Adult brains have four regions: 1. Cerebral hemispheres 2. Diencephalon 3. Brain stem, consisting of: • Midbrain • Pons • Medulla 4. Cerebellum

Gray matter: short, nonmyelinated neurons and cell bodies White matter: myelinated and nonmyelinated axons The basic pattern found in the CNS • A central cavity is surrounded by gray matter, with white matter external to gray matter • Spinal cord exhibits this basic pattern; however, pattern changes with ascent into brain stem. • Brain stem has additional gray matter nuclei scattered within white matter. Cerebral hemispheres (cerebrum) and cerebellum contain outer layer of gray matter called the cortex

Ventricles • Fluid-filled chambers that are continuous with one another and to the central canal of the spinal cord • Filled with cerebrospinal fluid (CSF) • Lined by ependymal cells (neuroglial cells)

Paired lateral ventricles are large, C-shaped chambers located deep in each hemisphere of the brain

Each lateral ventricle is connected to the third ventricle • The third ventricle is connected to the fourth ventricle via the cerebral aqueduct, which is continuous with central canal of the spinal cord

Surface markings: • Gyri: ridges • Sulci: shallow grooves • Fissures: deep grooves • Longitudinal fissure • Separates two hemispheres • Transverse cerebral fissure • Separates cerebrum and cerebellum

First four lobes of the cerebral hemispheres are named after overlying skull bones

A fifth lobe, Insular lobe, is buried under portions of temporal, parietal, and frontal lobes

Each hemisphere has three basic regions: • Cerebral cortex of gray matter superficially • White matter internally, with the basal nuclei deep within white matter • Basal nuclei (Ganglia)

The cerebral cortex is the site of the conscious mind: • Awareness • Sensory perception • Voluntary motor initiation • Communication • Memory storage Thin (2–4 mm) superficial layer of gray matter • Composed of neuron cell bodies, dendrites, glial cells, and blood vessels, but no axons 40% of mass of brain

The cerebral whit matter is responsible for communication between cerebral areas and between the cortex and lower CNS Classified based on the direction they run: • Association fibers are horizontal running fibers that connect different parts of same hemisphere • Commissural fibers are horizontal fibers that connect gray matter of two hemispheres • Projection fibers are vertical fibers that connect hemispheres with lower brain or spinal cord

The basal nuclei is closely associated with the diencephalon and the midbrain Each hemispherebs basal nuclei include a: • Caudate nucleus • Putamen

The basal nuclei is closely associated with the diencephalon and the midbrain Functions of basal nuclei: • Influence muscle movements • Play role in cognition and emotion • Regulate intensity of slow or stereotyped movements • Filter out incorrect/inappropriate responses • Inhibit antagonistic/unnecessary movements

Consists of three paired gray-matter structures • Thalamus • Hypothalamus • Epithalamus Functions of basal nuclei: • Influence muscle movements • Play role in cognition and emotion • Regulate intensity of slow or stereotyped movements • Filter out incorrect/inappropriate responses • Inhibit antagonistic/unnecessary movements

Consists of three paired gray-matter structures • Thalamus • Hypothalamus • Epithalamus

Thalamus: Egg-shaped nuclei that makes up 80% of the diencephalon Main function is to act as relay station for information coming into the cortex • Impulses from hypothalamus for regulating emotion • Impulses from cerebellum and basal nuclei to help direct motor cortices • Impulses for memory or sensory integration

Hypothalamus: Located below the thalamus Main function is to control the autonomic nervous system • Blood pressure • Heart rate • Pupil size • Body temperature • Endocrine system

Epithalamus: Most dorsal portion of the diencephalon Contains pineal gland • Secretes melatonin that helps regulate sleep-wake cycle

Consists of the midbrain, pons, and medulla oblongata • Similar in structure to spinal cord but contains nuclei embedded in white matter • Controls automatic behaviors necessary for survival • Regulating voluntary movement

Midbrain nuclei that play a role in pain suppression and fight-or-flight response

Pons are composed of conduction tracts • Longitudinal fibers connect higher brain centers and spinal cord • Transversal/dorsal fibers relay impulses between motor cortex and cerebellum

Located dorsal to the pons and medulla • Processes input from cortex, brain stem, and sensory receptors • Plays a role in balance

The CNS does not sit naked encased in bone, it is protected by several layers of connective tissue, bone, and integument - Skin - Bone; skull or vertebrae - Dura mater - Arachnoid - Subarachnoid Space filled with fluid (CSF) - Pia mater Meninges

Dura mater = tough, non-elastic “bag” surrounding brain and spinal cord

Arachnoid membrane = web-like layer underneath Dura mater (blood can collect here after an injury and lead to swelling)

Pia mater = thin membrane that lies on top of nervous tissue

Subarachnoid Space separates Pia mater from Arachnoid and Dura mater

The CNS has a fluid-filled canal system – brain ventricles to the spinal cord canal, which is filled with CSF and has several functions • Homeostatic Control to the CNS • Chemical Environment - Ions(Na+, K+, Ca2+, …..), Metabolites (Glucose), Metabolic waste disposal • Protection of the CNS • Hydraulic buffer between CNS and Bone that keeps the CNS from making direct contact with bone • Buoyancy • The human brain ~1400g of jelly-like mass that is not supported by any internal skeletal or other mechanical structures. CSF creates a “hydroskeleton”

Spinal roots and nerves leave the vertebral column at each vertebral joint

Roots are part of PNS • Dorsal Roots = Afferent Sensory Neurons • Ventral Roots = Efferent Motor Neurons • Spinal Nerve = efferent and afferent fibers are mixed

The spinal cord: 8 Cervical nerves 12 Thoracic nerves 5 Lumbar nerves 4 Sacral nerves Cauda equina (“Ponytail)

The distal part of the spinal cord looks like a horse tail: • Cauda equina (cauda = tail, equs = horse) The spinal cord feather into several strands (individual spinal nerves) in the lumbar and sacral area • During development the vertebral column grows faster than the spinal cord and nerves have to “chase” after their “exit ports” between the vertebrae

Gray matter: short, nonmyelinated neurons and cell bodies White matter: myelinated and nonmyelinated axons The basic pattern found in the CNS • A central cavity is surrounded by gray matter, with white matter external to gray matter • Spinal cord exhibits this basic pattern; however, pattern changes with ascent into brain stem

Nerves (like muscles) are wrapped in layers of protective cells or connective tissue • Myelin Sheath is formed by glia cells, not formed by connective tissue • Endoneurium wraps individual axons (endomysium in muscles) • Perineurium wraps axons bundles (perimysium in muscles) • Epineurium; wraps nerves formed by axon bundles (fascicles) • Blood vessels run along nerves, providing a supply of O2 and nutrients