pathway is damaged:
Dopamine release to the anterior pituitary decreases.
Without dopamine inhibition, the lactotrophs in the anterior pituitary secrete prolactin unchecked.
This leads to hyperprolactinemia, which can cause symptoms such as:
Galactorrhea (milk production unrelated to pregnancy or breastfeeding)
Amenorrhea or irregular menstrual cycles in women
Decreased libido and infertility in both sexes
Explain the REM sleep stage, which brain wave predominates, and how the suprachiasmatic nucleus contributes to its regulation.
REM (Rapid Eye Movement) sleep is a stage of sleep characterized by vivid dreaming, rapid eye movements, and muscle atonia (near-complete paralysis of skeletal muscles). It occurs cyclically, usually beginning about 90 minutes after sleep onset and recurring every ~90–120 minutes throughout the night. The predominant EEG pattern resembles beta waves (high-frequency, low-amplitude). REM sleep is characterized by vivid dreaming, muscle atonia, and elevated autonomic activity. The suprachiasmatic nucleus (SCN) in the hypothalamus acts as the master circadian clock, receiving input from retinal light receptors to synchronize sleep-wake cycles, including the timing of REM phases, with external day-night rhythms.
Given that both divisions innervate many of the same organs but produce opposite effects, propose a scenario (e.g., during exercise) where the sympathetic and parasympathetic systems must finely balance each other.
Scenario: Moderate Exercise
Situation: You start jogging or cycling.
Sympathetic Activation (Fight or Flight Response)
Heart rate increases to pump more blood to muscles.
Bronchioles dilate to allow more oxygen into the lungs.
Blood vessels to skeletal muscles dilate, while vessels to the digestive tract constrict.
Energy mobilization: Glycogen breakdown and glucose release from the liver.
Parasympathetic Modulation (Fine-Tuning / Safety Check)
Prevents heart rate from spiking too high at the very start of exercise.
Maintains digestive secretions at low levels to avoid abrupt disruption.
Reduces excessive vasoconstriction in non-essential tissues, helping maintain stable blood pressure.
Balancing Act
Sympathetic system provides rapid, generalized activation for performance.
Parasympathetic system modulates the response, preventing overshoot and maintaining homeostasis.