A&P Ch 14 Intro to the brain and brain stem

Rostral

-Toward the forehead

Caudal

-Toward the spinal cord

Brain weight

-About 1600g (3.5 lb) for men

-1450g for woman

Cerebrum

-83% of brain volume

-Cerebral hemispheres

-Gyri and sulci

-Longitudinal fissure

-Corpus callosum

Longitudinal fissure

-Deep groove that separates cerebral hemispheres

Gyri

-Raised areas

Sulci

-Shallow grooves

Corpus callosum

-Thick nerve bundle at bottom of longitudinal fissure that connects hemispheres

-White fibrous tract

Cerebellum location

-Occupies posterior cranial fossa

-Separated from cerebrum by transverse cerebral fissure

vermis

-Connects both halves of cerebellar hemispheres

Folia

-Cerebellum

-Superficial cortex of gray matter with folds

Arbor vitae

-Cerebellum

-"tree of life"

-branching white mater

Cerebellum

-contains over 50% of brain neurons ~ 100 billion

-Many small granule cells

-Large Purkinje cells have axons that synapse on deep nuclei

-~10% of brain volume

-Also has sulci, gyri, and fissures

-Small in many hyperactive children

Brain stem location

-What remains of the brain if the cerebrum and cerebellum are removed

Brain stem

-Midbrain

-Pons

-Medulla oblongata

Gray matter

-The seat of neurosomas, dendrites, and synapse

-Dull color due to little myelin

-Surface of brain

-Forms nuclei deep within brain

White mater

-Bundles of axons

-Lies deep in brain

-Pearly white color from myelin

White mater function

-Composed of tracts, or bundles of axons, that connects one part of the brain to another, and the spinal cord

Meninges

-Three connective tissue membranes that envelope the CNS

-Protect the CNS and provide structural framework for its arteries and veins

Meninges Location

-Lies between the nervous tissue and bone

Meningitis

-Inflammation of the meninges

-Serious disease of infancy and childhood

Meningitis causes

-Caused by bacterial or viral invasion of the CNS

-Especially between 3 months and two years of age

Cranial dura mater

-Outer periosteal

-Inner meningeal

-Folds inward to extend between parts of the brain

Cranial dura mater location

-Layers separated by dural sinuses

-Pressed closely against cranial bones

=No epidural space

=Only attached to bone around foramen magnum, stella turcica, crista galli, and sutures of the skull

Periosteal

-Equivalent to periosteum of cranial bones

Meningeal

-Continuous into vertebral canal and forms dural sheath around spinal cord

Dural sinuses

-Separates layers of cranial dura mater

-Collect blood circulating though brain

Arachnoid mater

-Transparent membrane over brain surface

Subarachnoid space

-Separates arachnoid mater from pia mater below

-Contains CSF

Subdural space

-Separates arachnoid from dura mater above in some spaces

Pia mater

-Very thin membrane that follows contours of brain, even dipping into sulci

-Not usually visible without a microscope

Ventricles

-Internal chambers within the brain

Lateral ventricles

-One in each cerebral hemispheres

-Interventricular foramen

Interventricular foramen

-Tiny pore that connects to third ventricle

Third ventricle

-Narrow medial space beneath corpus callosum

-Connects to cerebral aqueduct

Cerebral aqueduct

-Runs through midbrain and connects to third and fourth ventricles

Fourth ventricle

-Small triangular chamber between pons and cerebellum

-Connects to central canal that runs through spinal cord

Choroid plexus

-Spongy mass of blood capillaries on the floor of each ventricle

Ependymal

-Type of neuroglia that lines ventricles and covers choroid plexus

-Produces CSF

Cerebrospinal fluid

-CSF

-Clear, colorless liquid that fills the ventricles and canals of CNS

-Bathes its external surface

CSF production

-Brain produces and absorbs 500 mL/day

-100-160 present at one time

-produced 40% in subarachnoid space

-Produced evenly by ependymal cells lining ventricles and by the choroid plexuses

CSF creation

-Begins with filtration of blood plasma through capillaries of the brain

-More sodium and chloride then plasma

-Less potassium, glucose, and very little protein

Bouyancy

-Allows brain to attain considerable size without being impaired by its own weight

Without CSF

-If it rested heavily on floor of cranium, the pressure would kill the nervous tissue

Shock absorbtion

-Protects the brain from striking the cranium when the head is jolted

severe jolting

-cause shaken child syndrome and concussions

Chemical stability

-Flow of CSF rinses away metabolic wastes from the nervous tissue and homeostatically regulates its chemical environment

Blood flow to brain

-2% of bodies weight

-receives 15% of the blood

-750 mL /min

Neurons and blood flow

-High demand for ATP, and therefore, O2 and glucose

-Constant supply of blood is critical

10 second interruption

-may cause loss of consciousness

1-2 min interruption

-Can cause significant impairment of neural function

going 4 min

-Causes irreversible brain damage

Blood barrier system

-Regulates what substances can get from bloodstream into tissue fluid of the brain

-Though crucial it can contain harmful agents

Gaurded points of entry

-Blood capillaries throughout the brain tissue

-Capillaries of the choroid plexus

Blood CSF barrier

-Protects brain at the choroid plexus

-Forms tight junctions between ependymal cells

Blood barrier allows

-is highly permeable to water, glucose

-lipid-soluble substances such O2, CO2, alcohol, caffeine, nicotine, and anesthetics

Brain barrier system

-BBS

-Can be an obstacle for delivering medication such as antibiotics and cancer drugs

-Can be damaged by trauma and inflammation

Circumventricular organs

-CVO

-Places in the third and fourth ventricles where barrier is absent

Circumventricular organ functions

-Blood has direct access to the brain

-Enables brain to monitor and respond to fluctuations in blood glucose, pH, osmolarity, and other variables

Medulla oblongata location

-Begins at foramen magnum of skull

-Extends about 3 cm rostrally and ends at a groove just below pons

-Slightly wider than pons

Pyramids location

-Pair of ridges on anterior surface resembling side-by-side baseball bats

-Four pairs of cranial nerves begin or end in medulla (VIII (in part), XI, X, and XII)

-Separated by anterior median fissure

Medulla oblongata function

-Houses neurosomas of second-order sensory neurons

-All ascending and descending fibers connecting to brain and spinal cord pass through

Olives

-Prominent bulges lateral to each pyramid

pyramids functions

-Carry motor signals to skeletal muscle

Inferior olivary nucleus

-Relay center for signals to cerebellum

reticular formation

-Loose network of nuclei extending throughout the medulla, pons, and mid brain

-Contains cardiac, vasomotor, and respiratory center

Pons location

-Anterior bulge in the brainstem, rostral to medulla

Pons function

-Reticular formation in pons contains additional nuclei concerned with sleep, respiration, and posture

-CN V, VI, VII and VIII

Pons sensory roles

-Hearing, equilibrium, taste, and facial sensation

Pons motor roles

-Eye movement, facial expressions, chewing, swallowing, urination, and secretion of saliva and tears

Cerebral peduncles pons

-Thick stalks on posterior pons that connect it (and the midbrain) to the cerebellum

Midbrain function

-Short segment of the brainstem that connects hindbrain to the forebrain

-contains cerebral aqueduct

=Surrounded by central gray matter involved in controlling pain

Midbrain

Contains...

-continuation of reticular formation

-Motor nuclei of two cranial nerves that control eye movement

-CN III and IV

Tectum

-Roof-like part of the midbrain posterior to cerebral aqueduct

-contains corpora quadrigemina

=Superior and inferior colliculi

Superior colliculi

-Upper pair of corpora quadrigemina

-Function in visual attention, tracking moving objects, and some reflexes

Inferior colliculi

-Lower pair of corpora quadrigemina

-Receives signals from the inner ear and relays them to other part of the brain, especially thalamus

Cerebral peduncles midbrain

-Two anterior midbrain stalks that anchor the cerebrum to the midbrain

-Each peduncle has three parts

=Tegmentum, substantia nigra, other (not important)

Tegmentum

-Dominated by red nucleus

-Pink color due to high density of blood vessels

-Connections go to and from cerebellum for motor controls

Substantia nigra

-Motor center that relays inhibitory signals to thalamus and basal nuclei preventing unwanted body movement

-Black nucleus pigmented with melanin

Substantia nigra senescence

-Degeneration of neurons leads to tremors of Parkinson disease

Reticular formation

-Loose web of gray matter that runs vertically though all levels of the brainstem

-Has connections with many areas of cerebrum

reticular formation location

-Occupies space between white fiber tracts and brainstem nuclei

-Has more than 100 small neural networks without distinct boundaries

reticular formation function

-Somatic motor control

-Adjust muscle tension

-Cardiovascular control

-Pain modulation

-sleep and consciousness

-Habituation

-Gaze center

-Central pattern generators

-Integrate visual, auditory, balance and motion stimuli into motor coordination

Adjust muscle tension

-Reticular formation

-To maintain tone, balance, and posture, especially during body movements

Gaze centers

-Reticular formation

-Allow eyes to track and fixate on objects

Central pattern generators

-Reticular formation

-Neural pools produce rhythmic signals to the muscles of breathing and swallowing

Cardiovascular control

-Reticular formation

-Cardiac and vasomotor centers of medulla oblongata

Pain modulation

-Reticular formation

-some pain signals ascend though the reticular formation

-Some descending analgesic pathways begin in the reticular formation

=End in the spinal cord where they block transmission of pain signals

Sleep and consciousness

-Reticular formation

-Plays a role a central role in consciousness, alertness and sleep

-Injury here can result in irreversible coma

Habituation

-Reticular formation

-Activating system modulates activity in cerebral cortex so that it ignores repetitive, inconsequential stimuli

Cerebellar peduncles

-Three pairs of stalks that connect brainstem and cerebellum

-Fibers carry signals to and from cerebellum

Inferior peduncles

-Connected to medulla oblongata

-Most spinal input enters the cerebellum through here

Middle peduncles

-Connected to medulla oblongata

-most input from rest of the brain enters here

Superior peduncles

-Connected to the midbrain

-Carries cerebellar output

Motor coordination

-Cerebellum has long been known to be important for this and locomotor ability

Cerebellum and nonmotor functions

-Comparing textures

-Perceiving space

-Recognizing objects from different views

-Maintaining judgment of time and Rythm

-directing eye movement that compensates for head movement

-Judging pitch and tone

-Verbal association

-Planning, scheduling, and emotional control

Forebrain

-Diencephalon

-Telencephalon

Diencephalon

-Encloses third ventricle

-Most rostral part of the brainstem

-hypo/thalamus, and epithalamus

Telencephalon

-Develops chiefly into the cerebrum

Thalamus location

-Ovoid mass on each side of the brain perched at the superior end of the brainstem beneath the cerebral hemispheres