Anatomy Chatper 15: Brain and cranial nerves

15.5 is not on the exam this is just 15.1-15.4

Major Landmarks

• Cerebrum

  • Two hemispheres

  • gyri: folds

  • sulci: grooves

  • Longitudinal (median) cerebral fissure: deep sulcus between hemisphere

• Cerebellum

  • also has folds

• Brainstem

  • crucial for survival

Lobes

• frontal

• parietal

• occupital

• temporal

• insula

Fissures

• longitudinal cerebral fissure

• central sulcus

• lateral sulcus

• transverse cerebral fissure

Gray and White Matter

• Gray Matter (superficial)

  • Outer part (cortex) of cerebrum and of cerebellum, as well as deep nuclei

  • Neursosomas (cell bodies), dendrites, and synapses

• White Matter (deep)

  • deep in brain

  • tracts: bundles of myelinated axon (often time mostly myelinated)

Meninges

• Dura mater: tough, outer layer

• Arachnoid mater: transparent, middle layer

• Pia mater: delicate, inner layer

Dura mater

• within cranium, the dura has two layer

  • periosteal layer

  • meningeal layer

• in some places, the layers separate to form dural sinuses

  • superior sagittal sinus

  • transverse sinus

• in some places, dural sheets occupy spaces separating major parts of the brain

  • falx cerebri: between hemispheres

    • bony sepration

  • tentorium cerebelli: between cerebrum and cerebellum

    • like a tent for cerebellum

ventricles

• House CSF

Lateral ventricles

• interventricular foramen

Third ventricle

• cerebral aqueduct

Fourth ventricle

• central canal

• choroid plexus

merge together come down go to spinal cord

Cerebrospinal fluid (CSF)

• clear, colorless liquid

• produced by choroid plexus within ventricles

• flows within ventricles, canals, and in subarachnoid space around CNS

• Absorbed by arachnoid granulations into blood of superior sagittal sinus

• Provides buoyancy, protection, and chemical stability

  • keeps brain where it needs to be

Pathway CSF flows

1. CSF is secreted by choroid plexus in each lateral ventricle.

2. CSF flows through interventricular 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 out two lateral apertures and one median aperture.

7. CSF fills subarachnoid space and bathes external surfaces of brain and spinal cord

8. At the arachnoid granulations, CSF is reabsorbed into venous blood of dural venous sinuses.

Blood supply and Brain Barrier system

Brain is only 2% of body weight but receives 15% of blood and uses 20% of oxygen and glucose

• blood-brain barrier (BBB)

  • seals capillaries in brain tissue

  • tight junctions between endothelial cells

• Blood-CSF barrier

  • seals choroid plexus within brain ventricles

  • tight junctions between ependymal cells

• Circumventricular organs (CVOs)

  • regions 3rd and 4th ventricles that lack BBB

  • allow brain to monitor blood chemistry

    • chemical dip sticks can be area of liability or protection

The Medulla oblongata

• Develops from myelencephalon

• Extends from formaen magnus to pons

Important nuclei

• cardiac center

• vasomotor center

• respiratory center

Has anterior surfaces bulges: pyramids (med) and olives (lat)

Houses many other internal structures:

• 4th ventricle and Cranial Nerves: 8 (VIII) ,9 (IX),10 (X) ,11 (XI)

EX: someone has a tumor in there medulla oblongata how would that impact their body:

• trouble breathing: can be elevated or decreased

• elevated blood pressures

• irregular heart beat

• paralysis

The brainstem

• Midbrain

• Pons

• Medulla oblongata

The Pons

• Develops from metencephalon

• Anterior aspect: large bulge

• Posterior aspect: peduncles that attach to cerebellum

• Internally, contains parts of several tracts and nerves

  • cranial nerves V-VIII (5-8)

The midbrain

• Develops from mesencephalon

• cerebral aqueduct passes through

• tectum (posterior aspect)

• cerebral peduncles (anterior aspect)

  • tegmentum with red nucleus

  • substantia nigra (*degenerates in parkinson’s)

  • cerebral crurs anchor cerebrum to brainstem

• Gives rise to Cranial nerves 3 (III) and 4 (IV)

The reticular formation

• Web of gray matter that runs through all levels of brainstem

Functions:

• Somatic motor control

• cardiovascular control

• pain modulation

• sleep and consciousness

• Habituation

The cerebellum

• Cerebellar hemispheres

• vermis (midline separator)

  • cortex of folia and sulci - gray matter

    • numerous granuel cells

    • large purkinje cells

• Arbor vitae: white matter

• Deep nuclei: gray matter

Functions of Hindbrain and Midbrain

• Medullar oblongata

  • centers for circulatory and respiratory control

  • sensory and motor functions for head/neck

• Pons

  • facial sensation and expression

  • control of chewing, respiration, and sleep

• Midbrain

  • red nucleus and substantia nigra = motor control

  • central gray= pain awareness

  • superior colliculus= visual attention

  • inferior colliculus= auditory attention

• Reticular formation

  • sleep and consciousness

  • varied sensory, motor, and involuntary functions

• Cerebellum

  • muscular coordination and fine motor control

  • varied cognitive functions

The Diencephalon

• part of the forebrain

• three divisions that surround the third ventricle

  • thalamus

  • hypothalamus

  • epithalamus

The thalamus

• Large ovoid mass that makes up four-fifths of diencephalon

  • Makes up most of diencephalon

• “Gateway to the cerebral cortex”

  • involved in sensation, movement, memory, and emotion

  • mnemonic MEMS

The Hypothalamus

• Extends from optic chiasm to mammillary bodies

• Major control center of the autonomic nervous system and endocrine system

Functions

• hormone secretions

• autonomic effects

• thermoregulation

• food and water intake

• sleep and circadian rhythms

• emotional responses

• memory

The epithalamus

• Pineal gland: an endocrine gland

• Habenula: relay from limbic system to midbrain

• Thin roof over the third ventricle

The cerebrum

• Derives from embryonic telencephalon of forebrain

• 2 cerebral hemispheres

  • separated by longitudnial cerebral fissure

  • connected by corpus callosum

• Gyri and sulci produce large surface area

Lobes of the Cerebrum

Frontal Lobe

• from frontal bone to central sulcus

• cognition, speech, and motor control

parietal lobe

• from central sulcus to parieto-occipital sulcus

• interprets signals of general senses and taste

Occipital lobe

• from parieto-occipital sulcus to occiptal bone

• principal visual center

  • visual center back of head

Temporal lobe

• from temporal bone to lateral sulcus

• hearing, smelling, learning, and memory

insula

• deep to lateral sulcus (not visible from surface)

  • taste, visceral sensation, and language

    • ex: of visceral sensation: hunger, nausea, fullness

Cerebral Cortex

• surface of the hemisphere (outermost aspects)

• 40% of mass of brain

Pyramidal cells

• triangle shaped with apex pointing to brain surface

• output neurons of cerebrum

  • out to the body

Limbic system

• Prominent parts include: cingulate gyrus, hippocampus, and amygdala

  • Know it is more of a region across areas not just one specific point.

• important functions for emotion and learning

• contains multiple gratification and aversion centers

Basal Nuclei

• Deep masses of cerebral gray matter

• consist of caudate nucleus, putamen, and globus pallidus

• involved in motor control

integrative brain functions

primary cortex

• primary sensory cortex is first cortical region to receive input for that sense

• primary motor cortex issues projection fibers to distribute motor commands

Association cortex

• any cortical area that is not primary

• interpretation of sensations, thought, memory, and motor planning

some functional regions of the cerebral cortex

vision

• occipital lobe

• primary visual cortex

Hearing

• temporal lobe and insula

• primary auditory cortex

Equilibrium (balance)

• cerebellum (mostly)

• several brainstem nuclei

Taste

• parietal lobe

• primary gustatory cortex

smell

• temporal and frontal lobes (mainly)

• orbitofrontal cortex (little bit)

Language

wernicke area

• posterior to lateral sulcus of left brain

• recognition of written and spoken language

Broca area

• inferior prefrontal cortex of the left brain

• speech

Ex: stroke depending where, can make a person have speech (make noises) but can’t process cognition and vice versa. So person isnt saying any actual words

Emotion

• Multiple area involved

• Amygdala outputs to hypothalamus and prefrontal cortex

Cognition

• Acquire and use knowledge

• Association area of cortex

Memory

• two types: procedural and declarative

• limbic areas involved

  • Amygdala creates emotional memories

  • Hippocampus consolidates declarative long-term memories

Lateralization of cerebral Functions

• Difference in function for each hemisphere

• categorical hemisphere: left

• representation hemisphere: right

Forebrain functions