Chapter 14 The Brain and Cranial Nerves

List the 3 major parts of the brain and describe their locations:

Cerebrum: 83% of the brain's volume and consists of a pair of half globes called the CEREBRAL HEMISPHERES. Each hemisphere is marked by thick folds called GYRI separated by shallow grooves called SULCI. A very deep median groove is the LONGITUDINAL FISSURE, separates the right and the left hemp. from each other. at the bottom of this fissure, the hemp is connected by a thick bundle of nerve fibers called the CORPUS CALLOSUM. Cerebellum: occupies the posterior cranial fossa inferior to the cerebrum, departed by its transverse cerebral fissure. It is also marked by fissures, sulk, gyro. The cerebellum is the second-largest region of the brain constituting about 10% of its volume but containing over 50% of its neurons. Brainstem: Defined by differently various authorities. All of the brain except for the cerebrum and cerebellum. It's major components, from rostural to caudal, are the diencephalon, midbrain, pons, and medulla oblongata. Many authorities however exclude the diencephalon since it can be classified with the cerebrum as part of the forebrain.

What are the major components of the BRAIN STEM?

Diencephalon Midbrain Pons Medulla oblongata

Hindbrain- Medulla Oblongata Centers: Name them and what they do.

- Cardiac Center: Adjusts rate and force of heart - Vasometer Center: Adjusts blood vessel diameter - Respiratory Centers: Control rate and depth of breathing - Reflex Centers: For coughing, sneezing, gagging, swallowing, vomiting salivation, sweating, movements of tongue and head.

Explain the arachnoid mater meninge.

-Transparent membrane over brain surface. -SUBARACHNOID SPACE separates it from pia mater below. -SUBDURAL SPACE separates it from dura mater above in some places.

Explain the pia mater meninge.

-Very thin membrane that follows contours of brain, even dipping into sulci. -Not usually visible without a microscope.

PONS: what type of tracts does the PONS have? What are the cranial nerves in the PONS? What are the roles of sensory and motor? What does the RETICULAR FORMATION in the PONS contain? What is the RETICULAR FORMATION concerned with?

Ascending sensory tracts, descending motor tracts and pathways in and out of cerebellum. Cranial nerves V, Vi, VII, and VIII SENSORY ROLES include hearing, equilibrium, taste, and facial sensations. MOTOR ROLES include eye movement, facial expressions, chewing, swallowing, urination, and secretion of saliva and tears. The reticular formation in pons contains additional nuclei concerned with: sleep respiration and posture.

Describe three functions of the cerebrospinal fluid.

BUOYANCY: Allows brain to attain considerable size without being impaired by its own weight. If it rested heavily on floor of cranium, the pressure would kill the nervous tissue. PROTECTION: protects the brain from striking the cranium when the head is jolted. SHAKEN CHILD SYNDROME and CONCUSSIONS do occur from severe jolting. CHEMICAL STABILITY: flow of CSF rinses away metabolic wastes from nervous tissue and homeostatic ally regulates its chemical environment.

Where does the HINDBRAIN (medulla oblongata) begin?How big is it? What are the external ridges on the anterior surface called? What is the prominent bugle lateral to each pyramid?

Beings at Foramen Magnum (middle hole) of the skull. It is slightly wider than a spinal cord. PYRAMID is the pair of external ridges on the anterior service of the HINDBRAIN. OLIVE is a prominent bulge lateral to each pyramid.

What connects the cerebellum to pons and midbrain?

CEREBRAL PEDUNCLES connects the cerebellum to the pons and midbrain.

Contrast the composition and locations of gray and white matter in the brain.

GRAY MATTER = Neurosomas, dendrites, and synapse. Forms the surface layer called the CORTEX over the cerebrum and cerebellum, and deeper masses called NUCLEI surrounded by WHITE MATTER. WHITE MATTER lies deep to the cortical gray matter in most of the brain, opposite from the relationship of gray and white matter in the spinal cord.As in the spinal cord, white matter is composed of TRACTS, or bundles of axons, which connect one part of the brain to another and to spinal cord.

Blood Supply to the Brain: Why is it important for the blood to flow to the brain? If there is an interruption what may be the effects to the brain?

Neurons have a high demand for ATP, and therefore, oxygen and glucose, so a constant supply of blood is critical to the nervous system. -10 second interruption of blood flow may cause loss of consciousness - 1-2 Minute interruption can cause significant impairment of neural function - 4 minutes with out blood causes irreversible brain damage - Blood-brain barrier: tight junctions

Medulla Oblongata: What contains descending fibers called corticospinal tracts?

PYRAMIDS- also carry motor signals to skeletal muscles.

What are the 4 four pairs of cranial nerves? Where do they begin and end? (same place)

The 4 pairs of cranial nerves begin or end in MEDULLA. IX glossopharyngeal X vagus XI accessory XII hypoglossal

Medulla Oblongata: What is the relay center for signals to the cerebellum?

The INFERIOR OLIVARY NUCLEUS is the relay center for signals to cerebellum.

What is the anterior bulge in the brainstem? Rostral to medulla

The PONS is the anterior bulge in the brainstem.

Medulla Oblongata: What is the loose network of gray matter?

The RETICULAR FORMATION is the loose network of gray matter.

Where does the CF originate and what route does it take through and around the CNS?

The cerebrospinal fluid (CSF) is a clear, colorless body fluid found in the BRAIN and SPINAL CORD. It is produced in the CHORID PLEXUSES of the ventricles of the brain, and absorbed in the ARACHNOID GRANULATIONS. FLOW OF CEREBROSPINAL FLUID: 1. CSF is secreted by chord plexus in each lateral ventricle. 2. CSF flows through inter ventricular foramina into third ventricle. 3. Choroid plexus in third ventricle adds more CSF. 4. CSF flows down cerebral aqueduct to fourth ventricle. 5. Choroid plexus in fourth ventricle adds more CSF. 6. CSF flows and two lateral apertures and one median aperture. 7. CSF fills subarachnoid space and bathes external surfaces of brain and spinal cord. 8. At arachnoid villi, CSF is reabsorbed into venous blood of dural venous sinuses.

What are the two layers of the DURAMATER? What are the layer separated by? What are the folds inward to extend between parts of the brain?

The duramater consists of the PERIOSTAL LAYER, equivalent to the periosteum of the cranial bones and an inner MENINGEAL LAYER. Only the meningeal layer continues into the vertebral canal, where it forms the dural sheath around the spinal cord. The layers are separated by DURAL SINUSES- collect blood circulating brain. FALX CEREBRI separates the two cerebral hemispheres. TENETORIUM CEREBELLI separates cerebrum, from cerebellum. FALX CEREBELLI separates the right and left halves of cerebellum.

Name the 5 secondary brain vesicles. Explain how the five secondary brain vesicles arise from the neural tube.

The forebrain divides into two of the vesicles, the TELENCEPHALON and DIENCEPHALON ; the midbrain remains undivided and retains the name MESENCEPHALON; the hindbrain divides in two two vesicles and the METENCEPHALON and MYELENCEPHALON.

What does the meninges do? Name the three meninges from superficial to deep. How does the dura mater of the brain differ from that of the spinal cord?

The meninges lie between the nervous tissue and bone. They protect the brain and provide structural framework for its arteries and veins. As in the spinal cord, the meninges are the DURAMATER, ARACHNOID MATER, and PIA MATER. The duramater its pressed closely against the cranial bone, with no intervening epidural space like the one around the spinal cord. It is NOT ATTACHED to the bone, however except in limited places: around the foramen magnum the sella tricia, the crust galli, and the sutures of the skull.

Define Gyri

Thick folds

Define Sulci

Thin folds

Ventricles and Cerebrospinal Fluid:

VENTRICLES: 4 internal chambers within the brain. Two LATERAL VENTRICLES- one in each cerebral hemp. -INTERVENTRICULAR FORAMEN: a tiny pore that connects to third ventricle. THIRD VENTRICLE single narrow medial space beneath corpus callosum. -CEREBRAL AQUEDUCT runs through midbrain and connects third to fourth ventricle. FOURTH VENTRICLE small triangular chamber between pons and cerebellum. -Connects to CENTRAL CANAL. Runs down through spinal cord. CHOROID PLEXUS: Spongy mass of blood capillaries on the floor of each ventricle EPENDYMA: Neuroglia that lines the ventricles and covers choroid plexus. - produces cerebrospinal fluid.