CH14: The Brain and Cranial Nerves

Question 1

List the major parts of the brain and any key subdivisions.

Answer 1

The adult brain consists of four major parts, the brainstem, cerebellum, diencephalon, and cerebrum.

The brain stem is continuous with the spinal cord and consists of the medulla oblongata, pons and midbrain

Superior to the brainstem is the diencephalon which consists of the thalamus, hypothalamus and epithalamus

Posterior to the brainstem is the cerebellum

Supported on the diencephalon and brainstem is the cerebrum, the largest part of the brain

Question 2

What extensions separate regions of the brain

Answer 2

Three extensions of the dura mater separate parts of the brain

The falx cerebri separates the two hemispheres (sides) of the cerebrum

The falx cerebelli separates the two hemispheres of the cerebellum

The tentorium cerebelli separates the cerebrum from the cerebellum

Question 3

What is the BBB and what substances most easily cross it?

Answer 3

The BBB is a highly selective barrier that consists primarily of tight junctions which seal endothelial cells of brain blood capillaries and thick basement membrane surrounding capillaries. It allows certain molecules to enter easily into the brain tissues and others to not

Molecules that easily diffuse across the lipid bilayer of endothelial cells are lipid-soluble molecules like 02, nicotine, CO2) and water

Some water soluble substances, like glucose are transported in by facilitated transport

Question 4

Describe what ventricles are and name them

Answer 4

Ventricles are cavities within the brain that contain CSF to protect and nourish neurons and neuroglia.

There is a lateral ventricle on each side of the cerebrum.

The third ventricle is a narrow, slit-like cavity along the midline superior to the hypothalamus and between right and left halves of the thalamus.

The fourth ventricle lies between the pons and medulla anteriorly and the cerebellum posteriorly

Question 5

What are the main functions of the CSF

Answer 5

The CSF has three basic functions in maintaining homeostasis
Mechanical protection: Serves as shock absorbing medium that protects the delicate tissues of the brain and spinal cord from jolts that would otherwise cause them to hit the bony walls of the cranial cavity. It also buoys the brain so that it is floating in the cranial cavity

Chemical protection: The CSF provides optimal chemical environment for accurate neuronal signaling. Even slight changes in the ionic composition of CSF within the brain can seriously disrupt production of action potentials and postsynaptic potentials

Circulation: The CSF is a medium for minor exchange of nutrients and waste products between the blood and adjacent nervous tissue

Question 6

What are pyramids in the brainstem?

Answer 6

Two elongated, ridged structures that are part of the medulla oblongata, a region of the brainstem.

The pyramids are located on the anterior (front) surface of the medulla oblongata, and they are part of the corticospinal tracts. These tracts are pathways that carry motor (voluntary movement) information from the cerebral cortex (the outer layer of the brain responsible for higher cognitive functions) to the spinal cord. In other words, the pyramids contain nerve fibers that transmit motor signals from the brain to control muscle movements.

Within the pyramids, motor fibers cross from one side of the brain to the other, a phenomenon known as the “pyramidal decussation.” This means that the left hemisphere of the brain controls motor functions on the right side of the body, and the right hemisphere controls motor functions on the left side of the body

Question 7

What is the olive of the brain stem?

Answer 7

Olives are two oval shaped swelling structures that are just lateral to each pyramid. They contain the inferior olivary nucleus, which receives inputs from the midbrain, cerebral cortex and spinal cord.

Question 8

What is the pons? What are its functions?

Answer 8

The pons is another structure of the brainstem that connects parts of the brain with one another. The pons functions in relaying nerve impulses related to voluntary skeletal muscle movements from cerebrum to cerebellum

Question 9

Name the key structures of the midbrain

Answer 9

The superior colliculi are reflex centers for visual activities through neural circuits from the eye muscles and also govern movements of the head, eyes and trunk in response to visual stimuli

The inferior colliculi are part of the auditory pathway and relay impulses from the hearing receptor in the inner ear to the brain, and are responsible for the reflex to loud noises

The cerebral peduncles conduct nerve impulses from motor areas in the cerebral cortex to the spinal cord, medulla and pons.

Question 10

Describe the cerebellum and its functions

Answer 10

The cerebellum is a highly folded region that is posterior to the brainstem and inferior to the cerebrum. It is separated from the cerebrum by the transverse cerebral fissure and the tentorium cerebelli. It consists of two hemispheres called the cerebellar hemispheres which is joined by the vermis,.

It functions to asses motion caused by the cerebrum and to smooth and coordinate complex movements and skeletal contractions, as well as regulating posture and balance.

Question 11

Describe the components and location of the diencephalon.

Answer 11

The diencephalon forms a central core of brain tissue just superior to the midbrain. It is almost completely surrounded by cerebral hemispheres and contains numerous nuclei involved in a wide variety of sensory and motor processing between higher and lower brain centers. The diencephalon extends from the brainstem to the cerebrum and surrounds the third ventricle.
The diencephalon consists of three main parts, the thalamus, hypothalamus and epithalamus. Projecting from the thalamus is the hypophysis, or pituitary gland

Question 12

Describe the diencephalon and its components.

Answer 12

The diencephalon forms a central core of brain tissue just superior to the midbrain, and is mainly surrounded by cerebral hemispheres. It consists of the thalamus, hypothalamus and epithalamus

The thalamus is the largest region of the diencephalon and is superior to the midbrain.
- The thalamus is the principal relay station for sensory impulses (except smell) that reach the cerebral cortex from other parts of the brain and the spinal cord. The thalamus also relays nerve impulses between different areas of the cerebrum and plays a role in the maintenance of consciousness.

The hypothalamus is a large caretaker of homeostasis, and contains a vast array of functions:

   - Controls and integrates activities of autonomic nervous system.
   - Produces hormones, including releasing hormones, inhibiting hormones, oxytocin, and antidiuretic hormone
   - Regulates emotional and behavioral patterns (together with limbic system).
  - Contains feeding and satiety centers (regulate eating), thirst center (regulates drinking), and suprachiasmatic nucleus (SCN) (regulates circadian rhythms).
     - Controls body temperature by serving as body’s thermostat.
    - Circadian rhythms (sleep clock)

The epithalamus consists of the pineal gland and habenular nuclei.

   - The pineal gland's main function is to produce melatonin which regulates the body's circadian rhythm
    - The habenular nuclei is involved in olfaction, and emotional repsonses to olfaction

Question 13

What separates the right and left hemisphere and what connects them?

Answer 13

The longitudinal cerebral fissure separates them and the corpus callosum connects them

Question 14

What are cerebral gryi, and name the types of gyri

Answer 14

Cerebral gyri (singular: gyrus) are the prominent, raised folds or convolutions on the surface of the cerebral cortex of the brain.

Cerebral sulci: Grooves that separate neighboring cerebral gyri

Interlobar sulci: Grooves that separate various lobes of the cerebrum

Cerebral fissures: Grooves that separate part of the brain

Question 15

Name the lobes of the cerebrum

Answer 15

The lobes are named after the bones that cover them: frontal, parietal, temporal and occipital lobes
A fifth part of the cerebrum, the insula, cannot be see at the surface of the brain because it lies deep to the parietal, frontal and temporal lobes

Question 16

List the 3 white matter tracts and their functinos

Answer 16

Association tracts: Contain axons that conduct nerve impulses between cerebral gyri in the same hemisphere

Commissural tracts: Contains axons that conduct nerve impulses from cerebral gyri in one cerebral hemisphere to corresponding cerebral gyri in the other cerebral hemisphere.

Projection tracts: Contains axons that conduct nerve impulse from cerebrum to lower parts of CNS (thalamus, brainstem and spinal cord)

Question 17

What are basal nuclei and what do the do?

Answer 17

Deep within each cerebral hemisphere are nuclei (masses of gray matter) that are collectively termed the corpus striatum or basal nuclei.

A major function of the corpus striatum is to help regulate initiation and termination of movements
The corpus striatum also control subconscious contractions of skeletal muscles. Examples include automatic arm swings while walking and true laughter in response to a joke (not the kind you consciously initiate to humor your anatomy and physiology instructor).

Question 18

What are the sensory areas of the brain?

Answer 18

Sensory areas of the brain integrate sensory experiences to generate meaningful patterns of recognition and awareness

The primary somatosensory cortex receives nerve impulses for touch, pressure, vibration, itch, tickle, temperature (coldness and warmth), pain, and proprioception (joint and muscle position) and is involved in the perception of these somatic sensations. A “map” of the entire body is present in the primary somatosensory cortex: each point within the area receives nerve impulse, and the size of the area receiving nerve impulses depends on the number of receptors present there rather than the size of the body part
This distorted somatic sensory map of the body is known as the sensory homunculus. The primary somatosensory cortex allows you to pinpoint where somatic sensations originate, so that you know exactly where on your body to swat that mosquito

Primary visual cortex: The primary visual cortex is responsible for receiving visual information and is involved in visual perception

Primary auditory cortex: The primary auditory cortex receives information for sound and is involved in auditory perception

Gustatory cortex: Receives impulses for taste and is involved in gustatory perception and taste discrimination

Olfactory cortex: Receives impulses for smell and is involved in olfactory perception

Question 19

Name and describe the motor areas of the brain

Answer 19

Motor output from the cerebral cortex flows mainly from the anterior part of each hemisphere. Among the most important motor areas are the following:

Primary motor cortex:The primary motor cortex is similar to the primary somatosensory cortex, in that it contains a “map” of the entire body, with each region within the area controlling voluntary contraction of specific muscles. This distorted muscle map of the body is called the motor homunculus
Electrical stimulation of any point on the primary motor cortex causes contraction of specific muscle fibers on the opposite side of the body.
Different muscles are represented unequally in the primary motor cortex. More cortical area is devoted to those muscles involved in skilled, complex, or delicate movement. For instance, the cortical region devoted to muscles that move the fingers is much larger than the region for muscles that move the toes

Premotor cortex: Located just anterior to the primary motor cortex, the premotor cortex sends impulses to the primary motor cortex that plan movements that cause specific groups of muscles to contract simultaneously or sequentially.
Such activities include typing, writing your name and playing a muscle instrument. The premotor cortex also serves as a memory bank for such coordinated movements
Broca’s area: From Broca’s area, nerve impulses pass to the premotor regions that control the muscles of the larynx, pharynx and mouth. The impulses from the premotor cortex result in specific, coordinated muscle contractions
Simultaneously, impulses propagate from Broca’s area to the primary motor cortex. From here, impulses also control the breathing muscles to regulate the proper flow of air past the vocal cords. The coordinated contractions of your speech and breathing muscles enable you to speak your thoughts
Frontal eye field: Located partially in and anterior to the premotor cortex and superior to Broca’s area, the frontal eye field controls voluntary scanning movements of the eyes, for example, those that you are now using to read this sentence :D

Question 20

Describe and name the association areas

Answer 20

Somatosensory association area: The somatosensory association area is just posterior and receives input from the primary somatosensory cortex and other part of the brain. This part of the brain allows you to determine the exact shape and texture of an object by feeling it, to determine the orientation of one object with another as they are felt, and to sense the relationship of one body part to another.
Another role of the somatosensory association area is the storage of memories of past somatic sensory experiences, enabling you to compare current sensations with previous experiences. For example, the somatosensory association area allows you to recognize objects such as a pencil and a paperclip simply by touching them

Visual association area: The visual association area receives sensory impulses from the primary visual cortex, and the thalamus. It relates past and present visual experiences and is essential for recognizing and evaluating what is seen. For example, the visual association area allows you to recognize an object such as a spoon simply by looking at it

Auditory association area: The auditory association area allows you to recognize a particular sound as speech, music, or noise

Orbitofrontal cortex: The orbitofrontal cortex receives sensory impulses from the olfactory cortex, allowing you to identify odors and discriminate among different odors

Wernicke’s area (VER-ni-kēz): Interprets the meaning of speech by recognizing spoken words. It is active as you translate words into thoughts.
The regions in the right hemisphere that
correspond to Broca’s and Wernicke’s areas in the left hemisphere also contribute to verbal communication by adding emotional content, such as anger or joy, to spoken words.

Common integrative area: The common integrative area receives impulses from several association areas and integrates them, allowing the formation of thoughts based on a variety of sensory inputs. It then transmits signals to other parts of the brain for the appropriate response to the sensory signals it has interpreted.

Prefrontal cortex: A developed portion of the brain in primates, especially humans, The prefrontal cortex is concerned with the makeup of a person’s personality, intellect, complex learning abilities, recall of information, initiative, judgment, foresight, reasoning, conscience, intuition, mood, planning for the future, and development of abstract ideas.
The prefrontal cortex is concerned with the makeup of a person’s personality, intellect, complex learning abilities, recall of information, initiative, judgment, foresight, reasoning, conscience, intuition, mood, planning for the future, and development of abstract ideas

Question 21

Describe the functions of the left and right side of our brains

Answer 21

Right side: The right side of the brain receives somatic sensory signals from and controls muscles on the left side of the brain. It is responsible for musical and artistic awareness, space and pattern perception, recognizing faces and understanding facial expressions, generating emotional content of language, generating mental images to compare spatial relationships, and identifying and discriminating among odors
Damage to the right side of the brain that corresponds to Broca’s and Wenicke’s areas in the left hemisphere speak in a monotonous voice, having lost the ability to impart emotional inflection to what they say

Left side: Receives somatic sensory signals from and controls muscles on the right side of the body. Functions for reasoning, numerical and scientific skills, ability to use and understand sign language, and ability to understand and use spoken and written language

Question 22

Name the 4 types of brain waves

Answer 22

Alpha waves: Alpha waves occur when people are awake and resting with their eyes closed, and disappear when they sleep
Beta waves: Appear when the nervous system is active during periods of sensory input and mental activity
Θ waves: Occurs when children and adults experience emotional stress
Delta waves: Occur during deep sleep in adults and in awake infants. Indicate brain damage if present in awake adults :(