Unit G (Nervous System Part 2)

Parts of the brain stem

Medulla oblongata, pons, midbrain

Medulla oblongata: main role

Relays sensory input and motor output between other parts of the brain

Which centers are in the medulla?

Heartbeat, breathing, swallowing

Pons: main role

Relays impulses from one side of the cerebellum to the other and between the medulla and midbrain

Which centers are in the pons?

Breathing centers

Midbrain: main role

Relays motor output from the cerebral cortex to the pons and sensory input from the spinal cord to the thalamus

Midbrain functions

Eye movement and response to auditory stimuli

Cerebellum function

Compares intended movement with reality to coordinate complex movement; regulates posture and balance

Parts of the diencephalon

Thalamus, hypothalamus, epithalamus

Thalamus function

Relays sensory input (touch, pressure, pain, temperature) to the cerebral cortex

Hypothalamus function

Controls ANS and pituitary gland activity (temperature, eating, drinking, waking state)

What does the epithalamus contain?

The pineal gland

What does the pineal gland secrete?

Melatonin

Cerebrum: sensory areas

Involved in perception

Cerebrum: motor areas

Control movement

Cerebrum: association areas

Have integrative functions

What part of the cerebrum handles emotion related to survival?

The limbic system

Are brain and spinal meninges continuous?

Yes

How many layers does the cranial dura mater have?

Two (unlike the spinal dura)

Where are the two cranial dural layers not fused?

Where they enclose the dural venous sinus

Where does the dural venous sinus drain?

Into the internal jugular vein

What does the falx cerebri separate?

The hemispheres of the cerebrum

What does the falx cerebelli separate?

The hemispheres of the cerebellum

What does the tentorium cerebelli separate?

The cerebrum from the cerebellum

Which meningeal layer is innermost?

Pia mater

What does the pia mater form around vessels?

A sheath around vessels that pass along the brain surface and penetrate inward

Which arteries supply blood to the brain?

Internal carotid and vertebral arteries

Which veins drain blood from the brain?

Internal jugular veins

What does the BBB do?

Protects the brain from harmful chemicals or pathogens in the blood

What forms the BBB (per slide)?

Astrocytes with tight junctions

How does glucose cross the BBB (per slide)?

Active transport from blood to brain

How do creatinine, urea, and most ions cross the BBB?

Slowly

Which substances do not cross the BBB at all?

Proteins and antibiotics

Which substances cross the BBB easily?

Hydrophobic (lipid-soluble) substances

Examples of easily crossing substances?

Oxygen, carbon dioxide, alcohol, anesthetics

What does CSF look like?

Clear and colorless

What are CSF’s general roles?

Protects the brain and spinal cord; carries oxygen, glucose, and other chemicals from blood to neurons and neuroglia

CSF volume?

80-150 mL

CSF production rate?

20 mL/hr (480 mL/day)

Why does CSF volume stay constant?

It is reabsorbed at the same rate it is produced

Components of CSF?

Glucose, proteins, lactic acid, urea, cations (K⁺, Na⁺, Ca²⁺, Mg²⁺), anions (Cl⁻, HCO₃⁻), white blood cells

Mechanical protection by CSF?

Buoys the brain and acts as a shock absorber

Chemical protection by CSF?

Provides an optimal environment for nerve signals

What are choroid plexuses?

Networks of capillaries that line the ventricles

What covers the choroid plexuses?

Ependymal cells (glia) with tight junctions

Why must substances pass through ependymal cells?

Tight junctions prevent leaking between cells

What barrier does this create?

The CSF-brain barrier

How is CSF formed from blood plasma?

By filtration and secretion

Where is CSF first formed?

Choroid plexuses of the lateral ventricles

How does CSF get from the lateral ventricles to the third?

Through the interventricular foramina

How does CSF get from the third to the fourth ventricle?

Through the cerebral aqueduct (aqueduct of the midbrain)

How does CSF leave the fourth ventricle?

Through the median and two lateral apertures into the subarachnoid space

Where else does CSF circulate?

The central canal of the spinal cord and the subarachnoid space around the brain and spinal cord

Where is CSF reabsorbed?

Through arachnoid villi, especially at the superior sagittal sinus

Length of the medulla

3 cm

Where does the medulla begin and end?

Begins at the foramen magnum, extends to the inferior border of the pons

What do the pyramids contain?

Bulges of white matter in the medulla

What is decussation of the pyramids?

About 90% of tracts cross sides in the medulla

What does decussation explain?

Why the left side of the brain controls the right side of the body

Medial lemniscus

A ribbon of white matter through the medulla, pons, and midbrain whose axons ascend to the thalamus

Cardiovascular center function

Controls rate and force of heartbeat

Medullary rhythmicity area function

Adjusts the rhythm of breathing

What does the inferior olivary nucleus do?

Relays impulses from proprioceptors to the cerebellum

Where is the olive?

An oval swelling just lateral to each pyramid

Gracile and cuneate nuclei: location

Posterior medulla

Gracile and cuneate nuclei: function

Relay touch, vibration, and conscious proprioception to the thalamus on the opposite side

Cranial nerve nuclei in the medulla

VIII, IX, X, XI, XII

Length of the pons

2.5 cm

Where is the pons?

Superior to the medulla, anterior to the cerebellum

What do pontine nuclei do?

Relay voluntary movement signals from the cortex to the cerebellum

Which areas of the pons help control breathing?

Pneumotaxic and apneustic areas

Cranial nerve nuclei in the pons

V, VI, VII, VIII

Another name for the midbrain

Mesencephalon

What passes through the midbrain?

The cerebral aqueduct, connecting the third and fourth ventricles

What are cerebral peduncles?

Tracts conducting impulses from the cerebrum to the spinal cord, pons, and medulla

What is the tectum?

The posterior midbrain with four rounded elevations (startle reflex)

Superior colliculi function

Reflex centers for vision

Inferior colliculi function

Auditory pathway

Substantia nigra neurotransmitter

Dopamine

Substantia nigra function

Helps control subconscious muscle activities

What is associated with substantia nigra neuron loss?

Parkinson’s disease

Why are the red nuclei red?

Rich blood supply and iron-containing pigment

Red nuclei function

Coordination of muscle movement

Cranial nerve nuclei in the midbrain

III (oculomotor), IV (trochlear)

What is the reticular formation?

A net-like mix of gray and white matter running through the brain stem

What does the RAS do?

Projects sensory axons to the cortex to maintain consciousness and awakening

Descending function of the reticular formation

Muscle tone

Where is the cerebellum?

The inferior, posterior aspect of the cranium

How large is the cerebellum compared to other brain parts?

Second largest

What is the transverse fissure?

A deep groove separating the cerebellum from the cerebrum

What does the tentorium cerebelli do?

Supports the posterior cerebrum and separates the cerebellum from the cerebrum

What is the vermis?

The central constricted area of the cerebellum (center of the butterfly)

What are the cerebellar hemispheres divided into?

Anterior and posterior lobes

What do the cerebellar hemispheres handle?

Subconscious aspects of skeletal movement

Where is the flocculonodular lobe?

The inferior surface of the cerebellum

Flocculonodular lobe function

Equilibrium and balance

What is the cerebellar cortex made of?

Gray matter in slender, parallel ridges (folia)

What are folia?

The slender, parallel ridges of the cerebellar cortex

What is the arbor vitae?

Tracts of white matter deep in the gray matter

Where are the cerebellar nuclei?

Gray matter deep in the white matter