Brain and Cranial Nerves

14a

Brain volume

1200 ml (750-2100 ml range)

Brain Weight

around 3 pounds (1.4 kg)

How many neurons and connections in brain?

100 Billion neurons, 500 trillion connections

Female and male differences

Males have greater volume, females have more connections

Gyri

rounded elevations

Sulci

Shallow grooves

Fissues

deeper grooves

Four “regions” of brain

Cerebrum

Cerebellum

Diencephalon

• Thalamus

• hypothalamus

Brainstem

• Midbrain

• pons

• medulla oblongata

During embryonic development, the CNS develops from

neural tube

Ventricular system of brain

• Lateral ventricles (2)

• Third ventricle

• fourth ventricle

• cerebral aqueduct

• intraventricular foramen

A

lateral ventricles

B

interventricular foramen

C

third ventricle

D

cerebral aqueduct

E

Fourth ventricle

F

central canal

G

Spinal cord

H

Medulla oblongata

I

Pons

J

Cerebral hemispheres

Ventricles of the brain

• fluid filled spaces/ openings

• continuous with spinal cord

• contain CSF fluid, ependymal cells

Cerebrospinal Fluid Function

• support (our brain floats)

• cushioning (absorbing impact)

• transport (nutrients, hormones, waste)*

  • still remember that brain is vascularized

What three structures (aside from scalp and skull) protect the brain?

• Cranial meninges (DAP)

• Blood Brain Barrier (BBB)

• CSF

CSF produced each day

500 ml/2 cups, but sometimes 150ml every moment

*Replaced every 8 hours

**Extra CSF absorbed into venous circulation (veins)

1

Periosteal cranial dura

2

Dural sinus

3

Meningeal cranial dura

4

Subdural space

5

Arachnoid mater

6

Dura Mater

7

Subarachnoid space

8

Pia Mater

9

Cerebral Cortex

Dura Mater

• outermost, fused to periosteum of cranial bones

• Subdural space (below it)

Arachnoid Mater

• “spiderlike”, has subarachnoid space

Pia Mater

• anchored by processes of astrocytes, sticks to surface of brain

Blood Brain Barrier (BBB)

• formed by capillary endothelial cells connected by tight junctions

• prevent materials from diffusing between endothelial cells

• Small capillaries that are 1 cell thick

• NOT fenestrated (no holes/apertures)

What glial cell maintains BBB?

• Astrocytes

  • ends “endfeet” of astrocytes surround blood vessel (capillary) that produces substance, which supports thigh junctions

  • regulates interstitial environment (between tissue)

    • determining ions, neurotransmitters needed for homeostasis, etc….

    • ex. not eating until 12, but brain uses glucose storage while thinking

What provides nutrients for astrocytes?

Pericytes

Transport across BBB

• lipid soluble (Oxygen, alcohol, CO2)

• lipid based sterol hormones (insulin, leptin, viruses)

• **NOT glucose, needs active transport

Circumventricular Organs

• have fenestrated capillaries

  • Hypothalamus (which secretes neurohormones ADH and Oxytocin)

  • Posterior Pituitary Gland (where ADH and Oxytocin move around)

  • Pineal Gland (melatonin)

  • Choroid Plexus (in each of the ventricles)

Choroid Plexus

• network of blood vessels, exchange between blood and CSF takes place here

• lines all ventricles of brains

Medulla Oblongata

• Cranial nerves 8-12

• Three groups of nuclei

  • Reflex center for autonomic activity

  • sensory and motor nuclei of cranial nerves

  • relay stations for sensory, motor pathways

Brainstem

• processes and relays info from spinal cord to higher brain (cerebellum, cerebrum)

  • two way street (sensory info goes up, motor info goes down)

    • thalamus, pons, medulla*

Medulla Oblongata Reflex Center (1st nuclei group’s automatic activity)

• cardiovascular

  • adjust HR, cardiac contractility, peripheral resistance in <3, blood vessels

• Respiratory Rhythmic

  • Set basic pace for respiration**

    • **pons also regulate breathing

Reticular Formation (a part of medulla)

• gray and white matter, relay station

Pons

• Largest part of brainstem, medial to midbrain and medulla oblongata

• 5-8 cranial nerve, no. 8 is shared

• also regulates breathing

  • Apneustic and pneumotaxic centers in gray matter region of pons

Apneustic and pneumotaxic centers

• respiratory rhythmicity centers, control respiration (shared task between pons and medulla)

Midbrain

• Most superior

• cranial nerves 3-4

• hand eye coordination, connect to cerebellum

• auditory and visual processing

• Substantia nigra is here

Substantia nigra

• Regulates basal nuclei activity in midbrain

• dopamine producing nuclei here

• production of neuromelanin

  • maintain consciousness

• controls body movements

• controls learning, mood, judgement decision-making

  • Diminished SN —> Parkinson’s disease

Cerebellum

• 10% of brain volume, 50% of total brain neurons found here

• posterior to brainstem, inferior to cerebrum

• Rich in Purkinje Cells (branched, dense, highly connected)

  • found in cerebellar cortex

  • axons are myelinated

Gray matter of Cerebellum

• Cerebellar cortex

• cerebellar nuclei

White Matter of Cerebellum

• Arbor Vitae (tree of life striations)

• cerebellar peduncles

A

Anterior

D

Posterior

B

Primary fissure

C

Folia

• more folia, more neurons

E

Vermis

• separates cerebellum into 2 lat. hemispheres

F

Intermediary zone

G

Horizontal fissure

• creates superior and inferior areas

H

Flocconobular lobe

A

Midbrain

B

Choroid plexus

C

Flocculonodular lobe

D

Medulla Oblongata

E

Posterior Lobe

F

Pons

G

White matter/arbor vitae

1

Superior Peduncle

2

Middle peduncle

3

Inferior peduncle

Cerebellum Functions

• hand eye coordination (guitar)

• rehearsing learned movements/ learning

• balance (muscle “tone”)

  • Coordination, tone, balance

    • relate back to somatic nervous system controlling skeletal muscle

Spinocerebellar pathways (tracks)

• cerebellum doesn’t work in isolation

• afferent/efferent (arrive/sensory and exit/motor)

• enter and exit through peduncles

Ataxia

• disturbance in muscle coordination

• temporary cause: alcohol

• slurred speech, awkward gait, trouble with fine motor movements

  • Dysmetria: type of ataxia

    • inability to control distance, speed, range of motion

Diencephalon (3 areas)

1. epithalamus

2. thalamus

3. hypothalamus

Epithalamus

• roof of dienceph, superior to 3rd ventricle

• anterior side has choroid plexus of 2 lat. ventricles

Pineal Gland

• near posterior portion of epithalamus

• melatonin production

Circadian rhythm and melatonin cycle

• body adjusts

• can be impacted/rewired with drugs

• blue light inhibits melatonin prod

Thalamus

• major part of diencephalon

• central relay****

• made of many nuclei

Nuclei is

cluster of nerve cell bodies in CNS

• analogous to PNS’s ganglia/ganglion

Hypothalamus

• floor of diencephalon

• has mamillary bodies (memory?)

Funct of Hypothalamus

• produce and secretes ADH (antidiuretic), oxytocin

  • sends to posterior pituitary gland

• Thermoregulation

• “Internal Thermostat”

  • Homeostasis

  • neg. feedback

• circadian rhythm

• auto centers: regulating blood pressure and heart rate

• Subconscious control of skeletal muscle

  • direct motor patterns associated with emotions

• Emotional, Behavioral drive

  • Feeding, thirst, satiety center

Limbic (“border”) Center

Emotion Center, basic emotional states

• works with hypothalamus

• link conscious funct of cerebrum to automatic functs of brainstem

• memory, storage, retrieval

Hippocampus

memory

Amygdala

“Fight or flight response, freeze”

• interface between limbic system & cerebrum & sensory organs

• sympathetic NS stimulated (typically)

Cerebrum

• Surface a: 2200

• largest part of brain

• highest level of thinking

  • somatosensory info

• cerebral cortex: outermost portion

What splits the cerebrum into 2 hemispheres?

Longitudinal Fissure

Basal Nuclei

• masses of gray matter, UNmyelinated neurons

• function via feedback loop with cerebral cortex

• constantly adjusting muscle tone

Commissural Fibers

White Matter connecting lobes of brain

• Fibers connecting 2 hemispheres

  • best example of c.fibers is Corpus Callosum

    • C.C. is cut to prevent seizures (epilepsy)

Frontal Lobe

• its anterior contains prefrontal cortex (developed by 25, last part to fully develop)

• motivation, planning, exec. funct, attention and focusing

• short term mem

What’s in the frontal lobe?

• Prefrontal Cortex

• Precentral gyrus

• Broca’s area

Parietal lobe

• posterior and dorsal to frontal lobe

  • proprioceptive (where body is in space)

  • mechanoreceptive (touch)

• language processing

• contains post-central gyrus

Post central gyrus

• contains somatosensory cortex (AFFERENT info, goes up to brain to be processed)

Temporal Lobe

• Inferior, posterior to frontal lobe

• Auditory complex (hearing), and some visual input

• Wernicke’s area

Wernicke’s area

• temporal lobe

• for comprehension of language (written and spoken)

• unilateral, dominant hemisphere

  • If Rightie, left side of brain

Occipital Lobe

Vision