Brain Stem Located b/w the cerebrum and the spinal cord –Provides a pathway for tracts running b/w higher and lower neural centers. Consists of the midbrain, pons, and medulla oblongata. –Each region is about an inch in length. Microscopically, it consists of deep gray matter surrounded by white matter fiber tracts. Produce automatic behaviors necessary for survival!

Midbrain Located b/w the diencephalon and the pons. –2 bulging cerebral peduncles on the ventral side contain: Descending fibers that go to the cerebellum via the pons Descending pyramidal tracts –Running through the midbrain is the hollow cerebral aqueduct which connects the 3 rd and 4 th ventricles of the brain. –The roof of the aqueduct (the tectum) contains the corpora quadrigemina 2 superior colliculi that control reflex movements of the eyes, head and neck in response to visual stimuli 2 inferior colliculi that control reflex movements of the head, neck, and trunk in response to auditory stimuli

Midbrain contains the headquarters of the reticular activating system and the nuclei for Cranial nerves 3&4 (oculomotor and trochlear). Cerebral aqueduct

Midbrain On each side, the midbrain contains a red nucleus and a substantia nigra SN. –Red nucleus contains numerous blood vessels and receives info from the cerebrum and cerebellum and issues subconscious motor commands concerned w/ muscle tone & posture –Lateral to the red nucleus is the melanin-containing SN, which contain dopamine releasing neurons that terminate in the basal nuclei.

Pons Literally means “bridge” Wedged b/w the midbrain & medulla. Contains: –Sensory and motor nuclei for 4 cranial nerves Trigeminal (5), Abducens (6), Facial (7),and Auditory/Vestibular (8) –Respiratory nuclei: Apneustic & pneumotaxic centers work w/ the medulla to maintain respiratory rhythm –Nuclei & tracts that process and relay info to/from the cerebellum –Ascending, descending, and transverse tracts that interconnect other portions of the CNS

Medulla Oblongata Most inferior region of the brain stem. Ventrally, 2 ridges (the medullary pyramids) are visible. –These are formed by the large motor corticospinal tracts. –Right above the medulla-spinal cord junction, most of these fibers cross- over (decussate).

Brainstem: - Medulla Oblongata = Most nerve impulses coming to brain from spinal cord cross over (decussation) in medulla

Continuous with spinal cord at foramen magnum. Contains 3 nuclei (“vital” centers) functions: - respiratory center - cardiac center - vasomotor center Continuous with spinal cord at foramen magnum. Contains 3 nuclei (“vital” centers) functions: - respiratory center - cardiac center - vasomotor center Medulla Oblongata

Brainstem: - Medulla Oblongata - reflexes  coughing, vomiting, swallowing, sneezing -contains two prominent enlargements on the anterior surface  pyramids - Medulla Oblongata - reflexes  coughing, vomiting, swallowing, sneezing -contains two prominent enlargements on the anterior surface  pyramids

Medulla Oblongata Contains sensory & motor nuclei of 5 cranial nerves: –Auditory/Vestibular (8), Glossopharyngeal (9), Vagus (10), Accessory (11), and Hypoglossal (12) Contains relay nuclei that pass somatosensory info to the thalamus and relay nuclei that conveys info from the spinal cord, cerebral cortex, and the brainstem to the cerebellar cortex.

How many brain structure can you ID?

Other structures:  limbic system = olfactory cortex, diencephalon & cerebrum functions: emotions & memory functions: emotions & memory Other structures:  limbic system = olfactory cortex, diencephalon & cerebrum functions: emotions & memory functions: emotions & memory

Limbic System

Reticular formation = Function: maintains a state of attention & wakefulness (consciousness) by arousal of the cerebral cortex of the cerebral cortex (sleep disorders: Narcolepsy & cataplexy) (sleep disorders: Narcolepsy & cataplexy) Reticular formation = Function: maintains a state of attention & wakefulness (consciousness) by arousal of the cerebral cortex of the cerebral cortex (sleep disorders: Narcolepsy & cataplexy) (sleep disorders: Narcolepsy & cataplexy)

Protection What is the major protection for the brain? There are also 3 connective tissue membranes called the meninges: Cover and protect the CNS Protect blood vessels Contain cerebrospinal fluid The 3 meninges from superficial to deep: Dura mater Arachnoid mater Pia mater

meninges = connective tissue membrane surrounding both the brain & spinal cord - 3 meninges (function  nourishes and protects) nourishes and protects) meninges = connective tissue membrane surrounding both the brain & spinal cord - 3 meninges (function  nourishes and protects) nourishes and protects)

Skin Galea Aponeurotica Connective Tissue Bone Dura Mater Arachnoid mater

- 3 meninges dura mater = tough outer, dura mater = tough outer, fibrous conn. tissue fibrous conn. tissue -Just inside cranium and is tightly attached to the periosteum of the skull. -Surrounded by epidural space in the vertebral column arachnoid mater = thin, arachnoid mater = thin, web-like layer web-like layer pia mater = innermost layer pia mater = innermost layer tightly bound to brain tightly bound to brain surface surface

subarachnoid space = space between arachnoid and pia mater contains Cerebral Spinal Fluid (CSF).

Meninges

Ventricles Ventricles are within the cerebral hemispheres and brain stem and consist of a series of interconnected cavitiesVentricles are within the cerebral hemispheres and brain stem and consist of a series of interconnected cavities Continuous with the central canal of the spinal cordContinuous with the central canal of the spinal cord Contain cerebrospinal fluidContain cerebrospinal fluid

Ventricles of the brain Largest-Lateral ventricles (1 st and 2 nd ventricles)Largest-Lateral ventricles (1 st and 2 nd ventricles) –Occupies part of the hemispheres and portions of the frontal, temporal and occipital lobes

Ventricles of the brain Third ventricle-a narrow space in the midline of the brain beneath the corpus callosumThird ventricle-a narrow space in the midline of the brain beneath the corpus callosum –Communicates with the lateral ventricles through openings in its anterior end  interventricular foramina

Ventricles of the brain Fourth ventricle-in the brain stem just anterior to the cerebellumFourth ventricle-in the brain stem just anterior to the cerebellum –Connected to the third ventricle via the cerebral aqueduct –Continuous with the central canal of the spinal cord and has openings in its roof that lead into the subarachnoid space of the meninges.

Ventricles & CSF - ventricles = fluid-filled - ventricles = fluid-filled ( Cerebral Spinal Fluid, CSF) ( Cerebral Spinal Fluid, CSF) cavities within brain cavities within brain - CSF clear fluid produced by - CSF clear fluid produced by the choroid plexus the choroid plexus  serves as protection and provides nourishment Ventricles & CSF - ventricles = fluid-filled - ventricles = fluid-filled ( Cerebral Spinal Fluid, CSF) ( Cerebral Spinal Fluid, CSF) cavities within brain cavities within brain - CSF clear fluid produced by - CSF clear fluid produced by the choroid plexus the choroid plexus  serves as protection and provides nourishment

Ventricles

Cerebrospinal Fluid Fills the space b/w the arachnoid and pia mater, as well as the internal cavities of the brain (ventricles) and spinal cord. Functions: –Shock absorption –Support –Nourishment A choroid plexus consists of a combination of specialized ependymal cells and permeable capillaries for the production of CSF. –2 extensive folds originate in the roof of the 3 rd ventricle (located b/w the lateral walls of the diencephalon) and extend through the interventricular foramina and cover the floors of the lateral ventricles. A region of choroid plexus is also found in the 4 th ventricle b/w the cerebellum and pons.

Ependymal cells selectively secrete capillary filtrate into the ventricles. They also remove waste products from the CSF and adjust its composition over time. CSF differs markedly from blood in its [soluble protein] and cellular content. About 500mL of CSF is produced per day. The total volume of CSF at any given moment is 150mL CSF circulates from the choroid plexus through the ventricles and the central canal of the spinal cord. As it circulates, there is unrestricted diffusion b/w it and the interstitial fluid of the CNS.

Flow of CSF CSF is absorbed into the general circulation at the arachnoid granulations CSF reaches the subarachnoid space through foramina in the wall and roof of the 4th ventricle. CSF then flows through the subarachnoid space surrounding the brain, spinal cord, and cauda equina Along the axis of the superior sagittal sinus, fingerlike extensions of the arachnoid membrane, called arachnoid villi, penetrate the dura. In adults, clusters of villi form arachnoid granulations.