Chapter 14: The Brain and Cranial Nerves Flashcards
What is the role of the brain in homeostasis?
The brain contributes to homeostasis by receiving sensory input, integrating information, making decisions, and executing responses through motor activities.
How many neurons and neuroglia make up the brain?
The brain contains about 90 billion neurons and about 100 billion neuroglia.
What are the major parts of the brain?
The major parts of the brain are the brainstem, cerebellum, diencephalon, and cerebrum.
How is the brain protected?
The brain is protected by cranial bones, cranial meninges, and the blood-brain barrier.
What are the cranial meninges, and how are they different from spinal meninges?
The cranial meninges consist of the dura mater, arachnoid, and pia mater. The difference from spinal meninges is that the cranial dura mater has two layers, while the spinal dura mater has only one.
What are the extensions of the dura mater in the brain?
The three extensions of the dura mater are: (1) the falx cerebri, (2) the falx cerebelli, and (3) the tentorium cerebelli.
What is the role of the falx cerebri?
The falx cerebri separates the two hemispheres of the cerebrum.
How is blood supplied to the brain?
Blood is supplied to the brain primarily by the internal carotid and vertebral arteries.
How much of the body’s oxygen and glucose does the brain consume?
The brain consumes about 20% of the oxygen and glucose used by the body, even during rest.
What is the blood-brain barrier (BBB)?
The BBB consists of tight junctions between endothelial cells of brain blood capillaries and a thick basement membrane. It regulates what substances pass from blood into brain tissue.
What substances can cross the blood-brain barrier easily?
Lipid-soluble substances (e.g., O2, CO2, steroid hormones, alcohol, nicotine, caffeine) and water molecules easily cross the BBB.
How do glucose and ions cross the blood-brain barrier?
Glucose crosses the BBB via facilitated transport, while ions cross very slowly.
What happens when blood flow to the brain is interrupted?
Even brief interruptions in blood flow (1-2 minutes) can impair brain function, and total oxygen deprivation for about 4 minutes can cause permanent injury.
Why is it important for people with diabetes to monitor their blood sugar?
Low blood sugar can cause mental confusion, dizziness, convulsions, loss of consciousness, and diabetic shock, which could lead to seizure, coma, or death.
What can cause a breakdown in the blood-brain barrier?
Trauma, certain toxins, and inflammation can cause the blood-brain barrier to break down.
What are the primary functions of the brainstem, cerebellum, and diencephalon?
The brainstem regulates basic life functions such as breathing and heart rate; the cerebellum coordinates movement; the diencephalon (thalamus, hypothalamus, epithalamus) regulates sensory and motor signals, and autonomic functions like temperature control.
What is CSF?
CSF (Cerebrospinal Fluid) is a clear, colorless liquid composed primarily of water that protects the brain and spinal cord from chemical and physical injuries.
What does CSF carry to neurons and neuroglia?
CSF carries small amounts of oxygen, glucose, and other necessary chemicals from the blood to neurons and neuroglia.
Where does CSF circulate?
CSF circulates through cavities in the brain and spinal cord, and around the brain and spinal cord in the subarachnoid space.
What is the normal volume of CSF in an adult?
The total volume of CSF is 80 to 150 mL (3 to 5 oz) in an adult.
What are the main components of CSF?
CSF contains small amounts of glucose, proteins, lactic acid, urea, cations (Na+, K+, Ca2+, Mg2+), anions (Cl− and HCO3−), and some white blood cells.
What are the ventricles in the brain?
The ventricles are four CSF-filled cavities in the brain: two lateral ventricles, a third ventricle, and a fourth ventricle.
What separates the two lateral ventricles?
The two lateral ventricles are separated by a thin membrane called the septum pellucidum.
Where is the third ventricle located?
The third ventricle is a narrow, slit-like cavity along the midline, superior to the hypothalamus, and between the right and left halves of the thalamus.
Where is the fourth ventricle located?
The fourth ventricle lies between the pons and medulla anteriorly and the cerebellum posteriorly.
What are the three basic functions of CSF?
- Mechanical protection, 2. Chemical protection, 3. Circulation.
What is the mechanical protection function of CSF?
CSF serves as a shock-absorbing medium that protects the brain and spinal cord from jolts, and also buoy the brain in the cranial cavity.
What is the chemical protection function of CSF?
CSF provides an optimal chemical environment for accurate neuronal signaling, ensuring proper ionic composition for action potentials and postsynaptic potentials.
How does CSF function in circulation?
CSF serves as a medium for minor exchange of nutrients and waste products between the blood and adjacent nervous tissue.
Where is most CSF produced?
Most CSF is produced in the choroid plexuses, which are networks of blood capillaries in the walls of the ventricles.
How is CSF formed?
Ependymal cells cover the capillaries of the choroid plexuses and secrete selected substances from blood plasma to form CSF.
What is the blood-CSF barrier?
The blood-CSF barrier is formed by tight junctions of ependymal cells, preventing harmful blood-borne substances from entering the CSF.
How does CSF circulate through the ventricles?
CSF flows from the lateral ventricles into the third ventricle via the interventricular foramina, then through the aqueduct of the midbrain to the fourth ventricle.
How does CSF leave the fourth ventricle?
CSF enters the subarachnoid space through three openings in the roof of the fourth ventricle: a median aperture and two lateral apertures.
Where does CSF circulate after leaving the fourth ventricle?
After leaving the fourth ventricle, CSF circulates in the central canal of the spinal cord and the subarachnoid space around the brain and spinal cord.
How is CSF reabsorbed into the blood?
CSF is reabsorbed into the blood through arachnoid granulations (villi), finger-like extensions that project into the dural venous sinuses.
What is the rate of CSF formation and reabsorption?
CSF is formed and reabsorbed at the same rate, approximately 20 mL/hr or 480 mL/day, keeping the pressure and volume constant.
What is the brainstem and what are its three main structures?
The brainstem is the part of the brain between the spinal cord and the diencephalon. Its three main structures are: 1. Medulla oblongata, 2. Pons, and 3. Midbrain.
Where does the medulla oblongata begin and end?
The medulla oblongata begins at the foramen magnum and extends to the inferior border of the pons, about 3 cm long.
What are the pyramids in the medulla and what is their function?
The pyramids are bulges on the anterior aspect of the medulla, formed by the corticospinal tracts. They control voluntary movements of the limbs and trunk.
What is the decussation of pyramids?
The decussation of pyramids is the crossing of 90% of the axons in the pyramids from one side of the medulla to the other, explaining why each side of the brain controls movements on the opposite side of the body.
What vital body functions are regulated by nuclei in the medulla?
Nuclei in the medulla regulate functions such as heartbeat, blood vessel diameter, and breathing rhythm.
What reflexes are controlled by the medulla?
The medulla controls reflexes like vomiting, swallowing, sneezing, coughing, and hiccupping.
What is the role of the inferior olivary nucleus in the medulla?
The inferior olivary nucleus regulates cerebellar neuron activity and helps make adjustments to muscle activity when learning new motor skills.
What sensory pathways are associated with nuclei in the medulla?
The medulla contains nuclei involved in sensory pathways for touch, pressure, vibration, proprioception, gustation (taste), audition (hearing), and equilibrium (balance).
Which cranial nerves have nuclei located in the medulla?
Cranial nerves with nuclei in the medulla include: 1. Vestibulocochlear (VIII), 2. Glossopharyngeal (IX), 3. Vagus (X), 4. Accessory (XI, cranial portion), and 5. Hypoglossal (XII).
What is the primary function of the pons?
The pons connects parts of the brain through bundles of axons and plays a role in sensory and motor pathways.
What are the two major structural components of the pons?
The two major components of the pons are the ventral region (synaptic relay station with pontine nuclei) and the dorsal region (ascending and descending tracts, cranial nerve nuclei).
What is the pontine respiratory group?
The pontine respiratory group, located in the pons, helps control breathing in coordination with the medullary respiratory center.
Which cranial nerves have nuclei located in the pons?
Cranial nerves with nuclei in the pons include: 1. Trigeminal (V), 2. Abducens (VI), 3. Facial (VII), and 4. Vestibulocochlear (VIII).
What is the role of the midbrain in the brainstem?
The midbrain connects the pons to the diencephalon and contains nuclei and tracts involved in motor control, visual and auditory reflexes, and muscle activity.
What are the cerebral peduncles?
The cerebral peduncles are paired bundles of axons in the midbrain that transmit nerve impulses from the motor areas of the cerebral cortex to the spinal cord, medulla, and pons.
What are the superior colliculi in the midbrain?
The superior colliculi are reflex centers for visual activities, controlling eye movements in response to visual stimuli.
What are the inferior colliculi in the midbrain?
The inferior colliculi relay auditory information from the inner ear and serve as reflex centers for the startle reflex in response to loud noises.
What is the substantia nigra and its role?
The substantia nigra is a darkly pigmented area in the midbrain where neurons release dopamine to help control subconscious muscle activities. Loss of these neurons is associated with Parkinson’s disease.
What are the red nuclei in the midbrain?
The red nuclei are involved in motor coordination and have a rich blood supply, giving them a reddish color.
What is the reticular formation?
The reticular formation is a broad region in the brainstem where white matter and gray matter are interspersed. It extends from the superior part of the spinal cord, through the brainstem, and into the inferior part of the diencephalon.
What functions do neurons in the reticular formation serve?
Neurons in the reticular formation serve both ascending (sensory) and descending (motor) functions.
What is the reticular activating system (RAS)?
The RAS is the ascending portion of the reticular formation. It consists of sensory axons that project to the cerebral cortex, directly or through the thalamus, and plays a key role in consciousness, wakefulness, and attention.
What are some sensory stimuli that activate the RAS?
Visual and auditory stimuli, mental activities, pain, touch, pressure, and receptors in the limbs and head that monitor body position can activate the RAS.
What is the role of the RAS in consciousness?
The RAS helps maintain consciousness, which is a state of wakefulness where an individual is alert, aware, and oriented. It is also active during arousal or awakening from sleep.
How does the RAS help with attention?
The RAS maintains attention by focusing on a single object or thought, preventing sensory overload by filtering out insignificant stimuli.
What happens when the RAS is inactivated?
Inactivation of the RAS results in sleep, a state of partial consciousness from which an individual can be aroused.
What occurs if the RAS is damaged?
Damage to the RAS results in coma, a state of unconsciousness where an individual cannot be aroused. In the deepest states of coma, even brainstem and spinal reflexes are lost, and if vital functions are impaired, the patient may die.
How do melatonin and general anesthetics affect the RAS?
Melatonin helps induce sleep by affecting the RAS, while general anesthetics turn off consciousness via the RAS.
What is the role of the descending portion of the RAS?
The descending portion of the RAS helps regulate muscle tone, heart rate, blood pressure, and respiratory rate by connecting to the cerebellum and spinal cord.
Why is there no input from smell receptors in the RAS?
The RAS does not receive input from receptors for the sense of smell, meaning strong odors, such as those from smoke, may not awaken someone from sleep.
What is the function of the medulla oblongata?
The medulla oblongata regulates heartbeat, blood vessel diameter, and breathing. It contains nuclei involved in sensory and motor functions, and coordinates activities like vomiting and swallowing. It also contains nuclei for several cranial nerves.
What is the function of the pons?
The pons contains sensory and motor tracts, relays impulses from the cerebral cortex to the cerebellum, helps control breathing, and contains nuclei for several cranial nerves.
What is the function of the midbrain?
The midbrain coordinates movements in response to visual and auditory stimuli and contributes to movement control through structures like the substantia nigra and red nucleus. It also contains nuclei for cranial nerves.
What role does the cerebellum play?
The cerebellum smooths and coordinates skeletal muscle contractions, regulates posture and balance, and may assist in cognition and language processing.
What does the thalamus do?
The thalamus relays almost all sensory input to the cerebral cortex and contributes to motor functions by transmitting information from the cerebellum and corpus striatum. It also plays a role in maintaining consciousness.
What are the functions of the hypothalamus?
The hypothalamus controls autonomic functions, produces hormones, regulates emotional and behavioral patterns, and controls body temperature, eating, drinking, and circadian rhythms.
What is the function of the epithalamus?
The epithalamus consists of the pineal gland (which secretes melatonin) and the habenular nuclei (involved in olfaction).
What functions are associated with the cerebral cortex?
Sensory areas of the cortex are involved in perception of sensory information, motor areas control voluntary movements, and association areas handle more complex functions such as memory, personality traits, and intelligence.
What is the role of the corpus striatum?
The corpus striatum helps initiate and terminate movements, suppresses unwanted movements, and regulates muscle tone.
What is the function of the limbic system?
The limbic system regulates emotions, including pleasure, pain, fear, affection, and anger.
What is the size of the cerebellum compared to the cerebrum?
The cerebellum is second in size only to the cerebrum.
Where is the cerebellum located in the brain?
The cerebellum is located inferior to the posterior portion of the cerebrum and posterior to the medulla and pons.
How does the surface of the cerebellum differ from that of the cerebrum?
Like the cerebrum, the cerebellum has a highly folded surface that increases the surface area of its outer gray matter cortex.
What percentage of the brain mass does the cerebellum account for?
The cerebellum accounts for about a tenth of the brain mass.
How much of the brain’s neurons are in the cerebellum?
The cerebellum contains nearly half of the neurons in the brain.
What separates the cerebellum from the cerebrum?
The cerebellum is separated from the cerebrum by the transverse cerebral fissure and the tentorium cerebelli.
What is the shape of the cerebellum when viewed superiorly or inferiorly?
The cerebellum resembles a butterfly with a central constricted area (vermis) and lateral “wings” (cerebellar hemispheres).
What are the functions of the anterior and posterior lobes of the cerebellum?
The anterior and posterior lobes govern subconscious aspects of skeletal muscle movements.
What is the function of the flocculonodular lobe?
The flocculonodular lobe contributes to equilibrium and balance.
What is the cerebellar cortex made of?
The cerebellar cortex is made of gray matter arranged in slender, parallel ridges called folia.
What is the name of the white matter in the cerebellum, and what does it resemble?
The white matter in the cerebellum is called the arbor vitae, and it resembles branches of a tree.
What are the cerebellar nuclei, and where are they located?
The cerebellar nuclei are regions of gray matter located deep within the white matter of the cerebellum.
What are cerebellar peduncles?
The cerebellar peduncles are three paired bundles of white matter that attach the cerebellum to the brainstem and facilitate communication between the cerebellum and other parts of the brain.
What are the functions of the superior cerebellar peduncles?
The superior cerebellar peduncles contain axons that extend from the cerebellum to the red nuclei of the midbrain and nuclei of the thalamus.
What is the function of the middle cerebellar peduncles?
The middle cerebellar peduncles carry impulses for voluntary movements from the pontine nuclei to the cerebellum.
What are the functions of the inferior cerebellar peduncles?
The inferior cerebellar peduncles carry sensory information from proprioceptors in the trunk, limbs, and head, as well as axons from the inferior olivary nucleus, and extend to the vestibular nuclei and reticular formation.
What is the primary function of the cerebellum?
The primary function of the cerebellum is to evaluate and coordinate the execution of movements initiated by the cerebral motor areas, ensuring smooth and accurate movements.
How does the cerebellum correct movement discrepancies?
When the cerebellum detects discrepancies in movement, it sends feedback signals to the motor areas of the cerebral cortex via the thalamus to correct the errors.
In addition to movement coordination, what other functions does the cerebellum regulate?
The cerebellum regulates posture and balance.
What kinds of activities depend on the cerebellum’s motor coordination?
Skilled muscular activities such as catching a baseball, dancing, and speaking rely on cerebellar coordination.
What nonmotor functions may the cerebellum be involved in?
The cerebellum may be involved in cognition, language processing, learning, and responding to anticipated rewards.
What imaging studies suggest additional functions of the cerebellum?
MRI and PET imaging studies suggest the cerebellum may play a role in processing sensory information.
What is the diencephalon and where is it located?
The diencephalon is a central core of brain tissue located just superior to the midbrain. It is surrounded by the cerebral hemispheres and contains nuclei involved in sensory and motor processing. It extends from the brainstem to the cerebrum and surrounds the third ventricle.
What are the main structures that make up the diencephalon?
The diencephalon includes the thalamus, hypothalamus, and epithalamus. The hypothalamus projects to the hypophysis (pituitary gland).
What are circumventricular organs in the diencephalon?
Circumventricular organs are parts of the diencephalon in the wall of the third ventricle, involved in monitoring and regulation of body processes.
Where do the optic tracts carrying neurons from the retina enter the diencephalon?
The optic tracts enter the diencephalon.
What percentage of the diencephalon is made up of the thalamus?
The thalamus makes up about 80% of the diencephalon.
What is the interthalamic adhesion and where is it located?
The interthalamic adhesion, or intermediate mass, is a bridge of gray matter that joins the right and left halves of the thalamus in about 70% of human brains.
What is the internal medullary lamina in the thalamus?
The internal medullary lamina is a Y-shaped sheet of white matter that divides the gray matter of the thalamus into right and left sides and contains myelinated axons.
What is the function of the thalamus?
The thalamus is the major relay station for sensory impulses reaching the cerebral cortex from other parts of the brain and spinal cord, and it also plays a role in motor functions and consciousness.
What are the seven major groups of nuclei in the thalamus?
The seven major groups are: anterior, medial, lateral, ventral, intralaminar, periventricular, and reticular.
What does the anterior nucleus of the thalamus do?
The anterior nucleus receives input from the hypothalamus and sends output to the limbic system, contributing to emotions and memory.
What is the function of the lateral group nuclei in the thalamus?
The lateral group nuclei integrate sensory information and function in emotions and memory. The lateral dorsal nucleus is involved in emotions, and the lateral posterior and pulvinar nuclei help integrate sensory data.
What is the role of the ventral anterior nucleus in the thalamus?
The ventral anterior nucleus receives input from the basal nuclei and sends output to the motor cortex, playing a role in movement control.
What is the function of the ventral posterior nucleus in the thalamus?
The ventral posterior nucleus relays sensory impulses related to touch, pressure, vibration, temperature, pain, and proprioception from the face and body to the cerebral cortex.
What is the role of the lateral geniculate nucleus?
The lateral geniculate nucleus relays visual impulses for sight from the retina to the primary visual cortex of the cerebrum.
What does the medial geniculate nucleus relay?
The medial geniculate nucleus relays auditory impulses for hearing from the ear to the primary auditory cortex of the cerebrum.
What are intralaminar nuclei responsible for?
Intralaminar nuclei are involved in arousal, sensory and motor integration, and connections with the reticular formation, cerebellum, and cerebral cortex.
What is the presumed function of the periventricular nucleus?
The periventricular nucleus is involved in memory and olfaction.
What does the reticular nucleus of the prethalamus do?
The reticular nucleus monitors, filters, and integrates activities of other thalamic nuclei.
What is the hypothalamus and where is it located?
The hypothalamus is a small part of the diencephalon located inferior to the thalamus.
How many major regions is the hypothalamus composed of, and what are they?
The hypothalamus is composed of four major regions: posterior (mammillary) area, intermediate (tuberal) area, anterior (supraoptic) area, and preoptic area.
What is the function of the posterior hypothalamic area?
The posterior hypothalamic area, including the mammillary bodies, serves as relay stations for reflexes related to the sense of smell.
What does the intermediate hypothalamic area contain?
The intermediate hypothalamic area contains the dorsomedial nucleus, ventromedial nucleus, arcuate nucleus, and the infundibular stalk that connects the pituitary gland to the hypothalamus.
What is the function of the anterior hypothalamic area?
The anterior hypothalamic area regulates autonomic functions and contains nuclei involved in producing hormones like oxytocin and antidiuretic hormone.
What are the primary functions of the hypothalamus?
The hypothalamus controls the autonomic nervous system, produces hormones, regulates emotional and behavioral patterns, controls eating and drinking, maintains body temperature, and regulates circadian rhythms.
What is the role of the hypothalamus in controlling the autonomic nervous system (ANS)?
The hypothalamus regulates the contraction of smooth and cardiac muscles, as well as the secretions of many glands, controlling vital functions like heart rate and digestion through the ANS.
How does the hypothalamus regulate body temperature?
The hypothalamus acts as a thermostat, regulating body temperature by stimulating activities that promote heat loss or heat production and retention depending on blood temperature.
What is the function of the suprachiasmatic nucleus (SCN)?
The SCN regulates circadian rhythms, helping synchronize biological activities (like the sleep-wake cycle) with the light-dark cycle, and it acts as the body’s internal biological clock.
How does the SCN influence circadian rhythms?
The SCN receives light-dark cues from the eyes and sends output to other hypothalamic nuclei, reticular formation, and pineal gland, synchronizing biological rhythms with the 24-hour day-night cycle.
What causes the internal clock in SCN neurons to operate in a 24-hour cycle?
The rhythmic turning on and off of clock genes in the SCN neurons creates alternating levels of clock proteins, leading to a 24-hour cycle of biological activity.
What is the epithalamus and where is it located?
The epithalamus is a small region located superior and posterior to the thalamus. It consists of the pineal gland and habenular nuclei.
What is the role of the pineal gland?
The pineal gland secretes the hormone melatonin, which helps regulate circadian rhythms. It responds to visual input from the eyes via the suprachiasmatic nucleus (SCN) of the hypothalamus, which stimulates melatonin secretion.
How does the pineal gland regulate circadian rhythms?
In response to visual input from the retina, the SCN stimulates the pineal gland through neural connections with sympathetic neurons. This causes the pineal gland to secrete melatonin in a rhythmic pattern, with low levels during the day and higher levels at night. These changing melatonin levels affect sleep, wakefulness, hormone secretion, and body temperature.
What other functions does melatonin serve beyond regulating circadian rhythms?
Melatonin induces sleep, serves as an antioxidant, and inhibits reproductive functions in certain animals. It promotes sleepiness due to its higher secretion during darkness and is used to help the body adjust to jet lag when taken orally.
What are the habenular nuclei and what is their role?
The habenular nuclei are involved in olfaction, specifically in emotional responses to odors. For example, they help us react emotionally to the scent of a loved one’s cologne or the smell of cookies baking.
What are circumventricular organs (CVOs)?
Circumventricular organs are parts of the diencephalon around the third ventricle that lack a blood-brain barrier, allowing them to monitor chemical changes in the blood. These organs include parts of the hypothalamus, pineal gland, and pituitary gland.
What are the functions of circumventricular organs (CVOs)?
CVOs coordinate homeostatic activities of the endocrine and nervous systems, such as regulating blood pressure, fluid balance, hunger, and thirst. They also play a role in the brain’s entry points for certain viruses, like HIV, which can cause neurological disorders.
Why are circumventricular organs (CVOs) important for the immune system?
Since CVOs lack a blood-brain barrier, they are thought to be sites of entry for HIV, the virus that causes AIDS, and may contribute to the development of conditions like dementia and other neurological disorders once the virus enters the brain.
What is the cerebrum often referred to as?
The “seat of intelligence.”
What functions does the cerebrum provide?
The cerebrum allows us to read, write, speak, make calculations, compose music, remember the past, plan for the future, and imagine things.
What are the components of the cerebrum?
The cerebrum consists of the cerebral cortex, cerebral white matter, and deep gray matter nuclei.
What is the cerebral cortex and where is it located?
The cerebral cortex is a region of gray matter that forms the outer rim of the cerebrum.
How thick is the cerebral cortex?
The cerebral cortex is 2-4 mm thick.
What happens to the cerebral cortex during brain development?
The cortex enlarges faster than the white matter, causing it to fold and form gyri (folds) and sulci (grooves).
What is the deepest groove in the cerebral cortex called?
The deepest grooves are called fissures.
What is the longitudinal fissure?
The longitudinal fissure is the most prominent fissure that separates the cerebrum into right and left hemispheres.
What connects the two cerebral hemispheres?
The corpus callosum, a broad band of white matter containing axons, connects the two hemispheres.
What are the lobes of the cerebrum?
The cerebrum has frontal, parietal, temporal, and occipital lobes.
What separates the frontal and parietal lobes?
The central sulcus separates the frontal and parietal lobes.
Where is the primary motor cortex located?
The primary motor cortex is located in the precentral gyrus, just anterior to the central sulcus.
Where is the primary somatosensory cortex located?
The primary somatosensory cortex is located in the postcentral gyrus, just posterior to the central sulcus.
